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Three-dimensional evaluation on digital casts of maxillary palatal size and morphology in patients with functional posterior crossbite

Three-dimensional evaluation on digital casts of maxillary palatal size and morphology in... Summary Background and objectives Some authors have recently postulated the possibility of a unilateral contraction of the palate in patients with crossbite. This study aimed to investigate palatal dimension size and morphology in subjects with functional posterior crossbite and to localize location of the contraction through a 3D analysis procedure. Materials and methods A study sample (SS) of 35 subjects (mean age 9.2 ± 0.8 years), diagnosed with functional crossbite, and a control sample (CS) of 35 subjects (mean age 9.4 ± 0.9 years) without crossbite were selected for this study. The digital models of each patient were analysed to assess palatal dimension size and symmetry by measuring linear distances between primary canines (D1) and fist molars (D2) to the median palatine plane and by performing and analysing the 3D deviation between the two specular models of the palatal vault for each patient. Results Our findings demonstrate a significantly narrower dimension of D2 for the crossbite side than at the non-crossbite side. The 3D deviation analysis demonstrates a lower matching percentage of the palatal vault models in the SS (83.36%) compared with the CS (92.82%) and a location of that the palatal contraction is at the alveolar bone level. Conclusions It can be assumed that there is a bilateral symmetrical contraction of the palatal vault and an asymmetric contraction of the alveolar process, but further studies are needed to corroborate this hypothesis. Introduction Posterior crossbite is one of the most frequent malocclusions in deciduous and mixed dentition, with a prevalence of 7–23% (1–4). It often appears unilaterally due to a functional shift of the mandible towards the crossbite side (5). This condition, known as functional posterior crossbite, is often caused by a mild bilateral maxillary constriction (6), which causes occlusal interference that leads to a functional shift of the mandible towards the crossbite side upon closure (3, 6, 7). The treatment of this condition often requires bilateral maxillary expansion (7). However, bilateral maxillary constriction together with functional crossbite has been questioned recently (8, 9). So, we found that subjects with functional crossbite may have asymmetric contracted maxillary morphology on the crossbite side (9) because it is narrower than the non-crossbite side (9). However, these findings were obtained on plaster casts by only measuring the inter-canine and inter-molar distances (8, 9). Measurements based on stone casts might not reliably assess palatal morphology and cannot exclude bias in assessing the transverse dimension of the maxillary arch (10), due to tooth inclination and angulation (10). To overcome such limits, three-dimensional (3D) images of dental casts or digital casts should be used. Interestingly, a previous study evaluated 3D palatal changes following unilateral posterior crossbite correction in primary dentition (10). Hence, to clarify these controversies, which could have clinical implications, palatal size and morphology in subjects with functional crossbite can be investigated with the aid of new 3D technology. Among these, the best-fit method or ‘fine matching’ overcomes the errors in manual ‘raw matching’, which consists of manual selection and the measurement of matchings (11). The aim of this study was first to measure and compare 2D palate sizes (i.e. semi-palatal widths) with the median sagittal plane and between crossbite and non-crossbite sides and second to investigate and compare palatal morphology and shape by mirroring the palatal vault and alveolar processes to assess whether there is any asymmetry between the two palatal halves. Materials and methods Study population To assess the power of the study, a power calculation was conducted using a specific research toolkit (DSS Research, Washington, DC, USA, https://www.dssresearch.com/knowledgecenter/toolkitcalculators/samplesizecalculators.aspx), which indicated that data from 18 participants would yield a confidence level of 95% and a Beta error level of 85% making it sufficient to determine statistically significant differences. Dental casts from 48 patients were randomly selected from a larger pool of subjects seeking orthodontic treatment at the Department of Orthodontics, Faculty of Dentistry, Catania University, Italy; the Department of Orthodontics, Faculty of Dentistry, La Sapienza, Rome University, Italy; and Department of Orthodontics, Faculty of Dentistry, University of Messina, Italy, between January 2015 and May 2016. To be included in the study sample (SS), all patients at the start of the treatment had to have a transverse maxillary deficiency and a crossbite on one side only, with buccal cusps of at least two or more maxillary posterior teeth occluding lingual to buccal cusps of the mandibular teeth, and a mandibular midline shift towards the crossbite site of ≥2 mm at the maximum intercuspal position and not at mouth opening, indicating a functional posterior cross bite (FPXB), as clinically assessed by an experienced orthodontist (ALG). Further inclusion criteria were Class I or edge-to-edge molar relationship, skeletal Class I relationship, pre-puberty cervical vertebral maturation as assessed on lateral cephalograms (CVMS1, CVMS2). The exclusion criteria were maxillary posterior teeth occluding entirely on the lingual side of the mandibular teeth, missing teeth (excluding the third molars) or non-erupted exfoliated primary teeth, craniofacial deformities, systemic diseases, previous orthodontic treatment, anterior crossbite, signs or symptoms of temporomandibular disorder, carious lesions, extensive restoration, or periodontal disease. The SS included 20 girls and 15 boys (mean age 9.2 ± 0.8 years) diagnosed with functional posterior crossbite (Table 1) of which 20 had a functional mandibular shift on the right side, 13 on the left. Table 1. Demography and clinical characteristics of the sample of the study. Sample characteristics Total (n = 70) Study sample (n = 35) Control sample (n = 35) Significance* Mean or n Mean or n Mean or n Mean age (years) 9.3 (±0.9) 9.2 (±0.8) 9.4 (±0.9) NS Sex NS  Male 31 15 16  Female 39 20 19 Skeletal maturity NS  CVMS I 32 14 13  CVMS II 38 21 22 Sample characteristics Total (n = 70) Study sample (n = 35) Control sample (n = 35) Significance* Mean or n Mean or n Mean or n Mean age (years) 9.3 (±0.9) 9.2 (±0.8) 9.4 (±0.9) NS Sex NS  Male 31 15 16  Female 39 20 19 Skeletal maturity NS  CVMS I 32 14 13  CVMS II 38 21 22 *P-value for comparison of group means by t-test or differences in proportion calculated by chi-square test. View Large Table 1. Demography and clinical characteristics of the sample of the study. Sample characteristics Total (n = 70) Study sample (n = 35) Control sample (n = 35) Significance* Mean or n Mean or n Mean or n Mean age (years) 9.3 (±0.9) 9.2 (±0.8) 9.4 (±0.9) NS Sex NS  Male 31 15 16  Female 39 20 19 Skeletal maturity NS  CVMS I 32 14 13  CVMS II 38 21 22 Sample characteristics Total (n = 70) Study sample (n = 35) Control sample (n = 35) Significance* Mean or n Mean or n Mean or n Mean age (years) 9.3 (±0.9) 9.2 (±0.8) 9.4 (±0.9) NS Sex NS  Male 31 15 16  Female 39 20 19 Skeletal maturity NS  CVMS I 32 14 13  CVMS II 38 21 22 *P-value for comparison of group means by t-test or differences in proportion calculated by chi-square test. View Large The control sample (CS) was matched by cervical vertebral maturation to minimize the confounding effect of growth and included 19 girls and 16 boys (mean age 9.4 ± 0.9 years). The inclusion and exclusion criteria were the same as the patient group, plus the absence of functional crossbite (Table 1). Approval for this cross-sectional study was obtained from the local Institutional Review Board, and signed informed consent from the parents of all the subjects was already obtained, prior to starting orthodontic treatment. Each subject received conventional dental impressions using a monophasic polyether impression material (Impregum Penta; ‘3M ESPE’, Seefeld, Germany) with stainless steel impression trays (Hi-Tray Metal; ‘Zhermack SpA’, Rovigo, Italy), which was poured, at most, after 4 hours with type IV stone (Ortostone; Techim Group, Milan, Italy). Then, all the maxillary casts were scanned using the D500 3D