This study aimed to investigate cheiloscopic patterns among monozygotic twins (MT), non-twin siblings (NTS) and unrelated individuals (UI). The sample consisted of 20 pairs of monozygotic twins (G1), 20 pairs of non-twin siblings (G2) and 20 pairs of unrelated individuals (G3). Lip thickness, commissures and grooves were evaluated and the latter were classified as: I - clear-cut vertical grooves; I’ - incomplete vertical grooves; II - branched grooves; III - intersecting; IV - reticular grooves and V - undetermined, in 8 labial regions (sub-quadrants). The data were analyzed using descriptive and inferential statistics, with a 5% significance level. Concordance Correlation Coefficient (CCC) and Kappa coefficient, with a 95% confidence interval, were employed to check for agreement rates between G1, G2 and G3 pairs. There was a weak correlation for lip thickness (<0.90) in the total group, with higher values in G1 (CCC from 0.25 to 0.83 and from 0.34 to 0.86, upper and lower lips, respectively), followed by G2 (CCC from -0.03 to 0.70 and from -0.21 to 0.62, upper and lower lips, respectively) and G3 (CCC from -0.25 to 0.56 and from -0.38 to 0.34, upper and lower lips, respectively). With regard to labial commissures, Kappa statistic values were found to be 1.00 for G1, 0.45 for G2 and -0.24 for G3. As for the main groove pattern by sub-quadrant, Kappa values ranged from 0.48 to 0.87 for G1, from 0.17 to 0.59 for G2, and from -0.18 to 0.19 for G3. Monozygotic twins presented a relevant percentage of cheiloscopic agreements. Similarities were also found among NTS, while UI showed greater differences compared to their pairs, highlighting the influence of hereditary relationships on inherited cheiloscopic features.
forensic sciences; forensic anthropology; forensic dentistry; lip; twins; monozygotic.