Journal of
Oral Rehabilitation
Journal of Oral Rehabilitation 2015 42; 588–599
Dental, skeletal asymmetries and functional characteristics in Class II subdivision malocclusions J. LI, Y. HE, Y. WANG, T. CHEN, Y. XU, X. XU, H. ZENG, J. FENG, Z. XIANG, C. XUE, X. HAN & D. BAI State Key Laboratory of Oral Disease, West China School of Stomatology Sichuan University, Chengdu, China
SUMMARY Treatment outcomes of Angle Class II subdivision malocclusions may be compromised because of the uncertainty of the aetiology. Previous studies have reported controversial ideas about the origins, but the existence of a primary contributor still remains unknown. Functional factors have been mentioned as a probable cause, but until now, there have been no supporting data. This study was a cross-sectional investigation of the characteristics of Angle Class II subdivision malocclusion, including dental, skeletal and functional factors, by comparison of the subdivision group and the normal occlusion group. The evaluations of dental and skeletal asymmetries of both groups were carried out by cone-beam computed tomography (CBCT) and analysis of dental casts. The functional deviations were evaluated by cast mounting and measuring. In the subdivision group, the asymmetric position of the glenoid fossa was found to be the most significant
Introduction Angle Class II subdivision malocclusion, with a Class I molar relationship on one side and Class II on the other, as a classic type of asymmetric occlusion, has long been a challenge for clinicians, not only for the difficulties in treatment planning, but also for the complexity of the origin (1). A recent retrospective study focused on classification and treatment outcomes of Angle Class II subdivision malocclusion has shown that even with excellent clinical skills and various options for treatment strategies, there were still up to 30% finished cases that fell short of complete correction, and the midline correction can be rather challenging and often incomplete (2). © 2015 John Wiley & Sons Ltd
skeletal asymmetry. No dentoalveolar asymmetry was found in this group. The most important finding was that, in subdivision malocclusions, functional deviation resulting in pseudoasymmetry occurred in 3286% of the study participants. This deviation is probably related to the disharmonious arch width between maxillary and mandibular dental arches in the premolar section. The origin of Angle Class II subdivision malocclusion is multifactorial, with dental, skeletal and functional factors included. Functional deviation occurs, probably due to dental arch width disharmony. Asymmetric position of the glenoid fossa may account for most of the skeletal asymmetry. KEYWORDS: dental occlusion, centric relation, orthodontics, cone-beam computed tomography, three-dimensional imaging, craniofacial anomalies Accepted for publication 29 March 2015
The factors contributing to Class II subdivision malocclusion can be multifactorial. Previous studies with 2-dimensional radiographs established the absence of skeletal asymmetries of mandibles as a factor in Class II subdivision malocclusion (3–5), whereas dental alveolar asymmetry was found to account for the greatest proportion of the origin (6, 7). Recent studies in which cone-beam computed tomography (CBCT) was applied showed that skeletal and dental asymmetries are possibly the main factors contributing to Class II subdivision malocclusion (8, 9). Minich (8) first discovered that the position of the maxilla is asymmetrical in relation to the cranial base; however, no comparison with the control group was carried out in that study. Positive results achieved by Sanders (9) with mandibular asymdoi: 10.1111/joor.12303
A CROSS-SECTIONAL CLINICAL STUDY metry showed that mandibular deficiency on the Class II side was the primary contributing factor. The data from this study are reliable and statistically significant, but the differences between the two groups are too small to be clinically significant. Functional deviation is another important component of the origin of any kind of asymmetric occlusion (10–12). It has been mentioned and presumed several times, but so far, no relevant data have supported any specific correlation between functional deviation and the cause of subdivision malocclusion. This cross-sectional investigation was designed to study the characteristics of Class II subdivision malocclusion: the dental, skeletal and functional factors contributing to subdivision malocclusion as evaluated by comparison of the subdivision group with the normal occlusion group.
facial midline, (iii) age between 18 and 25 years and (iv) numbers 2 through 9 of the inclusion criteria (above) for the subdivision group. The subdivision group, the experimental group, consisted of 70 consecutive patients, 38 boys and 32 girls, with an average age of 1235 years. The normal occlusion group, the control group, consisted of 64 consecutive patients, 27 boys and 37 girls, with an average age of 2055 years. Participants volunteered for the study. The experiments were undertaken with the understanding and written consent of each participant and according to ethical principles. Approval of the procedures for this research was obtained from the Ethics Committee of the Sichuan University. In this study, the examination and analysis methods for the experimental and control groups, including the related index of dental, skeletal and functional factors, consisted of the following three parts.
