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Prediction of Transverse Maxillary Dimension Using Orthodontic Models Melchiades Alves de Oliveira, Jr, DDS, PhD, Max Domingues Pereira, MD, PhD, Claudia Toyama Hino, DDS, PhD, Anelisa Bittencourt Campaner, MD, PhD, Marco Antonio Scanavini, DDS, PhD, Lydia Masako Ferreira, MD, PhD São Paulo, Brazil The main objective of this study was to quantify the transverse maxillary dimensions using orthodontic cast models of individuals with natural normal occlusion. Sixty-eight pairs of orthodontic models were evaluated with the respective posteroanterior radiographies of white adults (38 women and 30 men; mean age, 17 years and 5 months). The models were placed in Class I molar occlusion, and on each pair, 4 points were marked on the alveolar buccal ridge (2 on the premolar region and 2 on the molar), determining the upper and lower transverse interpremolar and intermolar dimensions. The variables analyzed in the 3 measurements, obtained from the cephalometric radiographies and the cast models, showed no statistical differences. The upper intermolar distance was 57.20 T 2.60 mm; the lower intermolar, 55.16 T 2.40 mm; the upper interpremolar, 42.17 T 2.19 mm, and the lower interpremolar; 39.67 T 1.77 mm. On the posteroanterior cephalograms, the maxillary width was 65.97 T 3.42 mm and the mandibular width was 87.92 T 4.60 mm. There was intraresearcher and interresearcher correlation. There was no sexual dimorphism. The method proposed in this study can predict the transverse maxillary dimension, applying the formula µm = 8.62 + 0.88xm (µm = expected upper intermolar distance, xm = lower intermolar distance) for the molar region, and µpm = 4.87 + 0.94xpm (µpm = expected upper interpremolar distance, xpm = lower interpremolar distance) for the premolar region. Key Words: Palatal expansion technique, Natural normal occlusion, Cephalometric From the Plastic Surgery Division of Federal University of São Paulo, Brazil. Address correspondence and reprint requests to Dr. Max Domingues Pereira, Rua Napoleão de Barros, 715-4- andar, CEP: 04024-002, São Paulo, SP, Brazil; E-mail: [email protected] T ransverse maxillary deficiency has been studied in terms of its etiology, forms of treatment, and devices used for its correction. However, the majority of these studies, which are available in the scientific literature, do not clearly demonstrate the method used to evaluate the transverse maxillary prediction. The methods of evaluating the transverse maxillary dimension can be classified into dental, radiographic, and clinical methods. In the dental method, the transverse dimension is obtained measuring the distance of the first molar and first premolar regions and is determined by mathematical equations. These equations have preestablished constants of the upper interpremolar and intermolar distances, with variable being the sum of the diameters of the upper incisors.1,2 On the other hand, this method may lead to error because of alterations in the form and size of some of the upper anterior dental elements. In the radiographic method, a specific radiographyVposteroanterior radiograph (PA)Vis used. The dimension of the maxillary and mandibular width is obtained based on values proposed by Ricketts et al,3 whereas Betts et al4 established a transverse maxillary index. Despite this method being the most commonly used to predict the transverse maxillary dimension, the lack of precision in the location of the points of the maxilla and the mandible may lead to miscalculations of the maxillomandibular width. The clinical method is based on visible observation of the palatal cusp tip of the upper molar, which should be in contact with the buccal cusp tip of the lower molar.5Y7 The clinical method should not be used to determine the prediction of maxillary expansion when surgically assisted rapid maxillary expansion (SARME) is required, due to the dental compensation that occurs in these cases. The aim of this study was to determine the prediction of the transverse maxillary dimension 1465 Copyright @ 2008 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited. THE JOURNAL OF CRANIOFACIAL SURGERY / VOLUME 19, NUMBER 6 November 2008 38 (55.88%) females aged from 16 to 21 years (average of 17.4 years). Their respective posteroanterior cephalometric radiographies were also evaluated. This study was approved by the Ethics Committee of the ‘‘Universidade Federal de São Paulo’’ Ethics Committee. Posteroanterior Radiographs Posteroanterior radiographs were obtained using the same radiographic device and standardized