Long-term F release from glass ionomer cements.

Fluoride release from three commercial glass ionomer filling cements and three glass ionomer luting cements was measured in the laboratory over a 12-month period. Fluoride release from these glass ionomer cements was compared with that released from a silicate, silicophosphate, and a fluoride-containing polycarboxylate cement. The fluoride released from the glass ionomer cements throughout the one-year period was similar, both in quantity and pattern, to that released by the silicate cement. The silicophosphate cement tended to release fluoride in somewhat lesser amounts, while the amount of fluoride released by the polycarboxylate was negligible after the first few days. Analysis of these data indicates that these glass ionomer cements probably possess anticariogenic properties similar to those of silicate cement.

Rheology of luting cements.

A rheometer has been developed to simulate the extrusion of luting cement from beneath a full crown during seating using clinically realistic shear rates. Five luting cements were studied, and differences in rheological behavior were illustrated. These measurements demonstrate the importance of consideration of the effects of shear rate on viscosity when evaluating a cement for optimal clinical utilization.

Effect of filler content and size on properties of composites.

Two series of dental composites, along with the unfilled resin matrix, were examined to determine the effects of filler level and size on selected properties. Both series were prepared by incorporating a silanated barium borosilicate filler into a visible-light-activated polyphenylene polymethacrylate resin matrix. One series had a filler particle size of 2 microns, with filler levels of 20, 40, 45, 50, and 53% (vol). The second series contained a 15-microns filler in amounts of 20, 40, 50, 60, and 65% (vol). Tests conducted included: depth of cure as evaluated by hardness, water sorption, compressive strength, stress-strain behavior under slow compression, toothbrush abrasion, and wear by hydroxyapatite. Analysis of the data indicated that increased filler levels resulted in increased hardness, compressive strength and stiffness, and decreased water sorption. Also, there was a slight trend toward improved depth of cure. Incorporation of the 2-microns filler decreased the abrasion resistance of the resins to toothbrushing as compared with the unfilled resin, while addition of the 15-microns filler improved resistance. All filled resins exhibited a significant improvement in resistance to wear by hydroxyapatite as compared with the unfilled resin. There was a trend for increased wear with increased filler level. The particle size of the filler appeared to have a moderate influence on the properties. When compared with 15-microns filled resins of the same filler levels, the 2-micron filled series appeared to have inferior properties in terms of depth of cure, compressive strength, water sorption, and resistance to toothbrush abrasion. Properties which were less affected by particle size were hardness, stiffness, and wear resistance to hydroxyapatite.

Properties of microfilled composite resins as influenced by filler content.

Two series of composite resins were prepared with a light-cured urethane dimethacrylate matrix to which varying amounts of two types of silanated silica particles were added. One series contained volume fractions ranging from 15.8 to 28.8% silica particles of 20 nm in diameter (Type I filler) and the other series volume fractions of from 24 to 49.4% of an agglomerated silica particle of 40 nm in diameter (Type II filler). Tests were conducted to determine the effect of filler level on: depth of cure as determined by hardness measurements; color stability in both UV light and water; water sorption with time; hardness; compressive strength; strain behavior in slow compression; and resistance to toothbrush abrasion and wear by hydroxyapatite. Analysis of the data obtained for these two microfilled series indicate that increased filler levels result in trends for increased depth of cure, color stability, hardness, compressive strength, and stiffness, while water sorption and resistance to both toothbrush abrasion and wear by hydroxyapatite were reduced. These trends were more pronounced for the Type II filler series than for the Type I filler series. However, there was a greater differential in filler levels within the Type II series than within the Type I series.

Thermal diffusion through amalgam and cement base: comparison of in vitro and in vivo measurements.

Thermal diffusion was measured in vitro and in vivo through amalgam and amalgam underlaid with bases of zinc phosphate, zinc oxide-eugenol, and calcium hydroxide cements. Although the magnitudes differed, there generally was good agreement between in vitro and in vivo data with respect to the relative rates of thermal diffusivity through amalgam restorations underlaid with bases of each of the three materials. In all tests, both in vitro and in vivo, the zinc oxide-eugenol base proved to be the best thermal insulator. Calcium hydroxide was the next best thermal barrier and was followed by zinc phosphate cement. In vitro tests indicated dentin to be a better thermal insulator than zinc phosphate cement but inferior to the zinc oxide-eugenol and calcium hydroxide base materials used here. Although a method has been presented here for the in vivo assessment of the efficacy of thermal insulating bases and a number of in vivo experiments were conducted, much research remains to be done in this area. Additional investigation is needed to better define the parameters of thermal change beneath various types of restoratives and also to establish more exactly the role of base thickness in providing thermal protection beneath clinical metallic restorations.

