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The Pterygoid Plate Implant:A Solution for Restoring thePosterior Maxiiia

Stuart L Groves, DDS. PviS'

Ttie sinus cavity ond ttie rarefied posterior maxillary bone make it difficultto place Impiants posterior ta the first premoiar. Placement of an implantinto ttie pterygaid plate area has been used to overcome these anatomicaOstacies. allawing successtui restoration at the area. Sixty-four implantswere pioced in 49 patients. Forty-three impiants are in function. There havebeen 7 foiiures. The technique is described and a typical case is iilustrated.(Int J Periodont Rest Denf 1994:14:513-523.)

•Private practice in oiai surgery, Büri<e. Virginia.

Reprint requests: Dr Stuart L. Graves, 5206 Lyngate CoLfrt. Burke,

Virginia 22015.

Restoring fhe dentition in fheposterior maxilla can be verychallenging.'"-* Firsf and sec-ond molars tend to be thefeeth initially lost to pathoses."Often implants are not placedin this region because of thepoor quality of bone or pneu-matlzafion of fhe sinus.^•''Piacemenf of a cantileveredresforafion or augmentationwifh a sinus liff has becomeconvenfional freatment for themaxilla.'"^" Placement of apterygoid plate fixture is analfernafive fhaf may be usedwith predictable success," Thisimplant passes through a pillarof bone composed of the max-illa, pyramidal process of fhepalafine bone, and the ptery-goid process of fhe sphenoid'^(Figs la to lc).

Anatomy

The tuberosity of the maxilla iscomposed of type III and typeIV cancellous bone. The pyra-midal process of fhe polafine

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Mandibular f.

StTloiiI aro'

Fig la (abave) Three separate bohes are ¡cined together in the pferygoid region-the posterior moxillo, the pyramidal process of the palafine. and the pterygoidprocess of the sphenoid.

Fig lb (top right) The ptetygoid fossd is bordered Oy the mediah and lateral ptery-goid piafes. Branches of fhe posferiot superior aiveoior nerve pass through thisregion. There are no ma/or arteries or veins The thickesf Puffress of bone ¡s medial fothe alveolar ridge.

Fig Ic (bottom right) The ideol piocement of fhe impianf is from midfuberosity infothe pterygoid fossa The hamuiar process is just medidi to fhe apex.

and fhe pterygoid process ofthe sphenoid ore dense corfi-coi bone. An ideally plocedimpionf will pass completelythrough the pterygoid processinto the pferygoid fossa (Figs 2ato 2c).

No anotomicolly significantsfrucfures are found in thisregion. A branch of fhe posteri-or superior aiveoior nerve pass-es befween fhe pferygoidpiates.'^ The pterygoid musclesoccupy the majority of spocebefween fhe plates. The inter-

nal maxillary artery crosses 1cm superior to fhe pterygo-moxiliary suture as it enters fhepterygopolat ine tossa. Themean disfance from fhe inferiorpterygomaxillary suture to thisartery is 25 mm."* In a Le Fort Iosfeotomy, the pferygoidplotes are sectioned trom thepalafine bane at the pterygo-maxillary sufure (Figs 3a ond3b). This is considered a safeareo becouse of fhe lack ofvital structures (Figs 4a and 4b).

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Fig 2a Tfie ideal placement of thepterygoid plate fixture is showing. Theanguiotion and position are deter-mined by the size at tne sinus cavity.

Fig 2b The typical position ot 20-mmimpiant is shown on o modei witti thelaterol tuberasity and iat&ial pterygoidplate remaved. Tfie fixture extends fromthe second molar region through thepterygoid buttress of bone inta thefossa.

Fig 2c The cephaiomerric radiographShaws the relotionship of the implant tathe facial skeleton. The ape*- extendspast the pterygoid buttress of bone.

Fig 3o (left) The internal maxiliaryartery courses superior and lateral tathe pterygomaxiliary suture and termi-nates in the sphenopalafine tosso.

Fig 3b (rignt) tn the Le Fort I osteoto-my, the separating chisel is movedthrough the pterygomaxiliary suture. Aslong as the chisel is kept below thesphenapalatine fossa, no yitol struc-tures are threatened.

Fig 4a The average height of thepterygoid maxillary suture IS 15 mmSuperior to this level, the sphenopala-tine fassa cantains fhe maxiilary nerveand ferminal branches ot the internaimaxiliary artery.

Fig 4b The distance from the secondmoiar area to the pterygoid buttress is15 mm The distance fram the sameorea at the tuberosity to the cranialbase is mare than 40 mm.

