The objective of this research was to evaluate the reliability of 2 methods (Andrews’ Element III analysis and Yonsei transverse analysis) in maxillary transverse deficiency diagnosis.
Plaster casts and cone-beam computed tomography images of 80 outpatients with skeletal Class I malocclusion (29 males and 51 females, mean age, 20.16 ± 8.22 years) were selected. Maxillary and mandibular width were measured, respectively, and independently by 2 examiners at an interval of 2 weeks, using Andrews’ Element III analysis and Yonsei transverse analysis. Intraclass correlation coefficients and Bland-Altman plots of intraexaminer and interexaminer reliability were evaluated. After diagnosis, Cohen’s kappa statistics were calculated to evaluate the diagnostic agreement.
The intraclass correlation coefficients were all above 0.85, indicating good to excellent reliability. Compared with Andrews’ Element III analysis, Yonsei transverse analysis had higher intraexaminer and interexaminer reliability in both maxillary and mandibular width measurements. Thirty-one to 42 of the patients were diagnosed with maxillary transverse deficiency by 2 examiners using 2 methods. The intraexaminer and interexaminer Cohen’s kappa values of Yonsei transverse analysis were all higher than those of Andrews’ Element III analysis.
Both Andrews’ Element III analysis and Yonsei transverse analysis had good to excellent reliability and substantial diagnostic agreement. Yonsei transverse analysis had higher reliability in maxillary and mandibular width measurements and higher diagnostic agreement, compared with Andrews’ Element III analysis.
Both methods have good to excellent reliability and substantial diagnostic agreement.
Yonsei transverse analysis had higher reliability in width measurements.
Yonsei transverse analysis had higher kappa agreement in diagnosis.
Cautions need to be paid to the transverse dimension routinely in orthodontic diagnosis.
A harmonious maxilla-mandibular transverse relationship is crucial for the function and stability of the dentition; the ideal transverse relationship is that the molars are centered and upright in the alveolar house and well-intercuspated. The maxillary transverse deficiency (MTD) is pervasive in patients with malocclusion. It is often accompanied by crossbites, dental crowding, and wide buccal corridors, and it is often compensated with the buccal tipping of the maxillary molars and lingual inclination of the mandibular molars leading to an exaggerated curve of Wilson, inclined force transition, and potential periodontal disadvantage. The transverse discrepancy is more easily to be ignored than the sagittal and vertical discrepancies, therefore, selecting an accurate and reliable MTD diagnostic method is essential before treatment planning begins.
Studies have found that dental arch width deficiency was one of the primary causes of dental crowding, and crowding was a major consideration in MTD diagnosis in the last century. By measuring plaster casts, Pont established an ideal relationship between maxillary incisor width and dental arch width; Schwarz and Gratzinger presented a method of dental arch width estimation according to different facial types, and Howe et al set a series of arch width normative data. However, at that time, most studies merely took the maxillary expansion as a means of space acquisition. The relationship between maxillary and mandibular widths had been rarely evaluated.
In recent years, Andrews and Andrews proposed The six elements of orofacial harmony . According to the authors, the mandibular width is naturally optimal in most patients; the maxillary width should be 5 mm greater than the mandibular width when the first permanent molars centered and upright in the alveolus. If the difference between maxillary and mandibular width was less than 5 mm, the patient was diagnosed with MTD. To calculate maxillary and mandibular widths after decomposition, distance and angular measurements of plaster casts were made.
Radiographs are also commonly used as an aid in MTD diagnosis. Ricketts , introduced a transverse diagnosis method using anteroposterior cephalometrics and determined a series of age-determined normative data. However, because of the image superimposition of anteroposterior cephalometrics and head rotation during radiographing, higher landmark identification errors and less reliability of this method were reported than those of the cone-beam computed tomography (CBCT) images. Recent studies reported multiple ways in MTD diagnosis using CBCT images. Miner et al , analyzed the transverse dimension using the cone-beam transverse method. By measuring maxillary and mandibular width at the palatal and lingual cortex, normative data were determined, and this method was proved to be valid. Shewinvanakitkul developed a method to measure buccolingual inclinations of posterior teeth using CBCT; afterward, the Case Western Reserve University’s transverse analysis was developed. Yehya Mostafa et al indicated that the Case Western Reserve University’s transverse analysis could significantly improve the orthodontic results. Koo et al introduced Yonsei University’s transverse analysis. The authors stated that the centers of resistance (CR) of the first permanent molars were not readily affected by the tipping of the teeth; thus, the CR could enable evaluation of the transverse dimension at the basal bone level. By measuring the maxillary and mandibular width at the estimated CR of first permanent molars, the authors provided the Yonsei Transverse Index of normal occlusions, which is −0.39 ± 1.87 mm.
As with any diagnostic test, the most important factors are validity and reliability. Reliability represents the repeated measurements by the same or different raters yielding the same results, and a diagnostic method with high reliability is crucial in orthodontic clinical practice. As far as we know, the reliability of Andrews’ Element III analysis and Yonsei transverse analysis has not been evaluated yet. Therefore, in this study, we aimed to evaluate the reliability of 2 methods in MTD diagnosis.
