Osteosclerosis is a metabolic bone disease characterized by generalized sclerosis of the skeleton, which is mediated by a reduction in bone resorption. Ultrastructural changes of ameloblasts and enamel mineralization in the tooth germs of osteosclerotic (oc/oc) mice were examined. In oc/oc mice, secretory ameloblasts exhibited well-developed cytoplasmic organization for protein synthesis and secretion, but lacked membrane infoldings in the plasma membranes of Tomes processes, which might have resulted in reduced enamel mineralization. In the forming enamel, deposition of hydroxyapatite crystals was partially disturbed. These results suggest that osteosclerosis induces inhibition of membrane infoldings in ion transporting-type cells, secretory ameloblasts, and causes hypomineralization of forming enamel. In oc/oc mice, hypoplasia of the enamel matrix was also observed. In such enamel, secretory ameloblasts lacked Tomes processes and contained many lysosomal autophagic vacuoles. These results suggest that oc/oc mice may be a possible experimental model for studying tooth morphogenesis and mineralization.

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Using 3-week-old male beagle dogs, the bone formation processes in the mandibular condylar head were examined by means of light and electron microscopy. There were two bone formative patterns in the mandibular condylar head : intramembranous and endochondral bone formation. In the peripheral area of the condylar head, connective tissue derived from the cartilaginous membrane invaded deeply into hyaline cartilaginous tissues and directly formed membranous bone. At the initial stage of membranous bone formation, TRAP-positive osteoclasts were not observed. Cartilaginous tissue was absorbed by mononuclear phagocytes (macrophages). In the central area of the condylar head, irregular endochondral bone formation was observed. In the endochondral bone formation, chondrocytic lacunae were opened by the removal of septal cartilage by macrophages. Shortly thereafter, a thin bone layer was deposited on the remaining calcified septal cartilage by invading osteoblasts. Multinucleated preosteoclasts in lacunar canals did not develop either a ruffled border or a clear zone in the cartilage matrix, but once the bone layer had been deposited on the remaining cartilage, these structures formed. Our results suggest that cartilage-bone replacement in the mandibular condylar head involves three sequential processes : (1) phagocytosis of calcified cartilage fragments by macrophages, (2) bone deposition on the remaining calcified septal cartilage, and (3) degradation of both bone and calcified cartilage by differentiated osteoclasts.

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The study was carried out to identify the common oro-dental problems in a developing country. To determine the level of knowledge among the common population regarding oral hygiene practices. To find out the relation of socio-economic, educational level and other factors with oro-dental diseases. The study involved 125 patients of a dental college hospital who visited the out patient department of the hospital for their treatment purpose. Information about their disease pattern were obtained by examining the patients mouth directly and information about dental care, oral hygiene, food habit, educational and economical status were obtained through a questionnaire and check list. Identified dental problems include dental caries 70.4%, gingivits 34.4%, periodontitis 11.2%, alveolar abscess 5.6%, attrition and mobility 3.2%. The highest number of dental caries occurred among the age group of 21-30 years and the lowest in the age group of 50 years. Only 53% people have knowledge how dental diseases are occuring. Only 27.2% dental caries occurred who brushed their teeth regularly before going to bed and 43.2% dental caries occurred who did not brushed before going to bed. So a significant relationship (p < 0.05) among brushing teeth before going to bed and dental caries is found. Comparatively highly educated and high-income group people suffered more than medium educated and low-income group people. The majority people who suffered from dental diseases used to take chocolate, sweets and biscuits as their snacks. Male suffered more (70%) than female. Dental caries, gingivitis, periodontitis, alveolar abscess, attrition, mobility are common oro-dental problems in the developing countries like Bangladesh. Various awareness programme for the common population in developing countries regarding regular practice of oral hygiene offered by the government, NGOs, dental professionals, WHO through mass-media, audio-visual equipments etc. can combat the current crisis to large extent.

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The aims of this study were to compare the effectiveness of FlexMaster^® nickel-titanium rotary and K-Flexofile^® hand instruments with regard to straightening of curved root canals and preparation time, and to evaluate the morphological aspects of instrumented root canal walls in extracted human teeth. A total of 60 root canals in molar teeth, with curvatures ranging between 0 and 35°, were divided into three groups of 20 root canals each, based on the degree of curvature. Half of each group was prepared using FlexMaster^® instruments by a crown-down preparation technique and the other half using K-Flexofile^® by a conventional technique. After each instrumentation, the root canals were flushed with 3 ml of 5.25% sodium hypochlorite and 3% hydrogen peroxide, alternatively, and 1 ml of 14% EDTA. Using radio-graphs taken before and after root canal preparation, the angles of root canal curvature of all specimens were determined. The preparation time was also recorded. All roots were bisected longitudinally and the canal walls were examined by scanning electron microscopy for morphological aspects. The use of FlexMaster^® instruments resulted in significantly less straightening of root canal curvatures and a shorter preparation time compared to K-Flexofiles^® (p <0.01). They resulted in less debris, but left a thicker smear layer at the apical third of root canal than the K-Flexofile^®. These results showed that rapid preparation of curved root canals with minimal canal straightening was possible using FlexMaster^® instruments, and the use of FlexMaster^® resulted in less debris, but a thicker smear layer than that of K-Flexofile^®.

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