Dental Asia November/December 2023

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CLINICAL FEATURE Digital palate analysis to verify the mirror twin phenomenon By Dr Botond Simon DMD, Dr George Freedman BSc, DDS, DiplABAD, and János Vág, DMD, PhD, Med Habil INTRODUCTION Mirror-image twin is a unique phenomenon where the features on one identical, or monozygotic, twin’s left side are mirrored on the other twin’s right side. For example, one twin may have a birthmark on their left cheek, while the other twin has a birthmark in the exact location but on the right cheek. The prevalence of mirror twins can only be estimated from indirect evidence. 1,2 Approximately 25% of monozygotic twins (n=75) in the US, 3 and 23% of monozygotic twins (n=375) in Belgium, 4 had discordant handedness, where one sibling is righthanded and the other is left-handed. However, handedness is determined mainly by the non-shared environment with fewer genetic influences. While mirror twins share identical DNA, they may have distinct personalities, interests and abilities, and they may also experience different health issues throughout their lives. Numerous studies have reported mirrorimage dental anomalies in twins: aplasia, 5 supernumerary teeth, 6 or dental fusion. 7 Contralateral craniofacial lesions such as cleft lip and palate, 8 hemifacial microsomia, 8 and unilateral condylar hyperplasia have been reported. 9 The pathological phenomena suggest the importance of mirror-imaging. 2 Recently, it has been demonstrated that palatal geometry measured on the intraoral scan can distinguish strangers and even identical twins with moderate certainty, facilitating human and victim identification. 10 After selecting possible matches, an additional superimposition of the palatal scan can confirm the identity. 11,12 However, recognising a twin relationship might be concealed by the opposite laterality of siblings. Therefore, this study’s primary aim was to assess the effect of sagittal mirroring All three scans of the 174 subjects, 522 on the fit between twin siblings’ scans. total scans, were cropped, and teeth were removed in the GOM Inspect Suite software. Compared to DNA analysis, the strength The cropped palatal model was duplicated, of the intraoral ante-mortem scan-based and one was mirrored in the y-axis, or the identification method is growing due to sagittal plane (Figs. 1A and B). The palatal the rapid spread of intraoral scanning. scans were aligned by the best-fit function However, the limitation is that dentists may using the iterative closest point algorithm. 17 focus on quadrant rehabilitation, limiting The mean absolute distance between aligned the scan to only one palate side. Similarly, a scans’ surfaces was calculated by dividing the severe accident may damage the half palate. integrated absolute distance by the area of Although the palatal side-to-side asymmetry the valid distance (Fig. 1C). is relatively small, 13 the total geometry and surface morphology may differ between sides. Assessment of twin mirroring: Betweensiblings comparison Therefore, the study’s secondary aim was to assess the fit between the mirrored scan and The three scans of one sibling were the original scan of the same individuals. superimposed with three scans of the other sibling in the original group, for nine MATERIAL AND METHODS superimpositions per subject. Additionally, Sample collection and preparation the three original scans of one sibling were A total of 174 participants were recruited superimposed with three mirrored scans of through the National Twin Registry: 61 the other sibling in the mirror group, for nine monozygotic twin pairs and 26 same-sex superimpositions per twin pair. A total of dizygotic twin pairs. 14,15 All participants agreed 2,610 measurements were made. to study participation by written informed consent and ethical approval 36699-2/2018/ Assessment of asymmetry: Between-replicates EKU was obtained. Zygosity was determined comparison using questionnaires. 16 Evidence of previous The original three scans within a subject were orthodontic treatment was also recorded. superimposed on each other in the original Each participant’s palate was scanned three group, for three superimpositions. The three times using a Planmeca Emerald intraoral mirrored scans were superimposed with a scanner, version number Romexis 5.2.1, as non-mirrored replicate in the mirror group, previously described. 11 for three superimpositions. Fig. 1A-C: The original scan (A) was mirrored on the y-axis (B). The complete surface comparison is shown after the best-fit alignment of the two scans (original vs mirrored) (C). The table indicates the integrated absolute distance (977.08mm 3 ) and the area of the valid distance (1,622.60mm 2 ). Their ratio makes up the mean absolute distance (0.602mm) 36 DENTAL ASIA NOVEMBER / DECEMBER <strong>2023</strong>
CLINICAL FEATURE Statistics The Wilcoxon test was used to compare the original and mirror mean absolute distance in the between-siblings and between-replicates comparisons. The Mann-Whitney U test was used to compare the monozygotic with the dizygotic twins. The number of twin pairs in which the difference between the scans increased following mirroring was tabulated, as well as the number of pairs in which the difference decreased. Then the ratio of increased to decreased was calculated. The proportion in monozygotic and dizygotic was compared by Chi-square statistics. All analyses were made by IBM SPSS Statistics, Version 27. A p-value less than 0.05 was considered statistically significant. The data in the text is given in the median and interquartile range. RESULTS Assessment of twin mirroring: Betweensiblings comparison The mean absolute distance between-siblings increased significantly (p
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Page 4 and 5: CONTENTS TRENDS 11 A growing region
Page 6 and 7: EDITOR’S NOTE Something in the Ai
Page 8 and 9: DENTAL UPDATES Straumann Group acqu
Page 10 and 11: DENTAL UPDATES Mirco Stiehle and Mi
Page 12 and 13: DENTAL UPDATES Chamlion partners wi
Page 14 and 15: TRENDS successful proof-of-concept
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Page 23 and 24: UNDER THE SPOTLIGHT A second artifi
Page 25 and 26: DENTAL PROFILE Furthermore, with th
Page 27 and 28: DENTAL PROFILE “Our main priority
Page 29 and 30: DENTAL PROFILE singular platform fo
Page 31 and 32: CLINICAL FEATURE Using a 3D-printer
Page 33 and 34: CLINICAL FEATURE Quadrant Dentistry
Page 35 and 36: CLINICAL FEATURE structurally compr
Page 37: CLINICAL FEATURE inclines, both in
Page 41 and 42: USER REPORT Taking the first step i
Page 43 and 44: USER REPORT The IOS price war: Adva
Page 45 and 46: USER REPORT Rubber dam isolation By
Page 47 and 48: BEHIND THE SCENES Communicating tow
Page 49 and 50: BEHIND THE SCENES Pressure or vacuu
Page 51 and 52: invis is a comprehensive approach t
Page 53 and 54: Dr Dagnelid (left) will be speaking
Page 55 and 56: IN DEPTH WITH In addition to the pa
Page 57 and 58: SCAN TO REGISTER THE LEADING DENTAL
Page 59 and 60: PRODUCT HIGHLIGHTS Pac-Dent introdu
Page 61 and 62: PRODUCT HIGHLIGHTS ASI Dental Speci
Page 63 and 64: DUAL CURING CORE & RESIN CEMENT 3 I
Page 65 and 66: EVENTS CALENDAR 2023 NOVEMBER 9 - 1
Page 67: INSIGHTS P A L M A D E M A L L O R

Dental Asia November/December 2023

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