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Temporomandibular Joint: Disorders, Treatments, and Biomechanics

SHIRISH INGAWALE1 and TARUN GOSWAMI1,2

1Department of Biomedical, Industrial and Human Factors Engineering, Wright State University, 3640, Col. Glenn Hwy,Dayton, OH 45435, USA; and 2Orthopaedic Surgery and Sports Medicine, Wright State University, Dayton, OH 45435, USA

(Received 5 May 2008; accepted 13 February 2009; published online 28 February 2009)

AbstractTemporomandibular joint (TMJ) is a complex,sensitive, and highly mobile joint. Millions of people sufferfrom temporomandibular disorders (TMD) in USA alone.The TMD treatment options need to be looked at more fullyto assess possible improvement of the available options andintroduction of novel techniques. As reconstruction witheither partial or total joint prosthesis is the potentialtreatment option in certain TMD conditions, it is essentialto study outcomes of the FDA approved TMJ implants in acontrolled comparative manner. Evaluating the kinetics andkinematics of the TMJ enables the understanding of structureand function of normal and diseased TMJ to predict changesdue to alterations, and to propose more efcient methods oftreatment. Although many researchers have conducted bio-mechanical analysis of the TMJ, many of the methods havecertain limitations. Therefore, a more comprehensive analysisis necessary for better understanding of different movementsand resulting forces and stresses in the joint components.This article provides the results of a state-of-the-art investi-gation of the TMJ anatomy, TMD, treatment options, areview of the FDA approved TMJ prosthetic devices, and theTMJ biomechanics.

KeywordsTemporomandibular joint (TMJ), Temporoman-

dibular disorder (TMD), TMJ implants, TMJ biomechanics.

BACKGROUND

Temporomandibular joint (TMJ) connects themandible or the lower jaw to the skull and regulatesthe movement of the jaw (see Fig. 1). It is a bi-condylarjoint in which the condyles, located at the two ends ofthe mandible, function at the same time. The TMJ isone of the most complex as well as most used joint in ahuman body.3,5,40 The important functions of the TMJare mastication and speech.

Temporomandibular disorder (TMD) is a genericterm used for any problem concerning the jaw joint.Injury to the jaw, temporomandibular joint, or muscles

of the head and neck can cause TMD. The most com-mon TMJ disorders are pain dysfunction syndrome,internal derangement, arthritis, and traumas.18,21,22

With millions of people suffering in the United Statesalone,21,32,87,115 TMD is a problem that should belooked at more fully. Since a large fraction of TMDcauses are currently unexplained, the betterunderstanding of the etiology of TMDs will help pre-vent not only occurrence of TMDs but also failure of animplanted joint in the same way as the joint it replaced.

The TMJ Bioengineering Conference, held in 2006,underlined the importance of collective research eortsfrom four major categories: tissue engineering, bio-mechanics, clinical community, and biology.22 AtWright State University, Dayton, Ohio; our researchefforts focus on developing 3-D models of asymptoticand diseased TMJs of men and women of different agegroups to enable better understanding of joint motionand forces. The nite element analysis of these modelscan provide useful information about the contactstresses that possibly contribute to the dysfunction ofthe joint. The similar approach can also be employedfor comparative evaluation of different TMJ implantdesigns.

TEMPOROMANDIBULAR JOINT (TMJ)

TMJ Anatomy

TMJ, a joint that connects the mandible to the skulland regulates mandibular movement, is a bi-condylarjoint in which the condyles, located at the two ends ofthe mandible, function at the same time. The movableround upper end of the lower jaw is called the condyleand the socket is called the articular fossa (see Fig. 1).Between the condyle and the fossa is a disc made ofbrocartilage that acts as a cushion to absorb stressand allows the condyle to move easily when the mouthopens and closes.5,46

The features that dierentiate and make the TMJ aunique joint are its articular surfaces covered by

Address correspondence to Shirish Ingawale, Department of

Biomedical, Industrial andHuman Factors Engineering,Wright State

University, 3640, Col. Glenn Hwy, Dayton, OH 45435, USA. Elec-

tronic mail: [email protected] and [email protected]

Annals of Biomedical Engineering, Vol. 37, No. 5, May 2009 ( 2009) pp. 976996DOI: 10.1007/s10439-009-9659-4

0090-6964/09/0500-0976/0 2009 Biomedical Engineering Society

976

brocartilage instead of hyaline cartilage. The bonystructure consists of the articular fossa; the articulareminence, which is an anterior protuberance continu-ous with the fossa; and the condylar process of themandible that rests within the fossa. The articularsurfaces of the condyle and the fossa are covered withcartilage.46 A dense brocartilaginous disc is locatedbetween the bones in each TMJ. The disc divides thejoint cavity into two compartments (superior andinferior).46,92 The two compartments of the joint arelled with synovial uid which provides lubricationand nutrition to the joint structures.40,92 The disc dis-tributes the joint stresses over broader area therebyreducing the chances of concentration of the contactstresses at one point in the joint. The presence of thedisc in the joint capsule prevents the bone-on-bonecontact and the possible higher wear of the condylarhead and the articular fossa.9,54,68,92 The bones areheld together with ligaments. These ligaments com-pletely surround the TMJ forming the joint capsule.

Functioning of TMJ

The most important functions of the TMJ are mas-tication and speech. Strong muscles control the move-ment of the jaw and the TMJ. The temporalis musclewhich attaches to the temporal bone elevates themandible. The masseter muscle closes the mouth and isthe main muscle used in mastication.45 Movement isguided by the shape of the bones, muscles, ligaments,and occlusion of the teeth. The TMJ undergoes hingeand gliding motion.3 The TMJ movements are verycomplex as the joint has three degrees of freedom, witheach of the degrees of freedom associated with a

separate axis of rotation. Rotation and anterior trans-lation are the two primary movements. Posteriortranslation and mediolateral translation are the othertwo possible movements of TMJ.24

TEMPOROMANDIBULAR DISORDER (TMD)

Temporomandibular disorder (TMD) is a genericterm used for any problem concerning the jaw joint.Injury to the jaw, temporomandibular joint, or musclesof the head and neck can cause TMD. Other possiblecauses include grinding or clenching the teeth, whichputs a lot of pressure on the TMJ; dislocation of thedisc; presence of osteoarthritis or rheumatoid arthritisin the TMJ; stress, which can cause a person to tightenfacial and jaw muscles or clench the teeth;aging.7,15,31,38,48,92,97 The most common TMJ disordersare pain dysfunction syndrome, internal derangement,arthritis, and traumas.18,21,22

TMD is seen most commonly in people between theages of 20 and 40 years, and occurs more often inwomen than in men.21,22,106,107 In 1996, the NationalInstitutes of Health estimated that 10 million Ameri-cans had painful TMJ dysfunction and more womenbeing affected by it than men. Some surveys havereported that 2025% of the population exhibitsymptoms of TMD while it is estimated that 30 millionAmericans suffer from it, with approximately onemillion new patients diagnosed yearly.21,32,87,115

Disc Displacement

Coordinated movement of condyle and disc isessential to maintain the integrity of the disc. Disc dis-placement is the most common TMJ arthropathy and isdened as an abnormal relationship between the artic-ular disc and condyle.26,97 As the disc is forced out of thecorrect position there is often bone on bone contactwhich creates additional wear and tear on the joint, andoften causes the TMD toworsen.15,97 Disc displacementgenerates a popping sound when the disc is rst forcedout of alignment as the mouth opens up and then againas the disc is forced back into place as the mouth isclosed. Clinically, this popping sound or clicking isregarded as an initial symptom of the temporoman-dibular joint internal derangement (TMJ-ID).97

The anterior disc displacement has dierent degreesof severity. Wilkes developed staging classications forthe TMJ related internal derangement, or disc dis-placement (see Table 1).31,108,109 These stages weredened based on clinical or radiological ndings, orbased on the anatomic pathology of the jaw. The earlystage included slight displacement with clicking, andno pain or dysfunction. The last stage included

The temporomandibular joint

Condyle

Ligament Disc

Articular fossa

Muscle

FIGURE 1. Anatomical structure of the temporomandibularjoint (TMJ). Source: American Association of Oral and Maxil-lofacial Surgeons.5

TMJ Disorders, Treatments, and Biomechanics 977

degenerative changes to the disc with possible perfo-ration, attening of bones, pain, and restrictedmotion.31,109 In an early stage, there is a simple discdisplacement in the closed mouth position, usuallyanteriorly, due to weakness of the discal ligaments.78,79

If the displaced disc returns to its normal position whenthe mouth is opened, accompanied by a popping sound,it is referred to as disc displacement with reduction(see Fig. 2).72,78,86 If the displaced disc does not returnto the normal position and acts as an obstacle duringattempted mouth opening, the joint appears as locked.This is referred to as disc displacement without reduc-tion.72,78,86 Almost 70% of TMD patients have discdisplacement.21,26 According to Tanaka et al.97 stressdistributions in the TMJ with a normal disc position aresubstantially different from those with anterior discdisplacement. It is suggested that the disc displacementinduces the change of stress distribution in the disc andthe increase of frictional coefcients between articularsurfaces, resulting in the secondary tissue damage.91,93

The internal derangement frequently precedes the onsetof TMJ osteoarthritis.92

Other Factors Causing TMD

Dierent types of functional malocclusion havebeen shown to be partly responsible for signs andsymptoms of TMD. The functional unilateral posterior

crossbite (FUPXB) might be a contributing factor formandibular dysfunction.75 The habitual body posture(HBP) during sleep is also speculated as being one ofthe possible reasons for disc displacement.41 A studyconducted by Hibi and Ueda41 suggests that HBPallows the ipsilateral condyle to displace posteriorlyand this posterior position causes anterior disc dis-placement. Juvenile chronic arthritis, a chronic arthritisin childhood with an onset before the age of 16 yearsand a duration of more than 3 months, is also reportedas a TMD risk factor.6

Animal studies indicate that the TMJ can adapt tochanging biomechanical stresses allowing aected tis-sues of the joint to maintain ecient function in thepresence of changing load demands. However, thisadaptability may be adversely aected by several fac-tors including advanced age, tissue perturbationscaused by previous traumatic injury, enhanced sym-pathetic tone and hormonal inuences.70 Milam andSchmitz70 suggested that direct mechanical injury,hypoxia-reperfusion injury, and neurogenic inam-mation are the mechanisms involved in degenerativeprocesses affecting the TMJ. Mechanical stresses leadto the accumulation of damaging free radicals in affectedarticular tissues of susceptible individuals.69,71,74

Free radicals are molecules capable of independentexistence that have one or more unpaired electrons intheir outer orbits.37 If allowed to proceed unchecked,

TABLE 1. Wilkes staging classification of internal derangement of TMJ with respect to clinical, radiologic, and surgical findings.

