Rafael Grajower

Improving the fit of crowns with die spacers

This investigation studied the dependence of seating crowns on the thickness of layers of spacers applied to dies. Extracted molars were prepared to designated taper angles. Artificial stone dies were prepared in polyether impressions of tooth preparations and covered with one to five layers of new or old spacer material in a predetermined manner. Wax patterns were invested to obtain a uniform and low expansion. Crowns were cast, luted to the teeth, invested in acrylic resin, ground parallel to the axes of the teeth, and inspected microscopically. The average thickness of layers of new and old spacer material was determined. The application of spacers up to the shoulder margins of dies decreased the elevation of the casting above the margin of the tooth preparation until an average minimum elevation above the shoulder of the preparation was obtained. A further increase in the spacer thickness did not affect the elevation, but increased the cement thickness at the axial walls. The average minimum elevation results mainly from individual protrusions on the casting surface. The optimum thickness of the spacer results in the minimum elevation at the margin together with a low cement thickness at the axial walls. Leaving the cervical part of the axial walls near the margin uncovered with spacer negates the effect of a thick spacer on the remaining die surface almost completely and is therefore contraindicated.

Compatibility of a composite resin with pulp insulating materials. A scanning electron microscope study

Abstract A scanning electron microscope investigation of the interface between Adaptic and pulp insulating materials was conducted. The surface roughness, as caused by insulated materials, was observed to decrease in the sequence ZOE, Dycal, ZPC, and Copalite. Uncured Adaptic dissolved a cavity varnish. The clinical significance of these observations has been discussed.

Fit of crown wax patterns after removal from the die.

The effects of loading the wax pattern before investment was determined. Various loads were placed on the pattern after its margin was remodeled. The patterns were replaced on the die with a load of 50 gm before investment. For loads of 0, 250, and 1000 gm, the average elevation of the pattern on the die was found to be greater by 29, 56, and 19 micron, respectively, than before removal from the die. Repetitive loading showed that the plastic deformation in wax was less in the second than in the first cycle for a specific load. This decrease in plastic deformation may explain the improved adaptation of the pattern after a load of 1000 gm.

Observations on cavity liners for composite resin restorations

Adhesion or surface roughness and discoloration at the interface between pulpinsulating materials and composite resins were taken as indications for interaction between the resins and the insulating materials. Some interaction occurred between all insulating materials and resins investigated. After separation of the restorative resins, the interaction of Dycal with the different composite resins varied considerably and decreased in the following sequence: Opotow, Natural, and Adaptic. The interactions of ZOE with Natural and with Adaptic were similar and more pronounced than the interaction at the Adaptic-Dycal interface but less pronounced than at the Dycal-Natural interface. A very thin film of Tubulitec was found to adhere to the composite resins in some areas. The adherence of liners containing calcium hydroxide to dentin was found to be generally stronger than the bond between these liners and composite resins. Separation of the composite resins caused tears in the varnishes and frequently in Hydroxyline. Almost completely intact layers of the varnish Copalite were observed on dentin, but Zahnlack apparently dissolved to a great extent in the resins. Among the liners containing calcium hydroxide, Dycal and Tubulitec were found to give rise to a high pH in samples of saliva, but Hydroxyline did not. Porosity and a folded surface were observed for Hydroxyline, indicating the entrapment of the solvent beneath a dry superficial layer.

