Biomedical subjects

T Dérand

Publications and source records attributed to T Dérand.

12 recordsLinked to original sources

PubMed1992

Bond strength of porcelain on cast vs. wrought titanium.

The bond strength of porcelain fused to cast and wrought titanium surfaces was calculated from fracture loads in a 4-point bending test. Two different porcelain were applied (O'Hara and Duceratin). The surface of Ti-cast specimens was treated in two different ways to produce variations in the impurity level before porcelain veneering. Microhardness measurements as well as scanning electron microscopy with EDX analysis were conducted. The results showed no significant difference in bond strength between the two porcelains. Nor was any difference in bond capacity found between thoroughly blasted castings and wrought titanium. Significantly lower bond strengths were observed for lightly blasted specimens and for specimens treated with Gold bonding agent. Impurities in the surface region of the castings were found to be due to contact with the investment during solidification. This indicates that a thin surface layer (50-100 microns) of the casting should be removed before firing of the porcelain.

Aluminum Oxide↗

PubMed1992

Cytotoxicity of corroded gallium and dental amalgam alloys. An in vitro study.

The cytotoxicity of one gallium and three different dental amalgam alloys was assessed in a cell culture system. Two evaluation methods were used, the filter method and an extraction method. Before being tested, set specimens of the alloys were stored in 0.9% NaCl solution for 1 and 10 weeks, to corrode. The alloys showed various degrees of cytotoxicity, ranging from mild to marked. Differences were found between the two testing methods, but in most cases no major differences in cytotoxicity were found between the Ga alloy and the amalgams. The results encourage further study and development of the Ga alloy, which is mercury-free.

Biocompatible Materials↗

PubMed1991

Reduction of cervical gaps in class II composite resin restorations.

Class II cavities prepared in brass models and in extracted teeth were restored with three light-cured composite resins. A transparent cone-shaped device (Light-tip) at the end of the light source was pressed into the filling material in the proximal box for curing the resin. A second layer was filled in the recess left by the cone and cured without the cone. Controls consisted of fillings cured in two layers. In the brass cavities the contraction gap was 10 microns (+/- 10.6) with use of the cone compared with 109.5 microns (+/- 46.5) in control fillings (p less than 0.001). Extracted teeth were restored without etching of the enamel. Cervical contraction gaps in control restorations were reduced by more than half with the use of the transparent cone technique.

Acrylic Resins↗

PubMed1991

Stress analysis of cemented or resin-bonded loaded porcelain inlays.

Ceramic inlays have become an interesting alternative to amalgam fillings. There are two main ways to affix the inlay to the tooth: by use of either a cement or a composite adhesion system. The aim of the investigation was to examine the two methods' influence on stresses in the inlay and the shear-stress state in the gluing materials. The finite element method (FEM) was used to calculate the stresses and displacements. A two-dimensional inlay was modeled with a 200-N point load on the occlusal surface just over the isthmus. Composite and cement linings were stimulated with and without adhesion, and the stresses were calculated. The results showed a marked compression of the dentin below the proximal part of the inlay. The direct effects of the different elastic constants of the two lining materials influenced the stresses in only a minor way. Complete adhesion reduced stresses in the inlay, compared with cemented inlays, with no adhesion along the pulpal wall. Higher shear stresses were also calculated in the cement compared with the composite.

Dental Bonding↗

PubMed1991

Root caries.

Increasing interest in root caries has resulted in several reports during the year. Problems with diagnosis, epidemiology, structural histopathology, and treatments have clarified some problems concerning root caries. Only active lesions should be registered, but it is important to search for lesions in the periodontal pocket. In several countries, root caries have been found in 30% to 50% of elderly people. In structural investigations, remineralization may occur as irregular precipitation of crystals clearly distinguishable from those of normal sound dentin. Presence of plaque with gram-positive bacteria is closely associated with root caries. Treatment with varnish containing chlorhexidine and thymol may have a reducing effect. Little has been written about the operative treatment of root caries.

Dental Caries↗

PubMed1991

Secondary caries related to various marginal gaps around amalgam restorations in vitro.

