A tensile test to facilitate identification of defects in dentine bonded specimens

A Comparison of Microtensile Bond Strength, Film Thickness, and Microhardness of Photo-Polymerized Luting Composites

The aim of this study was to evaluate the effect of CAD/CAM composite thickness on micro-tensile bond strength (µTBS), microhardness (HV), and film thickness (FT) of different luting composites. Composite blocks (6.8 mm × 6.8 mm) were divided into 12 groups according to: CAD/CAM thickness and luting composite. For each group, 21 rods (1 mm × 1 mm) were tested in tension at crosshead speed of 1 mm/min. Fracture modes were categorized as adhesive, mixed, and cohesive. Microhardness (n = 5/group) was assessed using microhardness tester. Film thickness (12-rods/group) was evaluated using a stereomicroscope (×40). Data were analyzed using the two-way ANOVA/Tukey’s HSD test (p = 0.05). Parameters “thickness”, “cement”, and “thickness x cement” showed significant difference on µTBS and HV (p < 0.05). At 2 mm, heated x-tra fil composite showed the highest µTBS (45.0 ± 8.5 MPa), while at 4 mm thickness, Grandio Flow revealed the lowest µTBS (33.3 ± 6.3 MPa). Adhesive, mixed, and cohesive failures were reported. The HV of all composites decreased when photo-polymerized through 4 mm thickness (p < 0.05). Regardless of CAD/CAM thickness, photo-polymerized composites can be successfully used for luting CAD/CAM composite.

Mechanical Stability and Proteolytic Activity of Resin-dentin Bonds Using the Cross-linked Dry Bonding Technique

OBJECTIVE

To evaluate the mechanical stability and the proteolytic activity of bonds created by a two-step, etch-and-rinse adhesive applied to cross-linked and air-dried etched dentin.

METHODS

Flat dentin surfaces were produced in 64 extracted sound human molars. The dentin was etched with 35% phosphoric acid for 15 seconds, and then the teeth were divided into groups according to the cross-linking solution applied on the etched dentin. Group 1: 5% grape seed extract (GSE), Group 2: 5% glutaraldehyde, Group 3: Gluma Desensitizer, or Group 4: deionized water (control). Solutions were applied for 60 seconds, followed by rinse and blot drying. Then, the teeth were separated into two subgroups where the etched dentin was kept moist or air-dried. The adhesive was applied followed by a composite resin buildup. After 24 hours, the teeth were cut into beams (0.81 mm2) that were tested for microtensile strength immediately or after 12 months of aging in a 37°C saliva-like buffer. Additional teeth (n=32) were bonded as described and cut into 0.5-mm-thick slabs. The slabs were prepared for nanoleakage (scanning electron microscopy) and in situ zymography (EnzChek Protease Assay Kit). Bond strength data were submitted to ANOVA and Tukey tests (α=0.05).

RESULTS

Significant reduction in immediate bond strength (ca 65%) and increase in proteolytic activity was seen when the etched dentin was air dried without previous cross-linking biomodification. Conversely, bond strengths did not differ from those produced on wet dentin when collagen was cross-linked before air drying, irrespective of the solution applied. For both moist and air-dried etched dentin, collagen cross-linking resulted in mechanically stable bonds and reduced proteolytic activity after 12 months of storage.

CONCLUSION

Bonds produced by the application of a two-step, etch-and-rinse adhesive to cross-linked, air-dried, etched dentin were mechanically stable and revealed reduced proteolytic activity after 1 year of aging.

Novel testing method to evaluate the mechanical strength of self-adhesive resin cements with reflection of cement thickness

This study aimed to propose an evaluation method for testing the mechanical strength of film-formed self-adhesive resin cements (SARCs) while reflecting cement layer thickness. Three commercially available dual-cure type SARCs were used for tensile and shear tests using specimens with varying thicknesses (0.05, 0.2, and 0.4 mm). There were no significant differences in tensile strengths among the various specimen thicknesses. In the shear test, there was a significant decrease in the strength with a reduction in specimen thickness. Stress distribution and fracture patterns were analyzed using in silico nonlinear dynamic finite element analysis. Finite element analysis demonstrated that stress distribution on the specimen surface was homogeneous even with different thicknesses in the tensile test, whereas it was inhomogeneous and induced different fracture patterns on the 0.05-mm-thick specimen in the shear test. These results suggest that the tensile test is useful for testing the mechanical strength of film-formed SARCs.

Evaluation of Restorative Techniques for Vertically Fractured Roots

The purpose of this study was to examine the effects of combining specific adhesive materials and various surface treatments on bonding durability and microleakage of vertically fractured roots. Adhesive models were prepared using bovine lower incisors. The experiment included the following five groups: SB-G group (control) (10% citric acid with 3% ferric chloride solution (10-3 solution) + an adhesive resin cement (4-META/MMA-TBB; Super-Bond^®)), EC group (self-cure bonding agent (UB) + core composite resin (EC)), EC-G group (10-3 solution + UB + EC), EC-P group (40% phosphate solution + UB + EC), and EC-E group (18% ethylenediaminetetraacetic acid (EDTA) solution + UB + EC). After applying a load of 50,000 cycles, microleakage, microtensile bond strength (μTBS), and failure modes were examined. Microleakage of the EC, EC-G, and EC-E groups was significantly lower than that of the EC-P group. The μTBS of the EC-G group was significantly higher than that of the other groups. All EC groups showed that mixed (cohesive and adhesive) and adhesive failures were the most prevalent types of failure modes. The EC-G group showed the highest bonding durability and the lowest microleakage results, which indicates a possible alternative to current adhesive and tooth surface treatments.

Etching time and bonding of adhesive systems to dentin of primary teeth: A systematic review and meta-analysis

BACKGROUND

Due to the chemical and morphological differences between primary vs. permanent teeth, the time reduction of the acid etching or acidic primer can result in higher values of bond strength.

AIM

To assess through a systematic review and meta-analysis the influence of the reducing etching (acid etching or acidic primer) time on the bond strength of adhesive systems to primary dentin.

DESIGN

A systematic search was carried out in 3 databases: PubMed, Web of Science and Scopus. Studies that evaluated the effect of reducing the etching time on the bond strength of adhesive systems to primary dentin were included. Meta-analyses were performed using a random-effects model, with subgroups for etch-and-rinse and self-etching adhesives, with a significance level of P < .05. The risk of bias and heterogeneity between studies (Cochrane and I2 tests) were assessed.

RESULTS

Eight studies were included in the systematic review and seven in the meta-analyses. The shortening etching time did not influence the immediate dentin bond strength for etch-and-rinse (Z = 0.07, P = .95) and self-etching adhesives (Z = 0.41, P = .69). After ageing, however, the shorting etching time improved the bond strength for etch-and-rinse adhesives (Z = 2.01, P = .04). All studies presented high bias risk.

CONCLUSIONS

Reducing the acid-etching time to primary dentin improves the long-term bond strength to this substrate.

