Stability of hard tissue profile after mandibular setback in sagittal split osteotomies: a longitudinal and long-term follow-up study

The aim of the study was to conduct a long-term follow-up on the stability of the hard tissues after bilateral sagittal split osteotomy (BSSO) with rigid internal fixation (RIF)to set back the mandible and to compare it with that of mandibular advancement performed by the same team of surgeons and with the same examination protocol. Seventeen consecutive patients (6 females and 11 males) could be re-examined 12.7 years (T5) after surgery. The previous examinations were before surgery (T1), 5 days (T2), and 6.6 (T3) and 14.4 (T4) months after surgery. Lateral cephalograms were traced by hand, digitized, and evaluated with the Dentofacial Planner software program. The x-axis for the system of co-ordinates ran through sella (point zero) and the line nasion-sella-line minus 7 degrees. The program determined the x- and y-values of each variable and the usual angles and distances. The effects of treatment were determined with Wilcoxon matched pairs, signed ranks test, with Bonferroni adjustment, and the relationship between variables with Spearman rank correlation coefficient. Relapse at point B was 0.94 mm or 15 per cent and at pogonion 1.46 mm or 21 per cent of the initial setback at T5. Relapse was mainly short-term (T4-T2), 13 per cent for point B and 17 per cent for pogonion. Gender correlated significantly with relapse (T5-T2) at point B (P = 0.002) and pogonion (P = 0.021), i.e. females in contrast to males showed further distalization of the mandible instead of relapse. No correlations were seen for age or the amount of surgical setback. The long-term results in mandibular setback patients were more stable when compared with the mandibular advancement patients examined previously. The initial soft tissue profile, the initial growth direction, and the remodelling processes of the hard tissues must be considered as reasons for long-term relapse. Growth direction positively influenced the long-term results in females: further distalization of the mandible occurred.     

Long-term hard and soft tissue relapse rate after genioplasty

PURPOSE: The purpose of this study was to assess hard and soft tissue stability 12 months after advancement genioplasty. MATERIAL AND METHODS: This is a retrospective study of 20 patients who underwent either advancement genioplasty alone (n = 11) or in combination with bilateral sagittal split osteotomy for mandibular advancement (n = 9). Lateral cephalometric radiographs were traced and immediate postoperative changes and 12-month postoperative changes were defined. The relapse rate for the pogonion, the soft tissue pogonion, and the soft tissue B point (Bs) were evaluated. The results were compared for combined mandibular advancement plus genioplasty versus genioplasty alone. Relapse rates were also correlated with the amount of advancement. All patients were treated with rigid internal fixation. RESULTS: After 12 months, the pogonion, the soft tissue pogonion, and the soft tissue B point had a mean relapse rate of -0.38 mm, -1.2 mm, and -1.5 mm (negative value indicates a relapse, and a positive value indicates prolapse), respectively, which was not significant at probability values of.45,.069, and.054, respectively. Relapse was not statistically related to the amount of advancement. There was no significant difference between the relapse rate for genioplasty alone versus combined bilateral sagittal split osteotomy and genioplasty, even with different amounts of advancement. CONCLUSIONS: Advancement genioplasty is an important and reliable technique for the esthetic treatment of the lower facial skeleton. The results indicate that there is no significant relapse after genioplasty and bilateral sagittal split osteotomy or genioplasty alone after 12 months when rigid internal fixation is used. The changes were minimal and hard to detect clinically. Genioplasty, with or without mandibular advancement, is a stable surgical procedure when used in conjunction with rigid internal fixation.     

