Analysis of dentoalveolar structures with novel ... · Analysis of dentoalveolar structures with...

ORIGINAL ARTICLE

Analysis of dentoalveolar structures withnovel corticotomy-facilitated mandibularexpansion: A 3-dimensional finiteelement study

Deepal Haresh Ajmera,a Pradeep Singh,b Chao Wang,c Jinlin Song,a Shui Sheng Xiao,d and Yubo Fane

Chongqing and Beijing, China

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Introduction: Surgically assisted mandibular arch expansion is an effective treatment modality for alleviatingconstriction and crowding. However, only mandibular symphyseal osteotomy is recommended for mandibulararch expansion. No relevant studies have compared the biomechanical responses of different corticotomy de-signs on mandibular expansion. Therefore, the aim of this study was to evaluate the effect of different cortico-tomy approaches and modes of loading on the expansion of adult mandibles using biomechanics. Methods:Nine finite element models including 2 novel corticotomy designs were simulated. Stress, strain, and displace-ment of crown, root, and bone were calculated and compared under different corticotomy approaches andloading conditions.Results: The biomechanical response seen in the finite element models in terms of displace-ment on the x-axis was consistent from anterior to posterior teeth with parasymphyseal step corticotomy andtooth-borne force application. In addition, the amount of displacement predicted by parasymphyseal stepcorticotomy in the tooth-bornemodewas greater comparedwith other models.Conclusions: These results sug-gest that parasymphyseal step corticotomy with tooth-borne force application is a viable treatment option for truebony expansion in an adult mandible. (Am J Orthod Dentofacial Orthop 2017;151:767-78)

gqing Key Laboratory of Oral Diseases and Biomedical Sciences; Chongq-unicipal Key Laboratory of Oral Biomedical Engineering of Higher Educa-Department of Orthodontics and Dentofacial Orthopedics, College oftology, Chongqing Medical University, Chongqing, China.gqing Key Laboratory of Oral Diseases and Biomedical Sciences; Chongq-unicipal Key Laboratory of Oral Biomedical Engineering of Higher Educa-Department of Oral and Maxillofacial Surgery, College of Stomatology,gqing Medical University, Chongqing, China.ge of Stomatology, Chongqing Medical University; Chongqing Key Labo-of Oral Diseases and Biomedical Sciences, Chongqing, China.rtment of Oral andMaxillofacial Surgery, College of Stomatology, Chongq-edical University, Chongqing, China.ratory for Biomechanics and Mechanobiology of Ministry of Education,l of Biological Science and Medical Engineering, Beihang University, Bei-hina.thors have completed and submitted the ICMJE Form for Disclosure oftial Conflicts of Interest, and none were reported.rted by the Program for Innovation Team Building at Institutions of WorldOrganization Education in Chongqing, the Program for Innovation Team

ng at Institutions of Higher Education in Chongqing in 2013, the Nationalal Key Specialty Constitution Program of China for 2013-2014, the Nationalal Science Foundation of China (grant number 11402042), and the Scientificrch Foundation of Chongqing (grant number cstc2015jcyjA10027).l Haresh Ajmera and Pradeep Singh contributed equally to this study andint first authors.ss correspondence to: Jinlin Song and Chao Wang, Chongqing Key Labo-of Oral Diseases and Biomedical Sciences and College of Stomatology,

gqing Medical University, Chongqing 400016, China; e-mail,[email protected]; [email protected], February 2016; revised and accepted, September 2016.5406/$36.007 by the American Association of Orthodontists. All rights reserved./dx.doi.org/10.1016/j.ajodo.2016.09.015

Atooth size-arch length discrepancy is a commonform of malocclusion seen in clinical practice.Clinical characteristics including decreased

mandibular arch length, narrow intercanine width,mandibular anterior teeth crowding, and posteriorbuccal crossbite are associated with transverse mandib-ular deficiency.1,2 Moreover, from the treatment aspect,it is often believed to be a critical factor in decisionmaking for surgical or nonsurgical expansion.

