PubMed · 5279877
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E A Fanning, T Brown. 1971. Primary and permanent tooth development.. https://doi.org/10.1111/j.1834-7819.1971.tb00979.x
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The purpose of this study was to evaluate the degradation of resin-dentin bonds after 1 year of water storage. Resin-dentin-bonded specimens were prepared with the use of an adhesive resin system (One-Step: Bisco). Half of the experimental specimens were sectioned perpendicular to the adhesive interface to produce a beam (adhesive area: 0.9 mm(2)) before being stored in distilled water at 37 degrees C for 1 year. The remaining half of the bonded specimens were sectioned into beams of similar dimensions after 1 year of water storage. Additional bonded specimens that had been stored in water for 24 h before sectioning into beams were used as controls. The beams in the two experimental groups and the control group were subjected to microtensile bond testing. Fractography was performed on all fractured beams with the use of FE-SEM. There were significant (p <.05) differences in bond strength among the control specimens (55.9 +/- 12.9 MPa), specimens that had been sectioned into beams after water storage (68.9 +/- 18.6 MPa), and specimens that had been sectioned into beams before water storage (28.1 +/- 9.3 MPa). Fractography revealed that the resin material was gradually extracted from the periphery to the center portion of the beam. This probably accounted for the decrease in bond strength after 1 year of water storage.
The longevity of dental restorations is dependent on many different factors, including those related to materials, the dentist, and the patient. The main reasons for restoration failure are secondary caries, fracture of the bulk of the restoration or of the tooth, and marginal deficiencies and wear. The importance of direct-placement, aesthetic, tooth-colored restorative materials is still increasing. Amalgam restorations are being replaced because of alleged adverse health effects and inferior aesthetic appearance. All alternative restorative materials and procedures, however, have certain limitations. Direct composite restorations require a time-consuming and more costly treatment procedure and are actually only indicated for patients with excellent oral hygiene. Glass ionomers can be considered only as long-term provisional restorations in stress-bearing posterior cavities. Future treatment regimens that are made possible by the development of sophisticated preparation techniques, improved dentin bonding agents, and resin-based restorative materials will result in the therapy of more small-sized lesions rather than large restorations. The importance of indirect inlay techniques will shift more and more toward the direct restoratives. As the cavities become smaller, it is to be expected that the use of improved direct restorative materials will provide excellent longevity even in stress-bearing situations.
OBJECTIVES: The purpose of this study was to compare the effects of the diameter, the length and the number of implants on stress distribution in the bone around the implants supporting three-unit fixed partial prostheses in the mandibular posterior edentulism. MATERIALS AND METHOD: A mandibular Kennedy II three-dimensional finite element model was constructed. Four fixed partial prostheses with two terminal implant supports of various lengths and diameters, and two fixed partial prostheses with three implant supports of various lengths were designed. In separate load cases, 400 N oblique, 200 N vertical, and 57 N horizontal forces were simulated. The tensile and the compressive stress values in the cortical bone around the collar of the implants and Von Mises stresses in the implants were evaluated. RESULTS: Although the change in the length of implants did not decrease the stress levels, lower tensile and compressive stress values were observed in the bone for wider implant placement configurations. Similar stress distributions and close stress levels were observed for two wider implant supports in comparison with the three-implant-supported fixed partial prostheses. CONCLUSION: With the use of two implants of 4.1-mm diameter and 10-mm length as terminal supports for three-unit fixed prostheses, the magnitude and the distribution of stresses in the cortical bone around the implant collar is within the normal physiological limits.