A retrospective cohort study was conducted to analyze the relapse rate of anterior open bite (AOB) correction comparing Le Fort I osteotomy with and without anterior segmentation. The risk factors that might contribute to relapse were also assessed. Lateral cephalograms obtained at six different times were analyzed. A total of 81 patients with AOB were recruited. Thirty-five patients underwent Le Fort I osteotomy without anterior segmentation and 46 patients underwent anterior segmentation. Le Fort I osteotomy with anterior segmentation resulted in significantly more AOB relapse when compared to that without anterior segmentation at 7 weeks postoperative (15.2% vs. 0%, P = 0.016). During the early postoperative period, factors that contributed to AOB relapse in Le Fort I osteotomy with anterior segmentation were AOB closure ≥4 mm and inferior positioning of the anterior segment >2 mm. Over the long term, AOB closure ≥4 mm and intraoral vertical ramus osteotomy as the only mandibular procedure were factors identified as causing more AOB relapse in those treated by Le Fort I osteotomy with anterior segmentation. In conclusion, Le Fort I osteotomy without anterior segmentation was found to be more stable in the surgical correction of AOB in the early and late postoperative periods.
Anterior open bite (AOB) malocclusion is a complex morphological and functional anomaly that can be defined as the lack of vertical overlapping in the upper and lower incisors when the posterior teeth are in maximum occlusion . It is impossible to consider AOB as a single entity as its aetiology is often multifactorial. Depending on age at presentation, treatment options may include the redirection of facial skeletal growth, habit control, and orthodontic tooth movements. However, severe cases of AOB in adults usually require more complex management that involves orthodontic treatment and orthognathic surgery.
Relapse after the treatment of AOB is relatively high when compared to other dentofacial deformities . Systematic reviews and meta-analyses looking into the relapse rate of surgical and non-surgical AOB correction have reported rates varying from as low as 0% to 70% . However, there is no general consensus in regard to the surgical treatment for AOB that would minimize the relapse rate.
A common aetiology of AOB is the posterior vertical maxillary excess, which interferes with the closure of the mandible. This causes a clockwise rotation of the mandible, thereby producing an anterior open bite, regardless of the presence or absence of an abnormal mandible. It usually presents with a flat maxillary occlusal plane and sometimes an exaggerated curve of Spee in the maxillary arch . The Le Fort I osteotomy is usually necessary to correct the vertical height of the maxilla by differentially impacting the maxilla and allowing anticlockwise rotation of the mandible with or without mandibular surgery . In some cases, anterior segmentation of the Le Fort I osteotomy may be helpful to allow independent repositioning of the anterior and posterior segments of the maxilla. It is also indicated to correct reversed occlusal curves and protruded anterior dentoalveolar segments . The segmentation of a Le Fort I osteotomy requires additional surgical time and skill, and carries the risk of increased morbidity, such as avascular necrosis and damage to the tooth roots at the osteotomy site . In AOB cases, the relapse rate with or without anterior segmentation of the Le Fort I osteotomy remains unclear.
The aims of this study were to evaluate the relapse rate of AOB correction comparing Le Fort I osteotomies with and without anterior segmentation, and to assess the risk factors that might contribute to the relapse in these two treatment modalities.
Materials and methods
This was a retrospective study of patients with AOB treated by orthognathic surgery. The inclusion criteria were: (1) age 18 years and above, (2) medically fit, (3) presenting an anterior open bite (i.e., lack of vertical contact between the incisors), (4) treated by bimaxillary orthognathic surgery, and (5) at least 24 months of postoperative follow-up. Patients who underwent single-jaw surgery, had undergone previous orthognathic surgery, had pathological lesions in the oral and maxillofacial region such as fibrous dysplasia and condylar resorption, or who had syndromic diseases affecting the craniofacial region such as cleft lip and palate were excluded.
Eligible patients were divided into two groups depending on the maxillary procedure they received. Patients in group A had a Le Fort I osteotomy without anterior segmentation (i.e., in one piece or two pieces with a midline split). Patients in group B had a Le Fort I osteotomy with anterior segmentation (i.e., in four pieces where the midline split is followed by segmentation behind the canines) (see Surgical procedure). The mandibular surgeries that the patients received were recorded. All patients underwent pre-surgical and post-surgical orthodontic treatment.
