Evaluation of bond strength in single-cone fillings of canals with different cross-sections.

AIM: To evaluate the effect of root canal cross-sectional shape on single-cone root filling bond strength, as well as to determine the percentage of gutta-percha-filled areas (PGFA) and sealer-filled areas (PSFA), establishing a relationship between these variables. METHODOLOGY: Distal roots of mandibular molars were selected using microcomputed tomography imaging and allocated into three groups (n = 10) according to canal shape: round, oval and long oval. The canals were prepared with an R40 reciprocating instrument and filled with matching single-cone gutta-percha and AH Plus sealer. Two 1-mm-thick dentine slices were obtained from each third of each root. PGFA and PSFA were calculated in digital images (x25 magnification) of each slice. Next, the slices were subjected to a push-out test and the failure modes (adhesive, cohesive or mixed) were assessed. Data were analysed using parametric tests (P < 0.05). RESULTS: In the coronal (2.17 ± 0.56MPa) and middle thirds (1.78 ± 0.45MPa), the round canals were associated with higher bond strength values (P < 0.01), with no difference between the groups for the apical third (P > 0.05). Adhesive and mixed failures predominated in round canals, whilst cohesive failures were more frequent in oval and long oval canals. Round canals had significantly higher PGFA and lower PSFA than all other groups (P = 0.000). The PGFA and PSFA had a positive (r = 0.521, P = 0.000) and a negative (r = -0.523, P = 0.000) correlation with bond strength, respectively. CONCLUSION: Bond strength values of gutta-percha and sealer were affected by canal shape. Higher percentage of gutta-percha-filled area resulted in higher bond strength to dentine.

Significant shear bond strength improvements of a resin-modified glass ionomer cement with a resin coating.

Previous evidence has suggested that resin-modified glass ionomer cements (RMGICs) may be sensitive to temperature and moisture changes for the first 24 hours after photopolymerization. To test the hypothesis that a resin coating placed over the surface of an RMGIC restoration would decrease the susceptibility to moisture and temperature conditions, 44 RMGIC samples were prepared in inverted-cone recesses drilled in epoxy resin plates. After abrasion of all samples with 800-grit silicon carbide paper to simulate a diamond bur finish on the surface, a coat of highly filled resin was applied to the experimental group (n = 22) and cured according to the manufacturer's instructions. The plates were thermocycled 500 times between 5°C and 55°C and then maintained at 37°C with 95% humidity. The thermocycled samples were bonded to a second epoxy resin plate filled with RMGIC and subjected to shear bond strength testing. The resin-coated group had a significantly greater mean shear bond strength than the control group (P < 0.05). The resin coating also appeared to affect the mode of failure by significantly increasing the number of mixed failures (P < 0.05). The results suggest that a resin coating protects RMGIC from moisture- and temperature-induced damage and increases shear bond strength.

Influence of Cavity Margin Design and Restorative Material on Marginal Quality and Seal of Extended Class II Resin Composite Restorations In Vitro.

PURPOSE: To investigate the influence of three cavity designs on the marginal seal of large Class II cavities restored with low-shrinkage resin composite limited to the enamel. MATERIALS AND METHODS: One hundred twenty (120) intact human molars were randomly divided into 12 groups, with three different cavity designs: 1. undermined enamel, 2. box-shaped, and 3. proximal bevel. The teeth were restored with 1. an extra-low shrinkage (ELS) composite free of diluent monomers, 2. microhybrid composite (Herculite XRV), 3. nanohybrid composite (Filtek Supreme XTE), and 4. silorane-based composite (Filtek Silorane). After artificial aging by thermocycling and storage in physiological saline, epoxy resin replicas were prepared. To determine the integrity of the restorations' approximal margins, two methods were sequentially employed: 1. replicas were made of the 120 specimens and examined using SEM, and 2. the same 120 specimens were immersed in AgNO3 solution, and the dye penetration depth was observed with a light microscope. Statistical analysis was performed using the Kruskal-Wallis and the Dunn-Bonferroni tests. RESULTS: After bevel preparation, SEM observations showed that restorations did not exhibit a higher percentage of continuous margin (SEM-analysis; p>0.05), but more leakage was found than with the other cavity designs (p<0.05). The lowest percentage of continuous margin was observed in ELS restorations (p<0.05). More fractured margins were observed in the undermined enamel cavity design groups (p<0.05). CONCLUSION: Bevel preparation failed to improve margin quality in large Class II composite restorations and is no longer recommended. However, undermined enamel should be removed to prevent enamel fractures.

A randomized controlled trial of cluster audit and feedback on the quality of dental sealant for rural schoolchildren.