Soft tissue stability after segmental distraction of the anterior mandibular alveolar process: a 5.5 year follow-up

Soft tissue changes were analysed retrospectively in 17 patients following distraction osteogenesis (DO) of the mandibular anterior alveolar process. Lateral cephalograms were traced by hand, digitized, superimposed, and evaluated at T1 (17.0 days), after DO at T2 (mean 6.5 days), at T3 (mean 24.4 days), at T4 (mean 2.0 years), and at T5 (mean 5.5 years). Statistical analysis was carried out using Kolmogorov–Smirnov test, paired t-test, Pearson's correlation coefficient, and linear backward regression analysis. 5.5 years postoperatively, the net effect for the soft tissue at point B′ was 88% of the advancement at point B while the lower lip (labrale inferior) followed the advancement of incision inferior to 24%. Increased preoperative age was correlated (p < 0.05) with more horizontal backward movement (T5–T3) for labrale inferior and pogonion′. Higher NL/ML′ angles were significantly correlated (p < 0.05) to smaller horizontal soft tissue change at labrale inferior (T5–T3). The amount of advancement at point B was significantly correlated with an upward movement (T5–T3) of labrale inferior (p < 0.01) and stomion inferior (p < 0.05). It can be concluded that further change in soft tissues occurred between 2.0 and 5.5 years postoperatively. The physiological process of ageing and loss of soft tissue elasticity should be considered as possible reasons.     

Soft tissue to hard tissue advancement ratios for mandibular elongation using distraction osteogenesis in children

Distraction osteogenesis is extensively used for the elongation of hypoplastic mandibles in children, yet the soft tissue profile response to this is not well understood. The pre- and posttreatment lateral cephalometric radiographs of 27 pediatric patients who underwent bilateral mandibular elongation using distraction osteogenesis were analyzed retrospectively to correlate horizontal soft tissue advancement with horizontal underlying bone advancement at B point and pogonion. Horizontal advancement (in millimeters) of bone and overlying soft tissue at these points was collected from the radiographs of each patient, and linear regression analysis was performed to determine the relationship of hard to soft tissue horizontal advancement at these points. A 1:0.90 mean ratio of bone to soft tissue advancement was observed at B point/labiomental sulcus and at pogonion/soft tissue pogonion (linear regression analysis demonstrated slopes [beta1 values] of 0.94 and 0.92, respectively). These ratios were consistent throughout the sample population and are highly predictive of the soft tissue response that can be anticipated. Magnitude of advancement, age, and sex of the patient had no effect on these ratios in our population. This study assists with our understanding of the soft tissue response that accompanies bony elongation during distraction osteogenesis which will allow us to more effectively treatment plan the orthodontic and surgical intervention that will optimize the patients' functional and esthetic outcome.     

Relapse after rigid fixation of mandibular advancement

In 19 subjects rigid fixation of bilateral sagittal split osteotomies was used for mandibular advancement. Five angles and four linear measurements were determined cephalometrically for two time intervals: before surgery to immediately after surgery (T1-T2), and immediately after surgery to six months to one year after surgery (T2-TL). A multiple regression analysis with a backward stepping procedure was used to determine relationships between relapse, as defined by the position of pogonion at T2-TL (PgT2) and B point during this same time interval (BT2). The only significant predictor of PgT2 was PgT1 (P less than 0.001) (amount of advancement of pogonion during the time interval T1-T2). When BT2 was examined, both the change in position of B point at T1-T2 (P less than 0.001) and the change in anterior facial height at T1-T2 (P less than 0.02) were significant predictors of relapse. There were no other predictors of relapse. Advancements of 6 to 7 mm or greater as measured at B or Pg deserve special attention as they were more predisposed to relapse. Methods for preventing relapse are discussed.     

Comparison of relapse in bilateral sagittal split osteotomies for mandibular advancement: rigid internal fixation (screws) versus inferior border wiring with anterior skeletal fixation

A retrospective study of 28 patients treated by bilateral sagittal split ramus osteotomies for mandibular advancement and stabilized by two different methods of fixation was performed. Fourteen patients received rigid fixation, and 14 patients had inferior border wiring with anterior skeletal fixation. The postoperative and long-term cephalograms (greater than 6 months) were analyzed in a horizontal and vertical direction for relapse. In the horizontal direction, the rigid group experienced a 1.5% relapse in point B and a 3.2% relapse in pogonion. In the vertical direction, the rigid group experienced a 4% relapse in point B and a 9% relapse in pogonion, while the wire osteosynthesis group had a 13% relapse in point B and a 6% relapse in pogonion. These results support the belief that rigid fixation is more stable than is wire osteosynthesis and that it helps prevent relapse in the long-term results.     

