Micro-osteoperforations

: Minimally invasiveaccelerated tooth movementMani Alikhani, Sarah Alansari, Chinapa Sangsuwon, Mona Alikhani,Michelle Yuching Chou, Bandar Alyami, Jeanne M. Nervina, andCristina C. Teixeira

& 20151073-87http://d

New Yoranimal studPropel Orthoa tool to facithis study. N

ConsortiUniversityDevelopmenMA; DeparDentistry, 3

Correspo

Safe, minimally invasive, and cost-effective treatments are being sought to

shortened orthodontic treatment time. Based on the well-known principle

that orthodontic force triggers inflammatory pathways and osteoclast

activity, we hypothesized that controlled micro-trauma in the form of

micro-osteoperforations (MOPs) will amplify the expression of inflammatory

markers that are normally expressed during orthodontic treatment and that

this amplified response will accelerate both bone resorption and tooth

movement. We tested our hypothesis in an animal model and in a human

clinical trial. In adult rats, MOPs treatment significantly increased molar

protraction with concomitant increase in inflammatory cytokine expression,

osteoclastogenesis, and alveolar bone remodeling. Likewise, in human

subjects, MOPs increased the rate of canine retraction concomitant with

increased TNFa and IL-1b levels in gingival crevicular fluid. Moreover, MOPs

treatment did not produce additional pain or discomfort in the patients

tested. Our data supports our conclusion that MOPs offers a safe, minimally

invasive, and easy mechanism to accelerate orthodontic tooth movement.

(Semin Orthod 2015; 21:162–169.) & 2015 Elsevier Inc. All rights reserved.

A major challenge in orthodontics isdecreasing treatment time without com-

promising treatment outcome. Assuming thatmechanotherapy and cooperation are optim-ized for any given patient, the rate-limiting stepin treatment time will be the patient’s biologicalresponse to mechanotherapy. Thus, identifyingand, more importantly, harnessing the cellularregulators of tooth movement are essential ifwe are to safely shorten orthodontic treatmenttime.

Elsevier Inc. All rights reserved.46/12/1801-$30.00/0x.doi.org/10.1053/j.sodo.2015.06.002

k University filed a patent on microperforations when theies were completed (J Dent Res. 89:1135-41; 2010).dontics Inc. licensed this patent from NYU and developedlitate the procedure. They did not participate in or supportYU purchased the Propel tools used in this study.

um for Translational Orthodontic Research, New YorkCollege of Dentistry, New York, NY; Department oftal Biology, Harvard School of Dental Medicine, Boston,tment of Orthodontics, New York University College of45 East 24th Street, New York, NY 10010.nding author: ct40@nyu.edu

Seminars in Orthodontics, Vol 21, No

Biology of tooth movement

The now well-known sequence of biologicalresponses to orthodontic forces begins withcompression and tension in the periodontal lig-ament (PDL). Compression and tension imme-diately deform and constrict blood vessels, anddamage cells in the periodontal tissues. The initialaseptic, acute inflammatory response is marked bya flood of chemokines and cytokines from local-ized cells, such as osteoblasts, fibroblasts, andendothelial cells. Many of these cytokines are pro-inflammatory and sustain the inflammatoryresponse by recruiting inflammatory cells andosteoclast precursors from the PDLs extravascularspace. Infiltrating inflammatory cells maintainhigh chemokine and cytokine levels to supportosteoclast precursor differentiation into multi-nucleated giant cells that perform the time-consuming process of resorbing alveolar bonethat is needed for teeth to move. Equally impor-tant is the continued presence of anti-inflammatory chemokines and cytokines, whichtemper the destructive pro-inflammatory andosteolytic processes. Thus, the more we knowabout the pro- and anti-inflammatory responses of

1623 (September), 2015: pp 162–169

Micro-osteoperforations 163

alveolar bone, PDL and inflammatory cells toorthodontic force, the better we can develop safetherapies that shorten overall orthodontictreatment time.

