Long-term skeletal and dental effects of mandibular symphyseal distraction osteogenesis

Hybrid mandibular Bologna midline distractor in combination with surgically assisted rapid maxillary expansion for transverse facial expansion: clinical and cephalometric results

Transverse maxillomandibular hypoplasia can be treated with surgically assisted rapid maxillary expansion (SARME) in association with mandibular symphyseal distraction (MSD). This paper introduces a hybrid mandibular Bologna midline distractor (BMD); the effectiveness of the distractor in combination with SARME for the treatment of transverse skeletal deficiency was evaluated. This two-centre study included 10 patients with a transverse arch width deficit>7 mm and dental crowding, in both the maxilla and mandible, treated with SARME and MSD. The study design was partly retrospective (seven patients) and partly prospective (three patients). Frontal and lateral cephalometric analyses, as well as measurements on dental models, were performed at three different times: before treatment, after the distraction, and 6 months after postoperative orthodontic treatment. The cephalometric analyses and measurements on dental impressions confirmed a balanced and stable skeletal and dental mandibular expansion. An average symphyseal expansion of 7.8 mm was obtained, resolving dental crowding without dental extractions. In conclusion, mandibular expansion performed with the BMD in combination with SARME appears to be a viable surgical approach to transverse maxillomandibular hypoplasia. This technique allows the surgeon to obtain a balanced skeletal and dental expansion, with a low level of relapse.

Differences in dentoskeletal and soft tissue changes due to rapid maxillary expansion using a tooth-borne expander between adolescents and adults: A retrospective observational study

Objective

The purpose of this study was to compare the differences in dentoskeletal and soft tissue changes following conventional tooth-borne rapid maxillary expansion (RME) between adolescents and adults.

Methods

Dentoskeletal and soft tissue variables of 17 adolescents and 17 adults were analyzed on posteroanterior and lateral cephalograms and frontal photographs at pretreatment (T1) and after conventional RME using tooth-borne expanders (T2). Changes in variables within each group between T1 and T2 were analyzed using Wilcoxon signed-rank test. Mann–Whitney U test was used to determine the differences in the pretreatment age, expansion and post-expansion durations, and dentoskeletal and soft tissue changes after RME between the groups. Spearman’s correlation between pretreatment age and transverse dentoskeletal changes in the adolescent group was calculated.

Results

Despite similar amounts of expansion at the crown level in both groups, the adult group underwent less skeletal expansion with less intermolar root expansion after RME than the adolescent group. The skeletal vertical dimension increased significantly in both groups without significant intergroup difference. The anteroposterior position of the maxilla was maintained in both groups, while a greater backward displacement of the mandible was evident in the adult group than that in the adolescent group after RME. The soft tissue alar width increased in both groups without a significant intergroup difference. In the adolescent group, pretreatment age was not significantly correlated with transverse dentoskeletal changes.

Conclusions

Conventional RME may induce similar soft tissue changes but different dentoskeletal changes between adolescents and adults.

Three-dimensional soft tissue evaluation after rapid maxillary expansion and mandibular midline distraction osteogenesis

OBJECTIVES

To evaluate the effects of rapid maxillary expansion (RME) and mandibular midline distraction osteogenesis (MMDO) on facial soft tissues using three-dimensional (3D) images.

MATERIALS AND METHODS

A total of 20 patients (average age 15.86 ± 2.17 years) were treated with RME and MMDO using tooth-borne distractors. Three-dimensional photographs of each patient were taken with a stereophotogrammetry system at baseline (T0), at the end of the distraction period (T1), and at the end of the consolidation period (T2). All data were analyzed using a dependent-samples t-test at a significance level of 5%.

RESULTS

Total and lower face height increased after MMDO (P < .05). Nasal and mouth width increased after RME as compared with baseline (P < .05). The labiomental angle increased at T1 and decreased at T2 (P < .05). After MMDO, the convexity angle increased while the mandibular angle decreased (P < .05). Upper and lower lip angles increased after RME (P < .05). The distance from the lower lip to the E plane increased after MMDO and decreased after RME (P < .05).

CONCLUSIONS

The MMDO and RME procedures provide an efficient nonextraction treatment alternative for transverse maxillomandibular deficiency. MMDO may improve the facial soft tissue profile in the transverse and vertical axis of the mandibular region.