I. Early stage

Clinical: No significant mechanical symptoms other then opening reciprocal clicking; no pain or limitation of motion

Radiological: Slight forward displacement; good anatomic contour of the disc; negative tomograms

Anatomic pathology: Excellent anatomic form; slight anterior displacement; passive in-coordination demonstrable

II. Early intermediate stage

Clinical: One or more episodes of pain; beginning major mechanical problems consisting of mid-to-late opening loud clicking; transient

catching, and locking

Radiological: Slight forward displacement; beginning disc deformity of slight thickening of posterior edge; negative tomograms

Anatomic pathology: Anterior disc displacement; early anatomic disc deformity; good central articulating area

III. Intermediate stage

Clinical: Multiple episodes of pain; major mechanical symptoms consisting of locking (intermittent or fully closed); restriction of motion;

difficulty with function

Radiological: Anterior disc displacement with significant deformity or prolapse of disc (increase thickening of posterior edge); negative

tomograms

Anatomic pathology: Marked anatomic disc deformity with anterior displacement; no hard tissue changes

IV. Late intermediate stage

Clinical: Slight increase in severity over intermediate stage

Radiological: increase in severity over intermediate stage; positive tomograms showing early-to-moderate degenerative

changesflattening of eminence, deformed condylar head, sclerosis

Anatomic pathology: Increase in severity over intermediate stage, hard tissue degenerative remodeling of both bearing surfaces

(osteophytosis); multiple adhesions in anterior and posterior recesses; no perforation of disc or attachments

V. Last stage

Clinical: Characterized by crepitus; variable and episodic pain chronic restriction of motion and difficulty with function

Radiological: Disc or attachment perforation; filling defects; gross anatomic deformity of disc and hard tissues; positive tomograms with

essentially degenerative arthritic changes

Anatomic pathology: Gross degenerative changes of disc and hard tissues; perforation of posterior attachment; multiple adhesions;

osteophytosis; flattening of condyle and eminence; subcortical cyst formation

Sources: Wilkes109; Gadd and Goswami31.

S. INGAWALE AND T. GOSWAMI978

free radical-mediated reactions can be extremelyharmful by damaging extracellular and cellular mole-cules, and by excessive activation of cellular pro-cesses.69,71,122 Free radicals may accumulate in articulartissues of the TMJ as a result of mechanical stressesgenerated during functional or parafunctional move-ments of the jaw, or with clenching or bruxism. Accu-mulation of free radicals in the articular tissues of theTMJ can cause signicant tissue damage, microblee-ding, and pain. In individuals predisposed to developexcessive mechanical stresses in the TMJ because ofunique structural or functional characteristics of mas-ticatory system, adaptive mechanisms of the TMJ maybe exceeded by free radical accumulation leading to adysfunctional state (i.e., disease state).71 Becausehemoglobin constitutes the largest iron store in thebody, it is speculated to be a potential source of redoxactive iron which can catalyze the formation of freeradicals that might be damaging to the joint.120122

Zardeneta et al.122 showed the presence of bronectinfragments, which may stimulate proinammatoryresponses, in samples obtained from symptomatichuman TMJs.42

The Gender Paradox

The majority of TMJ patients is female, agedbetween 20 and 40 years.21,106,107 The female to male

patient prevalence is reported to be varying from 3:1 to8:1.14,21,22,36,87 Because of the high predilection for theTMJ symptoms in women compared with men, andbecause these symptoms are more common duringchildbearing years, some researchers suggest that thefemale sex hormones may have a role in the patho-genesis of the TMJ disorders. Sex hormones are knownto inuence the differentiation, growth and develop-ment, and metabolism of connective tissues. A studyconducted by Abubaker et al.1 suggests that sex hor-mones affect the extracellular matrix of the TMJ discof female and male rats.1 These effects on the bio-chemical composition of the disc can theoretically alterthe biomechanical properties of the connective tissuesuch as those in the TMJ. Unfortunately, it is not yetknown whether the female sex hormones or theestrogen receptors or some other factors are responsi-ble for the TMD gender paradox.22

TREATMENT OPTIONS FOR TMD

Treatments for the various TMJ disorders rangefrom physical therapy and nonsurgical treatments tovarious surgical procedures. Usually the treatmentbegins with conservative, nonsurgical therapies rst,with surgery left as the last option. The majority ofTMDpatients can be successfully treated by non-surgical

FIGURE 2. A schematic representation of the position of the TMJ disc in three different conditions: a healthy joint, anterior discdisplacement with reduction (ADDWR), and anterior disc displacement without reduction (ADDWOR). Source: Perez-Palomar andDoblare78.


therapies and surgical interventions may be requiredfor only a small part of TMD population. All non-surgical treatment options must be exhausted beforeundertaking the invasive methods for the managementof TMD. Many of the treatments listed below oftenwork best when used in combination. The correctcourse of action may vary, for example: medication,therapy, splints, arthrocentesis, discectomy, or pros-thesis.15 The initial treatment does not always work andtherefore more intense treatments such as jointreplacement may be a future option. The success ofjoint replacement surgeries signicantly depends on thenumber of prior surgeries with better outcomes forpatients with fewer previous TMJ surgeries.66,67,84,112,115

Self-Care

Physical therapy is often used by TMD patients tokeep the synovial joint lubricated, and to maintain fullrange of the jaw motion. One such exercise for the jawis to open the mouth to a comfortable fully-openposition and then to apply slight additional pressure toopen the mouth fully. Another exercise includesstretching the jaw muscles by making various facialexpressions.31 Avoiding extreme jaw movements, tak-ing medications, applying moist heat or cold packs,eating soft foods are other ways that may keep thedisorder from worsening.40

Splints

Splints are plastic mouthpieces that t over the upperand lower teeth (see Fig. 3). They prevent the upper andlower teeth from coming together, lessening the effectsof clenching or grinding the teeth. The splints alsocorrect the bite by positioning the teeth in their mostcorrect and least traumatic position.18 Dental splints

are often used as a short-term treatment during ortho-dontic management, before orthodontic therapy, or ifthe TMJ disorders occur during dentofacial orthopedicprocedures.25 Bruxism is believed to cause the TMJdysfunction due to tooth attrition and subsequentmalocclusion; myofascial strain, fatigue or brosis ofmasticatory muscles; and capsulitis and adhesionswithin the TMJ joint space.47 Splints are used to helpcontrol bruxism,17,19,33,34,47,81,85,95,117 a TMD risk fac-tor in some cases. Splints are effective in reducing theintensity of pain for patients with pain in jaw andmasticatory muscles by compensating for or correctingperceived bite defects of the sufferer.17,19,33 The studieson evidence-based medicine for splint therapy, how-ever, have shown equivocal results.2,28,29,57,60,101 Thelong-term effectiveness of this therapy has been widelydebated and remains controversial.17,19,85,117

Surgery

Surgery can play an important role in the manage-ment of TMDs. As dierent surgical approaches fortreating the same condition are often recommended inthe literature, it is essential to understand whichapproach can be more benecial when surgery is nee-ded. Conditions that are always treated surgicallyinvolve problems of overdevelopment or underdevel-opment of the mandible resulting from alterations ofcondylar growth,mandibular ankylosis, and benign andmalignant tumors of the TMJ.59 The surgical treatmentssuch as arthrocentesis, arthroscopy, discectomy, andjoint replacement are discussed below.

Arthrocentesis

Arthrocentesis is the simplest form of surgicalintervention into the TMJ performed under generalanesthesia for sudden-onset, closed lock cases (restrictedjaw opening) in patients with no signicant prior historyof TMJ problems.4,18 Arthrocentesis is not only the leastinvasive of all surgical procedures but also carries a verylow risk. It involves inserting needles inside the affectedjoint and washing out the joint with sterile uids (seeFig. 4). Occasionally, the procedure may involveinserting a blunt instrument inside the joint to dislodge astuck disc.4,18,61

Arthroscopy

Arthroscopy is a surgery performed to put thearticular disc back into place. During this surgery asmall incision is made in front of the patients ear toinsert a small, thin instrument that contains a lens andlight. This instrument is connected to a video screen,allowing the surgeon to examine the TMJ and sur-rounding area. Depending on the cause of the TMD,

FIGURE 3. A dental guard or splint. Source: Dental CareOttawa.20


the surgeon may remove inamed tissue or realign thedisc or condyle.18,35 However, if the ligament and ret-rodiscal tissue was previously stretched beyond itselastic range, then just popping the disc back into placeis only a temporary x as the joint still would not workas well as usual. Therefore, an anchorMitek minianchorand articial ligaments have been used forseveral years to stabilize the articular disc to the pos-terior aspect of the condyle (see Fig. 5).27,110,111

When disc repositioning and stabilization are indi-cated, the Mitek mini anchor system oers signicantadvantages over other disc repositioning methods.27,62,114

The Mitek mini anchor has been analyzed in variousstudies to assess its performance. A 2-year follow-up

study showed a success rate of 90% in reference toincisal opening, jaw and occlusal stability, and signif-icant reduction in presurgical pain level.110 Fields andWolford27 have demonstrated osseointegration of theMitek anchor in human condyles. The Mitek anchorsare reported to remain intact and biocompatible for aslong as 59 months.27 Mehra and Wolford62 reportedthat, in 105 patients (188 discs) treated with Mitek minianchors, the radiographic evaluation for the follow-upover 1484 months demonstrated no signicant con-dylar resorption or positional changes of the anchors.They also reported a statistically signicant reductionin TMJ pain, facial pain, headaches, the TMJ noisesand disability; and improvement in jaw function anddiet. The Mitek mini anchor also provides an effectivemethod for prevention of condylar dislocation whilepermitting some controlled translation.114

Discectomy

Discectomy is a surgical treatment, which isoften performed on individuals with severe TMD, toremove the damaged and very often dislocatingarticular disc without going to a more extreme treat-ment such as a joint prosthetic.18 However, removal ofthe painful pathologic disc causes the TMJ reducedabsorbency and increased loading during articula-tion.39,90,92 Although materials such as tendon allo-grafts are advocated for the use of disc replacement,there are no ideal inter-positional materials that canprotect articular cartilage from degenerative changesfollowing discectomy.39

