Skeletal stability of surgery-first bimaxillary orthognathic surgery for skeletal class III malocclusion, using standardized criteria

Abstract

The purpose of this study was to compare the postoperative stability following bimaxillary surgery performed either with or without preoperative orthodontic treatment, in class III malocclusion patients. These patients were enrolled using standardized inclusion criteria. Forty patients with a class III malocclusion were included in this retrospective study. Inclusion criteria were class III malocclusion with and without premolar extraction, <3 mm midline deviation, and <5 mm arch width discordance. Patients were assigned to the conventional bimaxillary surgery group ( n = 20) or the surgery-first bimaxillary surgery group ( n = 20). Serial cephalometric radiographs obtained before surgery (T0), at 2 months after surgery (T1), and at 6 months after surgery (T2) were used to assess the variation in surgical change (T0 to T1) and postsurgical change (T1 to T2). Eight linear and three angular parameters were used to evaluate postoperative stability. With respect to postsurgical changes, significant differences were observed in the changes for the vertical reference plane to the posterior nasal spine, horizontal reference plane to B-point, and occlusal plane angle in both groups. No statistically significant differences in the relapse rates were observed between the two groups. No significant differences were observed between the two groups in terms of the postoperative stability.

Orthognathic surgery is used to correct skeletal discrepancies in the facial area. Moreover, it may improve functional aspects such as mastication and pronunciation, and aesthetic appeal. In the past, orthognathic surgery was focused on improving skeletal incongruities. More recently, however, in addition to correcting malocclusion, orthognathic surgery is increasingly in demand to improve patient aesthetics. Conventional orthognathic surgery requires preoperative orthodontic treatment, which increases the treatment period, and postoperative orthodontic treatment for stabilization. Preoperative orthodontic treatment may take 12–24 months, and because of the compensation process, facial aesthetics and mastication may deteriorate during this period, leading to patient discomfort. In order to offset this disadvantage, Nagasaka et al. proposed a surgery-first approach to orthognathic surgery in 2009. This approach has the advantage of a significantly shortened treatment duration. Moreover, improvements in the facial profile may be observed immediately, leading to greater patient cooperation during treatment. In addition, tooth movement is accelerated during postoperative treatment because of the regional acceleratory phenomenon.

There are fewer reports in the literature describing surgery-first orthognathic surgery than conventional orthognathic surgery. Thus, the outcomes and prognosis of the surgery-first approach remain controversial. Moreover, it is challenging to precisely predict the tooth movement preoperatively and the movement setting during surgery. The unstable occlusions that are usually observed after surgery may hinder long-term skeletal stability, leading to relapse. Postoperative stability may be influenced by various factors, including surgical factors, skeletal structure, and dental issues. Surgical factors, which include surgical and fixation protocols, as well as skeletal and dental issues, such as overbite, overjet, and divergent occlusal planes, can all influence postoperative stability. Furthermore, the initial studies on surgery-first orthognathic surgery did not propose rigid standardized inclusion criteria, leading to uncertainty in the analysis of the outcomes.

This study used cephalometric analysis to evaluate the postoperative stability of the surgery-first orthognathic surgery approach for malocclusion in class III patients who satisfied specific rigid inclusion criteria set by the study department. Consequently, the conventional and surgery-first orthognathic surgery approaches could be compared in terms of the postoperative stability, and could be analyzed considering the factors contributing to relapse. This study aimed to identify inclusion criteria as a guideline for the surgery-first approach that would be acceptable with regards to surgical relapse.

Patients and methods

A total of 229 patients underwent bimaxillary orthognathic surgery in the department of oral and maxillofacial surgery of the university dental hospital in Korea between 2011 and 2012. These cases were analyzed retrospectively. A surgery-first bimaxillary surgery approach has been implemented in this department for patients meeting specific rigid criteria. Initially, 26 patients met the standardized inclusion criteria and were identified retrospectively as surgery-first bimaxillary surgery cases. However six cases were excluded as their follow-up visits were incomplete. This study therefore included the remaining 20 surgery-first patients. For uniformity of the study groups, the same numbers of patients also meeting the specific criteria were selected for the conventional bimaxillary orthognathic surgery group. Thus the 40 patients were assigned to the following two groups: conventional bimaxillary surgery (CS group) and surgery-first bimaxillary surgery (SF group).