according to the technique described by Ricketts.8 To determine the transverse maxillary and mandibular dimensions, an anatomic outline was drawn over each PA,9 with the width of the maxilla ( JD-JE) and the mandibula (AG-GA) outlined according to Ricketts et al.3 The PAs were used to determine if the samples had values similar to those proposed by Ricketts et al.3 Orthodontic Cast Models Fig 1 Metal ruler positioned on the side of the orthodontic models, parallel to the mesiobuccal sulcus of the first lower molar. using the buccal ridge of the alveolar process in orthodontic cast models from patients with natural normal occlusion. MATERIALS AND METHODS P airs of upper and lower orthodontic cast models were obtained from 68 white individuals with natural normal occlusion, with 30 (44.12%) males and The orthodontic cast models were built up using white plaster stone. The orthodontic cast models were placed in Angle Class I occlusion and supported on a firm, flat base to demarcate the points on the left and right surfaces. A metal ruler was positioned touching the lateral bases, perpendicularly to the occlusal surface, and parallel to the buccal surface, demarcating a small segment of vertical straight line, crossing the horizontal lines on the upper and lower alveolar bones, and giving the points to determine the transverse dimensions in the first molar and first premolar regions (Fig 1). Fig 2 Orthodontic cast models in occlusion. A, Right side with points A1, B1, C1, and D1. B, Left side with points A2, B2, C2, and D2. 1466 Copyright @ 2008 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited. TRANSVERSE MAXILLARY DIMENSION / de Oliveira et al Point D. Intersection of the horizontal line of the alveolar buccal ridge of the mandibula, with the segment of the vertical line passing through the tip of the buccal cusp of the lower premolar (D1Vright side; D2Vleft side) After determining the points on the upper and lower orthodontic cast models, the distance between the region of the upper and lower first molar and first premolar were measured and denominated as follows (Fig 3): Fig 3 Orthodontic cast models with the occlusal surfaces turned up, indicating distances 1, 2, 3, and 4. The reference used in the molar region was the mesiobuccal sulcus of the first lower molar, and in the premolar region, the reference was the center of the buccal cusp of the lower first premolar. The intersection with the horizontal line of the buccal ridge of the alveolar process with the segments of vertical lines determined the points where they intersect (Fig 2): Point A. Intersection of the horizontal line of the alveolar buccal ridge of the maxilla, with the segment of the vertical line passing through the mesiobuccal sulcus of the first lower molar (A1Vright side; A2Vleft side) Point B. Intersection of the horizontal line of the alveolar buccal ridge of the mandibula, with the segment of the vertical line passing through the mesiobuccal sulcus of the first lower molar (B1Vright side; B2Vleft side) Point C. Intersection of the horizontal line of the alveolar buccal ridge of the maxilla, with the segment of the vertical line passing through the tip of the buccal cusp of the lower premolar (C1Vright side; C2Vleft side) Upper intermolar distance (Dist1)Vdistance between points A1 to A2 Lower intermolar distance (Dist2)Vdistance between points B1 to B2 Upper interpremolar distance (Dist3)Vdistance between points C1 to C2 Lower interpremolar distance (Dist4)Vdistance between points D1 to D2 Three measurements were performed by 2 researchers. The first researcher performed 2 measurements with an interval of 15 days between the first (M1P1) and the second (M2P1). The second researcher performed a third measurement (M1P2). A digital caliper was used to obtain all the measurements, for both the posteroanterior cephalometric radiographs and orthodontic cast models. After each measurement had been taken, the lines and points were erased using a soft white eraser. STATISTICAL METHOD T he variables for the PAs analyzed were the maxillary and the mandibular width. For the orthodontic cast models, the variables were as follows: the upper intermolar distance (Dist1), the lower intermolar distance (Dist2), the upper interpremolar distance (Dist3), and the lower interpremolar distance (Dist4). Table 1. Mean, Median, Standard Deviation, Maximum, and Minimum, in Millimeters, for the Transverse Maxillary and Mandibular Dimensions Measurements, Determined in the Posteroanterior Radiographs Transverse Transverse Transverse Transverse Transverse Transverse maxillary dimensionVM1 P1 maxillary dimensionVM2 P1 maxillary dimensionVM1 P2 mandibular dimensionVM1 P2 mandibular dimensionVM2 P1 mandibular dimensionVM1 P2 Mean Median Standard Deviation Minimum Maximum 66.03 65.93 65.96 87.43 88.52 87.81 66.09 65.76 66.13 87.33 88.15 87.41 3.13 3.49 3.62 4.51 4.62 4.84 60.05 59.64 58.77 77.34 78.85 76.56 74.07 73.90 74.32 99.43 98.79 99.92 M1P1 indicates measurement 1 of the first researcher; M2P1, measurement 2 of the first researcher; M1P2, measurement 1 of the second researcher. 