Maxillomandibular Transverse Osteodistraction: A Multidisciplinary Case Report with 30-Month Follow-Up

Aim

To describe a multidisciplinary treatment to correct a severe II class malocclusion with reduced both maxillary and mandibular transverse dimensions and dental crowding. Case Report. A 17-year-old young woman presented with an increased overjet complaining chiefly of forwardly placed upper front teeth and unpleasant smile aesthetics. The patient facially exhibited a gently convex profile, severe mentalis strain on lip closure, and dark buccal corridors. The intraoral assessment indicates Class II molar relationship bilaterally, mandibular and maxillary anterior crowding, and narrow shape of upper and lower arches. The cephalometric evaluation of the lateral radiograph of the skull evidences a skeletal Class II with a reduction of lower face height. Based upon the diagnostic records and consultation with the patient, surgically assisted expansion of both arches using bone-borne distractors, comprehensive orthodontic treatment, and combined jaw surgery was planned.

Results

This approach permitted achieving most of the desired objectives in approximately 30 months. The follow-up records 30 months after treatment conclusion showed a stable occlusion. No complications were clinically and radiographically noticeable during the follow-up.

Bimaxillary transverse constriction in adults: Short-term follow-up of non-surgical arch expansion

OBJECTIVE

Concurrent maxillary and mandibular expansion is a treatment option for patients with maxillary and mandibular transverse constriction. These patients do not present with crossbite but require expansion due to narrow arches and associated crowding, dark buccal corridors and decreased anterior arch contour. The objective of the study is to first establish Bimaxillary Transverse Constriction as an under-recognized malocclusion and second to evaluate whether in adults the maxillary and mandibular arches can be successfully and safely expanded.

SETTING AND SAMPLE POPULATION

Pre- and post-treatment study models and lateral cephalograms of 31 adults with Bimaxillary Transverse Constriction expanded non-surgically were analysed. Thirty adult orthodontic patients who did not require expansion served as a control. Expanders were turned no more frequently than every other day in the maxilla and every third day in the mandible.

MATERIALS AND METHODS

Measurements in both arches made on OrthoCAD models were transarch widths, molar and premolar axial angulation, clinical crown height of posterior teeth and cuspids, and mandibular divergence. Retrospective comparison of the 2 groups used independent Student's t tests for mean differences between groups.

RESULTS

At pre-treatment, the expansion group demonstrated significant transverse constriction compared with the control. Increased widths were achieved in the expansion group (4 mm in the maxilla and 2.5 mm in the mandible), while the control group was unchanged. The mandibular plane was unchanged. There was no buccal attachment loss.

CONCLUSION

Non-surgical expansion in the maxilla and mandible is a viable treatment option for adult patients with Bimaxillary Transverse Constriction.

Mandibular Midline Distraction Osteogenesis with a Bone-borne, Tooth-borne or Hybrid Distraction Appliance: a Systematic Review

Objectives

The objective of the present systematic review was to assess the transverse skeletal and dental arch expansion and relapse after mandibular midline distraction osteogenesis with a bone-borne, tooth-borne or hybrid distraction appliance.

Material and Methods

A MEDLINE (PubMed), Embase and Cochrane library search in combination with a hand-search of relevant journals was conducted. Human studies published in English until the 3^rd of July, 2018 were included.

Results

Two comparative and seven non-comparative studies characterized by high risk of bias fulfilled the inclusion criteria. Transverse mandibular widening was achieved with the different types of distraction appliance displaying a horizontal V-shaped opening with larger anterior transverse expansion declining progressively towards the posterior part of the mandible. Bone-borne and hybrid appliance facilitate more skeletal expansion compared with tooth-borne appliance, whereas comparable dental arch expansion was achieved with the different types of distraction appliance. Skeletal and dental arch relapse with the different type of appliance was limited and comparable. However, frequency of complications was higher with bone-borne appliance compared with tooth-borne or hybrid appliance.

Conclusions

Mandibular midline distraction osteogenesis with bone-borne, tooth-borne or hybrid distraction appliance is an effective treatment modality to correct severe transverse mandibular discrepancies, although the skeletal and dental arch expansion pattern was dissimilar with the different types of appliance. However, dissimilar evaluation methods, different outcome measures, various methodological confounding factors posed serious restrictions reviewing the literature in a quantitative systematic manner. Hence, well-designed long-term randomized controlled trials applying three-dimensional technology, patient-related outcome measures and an economic perspective are needed before definite conclusions can be provided.

[Symphyseal bone distraction (part 1): benefit / risk ratio. A systematic literature review]

INTRODUCTION

The purpose of this systematic literature review is to evaluate the benefit / risk ratio of mandibular symphyseal distraction osteogenesis.

MATERIALS AND METHODS

Searches were made on Pubmed/Medline and Cochrane for randomized clinical trials and case series involving mandibular symphyseal distraction over the past 20 years with a patient sample greater than or equal to 10.

