Influence of different elastic moduli of dowel and core on stress distribution in root.

This study was carried out to investigate the influences of elastic moduli of the dowel-core combination on the stress distribution in the root by the use of 2-dimensional finite element analysis. The peak stress at the dowel-cement interface was influenced strongly by a change of elastic modulus of the post (from 20,000 kg/mm2 as a hard prefabricated post to 8,000 kg/mm2 as a custom cast post) for both vertical and 45 degree oblique loading (rho > 90%). Peak dentinal stress adjacent to the luting cement layer depended only on the post material for vertical loading (rho [symbol: see text] 99%). In contrast, the post and core materials (from 8,000 kg/mm2 as cast core to 300 kg/mm2 as composite resin core) acted in cooperation on the stress magnitude for oblique loading, but the influence of the core material was stronger than that of the post (rho of core [symbol: see text] 41% and rho of post [symbol: see text] 26%). On the other hand, at the marginal region the effect of the core material contributed more than 86% to the peak stress value for both loadings, and the post material affected at most about 11% of the bending resistance.

The effect of an oral prosthesis on the quality of life for head and neck cancer patients.

The quality of life (QOL) in patients with cancer in the head and neck regions has become an increasingly important factor in medical treatment. We examined the effect of a prosthesis on the QOL based on the patients' own subjective evaluations. Sixty-eight head and neck cancer patients who had been treated in the Department of Prosthetic Dentistry of the Faculty of Dentistry, Kyushu University, were compared with 35 denture wearers as a control. General denture satisfaction in the control group showed a statistical correlation with eating (P<0.01, t-test; rho = 0.72, Spearman rank correlation), aesthetic satisfaction (P<0.01, rho = 0.57) and pain (P<0.01, rho = 0.51). On the other hand, for cancer patients, general denture satisfaction showed a statistical correlation with not only eating (P<0.01, rho = 0.34), aesthetic satisfaction (P<0.01, rho = 0.33) and pain (P<0.01, rho = 0.41) but also health (P<0.01, rho = 0.33) and mental well-being (P<0.01, rho = 0.41). A statistical correlation between the Denture score and the QOL score was thus observed in cancer patients (P<0.0001, rho = 0.56), while the correlation for the control group was not statistically significant. This study showed that oral prostheses for head and neck cancer patients are important factors not only for eating but also for the overall patient QOL.

GBR in human extraction sockets and ridge defects prior to implant placement: clinical results and histologic evidence of osteoblastic and osteoclastic activities in DFDBA.

This study evaluated new bone formation in 3 types of osseous defects following treatment with demineralized freeze-dried bone allografts (DFDBA) and cell-occlusive membranes. For 8 patients electing to receive implant treatment, a distinction was made among 3 clinical situations: (1) existing alveolar ridge defects; (2) extraction sockets with lost buccal plate; and (3) extraction sockets with an intact alveolus. Implants were placed a mean of 6 months after the regenerative procedure. Clinical examination of bone width and height at the time of implant placement showed sufficient augmentation or preservation, and implants were inserted without incident. Histologic examination of hard tissue biopsies obtained from the implant sites revealed no discernible differences among the 3 types of defects. Specifically, all sites demonstrated DFDBA particles surrounded by woven or lamellar bone. No fibrous encapsulation of DFDBA or inflammatory reaction was observed. Osteoblasts were found lining marrow spaces. Howeship's lacunae, with and without resident osteoclasts, were clearly seen in several DFDBA particles; this finding supports the belief that DFDBA undergoes osteoclasis in vivo. These results demonstrate that commercially available DFDBA has osteoconductive properties that lead to appositional new bone growth in both self-contained and non-self contained osseous defects.

Histologic evaluation of human extraction sockets treated with demineralized freeze-dried bone allograft (DFDBA) and cell occlusive membrane.

