Introduction
This study aimed to investigate changes in bite force (BF) and occlusal contact area after anterior open-bite (AOB) treatment and compare the changes in surgical vs nonsurgical treatment.
Methods
This retrospective study included patients with AOB compared with normal occlusion. AOB was corrected by either intrusion of the maxillary molars (intrusion group, n = 19) or orthognathic surgery (surgery group, n = 37). The control group (n = 35) had a normal overbite relationship. Records of lateral cephalograms, BF, and occlusal contact area taken before (T0), immediately after (T1), and 2 years after (T2) orthodontic treatment were compared within and among the 3 groups.
Results
The open-bite group, including intrusion and surgery groups, had a lower BF and less occlusal contact area than the control group at T0 and T1 ( P <0.001). However, there were no significant differences among the 3 groups at T2 ( P >0.05). The intrusion and surgery groups showed no significant differences throughout the observation period extending from T0 to T2 ( P >0.05). Although BF and occlusal contact area decreased at T1 compared with T0, they increased during retention and showed higher values at T2 than at T0.
Conclusions
Treatment of AOB improved BF and occlusal contact area 2 years posttreatment. Orthognathic surgery and molar intrusion using orthodontic miniscrews can improve occlusal function similarly. Orthodontists can select either method depending on malocclusion severity and patient demand.
Highlights
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There were control and 2 open-bite treatment groups (intrusion and surgery).
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We compared changes in occlusal contact area (OCA) and bite force (BF) among groups.
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Improvement levels in OCA and BF did not differ between the 2 open-bite groups.
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Three groups showed no differences in OCA and BF 2 years posttreatment.
Anterior open-bite (AOB) indicates a lack of incisal overlap or incisal contact, which can cause problems in mastication and pronunciation. AOB can be grouped into skeletal or dental open bite categories depending on the etiology. Skeletal open bite results from genetically predetermined growth patterns or condylar resorption because of osteoarthritis of the mandibular condyle and is characterized by backward rotation of the mandible, whereas dental open bite displays a normal vertical skeletal pattern but lacks incisal overlap because of labioversion of the anterior teeth or inadequate eruption of the anterior teeth associated with a protrusive tongue thrust or thumb sucking habit.
Treatment of AOB in adults can be performed by orthognathic surgery or orthodontic camouflage, depending on etiology and severity. Orthognathic surgery is indicated to correct AOB if the vertical discrepancy is severe and is accompanied by a sagittal or transverse discrepancy, such as a Class III relationship and facial asymmetry. In contrast, if the degree of open bite is mild to moderate, orthodontic tooth movement can resolve AOB by extrusion of the anterior teeth, intrusion of the posterior teeth, or both. Historically, using conventional orthodontic techniques, it has been difficult to intrude on both maxillary and mandibular buccal segments. However, since the introduction of orthodontic miniscrews, it has been possible to correct AOB noninvasively by molar intrusion using orthodontic miniscrews to produce counterclockwise rotation of the mandible when exposure of the maxillary incisors is appropriate. , With orthognathic surgery, the masticatory muscles are detached, and immediate skeletal changes are manifested, whereas, with nonsurgical correction, slow intrusion of the buccal teeth allows the mandible to rotate counterclockwise without any need for muscular reattachment gradually. Changes in skeletal pattern and dentition affect the masticatory muscles and occlusal contact area (OCA), consequently influencing the bite force (BF). Therefore, the functional changes may differ depending on the modality after AOB treatment.
Regardless of its etiology, patients with AOB have low BF and less OCA. The low BF can decrease chewing efficiency, possibly attributing to AOB relapse. , The BF decreased immediately after orthodontic treatment, including in orthognathic surgery patients but increased gradually. , As AOB treatment would increase the OCA, which highly correlates with BF, , BF can be expected to increase after orthodontic treatment. However, there has been little investigation of changes in BF after orthodontic treatment in AOB patients.
BF can be measured using a BF transducer such as a pressure-sensitive sheet , or a digital occlusal analysis system ( Supplementary Fig 1 ). , The Dental Prescale System (Fuji Film Corp., Tokyo, Japan), which uses a thin pressure-sensitive sheet, has been widely used for the measurements because it best reflects the natural dentition with few errors simply and objectively. The purpose of this study was to investigate changes in BF and OCA after AOB treatment using the Dental Prescale System (Fuji Film Corp.) and to compare the changes according to treatment modality: orthognathic surgery vs nonsurgical correction by molar intrusion. The changes were also compared with those of the control group, which had a normal occlusion but had been treated with minor tooth movement.
