Staining calcified dental tissues with food.

The discoloration of enamel caused by food substances was found to be superficial and for dentin and cementum ingressive. Discoloration of cementum exceeded that of dentin, and dentin stained more than enamel. Coffee and soy sauce stained the calcified dental tissues more than the cola beverage and tea. The longer the staining time, the deeper was the discoloration.

Retention of cast crowns cemented to amalgam and composite resin cores.

An in vitro study was conducted to determine the tensile bond strength of complete cast gold restorations cemented with zinc phosphate cement on composite resin and amalgam crown cores. The samples were thermocycled and tested at 1-week, 1-month, and 3-month intervals. Results of the study showed that: (1) the amalgam core provides more retention for the cast gold crown than does the composite resin core and (2) the composite resin core provides increasing retention over a longer time period.

Auxiliary retention for complete crowns provided by cement keys.

1. Cement keys were an effective means of increasing the retention of complete cast gold crowns to preparations in extracted teeth. 2. Single grooves placed in either the dentin or in the crown alone were not effective in increasing retention in 30-degree crowns. In 7-degree crowns, a single groove in the crown gave better retention than a single groove in the dentin. 3. Crowns with a 7-degree taper had greater retentive strengths than 30-degree crowns treated identically. The retentive strength of 7-degree crowns with cement keys approached the tensile strength of zinc phosphate cement.

Marginal leakage: entry side and exit side-clinical implications.

The marginal leakage along the proximal walls of Class II amalgam restorations was studied. The influence of the direction of the bur rotation to tooth structure in cavity preparation was the primary concern of investigation. Also, the effect of different cavity wall finishing techniques created by exit and entry action of the rotating bur and that of two different types of amalgam on the marginal leakage was studied. The degree of marginal leakage was not significantly different among any of the treatment groups.

Microleakage of pin-retained amalgam and composite resin bases.

The marginal leakage of a composite resin (Adaptic) and an amalgam (Tytin) utilized as pin-retained bases was studied. The results indicated that the amalgam bases had less leakage than composite resin bases. No significant difference was found between the degree of leakage at enamel margins and dentinal margins.

Marginal leakage of compacted gold, composite resin, and high-copper amalgam restorations.

Amalgam and compacted gold were found to have the least marginal leakage in Class V cavities. Composite resin with acid etching performed at an acceptable level. Without acid etching the marginal seal was unsatisfactory. The following conclusions can be drawn: 1. High-copper amalgam and compacted gold are the materials of choice for Class V restorations when esthetics are not of primary concern. 2. If composite resins are to be used, they should be placed with an acid-etch technique.

The ability of foods to stain two composite resins.

In this bench study, coffee and soy sauce stained composite resin restorations to a significantly greater degree than did tea or cola beverage. Generally, the greatest degree of staining with all samples occurred during the first week of the study time. The stain penetration was superficial and was estimated to be 5 mu or less.

The fracture strength of amalgam overlying base materials.

Conclusions reached within the constraints of this study showed the following: 1. Fracture strength of Class II amalgam restorations decreased as the thickness of the bases increased. 2. Fracture strengths of amalgam restorations based with different thicknesses of zinc phosphate cement underline with 0.5 mm Dycal were not different from each other. 3. The strength of the restorations varied with the type of base. Zinc phosphate cement is equal to no base and superior to zinc phosphate cement plus Dycal, which is equal to Dycal. Dycal is superior to Cavitec, which is the same as Cavitec plus Dycal. 4. The base materials did not fracture. The amalgam restorations were stronger over a base with a higher modulus of elasticity, indicating that modulus of elasticity of a base is more important than compressive strength in supporting an amalgam restoration. 5. There is no advantage (no improvement in resistance to fracture of the amalgam restoration) to be gained from placing zinc phosphate cement over Dycal. 6. When a calcium hydroxide liner is not needed, the cements with a higher modulus of elasticity, such as zinc phosphate cement and reinforced ZOE, will provide for stronger amalgam restorations than Cavitec and unreinforced ZOE.