scanner (3Shape A/S, Copenhagen, Denmark) according to the manufacturer’s instructions: full arch scan time 90 seconds, 2 resolution cameras of 1.3 megapixels, red laser featuring an accuracy of 10 μm as reported by the manufacture. The 3Shape system has been validated and described previously (12, 13). Each dental cast was scanned from 10 or more angles and then combined and rendered into a 3D stereo-lithographic model by using a specific software (ScanItOrthodontics™ 2015, version 5.6.1.6, ‘3Shape A/S’, Copenhagen, Denmark). After scanning, the stereo-lithographic files were stored. The digital models of the scanned printed models were exported to Geomagic Qualify software (3D Systems, Rock Hill, Washington, DC, USA) to perform a superimposition model and exported to Ortho Analyzer software (3Shape) to measure distances. To analyse the transverse dimensions of the maxillary arch, a median palatal plane (MPP) was traced on digital casts through two landmarks identified along the median palatal raphe (14) (Figure 1). One landmark (point 1) was identified as the point on the median palatal raphe adjacent to the second ruga. The second point (point 2) was identified on the median palatal raphe 1 cm distal to point 1. Figure 1. View largeDownload slide The median palatal plane (MPP) was drawn through two landmarks detected along the median palatal raphe and showed in red. The first landmark identified the point on the median palatal raphe adjacent to the second ruga (Point 1). The second landmark was placed on the median palatal raphe 1 cm distal to the first point (Point 2). D1 and D2 represent respectively the linear distance from the midpoint of the dento-gingival junction of the primary canine and first molar to the MPP. Figure 1. View largeDownload slide The median palatal plane (MPP) was drawn through two landmarks detected along the median palatal raphe and showed in red. The first landmark identified the point on the median palatal raphe adjacent to the second ruga (Point 1). The second landmark was placed on the median palatal raphe 1 cm distal to the first point (Point 2). D1 and D2 represent respectively the linear distance from the midpoint of the dento-gingival junction of the primary canine and first molar to the MPP. After identification of MPP, the following measurements were performed (Figure 1): D1: the distance between the midpoint at the dento-gingival junction of the primary canine from the crossbite and non-crossbite sides compared with the MPP and D2: the distance between the midpoint of the dento-gingival junction of the first molar from the crossbite and non-crossbite sides compared with the MPP. In the CS, measuring the same distances on the right and left palatal halves. To check for crossbite/non-crossbite symmetry, digital casts from each patient were superimposed through a semi-automatic surface-to-surface matching technique, using 3D reverse modelling software (Geomagic Control™ X, version 2017.0.0, ‘3D Systems’, Rock Hill, USA), which also calculated the deviation between the mirrored and un-mirrored 3D palatal models. To define the palate surface of the 3D model to be analysed, a gingival plane had to pass through all the most apical points of the dento-gingival junction of all the teeth (from 1st right molar to 1st left molar, Figure 2A). Figure 2. View largeDownload slide The gingival plane (A) was assessed by linking the most apical point of the dento-gingival junction of all teeth at the palatal tooth face. Then the palatal vault model was created (B), mirrored (C), and roughly superimposed using the MPP plane and its perpendicular plane (D). Then a ‘best-fit’ alignment was done to enhance the superimposition (E) quality. Figure 2. View largeDownload slide The gingival plane (A) was assessed by linking the most apical point of the dento-gingival junction of all teeth at the palatal tooth face. Then the palatal vault model was created (B), mirrored (C), and roughly superimposed using the MPP plane and its perpendicular plane (D). Then a ‘best-fit’ alignment was done to enhance the superimposition (E) quality. The workflow for the superimposition of the palate is described below in four steps. Step 1. Mirroring: Converting the image orientation from right-left, antero-posterior, and infero-superior to left-right, antero-posterior, and infero-superior (Figure 2B–C); Step 2. First registration: Initial manual superimposition of the two models to shorten the time needed for the subsequent automatic superimposition; Thus, pairs of models (the original and the mirrored one of the same patient) were oriented and roughly registered by using the MPP and a line drawn perpendicularly through point 2 of the MPP. (Figure 2D); Step 3. Final registration: Final registration was performed using the ‘Best-fit alignment’ option in the Geomagic Control X software. After defining the reference dataset, the precision of the registration was set to at least 0.3 mm (tolerance type: ‘3D Deviation’), and the number of polygons for surface representation was set to the maximum of 100 000, the corresponding polygons of the selected reference areas were automatically superimposed (Figure 2E); and Step 4. Superimposition and 3D analysis: The distances between corresponding areas of the original maxillary cast and the corresponding mirrored one were compared to obtain colour-coded maps (Figure 3) in which the yellow-to-red fields indicated that the definitive casts were larger than the master model and the turquoise-to-dark blue fields indicated that the definitive casts were smaller than the master model. The tolerance range in green of the 3D deviation analysis was set to ±0.50 mm with a maximum of 2 mm. All the values in this range indicated the matching percentage between the two specular 3D models. Figure 3. View largeDownload slide 3D deviation analysis between the two specular palatal models. RGB coloured scale bar (millimetres) is reported on the right: the top (red) and the bottom (blue) of the scale indicate the maximum positive and negative deviations. Green indicates the tolerance range. The image shows palatal (A) and lateral (B–C) views. As shown, mismatching is mainly localized in the dento-alveolar process area. Figure 3. View largeDownload slide 3D deviation analysis between the two specular palatal models. RGB coloured scale bar (millimetres) is reported on the right: the top (red) and the bottom (blue) of the scale indicate the maximum positive and negative deviations. Green indicates the tolerance range. The image shows palatal (A) and lateral (B–C) views. As shown, mismatching is mainly localized in the dento-alveolar process area. To minimize random error and systematic errors, all measurements were performed by a single examiner, with 25 years orthodontic experience (RL). The examiner measured only five models each day to avoid fatigue. The models were measured in blind sequence. Statistical analysis Descriptive statistics were carried out to analyse the demographic and clinical characteristics of the SS and CS groups. The Student’s t-test and chi-square test compared numerical (age) and categorical (gender, skeletal maturity) characteristics between SS and CS. All the measurements were recorded on Microsoft Excell® spreadsheet (Microsoft, Redmond, Washington, DC, USA) and analysed using SPSS® version 24 Statistics software (IBM Corporation, 1 New Orchard Road, Armonk, New York, USA) with P-value < 0.05 considered statistically significant. The Kolmogorov–Smirnov test was used to test the normality of the data. Data matching the two hemi-palatal structures and linear measurements were normally distributed, while data of the two semi-palatal volumes showed no homogeneous variance. Parametric tests were used to evaluate and compare measurements. Student’s t-test assessed width differences compared with MPP (D1, D2) between the crossbite and non-crossbite sides of the SS and between the right and left sides of the CS. The matching (symmetry) percentages of the two semi-palatal volumes were investigated in both groups by independent Student’s t-test. The Wilcoxon signed-rank test was used to assess differences between the two hemi-palatal volumes in both SS and control group. Furthermore, to assess intra-rater repeatability, 10 digital casts from the SS and CS were measured again (T2), by the same operator after a washout period of 4 weeks. The Intraclass Correlation Coefficient (ICC) was applied between the two measurements to assess intra-examiner reliability. The method error was also assessed using Dahlberg’s formula. Statistical data analysis was performed using SPSS Statistics software (IBM Corporation, 1 New Orchard Road, Armonk, New York, USA). The level of significance was set at P < 0.05. Results The descriptive statistics of the SS and CS are reported in Table 1. Any statistically significant differences were obtained by comparing the two groups. The examiner’s ICC values, widths, and matchings showed that the measurement sets correlated highly (ICC values ranged from 90.7 to 99.0%). The method error was 91.97 mm3 for volumetric measurements, 0.17 mm for D1 measurements, 0.14 mm for D2 measurements, and 1.23% for hemi-palate matching. 