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The thici<est orea of sup-porfing bone is iaoafed in fhemiddie parf ot the pterygoidprocess between the piates.Thiis is 3 to 4 mm medial fo tfieaiveoiar ridge; an implant musttherefore be angied siightlymedially to bisect this densejuncture ot bone In the pfery-goid region. Thie fiamularprocess on the mediai ptery-goid plate is easily palpable inti^e oropharynx. The impiant isplaced just iateral to this i<eyiandmark. The average vi/idffiof dense bone at the junctureof the palatine and sphenoidprocesses is ó mm (Figs 5a and5b). It an implant is passedthrough this pillar of bone at anangie of 45 degrees, it incorpo-rates 8 to 9 mm of dense corti-cal bone. Frequently the screwaccess hoie w\\\ be tound in tinecentrol fossa ot the first molar(Figo),

Fig ó Ttie amounf ot bone surround-ing a !O-mm implant is compared tothat surrounding a 20-mm pterygoidplate implant. The screw access areafor both IS the ocdusal aspect of thefirst molar

Fig 5a (above) An implant with o 45-degree angle thot posses through thepterygaid buttress engages 8 mm ofdense cortical bone. The apex pra-trudes 2 mm Into the fossa.

Fig 5b (right) The thickness of thepferygoid buttress is 6 mm.

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Fig lu Radiograph lowing typicalpterygoid piate implont.

Fig 7b (left) The impiant is incorporat-ed info o four-unit fixed prosfhesis. Theview of fhe sfonddrd dbutmenf exitinggingiva reveots healthy tissue aroundI ne obutment.

Fig 7c (right) Tiie buccal view of fhefour-unit prosfhesis is shown.

Preoperatlve evaluation

A high-quality panoramic radi-ograph is usually all that is nec-essary to evaluóte the arearadiographically. Considerationshould be given to the degreeof pneumatization of the sinus,the shape of the tuberosity,and the relative density of thebone of the pterygoid plates.Knife-edged maxiilory ridgesare rarely o problem in this

area, becouse the maxiilatends to increase in width as itapproaches the second ondthird molars. Computerizedtomography provides a clearerpicture, but has been used bythe outhor only in patients withsevere maxillary atrophy. Thesize of the sinus determinesboth the angle ond anteropos-terior placement of the implant(Figs 7a to 7c).

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f ig Sa Preoperatively, the sinus ismoderately pneumatized in ft\e leftmoxillo, The ieft second premolar anafirst molar were extracted 1 mantn priorto implont placement.

Surgical technique

The surgical fechnique is shownin Figs 8a fo 8h, Locol anesthesiais achieved with lidocoine 2%with epinephrine 1:100,000, Infil-trations are made in thegreater polafine area of fhesoff palate and the lateral buc-cal vestibule, and posterolater-al to the tuberosity,

A full-thickness incision ismade a few millimeters medialto the crest of fhe tuberosifyfrom fhe pterygomaxi l laryfissure to the premolarregion, A relaxing incision isplaced anteriorly, A muco-periosteol f lap is elevafedbuccally, exposing fhe fuber-osify in ifs enfirefy. A "labialveneer" sfenf is preferredfor the flexibility if affords the

surgeon in location and angleof the fixture. Because of the45- fo 50-degree angulation ofthe fixfure, the crew accessarea will be in the central fossoof the firsf molar. The implantangle is determined by fhe tloorof the sinus and fhe verticalheight of bone in the tuberosi-ty. The normal tendency whenthis procedure is attempted forthe firsf fime is to place the Hxfuretoo far anteriorly wifh foo littlehorizontal angulation.

A guide hole 3 to 4 mmdeep is placed in the secondmolar area of the tuberositywith a No, 4 or 6 round bur. Toestablish the final depth andangle of the fixture placement,a long-shaft 2-mm twist drill ona bur extension is used. Thehamular process is palpated

and the drill is directed 5 mmlaterally at approximately 45degrees to the occlusol plane.This process is the primaryguide used to determine thethickest part ot fhe pterygoidpillar of bone. It the correctpath is followed, the twist drillwill encounter dense corticalbone of fhe pferygomaxillarysufure area at 10 to 14 mmdeep. The drill will slow downnoticeobly, then speed upagain affer it passes throughthe pteiygoid process. The drillis removed and a probe isp laced in fhe hole in anattempf fo feel fhe sinus cavity.If the floor of fhe sinus has beenperforafed, a new site must belacated at least 3 mm posteriorto the previous one. The long-shaft pilot and twist drills are

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Fig 8b A depfh prabe is piaced onthe tiamular process to fielp ih the ori-entation Ttie ideal impiaht placementis 5 mm iaterol fo this process. This struc-ture is frequently palpated during thedrilling phase.

