Andreas Rathke

Effectiveness of bonding fiber posts to root canals and composite core build-ups

This study investigated the effects of fiber posts, silanization, and luting agents on the interfacial strength to root dentin and composite cores. Root canals of 120 crownless human teeth were instrumented. Three different posts (opaque and translucent), with and without silane treatment, were bonded using etch-and-rinse, self-etch, and self-adhesive luting agents. The restored roots were built up with dual-curing composite. After storage in water for 24 h at 37 degrees C, 2-mm-thick slices were cut from each sample: one from the composite core and one from the restored root. Interfacial push-out bond strengths of the posts were determined in a universal testing machine. Failure modes were analyzed using scanning electron microscopy. The post type and the luting agent had significant effects on both the post-to-dentin and post-to-core strengths. Silanization did not significantly influence post-to-dentin strengths, but enhanced post-to-core strengths. With etch-and-rinse luting agents, debonding occurred predominantly between the post and the cement, while the self-etch and self-adhesive luting agents showed more failures on root dentin. No failures occurred between the composite core and the cement. The combination of translucent posts and etch-and-rinse dual-curing luting agents can positively influence the retention of fiber posts in root canals. Silanization seems to be less relevant for intra-root canal bonding, but may have beneficial effects on post-to-core strengths.

Effects of self-curing activator and curing protocol on the bond strength of composite core buildups.

PURPOSE To determine the effect of the polymerization mode of simplified bonding systems and the corresponding core buildup resin composite on the bond strength to dentin. MATERIALS AND METHODS Composite core buildups were bonded to flat prepared dentin surfaces of 320 human molars using a two-step etch-and-rinse (Excite, ER) and a two-step self-etching (AdheSE, SE) bonding system. Bonding systems were used both with and without their respective self-curing activators (Excite DSC, ER+SC; AdheSE DC, SE+SC). Six curing protocols for the dual-curing composite (MultiCore Flow) were examined: self-curing for 5 min (a); irradiation with light from each aspect for 10 s (b), 20 s (c), and 40 s (d); and irradiation with light from the occlusal aspect only for 60 s (e) and 120 s (f). Shear bond strengths were measured immediately after curing. Additional measurements were performed after water storage of the specimens for 24 h at 37°C. These specimens had been cured according the curing protocols given in the manufacturers instructions (groups a and d). Failure modes were analyzed using scanning electron microscopy. RESULTS Immediate bond strengths were significantly different among the bonding systems (p < 0.001): SE > ER > ER+SC > SE+SC. Immediate bond strengths of ER and SE were significantly lower when the composite was self-cured (p < 0.05). The use of SC activators reduced the bond strength and promoted adhesive failures to dentin. A severe incompatibility problem was observed between the composite and SE+SC. CONCLUSION Dentin bonding of dual-curing composite core buildups in combination with simplified bonding systems is still unsatisfactory, even when SC activators are employed. For adequate bonding to dentin, polymerization of the dual-curing composite should always be light initiated.

Effectiveness of the bond established between ceramic inlays and dentin using different luting protocols.

PURPOSE To evaluate the ceramic-to-dentin bond following luting with light- and dual-curing resin composites using different adhesive techniques. MATERIALS AND METHODS Dentin surfaces from 160 human molars were ground flat and randomly divided into eight groups (n = 20). Vita Mark II ceramic disks measuring 2 and 4 mm in thickness were bonded to the dentin with one of the following luting systems: Syntac/Tetric Ceram (ST), Syntac/Variolink II (SV), OptiBond Solo Plus/ Prodigy (OP), OptiBond Solo Plus/Nexus 2 (ON). Two different irradiation times (60 s, 120 s) were used per luting system, each without (-PC) and with (+PC) precuring the respective adhesive layer. After storage in water for 24 h at 37°C, the bonded specimens were sectioned perpendicularly to the adhesive interface into 1-mm-thick sticks. Three sticks per specimen were loaded to failure under tension in the Zwicki 1120. Failure analysis was performed using a scanning electron microscope (SEM). RESULTS Four-way ANOVA showed that the ceramic thickness, the type of luting system used, and the adhesive precuring had a significant effect on the microtensile bond strength. The longer irradiation times did not significantly increase the bond strength. The highest values were recorded with SV/+PC (27.9 ± 4.3 MPa) and the lowest with ST/-PC (10.2 ± 3.5 MPa). Under the SEM, failed specimens that had not been precured showed significantly more exposed dentin than those which had been precured (chi-square test). CONCLUSION The precuring step of light-curing bonding systems and the use of dual-curing luting composites were shown to optimize the dentin bond under thick ceramic layers.