2D measurements In patients with posterior crossbite, the palatal width measured at the primary canine was around 2 mm narrower on the crossbite side (D1-CB) and 1 mm at the non-crossbite (D1-non-CB) side compared with controls; D1-CB was found to be 1 mm narrower than D1-non-CB (P < 0.05) (Table 2). No significant differences were found between the crossbite side and non-crossbite side. (P > 0.05). The first molar width respect to MPP on the non-crossbite side (D2-non-CB) was around 1 mm smaller than the same measurements obtained from the CS (D2-Side A, D2-Side B); on the other hand, an even narrower distance was recorded on the crossbite side (D2-CB) because the difference compared with the CS was more than 2.5 mm. A statistically significant difference was obtained by comparing D2-non-CB and D2-CB (P < 0.05; Table 2). Table 2. Inferential statistics for observation and control groups. Comparison between linear semi-palatal measurements. Total D1 (mm) Significance D2 (mm) Significance Study sample FPXB side 35 11.42 (±1.32) * 13.55 ± (1.32) * No FPXB side 35 12.37 (±1.15) 15.07 ± (1.40) Control sample Side A (right) 35 13.71 (±1.48) NS 16.19 ± (1.18) NS Side B (left) 35 13.64 (±1.47) 16.36 ± (1.27) Total D1 (mm) Significance D2 (mm) Significance Study sample FPXB side 35 11.42 (±1.32) * 13.55 ± (1.32) * No FPXB side 35 12.37 (±1.15) 15.07 ± (1.40) Control sample Side A (right) 35 13.71 (±1.48) NS 16.19 ± (1.18) NS Side B (left) 35 13.64 (±1.47) 16.36 ± (1.27) Values based on paired Student’s t-tests. D1 = distance between mild palate plane and the centre of dento-gingival junctions of primary canine. D2 = distance between mild palate plane and the centre of dento-gingival junctions of first molar. NS = non significant. *P < 0.05. View Large Table 2. Inferential statistics for observation and control groups. Comparison between linear semi-palatal measurements. Total D1 (mm) Significance D2 (mm) Significance Study sample FPXB side 35 11.42 (±1.32) * 13.55 ± (1.32) * No FPXB side 35 12.37 (±1.15) 15.07 ± (1.40) Control sample Side A (right) 35 13.71 (±1.48) NS 16.19 ± (1.18) NS Side B (left) 35 13.64 (±1.47) 16.36 ± (1.27) Total D1 (mm) Significance D2 (mm) Significance Study sample FPXB side 35 11.42 (±1.32) * 13.55 ± (1.32) * No FPXB side 35 12.37 (±1.15) 15.07 ± (1.40) Control sample Side A (right) 35 13.71 (±1.48) NS 16.19 ± (1.18) NS Side B (left) 35 13.64 (±1.47) 16.36 ± (1.27) Values based on paired Student’s t-tests. D1 = distance between mild palate plane and the centre of dento-gingival junctions of primary canine. D2 = distance between mild palate plane and the centre of dento-gingival junctions of first molar. NS = non significant. *P < 0.05. View Large In the control group, the right and left side widths measured at the midline showed perfect symmetry at the canine and molar levels. 3D measurements The colour map analysis of the superimposition of the posterior crossbite models was an intense blue in the buccal area of the superimposed models on one side and intense red on the other. The palatal vault demonstrated a prevalence of green, which indicates insignificant differences. Palatal asymmetry was confined to the lower part of the palate at the alveolar processes level as shown in Figure 3. A prevalence of green at the palatal vault and alveolar process was observed in the CS group, indicating a higher matching percentage (Table 3). Table 3. Inferential statistics for observation and control groups. Comparison between emi-volumes measurements. Total Mean volume (mm3) Minimum Maximum Quartile Significance 25° 50° 75° Study sample FPXB side 35 3226.42 (±619.81) 2418.16 5046.49 2723.29 3038.86 3376.92 * No FPXB side 35 3428.92 (±653.75) 2368.77 5225.39 2987.36 3271.49 3690.1 Control sample Side A (right) 35 4133.74 (±913.46) 2923.38 6455.8 3441.06 3931.24 4716.78 NS Side B (left) 35 4122.60 (±904.54) 2911.85 6395.81 3432.34 3913.22 4734.84 Total Mean volume (mm3) Minimum Maximum Quartile Significance 25° 50° 75° Study sample FPXB side 35 3226.42 (±619.81) 2418.16 5046.49 2723.29 3038.86 3376.92 * No FPXB side 35 3428.92 (±653.75) 2368.77 5225.39 2987.36 3271.49 3690.1 Control sample Side A (right) 35 4133.74 (±913.46) 2923.38 6455.8 3441.06 3931.24 4716.78 NS Side B (left) 35 4122.60 (±904.54) 2911.85 6395.81 3432.34 3913.22 4734.84 Values based on Wilcoxon signed-rank test. NS = non significant. *P < 0.05. View Large Table 3. Inferential statistics for observation and control groups. Comparison between emi-volumes measurements. Total Mean volume (mm3) Minimum Maximum Quartile Significance 25° 50° 75° Study sample FPXB side 35 3226.42 (±619.81) 2418.16 5046.49 2723.29 3038.86 3376.92 * No FPXB side 35 3428.92 (±653.75) 2368.77 5225.39 2987.36 3271.49 3690.1 Control sample Side A (right) 35 4133.74 (±913.46) 2923.38 6455.8 3441.06 3931.24 4716.78 NS Side B (left) 35 4122.60 (±904.54) 2911.85 6395.81 3432.34 3913.22 4734.84 Total Mean volume (mm3) Minimum Maximum Quartile Significance 25° 50° 75° Study sample FPXB side 35 3226.42 (±619.81) 2418.16 5046.49 2723.29 3038.86 3376.92 * No FPXB side 35 3428.92 (±653.75) 2368.77 5225.39 2987.36 3271.49 3690.1 Control sample Side A (right) 35 4133.74 (±913.46) 2923.38 6455.8 3441.06 3931.24 4716.78 NS Side B (left) 35 4122.60 (±904.54) 2911.85 6395.81 3432.34 3913.22 4734.84 Values based on Wilcoxon signed-rank test. NS = non significant. *P < 0.05. View Large There were statistically significant (P < 0.05; Table 4) differences in the percentage of palatal volume matching: 83.36% in SS group and 92.82% in the CS group. Table 4. Comparison of emi-palate volumes matching between observation and control group. Total Matching (mean; %) SD Mean difference (%) 95% Confidence interval of the difference Significance Upper Lower Study sample 35 83.36 3.68 9.46 11 7.92 * Control sample 35 92.82 2.66 Total Matching (mean; %) SD Mean difference (%) 95% Confidence interval of the difference Significance Upper Lower Study sample 35 83.36 3.68 9.46 11 7.92 * Control sample 35 92.82 2.66 Values based on independent Student’s t-test. NS = non significant. *P < 0.05. View Large Table 4. Comparison of emi-palate volumes matching between observation and control group. Total Matching (mean; %) SD Mean difference (%) 95% Confidence interval of the difference Significance Upper Lower Study sample 35 83.36 3.68 9.46 11 7.92 * Control sample 35 92.82 2.66 Total Matching (mean; %) SD Mean difference (%) 95% Confidence interval of the difference Significance Upper Lower Study sample 35 83.36 3.68 9.46 11 7.92 * Control sample 35 92.82 2.66 Values based on independent Student’s t-test. NS = non significant. *P < 0.05. View Large Discussion Posterior crossbite is a frequent malocclusion that may develop and improve at any point between the eruption of the deciduous teeth to the eruption of the permanent teeth (15). It may be due to skeletal, soft tissue, dental, or respiratory factors or develop as the result of oral habits (15). Among treatment options, widening the upper teeth, arch, or palate is one of the most frequent clinical approaches (16, 17). Knowing whether there is a symmetric or asymmetric contraction of the palate and upper arch in patients with functional posterior crossbite and the chance of identifying morphological palate characteristics may be helpful for the appropriate treatment of this condition. The objective of this study was to use new digital technologies to see whether there is symmetrical or asymmetrical contraction of the palate in FPXB patients because the assumption that there is a mild bilateral contraction of the entire palate in functional crossbite has been recently questioned (8–10), in favour of a monolateral contraction. In our study, the palatal size and morphology of functional crossbite patients were evaluated using 3D laser scans of digital casts by surface-based superimposition because assessing size and shape using conventional 2D dental casts also raises the important