Microhardness of Sclerotic Dentin

Dentin becomes transparent or sclerotic as the result of the obliteration of the tubules by a highly radiopaque material (NALBANDIAN et al, J Dent Res 39:598-607, 1960). Data concerning the relative hardness of transparent dentin, with respect to opaque dentin, are inconsistent. (CRAIG et al, J Dent Res 38:624-630, 1959; RAUTiOLA and CRAIG, J Periodont 32:113-123, 1961). The ash content of tubular dentin was found to be higher than of sclerotic dentin, and the Ca/P ratio of the former material was shown to be higher than that of the latter material when both types of dentin were taken from apical sections (SIMON and ARMSTRONG, JADA 28: 1115-1120, 1941; MANLEY and BROOKS, J Dent Res 26:427-434, 1947; MOORE and LEAVER, Int J Forens Dent 2:13 16, 1974). Hardness of sclerotic dentin was determnined. Teeth with one root were extracted from adult patients. Twenty longitudinal and 15 transverse root sections were prepared. The transition between transparent and opaquie dentin was marked with a fine probe. Vickers microhardness was measured with a load of 200 grams. The indentions were made further than 0.7 mm from the cementLum and the root canal. Opaque dentin was softer than adjacent transparent dentin btut harder than most distant and apical dentin (table). The hard transparent region was as narrow as 200 gm on some transferse sections but more than 600 gm wide on longitudinal sections. The inconsistent results from earlier reports may be attributed to measurements of sclerotic dentin at varying distances from tubular dentin. Obliteration of tubules with a calcified material increases the

A temporary space maintainer using acrylic resin teeth and a composite resin.

A one-session technique for preparing a temporary space maintainer has been described. The technique consists of attaching an acrylic resin pontic to etched surfaces of natural adjacent teeth by means of a composite resin. The main advantages of this technique are elimination of premature tooth preparation, good esthetics, fair strength, low cost, and rapid completion of the restoration without the need of a dental laboratory.

Marginal adaptation of glass-ionomer cements.

The effect of thermocycling on the marginal adaptation of two glass-ionomer cements was determined by means of scanning electron microscopy. Small gaps in the cement as well as at the enamel-cement interface were observed after curing, but these phenomena were not enhanced by thermocycling. Localized areas of surface deterioration were observed for both cements after thermocycling.

Effect of manipulative variables on the accuracy of crown wax patterns

An instrument was developed to carve wax patterns in a reproducible manner. The methods of wax application to the die and wax removal during carving were similar to routine laboratory procedures. The wax patterns were invested in stone with the dies on which they were prepared, and sectioned to allow the determination of their adaptation on sectioned samples. Shrinkage of wax patterns on dies was found to create a marginal gap at shoulders and bevels. Further shrinkage observed after removal from the die was attributed to relaxation of elastic stresses in the wax. Carving of bevels improved adaptation to the die for samples with large gaps at the shoulder. This improved adaptation can be attributed to plastic deformation in the wax bevel. Remodeling of pattern margins was found to improve adaptation to the die, especially if carried out after the pattern was removed and replaced on the die. Remodeling the margin should involve heating with a spatula of a narrow band of wax around the margin up to the axial die wall over the entire shoulder width.

Temporary space maintainers retained with composite resin. Part II: Fracture load in vitro.

The average fracture load during occlusal loading of pontics which were bonded to natural abutment teeth in vitro was found to be 56.1, 57.5 and 74.2 kg for natural, acrylic resin, and Restodent pontics, respectively. Coating the roots of the abutment teeth with a thin layer of silicone rubber before embedding them in stone slightly reduced the strength of the fixed partial dentures. Thermocycling the specimens with coated roots caused a considerable decrease in strength to fracture loads of 33.0, 17.9, and 37.3 kg for natural, acrylic resin, and Restodent pontics, respectively. Fracture of the enamel of natural tooth pontics was observed in a few specimens. The superior strength of the fixed partial dentures with natural tooth and Restodent pontics would indicate that these pontics are superior for clinical trials rather than acrylic resin pontics.

Tooth preparation for full coverage—basic principles and rationalized clinical procedures

The basic principles of tooth preparation for full coverage are discussed and an efficient method is described for the operative procedure. The purpose of each of the four stages in this technique and of the five different diamond instruments which are used in their performance, is discussed. Modifications of the procedure are given for posterior and anterior teeth as well as for teeth with periodontal involvement. Comparing the relative merit of different types of finishing lines, the chamfer type was found most suitable for the majority of preparations.