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Reduction of Pax9 gene dosage in an allelic series of mouse mutants causes hypodontia and oligodontia.

Missing teeth (hypodontia and oligodontia) are a common developmental abnormality in humans and heterozygous mutations of PAX9 have recently been shown to underlie a number of familial, non-syndromic cases. Whereas PAX9 haploinsufficiency has been suggested as the underlying genetic mechanism, it is not known how this affects tooth development. Here we describe a novel, hypomorphic Pax9 mutant allele (Pax9neo) producing decreased levels of Pax9 wild-type mRNA and show that this causes oligodontia in mice. Homozygous Pax9neo mutants (Pax9neo/neo) exhibit hypoplastic or missing lower incisors and third molars, and when combined with the null allele Pax9lacZ, the compound mutants (Pax9neo/lacZ) develop severe forms of oligodontia. The missing molars are arrested at different developmental stages and posterior molars are consistently arrested at an earlier stage, suggesting that a reduction of Pax9 gene dosage affects the dental field as a whole. In addition, hypomorphic Pax9 mutants show defects in enamel formation of the continuously growing incisors, whereas molars exhibit increased attrition and reparative dentin formation. Together, we conclude that changes of Pax9 expression levels have a direct consequence for mammalian dental patterning and that a minimal Pax9 gene dosage is required for normal morphogenesis and differentiation throughout tooth development.

Alleles↗

A 5-year study of attachment loss in community-dwelling older adults: incidence density.

This is the second of three papers that present trends in attachment loss and tooth loss over a 5-yr period in a population of community-dwelling elderly black and whites. The first paper in this series showed that in addition to subject attrition during the 5 yr of the study, teeth also were lost. This loss of subjects and teeth resulted in trends that were not always consistent over time, because people were lost from the study and teeth with more active and advanced periodontal disease were more likely to be lost. In these instances, the incidence density (time-to-event) analytic strategy is useful. Incidence density is the average rate of occurrence for a fixed follow-up period. In 1988, the University of North Carolina School of Dentistry initiated the Piedmont 65+ Dental Study, which was designed to elicit 800 dentate respondents in the 5-county area who were examined again at 18, 36 and 60 months. Our findings indicated that for every 1000 sites followed for 1 yr in this population, 20.6 sites will experience attachment loss of 3+mm. Incidence densities varied greatly by subgroup, indicating that certain characteristics predispose sites for attachment loss. A multivariate logistic regression model indicated that people who are smokers, Porphyromonas gingivalis positive, have 5 or more missing teeth, are not high school graduates, and have not had a dental visit in the last 5 yr are at higher risk of attachment loss. Posterior teeth and mesiobuccal sites are at higher risk. We conclude that incidence density analyses are useful for longitudinal periodontal data and we illustrate the use of incidence density rates to plan clinical trials.

Aged↗

Craniographic examination of the condylar angle and the maxillary incisal palatal angle in Bedouin skulls.

Craniographic registrations were used to examine 25 Bedouin skulls. The skulls were divided into three groups according to the anatomy and position of the maxillary incisor. Correlations between condylar guidance angle, maxillary incisal palatal angle, attrition, and flaring were investigated. No correlation was found between the condylar and maxillary incisal palatal angles. In the presence of severe attrition and/or flaring, the maxillary incisal palatal angle was reduced and mild reduction was also found in the condylar guidance angle. A strong correlation was found between the level of attrition and flaring.

Cephalometry↗

Quantitative in vivo wear of human enamel.

In this study, the attrition wear, also called occlusal-contact-area wear, of human enamel was measured quantitatively with a computerized three-dimensional measuring technique over a period of four years. Tooth replicas from a clinical trial were used. A running-in wear period after restorative treatment, followed by steady-state wear, was suggested. The average steady-wear rate on occlusal contact areas was about 29 microns per year for molars and about 15 microns per year for premolars.

Adolescent↗

Educational material of dental anatomy applied to study the morphology of permanent teeth.

The purpose of this report is to present educational material that would allow the dental student to learn to easily identify the morphologic characteristics of permanent teeth, and how they fit together (occlusion). In order to do this, macro models of permanent teeth with no attrition were carved in wax and later molded with alginate. These molds were filled with plaster, dental stone and/or cold-cured acrylic resin. The large individual dental stone tooth models were mounted on a wax base, thus obtaining maxillary and mandibular arches which were occluded. These dental arches were molded with plaster or dental stone. The authors suggest that these types of macro models allow an excellent visualization of the morphologic characteristics of permanent teeth and occlusion. Dental students are able to carve the permanent dentition in wax with great facility when they can observe macro models.

Acrylic Resins↗

Occlusal relations and periodontal status in human adults.

A group of 66 adults provided the population for study of relations between various clinical parameters and periodontal status. Dental and habit histories and plaque scores were acquired. Occlusal features included classification of malocclusion, analysis of centric displacement, establishment of patterns of lateral and protrusive excursions, identification of tooth contacts and presence of wear facets. Periodontal analysis included pocket depths, radiographic manifestations and extent of mobility. Class I malocclusion predominated and the majority of patients did not have coincidental centric relation and centric occlusion. Group function is the most common lateral excursive pattern in the adult. Nonfunctional contacts are common as is enamel attrition. Results indicate no significant deleterious influence on the status of the periodontium by occlusal disharmonies.

Adolescent↗

Prevalence of malocclusion in medieval and modern Danes contrasted.

A comparison was made of frequencies of anomalies of the dentition, occlusion, and space conditions for the permanent dentition in the skeletal remains of 278 medieval Danes and in 1258 contemporary Danes. The congenital anomalies of the dentition were equally common in the samples. Extreme maxillary overjet and distal molar occlusion, deep bite, and crowding were considerably less frequent in the Middle Ages. The frequencies of mesial molar occlusion and crossbite, but not that of midline displacement, were higher in the medieval sample, especially in the older subjects. It is suggested that the observed differences in malocclusion prevalence were related to exogenous factors, primarily the pronounced dental attrition.

Adolescent↗