Material and methods
This retrospective study included intrusion (n = 19), surgery (n = 37), and control (n = 35) groups. From 2,890 patients who had visited OOO Dental Hospital for orthodontic treatment between 2008 and 2013, overbite (OB) was used to select AOB (<0 mm; n = 376) and control groups, whose AOB ranged from 1 mm to 4 mm (n = 1002), initially. In addition, the following inclusion and exclusion criteria were applied ( Fig 1 ). The inclusion criteria were (1) aged 18-40 years before treatment (T0); (2) female to minimize the effects of sex difference; (3) hyperdivergent facial profile, which was confirmed by Frankfort-mandibular plane angle (FMA) of >28°; (4) mild facial asymmetry (menton deviation <2 mm, which was confirmed from the initial posteroanterior cephalogram); (5) full eruption of the maxillary and mandibular second molars at T0; and (6) availability of lateral cephalograms and records of BF at T0, immediately after (T1), and 2 years posttreatment (T2). The exclusion criteria were (1) any missing teeth except for the third molars; (2) orthodontic extraction; (3) temporomandibular disorder; (4) history of previous orthodontic treatment; (5) systemic disease, cleft lip, cleft palate, or craniofacial disorder; and (6) use of a removable retainer to cover the occlusal surface. Of 97 patients who met the above criteria for the open bite group, 41 patients were excluded because their maxillary or mandibular anterior teeth showed extrusion during treatment. Nineteen patients whose AOB had been resolved by maxillary molar intrusion were assigned to the intrusion group, whereas 37 who had had orthognathic surgery were assigned to the surgery group. The orthognathic surgery on those in the surgery group addressed mandibular prognathism or long face. The 191 subjects in the control group were screened on the basis of the same inclusion/exclusion criteria. Then, 35 patients with Class I molar relationships (within a range of 2 mm of the ideal Class I molar relationship) at T0 were finally selected for the control group, whereas 156 subjects were excluded because of Class II or III molar relationships ( Table I ).
| Variables | Intrusion (n = 19) | Surgery (n = 37) | Control (n = 35) | P value |
|---|---|---|---|---|
| Age (y) | 21.4 ± 5.6 | 22.2 ± 5.7 | 21.1 ± 5.7 | 0.744 |
| Treatment duration (mo) | 27.3 ± 4.2 a | 23.8 ± 4.2 b | 22.1 ± 2.8 b | <0.001 ∗∗∗ |
| ANB (°) | 5.8 ± 1.5 a | 1.2 ± 2.3 b | 2.9 ± 1.7 c | <0.001 ∗∗∗ |
| FMA (°) | 39.1 ± 4.9 | 38.2 ± 5.3 | 36.2 ± 3.0 | 0.067 |
| Gonial angle (°) | 129.2 ± 5.1 | 128.1 ± 6.1 | 127.3 ± 4.9 | 0.471 |
| Anterior facial height (mm) | 132.0 ± 6.1 a | 136.4 ± 3.5 b | 130.2 ± 6.2 a | <0.001 ∗∗∗ |
| Posterior facial height (mm) | 77.3 ± 6.8 | 78.2 ± 5.6 | 78.5 ± 4.6 | 0.757 |
| U6-HRP (mm) | 81.0 ± 3.9 | 81.8 ± 2.6 | 80.9 ± 3.0 | 0.867 |
| Overbite (mm) | −1.9 ± 1.3 a | −2.3 ± 1.8 a | 2.8 ± 1.1 b | <0.001 ∗∗∗ |
| Overjet (mm) | 5.0 ± 2.1 a | 1.3 ± 3.3 b | 2.9 ± 0.9 c | <0.001 ∗∗∗ |
Institutional Review Board (IRB) approval (IRB no. 3-2017-0306) was obtained from Gangnam Severance Hospital before data collection. The IRB waived written informed consent because of the study’s retrospective nature.