Evaluation of Caries-Free Restorations Bonded with Various Adhesive Systems: In Vitro Study

Purpose. Secondary caries originate from a leakage pathway where oral acids can penetrate faster and demineralize the tooth substrate deeper which can be visualized by dye penetration. The ability to prevent secondary caries by contemporary adhesive systems was evaluated in this study. Dye penetration distance through leakage and into the tooth substrate adjacent to Class V restorations after artificial caries exposure was compared. Materials and Methods. Previously frozen extracted human molars were used to prepare the Class V cavities at the CEJ on axial surfaces. All cavities were restored with either the resin-composite or amalgam with or without resin adhesives: dry bonding: Super-Bond D-Liner II Plus; moist bonding: All-Bond 2; and self-etch bonding: AQ Bond and Clearfil Protect Bond. Two subgroups of Super-Bond D-Liner II Plus were immersed for 14 days at 37°C either in artificial saliva (negative control) or the artificial caries solution. The other groups were soaked in the artificial caries solution. The distance of dye penetration into the adjacent enamel, cementum/dentin, and tooth-resin interfaces was measured after immersion in 0.5% basic fuchsin dye for 24 h. The tooth-resin interfacial layer was investigated using SEM. Results. No dye penetration into the tooth-resin interface was found in Super-Bond D-Liner II Plus and AQ Bond groups which demonstrated a constant hybrid layer after a chemical challenge. The leakage distance at the cementum/dentin-resin interface of All-Bond 2, Clearfil Protect Bond, and non-adhesive amalgam (positive control) groups was significantly higher than the distance of dye penetration into the adjacent demineralized root surface (p<0.05). Conclusion. Caries associated with either amalgam or resin-composite restorations can be prevented using resin adhesives which can penetrate into the intact tooth substrate to form a stable hybrid layer. With caries-free restorations, tooth vitality may be conserved lifelong.

Comparison of the shear bond strength of self-adhesive resin cements to enamel and dentin with different protocol of application

AIM

The aim of the present study was to determine the shear bond strength of self-adhesive resin cements to enamel and dentin with and without surface treatments, and compare them with conventional resin cement as the control group.

METHODS

In this experimental study, buccal and lingual surface of the thirty sound human premolars were polished in order to obtain a flat surface of enamel (E) in buccal, and dentin (D) in lingual. Sixty feldspathic ceramic blocks (2×3×3 mm) were prepared and randomly divided into six groups (n=10). Each block was cemented to the prepared surface (30 enamel and 30 dentin surface) according to different protocol: E1 and D1; RelyX ARC as control group, E2, D2; RelyX Unicem, E3, D3; acid etching +RelyX Unicem. The specimens were termocycled and subjected to shear forces by a universal testing machine at a cross head speed of 0.5 mm/min. The mode of fracture were evaluated by stereomicroscope. Data were analyzed with descriptive statistical methods using SPSS version 15. One-way ANOVA, and post hoc Tukey tests were used to compare bond strengths between the groups with different adhesives at α=0.05.

RESULTS

Statistical analysis showed no significant differences within the enamel subgroups, but there were significant differences within the dentinal subgroups, and statistically significant differences were found between the groups D1and D3 (p=0.02). Comparison between similar enamel and dentinal subgroups showed that there was a significant difference just between the subgroups E3 and D3 (p=0.01).

CONCLUSION

Elective etching of enamel did not lead to significant increase in the shear bond strength of RelyX Unicem in comparison to RelyX ARC. On the other hand, elective etching of dentin reduces the bond strength of RelyX Unicem with the dentin.

Direct Tensile Strength and Characteristics of Dentin Restored with All-Ceramic, Resin-Composite, and Cast Metal Prostheses Cemented with Resin Adhesives

A dentin-cement-prosthesis complex restored with either all-porcelain, cured resin-composite, or cast base metal alloy and cemented with either of the different resin cements was trimmed into a mini-dumbbell shape for tensile testing. The fractured surfaces and characterization of the dentin-cement interface of bonded specimens were investigated using a Scanning Electron Microscope. A significantly higher tensile strength of all-porcelain (12.5 ± 2.2 MPa) than that of cast metal (9.2 ± 3.5 MPa) restorations was revealed with cohesive failure in the cement and failure at the prosthesis-cement interface in Super-Bond C&B group. No significant difference in tensile strength was found among the types of restorations using the other three cements with adhesive failure on the dentin side and cohesive failure in the cured resin. SEM micrographs demonstrated the consistent hybridized dentin in Super-Bond C&B specimens that could resist degradation when immersed in hydrochloric acid followed by NaOCl solutions whereas a detached and degraded interfacial layer was found for the other cements. The results suggest that when complete hybridization of resin into dentin occurs tensile strength at the dentin-cement is higher than at the cement-prosthesis interfaces. The impermeable hybridized dentin can protect the underlying dentin and pulp from acid demineralization, even if detachment of the prosthesis has occurred.

Effects of endodontic tri-antibiotic paste on bond strengths of dentin adhesives to coronal dentin

Objectives

The aim of this study was to evaluate the effects of tri-antibiotic paste (TAP) on microtensile bond strengths (MTBS) of dental adhesives to dentin.

Materials and Methods

Sixty extracted molars had their occlusal surfaces flattened to expose dentin. They were divided into two groups, i.e., control group with no dentin treatment and experimental group with dentin treatment with TAP. After 10 days, specimens were bonded using self-etch (Filtek P90 adhesive) or etch-and-rinse (Adper Single Bond Plus) adhesives and restored with composite resin. Teeth were sectioned into beams, and the specimens were subjected to MTBS test. Data were analyzed using two-way ANOVA and post hoc Tukey tests.

Results

There was a statistically significant interaction between dentin treatment and adhesive on MTBS to coronal dentin (p = 0.003). Despite a trend towards worse MTBS being noticed in the experimental groups, TAP application showed no significant effect on MTBS (p = 0.064).

Conclusions

The etch-and-rinse adhesive Adper Single Bond Plus presented higher mean bond strengths than the self-etch adhesive Filtek P90, irrespective of the group. The superior bond performance for Adper Single Bond when compared to Filtek P90 adhesive was confirmed by a fewer number of adhesive failures. The influence of TAP in bond strength is insignificant.

Posterior composite restoration update: focus on factors influencing form and function

Restoring posterior teeth with resin-based composite materials continues to gain popularity among clinicians, and the demand for such aesthetic restorations is increasing. Indeed, the most common aesthetic alternative to dental amalgam is resin composite. Moderate to large posterior composite restorations, however, have higher failure rates, more recurrent caries, and increased frequency of replacement. Investigators across the globe are researching new materials and techniques that will improve the clinical performance, handling characteristics, and mechanical and physical properties of composite resin restorative materials. Despite such attention, large to moderate posterior composite restorations continue to have a clinical lifetime that is approximately one-half that of the dental amalgam. While there are numerous recommendations regarding preparation design, restoration placement, and polymerization technique, current research indicates that restoration longevity depends on several variables that may be difficult for the dentist to control. These variables include the patient’s caries risk, tooth position, patient habits, number of restored surfaces, the quality of the tooth–restoration bond, and the ability of the restorative material to produce a sealed tooth–restoration interface. Although clinicians tend to focus on tooth form when evaluating the success and failure of posterior composite restorations, the emphasis must remain on advancing our understanding of the clinical variables that impact the formation of a durable seal at the restoration–tooth interface. This paper presents an update of existing technology and underscores the mechanisms that negatively impact the durability of posterior composite restorations in permanent teeth.

Influence of blood contamination before or after surface treatment on adhesion of 4-META/MMA-TBB resin to root dentin

The purpose of this study was to evaluate the influence of blood contamination before or after surface treatment on adhesion of 4-META/MMA-TBB resin. After bovine root dentin surfaces were contaminated with blood before or after dentin surface treatment with 10-3 solution, the contaminated surface was rinsed with water, air-dried, or re-treated with 10-3 solution. Dye leakage and microtensile bond strength (MTBS) of 4-META/MMA-TBB resin to dentin were measured after storage in water for 24 h. When blood contamination occurred before surface treatment, there was no significant difference in the leakage value and MTBS as compared with that of the uncontaminated group. When blood contamination occurred after surface treatment, the leakage value increased and MTBS significantly decreased (p<0.05) even if the blood was washed away. However, when the surface was re-treated with 10-3 solution after rinsing with water, the leakage value and MTBS were restored to those of the uncontaminated group.