RESULTS

Of the 92 articles, 25 met the inclusion criteria. A controlled trial was selected, but no randomized trial. The other studies were all case series, 16 retrospective and 8 prospective. Distractors with bone or hybrid anchorage appear to lead to more periodontal and infectious complications due to the buccal position of the jack. Most complications are benign. However, the most difficult event to deal with is distraction device fracture. Symphyseal midline distraction increases the transverse dimension efficiently, reliably and sustainably, and appears to have no demonstrated deleterious effects on the ATMs for the three types of distractors.

DISCUSSION

Tooth-borne devices are recommended in most cases given their benefit / risk ratio. Furthermore, they do not require a second surgical procedure to remove them.

CONCLUSION

Mandibular symphyseal distraction osteogenesis is a reliable therapy whose exact limits and reproducibility remain to be defined by future prospective studies.

[Symphyseal bone distraction (part 2): which protocol in 2018? A systematic literature review]

INTRODUCTION

The aim of this systematic literature review is to propose a clinical protocol in 2018 by comparing therapeutic efficacy and undesirable effects of the technique.

MATERIALS AND METHODS

Searches were made on Pubmed/Medline and Cochrane for randomized clinical trials and case series involving mandibular symphyseal distraction over the past 20 years with a patient sample greater than or equal to 10.

RESULTS

Of the 92 articles, 25 met the inclusion criteria. A controlled trial was selected, but no randomized trial. The other studies were all case series, 16 retrospective and 8 prospective. Dental crowding over 7 mm, with or without compensation, is an indication for mid-symphyseal distraction. Pre-surgical orthodontic treatment ensures root divergence between the mandibular incisors. Tooth-borne devices are recommended in first intention. Surgical intervention (ambulatory) under local anesthesia and intravenous sedation is considered. The latency period before activation of the jack is 6 days. Activations are performed by the orthodontist and subsequently by the patient at a rate of 1 mm per day, with four activations daily. Orthodontic movements are resumed two weeks after activations are discontinued. The distractor is removed within two to three months after installation.

CONCLUSION

Although the main features of the mid-symphyseal distraction protocol were drawn up essentially in the light of expert opinion, they still need to be refined by controlled trials.

Three-dimensional evaluation of mandibular midline distraction: A systematic review

OBJECTIVE

To provide a literature overview on mandibular midline distraction (MMD) using three-dimensional (3D) imaging analysis techniques. Regarding different distractor types, the focus was on changes in position and/or morphology of the mandibular condyle and temporomandibular joint (TMJ), skeletal effects, dental effects, soft tissue effects, and biomechanical and masticatory effects, specifically on the mandible and TMJ.

METHODS

Studies up to March 27 2017 were included, in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement guidelines, using Embase, Medline OvidSP, Web-of-science, Scopus, Cochrane, and Google Scholar.

RESULTS

Thirty-one full-text papers were assessed for eligibility and 15 met the inclusion criteria: prospective (2), retrospective (2), case-report (1) and computational analysis (10). All included studies were graded low (level 4-5) for quality of evidence, using the Oxford Centre for Evidence-Based Medicine criteria.

CONCLUSION

There is a limited number of studies available, with low levels of evidence and small sample sizes. Bone-borne distraction seems preferable when taking skeletal effects into account. Tooth-borne distraction leads to significant dental tipping. Hybrid distractors combined with parasymphyseal step osteotomy seem to be the most stable under functional masticatory loads. The effects of chewing appeared to be marginal during the latency period. No permanent TMJ symptoms were reported, and little is known about soft tissue effects.

SYSTEMATIC REVIEW REGISTRATION

International Prospective Register of Systematic Reviews, PROSPERO CRD42014010010.

Mandibular Widening by Distraction Osteogenesis in the Treatment of a Constricted Mandible and Telescopic Bite

Objective

Documentation of the application of mandibular widening by distraction osteogenesis and orthodontics.

Patients

Three patients with telescopic bite resulting from an extremely constricted mandible related to hypoglossia-hypodactyly syndrome.

Intervention

Mandibular widening by distraction osteogenesis using an extraoral device and subsequent orthodontic treatment.

Results

The extremely constricted mandible and telescopic bite were dramatically improved by mandibular widening using distraction osteogenesis and subsequent orthodontics. Two of the three patients had transient complications; one reported temporomandibular joint pain and the other showed evidence of periodontal damage.

Conclusion

Mandibular widening by distraction osteogenesis is an effective technique for the treatment of telescopic bite resulting from an extremely constricted mandible.

