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Biomedical subjects

C L Davidson

Publications and source records attributed to C L Davidson.

At least 55 records · Page 3Linked to original sources
PubMed1996

Influence of filler parameters on the mechanical coherence of dental restorative resin composites.

Next to the presence of (chemical) coupling between filler and resin, filler particle size is important for the mechanical coherence of dental resin composites which are used for posterior restorations. In the range of the current composites a smaller particle size is desirable. The better mechanical coherence for composites with smaller particles found in an in vitro erosive wear test is probably related to the size of food fibres, which are part of the erosive medium. It appears that there is a critical value of the filler particle size (1.3-1.5 microns), under which the food fibres are not able to penetrate in the interparticle space, so the erosive capability of the erosive medium will be reduced.

Adhesiveness↗
PubMed1996

Influence of enzymes and plaque acids on in vitro wear of dental composites.

The purpose of this investigation was to test the effect of an enzymatic and an acidic medium on in vitro wear of dental resin composites and an amalgam. Wear was evaluated in two-body and three-body wear conditions. The third body was a food slurry either in water, an esterase solution or an acid solution at a composition and concentration as found in caries active plaque fluid. In the two-body tests the slurry was left out. Under three-body wear conditions neither the enzyme nor the acids showed any significant (P < 0.05) effect on wear. Enzyme inactivation from a large excess of food constituents in the slurry or the absence of an effect from surface diffusion rates of the acids resulted in the lack of an effect on wear. The two-body/acids wear rates were statistically (P < 0.05) lower than the two-body/water wear rates caused by increased lubrication from the acids between sliding surfaces. A significant (P < 0.05) increase in wear was found in the two-body/enzyme experiments, showing that the enzymatic activity can start directly at the outer surface of the composites.

Acids↗
PubMed1996

Shear bond strength of four dentinal adhesives applied in vivo and in vitro.

OBJECTIVES: The purpose of this study was to determine whether dentine bonding performed under clinical conditions is as reliable as laboratory bonding. METHODS: Freshly cut dentine was used in vivo or in vitro as a substrate for the bonding of various adhesive systems. Bond strength was measured in shear loading. RESULTS: Clearfil Liner Bond, Optibond and All Bond 2 showed better results when applied in vivo than in vitro. Scotchbond Multipurpose showed the opposite effect but the bond strength was, for both conditions, superior to the other three products. Only All Bond 2 presented statistically significant differences in bond strength between in vivo and in vitro applied bonding. CONCLUSIONS: The results indicate that, with the new hydrophilic dentine bonding systems, in vitro application does not lead to substantially different results when compared with, in vivo application.

Adhesives↗
PubMed1996

In vivo resin-dentin interdiffusion and tag formation with lateral branches of two adhesive systems.

The close contact of the primer and the conditioned dentin is critical in the bonding of resin composites to dentin. In this study two different adhesive primers were tested in vivo with a separate conditioning procedure (Scotchbond Multipurpose) and a self-etching primer (Clearfil Liner Bond 2). The formation of lateral branches of tubule tags was investigated to substantiate the effectiveness of infiltration as a contribution to retention. Scanning electron microscopy revealed the formation of a resin-dentin interdiffusion zone and penetration into the lateral canals of the tubules for both primers. The resin tags with lateral branches were observed primarily at the floor of the class II cavities. In vivo effectiveness of self-etching priming was demonstrated.

Acid Etching, Dental↗
PubMed1996

Light initiation of dental resins: dynamics of the polymerization.

Literature has shown that slowing down the curing rate of light-initiated resin composites by lowering the light intensity of the light source improved the integrity of the adhesive composite-cavity interface as a result of a more gradual contraction stress development. This study investigated how the curing rate could be controlled by varying the concentrations of the photoinitiator components in BisGMA-TEGDMA resin. Conversions and curing rates were evaluated by linear contraction experiments and Fourier transform infrared spectroscopy. Curing rates could be moderated significantly be reducing the concentrations of both photoinitiator and reducing agent without affecting the conversion, provided that the light exposure with a standard dental light curing unit lasts for 60 s.

