The Journal of Adhesive Dentistry, 04/2004

The objective of this study was to analyze the stress concentration factor (Kt) in specimens of uniform material with the most commonly used geometry (square hourglass) during microtensile tests using finite element analysis. Standardization is emphasized with the aim of obtaining the most representative nominal strength of the material. Eighty cases were simulated using three-dimensional models, in which we varied the fixation of specimens in the jig (f = 1 or 2 sides), the height of this fixed region (h = 1 or 2.75 mm), the specimen width (D = 1.5, 2, 3, 4 or 5 mm), and the radius of curvature of the notch (r = 0.2, 0.5, 0.7 or 1 mm). The cross-sectional area (1 mm2) remained constant in all analyses. The stress concentration factor Kt (maximum tensile stress/nominal tensile stress) was calculated. A 150% difference was observed from the lowest Kt value (1.3) to the highest one (3.2). Results indicated that the radius of curvature is a very influential geometric parameter in microtensile strength tests (variation in Kt values up to 47.4%). For two-side fixed specimens, the Kt values varied from 3 to 4%, while the one-side fixed models resulted in variations from 11 to 15%. Variations in the specimen geometry and mode of load application can be responsible for part of the different strength values obtained in microtensile tests. The specimen fixation by two sides is a simple and easily performed method to reduce the stress concentration factor and its variations induced by specimen geometry and test assembly. Keywords: finite element analysis, composite resins, mechanical stress, materials testing

The aim of this study was to investigate the influence of testing speed on the microtensile bond strength values of two adhesive systems to dentin. A flat dentin surface was exposed after grinding the occlusal enamel of 10 human third molars. The adhesive systems (n = 5 each) Single Bond and Clearfil SE Bond were applied according to the manufacturers' instructions, and composite resin crowns (Z250) were constructed incrementally. After 24 h in distilled water at 37°C, each tooth was longitudinally sectioned in both the x and y directions, under a cutting speed of 300 rpm, to obtain sticks with a cross-sectional area of 0.8 mm2. The sticks from each tooth were divided into 5 groups to be tested under crosshead speeds of 0.1, 0.5, 1.0, 2.0, and 4.0 mm/min. The fracture pattern was analyzed microscopically after debonding (400X). A two-way ANOVA having adhesive system (2 levels) and testing speed (5 levels) as main factors was used to compare the microtensile bond strengths. The two-way ANOVA did not detect statistically significant differences either for the interaction (p = 0.80) or for the crosshead speed (p = 0.69). Differences were only detected between adhesive systems (p = 0.001), with Single Bond showing higher bond strength values than Clearfil SE Bond. The crosshead speed used for microtensile bond strength tests does not influence the bond strength values, regardless of the adhesive system employed. Keywords: microtensile test, crosshead speed, resin-dentin bond strength

The purpose of this study was to compare the microtensile bond strength (µTBS) of three adhesives to bovine enamel prepared with 600-grit silicon carbide paper, diamond rotary instrument, or carbide bur. Bovine teeth (n = 36) were randomly divided into three treatment groups and bonded using a total-etch adhesive (Single Bond, 3M ESPE), a self-etching primer system (Clearfil SE Bond, Kuraray), or a self-etching adhesive (One-Up Bond F, Tokuyama). A 4-mm composite crown was built on the bonded surfaces and specimens were stored in water for one day at 37°C. Specimens were sectioned into 0.7-mm-thick slabs, trimmed to a cross-sectional area of 1 mm2, and loaded to failure at a crosshead speed of 1 mm/min using a tabletop tester (EZ-Test, Shimadzu). Microtensile bond strength data were analyzed using ANOVA and Fisher's PLSD test (α = 0.05). The bond strength of each self-etching system was lower when the enamel was prepared using a diamond or carbide bur, rather than with 600-grit silicon carbide paper. Differences in µTBS between carbide- and diamond-prepared surfaces were not significant. The surface preparation method did not affect the total-etch system. Different preparation instruments are unlikely to affect resin-enamel bond strengths. Keywords: adhesion, enamel bonding, burs, self-etching primer