Influence of dentin substrates to simplify wet-bonding: a leakage-free and reliable tensile strength interface for long-lasting restorations

The wet-bonding procedure can be simplified by eliminating the primer. An aqueous mixture of 1% citric acid and 1% ferric chloride (1-1) was hypothesized as providing an easier dehydratable thinner substrate to which 4-META/MMA-TBB resin can adhere reliably. The 1-1 was applied for 10 s and rinsed off with water for 10 s. Demineralized dentin under four conditions was prepared before bonding to PMMA rod using 4-META/MMA-TBB resin: air-dried 10 s (D-NP); air-dried 10 s, primed 60 s with 5% 4-META in acetone (D-P); blotted dry 10 s (W-NP); blotted dry 10 s, primed 60 s (W-P). The tensile strengths (MPa) using mini-dumbbell specimens were 4.0 ± 2.4 for D-NP, 10.6 ± 5.4 for D-P, 38.3 ± 4.4 for W-NP, and 42.9 ± 3.3 for W-P. There was no significant difference between W-NP and W-P with cohesive failure in the dentin and the cured resin. In the wet groups, the hybridized dentin was stable against both HCl and NaOCl challenges. TEM examination and a leakage tests confirmed a perfect seal with a leakage-free interface of W-NP. These results suggest that this primer-less wet-bonding is promising method to protect the underlying intact dentin and pulp, thus providing long-lasting dental treatment.

Morphological and microtensile bond strength evaluation of three adhesive systems to caries-affected human dentine with chemomechanical caries removal

OBJECTIVES

To evaluate the influence of chemomechanical caries removal on bond strengths of three adhesive systems to caries-affected human dentine.

METHODS

45 extracted human third molars with occlusal moderate caries were used. One half of each cavity was prepared with chemomechanical method and the other half with bur as the control. Three adhesive systems, Prime&Bond NT (Dentsply, Germany) without any previous conditioning, an etch-and-rinse adhesive (One-Step, Bisco, USA) and a self-etching adhesive (Adper Prompt-L-Pop, 3M ESPE, USA), were applied. The compomer or resin crowns were, then, built up. The prepared specimens were sectioned for scanning electron microscopy (SEM) examination and microtensile bond strength (MTBS) testing. Data were analysed using two-way ANOVA with subsequent application of Student-Newman-Keuls test at p<0.05.

RESULTS

Opened dentinal tubules and less smear layer were visible by SEM after chemomechanical caries removal, whilst an obvious smear layer covering the dentine surface with occluded tubules was exhibited after bur excavation. Resin tags were seen only in specimens with chemomechanical excavation when Prime&Bond NT system was applied. Statistical analysis of the values of MTBS failed to show significant difference between caries removal methods. However, the values of MTBS for One-Step system achieved with two caries removal methods were both significant higher than other adhesive systems.

CONCLUSIONS

Chemomechanical caries removal did not influence the bond strengths of the adhesive systems used in this study to caries-affected human dentine. Highest bond strength was achieved with application of etch-and-rinse adhesive system.

Chlorhexidine increases the longevity of in vivo resin-dentin bonds

The aim of this study was to evaluate the mechanical stability of resin-dentin bonds produced in vivo in the presence of chlorhexidine. Children presenting at least one pair of contralateral primary molars with occlusal carious lesions were enrolled in the study. After cavity preparation and phosphoric acid etching, dentin was treated with 5 microl of either 2% chlorhexidine (experimental group) or deionized water (control group) [corrected].Thirteen pairs of teeth were restored and were collected after physiological exfoliation. The periods in oral function after restoration were divided as follows: up to 30 d; and 1-5, 10-12, and 18-20 months. Beam-shaped specimens (0.81 mm(2)) were obtained and subjected to microtensile bond-strength testing. A significant decrease of the bond strength was observed in the control group starting at the 1-5 month period (30.6%), while in the experimental group this decrease started only after 10-12 months of function (26.3%). The use of chlorhexidine as an adjuvant to the adhesion to dentin did not produce any detrimental effect to the immediate bond strength and was capable of reducing the rate of resin-dentin bond degradation within the first few months after restoration.

Effect of dentinal water on bonding of self-etching adhesives

This study examined the effect of dentinal water on bonding, comparing one-bottle and two-step self-etching adhesives using microtensile bond test and scanning electron microscope. The bond strength of resin to dentin was measured for wet dentin (control) and dry dentin substrates. Wet dentin is the normal substrate for bond testing, whereas dry dentin was dehydrated in a desiccator at different drying times (5 to 60 min) before bonding. After bond testing, the fractured surfaces were examined. Although no correlation was found for two-step self-etching adhesives, the bond strength of the dry-dentin was significantly increased with the increase in the drying-time for one-bottle adhesives. With increased drying-time, the amount of water-bubbles was decreased for one-bottle adhesives; however, no bubble formation was seen in two-step adhesives in any group. The hydrophilic resin adhesive may entrap the water from dentin by osmosis during and after bonding. This effect may depend on the "hydrophilicity" of adhesives.

EDTA or H3PO4/NaOCl dentine treatments may increase hybrid layers' resistance to degradation: a microtensile bond strength and confocal-micropermeability study

OBJECTIVES

The aim of this study was to reduce hybrid layer degradation created with simplified dentine adhesives by using two different methods to condition the dentine surface.

METHODS

A smear-layer was created on flat dentine surfaces from extracted human third molars with a 180-grit/SiC-paper. Dentine specimens were conditioned before bonding with the following procedures: 37% H(3)PO(4); H(3)PO(4)/0.5% NaOCl; 0.1M EDTA; 0.1M EDTA/0.5% NaOCl. Two etch-and-rinse adhesives: (Scotchbond 1XT or Optibond Solo Plus) were applied and light-cured. Composite build-ups were constructed. The bonded teeth were sectioned into beams, stored in distilled water (24h) or 12% NaOCl solution (90 min) and finally tested for microtensile bond strengths (microTBS). Additional dentine surfaces were conditioned and bonded as previously described. They were prepared for a pulpal-micropermeability confocal microscopy study and finally observed using confocal microscopy.

RESULTS

microTBS results revealed that both adhesives gave high bond strengths to acid-etched dentine before, but not after a 12% NaOCl challenge. Bonds made to acid-etched or EDTA-treated dentine plus dilute NaOCl, gave high microTBS that resisted 12% NaOCl treatment, as did EDTA-treated dentine alone. A confocal micropermeability investigation showed very high micropermeability within interfaces of the H(3)PO(4), etched specimens. The lowest micropermeability was observed in H(3)PO(4)+0.5% NaOCl and 0.1M EDTA groups.

CONCLUSIONS

The use of dilute NaOCl (0.5%) after acid-etching, or the conditioning of dentine smear layers with 0.1M EDTA (pH 7.4) produced less porous resin-dentine interfaces. These dentine-conditioning procedures improve the resistance of the resin-dentine bond sites to chemical degradation (12% NaOCl) and may result in more durable resin-dentine bonds.

