By Dr Botond Simon DMD, Dr George Freedman BSc, DDS, DiplABAD, and János Vág, DMD, PhD, Med Habil
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 mirror image 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 on the fit between twin siblings’ scans.
Compared to DNA analysis, the strength of the intraoral ante-mortem scan-based identification method is growing due to the rapid spread of intraoral scanning. However, the limitation is that dentists may focus on quadrant rehabilitation, limiting the scan to only one palate side. Similarly, a severe accident may damage the half palate. Although the palatal side-to-side asymmetry is relatively small,13 the total geometry and surface morphology may differ between sides. Therefore, the study’s secondary aim was to assess the fit between the mirrored scan and the original scan of the same individuals.
References available upon request.
To read the full article, click here or refer to Dental Asia November/December 2023 issue.