Restoration microleakage is thought to be determined by the method and location of cavity preparation, enamel etching, and dentin conditioning, as well as the restorative material. This study compared the microleakage of composite restorations placed in preparations cut with carbide and diamond burs and those treated with different bonding/conditioning agents. Class V preparations (3 x 2 x 2 mm) were cut wholly in enamel or in enamel and cementum in 100 human premolars. Twenty teeth were prepared with carbide burs and the preparations etched and conditioned with Prime&Bond NT but not restored. A second set of 20 teeth had enamel-only preparations cut with carbides (n = 10) or diamonds (n = 10), and the preparations etched, conditioned (Prime&Bond NT) and restored with Prisma TPH. The other 60 teeth were divided into 3 groups of 20 teeth each with enamel-only (n = 10) or enamel/cementum preparations (n = 10). The 3 groups of teeth were conditioned with Optibond Solo, Clearfil SE Bond or Prompt-L-Pop prior to restoration with Prisma TPH. Two mm of root was resected from all teeth, pulpal tissue removed, and insulated copper wires inserted via the root canals to contact with the pulp chamber roof before the tooth-wire interfaces and root surfaces were sealed. The teeth were immersed in 0.9% NaCl and leakage assessed over 30 d by iR drop across a resistor in series with a DC source and stainless-steel counter electrode. Differences (p < 0.05) in leakage were found for enamel preparations cut with carbides and diamonds, and the relationship of leakage vs time was linear. Enamel/cementum preparations showed greater leakage, and the relationship of leakage vs time was sigmoidal. Conditioned-only preparations showed the same leakage as those conditioned and restored, while preparation leakage varied with the conditioning agent. Cavity preparation location, method of cutting, and the conditioning agent markedly affect leakage behavior. Keywords: restoration leakage, cavity preparations, dental burs, dentin conditioning

To determine the shear bond strength (SBS) of different established (Resulcin Aqua Prime & Monobond N: RA, Prompt L-Pop III: PLP) and experimental (AC-Bond: AC, AC-Bond + Desensitizer: ACD) self-etching adhesives in comparison to fourth (Optibond FL: FL) and fifth generation (Excite: EX, Gluma Comfort Bond: CB) adhesives. All adhesives were applied on flat enamel and dentin surfaces and light cured following manufacturers' directions. Tetric Ceram A2 composite cylinders 3.5 mm in diameter and 2.0 mm in height were sheared off (1 mm/min) after thermocycling (5 to 55°C, 5000x). The t-test (5% level, Bonferroni-correction) was used for statistical analysis. SBS in enamel: RA: 27.0 ± 5.8 MPa, PLP: 15.9 ± 3.4 MPa, AC: 28.1 ± 4.4 MPa, ACD: 22.2 ± 4.1 MPa, FL: 33.2 ± 3.2 MPa, EX: 30.5 ± 5.1 MPa, CB: 30.1 ± 3.7 MPa. SBS in dentin: RA: 25.8 ± 5.7 MPa, PLP: 20.7 ± 2.9 MPa, AC: 27.0 ± 4.5 MPa, ACD: 20.7 ± 3.7 MPa, FL: 34.4 ± 3.8 MPa, EX: 30.0 ± 4.6 MPa, CB: 27.9 ± 2.6 MPa. FL resulted in significantly (p < 0.002) higher SBS in enamel and dentin than RA, AC, ACD, and PLP, and in higher SBS to dentin than CB. In enamel and dentin, RA performed significantly superior to PLP, but was not different from AC and ACD. EX and CB were both on the same level of significance as AC and RA, but showed superior results to ACD and PLP (enamel and dentin). PLP resulted in significantly lower SBS values in enamel and dentin than all the other materials investigated, except ACD in dentin, to which it was equivalent. Resulcin Aqua Prime & Monobond N and AC-Bond were not significantly different than established 5th generation products. AC-Bond + Desensitizer and Prompt L-Pop have significantly different SBS from established 4th and 5th generation products. Future studies are required to investigate marginal integrity to determine if self-etching adhesives are an adequate alternative to one- and multi-bottle systems. Keywords: self-etching adhesives, 6th generation, in vitro study, shear bond strength