Joint Replacement

Joint replacement is a surgical procedure in whichthe severely damaged part of the TMJ is removed andreplaced with a prosthetic device. While more conser-vative treatments are preferred when possible, in severecases or after multiple operations, the current end stagetreatment is joint replacement.92 If either a condyle ora fossa component of the TMJ is replaced, the surgeryis called partial joint replacement. In total jointreplacement, condyle and fossa are both replaced (seeFig. 6). Joint replacement is performed in certain cir-cumstances such as bony ankylosis, recurrent brousankylosis, severe degenerative joint disease, asepticnecrosis of the condyle, advanced rheumatoid arthritis,two or more previous TMJ surgeries, absence of theTMJ structure due to pathology, tumors involving thecondyle and mandibular ramus area, loss of the con-dyle from trauma or pathology.15,63,83,84,112,113 Thereare now long-term studies available in the literaturethat support the safety and efcacy of joint replace-ment under appropriate circumstances.65 However,before a joint replacement option is ever considered for

FIGURE 5. The Mitek mini anchor for repositioning and sta-bilization of TMJ disc. It is composed of a titanium alloy body,5 mm in length and 1.8 mm in diameter. Two nickel titaniumwings provide the intra bony locking mechanism while aneyelet in the body allows attachment of sutures which func-tion as artificial ligaments. Source: Wolford.110

FIGURE 4. Arthrocentesis. Source: Mayo Foundation forMedical Education and Research.61


a patient, all non-surgical, conservative treatmentoptions must be exhausted; and all conservative sur-gical methodologies should be employed.83,84

TMJ IMPLANT DEVICES

TMJ devices are used as endosseous implants forarticular disc replacements, condylar replacements,fossa replacements, and total joint prostheses. Theimportant characteristics for a TMJ implant to besuccessful are biocompatible materials; functionallycompatible materials; low wear, and fatigue; adapt-ability to anatomical structures; rigidly stabilizedcomponents; and corrosion resistant and non-toxicnature.115 van Loon et al.106 have stipulated the spe-cic requirements for the TMJ prosthesis to be a suc-cessful treatment option for the TMD patients (seeTable 2). They highlight the life expectancy of TMJimplant as one of the most critical requirements. Inorder to reduce the frequency of painful revision sur-gery, a TMJ device should have an expected lifetime ofmore than 20 years. As the maximum life of most TMJprosthetics is 1015 years, Gadd and Goswami31 sug-gested that the locking screws and locking compressionplate for the condylar part of the prosthetic should beresearched to increase implant stability and to avoidbone loss due to revision surgery.

A total TMJ prosthesis was not described until1974.50 Till then, surgeons had concentrated onimplanting either a fossa or a condylar head, but notboth.88 Although alloplastic TMJ prostheses were inuse since early 1960s; those became popular in 1980swith the introduction of the Vitek-Kent prosthesis.Many other companies then introduced their own de-signs of alloplastic TMJ devices.113 However, many ofthe alloplastic devices failed in delivering the intendedresults due to their vulnerability to the repeated

mechanical stresses encountered in the TMJ withfunctional movements of the jaw. The predicted in vivoservice life of such devices was one to three years.68

The United States Food and Drug Administration(FDA), in 1993, halted the manufacture of the TMJimplantsexcept for Christensen and Morgan im-plants which were on the market prior to the enactmentof the medical device law in 1976102due to lack ofsafety and efcacy information to support its indicateduse.113 In 1993, the Dental Products Advisory Panelreclassied TMJ implants into Class IIIthe highestrisk category.102,104 This means that all manufacturersof TMJ devices would be required to submit a Pre-market Approval Application (PMA)demonstratingsafety and effectivenesswhen called for by the FDA.On December 30, 1998, the FDA called for PMAs fromall manufacturers of the TMJ implants.102,104 Althoughmany individuals and research groups introduced dif-ferent designs of the TMJ prosthetic devices, only fourTMJ implants (from three manufacturers) are ap-proved by FDA since December 30, 1998: (1) Chris-tensen/TMJ Implants, Inc., total joint implant, (2)Christensen/TMJ Implants, Inc., partial joint implant,(3) Techmedica/TMJ Concepts implant, and (4) WalterLorenz/Biomet implant.102,104,105,113

Christensen TMJ Implant

The Christensen TMJ implant system was intro-duced in early 1960s.32,88 Later, in 1995, it wasdescribed as a total joint replacement system for theTMJ.88 The Christensen prosthesis system includeseither a partial or total TMJ prosthesis available as astock device (see Fig. 7). The Christensen fossa emi-nence prosthesis (FEP) is fabricated entirely of CobaltChrome (CoCr) alloy and is approximately 2035 mmacross and 0.5 mm thick with a polished articulatingsurface.32,83 This device can support either unilateral orbilateral partial joint reconstruction. The Christensen

TABLE 2. Design requirements for a TMJ prosthesis.

No. Description

1 Imitation of condylar translation during mouth opening

2 Unrestricted mandibular movements

3 Correct fit to the skull

4 Correct fit to the mandible

5 Stable fixation to the bony structures

6 Expected lifetime of more than 20 years

7 Low wear rate

8 Wear particles tolerated by the body

9 Biocompatible materials

10 Sufficient mechanical strength

11 Simple and reliable implantation procedures

Source: van Loon et al.106

FIGURE 6. Temporomandibular joint replacement. Source:Mayo Foundation for Medical Education and Research.61


condylar prosthesis has a CoCr alloy frame work witha molded Polymethylmethacrylate (PMMA) head andis available in three lengths of 45, 50, and 55 mm.CoCr bone screws and drill bits sized to the screws areused to x the FEP to the base of the skull and condylardevice to the ramus.32,83,99

Christensens implant registry data, from 1993 to1998, shows that 55% of the patients who receivedeither partial or total Christensen TMJ prostheses wereunder the age of 40, and 83% were under the age of 50.The number of women in the registry (3081, 87%)compared with men (434, 12%) emphasizes the genderparadox.32 A total of 58% of the patients receivedpartial joint prostheses while total TMJ prostheseswere placed in 42% patients.32

Chase et al.15 studied effectiveness of the ChristensenTMJ prosthesis system in treating patients with severeTMD. The study dealt with patients who wererecalcitrant to nonsurgical treatments or had had priorsurgical procedures that did not alleviate their symp-toms. The results of this study indicated that theChristensen TMJ prosthesis system might offer atreatment modality for severe TMJ dysfunction with ahigh degree of success.15 Wolford et al.112 reported thata metal condylar head against a metal fossa in theChristensen TMJ prosthesis device can increase themetal wear debris, create stress loading of the fossacomponent, causemetalosis and corrosion, and increaseexposure of elements in hypersensitive patients.

Techmedica/TMJ Concepts TMJ Implant

Techmedica, Inc. developed the joint prosthesis in1989 as a custom-made device (see Fig. 8). However, inJuly 1993, FDA halted the manufacture of any TMJ

devices developed after 1976, due to lack of safety andefcacy information to support its indicated use. In1997, Wolford et al.116 presented a 5-year follow-upstudy on 36 patients with 65 TMJs reconstructed withthe Techmedica (now known as TMJ Concepts) totaljoint prosthesis. This study reported the overall successrate of 90% for long-term occlusal and skeletal sta-bility and pain reduction of 89% after reconstruction.Based on outcomes of this ve year study, in 1997, the

FIGURE 7. The Christensen prostheses. (a) Fossa eminence prosthesis. (b) Total prosthesis. Source: TMJ Implants, Inc.100

FIGURE 8. The Techmedica/TMJ Concepts prosthesis.Source: Wolford et al.112


Techmedica/TMJ Concepts implant was approved bythe FDA.110,112,113

The Techmedica/TMJ Concepts total joint pros-thesis uses materials that are well proven in orthopedicjoint reconstruction for hip and knee replace-ments.112,113 The fossa component of this device ismade from commercially pure titanium mesh(ASTM F67 & F1341) with an articular surface madeof ultra-high-molecular-weight polyethylene (UHMWPEASTM F648).83,84,99,110,112 The body of condylarcomponent is made from medical grade titanium alloy(ASTM F136) with a condylar head of cobaltchro-miummolybdenum alloy (ASTM F1537).83,84,99,110,112

Both the fossa and condylar components are securedwith titanium alloy (Ti6Al4V) screws.83

Prior to joint replacement surgery, the patientundergoes a computed tomography (CT) scan of jawsaccording to a specic protocol.83,113,115 Using the CTdata, a 3-dimensional plastic model of the TMJ andassociated jaw structures is made using stereolithographictechnology, a rapid prototyping technology, to producean anatomically accurate plastic model.83,99,113,115 Thismodel allows selective repositioning of the mandible onthe model into a predetermined functional and estheticposition.113,115 The condyle is removed and any necessarybony recontouring of the fossa and mandibular ramus iscompleted and marked on the plastic model, since all thealterations on themodelmust be accurately duplicated onthe patient intraoperatively.99,113 A custom-made Tech-medica/TMJ Concepts total joint prosthesis conformingto the patients specic anatomical morphology and jawinterrelationship is then fabricated on the plasticmodel.113,115 The data generated in the computer is uti-lized to guide multi-axis milling systems in shaping theimplants to the anatomy found on the anatomical mod-els.99 To ensure optimum t, implant shapes are nalizedby hand contouring with careful attention to anatomicaldetails.99

Compared to the o-the-shelf implant devices, apatient-tted Techmedica/TMJ Concepts prosthesisprovides a better t and stabilization of its componentsto the host bone thereby mitigating any micro-move-ment leading to loosening of the components andmaximizing the opportunity for osseointegration ofcomponents and xation screws.65,67,112 Osseointegra-tion can contribute to improved patient function anddecreased micro-movement, which limits overall pros-thesis wear and stress.112 Based on material selection,treatment philosophy, and clinical experience, thisimplant is reported to have provided the service life ofup to 14 years without evidence of untoward wear orfailure.65,113,115

A prospective study by Wolford et al.115 evaluatedthe ve to eight year subjective and objective results of42 consecutive patients who had TMJ reconstruction

using the Techmedica/TMJ Concepts custom madetotal joint prosthesis. This study demonstrated that theTechmedica/TMJ Concepts total joint prosthesis is aviable technique for TMJ reconstruction as a primaryprocedure and for patients with previous multiple TMJsurgeries and severely damaged joint.

