Chiayi Shen

Work of adhesion of resin on treated lithia disilicate-based ceramic.

OBJECTIVE This study is to test the hypothesis that chemical etching and silane coating of a ceramic surface will influence the work of adhesion (WA) of adhesive resin to dental ceramic. METHODS A hot-pressed lithia disilicate-based ceramic was used as a model material to investigate the influence of probing media and surface treatments on WA using a dynamic contact angle analyzer. Eighty ceramic specimens were randomly divided into eight experimental groups and treated as follows: (1 and 3) as polished; (2 and 4) etched with 9.5% hydrofluoric acid (HF) for 1 min; (5) etched with 4% acidulated phosphate fluoride (APF) for 2 min; (6) silane coated; (7) etched with HF for 1 min and silane coated; (8) etched with APF for 2 min and silane coated. Advancing and receding contact angles (theta(a) and theta(r)) were measured using high purity water (gamma = 72.6 mN/m) for groups 1 and 2, and a liquid resin (gamma = 39.7) for groups 3-8 as probing liquids. RESULTS The liquid resin medium yielded a lower WA than water. Silanization produced a significantly lower WA (p < 0.001) than non-silanated surfaces. Etching alone consistently yielded a greater WA for all surface treatments (p < 0.001). SIGNIFICANCE The silanated ceramic surface exhibited a lower surface energy and did not enhance bonding to the liquid resin by work of adhesion.

The effect of glutaraldehyde base disinfectants on denture base resins

The effect of two alkaline glutaraldehyde base disinfectants on a heat-cured denture base resin was evaluated by the flexural strength, the repair flexural strength, and the surface morphology of the material that had been immersed up to 12 hours in the disinfecting solutions. The flexural strength of the material was not significantly affected by either disinfectant. The disinfectant with phenolic buffer caused surface pitting of the material after 10 minutes of immersion, and softening and swelling of the surface after 2 hours of immersion. No apparent surface change was observed with the regular alkaline formulation, however. Between the two repair resins, the autopolymerized resin yielded greater repair flexural strength than the light-cured repair resin. However, the repair flexural strength of autopolymerized resin seemed to be influenced by either disinfecting solution whereas the light-cured repair resin was not affected.

Strength of denture repairs as influenced by surface treatment

A c r y l i c resin is an indispensable material in removable prosthodonties. Unfortunately, removable restorations that are made totally or partially of acrylic resin will fracture if dropped or stressed beyond their fracture strength. Several techniques and materials have been used to repair fractured dentures. The ultimate goal is to restore the original strength of the denture and to avoid further fracture. However, this goal cannot always be attained. For example, the highest transverse strength for repaired dentures is about 80% of the original strength when heat-cured resin is used. ~ Furthermore, the fracture of the repaired specimens often occurs at the junction of the old and new materials rather than through the center of the repair where the load is applied. This finding clearly indicates that the interface of the old and new materials is the location of stress concentration during transverse strength testing, regardless of the technique used. Denture repairs involve joining two parts of a fractured denture with a denture repair material. In essence, the success of denture repairs relies on the phenomenon of adhesion. Surface preparation of the sites to be joined is of paramount importance to assure a long service life. 2 Correct surface preparation means a strong bonding interface, which can improve the repair strength and reduce stress concentration. Normally, the surfaces to be joined are ground with a handpiece to a desirable profile and cleaned; the surface is treated with monomer before the repair materials are inserted? Research in denture repairs has concentrated on the effect of edge profile (one method of surface preparation) or on repair materials. Polymer surfaces can be etched by appropriate chemicals, a process which changes considerably the morphology and chemical properties of the surface and promotes better adhesion? The concept of etching to improve bonding has not been clearly addressed or applied to denture repair. The purpose of this study was to

Controlled Release of Chlorhexidine from UDMA-TEGDMA Resin

Chlorhexidine salts are available in various formulations for dental applications. This study tested the hypothesis that the release of chlorhexidine from a urethane dimethacrylate and triethylene glycol dimethacrylate resin system can be effectively controlled by the chlorhexidine diacetate content and pH. The filler concentrations were 9.1, 23.1, or 33.3 wt%, and the filled resins were exposed to pH 4 and pH 6 acetate buffers. The results showed that Fickian diffusion was the dominant release mechanism. The rates of release were significantly higher in pH 4 buffer, which was attributed to the increase of chlorhexidine diacetate solubility at lower pH. The higher level of filler loading reduced the degree of polymerization, leading to a greater loss of organic components and higher chlorhexidine release rates.