What we know about cytokine effects on therate of tooth movement is very consistent—blocking pro-inflammatory cytokines increasesthe time needed to move teeth in differentanimal models.1–6 Taken together, these studiesstrongly support the conclusion that pro-inflammatory cytokines are essential mediatorsof orthodontic tooth movement. More impor-tantly, these data clearly compel us to developmethods to harness and titrate the pro-inflammatory responses to safely accelerateorthodontic tooth movement.

Accelerating tooth movement

In general, there are 2 methods to accelerate therate of tooth movement. The first involvesapplying physical and chemical stimulants toactivate bone remodeling pathways. Importantly,these pathways are not the pathways that areactivated during routine orthodontic toothmovement. Rather, these stimulant-activatedpathways trigger exaggerated uncoupled activa-tion of localized cells to resorb, or form bone inways that do not mimic the natural coupled cel-lular responses to orthodontic forces. In contrast,the second approach intensifies the naturallycoupled bone remodeling pathways that areactivated by orthodontic forces. Utilizing thelatter approach here, we present a simple andsafe method to accelerate tooth movement thatharnesses and amplifies the patient’s normalbiological response to orthodontic forces.

This novel method to accelerate toothmovement is based on the natural inflammatoryresponse of the body to physical trauma. Wehypothesize that controlled micro-trauma in theform of micro-osteoperforations (MOPs; whichmaintain the integrity and architecture of hardand soft tissue) will amplify the expression ofinflammatory markers that are normallyexpressed during orthodontic treatment and thatthis amplified response will accelerate both boneresorption and tooth movement. To test ourhypothesis, we used MOPs in an animal model ofaccelerated tooth movement,7 followed byhuman clinical trials of the MOPs protocol.8,9

From rats to humans

In our study on rats, the rate of tooth movementincreased significantly, with tooth movementoccurring twice as fast in the MOP group com-pared with the O group (Fig. 1B). Cytokine/cytokine receptor expression increasedsignificantly 24 hours after force application inthe MOP and O groups compared with the Cgroup (Fig. 1C). Moreover, 21 cytokines weresignificantly higher in the MOP group than the Ogroup. Histology revealed increased alveolarbone resorption in both the MOP and Ogroups compared to the C group. The MOPgroup showed a significantly greater rate ofalveolar bone resorption than in the O group,and a subsequent increase in PDL thickness(Fig. 1D). Immunohistochemical staining ofTRAP-positive osteoclasts (Fig. 1D) revealed athreefold increase in osteoclast number in theMOP group compared with the O group.

Using a canine retraction model in humans,we confirmed the results of our animal study.After 28 days of canine retraction, we observed asignificant increase in canine retraction in theMOP group compared with both C group and CLside (Fig. 2B). Dental cast measurements showeda 2.3-fold increase in canine retraction comparedwith both C group and CL side (Fig. 2C). GCFprotein analysis showed increased cytokine andchemokine expression after 24 hours of forceapplication compared with pre-retraction levelsfor the same patients. Moreover, cytokines weresignificantly higher in theMOP group than in theC group (Fig. 2D). After 28 days, all cytokinelevels were decreased back to pre-retractionlevels with the exception of interleukin-1-beta(IL1-β). In the MOP group, IL1-β levels at 28 dayswas still significantly higher (5.0- and 3.6-fold,respectively) than the pre-retraction levels(Fig. 2D). In addition, we recorded pain anddiscomfort levels using a self-reporting numericscale which ranged from 0 to 10 (0 ¼ “no pain”and 10 ¼ “worst possible pain”) on the day ofappliance placement, the day of canine retrac-tion, and 24 hours, 7 days, and 28 days afterretraction was initiated. All patients reportedmild to moderate discomfort compared to pre-retraction levels (Table). Importantly, MOPstreatment did not produce increased levelsof pain compared to conventional, non-MOPscanine retraction treatment, with patients

