Effects of etchants, surface moisture, and resin composite on dentin bond strengths

This in vitro study evaluated the effects of etchant type, surface moisture, and resin composite type on the shear bond strength of dentin adhesives. Three adhesives which bond to etched dentin were used in the study: All-Bond 2, Amalgambond, and Clearfil Photo Bond. Occlusal enamel was removed from 200 human molars to expose dentin. The dentin surfaces were etched, treated with a dentin adhesive system, and bonded with resin composite. After thermocycling and storage, the composite columns were fractured from dentin using an Instron machine. Bond strengths were calculated and subjected to a statistical analysis. Etchant type, surface moisture, and resin composite type all had significant effects on dentin bond strengths. Overall, the highest bond strengths were obtained with 10/3 etchant, moist dentin, and hybrid composite. The highest bond strengths for All-Bond 2 and Amalgambond were obtained by using the manufacturer's recommended etchant, moist dentin, and a hybrid composite. The mean bond strengths for All-Bond and Amalgambond under these conditions were 22.5 and 19.0 MPa, respectively. Clearfil Photo Bond had significantly lower bond strengths, but was relatively unaffected by changes in experimental conditions.     

Cysteine and glutathione deficiency in AIDS patients: a rationale for the treatment with N-acetyl-cysteine

The purpose of this study was to determine the effect of accidental dentin primer contact with etched enamel on shear bond strength of composite resin to enamel. Four dentin bonding systems were included in this study: GLUMA Dentin Bond, Scotchbond, and Prisma Universal Bond 2 and 3. Eighty extracted human permanent anterior teeth were used and divided in eight test groups. The vestibular surfaces were ground and acid etched. For each dentin bonding system 10 samples were treated with dentin primer prior to placement of resin. Shear bond testing showed that enamel contact with dentin primer in the above two systems decreased the shear bond strength between composite and enamel by 31 to 44%.     

Dyes for caries detection influence sound dentin bond strength

This study evaluated the influence of caries-detection dyes on the in vitro tensile bond strength of adhesive materials to sound dentin. Caries-free human molars were ground to expose superficial dentin. Two dyes (a commercial 0.5% basic fuchsin in propylene glycol and Cari-D-Tect) were applied to sound dentin and rinsed. Subsequently, the dentin was etched with phosphoric acid (35%) and rinsed, leaving a moist dentin surface. The adhesive (Prime & Bond 2.0) was applied in two layers and light cured. A composite (TPH Spectrum), a compomer (Dyract), and a hybrid ionomer (Advance) were used to prepare the bond-strength specimens with a 3-mm-in-diameter bonding area. Control groups were made without use of dyes. Six specimens were prepared for each group. After 24 hours in distilled water, tensile bond strength (MPa) was measured using a testing machine. Analysis of variance was used to evaluate the data. Without dyes, bond strengths of TPH Spectrum and Dyract with Prime and Bond 2.0 were similar and both values were significantly (P < 0.05) higher than that of Advance with Prime & Bond 2.0. Dyes for caries detection reduced the bond strength of TPH Spectrum and Dyract but not Advance when used with Prime and Bond 2.0.     

Snow on cholera--the special lecture in the Second British Epidemiology and Public Health Course at Kansai Systems Laboratory on 24 August 1996

The purpose of this study was to evaluate the resin-dentin interfacial morphology and shear bond strength of several new and experimental dentin bonding systems classified as single-bottle/total etch, multi-step/total etch, and self-etching. Class 1 and 5 cavities were prepared from freshly extracted permanent molars and restored with composite resin. Each bonded sample was cross sectioned and one-half was completely demineralized and deproteinized, while the other half was polished along the cut surface to permit measurement of the thickness of resin-infiltrated dentin layer (RIDL) within intertubular dentin (iRIDL) and around the peritubular walls (pRIDL) of resin tags by SEM. Shear bond strength was measured for all the systems 2 minutes after photocuring. SEM showed iRIDL and resin tags of different morphology depending on material and dentin location. The iRIDL was thinner in superficial dentin and thicker in deep dentin. Peritubular RIDL (pRIDL) was thinner than intertubular RIDL. Bond strength measurements varied from 12 to 21 MPa, depending on the materials used. Self-etching primer systems exhibited the highest bond strength, although one of the one-step/total etch systems also yielded very high values. The contribution of pRIDL to adhesion onto superficial dentin is limited by the small number of tubules. Single-component bonding agents produced SEM morphology and bond strengths similar to those of multi-step systems. Self-etching systems, despite their limited RIDL thickness, produced the highest immediate bond strengths. Bond strength did not correlate well with the thickness and morphology of RIDL.     