Effect of surface topography on the bond strength of a composite to three different types of ceramic

STATEMENT OF PROBLEM Mechanical retention based on the surface topography is critical for the success of chairside repair of chipped or fractured ceramic prostheses with a composite. PURPOSE The purpose of this study was to investigate whether the tensile bond strength of a composite to 3 dental ceramics was affected by surface roughening procedures on the ceramics. MATERIAL AND METHODS Three ceramics, Eris (ERV), Empress 1 (E1C), and an experimental ceramic (EXC), were used to fabricate 12 rectangular blocks (5 x 5 x 10 mm). After polishing with a series of SiC papers (120 through 1200 grit size), 4 surfaces were created on each ceramic as follows: 1) as-polished (P); 2) airborne-particle abraded with 50 microm Al(2)O(3) (A); 3) etching with 5% hydrofluoric acid gel (E); and 4) a combination of airborne particle abrasion and etching (A/E). An adhesive (Heliobond) was applied on the roughened ceramic surface and a composite (Tetric Ceram) was built-up incrementally. Twelve groups of different ceramic/surface treatment combinations were prepared. Twenty ceramic/composite specimens per group (0.9 x 0.9 x 20 mm) were obtained from each block with a slow speed diamond saw. Each specimen was subjected to a tensile force at a crosshead speed of 0.5 mm/min using a universal testing machine until failure. The mode of failure was determined by scanning electron microscopy. ANOVA and Duncans multiple range test (alpha=.05) were used to analyze the bond strength values. RESULTS Specimens of all as-polished groups and EXC(A) group separated during sectioning. The mean bond strength values (SDs) in MPa for the remaining groups were as follows: ERV(A): 2.6 (0.8); E1C(A): 2.8 (1.1); ERV(E): 3.1 (1.3); ERV(A/E): 9.3 (1.3); E1C(E): 10.5 (1.5); E1C(A/E):13.5 (3.3); EXC(E): 19.2 (4.7); and EXC(A/E): 23.1 (5.4). ANOVA showed statistically significant differences in the bond strength for both ceramics (P<.0001) and surface treatments (P<.0001). Duncans analysis yielded following statistical subsets of the bond strength values: EXC > E1C > ERV by ceramic; A/E > E > A by surface treatment. The mode of failure was a combination of adhesive and cohesive failures. CONCLUSION The tensile bond strength of a composite to ceramic was significantly different depending on the surface topography of ceramic. Among the surfaces investigated, combined surface roughness was the most effective surface topography in terms of the bond strength increase.

Interactive Effect of Stress and Temperature on Creep of PFM Alloys

The creep rates of six alloys for porcelain-fused-to-metal (PFM) restorations were determined as a function of flexural stress and temperature. Although two Pd-Cu alloys demonstrated excellent resistance to creep at low-stress, high-temperature conditions, they were especially susceptible to deformation at high stresses and temperatures near the glass transition temperature of dental porcelains. In comparison, a Ni-Cr alloy and a Pd-Co alloy demonstrated superior creep resistance at high-stress, low-temperature conditions. This indicates a relatively low potential for deformation due to stresses which may result from a thermal contraction differential between these two alloys and incompatible dental porcelains.