Complications in Mandibular Midline Distraction

Mandibular midline distraction (MMD) is a relatively new surgical technique for correction of transverse discrepancies of the mandible. This study assesses the amount and burden of complications in MMD. A retrospective cohort study was performed on patients who underwent MMD between 2002 and 2014. Patients with congenital deformities or a history of radiation therapy in the area of interest were excluded. Patient records were obtained and individually assessed for any complications. Complications were graded using the Clavien-Dindo classification system (CDS). Seventy-three patients were included of which 33 were males and 40 were females. The mean follow-up was 2.1 years. Twenty-nine patients had minor complications, grades I and II. Two patients had a grade IIIa and three patients had a grade IIIb complication. Common complications were pressure ulcers, dehiscence, and (transient) sensory disturbances of the mental nerve. This study shows that although MMD is a relatively safe method, complications can occur. Mostly the complications are mild, transient, and manageable without the need for any reoperation.

Comparison of two preoperative protocols for mandibular symphyseal distraction osteogenesis to reduce the risk of tooth damage

Two techniques to separate the lower incisors prior to mandibular symphyseal distraction osteogenesis (MSDO) were evaluated with respect to avoiding tooth damage.

METHODS

Fifty patients (20.2 ± 7.0 years) requiring MSDO were treated with a tooth-borne appliance by utilizing two preoperative protocols to separate the central incisors: i) brackets and a V-bent wire with an open coil spring (two-step; TS; n = 24) and ii) a wire attached from the appliance to the central incisors with subsequent dento-alveolar expansion prior to surgery (one-step; OS; n = 26). The distance between the lower incisors was measured preoperatively on radiographs and measurements at the cast models were performed. Complications and radiographs were analyzed.

RESULTS

The mean distance (±SD) between the lower central incisors for OS and TS prior to surgery was 3.44 ± 1.05 and 3.18 ± 1.13 mm, respectively. The mean expansion for OS and TS was 4.3 ± 2.9 and 4.3 ± 2.7 mm at the dental level and 3.8 ± 3.2 and 4.0 ± 2.1 mm at the bone level, respectively. Four patients undergoing the TS and one patient undergoing the OS showed transient dental complications.

CONCLUSION

Pre-surgical dento-alveolar expansion by utilizing a one-step technique to separate the lower central incisors reduces the risk of permanent tooth damage and weakens the mandibular bone in the midline.

Long-term skeletodental stability of mandibular symphyseal distraction osteogenesis: Tooth-borne vs hybrid distraction appliances

OBJECTIVE

To evaluate and compare the long-term skeletodental stability of mandibular symphyseal distraction osteogenesis (MSDO) achieved with the use of tooth-borne vs. hybrid distraction appliances.

MATERIALS AND METHODS

Posttreatment and follow-up orthodontic records were collected for 33 patients. The 14 patients who underwent distraction with a tooth-borne appliance had a mean follow-up of 5.08 years. The 19 patients who underwent distraction with a hybrid appliance had a mean follow-up of 6.07 years. Records included intraoral photographs, study models, postero-anterior cephalometric radiographs, and lateral cephalometric radiographs. Total changes of 16 measurements were analyzed to compare patients who underwent the tooth-borne vs. the hybrid distraction.

RESULTS

Both groups shared several similar and significant (P < .05) changes from posttreatment to follow-up records. Cast analysis showed a decrease in intercanine width and arch length and an increase in irregularity index. The postero-anterior cephalometric radiograph showed an increase in the width of the interincisal apices. The lateral cephalometric radiograph showed a decrease in the MP-L1 angle. The only statistically significant difference between the two appliances was the intercentral incisor contact point.

CONCLUSION

Changes found are consistent with those found in untreated and orthodontically treated individuals over time. The long-term changes in the current patient sample can be determined to be expected and acceptable. MSDO is a viable treatment option with the use of either a hybrid or tooth-borne appliance.

Biomechanical Effects of Novel Osteotomy Approaches on Mandibular Expansion: A Three-Dimensional Finite Element Analysis

PURPOSE

Surgically assisted mandibular arch expansion has proved to be an effective treatment modality in alleviating constriction and crowding issues. However, only mandibular symphyseal distraction osteogenesis has been in favor for the purpose of mandibular arch expansion. In addition, no relevant study has compared the biomechanical response of different osteotomy designs on mandibular expansion. The present study evaluated the effect of different osteotomy approaches and modes of loading on the expansion of the adult mandible using biomechanics.

