A comparison of Class II open bite correction by maxillary or mandibular surgery

Introduction

The purpose of this study was to compare treatment outcomes for anterior occlusion and vertical skeletal stability after maxillary or mandibular surgery for correction of Class II malocclusion with a mild to moderate open bite.

Methods

The records of 57 consecutive patients were retrieved; 30 had undergone 1-piece Le Fort I osteotomy, and 27 had undergone a bilateral sagittal split osteotomy (BSSO), without additional surgery. Lateral cephalograms at 6 stages were available (pretreatment to 3 years postsurgery).

Results

After the surgery, 87% of the Le Fort I patients and 63% of the BSSO patients had a positive overbite, and at the 6-month follow-up, the percentages were 90% and 74%, respectively. At 3 years after surgery, 74% of the Le Fort I patients and 42% of the BSSO patients had a positive overbite. The anterior facial height decreased in the Le Fort I subsample and increased in the BSSO subsample, and the mandibular plane angle decreased in both. The Le Fort I subsample generally remained stable, whereas clinically significant relapse of the mandibular plane angle (≥2°) occurred in 80% of the BSSO subsample.

Conclusions

When taking into account the limitations of retrospective clinical studies, several conclusions can be drawn. A significant improvement of the anterior occlusion can be expected in most patients when either maxillary or mandibular surgery is used for correction of Class II open bite. However, there will be individual patients in whom considerable posttreatment changes occur in both the anteroposterior and vertical dimensions. Although individual morphology needs to be taken into account, it seems that both short- and long-term stability are likely to be greater after Le Fort I surgery compared with BSSO.

Highlights

  • Le Fort I and bilateral sagittal split osteotomy (BSSO) surgery in skeletal Class II open bite were compared.

  • There was greater improvement in open bite correction after Le Fort I compared with BSSO.

  • There was more frequent posttreatment relapse to open bite after BSSO surgery.

  • Anterior face height decreased after Le Fort I surgery and increased after BSSO.

  • There was a significant relapse in the mandibular plane angle after BSSO surgery.

Open bite malocclusions represent a challenge to sustaining acceptable treatment outcomes, even when orthodontic treatment is supplemented with orthognathic surgery in adults. Historically, the surgical correction of a skeletal Class II open bite was by forward and upward rotation of the distal part of the mandible in a bilateral sagittal split osteotomy (BSSO), with wire osteosyntheses and intermaxillary fixation. Later, the mandibular approach was to some extent replaced by the more stable maxillary surgery (Le Fort I). Rigid fixation has now generally replaced wire osteosyntheses, and the mandibular procedure (BSSO) has again become a relevant alternative because of improved stability and an increased focus on facial appearance.

The choice of osteotomy is largely dependent on the individual’s skeletal morphology. Bimaxillary surgery is usually required for the treatment of severe Class II open bite, whereas either maxillary or mandibular surgery may be used to treat mild to moderate Class II open bite. When there is excess vertical growth of the posterior maxilla, a Le Fort I osteotomy with impaction to decrease the posterior facial height will allow anterior autorotation of the mandible. Alternatively, an open bite combined with a short and retrognathic mandible may be an indication for an elongation of the mandibular body by BSSO. The BSSO procedure may provide better control of overjet correction because the surgeon can advance and rotate the mandible. Overjet correction following Le Fort I, by autorotation of the mandible, is less predictable.

Previous studies have demonstrated varying stability after surgical correction of open bite. It is difficult to compare studies because of differing study designs and samples. We have been unable to identify any studies that specifically compare the results after Le Fort I osteotomy and BSSO in patients for whom either surgery may be indicated.

The purpose of the present study was to compare treatment outcomes for anterior occlusion and vertical skeletal stability after maxillary or mandibular surgery for the correction of Class II mild to moderate open bite by examining (1) the changes in dental and skeletal morphology during various time intervals from pretreatment to 3 years postsurgery; (2) the proportion of patients with positive overbite at various time points during a 3-year postsurgery period; and (3) the proportion of patients with skeletal relapse of clinical significance (≥2 mm or ≥2°).