How the lower face soft tissue changes after mandibular advancement or setback

To contribute as an auxiliary tool for orthodontic and orthognathic planning and treatment, short-term changes on the lower face soft and hard tissues were investigated. All subjects presented adequate maxillary relation with the cranial base. The treatment was done by mandibular advancement in patients with skeletal class II or setback in skeletal class III, by the same oral surgeon, using the same technique, and rigid internal fixation. Lateral cephalograms were traced at the following intervals: T0--immediately before the surgical procedure, T1--6 months after surgery, and T2--1 year after surgery. The postoperative data of the lower face revealed highly significant changes for the soft tissue pogonion and lower lip, in the mandible advancement cases, whereas the underlying bone and dental structures remained constant. For the mandible setback cases, just the hard tissue pogonion variable displayed a statistically significant change.     

Bilateral sagittal split osteotomy for correction of mandibular prognathism: long-term results.

PURPOSE: To identify the long-term maxillomandibular changes after surgical correction of mandibular prognathism using bilateral sagittal split osteotomy (BSSO). PATIENTS AND METHODS: Twenty patients who underwent BSSO to setback the mandible and had cephalometric radiographs taken preoperatively and postoperatively at 6 weeks, 1 year, and long-term follow-up (mean, 28 months). The cephalograms were traced and measured to determine the operative and postoperative changes. Correlation analyses were performed to see the relationship between the magnitude of setback and the amount of long-term postsurgical change at B point and pogonion. RESULTS: The mean surgical setback was 8.2 mm at B point and 8.8 mm at pogonion. The mean long-term horizontal relapse was 2.3 mm (28.0%) at B point and 3.0 mm (34.1%) at pogonion. Out of 20 patients, 12 (60.0%) relapsed horizontally greater than 2 mm at B point and 13 (65.0%) at pogonion. The mean vertical surgical changes showed downward displacement of B point (2.3 mm) and pogonion (2.0 mm). The mean long-term vertical relapse was 1.6 mm (69.6%) at B point and 1.7 mm (85.0%) at pogonion. CONCLUSION: There was no correlation between the magnitude of setback and the amount of relapse at B point and pogonion. However, there was significant correlation between the magnitude of vertical, downward surgical displacement and the amount of vertical relapse at B point and pogonion. The majority of the maxillofacial changes occurred within 1 year postoperatively.     

Soft tissue response to mandibular advancement and genioplasty.

Changes in facial esthetics after orthognathic surgery should be predictable if the results are to be satisfactory. The skeletal elements are moved in a planned and controlled manner, but the soft tissue drape is not as precisely managed. This study was on 31 patients who had undergone a mandibular advancement by means of a sagittal split osteotomy, 17 of whom had also received an advancement genioplasty and 6 received a maxillary impaction. The results showed a consistent 1:1 ratio of soft to hard tissue advancement at pogonion and B point, and that predictions could be accurate in both anteroposterior and vertical directions. When a genioplasty was added to the advancement, however, the results were much less consistent. The mean ratio was 0.9:1 of soft tissue to skeletal movement at pogonion, but the average difference between hard and soft tissue movement was +/- 2.6 mm. Thus the prediction of anteroposterior soft tissue changes was quite inaccurate. Changes in the vertical dimension were also more marked in the genioplasty group. The lower lip also showed a variable response, particularly in the genioplasty group, where the mean ratio was 0.5 mm lip advancement per 1.0 mm skeletal change, but again a range of 4.0 mm in either direction. There were no meaningful changes 1 year after surgery.     