THE OBJECTIVE: To examine whether audit and feedback could improve the quality of the application of dental sealant in rural Thai school children. RESEARCH DESIGN: A single blind, cluster randomized controlled trial was conducted. CLINICAL SETTING: Hospital-based and school-based school sealant applied by dental nurses in Southern province of Thailand. PARTICIPANTS: Dental nurses and school children who received dental sealant were involved. INTERVENTION: The intervention consisted of confidential feedback of data and tailor-made problem-solving workshops. MAIN OUTCOME MEASURES: Sealant quality was measured by sealant retention and caries on sealed surfaces at six-month after sealing. The teeth examinations were done among different groups of children prior and after the intervention. RESULTS: After the intervention, the sealant retention rate increased dramatically in the intervention group, whereas in the control group the rate was similar to that found at baseline. The rate of caries after the intervention was stable in the intervention group and increased slightly in the control group. At the beginning of the study, the adjusted odds ratio of complete sealant retention between the intervention and control group was 0.47 which increased to 1.99 at the end of the study. However, no effect on caries on sealed surfaces was observed. CONCLUSIONS: The intensive focus on actual problems during the audit and feedback improved the dental nurses' performance and the quality of the dental service, although it had no statistical impact on the incidence of caries.

An in situ evaluation of the polymerization shrinkage, degree of conversion, and bond strength of resin cements used for luting fiber posts.

STATEMENT OF PROBLEM: The behavior and magnitude of the deformations that occur during polymerization and the behavior of the luting agents of glass fiber posts inside the root canal require quantification. PURPOSE: The purpose of this in vitro study was to investigate the in situ polymerization shrinkage, degree of conversion, and bond strength inside the root canal of resin cements used to lute fiber posts. MATERIAL AND METHODS: Thirty maxillary canines were prepared to lute fiber posts. The teeth were randomly divided into 2 groups (n=15) according to the cementation system used, which included ARC, the conventional dual-polymerized resin cement RelyX ARC, and the U200 system, a self-adhesive resin cement, RelyX U200. Two fiber optic sensors with recorded Bragg gratings (FBG) were attached to each post before inserting the resin cement inside the root canal to measure the polymerization shrinkage (PS) of the cements in the cervical and apical root regions (µÎµ). Specimens were sectioned (into cervical and apical regions) to evaluate bond strength (BS) with a push-out test and degree of conversion (DC) with micro-Raman spectroscopy. Data were statistically analyzed with 2-way ANOVA and the Tukey honestly significant difference post hoc test (α=.05). RESULTS: The ARC and U200 system showed similar PS values (-276.4 ±129.2 µÎµ and -252.1 ±119.2 µÎµ, respectively). DC values from ARC were higher (87.5 ±2.7%) than those of U200 (55.9 ±9.7%). The cervical region showed higher DC values (74.8 ±15.2%) and PS values (-381.6 ±53.0 µÎµ) than those of the apical region (68.5 ±20.1% and -146.9 ±43.5 µÎµ, respectively) for both of the resin cements. BS was only statistically different between the cervical and apical regions for ARC (P<.05). CONCLUSIONS: The ARC system showed the highest PS and DC values compared with U200; and for both of the resin cements, the PS and DC values were higher at the cervical region than at the apical region of the canal root. BS was higher in the cervical region only for ARC.

Effect of surface treatment and aging on bond strength of composite resin onlays.

STATEMENT OF PROBLEM: Additional polymerization of indirect composite resins enhances their physical properties but lessens the potential for chemical bonding. PURPOSE: The purpose of this in vitro study was to evaluate the influence of different surface treatments and 6-month water storage on the microtensile bond strength (µTBS) of composite resin onlays. MATERIAL AND METHODS: Composite resin onlays (Filtek Z250) randomly received 6 different surface treatments: (1) airborne-particle abrasion with 27-µm alumina particles+Adper Scotchbond 1XT adhesive application, (2) airborne-particle abrasion with alumina particles+silane application (ESPE SIL)+Adper Scotchbond 1XT, (3) airborne-particle abrasion with alumina particles+Scotchbond Universal adhesive, (4) tribochemical silica coating with 30-µm particles (CoJet Sand)+Adper Scotchbond 1XT adhesive, (5) tribochemical silica coating+silane application+Adper Scotchbond 1XT, and (6) tribochemical silica coating+Scotchbond Universal adhesive. Onlays were luted to fresh composite resin specimens with RelyX Ultimate resin cement. Bonded assemblies were stored in water for 24 hours or 6 months at 37°C and subjected to the µTBS test. Additional surface-treated composite resin onlays were analyzed with a contact profilometer to determine average roughness, and micromorphologic changes were analyzed with scanning electron microscopy. RESULTS: Airborne-particle abrasion with alumina followed by Adper Scotchbond 1XT or Scotchbond Universal adhesive application provided the highest bond strength values at 24 hours. Lower values were obtained after tribochemical silica coating. After 6 months of artificial aging, airborne-particle abrasion with alumina or silica-coated alumina particles followed by Scotchbond Universal application yielded the greatest bond strength results. Airborne-particle abrasion with alumina produced the highest roughness values and a more irregular surface. CONCLUSION: Adhesive selection seems to be relevant to the µTBS of luted composite resin onlays after 6 months of water aging, as specimens treated with Scotchbond Universal, after alumina airborne-particle abrasion or tribochemical silica coating, yielded the highest values and better aging stability.