Evaluation of sources of uncertainties in microtensile bond strength of dental adhesive system for different specimen geometries

OBJECTIVE

The aim of this research is to use finite element analysis (FEA) to quantify the effect of the sample shape and the imperfections induced during the manufacturing process of samples on the bond strength and modes of failure of dental adhesive systems through microtensile test. Using the FEA prediction for individual parameters effect, estimation of expected variation and spread of the microtensile bond strength results for different sample geometries is made.

METHODS

The estimated stress distributions for three different sample shapes, hourglass, stick and dumbbell predicted by FEA are used to predict the strength for different fracture modes. Parameters such as the adhesive thickness, uneven interface of the adhesive and composite and dentin, misalignment of axis of loading, the existence of flaws such as induced cracks during shaping the samples or bubbles created during application of the adhesive are considered. Microtensile experiments are performed simultaneously to measure bond strength and modes of failure. These are compared with the FEA results.

RESULTS

The relative bonding strength and its standard deviation for the specimens with different geometries measured through the microtensile tests confirm the findings of the FEA. The hourglass shape samples show lower tensile bond strength and standard deviation compared to the stick and dumbbell shape samples. ANOVA analysis confirms no significant difference between dumbbell and stick geometry results, and major differences of these two geometries compared to hourglass shape measured values. Induced flaws in the adhesive and misalignment of the angle of application of load have significant effect on the microtensile bond strength. Using adhesive with higher modulus the differences between the bond strength of the three sample geometries increase.

SIGNIFICANCE

The result of the research clarifies the importance of the sample geometry chosen in measuring the bond strength. It quantifies the effect of the imperfections on the bond strength for each of the sample geometries through a systematic and all embracing study. The results explain the reasons of the large spread of the microtensile test results reported by various researchers working in different labs and the need for standardization of the test method and sample shape used in evaluation of the dentin-adhesive bonding system.

Effect of Antibacterial Varnishes Applied to Root Dentin on Shear Bond Strength of Tooth-colored Restorative Materials

The application of antibacterial varnish affects the shear bond strength of tooth-colored restorative materials after six months.

Compressive Fracture Resistance of Porcelain Laminates Bonded to Enamel or Dentin with Four Adhesive Systems

PURPOSE

To measure the compressive strength of porcelain laminates of 0.5 or 1.0 mm thickness when bonded to enamel or dentin using these resin cements: All-Bond 2 + Choice, Panavia 21, Scotchbond + Opal, and Super-Bond C&B.

MATERIALS AND METHODS

The buccal and lingual aspects of human molars were sectioned to prepare specimens at least 3 x 3 x 3 mm in size. Thirty horizontally flat enamel surfaces were prepared with a diamond disc for each group using a milling machine. Ten enamel specimens were randomly selected to test the fracture strength of 0.5-mm thick porcelain laminates without resin cement, and the data were recorded for a control group. The enamel specimens of each group were divided into two subgroups of 15 specimens to bond with either 0.5- or 1.0-mm thick porcelain laminates. Four resin cements were used for bonding of individual groups. All bonded specimens were stored in 37 degrees C for 24 hours before fracture testing. The horizontally flat dentin surfaces were prepared on the fractured bonded specimens using a diamond disc for each group. Ten 0.5 mm porcelain laminates were randomly selected to test the fracture strength on dentin (control group). The bonded laminates to dentin were prepared using the same procedure as for enamel. The fracture strengths were statistically analyzed at alpha= 0.05.

RESULTS

Statistically significant differences in mean fracture strengths between groups were revealed. No significant difference in fracture strengths of control specimens between enamel and dentin was found. Super-Bond C&B provided a higher fracture resistance of porcelain than the other resin cements. Increasing the thickness of porcelain laminate increased the fracture strength. The 0.5-mm thick porcelain bonded to enamel had higher fracture strength than that of 1.0-mm thick porcelain bonded to dentin when using Super-Bond C&B and Scotchbond + Opal cements.

CONCLUSIONS

Bonding techniques and curing systems of resin cements influenced the fracture resistance of porcelain laminates. Dry bonding with auto-polymerization of Super-Bond C&B resin provided the highest fracture resistance of porcelain. Porcelain bonded to enamel with this resin had a much higher fracture strength than when bonded to dentin.

Interfacial characteristics of adhesive luting resins and composites with dentine

PURPOSE

To evaluate the interfacial characteristics of five adhesive resin luting agents with dentine including tensile bond strength, failure mode, extent of demineralisation, morphological changes and hybrid layer formation.

MATERIALS AND METHODS

The products tested were Bistite II DC (BDC), C&B Super-Bond (CBM), M-Bond (MBD), Panavia-F (PAF) and Rely-X Unicem (RXU). For tensile bond strength measurements (TBS), metallic rods were bonded to standardised dentine surface areas (n=10), thermal-cycled (3000x 5-55 degrees C, 4 cycles/min) and debonded at 1mm/min crosshead speed. The failure mode was examined on dentine surfaces by LV-SEM (n=10), whereas the thickness of the hybrid layer by HV-SEM (n=4). FT-IR microscopy (n=4) and ESEM (n=4) were used to assess the extent of demineralisation and the morphological changes induced on dentine by the conditioning and priming treatments.

RESULTS

TBS (MPa) values were BDC (13.01), MBD (9.19) and PAF (7.07) significantly different from CBM (4.79) and RXU (4.47). The percentage of debonded dentine area covered with resin showed the highest values in BDC (47.80) and MBD (38.12) significantly different from CBM (17.20), PAF (16.47), and RXU (16.50). The extent of demineralisation for CBM was 100%. No statistical differences were found among BDC (60.86%), MBD (60.22%) and PAF (51.99%). RUX (45.03%) showed the lowest value. CBM induced the most pronounced tubule funneling and intertubular dissolution, followed by PAF, BDC and MDB. RXU partially removed the smear layer without opening tubule orifices. The thickest hybrid layer was found in CBM (4.17microm) followed by MBD (2.39microm). No statistically significant differences were found between PAF (0.95microm) and BDC (1.12microm), whereas RXU showed no detectable hybrid layer.

SIGNIFICANCE

Significant differences were found in the interfacial properties among the materials tested, that may lead to differences in their clinical performance.

Diffusion-induced water movement within resin–dentin bonds during bonding

It is thought that water-filled channels and nanovoids in resin-dentin bonds represent potential sites for degradation of bonds or hydrolysis of collagen or both. How water gains access to bonded interfaces is not clear. This study evaluated the diffusion-induced water uptake through resin-dentin interfaces during bonding. Two light-cured total-etch adhesive systems (Excite and One-Step Plus) and a chemical-cured adhesive (Amalgambond Plus) were used in this study. Dentin disks were placed in a split-chamber device, and the fluid movement across dentin was measured, with and without a physiological pressure, during bonding procedures and 24 h after bonding. For light-cured adhesives in the experimental groups, a 6 min interval of dark storage was conducted prior to light-curing, to evaluate the diffusion of water through the uncured resin monomers, and to test the effect of prolonged infiltration time of adhesives on water permeability of bonds. Prolonged adhesive infiltration reduced the water permeability of resin-dentin bonds for light-cured adhesives. Water gradients produced by bonding systems contribute to water movement across the dentin-adhesive interfaces during bonding procedures. Differences in chemical formulations for adhesive systems may lead to differences in the extent of diffusion-induced water movement and the amount of water within the resin-dentin bonds.

Tensile bond strength of Er,Cr:YSGG laser-irradiated human dentin and analysis of dentin-resin interface

OBJECTIVES

As the bond strength of composite resin to Er,Cr:YSGG laser-irradiated dentin has not yet been evaluated, the objectives of this study were to investigate the tensile bond strength and to analyze the resin-dentin interface among bur-cut/acid-etched, Er,Cr:YSGG laser-ablated/acid-etched and Er,Cr:YSGG laser-ablated human dentin.

