Primary tooth size asymmetry in twins and singletons

Tooth shape asymmetry in post-canine dentition: Evidence-based morphometric insights

Background

This study investigates the potential existence of asymmetry in the shape of tooth and location of landmarks of tooth anatomy and its variation between sexes.

Methods

Our study evaluated dental symmetry in 160 patients aged 13-20 years, focusing on post-canine dentition. Using 3D geometric morphometrics, the research evaluated the variations in the anatomical landmarks between left and right side.

Results

Analysis of the landmarks revealed that 20-30 % of the principal components explained 80 % of the shape variation. No significant difference in centroid size was found between sexes, but significant shape differences were noted in all teeth except the 3-cusp type mandibular second premolar. Asymmetry was more in the premolar segment in the maxillary arch and in the two-cusp type of mandibular second premolar and the mandibular first molar in the mandibular arch.

Conclusion

The research underscores the evolutionary advantage of bilateral symmetry and the presence of fluctuating asymmetry, possibly linked to genetic or environmental stressors. It emphasizes the importance of understanding dental asymmetry for effective treatment planning and diagnosis, in restorative dentistry and orthodontics.

Sex-specific effects of environmental temperature during gestation on fluctuating asymmetry in deciduous teeth

OBJECTIVES

External environmental heat exposure during gestation impacts the physiology of human development in utero, but evidence for these impacts has not yet been explored in dentition. We examined deciduous teeth for fluctuating asymmetry (FA), a measure of developmental instability, together with gestational environmental temperature data drawn from historical weather statistics.

MATERIALS AND METHODS

We measured dental casts from the longitudinal Burlington Growth Study, representing 172 participants (ages 3-6 years) with health records. FA was calculated from crown dimensions and intercuspal distances that develop during gestation. Multiple regression separated by sex (nfemale = 81) examined the effects of mean temperatures in each trimester, controlling for birth year.

RESULTS

In females, increased temperatures during the first trimester are significantly associated with an increase in FA (p = 0.03), specifically during the second and third prenatal months (p = 0.03). There is no relationship between temperature and FA for either sex in the second or third trimesters, when enamel is formed.

DISCUSSION

Dental instability may be sensitive to temperature in the first trimester in females during the scaffolding of crown shape and size in the earliest stages of tooth formation. Sexual dimorphism in growth investment strategies may explain the differences in results between males and females. Using enduring dental characteristics, these results advance our understanding of the effects of temperature on fetal physiology within a discrete period.

Facial asymmetry and chewing sides in twins

OBJECTIVE

To resolve how the preferred chewing side (PCS) affects facial asymmetry in twins, whether there are differences between monozygotic (MZ) and dizygotic (DZ) twins, and whether the twins with PCS have more asymmetric faces compared to symmetrically chewing twins.

MATERIAL AND METHODS

The study included 106 Lithuanian twin pairs of the same sex, 59 MZ and 47 DZ pairs. The data were analysed from facial 3D images and manually added landmarks. 3D images were analysed by Rapidform2006 software and statistical analyses were done by using the R software environment version 4.1.0.

RESULTS

The contralateral effect of PCS and larger chin side was dominant among right and non-right side chewing twins. Being female increased the whole face symmetry.

CONCLUSION

The volume of the chin becomes larger on the side opposite to the twins' habitual chewing side. As the results are quite similar in both twin types, functional factors are more prominent than heredity.

Relations of laterality and chewing sidedness in twins

OBJECTIVES

To study, whether there are associations between chewing side preference and other lateralities, whether there is a genetic origin for preferred chewing side (PCS), relations to sex, birth order and orthodontic treatment.

MATERIALS AND METHODS

The study included 113 twin pairs, 57 pairs monozygotic, 47 pairs same sex dizygotic and 9 pairs of opposite sex. The lateralities of preferred chewing side, footedness and eyedness were assessed by functional tests and handedness was checked by asking.

RESULTS

Right-handed, -footed and -eyed as separated groups, and true-right sided (combined), were evenly distributed by preferred chewing side. By contrast, left-handed, -footed, -eyed and non-right sided used more left or both sides when chewing. Birth order affected preferred chewing side among monozygotic: the first-born twin was more likely to have the preferred chewing side on the non-right, whereas second-born twins used right side. Gender, zygosity and orthodontic treatment were not statistically significant factors.

LIMITATIONS

Examination of chewing sidedness could have been done in several different ways to provide a definite result. Sample size of opposite sex twins was very small.

CONCLUSIONS

Preferred chewing side generally seemed to follow the side where other lateralities occur; however, monozygotic twins seemed to be more receptive to it. True-right sided were more evenly distributed than non-right sided by the preferred chewing side.