MATERIALS AND METHODS

To address the research purpose, 9 finite element (FE) models, including 2 novel osteotomy designs, were simulated. Stress, strain, and displacement of crown, root, and bone were calculated and compared under different osteotomy approaches and loading conditions.

RESULTS

The biomechanical response envisaged by the FE models in terms of displacement on the X axis was consistent from the anterior to posterior teeth with parasymphyseal step osteotomy and a hybrid mode of force application. In addition, the amount of displacement predicted by parasymphyseal step osteotomy with the hybrid mode was greater compared with that of the other models.

CONCLUSIONS

The results of our study suggest parasymphyseal step osteotomy with the hybrid mode is a viable treatment option for true bony expansion in the adult mandible.

Alternate rapid maxillary expansion-constriction and tooth-borne symphyseal distraction osteogenesis : A case report demonstrating treatment of a patient with severe crowding

Surgically assisted rapid mandibular expansion is a contemporary treatment alternative to enable genuine skeletal mandibular widening. Mandibular widening via a tooth-borne distractor is a practical and noninvasive clinical approach. Recently, to expand and protract the maxilla, the alternate rapid maxillary expansion-and-constriction procedure was suggested. In this case report, we describe a female patient (12 years 7 months old) having severe maxillary and mandibular crowding who underwent repeated alternate rapid maxillary expansion and constriction in combination with tooth-borne symphyseal distraction osteogenesis.

Interproximal wear versus incisors extraction to solve anterior lower crowding: a systematic review

OBJECTIVE

To determine by means of a systematic review the best treatment, whether interproximal wear or incisor extraction, to correct anterior lower crowding in Class I patients in permanent dentition.

METHODS

A literature review was conducted using MEDLINE, Scopus and Web of Science to retrieve studies published between January 1950 and October 2013. In selecting the sample, the following inclusion criteria were applied: studies involving interproximal wear and/or extraction of mandibular incisors, as well as Class I cases with anterior lower crowding in permanent dentition.

RESULTS

Out of a total of 943 articles found after excluding duplicates, 925 were excluded after abstract analysis. After full articles were read, 13 were excluded by the eligibility criteria and one due to methodological quality; therefore, only fours articles remained: two retrospective and two randomized prospective studies. Data were collected, analyzed and organized in tables.

CONCLUSION

Both interproximal wear and mandibular incisor extraction are effective in treating Class I malocclusion in permanent dentition with moderate anterior lower crowding and pleasant facial profile. There is scant evidence to determine the best treatment option for each case. Clinical decision should be made on an individual basis by taking into account dental characteristics, crowding, dental and oral health, patient's expectations and the use of set-up models.

Symphyseal distraction in the context of orthodontic treatment: a series of 35 cases

INTRODUCTION

Use of symphyseal distraction osteogenesis to treat a mandibular bone deficit with tooth-jaw discrepancy due to lack of space makes it possible to avoid the risks associated with the techniques usually envisaged (stripping, labioversion of incisors, extractions).

PATIENTS AND METHOD

This retrospective study presents the symphyseal distraction technique used in the maxillofacial surgery department of Lille University Hospital between January 1998 and March 2013. Treatment efficacy, complications and the stability of results were all evaluated.

RESULTS

Thirty-five patients were included in the study. The gain of inter-mental-foramen space was on average 7 mm (3-12, standard deviation 1.8 mm). A good occlusal result with dental Class I and no labioversion of the lower incisors was obtained in 27 of the 35 patients (77%).

CONCLUSION

Mandibular distraction by symphyseal osteotomy seems to be a quick, safe treatment for an anterior transversal mandibular deficit giving results that are stable over time. Its success depends on good collaboration between the orthodontist and the surgeon, and on strict patient selection.

Dentate transport discs can be used to reconstruct large segmental mandibular defects

PURPOSE

This study tested the use of a dentate transport segment for the reconstruction of a large U-shaped defect in the anterior segment of the canine mandible using a novel curved reconstruction plate. The quality and quantity of bone regenerate formed by dentate versus edentulous transport segments were compared.

MATERIALS AND METHODS

In 5 adult foxhound dogs, a defect of 70 to 75 mm was created in the canine mandible by excising the mandible anterior to the right and left fourth premolars. Reconstruction was performed by trifocal distraction osteogenesis using a bone transport reconstruction plate (BTRP-02), with 2 transport units being activated simultaneously, one on either side of the defect, 1 dentate and 1 edentulous. Bilateral distraction proceeded at a rate of 1 mm/day until the segments docked against each other in the midline. After 39 to 44 days of consolidation, the animals were euthanized. The quantity and quality of bone regeneration on the 2 sides were compared using micro-computed tomography.

