All PhD Theses

C.U. Joss

Distraction osteogenesis of the anterior mandibular process

07-12-2015

A scientific essay in Medical Sciences

DOCTORAL THESIS defended in public on 7th of December 2013

SUMMARY

Chapter 1 introduces the topic of non-surgical and surgical modalities in orthodontics to treat Class II malocclusions. Epidemiologic surveys, incidence, etiologic factors, and treatment indications of Class II malocclusions are shortly discussed. Furthermore the features of Class II malocclusions are presented. Different treatment approaches are necessary if orthodontic treatment for Class II malocclusions is carried out in growing children and adolescences or in non-growing individuals. For growing individuals, various types of functional and other appliances as well as treatment principles to enhance mandibular growth are addressed in this chapter. Two basic treatment options are described in non-growing individuals: Orthodontic  camouflage therapy (with or without additional genioplasty) and surgical correction of the dysgnathia in combination with orthodontic treatment. Finally, the bilateral sagittal split osteotomy for mandibular advancement (BSSO), the distraction osteogenesis (DO), and the DO of the anterior mandibular alveolar process are explored.

In chapter 2 the results of the study concerning the soft tissue changes after BSSO for mandibular advancement are presented. The purpose of the systematic review was to evaluate the soft tissue/hard tissue ratio i n BSSO with rigid internal fixation (RIF) or wire fixation (WF) of the osteotomy segments. The databases PubMed, Medline, CINAHL, Web of Science, Cochrane Library, and Google Scholar Beta were  searched. From the original 711 articles identified, 12 were finally included. Only 3 studies were prospective and 9 were retrospective. The postoperative follow-up ranged from 3 months to 12.7 years for RIF and 6 months to 5 years for WF. The short- and long-term ratios for the lower lip to lower incisor for BSSO with RIF or WF were 50%. No difference between the short- and long-term ratios for the mentolabial-fold to point B and soft tissue pogonion to pogonion could be observed. It was a 1:1 ratio. One exception was seen for the long-term results of the soft tissue pogonion to pogonion in BSSO with RIF; they tended to be greater than a 1:1 ratio. The upper lip mainly showed retrusion but with high variability. Despite a large number of studies on the short- and long-term effects of mandibular advancement by BSSO, the results of the present systematic review have shown that evidence-based conclusions on soft tissue changes are still unknown. This is mostly because of the inherent problems of retrospective studies, inferior study designs, and the lack of standardized outcome measures. Well-designed prospective studies with sufficient sample sizes that have excluded patients undergoing additional surgery (ie, genioplasty or maxillary surgery) are needed.

Chapter 3 describes a retrospective study on 33 patients (27 females; 6 males) analysed for skeletal and dental relapse before 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), and at T4 (mean 2.0 years). Lateral cephalograms were traced by hand, digitized, superimposed, and evaluated. Skeletal correction (T3-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 (T4-T3) measured -0.8 mm or 19.0% at point B (p < 0.001) and -1.6 mm or 25.0% at incision inferior (p < 0.001). Age, gender, amount and type (rotational versus translational) of advancement were not correlated with the amount of relapse. High angle patients (NL/ML'; p < 0.01) and patients with large gonial angle ( p < 0.05) showed significantly smaller relapse rates at point B. Overcorrection of the overjet achieved by the distraction was seen in a third of the patients and could be a reason for relapse. Considering the amount of skeletal relapse the DO could be an alternative to bilateral sagittal split osteotomy for mandibular advancement in selected cases.

Chapter 4 presents the evaluation of soft tissue changes in adult patients treated with DO 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). DO of the anterior mandibular alveolar process is  a valuable alternative for mandibular advancement regarding soft tissue change and predictability.

Chapter 5 addresses the neurosensory status and craniomandibular function after DO. 19 patients (mean age 35.2 years, range 17.8 -58.8 years) treated by combined surgical orthodontic treatment with DO of the anterior mandibular alveolar process (DO-group) were compared with a control-group of 41 orthodontically treated patients (mean age 22.9 years, range 15.1-49.0 years). Clinical examination took place on average 5.9 years (DO-group) and 5.4  years (control-group) after treatment ended. Neurosensory status was determined by two-point discrimination (2-pd) and the pointed and blunt test. Lateral cephalograms evaluated advancement of the mandibular alveolar process and possible relapse. There was no  significant difference in  craniomandibular function  and neurosensory status between the groups. Age was significantly correlated with 2-pd  at the lips (DO-group: p  = 0.01, = 0.575; control-group: p = 0.039, R = 0.324) and chin (DO-group: p = 0.029, R = 0.501; control- group: p = 0.008, R = 0.410). Younger patients had smaller 2-pd values. Gender, age, the amount of advancement, and relapse at point B or incision inferior show no correlation with craniomandibular function and neurosensory impairment. DO of the mandibular anterior alveolar process is a valuable and safe method with minor side effects regarding neurosensory impairment.

Chapter 6 describes 17 patients (14 female; 3 male) which were retrospectively analysed for skeletal and dental long-term relapse before 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. 

In chapter 7 long-term soft tissue changes of 17 patients following DO of the mandibular anterior alveolar process are presented. 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.

Chapter 8 is a general discussion of the clinical significance of  the results of the different studies as well as the strengths and weakness are discussed. Methodological considerations, suggestions and trends for future research are presented.