All bimaxillary surgeries, including Le Fort I osteotomy (LFI) and bilateral sagittal split osteotomy (BSSO), were performed by a single surgeon. Rigid internal fixation was used during bimaxillary surgeries. In order to ensure consistency of results, three inclusion criteria were set: (1) cases of class III malocclusion with and without premolar extraction for orthodontic purposes; (2) mild asymmetry, defined as a deviation of <3 mm from the teeth midline to facial midline; (3) an arch width discordance of <5 mm between the upper and lower jaws. Patients with a trauma, congenital syndromes, class II malocclusion, severe asymmetry, and an arch width discordance of >5 mm were excluded from this study.

In the SF group, no active preoperative orthodontic treatment was conducted in any of the patients. In the CS group, the average preoperative orthodontic treatment period was 14.7 months. Postoperative orthodontic treatment was started 4 weeks after surgery in both groups. All patients underwent LFI and BSSO under general anaesthesia. The maxilla was fixated using four 4-hole metal plates in the piriform rim and zygomaticomaxillary buttress areas. The mandible was fixed using metal plates and metal screws. Maxillomandibular fixation was performed with a surgical stent that had ball clasps for retention, and was applied for 5 days. Thereafter, mouth opening exercises and physical therapy were implemented with the aid of a maxillary retention surgical stent, for approximately 4 weeks.

Patient demographic data and relevant records pertaining to the surgery were acquired from the medical charts. Serial cephalometric radiographs were collected during patient examinations performed preoperatively (T0), at 2 months postoperative (T1), and at 6 months postoperative (T2). SimPlant software (Materialise, Leuven, Belgium) was used to analyze the T0, T1, and T2 radiographs. All lateral cephalometric radiographs were taken using the same cephalostat, in maximum intercuspal position, and were traced by a single observer in order to eliminate inter-examiner error in the tracing procedure. Differences in the extent of surgical change (T0 to T1) and postsurgical change (T1 to T2) were recorded by overlapping the cephalometric radiographs.

All landmarks and reference points for linear and angular parameters were determined as shown in Fig. 1 . The horizontal reference plane (HRP) was considered as a standard for vertical measurement. The HRP was set to pass through the nasion and 7° superior to the sella–nasion line. The vertical reference plane (VRP) was used to determine the standard for horizontal measurement and was set to be perpendicular to the HRP and pass through sella. Fig. 1 shows the locations of the landmarks in relation to the corresponding reference lines, recorded in linear measurements. Based on the HRP, posterior movement of the parameters was assigned a positive value, and anterior movement was assigned a negative value. Similarly, based on the VRP, superior movement of the parameters was assigned a positive value, and inferior movement was assigned a negative value. Postoperative stability was measured as the change in a particular value.

Fig. 1
Anatomical landmarks and reference lines used in the cephalometric analysis. S, sella; N, nasion; A, A-point; B, B-point; PNS, posterior nasal spine; U1, maxillary central incisor; U6, maxillary first molar; L1, mandibular central incisor; L6, mandibular first molar; Occ. plane, occlusal plane; Me, menton; Go, gonion; Mn. plane, mandibular plane; HRP, line passing through nasion and 7° superior to the sella–nasion line; VRP, line passing through sella and perpendicular to HRP.

Eight linear parameters (measured in millimetres) and three angular parameters (measured in degrees) were included in this study ( Table 1 ). The statistical analysis was performed using IBM SPSS Statistics for Windows version 21.0 software (IBM Corp., Armonk, NY, USA). The paired t -test was used to evaluate surgical change (T0 to T1) and postsurgical change (T1 to T2) for the CS and SF groups, in order to examine the differences in measurement parameters. An independent t -test was performed to compare the relapse rates for the CS and SF groups. The differences were considered significant at P < 0.05.

Table 1
Measurements and anatomical landmarks.
Measurements Anatomical landmarks
Horizontal (mm) VRP to ANS: Distance from VRP to ANS
VRP to PNS: Distance from VRP to PNS
VRP to A: Distance from VRP to A-point
VRP to B: Distance from VRP to B-point
Vertical (mm) HRP to ANS: Distance from HRP to ANS
HRP to PNS: Distance from HRP to PNS
HRP to A: Distance from HRP to A-point
HRP to B: Distance from HRP to B-point
Angular (°) SNA: Angle between SN line and A-point
SNB: Angle between SN line and B-point
Occlusal plane angle: Angle between HRP and occlusal plane

ANS, anterior nasal spine; HRP, line passing through nasion and 7° superior to the sella–nasion line; PNS, posterior nasal spine; SNA, sella–nasion–A-point angle; SNB, sella–nasion–B-point angle; VRP, line passing through sella and perpendicular to HRP.

