Surface degradation of lithium disilicate ceramic after immersion in acid and fluoride solutions.

PURPOSE: To analyze whether immersion in sodium fluoride (NaF) solutions and/or common acidic beverages (test solutions) would affect the surface roughness or topography of lithium disilicate ceramic. METHODS: 220 ceramic discs were divided into four groups, each of which was subdivided into five subgroups (n = 11). Control group discs were immersed in one of four test beverages for 4 hours daily or in artificial saliva for 21 days. Discs in the experimental groups were continuously immersed in 0.05% NaF, 0.2% NaF, or 1.23% acidulated phosphate fluoride (APF) gel for 12, 73, and 48 hours, respectively, followed by immersion in one of the four test beverages or artificial saliva. Vickers microhardness, surface roughness, scanning electron microscopy (SEM) associated with energy dispersive spectroscopy, and atomic force microscopy (AFM) assessments were made. Data were analyzed by nested analysis of variance (ANOVA) and Tukey's test (α = 0.05). RESULTS: Immersion in the test solutions diminished the microhardness and increased the surface roughness of the discs. The test beverages promoted a significant reduction in the Vickers microhardness in the 0.05% and 0.2% NaF groups. The highest surface roughness results were observed in the 0.2% NaF and 1.23% APF groups, with similar findings by SEM and AFM. Acidic beverages affected the surface topography of lithium disilicate ceramic. Fluoride treatments may render the ceramic surface more susceptible to the chelating effect of acidic solutions.

Repairing ceramic restorations: final solution or alternative procedure?

This article provides an overview of dental ceramics. It addresses possible modes of failure and factors that may influence the decision to either repair or replace ceramic restorations. The authors' intention was to present ceramic repair as a reliable, low-cost, low-risk technique.

Fluoride prophylactic agents effect on ceramic bracket tie-wing fracture strength.

OBJECTIVE: To test the hypothesis that fluoride prophylactic agents do not affect the fracture strength and fracture morphology of the tie-wing complex of ceramic brackets. MATERIALS AND METHODS: The fracture strength of the distal incisal tie-wing of two polycrystalline brackets, Clarity and Mystique, and a monocrystalline bracket, Inspire, was measured after the brackets were exposed to either Prevident, Phos-flur gel, or distilled water (control). Scanning electron microscopy was used to qualitatively evaluate the tie-wing intact and fractured surfaces. RESULTS: A two-way analysis of variance and Fisher-Hayter post hoc test, alpha = .05, indicated a significant decrease in tie-wing fracture strength following both fluoride treatments when compared with the distilled water control only with the monocrystalline bracket. None of the bracket brands exhibited any qualitative differences in the tie-wing intact or fracture surfaces as a function of fluoride treatment. CONCLUSIONS: The hypothesis is rejected. Based on the results, using topical fluoride agents with monocrystalline brackets might be contraindicated because of increased tie-wing fracture susceptibility.

Effect of fluoride and 10% carbamide peroxide on the surface roughness of low-fusing and ultra low-fusing porcelain.

STATEMENT OF PROBLEM: The effect of repeated applications of fluoride solutions and 10% carbamide peroxide on the surface roughness of newer dental porcelains is not completely known. PURPOSE: The purpose of this study was to compare the surface roughness of 3 different porcelains when exposed to 2 fluoride solutions, a 10% solution of carbamide peroxide, and distilled water. MATERIAL AND METHODS: Forty discs (10-mm diameter, 2 mm thick) were made of each of the following porcelains: feldspathic porcelain (Ceramco II), low-fusing porcelain (Finesse), and an aluminous porcelain (All-Ceram). Each disc was abraded with a medium-grit diamond bur and auto-glazed. One side of each disc was abraded with a diamond bur and polished using a porcelain polishing kit to simulate a chairside adjustment and polishing. The discs (10 specimens/group) were immersed in 1.23% APF, 0.4% stannous fluoride, 10% carbamide peroxide, and distilled water for 50 seconds (control). The discs in the 10% carbamide peroxide solution were immersed for 48 hours. The surface of each disc was evaluated with surface profilometry (0.1 mm/s speed, 600-microm range). The data were analyzed by factorial analysis of variance and a Tukey multiple comparison test, (alpha=.05). RESULTS: The data showed that the acidulated phosphate fluoride etched the auto-glazed surface of all 3 porcelains. For Finesse specimens, the mean Ra values for the auto-glazed surface were significantly higher than that of the control after immersion in 1.23% APF (mean Ra 0.3 +/- 0.06 microm, P<.031). All-Ceram auto-glazed surface specimens had a significantly higher mean Ra value when immersed in the 3 solutions than the control (1.23% APF, 0.4% stannous fluoride, and 10% carbamide peroxide, 0.245 +/- 0.115 microm, 0.22 +/- 0.104 microm, 0.22 +/- 0.04 microm, respectively; P<.002). Ceramco II specimens were affected by all 3 solutions, with the auto-glazed surface having higher Ra values (1.23% APF, 0.4% stannous fluoride, and 10% carbamide peroxide, with mean Ra values of 0.35 +/- 0.1 microm, 0.26 +/- 0.08 microm, and 0.24 +/-.0.05 microm, respectively, P=.001). Immersion in the 3 solutions had no effect on the polished surfaces of all-ceramic specimens tested. CONCLUSION: Prior to the use of fluoride and 10% carbamide peroxide, dentists should ascertain the type of porcelain restoration present to prevent a roughened surface from occurring.

