Exploring directional and fluctuating asymmetry in the human palate during growth

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.

The Virtual Database of the Documented Human Osteological Collection (DHOC) of the Certosa Cemetery of Bologna (Italy, 19th-20th Century)

This article aims to introduce a new virtual database of skeletal human remains from the Documented Human Osteological Collection (DHOC) of the Certosa Cemetery of Bologna (Emilia Romagna, northern Italy) housed at the University of Bologna. The Virtual DHOC of the Certosa Cemetery of Bologna (VirtualDHOC) is stored in the publicly accessible 3D data repository MorphoSource, and consists of 3D models or micro-Computer Tomography scans of skeletal elements of a subsample of the 425 individuals. These skeletons, mostly complete and well-preserved, pertain to individuals of different ages, ranging from fetuses/newborns to 91 years old, for which the sex is known, who died in the city of Bologna between 1898 and 1944. This collection represents an important scientific resource for the study of human skeletal remains and to test methods and techniques in the field of bioarchaeology, forensics, and paleoanthropology. The digitization of a comprehensive database of 3D scans and 3D bones is an ongoing project that will implement the Virtual DHOC of the Certosa Cemetery of Bologna over the next few years. The Virtual DHOC of the Certosa Cemetery of Bologna aims to share the data contained therein with other researchers, contributing to the dissemination of knowledge and the promotion of scientific research in anthropology, while also ensuring the virtual preservation and accessibility of this collection for future generations. This simultaneously responds to various ethical concerns and best practices about the treatment and management of human skeletal remains.

Influence of nasal septum deviation on fluctuating asymmetries of the nasomaxillary complex: A cross-sectional study

An important parameter in diagnostic analysis and treatment planning of different biological areas is facial symmetry, and several etiological factors have been attributed to skeletal facial asymmetry. Although causality cannot be determined, previous studies have reported a relationship between the anatomical deviation of the nasal septum and facial development. Diagnosis is critical for patients in growth stages due to the association between nasal septum deviation (NSD) and abnormal growth of the nasomaxillary complex. To understand this relationship, this study aimed to investigate the influence of nasal septum deviation on fluctuating asymmetries (FA) of the nasomaxillary complex at different stages of skeletal maturation. Another goal was to determine whether an association exists between the degrees of septal deviation severity and asymmetry of the nasomaxillary complex. This was a retrospective, cross-sectional observational study comprising 60 selected cone-beam computed tomography (CBCT) scans that were divided into four groups (n = 15) according to the degree of septal deviation and skeletal maturation: mild deviation (MD; <10°), moderate to severe deviation (MSD; ≥10°), early group (EG), and late group (LG). The angle and area of deviation were measured for the greatest NSD, and a geometric morphometric approach was used to evaluate the nasal septum (NS) shape. The morphology of the nasomaxillary complex and the presence of fluctuating asymmetries were evaluated using 23 two-dimensional landmarks on the nasomaxillary complex (nasal, lateral, and palatal regions) with Procrustes ANOVA and Mann-Whitney test. Additionally, Spearman's correlation and multivariate regression were used to correlate the NSD with asymmetries in these regions. No significant differences were observed in the Procrustes FA scores of the nasomaxillary complex between the MD-EG × MSD-EG and MD-LG × MSD-LG (p > 0.05). However, the results of the multivariate regression revealed more specific aspects of asymmetry (asymmetry component), there was a positive correlation between the NSD angle and the palatal regions (p = 0.035 and p = 0.047, middle and posterior, respectively), and the nasal septum shape and anterior palatal regions (p = 0.039). The nasal and lateral regions did not correlate with the NSD angle in the multivariate regression analysis (p > 0.05). The results of this study indicate that there were no significant differences in the fluctuating asymmetry of the nasomaxillary complex between the mild and moderate to severe nasal septum deviation groups, in both early and late skeletal maturation stages. However, a positive correlation was observed in the degree of nasal septum deviation angle and asymmetry components of the middle and posterior palatal regions, likewise between the nasal septum shape and asymmetry components of the anterior palatal region. The diagnosis of nasal septum deviation by both physicians and dentists is important, as a relationship was observed with fluctuating asymmetry component of the palatal region. This information can guide the decision of the treatment planning for these individuals, and should be considered, especially in cases of severe septum deviation, due to the great anatomical proximity of these structures.

Correlations of palatal surface area with anthropometric dimensions of the head and face

Purpose

Saliva distribution over the palatal surface plays an important role in the perception of dry mouth. It is envisaged that non-invasive estimation of the palatal surface area by anthropometric measurements of the head and face can be useful in the assessment of oral dryness. For this purpose, the relationship between the palatal surface area and anthropometric measurements of the head and face was investigated.

Methods

The palatal surface was measured in 51 healthy volunteers using an intra-oral scanner. The distances between anthropometric landmarks of the head and face were determined using an anatomical sliding caliper. Correlations between the palatal surface area and the anthropometric landmarks were investigated.

Results

The median palatal surface area for the total study population was found to be 2120.6 mm². Virtually, all anthropometric measurements showed significant differences between females and males. Various head and face measurements had a significant correlation with the palatal surface area. However, these correlations disappeared when the participants were stratified based on their sex, with the exception of mandibular length and palatal width in females.

Conclusion

The surface area of the palate correlates with nearly all anthropometric measurements of the head and face included in this study. Yet, the clinical applicability seems limited to females.

