A robust alternative to assessing three-dimensional relative enamel thickness for the use in taxonomic assessment.

OBJECTIVE: Three-dimensional relative enamel thickness (3DRET) is important for assessing hypotheses about taxonomy, phylogeny, and dietary reconstruction for primates. However, its weaknesses have not been thoroughly investigated. Here, we analyze its weaknesses and propose an index aiming at better taxonomic discrimination. MATERIALS AND METHODS: The dimensionless 3D index, ratio of enamel-thickness to dentine-thickness (3DRED), which is defined as the cubic root of the ratio of 3D average enamel thickness (3DAET) to 3D average dentine thickness (3DADT), is proposed here. To compare 3DRET and 3DRED and their sensitivity to voxel size, a fossil orangutan molar was scanned 14 times with different resolutions ranging from 10 to 50 µm. Enamel thickness analysis was carried out for each resultant digital model. In addition, enamel thickness measurements of 179 mandibular permanent molars (eight genera) were analyzed, followed by investigating the relationship between 3DRET and 3DAET and between 3DRED and 3DAET. RESULTS: Regarding sensitivity, 3DRED is more robust than 3DRET. In addition, 3DRET is correlated with 3DAET by linear curve with regression coefficients approximating or larger than 0.8 in most cases, while 3DRED shows less correlation with 3DAET. Furthermore, there are clear separations between different taxa in the bivariate plot of 3DRED against 3DAET, indicative of the taxonomic value of 3DRED. CONCLUSION: Under certain conditions, 3DRED promises to be a robust and reliable alternative to 3DRET in taxonomic study.

Comparison of dental measurement systems for taxonomic assignment of Neanderthal and modern human lower second deciduous molars.

Traditional morphometric approaches for taxonomic assignment of Neanderthal and modern human dental remains are mainly characterized by caliper measurements of tooth crowns. Several studies have recently described differences in dental tissue proportions and enamel thickness between Neanderthal and modern human teeth. At least for the lower second deciduous molar (dm(2)), a three-dimensional lateral relative enamel thickness index has been proposed for separating the two taxa. This index has the advantage over other measurements of being applicable to worn teeth because it ignores the occlusal aspect of the crown. Nevertheless, a comparative evaluation of traditional crown dimensions and lateral dental tissue proportion measurements for taxonomic assignment of Neanderthal and modern human dm(2)s has not yet been performed. In this study, we compare various parameters gathered from the lateral aspects of the crown. These parameters include crown diameters, height of the lateral wall of the crown (lateral crown height = LCH), lateral enamel thickness, and dentine volume of the lateral wall, including the volume of the coronal pulp chamber (lateral dentine plus pulp volume = LDPV), in a 3D digital sample of Neanderthal and modern human dm(2)s to evaluate their utility in separating the two taxa. The LDPV and the LCH allow us to discriminate between Neanderthals and modern humans with 88.5% and 92.3% accuracy, respectively. Though our results confirm that Neanderthal dm(2)s have lower relative enamel thickness (RET) index compared with modern humans (p = 0.005), only 70% of the specimens were correctly classified on the basis of the RET index. We also emphasize that results of the lateral enamel thickness method depend on the magnitude of the interproximal wear. Accordingly, we suggest using the LCH or the LDPV to discriminate between Neanderthal and modern human dm(2)s. These parameters are more independent of interproximal wear and loss of lateral enamel.

Valoración de los métodos de predicción de tamaños dentarios en dentición mixta / Assessment of the mixed dentition methods to predict unerupted teeth

Desde siempre, conocer el tamaño de los dientes no erupcionados, caninos y premolares, en dentición mixta, ha sido un claro reto en ortodoncia. El objetivo del presente trabajo es mostrar todos los métodos existentes en la bibliografía para realizar la predicción del tamaño de estos dientes, así como sus ventajas e inconvenientes. Estos métodos pueden clasificarse en 4 grandes grupos: los basados en ecuaciones de regresión; los basados en mediciones directas en radiografías; los que combinan elementos de los 2 anteriores, y otro método no clasificable en ninguno de los anteriores. Los métodos basados en ecuaciones de regresión son rápidos de realizar pero presentan coeficientes de correlación bajos y de poca fiabilidad; los que usan mediciones directas sobre radiografías periapicales presentan el problema de obtener imágenes distorsionadas en ocasiones, lo cual limita la exactitud de estas técnicas; los métodos combinados son los más fiables, aunque son los que más tiempo consumen y son más complejos de realizar. Por último, se presenta un método digital de gran fiabilidad y sencillo y rápido de realizar, no clasificable en ninguno de los grupos anteriores. Se trata de un método basado en la interpolación de tamaños de los dientes utilizando listas de tamaños dentarios y dientes de referencia ya erupcionados

The estimation of the size of unerupted permanent teeth, canines and premolars, in mixed dentition has always been considered an essential aspect in orthodontics. The aim of the present study is to show all the methods that have been developed to make these predictions and their advantages and disadvantages. Four main methods have been used to estimate the mesiodistal crown widths of unerupted canines and premolars: calculations from prediction equations and tables, direct measurements on radiographs, combination of radiographic measurements and prediction tables and other independent method. Methods with a regression equation that relate the widths of unerupted teeth to the widths of erupted teeth are easy and fast to use but not very reliable, methods of measuring unerupted teeth on radiographs depend on the quality of the x-ray films available for use and methods that combine regression equations and radiographs present great accuracy but are time consuming and difficult to use. Finally, we present a new digital computerized-aid method to predict the size of unerupted teeth in mixed dentition using several reference teeth already erupted and mesiodistal teeth tables

Evaluation of the root canal configurations of the mandibular and maxillary permanent teeth by gender in the Turkish population.

A key objective of successful nonsurgical endodontic treatment is obturation of the root canal systems. One factor in achieving this goal is the knowledge of possible root canal morphologies. Root canal morphology may exhibit variation as a result of many factors, including ethnic origin. In this study, 1400 male and 1400 female extracted mandibular and maxillary permanent teeth were evaluated for patterns in root canal morphology. The mandibular and maxillary teeth were divided into seven groups of tooth type (e.g. centrals, laterals, canines, first premolars, second premolars, first molars, and second molars), subdivided into gender, and classified by root canal morphologies. Vertucci's classification was taken as a reference during the evaluation. Although a majority of the specimens corresponded to this classification scheme, the analysis of this large data set revealed 14 additional root canal morphologies.