Materials and methods Evaluation with CBCT Samples The study sample for the subdivision group was selected from among the Chinese patients seeking orthodontic treatment at the Department of Orthodontics, West China Hospital of Stomatology, Chengdu, China, from 2010 to 2014. Intra-oral and dental cast examinations were carried out to identify the subdivision group based on the following inclusion criteria: (i) the presence of a complete Class I molar relationship on one side of the dental arch, and at least a half-step Class II molar relationship on the other; (ii) all permanent teeth erupted, except the third molars; (iii) no previous orthodontic treatment; (iv) symmetric and no more than 3 mm crowding or spacing of both arches; (v) no premature loss of deciduous teeth; (vi) no malformed teeth or missing teeth, or teeth with gross decay, no restorations; (vii) no history of facial trauma, or any factors that may affect the normal growth of the craniofacial complex; (viii) no craniofacial deformities; (ix) no signs or symptoms of temporomandibular joint dysfunction (TMD) based on the clinical history; and (x) age between 11 and 25 years. The samples for the normal occlusion group were selected from among Chinese students at Sichuan University from 2010 to 2014, and the inclusion criteria were as follows: (i) Angle Class I molar and canine relationship on both sides of the dental arch, (ii) both upper and lower midlines coincide with the © 2015 John Wiley & Sons Ltd
This part included CBCT scans and measurements, by which dental and skeletal factors were analysed. The three-dimensional (3D) scans were acquired by means of a cone-beam computed tomography (CBCT) unit*. All images were taken at the same settings, which were 5 mA, 80 kV and a 14 9 10 inch field of view. The data obtained were exported as DICOM format files and imported into Mimics software (version 16.0†) for analysis and measurement. With Mimics, after the craniofacial structures were reconstructed, three perpendicular planes were set to be the reference planes (Fig. 1a, Table 1). The horizontal plane was constructed by three landmarks, the most superior point of the infraorbital rim on the right and left sides and the most superior point of the right porion. The middle sagittal plane was constructed perpendicular to the horizontal plane with two points, the most middle point of the suture nasofrontalis and the most superior point on the crista galli. The coronal plane was perpendicular to the horizontal plane, with the most medial point of the frontozygomatic suture of both sides on it. In total, 38 anatomic landmarks were selected and entered into the measurement and analysis module of
*Morita, Kyoto, Japan. †
Materialise, Leuven, Belgium.
589
590
J . L I et al. (a)
(b)
(c)
(d)
Fig. 1. Reconstruction of craniofacial structures: (a) Setting of three perpendicular reference planes. (b–d) skeletal land marks located on the reconstructed models.
Mimics and then located on the reconstructed models (Fig. 1b–d). The evaluation was composed of three parts: (i) dentoalveolar asymmetry (Table 2); (ii) skeletal asymmetry in which asymmetries of the maxilla, the mandible and the temporomandibular joint were included (Table 3); and (iii) temporomandibular joint space (Table 4). The data obtained were then exported into a database for further analysis. Dental cast analysis Landmarks difficult to identify on CBCT reconstructed images were located on dental casts, and evaluation of dental asymmetries which could not be carried out by software was performed by cast analysis (Table 2). The data obtained were entered into the database and integrated with those variables for dental asymmetry obtained by CBCT evaluation. Evaluation of functional factors The functional factors were investigated by determination of the centric relation (CR)–centric occlusion
(CO) discrepancies of both the experimental and control groups. To eliminate interoperator error, all operations were carried out by only one operator. The CO wax bites were taken in centric occlusion with a two-layer Moyco wax piece and put into cold water for further analysis. The CR wax bites were taken according to the Roth power centric technique in a modified way, by which the mandible of a patient was guided with gentle assistance into a stable and comfortable position after the deprogramming process and was recorded with two pieces of bite registration wax‡, including anterior and posterior sections. After the wax bites hardened by being cooled in ice water, they were replaced and checked to ensure that the closest CR record available was achieved. The validity and reproducibility of taking wax bites were accessed by taking both the CO and CR wax bites 2 weeks apart in 40 randomly selected samples. The readings of the molar relationships were analysed by Student t-test. The results showed that there has
‡
Delar, Lake Oswego, OR, USA. © 2015 John Wiley & Sons Ltd
A CROSS-SECTIONAL CLINICAL STUDY Table 3. Variables for the evaluations of skeletal asymmetry Variables Maxilla Palatal plane inclination Mandible Sagittal Corpus length Mandibular length Ramus width Gonial angle Vertical Ramus height Gonial angle height Transverse Mandibular inclination Condyle Inclination of condylar head Condylar head length Condylar head width Glenoid fossa Height Depth Anterior–posterior relative position between left and right side