Results

The CS group ( n = 20) comprised 13 men and seven women (average age 25.25 ± 3.77 years). The SF group ( n = 20) comprised 12 men and eight women (average age 22.60 ± 5.39 years).

For the CS group, statistically significant differences were observed for all measurements following surgery (surgical change, T0 to T1), whereas significant differences were observed only for the VRP to the posterior nasal spine (PNS), HRP to B-point, and occlusal plane angle (OPA) ( P < 0.05) during the postsurgical period (post-surgical change, T1 to T2). The mean postsurgical change at the PNS was 1.422 ± 2.238 mm anteriorly and at the B-point was 2.744 ± 1.810 mm superiorly. OPA increased by 1.362 ± 1.505°. The remaining variables showed no significant differences ( P > 0.05, Table 2 ).

Table 2
Evaluation of the changes in the conventional bimaxillary surgery group: paired t -tests.
Measurement a T0–T1 T1–T2
Difference SD P -value Difference SD P -value
VRP to ANS −1.527 2.400 0.010 * −0.305 2.140 0.532
HRP to ANS 3.191 2.306 0.000 * 0.282 1.761 0.483
VRP to PNS −3.525 3.549 0.000 * −1.422 2.238 0.010 *
HRP to PNS 7.178 2.264 0.000 * −0.508 1.337 0.106
VRP to A −3.406 2.276 0.000 * 0.422 1.694 0.279
HRP to A 3.982 1.754 0.000 * 0.582 1.772 0.158
VRP to B 7.717 3.458 0.000 * −0.855 2.001 0.071
HRP to B 4.096 3.892 0.000 * 2.744 1.810 0.000 *
SNA −2.783 1.913 0.000 * 0.336 1.361 0.283
SNB 3.746 1.611 0.000 * −0.198 0.824 0.296
Occlusal plane angle −3.216 2.828 0.000 * 1.362 1.505 0.001*
T0, before surgery; T1, 2 months after surgery; T2, 6 months after surgery; SD, standard deviation.

a For definitions, see Table 1 .

* Statistically significant.

For the SF group, all measurements with the exception of VRP to the anterior nasal spine (ANS) showed statistically significant differences following surgery (surgical change, T0 to T1). During the post-surgical period (postsurgical change, T1 to T2), significant differences were observed for the VRP to the PNS, HRP to the PNS, VRP to B-point, HRP to B-point, SNB, and OPA ( P < 0.05). The mean postsurgical change at the PNS was 1.169 ± 2.307 mm anteriorly and 1.116 ± 1.710 mm inferiorly. The mean postsurgical change at the B-point was 1.086 ± 1.371 mm anteriorly and 1.747 ± 2.063 mm superiorly. SNB decreased by 0.656 ± 1.049° and OPA increased by 1.157 ± 2.668°. The remaining variables showed no significant differences ( P > 0.05, Table 3 ).

Table 3
Evaluation of the changes in the surgery-first bimaxillary surgery group: paired t -tests.
Measurement a T0–T1 T1–T2
Difference SD P -value Difference SD P -value
VRP to ANS −0.462 3.371 0.569 0.527 2.975 0.462
HRP to ANS 2.185 1.946 0.000 * −0.071 1.455 0.839
VRP to PNS −3.075 2.959 0.000 * −1.169 2.307 0.046 *
HRP to PNS 6.118 2.713 0.000 * −1.116 1.710 0.013 *
VRP to A −2.559 3.322 0.005 * −0.039 2.237 0.942
HRP to A 2.876 1.867 0.000 * 0.112 1.483 0.753
VRP to B 7.094 4.676 0.000 * −1.086 1.371 0.004 *
HRP to B 4.132 2.717 0.000 * 1.747 2.063 0.002 *
SNA −2.518 2.263 0.000 * 0.391 1.299 0.219
SNB 3.151 1.929 0.000 * −0.656 1.049 0.017 *
Occlusal plane angle −3.141 3.271 0.001 * 1.557 2.668 0.024 *
Only gold members can continue reading. Log In or Register to continue

Jan 16, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Skeletal stability of surgery-first bimaxillary orthognathic surgery for skeletal class III malocclusion, using standardized criteria
Premium Wordpress Themes by UFO Themes