Compared with maxillary deficiency, transversemandibular deficiency has received little attentionfrom researchers recently. A variety ofnonsurgical methods including the Schwarz and bihelixappliances have been used, with limited dimensionalchange and questionable long-term stability.3-8

Expansion of the mandibular arch reported in thesestudies was localized to alveolar bone and mostlyresulted in inclination of the teeth, without changes inthe mandibular body. Moreover, a compromisedperiodontium caused by excessive dental expansionand proclination in addition to compromised facialesthetics have been noticed as disadvantages for suchtreatments. However, the results of combined surgicaland orthodontic treatment for adults requiring an

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increase in the lateral dimension have shown promisingresults. Recent reports have shown that corticotomy-assisted orthodontic treatment is a well-accepted optionwith a predictable outcome that offers solutions to manylimitations associated with orthodontic treatment.

The first evidence of application of corticotomy in or-thopedics comes from the early 1900s.9 Since then,corticotomy-assisted orthodontic treatment has beenused as an effective treatment alternative for the correc-tion of various dentoalveolar discrepancies.10-13 Apatented technique called accelerated osteogenicorthodontics was also introduced by Wilcko et al14,15

in this regard. Corticotomy-assisted orthodontic treat-ment involves selective alveolar decortication to inducea state of increased tissue turnover that is followed byfaster tooth movement, resulting in reduced treatmenttime. In addition, corticotomy-assisted orthodontictreatment offers other advantages such as safer expan-sion of constricted arches and enhanced postorthodon-tic treatment stability.

Three-dimensional (3D) finite element (FE) analysis isa contemporary research tool for numeric simulation ofmechanical processes of a real physical system that offersseveral advantages, including accurate representation ofcomplex geometries and easy model modification.16

Also, it is considered a valid and reliable approach forquantitative evaluation of stress-strain and displace-ment in the dentoalveolar structures.17 Moreover, it pro-vides the freedom to simulate orthodontic force systemsapplied clinically, in addition to evaluation and predic-tion of the dentoalveolar response to the mechanicalloads in 3D spaces, thereby limiting the number of ani-mal experiments.

The physiologic characteristics of bone to adapt tothe mechanical environment when subjected to me-chanical load by means of 2 inherent mechanisms—bone modeling and bone remodeling—are well known.Moreover, the concept of selective decortications fol-lowed by increased tissue turnover and transient osteo-penia might be implied for correction of transversemandibular deficiency. Hence, it can behypothesized that with the change in the design ofcorticotomy, accompanied by different modes of forceapplication, the biomechanical response of the bone tis-sue might change, and advanced mandibular expansioncan be achieved that further contributes substantially tobetter treatment outcomes. With this intent, this studywas aimed to compare the biomechanical effects ofdifferent modes of force application on 3 corticotomydesigns and to select an optimal approach for clinicaladoption with respect to a corticotomized mandible.Although a number of studies have used the FE methodto investigate the biomechanics and mechanobiology of

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mandibular symphyseal osteotomy, to the best of ourknowledge, this is the first study of its kind, comparing3 corticotomy cuts including 2 novel corticotomy ap-proaches with different modes of force application usingthe FE method.

MATERIAL AND METHODS

A cone-beam computed tomography scan projectionof an adult mandible was obtained from the Departmentof Oral and Maxillofacial Radiology, College of Stoma-tology, Chongqing Medical University, in Chongqing,China. This scan (slice thickness, 1 mm; pixel size,0.42 mm) served as the pattern for construction of themathematical model. Processing of the data was per-formed using Mimics software (version 9.0; Materialise,Leuven, Belgium). The generated DICOM file was im-ported into the Mimics software for semiautomaticedge detection, followed by meshing of surface elementsusing an automated meshing module (Geomagic Studio;Geomagic, Morrisville, NC) to construct the 3D analyticalmodel of the mandible and dentition through threshold-ing, region growing, and calculating 3D operations. Thestudy protocol was approved by the ethics committee ofChongqing Medical University, and informed consentwas obtained from the subject before the study.