The influence of the depth of substrate dentin surface and thickness of the current restorative samples on bond strength

The effect of sample thickness and dentin depth on bond strength of composite, compomer and resin modified glass ionomer have been investigated. The occlusal surfaces of 84 non carious human third molars were used for bonding. 4 subgroups were tested, superficial dentin with sample thickness 1 and 2 mm and deep dentin with sample thickness 1 and 2 mm respectively SBMP + /Z 100 composite showed 26 +/- 3.2, 22.3 +/- 4.5, 17 +/- 3.2 and 21.8 +/- 4.2 MPa shear bond strength to S. dentin 1 mm, deep dentin 1 and 2 mm and S. dentin 2 mm respectively. Compoglass reported 10.4 +/- 1.57, 9.1 +/- 2.3, 5.0 +/- 0.6 and 9.24 +/- 3.1 MPa while, Vitremer achieved 4.7 +/- 0.49, 3.2 +/- 0.39, 3.0 +/- 0.81 and 3.2 +/- 0.53 MPa. It is concluded that the highest bond strength can be achieved to superficial dentin in thickness or increments not more than 1 mm. And that both dentin depth and sample thickness might influence the quality of the bond to dentin with an effect that varies from one material to another depending upon the mechanism of bond of each material and its chemical composition.     

Initial tensile bond strength of resin-modified glass ionomers and polyacid-modified resins on perfused primary dentin

The objective of this study was to evaluate the initial tensile bond strength of a resin-modified glass ionomer (Photac-Fil) and two polyacid-modified composite resins (Compoglass, Dyract) to primary dentin. A hybrid composite resin (Tetric) and two chemical cured glass ionomers (BaseLine, Hi-Dense) served as controls. Ninety caries-free dentinal discs were ground flat and perfused with Ringer's solution. Dentinal surfaces were conditioned (except for Base Line). From each material, fifteen standardized specimens were attached to the dentin. Light-curing of the respective materials followed (1 min), and adhesion was tested with a universal testing machine 15 min after application. The highest initial bond strength was observed with Tetric (5.17 MPa). Closed test procedure (Kruskal-Wallis) showed significant differences between all materials (P < 0.05), except for Compoglass (1.82 MPa) vs. Dyract (2.35 MPa), and BaseLine (0.37 MPa) vs. Photac-Fil (0.42 MPa). The condensable glass ionomer Hi-Dense revealed a mean tensile bond strength of 0.79 MPa. Adhesion of (polyacid-modified) composite resins is superior to the other tested glass ionomer materials, when applied to perfused primary dentin.     

Quantitative contribution of the collagen network in dentin hybridization

PURPOSE: To determine the quantitative contribution of dentin hybridization to bonded assembly strength and demonstrate the micromorphology of the interface with and without collagen present. MATERIALS AND METHODS: Four groups of 10 molar teeth were finished to a 320 grit dentin smear layer. Two groups served as controls and two experimental groups were subjected to collagenase digestion of the collagen exposed by acid conditioning. All-Bond 2 and Amalgambond were used to bond Bisfil and Epic resin composite, respectively. Stored in water at 37 degrees C for 24 hours the assemblies were tested in a shear mode at a crosshead speed of 5 mm/minute. Means and standard deviations were subjected to analysis for statistical significance. Twenty four teeth in four groups were examined by scanning (SEM) and transmission electron microscopy (TEM) for the relationship between resin and conditioned dentin with and without the collagen network. RESULTS: All-Bond 2 and Amalgambond controls were 28.41 +/- 3.9 and 19.04 +/- 5.96 MPa, collagenase-treated groups scored 26.43 +/- 2.90 and 19.70 +/- 4.25 MPa respectively. No significant difference existed between the control and experimental groups. SEM showed an intertubular collagen network with patent tubules and a pronounced porous, irregular dentin topography following collagen digestion. A distinct hybrid zone and tubular penetration was observed but the collagenase-treated specimens showed only resin in the tubules and their lateral extensions. TEM confirmed the absence of a distinct hybrid zone in the collagenase groups with a tight, gap-free junction between the resin and the undemineralized dentin. An electron dense zone (< 50 nm) at the leading edge of conditioning was observed for All-Bond 2 and Amalgambond groups. It was concluded that the resin-reinforced or hybridized, collagenous network does not detract from, nor contribute any significant quantitative value per se to dentin bonding with the systems tested.     