In the intrusion group, 8 orthodontic miniscrews (Orlus, Ortholution, Seoul, South Korea) had been implanted into the buccal and palatal interradicular alveolar bone between the first and second premolars and between the first and second molars to intrude the maxillary molars. The posterior teeth from the first premolar to the second molar were splinted with brackets (0.018-in slot) and sectional stainless-steel wires (0.017 × 0.025-in) on the buccal side, and metal buttons were bonded on the lingual side of each tooth. An elastic module, engaged between each tooth bracket/button and miniscrew on the buccal/palatal side, delivered 20-30 g of intrusion force per each posterior tooth. Until ≥1 mm of OB was obtained, the maxillary molars were intruded by an average of 1.7 mm over 5.2 ± 1.3 months, as retrospectively measured from lateral cephalograms. In the surgery group, all subjects underwent preoperative and postoperative orthodontic treatment and bimaxillary surgery by the same surgeon, LeFort I osteotomy, and bilateral intraoral vertical ramus osteotomy. The amount of surgery was precisely determined on the basis of surgical treatment objectives for each patient. The average amount of posterior impaction was 3.2 mm, and the mandible was moved to fit the maxillary position. During the first 2 weeks of postsurgery, maxillomandibular fixation was maintained; after that, all patients were asked to perform active physical therapy until they could open their mouths by at least 40 mm. Postoperative orthodontic treatment was conducted for 6.2 ± 1.9 months. In the control group, crowding relief, space closure, or total arch movement using interarch elastics or miniscrews were performed to achieve ideal occlusion. After treatment, fixed lingual retainers were bonded to the maxillary and mandibular anterior teeth with additional removable circumferential retainers in all groups. In both the intrusion and surgery groups, a hole was created around the incisive papilla to train tongue positioning, as a protrusive tongue position at rest can contribute to relapse. , The orthodontic treatment for all 3 groups was carried out by 3 orthodontic residents under the supervision of one expert orthodontist.
Lateral cephalograms and pressure-sensitive films (Dental Prescale 50H, type R) taken at T0, T1, and T2 were used for measurements. A horizontal reference plane (HRP) was registered on the lateral cephalograms as a straight line passing through the nasion and rotated 7° clockwise to the SN plane ( Fig 2 ). SNA, SNB, ANB, FMA, and gonial angle were measured for angular measurements, whereas anterior and posterior facial heights (AFH and PFH, respectively), perpendicular distance of the maxillary first molar (U6) to the HRP (U6-HRP), OB, and overjet were measured for linear measurements using V-ceph software (version 5.5; CyberMed, Osstem, Seoul, South Korea).
The Dental Prescale System (Fuji Film Corp), representing the static occlusal function, was used to measure BF and OCA. The patients were asked to bite on a thin pressure-sensitive film in maximum intercuspation with maximum force for 5 seconds while seated upright. The films were scanned and analyzed using an image scanner (Occluzer FPT 707), calculating BF and OCA ( Supplementary Fig 1 ).
One trained orthodontist (J.L.) scanned the pressure-sensitive films for BF and OCA, whereas 2 trained orthodontists (J.L. and Y.J.C.) independently measured all lateral cephalograms.
Statistical analysis
Interexaminer reliability was tested using intraclass correlation coefficients (ICC). The ICCs ranged from 0.877 to 0.965, indicating high reliability. In addition, 25 radiographs among lateral cephalograms taken at T1, T2, and T3 were randomly selected, and degree of agreement between 2 examiners was evaluated using Bland-Altman plot ( Supplementary Fig 2 ). Because the measurements are highly reproducible, the measurements by one orthodontist (J.L.) were used for the statistical analysis. To test intraexaminer reliability, the cephalometric measurements on 20 randomly selected subjects were repeated at a 2-week interval by one examiner (J.L.), and ICC were calculated. The ICCs ranged from 0.906 to 0.999, indicating high reliability. All the variables were tested for normality by Shapiro-Wilk’s tests and showed normal distributions. A power analysis confirmed the sample size should be >17 per group with 95% power at a significance level of 0.05.
For the cephalometric measurements, 1-way and repeated measures analysis of variance were used to compare the measurements of the 3 groups at each time point and among the 3-time points within each group, respectively. A linear mixed model was used to assess changes in the BF and OCA by testing the interaction among time and groups with age, FMA, gonial angle, AFH, PFH, PFH/AFH, and U6-HRP as covariates. All tests were conducted at a significance level of P <0.05 using SAS (version 9.3; SAS Institute Inc, Cary, NC).
