The purpose of this study was to evaluate the buccal and lingual alveolar bone thickness and buccolingual inclination of maxillary posterior teeth in patients with severe skeletal Class III malocclusion with and without mandibular asymmetry and compare with those in patients with skeletal Class I malocclusion.
Cone-beam computed tomography images of 69 patients with severe skeletal Class III malocclusion and 30 patients with skeletal Class I malocclusion were collected and reconstructed with Dolphin 3D software. Based on the distance from menton to the sagittal plane (d), the patients with skeletal Class III malocclusion were divided into a symmetry group (d ≤ 2 mm) and an asymmetry group (d ≥ 4 mm). Buccal and lingual alveolar bone thickness and buccolingual inclination of maxillary posterior teeth were measured and compared. Correlations among dental measurements, severity of sagittal discrepancy, and mandibular deviation were analyzed.
Maxillary posterior teeth on the deviated side in Class III asymmetry group and symmetry group were buccally inclined compared with the Class I group ( P < 0.001). A significant negative correlation was noted between buccolingual inclination of maxillary posterior teeth and ANB value with Spearman correlation coefficient of maxillary first molar, second premolar, and first premolar of –0.687, –0.485 and –0.506, respectively ( P < 0.001). Maxillary first molar showed thinner buccal alveolar bone on deviated side in asymmetry group and symmetry group of Class III, compared with the Class I group, with average values of 1.21 mm, 1.19 mm, and 1.83 mm, respectively ( P < 0.05). The maxillary first premolar also showed thinner buccal alveolar bone on deviated side in Class III asymmetry group compared with the Class I group, with average values of 0.87 mm and 1.28 mm, respectively ( P < 0.05).
Decompensation of buccally inclined posterior teeth in patients with skeletal Class III malocclusion should be more cautious owing to thinner buccal alveolar bone to avoid a high risk of fenestration and dehiscence.
Maxillary posterior teeth in Class III groups were buccally inclined compared with Class I.
The buccolingual inclination of maxillary posterior teeth was negatively correlated with ANB.
First molars and premolars had thinner buccal alveolar bone on the deviated side.
Skeletal Class III malocclusion is a kind of maxillofacial deformity with high prevalence in Asian populations, displaying sagittal discrepancy between maxilla and mandible. Facial asymmetry happens more frequently in patients with skeletal Class III malocclusion with overdeveloped mandible. Patients with skeletal Class III malocclusion with mandibular asymmetry have both sagittal and transverse skeletal discrepancies, leading to a great challenge to orthodontists.
Patients with severe skeletal Class III malocclusion with or without mandibular asymmetry usually require orthognathic surgery to normalize skeletal deformity, and presurgical orthodontic treatment directly influences the effects and long-term stability.
Patients with skeletal Class III malocclusion usually present with proclined maxillary incisors and retroclined mandibular incisors to compensate for sagittal discrepancy. In transverse dimension, patients with symmetrical skeletal Class III malocclusiont end to have buccally inclined upper posterior teeth and lingually inclined lower posterior teeth. However, the inclination of posterior teeth in patients with skeletal Class III malocclusions with mandibular asymmetry is different between deviated and nondeviated sides.
Dental decompensation in presurgical orthodontic treatment relies on adequate supporting periodontal tissue. Previous research on alveolar bone in patients with skeletal Class III malocclusion mainly focused on anterior teeth, indicating that patients with skeletal Class III malocclusion presented with thinner alveolar bone in the anterior area compared with patients with skeletal Class I malocclusion and morphology of alveolar bone in mandibular central incisor region adapted to the inclination of teeth. , Assessment of alveolar bone boundary around posterior area is also necessary to facilitate planned dental decompensation and avoid periodontal complications, including fenestration and dehiscence, during presurgical decompensation process. , Sendyk et al research noted that buccal and lingual alveolar bone thickness of teeth in patients with symmetrical skeletal Class III malocclusion was thinner compared with patients with normal occlusions.
Assessment of posterior teeth inclination and alveolar bone thickness in previous studies usually relied on dental casts or 2-dimensional anteroposterior radiographs. , However, dental casts could not reflect true inclination of the root, and evaluation on 2-dimensional anteroposterior radiographs had shortcomings of magnification, geometric distortion, superimposed structures, and inconsistent head position. Compared with traditional methods, cone-beam computed tomography (CBCT) could overcome these shortcomings and measure the inclination as well as alveolar bone thickness of teeth with great accuracy on different levels and dimensions. , , ,
The purposes of this study were to (1) assess buccolingual inclination and alveolar bone thickness of maxillary posterior teeth in patients with severe skeletal Class III malocclusion with and without mandibular asymmetry and compare with that in patients with skeletal Class I malocclusion; and (2) investigate the potential correlations among buccolingual inclination and alveolar bone thickness of maxillary posterior teeth, severity of mandibular deviation, and sagittal discrepancy.