Light↗
PubMed1996

Early and long-term wear of conventional and resin-modified glass ionomers.

Various studies have shown that glass ionomers are susceptible to brittle fracture and acid conditions and that they undergo long-term changes in their mechanical properties. Little information is available on how brittleness, acid susceptibility, and long-term changes are reflected in the wear characteristics of glass ionomers. The purpose of this study was to evaluate long-term changes in conventional glass ionomers, metal-reinforced glass ionomers (including a cermet), and (light-curing) resinmodified glass ionomers by wear experiments simulating the wear process in occlusal contact-free areas. The wear tests were conducted periodically over a period of one year. In addition, wear was determined after one year at a pH of 5 or 6, for assessment of acid susceptibility, and at a condition as found in the occlusal contact areas. All materials showed high early-wear rates which decreased significantly during the one-year test period. This long-term process may be related to a slow progression of the acid-base reaction extending over several months. At each stage, the resinmodified glass ionomers wore significantly faster than the acid-base setting glass ionomers. Most of these materials were not affected at a pH of 6.0, while at a pH of 5.0 only the conventional and the metal-reinforced glass ionomers showed increased wear. Direct contacts with the antagonist led to a significant increase in wear in comparison with contact-free wear, probably as a result of sub-surface fatigue phenomena. In view of the unfavorable wear characteristics of the resin-modified glass ionomers and the high early wear of the conventional glass ionomers, including the metal-reinforced glass ionomers, it was concluded that none of these materials can yet be recommended for use in high-stress-bearing situations.

Aluminum Silicates↗
PubMed1996

[The ideal restorative material].

Dental restorative materials have to fulfill a variety of requirements. Based on practical application, a characterization is presented of the advantages and disadvantages of the different existing materials and which are still in a stage of development. Attention is given to ease of handling and functionality. It is concluded that neither a universally applicable nor an ideal material is available for restorative dentistry.

Dental Amalgam↗
PubMed1996

Sealing performance of Scotchbond Multi-Purpose-Z100 in Class II restorations.

PURPOSE: To evaluate the sealing ability of Class II Scotchbond Multi-Purpose/Z100 composite restorations placed under in vivo and in vitro conditions. MATERIALS AND METHODS: For the in vivo part, Class II preparations were cut in posterior teeth which were scheduled for extraction for periodontal reasons. The cervical margins ended in dentin-cementum, 1 mm below the CEJ. The teeth were extracted after 2-3 months of clinical service. The in vitro part was performed in extracted posterior teeth, free from restorations and caries, following the same in vivo protocol. The in vivo and in vitro samples were processed and evaluated for marginal leakage. RESULTS: Leakage by dye penetration was observed at the cervical margins in 70% of the in vivo and in 50% of the in vitro specimens. All in vivo samples with no leakage at the cervical margin were restored where the adjacent interproximal tooth was missing. In more than 40% of the restorations placed in vivo, leakage was also found at the occlusal margins. Statistically significant differences were found at the cervical margins between in vivo and in vitro groups (P < 0.05). The in vitro samples can be of only limited value in predicting clinical performances of an enamel-dentin bonding system in Class II restorations.

Aged↗
PubMed1996

Dentin contamination protection after mechanical preparation for veneering.

PURPOSE: To evaluate in vivo the efficacy in preventing post-operative sensitivity and bacterial invasion of primed dentin that was left unprotected for 4 days after laminate veneer preparation. MATERIALS AND METHODS: Twelve vital, periodontically involved anterior teeth were prepared for experimental laminate veneers and divided into three groups: (1) Control group, in which the prepared surfaces were left unprotected after preparation; (2) Prepared dentin surfaces were cleaned with Tubulicid Red Label and covered with Tubulitec Primer; (3) All-Bond 2 Primer was applied to the prepared dentin surface. Post-operative sensitivity was evaluated immediately and a second appointment, 4 days later. The teeth were then extracted and examined by SEM. RESULTS: The application of a primer (Groups 2 and 3) prevented all sensitivity. After 4 days, the teeth in Group 1 were still sensitive to air blasts. Bacterial penetration into the unprotected tubules was observed in Group 1, but not in Groups 2 and 3.

