STATEMENT OF PROBLEM: Removable partial denture and complete denture often require denture base relines to improve the fittness against tissue-bearing mucosa because of the gradual change in edentulous ridge contour and resorption of underlyng bony structure. Self-curing hard reline resins offers the immediate and relatively inexpensive means to be recondition the surface of denture base directly. However weak bond between denture base resin and reline material can harbor bacteria, promote staining, or result in complete separation of the two materials. PURPOSE: The purpose of this study was to evaluate the effect of denture cleansers on bond strength and surface hardness of reline resin to denture base resin Denture base resin beams(60.0x15.0x3.0 mm) were made with Lucitone 199. MATERIAL AND METHODS: 10mm section was removed from the center of each specimen. The samples were replaced in the molds and the space of 10mm sections were packed with Tokuso Rebase reline material. The specimens were immersed in denture cleansers(Polident, Cleadent) and were evaluated after 1week, 2weeks, and 4weeks. The bond strength and surface hardness of self-curing hard reline materials to heat-curing denture base resin were measured using an UTM(universal testing machine). RESULTS AND CONCLUSION: 1) There was no significant difference of usage, kind, and denture cleaner by application time on the bonding strength of self-curing hard reline resin to denture base resin. 2) There was no significant difference of usage, kind, and denture cleaner by application time on the surface hardness, but the surface hardness showed decreasing tendency, as the time of immersion was extended 3) The failure modes of the specimens was initially adhesive failure and finally cohesive failure of self-curing hard reline resin.

PURPOSE: The purpose of this sudy was to compare the fracture resistance of the IPS Empress ceramic crown with 1.0mm width rounded shoulder, which is usually recommended in all ceramic crown, and 0.5mm width chamfer finish lines on the maxillary central incisor. MATERIAL AND METHOD: After 15 metal dies were made for each group, the IPS Empress all ceramic crowns were fabricated and cemented with resin cement(Bistite resin cement, Tokuyama Soda Co. LTD., Japan) on the metal die. The cemented crowns were mounted on the positioning jig and the universal testing machine(Zwick Z020, Zwick Co, Germany)was used to measure the fracture strength, with loading on the incisal edge. And also, three-dimensional finite element stress analysis was used to measure the stress distribution with the various types of the finish lines(1.0mm width rounded shoulder, 0.5mm width chamfer), the loading site(incisal edge, incisal 1/3), and the type of loading(concentration loading, distribution loading). RESULTS AND CONCLUSION: 1. In the fracture resistance experiment according to the finish line, the mean fracture strength of rounded shoulder(876N) and the mean fracture strength of chamfer(882N) did not show any significant difference between each other(p<0.05). 2. The stress distribution of all ceramic crown in three dimensional finite element analysis showed concentration aspect at loading point and cervical area of labial surface. 3. In metal die, there were no differences in stress distribution between finish lines, but in natural teeth model, chamfer finish line showed higher stress than rounded shoulder finish line. 4. When force was loaded on the incisal edge, the stress was concentrated on the incisal edge and the cervical area of labial surface. When force was loaded on the incisal 1/3, the stress concentrated on the cervical area of labial surface and the cingulum area. 5. Generally, natural teeth model showed higher and various stress than the metal die.