Dual NF1-requiring effect of human neurotropic JC virus composite pentanucleotide repeat elements on early and late viral gene expression

OBJECTIVE: The purpose of this study was to prepare a light-cured adhesive applicable for orthodontics by mixing monomers and a polymerized reactive organic composite filler (prepolymerized trimethylolpropane trimethacrylate-filler, TMPT-filler). METHODS: The monomer component was a mixture of 3.0 wt% 2-hydroxy-3-(2-naphthoxy)propyl methacrylate (HNPM) in triethylene glycol dimethacrylate. This was applied to extracted bovine tooth enamel after acid etching with 65 wt% phosphoric acid for 30 s. After 24 h in 37 degrees C water, the tensile bond strength was measured, and the data were analyzed with Duncan's new multiple range test (p < 0.01 or 0.05). RESULTS: The tensile bonding strength to enamel etched with 65 wt% phosphoric acid was 13.1 +/- 0.5 MPa, and the thermal stability of the bond was excellent. SEM examination of the cross-sectioned specimens modified with HCl demineralization showed that when the diffusion time prior to light irradiation was only 1 min, a well-developed resin honeycomb-like structure was created in the enamel surface in the formulation containing HNPM. SIGNIFICANCE: Monomer impregnation beyond the etched enamel surface was important for resin-enamel bonding, increasing bonding strength and thermal stability. HNPM was effective in enhancing monomer diffusion and impregnation of the etched enamel surface.     

Dynamic three-dimensional display of common congenital cardiac defects from reconstruction of two-dimensional echocardiographic images

PURPOSE: To investigate the effects of acetone or water based Gluma primers on bonding efficacy when applied to acid-etched wet, dry or rewetted dentin. MATERIALS AND METHODS: Shear bond strength (SBS, 24 hours) was measured on human dentin etched with 20% phosphoric acid gel and rinsed with water in the wet (blot dried), the conventional (2 seconds air blast), the dry (10 seconds air drying), and the rewetted stage (10 seconds air drying, remoistening and blot drying). The priming solution was either the original water based or an acetone based experimental Gluma primer. Cavity sealing performance and depth of resin impregnation were determined by solvent and by technique along the margins of 4.5 mm wide cylindrical dentin cavities with 90 degree cavosurface angle. RESULTS: The SBSs of the wet technique groups were approximately 18 MPa, irrespective of the primer solvent. Conventional drying gave an SBS almost as high (16.5 MPa). Rewetting was highly effective with acetone as the primer solvent. The dry techniques resulted in moderate (water) and poor (acetone) bond strengths. The cavity margins of acetone based primer treated specimens were consistently gap free with the wet technique. The other seven groups showed between two and six gaps in each group of six specimens. The resin impregnated layer (RIL) thicknesses were 12.5 microns approximately in the wet groups, and thus identical with the total depth of demineralization resulting from the 30-second etching. The alternative techniques showed significantly thinner RILs particularly in the dry groups (7.5 microns).     

Bonding of amalgam to composite: tensile strength and morphology study

OBJECTIVES: The present study was based on the premise that it may be possible to produce useful dental restorations by bonding freshly triturated amalgam to a cured composite restoration (Group 1 specimens), or by bonding uncured composite to hardened amalgam (Group 2 specimens). METHODS: To determine the validity of this premise, a phosphonate adhesive resin cement was used to produce simulated, layered dental restorations for each test group. RESULTS: The mean tensile bond strength of 24 hour-old Group 1 specimens (6.74 MPa +/- 1.63 MPa) was almost twice that of 24 hour-old Group 2 specimens. Cohesive failure of the amalgam-substrate layer was a prominent feature of the fracture pattern of Group 1 specimens. On the other hand, rupture of all Group 2 specimens occurred mainly along the adhesive-amalgam interface. Findings from SEM examination of the layers of amalgam, adhesive cement, and resin composite of intact Group 1 specimens suggested that inclusions of adhesive resin cement may be the cause of the persistent cohesive failure of the amalgam layer. SIGNIFICANCE: It may be possible to improve the strength of bonded couples made from freshly triturated amalgam and cured resin composite by minimizing the thickness of the adhesive layer.     

