Ex vivo investigation on the effect of minimally invasive endodontic treatment on vertical root fracture resistance and crack formation.

The evidence base on minimally invasive endodontic (MIE) treatment is limited. This study investigated the influence of MIE shaping on vertical root fracture (VRF) resistance and crack formation of root canal filled teeth. Human maxillary central incisors were randomized into six groups (n = 18, power = 0.9) and embedded in acrylic blocks with artificial periodontal ligaments. The root canals were either instrumented to size #40 and 0.04 taper (+MIE) or enlarged to ISO size #80 (-MIE). The canals were filled with cement-based (C) or adhesive resin-based (A) sealers in single-cone technique. The controls received no treatment or were left unfilled. After chewing simulation (staircase method, 25-150 N, 120,000×), the crack formation on the root surface was analyzed using stereomicroscope/digital imaging and classified (no defect, craze line, vertical crack, horizontal crack). Subsequently, the samples were loaded until fracture. The incidence of defects (56% vertical cracks) was not significantly different between the groups (p ≥ 0.077). VRF resistance was significantly higher in untreated teeth than in +MIE/C (p = 0.020) but did not significantly differ between the other groups (p ≥ 0.068). Minimal canal shaping did not reduce the risk of vertical root fracture and defects of root canal filled teeth.

Vertical root fracture resistance and crack formation of root canal-treated teeth restored with different post-luting systems.

The aim was to investigate the vertical root fracture (VRF) resistance and crack formation of root canal-treated teeth restored with different post-luting systems. Human maxillary lateral incisors of similar size were decoronated, assigned to five groups (n = 18, power = 0.9) and embedded in acrylic blocks with artificial periodontal ligament. After root canal filling, post spaces were prepared to place coated fiber-reinforced composite (FRC) or sandblasted titanium (Ti) posts of the same shape and size. Half of the posts were zinc phosphate cemented (C), while the other half was adhesively luted (A). Untreated teeth served as control. After thermal cycling and staircase loading in a chewing simulator, the crack formation on the root dentin surface was microscopically examined and classified as no defect, craze line, vertical crack, and horizontal crack. Subsequently, the samples were loaded until root fracture. Data were analyzed by one-way ANOVA, Tukey's test, and Fisher's exact test. All samples survived the chewing simulation without VRF, but crack formation was significantly different between the groups (P = 0.009). The control showed significantly fewer defects than FRC/C, Ti/C, and Ti/A (P = 0.001, P = 0.008, P = 0.008, respectively). FRC/C showed the highest incidence of vertical cracks. FRC/A had the lowest incidence of defects. There was no significant difference in VRF resistance between the groups (P = 0.265). Adhesively luted FRC posts did not increase VRF resistance but reduced the risk of defects. Most defects were craze lines and vertical root cracks.

One-year clinical results of restorations using a novel self-adhesive resin-based bulk-fill restorative.

This prospective study assessed the dual-curing self-adhesive bulk-fill restorative Surefil one. The restorations were placed and reviewed by dental practitioners who are members of a practice-based research network in the United States. Seven practitioners filled 60 cavities (20 class I, 19 class II and 21 class V) in 41 patients with Surefil one without adhesive, according to the manufacturer's instructions. The restorations were evaluated using modified USPHS criteria at baseline, 3 months, and 1 year. Patients were also contacted to report postoperative hypersensitivity one to four weeks after placement. The only patient that showed moderate hypersensitivity after 1 year had previously reported symptoms that were unlikely associated to the class I molar restoration. One class II restoration in a fractured maxillary molar was partially lost. The remaining restorations were found to be in clinically acceptable condition resulting in an annual failure rate of 2%. Color match showed the lowest number of acceptable scores (88%) revealing significant changes over time (P = 0.0002). No significant differences were found for the other criteria (P > 0.05). The novel self-adhesive bulk-fill restorative showed clinically acceptable results in stress-bearing class I and II as well as non-retentive class V cavities at 1-year recall.

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 Fisher's 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 Tukey's test. Failure modes were analyzed with Fisher's 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.

Antibacterial activity of calcium hydroxide and chlorhexidine containing points against Fusobacterium nucleatum and Parvimonas micra.

