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A variety of cusp-tip pits were observed with the scanning electron microscope (SEM) on canines and molars of both deciduous and permanent dentitions. Larger pits or craters usually were single and funnel-shaped with a narrow 100 micron base widening to 300-400 micron peripheral opening; smaller pits were in groups. As defects occur precisely in the tips of cusps, developing cusps fetal dentitions were examined for a consistent structural pattern which could explain cusp-tip pit development.

The enamel--dentin junction of human and Macaca irus teeth has been studied using light and scanning and transmission electron microscopy. There are differences between species and within the same tooth. Scalloping, when present, is more developed in the cuspal areas and approximally, and the scallops appear to be formed at the time of maturation of the hard tissues. Enamel tufts and spindles are briefly discussed. The depth of scallops was less in the human deciduous than in the permanent teeth, but no differences were noted between monkey deciduous and permanent dentitions.

In the absence of data on the dynamics of cementum apposition, one female Macaca fascicularis monkey, born July 1984 and sacrificed July 1985, was sequentially injected with calcein and xylenol orange 10 times, about every 33 days. Following fixation in formalin, the right and left maxillary and mandibular jaw segments were embedded in MMA and serially sectioned in the mesio-distal or bucco-oral directions, adapting the plane of sectioning to the various root axes. A total of 230 ground sections were produced. A selected set of sections then served for estimating the interval distances between the various lines of fluorescence and for calculating the daily rates of apposition of acellular and cellular cementum as well as of crown and root dentine of all deciduous and the first permanent molar teeth, using fluorescence microscopy and morphometric equipment. The resulting data were as follows: Acellular cementum formed at a rate of 0.10 +/- 0.02 microns/day, cellular cementum with initial rates of 0.4 to 3.1 and appositional rates of 0.1 to 0.5 microns/day. In comparison, crown dentine of the first permanent molar formed with a stable rate of about 3.1 microns/day, while the rate of root dentine formation varied from 4.6 to 2.7 microns/day in deciduous teeth, and from 2.2 to 3.2 microns/day in first permanent molars. Roots of deciduous teeth grew with an initial rate of 30 to 35 microns/day and this slowed down further apically to 10 to 14 microns/day. Roots of the first permanent molars formed with initial rates of 10 to 18 microns/day only.

The mineralized parts of the teeth of 17 human fetal dentitions, aged 15-38 weeks, were measured mesio-distally and occluso-cervically. The growth pattern of the incisors, with particular emphasis on the changes at the developing incisal edge was studied. Contralateral teeth in the same arch developed at approximately the same rate and with mirror-image morphology. Mineralization started in the upper and lower central incisors, followed by the corresponding lateral incisors. It then progressed at approximately the same rate for both incisors. At first, mesio-distal enamel growth was more significant, but was surpassed by occluso-cervical development later. Five development stages were identified as the incisors developed from a central lobe to the mature form. The main component of growth for the mesial lobe was in the incisal direction, and for the distal lobe in a distal direction, resulting in the characteristic approximal asymmetry of these teeth.

The effects of various enamel pretreatments on bond strengths between primary enamel and resin were investigated. Pretreatments included: removal of the outer enamel surface, varied exposure to phosphoric acid, and the use of an organic coupling agent. Results indicated highest bond strengths utilizing acid pretreatments and an organic coupling agent.

Eighty-five deciduous teeth, divided into five groups, were examined using a scanning electron microscope. The first two groups were etched for 60 and 120 sec respectively; the third and fourth groups were lightly milled and then etched for 60 and 120 sec respectively. In the first two groups, etching produced very few histological modifications. In the milled groups removal of the prismless enamel exposed the prisms to dissolution by the phosphoric acid. It was found that pretreatment and an etching time of 120 sec produced a constant and regularly distributed loss of inter- and intraprismatic substances.

Examination of microradiographs from the deciduous teeth of pigs revealed large lacunae or radiolucent zones close to the cemento-dentinal junction. Electron microscopic studies of the ground sections showed areas of irregularly shaped zones devoid of mineral and filled with collagen fibers. In the wide unmineralized zones, spherical clusters of crystallites were noted. Several cementum lacunae bordered by a broad rim of unmineralized collagen fibers were noted and some lacunae also contained zones of a moderately electron dense material. This material did not yield a diffraction pattern, while the mineralized part of the cementum gave the diffraction pattern typical of hydroxyapatite.