With the help of Rapidform software (version 6.5;INUS, Seoul, Korea), we performed scaling and Booleanoperations on the surface model of individual teeth andmandibular bone to produce cortical bone, trabecularbone, and periodontal ligament with average thicknessesof 2.0, 2.0, and 0.2 mm, respectively, thereby creatingparametric solids from 3D scans. For the purpose ofgenerating the geometric model, 5 materials includingteeth, mucosa, trabecular bone, cortical bone, and peri-odontal ligament were assembled; they were assumed tobe linearly elastic, homogeneous, and isotropic as shownin Figure 1. Furthermore, the orthodontic appliances andminiscrew implants were designed and modeled in CADsoftware (Solid Works, Dassault Systems, Concord,Mass). All components were saved in initial graphics ex-change specification format and imported into ANSYS(Swanson Analysis Systems, Houston, Tex).

The constructed model was then exported to the FEsoftware ANSYS, which divided the geometric modelinto finite elements; these elements were connected toadjacent elements by nodes, thereby creating a numericrepresentation of the geometric model. Table I gives thetypes and numbers of elements and nodes. Furthermore,to simulate the temporomandibular joint (TMJ), 2 blocksof temporal bone were made, and the space betweentemporal bone and condyles was filled by a 2-mm thicklayer of articular disc. With regard to boundary condi-tions for the TMJ, constraints were placed on the 2

Journal of Orthodontics and Dentofacial Orthopedics

Fig 1. Materials used to assemble a model.

Table I. Numbers of elements and nodes

Material Elements NodesCortical bone 15040 28112Trabecular bone 20735 36206Periodontal ligament 35772 72547Teeth 10636 20375

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bone blocks in all 3 axes (Fig 2). Geometric and FEmodels used in the study are shown in Figure 2, A andB, respectively). Subsequently, the simulated FE modelbehaved like the actual prototype after the allocationof material properties such as Young's modulus andPoisson's ratio (lateral strain/longitudinal strain). Thematerial properties were determined from the values inthe literature18-20 (Table II).

Three corticotomy cuts including midline symphysealcorticotomy, angulated midline symphyseal cortico-tomy, and parasymphyseal step corticotomy were per-formed on the simulated FE models. Following themodern conservative approach, only the buccal cortexwas perforated, whereby the vertical cut for the angu-lated midline symphyseal corticotomy was performedin the usual fashion between the central incisors, ex-tending below their roots, followed by an angulatedcut of almost 120� that extended laterally until the infe-rior border of mandible (Fig 3, B). Furthermore, the para-symphyseal step corticotomy cut was oriented in astepwise manner, including a vertical corticotomy be-tween the canine and first premolar that extended belowthe canine root and was brought medially as a horizontalcut extending up to the contralateral canine-premolarregion followed by a vertical corticotomy to the inferiorborder of the mandible (Fig 3, C).

Nine FE models including 3 diverse modes of forceapplication and 3 corticotomy approaches were de-signed and structured in this study (Fig 4). The cortico-tomy approaches we used differed in the designs; thesymphyseal corticotomy was performed in 3 models,whereas the other 6 models included 2 novel cortico-tomy designs respectively, as shown in Figure 4, D-I.

American Journal of Orthodontics and Dentofacial Orthoped

Each corticotomy approach was subjected to a tooth-borne, bone-borne, or hybrid device. Pure horizontalmechanical loads were applied in all 9 models, andeach model was analyzed for stress, strain, and displace-ment (amount and direction in relation to the x-axis) onthe tooth (crown and root) and the bone. The baselinecharacteristics of the study design are listed in Table III.