This study evaluated new bone formation in human extraction sockets treated with demineralized freeze-dried bone allografts (DFDBA) and celloc occlusive membranes. Hard tissue biopsies of 7 sites in 6 patients were obtained 14 weeks to 13 months following extraction and grafting. Histologic analysis revealed that individual particles of DFDBA were discernible up to 13 months in situ. In all samples, all particles of DFDBA were well incorporated within new bone, which exhibited osteocyte-containing lacunae. Distinct cement lines clearly demarcated the DFDBA particles from the surrounding, intimately-apposed woven and lamellar bone. The marrow demonstrated a mild degree of fibrosis without signs of inflammatory reaction. There was also a notable lack of fibrous encapsulation of the allograft, and little osteoclasis was observed. Our findings demonstrate that commercially available DFDBA has the potential to function physically as a nidus for appositional new bone growth in alveolar sockets following tooth extraction. Further investigations of the biological activity of DFDBA in situ are warranted.

Effect of selected beta-blockers on supragingival calculus formation.

Supragingival plaque and calculus indices, salivary flow rates, pH, ionic and total calcium concentrations, total phosphate concentration, and the number of cervical restorations and caries lesions were measured in 29 subjects using systemic beta-(beta) blockers and in 28 subjects who were not taking any systemic medication. After 8 weeks of normal oral hygiene following an oral prophylaxis, a second comparison of each of the above quantities was made. With the exception of the calculus indices and the incidence of cervical restorations, no significant differences were found for any of the measured quantities between the medicated and non-medicated groups at either examination. The medicated group showed significantly lower mean calculus values than the non-medicated group at both examinations and a higher incidence of cervical restorations at the baseline examination, suggesting that beta-blockers decrease the rate of mineralization in the oral cavity. Since beta-blockers did not appear to alter stimulated salivary pH, flow rate, phosphate, ionic calcium or total calcium concentrations, their effect on the mineralization processes must be attributed to other mechanisms. Two hypotheses appear plausible: changes in salivary mineralization rates caused by either direct physico-chemical effects of the secreted beta-blockers in the saliva, or by alterations in the salivary protein/glycoprotein composition, enzymes and oral bacterial flora owing to systemic pharmacological effects of beta-blockers.

Factors correlated with caraniomandibular disorders in young and older adults.

This study was conducted to examine prevalence of craniomandibular disorders in young adults compared with that in older subjects. In addition, the relationship between various oral conditions and this dysfunction was studied. No difference was found in the incidence of craniomandibular disorders between the groups. Classification according to the Helkimo index showed significant difference in complaints of craniomandibular disorders symptoms between the groups. Most of the older patients did not complain of mild disorders. The results suggest that conditions such as the number of teeth, presence or absence of dentures, and the type of denture worn are not important factors in the pathogenesis of craniomandibular disorders.

Numeric approach to the biomechanical analysis of thermal effects in coated implants.

A two-dimensional, finite element method was used to examine the influence of material selection and suprabony exposure of the implant coating on thermal and mechanical stress distribution. Hydroxyapatite coating reduced the heat conduction to the surrounding tissue because of its low thermal conductivity. However, thermal stress resulted from thermal expansion of the hydroxyapatite and titanium core. This might influence the success of hydroxyapatite-coated implants because the biomechanical properties of ceramics are so poor for tensile and shearing stress. In addition, this tendency becomes more pronounced when the hydroxyapatite coating surface extends beyond the cortical bone.

Phenotypic characteristics and DNA relatedness in Prevotella intermedia and similar organisms.

We have recently isolated from the gingival pockets, periapical lesions and saliva some anaerobic gram-negative, black-pigmented rods. Many of these isolates exhibited phenotypic characteristics similar to Prevotella intermedia (Bacteroides intermedius). However, several of these isolates, although resembling P. intermedia in most of the phenotypic expressions, were capable of fermenting lactose, a biochemical characteristic atypical of P. intermedia. These atypical clinical isolates (strains capable of fermenting lactose) and isolates exhibiting more typical phenotypic characteristics (i.e., lactose nonfermenting) were definitively identified as P. intermedia by DNA-DNA hybridization using a photoprobe biotin method. Quantitative hybridization of clinical isolates with labeled DNA of P. intermedia-type strains (ATCC 25611 and ATCC 33563) showed that almost all the clinical strains isolated from disease sites of adults belonged to the ATCC 25611 group, whereas strains isolated from the saliva of children belonged to the ATCC 33563 group. These data, together with the phenotypic characterization of the isolates, suggested that P. intermedia is a heterogeneous species both phenotypically and genetically.