1467 Copyright @ 2008 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited. THE JOURNAL OF CRANIOFACIAL SURGERY / VOLUME 19, NUMBER 6 November 2008 Table 2. Mean, Median, Standard Deviation, Maximum, and Minimum of the 3 Measurements, Values in Millimeters for Upper Intermolar Distance (Dist1), Lower Intermolar Distance (Dist2), Upper Interpremolar Distance (Dist3), and Lower Interpremolar Distance (Dist4), Calculated Using the Orthodontic Cast Models Upper Upper Upper Lower Lower Lower Upper Upper Upper Lower Lower Lower intermolar distance (Dist1)VM1P1 intermolar distance (Dist1)VM2P1 intermolar distance (Dist1)VM1P2 intermolar distance (Dist1)VM1P1 intermolar distance (Dist1)VM2P1 intermolar distance (Dist1)VM1P2 interpremolar distance (Dist3)VM1P1 interpremolar distance (Dist3)VM2P1 interpremolar distance (Dist3)VM1P2 interpremolar distance (Dist4)VM1P1 interpremolar distance (Dist4)VM2P1 interpremolar distance (Dist4)VM1P2 Average Median Standard Deviation Minimum Maximum 57.28 57.20 57.13 55.23 55.19 55.05 42.31 42.12 42.07 39.81 39.63 39.57 57.32 57.26 56.99 54.88 54.79 54.65 42.15 42.17 42.16 39.62 39.26 39.14 2.61 2.56 2.63 2.41 2.41 2.38 2.15 2.23 2.19 1.78 1.79 1.73 52.57 52.19 52.21 50.71 50.74 50.64 37.81 37.96 37.75 36.07 35.97 36.22 64.03 63.66 63.73 61.30 61.56 61.24 48.31 47.89 47.90 43.65 43.50 43.39 M1P1 indicates measurement 1 of the first researcher; M2P1, measurement 2 of the first researcher; M1P2, measurement 1 of the second researcher. The mean, median, and standard deviation were calculated, and the Kolmogorov-Smirnov test was carried out for these variables, to determine any similarity in the distribution of the sample. Once confirmed, we used the average values for the 3 measurements. The intraresearcher and interresearcher reproducibility of the median values was calculated using the interclass coefficient correlation method. The Mann-Whitney test was used to verify any sexual dimorphism differences in the variables for the orthodontic cast models. Analysis of variance was used to determine the transverse maxillary dimensions in the orthodontic cast models, to confirm the existence of the straight line linear regression equation, to validate the simple linear regression equation by the least squared method. The level of significance for rejection of the null hypothesis was fixed at a value of equal to or less than 0.05 (5%). RESULTS T here was no observed statistical intraresearcher or interresearcher difference ( P e 0.05), applied to the variables from the posteroanterior cephalometric radiographies and the orthodontic cast models. In the posteroanterior cephalometric radiographies (PA), the maxillary width (JD-JE) and the mandibular width (AG-GA) were, respectively, 65.97 T 3.42 and 87.92 T 4.60 mm (Table 1). In the orthodontic cast models, the mean upper intermolar distance (Dist1) was 57.20 T 2.60 mm, the mean lower intermolar distance (Dist2) was 55.16 T Fig 4 Coefficients of the intraresearcher correlation (M1P1 M2P1) and intraresearcher correlation (M1P1 M2P1) and (M2P1 M1P2) for the orthodontic cast models, and the posteroanterior cephalometric radiographies. M1P1 indicates measurement 1 of the first researcher; M2P1, measurement 2 of the first researcher; M1P2, measurement 1 of the second researcher; Dis1, upper intermolar distance; Dist2, lower intermolar distance; Dist3, upper interpremolar distance, Dist4, lower interpremolar distance; Max. Width, maxillary width; Mand. Width, mandibular width. 1468 Copyright @ 2008 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited. TRANSVERSE MAXILLARY DIMENSION / de Oliveira et al Fig 5 Expected upper intermolar distance after applying the formula to predict the transverse maxillary dimension based on the lower intermolar distance (Dist2). 