Effect of age on alveolar bone turnover adjacent to maxillary molar roots in male rats: A histomorphometric study.

OBJECTIVE: The effect of age on alveolar bone turnover adjacent to maxillary molar roots of male rats was assessed histomorphometrically with special focus on bone formation and resorption. DESIGN: A total of 110 male Wistar rats ranging in age from 6 to 100 weeks were used for this study. Histomorphometric parameters were measured in fluorescence-labeled undecalcified ground and paraffin-embedded decalcified sections of the alveolar wall around the disto-lingual roots of the maxillary first molars. Bone formation was measured statically by determining the percentage of the bone surface that was double-labeled surface (dLS/BS), bone formation rate (BFR/BS), and mineral apposition rate (MAR). Bone resorption was quantified statically in terms of the number of osteoclasts (N.Oc/BS) and the percentage of the bone surface covered with osteoclasts (Oc.S/BS). RESULTS: For the total surface of the alveolar wall, the values obtained for all parameters of both bone formation and resorption decreased with advancing age. All these values rapidly decreased during the early part of the life span, from 6 to 30-40 weeks of age, of the rats. A site-specific difference between the distal and mesial sides of the alveolar wall was found for each age group. dLS/BS and BFR/BS were significantly greater (p < 0.0001) on the mesial side than on the distal one. On the other hand, the distal side showed significantly greater (p < 0.0001) value for N.Oc/BS and Oc.S/BS did the mesial one. However, there were no significant age-related changes in dLS/BS and BFR/BS on the distal side or in N.Oc/BS and Oc.S/BS on the mesial side throughout observation period. CONCLUSION: The results of the present study demonstrate that alveolar bone turnover of male rats decreased rapidly with advancing age but that in order to maintain the integrity of the tooth function mechanical stress may still have participated in bone formation and resorption of the alveolar wall even in rats 100-week old.

Scanning electron microscopy of the three different types of cementum in the molar teeth of the guinea pig.

The aim of this study was to observe the three-dimensional distribution and structural characteristics of the three different types of cementum in the molar teeth of guinea pig by means of scanning electron microscopy. Twenty-five 4-week-old male guinea pigs were used in this study. Using decalcified and undecalcified specimens with or without NaOH maceration, we examined the mandibles, maxillae and extracted molars by scanning electron microscopy. Guinea pig molars consist of two longitudinal, deeply folded lamina cores covered by enamel on all surfaces, except the buccal surface of the upper molars and the lingual surface of the lower molars. In the regions without enamel, we observed continuous thin belt-like layers of conventional acellular cementum on the dentin surface. On the enamel-covered surfaces, two different types of coronal cementum were found: small circular islands of coronal cementum called cementum pearls, which were distributed widely at almost regular intervals on the peripheral enamel surface from the apical fifth to the occlusal surface; and cartilage-like cementum, which occupied almost all of the occlusal half of the two longitudinally folded grooves. The present study demonstrated the unique distribution pattern of the three different types of cementum in guinea pig molars. These cementum types may contribute to the requirements for many different functions such as mastication, anchorage and continuous tooth eruption.