In 2002, Mercuri et al.,67 in a 107 months (standarddeviation 15.5 months) follow-up study of 97 patientstreated with Techmedica/TMJ Concepts, reported a76% reduction in mean pain score, a 68% increase inmean mandibular function and diet consistency score,and a 30% increase in mandibular range of motionafter 10 years. In 2007, Mercuri et al.,65 in a meanfollow-up of 11.4 years (standard deviation 3.0; range014) study of the patient-tted Techmedica/TMJConcepts total reconstruction system, reported a sig-nicant reduction in pain scores, an increase in man-dibular function and diet consistency scores, andimprovement in mandibular range of motion after14 years. Both studies found the long-term quality oflife improvement scores to be statistically related to thenumber of previous TMJ operations the patient hadundergone.65,67 Comparison analysis demonstratedsignicantly better outcomes for patients with fewerprevious TMJ surgeries and without exposure to allo-plastic TMJ devices.65,67 In 2008, Mercuri et al.64

published the results of 20 TMJ reankylosis patients(total of 33 joints) treated with Techmedica/TMJConcepts total TMJ prosthesis system with theautogenous fat grafted around the articulating portionof the prosthesis at implantation. The follow-up datafor 50.4 28.8 months showed improvement inreported pain; increased jaw function; diet consistency;and a signicant improvement in postreplacementmaximum interincisal opening and quality of life.

Dingworth et al.23 and Wolford et al.112 publishedthe results of rst direct clinical comparison of pre-implantation and postimplantation subjective andobjective data from two similar groups of patients whounderwent reconstruction with two different TMJreconstruction systems. These studies evaluated 23patients treated with Christensen prostheses (followedfor a mean of 20.8 months) along with 22 patientsimplanted with Techmedica/TMJ Concepts prostheses(followed for a mean of 33 months). The investigatorsreported statistically signicant improved outcomesrelative to post-surgical incisal opening, pain, jawfunction, and diet for the Techmedica/TMJ Conceptsprosthesis group compared to the Christensen pros-thesis group.23,112

W. Lorenz/Biomet TMJ Implant

The W. Lorenz TMJ implant is a ball and sockettype prosthetic joint similar to a knee or hip implant


(see Fig. 9). This device is made of common materialswith over 30 years of successful use in orthopedic jointreplacement.84,103 The condylar component is manu-factured from CobaltChromiumMolybdenum (CoCrMo, ASTM F799) alloy with a roughened titaniumporous coating on the host bone side of the ramalplate.83,84,103 The ramus of mandibular component isavailable in lengths of 45 mm, 50 mm, and 55 mm. Thefossa component is manufactured from a specic gradeof ultra-highmolecularweight polyethylene (UHMWPE)calledArComwhich has shown a 24%reduction inwearcompared to traditional UHMWPE.83,84,103 The swanneck curvature on the medial surface of condylar neckavoids the inherent tting problems of the right angledesign found in most metallic condylar prosthesis.83,84

The fossa is available in three sizes with predrilled holesfor the screws. It also has an exaggerated circumferentiallipping to protect the condyle from possible heterotopicbone formation and to avoid condylar dislocation.83,84

Both the condyle and fossa implants are attached tobone using self-retaining, self-tapping bone screwsmadeof titanium alloy (Ti6Al4V).83,84,103

After three year follow-up of 50 patients (69 joints;31 unilateral and 19 bilateral) reconstructed with Lor-enz/Biomet prosthesis, Quinn83,84 reported signicantimprovement in pain intensity, mouth opening, andfunctional diet capability. This study also reported onecomplication of staph scalp infection, necessitating theremoval of fossa prosthesis after 10 months of service.According to FDA documentation, a total of 268 joints(92 unilateral and 88 bilateral) were reconstructed withW. Lorenz/Biomet total TMJ replacement system afterappropriate non-surgical treatment and/or previousimplant failure.103 The average patient follow-up for19.6 months demonstrated improvement in patientscondition through decrease in pain, increase of func-tion, increase in maximal incisal opening, and satis-faction with the treatment outcome.103 Barbick et al.7

have demonstrated that the Lorenz/Biomet prosthesis

ts satisfactorily in the majority of patients undergoingsurgical Techmedica/TMJ Concepts custom jointreplacement with minimal anatomical reduction. TheLorenz/Biomet total prosthesis has not been studied inpregnant women or children, therefore, the safety andeffectiveness for these patients is not known.103 Thesafety and effectiveness of revision surgery using asecond set ofW. Lorenz/Biomet total TMJ replacementsystem implants is not known.

The information about the FDA approved TMJimplants is summarized in Table 3. Outcomes of someselective studies of patients treated with FDAapproved total TMJ devices are summarized inTable 4. Investigating the outcomes of FDA approvedimplants in a controlled comparative manner, andevaluating biological characteristics of failed implantscompared to controls is essential to determine themechanism of implant failure. More rigorous com-parative evaluations of the available implants can bepossible with the advent of the TMJ Implant Registryand Repository (TIRR).22

ALLOPLASTIC MATERIALS

As the use of an alloplastic material eliminates thedonor site morbidity and the need for tissue harvesting,several dierent alloplastic materials have been used toreplace lost articular tissues of the TMJ.65,68 Allo-plastic materials used as medical devices have tradi-tionally been viewed as biologically inert substancesthat can be designed to achieve desirable mechanicalproperties.30,68,123 Silicone rubber and Proplast/Teon(PT) were widely used materials in alloplastic TMJimplants from mid 1970s to late 1980s. Silicone rubberwas used as permanent or temporary interpositionalmaterial in TMJ reconstructive surgery since animalstudies had revealed that silicone rubber implantsplaced into the TMJ after discectomy were typicallyencapsulated by a brous reactive tissue capable offunctioning as a pseudo-disc.68 Implants composedprimarily of carbon ber and polytetrauoroethylene(PTFE/Teon or PT) were introduced in the mid 1970sto reconstruct the TMJ after discectomy.68 Earlyreported successes with the use of these materialsincluded greater implant stability, and soft-tissueingrowth into the more porous PT implants.68

Adverse Tissue Responses to Alloplastic Materials

In many TMJ patients, alloplast materials initiallyprovided pain relief and improved function of the joint.However, in most patients, these implant materials(silicone rubber and PT) were found to gradually breakdown as they could not suciently withstand the

FIGURE 9. The W. Lorenz/Biomet TMJ prostheses. (a) Con-dylar prosthesis. (b) Total prosthesis. Source: Biomet Micro-fixation.11


contact stresses generated during functional movementsof the jaw.30,83,110 The structural failure of the implantsresulted in formation of microparticulate implant debriswhich elicited a foreign-body response characterized bythe presence of multinucleated giant cells.68 Thebreakdown particles provoked the foreign body giantcell reactions resulting in severe pain, headaches,inammation, brosis, malocclusion, progressive boneand soft-tissue destruction, and severely limited jointfunction often requiring further surgery.30,83,110,113

Zardeneta et al.123 suggested that the severity of thebiologic response to implant debris may be dependentlargely on the size of the debris particles. Implantsreduced to small particles elicit a more intenseinammatory response than implants degraded tolarger particles.68,110,123 The inammatory response toPT or silicone rubber debris continues despite removalof the failed implants because these materials are notsubstantially degraded in vivo.68,110 Patients with pre-vious exposure to failed materials and bony destruc-tion resulting from foreign body inammatory reactionare likely to experience high pain and poor long-termoutcomes with alloplastic reconstruction.89 In suchrevised reconstruction cases, implants showed thepotential to fragment in situ resulting in nonbiode-gradable particles that stimulate a giant cell reaction

and lead to degeneration of local structures, pain, andlimitation of mandibular opening.89

The next generation of joint replacements willincorporate live tissues in an eort to reconstruct thejoint to its normal state. The TMJ tissue engineeringstrategies, in the long-term, may need to combine thedisc and mandibular condyle along with other tissuessuch as retrodiscal tissue in a single implant.22

Understanding the development and break-down mechanisms of the TMJ lubrication may enableus to develop a good as new treatment remedy forTMDs.92

LOADING AND KINEMATICS OF TMJ

Mandibular motions result in static and dynamicloading in the TMJ. During natural loading of the joint,combinations of compressive, tensile, and shear loadingoccur on the articulating surfaces.92 The analysis ofmandibular biomechanics helps us understand theinteraction of form and function, and mechanism ofTMDs necessary to develop methods to prevent, diag-nose, and cure joint disorders.10,38,48,52,56,58 It also aidsin the improvement of the design and the behavior ofprosthetic devices, thus increasing their treatment

TABLE 3. Summarized information about the FDA approved TMJ implants.

TMJ implant Property

Prosthesis

FeaturesFossa eminence Condylar

Christensen/TMJ

Implants, Inc.

Materials CoCr alloy CoCr alloy. PMMA for head. Mainly a stock device

Serves as partial as well as

total prosthesis

The company has its own

implant registry

Some researchers believe

that the metal head

against the metal fossa

can cause more metal

wear debris

Dimensions 20 mm x 35 mm (across)

0.5 mm (thick)

45, 50, 55 mm

Available sizes 44 3

Accessories CoCr bone screws, drill bits CoCr bone screws, drill bits

Techmedica/TMJ

Concepts

Materials Pure titanium (ASTM F67 &

F1341). UHMWPE (ASTM

F648) for articular surface

Medical grade titanium

alloy (ASTM F136).

CoCrMo alloy (ASTM

F1537) for head

A custom-made device

Service life is reported up

to 14 years without

evidence of untoward

wear or failureDimensions Patient-specific Patient-specific

Available sizes Patient-specific Patient-specific

Accessories Ti6Al4V alloy screws Ti6Al4V alloy screws

W. Lorenz/Biomet Materials A specific grade UHMWPE

(ArCom)

CoCrMo alloy (ASTM

F799) +

Roughened titanium porous

coating.

The swan-neck curvature

of condylar component

offers better fitting of the

device

Service life is reported up

to 3 years without

evidence of untoward

wear or failure.

Long-term follow-up is

not available

Dimensions 45, 50, 55 mm

Available sizes 3 3

Accessories Ti6Al4V alloy screws Ti6Al4V alloy screws


TA

BL

E4.

