Osseous genioplasty in conjunction with bimaxillary orthognathic surgery: a review of 262 consecutive cases

Abstract

The purpose of this study was to evaluate the results of osseous genioplasty with bimaxillary orthognathic surgery. A retrospective consecutive case series of patients treated by a single surgeon between 2004 and 2013 was studied. All underwent Le Fort I, sagittal ramus osteotomies, septoplasty, inferior turbinate reduction, and osseous genioplasty. The outcome variables included the presenting chin dysmorphology, complications, and assessment of morphologic change. A Steiner analysis was completed for each subject’s interval cephalogram. Two hundred sixty-two subjects met the inclusion criteria. Their mean age at operation was 25 (range 13–63) years. Chin osteotomy complications included one wound infection (0.4%), and two of the 1572 mandibular anterior teeth at risk sustained a pulpal injury. None of the subjects required revision. For subjects undergoing chin advancement, the mean change was +3.5 (range +3 to +6) mm. A majority also underwent counterclockwise rotation of the mandible (62%). For those undergoing chin lengthening, the mean change was +5 (range +3 to +12 mm) mm, and for those undergoing vertical shortening, the mean change was −3.5 (range −3 to −7) mm. Osseous genioplasty is confirmed to be a safe method to reshape the chin. When osseous genioplasty is performed in conjunction with bimaxillary orthognathic surgery, only a modest horizontal change is required to achieve the preferred pogonion projection.

Hugo Obwegeser introduced the intraoral osseous genioplasty into clinical practice in 1957. More than half a century later, this relatively simple technique remains misunderstood and misused. An individual may arrive for a surgical consultation with a specific request for either a ‘chin implant’ or an ‘osseous genioplasty’. In these circumstances, comprehensive evaluation often confirms the presence of a dentofacial deformity requiring more extensive treatment. If the surgeon honours the patient’s request by completing a genioplasty in the presence of a jaw deformity, an unfavourable aesthetic result is a potential adverse outcome. A case in point is the individual with mandibular deficiency and procumbent incisors, who requests a ‘chin implant’ to improve lower face projection in the profile view. When a surgeon agrees to do so, the temptation is to advance pogonion too far in front of B-point to accomplish the desired profile projection. This is likely to result in an unattractive deep labiomental fold and a ‘button’ appearance to the chin.

A review of the literature confirms few cohort studies with significant numbers of subjects assessing the indications and morphologic results of osseous genioplasty and none that focus specifically on bimaxillary dentofacial deformities. The purpose of this retrospective cohort study was to evaluate the presenting chin dysmorphology and results achieved in a consecutive series of subjects undergoing osseous genioplasty in conjunction with bimaxillary orthognathic surgery. It was hypothesized that when an osseous genioplasty is carried out in conjunction with bimaxillary orthognathic surgery, the degree of chin ‘osteotomy site’ surgical correction need only be modest, as no camouflage aesthetic manoeuvres are required. The specific aims of this study were (1) to review the morphologic indications for genioplasty carried out for a spectrum of dentofacial deformities scheduled for bimaxillary orthognathic correction, (2) to document complications arising from osseous genioplasty in the study group, and (3) to document the chin region morphologic change achieved in comparison to normative data.

Materials and methods

Study design and subjects

To address the research objectives, a retrospective cohort study was designed and implemented. The sample was derived from the patients treated by one surgeon (JCP) in a private practice setting, with surgery carried out at a single hospital between 2004 and 2013. The study sample included an index group of subjects all with a bimaxillary developmental dentofacial deformity also involving the chin and symptomatic chronic obstructive nasal breathing. The nasal obstruction was documented to be unresponsive to medical therapy and was confirmed by an independent otolaryngologist to require septoplasty and reduction of the inferior turbinates. All study subjects were considered to have completed jaw growth at the time of orthognathic correction based on the clinical judgement of the treating orthodontist and surgeon. This included a review of serial radiographs and dental models, and a clinical examination. The subjects then underwent surgery that included, at a minimum, Le Fort I osteotomy, bilateral sagittal ramus osteotomies of the mandible, osseous genioplasty, septoplasty (submucosal resection), and reduction of the inferior turbinates.

All subjects underwent coordinated perioperative orthodontic treatment as part of their orthognathic correction. The primary orthodontic objective in each case was to remove dental compensations, then achieve a stable occlusion and long-term dental health when coordinated with surgery. When present, maxillary arch skeletal anomalies were treated with segmental osteotomies. Bicuspid extractions were carried out depending on the extent of dental crowding and need to create space for the relief of compensation.