2.40 mm, the mean upper interpremolar distance (Dist3) was 42.17 T 2.19 mm, and the mean lower interpremolar distance (Dist4) was 39.67 T 1.77 mm (Table 2). As much for the orthodontic models as for the PA, values above 0.8 were observed for all variables (Fig 4). The variables for the orthodontic cast models showed no sexual dimorphism. The equation µm = 8.62 + 0.88xm was determined in the molar region, where µm = the expected upper intermolar distance and xm = lower intermolar distance. The equation was only valid when the lower intermolar distance (Dist2 = xm) was between 61.37 and 50.76 mm (Fig 5). The equation µpm = 4.87 + 0.940xpm was determined for the premolar region, where µpm = the expected upper interpremolar distance and xpm = lower interpremolar distance, but it was valid only when the lower interpremolar distance (Dist4 = xpm) was between 43.51 and 36.09 mm (Fig 6). DISCUSSION A ll the existing methods for predicting the transverse maxillary dimensions have clinical applicability, but with drawbacks. In the dental method, cast models are used to predict the transverse maxillary dimension based on the teeth, whereas the new method enables the selection of measuring site based on the bone structure. The dental method is based on the sum total of the mesiodistal dimensions of the upper incisors, using the formula denominated indices, which vary, according to studies by different authors, to numerically determine the transverse dimension and the correct form of the dental arch, without taking into consideration the bone structure that Fig 6 Expected upper interpremolar distance after applying the formula to predict the transverse maxillary dimension based on the lower interpremolar distance (Dist4). 1469 Copyright @ 2008 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited. THE JOURNAL OF CRANIOFACIAL SURGERY / VOLUME 19, NUMBER 6 was analyzed in this study. Thus, any alterations in the form and size of the upper incisors could influence the results and cause them to be misleading. These indices should be evaluated and validated for each geographic region and ethnic group before being adopted.1,2,10 The radiographic method is carried out using PA, which is useful for evaluating the width-height ratio of the surface. However, the interpretation of these posteroanterior cephalometric radiographs has never been an easy task.11 The use of posteroanterior cephalometric radiograph is important for the diagnosis of cross bite and the evaluation of orthopedic modifications inherent to rapid disjunction of the midpalatal suture according to Marshall, 11 Vanarsdall and White,12 and Sato et al.9 In this study, the resulting values for the maxillary and mandibular widths are compatible with those of Ricketts et al,3 Sato et al,9 and Betts et al.4 The need for this complementary radiography was a limiting factor for this method because its analysis does not form part of the daily clinical routine, unlike orthodontic cast models, which are routinely used for assessment before treatment. The study of Vanarsdall and White12 reports that posteroanterior cephalometric radiographs are widely rejected by orthodontists. For Hixon13 and Yoon et al,14 one of the reasons for this is the difficulty in standardizing the cephalometric points that are marked out, and as a result, there is a wide variation in the measurements. Another reason for the rejection by orthodontists, according to Baumrind and Frantz,15 is that the overlapping of images and projections, caused by adjacent structures, makes it difficult to identify some anatomic structures and cephalometric points. Grummons and Van De Coppello,16 on the other hand, argue that this reluctance is mainly due to the difficulty in identifying the reference points due to the poverty of the radiographic technique and concerns over exposure to radiation. Therefore, the width of the maxilla and the mandibula may present dimensions with a variation, which could lead to an inadequate diagnosis and, consequently, to a wrong treatment. In relation to the present study, there was no error in the markings of the points because of the extensive training of the researchers. However, the points in the cast models showed intraresearcher and interresearcher correlation indices that were higher than those obtained in the posteroanterior cephalometric radiographs. Using the posteroanterior cephalometric radiograph, Betts et al4 created a transverse maxillary index, in which a maxillomandibular difference higher November 2008 than 5.0 mm was established as a skeletal alteration, with SARME being recommended for the patients with complete bone maturity. Compared with the new method, radiography has another limitation: the fact that it is not possible to determine whether the transverse maxillary deficiency molar and/or premolar region, because the region of the measurement is posterior, leaving the anterior