Resu

lts

of

the

tota

lT

MJ

reco

nstr

ucti

on

wit

hF

DA

ap

pro

ved

devic

es.

Devic

eS

ourc

e

Popula

tion

Num

ber

of

prior

TM

J

surg

eries

Follo

w-u

pR

esults

Patients

Join

ts

Christe

nsen

TM

J,

Inc.

Chase

et

al.

15

21

34

2.9

110

yr

(Mean

=2.4

yr)

95%

had

pain

impro

vem

ent

86%

had

incre

ase

dabili

tyto

eat

91%

had

impro

ved

incis

or

openin

g

No

failu

res

or

com

plic

ation

report

ed

Christe

nsen

TM

J,

Inc.

Quin

n83

90

109

?36108

month

s

(Mean

=73.1

month

s)

9fr

actu

res

ofth

econdyla

rpro

sth

eses,

at

an

avera

ge

of

5.8

yr

aft

er

pla

cem

ent,

were

report

ed.

These

factu

res

were

att

ribute

dto

uncorr

ecte

dpara

func-

tionalhabits

and

devic

efixation

Christe

nsen

TM

J,

Inc.

Gera

rdand

Hudson

32

17

26

?1284

month

s

(Mean

=50

month

s)

82%

had

apain

impro

vem

ent

88%

had

impro

ved

funct

ion

82%

had

impro

ved

inte

rincis

alopenin

g

One

condyla

rand

one

TJR

pro

sth

esis

required

repla

cem

ent

Christe

nsen

TM

J,

Inc.

Specu

land

et

al.8

845

60

?1120

month

s

(Media

n=

14.5

month

s)

97%

had

overa

llfu

nctionalim

pro

vem

ent

77%

could

eat

all

types

of

food

76%

report

ed

satisfa

ction

with

the

treatm

ent

No

pro

sth

esis

required

repla

cem

ent

Techm

edic

aT

MJ

Concepts

,In

c.

Wolfo

rdet

al.1

12

36

65

?5

years

90%

overa

llsucc

ess

rate

for

long-t

erm

occlu

saland

skele

talsta

bili

ty

89%

had

pain

reductio

n

Techm

edic

aT

MJ

Concepts

,In

c.

Wolfo

rdet

al.1

15

38

69

2.9

(range:

016)

6096

month

s

(Mean

=73.5

month

s)

Sta

tistically

sig

nifi

cant

impro

vem

ent

in

incis

alopenin

g,

jaw

function,

and

pain

level;

and

long-t

erm

sta

ble

occu

lsio

nin

all

case

s

Sta

tistically

sig

nifi

cantdecre

ase

inla

tera

l

excurs

ion

move

ments

Com

plic

ations

occu

rred

insix

patients

Techm

edic

aT

MJ

Concepts

,In

c.

Merc

uri

et

al.6

658

97

4.2

(range:

012)

60120

month

s

(Mean

=107.4

month

s)

76%

had

reductio

nin

mean

pain

score

s

68%

had

incre

ase

inm

andib

ula

rfu

nct

ion

and

die

tconsis

tency

score

s

30%

impro

vem

entin

mandib

ula

rra

nge

of

motio

naft

er

10

years

Aft

er

5years

of

impla

nta

tion,

one

case

required

repla

cem

ent

of

ara

mus

com

ponent

due

toscre

wlo

osenin

g

Techm

edic

aT

MJ

Concepts

,In

c.

Merc

uri

et

al.6

561

102

4.9

(range:

028)

014

years

(Mean

=11.4

years

)

Pain

levels

,m

andib

ula

rfu

nct

ion,

die

t

consis

tency,and

maxim

um

inte

rincis

al

openin

gin

cre

ased

sig

nifi

cantly

over

tim

e

85%

had

impro

ved

qualit

yof

life


efciency.56 As the TMJ components are difcult toreach and as the applications of experimental devicesinside the TMJ cause damage to its tissue, the directmethods are not used often.

In Vivo Testing

Some of the earlier studies suggest that the TMJ can,in certain specic combination of muscle forces, be aforce-free joint.13 These studies were contrasted byobservations of Brehnan et al.12 and Hylander45 whoshowed through the direct measurements that consid-erable forces were exerted on the TMJ during occlusionas well as mastication.13 In face of these contraryreports, Breul et al.13 performed stress investigationusingMRI scans of the TMJ in ve different positions ofocclusion. For each position of the condyle, themomentary center of rotation in the head of the man-dible and the tangent attached to the temporal surfacewere determined.13 The line connecting these two pointsindicated the direction of the resulting compressiveforce. Bymeans of the force and the estimated extensionof the area available to the force transmission, the stressdistribution was calculated independently from theposition.13 This analysis showed that the TMJ wassubjected to pressure forces during occlusion as well asduring mastication and it was slightly eccentricallyloaded in all positions of occlusion.13

Korioth and Hannam55 indicated that the differen-tial static loading of the human mandibular condyleduring tooth clenching was task dependent and boththe medial and lateral condylar thirds were heavilyloaded. Huddleston Slater et al.44 suggested that whenthe condylar movement traces coincide during chew-ing, there is compression in the TMJ during the closingstroke. However, when the traces do not coincide, theTMJ is not or only slightly compressed during chew-ing.44 Naeije and Hofman73 used these observations tostudy the loading of the TMJ during chewing andchopping tasks. Mandibular movements of ten healthysubjects were recorded using a jaw movement record-ing system during chewing and chopping of a latex-packed food bolus on the left or right side of themouth. Distances traveled by the condylar kinematiccenters were normalized with respect to the distancestraveled during maximum opening.73 The coincidenceof the opening and closing condylar movement traceswere judged without knowing their origin. The analysisshowed that the distances traveled by the condylarkinematic centers were shorter on the ipsilateral sidethan on the contralateral; and the kinematic centers ofall contralateral joints showed a coincident movementpattern during chewing and chopping.73 The indicationthat the ipsilateral joint is less heavily loaded duringchewing than the contralateral joint may explain why

TA

BL

E4.

co

nti

nu

ed

.

Devic

eS

ourc

e

Popula

tion

Num

ber

of

prior

TM

J

surg

eries

Follo

w-u

pR

esults

Patients

Join

ts

Lore

nzB

iom

et

Quin

n84

50

69

5.7

(range:

013)

3years

22

of

the

patients

have

had

the

join

ts

infu

nct

ion

for

longer

than

3years

Sig

nifi

cantim

pro

vem

entin

pain

inte

nsity,

mouth

openin

g,

&fu

nct

ionaldie

t

capabili

ty.

One

com

plic

ation

required

rem

ovalof

fossa

com

ponent


patients with joint pain occasionally report less painwhile chewing on the painful side.

Hansdottir and Bakke38 evaluated the effect of TMJarthralgia on mandibular mobility, chewing, and biteforce in TMD patients (categorized as disc derange-ments, osteoarthritis, and inammatory disorders)compared to healthy control subjects. The pressurepain threshold (PPT) was measured with an electronicalgometer during slight jaw opening. The PPT valuewas determined as the amount of pressure applied atwhich the sensation of pressure changed to pain.38

Maximum unassisted jaw opening was measured witha ruler at the central incisors.38 Unilateral bite forcewas recorded with a strain-gauge transducer placed onthe mandibular rst molar. The transducer was cov-ered with polyvinyl chloride tubes for protection, andthe force was measured during maximum clenches (2-sduration) as the stored peak values on the digital dis-play.38 The PPT, maximum jaw opening, and bite forcewere signicantly lower in the patients as compared tothat in controls. The patients were also found to havelonger duration of chewing cycles. The bite force andjaw opening in patients were signicantly correlatedwith PPT.38 The most severe TMJ tenderness (i.e.,lowest PPT) and the most impeded jaw function withrespect to jaw opening and bite force were found to bemore severe in the patients with inammatory disor-ders than the patients with disc derangement or oste-roarthritis.38

In Vitro Testing

Indirect techniques such as humanoid roboticapproach, physical modeling using photo-elastic sys-tems, moire fringe technique, and laser holographicinterferometry were tried by researchers to evaluatemandibular biomechanics.8,10,82,90,96 However, thesemethods had limited success due to their ability toevaluate only the surface stress of the model but not itsmechanical properties.

Mechanical Testing

Osteoarthritis of the TMJ is associated with artic-ular cartilage degradation and eventual joint destruc-tion due to collagen damage caused by excessive shearstrain.96,119 As shear strain can result in fatigue,damage, and deformation; data on shear behaviormight help a better understanding of tissue damage inthe articular cartilage.94,96 Previously it was reportedthat the shear stress is very sensitive not only to thefrequency and direction of the loading but also to theamount of shear and compressive strain.94 To char-acterize the dynamic shear properties, Tanaka et al.96

tested the shear response of cartilage of 10 porcine

mandibular condyles using an automatic dynamicviscoelastometer. The results showed that the shearbehavior of mandibular condylar cartilage is depen-dent on the frequency and amplitude of the appliedshear strain suggesting a signicant role of shear strainon the interstitial uid ow within the cartilage.

As TMJs are mostly used dynamically duringhabitual tasks, dynamic analyses seem to be the mostappropriate. Beek et al.8 performed sinusoidal inden-tation experiments and reported that the mechanicalbehavior of disc was nonlinear and time-dependent.Beek et al.10 simulated these experiments using axi-symmetric nite element model and showed that aporoelastic material model can describe the dynamicbehavior of the TMJ disc. Tanaka et al.90 carried out aseries of measurements of frictional coefcients on 10porcine TMJs using a pendulum-type friction tester.The results showed that the presence of the disc reducesthe friction in the TMJ by reducing the incongruitybetween the articular surfaces and by increasing syno-vial uid lubrication. This study highlighted impor-tance of alternatives to discectomy to treat internalderangement and osteoarthritis of the TMJ.