Soft tissue stability in segmental distraction of the anterior mandibular alveolar process. A 2-year follow-up

This study evaluated soft tissue changes in adult patients treated with distraction osteogenesis (DOG) of the anterior mandibular alveolar process and related it to different parameters. 33 patients (27 females; 6 males) were analysed retrospectively before surgery at T1 (17.0 days), after surgery at T2 (mean 6.5 days), at T3 (mean 24.4 days), and at T4 (mean 2.0 years). Lateral cephalograms were traced by hand, digitized, superimposed, and evaluated. Statistical analysis was carried out using Kolmogorov-Smirnov test, paired t test, Pearson's correlation coefficient, and linear backward regression analysis. 2 years postoperatively (T4), the net effect of the soft tissue at point B' was 100% of the advancement at point B whilst the lower lip (labrale inferior) followed the advancement of incision inferior to 46%. Increased preoperative age was correlated (p<0.05) with more horizontal backward movement (T4-T3) for labrale superior and pogonion'. Higher NL/ML' angles were significantly correlated (p<0.05) with smaller horizontal soft tissue change at point B'. Gender and the amount of skeletal and dental advancement were not correlated with postoperative soft tissue changes (T4-T3). DOG of the anterior mandibular alveolar process is a valuable alternative for mandibular advancement regarding soft tissue change and predictability.     

Analysis of soft tissue profile changes after mandibular advancement surgery

The aim of this study was to analyze changes in soft tissue profile after mandibular advancement surgery, with special emphasis on the effect of skeletal relapse and different Class II facial patterns. The cephalometric radiographs of 30 consecutive patients (24 women and 6 men, mean age 23 years) who underwent sagittal split osteotomy were studied. The radiographs were taken immediately before operation, at one week and 14 months postoperatively. To analyze the possible influence of hyper- and hypodivergent facial patterns, the patients were classified into low- (4 patients), medium- (16 patients) and high-angle (10 patients) groups according to the magnitude of the mandibulonasal plane angle. The main movement occurred in the horizontal plane. Soft tissue pogonion and mentolabial fold were found to follow the underlying skeletal structures in a nearly 1:1 ratio. On final follow-up, skeletal relapse of 1.3 mm was measured at B-point and of 1.5 mm at pogonion. Taking the skeletal relapses into account, the ratios of both corresponding soft tissue references (alternative ratios) dropped to 60%. Soft tissue pogonion is the most reliable reference for the planning of mandibular advancement. The ratio of soft tissue movement to final skeletal position at the chin amounts to 60% for a realistic prediction. However, the low-angle group differed from other groups by showing a markedly low soft-to-hard tissue ratio of only 14% at pogonion and a high ratio of 109% at the mentolabial fold. However, these differences in ratios between the groups were statistically not significant.     

Long-term stability of isolated advancement genioplasty,and influence of associated risk factors: A systematic review

The aim of this review was to investigate the skeletal and soft tissue stability of isolated advancement genioplasty after more than 1 year, and to observe the influence of associated risk factors.A literature search was performed on PubMed, Web of Science, Embase, ScienceDirect, and Cochrane. Only studies with at least 10 patients who underwent an isolated advancement genioplasty, and with a follow-up period of at least 1 year, were included.Of the 2224 records initially identified, eight articles met the eligibility criteria. The mean age of the total study population was 23 years and ranged from 19.1 to 26.5 years in the individual studies. The average surgical advancement at pogonion was 8.2 mm and ranged from 6.2 to 11.7 mm in the individual studies. After 1 year, the horizontal hard tissue relapse at the level of pogonion varied from 0.1 to 2.1 mm. In two studies, this was reported as statistically significant. Regarding the soft tissue, the horizontal relapse varied from 0.3 to 2.9 mm, which was also considered statistically significant in two studies.Isolated advancement genioplasty was found to be a predictable and stable orthognathic procedure in the sagittal plane at both soft and hard tissue levels. The amount of relapse was not associated with the fixation method or with the amount of surgical advancement.     

Skeletal Relapse Following Sagittal Split Ramus Osteotomy Advancement

Background

Sagittal split ramus osteotomy (SSRO) is an accepted and standard procedure to address mandibular corpus deficiency. The relapse following the mandibular advancement has a negative impact both on clinician and patient.