A mucosal incision was made 5 mm above the attached gingiva from the zygomatic buttress on one side to the other. A mucoperiosteal flap was raised to expose the lateral wall of the maxilla to the infraorbital foramen superiorly, the piriform aperture, and the pterygomaxillary fissure posteriorly. A retractor was placed to engage the pterygomaxillary fissure. The mucoperiosteum from the lateral nasal wall to the inferior turbinate bone was raised and protected. An osteotomy was performed along the lateral wall of the maxilla with a bur and completed with an osteotome to reach the pterygoid process. A lateral nasal osteotomy was performed. The mucoperiosteum along the nasal floor and latero-inferior surface was raised and the nasal septum osteotomized. A posterior osteotomy was made through the tuberosity at the site of the extraction sockets of the upper third molars or distal to the last molars. The maxilla was then down-fractured and mobilized.
For group A (without anterior segmentation) ( Fig. 1 ), the maxilla was fitted into the wafer in one piece, or was segmented at the midline into two pieces. For group B (with anterior segmentation) ( Fig. 2 ), a midline split followed by osteotomies behind the canines (through extraction sockets of the first premolars or spaces created orthodontically distal to the canines) were performed to create a Le Fort I in four pieces. The segments were mobilized to establish the occlusion with a surgical guide and a custom-made arch bar. Four titanium miniplates with 6-mm screws on each side were used for fixation at the piriform rims and zygomatic buttresses on each side.
With regard to the mandibular procedures, the patients received a mandibular ramus osteotomy with or without anterior mandibular surgery (anterior subapical osteotomy and/or genioplasty). An anterior subapical osteotomy was mainly performed for a body setback movement or uprighting of the anterior mandibular segment. In accordance with the study centre protocol, the bilateral sagittal split ramus osteotomy (SSRO) with miniplate fixation was used for mandibular advancement, while the bilateral intraoral vertical ramus osteotomy (IVRO) with intermaxillary fixation was used for mandibular setback.
Study variables and data collection
Standardized lateral cephalometric radiographs were taken pre-surgery (T1), immediately postoperative (T2), and postoperatively at 7 weeks (T3), 6 months (T4), 12 months (T5), and 24 months (T6). Cephalometric tracings were performed on acetate paper by one examiner. The cephalometric tracings from the same patient at the different follow-up time points were superimposed at the cranial base. Landmarks for tracing included sella (S), nasion (N), posterior nasal spine (PNS), anterior nasal spine (ANS), incisal edge of the upper incisor (U1), upper incisor root apex (U1-A), tip of the mesial cusp of the last fully erupted upper molar (UM) and lower molar (LM), incisor edge of the lower incisor (L1), and root apex of the lower incisor (L1-A). A reference frame was constructed using the SN line, x -axis, and y -axis for measurement of the surgical movement and post-surgical changes.
The anterior maxilla was represented by the ANS and U1, while the posterior maxilla was represented by the PNS and UM. The occlusal plane (OP) was made by joining a line from U1 to UM, and the upper incisor angle (UIA) was made by a line joining the upper incisor edge (U1) to the root apex of the upper central incisors. Overbite was measured as the vertical distance between the incisal edges of the upper and lower incisors projected perpendicular to the x -axis. A summary of the cephalometric landmarks and planes used can be found in Table 1 and Fig. 3 .
|Sella||S||Centre of the pituitary fossa of the sphenoid bone|
|Nasion||N||Intersection of the internasal suture with the frontonasal suture at midsagittal plane|
|Upper incisal tip||U1||Tip of the upper central incisor|
|Anterior nasal spine||ANS||Tip of the bony anterior nasal spine at the inferior margin of the piriform aperture, in the midsagittal plane|
|Upper molar||UM||Mesial cusp tip of the last erupted upper molar|
|Posterior nasal spine||PNS||Most posterior point on the bony hard palate in the midsagittal plane|
|Lower incisor tip||L1||Tip of the lower central incisor|
|SN line||SN||The line that is formed by connecting sella and nasion|
|x -axis||x -axis||A line passing through sella rotated by 7° clockwise from the SN line to approximate the Frankfort horizontal plane|
|y -axis||y -axis||A line perpendicular to the x -axis passing through sella|
|Upper incisor angle||UIA||The incisor angulation in relation to the x -axis|
|Occlusal plane||OP||The upper occlusal plane drawn from the upper incisal tip to the tip of the mesial cusp of the upper molar|
|Overbite||OB||The vertical distance between two lines crossing the incisal tip of the upper and lower central incisors parallel to the x -axis|
The vertical distances on the tracings were measured manually using an electronic digital sliding caliper (Aerospace Digital Caliper); the angular measurements were made with a protractor. To assess reproducibility, 10% of the sample was selected randomly for second tracing after an interval of 3 days and the data subjected to intra-operator reliability testing.