Patients were excluded if their jaw deformity was syndromic, cleft-related, revision orthognathic surgery, post-traumatic, or tumour-related. Patients not residing in North America were also excluded, as long-term follow-up was geographically inconsistent. All subjects included in the study were confirmed to be cardiovascularly stable and without pulmonary disease, renal disease, or a known coagulation disorder. The study protocol was reviewed and approved by the necessary institutional review board.

Study variables

Demographic, anatomic, and operative predictor variables were studied.

The demographic variables collected included the subject’s age at the time of operation, sex, and the removal of mandibular bicuspids to relieve dental compensation.

The anatomic variable of the presenting pattern of developmental dentofacial deformity was studied. At presentation, each subject was classified into one of six abnormal jaw growth patterns, including primary mandibular deficiency, maxillary deficiency with relative mandibular excess, asymmetric mandibular excess, short face, long face, and bimaxillary dental protrusion. There was also an atypical category, which included dentofacial deformities strongly influenced by parafunctional habits such as thumb sucking.

Operative variables assessed included the osseous genioplasty design and the method of fixation. The osseous genioplasty design was consistent for 258 of the 262 study subjects. Four of the subjects underwent pogonion recontouring (rotary drill with a bone cutting bur) rather than an osteotomy. The technique used for the 258 subjects undergoing the chin osteotomy is described.

Outcome variables studied included the presenting chin dysmorphology, complications of osseous genioplasty, and assessment of the chin region morphologic change achieved. The outcome variable of presenting chin dysmorphology was documented from a review of the presurgical assessment performed for each subject. The presenting chin dysmorphology was described in the vertical (i.e., excess, satisfactory, deficient) and horizontal (i.e., excess, satisfactory, deficient) dimensions.

Complications associated with the osseous genioplasty were categorized as dental, periodontal, infectious, need for surgical revision, and need for hardware removal. Injury to a dental root of an anterior mandibular tooth (cuspid-to-cuspid) was recorded to have occurred when damaged at operation. This was documented through a review of the operative report and confirmed on the 5-week postoperative panoramic radiograph. Injury to the dental pulp of an anterior mandibular tooth (cuspid-to-cuspid) was recorded to have occurred if either the dental crown darkened or if a dental abscess occurred at any time within 1 year after surgery. The required treatment (i.e., root canal therapy) was also documented. Direct injury to the periodontium within the anterior mandibular region (cuspid-to-cuspid) was coded to have occurred if a review of the operative report and of the 5-week postoperative radiographs documented an osteotomy through the lamina dura or widening of the periodontal ligament space (compared to preoperative). After surgical healing, each subject was also critically analyzed to determine any change in gingival levels along the labial aspect of the anterior mandibular dentition (cuspid-to-cuspid). This was documented by comparing the pre- and late postoperative labial gingival levels (mean of 2 years after surgery) at each anterior mandibular tooth for each subject. The gingival levels associated with each tooth were assessed as either reduced, or no significant change. The precise aetiology of the gingival recession (i.e., orthodontic, surgical, or mechanical) was not studied. A wound infection was recorded to have occurred if there was drainage or abscess formation in the chin region at any time within 1 year after surgery. The required treatment (i.e., second course of antibiotics and surgical drainage) was also documented. Any need for re-operation in the chin region (excluding skeletal, soft tissue, or hardware removal) within the first year after surgery was recorded as a potential complication or unfavourable outcome.

The outcome variable of chin region morphology achieved was determined from measurements taken from the 5-week postoperative lateral cephalometric radiograph for each subject in comparison to normative data (Steiner analysis) and to each subject’s preoperative cephalogram. The specific cephalometric measurements studied included (1) lower incisor to inferior mandibular border angle, (2) pogonion to nasion–B-point (NB) distance (mm), and (3) lower incisor to menton height (mm). The pre- and post-surgery lateral cephalometric radiographs were also compared for each subject to measure osteotomy site vertical and horizontal changes achieved at operation.

Collection, management, and analysis of data

Data were abstracted from the hospital and outpatient medical records and then recorded on a standardized data collection form by two researchers/observers (EC and RPC). These included data from each subject’s pre- and postoperative lateral cephalometric radiograph. The cephalograms were calibrated to yield a 1:1 radiograph to actual size ratio. A Steiner analysis was performed on each acceptable quality lateral cephalogram. Exclusion criteria for quality of the radiographs included the following: lack of a magnification scale, poor radiation exposure, and all areas for study not fully visualized.