The objective of this study was to investigate the effect of light- or chemical initiation on the polymerization reaction of dual-cured composite core buildup materials (CM) with respect to their shear bond strength to dentin treated with self-etching adhesives (SE), in the presence or absence of a low-viscosity composite liner (LI). Two SEs (Clearfil SE Bond and Unifil Core Bond), their respective CMs (DC Core Paste and Unifil Core), and a LI (Protect Liner F) were tested. After removing the labial enamel surfaces of 8 bovine incisors, each flat dentin surface was sectioned into 4 pieces with similar surface areas (30 mm2). The dentin surfaces were wet abraded with 600-grit SiC paper and randomly divided into 8 groups. Experimental groups comprised the use of a SE and its respective CM with or without an intermediate application of the LI and with or without CM light activation. Three cylinders of CM (0.5 mm high and 0.75 mm in diameter) were applied to each bonded dentin surface (n = 12), using a tygon tubing mold. After water storage for 24 h, specimens were subjected to microshear testing. Data were statistically analyzed by two-way ANOVA and Tukey's test (5%). For both SEs, LI application and CM light activation showed significantly higher bond strengths than the groups in which an intermediate LI was not used or the CMs were only chemically cured. The bond strength of CM to dentin using SE is reduced if the LI and light activation are not employed. Keywords: adhesive systems, resin core, bond strength, dentin, composite activation

The aim of this study was to evaluate the effect of sodium hypochlorite (NaOCl) on the shear bond strength (SBS) using three bonding systems in primary dentin. Forty-five sound extracted primary molars were selected. The crowns were longitudinally sectioned, embedded in polystyrene resin, and flattened until a dentin surface was reached. The samples were assigned to 6 groups (n = 15): G1, Single Bond (SB); G2, NaOCl + SB; G3, Prime & Bond 2.1 (PB); G4, NaOCl + PB; G5, Clearfil SE Bond (CSE); G6, NaOCl + CSE. All the adhesive systems were applied according to the manufacturers' instructions, except for the application of 10% NaOCl solution for 60 s in groups 2, 4 (after acid etching), and 6 (before applying adhesive system). The composite resin was placed in increments in a mold and light cured for 20 s. The samples were stored in distilled water at 37°C for 24 h and submitted to SBS testing with a crosshead speed of 0.5 mm/min. The failure sites were observed with SEM. The data were treated with ANOVA and Tukey's tests (p < 0.05). There was no statistically significant difference between the groups with or without treatment of the substrate with NaOCl, regardless the material used. The SBS averages in MPa (± SD) were: G1: 15.8(1.9)a; G2: 14.6(1.3)a; G3: 10.2(0.7)a; G4: 9.9(0.2)a; G5: 13.3(1.2)a; and G6: 10.7(1.0)a. There was a statistically significant difference between the materials (SB >= CSE >= PB). Mixed failure was the failure type most frequently observed for all groups. Dentin surface treatment with NaOCl did not affect the resin-dentin bonding strength in primary teeth. Keywords: sodium hypochlorite, primary teeth, dentin bonding

To measure the microtensile bond strength to enamel and dentin of three self-etching adhesives in comparison with a total-etch two-step system as a control. A total of 40 extracted human molars were stored in saline solution until use, then divided into 4 groups of 10 teeth (one group per adhesive system). Half of each of these groups underwent bond strength tests on enamel, and the other half was used for adhesion testing on dentin. The following experimental groups (n = 5) were then formed: E(1) Adper Prompt-L-Pop (AP, 3M ESPE) on enamel; E(2) Xeno CF II (X, Sanking Kogyo) on enamel; E(3) AdheSE (AS, Ivoclar-Vivadent) on enamel; E(4) Excite (EX, Ivoclar-Vivadent) on enamel; D(1) AP on dentin; D(2): X on dentin; D(3) AS on dentin; D(4) EX on dentin. Each tooth yielded 15 to 20 sticks about 0.9 x 0.9 mm in cross-sectional area for microtensile testing. Specimens were loaded in tension at a crosshead speed of 0.5 mm/minute, and bond strength at failure was calculated in MPa. A two-way ANOVA was applied to test for significance of the differences among the groups. The bond strength values of Excite (the control) were significantly higher than those of the test products on enamel (42.92 ± 4.8 MPa) and on dentin (45.80 ± 5.79 MPa). The self-etching adhesives AdheSE (28.48 ± 4.71 MPa) and Xeno CF II (27.22 ± 2.74 MPa) revealed significantly stronger adhesion than Adper Prompt-L-Pop (20.16 ± 2.07 MPa) on dentin. On enamel, all self-etching test materials performed similarly. The substrate did not appear to have a significant influence on adhesion, as each material reached comparable levels of bond strength on enamel and dentin. On both substrates the self-etching adhesives tested performed significantly worse than did the total-etch system. Keywords: bond strength, enamel, dentin, adhesive system