METHODS

Crown dentin disks prepared from extracted human third permanent molars were used for the observation of surface morphological changes by scanning electron microscope (SEM). The laser energy parameters were 3.5 W and 20 Hz with water spray (air pressure level, 80%; water pressure level, maximum level). Another group of crown dentin disks were prepared for composite resin restoration and observation of resin-dentin bond interface after demineralization in 6N hydrochloric acid (HCl) for 1 min and deproteinization in 1% sodium hypochlorite solution (NaOCl) for 10 min. The tensile bond strengths of the three groups were measured by a universal testing machine at a crosshead speed of 0.5 mm/min. Fracture types at the dentin-resin interface were analyzed using the digital stereoscopic microscope and fractured surfaces of the debonded specimens were examined by SEM.

RESULTS

All three groups showed that the treated surfaces were free of dentin debris and smear layer. The peritubular dentin protruded from the surrounding intertubular dentin after laser irradiation. The dentin-resin interface treated with Er,Cr:YSGG laser irradiation and acid etching demonstrated numerous resin tags converging into a bulge and then diverging again. The length of resin tags was greater than 100 microm. The tensile bond strengths of bur-cut/acid-etched, laser-ablated/acid-etched and laser-ablated human dentin were 5.37+/-1.51, 5.17+/-1.41 and 3.29+/-0.86 MPa, respectively. No statistical significance was found between the bur-cut/acid-etched and laser-ablated/acid-etched groups. The predominant fracture modes of bur-cut/acid-etched, laser-ablated/acid-etched and laser-ablated human dentin were Type 1 (50%), Type 2 (70%) and Type 1 (70%), respectively.

SIGNIFICANCE

Er,Cr:YSGG laser irradiation affects adversely adhesion of resin to dentin but acid etching following laser irradiation could increase the tensile bond strength as high as that of bur-cut/acid-etched human dentin.

Shortening of primary dentin etching time and its implication on bond strength

OBJECTIVE

The aim of this study was to investigate the influence of shortening the etching time on the bond strength of a conventional and a self-etching primer adhesive system used in primary tooth dentin.

METHODS

Flat dentin surfaces were obtained from 24 primary molars, randomly assigned to 4 experimental groups. The adhesive systems Single Bond and Clearfil SE Bond were applied in two groups according to the manufacturers' recommendations. In the other two groups, the adhesives were applied after half-time of acid etching, 7 s for Single Bond and 10 s for Clearfil SE Primer. Resin crowns were built up and after 24 h storage in water at 37 degrees C, the teeth were sectioned to produce beams with cross-sectional area of approximately 0.49 mm2. Specimens were tested in tension at 0.5 mm/min until failure. Fractured specimens were analyzed to determine the failure mode.

RESULTS

Tensile bond strengths for Single Bond in primary dentin were higher than for Clearfil SE Bond. Shortening of acid etching time improved bond strength only for Single Bond, while no statistically significant difference was observed for Clearfil SE Bond when both etching times were compared.

SIGNIFICANCE

No detrimental effect on bond strength was observed when the time of acid etching was shortened in 50%. Shortening the time for a procedure in a small child without compromising the quality of the work is a very important finding for the practicing pediatric dentist.

Importance of mini-dumbbell specimen to access tensile strength of restored dentine: historical background and the future perspective in dentistry

OBJECTIVES

The development of adhesive resins to dentine enables resin restorations to be more durable. Several bond strength measurement techniques for measuring adhesion have been proposed. A standardised method is needed which produced higher and more consistent bond strength values which allow bond stability and the bonding mechanism to be studied. Our aim was to investigate mainly the adhesives and not the substrate.

DATA SOURCES

This review is based on the literature on an adhesive, 4-META/MMA-TBB resin and conditioners to modify dentine substrates. The latter is a very important topic for developing our understanding of the bonding to dentine. The objective of the review is to explain the efficacy of the mini-dumbbell specimen in measuring the tensile strength of resin to dentine and to analyze the resin to dentine interface. Both the adhesive and the substrate control the quality of hybridized dentine.

CONCLUSIONS

By creating an impermeable acid resistant barrier to both biological and chemical stimuli between the exposed dentine and the restored tooth surface we are able to protect exposed dentine from caries (infection) at the same time as protecting the pulp and preventing toothache. This barrier also helps maintain tooth vitality and for the purposes of this article is termed 'artificial enamel'. Microleakage free restorations are possible through the introduction of this 'impermeable artificial enamel' barrier.

Effect of remaining demineralised dentine on dental microleakage accessed by a dye penetration: how to inhibit microleakage?

OBJECTIVES

To demonstrate that microleakage has taken place at the defect, which was analysed previously by a tensile test using dumbbell shaped specimens trimmed from bonded resin/dentine restorations, and to suggest how microleakage can be inhibited reliably in dental treatment.

METHODS

A total of 60 Class V box cavities were prepared at the cemento-enamel junction on fresh bovine incisors and randomly divided into four groups of 15 specimens each. Exposure times of etching for 10:3 conditioner were set at 10, 30 or 60 s, and for 10% phosphoric acid (positive control) at 10 s. The cavity walls were rinsed with water for 10 s, air-dried for 10 s and hybridised with 4-META/MMA-TBB resin. All the cavities were filled with a light cured resin composite and stored in 37 degrees C water for 24 h and then immersed in 15% methylene blue for 2 h. The length of dye penetration along the interface was graded by defined criteria and analysed using Kruskal-Wallis and Mann-Whitney tests. The dye penetration patterns were examined by light microscopy and the remaining demineralised dentine was analysed by Transmission Electron Microscopy (TEM).

RESULTS

The least leakage score was obtained in 10s-10:3 etched group with 12 out of 15 specimens demonstrating no leakage. Leakage was significantly lower at the cementum margin than for the other three groups. No significant difference in the extent of greatest dye penetration was found between the 60s-10:3 and 10s-phosphoric etched groups. Dye penetration along the cementum margins was significantly higher than that of the enamel margins in all groups, except the 10s-10:3 etched group. TEM examination confirmed that there were exposed collagen fibrils in the remaining demineralised dentine, where microleakage had taken place.

SIGNIFICANCE

It could be concluded from this study that microleakage has taken place at the defect in the bonded specimens which has correlations with zones of incompletely infiltrated demineralised dentine that was observed using TEM. A reliable method of inhibiting microleakage is the presence of well prepared hybridised dentine.

The influence of the dentin smear layer on adhesion: a self-etching primer vs. a total-etch system

OBJECTIVE

To determine the effect of dentin smear layers created by various abrasives on the adhesion of a self-etching primer (SE) and total-etch (SB) bonding systems.

METHODS

Polished human dentin disks were further abraded with 0.05 micro m alumina slurry, 240-, 320- or 600-grit abrasive papers, # 245 carbide, # 250.9 F diamond or # 250.9 C diamond burs. Shear bond strength (SBS) was evaluated by single-plane lap shear, after bonding with SE or SB and with a restorative composite. Smear layers were characterized by thickness, using SEM; surface roughness using AFM; and reaction to the conditioners, based on the percentage of open tubules, using SEM.

