Y. Michaeli

The effect of aging on tooth morphology: a study on impacted teeth.

The effect of age on dental tissues was studied on histologic sections of totally impacted teeth obtained from patients between 11 and 76 years of age. Impacted teeth were used in order to obviate the influence of the environmental effects prevalent in the oral cavity. The presence of concentric denticles and diffuse calcifications was determined, and the width of secondary dentin, predentin, and cementum was measured. The width of predentin and cementum increased linearly with age, whereas the aging process of secondary dentin formation and diffuse calcifications followed a different pattern. The incidence of concentric denticles was identical for all age groups.

Role of Attrition and Occlusal Contact in the Physiology of the Rat Incisor: III. Prevention of Attrition and Occlusal Contact in the Nonarticulating Incisor

Removal of occlusal contact in the absence of attrition liberates the growth potential of the rat incisor, which is expressed in a doubled rate of axial growth and eruption. The differentiation times, the life spans and the rates of apposition of dental hard tissue-forming cells, however, are independent of the rates of growth and eruption.

Aging of tissues of the roots of nonfunctional human teeth (impacted canines)

In order to examine the aging of dentin and cementum, seventy-two impacted human canines, nonfunctional and not affected by external factors, such as attrition, abrasion, caries, etc., were surgically extracted. Ground sections were prepared and the areas of sclerotic dentin and cementum were measured with the aid of a planimeter and expressed as a percentage of the total root area. It was found that there is a significant increase in sclerotic dentin and apposition of cementum with an increase in age.

Role of Attrition and Occlusal Contact in the Physiology of the Rat Incisor: X. The Part Played by the Periodontal Ligament in the Eruptive Process

Removal of the proliferating base of the rat incisor did not influence the rate of eruption which responded to changes in impediment to eruption in a fashion similar to that for control teeth. It is the periodontal ligament rather than the proliferating cells that is responsible for tooth eruption. The elements of the periodontal ligament apparently responsible for tooth movement are the mature fibroblasts.

Role of Attrition and Occlusal Contact in the Physiology of the Rat Incisor: IV. Prevention of Attrition in the Articulating Incisor

Basal growth in the rat incisor is controlled by occlusal restraint. The result of these two antagonistic forces is eruption, which is mediated via the periodontal ligament. The amount of eruption depends on the relation between the quality of the periodontal tissues and the amount of occlusal interference. If eruption does not rise above a certain minimum, odontogenesis proceeds abnormally.

A Three-dimensional Evaluation of the Effects of Functional Occlusal Forces on the Morphology of Dental and Periodontal Tissues of the Rat Incisor

We examined the effect of function on tooth and periodontal ligament (PDL) morphology in 40 lower incisors of adult female rats. Ten teeth were exposed to occlusal hyperfunction for three months, ten to hypofunction for three weeks, ten to hypofunction for three months, while ten teeth in normal occlusion served as control. Transverse ground sections were cut at various levels perpendicular to the tooth long axis, and their distances from the apex were calculated. The outlines of the tissues were traced and fed into a computer. We plotted the measurements according to their location and fitted them by second-order polynomials. We calculated tissue volume for the proximal 18 mm of bone-embedded tooth. Hyperfunction affected tooth shape, in that it became more rounded. The volumes of the dental tissues remained unchanged, while width and volume of the cementum-bordering PDL increased. Hypofunction did not alter tooth shape, but influenced its size: After three weeks, tooth circumference decreased, and after three months, it expanded. Dentin width was reduced, with concomitant increase of pulp size. The amount of enamel diminished initially, but after three months returned to normal values. The PDL bordering enamel expanded proportionally to the duration of hypofunction. The changes in socket size reflected the total dimensional variations in the tooth and its PDL. The results demonstrate that the shape and size of growing teeth and their periodontium are influenced by functional occlusal forces.

Incisors of the Rabbit: Morphology, Histology, and Development

A detailed morphologic and histologic description of each deciduous and permanent incisor of the rabbit is presented, together with the chronology of their prenatal and postnatal development. The deciduous incisors are teeth of limited growth, but the permanent incisors grow continuously.

Role of Attrition and Occlusal Contact in the Physiology of the Rat Incisor: IX. Impeded and Unimpeded Eruption in Lathyritic Rats

In the rat, the administration of a lathyrogenic agent reduced both impeded and unimpeded eruption rates of incisors. Unimpeded eruption rates were greater than impeded eruption rates. The general eruption pattern in the experimental rats was, however, similar to that in the control rats. Thus, eruption was possible even in rats with a lathyrogenically impaired periodontal ligament.

Kinetics of the inner enamel epithelium in the adult rat incisor during accelerated eruption.

Inner enamel epithelial (IEE) cell production was compared in accelerated and normal eruption (control). Each group consisting of thirty rats received 1 μCi/g tritiated thymidine. The animals were sacrificed at short time intervals up to 14 hr after injection. The excised incisors were cut mid‐sagittally and processed autoradiographically.

Role of Attrition and Occlusal Contact in the Physiology of the Rat Incisor: II. Diurnal Rhythm in Eruption and Attrition

Rates of eruption and of attrition were measured on impeded and unimpeded rat incisors at 6 AM and 6 PM. The rhythm of unimpeded eruption and attrition was diurnal. The rates increased during the night, as do rates of other physiologic processes in the nocturnal animal. When eruption was impeded however, this rhythm was reversed by the inhibiting force of occlusal contact.