Material and methods

This study sample consisted of the records of consecutively treated Class II open bite patients retrieved from the files of the Department of Orthodontics, University of Oslo, who were operated on at the Department of Maxillofacial Surgery at the University of Oslo between 1990 and 2014. Joint planning of treatment and monitoring of the patients took place at the Department of Orthodontics, University of Oslo, and orthodontic treatment was carried out by postgraduate students under supervision at the Department of Orthodontics or by orthodontic specialists in private practice. Lateral cephalograms were obtained before treatment (T0), within 1 week before surgery (T1), within 1 week after surgery (T2), and 6 months (T3), 1 year (T4), and 3 years after surgery (T5). The following inclusion criteria had to be met: (1) an initial diagnosis of Class II malocclusion and anterior open bite; (2) either 1-piece Le Fort I or BSSO, and only rigid fixation; (3) pre- and postsurgical orthodontic treatment; (4) nongrowing individuals; and (5) available lateral cephalograms of sufficient quality at both pre- and postsurgery stages (T1 and T2), and at a minimum of 3 of the other 4 observation stages (T0, T3, T4, T5).

Patients who had undergone bimaxillary surgery or other auxiliary osteotomies (eg, genioplasty) were excluded from the study. Patients with craniofacial syndromes, cleft-lip-palate anomalies, or dentofacial trauma were also omitted. A tentative treatment plan was outlined at the initial consultation (T0), and the final decision on surgical procedure was made by the patient and surgeon together before surgery (T1). Several surgeons (7) were involved in the orthognathic team, and each operation was performed by 2 surgeons working together.

A standard 1-piece Le Fort I osteotomy was performed as described by Espeland et al. Reference marks were made on the lateral aspects of the maxilla before performing the osteotomies. Two L-shaped 1.0-mm miniplates (Walter Lorentz Co, Jacksonville, Fla; Leibinger CMF Modular Wurzburg Stryker, Freiburg, Germany) were placed on either side of the maxilla, each with 4 screws (2.0-mm diameter). Two screws were placed above and 2 below the osteotomy.

A modified version of BSSO as described by Epker was used, and the segments were stabilized with 3 bicortical screws (2.0 mm) with washers as described by Mobarak et al. Two screws were placed above and 1 below the inferior alveolar nerve canal in the retromolar area. Eight patients had miniplates instead of, or in combination with, the screws.

A software program (Facad, Ilexis AB, Linkõping, Sweden) was used for cephalometric analysis, to trace dental and skeletal landmarks. Changes in landmark positions were recorded using a coordinate system; the x-axis was drawn 7.0° below the nasion-sella line through sella. The y-axis, also passing through sella, was then drawn perpendicular to the x-axis. The x-y axes were transferred to each cephalogram by superimposition, using the best fit of stable structures in the cranial base. Figure 1 shows the cephalometric landmarks and reference lines used. Definitions of landmarks and measurements have been presented previously. , Anterior open bite was measured as the distance between the incisal edges perpendicular to the maxillary occlusal plane. Three different cephalostats were used, the images were calibrated using the Facad tracing program, and all linear measurements were corrected for magnification. Digital images were transferred directly to Facad and the nondigital images were scanned at 300 dpi on an Epson scanner and then transferred to Facad. The same examiner carried out all the tracings and superimpositions (N.T.). For skeletal variables, clinically significant relapse was defined as changes ≥2 mm or ≥2⁰. An anterior open bite (≤0 mm) at T5 was also considered to represent clinically significant relapse.

Fig 1
Cephalometric landmarks, reference lines, and measurements.

The study was reported to the Regional Ethical Committee, but as the study was evaluating the quality of treatment that patients had already received, the committee concluded that approval from the Regional Ethical Committee was not necessary.