Effect of ceramic surface treatment on tensile bond strength to a resin cement.

PURPOSE: The objective of this study was to test the following hypotheses: (1) hydrofluoric acid (HF)-treated ceramic surfaces produce the highest tensile bond strength to resin cements, independent of the ceramic microstructure and composition; and (2) the tensile bond strength test is appropriate for analysis of interfacial adhesion for ceramic-bonded-to-resin systems. MATERIALS AND METHODS: Ceramic specimens were polished with 1-micron alumina abrasive and divided into four groups of 10 specimens for each of seven ceramic types. One of the following surface treatments was applied: (1) 10% ammonium bifluoride (ABF) for 1 minute; (2) 9.6% HF for 2 minutes; (3) 4% acidulated phosphate fluoride (APF) for 2 minutes; and (4) a silane coupling agent. The surface-treated areas were coated with an adhesive resin and bonded to a resin cement. Specimens were loaded to failure in tension using a testing machine. Tensile bond strength data were statistically analyzed, and fracture surfaces were examined to determine the mode of failure. RESULTS: Silane-treated surfaces showed statistically higher mean tensile bond strength values than surfaces treated with any etchant (HF, ABF, APF). HF produced statistically higher mean tensile bond strengths than ABF and APF. All failures occurred in the adhesion zone. CONCLUSION: The tensile bond strength test is adequate for analysis of the adhesive zone of resin-ceramic systems. The chemical adhesion produced by silane promoted higher mean bond strength values than the micromechanical retention produced by any etchant for the resin-ceramic systems used in this study.

Effect of etching and sandblasting on bond strength to sintered porcelain of unfilled resin.

This study determined the bond strength of an unfilled resin joined to a feldspathic porcelain for the purpose of evaluating the retentive performance of the prepared material surfaces. Porcelain disks (VMK 68 dentin) were either air abraded with alumina (AAA) or etched with one of the following five etchants: (1) ammonium hydrogen bifluoride (AHB); (2) acidulated phosphate fluoride (APF); (3) hydrofluoric acid (HFA); (4) phosphoric acid (PHA); and (5) sulfuric acid-hydrofluoric acid (SHF). Specimens ground with abrasive paper were also used as controls. After surface preparation, the two different sized porcelain disks were bonded together with a methyl methacrylate-based resin initiated with tri-n-butylborane (MMA-TBB resin). Shear bond strengths were determined both before and after thermocycling. Before the thermocycling, the greatest bond strengths (21.3 and 23.7 MPa) were generated with the use of the SHF and HFA agents, followed by the AHB agent (18.4 MPa). Reduction in bond strength after thermocycling was significant for all groups, although the SHF- and HFA-treated groups exhibited bond strengths greater than 15 MPa even after the thermocycling. The results indicated the effectiveness of the SHF- or HFA-etching for retaining the acrylic resin to the porcelain. However, ageing testing also revealed insufficient retentive characteristics of the acrylic resin by etching alone.

Microtensile strength of composite bonded to hot-pressed ceramics.

PURPOSE: The objective of this in vitro study employing the microtensile test was to test the hypothesis that the tensile bond strength of hot-pressed ceramics to composite is controlled by the ceramic microstructure and the ceramic surface treatment. MATERIALS AND METHODS: Hot-pressed IPS Empress (E1) and IPS Empress 2 (E2) ceramic blocks were polished with 1-micron alumina abrasive and treated as follows: group 1: 9.6% hydrofluoric acid (HF) on E1; group 2: 4% acidulated phosphate fluoride (APF) on E1; group 3: silane (S) on E1; group 4: HF + S on E1; group 5: APF + S on E1; group 6: HF on E2; group 7: APF on E2; group 8: S on E2; group 9: HF + S on E2; group 10: APF + S on E2. The surfaces as described above were then treated with Scotchbond Multi-Purpose Plus and covered with composite (Z-100). From the blocks obtained in this manner, specimens for microtensile testing were created by sectioning. Twenty bar specimens for each group were loaded to failure under tension using an Instron testing machine. RESULTS: Mean tensile bond strength (MPa) and standard deviation values are as follows: (1) 9.9 +/- 1.2; (2) 0; (3) 27.2 +/- 4.8; (4) 20.6 +/- 3.0; (5) 13.6 +/- 4.5; (6) 41.7 +/- 6.7; (7) 19.1 +/- 2.6; (8) 30.1 +/- 5.3; (9) 56.1 +/- 4.1; (10) 36.9 +/- 3.9. All fractures occurred within the adhesion zone. SEM images of chemically etched specimens revealed that HF produced greater surface degradation and greater bond strength than APF for both E1 and E2 ceramics. The mean bond strength of groups 6 through 10 (E2) was significantly greater than that of groups 1 through 5 (E1) for each treatment condition. CONCLUSION: The tensile fracture resistance of the composite-ceramic adhesion zones is controlled primarily by ceramic microstructure and ceramic surface treatment.