region with no reference for the transverse dimension. The clinical method is the most widely used evaluation procedure for the correction of transverse maxillomandibular deficiency in young patients. The transverse correction will be complete when observed, through clinical visibilization, that the palatal cusp of the upper molars was riding up on the buccal cusps of the lower molars.5,7,17Y21 Due to the fact that the method of clinical visibilization is based on the teeth, it becomes inadequate when there is a transverse deficiency of the lower dental arch because the real upper deficiency is camouflaged by the simultaneous deficiency of the lower arch. If the lower posterior teeth have a lingual axial inclination of more than 30 degrees, which is considered not normal, according to Andrews and Andrews,22 the amount of expansion of the maxilla may be insufficient, compromising the final result of the occlusion in the transverse direction. Therefore, the clinical method should not be used for adult patients requiring SARME because they present dentoalveolar compensation of the lower dental arch in the transverse direction. Hence, this method is inadequate because it uses the teeth as a reference, like the dental method. The new method proposed in this study does not have this inadequacy once it uses the bone structure as a reference, and because it is transversely corrected, so will the teeth be corrected. After correction of the axial inclinations of the lower molars, insufficiency of the transverse maxillary dimension is observed. For this method to be used successfully, transversal treatment of the mandibula should be carried out before SARME. The methodology proposed in this study for adult patients with transverse maxillary deficiency establishes the bone structure as the basis for determining the desired transverse maxillary dimension. This results in a prediction with less risk of error for palatal expansion, giving a transverse maxillomandibular balance. Furthermore, orthodontic cast models are used, which can be produced in the clinical use itself. 1470 Copyright @ 2008 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited. TRANSVERSE MAXILLARY DIMENSION / de Oliveira et al The measurement references of this method are the bone bases of the maxilla and mandibula. The points of reference showed to be easy to locate, which can be evaluated by the high intraresearcher and interresearcher correlation index between the intermolar and interpremolar maxillary and mandibular distances. Because the teeth are not used to analyze the transverse maxillomandibular relation, the initial morphology of the lower dental arch does not interfere in the amount of maxillary expansion, independent of the axial inclination of the posterior teeth. It is also feasible for evaluating the maxillary bone base in 2 regions: a more posterior region, which is based on the first molar, and another anterior region, in the dental arch, located in the first premolar. It is therefore possible to evaluate whether the maxillary atresia occurs in the posterior and/ or anterior region, enabling the treatment to be directed according to the area of the maxilla that requires expansion. The possible benefits of this procedure include the following: elimination of the need for complementary radiography (posteroanterior radiography), its easy applicability, the possibility of its use independent of the correction method (SARME or surgical expansion), assistance in the diagnosis of the type of transverse deficiency (skeletal or dentoalveolar), and its ability to determine whether the maxillary atresia is in the molar or premolar region. The prediction of the transverse maxillary dimension can be obtained using the alveolar buccal ridge of the orthodontic cast model of the maxilla and mandibula, which clinical applicability consists on those steps: For first molar region, the expected upper intermolar distance (µm) is obtained by the equation: µm = 8.62 + 0.88xm, with µm being the expected upper intermolar distance and xm being the actual lower intermolar distance. The prediction of the transverse maxillary dimension for the first molar region is calculated by the difference between the expected upper intermolar distance (µm) and the actual intermolar distance (Dist1). For the region of the first premolar, the expected upper interpremolar distance (µpm) is obtained by the equation: µpm = 4.87 + 0.94xpm, with µpm being the expected upper interpremolar distance and xpm being the actual lower interpremolar distance. 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