Results
The demographic features were different in the 3 groups at T0 ( Table I ). Although age, FMA, gonial angle, PFH, and U6-HRP were not significantly different ( P >0.05), treatment duration, ANB, AFH, OB, and OJ were significantly different ( P <0.001). Table II shows changes in the cephalometric measurements of each group at T0, T1, and T2. In the intrusion group, OB increased by 4.0 mm during treatment but decreased by 0.9 mm during 2-year retention. In the surgical group, it increased by 4.5 mm during treatment but decreased by 0.8 mm during 2-year retention. In the control group, OB was approximately 2.2-2.8 mm throughout the observation period.
| Intrusion (n = 19) | Surgery (n = 37) | Control (n = 35) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Variables | T0 | T1 | T2 | P value | T0 | T1 | T2 | P value | T0 | T1 | T2 | P value |
| SNA (°) | 80.1 ± 3.6 | 79.6 ± 3.6 | 79.6 ± 3.6 | 0.895 | 81.0 ± 3.4 | 81.6 ± 3.8 | 81.6 ± 3.9 | 0.742 | 80.3 ± 3.0 | 80.3 ± 3.0 | 80.4 ± 3.0 | 0.993 |
| SNB (°) | 74.3 ± 3.7 | 74.7 ± 3.8 | 74.6 ± 3.7 | 0.940 | 79.8 ± 4.4 | 78.7 ± 3.7 | 79.0 ± 3.8 | 0.420 | 77.5 ± 3.4 | 77.5 ± 3.4 | 77.5 ± 3.4 | 1.000 |
| ANB (°) | 5.8 ± 1.5 | 4.9 ± 1.6 | 5.0 ± 1.5 | 0.165 | 1.2 ± 2.3 a | 2.9 ± 1.6 b | 2.9 ± 1.7 b | <0.001 ∗∗∗ | 2.9 ± 1.7 | 2.9 ± 1.7 | 2.9 ± 1.7 | 0.981 |
| FMA (°) | 39.1 ± 4.9 | 37.3 ± 5.3 | 37.7 ± 5.2 | 0.598 | 38.2 ± 5.3 | 38.6 ± 5.1 | 39.1 ± 5.3 | 0.832 | 36.2 ± 3.0 | 36.5 ± 3.2 | 36.4 ± 3.1 | 0.854 |
| Gonial angle (°) | 129.2 ± 5.1 | 129.5 ± 5.2 | 129.5 ± 5.1 | 0.985 | 128.1 ± 6.1 | 128.2 ± 6.1 | 128.2 ± 6.1 | 0.995 | 127.3 ± 4.9 | 127.0 ± 5.0 | 127.1 ± 4.9 | 0.982 |
| AFH (mm) | 132.0 ± 6.1 | 129.9 ± 6.3 | 130.4 ± 6.3 | 0.582 | 136.4 ± 3.5 a | 131.8 ± 3.3 b | 132.8 ± 3.1 b | <0.001 ∗∗∗ | 130.2 ± 6.2 | 131.0 ± 6.2 | 130.8 ± 6.2 | 0.829 |
| PFH (mm) | 77.3 ± 6.8 | 76.7 ± 6.8 | 76.8 ± 6.8 | 0.966 | 78.2 ± 5.6 a | 72.4 ± 5.1 b | 72.8 ± 5.1 b | <0.001 ∗∗∗ | 78.5 ± 4.6 | 78.8 ± 4.6 | 78.7 ± 4.6 | 0.964 |
| U6-HRP (mm) | 75.0 ± 3.9 | 73.3 ± 4.0 | 73.6 ± 3.9 | 0.322 | 75.3 ± 2.6 a | 72.1 ± 2.8 b | 72.8 ± 2.7 b | <0.001 ∗∗∗ | 75.0 ± 3.0 | 76.0 ± 3.0 | 75.9 ± 3.0 | 0.370 |
| OB (mm) | −1.9 ± 1.3 a | 2.1 ± 0.8 b | 1.2 ± 0.8 b | <0.001 ∗∗∗ | −2.3 ± 1.8 a | 2.2 ± 0.4 b | 1.4 ± 1.0 b | <0.001 ∗∗∗ | 2.8 ± 1.1 a | 2.3 ± 0.4 b | 2.2 ± 0.6 b | 0.004 ∗∗ |
| OJ (mm) | 5.0 ± 2.0 a | 3.2 ± 0.9 b | 3.5 ± 1.1 b | <0.001 ∗∗∗ | 1.3 ± 3.3 a | 3.0 ± 0.6 b | 3.3 ± 1.1 b | <0.001 ∗∗∗ | 2.9 ± 0.9 | 2.5 ± 0.4 | 2.6 ± 0.5 | 0.061 |
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