The aim of this study was to compare bonding of composite resin luting cement to a fiber-reinforced composite (FRC) root canal post with either a cross-linked or a semi-interpenetrating polymer network (IPN) polymer matrix. Four different types of prefabricated FRC posts with a cross-linked polymer matrix and two types of FRC posts with a semi-IPN polymer matrix which were individually formed were tested. Serrated titanium posts served as the reference. An auto-polymerizing resin luting cement was used for cementing the posts into the holes of composite resin disks. The pull-out force was measured using a universal testing machine after the post/cement/disk system had been stored dry or thermocycled (5°C/55°C, 6000x) in water. The bonding sites of the posts were examined with SEM. The FRC posts with a semi-IPN polymer matrix gave significantly higher pull-out force values than the prefabricated FRC posts with a smooth surface and a cross-linked polymer matrix (p < 0.004). The highest pull-out force was obtained with serrated titanium posts. Both the type of FRC post and thermocycling had a significant effect on the pull-out force (n = 8, ANOVA p < 0.001 and p < 0.007, respectively). SEM photomicrographs confirmed the results. This study showed that FRC posts with a semi-IPN polymer matrix bonded better to composite resin luting cement than did prefabricated FRC posts with a cross-linked polymer matrix, although their pull-out force was not as high as that of the mechanically interlocked serrated titanium posts. Keywords: root canal posts, fiber reinforced composite, fiber reinforced composite root canal posts, pull-out force, SEM

The objective of this study was to test the following hypothesis: the silica coating on ceramic surface increases the bond strength of resin cement to a ceramic. In-Ceram Alumina blocks were made and the ceramic surface was treated: G1 - sandblasting with 110-µm aluminum oxide particles; G2 - Rocatec System: tribochemical silica coating (Rocatec-Pre powder + Rocatec-Plus powder + Rocatec-Sil); G3 - CoJet System: silica coating (CoJet-Sand) + ESPE-Sil. The ceramic blocks were cemented to composite blocks with Panavia F resin cement (under a load of 750 g/1 min). The cemented blocks were stored in distilled water at 37°C for 7 days and sectioned along the x and y axes with a diamond disk. Samples with an adhesive area of ca 0.8 mm2 (n = 45) were obtained. The samples were attached to an adapted device for the microtensile test, which was performed in a universal testing machine (EMIC) at a crosshead speed of 1 mm/min. The obtained results were submitted to ANOVA and Tukey's test. Mean values of tensile strength (MPa) and standard deviation values were: (G1) 16.8 ± 3.2; (G2) 30.6 ± 4.5; (G3) 33.0 ± 5.0. G2 and G3 presented greater tensile strength than G1. There was no significant difference between G2 and G3. All the failures took place at the ceramic/resin cement interface. The silica coating (Rocatec or CoJet systems) of the ceramic surface increased the bond strength between the Panavia F resin cement and alumina-based ceramic. Keywords: bond strength, aluminous ceramic, surface treatment, silica coating, microtensile test

The aim of this study was to evaluate the clinical performance of ceramic inlays and onlays made with two systems: sintered (Duceram [D], DeguDent) and pressable (IPS Empress [IPS], Ivoclar-Vivadent) after 1 year. Seventy-four restorations - 37 IPS and 37 D - were cemented in 34 patients. Twenty-four premolars and 50 molars received Class II cavity preparations, totaling 28 onlays and 46 inlays. The restorations were evaluated by two independent investigators at baseline, 6 months, and 1 year, according to modified USPHS criteria. Fisher and McNemar statistical tests were employed to assess the survival rate. After one year, 100% of the restorations were assessed and all the restorations were considered clinically excellent or acceptable. Among the analyzed criteria, only the following received "Bravo" ratings: marginal discoloration: IPS (24.32%), D (13.51%); marginal integrity: IPS (10.81%), D (8.11%); color match: IPS (5.41%), D (5.41%); surface texture: IPS (2.70%), D (10.81%). No "Charlie" or "Delta" scores were given to the restorations. Among the analyzed criteria, only marginal discoloration differed statistically significantly from the results of the baseline examination for IPS Empress ceramic restorations (p = 0.008). No significant differences were found between the two ceramics. The two ceramic systems demonstrated excellent clinical performance after a period of 1 year. Keywords: ceramic, onlays, inlays, clinical study