issue of reducing a 3D object to a 2D image (18). According to this reverse engineering, each virtual palate can be mirrored at an arbitrary point. This procedure, also designated as 3D surface-to-surfacematching, provides morphological differences between the two semipalatalhalves, the3D differences of the superimposed models are translated into colour codes, which represent the distances between corresponding points (18). In two previous studies (8, 9), palatal size was obtained by measuring inter-canine and inter-molar linear distances compared with the midpalatal suture of the maxilla. Findings from these investigations demonstrated upper dental arch asymmetry in patients with unilateral crossbite, the crossbite side being narrower than the non-crossbite side. However, these results could be biased due to tooth inclination and the poor reliability of midline allocation based on dental casts (19). These issues were overcome by another study (10), where the palate symmetry was evaluated in terms of palatal shell overlapping, by mirroring the palatal vault of children in primary dentition affected by posterior crossbite (10). So, the issue of palatal symmetry or asymmetry in unilateral crossbite is not clear. So, with 3D technology, this study analysed the palatal morphology of mixed dentition patients with posterior crossbite and precisely quantified and detected areas of asymmetry using the mirroring technique. This technique was carried out because shape analysis has become of increasing interest to the medical image analysis community, due to its potential for precisely locating and quantifying morphological changes between healthy and pathological structures (20). The results of our study demonstrated a mild asymmetric palate of the upper jaw in patients with functional posterior crossbite. We recorded palate widths on the crossbite side about 1 mm narrower at the molar and primary canine levels compared with the non-crossbite side, and these results agree with previous findings (9). Furthermore, these width differences, although not severe, were statistically significant. Also, the matching per cent of palatal shell overlapping by mirroring palates was different comparing the study group to controls. The matching per cent was 79.5% in the SS, compared with the CS of 88%. Our findings are hardly comparable with the only previous study carried out with the same digital technique investigating palatal symmetry in primary dentition children with functional crossbite (10), and our sample was intermediate–late dentition patients. However, in functional posterior crossbite patients, there has been described a worsening of facial asymmetry in the middle of the face at both the early/intermediate and late mixed dentition phases (21); thus, it could be speculated that the same could happen for the upper dental arch explaining the difference in results from our study compared with the previous one (10). Interestingly, in our crossbite patient sample, palatal asymmetry or mismatching of the palatal vault was mostly localized at the alveolar bone level, as revealed by the mirroring technique and colour map. In unilateral crossbite patients, it can be assumed that there is a bilateral symmetric contraction of the palatal vault and an asymmetric contraction of the upper arch alveolar process. According to our results, it can be hypothesized that the bending of the alveolar structures and buccal tipping of the posterior maxillary teeth, as a consequence of the functional shift of the mandible, could have a role in determining the sectional constriction of the palate as our sample showed. This could somehow explain the success rate of the early treatment of this malocclusion with selective grinding or occlusal adjustment of the primary dentition (22), which with or without the addition of a removable upper expansion device seems to be effective in preventing posterior crossbite in primary dentition from being perpetuated to the mixed and permanent dentitions (14). This eliminates occlusal interference as an opportunity to restore form and function. Nevertheless, since the differences in palatal arch sizes and morphology between crossbite and non-crossbite sides are mild and not severe, asymmetric expansion of the palatal arch does not seem to be clinically justified. Furthermore, the use of appliances that expand the dento-alveolar complex as well as selective adjustment and occlusal guiding are corroborated at least for the early intervention of functional posterior crossbite (14). However, this study has some limitations. We used a second generation of superimposition approaches based on ‘fine matching’. The effect of outliers is reduced, while accuracy and reliability markedly improves when serial 3D models are superimposed (11). This new technique reduces the errors associated with manually selecting superimposition points (11). It should be acknowledged that very recently, a novel method for superimposing digital maxillary 3D models has been proposed (11), which combines ‘raw matching’, ‘fine matching’, and ‘deformation analysis’, and has proved robust in evaluating palatal changes. There are two more issues with this study since it was only carried out on mixed dentition, while a sample of serial models taken with a moderate interval could have been of clinical aid in establishing the exact period of bending of the alveolar processes and therefore treatment planning. Moreover, teeth inclination differences between the study group and controls for the crossbite side and non-crossbite side were not assessed in our study, which was designed to investigate palate morphology, but they could have confirmed our results. Conclusions Semi-palatal widths on the crossbite side are smaller than those on the non-crossbite side and in controls. Palatal volume matching percentages are smaller in patients with functional crossbite (83.36%) than in controls (92.82%) as assessed by the mirroring technique. In patients with functional crossbite, the mismatching is observed mainly at the alveolar processes level. Further studies should evaluate if the use of 3D models and surface-to-surface mirroring could enhance the assessment of palatal asymmetry and the early treatment of posterior crossbite by selective adjustment and occlusal guiding to raise the success rates of this kind of therapy and establish criteria for defining success. Conflict of interest None to declare. References 1. da Silva Filho , O.G. , Santamaria , M. Jr and Capelozza Filho , L . ( 2007 ) Epidemiology of posterior crossbite in the primary dentition . The Journal of Clinical Pediatric Dentistry , 32 , 73 – 78 . Google Scholar Crossref Search ADS PubMed 2. de Sousa , R.V. , Ribeiro , G.L. , Firmino , R.T. , Martins , C.C. , Granville-Garcia , A.F. and Paiva , S.M . ( 2014 ) Prevalence and associated factors for the development of anterior open bite and posterior crossbite in the primary dentition . Brazilian Dental Journal , 25 , 336 – 342 . Google Scholar Crossref Search ADS PubMed 3. Kennedy , D.B. and Osepchook , M . 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Primožic , J. , Baccetti , T. , Franchi , L. , Richmond , S. , Farčnik , F. and Ovsenik , M . ( 2013 ) Three-dimensional assessment of palatal change in a controlled study of unilateral posterior crossbite correction in the primary dentition . European Journal of Orthodontics , 35 , 199 – 204 . Google Scholar Crossref Search ADS PubMed 11. Ganzer N , Feldmann I , Liv P and Bondemark L . A novel method for superimposition and measurements on maxillary digital 3D models-studies on validity and reliability . European Journal of Orthodontics . 2017 , 40 , 45 – 51 . Google Scholar Crossref Search ADS 12. Hayashi , K. , Sachdeva , A.U. , Saitoh , S. , Lee , S.P. , Kubota , T. and Mizoguchi , I . ( 2013 ) Assessment of the accuracy and reliability of new 3-dimensional scanning devices . American Journal of Orthodontics and Dentofacial Orthopedics , 144 , 619 – 625 . Google Scholar Crossref Search ADS PubMed 13. Sousa , M.V. , Vasconcelos , E.C. , Janson , G. , Garib , D. and Pinzan , A . ( 2012 ) Accuracy and reproducibility of 3-dimensional digital model measurements . American Journal of Orthodontics and Dentofacial Orthopedics , 142 , 269 – 273 . Google Scholar Crossref Search ADS PubMed 14. Maurice , T.J. and Kula , K . ( 1998 ) Dental arch asymmetry in the mixed dentition . The Angle Orthodontist , 68 , 37 – 44 . Google Scholar PubMed 15. Harrison JE and Ashby D . ( 2001 ) Orthodontic treatment for posterior crossbites . Cochrane Database Systematic Reviews . Cd000979 . 