Definition
Angulation between ANS-PNS and middle sagittal plane
Distance between GoR (GoL) and Me Distance between CdSR (CdSL) and Me The horizontal distance between JR (JL) point and posterior border of mandibular ramus Angulation between CdPR (CdPL) and Me Distance between CdPR (CdPL) and Me Distance between GoR (GoL) to horizontal plane Angulation (absolute value) between GoR and sagittal plane minus angulation between GoL and sagittal plane. Angulation between CdPR(CdPL)-CdAR(CdAL) to middle sagittal plane Distance between CdPR(CdPL) and CdAR(CdAL) Distance between CdMR(CdML) and CdLR(CdLL) Distance between GFSR(GFSL) and horizontal plane Distance between GFCR(GFCL) and middle sagittal plane Distance between perpendicular foot of GFCR and GFCL to middle sagittal plane
Table 4. Variables for the evaluations of functional deviation Joint space Anterior joint space Posterior joint space Superior joint space Value of molar relationship (left and right sides, CR and CO), VMR-CR/CO (mm)
DVMR
Distance between GFAL(GFAR) and CdAL(CdAR) Distance between GFPL(GFPR) and CdPL(CdPR) Distance between GFSL(GFSR) and CdSL(CdSR) A horizontal millimetre difference of molar relationship between Class I relationship: when premolars and molars on one side, all reach Angle class I relationship, VMR-CR/CO=0. The distal/mesial displacement of lower premolars and molars on one side was measured and recorded as an arithmetically positive/negative value for each tooth, and the sum of the three values was accounted as the VMR-CR on this side. VMR-CR minus VMR-CO: DVMR is in proportional to the degree of functional deviation on one side
subdivision group was greater than that on the Class II side (P < 005). The fossa on the Class II side was comparatively more anterior than that on the Class I side, compared with the difference between left and right sides of the control group (P < 001). When the functional factors were evaluated, 58 patients (8286% of the total) in the subdivision group showed CO-CR discrepancies. In only 23 © 2015 John Wiley & Sons Ltd
patients (3286% of the total), the DVMR of Class I and Class II sides differed greatly. The others in the group showed minor CO-CR discrepancies (symmetric, and
Oral Rehabilitation
Journal of Oral Rehabilitation 2015 42; 588–599
Dental, skeletal asymmetries and functional characteristics in Class II subdivision malocclusions J. LI, Y. HE, Y. WANG, T. CHEN, Y. XU, X. XU, H. ZENG, J. FENG, Z. XIANG, C. XUE, X. HAN & D. BAI State Key Laboratory of Oral Disease, West China School of Stomatology Sichuan University, Chengdu, China
SUMMARY Treatment outcomes of Angle Class II subdivision malocclusions may be compromised because of the uncertainty of the aetiology. Previous studies have reported controversial ideas about the origins, but the existence of a primary contributor still remains unknown. Functional factors have been mentioned as a probable cause, but until now, there have been no supporting data. This study was a cross-sectional investigation of the characteristics of Angle Class II subdivision malocclusion, including dental, skeletal and functional factors, by comparison of the subdivision group and the normal occlusion group. The evaluations of dental and skeletal asymmetries of both groups were carried out by cone-beam computed tomography (CBCT) and analysis of dental casts. The functional deviations were evaluated by cast mounting and measuring. In the subdivision group, the asymmetric position of the glenoid fossa was found to be the most significant
Introduction Angle Class II subdivision malocclusion, with a Class I molar relationship on one side and Class II on the other, as a classic type of asymmetric occlusion, has long been a challenge for clinicians, not only for the difficulties in treatment planning, but also for the complexity of the origin (1). A recent retrospective study focused on classification and treatment outcomes of Angle Class II subdivision malocclusion has shown that even with excellent clinical skills and various options for treatment strategies, there were still up to 30% finished cases that fell short of complete correction, and the midline correction can be rather challenging and often incomplete (2). © 2015 John Wiley & Sons Ltd
skeletal asymmetry. No dentoalveolar asymmetry was found in this group. The most important finding was that, in subdivision malocclusions, functional deviation resulting in pseudoasymmetry occurred in 3286% of the study participants. This deviation is probably related to the disharmonious arch width between maxillary and mandibular dental arches in the premolar section. The origin of Angle Class II subdivision malocclusion is multifactorial, with dental, skeletal and functional factors included. Functional deviation occurs, probably due to dental arch width disharmony. Asymmetric position of the glenoid fossa may account for most of the skeletal asymmetry. KEYWORDS: dental occlusion, centric relation, orthodontics, cone-beam computed tomography, three-dimensional imaging, craniofacial anomalies Accepted for publication 29 March 2015