Statistical analyses

The pretreatment data are presented using standard summary statistics (mean, standard deviation, and minimum and maximum values), and the treatment stages are presented as least-square means with a 95% confidence interval. A mixed model repeated measures analysis of variance was performed to assess the effect of the interventions and time on the outcome variables at the various time points. The core set of adjustment variables were age, gender, and time. In addition, the baseline measurement was included as a covariate in order to eliminate regression toward the mean for the estimated effect of the different treatments, as well as pairwise comparisons. Little’s test indicated that data were missing completely at random. Scheffé test was applied to assess the timepoint(s) for the significant difference between pairs of treatments as well as change within a treatment sample. Cook distance, the covariance ratio statistic, and the covariance trace statistics were applied to assess the validity of the model for the repeated measures mixed model analyses. To ascertain the robustness of the findings, a bootstrap regression analysis with 1000 replications was performed, adjusting for the baseline values as well as the variables mentioned above. The analyses were carried out using Statistical Analysis System (SAS Institute Inc, Cary, NC). All P values <0.05 were considered significant. A chi-square test was carried out for comparison of the samples with respect to the frequency of positive overbite at the various time points. Reproducibility of the cephalometric tracings was examined by duplicate tracings of 20 images, performed at least 2 weeks apart, with images chosen at random. The error of the method was analyzed by the intraclass correlation coefficient and Dahlberg calculation. The paired t test was applied to examine the systematic error. , The statistical analyses were carried out in SPSS for Windows (SPSS, Chicago, Ill).

Results

From a total of 57 patients fulfilling the criteria, 30 (8 male, 22 female) had Le Fort I, and 27 (3 male, 24 female) had BSSO surgery. The age at surgery ranged from 17 to 43 years (mean 25.4 years; standard deviation, 6.3 years).

The error of the method showed intraclass correlation coefficient values between 96.6% (ANS) and 99.7% (Me). Dahlberg calculations showed that the measurement error was <1.0 mm or <1.0° for all variables except for the mandibular plane angle (ML/NSL; 1.6°). No variable showed a difference between duplicate measurements that were significant at the 10% level.

The pretreatment (T0) dental and skeletal morphology is presented in Table I . In general, the sample can be described as having a retrognathic mandible, a high mandibular plane angle, an increased overjet, and a mild to moderate anterior open bite. The mean inclination of the mandibular incisors was within the normal range, whereas the mean inclination of the maxillary incisors was above the normal range. The mean overjet and overbite as well as the mean SNA and ANB angles were significantly different between subsamples. Because of the wide range in several variables, the subsamples overlapped even though there was a statistically significant difference between them ( Fig 2 ).

Table I
Pretreatment (T0) characteristics
Variable Le Fort I (n = 25) BSSO (n = 20)
Mean SD Min Max 95% CI Mean SD Min Max 95% CI
Age at surgery (y) 24.4 5.8 17.0 34.0 22.0, 26.8 27.1 7.1 18.0 43.0 23.8, 30.4
SNA (°) 78.5 3.6 68.3 83.1 77.0, 80.0 80.4 3.6 73.7 85.1 78.7, 82.1
SNB (°) 73.1 3.9 63.7 79.6 71.5, 74.7 72.7 3.3 68.7 78.3 71.2, 74.2
ANB (°) 5.4 1.9 2.1 9.8 4.6, 6.1 7.7 2.2 4.3 11.8 6.6, 8.7
ML/NSL (°) 43.3 7.4 33.7 60.3 40.3, 46.4 42.3 5.7 23.1 51.8 39.6, 44.9
NL/NSL (°) 8.9 3.9 2.6 16.7 7.3, 10.5 8.7 2.7 3.7 14.1 7.5, 10.0
iLs/FH (°) 115.5 5.8 104.9 127.7 113.1, 117.9 111.0 6.1 99.2 123.2 108.1, 113.8
iLi/ML (°) 90.0 6.8 70.2 101.3 87.2, 92.8 92.4 5.8 79.9 101.1 89.7, 95.1
Overjet (mm) 7.0 1.9 3.7 12.8 6.3, 7.8 8.5 1.6 6.1 12.3 7.7, 9.2
Overbite (mm) –3.3 1.5 –5.7 –0.3 –3.9, –2.7 –1.9 1.1 –5.3 0.0 –2.4, –1.4

SD , standard deviation; Min , minimum; Max , maximum; CI , confidence interval.

P <0.05.

Fig 2
Boxplots showing median, interquartile range, maximum and minimum values, and outliers for pretreatment (T0) overjet and overbite.

The mean changes in dental and skeletal cephalometric variables at each of the treatment and follow-up intervals are presented in Table II (Le Fort I) and Table III (BSSO).