Formal models for the study of the relationship between fluctuating asymmetry and fitness in humans

OBJECTIVES

To evaluate three of the main verbal models that have been proposed to explain the relationship between fluctuating asymmetry and fitness in humans: the "good genes," the "good development," and the "growth" hypotheses.

MATERIALS AND METHODS

A formal model was generated for each verbal model following three steps. First, based on the literature, a theoretical causal model and the theoretical object of inquiry were outlined. Second, an empirical causal model and the targets of inference were defined using observational data of facial asymmetries and life-history traits related to fitness. Third, generalized linear models and causal inference were used as the estimation strategy.

RESULTS

The results suggest that the theoretical and empirical assumptions of the "good genes" hypothesis should be reformulated. The results were compatible with most of the empirical assumptions of "the good development" hypothesis but suggest that further discussion of its theoretical assumptions is needed. The results were less informative about the "growth" hypothesis, both theoretically and empirically. There was a positive association between facial fluctuating asymmetry and the number of offspring that was not compatible with any of the empirical causal models evaluated.

CONCLUSIONS

Although the three hypotheses focus on different aspects of the link between asymmetry and fitness, their overlap opens the possibility of a unified theory on the subject. The results of this study make explicit which assumptions need to be updated and discussed, facilitating the advancement of this area of research. Overall, this study elucidates the potential benefit of using formal models for theory revision and development.

Direct evidence that late Neanderthal occupation precedes a technological shift in southwestern Italy

OBJECTIVES

During the middle-to-upper Paleolithic transition (50,000 and 40,000 years ago), interaction between Neanderthals and Homo sapiens varied across Europe. In southern Italy, the association between Homo sapiens fossils and non-Mousterian material culture, as well as the mode and tempo of Neanderthal demise, are still vividly debated. In this research, we focus on the study of two human teeth by using 3D geometric morphometric approaches for a reliable taxonomical attribution as well as obtaining new radiometric dates on the archeological sequence.

MATERIAL AND METHODS

This work presents two lower deciduous molars uncovered at Roccia San Sebastiano (Mondragone-Caserta, Italy), stratigraphically associated with Mousterian (RSS1) and Uluzzian (RSS2) artifacts. To obtain a probabilistic attribution of the two RSS teeth to each reference taxa group composed of Neanderthals and Homo sapiens, we performed and compared the performance of three supervised learning algorithms (flexible discriminant analysis, multiadaptive regression splines, and random forest) on both crown and cervical outlines obtained by virtual morphometric methods.

RESULTS

We show that RSS1, whose Mousterian context appears more recent than 44,800-44,230 cal BP, can be attributed to a Neanderthal, while RSS2, found in an Uluzzian context that we dated to 42,640-42,380 cal BP, is attributed to Homo sapiens.

DISCUSSION

This site yields the most recent direct evidence for a Neanderthal presence in southern Italy and confirms a later shift to upper Paleolithic technology in southwestern Italy compared to the earliest Uluzzian evidence at Grotta del Cavallo (Puglia, Italy).

Exploring directional and fluctuating asymmetry in the human palate during growth

Objectives

Palate morphology is constantly changing throughout an individual's lifespan, yet its asymmetry during growth is still little understood. In this research, we focus on the study of palate morphology by using 3D geometric morphometric approaches to observe changes at different stages of life, and to quantify the impact of directional and fluctuating asymmetry on different areas at different growth stages.

Materials and Methods

The sample consists of 183 individuals (1–72 years) from two identified human skeletal collections of 19th and early 20th Century Italian contexts. A 3D‐template of 41 (semi)landmarks was applied on digital palate models to observe morphological variation during growth.

Results

Asymmetrical components of the morphological structure appears multidirectional on the entire palate surface in individuals <2 years old and become oriented (opposite bilateral direction) between 2 and 6 years of age. Specifically, directional asymmetry differentially impacts palate morphology at different stages of growth. Both the anterior and posterior palate are affected by mild alterations in the first year of life, while between 2 and 6 years asymmetry is segregated in the anterior area, and moderate asymmetry affects the entire palatal surface up to 12 years of age. Our results show that stability of the masticatory system seems to be reached around 13–35 years first by females and then males. From 36 years on both sexes show similar asymmetry on the anterior area. Regarding fluctuating asymmetry, inter‐individual variability is mostly visible up to 12 years of age, after which only directional trends can be clearly observed at a group level.

Discussion

Morphological structure appears instable during the first year of life and acquires an opposite asymmetric bilateral direction between 2 and 6 years of age. This condition has been also documented in adults; when paired with vertical alteration, anterior/posterior asymmetry seems to characterize palate morphology, which is probably due to mechanical factors during the lifespan. Fluctuating asymmetry is predominant in the first period of life due to a plausible relationship with the strength of morphological instability of the masticatory system. Directional asymmetry, on the other hand, shows that the patterning of group‐level morphological change might be explained as a functional response to differential inputs (physiological forces, nutritive and non‐nutritive habits, para‐masticatory activity as well as the development of speech) in different growth stages. This research has implications with respect to medical and evolutionary fields. In medicine, palate morphology should be considered when planning orthodontic and surgical procedures as it could affect the outcome. As far as an evolutionary perspective is concerned the dominance of directional asymmetries in the masticatory system could provide information on dietary and cultural habits as well as pathological conditions in our ancestors.