Depth of cure of bulk-fill flowable composite resins.

In recent years, manufacturers have introduced flowable composite resins that reportedly can be placed in increments of 4 mm or greater. The purpose of this study was to evaluate the depth of cure of bulk-fill flowable composite resins (SureFil SDR Flow, Grandio Flow, and Venus Bulk Fill) and a conventional flowable composite resin (Revolution Formula 2). Depth of cure was measured in terms of bottom-maximum Knoop hardness number (KHN) ratios and the International Organization for Standardization (ISO) 4049 scrape technique. Shades A2 and A3 of SureFil SDR Flow, Grandio Flow, and Revolution Formula 2 were tested. Venus Bulk Fill was tested in its only available shade (universal). Specimens in thicknesses of 2, 3, 4, 5, and 6 mm were polymerized for 20 or 40 seconds, and a hardness tester was used to determine the hardness ratios for each shade at each thickness. For the scraping technique, after specimens were exposed to the curing light, unpolymerized composite resin was removed with a plastic instrument, the polymerized composite was measured, and the length was divided by 2 per ISO guidelines. According to the KHN ratios and the scrape test, Venus Bulk Fill predictably exceeded the manufacturer's claim of a 4-mm depth of cure at both 20 and 40 seconds of curing time. The overall results for depth of cure showed that Venus Bulk Fill ≥ SureFil SDR Flow ≥ Grandio Flow ≥ Revolution Formula 2.

Bond strength of repaired amalgam restorations.

This in vitro study investigated the interfacial flexural strength (FS) of amalgam repairs and the optimal combination of repair materials and mechanical retention required for a consistent and durable repair bond. Amalgam bricks were created, each with 1 end roughened to expose a fresh surface before repair. Four groups followed separate repair protocols: group 1, bonding agent with amalgam; group 2, bonding agent with composite resin; group 3, mechanical retention (slot) with amalgam; and group 4, slot with bonding agent and amalgam. Repaired specimens were stored in artificial saliva for 1, 10, 30, 120, or 360 days before being loaded to failure in a 3-point bending test. Statistical analysis showed significant changes in median FS over time in groups 2 and 4. The effect of the repair method on the FS values after each storage period was significant for most groups except the 30-day storage groups. Amalgam-amalgam repair with adequate condensation yielded the most consistent and durable bond. An amalgam bonding agent could be beneficial when firm condensation on the repair surface cannot be achieved or when tooth structure is involved. Composite resin can be a viable option for amalgam repair in an esthetically demanding region, but proper mechanical modification of the amalgam surface and selection of the proper bonding system are essential.

Effect of moisture and moisture-insensitive primer on bond strength of composite resin to enamel and dentin.

This article sought to compare the influence of moisture and the effect of moisture-insensitive primer (MIP) on shear bond strength (SBS). This study divided 160 extracted teeth randomly into 2 groups (n = 80): Group 1 (enamel) and Group 2 (dentin). Groups 1 and 2 were divided into 4 subgroups (n = 20), according to the surface treatment administered. Subgroup A samples were etched and primed, and received composite resin; Subgroup B samples were etched, contaminated with artificial saliva, and primed before application of composite resin; Subgroup C samples were etched, primed, and contaminated before application of composite resin. Subgroup D samples were etched, primed, contaminated, and primer was applied a second time before application of composite resin. All the specimens were stored in distilled water and thermocycled for 500 cycles; at that point, SBS was tested. According to Tukey's test, only the mean values in Subgroups A and C revealed statistically significant differences (P < 0.05). The use of MIP on contaminated etched tooth surfaces achieved comparable bond strength to noncontaminated tooth surfaces and might have a role in restorative dentistry cases where moisture contamination is inevitable.

Bond strength of resin cements to zirconia conditioned with primers.