The mandibular incisor inclination was measured with reference to the inferior border of the mandible (lower incisor to inferior mandibular border angle) ( Fig. 1 ). The vertical change achieved was measured as the difference in height from the lower incisal occlusal tip to menton (mm) before and after surgery (lower incisor to menton height) ( Fig. 2 ). The horizontal change in pogonion position was measured in relation to a vertical facial reference line. The vertical reference line was drawn through nasion and B-point. The distance from this line to pogonion, measured in a perpendicular plane, was designated as the horizontal change (mm) achieved (pogonion to NB distance, mm) ( Fig. 3 ).

Fig. 1
Measurement of the mandibular incisor inclination, prior to surgery. Using a lateral cephalometric radiograph taken prior to surgery, the mandibular incisor inclination was measured with reference to the inferior border of the mandible (lower incisor to inferior mandibular border angle). A line connecting gonion to menton formed the inferior border of the mandible. A second line was drawn through the long axis of the mandibular incisors. The angle formed by the two lines was measured and represented the incisor inclination. In this example, the incisor inclination is 81°.

Fig. 2
Measurement of the vertical height of the chin, prior to and after surgery. Using a lateral cephalometric radiograph, the vertical change achieved was measured as the difference in height of the lower incisal occlusal tip to menton (lower incisor–menton height) (mm) before and after surgery. In this example, the vertical chin height was (A) 39 mm prior to surgery, and (B) 40 mm after surgery.

Fig. 3
Measurement of the pogonion to B-point distance, prior to and after surgery. Using a lateral cephalometric radiograph, the pogonion position to B-point was measured by first drawing a line through nasion and B-point. The distance from this line to pogonion, measured in a perpendicular plane, was designated as the pogonion projection (pogonion–NB distance, mm). In this example, the measurement was (A) 0 mm prior to surgery, and (B) 4 mm after surgery.

The actual chin osteotomy site horizontal change was measured by first drawing a line along the inferior border of the mandible (gonion and menton). A perpendicular line was drawn through pogonion to the inferior border of the mandible. A second perpendicular line was drawn through B-point to the inferior border of the mandible. The difference in the distance (mm) between the two perpendicular lines, as measured before and after surgery, represented the actual horizontal change at the osteotomy site ( Fig. 4 ).

Fig. 4
Measurement of the actual osteotomy site horizontal change, prior to and after surgery. Using a lateral cephalometric radiograph, the actual chin osteotomy site horizontal change was measured in millimetres by first drawing a line through the inferior border of the mandible (gonion and menton). Next a perpendicular line was drawn through pogonion to the inferior border of the mandible. Then a second perpendicular line was drawn through B-point to the inferior border of the mandible. The difference in the distance (mm) between the two perpendicular lines, measured before and after surgery, represented the actual horizontal change. In this example, the measurement was (A) 7 mm prior to surgery, and (B) 9 mm after surgery. The actual horizontal advancement was 2 mm.

No subjects were lost to follow-up and no records or data points were missing for any of the subjects for any parameters in the study.

Statistical analysis

The data were entered into a database that was created and analyzed using Microsoft Access (Microsoft, Inc., Redmond, WA, USA). The mean values and standard deviations (SD) of four cephalometric variables were calculated including (1) pogonion to B-point projection (after chin advancement and setback), (2) vertical change (lengthening and shortening), (3) actual horizontal change at the osteotomy site (advancement and setback), and (4) mandibular incisor inclination (extraction and non-extraction subgroups). Except for the mandibular inclination measurement, differences in pre- and postoperative measurements for each variable were examined using analysis of variance (ANOVA). For mandibular incisor inclination, the preoperative measurement in the premolar extraction subgroup was compared to the measurement in the non-extraction subgroup using ANOVA. A P -value of <0.05 was considered significant.

Results

Demographic characteristics

Two hundred and sixty-two consecutive subjects presenting for treatment and meeting the inclusion criteria were included in this study. All subjects underwent perioperative orthodontics to relieve dental compensations. Sixty-six of the 262 subjects (25%) underwent lower bicuspid extractions to relieve dental compensations in the mandible. The patterns of presenting developmental dentofacial deformity in the study group included the following: long face (78/262, 30%), maxillary deficiency with relative mandibular excess (66/262, 25%), asymmetric mandibular excess (51/262, 19%), primary mandibular deficiency (40/262, 15%), short face (15/262, 6%), bimaxillary dental protrusion (5/262, 2%), and atypical dentofacial deformity (7/262, 3%).

The mean age of the subjects at operation was 25 years (range 13–63 years); 134 of the subjects were female (51%). The chronologically young subject (13+ years of age) had a long face class II jaw growth pattern. She also had symptomatic obstructive sleep apnea and chronic obstructive nasal breathing. All the permanent teeth were erupted and orthodontically aligned. Based on clinical and radiographic analysis, she was judged to be jaw growth mature at the time of orthognathic correction. At the close of the study, she was 18 years of age. She has maintained the planned occlusion, an open airway, and preferred facial aesthetics. Thirty-seven of the 262 subjects (14%) were 40 years of age or older at the time of operation.