Material and methods
This cross-sectional study was accepted by the Research Ethics Committee of Shandong University Dental School (Protocol No. 20190505). Among the outpatients who visited the Department of Orthodontics of School of Stomatology, Shandong University in 2018, 80 were included in this study. The inclusion criteria were as follows: (1) the subjects were aged at least 12 years with full permanent dentitions; (2) all maxillary and mandibular first permanent molars had fully erupted to the occlusal plane; and (3) skeletal Class I relationship (ANB angle was greater than 1° and less than 4°). The exclusion criteria were as follows: (1) subjects with any of the first permanent molars have abnormal root morphology, restoration, fracture, or cavity; (2) periodontal disease; and (3) previous orthodontic treatment.
CBCT scans (NewTom 5G; NewTom, Verona, Italy) at a 0.30-mm voxel resolution with the scanning parameter of 110 kV, 5 mA, were selected from the past orthodontic records. They were not specifically taken for this research but to evaluate other craniofacial patterns, for example, the impacted third molars. The corresponding plaster casts were also selected. All the CBCT data and plaster casts were coded and randomized to blind the investigators who made the measurements.
Andrews’ Element III analysis was based on the plaster casts measurements. The facial axis (FA) points were defined as the midpoint of the buccal groove of the first permanent molars. The WALA ridge was defined as the most prominent portion of a mandible’s mucogingival junction. First, distances and angles were measured. A digital caliper with an accuracy of 0.01 mm was used to measure the distance between the maxillary FA-FA points of the bilateral first molars, as well as the distance between the WALA-WALA ridge at the side of mandibular first molars. An Andrews ruler was used to measure the angulation between the FA of maxillary first molars and the occlusal plane. The plastic rod was placed parallel to the FA of the crown; thus, the angulation could be read on the ruler ( Fig 1 ). Second, researchers estimated the amount of horizontal change that would occur between the FA-FA distances when the molars were optimally angulated. According to Andrews’ Element III analysis, every 5° molar inclination change indicates 1-mm difference in maxillary width. Then, the estimated amount of change was subtracted from the original FA-FA distances; the result represents the maxillary width after decompensation. The mandibular width was the WALA-WALA distance minus 4 mm. Finally, we subtracted the mandibular width from the maxillary width, and if the difference is less than 5 mm, the patient was diagnosed with MTD.
Yonsei transverse analysis was based on the measurements of CBCT images. The Digital Imaging and Communications in Medicine format CBCT data were transferred into Materialise’s Interactive Medical Image Control System (MIMICS) (version 19.0; Materialise, Leuven, Belgium) software package. The estimated CR points were located at the middle of the root furcation of the first permanent molars. To make the procedure more precise, the location of the points was checked on different cutting slices in 3 planes of space, including the sagittal, coronal, and transverse views. Then the distance between the estimated CR points could be calculated automatically in MIMICS ( Fig 2 ). Then we subtracted the mandibular width from the maxillary width. According to Yonsei Transverse Index, if the difference was less than −2.26 mm, the patient was diagnosed with MTD. ,
All the measurements were carried out by 2 practiced researchers (C.Z. and X.T.) independently at a 2-week interval. The researchers used the same computer, digital caliper, and Andrews ruler to prevent performance bias. The agreement of dichotomous diagnosis MTD and harmonious was evaluated with kappa statistics.
Sample size calculation for the kappa agreement evaluation was performed using PASS (version 15.0; NCSS, LLC, Kaysville, Utah) software, with an alpha of 0.05, power of 0.8, k 1 of 0.9, and k 0 of 0.7, the number of the subjects should be at least 79. Thus, 80 subjects were included. Statistical analysis was performed using SPSS (version 21.0; IBM, Armonk, NY) and MadCalc (version 18.11.3; MadLogic, Ostend, Belgium) software package. The mean of the 2 measurements of the same examiner at different times was calculated to represent the final measurement of the examiner. First, the intraclass correlation coefficients (ICC; 2-way random, single measurements) were used to assess the intraexaminer and interexaminer reliability of the maxillary and mandible width measurements. The agreement was classified according to the following ICC values: excellent (>0.9), good (0.75-0.9), moderate (0.5-0.75), or poor (<0.5). A P value less than 0.05 indicated statistical significance. Second, the Bland-Altman plots were drawn, in which the 95% limits of agreement were defined as the mean difference plus and minus 1.96 times the standard deviation of the differences. The bias should ideally be near zero, and the values between the limits of the agreement lines were considered to be acceptable. The smaller range between these 2 limits, the better the agreement. Third, after diagnosis, Cohen’s kappa coefficients were calculated to evaluate the clinical determination of harmonious vs MTD of the 2 methods. The levels of agreement reflected by the kappa values were considered 0-0.20 as slight, 0.21-0.40 as fair, 0.41-0.60 as moderate, 0.61-0.80 as substantial, and 0.81-1 as almost perfect agreement.
Twenty-nine males and 51 females were included in this study, with a mean age of 20.16 ± 8.22 years. The clinical examination showed that only 19 of the 80 patients had posterior crossbites.
The ICC with 95% confidence intervals for intraexaminer and interexaminer reliability of the 2 methods are presented in Table I . The ICC values were all above 0.85, indicating good to excellent reliability. Compared with Andrews’ Element III analysis, Yonsei transverse analysis had higher intraexaminer and interexaminer reliability in both maxillary and mandibular measurements.