Material and methods
All patient images in this study were collected in the Department of Oral Maxillofacial Surgery and Department of Orthodontics, Peking University School and Hospital of Stomatology. This project was approved by the Biomedical Ethics Committee of Peking University School and Hospital of Stomatology.
After applying the inclusion and exclusion criteria, 69 patients with skeletal Class III malocclusion were included in the sample ( Table I ). The inclusion criteria for the Class III group were as follows: (1) aged at least 16 years; (2) Mongolian; (3) permanent dentition; (4) no prior orthodontic or orthognathic treatment; (5) skeletal Class III (ANB angle, < 0°; Wits appraisal, ≤ –3.6 mm); (6) anterior teeth in crossbite or edge-to-edge position; and (7) MP-SN ≥ 27°. Exclusion criteria included: (1) congenitally missing teeth, retained deciduous teeth, or impacted teeth; (2) severe crowding in posterior teeth; (3) crowns or significant restorations in posterior teeth; (4) maxillary sinus obviously bulging into buccal or lingual alveolar bone of maxillary posterior teeth; (5) severe periodontitis; (6) systemic diseases; and (7) cleft lip or palate, temporomandibular joint disease. In addition, 30 patients with skeletal Class I malocclusion were included with the following inclusion criteria: (1) ANB angle between 0.7° and 4.7°; (2) mandibular deviation < 2 mm; and (3) other inclusion criteria the same as that for skeletal Class III subjects. Exclusion criteria included: (1) severe crowding or crossbite in posterior teeth; (2) crossbite or edge-to-edge position in anterior teeth; and (3) the same exclusion criteria as patients with skeletal Class III malocclusion.
|Characteristics||Group III (asymmetry) n = 39||Group III (symmetry) n = 30||Group I n = 30||Multiple comparison|
|Age (y)||20.2 ± 3.00||21.3 ± 4.62||22.9 ± 4.16|
|ANB (°)||–3.7 ± 2.88||–4.2 ± 2.86||2.8 ± 1.57||AS = S < I|
|Wits (mm)||–12.3 ± 4.44||–12.8 ± 5.22||–1.3 ± 2.34||AS = S < I|
|Mandibular deviation (mm)||7.5 ± 3.03||0.9 ± 0.67||0.9 ± 0.66||I = S < AS|
|MP-SN (°)||37.5 ± 6.76||36.8 ± 7.00||34.8 ± 5.36||AS = S = I|
Patients with skeletal Class III malocclusion were further divided into 2 subgroups according to the degree of mandibular deviation from midsagittal plane measured on 3-dimensional CBCT images: (1) group III (asymmetry), which included 39 patients (25 males, 14 females; average age, 20.2 ± 3.00 years) with mandibular deviation more than 4 mm; and (2) group III (symmetry), which included 30 patients (10 males, 20 females; average age, 21.3 ± 4.62 years) with mandibular deviation < 2 mm. Twenty-one patients with mandibular deviation from 2 to 4 mm were excluded from the study. Group I included 30 patients (10 males, 20 females; average age, 22.9 ± 4.16 years) with mandibular deviation < 2 mm. The mandibular deviation was evaluated by menton (Me) deviation to the midsagittal plane. The deviated side was defined as the side Me shifted toward the midsagittal plane, while the other side was defined as the nondeviated side ( Table II ).
|Or (orbitale)||Lowest point of skeletal infraorbital margin|
|Po (porion)||Most superior point of skeletal external auditory meatus when the meatus is entirely encircled in bone|
|N (nasion)||Most anterior and median point along the frontonasal suture|
|Ba (basion)||Most inferior point along the anterior border of the foramen magnum|
|Me (menton)||Most inferior point of skeletal symphysis|
|Horizontal plane (Frankfort plane)||Plane passing through bilateral orbitale and right porion|
|Midsagittal plane||Plane perpendicular to horizontal plane, passing through nasion and basion|
|Coronal plane||Plane perpendicular to the above 2 planes, passing through basion|
The sample size calculation was based on buccal and lingual alveolar bone thickness of maxillary posterior teeth measured at 3 mm apical to the mandibular cementoenamel junction in Sendyk et al study and a standard deviation of 0.6 mm of maxillary second molar was reported. If 0.35 mm was set as clinically relevant difference, a minimum sample size of 20 subjects was required per group to achieve a significant analysis, with a significance level of 0.05 and a statistical power of 90%. The sample size was calculated using the Power Analysis and Sample Size software (version 11; NCSS, Kaysville, Utah).