To investigate the cytodifferentiation and degeneration of odontoclasts in physiologic root resorption, we studied deciduous incisors undergoing resorption in 6-month-old kittens by electron microscopy of ultrathin sections. The endogenous peroxidase activity within the cells was also examined by incubating the tissue slices in diaminobenzidine-H2O2 medium. The resorbing tissues, consisting of multinucleated giant cells, macrophages, granular leukocytes, fibroblasts and many blood vessels, were observed at the resorbing surface of the root dentine. Macrophages and granular leukocytes exhibited endogenous peroxidase activity, but mononuclear and multinucleated preodontoclasts and multinucleated odontoclasts did not. These preodontoclasts contained abundant mitochondria, a moderate amount of rough endoplasmic reticulum, stacks of Golgi membranes, lysosomes and numerous polyribosomes scattered throughout the cytoplasm. Many cellular processes extended from their cell surfaces by which the preodontoclasts appeared to fuse to one another during their multinucleation. Concomitant with the multinucleation process, the preodontoclasts developed numerous pale vacuoles throughout the cytoplasm. These vacuoles seemed to arise from some smooth endoplasmic reticula, perhaps representing Golgi-endoplasmic reticulum-lysosome, and the Golgi saccules. However, the preodontoclasts did not yet form a ruffled border and clear zones. When these preodontoclasts came into direct contact with resorbing dentine surfaces, they began to form the clear zones against dentine surfaces. Characteristically, numerous pale vacuoles were accumulated in the cytoplasm adjacent to the clear zone, then they penetrated into the cytoplasm of the clear zone, and with this, ruffles of the plasma membranes appeared. Through a further movement of more pale vacuoles towards the ruffled plasma membranes, the odontoclasts developed typical ruffled borders against the resorbing dentine surfaces. At this differential phase, little pale vacuoles appeared in the Golgi area, but the cisterns of the Golgi apparatus themselves reached their greatest extent during cellular differentiation. Fully differentiated odontoclasts frequently extended long broad cellular processes into the dentinal tubules exposed to the resorption lacunae. Although some odontoclastic processes penetrating the dentinal tubules contained vacuoles and lysosomal structures, most processes lacked any cytoplasmic organelles, and their cytoplasm resembled that of the clear zone. But these processes never exhibited ruffled-border-like structures.(ABSTRACT TRUNCATED AT 400 WORDS)

The phospholipid composition and ultrastructure of pulp are found to be qualitatively different at different stages of ontogenetic development (in the first and permanent dentition). An intensified functional load (with higher dental abrasion) prevents completion of the differentiation of cellular and noncellular elements of pulp even in permanent teeth.

"Phantom tooth" or "odontodysplasia" is one of the most unusual and rare of dental abnormalities, being characterised: Clinically, by the topography of the lesions, the involvement of both sets of teeth and abnormalities in the size and form of the teeth which remain unrupted or only partially evolved. Radiologically, by transparency of the teeth to X-rays. Histologically, by disorganisation of the dental structures and a highly characteristic appearance of the enamel and, in particular, dentine. On the basis of one case, the authors review in detail each aspect of these characteristics, paying special attention to histology and the information obtained using the sweep electron microscope.

In this paper the average diameter of enamel crystallites in mature, deciduous and fluorosed human enamel as well as in bovine enamel (in vivo and in vitro remineralized) is discussed. The investigation was carried out on broken surfaces of the various kinds of enamel with a scanning electron microscope. Corrections have been applied for the thickness of the gold-layer deposited. The average crystallite diameters for sound, deciduous and fluorosed human enamel were : 36 nm; 46 nm and 81 nm, respectively. The values for sound, remineralized in vitro and remineralized in vivo bovine enamel were 57 nm; 97 nm and 63 nm, respectively. The results indicate furthermore that if a correction for the sputtered goldlayer is applied, the results for SEM and TEM microscopy are in good agreement with each other. The difference between in vivo and in vitro remineralized bovine enamel is most likely due to differences in speed of remineralization and/or the presence of saliva.