Finite Element Modeling

The nite element modeling has been used widely inbiomechanical studies due to its ability to simulate thegeometry, forces, stresses and mechanical behavior ofthe TMJ components and implants during simulatedfunction.16,52,53,56,7680,82,91,94,98 Experimental or clini-cal validation of theoretical predictions should be thegoal in any simulation endeavor.56 Chen et al.16 per-formed stress analysis of human TMJ using a two-dimensional (2D) nite element model developed frommagnetic resonance imaging (MRI). Although thereare limitations for using a 2D nite element model toestimate stress/strain for a three-dimensional (3D)joint, it is possible to estimate the relative changes ofthe stresses corresponding to a 2D motion of the TMJ.However, the 3D models are more realistic.16

Figure 10 shows the meshes of the TMJ model. Themaximum von Mises stress, seen at the posterior por-tion of the disc, was about 8.0 MPa. The compressivestress (about 8.0 MPa) was much higher than thetensile stress (3.7 MPa). Due to convex nature of thecondyle, the compressive stresses were dominant in thecondylar region whereas the tensile stresses weredominant in the fossa-eminence complex owing to itsconcave nature.16

Although TMJ is a bicondylar joint, very few niteelement simulations have analyzed the dierentresponses of two sides of the joint. Beek et al.9 devel-oped a 3D linear nite element model and analyzed thebiomechanical reactions in the mandible and in the


TMJ during clenching under various restraint condi-tions. Tanaka et al.91,98 developed a 3D model toinvestigate the stress distribution in the TMJ duringjaw opening, analyzing the differences in the stressdistribution of the disc between subjects with andwithout internal derangement. In 2008, Tanakaet al.,93 from the results of nite element model of theTMJ based on magnetic resonance images, suggestedthat increase of the frictional coefcient betweenarticular surfaces may be a major cause for the onset ofdisc displacement.

All of the above mentioned simulations consideredsymmetrical movements of mandible, and the modelsdeveloped only considered one side of the joint. Perez-Palomar and Doblare76 used the combination of thenite element models of the TMJ comprising the twojoints and models for soft components to studyclenching of mandible. However, these movementswere considered to be symmetric. In 2005, Koolstraand van Eijden52 developed a combination of rigid-body model with a nite element model of both discsand the articulating cartilaginous surfaces to simulatethe opening movement of the jaw. Using the samemodel, Koolstra and van Eijden53 performed niteelement analysis to study the load-bearing and main-tenance capacity of the TMJ. The results indicated thatthe construction of the TMJ permits its cartilaginous

structures to regulate their mechanical propertieseffectively by imbibitions, exudation and redistributionof uid; and refreshment of this uid can be performedduring normal function. However, these studies didnot dynamically simulate the TMJ as a two-sided jointincorporating both discs and the most relevant liga-ments and considering a nonsymmetrical movement ofthe jaw.

In 2006, Perez-Palomar and Doblare77 developed a3D nite element model that included not only the twodiscs but also the most important ligaments and thethree body contact between all elements of the joints,and analyzed biomechanical behavior of the softcomponents during a nonsymmetrical lateral excursionof the mandible to investigate possible consequences ofbruxism. The right lateral movement of the mandiblewas performed in which case the right joint becomesthe ipsilateral TMJ (or working side) and the left jointbecomes the contralateral one (or nonworking side)(see Fig. 11).77 The study reported maximum principalstresses in the posterior band of the ipsilateral disc (upto 2.5 MPa) and anterior band of the contralateraldisc; higher compressive stresses (up to 3.2 MPa) in theposterior band and lateral part of the ipsilateral disc(as it was compressed posteriorly against the temporalbone); higher shear stresses (3.2 MPa) in the contra-lateral disc in the lateral part of the posterior band;

FIGURE 10. Meshes of the TMJ model consisting of the disc, condyle and the fossa-eminence complex. Source: Chen et al.16


and higher tensile stress in the contralateral ligamentsthan that in the ipsilateral ligaments.77 This studysuggested that a continuous lateral movement of thejaw may lead to perforations in the lateral part of bothdiscs, conforming with the indications by Tanakaet al.91,94,98 Later, in 2007, Perez-Palomar andDoblare79 suggested that unilateral internal derange-ment is a predisposing factor for alterations in theunaffected TMJ side. However, it would be necessaryto perform an exhaustive analysis of bruxism with theinclusion of contact forces between upper and lowerteeth during grinding.

Nearly 40% of the rear-end impacts during vehicleaccidents produce whiplash injuries.43 Whiplash injuryis considered as a signicant TMD risk factor and hasbeen proposed to produce internal derangements of theTMJ.49,80 However, this topic is still subject todebate.22 In 2008, Perez-Palomar and Doblare,80

published the results of nite element simulations ofthe dynamic response of TMJ in rear-end and frontalimpacts to predict the internal forces and deformationsof the joint tissues. The results, similar to suggested byKasch et al.,49 indicated that neither a rear-end impactat low-velocity nor a frontal impact would producedamage to the soft tissues of the joint suggesting thatwhiplash actions are not directly related with TMDs.80

However; since this study has its own limitations suchas analysis of only one model, for low-velocity impacts,without any restrictions like contact with some com-ponent of the vehicle; there is a need for more reliablenite element simulations to obtain more accuratenumerical results.

Eects of TMJ Surgery

To assess the surgical replacement of TMJ, pre- andpost-surgical in vivo kinetics and kinematics of jaw hadbeen reported in the literature.51,66,118 TMJ recon-struction using the partial or total TMJ prosthetics, in

most cases, improves range of motion and mouthopening in the TMJ patients. However, loss of trans-lational movements of the mandible on the operatedside has been often observed, especially in anteriordirection, owing to various factors like loss of ptery-goid muscle function, scarring of the joint region andthe muscles of mastication.118 Komistek et al.51

assessed in vivo kinematics and kinetics of the normal,partially replaced, and totally replaced TMJs. Underuoroscopic surveillance, the subjects were asked toopen and close their jaw on a force transducer placedbetween their molars nearest the joint. A data acqui-sition system recorded the bite force. The kinematicdata derived from uoroscopy and the data outputfrom the force transducer were input into a mathe-matical model of the human jaw to determine thekinetics of the TMJ.51 Less translation was reported inthe implanted fossa and total TMJ joints than in thenormal joints. The study suggests that total TMJimplants only rotate and do not translate; and themuscles do not apply similar forces at the joint whenthe subject has a total TMJ implant, compared to asubject who has a normal, healthy TMJ.

In the post-TMJ replacement follow-up studies,Mercuri et al.67 obtained the measures of mandibularinterincisal opening and lateral excursions from directmeasurements using the measuring scale provided inthe survey, mailed to patients with instructions as to itsuse. The assessment showed a 24% and a 30%improvement in mouth opening after 2 years and10 years, respectively. On the other hand, at 2 yearspost-implantation there was a 14% decrease in leftlateral excursion and a 25% decrease in right lateralexcursion from the pre-implantation data.65,67 As theloss of lateral jaw movement is a great disadvantage tototal TMJ prosthesis replacement, a future prosthesismust allow some lateral translation as well as theanterior movement of mandible on the operated sidewhen the mouth is opened.105

Most studies have collected the data by subjectivesurveys or mandibular incisor motion rather thancondylar motion. Yoon et al.118 followed a kinematicmethod that tracks the condylar as well as incisorspath of the TMJ motion. An electromagnetic trackingdevice and accompanying software were used to recordthe kinematics of the mandible relative to temporalbone during openingclosing, protrusive, and lateralmovements.118 This was achieved using an electro-magnetic sensor attached each to the upper and lowerplastic dental brackets, a magnetic source, and a digi-tizing probe used to locate anatomic points for deninganatomic coordinate systems and landmarks of inter-est.118 Mean linear distance (LD) of incisors duringmaximal mouth opening for the surgical patient groupwas 18% less than the normal subjects. Mean LD for

FIGURE 11. Schematic diagram of a lateral movement of themandible: (I) ipsilateral condyle, (C) contralateral condyle.Source: Perez-Palomar and Doblare.77


mandibular right and left condyles was symmetrical inthe normal group; however, in the surgical patientgroup, measurements for operated condyle and unop-erated condyle were asymmetric and reduced as com-pared with normal subjects by 57 and 36%,respectively (see Fig. 12).118 In protrusive movements,operated and unoperated condyles of surgical patientstraveled less and signicantly differently as comparedwith condyles of normal subjects, which moved almostidentically. For the surgical patient group, the meanincisor LD away from the operated side and towardthe operated side as compared with the normal groupincisors were reduced by 67 and 32%, respectively.118

Various research articles on the TMJ underline theimportance of biomechanical analysis of the naturaljoint to better understand the structural and functionalaspects; and of the reconstructed joint to assess theimplant function and performance. Numerous workshave focused primarily on calculating absolute mag-nitude of TMJ loading with nite element models.Most of the methods reported in the literature havecertain limitations due to the complex nature of thejoint and also due to certain limitations of the tech-niques and software packages used for modeling andanalysis. The reported magnitudes of TMJ loadingdier signicantly from one another because of dif-ference in simulation conditions. The direct measure-ments also indicate a large discrepancies.92 Due tothese reasons; there is currently no universally agreed-upon value of TMJ loading.92 Therefore, a morecomprehensive biomechanical analysis of the TMJ isessential for better understanding of the movements,applied forces, and resultant stresses in the naturaland/or articial joint components.

CONCLUSION

The temporomandibular disorder (TMD) symp-toms are exhibited by a large portionnearly 20 to

25%of the population and, hence, this problemshould be looked at more fully. Though majority of theTMD conditions can be successfully managed by var-ious non-surgical and less-invasive treatments, jointreplacement becomes the only potential remedy forcertain TMD conditions. Assessing the outcomes ofthe FDA approved TMJ implants in a controlledcomparative manner, and evaluating biological char-acteristics of failed implants compared to controls areessential to determine mechanism of implant failure.The biomechanical analysis is a useful tool tounderstand the normal function, predict changes dueto alterations, and propose methods of articialintervention for the treatment of diseased or damagedTMJ. The patient-specic computer models can beused to estimate non-measurable TMJ loads throughnite element analysis to understand the underlyingmechanisms of TMD, necessary for developing andimproving the methods to prevent, diagnose and curejoint disorders.