The factors contributing to Class II subdivision malocclusion can be multifactorial. Previous studies with 2-dimensional radiographs established the absence of skeletal asymmetries of mandibles as a factor in Class II subdivision malocclusion (3–5), whereas dental alveolar asymmetry was found to account for the greatest proportion of the origin (6, 7). Recent studies in which cone-beam computed tomography (CBCT) was applied showed that skeletal and dental asymmetries are possibly the main factors contributing to Class II subdivision malocclusion (8, 9). Minich (8) first discovered that the position of the maxilla is asymmetrical in relation to the cranial base; however, no comparison with the control group was carried out in that study. Positive results achieved by Sanders (9) with mandibular asymdoi: 10.1111/joor.12303
A CROSS-SECTIONAL CLINICAL STUDY metry showed that mandibular deficiency on the Class II side was the primary contributing factor. The data from this study are reliable and statistically significant, but the differences between the two groups are too small to be clinically significant. Functional deviation is another important component of the origin of any kind of asymmetric occlusion (10–12). It has been mentioned and presumed several times, but so far, no relevant data have supported any specific correlation between functional deviation and the cause of subdivision malocclusion. This cross-sectional investigation was designed to study the characteristics of Class II subdivision malocclusion: the dental, skeletal and functional factors contributing to subdivision malocclusion as evaluated by comparison of the subdivision group with the normal occlusion group.
facial midline, (iii) age between 18 and 25 years and (iv) numbers 2 through 9 of the inclusion criteria (above) for the subdivision group. The subdivision group, the experimental group, consisted of 70 consecutive patients, 38 boys and 32 girls, with an average age of 1235 years. The normal occlusion group, the control group, consisted of 64 consecutive patients, 27 boys and 37 girls, with an average age of 2055 years. Participants volunteered for the study. The experiments were undertaken with the understanding and written consent of each participant and according to ethical principles. Approval of the procedures for this research was obtained from the Ethics Committee of the Sichuan University. In this study, the examination and analysis methods for the experimental and control groups, including the related index of dental, skeletal and functional factors, consisted of the following three parts.
Materials and methods Evaluation with CBCT Samples The study sample for the subdivision group was selected from among the Chinese patients seeking orthodontic treatment at the Department of Orthodontics, West China Hospital of Stomatology, Chengdu, China, from 2010 to 2014. Intra-oral and dental cast examinations were carried out to identify the subdivision group based on the following inclusion criteria: (i) the presence of a complete Class I molar relationship on one side of the dental arch, and at least a half-step Class II molar relationship on the other; (ii) all permanent teeth erupted, except the third molars; (iii) no previous orthodontic treatment; (iv) symmetric and no more than 3 mm crowding or spacing of both arches; (v) no premature loss of deciduous teeth; (vi) no malformed teeth or missing teeth, or teeth with gross decay, no restorations; (vii) no history of facial trauma, or any factors that may affect the normal growth of the craniofacial complex; (viii) no craniofacial deformities; (ix) no signs or symptoms of temporomandibular joint dysfunction (TMD) based on the clinical history; and (x) age between 11 and 25 years. The samples for the normal occlusion group were selected from among Chinese students at Sichuan University from 2010 to 2014, and the inclusion criteria were as follows: (i) Angle Class I molar and canine relationship on both sides of the dental arch, (ii) both upper and lower midlines coincide with the © 2015 John Wiley & Sons Ltd
This part included CBCT scans and measurements, by which dental and skeletal factors were analysed. The three-dimensional (3D) scans were acquired by means of a cone-beam computed tomography (CBCT) unit*. All images were taken at the same settings, which were 5 mA, 80 kV and a 14 9 10 inch field of view. The data obtained were exported as DICOM format files and imported into Mimics software (version 16.0†) for analysis and measurement. With Mimics, after the craniofacial structures were reconstructed, three perpendicular planes were set to be the reference planes (Fig. 1a, Table 1). The horizontal plane was constructed by three landmarks, the most superior point of the infraorbital rim on the right and left sides and the most superior point of the right porion. The middle sagittal plane was constructed perpendicular to the horizontal plane with two points, the most middle point of the suture nasofrontalis and the most superior point on the crista galli. The coronal plane was perpendicular to the horizontal plane, with the most medial point of the frontozygomatic suture of both sides on it. In total, 38 anatomic landmarks were selected and entered into the measurement and analysis module of
*Morita, Kyoto, Japan. †
Materialise, Leuven, Belgium.
