An evaluation of the time-dependent dimensional stability of elastomeric impression materials / 대한치과보철학회지

Statement of Problem: The accuracy and dimensional stability of elastomeric impression materials have been the subject of numerous investigation. Few studies have addressed the effect of changes in time on the dimensional stability of impression materials. Purpose: The purpose of this investigation was to evaluate the effects of elastomeric impression materials and storage time on dimensional stability. Materials and methods: A total of 75 impressions were made of epoxy resin dies mimicked prepared 3-unit fixed partial denture. The dies had 1 buccolingual, 1 mesiodistal and 1 occlusogingival lines and interpreped dot. Impression materials investigated included two polyether impression materials and three polyvinylsiloxane impression material. 15 specimens were made of each impression material and poured by type IV stone over times(30 minutes, 24 hours, 72 hours) after mixing; the same examiner measured each specimen 3 times at a magnification of 3.5*. All statistical tests were performed with the level of significance set at .05. Results: The results indicated that significant difference at any measuring point of stone dies of the polyvinylsiloxane and polyether impression materials when measurements at 30 minutes, 24hours, and 72 hours were compared; the length of measuring point increased significantly as time passed by. However, this result is not significant clinically. Analysis also showed significant differences at any measuring point when polyvinylsiloxane and polyether impression materials were compared and significant differences clinically. Conclusion: Under the conditions of this study, the shrinkage rate of the polyvinylsiloxane and polyether impression materials significantly increased as time passed by. The polyether impression materials showed higher shrinkage significantly, while the shrinkage rate of all five materials showed a significant time-dependent increase.

Bond strength of resin cements to zirconia ceramic / 대한치과보철학회지

STATEMENT OF PROBLEM: Although zirconium oxide ceramics are more and more commonly used in restorative dentistry, for many clinical applications only limited data can be found in the literature. However, it is quite clear that hydrofluoric acid etching is impossible with zirconia ceramics. Therefore, other bonding techniques are required in order to lute these materials adhesively. PURPOSE: The purpose of this study was to evaluate the effects of surface treatments on shear bond strengths between two resin cements and a zirconia ceramic. MATERIALS AND METHODS: Experimental industrially manufactured yttrium-oxide-partially-stabilized zirconia ceramic discs (Adens, Korea) were used for this study. The ceramic specimens divided into five experimental groups and a control group (as received). Five surface treatments were studied. 1) sandblasting with 110 micrometer Al2O3 at 3 bars pressure 13 seconds at a distance of 10mm, 2) flame-treated with the Silano-Pen for 5 s/cm2, 3) grinding with a diamond bur, 4) sandblasting + Silano-Pen treatment, 5) diamond bur preparation+ Silano-Pen treatment. Acrylic plastic tube (5 mm in height and 3 mm in diameter) were filled with composite to fabricate composite cylinders. The composite cylinders were bonded to the ceramic specimens with either Superbond C & B or Panavia F resin luting agents. All cemented specimens were tested under shear loading until fracture on universal testing machine at a crosshead speed 1mm/min, the maximum load at fracture was recorded. Shear bond strength data were analyzed with oneway analysis of variance and Tukey HSD tests (p<.05). Treated ceramic surfaces and fracture surfaces after shear testing were examined morphologically using scanning electron microscope. Results: Ceramic surface treatment with Silano-Pen after sandblasting improved the bond strength of Superbond C & B resin cement. Superbond CandB resin cement at Silano-Pen after sandblasting(27.4 +/- 3.8 MPa) showed statistically higher shear bond strength than the others. CONCLUSION: Within the limitation of this study, Superbond C & B resin cement are suitable for cementation of zirconia ceramics and flame-treated with the Silano-Pen after sandblasting is required to enhance the bond strength.

Physical Properties Of Relining Denture Base Resins With Different Polymerizing Methods / 대한치과보철학회지

This study would like to measure and compare water sorption and solubility of acrylic resins, with 3 different polymerizing methods, and tensile strength between denture base resin and relining resins. For this experiment, 3 different acrylic resins were used; heat polymerizing resin: Vertex (Dentmex, Zeist,Holland), autopolymerizing resin: Tokuso Rebase (Tokuyama Corp, Tokyo, Japan), and light curing resin: Mild Rebaron LC (GC Corp, Tokyo, Japan) The results were as follows; 1. Tokuso Rebase showed the lowest water sorption, followed by Mild Rebaron LC and Vertex. Among resins, there were some signigicant differences (P0.05). About 50% of Rebaron LC showed cohesive fracture. 4. Tensile strength has more decreased after thermocycling than before, but there was no statistical difference (P>0.05).