16. Bazargani , F. , Feldmann , I. and Bondemark , L . ( 2013 ) Three-dimensional analysis of effects of rapid maxillary expansion on facial sutures and bones . The Angle Orthodontist , 83 , 1074 – 1082 . Google Scholar Crossref Search ADS PubMed 17. Lagravere , M.O. , Major , P.W. and Flores-Mir , C . ( 2005 ) Long-term skeletal changes with rapid maxillary expansion: a systematic review . The Angle Orthodontist , 75 , 1046 – 1052 . Google Scholar PubMed 18. Gkantidis , N. , Schauseil , M. , Pazera , P. , Zorkun , B. , Katsaros , C. and Ludwig , B . ( 2015 ) Evaluation of 3-dimensional superimposition techniques on various skeletal structures of the head using surface models . PLoS One , 10 , e0118810 . Google Scholar Crossref Search ADS PubMed 19. Almeida , M.A. , Phillips , C. , Kula , K. and Tulloch , C . ( 1995 ) Stability of the palatal rugae as landmarks for analysis of dental casts . The Angle Orthodontist , 65 , 43 – 48 . Google Scholar PubMed 20. Ho , J.T. , Schreurs , R. , Milstein , D.M. , Dubois , L. , Maal , T.J. , de Lange , J. and Becking , A.G . ( 2016 ) Measuring zygomaticomaxillary complex symmetry three-dimensionally with the use of mirroring and surface based matching techniques . Journal of Cranio-maxillo-facial Surgery , 44 , 1706 – 1712 . Google Scholar Crossref Search ADS PubMed 21. Primozic , J. , Perinetti , G. , Richmond , S. and Ovsenik , M . ( 2013 ) Three-dimensional evaluation of facial asymmetry in association with unilateral functional crossbite in the primary, early, and late mixed dentition phases . The Angle Orthodontist , 83 , 253 – 258 . Google Scholar Crossref Search ADS PubMed 22. Lindner , A . ( 1989 ) Longitudinal study on the effect of early interceptive treatment in 4-year-old children with unilateral cross-bite . Scandinavian Journal of Dental Research , 97 , 432 – 438 . Google Scholar PubMed © The Author(s) 2018. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The European Journal of Orthodontics Oxford University Press

Three-dimensional evaluation on digital casts of maxillary palatal size and morphology in patients with functional posterior crossbite

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Oxford University Press
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© The Author(s) 2018. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com
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0141-5387
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10.1093/ejo/cjx103
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Abstract

Summary Background and objectives Some authors have recently postulated the possibility of a unilateral contraction of the palate in patients with crossbite. This study aimed to investigate palatal dimension size and morphology in subjects with functional posterior crossbite and to localize location of the contraction through a 3D analysis procedure. Materials and methods A study sample (SS) of 35 subjects (mean age 9.2 ± 0.8 years), diagnosed with functional crossbite, and a control sample (CS) of 35 subjects (mean age 9.4 ± 0.9 years) without crossbite were selected for this study. The digital models of each patient were analysed to assess palatal dimension size and symmetry by measuring linear distances between primary canines (D1) and fist molars (D2) to the median palatine plane and by performing and analysing the 3D deviation between the two specular models of the palatal vault for each patient. Results Our findings demonstrate a significantly narrower dimension of D2 for the crossbite side than at the non-crossbite side. The 3D deviation analysis demonstrates a lower matching percentage of the palatal vault models in the SS (83.36%) compared with the CS (92.82%) and a location of that the palatal contraction is at the alveolar bone level. Conclusions It can be assumed that there is a bilateral symmetrical contraction of the palatal vault and an asymmetric contraction of the alveolar process, but further studies are needed to corroborate this hypothesis. Introduction Posterior crossbite is one of the most frequent malocclusions in deciduous and mixed dentition, with a prevalence of 7–23% (1–4). It often appears unilaterally due to a functional shift of the mandible towards the crossbite side (5). This condition, known as functional posterior crossbite, is often caused by a mild bilateral maxillary constriction (6), which causes occlusal interference that leads to a functional shift of the mandible towards the crossbite side upon closure (3, 6, 7). The treatment of this condition often requires bilateral maxillary expansion (7). However, bilateral maxillary constriction together with functional crossbite has been questioned recently (8, 9). So, we found that subjects with functional crossbite may have asymmetric contracted maxillary morphology on the crossbite side (9) because it is narrower than the non-crossbite side (9). However, these findings were obtained on plaster casts by only measuring the inter-canine and inter-molar distances (8, 9). Measurements based on stone casts might not reliably assess palatal morphology and cannot exclude bias in assessing the transverse dimension of the maxillary arch (10), due to tooth inclination and angulation (10). To overcome such limits, three-dimensional (3D) images of dental casts or digital casts should be used. Interestingly, a previous study evaluated 3D palatal changes following unilateral posterior crossbite correction in primary dentition (10). Hence, to clarify these controversies, which could have clinical implications, palatal size and morphology in subjects with functional crossbite can be investigated with the aid of new 3D technology. Among these, the best-fit method or ‘fine matching’ overcomes the errors in manual ‘raw matching’, which consists of manual selection and the measurement of matchings (11). The aim of this study was first to measure and compare 2D palate sizes (i.e. semi-palatal widths) with the median sagittal plane and between crossbite and non-crossbite sides and second to investigate and compare palatal morphology and shape by mirroring the palatal vault and alveolar processes to assess whether there is any asymmetry between the two palatal halves. Materials and methods Study population To assess the power of the study, a power calculation was conducted using a specific research toolkit (DSS Research, Washington, DC, USA, https://www.dssresearch.com/knowledgecenter/toolkitcalculators/samplesizecalculators.aspx), which indicated that data from 18 participants would yield a confidence level of 95% and a Beta error level of 85% making it sufficient to determine statistically significant differences. Dental casts from 48 patients were randomly selected from a larger pool of subjects seeking orthodontic treatment at the Department of Orthodontics, Faculty of Dentistry, Catania University, Italy; the Department of Orthodontics, Faculty of Dentistry, La Sapienza, Rome University, Italy; and Department of Orthodontics, Faculty of Dentistry, University of Messina, Italy, between January 2015 and May 2016. To be included in the study sample (SS), all patients at the start of the treatment had to have a transverse maxillary deficiency and a crossbite on one side only, with buccal cusps of at least two or more maxillary posterior teeth occluding lingual to buccal cusps of the mandibular teeth, and a mandibular midline shift towards the crossbite site of ≥2 mm at the maximum intercuspal position and not at mouth opening, indicating a functional posterior cross bite (FPXB), as clinically assessed by an experienced orthodontist (ALG). Further inclusion criteria were Class I or edge-to-edge molar relationship, skeletal Class I relationship, pre-puberty cervical vertebral maturation as assessed on lateral cephalograms (CVMS1, CVMS2). The exclusion criteria were maxillary posterior teeth occluding entirely on the lingual side of the mandibular teeth, missing teeth (excluding the third molars) or non-erupted exfoliated primary teeth, craniofacial deformities, systemic diseases, previous orthodontic treatment, anterior crossbite, signs or symptoms of temporomandibular disorder, carious lesions, extensive restoration, or periodontal disease. The SS included 20 girls and 15 boys (mean age 9.2 ± 0.8 years) diagnosed with functional posterior crossbite (Table 1) of which 20 had a functional mandibular shift on the right side, 13 on the left. Table 1. Demography and clinical characteristics of the sample of the study. Sample characteristics Total (n = 70) Study