Bond strength to crown and root dentin

PURPOSE: To investigate (1) the tensile bond strengths of four commercial dentin bonding systems to bovine crown and root dentin and (2) the structure of the hybrid layers for each system bonded to the two dentin substrates. MATERIALS AND METHODS: Superficial surfaces were exposed in bovine crown and root dentin. The teeth were embedded in plaster and a 3 mm diameter bonding area was demarcated. The four bonding systems used were All-Bond 2, Super-Bond D-Liner Plus, Clearfil Liner Bond II, and ProBond. Bonding procedures followed the manufacturers' instructions with the exception of Super-Bond D-Liner Plus where the primer was left in situ for 60 seconds. Tensile bond strengths were tested after 24-hour storage in 37 degrees C deionized water. Specimens were also prepared for SEM observation of the hybrid layer, after treatment with 10% phosphoric acid, and 10% phosphoric acid and 5% sodium hypochlorite. RESULTS: Statistically lower bond strengths to crown dentin when compared with root dentin were observed for All-Bond 2, whereas Liner Bond II showed the opposite (P < 0.01). Both ProBond and Super-Bond D-Liner Plus showed no statistical differences between crown and root dentin (P > 0.05). Hybrid layers could be observed for All-Bond 2, Liner Bond II and Super-Bond D-Liner Plus, with no apparent differences between the hybrid layers of crown and root dentin. In the case of ProBond, where the smear layer was not removed during the priming stage, it appeared that the primer had infiltrated and caused hybridization of the smear layer. The differences in bond strength were thought to be related to the different bonding mechanisms of each material, as well as possible variations in the crown and root dentin substrates.     

Effects of aminobenzoic acid derivatives with 4-AET/HEMA in self-etching primer on bonding to ground dentin

The effect of the inclusion of aminobenzoic acid derivatives (ABAD) in a self-etching primer comprising 4-acryloxyethyltrimellitic acid (4-AET), HEMA and water on shear bond strength to ground dentin was investigated. The mean bond strengths to dentin were significantly increased by the inclusion of 0.307 mol% ABAD in the 4-AET/HEMA primer, when compared with the control (0 wt% ABAD) (p < 0.01). A particularly high value (38.0 MPa) of shear bond strength was obtained in the use of the primer containing p-nitroanthranilic acid (p-NAA). It seemed to assume that the effect of p-NAA could be caused by the strong electron-withdrawing group of -NO2. From SEM observation, it was found that bonding resin appeared to adhere strongly to the ground dentin without formation of any resin-tags in the dentinal tubules. It was thought that the ABAD with 4-AET/HEMA could perform facilitating photo-polymerization at the bonding interface, and resulted in increased bond strength to ground dentin, and that the bond strength could be affected by the electronegativities of substitutional groups of ABAD.     

Effects of moxonidine and clonidine on renal function and blood pressure in anesthetized rats

OBJECTIVES: This study was conducted 1) to characterize through SEM analysis the resin-dentin interface produced by single-bottle primer/adhesives and a three-component system [Scotchbond Multi-Purpose (3M Dental)] and 2) to evaluate the shear bond strength to dentin of these adhesive systems. METHODS: Single-bottle primer/adhesives [Bond 1 (Jeneric/Pentron), Single Bond, (3M Dental Products); One Step (Bisco Inc.), OptiBond Solo (Kerr Corp.), Prime & Bond 2.1 (L.D. Caulk-Dentsply), Syntac Single-Component (Ivoclar-Vivadent), Tenure Quilk with Fluoride (Den-Mat)] were used according to manufacturers' instructions to bond resin composite to flat dentinal surfaces of extracted human third molars (n = 15). All samples were thermocycled 300x. Twelve specimens per group were used to measure shear bond strength and three specimens were used to evaluate the interfacial morphology under SEM. A one-way ANOVA and Turkey's test were used to assess the results. RESULTS: Mean shear bond strengths in MPa +/- SD for the groups ranged from 22.27 +/- 4.5 MPa for Single Bond to 7.6 +/- 3.9 MPa for Syntac Single-Component. The statistical analysis indicated that Single Bond produced significantly higher (p < 0.001) bond strengths than Syntac Single-Component, Prime & Bond 2.1, Bond 1 and Tenure Quik With Fluoride. Bond strengths for Syntac Single-Component were significantly lower than One-Step, OptiBond Solo, Scotchbond Multi-Purpose Plus and Single Bond. SEM examination clearly revealed the formation of a distinct hybrid layer for all adhesive systems; however, minor variations in ultrastructure existed among products. SIGNIFICANCE: Some single-bottle primer/adhesive present in vitro bond strengths and hybrid layer formation similar to those found for the conventional three-component adhesive system tested.     

