OBJECTIVE: The purpose of this study is to determine the eruption patterns of maxillary and mandibular first molars from the first occlusal contacts to adulthood. Previous studies have failed to obtain measurements into adulthood or have not been longitudinal in design. By using a measurement during the subjects' adulthood, a better estimate of the changes that occur between the tooth and the gingival margin throughout growth and aging can be obtained. METHODS: The material for this research project was obtained from the Meredith Facial Growth Study from the University of Iowa Orthodontics Department. Records from a set of 64 subjects (35 males and 29 females) were used. Each of these patients had intraoral models taken throughout adolescence into adulthood. A final model was available for each subject in their twenties. Twenty-eight subjects had final records available in their forties (14 males and 14 females). Measurements were recorded for the maxillary first molars (Teeth 3 and 14), and the mandibular first molars (Teeth 19 and 30). Measurements were taken at eleven time points for all sixty-four subjects starting at year 8 and yearly until age 18 with a final measurement taken on a model from the patient's twenties. A subset of twenty-eight subjects contained measurements in their forties. Bitewing Radiographs were also used to measure changes in alveolar bone height at 12, 20, and 40. RESULTS AND CONCUSIONS: Alveolar bone heights and their changes over time measured from the CEJ indicate that the sample population had a stable periodontium. Crown heights at age 20 and 40 were significantly greater than age 11. At age 40, crown heights were significantly greater than age 20. Teeth continue to erupt into a patient's forties in the absence of bone loss and attrition.

Le terme « cément » est utilisé pour désigner l’ensemble des tissus conjonctifs minéralisés retrouvés sur la surface externe de la racine d’une dent ainsi que sur certaines zones de l’émail ou au niveau du foramen apical. Il appartient à deux unités fonctionnelles : la dent et le parodonte et constitue avec l’os alvéolaire un point d’attache essentiel du ligament alvéolo-dentaire. Dans certaines conditions non encore élucidées la synthèse de l’une de ses variétés, le cément cellulaire mixte stratifié, est excessive, elle dépasse la « normalité » : il s’agit d’une hypercémentose. Une revue critique de la littérature nous a permis de mettre en évidence un certain nombre de problématiques concernant sa définition, sa classification, sa fréquence, ses étiologies et certaines de ses caractéristiques anatomiques. Afin d’y répondre nous avons élaboré un protocole d’étude dont le matériel comprenait trois séries d’Hommes sub-actuels (675 individus ; 8861 dents dont 419 hypercémentosées) et dont les méthodes ont fait appel à la photographie, la radiographie, la stéréomicroscopie, la microscopie électronique à balayage et l’histologie. Au terme de notre étude nous avons mis au point une définition et une classification de l’hypercémentose reposant sur des critères reproductibles, nous avons évalué sa fréquence au sein de grands échantillons et déterminé ses principales étiologies (éruption continue liée à la perte des dents antagonistes, parodontite apicale, atteintes parodontales, inclusion dentaire, pathologies générales, syndromes génétiques, hérédité, idiopathie). Nous avons également fourni certaines données inédites concernant les épaisseurs du cément hyperplasique et l’anatomie des foramens apicaux. Nos résultats ont enfin été appliqué à un certain nombre de dents néandertaliennes ce qui nous a permis de reconsidérer l’hypothèse selon laquelle l’importance des contraintes occlusales au sein de ce taxon est la cause principale des hypercémentoses. / The term "cement" is used to refer to all mineralised connective tissue found on the external surface of the root of a tooth and also on certain areas of the enamel or around the apical foramen. It pertains to two functional units, the tooth and the periodontium, and together with the alveolar bone forms an essential point of attachment for the periodontal ligament. In certain conditions that have still to be clarified, synthesis of one variety of cement, cellular mixed stratified cementum, is excessive, going beyond "normal" levels: this is hypercementosis. From a review of the literature, we identified a certain number of questions relating to the definition, classification, frequency, and etiologies of this term, and also to some of its anatomical characteristics. To find answers to these questions, we set up a study protocol on material consisting of three series of modern Humans (675 individuals; 8,861 teeth, 419 with hypercementosis), using photography, radiography, stereomicroscopy, scanning electron microscopy and histology techniques. From this we were able to produce a definition and a classification of hypercementosis based on reproducible criteria, we assessed frequency using a large set of samples and determined the main etiologies (continuous eruption associated with the loss of opposing teeth, apical periodontitis, periodontal injuries, dental inclusion, general pathologies, genetic syndromes, heredity, idiopathy). We were also able to provide new data on hyperplastic cement thicknesses and the anatomy of apical foramens. Finally, our results were applied to a number of Neanderthal teeth, which led us to reconsider the hypothesis according to which the importance of occlusal stress in this taxon is the main cause of hypercementosis.