Influence of certain manipulative variables on the static creep of amalgam.

The effects of trituration time on the creep of eight commercial dental amalgams was determined. The data show that trituration time does influence the creep of amalgam, but its magnitude varies from one alloy to another. The condensing procedure also influences creep.

Fluoride distribution in teeth using a silicate model.

The fluoride determinations were done on enamel biopsies taken before and after restoration of extracted teeth with silicate cement. Two sites, one near the restoration and one 3 mm or more away from the restoration, were assayed. No difference was noted in pre- and post-restoration biopsies when teeth were restored with a fluoride-free silicate. Post-restoration biopsies at sites near and away from the restoration were significantly higher in fluoride as compared to pre-restoration biopsies when the teeth were restored with a fluoride-containing silicate.

Addition of fluoride to pit and fissure sealants--a feasibility study.

The data obtained in this in vitro study indicate that contact with pit and fissure sealants to which NaF has been added in amounts ranging from 2 to 5% substantially increases the fluoride content of the enamel and reduces its solubility in acid. The properties of the materials do not seem to be impaired by the addition of fluoride in these amounts. It thus appears that this approach to providing a backup anticariogenic mechanism may, indeed, be feasible. However, further investigation must be done to confirm the anticariogenic effect and to establish the most efficacious means of fluoride incorporation in the materials.

Effect of root canal treatments on dentin permeability.

Calcium hydroxide has been used to slow or reverse external root resorption subsequent to trauma. In this study, an experimental model was established to study the diffusion of calcium ions from the canal to the root periphery after various intracanal treatments. Analyses of calcium ion concentrations from extraradicular samples revealed that dentin specimens varied in their rates of diffusion of calcium and that treatment of the canals with various agents affected the amounts of calcium recovered.

Influence of selected variables on adhesion testing.

Three variables associated with adhesion testing were examined: (1) the test mode, shear and tension; (2) design of the tensile apparatus; and (3) tooth substrate, human and bovine. Findings revealed no significant differences in bond strength by one tensile test and a shear test. However, the shear test produced more true adhesive failures; thus it may be preferable to use a shear test for adhesion testing. Bond strengths with some adhesive systems differed significantly when tested by two different tensile apparatus. Design of the test apparatus appeared to affect values. Bond strength measurements obtained with human and bovine enamel were essentially comparable. Values with dentin varied. There appeared to be a trend for higher bond strength values with bovine than with human dentin.

An in vitro study of certain properties of a glass ionomer cement.

A glass ionomer cement was tested for its release of fluoride, effect on solubility of enamel, bond to enamel, and ability to seal the cavity. It was comparable to silicate cement in its release of fluoride and its effect on solubility of enamel. The strength of the bond of the cement to tooth structure was similar to polycarboxylate cement, and it appeared to be quite effective in sealing cavities.

The influence of mixing speed on the setting rate of high-copper amalgams.

This study was undertaken to assess the effect of mixing speed on the setting rate of high-copper dental amalgam. The surface hardness during setting of two representative brands of dental amalgam was related to working and carving times determined by clinicians. From this information, a means of evaluating setting rate of amalgam based on surface hardness was developed.

In vivo disintegration of luting cements.

The in vivo disintegration of luting cements was determined at 6- and 12-month intervals in two test series of 20 participants each. Four cements were inserted in the wells located in the mesial and distal surfaces of cast crowns. Glass ionomer, silicophosphate, polycarboxylate, and zinc phosphate cements prepared with recommended powder/liquid ratios are discussed, and are ranked with respect to disintegration at 6 and 12 months.

Margin quality and microleakage of Class II composite resin restorations.

Margin quality and isotope microleakage analyses of Class II restorations placed in extracted human molars were compared using various composite resins and placement techniques. At occlusal margins, the traditional (experimental) composite resin restoration placed by the incremental technique showed less microleakage than did the traditional (commercial) [corrected] composite resin restoration placed by the bulk technique. In each group, the occlusal and proximal adaptations had significantly higher "excellent margin" than did the cervical adaptation. Thus, the marginal adaptation at the cervical aspect of conventional Class II composite resin restorations may present a problem with respect to microleakage.