New ceramic primers, which reportedly enhance bonding of resin cements to zirconia, have been marketed recently. The purpose of this study was to compare the shear bond strength of 3 resin cements to zirconia conditioned with 4 ceramic primers. Zirconia blocks were conditioned with 4 different primers (Z-Prime Plus, MonoBond Plus, CLEARFIL CERAMIC PRIMER, and AZ Primer) or no primer (control). The zirconia blocks were placed in a jig, and 1 of 3 resin cements (Multilink Automix, RelyX Unicem, Panavia F 2.0) were mixed, injected into a mold, and light cured. The specimens were tested in shear on a universal testing machine after 24 hours of storage in distilled water. The shear bond strength of the resin cements to zirconia varied based on the type of primer. Z-Prime Plus provided the highest shear bond strength to zirconia, and was significantly greater than the control (no primer) with all 3 resin cements.

Should acid etching be performed prior to nonvital bleaching?

This study sought to measure the microtensile bond strength of a nanofilled composite resin to human dentin after phosphoric acid etching followed by nonvital bleaching. Scanning electron microscopy was used to analyze fracture modes. Twenty extracted sound human maxillary premolars were prepared for Class I defects and assigned randomly to 4 groups (n = 5): Group 1 (control group) samples were unbleached and had no previous acid etching; Group 2 samples were bleached only, Group 3 samples were acid-etched for 15 seconds prior to bleaching, and Group 4 samples were acid-etched for 30 seconds prior to bleaching. There were no statistically significant differences of bond strength values among Groups 1-3; however, the mean values of Group 4 were statistically lower compared with the other groups.

Carrier-based root canal filling materials: a literature review.

A review of the literature on the use of carrier based obturation materials focusing on Thermafil and Resilon based obturator (RealSeal 1) are presented in this article. The review addressed the history, apical leakage, coronal leakage, biocompatibility, sealing ability and clinical success of Thermafil and RealSeal 1. Based on the studies gathered, this review concluded that both treatment techniques (Thermafil and RealSeal 1) did not provide excellent apical sealing ability. More research should be done to try to overcome their main drawback, its sealing ability.

Prediction and diagnosis of clinical outcomes affecting restoration margins.

The longevity of dental restorations is largely dependent on the continuity at the interface between the restorative material and adjacent tooth structure (the restoration margin). Clinical decisions on restoration repair or replacement are usually based upon the weakest point along that margin interface. Physical properties of a restorative material, such as polymerisation shrinkage, water sorption, solubility, elastic modulus and shear strength, all have an effect on stress distribution and can significantly affect margin integrity. This review will focus on two aspects of margin deterioration in the oral environment: the in vitro testing of margin seal using emersion techniques to simulate the oral environment and to predict clinical margin failure and the relationship between clinically observable microleakage and secondary caries. The many variables associated with in vitro testing of marginal leakage and the interpretation of the data are presented in detail. The most recent studies of marginal leakage mirror earlier methodology and lack validity and reliability. The lack of standardised testing procedures makes it impossible to compare studies or to predict the clinical performance of adhesive materials. Continual repeated in vitro studies contribute little to the science in this area. Clinical evidence is cited to refute earlier conclusions that clinical microleakage (penetrating margin discoloration) leads to caries development and is an indication for restoration replacement. Margin defects, without visible evidence of soft dentin on the wall or base of the defect, should be monitored, repaired or resealed, in lieu of total restoration replacement.

Apical periodontitis in association with the quality of root fillings and coronal restorations: a 14-year investigation in young Greek adults.

PURPOSE: To examine the possible association between the presence of apical periodontitis (AP) and the quality of endodontic treatment and coronal restoration over a time period of 14 years. MATERIALS AND METHODS: 1781 panoramic radiographs of freshmen cadets, taken between the years 1995-2008 were included in this study. The periapical status was evaluated using the Periapical Index (PAI) scoring system. The chisquare test and logistic regression analysis were used to examine associations between apical disease and the quality of both the root filling and the coronal restoration. RESULTS: 62.3% of the examined teeth demonstrated AP. The number of root-filled teeth and the prevalence of AP were found to be higher in OPGs taken between 1995 and 2001 than those taken between 2002 and 2008. Both the quality of the coronal restoration and the quality of the root filling (length and lateral seal) were found to be correlated with the presence of AP, but the factor most significantly associated seemed to be the coronal restoration (OR = 0.404, 95% CI: 0.174-0.940). CONCLUSION: The quality of the endodontic treatment in young Greek adults was poor but improved over the years. Both the quality of the endodontic treatment and coronal restoration appeared to affect the periapical status of the treated teeth. The factor that probably most determined the periapical health was the quality of the coronal restoration.