Fig 6c The standard incision is madefrom the posterior tuberosify, stighfiymedial fo the alveolar crest ta ffie pre-molar area.

Fig 8d A guide hole is placed with theaid of a lobioi veneer sfenf.

Fig Be (ieft) A long-shaft 2-mm twistdrill on a bur extension is sunk throughthe pterygoid buttress.

FigSf (right) An 18-mm implant ispiaced without counfersini<ing.

FigBg (leff) Final placement of theirriplani with cover screw is shown. Theimplant heod is flush wifh fhe corlicolbone of the tuberosity.

Fig 8ti (right) The implahf is parallel fothe flaor af the sinus and protrudesthrough fhe pferygoid process of sphe-noid bohe.

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used similarly. It is imporfanf fopass compietely through thepterygoid plate buttress ofbone. There is no oounfersink-ing.

After fhe impianf site hasbeen completely prepared, adepth probe with an eniargedtip is used to explore fhe siteand determine the length ofthe impiant fo be used. Care istaken to check that the sinushas not been perforated. Theimpianf shouid pass compiete-ly through the pterygoidprocess fo esfablish bicorfioalstabiiizafion,

A fixture that wiil extend 3fo 4 mm past the pferygoidprocess and into the fossa isselected. This is usually a seif-fapping 15- to 20-mm thread-ed implant, if is easiiy placedwith a long fixture mount. Theimplant should be seated sothat the hex head is buried inthe cortex of fhe fuberosity. Acover screvi/ is then piaced.

Soft tissue piasty or tuberosi-fy reduction is often performedat ciosure. The incision is closedwifh 3-0 resorbabie suture on aNo. ó cutting needle with con-tinuous suturing,

The patient is allowed towear the prosthesis immediate-ly affer surgery. The denfure isrelieved in fhe tuberosity to pre-vent premoture loading. Thepatient is placed on antibioticsfor 1 week. Penicillin 500 mgfour times per day is preferred.if the patient is sensitive to peni-ciliin, cephaiosporin or clin-damycin can be substituted.

At reentry in 6 months, theimpiant is reverse torque tested(10 Ncm) fo ensure osseoinfe-gration. A standard abutmentis usually placed. Where theangulation has exceeded óOdegrees, an angled abufrmenfhas been used.

Discussion

To date, 64 pterygoid platefixtures have been piaced in 49patients. Forty-three arepresently loaded and in func-tion. There have been 7 faii-ures, All failures were obviousat fhe second stage, whentheir mobility was tested, Noneof fhe impianfs has f a i l e dunder function. This wouid indi-cate that implants, uniiketeeth, respond weii to nonaxiailoading. The occiusai plane, inrelation fo fhe impiant axis,seems to exert no significant

influence on the peri-implantheaifh or stabiiity.'^

Advantages of pferygoid plateimpianfs

1. No bone graft is necessary.

2. integrity of fhe sinus is pre-setved,

3. The architecture of thesinus (eg, septafed sinus) israreiy a technical probiem,

4. The outcome is predicfabiysuccessful (of 5Ó fixturespiaced, six have beenunsuccessful).

5. The anterior-posterior spreadis maximized; fhere is noneed for cantilevering.

6. The fixture is pioced at aneasy angle to restore.

7. There is iittie morbidity.

8. Tuberosify reduction orother tissue plasfy can bedone simultaneously.

9. Treatment fime is shorterthan wifh sinus grafting.

Disadvantages ot pterygoidplate impianfs

1. The procedure is techniquesensitive—it is a semiblindprocedure through 15 fo 20mm of bone.

2. Adequafe bone supporf isnecessary in fhe tuberosityand pterygoid piafe region.

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Fig 9a (\efí) in the ideal placement,the anterior-posterior spread is maxi-mized. (Courtesy of Dr Daniei Sullivan.)

Fig 9b (right) A spark erosion frame-work is fitted an standard aPutments foran overdenture. (Courtesy of Dr DanielSullivan.)

Fig Wa (ieft) Typically, the fixture isplaced at a 45- to 50-degree angie.(Courtesy of Dr Abraham ingber.)

Fig 10b (nghf) The fixture is placed atan easy-access ongle for placingrestorative components. (Courtesy ofDr Abraham ingber.)