RESULTS

The defect reconstruction was successful. The amount and quality of bone formed by the transport segments were similar on the 2 sides. There were no major differences in the bone volume fraction and density of the regenerate bone formed by the 2 transport segments. The bone volume fraction and density of the regenerate bone were considerably lower than those of the host bone in the distal segments, likely owing to the short consolidation period.

CONCLUSIONS

Bone transport remains a viable option in reconstructing anterior segmental defects in the mandible. The use of dentate or edentulous transport segments for reconstruction provides options for the surgeon in often highly compromised patients requiring these surgeries.

Effects of a hinged expansion screw for median mandibular distraction treatment on the lower first molars regarding tooth inclination and intermolar transverse distance

OBJECTIVES

The goal of this study was to assess the extent to which median mandibular distraction via a cemented and screw-retained full-coverage splint appliance employing a hinged expansion screw causes inclination changes in the lower first molars and widens the dental arch.

METHODS

Our study included 17 patients (12 females and 5 males; average age 16 years and 3 months) who presented with transverse space deficits and pronounced dental crowding. Baseline and final mandibular casts reflecting the situations before and after 6 weeks of median distraction therapy were created, scanned, and matched via their coordinate systems. Perpendiculars were drawn at the geometric centers between the cusp tips of teeth 36 and 46 and projected against the frontal plane. The intersection angles yielded single-tooth and total inclination values for both molars, and the difference between the intermolar distances measured at the geometric centers of both teeth provided the amount of transverse expansion.

RESULTS

An intraclass correlation coefficient (ICC) of >0.99 was obtained in a series of three measurements. After distraction treatment, the total inclination values between teeth 36 and 46 changed by +2.93 ± 9.14°. The corresponding single-tooth inclinations changed by +0.68 ± 6.32° and -2.25 ± 4.33°, respectively. Both molars underwent similar degrees of buccal or lingual tipping. Compared to a mean expansion of +6.9 ± 1.83 mm at the distraction screw, a distance increase of only +3.77 ± 1.27 mm along the transversal connecting teeth 36 and 46 was recorded. Pearson's correlation coefficient was 0.336 between total tipping and intermolar expansion (p=0.187) and -0.426 between total tipping and patient age (p=0.088).

CONCLUSION

Expansion amounts were approximately twice as long at the expansion screw as between the first molars. This V-shaped expansion pattern was due to the hinged connections between each expansion screw and the full-coverage splints. The buccal and lingual tipping of molars measured may be due to varying heights of the posterior alveolar ridge during mixed dentition or to anatomy-related differences in the expansion-screw position. In all cases we observed a mainly parallel opening of the distraction gap on the vertical plane.

Model to assess duration of distraction compared with degree of incisal crowding in symphyseal distraction osteogenesis

Our aim was to evaluate symphyseal distraction in relation to duration of expansion, and to propose an optimised procedure. Eighteen patients (mean (SD) age 19 (7) years) with transverse mandibular deficiency were treated by symphyseal distraction osteogenesis. The mean (SD) anterior dental crowding measured was 6.8 (4.2) mm. We retrospectively compared the width of expansion between the canines (ICE) and expansion between the first molars (IFME) after symphyseal distraction according to the distraction time. The median (range) duration of expansion was 13.6 (7-21) days. The median (range) ICE distraction width was 5.5 (3.4-8) mm and IFME width 3.3 (1-7.9) mm (p<0.001). There was a significant correlation between expansion width and distraction time (p<0.001). The transverse anterior and posterior expansion widths differed significantly until 14 days after expansion. The expansion ratio (ICE:IFME) decreased as expansion time increased. The results suggest that the duration of activated expansion can be predicted from the degree of incisal crowding using the formula: distraction time (days)=0.84+3.4×[IC (mm)]-0.2×[IC (mm)](2).

A finite element study on the effects of midsymphyseal distraction osteogenesis on the mandible and articular disc

OBJECTIVE

To evaluate the biomechanical effect of midsymphyseal distraction osteogenesis with three types of distractors on the mandible and articular disc using a three-dimensional finite element model analysis.

MATERIALS AND METHODS

A virtual model of the mandible was produced from computed tomography scan images of a healthy 27-year-old man. On the finite element model of the mandible, expansion of the bone-borne, tooth-borne, and hybrid type distractors were simulated with the jaw-closing muscles. The displacement and stress distribution of the mandible and articular disc were analyzed.