RESULTS

Overall, SBS was lower when SB was used than when SE was used. SBS decreased with increasing coarseness of the abrasive in the SE group. Among burs, the carbide group had the highest SBS, and 320- and 240-grit papers had SBS close to the carbide group. Surface roughness and smear layer thickness varied strongly with coarseness. After conditioning with SE primer, the tubule openness of specimens abraded by carbide bur did not differ from 240- or 320-grit paper, but did differ from the 600-grit.

SIGNIFICANCE

Even though affected by different surface preparation methods, SE yielded higher SBS than SB. The higher SBS and thin smear layer of the carbide bur group, suggests its use when self-etching materials are used in vivo. Overall, the 320-grit abrasive paper surface finish yielded results closer to that of the carbide bur and its use is recommended in vitro as a clinical simulator when using the SE material.

AFM observation of collapse and expansion of phosphoric acid-demineralized dentin

The objective of this study is to provide additional data regarding morphological changes that occur to dentin matrices following demineralization with etchants. Our understanding of the mechanism of diffusion of comonomers into the demineralized substrate is very limited. It has been hypothesized that certain water-soluble polyelectrolytes (acidic proteins) and neutral proteins in dentin can influence the collapse of demineralized dentin when it is air dried. Some of these solubilized substances are thought to aggregate by the action of Ca cations, which become dissolved during H(3)PO(4) etching, ultimately resulting in some degree of collapse. In the current study, dentin surfaces were examined by atomic force microscopy (AFM) before and after treatment by 10% H(3)PO(4)containing increasing concentrations of CaHPO(4). Reversal of matrix collapse by aqueous 30% 2-hydroxyethyl methacrylate (HEMA) was evaluated by AMF for 60 min. The results demonstrate two forms of matrix collapse; we speculate that one form is induced by acidic noncollagenous polyelectrolytes and the other by neutral peptides. Our data indicate that further evaluation of the influence of endogenous noncollagenous proteins must be studied to understand the mechanism of the collapse and reexpansion dynamics of demineralized dentin networks.

Improved wet bonding of methyl methacrylate-tri-n-butylborane resin to dentin etched with ten percent phosphoric acid in the presence of ferric ions

The objective of this study was to determine the influence of dissolved dentinal substances in demineralized dentin on the hybridization of resin for bonding to dentin. It was hypothesized that these substances, including polyelectrolytes, significantly change the substrates, which could then be assessed by the addition of Na(+), Ca(2+), or Fe(3+) in 10% phosphoric acid. Bovine dentin specimens were etched for 10 s with a solution of 10% phosphoric acid (control) or of 22.0 mM dissolved sodium chloride (10P-Na), calcium chloride (10P-Ca), or ferric chloride (10P-Fe). The specimens were then rinsed, blot-dried, and primed three times with 5% 4-methacryloyloxyethyl trimellitate anhydride in acetone for 60 s. Methyl methacrylate-tri-n-butylborane resin was then applied. The tensile bond strength of each of the dumbbell-shaped specimens was then measured. The fractured surfaces and modified cross-sections were examined by scanning electron microscopy. The cross-sections were soaked in 6N HCl for 10 s and then in 1% sodium hypochlorite for 30 min to determine the resin content in the hybridized specimens. Shrinkage of the demineralized dentins upon drying was assessed by atomic force microscopy. The tensile bond strengths were 10.8 +/- 4.5 (control), 15.0 +/- 7.0 (10P-Na), 19.3 +/- 5.5 (10P-Ca), and 27.8 +/- 8.1 (10P-Fe) MPa. The atomic force microscopy studies showed that Fe(3+) minimized the shrinkage by drying for 10 s but Ca(2+) and Na(+) did not decrease the shrinkage the same as the control. The results support the hypothesis that the monomer permeability of wet demineralized dentin is effectively improved by dissolving ferric ions in the phosphoric acid, resulting in a greater bond strength and higher resin content in the hybridized dentin. The dissolved dentinal substances, including the polyelectrolytes, had a significant influence on the characteristics of the demineralized dentin, changing the degree of hybridization and bonding.

Influence of dentinal polyelectrolytes on wet demineralized dentin, a bonding substrate

The objective of this study was to show the influence of dissolved dentinal polyelectrolytes on the characteristics of dentin (bonding substrate) demineralized by citric acid in the absence or presence of ferric chloride. The demineralizing agent was an aqueous mixture of 0, 1, 3, or 10% ferric chloride in 10% citric acid (10-0, 10-1, 10-3, 10-10, respectively). The hypothesis was that the concentration of dissolved dentinal noncollagenous substances, mainly polyelectrolytes soluble in water, must be decreased by their aggregation with ferric ions, which changes the characteristics of demineralized dentin, the rates of demineralization, and dehydration. Cervical bovine dentin was prepared in 3 x 2 x 2-mm blocks, each weighing 20.0 +/- 0.5 mg. The rate of demineralization was investigated by measuring the weight loss resulting from demineralization by immersion in 10 mL of conditioner at 2-h intervals. The dehydration rate of wet demineralized dentin was determined using two methods: (1) weight loss in a desiccator under 263 Pa pressure and (2) differential scanning calorimetry (DSC). Twenty, 12, 8, and 4 h were required to complete demineralization of the blocks with the 10-0, 10-1, 10-3, and 10-10 solutions, respectively. The 10-10 wet demineralized dentin showed the highest rate of dehydration, followed in descending order by the 10-3, 10-1, and 10-0 specimens. Ferric chloride in dentin conditioners provided both a higher rate of dentin demineralization and a higher dehydration rate of wet demineralized dentin. These results suggest that in the presence of ferric chloride, a decreasing amount of dissolved polyelectrolytes aggregated with ferric ions in the substrates may increase the permeability of dentin to water and citric acid. Improvement of monomer permeability is essential to the preparation of good hybridized dentin, providing a more stable and reliable bonding and also protecting the dentin and pulp from infection. A further study of bonding substrates is required in order to understand the role of hybridized dentin in improved dental treatment.

In vitro degradation of resin-dentin bonds analyzed by microtensile bond test, scanning and transmission electron microscopy

Our knowledge of the mechanisms responsible for the degradation of resin-dentin bonds are poorly understood. This study investigated the degradation of resin-dentin bonds after 1 year immersion in water. Resin-dentin beams (adhesive area: 0.9mm(2)) were made by bonding using a resin adhesive, to extracted human teeth. The experimental beams were stored in water for 1 year. Beams that had been stored in water for 24h were used as controls. After water storage, the beams were subjected to microtensile bond testing. The dentin side of the fractured surface was observed using FE-SEM. Subsequently, these fractured beams were embedded in epoxy resin and examined by TEM. The bond strength of the control specimens (40.3+/-15.1MPa) decreased significantly (p<0.01) after 1 year of water exposure (13.3+/-5.6MPa). Loss of resin was observed within fractured hybrid layers in the 1 year specimens but not in the controls. Transmission electron microscopic examination revealed the presence of micromorphological alterations in the collagen fibrils after 1 year of water storage. These micromorphological changes (resin elution and alteration of the collagen fibrils) seem to be responsible for the bond degradation leading to bond strength reduction.

A morphological and micro-tensile bond strength evaluation of a single-bottle adhesive to caries-affected human dentine after four different caries removal techniques

OBJECTIVES

This study evaluated the influence of different caries removal techniques (conventional bur; chemomechanical removal/Carisolv()-MediTeam; a sonic preparation system/SonicsysMicro-Kavo and air abrasion/PrepStar-Danville Engineering) on microtensile bond strength to caries-affected human dentine.