RESULTS

The results are shown in Figures 5-7.The graphic representation of tooth number vs

maximum von Mises stress under different corticotomyconditions is shown in Figure 5. Von Mises stress onthe crown was observed to be maximum with the hybridmode at the canine region (Fig 5,A-C) in all corticotomydesigns. In contrast to the hybrid mode, which showed alocalized effect, the tooth-borne mode produced consis-tent stress, which gradually declined posteriorly (Fig 5,A-C). Likewise, when stress concentration on the rootwas analyzed, a similar response was observed in the an-gulated symphyseal corticotomy with respect to thehybrid mode, which produced maximum stress at thecanine region (Fig 5, E). Conversely, stress concentrationon the root in the midline symphyseal and step corticot-omies was more pronounced at the canine and premolarregion with the tooth-borne and hybrid modes, respec-tively (Fig 5, D and F). Interestingly, the results of stressdistribution patterns on bone were quite different fromthe above-mentioned results. Here, the tooth-bornemode produced almost equivalent stress anteriorly inthe angulated corticotomy followed by a steady fall pos-teriorly (Fig 5,H). Also, the magnitudes of stress concen-tration on bone in the midline and step corticotomieswere maximum at the mandibular anterior region withthe tooth-borne mode and progressively plunged poste-riorly (Fig 5, G and I). Furthermore, the bone-bornemode produced minimal von Mises stress at crown,root, and bone compared with the tooth-borne andhybrid modes, irrespective of the corticotomy design(Fig 5).

Likewise, a similar strategy was used to analyze thedistribution of strain on the tooth (crown and root)and the bone as shown in Figure 6. The graphic depic-tion of strain distribution shows that the pattern ofstrain produced on the crown (Fig 6, A-C) was

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Fig 2. A, Basic geometric model of the mandible; B, FE model of the mandible.

Table II. Material properties

MaterialPoisson'sratio

Young'smodulus(MPa) Reference

Teeth 0.3 20.7E3 Lee and Baek18

Periodontal ligament 0.45 50 Lin et al19

Trabecular bone 0.3 9.7E2 Aversa et al20

Cortical bone 0.3 10.7E3 Aversa et al20

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analogous to the stress patterns in all corticotomies,wherein the hybrid mode produced maximum strain onthe crown. The peaks of the strain distribution graphfor the root (Fig 6, D-F) show greater strain concentra-tions at the canine region with the tooth-borne mode inthe midline corticotomy and in the hybrid mode in theangulated and step corticotomies, respectively. Further-more, noticeable results were obtained when strain dis-tribution was plotted for bone. Figure 6, G-I, showsconsiderable strain on bone anteriorly with the tooth-borne means of loading, with a consistent drop posteri-orly in all corticotomy approaches. The patterns of straindistribution on bone with respect to the midline and stepcorticotomies were comparable with the stress patterns(Fig 6, G and I). Our results show that the bone-bornemode failed to produce significant strain on crown,root, and bone in all the corticotomy cuts (Fig 6).

Considering the influence of the different cortico-tomy cuts and modes of load application on displace-ment, we analyzed the displacement of tooth (crownand root) and bone on the x-axis of the coordinate sys-tem (Fig 7). Figure 7, A-C, depicts a steady rise indisplacement of the crown until the canine region, fol-lowed by a constant displacement posteriorly in all thecorticotomy designs with the tooth-borne mode. Inaddition, the hybrid means also displayed a steady riseuntil the canine region; however, the effect decreased


posteriorly. Interestingly, a trivial effect of the corti-cotmy designs was observed with respect to displace-ment of root and bone (Fig 7, D-I). Here, all thecorticotomies showed a persistent rise in the displace-ment of root and bone from anterior to posterior withthe tooth-borne mode. Also as expected, the tooth-borne mode showed more displacement of bone at thecentral incisor region compared with the lateral incisorregion in the midline corticotomy (Fig 7, G). However,after an initial constant displacement of root, a plungewas seen posteriorly with the hybrid mode for all corti-cotomies. Furthermore, in contrast to these results, thebone-borne mode displayed a constant anterior-to-posterior displacement of crown, root, and bone in thestep corticotomy, albeit the effect was not significant(Fig 7, A, C, D, F, G, and I). Displacementspredicted by different osteotomy designs with hybridmode at the second premolar level obtained from 3DFE models are shown in Figure 8.

