The purpose of this study was to evaluate the effect of using the transverse analysis developed at Case Western Reserve University (CWRU) in Cleveland, Ohio. The hypotheses were based on the following: (1) Does following CWRU’s transverse analysis improve the orthodontic results? (2) Does following CWRU’s transverse analysis minimize the active treatment duration?
A retrospective cohort research study was conducted on a randomly selected sample of 100 subjects. The sample had CWRU’s analysis performed retrospectively, and the sample was divided according to whether the subjects followed what CWRU’s transverse analysis would have suggested. The American Board of Orthodontics discrepancy index was used to assess the pretreatment records, and quality of the result was evaluated using the American Board of Orthodontics cast/radiograph evaluation. The Mann-Whitney test was used for the comparison.
CWRU’s transverse analysis significantly improved the total cast/radiograph evaluation scores ( P = 0.041), especially the buccolingual inclination component ( P = 0.001). However, it did not significantly affect treatment duration ( P = 0.106).
CWRU’s transverse analysis significantly improves the orthodontic results but does not have significant effects on treatment duration.
Using the transverse analysis will result in higher-quality results.
The transverse analysis is reliable.
To ignore the transverse dimension may affect the quality of the results.
The key to successful orthodontic treatment is thorough diagnosis and treatment planning. Diagnosis must be broad and comprehensive, and should not overlook any aspect of the problem. The introduction of the cephalostat by Holly Broadbent and T. Wingate Todd in the 1920s revolutionized the diagnostic tools, by allowing us to study the skeletal and dental relationships in more depth, especially in the anteroposterior and vertical dimensions. Since the lateral cephalogram is a 2-dimensional presentation of a 3-dimensional (3D) structure, the transverse dimension was not as thoroughly studied and was often left out during diagnosis and treatment planning. This is despite the fact that the importance of the transverse dimension has been brought to our attention by various authors. In a classic study, Andrews evaluated 120 casts of nonorthodontic patients with normal occlusion and developed “the 6 keys to normal occlusion,” which became a foundation for orthodontic treatment. One of those 6 keys is the buccolingual inclination of crowns, which Andrews thought was essential for harmonious occlusion. Furthermore, Andrews and Andrews studied the 6 elements to orofacial harmony and stated that maxillary arch width should be compatible with mandibular arch width for optimal orofacial harmony. The importance of the transverse dimension was further confirmed when the American Board of Orthodontics (ABO) incorporated the buccolingual inclination of the posterior teeth in the cast-radiograph evaluation, used for assessing the quality of orthodontic treatment. Moreover, Sarver and Ackerman discussed the importance of assessing the transverse dimension for achieving an esthetic smile. They stated that improving the transverse dimension can dramatically enhance the smile by optimizing the buccal corridors and the transverse dimension of the smile. Kusnoto et al investigated the orthodontic correction of transverse arch asymmetries and noticed that asymmetry in the transverse dimension was not corrected. Also, there were no differences between growing and nongrowing responses in transverse asymmetry correction.
McNamara indicated that maxillary transverse deficiency may be one of the most pervasive skeletal problems in the craniofacial region. In a classic article, Haas stated that the prime objective of palatal expansion is to coordinate the maxillary and mandibular denture bases. Lagravère et al performed a meta-analysis of immediate changes with rapid maxillary expansion (RME) and found that the greatest changes after RME were dental and skeletal transverse changes. A few vertical and anteroposterior immediate changes were statistically significant, although they were clinically negligible. Furthermore, Lagravère et al compared the transverse, vertical, and anteroposterior skeletal and dental changes in adolescents receiving expansion treatment with bone-anchored maxillary expansion vs traditional rapid maxillary expansion. They concluded that both expanders showed similar results. The greatest changes were seen in the transverse dimension; changes in the vertical and anteroposterior dimensions were negligible. Dental expansion was also greater than skeletal expansion.
In a classic article, El-Mangoury pointed out that the mandibular intercanine width tended to relapse toward its original pretreatment value. This suggests that at the end of active treatment, the mandibular intercanine width should be maintained as it was originally.