Figure 1. MOPs accelerate tooth movement in rats. Rats were divided into 3 groups. The experimental group(MOP) received 3 shallow MOPs (black dots) in the cortical bone 5 mm mesial to the maxillary first molar and aspring connecting the maxillary first molar to the incisors to apply a mesial force (A). The sham group (O)received the same mesializing spring but no MOPs. The control group (C) received passive springs and no MOPs.(B) Magnitude of tooth movement after 28 days of orthodontic force (C, control; O, orthodontic force only; MOP,orthodontic forceþmicro-osteoperforations). The MOP group showed the greatest magnitude of movement. (C)RT-PCR analysis of cytokine gene expression. Data presented as fold increase in cytokine expression in the O andMOP groups compared with C group. Data shown is mean � SEM of 3 experiments. (D) Histological sectionsstained with hematoxylin and eosin (top panels) show increased periodontal space (p) thickness around themesiopalatal root (r) of the first molar and increase in bone (b) resorption in both the O and MOP groups.Immunohistochemical staining (bottom panels) shows an increase in osteoclast activity represented by theincreased number of TRAP-positive osteoclasts (arrowhead) in both the O and MOP groups.

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Figure 2. MOPs treatment accelerated canine retraction in a human clinical study. In a randomized, single-center,single-blinded study, 20 subjects were randomly divided into control and experimental groups. Both groupsreceived similar treatment until the initiation of canine retraction. At that time, the experimental group received 3MOPs between the canine and the second premolar on one side only, while the contralateral side served asadditional control (CL). The control group (C) did not receive MOPs. The rate of canine retraction wasdetermined from dental cast analysis of impressions taken immediately before initiating canine retraction and after28 days of retraction. (A) Diagram showing the setup during canine retraction. A power arm extending from thevertical slot of the canine bracket to the level of the canine center of resistance (green dot) was connected by a NiTicoil (continuous 50 cN force) to a temporary anchorage device (blue dot) placed between the second premolar andthe first molar at the level of the CR of the canine. The 3 MOPs (red dots) were placed between the canine and thesecond premolar prior to retraction. (B) After 28 days of force application, the distance between the canine andthe lateral incisors was measured using a digital caliper. The canine retraction is significantly greater in the MOPgroup than in the O group (orthodontic force alone or contralateral side). (C) Canine retraction in MOP groupincreased 2.3-fold after 28 days of retraction compared with the control group and the contralateral side of theexperimental group. (D) Cytokine levels in the gingival crevicular fluid collected from the distobuccal crevices ofthe canine before retraction and 24 hours, 7 days, and 28 days after force application cytokine protein activity wasassayed by enzyme-linked immunoassay (ELISA) and shows significantly higher levels in the MOP group than inthe C group. Data is presented as pg/uL. nSignificantly higher than control (p o 0.05). (For interpretation of thereferences to colour in this figure legend, the reader is referred to the web version of this article.)

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Table. Pain and Discomfort Assessment for Control (O) and Experimental (MOP) Groups Using a NumericalRating Scale (NRS)

Day of Canine Retraction 1 d 7 d 14 d 28 d

Control (O) 18 � 0.3 3.4 � 0.5 2.1 � 0.7 1.6 � 0.5 1.1 � 0.4Experimental (MOP) 1.4 � 0.2 3.1 � 0.4 2.2 � 0.6 1.4 � 0.5 1.2 � 0.2

Pain scores in the control and experimental groups, Values represent the average for each group � SD.

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reporting only moderate discomfort that wasbearable and did not require any medication.