DISCUSSION

Although extraction and nonextraction arguments inorthodontics have continued over a long period, duringthe past decade there has been renewed interest inproviding routine relief of crowding without premolarextractions. In this regard, arch expansion can beachieved to solve the space deficiency problems, withoutthe need for extractions. Previous studies have alsoshown substantial results after surgically assisted maxil-lary arch expansion. However, clinicians have been skep-tical about attempting a true mandibular expansion.Relatively few studies have addressed surgically assistedtrue mandibular expansion. The results of previous FEstudies have provided useful insights toward the predic-tion of the changes in dentoalveolar structures after loadapplication, which was the basis of this study. Therefore,we studied the biomechanical effects of different


Fig 4. Allocation of different loading conditions on FE model: A-C, midline symphyseal corticotomywith different loads (tooth-borne, bone-borne, and hybrid, respectively); D-F, angulated midline sym-physeal corticotomy with different loads (tooth-borne, bone-borne, and hybrid, respectively);G-I, para-symphyseal step corticotomy with different loads (tooth-borne, bone-borne, and hybrid, respectively).

Fig 3. Designs of corticotomy approaches: A, midline symphyseal corticotomy; B, angulated midlinesymphyseal corticotomy; C, parasymphyseal step corticotomy.

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corticotomy cuts and modes of load application on den-toalveolar structures.

With some modern refinements, the procedure ofKole,21 that included interradicular corticotomies


and supra-apical osteotomies, is the basic techniquethat is used today. In the 1970s, Suya22 introduceda modification to Kole's technique that had a signifi-cant influence on today's standard corticotomies.


Table III. Baseline characteristics of the study design

Biomechanicalparameteranalyzed

Mode of loadapplication

Corticotomydesign*

Part I Stress(crown, root, bone)

Tooth borne Midline

AngulatedStep

Bone borne MidlineAngulatedStep

Hybrid MidlineAngulatedStep

Part II Strain(crown, root, bone)

Tooth borne Midline

AngulatedStep



Part III Displacement(crown, root, bone)

Tooth borne Midline

AngulatedStep



*Midline, Midline symphyseal corticotomy; angulated, angulatedmidline symphyseal corticotomy; step, parasymphyseal step cortico-tomy.

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Later, Wilcko et al23,24 called the procedure(periodontally) accelerated osteogenic orthodonticsby combining the corticotomy-facilitated orthodontictechnique with alveolar augmentation. An acceleratedtooth movement after corticotomy, caused byincreased bone turnover, is brought about by the bio-logic process known as the regional acceleratory phe-nomenon.11,12,25,26 As much as a 5-fold increase inbone turnover has been reported adjacent to cortico-tomy sites27 including a 3-fold increase in the numberof osteoclasts and a 4-fold increase in the number ofosteoblasts.28 Despite this, only the symphyseal os-teotomy has been in favor for the mandibular expan-sion. Therefore, in this study, new corticotomyapproaches with minor cuts were introduced bychanging the site and design of the corticotomy tominimize surgical injury and difficulty of operation.Furthermore, we used extreme care to preserve ante-rior tooth roots while performing corticotomies.


In this study, we found that a change in the cortico-tomy approach can affect the mechanical response ofthe dentoalveolar structures. The expansion predictedfor a step corticotomy appears to be more significantcompared with midline and angulated corticotomies.In particular, a step corticotomy with the tooth-bornemode achieved substantial expansion presumablybecause of selective decortications of alveolar bonethat resulted in increased bone turnover and transientosteopenia adjacent to the corticotomy sites. Thecorticotomy-facilitated orthodontic technique initiatedthe regional acceleratory phenomenon; second, thedesign of the step corticotomy allowed controlleddisplacement of the corticotomized alveolar bone bilat-erally through the fixation points of the tooth-bornemode that were located on the teeth.