In a similar vein, Housley et al indicated that transverse expansion was more stable in the posterior region of the mandibular dental arch than in the anterior region, and that the mandibular intercanine width increase could be maintained only by fixed retention.
Initially, Marshall et al assessed the transverse molar movements during growth and concluded that, on average, the maxillary molars erupt with buccal crown torque and upright with age. Mandibular molars erupt with lingual crown torque and upright with age also. These molar crown torque changes were accompanied by concurrent increases in maxillary and mandibular intermolar widths. Later, Hesby et al studied the transverse skeletal and dentoalveolar changes during growth and found that the transverse molar movements during growth mirror the maxillary and mandibular cross-arch alveolar process width increases.
Enlow and Hans discussed dentoalveolar compensations: the natural tendency of the teeth to maintain contact and normal interarch relationships. They stated that intrinsic adjustments during growth are an important biologic concept, since they allow regional parts to stay in a state of functional and structural equilibrium. Moreover, Solow mentioned that transverse skeletal jaw discrepancies are partly compensated by “dentoalveolar compensation” through adjustments of the buccolingual molar angulations.
Hans et al discussed how the evolution of imaging introduced cone-beam computed tomography (CBCT), which brought us to a new era of diagnostics. It gave us a 3D image, allowing us to study the cranium in all 3 planes. Mostafa indicated that the introduction of 3D CBCT imaging is revolutionizing the orthodontic diagnostic philosophy. Furthermore, Palomo et al discussed the variety of orthodontic clinical applications of CBCT, along with the methods and clinical applications of CWRU’s transverse analysis. Larson indicated that it is the imaging of choice for comprehensive orthodontic treatment. Among the many applications of 3D imaging in orthodontics that are not possible with 2-dimensional images is a more thorough analysis of the transverse dimension, where a cross-sectional axial view allows measurement of the buccolingual inclinations of the molars and canines.
In 5 consecutive years, CWRU’s transverse analysis was developed by Shewinvanakitkul, Evangelinakis, Shewinvanakitkul et al, Karamitsou, Miyamoto, Copeland, Streit, and Palomo et al. Shewinvanakitkul developed a new technique to measure buccolingual inclinations using CBCT. Palomo et al specified the methods and clinical applications of CWRU’s transverse analysis. These studies produced a reliable method to measure the buccolingual inclinations of molars and canines, and gave us their norms ( Fig 1 ). Measuring the molar angulations according to CWRU’s transverse analysis method was done as follows. After orienting the head ( Fig 2 ), the buccolingual inclination of each maxillary first molar was measured through the angle outlined between the palatal long axis of the tooth (the line joining the mesiopalatal cusp tip with the palatal root apex) and a tangent to the inferior border of the nasal cavity ( Fig 3 ). The buccolingual inclination of each mandibular first molar was measured through the angle formed between the long axis of the tooth (the line connecting the central groove with the apex of the mesial root) and a tangent to the inferior border of the mandible ( Fig 4 ).
Mostafa concluded that CWRU’s transverse analysis significantly improves the orthodontic results.
The purpose of this study was to retrospectively test the diagnostic importance of the molar angulation component of CWRU’s analysis and its effect on treatment results by (1) evaluating the orthodontic pretreatment and posttreatment records with CWRU’s transverse analysis, (2) assessing the pretreatment records using the ABO discrepancy index, and (3) appraising the posttreatment study casts using the ABO cast/radiograph evaluation.
Cangialosi et al introduced the discrepancy index to measure case complexity before treatment. It measures objectively the following disorders: overjet, overbite, anterior open bite, lateral open bite, crowding, buccal posterior crossbite, lingual posterior crossbite, occlusion, ANB angle, IMPA, and SN-GoGn angle. The greater the number of these conditions in a patient, the greater the complexity, the higher the score, and the greater the challenge for the orthodontist.