METHODS

Occlusal surfaces of extracted human permanent third molars with coronal dentine caries extending approximately halfway through the dentine was ground perpendicular to the long axis of the tooth to expose a flat surface of normal dentine surrounding the carious lesion with laser fluorescence values of approximately 30 (DIAGNODent), KaVo). Carious lesions were excavated with one of the four techniques until laser fluorescence values decreased to 15 in the center of the lesions. An ethanol-based dentine adhesive (Single Bond, 3M) was used to bond composite resin (P60, 3M) to the substrate. Vertical slices (n=11/group), approximately 0.8 mm thick were made through the caries-affected portions of each tooth, perpendicular to the bonding surface. Specimens were subjected to tensile stress at a crosshead speed of 1 mm/min. Data were analyzed by Kruskal-Wallis test. SEM investigation was performed for the qualitative evaluation of resin-dentine hybridization.

RESULTS

The microtensile bond strengths were as follows (mean+/-SD in MPa): 6.4+/-5.3 (bur), 8.4+/-3.3 (Carisolv), 8.5+/-5.9 (Sonicsys Micro), and 8.8+/-8.8 (air abrasion). Statistical analysis did not show significant differences between any of the treatment modalities (p=0.160). Tensile fracture was cohesive within caries-affected dentine in all specimens.

CONCLUSIONS

The four different caries removal techniques used within this study did not influence the bond strength of the tested dentine adhesive to caries-affected human dentine.

Degradation patterns of different adhesives and bonding procedures

Various types of resin adhesives and procedures are available in the clinical field, so comprehensive understanding of degradation is required for each material and bonding procedure. The objective of this study was to investigate the bond durability for different adhesives and bonding procedures. Resin-dentin bonded beams were prepared with the use of two adhesives (One-Up Bond F/self-etching primer system and One Bond/total-etch adhesive) and two experimental groups for the bonding procedure (wet and dry bonding of the total-etch adhesive). Those samples were soaked in water for 24 h(control), 6 and 12 months. After the water immersion, the bond strengths were measured by the microtensile bond test, and subsequently fractography was performed with the use of SEM. Statistically significant reduction of the bond strength (p < 0.05) was apparent after 12 months of water exposure in the range 22-48% of the control. The bonding resin was eluted from the hybrid layer of the self-etching and the total-etch adhesives for the wet bonding. Micromorphological alterations were found due to the hydrolysis of collagen fibrils with the total-etch adhesive for the dry bonding mode. These pathologic alterations were in accord with the bond strength.

SEM and TEM analysis of water degradation of human dentinal collagen

Recently several long-term studies have reported evidence of the hydrolytic degradation of collagen fibrils based on fractured surface observations after bond testing. Those studies suggested that one cause of the decline in the bond strength was the degradation of the collagen fibrils within the bonds. However, one concern has been raised that the dentinal collagen fibrils may be stable in water that does not contain oral bacteria or enzymes. Therefore, the present study aimed to clarify the micromorphological change in naked collagen fibrils after 500 days of water storage. To prepare exposed collagen fibrils, sectioned and polished human dentin surfaces were acid conditioned for 15 s with the use of two commercially available acid conditioners: All-Etch (10% phosphoric acid) and Uni-Etch (32% phosphoric acid) (Bisco, Inc.). Those specimens were stored in distilled water at 37 degrees C for 1 day (control) for 500 days. After the storage periods, the samples were examined with the use of SEM and TEM. Under SEM and TEM examination, micromorphological alterations (disarrangement of collagen web, widening the interfibrillar space, and the thinning diameter of collagen fibrils) were found in the specimens after 500 days in water.

Degradation of resin-dentin bonds using NaOCl storage

OBJECTIVE

Several recent studies have reported collagen hydrolysis within bonds over the long-term. This may be one reason for the degradation of the bonds. This study therefore aimed to determine the effects of NaOCl on adhesive system bonds (total-etch bonding system vs. self-etching primer system) to dentin in order to accelerate the durability testing.

METHODS

Resin-dentin bonded specimens were produced using Liner Bond 2V (Kuraray), a self-etching primer system, and OptiBond SOLO (Kerr), a total-etch bonding system, according to the manufacturers' instructions. The bonded specimens were serially sectioned in both x and y directions across the adhesive interface to obtain beams (adhesive area: 0.9 mm(2)). The specimens were immersed in 10% NaOCl solution for 1-5h after being stored in water at 37 degrees C for 24h. Control specimens were tested without exposure to NaOCl. After storage, micro-tensile bond tests were performed. Results were analyzed by two-way ANOVA and Fisher's PLSD tests (p<0.05). All fractured surfaces were observed by SEM, and examined using an image analyzer.

RESULTS

The bond strengths decreased with increasing storage time in NaOCl. Fractography showed that NaOCl had a greater effect on the bond structure of OptiBond SOLO than on that of Liner Bond 2V, although both adhesives were susceptible.

SIGNIFICANCE

Deterioration of the bonds was responsible for the effect of NaOCl on the hybrid layer. This deterioration may occur in humans in cases of deproteinization within the bonds.

Dental biomaterials and the healing of dental tissue

This paper addresses the application of new adhesive technologies to dentistry. The bonding of synthetic polymers to dentin is difficult and it has taken a long time to produce reliable methods. Success has been achieved suing a 4-methacryloyloxyethyltrimellitate anhydride/methyl methacrylate-tri-n-butyl borane system which allows the generation of a layer of hybridised dentin. This provides a pseudo-wound-healing layer that resists demineralisation and degradation, is impermeable and inhibits secondary caries and hypersensitivity.

Deproteinizing effects on resin-tooth bond structures

This study investigated the effects of NaOCl on resin-tooth bonds to simulate the situations of long-term durability and caries invasion. Resin-tooth bonded specimens were produced with the use of two resin adhesives (Excite and One-Bond). Resin-tooth bonded beams (adhesive area; 0.9 mm2) were serially sectioned and the specimens were immersed in 10% NaOCl medium for 0 (control), 2, 4, and 6 h after being stored in water for 24 h. After immersion, microtensile bond tests were performed. SEM fractography was conducted to calculate each failure mode by image analysis. In addition, the adhesive interface was examined with the use of TEM. In the control specimens, enamel bond strengths had no difference between Excite (45.6 +/- 15.0) and One-Bond (56.9 +/- 12.9). On the other hand, dentin bond strengths had significant difference between Excite (80.6 +/- 21.2) and One-Bond (50.7 +/- 11.2). The bond strengths decreased with increased storage time for both systems with enamel and dentin bonds. The deteriorated mineralized dentin of beams resulted in bond-strength reduction for resin-enamel bonds. For dentin bonding, the adhesive interface was gradually dissolved from the outer to the center portion of the beam. The depletion of collagen fibrils within the demineralized dentin or hybrid layer deformation was found under SEM and TEM examinations. These morphological changes are responsible for bond strength reduction of resin-dentin bonds.

Comparison of microleakage of three acid-base luting cements versus one resin-bonded cement for Class V direct composite inlays

STATEMENT OF PROBLEM

Demineralized dentin beneath set cement may adversely affect microleakage under fixed restorations.

PURPOSE

Microleakage of direct composite inlays cemented with acid-base cements and a methyl methacrylate resin cement were evaluated to determine their effect on the integrity of the underlying hybridized dentin.