Adult↗
PubMed1996

Dentin infiltration by three adhesive systems in clinical and laboratory conditions.

PURPOSE: To evaluate in vivo and in vitro the formation of hybrid layer, resin tags and adhesive lateral branches, by use of three different enamel dentin bonding systems. MATERIALS AND METHODS: The dentin adhesives were tested on flat dentin preparations made on buccal surfaces of vital, periodontally compromised teeth. The samples were randomly divided in four groups: Group 1: Prime & Bond 2.0; Group 2: Scotchbond Multi-Purpose Plus; Group 3: Clearfil Liner Bond 2 (the self-etching primer was applied for 30 seconds on the enamel and dentin); Group 4: Clearfil Liner Bond 2 (the self-etching primer was applied for 60 seconds on the enamel and dentin). The sample teeth were extracted immediately after the bonding was cured. The same procedure described for the in vivo samples was performed in vitro on extracted molars. All the samples were split-fractured along their long axis. Half of the samples were used to visualize the hybrid layer and the other half to observe the morphology of resin tags by use of scanning electron microscopy. RESULTS: All the tested products formed a hybrid layer, both in vivo and in vitro. In many areas of the samples of Groups 1, 2 and 4, characteristic reverse cone-shaped tags with their corresponding adhesive lateral branches were evident. In contrast to this, resin tags found in samples of Group 3 were narrower at the tubule orifices, and adhesive lateral branches were scarce. The length of the resin tags observed in the samples of Groups 1 and 2 were longer than those found in Groups 3 and 4. The morphology of the hybrid layer of the in vivo samples was similar to that of the in vitro samples.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1995

The influence of water sorption on the development of setting shrinkage stress in traditional and resin-modified glass ionomer cements.

OBJECTIVES: The aim of this study was to determine the setting stress development for some traditional and resin-modified glass ionomer cements and to assess the effect of early water exposure to this stress. METHODS: The development of the setting stress of the glass ionomer cements was determined in a tensilometer set-up as described earlier by Feilzer et al. (1987). RESULTS: The results of this study show the influence of water sorption on the development of setting shrinkage stress in bonded glass ionomer cements. When curing took place under isolated conditions (no hydration or dehydration), all the traditional glass ionomer cements investigated fractured spontaneously, either adhesively and/or cohesively, due to the developing stress. Early exposure to water led to stress relief and prevented spontaneous fracturing. For the light-cured products, no spontaneous failures were observed under isolated conditions. Stress relief due to water sorption reversed the contraction stress into an expansion stress. SIGNIFICANCE: Exposure of traditional glass ionomer cements to water at an appropriate time by the use of permeable matrix systems is advised. Whether the conversion of contraction stresses into expansion stresses as observed for the resin-modified products, is beneficial for a restoration requires further study.

Absorption↗
PubMed1995

Dentine permeability and bond quality as affected by new bonding systems.

OBJECTIVES AND METHODS: The relationship between dentine bonding and the condition of dentine for four dentine bonding systems (All Bond 2, Clearfil Liner Bond, Scotchbond MP and XR Bond) has been examined. Different dentine conditions were evaluated and correlated with adhesion values. Dentine permeability was calculated using a hydraulic pressure apparatus working under physiological pulpal pressure (6.9 kPa), while remaining dentine thickness (RDT) was measured using pincer calipers. Scanning electron microscopic (SEM) examinations were effected to analyse dentine morphology. These evaluations were considered as an index of the condition of dentine. Shear bond strength tests were used to evaluate adhesion. Dentine samples after the bonding systems application were stored for 24 h under pulpal pressure before bond strength was tested. RESULTS: Scanning electron microscopy examinations indicated that the application of bonding system conditioners caused the removal of smear layer, the demineralization of dentine and the formation of a layer of collapsed collagen fibrils in the intertubular and peritubular dentine. Primers were able to infiltrate the collagen fibrils. A layer of resin infiltrated/reinforced dentine (the so-called 'hybrid layer') was observed for All Bond 2, Clearfil Linear Bond and Schotchbond MP. CONCLUSIONS: Significant correlations were observed only for XR Bond, which proved very sensitive to RDT and dentine permeability despite the presence of smear layer. The other three materials did not show any correlation with dentine conditions. By contrast they showed the highest bond values.