Strengthening of Feldspathic Porcelain by Ion Exchange and Tempering

This study investigated the effectiveness of tempering and ion-exchange treatments on crack growth and bi-axial flexural strength of seven feldspathic porcelains. The results showed that tempering treatment was more effective in strengthening porcelain than was the ion-exchange process as measured by the bi-axial flexural strength. However, the results of initial crack size induced by a microhardness tester showed that ion-exchange yielded a surface that was more resistant to crack initiation than was that yielded by the tempering treatment. EDX and microprobe analyses showed that there was evidence of exchange between Na+ within the porcelain surface and K+ from the ion-exchange agent applied on the surface.

Strengthening of porcelain by ion exchange subsequent to thermal tempering

The purpose of this study was to test the hypothesis that high-leucite content feldspathic porcelain can be strengthened best by thermal tempering followed by ion exchange, compared with either thermal tempering or ion exchange alone. The results of biaxial flexure testing indicate that thermal tempering was the most effective way of strengthening the porcelain among the three methods tested. The combined procedure did not yield the greatest strengthening effect as hypothesized, but one that is only slightly stronger than that produced by ion exchange alone. Weibull analysis indicated that the ion-exchange treatment resulted in a narrower distribution of biaxial flexural strength compared with that of untreated or thermally tempered porcelain. The narrower distribution of biaxial flexural strength is considered desirable for enhancing the longevity of ceramic-based dental restorations.

Effect of CaF2 Content on Rate of Fluoride Release from Filled Resins

Information on the time-dependent release of fluoride from filled resins containing fluoride particles as a function of particle content and solution pH is limited. This study characterized the fluoride ion release from filled resins containing CaF2 particles as a function of filler content and pH. Urethane dimethacrylate and triethylene glycol dimethacrylate resins were used to make filled-resin disks containing 9.09, 23.08, or 33.33 mass% CaF2 filler. Fluoride ion release for the 9.09 mass% concentration was independent of pH. Increasing the filler content from 9.09 to 33.33 mass% increased the fluoride release rate in pH 4.0 buffer solution, because of greater surface degradation. Fluoride ion release from disks stored in pH 6.0 buffer solutions occurred mainly by diffusion from disk surfaces, while fluoride release from disks in pH 4.0 buffers was controlled by diffusion from disk surfaces and degeneration of the resin matrix, which exposed more CaF2 particle surface area.

Effect of metal selection and porcelain firing on the marginal accuracy of titanium-based metal ceramic restorations

STATEMENT OF PROBLEM Titanium is the most biocompatible metal used for dental casting; however, there is concern about its marginal accuracy after porcelain application since this aspect has direct influence on marginal fit. PURPOSE The purpose of this study was to determine the effect that metal selection and the porcelain firing procedure have on the marginal accuracy of metal ceramic prostheses. MATERIAL AND METHODS Cast CP Ti, milled CP Ti, cast Ti-6Al-7Nb, and cast Ni-Cr copings (n=5) were fired with compatible porcelains (Triceram for titanium-based metals and VITA VMK 95 for Ni-Cr alloy). The Ni-Cr alloy fired with its porcelain served as the control. Photographs of metal copings placed on a master die were made. Marginal discrepancy was determined on the photographs using an image processing program at 8 predetermined locations before airborne-particle abrasion for porcelain application, after firing of the opaque layer, and after firing of the dentin layer. Repeated-measures 2-way ANOVA was used to investigate the effect of metal selection and firing stage, and paired t tests were used to determine the effect of each firing stage within each material group (alpha=.05). RESULTS ANOVA showed that both metal selection and firing stage significantly influenced the measured marginal discrepancy (P<.001), and there was interaction between the 2 variables (P<.001). Student-Newman-Keuls multiple comparison tests showed that there were significant differences between any 2 metals compared, at each stage of measurement. Paired t tests showed that significant changes in marginal discrepancy occurred with opaque firing on milled CP Ti (P=.017) and cast Ti-6Al-7Nb alloy (P=.003). CONCLUSIONS Titanium copings fabricated by CAD/CAM demonstrated the least marginal discrepancy among all groups, while the base metal (Ni-Cr) groups exhibited the most discrepancy of all groups tested.