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C A Fernandes

Publications and source records attributed to C A Fernandes.

5 recordsLinked to original sources
PubMed2001

Tensile strength of human dentin as a function of tubule orientation and density.

PURPOSE: This study investigated the ultimate tensile strength (UTS) of human dentin as a function of tubule orientation and density. MATERIALS AND METHODS: Slabs of dentin (ca 0.7 mm thick) were obtained from human third molars by either transversally or longitudinally sectioning the crowns with an Isomet saw. The slabs were gently trimmed to reduce the central area of the coronal dentin to a cross-sectional area of approximately 0.5 mm2. The longitudinally sectioned slabs were either trimmed from the mesial and distal sides or from the occlusal and pulpal aspects to permit the tensile load to be applied either parallel or perpendicular to the tubule orientation. The transversally sectioned specimens were obtained at several distances from the pulp and were used to evaluate the effects of tubule density. The trimmed specimens were tested in tension on a Kratos testing machine at 0.5 mm/min. After failure, the UTS of each was calculated and expressed in MPa. The fractured ends of the transversally sectioned specimens were viewed under SEM to calculate the number of tubules per mm2 at the site of fracture, and its relation with the UTS was investigated by regression analysis. RESULTS: The UTS of dentin is higher when the load is applied perpendicular to the tubule orientation (80 +/- 13 MPa) than when applied parallel to tubule orientation (58 +/- 11 MPa, p < 0.05). There was a tendency for dentin to be weaker as the number of tubules at the site of fracture increased, although this relationship was not statistically significant (R2 = 0.051, p > 0.05). CONCLUSION: The UTS of dentin is dependent on the tubule direction. Dentin tends to be weaker as the number of tubules per area increases.

Dental Stress Analysis↗
PubMed2000

Effects of prism orientation on tensile strength of enamel.

PURPOSE: This study tested the hypothesis that the tensile strength of enamel varies according to prismatic orientation. MATERIALS AND METHODS: Eight extracted, caries-free human third molars were thoroughly cleaned with pumice and water. The entire enamel surface was conditioned with 37% phosphoric acid for 30 s, air dried, and bonded with Single Bond adhesive system. Several layers of composite (Z-100) were incrementally applied to the crown to build up a "cube-like" resin structure approximately 5 mm thick covering the entire crown of the teeth. The teeth were stored for 24 h in water at 37 degrees C, and then the crown was serially, vertically sectioned in a mesio-distal direction to obtain several slices approximately 0.7 mm thick. The slices were sectioned into halves, and each half was gently trimmed from both sides with a diamond bur to reduce the cross-sectional area to a "neck" located in enamel, either on the external slope or functional slope of the cusps. The specimens were trimmed to permit testing of enamel with its prisms either oriented parallel (PL) or perpendicular (PD) to the applied load. The trimmed specimens were glued to the fixtures of a Vitrodyne tester and stressed in tension at 0.5 mm/min. SEM images were taken from the fractured surfaces to examine the site of failure and confirm the prism orientation. RESULTS: Mean tensile strength of enamel was 24.7 +/- 9.6 MPa (n = 22) for PL and 11.4 +/- 6.3 MPa (n = 22) for PD oriented enamel prisms (t value = -5.45, p < 0.05). There was no significant difference between specimens originating from different slopes of the cusps (p > 0.05). CONCLUSION: The results showed that tensile strength of enamel is dependent on the prismatic orientation.

Acid Etching, Dental↗
PubMed1999

The microtensile bond test: a review.

PURPOSE: The purpose of this review is to describe all of the various modifications of the microtensile bond test in one paper, so that investigators can select the modification that best suits their needs. METHODS: The essence of the microtensile test is the division of resin-bonded teeth into slabs between 0.5 and 1.0 mm thick that are then trimmed in such a manner that tensile force will be concentrated on the bonded interface during testing. Among the many advantages of the technique are that each tooth produces multiple specimens. Further, there is no need for a matrix to limit the bonded surface area, since the area is determined by the dimensions of the trimmed specimens. RESULTS: The various modifications of the microtensile test have been used to measure differences in regional bond strength across occlusal dentin, down the external surface of teeth from crown through roots, down the internal surface of root canals from cervical to apical thirds, as well as to compare normal vs caries-affected occlusal dentin and normal vs sclerotic cervical dentin. The technique is ideal for evaluating the long-term durability of resin-hard-tissue bonds. CONCLUSION: The microtensile test methods offer versatility that cannot be achieved by conventional methods. It is more labor-intensive than conventional testing, but holds great potential for providing insight into the strength of adhesion of restorative materials to clinically relevant sites and substrates.

Dental Bonding↗
PubMedDate not supplied

[Geriatric nursing].

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Geriatric Nursing↗