REFERENCES

1Abubaker, A. O., P. C. Hebda, and J. N. Gunsolley.Effects of sex hormones on protein and collagen contentof the temporomandibular joint disc of the rat. J. OralMaxillofac. Surg. 54:721727, 1996. doi:10.1016/S0278-2391(96)90690-4.2Al-Ani, M. Z., S. J. Davies, R. J. M. Gray, P. Sloan, andA. M. Glenny. Stabilisation splint therapy for temporo-mandibular pain dysfunction syndrome. Cochrane Data-base of Systematic Reviews. Issue 1, 2004. Art. No.: CD002778. doi:10.1002/14651858.CD002778.pub2. Retrievedon 01/22/2009, from http://mrw.interscience.wiley.com/cochrane/clsysrev/articles/CD002778/pdf_fs.html.3Alomar, X., J. Medrano, J. Cabratosa, J. A. Clavero,M. Lorente, I. Serra, J. M. Monill, and A. Salvador.Anatomy of the temporomandibular joint. Semin. Ultra-sound CT MRI 28:170183, 2007.4Alpaslan, C., M. F. Dolwick, and M. W. Heft. Five-yearretrospective evaluation of temporomandibular jointarthrocentesis. Int. J. Oral Maxillofac. Surg. 32:263267,2003. doi:10.1054/ijom.2003.0371.5American Association of Oral and Maxillofacial Sur-geons (AAOMS). The temporomandibular joint (TMJ).Retrieved on 10/14/2007, from http://www.aaoms.org/tmj.php.6Bakke, M., M. Zak, B. L. Jensen, and F. K. Pedersen.Orofacial pain, jaw function, and temporomandibulardisorders in women with a history of juvenile chronicarthritis or persistent juvenile chronic arthritis. Oral Surg.Oral Med. Oral Pathol. Oral Radiol. Endod. 92:406414,2001. doi:10.1067/moe.2001.115467.7Barbick, M., M. F. Dolwick, S. Rose, and S. Abra-mowicz. Adaptibility of Biomet Lorenz tmj prosthesis tojoints that were previously treated with the tmj conceptscustom joint prosthesis. Oral Med. Oral Pathol. OralRadiol. Endod. 106(2):e17, 2008. doi:10.1016/j.tripleo.2008.05.058.

FIGURE 12. Condyle kinematics healthy and diseased TMJsduring openingclosing and protrusive movements. Source:Yoon et al.118


8Beek, M., M. P. Aarnts, J. H. Koolstra, A. J. Feilzer, andT. M. G. J. van Eijden. Dynamical properties of thehuman temporomandibular joint disc. J. Dent. Res.80:876880, 2001. doi:10.1177/00220345010800030601.9Beek, M., J. Koolstra, L. van Ruijven, and T. van Eijden.Three dimensional nite element analysis of the cartilag-inous structures in the human temporomandibular joint.J. Dent. Res. 80:19131918, 2001. doi:10.1177/00220345010800101001.

10Beek, M., J. H. Koolstra, and T. M. G. J. van Eijden.Human temporomandibular joint disc cartilage as aporoelastic material. Clin. Biomech. 18:6976, 2003. doi:10.1016/S0268-0033(02)00135-3.

11Biomet Microxation. Retrieved on 02/04/2009, fromhttp://www.lorenzsurgical.com/downloads/BMF-7014%20TMJBro%20(d)4Final.pdf.

12Brehnan, K., R. L. Boyd, J. Laskin, C. H. Gibbs, andP. Mahan. Direct measurement of loads at the temporo-mandibular joint in macaca arctoides. J. Dent. Res. 60:18201824, 1981.

13Breul, R., G. Mall, J. Landgraf, and R. Scheck. Biome-chanical analysis of stress distribution in the humantemporomandibular-joint. Ann. Anat. 181:5560, 1999.doi:10.1016/S0940-9602(99)80090-9.

14Campbell, J. H., M. S. Courey, P. Bourne, et al. Estrogenreceptor analysis of human temporomandibular disc.J. Oral Maxillofac. Surg. 51:1101, 1993.

15Chase, D. C., J. W. Hudson, D. A. Gerard, R. Russell,K. Chambers, J. R. Curry, J. E. Latta, and R. W. Christen-sen. The Christensen prosthesis: a retrospective clinicalstudy. Oral Surg. Oral Med. Oral Pathol. 80:273278, 1995.

16Chen, J., U. Akyuz, L. Xu, and R. M. V. Pidaparti. Stressanalysis of the human temporomandibular joint.Med. Eng.Phys.20:565572, 1998. doi:10.1016/S1350-4533(98)00070-8.

17Chung, S. C., Y. K. Kim, and H. S. Kim. Prevalence andpatterns of nocturnal bruxofacets on stabilization splints intemporomandibular disorder patients. Cranio 18:92, 2000.

18Cleveland Clinic. Health information. Retrieved on 09/21/2007, from http://www.clevelandclinic.org/health/.

19Dao, T. T., and G. J. Lavigne. Oral splints: the crutchesfor temporomandibular disorders and bruxism? Crit. Rev.Oral Biol. Med. 9:345361, 1998. doi:10.1177/10454411980090030701.

20Dental Care Ottawa. Retrieved on 04/09/2008, from http://www.dentalcareottawa.com/Smile%20Spa%20Images/EQUIPMENT%20PICTURES/SoftSplint.gif.

21Detamore, M. S., and K. A. Athanasiou. Structure andfunction of the temporomandibular joint disc: implica-tions for tissue engineering. J. Oral Maxillofac. Surg.61(4):494506, 2003. doi:10.1053/joms.2003.50096.

22Detamore, M. S., K. A. Athanasiou, and J. Mao. A call toaction for bioengineers and dental professionals: directivesfor the future of TMJ bioengineering. Ann. Biomed. Eng.35(8):13011311, 2007. doi:10.1007/s10439-007-9298-6.

23Dingworth, D. J., L. M. Wolford, R. M. Talwar,et al. Comparison of two total joint prosthesis systemsused for TMJ reconstruction. J. Oral Maxillofac. Surg.56(Suppl. 4):59, 1998.

24Dutton, M. Orthopaedic Examination, Evaluation, &Intervention. New York: McGraw Hill, 2004.

25Eberhard, D., H. P. Bantleon, and W. Steger. The efcacyof anterior repositioning splint therapy studied by mag-netic resonance imaging. Eur. J. Orthod. 24:343352,2002. doi:10.1093/ejo/24.4.343.

26Farrar, W. B., and W. L. McCarty, Jr. The TMJ dilemma.J. Ala. Dent. Assoc. 63:19, 1979.

27Fields, R. T., and L. M. Wolford. The osseointegration ofMitek mini anchors in the mandibular condyle. J. OralMaxillofac. Surg. 59:14021406, 2001. doi:10.1053/joms.2001.28268.

28Forssell, H., and E. Kalso. Application of principles ofevidence-based medicine to occlusal treatment for tem-poromandibular disorders: are there lessons to be learned?J. Orofac. Pain 18:922, 2004; discussion 2332.

29Forsell, H., E. Kalso, P. Koskela, R. Vehmanen,P. Puukka, and P. Alanen. Occlusal treatments in tem-poromandibular disorders: a qualitative systematic reviewof randomized controlled trials. Pain 83:549560, 1999.doi:10.1016/S0304-3959(99)00160-8.

30Fricton, J. R., J. O. Look, E. Schiffman, and J. Swift. Long-term study of temporomandibular joint surgery with allo-plastic implants compared with nonimplant surgery andnonsurgical rehabilitation for painful temporomandibularjoint disc displacement. J. Oral Maxillofac. Surg.60(12):14001411, 2002. doi:10.1053/joms.2002.36091.

31Gadd, A., and T. Goswami. Temporomandibular disorderand joint replacement. Biomed. Mater., Paper No. BMW-RANL-7PJRW3, 2009.

32Gerard, D. A., and J. W. Hudson. The Christensen tem-poromandibular joint prosthesis system: an overview.TMJournal, 2002. Retrieved on 09/20/2007, from http://tmjournal.com/library/CP-009.pdf.

33Glaros, A. G., Z. Owais, and L. Lausten. Reduction inparafuncational activity: a potential mechanism for theeffectiveness of splint therapy. J. Oral Rehabil. 34:97104,2007. doi:10.1111/j.1365-2842.2006.01660.x.

34Glass, E. G., A. G. Glaros, and F. D. McGlynn. Myo-fascial pain dysfunction: treatments used by ADA mem-bers. Cranio 11:2529, 1993.

35Going, R. B., Jr Arthroscopy in the Conservative Man-agement of TMD. Temporomandibular Disorders. 2nd ed.New York: Churchill Livingstone, pp. 217236, 1994.

36Gray, R. J. M., S. J. Davies, and A. A. Quayle. Tempo-romandibular Disorders: A Clinical Approach. London:British Dental Association, 1995.

37Halliwell, B., and J. M. C. Gutteridge. Free Radicals inBiology and Medicine. Oxford: Clarendon Press, 1995.

38Hansdottir, R., and M. Bakke. Joint tenderness, jawopening, chewing velocity, and bite force in patients withtemporomandibular joint pain and matched healthy con-trol subjects. J. Orofac. Pain 18:108113, 2004.

39Haruki, S. Stored tendon allograft for TMJ disc replace-ment following discectomy in rabbit. J. Oral Maxillofac.Surg. 63(8):98, 2005.

40Hebert, L.A.OvercomingTMJ: There isHope. Greenville,ME: IMPACC USA, 1996.

41Hibi, H., and M. Ueda. Body posture during sleep anddisc displacement in the temporomandibular joint: a pilotstudy. J. Oral Rehabil. 32:8589, 2005. doi:10.1111/j.1365-2842.2004.01386.x.

42Homandberg, G. A., R. Meyers, and D. L. Xie. Fibro-nectin fragments cause chondrolysis of bovine articularcartilage slices in culture. J. Biol. Chem. 267:3597, 1992.

43Huang, S. C. Dynamics modeling of human temporo-mandibular joint during whiplash. Bio-Med. Mater. Eng.9:233241, 1999.

44Huddleston Slater, J. J., C. M. Visscher, F. Lobbezoo,and M. Naeije. The intra-articular distance within the TMJ


during free and loaded closing movements. J. Dent. Res.78:18151820, 1999. doi:10.1177/00220345990780120801.

45Hylander, L. W. An experimental analysis of temporo-mandibular joint reaction force in macaques. Am. J. Phys.Anthropol. 51:433456, 1979. doi:10.1002/ajpa.1330510317.

46Ide, Y., K. Nakazawa, T. Hongo, J. Taleishi, andK. Kamimura. Anatomical Atlas of the Temporoman-dibular Joint. Chicago: Quintessence Pub. Co., 1991.

47Kalamir, A., H. Pollard, A. L. Vitiello, and R. Bonello.TMD and the problem of bruxisma review. J. BodyworkMov. Ther. 11:183193, 2007. doi:10.1016/j.jbmt.2006.11.006.