Three of the subjects (1%) had used oral bisphosphonates for the management of osteoporosis. Prior to surgery, each had been off the medication for at least 6 months (range 6 months to 5 years). All 262 subjects had pre- and postoperative panoramic and lateral cephalometric radiographs. Exclusion criteria for quality of the radiographs limited the cephalometric analysis component of the study to 186 of the 262 subjects.

Complications of osseous genioplasty

There was one case of infection in the 262 consecutive osseous genioplasties (0.4%) ( Table 1 ). This was a chin region wound infection in a 27-year-old male with a long face growth pattern who underwent a vertical shortening (2 mm) and horizontal advancement (4 mm) genioplasty. Tenderness and spontaneous intraoral drainage occurred 6 days after surgery and required a second course of antibiotics and the placement of a Penrose drain for 8 additional days. The infection did not delay osteotomy site healing or affect the long-term outcome.

Table 1
Complications of osseous genioplasty.
Complication Occurrence
Infection 1/262 subjects (0.4%)
Direct dental injury 0/1572 teeth at risk
Pulpal injury requiring RCT 2/1572 teeth at risk (0.1%) a
Gingival recession 8/1572 teeth at risk (0.5%) a
Need for chin revision 0/262 subjects
Need for hardware removal 0/262 subjects
RCT, root canal therapy.

a 262 × 6 anterior teeth = 1572.

A review of each subject’s operative report and postoperative panoramic radiograph confirmed that none of the study subjects ( n = 262) sustained a direct injury to a dental root or to the periodontium. There was no case of abscessed anterior mandibular teeth during the duration of the study. Two of the 1572 mandibular anterior teeth (cuspid-to-cuspid) sustained a pulpal injury with a darkened crown. Each underwent successful root canal therapy and internal bleaching.

The analysis of periodontal status after osseous genioplasty included 1572 sites (262 subjects × 6 gingival sites). The findings confirmed 8/1572 sites (0.5%) with reduced gingival levels in five subjects. All other gingival sites maintained their presurgical position. For those sites that sustained gingival recession, the most frequent location was the labial aspect of a central incisor (five sites), followed by the labial aspect of a lateral incisor (three sites). Two of the five subjects with progressive recession were over 40 years of age and had exhibited pre-treatment gingival loss. Two of five subjects with gingival recession had undergone bicuspid extractions to correct crowding of the mandibular arch prior to surgery.

None of the study subjects followed for a minimum of 12 months after surgery required a revision procedure to the chin (skeletal or soft tissue).

Need to remove chin fixation hardware

Two hundred fifty-eight of the 262 osseous genioplasties (98%) were rigidly fixed with two surgeon-contoured straight titanium plates and screws. Ten (4%) of the subjects required vertical lengthening to the extent that an interpositional graft was placed. Allogeneic iliac corticocancellous bone was the graft material used in each case. In these subjects, an additional surgeon-contoured straight titanium microplate was placed across the grafted region and then secured with screws. Four of the subjects underwent chin (pogonion) region recontouring that did not require the placement of fixation hardware. None of the consecutive osseous genioplasties carried out required fixation hardware removal during the observation period.

Morphological indications for genioplasty

Prior to surgery, 87% of chins were at least somewhat retrusive in the horizontal plane, while 5% were protrusive. In the vertical dimension, 54% of the chins had a degree of excess height, while 22% were at least somewhat deficient in height. Ten of the subjects (4%) required vertical lengthening of the chin to the extent that an interpositional graft was placed.

Chin morphology achieved (cephalometric analysis)

Fifty-four percent of subjects underwent a degree of vertical shortening of the chin (range 1–7 mm) and 22% underwent at least some chin lengthening (range 1–12 mm). A review of the data confirmed that the study subjects undergoing just 1 or 2 mm of vertical change did so in conjunction with a planned significant horizontal change as the primary indication for osseous genioplasty. For those undergoing vertical shortening as the primary indication ( n = 57, 31%), the average reduction was −3.5 mm (range −3 to −7 mm) ( Fig. 5 ). For those undergoing vertical lengthening as the primary indication ( n = 22, 12%), the average change was +5 mm (range +3 to +12 mm) ( Fig. 6 ).

Jan 16, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Osseous genioplasty in conjunction with bimaxillary orthognathic surgery: a review of 262 consecutive cases
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