sample (n = 35) Control sample (n = 35) Significance* Mean or n Mean or n Mean or n Mean age (years) 9.3 (±0.9) 9.2 (±0.8) 9.4 (±0.9) NS Sex NS  Male 31 15 16  Female 39 20 19 Skeletal maturity NS  CVMS I 32 14 13  CVMS II 38 21 22 Sample characteristics Total (n = 70) Study sample (n = 35) Control sample (n = 35) Significance* Mean or n Mean or n Mean or n Mean age (years) 9.3 (±0.9) 9.2 (±0.8) 9.4 (±0.9) NS Sex NS  Male 31 15 16  Female 39 20 19 Skeletal maturity NS  CVMS I 32 14 13  CVMS II 38 21 22 *P-value for comparison of group means by t-test or differences in proportion calculated by chi-square test. View Large Table 1. Demography and clinical characteristics of the sample of the study. Sample characteristics Total (n = 70) Study sample (n = 35) Control sample (n = 35) Significance* Mean or n Mean or n Mean or n Mean age (years) 9.3 (±0.9) 9.2 (±0.8) 9.4 (±0.9) NS Sex NS  Male 31 15 16  Female 39 20 19 Skeletal maturity NS  CVMS I 32 14 13  CVMS II 38 21 22 Sample characteristics Total (n = 70) Study sample (n = 35) Control sample (n = 35) Significance* Mean or n Mean or n Mean or n Mean age (years) 9.3 (±0.9) 9.2 (±0.8) 9.4 (±0.9) NS Sex NS  Male 31 15 16  Female 39 20 19 Skeletal maturity NS  CVMS I 32 14 13  CVMS II 38 21 22 *P-value for comparison of group means by t-test or differences in proportion calculated by chi-square test. View Large The control sample (CS) was matched by cervical vertebral maturation to minimize the confounding effect of growth and included 19 girls and 16 boys (mean age 9.4 ± 0.9 years). The inclusion and exclusion criteria were the same as the patient group, plus the absence of functional crossbite (Table 1). Approval for this cross-sectional study was obtained from the local Institutional Review Board, and signed informed consent from the parents of all the subjects was already obtained, prior to starting orthodontic treatment. Each subject received conventional dental impressions using a monophasic polyether impression material (Impregum Penta; ‘3M ESPE’, Seefeld, Germany) with stainless steel impression trays (Hi-Tray Metal; ‘Zhermack SpA’, Rovigo, Italy), which was poured, at most, after 4 hours with type IV stone (Ortostone; Techim Group, Milan, Italy). Then, all the maxillary casts were scanned using the D500 3D scanner (3Shape A/S, Copenhagen, Denmark) according to the manufacturer’s instructions: full arch scan time 90 seconds, 2 resolution cameras of 1.3 megapixels, red laser featuring an accuracy of 10 μm as reported by the manufacture. The 3Shape system has been validated and described previously (12, 13). Each dental cast was scanned from 10 or more angles and then combined and rendered into a 3D stereo-lithographic model by using a specific software (ScanItOrthodontics™ 2015, version 5.6.1.6, ‘3Shape A/S’, Copenhagen, Denmark). After scanning, the stereo-lithographic files were stored. The digital models of the scanned printed models were exported to Geomagic Qualify software (3D Systems, Rock Hill, Washington, DC, USA) to perform a superimposition model and exported to Ortho Analyzer software (3Shape) to measure distances. To analyse the transverse dimensions of the maxillary arch, a median palatal plane (MPP) was traced on digital casts through two landmarks identified along the median palatal raphe (14) (Figure 1). One landmark (point 1) was identified as the point on the median palatal raphe adjacent to the second ruga. The second point (point 2) was identified on the median palatal raphe 1 cm distal to point 1. Figure 1. View largeDownload slide The median palatal plane (MPP) was drawn through two landmarks detected along the median palatal raphe and showed in red. The first landmark identified the point on the median palatal raphe adjacent to the second ruga (Point 1). The second landmark was placed on the median palatal raphe 1 cm distal to the first point (Point 2). D1 and D2 represent respectively the linear distance from the midpoint of the dento-gingival junction of the primary canine and first molar to the MPP. Figure 1. View largeDownload slide The median palatal plane (MPP) was drawn through two landmarks detected along the median palatal raphe and showed in red. The first landmark identified the point on the median palatal raphe adjacent to the second ruga (Point 1). The second landmark was placed on the median palatal raphe 1 cm distal to the first point (Point 2). D1 and D2 represent respectively the linear distance from the midpoint of the dento-gingival junction of the primary canine and first molar to the MPP. After identification of MPP, the following measurements were performed (Figure 1): D1: the distance between the midpoint at the dento-gingival junction of the primary canine from the crossbite and non-crossbite sides compared with the MPP and D2: the distance between the midpoint of the dento-gingival junction of the first molar from the crossbite and non-crossbite sides compared with the MPP. In the CS, measuring the same distances on the right and left palatal halves. To check for crossbite/non-crossbite symmetry, digital casts from each patient were superimposed through a semi-automatic surface-to-surface matching technique, using 3D reverse modelling software (Geomagic Control™ X, version 2017.0.0, ‘3D Systems’, Rock Hill, USA), which also calculated the deviation between the mirrored and un-mirrored 3D palatal models. To define the palate surface of the 3D model to be analysed, a gingival plane had to pass through all the most apical points of the dento-gingival junction of all the teeth (from 1st right molar to 1st left molar, Figure 2A). Figure 2. View largeDownload slide The gingival plane (A) was assessed by linking the most apical point of the dento-gingival junction of all teeth at the palatal tooth face. Then the palatal vault model was created (B), mirrored (C), and roughly superimposed using the MPP plane and its perpendicular plane (D). Then a ‘best-fit’ alignment was done to enhance the superimposition (E) quality. Figure 2. View largeDownload slide The gingival plane (A) was assessed by linking the most apical point of the dento-gingival junction of all teeth at the palatal tooth face. Then the palatal vault model was created (B), mirrored (C), and roughly superimposed using the MPP plane and its perpendicular plane (D). Then a ‘best-fit’ alignment was done to enhance the superimposition (E) quality. The workflow for the superimposition of the palate is described below in four steps. Step 1. Mirroring: Converting the image orientation from right-left, antero-posterior, and infero-superior to left-right, antero-posterior, and infero-superior (Figure 2B–C); Step 2. First registration: Initial manual superimposition of the two models to shorten the time needed for the subsequent automatic superimposition; Thus, pairs of models (the original and the mirrored one of the same patient) were oriented and roughly registered by using the MPP and a line drawn perpendicularly through point 2 of the MPP. (Figure 2D); Step 3. Final registration: Final registration was performed using the ‘Best-fit alignment’ option in the Geomagic Control X software. After defining the reference dataset, the precision of the registration was set to at least 0.3 mm (tolerance type: ‘3D Deviation’), and the number of polygons for surface representation was set to the maximum of 100 000, the corresponding polygons of the selected reference areas were automatically superimposed (Figure 2E); and Step 4. Superimposition and 3D analysis: The distances between corresponding areas of the original maxillary cast and the corresponding mirrored one were compared to obtain colour-coded maps (Figure 3) in which the yellow-to-red fields indicated that the definitive casts were larger than the master model and the turquoise-to-dark blue fields indicated that the definitive casts were smaller than the master model. The tolerance range in green of the 3D deviation analysis was set to ±0.50 mm with a maximum of 2 mm. All the values in this range indicated the matching percentage between the two specular 3D models. Figure 3. View largeDownload slide 3D deviation analysis between the two specular palatal models. RGB coloured scale bar (millimetres) is reported on the right: the top (red) and the bottom (blue) of the scale indicate the maximum positive and negative deviations. Green indicates the tolerance range. The image shows palatal (A) and lateral (B–C) views. As shown, mismatching is mainly localized in the dento-alveolar process area. Figure 3. View largeDownload slide 3D deviation analysis between