48Kang, H., G. Bao, and S. Qi. Biomechanical responses ofhuman temporomandibular joint disc under tension andcompression. Int. J. Oral Maxillofac. Surg. 35:817821,2006. doi:10.1016/j.ijom.2006.03.005.

49Kasch, H., T. Hjorth, P. Svensson, L. Nyhuus, and T. S.Jensen. Temporomandibular disorders after whiplash in-jury: a controlled, prospective study. J. Orofac. Pain16(2):118128, 2002.

50Kiehn, C. L., J. D. Des Prez, and C. F. Converse. A newprocedure for total temporomandibular joint replacement.Plast. Reconstr. Surg. 53:221226, 1974. doi:10.1097/00006534-197402000-00022.

51Komistek, R. D., D. A. Dennis, J. A. Mabe, and D. T.Anderson. In vivo kinetics and kinematics of the normaland implanted TMJ. J. Biomech. 31:13, 1998. doi:10.1016/S0021-9290(98)80028-6.

52Koolstra, J., and T. M. G. J. van Eijden. Combined nite-element and rigid-body analysis of human jaw jointdynamics. J. Biomech. 38:24312439, 2005. doi:10.1016/j.jbiomech.2004.10.014.

53Koolstra, J., and T. M. G. J. van Eijden. Prediction ofvolumetric strain in the human temporomandibular jointcartilage during jaw movement. J. Anat. 209:369380,2006. doi:10.1111/j.1469-7580.2006.00612.x.

54Koolstra, J., and T. M. G. J. van Eijden. Viscoelasticbehavior of the temporomandibular joint disc duringmasticatory dynamics. J. Biomech. 39(Suppl. 1):49, 2006.doi:10.1016/S0021-9290(06)83740-1.

55Korioth, T. W. P., and A. G. Hannam. Mandibular forcesduring simulated tooth clenching. J. Orofac. Pain 8(2):178189, 1994.

56Korioth, T. W. P., and A. Versluis. Modeling themechanical behavior of the jaws and their related structuresby nite element (FE) analysis. Crit. Rev. Oral Biol. Med.8(1):91104, 1997. doi:10.1177/10454411970080010501.

57Kreiner, M., E. Betancor, and G. T. Clark. Occlusal sta-bilization appliances. Evidence of their efcacy. J. Am.Dent. Assoc. 132:770777, 2001.

58Kubein-Messenburg, D., H. Nagerl, and J. Fanghanel.Elements of a general theory of joints. Anat. Anz. 170:301308, 1990.

59Laskin, D. M. Indications and Limitations of TMJ Sur-gery. TMDs: Temporomandibular Disorders: An Evi-dence-Based Approach to Diagnosis and Treatment.Chicago: Quintessence, 2006.

60Marbach, J. J., and K. G. Raphael. Future directions inthe treatment of chronic musculoskeletal facial pain: therole of evidence-based care. Oral Surg. Oral Med. OralPathol. Oral Radiol. Endod. 83:49183, 1997. doi:10.1016/S1079-2104(97)90110-4.

61Mayo Foundation for Medical Education and Research.Retrieved on 10/10/2007, from http://www.mayoclinic.org/tmj/.

62Mehra, P., and L. M. Wolford. The Mitek mini anchor forTMJ disc repositioning: surgical technique and results.Int. J. Oral Maxillofac. Surg. 30:497503, 2001. doi:10.1054/ijom.2001.0163.

63Mercuri, L. G. The use of alloplastic prostheses for tem-poromandibular joint reconstruction. J. Oral Maxillofac.Surg. 58:7075, 2000. doi:10.1016/S0278-2391(00)80020-8.

64Mercuri, L. G., F. A. Ali, and R. Woolson. Outcomes oftotal alloplastic replacement with periarticular autogenousfat grafting for management of reankylosis of the tem-poromandibular joint. J. Oral Maxillofac. Surg. 66:17941803, 2008. doi:10.1016/j.joms.2008.04.004.

65Mercuri, L. G., N. R. Edibam, and A. Giobbie-Hurder.Fourteen-year follow-up of a patient-tted total tempo-romandibular joint reconstruction system. J. Oral Max-illofac. Surg. 65:14401448, 2007. doi:10.1016/j.joms.2007.04.004.

66Mercuri, L. G., N. R. Edibam, and A. Giobbie-Hurder.Long-term outcomes after total alloplastic temporoman-dibular joint reconstruction following exposure to failedmaterials. J. Oral Maxillofac. Surg. 62(9):10881096,2004. doi:10.1016/j.joms.2003.10.012.

67Mercuri, L.G., L.M.Wolford, B. Sanders, et al. Long-termfollow-up of the CAD/CAM patient tted total temporo-mandibular joint reconstruction system. J. Oral Maxillo-fac. Surg. 60:14401448, 2002. doi:10.1053/joms.2002.36103.

68Milam, S. B. Failed implants and multiple operations.Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod.83(1):156162, 1997. doi:10.1016/S1079-2104(97)90107-4.

69Milam, S. B. The process of lubrication impairment and itsinvolvement in temporomandibular joint disc displace-ment: a theoretical concept (Discussion). J. Oral Maxillo-fac. Surg. 59:45, 2001. doi:10.1053/joms.2001.19282.

70Milam, S. B., and J. P. Schmitz. Molecular biology oftemporomandibular joint disorders: proposed mecha-nisms of disease. J. Oral Maxillofac. Surg. 53:14481454,1995. doi:10.1016/0278-2391(95)90675-4.

71Milam, S. B., G. Zardeneta, and J. P. Schmitz. Oxidativestress and degenerative temporomandibular joint disease:a proposed hypothesis. J. Oral Maxillofac. Surg. 56:214223, 1998. doi:10.1016/S0278-2391(98)90872-2.

72Molinari, F., P. F. Manicone, L. Raffaelli, R. Raffaelli,T. Pirronti, and L. Bonomo. Temporomandibular jointsoft-tissue pathology. I: Disc abnormalities. Semin.Ultrasound CT MRI 28(3):192204, 2007.

73Naeije, M., and N. Hofman. Biomechanics of the humantemporomandibular joint during chewing. J. Dent. Res.82(7):528531, 2003. doi:10.1177/154405910308200708.

74Nitzan, D. W. Intraarticular pressure in the functioninghuman temporomandibular joint and its alteration byuniform elevation of the occlusal plane. J. Oral Maxillofac.Surg. 52:671, 1994. doi:10.1016/0278-2391(94)90476-6.

75Pellizoni, S. E. P., M. A. C. Salioni, Y. Juliano, A. S.Guimaraes, and L. G. Alonso. Temporomandibular jointdisc position and conguration in children with functionalunilateral posterior crossbite: a magnetic resonanceimaging evaluation. Am. J. Orthod. Dentofac. Orthoped.129(6):785793, 2006.

76Perez-Palomar, A., and M. Doblare. The effect of collagenreinforcement in the behavior of the temporomandibularjoint disc. J. Biomech. 39:10751085, 2006. doi:10.1016/j.jbiomech.2005.02.009.

77Perez-Palomar, A., and M. Doblare. Finite elementanalysis of the temporomandibular joint during lateral


excurision of the mandible. J. Biomech. 39:21532163,2006. doi:10.1016/j.jbiomech.2005.06.020.

78Perez-Palomar, A., and M. Doblare. An accurate simu-lation model of anteriorly displaced TMJ discs with andwithout reduction. Med. Eng. Phys. 29:216226, 2007.doi:10.1016/j.medengphy.2006.02.009.

79Perez-Palomar, A., and M. Doblare. Inuence of unilat-eral disc displacement on the stress response of thetemporomandibular joint discs during opening and mas-tication. J. Anat. 211:453463, 2007.

80Perez-Palomar, A., and M. Doblare. Dynamic 3D FEmodelling of the human temporomandibular joint duringwhiplash.Med. Eng. Phys. 30:700709, 2008. doi:10.1016/j.medengphy.2007.07.009.

81Pierce, C. J., R. J. Weyant, H. M. Block, and D. C. Nemir.Dental splint prescription patterns: a survey. J. Am. Dent.Assoc. 126:248, 1995.

82Pileicikiene, G., E. Varpiotas, R. Surna, and A. Surna.The three dimensional model of the human masticatorysystem, including the mandible, the dentition and thetemporomandibular joints. Stomatologija Balt. Dent.Maxillofac. J. 9:2732, 2007.

83Quinn, P. D. Alloplastic reconstruction of the temporo-mandibular joint. Sel. Read. Oral Maxillofac. Surg. 7(5):123, 1999.

84Quinn, P. D. Lorenz prosthesistotal temporomandibu-lar joint reconstruciton. Oral Maxillofac. Surg. Clin.North Am. 12(1):93104, 2000.

85Raphael, K. G., J. J. Marbach, J. J. Klausner, M. F.Teaford, and D. K. Fischoff. Is bruxism severity a pre-dictor of oral splint efcacy in patients with myofascialface pain? J. Oral Rehabil. 30:1729, 2003. doi:10.1046/j.1365-2842.2003.01117.x.

86Schwartz, H. C., and R. W. Kendrick. Internal derange-ment of the temporomandibular joint: description ofclinical syndromes. Oral Surg. Oral Med. Oral Pathol.58(1):2429, 1984. doi:10.1016/0030-4220(84)90358-X.

87Solberg, W. K., M. W. Woo, and J. B. Houston. Preva-lence of mandibular dysfunction in young adults. J. Am.Dent. Assoc. 98:2534, 1979.

88Speculand, B., R. Hensher, and D. Powell. Total pros-thetic replacement of the TMJ: experience with two sys-tems 19881997. Br. J. Oral Maxillofac. Surg. 38(4):360369, 2000. doi:10.1054/bjom.2000.0338.

89Ta, L. E., J. C. Phero, S. R. Pillemer, H. Hale-Donze,N. McCartney-Francis, A. Kingman, M. B. Max, S. M.Gordon, S. M. Wahl, and R. A. Dionne. Clinical evalu-ation of patients with temporomandibular joint implants.J. Oral Maxillofac. Surg. 60(12):13891399, 2002. doi:10.1053/joms.2002.36089.

90Tanaka, E., D. A. Dalla-Bona, T. Iwabe, N. Kawai,E. Yamano, T. van Eijden, M. Tanaka, M. Miyauchi,T. Takata, and K. Tanne. The effect of removal of the discon the friction in the temporomandibular joint. J. OralMaxillofac. Surg. 64:12211224, 2006. doi:10.1016/j.joms.2006.04.017.

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