Traditionally, the evaluation of orthodontic treatment outcomes has been done through the subjective opinions of experienced orthodontists. In 1998, Casko et al introduced the ABO ruler and the ABO’s cast/radiograph evaluation for assessing posttreatment dental casts and panoramic radiographs. It is composed of the following 8 criteria: alignment, marginal ridges, buccolingual inclination, occlusal relationships, occlusal contacts, overjet, interproximal contacts, and root angulation. The cast/radiograph evaluation reduces subjectivity when assessing the quality of orthodontic finishing and helps to evaluate cases submitted to the phase II ABO examination for board certification or recertification. However, the root angulation category was not measured or included in the cast/radiograph evaluation score in this study.
The sample was divided into 2 groups according to whether the subjects were treated according to CWRU’s transverse analysis, specifically the molar angulation component, since the canine angulations were not necessary for our study. This was a retrospective cohort study.
The expected results were that CWRU’s transverse analysis not only improves the orthodontic results but also minimizes the active treatment duration. If these results are achieved, diagnostic strategies could be applied whereby the treatment plan and mechanotherapy are evidence-based on a clear vision of the desired orthodontic posttreatment outcomes, satisfying different physiologic and esthetic requisites for each patient.
Material and methods
A retrospective cohort research study was executed on the basis of a randomly selected sample from the core clinic at CWRU. The sample consisted of 100 subjects, of whom 85 met the inclusion criteria. One subject was excluded because he was planned for orthognathic surgery at the posttreatment time, and 14 subjects were excluded for lack of adequate posttreatment records. The sample was divided into 2 groups according to whether the subjects were treated according to what CWRU’s transverse analysis would have suggested.
Inclusion criteria: randomly selected subjects who started orthodontic treatment in the core clinic at CWRU in 2010 and completed active treatment.
Exclusion criteria: incomplete pretreatment records (pretreatment CBCT scans, study casts, intraoral and extraoral photographs), incomplete posttreatment records (study casts, intraoral and extraoral photographs), or patients who were planned for surgery at the time of posttreatment records.
Table I shows the descriptive demographics of the sample. The sample was predominantly white, with only 6 subjects from other ethnicities. The sample included 49 girls and 36 boys, and the predominant pretreatment age group was 12 to 13 years (42 subjects).
n = 46
|Did not follow
n = 39
The materials used for the study were (1) pretreatment records (pretreatment CBCT scans, study casts, intraoral and extraoral photographs), (2) initial treatment plans and progress notes, (3) posttreatment records (posttreatment CBCT scans, study casts, intraoral and extraoral photographs), and (4) the ABO measuring gauge.
The protocol was approved by CWRU’s institutional review board. The sample was divided into 2 groups on the basis of whether the subjects were treated according to CWRU’s transverse analysis. These 2 groups “followed” what the CWRU transverse analysis would have suggested or “did not follow” the CWRU transverse analysis.
In the “followed” group (n = 46) ( Fig 5 ), treatment would include RME for subjects with either 1 maxillary molar having an abnormal buccolingual inclination (more than 1 SD above the mean), or 1 mandibular molar having an abnormal buccolingual inclination (more than 1 SD below the mean). Furthermore, in the “followed” group, treatment would include archwire expansion or cross elastics for subjects who had at least 1 maxillary molar having an abnormal buccolingual inclination (more than 1 SD below the mean).
Patients who had normal buccolingual inclinations, without a crossbite, and did not have expansion, were also included in the “followed” group ( Fig 5 ).
The “did not follow” group included all subjects who did not meet any of these criteria (n = 39) ( Fig 6 ).
For example, patient A had a pretreatment discrepancy index of 14 and had a maxillary left first molar with a deficient angle (91.6°) that was in crossbite, which is lower than the norm of 100° ± 4° ( Fig 7 ). This suggests that the crossbite is likely due to deficient dental inclination and not a true transverse discrepancy. Thus, increasing the buccal inclination could correct the crossbite. The patient was treated with unilateral cross elastics and thus fell into the “followed” group, since his crossbite was due to a deficient maxillary molar angle and not a transverse discrepancy. The final result ( Fig 8 ) shows that his maxillary left molar had an angle of 102.2°, which is within the normal range, and that his crossbite was alleviated. The final cast/radiograph evaluation score was 17, and no first molar scored a point on the buccolingual inclination aspect.