RESULTS

With the bone-borne appliance the alveolar process area was displaced more than the basal bone area. The tooth-borne appliance displaced the mandibular body in a parallel manner and showed high level of the von Mises stress in the alveolar process and the ramal region as well as in the condylar neck area. The hybrid type showed medium amount of displacement and stress distribution compared with the bone-borne and tooth-borne type. At the articular disc the compressive stress was concentrated in the anteromedial and posterolateral area, and it was highest in the tooth-borne distractor, followed by hybrid appliance and bone-borne appliance.

CONCLUSIONS

The tooth-borne distractor produced more parallel bony widening in the midsymphyseal area and larger expansion in the molar region; however, it induced higher stress concentration on the articular disc than the hybrid appliance and bone-borne appliance. Whether any long-term side effects on the temporomandibular joint are anticipated, especially in tooth-borne distractor, remains to be investigated.

EFFECTS OF AGING ON THE LATENCY PERIOD IN MANDIBULAR DISTRACTION OSTEOGENESIS: A COMPUTATIONAL MECHANOBIOLOGICAL ANALYSIS

Mandibular symphyseal distraction osteogenesis is a clinical procedure utilized in orthodontics for solving problems of dental overcrowding on the mandibular arch. A critical issue is to evaluate the optimal duration of the latency period between the osteotomy and the first aperture of distraction device. In fact, the latency period should change with the patient's age. To this end, a computational mechanobiological model has been developed in order to find optimal durations of latency period for young, adult, and elder patients. The model is implemented in a finite element framework simulating the process of tissue differentiation in the bone callus formed after osteotomy. The biophysical stimulus regulating the tissue differentiation process is hypothesized to be a function of the octahedral shear strain and interstitial fluid flow velocity. The resulting spatial distribution of stiffness properties in the callus region is analyzed in order to assess the risk of premature bone union of osteotomy edges. The three-dimensional (3D) finite element model (FEM) of human mandible is reconstructed from computed tomography (CT) scans and also includes a tooth-borne device. Under unilateral occlusion, the mandible is submitted to full mastication loading or to mastication forces reduced by 70%. The results show that optimal durations of the latency period for preventing premature bone union are about 5–6 days for the young patient, 7–8 days for the adult patient, and 9–10 days for the elder patient. These durations seem rather insensitive to the magnitude of mastication forces. Finally, distraction force values predicted by the present mechanobiological model are in good agreement with data reported in the literature.

[Comparative analysis of linear morphometric parameters of the humane mandibula obtained by direct and indirect measurement]

BACKGROUND/AIM

Reconstruction of lost, damaged or distorted mandibular bone presents a challenge from the functional side, as well as from the esthetic point of view. The aim of this study was to determinate potential differences between values of the basic linear moprhometric parameters (LMPs) obtained by direct and indirect manual measurement of the same humane mandibles, with accuracy testing of indirect measurement, which are routinely used in every-day clinical practice. The results are essential for defining of parametric model of the "standard mandible" and virtual modeling of the humane mandible in future researches as well as in clinical medicine.

METHODS

A total number of 12 dry bony mandibles of human adults were studied. According to the standard anatomical landmarks, 10 standard LPMs were measured on each mandible by different manual methods: directly by a sliding caliper with nonius, and indirectly using standard software on two-dimensional (2D) reconstructions of mandibular multislice computed tomography (MSCT) scans. The values obtained by the different measuring methods were matched for the same LMPs.

RESULTS

Statistically significant differences between compared LMPs values obtained by different measuring methods, appeared in the gnathio-interdental distance (Gn-IdD), as well as in the gnathio-condylar distance (Gn-CoD), bilaterally. In both parameters, significantly higher mean values (with percent of difference) were obtained by direct versus indirect measurement: Gn-IdD (21.57%; 29.2 mm vs 22.9 mm; p = 0.004); Gn-CoD left side (14.1%; 122.7 mm vs 105.4 cm; p = 0.001); Gn-CoD right side (11.87%; 124.7 mm vs 109.9 mm; p = 0.009).

CONCLUSION

According to the observed inaccuracy of indirect measurement, we recommended the use of a correction factor for calculation of both Gn-IdD and Gn-CoD real vales, in defining of parametric model of the "standard mandible" based on indirect morphometry on 2D reconstructions of mandibular MSCT scans. Additional studies with larger number of specimens and quantification of anatomical variations regarding to sex, age, dentition status and ethnic origin, additionally should increase measurement accuracy and consequently reliability of future parametric model of the human mandible.