Cyclic Loading of Incisors Restored with Different Post Systems

Objective: To evaluate the fatigue resistance of different post systems by submitting them to cyclic loading. Methods: Human maxillary central incisors of similar dimensions were decapitated, root filled and embedded in acrylic blocks with simulated periodontal ligaments. Post spaces were prepared to a depth of 8 mm and restored with one of the following prefabricated posts: a 1.5 mm diameter titanium post (Mooser) (A), a 1.7 mm diameter zirconia ceramic post (Cosmopost) (B), a 1.4 diameter quartz fiber post (Aestheti-Plus) (C), and glass fiber posts (FRC Postec) of 1.5 mm (D) and 2.0 mm in diameter (E). All the posts were covered with metal copings, stored in 37°C water for 48 h, and then cyclically loaded with 25 N peak load at a 45° angle to the axial direction in a loading machine (Zwick 1465). Every 250 cycles (0.2 Hz frequency), the peak load was increased by 25 N until failure occurred. The equivalent load was calculated with the formula: eq 1 P ( )/1000 = = ⋅ ∑ n ii i PN , where Pi is the peak load, which is repeated for Ni cycles. Results: Failure modes were yielding (A) and post fracture (B-E). ANOVA post hoc Tukey test showed significantly higher mean loading cycles and mean equivalent loads for (A) than for the other post groups (p 0.05). Conclusion: For severely damaged upper incisors without ferrule, metal posts demonstrated higher fatigue resistance than fiber-reinforced composite or zirconia posts and thus may be preferable over non-metal posts.

Durability of fiber post-to-composite bonds achieved by physical vapor deposition and tribochemical silica coating.

PURPOSE To evaluate post-to-composite bonds in terms of their durability, achieved either by physical vapor deposition (PVD) or tribochemical silica coating (TSC) compared to coupling strategies for fiber posts at chairside. MATERIALS AND METHODS Thirty uncoated fiber posts (DT Light) each were either left untreated (control) or silanized with a one-bottle (Monobond Plus) or a two-bottle (Clearfil SE Bond/Porcelain Bond Activator) silane at the chairside. Thirty coated fiber posts each had already been silica coated and silanized by the manufacturer using PVD (DT Light SL) or TSC (DentinPost Coated) deposition techniques. Surface analysis was carried out by profilometry and x-ray microanalysis. All the posts were surrounded by 2-mm-thick disks of a dual-curing composite resin (MultiCore Flow). After water storage for 24 h at 37°C, the specimens in each group were randomly divided into three subgroups (n=10) and subjected to 0, 1500, and 20,000 thermocycles (5°C to 55°C) prior to push-out testing. Failure modes were evaluated by optical and scanning electron microscopy. The statistical significance was determined with two-way ANOVA, the Student-Newman-Keuls test, and Fishers exact test. RESULTS The conditioned posts had significantly higher interfacial bond strengths than the control posts after thermocycling (p<0.05). Extended thermocycling significantly reduced the interfacial strength of chairside silanized posts (p<0.05). This effect was not significant with industrially coated posts (p>0.05). Coatings deposited by TSC reached the highest bond values (p<0.05) and showed predominantly adhesive failures in the form of coating delamination (p<0.0001). In contrast, the other coupling strategies showed significantly lower values and adhesive failures between the post and the composite. CONCLUSION PVD and TSC techniques enhanced the bond durability of fiber posts. TSC led to a superior post-tocomposite bond, probably based on more effective micromechanical adhesion due to the higher surface roughness.

Reconsidering the double etching of enamel: do self-etching primers contaminate phosphoric acid-etched enamel?

PURPOSE To evaluate the composite-to-enamel bond following double etching of the enamel using phosphoric acid and different self-etching (SE) bonding systems with and without the application of their respective acidic primers. MATERIALS AND METHODS The enamel surfaces of 90 human molars were ground (600 grit) flat and randomly divided into nine groups (n = 10). Three two-step SE systems (AdheSE, ASE; Clearfil SE Bond, CSE; OptiBond Solo Plus SE, OSE) were tested, both with and without primer application on enamel pre-etched with phosphoric acid under dry bonding conditions. As the controls, the SE systems were applied according to their original directions without pre-etching. All the specimens were built up with a microhybrid composite resin (Arabesk Top). After water storage for 24 h at 37°C, the bonded specimens were sheared to failure in the Zwicki 1120. Etching and failure patterns were evaluated using a scanning electron microscope (SEM). Shear bond strength was analyzed with two-way ANOVA and Tukeys test. Failure modes were analyzed with Fishers exact test. RESULTS Without pre-etching, CSE showed significantly higher bond strengths than ASE and OSE (p < 0.05). Enamel etching prior to the application of the SE systems tended to result in higher bond strengths, but significantly increased the values only for ASE (p < 0.05). Contamination of the pre-etched enamel with the SE primer decreased the bond strength by values of 19% for ASE (p > 0.05), 36% for CSE (p < 0.05), and 75% for OSE (p < 0.05). SEM analysis showed that omission of the priming step significantly increased the number of cohesive failures within the resin for OSE (p < 0.0001). CONCLUSION Additional etching with phosphoric acid before the application of SE systems does not necessarily result in better enamel bonding, since unavoidable primer contamination of the pre-etched enamel was shown to significantly reduce the bond strength for two of the three systems tested.