Conclusion

Long-term evaluafion is need-ed fo assess fhe viobility ofimplant placement in tfie pfery-goid piate regicn. The ptery-goid plate fixture has beenused successfuliy vi/ith fixedprostfieses, spari< erosion pros-theses, and framework-supporf-ed overdentures (Figs 9a fo10b). iVlany of the impianfsfiave been in function for morethan 4 years. To date none hasbeen iosf after loading.

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Figllo ' ,. . ..'•-.-••.' \iOS previouslyscheduled to receive bitoterdi sinus lifts.Because sinuses are septafed bilateral-ly and because the patient suffers fromchronic sinusitis (evidenced byincreased density in the Sinus), thepianned procedure was cancelledand pterygoid pidle fixtures will beplooed instead. Note the dense bonepresent biiaterolly in the pterygoid but-tress areo.

Fig l i b Piocemenf of the pterygoid plate fixtures has been successful. A spork ero-sion overdenture is in place.

Fig 12 A pferygoid plate tixfure hasbeen piaced after a sinus groft faiiedThe prosthesis has been in function formote than 4 yeors.

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The sinus cavity (Figs 11aand l i b ) and rarified posteriormaxillary bone create a diffi-cult problem for implanf piace-menf posterior to the first pre-molar. The pterygoid platefixture has proved to be a pre-dictably successtui solution withlow morbidity (Fig 12).

Acknowledgements

Special ttianks to Ms Cindy C, Blaiackond Ms Jen Eimare for assistanoe in tiiisstudy and to Dr Gary Reiser for assis-tance in preparation ot this artioie.

References

1, Jattin RA, Berman CL, The excessiveloss ot Brónemark tixtures in type IVbone: A 3-yeai anoiysis, JPeriodontoi 1991:2:2-4,

2, DaSiiva JD, Sctinitman PA, WohtiePS, Wong HN, Kooh GG, influence otsite on impiant suivlval: ó year results(abstract). J Dent Res 1992:71:256,

3, Weber HP, Fioreiiine JP, Ttie biologyand morpinology of the impiont-tis-sue interfaoe. AO 1992:8561,04,

4, Hirsohfieid L, Wasserman B. A long-term survey ot tooth ioss in óOO tieat-ed per iodonto l pat ients, JPeriodontoi 1978:49:225-237,

5, Laney WR, Harris D, Krogh PiHJ, ZarbG, Osseointegrated impiants tor sin-gie- tooth repiacement : Progressreport trom a muiticenter prospeo-tive study after 3 years Int J OralMoKioiiofac impionts lW4:9:4Ç-5d,

ó. Henry PJ, Toiman DE, Boiender. CL,The applicabiiity of osseointegratedimpiants in the treatment of portialiyedentuious patients: Three yeorresults of a prospective multioenterstudy. Quintessence int 1993,24:123-129,

7. Hali iHD. Porticulate bone gratt ofthe moxillary sinus and aveolar ridgefor Brânemark impiants. Presentedat the Annuai Meet ing ot theAcaaemy of Osseointegration,Dailas, March 1990,

8. Kent JN, Block MS, Simuitaneousmaxillory sinus tloor bone grattingand piacement ot hvdro!<ylQpotitecoated implants, J Orai MaxiliotooSufg 1989:47:238-242,

9. totum H, Maxiilary and sinus impiantreconstruction. Dent Ciin North Am1986:30:207-223,

10, Haii HD, MoKenno SJ, Bone giaft ofthe maxiiiary sinus fioor forBrânemark implants: A preliminaryreport, Orai MaKiiiofac Surg ClinNorth Am 1991(Nov):3C4).

11. Krogh PHJ. Anatomic and surgioaiconsiderat ions in the use otosseointegrated impiants in theposteiior maxilla. Oral MaxiiofacSurg Clin North Am 1991:3:853-868.

12, Khayat P, Nader N, t he use ofosseointegrated implonts in themoxiiiary tuberosity, Proct PerioAesthet Dent 19946:53-61.

13. Grant JC8. Atias of Anatomy,Boitimore, MD: Wiiiiams and Wiikins,1972576.

14, Turvey T, Fonseoa R, the anatomyof the internai maxiilary artery: Itsrelationship in maxiiiary surgery. JCrai Surg 1980:38 92-95.

15. Mericske-Stern R Forces onrmpiants supporting overdentures:A preliminary study oí moiphologicand cephaiometric considérations,int J Oral Maxil iofao impiants1W3:8: 254-263.

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