Modified bonding technique for a standardized and effective indirect bonding procedure.

This article describes a modified technique for indirect bonding. Crucial variables that influence the procedure are analyzed and discussed to help the clincian use the indirect bonding techinique routinely.

Effect of enamel surface treatment on the bond strength of metallic brackets in rebonding process.

Bond failure after rebonding for newly placed brackets can be reduced by appropriate enamel surface treatment. This in vitro study investigated the effect of two enamel surface treatments on the bond strength of metallic brackets in the rebonding process. After debonding the brackets and removing the residual adhesive on the enamel surface of 50 upper premolar teeth, the teeth were divided into two equal groups. In the first group, the enamel surface was etched with phosphoric acid 37 per cent, and in the second group, the teeth were sandblasted prior to acid etching. After bonding of the new brackets, the shear bond strength (SBS), probability of bond failures, and adhesive remnant index (ARI) were determined and compared with the t-test, Weibull analysis, and chi-square test. Mean SBS in both groups did not differ significantly (P = 0.081). Most bond failures occurred with ARI scores of 2 and 3, and the difference between the two groups was statistically significant (P < 0.001). Weibull analysis showed that for a given stress, the probability of failure differed between groups. Enamel surface preparation with sandblasting prior to acid etching did not significantly improve SBS in bracket rebonding and left more residual adhesive remnants on the enamel surface.

Extension for prevention: margin placement.

This article will review the concept of extension for prevention popularized by G.V. Black around the early 1900s. Concepts of extension and prevention have changed over the years with a more informed knowledge of the caries process, improved materials, cutting instruments, and techniques. The reasons for placement of the outline form relative to the tooth morphology, gingival tissue, relationship to adjacent teeth, and the choice of material will be described for all of the materials used in restorative dentistry. Research will be cited to support the scientific basis for outline form placement.

The bonding property and cytotoxicity of a dental adhesive incorporating a new antibacterial monomer.

The incorporation of polymerisable cationic monomers has been attempted to generate dental resinous materials with antibacterial activity. This study tested whether the incorporation of a cationic monomer, methacryloxylethyl cetyl dimethyl ammonium chloride (DMAE-CB), into a commercial dental adhesive would influence the bonding property and biocompatibility of the parental adhesive, and whether DMAE-CB could leach out from the cured modified adhesive. Microtensile bond strengths of DMAE-CB-incorporated adhesive and its parental adhesive to dentin were compared. Dentin discs bonded with modified adhesive were incubated in artificial saliva at three different temperatures for 90 days to obtain eluents. The cytotoxicity of DMAE-CB monomer and adhesive eluents were tested with 3-(4, 5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cleavage assay (MTT assay). High-performance liquid chromatography (HPLC) was performed with the eluents of the modified adhesive. The results indicated that the incorporation of DMAE-CB into the dental adhesive did not adversely influence its bonding strength to dentin (P > 0·05). Although DMAE-CB monomer exhibited toxicity against L929 cells at the concentration of 2 µg mL(-1) or higher (P < 0·05), the eluents of DMAE-CB-incorporated adhesive did not show significant influence on cell growth (P > 0·05). Moreover, HPLC analysis detected four substances' peak baseline separation for the eluents of modified adhesives, which was identical to the eluent of the parental adhesive, indicating no detectable DMAE-CB monomer leaching even after soaking for 90 days. Those results suggest that DMAE-CB could be incorporated into the dental adhesive stably without compromising the bonding efficiency and biocompatibility of its parental adhesive.

Metal-ceramic bond: how to improve?

Metal-ceramic restorations include the positive features of metal (strength, durability and stability) and ceramics (esthetics). The strong bond on the metal-ceramic interface is the basic prerequisite for the durability of the metal-ceramic restoration. The heating of metal construction results in the diffusion of certain atoms (tracers) on the surface. There they react with atmospheric oxygen creating in oxides which remain on the cast surface, because the reversible diffusion is prevented. Atoms of silica in ceramic are bound with these oxides as a result of which a metal-tracer-ceramic compound is formed and a chemical bond is realised. In addition to forming an oxide layer, the oxidation heat treatment (OHT) is applied for all alloys in order to remove the entrapped gas and eliminate surface contaminants. Surface metal preparation before porcelain application may also affect the bond strength of metal and ceramics. Roughened surface by sandblasting enables mechanical interlocking and an increased surface for bonding metal and ceramics. Applying a bonding agent may improve the quality of the bond of certain metal-ceramic restorations. Due to the continued oxidation of titanium and creation of a non-adherent oxide layer, the bond strength between titanium and ceramics is weak, which is attempted to be resolved by firing in an argon atmosphere.