OBJECTIVE: Up to 90% of the flora of an infected root canal consists of obligate anaerobic bacteria. However, most studies have centred on microaerophiles. This quantitative assay investigated the antibacterial effects against Fusobacterium nucleatum and Parvimonas micra of gutta-percha (GP) points containing either calcium hydroxide (Ca(OH)(2)) or chlorhexidine (CHX) compared to those of conventional GP points. METHODS: Standardized root canals were prepared in 192 bovine incisors. The canals were sterilized and then inoculated with one of two bacterial species (n=96 teeth per bacterium). After anaerobic incubation at 37°C, the inoculum was removed and the canals were filled with one of the three points. Control teeth were filled with a saline/serum mixture. After 0, 1, 4 and 8 days of anaerobic incubation, the numbers of viable bacteria (CFU/ml) were determined on both the points and the canal wall dentin. Six replicates were carried out for each experiment. RESULTS: None of the points completely eradicated the bacteria in the canal. GP+CHX was significantly more effective than GP+Ca(OH)(2) and GP (P<.05 in each case). The inhibitory effect of GP+Ca(OH)(2) did not significantly differ from that of GP (P>.05). Compared to the controls, the antibacterial effect of the medicated points was reached initially. CONCLUSION: Within the limitations of the in vitro model, the incorporation of commonly used medicaments in GP does not offer a long-lasting antibacterial advantage over non-medicated GP.

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.

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 manufacturer's 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.

Antibacterial activity of a triclosan-containing resin composite matrix against three common oral bacteria.

This study investigated the antibacterial effect of a resin composite matrix with or without incorporated triclosan (0.3 wt%) on Streptococcus mutans, Actinomyces viscosus and Lactobacillus casei. In the quantitative assay, bacterial suspensions were filled into 20-µl cavities within temporary restorative resins. After 0, 4, 8, 12, 24 and 48 h of incubation, the suspensions were removed from the restoratives and the numbers of viable bacteria were determined. Bacterial suspensions incubated without restoratives served as the controls. Ten replicates were carried out for each experiment. The resin composite containing triclosan demonstrated variable degrees of antibacterial activity against the microorganisms, revealing a significant inhibitory effect on S. mutans within 12 h compared to the control. The viable counts of A. viscosus significantly decreased after 24 h. A significant reduction of L. casei was observed after 48 h. The unloaded resin composite did not reveal a marked antibacterial effect. The resin composite loaded with triclosan might be beneficial in preventing cavity contamination and minimizing the risk of pulpal irritation in the short-term.

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.

Effect of different surface treatments on the composite-composite repair bond strength.

The aim of this study was to investigate the effect of different mechanical and adhesive treatments on the bond strength between pre-existing composite and repair composite using two aging times of the composite to be repaired. Standardized cylinders were made of a microhybrid composite (Spectrum TPH) and stored in saline at 37 degrees C for 24 h (n = 140) or 6 months (n = 140). Three types of mechanical roughening were selected: diamond-coated bur followed by phosphoric acid etching, mini sandblaster with 50-microm aluminum oxide powder, and 30-microm silica-coated aluminum oxide powder (CoJet Sand), respectively. Adhesive treatment was performed with the components of a multi-step bonding system (OptiBond FL) or with a one-bottle primer-adhesive (Excite). In the CoJet Sand group, the effect of a silane coupling agent (Monobond-S) was also investigated. The repair composite (Spectrum TPH) was applied into a mould in three layers of 1 mm, each separately light-cured for 40 s. Repair tensile bond strengths were determined after 24-h storage. Mechanical and adhesive treatment had significant effects on repair bond strength (P < 0.001). The age of the pre-existing composite had no significant effect (P = 0.955). With one exception (CoJet Sand/OptiBond FL Adhesive), adhesive treatments significantly increased repair bond strengths to 6-month-old composite when compared to the controls without adhesive. Adhesive treatment of the mechanically roughened composite is essential for achieving acceptable repair bond strengths. The more complicated use of silica-coated particles for sandblasting followed by a silane coupling agent had no advantage over common bonding systems.

Dentin diffusion of HEMA released from etch-and-rinse and self-etch bonding systems.

The aim of this in vitro study was to determine the diffusion of 2-hydroxyethyl methacrylate (HEMA) released from different bonding systems (BS) through dentin. Occlusal cavities with a remaining dentin thickness (RDT) of 0.5 mm (n=90) and 0.25 mm (n=80), respectively, were prepared in dentin discs of non-carious human molars. Artificial pulp chambers were attached to the pulpal side of each dentin disc. Bonding systems were applied with (Clearfil SE Bond, OptiBond FL, OptiBond Solo Plus) or without (AdheSE, Adper Prompt L-Pop, Clearfil SE Bond, OptiBond FL, OptiBond Solo Plus Self Etch, Xeno III) prior phosphoric acid etching. HEMA was detected by gas chromatography/mass spectrometry (n=10 per BS and RDT). The highest mean HEMA concentration was found in the 0.25 mm RDT group treated with OptiBond FL (13.3 microg) and the lowest mean HEMA concentration was detected in the 0.5 mm RDT group treated with AdheSE (0.5 microg). At 0.25 mm RDT the quantities of HEMA recovered in the artificial pulp chambers were significantly higher than at 0.5 mm RDT, except for Clearfil SE Bond. Etching with phosphoric acid increased the detected HEMA quantities compared with self-etch BS. In deep cavity preparations, etching with phosphoric acid should be avoided in favor of the use of self-etch BS.