Table II
Skeletal and dental changes at different time intervals following Le Fort I treatment
Variable T0 to T1 T1 to T2 T2 to T3 T2 to T5 T3 to T5
Mean SD 95% CI Mean SD 95% CI Mean SD 95% CI Mean SD 95% CI Mean SD 95% CI
Skeletal changes
Horizontal
A –0.1 1.0 –0.5, 0.3 0.7 1.8 0.1, 1.4 –0.4 0.5 –0.6, –0.2 –0.7 1.0 –1.1, 0.3 –0.4 ∗∗ 0.8 –0.7, –0.1
B –0.2 1.4 –0.8, 0.5 1.9 2.1 1.1, 2.8 –0.1 1.1 –0.6, 0.3 –0.4 1.2 –0.9, 0.0 –0.4 1.2 –0.8, 0.1
Pg 0.0 1.6 –0.7, 0.7 2.3 2.4 1.3, 3.3 0.1 1.2 –0.4, 0.6 –0.4 1.4 –1.0, 0.1 –0.6 1.4 –1.1, 0.0
Vertical
ANS 0.0 0.7 –0.3, 0.3 0.8 2.0 0.0, 1.6 –0.3 ∗∗ 0.9 –0.6, 0.0 –0.1 1.4 –0.7, 0.4 0.0 1.1 –0.4, 0.5
PNS 0.2 0.6 0.0, 0.5 –4.1 ∗∗∗ 1.5 –4.7, –3.6 0.4 0.7 0.1, 0.6 0.6 ∗∗∗ 0.7 0.4, 0.9 0.1 0.5 –0.1, 0.4
Me 0.3 1.3 –0.4, 0.9 –2.0 ∗∗∗ 1.6 –2.7, –1.4 –0.1 1.0 –0.6, 0.3 0.0 1.3 –0.5, 0.5 0.0 0.8 –0.3, 0.3
Angular
SNA 0.0 0.9 –0.4, 0.4 0.5 ∗∗ 1.7 0.0, 1.2 –0.4 0.6 –0.6, –0.2 –0.5 ∗∗ 0.7 –0.8, –0.2 –0.1 0.7 –0.4, 0.2
SNB –0.1 0.7 –0.4, 0.3 0.7 ∗∗ 0.9 0.3, 1.1 –0.1 0.6 –0.3, 0.1 –0.1 0.7 –0.4, 0.1 –0.1 0.7 –0.4, 0.2
ANB 0.1 0.9 –0.3, 0.6 –0.1 1.6 –0.7, 0.4 –0.3 0.7 –0.6, 0.0 –0.4 0.9 –0.7, 0.0 0.0 0.9 –0.4, 0.3
ML/NSL –0.4 1.6 –1.2, 0.4 –1.4 1.7 –2.1, –0.6 –0.3 1.2 –0.7, 0.2 0.0 1.3 –0.5, 0.5 0.2 1.2 –0.2, 0.7
NL/NSL –0.3 1.0 –0.7, 0.1 5.8 ∗∗∗ 2.8 4.7, 6.9 –0.7 1.2 –1.1, –0.2 –0.7 1.9 –1.5, 0.0 0.0 1.3 –0.5, 0.5
Dental changes
iLs/FH (°) –2.8 5.3 –5.0, –0.6 –5.4 ∗∗∗ 2.2 –6.9, –3.8 0.1 4.4 –1.6, 1.8 1.8 ∗∗ 3.3 0.5, 3.1 2.0 3.2 0.7, 3.2
iLi/ML (°) 3.2 5.6 0.9, 5.5 –0.9 ∗∗ 4.1 –1.8, –0.1 1.1 2.5 0.1, 2.1 0.6 3.3 –0.8, 1.9 –0.4 2.1 –1.3, 0.4
Overjet –2.0 ∗∗∗ 1.6 –2.8, –1.2 –2.0 ∗∗∗ 1.8 –2.7, –1.4 –0.2 0.9 –0.6, 0.1 0.6 ∗∗ 1.2 0.1, 1.1 0.8 0.8 0.5, 1.1
Overbite 1.2 ∗∗∗ 2.1 0.7, 1.8 2.8 ∗∗∗ 1.5 2.3, 3.3 0.2 0.9 –0.1, 0.5 –0.2 1.0 –0.6, 0.2 –0.4 0.8 –0.7, 0.0
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May 12, 2020 | Posted by in Orthodontics | Comments Off on A comparison of Class II open bite correction by maxillary or mandibular surgery
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