On the other hand, patient B had a maxillary left first molar with excessive angulation (104.9°), which is greater than the norm ( Fig 9 ). Moreover, the mandibular first molars had deficient angles (right first molar, 58.4°; left first molar, 56.7°), which are below the norm of 75°. This indicates a possible dental compensation for a transverse deficiency, which was not addressed since the treatment plan did not include expansion. Accordingly, the subject fell into the “did not follow” group. The total final cast/radiograph evaluation score was 17; the maxillary left first molar (109°) and mandibular right first molar (68.3°) each scored 1 point on the buccolingual inclination aspect ( Fig 10 ). If the CWRU’s transverse analysis was used, the biomechanics would have included RME, and the final cast/radiograph evaluation score may have been better.
The following 7 independent variables were recorded: crossbite status, maxillary expansion, active treatment duration, pretreatment and posttreatment ages, sex, and race. Eleven dependent variables were measured: 4 pretreatment buccolingual inclinations and 4 posttreatment buccolingual inclinations with CWRU’s transverse analysis, 1 dichotomized CWRU variable (followed or did not follow CWRU’s transverse analysis), the discrepancy index, and the cast/radiograph evaluation score.
The already existing CBCT scans used here were taken with a CB MercuRay (Hitachi Healthcare Americas, Twinsburg, OH, USA.) with custom low-dose settings of 2 mA, 120 kVp, 12-in field of view, 512 slices, 0.377-mm slice thickness, resolution of 1024 × 1024 pixels, 12 bits per pixel, and 4096 gray scale. For CWRU’s transverse analysis, the pretreatment buccolingual inclinations of the maxillary and mandibular permanent first molars were determined for each quadrant (as described by Shewinvanakitkul et al, Karamitsou, and Mostafa ) using Dolphin Imaging Software (version 11.8; Dolphin Imaging and Management Solutions, Chatsworth, Calif).
For the discrepancy index, the pretreatment records were evaluated to objectively measure the complexity, which included the following disorders: overjet, overbite, anterior open bite, lateral open bite, crowding, buccal posterior crossbite, lingual posterior crossbite, occlusion, ANB angle, IMPA, SN-GoGn angle, and other complexities. For the cast-radiograph evaluation, the posttreatment dental casts were scored with the following 7 criteria: marginal ridges, buccolingual inclinations, interproximal contacts, occlusal contacts, occlusal relationships, rotations/alignment, and overjets. The eighth component of the cast/radiograph evaluation—root angulation—was not measured or included in the cast/radiograph evaluation score in this study. The ABO measuring gauge was used for the cast/radiograph evaluation scoring. All statistical analyses were done with SPSS software (version 22.0; IBM, Armonk, NY).
For intrarater reliability, the primary investigator (R.Y.M.) used CWRU’s transverse analysis to measure the buccolingual inclinations of the maxillary and mandibular permanent first molars on 30 subjects. This investigator also estimated the ABO’s discrepancy index with the pretreatment records of 30 subjects and gauged the cast/radiograph evaluation measurements with the posttreatment orthodontic casts of 30 subjects. After 4 weeks, all of the above measurements were repeated by the same investigator.
For interrater reliability, another investigator (R.M.B.) measured the buccolingual inclinations of the maxillary and mandibular first molars, as well as the ABO cast/radiograph evaluation with the posttreatment casts of 30 subjects. The Cronbach alpha test was used for the reliability analyses of the intrarater and interrater reliabilities.
To satisfy the major assumptions of parametric statistical testing, the normality of the data distribution was evaluated using the Shapiro-Wilk test. The aspects measured were the cast/radiograph evaluation, the discrepancy indexs, and active treatment duration. Their P values were less than 0.015, indicating that the data were nonparametric in distribution. The data were analyzed with the independent-sample Mann-Whitney test, because of the nonparametric distribution. P ≤0.05 was used to assign statistical significance.