Effect of topical fluoride agents on the morphologic characteristics and composition of resin composite restorative materials.

STATEMENT OF PROBLEM: The high reactivity of fluoride agents used in topical fluoride treatments have raised important questions on their potential adverse effects on restorative materials. PURPOSE: The purpose of this study was to evaluate the effect of topical fluoride agents used for office or home treatments on the surface morphologic characteristics and composition of composite restoratives. MATERIAL AND METHODS: The fluorides used were Act, Phosflur, Gel II, Prevident, Stop, Butler APE, Nupro, and Omni Gel & Rinse. The composites tested were Brilliant DI, Heliomolar Ro, Herculite XRV, and P-50. The pH of the fluorides was measured as received and after dilution with water at a 1:3 volume ratio. The composites were subjected to the fluoride treatments until the total number of applications simulated the equivalent of 4 years under treatment. The changes induced on the surface morphologic features and composition of the restoratives were assessed by multiple internal reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, and x-ray microanalysis. RESULTS: All fluorides showed an acidic pH that was not significantly changed after dilution, except Stop, which exhibited a significant pH reduction. All fluorides increased the amount of loosely bound water in the composite matrix. Butler APF gel was the most aggressive for Brilliant DI and Herculite XRV, leading to excessive surface degradation, porosity, destruction of the filler-matrix interface, filler dissolution, and debonding. A reduction in the extent of remaining C = C bonds was observed in Herculite XRV after Butler APF treatment; Phosflur, Gel II, and Prevident had a milder effect. Treatment of Brilliant Dl and Herculite XRV with Omni Gel & Rinse resulted in the formation of a stable precipitation layer rich in barium, phosphorus, tin, oxygen, and fluoride. P-50 was severely affected at the resin-matrix interface after Stop treatment, whereas Omni Gel & Rinse induced fewer surface changes. Heliomolar Ro was the least affected restorative regardless of the type of fluoride used.

The effect of topical fluorides on ceramic brackets.

Topical fluorides are frequently prescribed to orthodontic patients to minimize development of initial carious lesions around brackets and bands. However, various topical fluorides are reported to cause surface changes and weight loss of dental materials composed of ceramic elements. Little is known of the effects of these fluorides on ceramic brackets. The purpose of this study was to determine the effects of topical fluorides (0.4% stannous fluoride, 0.5% acidulated phosphate fluoride, and 1.1% sodium fluoride) as compared with water, on the weight and on the surface of the wings and slots of aluminum oxide ceramic brackets. The brackets (n = 10 each treatment agent) were weighed before 6-minute immersions in the treatment agent, rinsed, dried, and reweighed for a total of 10 immersions. The surface appearance of the wings and the slots of the brackets (n = 5 each treatment group) were evaluated with scanning electron microscopy. No statistically significant changes in weight were found among the groups. Surface changes were not observed in either the slots nor the wings of ceramic brackets. Therefore it was concluded that the commercially available topical fluorides when applied as per the regimen in this study to the aluminum oxide ceramic brackets did not cause surface damage or significant weight loss as compared with controls (water).

The bond strength of orthodontic resins to porcelain.

Orthodontic brackets were bonded to one of two porcelain surfaces using a self-cured or one of two light-activated orthodontic bonding resins. The porcelain surfaces were either glazed (control) or deglazed (experimental) by being subjected to either 1.23% APF for 4 minutes or roughened with a Busch silent wheel. The bonds were tested to failure in shear mode on a universal mechanical testing machine. For one porcelain, there was no significant difference in the mean bond strengths between the control and the APF-treated surface, but for the second porcelain the mean bond strength was significantly greater when the surface was de-glazed by abrasion. It is considered that the mean bond strengths may be inadequate to withstand manipulations associated with routine orthodontic therapy.

In vitro effect of topical fluorides on sealant materials.

The purpose of this study was to determine by visual inspection and by scanning electron microscopy (SEM) whether commercially available, topical, acidulated phosphate fluoride (APF) and neutral sodium fluoride (NaF) agents cause surface roughening of five sealant materials: two unfilled resins, two filled resins, and one glass-ionomer material. In addition, the effect of treatment with 1.23% APF and sonification on weight of an unfilled and a filled sealant was compared to treatment with controls. Unfilled sealants exhibited no surface changes visually or on micrographs following any treatment. Filled sealants and the glass-ionomer sealant exhibited visually apparent changes depending on the treatment. SEM inspection of filled sealants with visually apparent changes showed loss of filler particles whereas the glass-ionomer sealant exhibited apparent destruction both of the matrix and the filler particle. No significant differences in weight were found between sonicated and unsonicated specimens. However, significant loss of weight was found with filled sealant specimens, but not unfilled sealant specimens, treated with 1.23% APF gel as compared with the specimens treated with water. The results of this in vitro study indicate that preventive therapies that combine use of topical fluorides and sealants may cause deterioration of filled sealants and glass-ionomer sealant material, but not unfilled sealants.