Bmp4 gene is expressed at the putative site of fusion in the midfacial region

The molecular mechanisms by which the primordia of the midface grow and fuse to form the primary palate portion of the craniofacial region are not well characterized. This is in spite of the fact that failure of growth and/or fusion of these primordia leads to the most common craniofacial birth defect in humans (i.e. clefts of the lip and/or palate). Bmp4 plays a critical role during early embryonic development and has previously been shown to play a role in epithelial-mesenchymal interactions in the craniofacial region of chicks. We analyze the expression of bmp4 in mouse as the midfacial processes undergo fusion to form the primary palate. We show that bmp4 is expressed in a very distinct manner in the three midfacial processes (lateral nasal, LNP, medial nasal, MNP, and maxillary processes, MxP) that ultimately fuse to form the midface. Prior to fusion of the midfacial processes, bmp4 is expressed in the ectoderm of the LNP, MNP, and MxP in a distinct spatial and temporal manner near and at the site of fusion of the midface. Bmp4 appears to demarcate the cells in the LNP and MNP that will eventually contact and fuse with each other. As fusion of the three prominences proceeds, some bmp4 expressing cells are trapped in the fusion line. Later, the expression of bmp4 switches to the mesenchyme of the midface underlying its initial expression in the ectoderm. The switch occurs soon after fusion of the three processes. The pattern of expression in the midfacial region implicates the important role of bmp4 in mediating the fusion process, possibly through apoptosis of cells in the putative site of fusion, during midfacial morphogenesis.     

Functional symmetries in the schmelzmuster and morphology of rootless rodent molars

Morphology and schmelzmuster of rootless cheek teeth of 25 extant rodent genera were studied in relation to jaw movement. A differentiation between leading and trailing edges is observed regularly in enamel thickness and schmelzmuster. Similarities between antagonists are interpreted as 'functional symmetries'. Differences in the enamel thickness, the schmelzmuster and orientation of cutting edges are controlled by functional and phylogenetic constraints. The heterogenous sample allows discrimination between these two constraints. The most obvious functional constraint leads to the almost regular occurrence of radial enamel on the push sides of cutting edges. The degree of functional symmetry seems to be determined by phylogenetic limitations.     

Enamel thickness and the helicoidal occlusal plane

In the present study 38 unworn maxillary molars (M¹ = 16, M²= 12, M³ = 10) of modern humans from a Slavic necropolis were sectioned through the mesial cusps in a plane perpendicular to the cervical margin of the crown. Five slightly worn M¹s and one slightly worn M³ were also used thus increasing the total sample to 44, but measurements made on the worn areas were coded as missing values. Seven measurements of enamel thickness as well as the heights of the protocone and the paracone dentine horns were recorded in order to analyze whether changes in these dimensions in anteroposterior direction can be related to the helicoidal occlusal plane. Uni- and multivariate analyses revealed that the distribution of enamel thickness within and between maxillary molars corresponds to a helicoidal occlusal wear pattern. Enamel thickness along the occlusal basin increases from anterior to posterior, which may lead to rapid development of a reverse curve of Monson in first molars when compared to posterior teeth. However, although these overall differences together with the serial, especially delayed eruption pattern of human molars, contribute to the marked expression of the helicoidal occlusal plane in Homo, differences in enamel patterning between molars indicate that a helicoidal plane is a structural feature of the orofacial skeleton. In contrast to first upper molars, second and third molars show absolutely and relatively thicker enamel under the Phase I wear facet of the paracone, i. e., the lingual slope of the paracone, than under the Phase II facet of the protocone, i. e., the buccal slope of that cusp. These proportional differences are most pronounced in M³, as evidenced by uni- and multivariate statistics. It thus appears that the pattern of enamel thickness distribution from M¹ to M³ follows a trend towards providing additional tooth material in areas that are under greater functional demands, that is, corresponding to a lingual slope of wear anteriorly and to a flat or even buccal one posteriorly. In addition, the heights of the dentine horns in anteroposterior direction change in a way that lends support to the hypothesis that the axial inclination of teeth could be one of the most important factors for the development of the helicoidal occlusal plane. Finally, the changes in morphology and enamel thickness distribution from first to third upper molars found in this study suggest that molars could be “specialized” in their function, i. e., from performing proportionally more shearing anteriorly to increased crushing and grinding activities posteriorly. © 1994 Wiley-Liss, Inc.     

Brief communication: Type II tooth cusp occurrence asymmetry in a human monozygotic twin pair

A Type II tooth cusp occurrence asymmetry proposed for human twins in 1974 but not observed until recently was described in a female monozygotic twin pair. Am J Phys Anthropol 105:93–95, 1998. © 1998 Wiley-Liss, Inc.     

Molar scaling in strepsirrhine primates

We examined how maxillary molar dimensions change with body and skull size estimates among 54 species of living and subfossil strepsirrhine primates. Strepsirrhine maxillary molar areas tend to scale with negative allometry, or possibly isometry, relative to body mass. This observation supports several previous scaling analyses showing that primate molar areas scale at or slightly below geometric similarity relative to body mass. Strepsirrhine molar areas do not change relative to body mass(0.75), as predicted by the metabolic scaling hypothesis. Relative to basicranial length, maxillary molar areas tend to scale with positive allometry. Previous claims that primate molar areas scale with positive allometry relative to body mass appear to rest on the incorrect assumption that skull dimensions scale isometrically with body mass. We identified specific factors that help us to better understand these observed scaling patterns. Lorisiform and lemuriform maxillary molar scaling patterns did not differ significantly, suggesting that the two infraorders had little independent influence on strepsirrhine scaling patterns. Contrary to many previous studies of primate dental allometry, we found little evidence for significant differences in molar area scaling patterns among frugivorous, folivorous, and insectivorous groups. We were able to distinguish folivorous species from frugivorous and insectivorous taxa by comparing M1 lengths and widths. Folivores tend to have a mesiodistally elongated M1 for a given buccolingual M1 width when compared to the other two dietary groups. It has recently been shown that brain mass has a strong influence on primate dental eruption rates. We extended this comparison to relative maxillary molar sizes, but found that brain mass appears to have little influence on the size of strepsirrhine molars. Alternatively, we observed a strong correlation between the relative size of the facial skull and relative molar areas among strepsirrhines. We hypothesize that this association may be underlain by a partial sharing of the patterning of development between molar and facial skull elements.     