Purpose

To analyse the hard tissue changes and to investigate relapse following SSRO advancement procedure.

Materials and Methods

A retrospective review of 21 patients treated by bilateral SSRO advancement at our institute was conducted. Lateral cephalograms obtained at pre-treatment (T1), pre-surgery (T2), 2 months (T3) and 2 years post-surgery (T4) were evaluated by an independent investigator. The data T2–T3 revealed immediate postoperative changes, and T3–T4 revealed skeletal relapse following surgery after 2 years.

Results

Twelve females and nine males with age ranging from 16 to 24 years underwent mandibular advancement. The mean follow-up period was 2 years 7 months ± 4 months. The mean mandibular advancement at pogonion was 5.1 ± 1.25 mm with significant improvement in SNB, ANB, CoGn, maxillo-mandibular differential and SN:GoPg ratio following surgery. Comparison of the outcomes following surgery revealed that the mean relapse at pogonion was 0.2 ± 0.44 mm. B point, mandibular corpus length, anterior and posterior facial height remained stable with no significant relapse following mandibular advancement.

Conclusion

Sagittal split ramus osteotomy within the range of mandibular advancement is a stable procedure.     

Predicting lower lip and chin response to mandibular advancement and genioplasty

The purposes of this retrospective study were to examine the multidimensional nature of soft tissue changes associated with mandibular advancement and genioplasty and to develop predictive models. Longitudinal lateral cephalograms of 62 nongrowing patients (27 men and 35 women) were taken in centric relation with the lips in repose within 4 weeks before surgery and at least 6 months postoperatively (median postsurgical duration was 11 months). The mandibular incisor and pogonion were advanced surgically approximately 6 mm and 11 mm, respectively. The lower lip lengthened slightly (2.5 +/- 3.8 mm), and its surface contour straightened because of thinning at labrale inferior (-2.8 +/- 2.0 mm); there was a slight thickening at the labiomental fold (1.0 +/- 2.3 mm) and a slight thinning at soft tissue pogonion (-0.8 +/- 2.2 mm). Multiple regression models (explaining from 80% to 94% and 66% to 82% of the variation for horizontal and vertical movements, respectively) showed that soft tissue response to advancement surgery depended on pretreatment tissue thickness, horizontal skeletal movement, vertical skeletal movement, and the position of the maxillary incisors. Similar amounts of variation were explained when the models were applied to an independent validation sample of 15 subjects. It was concluded that lower lip and chin response to mandibular advancement and genioplasty is multifactorial but can be accurately and reliably predicted.     

Prospective clinical trial comparing the effects of conventional Twin-block and mini-block appliances: Part 2. Soft tissue changes.

PURPOSE: The aims of this prospective clinical trial were to compare the soft tissue effects of Twin-block (TB) and mini-block (MB) functional appliances by using lateral cephalograms and optical surface laser scans and to evaluate the extent of posttreatment relapse with both appliances. MATERIAL: Seventy Class II Division 1 patients meeting set inclusion criteria were matched by age and sex. The matched pairs were randomly allocated to treatment with either the TB or the MB appliance. The appliances were worn full time for 9 months (phase I), followed by a 3-month observation phase of no appliance wear (phase II). Lateral cephalograms were taken at the start of treatment and at 12 months, and laser scans were taken at 0, 3, 9, and 12 months. RESULTS: Radiographically, there was a greater advancement of the soft tissue pogonion in the TB group (median, TB: 4.0 mm; MB: 1.8 mm; P = .004), whereas the soft tissue anterior face height increased similarly in both groups (median, TB: 4.4 mm; MB: 4.3 mm). Optical surface scans confirmed the cephalometric changes. There were a greater forward movement of soft tissue pogonion in the TB group during active treatment (median change, TB: 3.2 mm; MB: 3.9 mm) and similar increases in the soft tissue total anterior face height (median change, TB: 3.2 mm; MB: 3.9 mm). There were negative changes of soft tissue pogonion (median, TB: -1.0 mm; MB: -0.9 mm) and vertical face height (median change, TB: -0.7; MB: -0.6) during phase II. CONCLUSIONS: The TB appliance produced the greater overall change in the soft tissue profile. However, there were clinically significant relapse changes in the immediate postfunctional phase.     

