Unicuspid and bicuspid tooth crown formation in squamates.

The molecular and developmental factors that regulate tooth morphogenesis in nonmammalian species, such as snakes and lizards, have received relatively little attention compared to mammals. Here we describe the development of unicuspid and bicuspid teeth in squamate species. The simple, cone-shaped tooth crown of the bearded dragon and ball python is established at cap stage and fixed in shape by the differentiation of cells and the secretion of dental matrices. Enamel production, as demonstrated by amelogenin expression, occurs relatively earlier in squamate teeth than in mouse molars. We suggest that the early differentiation in squamate unicuspid teeth at cap stage correlates with a more rudimentary tooth crown shape. The leopard gecko can form a bicuspid tooth crown despite the early onset of differentiation. Cusp formation in the gecko does not occur by the folding of the inner enamel epithelium, as in the mouse molar, but by the differential secretion of enamel. Ameloblasts forming the enamel epithelial bulge, a central swelling of cells in the inner enamel epithelium, secrete amelogenin at cap stage, but cease to do so by bell stage. Meanwhile, other ameloblasts in the inner enamel epithelium continue to secrete enamel, forming cusp tips on either side of the bulge. Bulge cells specifically express the gene Bmp2, which we suggest serves as a pro-differentiation signal for cells of the gecko enamel organ. In this regard, the enamel epithelial bulge of the gecko may be more functionally analogous to the secondary enamel knot of mammals than the primary enamel knot.

First premolar morphometry: a study in 54 cases / Morfometría de primeros premolares: un estudio de 54 casos

First lower premolars are the teeth with greater variations following third molars. Fifty four first premolars extracted by orthodontic indication from patients in Temuco, Chile, were studied and classified by age, sex and maxillar and mandible location. The following parameters were measured: vestibular-palatine diameter (VP), mesiodistal (MD) diameter, coronary height (C-O), root length and total length. The data were statistically analyzed and tabulated. The results exhibited that first upper premolars showed higher values in the VP diameter and root length compared with the lower, noting significant differences. Further, male sex showed higher values on most measures compared with females, except in root length. Finally a difference in root length was observed between first upper and lower premolars.

Los primeros premolares inferiores son las piezas dentarias con mayores variaciones después de los terceros molares. Se estudiaron 54 primeros premolares extraídos por ortodoncia de pacientes de la ciudad de Temuco, Chile, los cuales fueron clasificados por edad, género y ubicación en los maxilares y en la mandíbula. Se midieron los siguientes parámetros: diámetro vestíbulo-palatino (V-P), mesio-distal (M-D), altura coronaria (C-O), longitud radicular y longitud total. Los datos fueron analizados estadísticamente y tabulados. Los resultados arrojaron que los primeros premolares superiores presentaron valores superiores en el diámetro V-P y la longitud radicular con respecto a los inferiores, observando diferencias estadísticamente significativas. Además, en los hombres se observaron valores superiores en la mayoría de las mediciones, a excepción de la longitud radicular. Finalmente, se observó una diferencia en la longitud radicular entre los primeros premolares maxilares y los mandibulares.

Early morphogenesis of heterodont dentition in minipigs.

The minipig provides an excellent experimental model for tooth morphogenesis because its diphyodont and heterodont dentition resemble that of humans. However, little information is available on the processes of tooth development in the pig. The purpose of this study was to classify the early stages of odontogenesis in minipigs from the initiation of deciduous dentition to the late bell stage when the successional dental lamina begins to develop. To analyze the initiation of teeth anlagens and the structural changes of dental lamina, a three-dimensional (3D) analysis was performed. At the earliest stage, 3D reconstruction revealed a continuous dental lamina along the length of the jaw. Later, the dental lamina exhibited remarkable differences in depth, and the interdental lamina was shorter. The dental lamina grew into the mesenchyme in the lingual direction, and its inclined growth was underlined by asymmetrical cell proliferation. After the primary tooth germ reached the late bell stage, the dental lamina began to disintegrate and fragmentize. Some cells disappeared during the process of lamina degradation, while others remained in small islands known as epithelial pearls. The minipig can therefore, inter alia, be used as a model organism to study the fate of epithelial pearls from their initiation to their contribution to pathological structures, primarily because of the clinical significance of these epithelial rests.

Rasgos morfológicos y métricos dentales coronales de premolares superiores e inferiores en escolares de tres instituciones educativas de Cali, Colombia / Morphologics and metric dental crown traits of upper and lower premolars in scholars of Cali, Colombia