Strength of secondary-cured resin composite inlay repairs

A study was designed to simulate the repair of an indirect resin composite restoration with conventionally cured resin composite. Two-part specimens were prepared to test the diametral tensile strength of the repair interface between the base material of an indirectly cured resin composite (Herculite XRV) and repairs carried out with three directly cured materials (Herculite XRV, TPH, and Charisma). The repairs were carried out with and without use of the bonding resin for the repair material. The diametral tensile strengths of all repaired specimens were significantly less than those of bulk unrepaired specimens. There were no significant differences between the diametral tensile strengths of repaired blocks when the repair materials were used without bonding resin. The use of an intermediate layer of bonding resin significantly increased the bond strengths obtained when Herculite XRV and TPH were used for repair. There was no significant difference between the strength values of Herculite XRV and TPH, but Charisma exhibited the lowest strengths of repaired specimens.     

Use of 2-isocyanatoethyl methacrylate and iron (II) perchlorate for bonding tri-n-butylborane-initiated luting agents to dentin

The present study investigated the effect of 2-isocyanatoethyl methacrylate (IEM) and iron (II) perchlorate on dentin adhesion. Four primers were evaluated, consisting of aqueous 2-hydroxyethyl methacrylate (HEMA) solutions containing 5, 10, 20 or 50 micromol/g iron (II) perchlorate. Five luting agents were prepared with methyl methacrylate (MMA), poly(methyl methacrylate) (PMMA), tri-n-butylborane (TBB) initiator and IEM. The concentrations of IEM in the luting agents were 0.2, 0.4, 0.8, 2.0 and 4.0 wt%. Extracted bovine teeth were ground to expose the dentin, etched with an aqueous solution of 10 wt% phosphoric acid, primed, and then bonded with stainless-steel rods; tensile bond strengths were determined after 1 d immersion in water. The highest bond strength (20.7 MPa) was recorded for the group using 10 micromol/g iron (II) perchlorate and 2.0 wt% IEM. The use of IEM was effective in decreasing the optimal concentration of iron (II) perchlorate, and this may contribute to the color stability of iron-containing pretreatment agents.     

Preconditioning with 15-minute ischemia extends myocardial infarct size after subsequent 30-minute ischemia in rabbits

In an attempt to compare the morphology of the resin-dentin interface in areas where the dentinal tubules run perpendicularly or at an angle to the cavity surface with that of areas where they run parallel to it, we studied a dentin adhesive system using transmission electron microscopy and fluorescence confocal laser scanning microscopy. The design of the study included the simulation of the normal hydrostatic pressure within the pulp and the dentinal tubules. Following acid etching of the dentinal surface with maleic acid/HEMA, the smear layer was removed, and a superficial zone was demineralized in such a way that the exposed collagenous dentin matrix retained its integrity. Confocal laser scanning microscopal investigations using primer labeled with rhodamine B showed that the penetration of the primer occurred not only vertically via surface porosities, but mainly laterally, via the dentinal tubules. The adhesive resin labeled with fluorescein completely infiltrated the demineralized layer, thereby forming a hybrid layer. The orientation of the dentinal tubules had a profound effect on the formation of the hybrid layer. In areas with perpendicular tubule orientation, the layer was 3.2 +/- 0.8 microns thick, showing solid 27.2 +/- 0.8 microns long resin tags in the dentinal tubules, and a network of tiny tags in their side-branches. In areas with parallel tubule orientation the layer was significantly thinner (1.3 +/- 0.6 microns) and resin tags were absent.     