Secondary caries lesions were produced in vitro by immersing human tooth-blocks with amalgam restorations every third day for 4 weeks in glucose- or sucrose-containing broth inoculated with a strain of Streptococcus mutans. The lesions at the cavity walls were related to various standardized micro-spaces (0, 30, 40, 60 and 80 microns) around the restorations. When a thick, sucrose induced layer of plaque covered the margin, dentine caries was found in all cases where a gap was present (30 microns or more). In the presence of a thin, glucose induced layer of plaque, dentine caries was detected only in the specimens with 60 and 80 microns gap-widths. Caries lesions were detected on the outer free enamel surfaces in all specimens. Lesions in the enamel of the cavity walls were observed with polarized light in 46% in the presence of sucrose- and in 21% in the presence of glucose-induced plaque.

Dental Amalgam↗

PubMed1989

Effect of topical F- solutions on caries-like lesions in root surfaces.

Topical F- solutions, NaF, SnF2, TiF4, or Fe-Al-NaF, were applied to root surfaces to examine the effect on caries-like lesions produced in vitro. Extracted premolars were treated with a solution for 10 min prior to a 20-day period in acid gel. The lesions were studied by microradiography and light microscopy, and concentration profiles of 12 elements were determined by secondary ion mass spectrometry. The results indicated that the solutions retarded the development of lesions. The greatest effect was obtained with TiF4 and SnF2 solutions. Element analyses revealed that high concentrations of F (up to 3.5%) accumulated in the outer third of the lesion and that SnF2 and TiF4 formed depots in the cementum, although both Sn and Ti also penetrated the lesion. NaF had a weaker effect on lesion formation, but induced a high F concentration in the demineralized zones. The Fe-Al-F solution affected the lesion only marginally and deposited a relatively low F concentration in the lesion, although Fe and Al penetration and depot formation were noted.

Adolescent↗

PubMed1989

Mercury vapor from dental amalgams, an in vitro study.

The aim of this investigation was to examine in vitro the rate of mercury vapor from different types of dental amalgams. Amalgam surfaces of three different states were used, polished, oxidized and corroded. The influence of temperature, tooth brushing and water on the specimens was also examined. The results showed great differences between the polished amalgams stored in air and amalgams corroded in artificial saliva. Single composition types released more mercury than conventional and dispersed ones. Higher temperature raised and water lowered the vapor rates. When the surfaces of the amalgams were brushed with a tooth paste, an instant increase of mercury vapor occurred.

Dental Amalgam↗

PubMed1977

Marginal failure of amalgam class II restoration.

Analysis of stresses in a bicuspid with an amalgam Class II restoration was carried out with the finite element method. When stresses were known, creep in the margin of the restoration was calculated. If the buccal cusp was loaded, the maximum compressive stresses were found in the buccal part of the restoration.

Dental Amalgam↗

PubMed1977

The principal stress distribution in a root with a loaded post in model experiments.

The principal stress distribution in a root with a loaded post was analyzed in model experiments, in which emphasis was directed to the cervical boundary of the root where the stresses are greatest. Maximum stresses were found in the inner proximal sides, and were stronger when the prepared root canal walls were parallel. When contact between post and root was reduced, stresses decreased. These findings point to the importance of sparing tooth substance in the proximal parts of the canal in order to reduce the risk of breaking the cement layer and loosening the post.

Crowns↗

PubMed1976

Creep in amalgam class V restorations.

The purpose of the investigation was to examine the creep rate in an amalgam Class V restoration. The stresses in a central bucco-lingual plane of a loaded bicuspid with a Class V restoration were computed with aid of the finite element method. When the stresses were known, the creep rate was calculated. The results showed that the creep rate of a load of 150 N varied between 0.6% and 3.5% per 104 s for amalgams with large differences between their viscoelastic behaviors. A gap between the restoration and the cavity margin will thus occur if a tooth is often heavily loaded.

Bicuspid↗

PubMed1975

The influence of the cement layer on the strength of porcelain crowns subjected to frequent loading.

The aim of this investigation was to find out whether the support of cemented porcelain crowns was altered by repeated loading. The experiments were carried out on porcelain caps cemented with zincphosphate cement to cores of dentine. One cap was made half the scale of the other. The proximal tensile stresses were determined from strains measured from attached strain gauges with a measuring bridge. The top of the caps were loaded at an angle of 60 degrees. The first measurement was made one hour after the cementation. A loading cycle of 6000 loadings was afterwards started. A second measurement was then made. The proximal tensile stresses were increased after the loading cycle. Only in the small model this increase was significant. This was probably because the cement layer was relatively thinner in the large model. The experiments suggested that repeated loading of porcelain crowns alter the support and then to increase the risk of fractures of the crowns. If the cement layer is thin, this risk is smaller.

Crowns↗