the two specular palatal models. RGB coloured scale bar (millimetres) is reported on the right: the top (red) and the bottom (blue) of the scale indicate the maximum positive and negative deviations. Green indicates the tolerance range. The image shows palatal (A) and lateral (B–C) views. As shown, mismatching is mainly localized in the dento-alveolar process area. To minimize random error and systematic errors, all measurements were performed by a single examiner, with 25 years orthodontic experience (RL). The examiner measured only five models each day to avoid fatigue. The models were measured in blind sequence. Statistical analysis Descriptive statistics were carried out to analyse the demographic and clinical characteristics of the SS and CS groups. The Student’s t-test and chi-square test compared numerical (age) and categorical (gender, skeletal maturity) characteristics between SS and CS. All the measurements were recorded on Microsoft Excell® spreadsheet (Microsoft, Redmond, Washington, DC, USA) and analysed using SPSS® version 24 Statistics software (IBM Corporation, 1 New Orchard Road, Armonk, New York, USA) with P-value < 0.05 considered statistically significant. The Kolmogorov–Smirnov test was used to test the normality of the data. Data matching the two hemi-palatal structures and linear measurements were normally distributed, while data of the two semi-palatal volumes showed no homogeneous variance. Parametric tests were used to evaluate and compare measurements. Student’s t-test assessed width differences compared with MPP (D1, D2) between the crossbite and non-crossbite sides of the SS and between the right and left sides of the CS. The matching (symmetry) percentages of the two semi-palatal volumes were investigated in both groups by independent Student’s t-test. The Wilcoxon signed-rank test was used to assess differences between the two hemi-palatal volumes in both SS and control group. Furthermore, to assess intra-rater repeatability, 10 digital casts from the SS and CS were measured again (T2), by the same operator after a washout period of 4 weeks. The Intraclass Correlation Coefficient (ICC) was applied between the two measurements to assess intra-examiner reliability. The method error was also assessed using Dahlberg’s formula. Statistical data analysis was performed using SPSS Statistics software (IBM Corporation, 1 New Orchard Road, Armonk, New York, USA). The level of significance was set at P < 0.05. Results The descriptive statistics of the SS and CS are reported in Table 1. Any statistically significant differences were obtained by comparing the two groups. The examiner’s ICC values, widths, and matchings showed that the measurement sets correlated highly (ICC values ranged from 90.7 to 99.0%). The method error was 91.97 mm3 for volumetric measurements, 0.17 mm for D1 measurements, 0.14 mm for D2 measurements, and 1.23% for hemi-palate matching. 2D measurements In patients with posterior crossbite, the palatal width measured at the primary canine was around 2 mm narrower on the crossbite side (D1-CB) and 1 mm at the non-crossbite (D1-non-CB) side compared with controls; D1-CB was found to be 1 mm narrower than D1-non-CB (P < 0.05) (Table 2). No significant differences were found between the crossbite side and non-crossbite side. (P > 0.05). The first molar width respect to MPP on the non-crossbite side (D2-non-CB) was around 1 mm smaller than the same measurements obtained from the CS (D2-Side A, D2-Side B); on the other hand, an even narrower distance was recorded on the crossbite side (D2-CB) because the difference compared with the CS was more than 2.5 mm. A statistically significant difference was obtained by comparing D2-non-CB and D2-CB (P < 0.05; Table 2). Table 2. Inferential statistics for observation and control groups. Comparison between linear semi-palatal measurements. Total D1 (mm) Significance D2 (mm) Significance Study sample FPXB side 35 11.42 (±1.32) * 13.55 ± (1.32) * No FPXB side 35 12.37 (±1.15) 15.07 ± (1.40) Control sample Side A (right) 35 13.71 (±1.48) NS 16.19 ± (1.18) NS Side B (left) 35 13.64 (±1.47) 16.36 ± (1.27) Total D1 (mm) Significance D2 (mm) Significance Study sample FPXB side 35 11.42 (±1.32) * 13.55 ± (1.32) * No FPXB side 35 12.37 (±1.15) 15.07 ± (1.40) Control sample Side A (right) 35 13.71 (±1.48) NS 16.19 ± (1.18) NS Side B (left) 35 13.64 (±1.47) 16.36 ± (1.27) Values based on paired Student’s t-tests. D1 = distance between mild palate plane and the centre of dento-gingival junctions of primary canine. D2 = distance between mild palate plane and the centre of dento-gingival junctions of first molar. NS = non significant. *P < 0.05. View Large Table 2. Inferential statistics for observation and control groups. Comparison between linear semi-palatal measurements. Total D1 (mm) Significance D2 (mm) Significance Study sample FPXB side 35 11.42 (±1.32) * 13.55 ± (1.32) * No FPXB side 35 12.37 (±1.15) 15.07 ± (1.40) Control sample Side A (right) 35 13.71 (±1.48) NS 16.19 ± (1.18) NS Side B (left) 35 13.64 (±1.47) 16.36 ± (1.27) Total D1 (mm) Significance D2 (mm) Significance Study sample FPXB side 35 11.42 (±1.32) * 13.55 ± (1.32) * No FPXB side 35 12.37 (±1.15) 15.07 ± (1.40) Control sample Side A (right) 35 13.71 (±1.48) NS 16.19 ± (1.18) NS Side B (left) 35 13.64 (±1.47) 16.36 ± (1.27) Values based on paired Student’s t-tests. D1 = distance between mild palate plane and the centre of dento-gingival junctions of primary canine. D2 = distance between mild palate plane and the centre of dento-gingival junctions of first molar. NS = non significant. *P < 0.05. View Large In the control group, the right and left side widths measured at the midline showed perfect symmetry at the canine and molar levels. 3D measurements The colour map analysis of the superimposition of the posterior crossbite models was an intense blue in the buccal area of the superimposed models on one side and intense red on the other. The palatal vault demonstrated a prevalence of green, which indicates insignificant differences. Palatal asymmetry was confined to the lower part of the palate at the alveolar processes level as shown in Figure 3. A prevalence of green at the palatal vault and alveolar process was observed in the CS group, indicating a higher matching percentage (Table 3). Table 3. Inferential statistics for observation and control groups. Comparison between emi-volumes measurements. Total Mean volume (mm3) Minimum Maximum Quartile Significance 25° 50° 75° Study sample FPXB side 35 3226.42 (±619.81) 2418.16 5046.49 2723.29 3038.86 3376.92 * No FPXB side 35 3428.92 (±653.75) 2368.77 5225.39 2987.36 3271.49 3690.1 Control sample Side A (right) 35 4133.74 (±913.46) 2923.38 6455.8 3441.06 3931.24 4716.78 NS Side B (left) 35 4122.60 (±904.54) 2911.85 6395.81 3432.34 3913.22 4734.84 Total Mean volume (mm3) Minimum Maximum Quartile Significance 25° 50° 75° Study sample FPXB side 35 3226.42 (±619.81) 2418.16 5046.49 2723.29 3038.86 3376.92 * No FPXB side 35 3428.92 (±653.75) 2368.77 5225.39 2987.36 3271.49 3690.1 Control sample Side A (right) 35 4133.74 (±913.46) 2923.38 6455.8 3441.06 3931.24 4716.78 NS Side B (left) 35 4122.60 (±904.54) 2911.85 6395.81 3432.34 3913.22 4734.84 Values based on Wilcoxon signed-rank test. NS = non significant. *P < 0.05. View Large Table 3. Inferential statistics for observation and control groups. Comparison between emi-volumes measurements. Total Mean volume (mm3) Minimum Maximum Quartile Significance 25° 50° 75° Study sample FPXB side 35 3226.42 (±619.81) 2418.16 5046.49 2723.29 3038.86 3376.92 * No FPXB side 35 3428.92 (±653.75) 2368.77 5225.39 2987.36 3271.49 3690.1 Control sample Side A (right) 35 4133.74 (±913.46) 2923.38 6455.8 3441.06 3931.24 4716.78 NS Side B (left) 35 4122.60 (±904.54) 2911.85 6395.81 3432.34 3913.22 4734.84 Total Mean volume (mm3) Minimum Maximum Quartile Significance 25° 50° 75° Study sample FPXB side 35 3226.42 (±619.81) 2418.16 5046.49 2723.29 3038.86 3376.92 * No FPXB side 35 3428.92 (±653.75) 2368.77 5225.39 2987.36 3271.49 3690.1 Control sample Side A (right) 35 4133.74 (±913.46) 2923.38 6455.8 3441.06 3931.24 4716.78 NS Side B (left) 35 4122.60 (±904.54) 2911.85 6395.81 3432.34 3913.22 4734.84 Values based on Wilcoxon signed-rank test. NS = non significant. *P < 0.05. View Large There were statistically significant (P < 0.05; Table 4) differences in the percentage of palatal volume matching: 83.36% in SS group and 92.82% in the CS group. Table 4. Comparison of emi-palate volumes matching between observation and control group. Total Matching (mean; %) SD Mean difference (%) 95% Confidence interval of the difference Significance Upper Lower Study sample 35 83.36 3.68 9.46 11 7.92 * Control sample 35 92.82 2.66 Total Matching (mean; %) SD Mean difference (%) 95% Confidence interval of the difference Significance Upper Lower Study sample 35 83.36 3.68 9.46 11 7.92 * Control sample 35 92.82 2.66 Values based on independent Student’s t-test. NS = non significant. *P < 0.05. View Large Table 4. Comparison of emi-palate volumes matching between observation and control group. Total Matching (mean; %) SD Mean difference (%) 95% Confidence interval of the difference Significance Upper Lower Study sample 35 83.36 3.68 9.46 11 7.92 * Control sample 35 92.82 2.66 Total Matching (mean; %) SD Mean difference (%) 95% Confidence interval of the difference Significance Upper Lower Study sample 35 83.36 3.68 9.46 11 7.92 * Control sample 35 92.82 2.66 Values based on independent Student’s t-test. NS = non significant. *P < 0.05. View Large Discussion Posterior crossbite is a frequent malocclusion that may develop and improve at any point between the eruption of the deciduous teeth to the eruption of the permanent teeth (15). It may be due to skeletal, soft tissue, dental, or respiratory factors or develop as the result of oral habits (15). Among treatment options, widening the upper teeth, arch, or palate is one of the most frequent clinical approaches (16, 17). Knowing whether there is a symmetric or asymmetric contraction of the palate and upper arch in patients with functional posterior crossbite and the chance of identifying morphological palate characteristics may be helpful for the appropriate treatment of this condition. The objective of this study was to use new digital technologies to see whether there is symmetrical or asymmetrical contraction of the palate in FPXB patients because the assumption that there is a mild bilateral contraction of the entire palate in functional crossbite has been recently questioned (8–10), in favour of a monolateral contraction. In our study, the palatal size and morphology of functional crossbite patients were evaluated using 3D laser scans of digital casts by surface-based superimposition because assessing size and shape using conventional 2D dental casts also raises the important issue of reducing a 3D object to a 2D image (18). According to this reverse engineering, each virtual palate can be mirrored at an arbitrary point. This procedure, also designated as 3D surface-to-surfacematching, provides morphological differences between the two semipalatalhalves, the3D differences of the superimposed models are translated into colour codes, which represent the distances between corresponding points (18). In two previous studies (8, 9), palatal size was obtained by measuring inter-canine and inter-molar linear distances compared with the midpalatal suture of the maxilla. Findings from these investigations demonstrated upper dental arch asymmetry in patients with unilateral crossbite, the crossbite side being narrower than the non-crossbite side. However, these results could be biased due to tooth inclination and the poor reliability of midline allocation based on dental casts (19). These issues were overcome by another study (10), where the palate symmetry was evaluated in terms of palatal shell overlapping, by mirroring the palatal vault of children in primary dentition affected by posterior crossbite (10). So, the issue of palatal symmetry or asymmetry in unilateral crossbite is not clear. So, with 3D technology, this study analysed the palatal morphology of mixed dentition patients with posterior crossbite and precisely quantified and detected areas of asymmetry using the mirroring technique. This technique was carried out because shape analysis has become of increasing interest to the medical image analysis community, due to its potential for precisely locating and quantifying morphological changes between healthy and pathological structures (20). The results of our study demonstrated a mild asymmetric palate of the upper jaw in patients with functional posterior crossbite. We recorded palate widths on the crossbite side about 1 mm narrower at the molar and primary canine levels compared with the non-crossbite side, and these results agree with previous findings (9). Furthermore, these width differences, although not severe, were statistically significant. Also, the matching per cent of palatal shell overlapping by mirroring palates was different comparing the study group to controls. The matching per cent was 79.5% in the SS, compared with the CS of 88%. Our findings are hardly comparable with the only previous study carried out with the same digital technique investigating palatal symmetry in primary dentition children with functional crossbite (10), and our sample was intermediate–late dentition patients. However, in functional posterior crossbite patients, there has been described a worsening of facial asymmetry in the middle of the face at both the early/intermediate and late mixed dentition phases (21); thus, it could be speculated that the same could happen for the upper dental arch explaining the difference in results from our study compared with the previous one (10). Interestingly, in our crossbite patient sample, palatal asymmetry or mismatching of the palatal vault was mostly localized at the alveolar bone level, as revealed by the mirroring technique and colour map. In unilateral crossbite patients, it can be assumed that there is a bilateral symmetric contraction of the palatal vault and an asymmetric contraction of the upper arch alveolar process. According to our results, it can be hypothesized that the bending of the alveolar structures and buccal tipping of the posterior maxillary teeth, as a consequence of the functional shift of the mandible, could have a role in determining the sectional constriction of the palate as our sample showed. This could somehow explain the success rate of the early treatment of this malocclusion with selective grinding or occlusal adjustment of the primary dentition (22), which with or without the addition of a removable upper expansion device seems to be effective in preventing posterior crossbite in primary dentition from being perpetuated to the mixed and permanent dentitions (14). This eliminates occlusal interference as an opportunity to restore form and function. Nevertheless, since the differences in palatal arch sizes and morphology between crossbite and non-crossbite sides are mild and not severe, asymmetric expansion of the palatal arch does not seem to be clinically justified. Furthermore, the use of appliances that expand the dento-alveolar complex as well as selective adjustment and occlusal guiding are corroborated at least for the early intervention of functional posterior crossbite (14). However, this study has some limitations. We used a second generation of superimposition approaches based on ‘fine matching’. The effect of outliers is reduced, while accuracy and reliability markedly improves when serial 3D models are superimposed (11). This new technique reduces the errors associated with manually selecting superimposition points (11). It should be acknowledged that very recently, a novel method for superimposing digital maxillary 3D models has been proposed (11), which combines ‘raw matching’, ‘fine matching’, and ‘deformation analysis’, and has proved robust in evaluating palatal changes. There are two more issues with this study since it was only carried out on mixed dentition, while a sample of serial models taken with a moderate interval could have been of clinical aid in establishing the exact period of bending of the alveolar processes and therefore treatment planning. Moreover, teeth inclination differences between the study group and controls for the crossbite side and non-crossbite side were not assessed in our study, which was designed to investigate palate morphology, but they could have confirmed our results. Conclusions Semi-palatal widths on the crossbite side are smaller than those on the non-crossbite side and in controls. Palatal volume matching percentages are smaller in patients with functional crossbite (83.36%) than in controls (92.82%) as assessed by the mirroring technique. In patients with functional crossbite, the mismatching is observed mainly at the alveolar processes level. 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Journal

The European Journal of Orthodontics – Oxford University Press

Published: Sep 28, 2018

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