The effect of microetching on the bond strength of metal brackets when bonded to previously bonded teeth: an in vitro study

The purpose of this in vitro study was to answer the following questions for three different metal brackets: (1) when rebonding a previously bonded tooth, how do shear bond strengths compare for new brackets, new microetched brackets, and debonded microetcher cleaned brackets? and (2) how do the different bracket types compare with respect to the time required to remove composite resin from their bonding pads with a microetcher? Ninety human premolars and canines previously debonded of metal brackets were randomly assigned to 9 groups of 10 teeth each. New, new etched, and debonded etched cleaned brackets of each type were bonded with composite resin onto teeth, and the bonds tested to failure for shear bond strength. An analysis of variance and Duncan's multiple range test were used to compare bracket/enamel bond strength. Within each bracket type no significant differences were found between mean bond strengths for new, new etched, and debonded etched conditions, a finding that supports the use of microetching to clean accidentally debonded brackets. Mean times for removal of resin from bonding pads with a microetcher varied from 9.3 seconds to 11.9 seconds, with bracket (M) requiring significantly less time for removal of resin.     

The effect of dentin primer on the tensile bond strength to human enamel

Four third-generation dentin bonding products (Scotchbond Multi-Purpose, Optibond, All-Bond 2, and Prisma Universal Bond 3) were tested to evaluate their tensile bond strength to enamel. Test enamel specimens were etched, primed, and polymerized according to each manufacturer's directions. Control specimens were treated identically except the primer application was eliminated. The results demonstrated that the dentin primer significantly increased the tensile bond strength of All-Bond 2, significantly decreased the tensile bond strength of Scotchbond Multi-Purpose and Optibond, and had no significant effect for Prisma Universal Bond 3. A one-way analysis of variance was run between the eight groups tested, and three significant subsets were found (P < .05). The subset with the highest mean tensile bond strengths consisted of Prisma Universal Bond 3 primed and nonprimed, All-Bond 2 primed, and Optibond nonprimed.     

Dentastic bond strength to dentin

PURPOSE: To evaluate the shear bond strength to the dentin of permanent teeth and failure site of Dentastic hydrophilic dentin bonding agent. MATERIALS AND METHODS: Forty permanent noncarious molar teeth stored in distilled water were obtained. The teeth were cleaned with pumice and a rubber cup. The mesio-buccal surface of the teeth was ground flat with hand pressure with a series of SiC paper ending with the 600 grit to provide a uniform surface on dentin to which the resin composite could be applied. After preparing the tooth surface, the teeth were stored in distilled water for 48 hours. They were then divided at random into four groups of 10 specimens each: Group 1: Dentastic, five coats of primer; Group 2: Dentastic, three coats of primer; Group 3: Dentastic, five coats of primer, light-cured adhesive before resin bonding; Group 4: Dentastic, three coats of primer, light-cured adhesive before resin bonding. All specimens were thermocycled (500x) and sheared in a testing machine. After shear testing, the debonded sites of all samples were examined with a stereomicroscope and a scanning electron microscope. RESULTS: The results in MPa were: Group 1: 22.63 +/- 6.24; Group 2: 23.35 +/- 5.14; Group 3: 23.58 +/- 5.66; Group 4: 27.26 +/- 8.22. ANOVA and Student-Newman-Keuls showed no statistically significant difference between the groups. In all groups, all specimens failed at the dentin (dentin cohesive failure = dentin fracture) or at the resin (resin cohesive failure = resin fracture). This means that the bond strength of the product is stronger than the cohesive strengths of the dentin and the resin.     

Effect of etchant, etching period, and silane priming on bond strength to porcelain of composite resin

The purpose of this study was to evaluate the effect of etching and silane priming on bond strength to a feldspathic porcelain (VMK 68) of a composite resin (Clearfil APX). Two hydrofluoric acid etchants (2.5% and 5%) and seven different etching times (0, 30, 60, 90, 120, 150, and 180 seconds) were used to etch the porcelain specimens respectively. A self-curing bonding agent containing a silane coupler (Clearfil Porcelain Bond) was used on both etched and unetched porcelain surfaces. Etched relief patterns were observed by means of a scanning electron microscope, and the bond strengths between the photocured composite resin and the porcelain were determined. Scanning electron micrographs revealed complicated etching patterns with increased etching time periods. Shear testing results showed that the bond strength to the unetched porcelain of the composite resin was very low, and that etching periods for more than 30 seconds effectively enhanced the bond strength. Of the two etching agents applied to the unsilanated porcelain, the buffered 2.5% etchant produced higher bond strengths than the 5% etchant for all etching time periods except for 180 seconds. Silane priming was effective and critical for improving bond strength to the porcelain. Application of the silane bonding agent to the porcelain after hydrofluoric acid etching appeared to be suitable for achieving consistent bonding between the composite resin and the porcelain.