Patient demographic data including age and sex were collected. The patients’ diagnoses, surgical treatments received, and all cephalometric tracing measurements were recorded. Ethical approval was obtained from the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster.
The primary outcome of this study was the AOB relapse rate at different follow-up time points. The secondary outcomes were the risk factors contributing to the relapse of AOB based on surgical movements (T2 − T1) of the anterior maxilla (ANS), the posterior maxilla (PNS), the maxillary occlusal plane (OP), and the upper incisor angulation, and also based on the mandibular procedures.
All data were gathered and entered into statistical software (IBM SPSS Statistics version 23.0; IBM Corp., Armonk, NY, USA). The intra-observer variations were analyzed using the paired t -test. Descriptive statistics, including frequencies, means and standard deviations (SD), were used to describe the demographic data of the samples and the preoperative cephalometric features for both groups. The mean overbite was obtained at the different postoperative time points for each group. The proportions of patients who showed relapse at the different postoperative times in each group were compared using the χ 2 test. Risk factors such as preoperative overbite, surgical changes at the anterior maxilla (ANS, U1), posterior maxilla (PNS, UM), upper incisal angle (UIA), and the occlusal plane (OP), and the mandibular procedures used were also tested with regard to the relapse rate using the χ 2 test.
A total of 81 patients (22 male, 59 female) with AOB were treated by bimaxillary orthognathic surgery. The mean age of the patients was 24.3 years (SD 6.0 years). The mean preoperative AOB was 3.9 mm (SD 2.3 mm). Thirty-five patients (43.2%) who had a Le Fort I osteotomy without anterior segmentation for the maxillary procedure formed group A; 13 of these patients (37.1%) had a midline split for sagittal plane segmentation. Group B consisted of 46 patients (56.8%) who had a Le Fort I osteotomy with anterior segmentation for the maxillary procedure.
Twenty-four patients (29.7%) had a SSRO, of whom 16 (66.7%) also had simultaneous anterior mandibular surgery. Thirty-nine patients (48.1%) had an IVRO, of whom 19 (48.7%) also had simultaneous anterior mandibular surgery. Eighteen patients (22.2%) had only anterior mandibular surgery.
A summary of the demographic data, preoperative AOB, and preoperative cephalometric measurements for group A and group B are presented in Table 2 . The preoperative AOB was 3.8 mm (SD 2.1 mm, range 0.8–9.5 mm) in group A and 4.0 mm (SD 2.5 mm, range 0.6–13.5 mm) in group B. There was no statistically significant difference between the two groups for these variables. The paired t -test for intra-operator reliability showed no significant difference, indicating that the landmarks were consistently and accurately identified.