Using the same canine retraction model inhumans, the effect of number of MOPs on therate of tooth movement was studied. In this study,rate of tooth movement was compared in 3groups: control that only received orthodonticforce (O), O þ 1 MOP group that in addition toorthodontic force received 1 MOP betweencanine and second premolar, and O þ 4 MOPgroup that in addition to orthodontic forcereceive 4 MOPs in the same position. At differenttime points after canine retraction, the rate oftooth movement and levels of inflammatorymarker IL1-α were evaluated as described before.In response to 4 MOPs, IL1-α activity in thegingival crevicular fluid increased fivefold whencompared with O group, 24 hours after MOPsprocedure and coil activation, and 3.5-fold after28 days (Fig. 3A), which was statistically wassignificant (po 0.05). While a slight increase wasobserved in the Oþ 1 MOP group in comparisonto O group at all time points studied, thesechanges were not statistically significant. Similarto the results of the previous clinical trial, 4 MOPswere able to increase the rate of tooth movementmore than 2 folds (p 4 0.05), while nosignificant difference between O group andO þ 1 MOP group was observed (Fig. 3B andC). These results demonstrate a direct relationbetween the magnitude of the trauma to thealveolar bone and activation of inflammatorymarkers, and therefore, the rate of toothmovement.

Discussion

The demand for accelerated tooth movement isheard from both orthodontists and their patients.Delivering on this demand has led researchersdown varied paths, including vibration, piezo-electricity, and light; just to name a few. Wehypothesize that harnessing and amplifyingthe body’s natural inflammatory responses to

orthodontic tooth movement using micro-osteoperforations in the alveolar bone wouldproduce a minimally invasive, safe and easilyperformed protocol to accelerate tooth move-ment. Our data from both the animal and humanstudies strongly support our hypothesis. Weconfidently conclude that MOPs treatment is aviable option for orthodontists who seek toshorten overall treatment time for their patients.

Shortening orthodontic treatment time offerssignificant value to clinicians and patients alike.Less time in fixed appliances reduces the risk forexternal apical root resorption10 and deminera-lization/caries11; patient burn-out is less likely;young patients will miss less school; parents orolder patients will miss less work. Our MOPsprotocol not only offers these advantages byshortening treatment time, its minimally invasiveapplication accelerates tooth movement withoutadditional discomfort for the patients.

Mechanistically, our animal studies showedthat MOPs significantly stimulated expressionof inflammatory markers and significantlyincreased the number of osteoclasts and boneresorption, as anticipated. Interestingly, weobserved that the increase in bone remodelingwas not limited to the area of the moving tooth,but extended to the tissues surrounding theadjacent teeth (data not shown). This most likelycontributed to the increase in the rate andmagnitude of tooth movement observed in thisstudy, thereby suggesting that the perforations donot need to be very close to the tooth to bemoved to accelerate the rate of tooth movement.

The results of our human clinical trial weresimilar to the rat study. Canine retraction in thepresence of MOP resulted in twice as muchdistalization as observed with the orthodonticforces alone. When compared to invasive surgicalapproaches to accelerate tooth movement, it isobvious that MOPs offers a number of advan-tages. This procedure is minimally invasive andflapless, allowing orthodontists to deliver care intheir offices.

Figure 3. Increasing the number of micro-osteoperforations increases the catabolic effect in humans. A total of 15subjects were randomly divided into control (O) and experimental groups. Using the same canine retration modelpreviously described, experimental groups received either 1 (O þ 1 MOP) or 4 (O þ 4 MOP) MOPs between thecanine and the second premolar prior to retraction, on one side of maxilla. (A) Levels of IL1α in the gingivalcrevicular fluid—as measured by protein activity was measured by enzyme-linked immunoassay (ELISA) beforeretraction, 24 hours, 7 days, and 28 days after force application. Data show significantly higher levels in the groupthat received 4 MOPs in comparison to control (O) and the O þ 1 MOP group. Data is presented as pg/uL.nSignificantly higher than O and O þ 1 MOP groups (p o 0.05). (B) Intraoral photos showing canine retractionafter 28 days of force application. (C) Canine retraction measured in casts was significantly greater in the O þ 4MOP group than in the O þ 1 MOP and O groups. nSignificantly different from O and O þ 1 MOP groups(p o 0.05).