589
590
J . L I et al. (a)
(b)
(c)
(d)
Fig. 1. Reconstruction of craniofacial structures: (a) Setting of three perpendicular reference planes. (b–d) skeletal land marks located on the reconstructed models.
Mimics and then located on the reconstructed models (Fig. 1b–d). The evaluation was composed of three parts: (i) dentoalveolar asymmetry (Table 2); (ii) skeletal asymmetry in which asymmetries of the maxilla, the mandible and the temporomandibular joint were included (Table 3); and (iii) temporomandibular joint space (Table 4). The data obtained were then exported into a database for further analysis. Dental cast analysis Landmarks difficult to identify on CBCT reconstructed images were located on dental casts, and evaluation of dental asymmetries which could not be carried out by software was performed by cast analysis (Table 2). The data obtained were entered into the database and integrated with those variables for dental asymmetry obtained by CBCT evaluation. Evaluation of functional factors The functional factors were investigated by determination of the centric relation (CR)–centric occlusion
(CO) discrepancies of both the experimental and control groups. To eliminate interoperator error, all operations were carried out by only one operator. The CO wax bites were taken in centric occlusion with a two-layer Moyco wax piece and put into cold water for further analysis. The CR wax bites were taken according to the Roth power centric technique in a modified way, by which the mandible of a patient was guided with gentle assistance into a stable and comfortable position after the deprogramming process and was recorded with two pieces of bite registration wax‡, including anterior and posterior sections. After the wax bites hardened by being cooled in ice water, they were replaced and checked to ensure that the closest CR record available was achieved. The validity and reproducibility of taking wax bites were accessed by taking both the CO and CR wax bites 2 weeks apart in 40 randomly selected samples. The readings of the molar relationships were analysed by Student t-test. The results showed that there has
‡
Delar, Lake Oswego, OR, USA. © 2015 John Wiley & Sons Ltd
A CROSS-SECTIONAL CLINICAL STUDY Table 3. Variables for the evaluations of skeletal asymmetry Variables Maxilla Palatal plane inclination Mandible Sagittal Corpus length Mandibular length Ramus width Gonial angle Vertical Ramus height Gonial angle height Transverse Mandibular inclination Condyle Inclination of condylar head Condylar head length Condylar head width Glenoid fossa Height Depth Anterior–posterior relative position between left and right side
Definition
Angulation between ANS-PNS and middle sagittal plane
Distance between GoR (GoL) and Me Distance between CdSR (CdSL) and Me The horizontal distance between JR (JL) point and posterior border of mandibular ramus Angulation between CdPR (CdPL) and Me Distance between CdPR (CdPL) and Me Distance between GoR (GoL) to horizontal plane Angulation (absolute value) between GoR and sagittal plane minus angulation between GoL and sagittal plane. Angulation between CdPR(CdPL)-CdAR(CdAL) to middle sagittal plane Distance between CdPR(CdPL) and CdAR(CdAL) Distance between CdMR(CdML) and CdLR(CdLL) Distance between GFSR(GFSL) and horizontal plane Distance between GFCR(GFCL) and middle sagittal plane Distance between perpendicular foot of GFCR and GFCL to middle sagittal plane
Table 4. Variables for the evaluations of functional deviation Joint space Anterior joint space Posterior joint space Superior joint space Value of molar relationship (left and right sides, CR and CO), VMR-CR/CO (mm)
DVMR
Distance between GFAL(GFAR) and CdAL(CdAR) Distance between GFPL(GFPR) and CdPL(CdPR) Distance between GFSL(GFSR) and CdSL(CdSR) A horizontal millimetre difference of molar relationship between Class I relationship: when premolars and molars on one side, all reach Angle class I relationship, VMR-CR/CO=0. The distal/mesial displacement of lower premolars and molars on one side was measured and recorded as an arithmetically positive/negative value for each tooth, and the sum of the three values was accounted as the VMR-CR on this side. VMR-CR minus VMR-CO: DVMR is in proportional to the degree of functional deviation on one side
subdivision group was greater than that on the Class II side (P < 005). The fossa on the Class II side was comparatively more anterior than that on the Class I side, compared with the difference between left and right sides of the control group (P < 001). When the functional factors were evaluated, 58 patients (8286% of the total) in the subdivision group showed CO-CR discrepancies. In only 23 © 2015 John Wiley & Sons Ltd
patients (3286% of the total), the DVMR of Class I and Class II sides differed greatly. The others in the group showed minor CO-CR discrepancies (symmetric, and