Biometric ratio in estimating widths of maxillary anterior teeth derived after correlating anthropometric measurements with dental measurements

doi: 10.1111/j.1741‐2358.2012.00648.x Biometric ratio in estimating widths of maxillary anterior teeth derived after correlating anthropometric measurements with dental measurements Objective: To correlate dental measurements i.e. combined mesiodistal width of six maxillary anterior teeth with facial measurements i.e. inner canthal distance, interpupillary distance and intercommissural width and acquire a biometric ratio to serve as a preliminary guide in selection of the maxillary anterior teeth. Background: In the absence of pre‐extraction records, the resultant denture can lead to patient dissatisfaction towards the aesthetic appeal of their dentures. The maxillary anterior teeth play a pivotal role in denture aesthetics. Various techniques and biometric ratios have been described in literature for selection of the maxillary anteriors. This study derives a biometric ratio for the same, obtained after correlating anthropometric measurements with dental measurements. Materials and methods: Two standardized digital photographs of the face were generated; one, when the facial muscles were relaxed and the other, when the subject was smiling; thereby, revealing the maxillary anterior teeth upto the canine tip. Inner canthal distance, interpupillary distance, intercommissural distance, distance between the tips of the maxillary canines and distance between the distal surfaces of the canines were measured. On the cast, the distance between tips of maxillary canines and distance between distal surfaces of maxillary canines were noted. The data was analysed using Spearman’s rank correlation coefficient. Results: A high correlation was found between the intercommissural measurement with distance between the tips of the canines on the photograph and between the tips of the canines on the cast with the interpupillary distance, giving a biometric ratio of 1:1.35 and 1:1.41 respectively. The least correlation was between the inner canthal distance and the tips of the canines measured on the photograph. Conclusions: Extra oral anthropometric measurements of the interpupillary distances and the intercommissural distances with the help of standardised photographs can help us determine the combined widths of the anterior teeth accurately, thus aiding their selection in the absence of pre‐extraction records.     

Relationships between the diet and dentition of Asian leaf monkeys

Colobines have been generally described as primates that use the anterior teeth minimally, but the posterior teeth extensively, to process leaves and related food items. However, variation among leaf monkeys in both anterior and posterior dental morphology has been recognized for decades. In this study, we turn to Hylander's (Science 189 (1975) 1095-1098) analysis of anterior incisor row length and Kay's (Adaptations for foraging in nonhuman primates, 1984) examination of relative molar crest length to test hypotheses proposed by them for Asian colobines. We present findings based on data from the largest Asian colobine sample measured to date. Our findings for incisor row length and molar cresting are not amenable to broad generalizations. In those instances when our morphological findings concur with those of Hylander (Science 189 (1975) 1095-1098) and Kay and Hylander (The ecology of arboreal folivores, 1978), the ecological evidence seldom supports the morphological predictions. The disassociation between diet and dental patterns may be a consequence of differential selection by fallback foods, anthropogenic disturbance or climatic shifts limiting preferred diets, or the use of food types as opposed to food mechanical properties for dietary categorization. We also found that in the case of both incisor row length and molar crest length, the patterns for males and females differed markedly. The reasons for these differences may in part be ascribed to the metabolic challenges faced by females and subsequent niche partitioning. We propose integrated analyses of the ingestive and digestive systems of our study taxa to clarify relationships among behavior, dental morphology, and diet in extant and extinct colobines.     

Comparative morphology of sensilla on antenna,maxillary palp and labial palp of larvae of white‐spotted and yellow‐spotted Asian long‐horned beetle,Anoplophora glabripennis Motschulsky (Coleoptera: Cerambycidae)

The Asian long‐horned beetle (ALB) is one of the most important wood‐boring insects worldwide that damages broad‐leaved trees, primarily poplar, willow, elm and maple. Based on the color of the spots on the elytra, the beetles are separated into white‐spotted (ALB‐W) and yellow‐spotted (ALB‐Y) Asian long‐horned beetles. In order to clarify the morphology of sensilla on antenna, maxillary palp and labial palp of ALB‐W and ALB‐Y larvae, we studied the typology, morphology, number and distribution of the sensilla by scanning electron microscopy. The results showed that: (i) the antennae of two biotypes had five types of sensilla, including three types of sensilla basiconica (b.) and two types of sensilla twig basiconica (s.tb); numbers of b.1, b.2, b.3 and s.tb1 on antenna were not significantly different (P > 0.05) between two biotypes, and the numbers of s.tb2 were significantly different (P < 0.05); (ii) the maxillary palp of two biotypes had four types of sensilla, including sensilla styloconica (st.), two types of s.tb and digitiform sensilla (ds.); the numbers of st. and ds. on the maxillary palp were not significantly different (P > 0.05) between two biotypes, and the numbers of s.tb1 and s.tb2 were significantly different (P < 0.05); (iii) the labial palp of two biotypes had four types of sensilla, including b., st. and two types of s.tb, and the numbers of b.3, st., s.tb1 and s.tb2 on the labial palp were not significantly different (P > 0.05) between two biotypes. We discuss the relationships between sensilla and damage caused by the larvae inside the host trees.