Stability of the mandibular arch is an area of primaryconcern in an arch expansion study such as ours. First, theamount of bony displacement predicted by the FE modelin the step corticotomy using the tooth-borne mode wasmaximum and consistent including significant increasesin intercanine, interpremolar, and intermolar widths,which were in contrast to the findings of Basciftciet al29 and Boccaccio et al.30 A previous study by Gardnerand Chaconas31 also confirmed that expansion ofmandibular interpremolar and intermolar dimensions ismore stable than intercanine expansion; this agreeswith our findings. In addition, although the absolutevalues differed, the response curves showed similartendencies with respect to displacements of crown androot, thus indicating bodily movement of the tooth, ratherthan inclination as observed in previous studies.3-8

Second, in contrast to maxillary expansion, mandibularexpansion has not been generally accepted as a viabletreatment because any increase in mandibularintercanine width is subject to relapse.32 Pressures exertedfrom the lips and cheeks are likely contributors tomandibular dental expansion posttreatment instabilityas suggested by Shellhart et al,33 although they concludedthat labial soft tissues adapt to simulated conventionaldental arch expansion with the decrease in pressuresgradually. Also, most recent follow-up studies haveconfirmed stable long-term outcomes with transverseexpansion of the mandibular arch (Sabuncuoglu et al,34

Handelman,35 O'Grady et al,36 and Brust andMcNamara37). Although these studies were performedon nonsurgical mandibular expansion, it is rational toinfer that the same should hold true for surgically assistedmandibular expansion until the completion of furtherlong-term stability studies. Furthermore, Boccaccioet al30 suggested that parasitic rotations generated bythe masticatory muscles become less significant overtime, resulting in greater stability. Therefore, it can be


Fig 5. Graphic representation of loading site vs maximum von Mises stress in different loading condi-tions: A-C, maximum von Mises stress on the crown for midline, angulated, and step corticotomies,respectively; D-F, maximum von Mises stress on the root for midline, angulated, and step corticoto-mies, respectively; G-I, maximum von Mises stress on the bone for midline, angulated, and step corti-cotomies, respectively.

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suggested that despite initial instability caused by thelabial soft tissues and masticatory muscles, stableoutcomes can be achieved gradually because of theadaptive behavior of muscles and soft tissues.

An additional factor to be considered is the effect ofmandibular distraction osteogenesis on the temporo-mandibular joint. Samchukov et al38 emphasized


compensation of lateral rotational movements of thecondyles after symphyseal distraction osteogenesis toprevent subsequent degenerative condylar changes,caused by inappropriate loading on the articular surfaceof the condyles. Conversely, a histological study by Bellet al39 showed only minor changes in the condyles aftersymphyseal distraction osteogenesis. Likewise,


Fig 6. Graphic depiction of strain distribution in different loading conditions: A-C, strain distribution onthe crown for midline, angulated, and step corticotomies, respectively; D-F, strain distribution on theroot for midline, angulated, and step corticotomies, respectively; G-I, strain distribution on bone formidline, angulated, and step corticotomies, respectively.

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Mommaerts40 and Kewitt et al41 suggested limitedmorbidity of TMJ function with respect to symphysealdistraction osteogenesis. Therefore, considering thosefindings, we believe that future prospective studies arerequired to precisely evaluate the biomechanical effectsof distraction osteogenesis on the TMJ afterangulated midline symphyseal and parasymphyseal step


corticotomies. Furthermore, because of the complexityof the TMJ, it is difficult to define accurately the bound-ary condition for the TMJ in the FE simulation, since theTMJ is comparatively resilient, with the condyles impact-ing against a fibrous articular disc in the anterior regionand articular ligament material in the posterior region.Therefore, it was assumed that there is relative


Fig 7. Response curves of loading site vs total displacement on the x-axis with respect to differentloading conditions: A-C, total displacement of the crown in midline, angulated, and step corticotomies,respectively; D-F, total displacement of the root in midline, angulated, and step corticotomies, respec-tively; G-I, total displacement of the bone in midline, angulated, and step corticotomies, respectively.