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As it was discussed earlier osteoclast recruit-ment depends on inflammatory marker expres-sion. This begs the question does inflammatorymarker expression depend on the magnitude ofthe trauma? Our clinical studies demonstratethat by increasing the number of MOPs,inflammatory maker expression, and magnitudeof tooth movement increased significantly.Therefore, one should expect procedures such asorthognathic surgery, corticotomies (where aflap is raised and numerous cuts and perforationsare made in the alveolar bone), or piezocision(where no flap is raised, and bone is accessedthrough small cuts through the gingiva, followedby bone injury by a piezoelectric device) to sig-nificantly increase the level of inflammatorycytokines beyond levels induced by MOPs, whichin comparison to these procedures is considereda very conservative insult to alveolar bone.Unfortunately, the increase in inflammatorymarker expression is not sustained for a longtime and after 2–3 months a significant decreasein cytokine activity is observed regardless of thetype of procedure or the magnitude of injury.Due to the need to repeat the procedures overthe course of orthodontic treatment, some of theabove procedures lose their practicality. There-fore, based on these observations the ortho-dontists should be able to decide whichprocedure best fits the needs of their patients.

Pain and external apical root resorption

The 2 main concerns about MOPs are pain androot resorption. MOPs are done under infiltrationof local anesthetic. Patients who received MOPsdid not demonstrate additional pain or discomfortwhen compared with patients who received onlyorthodontic treatment and did not require addi-tional pain medications or additional care otherthan regular oral hygiene. External apical rootresorption (EARR) is not increased followingMOPs treatment. One main reason for EARR ishigh stress that produces a cell-free zone when atooth is pushed towards dense bone.12 In theseareas, osteoclasts are recruited from thesurrounding PDL and endosteal surfaces. Theprolonged presence of osteoclasts, rather than thenumber of osteoclasts, causes EARR. While MOPssignificantly increased the number of osteoclasts,these osteoclasts are on the adjacent endostealbone surface not in the PDL (data not shown).

Moreover, since MOPs decreases the density ofthe adjacent alveolar bone, the cell-free zone issmaller and cleared faster, which would preventprolonged osteoclast activity adjacent to toothroots. Thus, EARR risk decreases significantly inMOPs treatment, even during tooth movementover long distances.

Clinical applications

MOPs can easily be incorporated into ourorthodontic mechanics. Application of MOPsduring leveling and aligning stages should bepostponed until adequate space has been cre-ated. While MOPs can increase the number ofosteoclasts, it will not change the side effects ofthe biomechanics plan and therefore similar toclassic mechanics, the teeth without adequatespace will not be able to engage in the mainarchwire. MOPs can facilitate one of the mostdifficult movements to accomplish in ortho-dontics; root movement. By activating osteoclastsand decreasing the bone density, application ofsimilar bodily movement mechanics can producefaster tooth movement and less stress on anchorteeth, since movement occurs in less time. Forthese reasons, MOPs are an excellent adjuncttechnique during protraction/retraction of asingle tooth or group of teeth. MOPs between theroots of teeth decreases the bone density whilethe bone density around anchor teeth remainsunchanged. This procedure is especially usefulwhen a tooth is moved into an edentulous spacewhere alveolar bone is dense with a narrow ridge.MOPs can significantly decrease the bone densityand allow faster and safer tooth movement whileenhancing alveolar bone remodeling in thatarea. MOPs should also be considered duringsegmental intrusion, during which there is apossibility of root resorption due to high stressarea around the root apex. While keeping theforce light, MOPs application around the apexprevents the prolonged cell-free zone that cancause root resorption. Clinicians should take intoconsideration that since the increase in cytokineactivity decreases after 2 months of MOPsapplication, repeating the procedure every othermonth is recommended. And if TADs are beingused to increase anchorage, application of MOPsadjacent to the location of the TADs should beavoided since decreased bone density around theTADs will likely decrease their stability.

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Conclusion

MOPs can be incorporated into routine ortho-dontic mechanics and at different stages oftreatment, facilitating alignment and rootmovement, reducing the possibility of rootresorption, stimulating bone remodeling in areasof deficient alveolar bone, and reducing thestress on anchor units. Therefore, MOPs offers apractical, minimally invasive and safe procedurethat can be repeated as needed to maximize thebiological response to orthodontic forces.

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