Stability of skeletal Class II correction with 2 surgical techniques: the sagittal split ramus osteotomy and the total mandibular subapical alveolar osteotomy.

Combined orthodontic and surgical treatment of severe Class II dentoskeletal deformities with the use of the bilateral sagittal split ramus osteotomy is a routine procedure in orthodontic practices. However, an alternative surgical technique, the total mandibular subapical alveolar osteotomy, could be used for the same purpose. The aim of this investigation was to compare the stability of the sagittal split ramus osteotomy with the total mandibular subapical alveolar osteotomy in the correction of dentoskeletal Class II malocclusions. Forty patients that exhibited Class II dentoskeletal relationships were included in the study. Twenty of these patients had mandibular advancement with the sagittal split ramus osteotomy; the remaining 20 patients had advancement of the whole lower alveolar segment with the total mandibular subapical alveolar osteotomy. The cephalograms studied were taken before the surgical procedure (T1 = 4 weeks before operation), immediately after the procedure (T2 = 10 days after surgery), and 1 year later (T3). The statistical analysis used to assess the results between and within the groups over the different time periods was the analysis of variance. The regression analysis was used to test the interdependence of soft tissue response to hard tissue movement. The results of this study show that both procedures are equally stable when correcting Class II malocclusions. This was proved by the stability of the correction of overjet, B point, and incisor-mandibular plane angle. There were no statistically significant differences between or within the groups in the position of these landmarks over time. There was a statistically significant change in the position of pogonion from T1 to T2 (P <.0028) between the groups, although at T3 this difference was not significant (P <.05). There were no significant changes in face height either within or between the groups over time. The hard/soft tissue interactions for the total mandibular subapical alveolar osteotomy were as follows: The lower lip advanced 60% to the incisor movement; soft tissue B' point responded with a 130% advancement in relation to the change in its hard tissue counterpart. Soft tissue pogonion advanced 90% in relation to the hard tissue landmark. The data suggest that the total mandibular alveolar osteotomy is the treatment of choice for the correction of severe dentoalveolar retrusive Class II malocclusion for which alteration of the mentolabial sulcus is desirable.     

Five-year outcome and predictability of soft tissue profiles when wire or rigid fixation is used in mandibular advancement surgery.

The purpose of this study was to follow the covariation of hard and soft tissue changes in Class II malocclusion subjects who received a bilateral sagittal split osteotomy. The subjects were randomized to receive wire or rigid fixation after the surgery. Subjects in the rigid group (n = 78) received 2-mm bicortical position screws, and those in the wire group (n = 49) received inferior border wires and 6 weeks of skeletal intermaxillary fixation with 24-gauge wires. Additionally, some subjects received genioplasty in both the rigid (n = 35) and the wire groups (n = 24). Soft and hard tissue profile changes were obtained from cephalometric films immediately before surgery and at various times up to 5 years postsurgery. Soft and hard tissue profile changes were referenced to a cranial-base X-Y coordinate system. Horizontal changes in mandibular incisor, lower lip, B-point, soft tissue B-point, pogonion, and soft tissue pogonion were calculated at each time. There was considerable skeletal relapse in the wire fixation group. Bivariate correlations and ratios between the hard and soft tissue changes were calculated for each time period. Hard to soft tissue correlations were the highest at the earlier times, although the ratios varied among the 4 groups. These results provide a solid basis for both short-term and long-term prediction.     