MATERIALS AND METHODS

Sixty Class V box preparations (3 mm x 3 mm x 1.5 mm) were precisely prepared in previously frozen bovine teeth with one margin in enamel and another margin in dentin. Direct composite inlays (EPIC-TMPT) for each preparation were divided into 4 groups of 15 specimens each and cemented with 3 acid-base cements (control group): Elite, Ketac-Cem, Hy-Bond Carbo-Cem, and 1 adhesive resin cement: C&B Metabond. All specimens were stored in distilled water for 24 hours at 37 degrees C before immersion in 0.5% basic fuchsin for 24 hours. The dye penetration was measured on the sectioned specimens at the tooth-cement interface of enamel and cementum margins and recorded with graded criteria under light microscopy (Olympus Vanox-T) at original magnification x 50, 100, and 200. A Kruskal-Wallis and the Mann-Whitney test at P<.05 were used to analyze leakage score.

RESULTS

All cementum margins of the 3 acid-base cements tested demonstrated significantly higher leakage scores than cementum margins for inlays cemented with the resin cement tested(P<.01). No leakage along the tooth-cement interface was found for inlays retained with the adhesive resin cement.

CONCLUSIONS

Within the limitations of this study, the 3 acid-base cements tested exhibited greater microleakage at the cementum margins than did the adhesive resin cement that was tested.

Fractured surface characterization: wet versus dry bonding

OBJECTIVE

Fractographic analysis was conducted to evaluate the resin-dentin bond structures made under wet and dry conditions.

METHODS

Resin-dentin bonded specimens were prepared using two adhesive resin systems (Single Bond/SB; 3M and All Bond 2/AB2; Bisco Inc) under wet and dry conditions. The specimens were sectioned perpendicular to the adhesive interface to produce a square bar-shaped specimen (adhesive area: 0.9 mm(2)) by means of a diamond saw. The mean bond tensile test was then conducted at a crosshead speed of 1.0 mm/min. The mean bond strengths were statistically compared with two-way ANOVA and Fisher's PLSD test (p<0.05). Subsequently, the fractured surfaces of all specimens were examined using SEM and the area fractions of failure modes (%) were measured using an image analyzer on SEM microphotographs.

RESULTS

No significant differences in tensile-bond strength were observed between SB (60.1+/-16.4MPa) and AB2 (69.8+/-17.4MPa) (p>0.05) under wet conditions. However, the bond strength either of SB or AB2 made under wet conditions was significantly greater than those made under dry conditions (SB: 26.2+/-12.5MPa and AB2: 6.8+/-3.3MPa) (p<0.05). Under fractographic analysis, the major portion at the fractured surface was occupied by the cohesive failure of bonding resin and the resin composite for the wet conditions, and the top of the hybrid layer for the dry conditions in both systems.

SIGNIFICANCE

The interaction between the top of the hybrid layer and the bonding resin influenced the bond integrity.

Over-etching effects on micro-tensile bond strength and failure patterns for two dentin bonding systems

OBJECTIVES

The purpose of this study was to determine (1) the weakest zone of resin-dentin bonds and (2) the relation between bond strength and failure mode to clarify the effect of demineralized dentin.

METHODS

Human premolars were sectioned to expose the dentin surfaces, and the dentin surfaces were conditioned with phosphoric acid for 15, 60, 120, or 180s. Resin-dentin bonded specimens were produced using two adhesives: One-Step (Bisco) and OptiBond Solo (Kerr). Each sample was sectioned to produce a beam (adhesive area: 0.9mm(2)). Microtensile bond tests were then conducted, and the mean bond strengths (n=12 for each group) were statistically compared using two-way ANOVA and Duncan's multiple-range test (p<0.05). The fractured surfaces of all specimens were examined using SEM, and the areas of failure were measured using an image analyzer.

RESULTS

For One-Step, the bond strength decreased with increase in acid-conditioning time (15s: 50.7+/-9.7, 60s: 40.8+/-11.0, 120s: 23.6+/-4.9 and 180s: 12.1+/-4.6MPa) (p<0.05). For OptiBond Solo, the bond strength in the case of 15s acid-conditioning time (42.6+/-7.9MPa) was significantly greater than that for the other times (60s: 31.9+/-10.3, 120s: 31.8+/-14.4 and 180s: 31.8+/-7.4MPa) (p<0.05). Fractography showed that the area percentage of the hybrid layer increased with increase in etching time for both systems.

CONCLUSIONS

The integrity of the hybrid layer, especially the top part, has an effect on bond strength.

Quantifying adhesive penetration in adhesive/dentin interface using confocal Raman microspectroscopy

Confocal Raman microspectroscopy (CRM) provides an important and novel means of analyzing the chemical composition of the adhesive/dentin (a/d) interface. The purpose of this study was to develop a method for quantitative determination of the degree of adhesive penetration at the a/d interface using CRM. Three commercial dentin adhesive systems [Scotchbond Multipurpose Plus (SBMP+), Single Bond (SB), and Primer Bond NT (PBNT)] based on the total etch and "wet" bonding technique were examined in this study. Human dentin specimens treated with these adhesives were analyzed with CRM mapping across the a/d interface. Also, Raman spectra were collected on model mixtures of adhesive and type I collagen, and the ratios of the relative intensities of the Raman bands corresponding to adhesive and collagen were used for the construction of calibration curves. By comparing the Raman band ratios of interface specimens to the calibration curves, the percent of adhesive as a function of spatial position across the a/d interface was determined. The results show that there is a gradual decrease in penetration as a function of position for all three adhesive systems while the adhesive concentration gradient decreases in the order of SBMP+ > SB > PBNT. These differences in penetration of the three adhesives at the a/d interface also are discussed relative to the composition and phase segregation in adhesives. Additionally, our results indicate that confocal Raman microspectroscopy is a reliable in situ analytical technique for simple and rapid quantitative determination of adhesive penetration at its interface with prepared dentin.

Effect of Phenyl-P/HEMA acetone primer on wet bonding to EDTA-conditioned dentin

OBJECTIVES

The purpose of this study was to examine the effect of 2-methacryloyloxyethyl phenyl phosphoric acid (Phenyl-P)/2-hydroxyethyl methacrylate (HEMA) acetone-based primer on moist dentin surfaces that were preconditioned with ethylenediaminetetraacetate (EDTA) to remove the smear layer.

METHODS

Bovine dentin were prepared with 180-grit paper, conditioned with 0.5M EDTA (pH 7.4) for 60s followed by water rinsing and then blot drying. Each surface was then primed with Phenyl-P/30 wt% HEMA in acetone for 10s followed by blot drying. A light-cured bonding agent was then applied, cured and trimmed to give dumbbell-shaped specimens. The Phenyl-P concentration ranged from 1 to 20 wt%. During the bonding procedure, no compressed air was used. After storage in water at 37 degrees C for one day, tensile bond strengths were measured and analyzed using one-way ANOVA. Dentin discs treated under the same conditions were observed under a scanning electron microscope (SEM).

RESULTS

When the concentration of Phenyl-P was 12 wt%, the highest mean tensile bond strength was obtained (27 MPa). It was significantly higher than that of the 3, 5, 15 or 20 wt% groups (9-11 MPa) (p<0.05). The samples of 1 wt% group were all broken during trimming the dumbbell-shaped specimens. SEM observations showed a 1 microm-thick layer of hybridized dentin after polished cross-sections were chemically challenged with 6N HCl for 30s and then 1% NaOCl for 60 min.

SIGNIFICANCE

The experimental Phenyl-P/HEMA acetone primer is effective in bonding resin to EDTA-conditioned dentin. Acetone as a solvent for Phenyl-P/HEMA primer has the clinical advantage of not requiring an air-stream to evaporate the solvent. The experimental bonding procedure can minimize the skin irritation by HEMA.