Acid Etching, Dental↗
PubMed1995

Influence of light intensity on polymerization shrinkage and integrity of restoration-cavity interface.

The results of this study showed that the use of high intensity curing light units negatively affected the integrity of the restoration-cavity interface in class V restorations This is explained by the high reaction rates of light curing resin composites. The interfacial integrity was better preserved with low light intensity as it extends the visco-elastic stage of the setting materials, thereby moderating the setting stress development. The ultimate polymerization shrinkages for both conditions were equal, which suggested equal degrees of conversion and thus equal material properties. The results may alleviate the trend in using higher intensity light curing units and in particular the development of units with laser beams in an attempt to further increase conversion rates.

Composite Resins↗
PubMed1995

Tensile strength of thin resin composite layers as a function of layer thickness.

As a rule, cast restorations do not allow for free curing contraction of the resin composite luting cement. In a rigid situation, the resulting contraction stress is inversely proportional to the resin layer thickness. Adhesive technology has demonstrated, however, that thin joints may be considerably stronger than thicker ones. To investigate the effects of layer thickness and contraction stress on the tensile strength of resin composite joints, we cured cylindrical samples of a chemically initiated resin composite (Clearfil F2) in restrained conditions and subsequently loaded them in tension. The samples had a diameter of 5.35 mm and thicknesses of 50, 100, 200, 300, 400, 500, 600, and 700 microns, 1.4 mm, or 2.7 mm. None of the samples fractured due to contraction stress prior to tensile loading. Tensile strength decreased gradually from 62 +/- 2 MPa for the 50-microns layer to 31 +/- 4 MPa for the 2.7-mm layer. The failures were exclusively cohesive in resin for layers between 50 and 400 microns thick. Between 500 and 700 microns, the failures were cohesive or mixed adhesive/cohesive, while the 1.4- and 2.7-mm layers always failed in a mixed adhesive/cohesive mode. For the resin composite tested, the contraction stress did not endanger the cohesive strength. It was concluded that if adhesion to tooth structure were improved, thinner adhesive joints might enhance the clinical success of luted restorations.

Composite Resins↗
PubMed1994

In vitro flexural fatigue limits of dental composites.

The flexural fatigue test equipment developed was used to study the fatigue behavior of dental restorative composites, using a "staircase" approach. Three commercial composites were tested after dry and wet storage conditions. The findings indicate that the method is accurate and reliable, and that changes due to water sorption are clearly reflected: The flexural fatigue limit decreases after water sorption. From the present results it seems that under environmentally controlled conditions, the fatigue behavior is characterized by a well-defined fatigue stress level above which the composites tested fail rapidly, and below which they survive.

Dental Materials↗
PubMed1994

Silane treatment of filler and composite blending in a one-step procedure for dental restoratives.

The aim of this study was to investigate whether a one-step procedure of silane treatment of filler and composite blending could also produce the strong resin-filler integrity, as can be obtained for dental composites in two steps by pretreating the filler with a silane coupling agent before blending. Resin mixtures containing either a silane-functional methacrylate or a non-silane-functional methacrylate were blended with silane pretreated or non-treated filler particles. The resin-filler integrity of the composites was determined from the wear performance in three-body wear tests. For composites with the non-silane-functional methacrylate the wear rates dramatically decreased when the silane pretreated filler was used instead of untreated filler, showing the efficacy of the silane treatment. For composites with the silane-functional methacrylate the decrease was small, indicating comparable resin-filler integrity for the one-step and the two-step procedures.

Analysis of Variance↗