Skeletal and dental stability of segmental distraction of the anterior mandibular alveolar process. A 5.5-year follow-up

17 patients (14 female; 3 male) were analysed retrospectively for skeletal and dental relapse before distraction osteogenesis (DO) of the mandibular anterior alveolar process at T1 (17.0 days), after DO at T2 (mean 6.5 days), at T3 (mean 24.4 days), at T4 (mean 2.0 years), and at T5 (mean 5.5 years). Lateral cephalograms were traced by hand, digitized, superimposed, and evaluated. Skeletal correction (T5–T1) was mainly achieved through the distraction of the anterior alveolar segment in a rotational manner where the incisors were more proclined. The horizontal backward relapse (T5–T3) measured ?0.3 mm or 8.3% at point B (non-significant) and ?1.8 mm or 29.0% at incision inferior (p < 0.01). Age, gender, amount and type (rotational vs. translational) of advancement were not correlated with the amount of relapse. High angle patients (NL/ML′; p < 0.01) showed significant smaller relapse rates at point B. Overcorrection of the overjet achieved by the distraction could be a reason for dental relapse. Considering the amount of long-term skeletal relapse the DO could be an alternative to bilateral sagittal split osteotomy for mandibular advancement in selected cases.     

Advancement genioplasty in Class I patients: predictability and stability of facial profile changes

This retrospective study evaluated the skeletal and soft tissue facial profile changes as well as the predictability and the short-term stability of the soft-tissue response to advancement genioplasty in Class I dental arch relationship patients. The study included 14 adult patients who presented a Class I dental arch but a Class II skeletal arch relationship and underwent advancement genioplasty exclusively. Lateral cephalograms taken immediately preoperatively (T1), immediately postoperatively (T2) and 1 year postoperatively (T3) were analysed. The hard tissue pogonion was sagittally advanced by an average of 7.9 mm (p < 0.001) (T1-T2). The soft tissue chin followed the sagittal skeletal chin movement and exceeded chin advancement due to the initial soft tissue swelling. In the vertical dimension, the skeletal chin moved 3.0 mm (p < 0.01) upwards whilst the soft tissue chin moved only 2.1 mm upwards (p < 0.01). All profile convexity angles increased significantly (p < 0.001), implying that the profile was straightened by the advancement of the chin. In the short term, advancement genioplasty was a predictable and stable procedure for chin correction. A ratio of 1:1 may be used to predict the sagittal soft tissue to bony movements for the period from before to 1 year after surgery.     

Effect of distraction osteogenesis on the severely hypoplastic mandible and inferior alveolar nerve function.

PURPOSE: The purpose of this study was to examine the effect of distraction osteogenesis surgery on the inferior alveolar nerve (IAN) and on the stability of the occlusion in patients undergoing mandibular osteotomy and advancement for correction of severe retrognathia. MATERIALS AND METHODS: Five patients (4 women and 1 man) underwent vertical posterior body osteotomy or bilateral sagittal split ramus osteotomy with the application of a distraction device for advancement of the mandible of 10 to 14 mm. After a period of latency, each mandible was advanced 1 mm per day until the patient achieved a Class I occlusion. Distraction devices were removed after a suitable period of consolidation (4 to 11 months). IAN sensory function was evaluated by 2-point discrimination, response to painful stimulus, and moving brush stroke identification. Testing of the IAN was performed on all patients at 7 different time intervals: preoperative (T0), postsurgery and predistraction (T1), within 7 days after the end of distraction (T2), 3 months after T2 (T3), 6 months after T2 (T4), 9 months after T2 (T5), and 1 year after T2 (T6). The same surgeon performed all IAN testing. RESULTS: There were no instances of malunion or fibrous union. At the 1-year follow-up, all 5 patients showed no relapse of their advancement as assessed by their maintenance of a Class I occlusion. Radiographic analysis was not done to discern skeletal versus dental stability. All 10 IANs were intact after the initial surgery. As time progressed, all 10 nerves showed improvement of function as measured by 2-point discrimination, response to painful stimulus, and moving brush stroke identification. At 1 year postsurgery, all 10 nerves showed function consistent with or very near presurgery levels. CONCLUSION: Stable mandibular advancements of 10 mm and greater can be successfully accomplished by distraction osteogenesis without producing significant damage to the IAN.