|Group A ( n = 35)||Group B ( n = 46)||P -value|
|Sex, n (%)||0.307|
|Male||11 (31.4%)||11 (23.9%)|
|Female||24 (68.6%)||35 (76.1%)|
|Age, years, mean ± SD||24.6 ± 6.4||24.1 ± 5.7||0.695|
|Preoperative cephalometric measurements, mean ± SD|
|OB (mm)||−3.8 ± 2.1||−4.0 ± 2.5||0.576|
|ANS (mm)||49.3 ± 5.0||48.9 ± 6.7||0.732|
|U1 (mm)||82.5 ± 7.4||82.1 ± 7.6||0.818|
|PNS (mm)||47.9 ± 3.6||47.7 ± 3.6||0.846|
|UM (mm)||58.8 ± 7.2||56.6 ± 7.4||0.171|
|OP (°)||8.1 ± 6.0||9.0 ± 5.2||0.486|
|UIA (°)||61.9 ± 9.1||59.6 ± 10.4||0.304|
|Surgical movements (T2−T1), mean ± SD|
|OB closure (mm)||5.4 ± 2.8||5.8 ± 2.9||0.471|
|ANS (mm)||−2.4 ± 3.7||−3.4 ± 3.8||0.222|
|U1 (mm)||−2.9 ± 5.4||−3.1 ± 5.0||0.907|
|PNS (mm)||−4.5 ± 2.8||−3.6 ± 2.9||0.169|
|UM (mm)||−4.0 ± 3.4||−3.9 ± 4.6||0.855|
|OP (°)||1.5 ± 3.7||1.6 ± 3.5||0.940|
|UIA (°)||1.7 ± 6.2||7.0 ± 6.5||0.000 a|
The cephalometric landmarks representing the surgical movements (T2 − T1) in both groups are listed and compared in Table 2 . The difference in landmark AOB at T2 and T1 represented the amount of overbite closure; this was 5.4 mm (SD 2.8 mm) in group A and 5.8 mm (SD 2.9 mm) in group B. For landmarks ANS, U1, PNS, and UM, a positive value represents inferior repositioning of the maxilla, whereas a negative value represents superior movement. There was no statistically significant difference in overbite closure, ANS, U1, PNS, or UM between the two groups at T2 − T1. For the landmark OP, a positive value represents clockwise rotation and a negative value indicates anticlockwise rotation. There was no statistically significant difference between the two groups for the change in OP. For the upper incisal angle landmark (UIA), a positive value indicates upright movement of the anterior maxillary segment. The UIA in group B was 7.0° (SD 6.5°), which was significantly greater than the UIA in group A without anterior segmentation (mean 1.7°, SD 6.2°) ( P = 0.000).
Primary outcome: AOB relapse
Patients with a negative overbite (OB) at postoperative follow-up were regarded as having AOB relapse. The overall relapse rate was 8.6% at 7 weeks postoperative (T3), 9.9% at 6 months postoperative (T4), 7.4% at 12 months postoperative (T5), and 12.3% at 24 months postoperative (T6). Table 3 shows the AOB relapse rates at the different postoperative follow-up points for group A and group B. At 7 weeks postoperative (T3), the relapse rate of group B was significantly higher than that of group A (15.2% (7/46) vs. 0% (0/35); P = 0.016). There was no significant difference in the relapse rate of AOB between the two groups at 6 months (T4), 12 months (T5), or 24 months (T6) postoperative. Although statistically non-significant, the AOB relapse rate of group A was higher than that of group B at 6 months postoperative (T4) (10.9% vs. 8.7%, P = 0.683), but group B relapsed more than group A at 12 months postoperative (T5) (10.9% vs. 2.9%, P = 0.156) and 24 months postoperative (T6) (17.4% vs. 5.7%, P = 0.106).
|Group A||Group B||P -value|
|1 week (T2)||10.9% (4/35)||8.7% (4/46)||0.683|
|7 weeks (T3)||0% (0/35)||15.2% (7/46)||0.016 b|
|6 months (T4)||10.9% (4/35)||8.7% (4/46)||0.683|
|12 months (T5)||2.9% (1/35)||10.9% (5/46)||0.156|
|24 months (T6)||5.7% (2/35)||17.4% (8/46)||0.106|
The mean preoperative overbite for the total sample was −3.9 mm (SD 2.3 mm, range −13.5 mm to −0.6 mm). The overall mean overbite was 1.7 mm (SD 1.5 mm, range −2.5 mm to 6.2 mm) at 1 week postoperative (T2). The mean overbite at 7 weeks, 6 months, 12 months, and 24 months postoperative was 1.6 mm (SD 1.4 mm, range −2.2 mm to 4.2 mm), 1.5 mm (SD 1.3 mm, range −1.7 mm to 4.3 mm), 1.6 mm (SD 1.3 mm, range −2.1 mm to 4.6 mm), and 1.3 mm (SD 1.1 mm, range −1.4 mm to 3.6 mm), respectively. Table 4 shows the mean overbite measurements for the preoperative and postoperative time points. There was no significant difference in the mean overbite between group A and group B at any of the postoperative follow-ups ( P > 0.05).
