Purpose:

The purpose of the study is to evaluate the stability of the mandibular narrowing in the treatment of transverse maxillomandibular discrepancies.

The management of transverse maxillomandibular discrepancies is a controversial and rarely discussed topic in both orthodontic and surgical literature. The author's original occlusographic analysis is used to evaluate the short-term stability of the mandibular narrowing following a vertical anterior and bilateral sagittal split osteotomy, in a prospective cohort study. This is the largest series in the literature.

Material and Method:

Between December 1996 and June 2006, 40 patients underwent mandibular narrowing for the correction of substantial transverse maxillomandibular discrepancies. The technique consisted of a combination of bilateral sagittal split osteotomy and a vertical anterior symphyseal or parasymphyseal osteotomy. There were 32 females and 8 males, ages from14 to 46 years with an average of 23 years. Preoperative evaluation consisted of clinical exam, PA and lateral cephalograms, orthopantomogram, periapicals and dental impressions for reference and model surgery. Nine patients had no other surgery. Twenty nine had the mandibular narrowing combined with a Le Fort I osteotomy, 3 had a genioplasty and 6 had a combination of mandibular narrowing, a Le Fort I osteotomy and a genioplasty. The fixation method for the anterior osteotomy was without preference using 1 or 2 screws, 1 or 2 plates or one of each. Postoperative evaluation was done at 1 and 2 weeks, 1, 3, 6 and 12 months with clinical exam, orthopantomogram, PA cephalogram and lower dental impression. The occlusographic analysis was done on all of the patients. The author's occlusographic analysis is obtained on a life-size image of the dental arch by simply placing the dental impression on a copy machine and superimposing the tracings of pre and post operative position of the mandibular segments. The analysis uses simple basic geometric measurements.

Results:

Twenty six patients came for the final evaluation. The follow-up period was 5 to 109 months with an average of 18 months. The degree of mandibular narrowing ranged from -4° to -14° (average -8.5°). The posterior displacement of the mandibular segment was 1to7 mm (average 3.7 mm) and the increase in the sagittal length of the mandible was 1 - 4 mm (average 2mm). The most interesting finding was the relapse which was 0 - 11° (average 4.7°). All but 5 patients have relapsed to various degrees and the relapse rate was 80%.

Conclusion:

The mandibular narrowing is a relatively new procedure which is used in the surgical treatment of maxillomandibular discrepancies. There has been no simple and precise method for the evaluation of the results. With the original occlusographic analysis of the author, which is a simple, quick and precise method, we have been able for the first time to demonstrate and quantify the outcome of the mandibular narrowing procedure. This is the largest series in the literature. We were able to identify the relapse and its rate of 80%. However the factor intervening in the relapse need to be identified and their impact measured in a larger series.