Analysis of the performance of different orthodontic devices for mandibular symphyseal distraction osteogenesis

The aim of this study was to investigate the performance of different orthodontic devices for mandibular symphyseal distraction osteogenesis (MSDO). Two performance parameters were analysed, the first of which concerned the stability guaranteed by a distractor in the fracture gap under mastication loads and the second the level of reliability with which a distractor transfers a given expansion to the mandibular bone, inasmuch as the more reliable the device the smaller the difference between the degree of expansion provided to the device and the displacement achieved on the mandibular arch. Hence, a non-linear finite element (FE) model of a human mandible with different devices (tooth-borne, bone-borne, and hybrid) was constructed and then utilized to assess the structural behaviour of the mandibular bone under distraction and mastication loads. An ad hoc algorithm was developed to simulate progressive expansion of the devices; a distraction protocol comprising a 10 day latency period and a 6 day distraction period was hypothesized. The first hypothetical expansion given to the device was 2 mm, and the five subsequent expansions were 1 mm. The results showed that the hybrid device was the most stable appliance under mastication loads, followed by the tooth- and bone-borne devices. However, parasitic rotations of the mandibular arms caused by mastication might counteract the benefits of distraction. The tooth-borne device was found to have the highest reliability in transferring expansion to the mandibular bone. For this device, mandibular expansion was less than the nominal aperture of the distractor by no more than 15 per cent. Lower values of reliability were achieved with the bone-borne device. As the values of the aperture of the appliances increased, the stability guaranteed in the fracture gap increased while the reliability in transferring expansion to the mandibular arch decreased.

Advancement of mandibular symphysis with distraction osteogenesis

This case report demonstrates the effects of mandibular symphysis advancement with distraction osteogenesis (DO) in a 21-year-old man with a Class I molar relationship, protrusive maxillary incisors, crowding in both arches, and increased overjet and overbite. Treatment consisted of maxillary arch leveling, mandibular incisor repositioning through mandibular symphysis advancement with DO, and subsequent mandibular arch leveling. The osteotomy line, between the canine and the first premolar, was extended from the interdental area to the lower border of the mandibular symphysis bilaterally. The distraction device was cemented after mobilization of the mandibular symphysis. The screws were activated (0.8 mm per day) after a latent period of 1 week. The amount of activation per side was 6.4 mm. After an 8-week consolidation period, the distraction appliance was removed. At the end of treatment, increases of SNB angle, effective mandibular length, SN/GoGn, anterior facial height, mandibular incisor inclinations, and labiomental angle were observed. Decreases of ANB angle, overjet, and distance from the lower lip to the esthetic line were noted. Even though this patient's long-term results are not yet available, the results so far are encouraging. Mandibular symphysis advancement with DO seems to be an effective method for correcting mandibular anterior crowding and an increased overjet.

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Facing a dental crowding, the orthodontist has several therapeutic options. If maxillary expansion is often used, mandibular orthodontic expansion is proscribed because of its tendency of inefficiency and relapse. Mandibular symphyseal distraction osteogenesis allows to remove this proscription. This therapeutic protocol consists in a pre-surgery orthodontic preparation phase followed by surgery (symphyseal osteotomy and placement of the distraction device), a latency period (five to seven days), then an activation period (most of the time 1 mm/day in two steps) followed by a consolidation period (three months) during which the orthodontic treatment can be resumed. Skeletal and alveolar expansion corrects dental crowding. This surgical technique is versatile, minimally invasive, and stable with time. Major indications are hypoplastic symphysis, anterior crowding, relapse of orthodontic treatments and some syndromes. This method can also be an answer to aesthetic concerns or an alternative for treatment of dental crowding. Face à un encombrement dentaire, l'orthodontiste dispose de plusieurs options thérapeutiques. Si au maxillaire, l'expansion est fréquemment utilisée, l'expansion mandibulaire orthodontique est proscrite, car inefficace et récidivante. La distraction symphysaire permet de lever cet interdit. Ce protocole thérapeutique comprend : une préparation orthodontique pré-chirurgicale, une chirurgie (ostéotomie symphysaire et pose du distracteur), une période de latence (cinq à sept jours), puis une période d'activation (le plus souvent 1 mm/j en deux fois) suivie d'une période de consolidation (trois mois) pendant laquelle le traitement orthodontique peut être repris. L'expansion basale et alvéolaire corrige l'encombrement dentaire. Cette technique est polyvalente, peu invasive et stable dans le temps. Ses indications majeures sont l'hyposymphysie, l'encombrement incisif, la récidive de traitements orthodontiques et certains grands syndromes. Cette méthode peut aussi être proposée pour répondre à des préoccupations esthétiques ou comme alternative aux traitements classiques de l'encombrement dentaire.