|Time point||Group A ( n = 35)||Group B ( n = 46)||P -value|
Table 5 shows the mean changes in overbite at the different postoperative follow-up times from 1 week postoperative (T2). There was a significant increase in the change in overbite at 24 months postoperative for group B, with a mean change of −0.6 mm ( P = 0.042). No significant change in overbite was noted for group A at any of the postoperative follow-up times. However, when the mean change in overbite was compared independently for groups A and B, no statistically significant difference was found between the two groups at any of the postoperative follow-up times.
|OB changes||Group A||Group B||P -value between groups|
|Mean||SD||Min||Max||P -value||Mean||SD||Min||Max||P -value|
|T3 − T2||0.1||1.4||−3.1||4.2||0.545||−0.3||1.8||−5.7||3.7||0.257||0.211|
|T4 − T2||−0.1||1.7||−5.7||3.2||0.616||−0.2||1.6||−4.0||4.7||0.403||0.876|
|T5 − T2||−0.0||1.7||−2.9||4.2||0.846||−0.3||1.8||−4.1||3.6||0.393||0.662|
|T6 − T2||−0.2||1.7||−4.7||3.2||0.407||−0.6||1.7||−4.5||2.6||0.042 a||0.442|
Secondary outcomes: risk factors for AOB relapse
The risk factors for AOB relapse were assessed based on the surgical movements of the anatomical landmarks, including the amount of AOB closure, the vertical movements of anterior maxilla (ANS) and posterior maxilla (PNS), and rotation of the occlusal plane (OP), as well as the types of mandibular surgery performed. Table 6 summarizes the comparisons of AOB relapse rates based on the amount of AOB closure, direction and amount of ANS and PNS movements, and rotation of the maxillary occlusal plane at the different postoperative follow-up times.
|P -value||6 months
|P -value||12 months
|P -value||24 months
|AOB closure ≥4 mm ( n = 55)||0.041 a||0.356||0.155||0.024 a|
|Group A||0 (0/21)||4.8% (1/21)||0 (0/21)||0 (0/21)|
|Group B||17.6% (6/34)||8.8% (3/34)||8.8% (3/34)||20.6% (7/34)|
|AOB closure <4 mm ( n = 26)||0.271||0.356||0.399||0.636|
|Group A||0 (0/14)||21.4% (3/14)||7.1% (1/14)||14.3% (2/14)|
|Group B||8.3% (1/12)||8.3% (1/12)||16.7% (2/12)||8.3% (1/12)|
|ANS inferior >2 mm ( n = 53)||0.028 a||0.654||0.288||0.288|
|Group A||0 (0/22)||13.6% (3/22)||9.1% (2/22)||9.1% (2/22)|
|Group B||19.4% (6/31)||6.5% (2/31)||12.9% (4/31)||12.9% (4/31)|
|ANS superior >2 mm ( n = 9)||0.134||0.453||–||0.134|
|Group A||0 (0/6)||16.7% (1/6)||0 (0/6)||0 (0/6)|
|Group B||33.3% (1/3)||0 (0/3)||0 (0/3)||33.3% (1/3)|
|PNS impaction 2–4 mm ( n = 20)||0.257||0.660||0.257||0.881|
|Group A||0 (0/11)||18.2% (2/11)||0 (0/11)||9.1% (1/11)|
|Group B||11.1% (1/9)||11.1% (1/9)||11.1% (1/9)||11.1% (1/9)|
|PNS impaction >4 mm ( n = 38)||0.191||0.401||0.906||0.906|
|Group A||0 (0/17)||5.9% (1/17)||5.9% (1/17)||5.9% (1/17)|
|Group B||9.5% (2/21)||14.3% (3/21)||4.8% (1/21)||4.8% (1/21)|
|Rotation of OP >2° ( n = 29)||0.099||0.104||0.343||0.220|
|Group A||0 (0/13)||15.4% (2/13)||0 (0/13)||7.7% (1/13)|
|Group B||18.8% (3/16)||0 (0/16)||6.3% (1/16)||25.0% (4/16)|
|Rotation of OP <2° ( n = 52)||0.075||0.636||0.271||0.271|
|Group A||0 (0/22)||9.1% (2/22)||4.5% (1/22)||4.5% (1/22)|
|Group B||13.3% (4/30)||13.3% (4/30)||13.3% (4/30)||13.3% (4/30)|