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displacement between the articular disc and bone, andthe FE models were calculated with a surface-to-surface frictional contact program. Hence, themandibular body was not “bonded” in our FE models,and displacement was analyzed along the x-axis.

Since bone remodeling is a significant aspect of a FEstudy such as this, it needs to be addressed. Bone


remodeling is a multifactorial process that depends onboth mechanical and biological factors. Mechanical fac-tors are related to the new distribution of loads causedby the site of appliance placement, the physical charac-teristics of the appliance (design), and the type ofanchorage (tooth-borne, bone-borne, or hybrld). Bio-logics are related to the subject's age, weight, and initial


Fig 8. Displacement vectors for different corticotomy designs with the tooth-borne (TB) mode ofloading at the second premolar level obtained from the 3D FE method. The predicted expansion ofmandibular bone can be appreciated from the direction of the displacement vectors in the parasymphy-seal step corticotomy with the tooth-borne mode.

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bone mass. Bone is a dynamic tissue that is tightly regu-lated by many homeostatic controls and constantly re-models itself to more efficiently endure externalforces.42,43 One key environmental regulator of bone ismechanical stimulation. Wolff's law recognizes theresponse of bone to mechanical stimulation and statesthat as a consequence to continuous loading, bonechanges its internal architecture according tomathematical rules and, as a secondary effect, alsochanges its shape.44 This alteration of the normalbiomechanics results in a phenomenon called adaptivebone remodeling.45 Also, the muscles attached to thesurface of compact bones can significantly influencethe intensity of a load and might contribute to thechange in the biomechanical properties of bone.46 Asimilar biomechanical response was observed in thisstudy, with the changes in osteotomy design and sitemode of load application. Furthermore, the above-mentioned theories of bone remodeling have beenused successfully in conjunction with the FE methodto predict density and bone adaptation. Althoughsome remodeling does take place at the site of forceapplication, the amount of bone remodeling was notevaluated in this study, since we are clinicians, and theimplementation of an extendable numeric algorithm tobuild up the remodeling process of bone due to mechan-ical stimulus was beyond the scope of this study.

The strengths of this study include a comprehensiveFE analysis on an adult mandible and using extracteddata for the assessment of potential mandibular boneexpansion. However, some limitations should be consid-ered for our study. First, FE analysis is a mathematical in-vitro study that may not simulate the clinical situationcompletely. For the creation of the FE models, the


materials used in this study were assumed to be isotropicand homogeneous. Therefore, the resultant stress valuesobtained may not be accurate quantitatively but aregenerally accepted qualitatively. Second, our study wasconstrained to biomechanical factors, and no animal ex-periments have been performed yet. Because of the lim-itations of the study, further research regarding 3D FEanalysis combined with experimental studies and long-term clinical evaluations is required to quantitativelyvalidate our numeric results.

CONCLUSIONS

Within the limitations of this study, our data mayprovide a valuable reference for future clinical andexperimental studies, concluding that (1) the design ofthe corticotomy and the type of loading can substan-tially influence the mechanical response of the dentoal-veolar structures in a corticotomized mandible, and (2)the expansion predicted for the parasymphyseal stepcorticotomy with the tooth-borne mode appears to bemore significant compared with the midline and angu-lated corticotomies.

Consequently, even though significant insights havebeen gained about mandibular expansion, furtherresearch is needed to clarify the role of mandibularexpansion stability for more substantiated results.

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