In vitro evaluation of the use of resin liners to reduce microleakage and improve retention of amalgam restorations.

This in vitro study evaluated the ability of three commercially available adhesive resins to reduce microleakage and provide retention between amalgam restorations and tooth structure. Results indicated that Amalgambond reduced leakage significantly more than Panavia EX, Prisma Universal Bond 2, and Copalite. In addition Amalgambond and Panavia EX exhibited the ability to bond amalgam to tooth structure. These results suggest that Amalgambond has the potential for serving successfully as a cavity liner with amalgam.

Direct surface pH determinations of setting cements.

Surface pH measurements were made over a 24-hour period for several luting cements and glass-ionomer lining and restorative materials. Of the luting cements, the water-mixed glass-ionomer cement, Ketac-Cem, had the lowest initial pH and the polycarboxylate, Durelon, had the highest. Three glass-ionomer lining materials showed differences in pH that increased over the entire test period. Two of the three visible-light-cured glass-ionomer liners evaluated showed similar pH values, while the third exhibited a considerably lower pH. The lower pH values found with the water-mixed glass-ionomer luting agent suggest that acidity may contribute to the posttreatment sensitivity associated with this material.

The effects of varied etching time and etching solution viscosity on bond strength and enamel morphology.

The effects of varied etching time and etching solution viscosity on bond strength were evaluated by measuring the tensile bond strength of a composite resin to bovine enamel. Also, six enamel surfaces were examined to evaluate the effect of acid treatment on the morphology of etched enamel using scanning electron microscopy. There was no significant difference in tensile bond strength between three etchants of differing viscosity or between etch times. Light microscopy revealed that most bond failures were cohesive in nature. When the three etchants of differing viscosity were compared under the scanning electron microscope, the liquid and the thin gel produced a more even etch pattern than the thick gel. In addition, the thin gel appeared to produce the most well-defined pattern of the three conditioners.

Efficacy testing of visible-light-curing units.

This study evaluated (1) the effect of known reductions in the output of curing lights on the depth of cure of various resins as determined by hardness measurements, and (2) the ability of the clinician to detect reduced light output by use of an explorer to compare the hardness of the top and bottom surfaces of resin specimens. Curing light output was reduced stepwise from 10 to 70% with neutral density filters. Hardness values indicated polymerization of the top surface to be generally unaffected by light blockage. Bottom surfaces were greatly affected: more with a 30-second than a 60-second cure time. Three clinicians utilized an explorer to compare the tops and bottoms of specimens of known hardness. Evaluators were unable to routinely detect differences of less than 20 to 30 Barcol numbers. The data indicate that a light meter is a more efficacious means of monitoring curing light performance than is a tactile test of resin surface hardness.

Class 5 composite resin restorations: margin configurations and the distance from the CEJ.

An in vitro study of 60 teeth examined the cervical microleakage of class 5 composite resin restorations in regard to preparation design and location from the cementoenamel junction (CEJ). Four groups of 15 teeth each were prepared for a class 5 composite resin restoration with the cervical margins finished as follows: a butt joint margin placed less than 1 mm from the CEJ, a beveled margin placed less than 1 mm from the CEJ, a butt joint placed greater than 1.5 mm from the CEJ, and a beveled margin placed greater than 1.5 mm from the CEJ. The teeth were acid etched, treated with an enamel bonding agent, and restored with a microfilled composite resin, and then sectioned for further analysis. The sectioned specimens were evaluated for cervical microleakage by Ca45 autoradiography. The butt joint margins placed less than 1 mm from the CEJ had significantly more microleakage than the other groups, indicating that all enamel margins of a class 5 composite resin restoration should be beveled to decrease microleakage regardless of their location relative to the cementoenamel junction.

Comparative study: bond strength and microleakage with dentin bond systems.

Four commercial bond agent-composite systems were tested with respect to the strength of the bond to bovine dentin and their ability to seal class 5 erosion lesions without cavity preparation. At seven days there was no significant difference in the bond strengths of the four bonding agents, Scotchbond, Gluma, Tenure, and Scotchbond 2. Restorations placed with Gluma had significantly less leakage than those placed with other bond agents. At 90 days the bond strength of Tenure was reduced and was significantly less than that of the other systems, while Gluma and Scotchbond 2 restorations exhibited significantly less leakage than Scotchbond and Tenure. There was an inverse correlation (r2 = .5460) between bond strength and marginal leakage of class 5 restorations.