CBCT images were taken with NewTom Scanner (NewTom AG, Marburg, Germany) set as follows: 15 × 15 cm field of view, 110 kV, 2.81 mA, 3.6-second exposure, with axial slice thickness of 0.3 mm. The CBCT images were saved as digital imaging and communications in medicine format and reconstructed in Dolphin 3D Imaging software (version 11.8; Dolphin Imaging and Management Solutions, Chatsworth, Calif). Landmarks were located with Dolphin software and judged on 3-dimensional sections. The location of each landmark was calculated based on 3-dimensional coordinates. To standardize the orientation of craniofacial structures, 3-dimensional reference planes were set: (1) horizontal plane was defined as Frankfort plane; (2) midsagittal plane was perpendicular to Frankfort plane, passing through nasion and basion point; and (3) coronal plane was perpendicular to the above 2 planes and passing through basion point. Landmarks and reference planes are defined and shown in Table II and Figure 1 .
On long-axis plane, angle between long axis of tooth and midsagittal line was defined as buccolingual inclination of the tooth. Definition and measurement of long axis of teeth are shown in Table III and Figures 2 and 3 . , , If a tooth was buccally inclined, inclination angle of the tooth was defined as positive, and if it was lingually inclined, inclination angle was defined as negative.
|Long-axis plane of teeth|
|Maxillary first molar||Plane perpendicular to midsagittal plane, passing through the central fossa and trifurcation of maxillary first molar|
|Maxillary premolar||Plane perpendicular to midsagittal plane, passing through the central fossa and furcation (multirooted) or root apex (single-rooted) of the premolar|
|Long axis of teeth|
|Maxillary first molar||Line passing through the central fossa and trifurcation|
|Maxillary premolar (multirooted)||Line passing through the central fossa and furcation|
|Maxillary premolar (single-rooted)||Line passing through the central fossa and root apex|
Buccal and lingual alveolar bone thickness and alveolar width were measured at the level of buccal furcation plane of maxillary first molars. To adjust measurement plane as follows , : (1) sagittal view: rotate the section to make long axis of tooth parallel to the vertical reference line ( Fig 4 , A ); (2) coronal view: rotate the section to ensure the horizontal line parallel to the palatal plane and nasal floor ( Fig 4 , B ); (3) axial view: position the section at the level of buccal furcation of maxillary first molar to get the measurement plane ( Fig 4 , C ). Measurements of buccolingual alveolar width and buccal and lingual alveolar bone thickness of teeth are described in Table IV and Figures 4-6 . , Dehiscence and fenestration were defined according to the criteria published by Evangelista. If bone defect happened in the measured horizontal plane, the value of bone thickness was marked as zero.
|Maxillary first molar||Distance of outer limits from buccal to lingual cortical plate, passing through the center of maxillary first molar’s trifurcation, nearly perpendicular to each cortical plate|
|Maxillary premolar||Distance of outer limits from buccal to lingual cortical plate, passing through the center of furcation (multirooted) or center of root (single-rooted) of maxillary premolar, nearly perpendicular to each cortical plate|
|Buccal alveolar bone thickness|
|Maxillary first molar||Distance between the most prominent point of mesiobuccal root and the nearest outer buccal cortical bone edge point|
|Maxillary premolar||Distance between the most prominent point of premolar root on buccal side and the nearest outer buccal cortical bone edge point|
|Lingual alveolar bone thickness|
|Maxillary first molar||Distance between the most prominent point of palatal root and the nearest outer lingual cortical bone edge point|
|Maxillary premolar||Distance between the most prominent point of premolar root on lingual side and the nearest outer lingual cortical bone edge point|
Landmarks of 20 patients chosen randomly were measured by 2 authors (X.N.H and X.Y.H) with 2-week interval to test interobserver and intraobserver reliability. Intraclass correlation coefficient was calculated with acceptable reproducibility of measurements. ( Table V ).
Paired t test was used to compare the parameters between deviated and nondeviated sides in each group ( Tables VI and VII ). If no significant difference was found, the average value was used. One-way analysis of variance and post-hoc Bonferroni test were used to compare the difference of the parameters among 3 groups ( Tables VIII-XI ). Spearman correlation test was used to evaluate the correlation among buccolingual inclination and alveolar bone thickness of maxillary posterior teeth, severity of mandibular deviation and sagittal discrepancy ( Tables XII and XIII ). All statistical tests were 2-sided, performed with SPSS software (version 23; IBM, Armonk, NY). Significance was defined as P < 0.05.
|Variable/tooth||Group III (asymmetry)||Group III (symmetry)||Group I|
|Maxillary first molar (°)||13.84 ± 6.43||6.11 ± 7.74||0.000 ∗||14.45 ± 4.93||13.80 ± 7.06||0.548||5.93 ± 5.41||5.21 ± 5.62||0.435|
|Maxillary second premolar (°)||7.96 ± 5.34||2.45 ± 5.85||0.000 ∗||5.47 ± 4.76||4.84 ± 5.10||0.573||0.14 ± 4.93||0.11 ± 5.75||0.972|
|Maxillary first premolar (°)||6.24 ± 5.22||–0.12 ± 4.54||0.000 ∗||3.32 ± 4.63||2.83 ± 4.11||0.536||–0.40 ± 3.65||–1.68 ± 4.10||0.069|