El objetivo de este trabajo fue determinar la frecuencia y variabilidad de doce rasgos morfológicos dentales coronales y de dos rasgos métricos dentales coronales en los primeros y segundos premolares superiores (UP1/UP2) e inferiores (LP1/LP2) de 112 modelos de yeso obtenidos de una muestra de jóvenes escolares del municipio de Santiago de Cali. Se trata de un estudio descriptivo transversal cuantitativo que evaluó doce rasgos morfológicos dentales coronales mediante los sistemas ASUDAS (Arizona State University Dental Anthropology System): cresta accesoria mesial, cresta accesoria distal y premolar tricúspide; Higa et al.: tubérculos intersticiales mesial y distal; van Reenen et al.: hipostilo, surco vestibular, cresta central, surco meso-lingual y surco disto-lingual; Hillson: número de cúspides linguales y patrón cuspideo. Y dos rasgos métricos dentales coronales, los dißmetros mesio-distal mediante el método de Moorrees et al. y vestíbulo-palatino (lingual) mediante el de Kieser et al. La frecuencia de los rasgos morfológicos y las dimensiones dentales evidencia que los primeros premolares cuentan con una morfología mucho mas simplificada y dimensiones menores (caninización; mientras que los segundos son mucho mas caracterizados y de mayor tamaño (molarización). La frecuencia de los rasgos morfológicos es ambigua, no presentan dimorfismo sexual y cuentan con bilateralidad en su expresión, a excepción del surco meso-lingual. La correspondencia entre los primeros y segundos premolares superiores e inferiores varía en cada rasgo. Las dimensiones dentales presentan bilateralidad y dimorfismo sexual a excepción de los segundos premolares inferiores. El dendograma obtenido sugiere que la muestra consiste en mestizos con características caucasoides, de fuerte influencia negroide y conservación mongoloide.

The objective is determining the frequency and variability, sexual dimorph, bilateral asymmetry and correspondence between twelve non-metric dental traits and two metric dental traits on the first and second upper and lower premolars in dental casts from 110 subjects from a Colombian racially mixed population. In this descriptive and quantitative study, frequency and variability of twelve non-metric dental crown traits were observed, through the ASUDAS (mesial and distal accessory crest and tricuspid premolar), Higa et al. (mesial and distal interstitial tubercle), van Reenen et al. (hypostile, bucal furrow, transverse ridge, meso-lingual furrow and disto-lingual furrow; and Hillson (lingual cusp number and groove pattern). The frequency of the metric and non-metric dental traits demonstrates that the first premolars present a minor dimensions and simplified morphology (caninization); whereas the second premolars ones are many characterized and of major size (molarization). The frequency of the non-metric dental traits is ambiguous; they do not present sexual dimorphism and present bilateral symmetry, with the exception of the meso-lingual furrow. The correspondence between the first and second upper and lower premolars changes in every trait. The dental dimensions present bilateral symmetry and sexual dimorphism with the exception of the second lower premolars. The dendogram suggests that the sample consists in mixed population with Caucasoid characteristics, negroid influence and mongoloid conservation.

Dental embryology, anatomy, development, and aging.

Equine practitioners should be knowledgeable of dental anatomy and development to enhance their skill of age estimation of horses. The permanent teeth of horses are continually undergoing changes in shape and appearance. These changes may be used to suggest a reasonable age range for a horse.

Ontogeny of postcanine tooth form in the ferret, Mustela putorius (Carnivora: Mammalia), and the evolution of dental diversity within the Mustelidae.

This study describes dental development within the ferret, Mustela putorius, through study of the form of the carnassial teeth and the upper first molar at progressive growth stages. Primordial teeth were serially sectioned in sagittal and transverse planes and three-dimensional reconstructions of tooth primordia were generated using MacReco software. Regional growth of the crown and asynchronous maturation of the dental tissues were observed in each tooth. The upper carnassial blade develops early and the tooth increases in length rapidly. Lingual growth of the upper carnassial is less pronounced and the protocone and its surrounding region mature late. The lower carnassial blade develops early and the talonid is late to mature. Development of the upper first molar differs from carnassial development in the early emphasis upon transverse growth and reduced lengthwise expansion. The early development of the carnassial blades in the ferret is shared with other carnivores, and may reflect the functional significance of this feature. Later stages of tooth ontogeny differ among carnivoran taxa and the specialized morphology of ferret teeth results from an apparently truncated period of late tooth ontogeny. This suggests that carnivoran species may share a common path of early development that specifies the ontogeny of homologous tooth features and that in later stages developmental differences result in species-specific tooth forms.

The origin of tooth cusps--a hypothesis.

An embryological concept is offered to explain the formation of tooth cusps. The epithelium is considered to play the active part in morphogenesis. The folding of the inner sheath of the enamel organ must be seen to be the origin of tooth cusps. This folding can be considered to be a consequence of the ability to span only a certain area without folding. The regularity of the folding--and thus the regularity of the molar occlusal pattern--might be a result of the unique material properties of the inner enamel epithelium.

Evidence for the presence of numerous protein components in immature bovine dental enamel.

The proteins and peptides of immature enamel were extracted from freshly slaughtered bovine embryos in solutions containing protease inhibitors. No detectable differences were noted in the number of components, their overall amino acid composition, or molecular weights from the proteins and peptides extracted 12-16 h postmortem in solutions which contained no protease inhibitors. These data indicate that the large number of components found in developing bovine enamel is not due to proteolysis occurring during their isolation. Significant amounts of protein components having molecular weights greater than approximately 15,000 were not detected. Therefore, if the ameloblasts initially synthesize only a few high molecular weight protein species, the present data imply that in vivo degradation of the high molecular weight enamel proteins occurs very rapidly after their synthesis and precedes the massive loss of protein which accompanies the final stages of enamel mineralization and maturation.