Nominal shear or fracture mechanics in the assessment of composite-dentin adhesion?

Reliability of an Innovative Slab Shear versus Microtensile Bond Strength Test: Mechanical and Finite Element Analysis

OBJECTIVE

 The aim of this study was to evaluate the efficiency of slab shear bond strength test (Slab_SBS) versus the microtensile in evaluation of the bond strength of different substrates.

MATERIALS AND METHODS

 Forty-eight extracted caries-free human third molars were utilized for teeth specimens' preparation. After flattening of all molars' occlusal table, the specimens were divided into two groups based on the type of utilized restorative material: nanohybrid resin composite and resin-modified glass ionomer (RMGI). Each group was further subdivided into three subgroups according to the subsequently applied bond strength test and specimen width; microtensile bond strength test (μTBS), Slab_SBS [2 mm] and Slab_SBS [3 mm]. Both testing methods were additionally applied on CAD/CAM specimens, nanohybrid resin composite blocks (composite-to-composite), and ceramic blocks (ceramic-to-ceramic). CAD/CAM specimens were prepared and cemented and then sectioned and subdivided as followed for teeth specimens' preparation. Pretest failures (PTF), bond strength, and failure mode of each specimen were recorded. Representative three-dimensional (3D) finite element analysis (FEA) models were developed to simulate μTBS and Slab_SBS specimens. Data were statistically analyzed using Shapiro-Wilk test and Weibull analysis.

RESULTS

 Pretest failures were only noted in the μTBS subgroups. Slab_SBS provided comparable bond strength to the μTBS of all substrates with adhesive mode of failure.

CONCLUSION

 Slab_SBS is easier to prepare with consistent and predictable outcome with no pretest failures during specimen preparation and better stress distribution.

Microshear Bond Strength of Bioactive Materials to Dentin and Resin Composite

OBJECTIVES

 The aim of this study was to comparatively evaluate microshear bond strength (μSBS) of bioactive ionic resin composite and resin-modified glass ionomer liner (RMGI) to dentin and resin composite.

MATERIALS AND METHODS

 The enamel of 11 posterior molar teeth was removed to expose dentin and then placed in acrylic blocks. Each specimen received three microcylindrical Tygon tubes filled with bioactive ionic resin composite (Activa Bioactive base/liner (PULPDENT: , MA, USA)), RMGI (Riva light cure SDI LTD, Bayswater, Australia), and resin composite (Filtek Z350xt, MN, USA). Composite discs (n = 11) were fabricated from nanofilled resin composite (Filtek Z350xt) and then fixed in acrylic blocks. Each specimen received two microcylindrical Tygon tubes filled with Activa Bioactive base/liner and Riva RMGI. All specimens were mounted individually to universal testing machine for μSBS test. Failure modes were analyzed using stereomicroscope and scanning electron microscope.

RESULTS

 Filtek Z350xt nanofilled resin composite showed the highest μSBS values. No statistical significant difference was found between Activa Bioactive and Riva RMGI (p > 0.05).

CONCLUSION

 Bioactive ionic resin composite liner exhibited similar bond strength as RMGI to dentin and resin composite.

The effect of diabetes mellitus on the shear bond strength of composite resin to dentin and enamel

Diabetes mellitus might be linked to the deterioration of certain physical properties of dentin and enamel. This study aimed to determine the effect of two types of diabetes on the shear bond strength of enamel and dentin, by using the single bond universal bonding system. Sixty specimens [from 15 teeth; 5 from each group-non-diabetic (ND), Diabetic type I (D1), and Diabetic type II (D2)], were prepared with equal amounts of dentin (n = 5) and enamel (n = 5). Enamel specimens (E20) were etched with 37% phosphoric acid, for 20 s, and dentin specimens (D15) were etched for 15 s. A standard shear bond strength test was performed on all specimens. Their failure modes were also studied under a scanning electron microscope, and the data were analyzed by using ANOVA and Post Hoc Tukey's test (a = 0.050). For the enamel groups, significant differences were only noticed between the ND and D1 (P < 0.050) groups, and between the ND and D2 (P < 0.050) groups. In the dentin groups, there was a significant difference only between the ND and D1 (P < 0.050) groups. The micrographs showed that the ND group had the highest number of specimens with cohesive failure and D1 had the highest number of specimens with adhesive failure. It can be concluded that both types of diabetes reduce the shear bond strength of composite resin on dentin and enamel. However, it seems that the negative effect of diabetes on shear bond strength of dental composite resin is more drastic in individuals with type I diabetes as compared with type II.

The microtensile bond strength test: Its historical background and application to bond testing

Microtensile bond strength (μTBS) test was introduced in 1994. Since then, it has been utilized profoundly across many bond strength testing laboratories, making it currently one of the most standard and versatile bond strength test. Although it is a static and strength-based method, together with the morphological and spectroscopic investigations, it has been contributing immensely in the advancement of dentin adhesive systems. μTBS test has a greater discriminative capability than the traditional macro-shear bond test. During the early stage of its development, the authors predicted that this testing method would enable evaluation of the adhesive performances of resins to excavated carious or sclerotic dentin and the regional bond strengths of various portions of the cavity. In addition, they also stated the possibility of comparing the long-term stability of resin adhesion at various portions of the cavity walls on teeth extracted at various times after insertion of bonded restorations. In this review, we discussed the historical background, inception and the application of the μTBS test and proposed directions for further improvement of this testing method.

Shear bond strength vs interfacial fracture toughness - Adherence to CAD/CAM blocks

OBJECTIVE

To compare shear bond strength (SBS) and interfacial fracture toughness (IK_IC) results when assessing the effect of surface roughness and thermocycling on the adherence of a resin composite luting agent (RCLA) to a CAD/CAM resin composite block (RCB).

METHODS

Tetric CAD HT along with the recommended bonding system, Adhese Universal and Variolink Esthetic LC, were used. Surface roughness was achieved with 600/320/60 grit SiC papers. Samples were stored 24h in 37°C water or thermocycled 10000× (5°C-55°C) prior to testing. Results were analyzed by univariate ANOVA and Scheffé modified t-tests (α=0.05). Fractured specimens were viewed with a stereo microscope and selected specimens with a scanning electron microscope.

RESULTS

SBS results showed a significant difference between the 60 grit group and the other groups, both after 24h and thermocycling. A large number of SBS samples showed cohesive fracture or subsurface damage in RCB. Thermocycling led to a significant decrease in SBS in all groups. IK_IC results showed no significant differences due to surface preparation after 24h storage in 37°C. After thermocycling, there was a significant difference between the 60 and the 600 grit groups. All K_IC samples fractured adhesively at the RCB surface. K_IC of the RCLA was significantly higher than IK_IC of all groups.

SIGNIFICANCE

The results endorse the use of fracture mechanics methodology for the assessment and characterization of adherence, while identifying difficulties in its implementation. The results suggest also that adherence to CAD/CAM RCB may be limited by the strength of the resin composite block - adhesive interface.

Assessment of Bonding Effectiveness of Adhesive Materials to Tooth Structure using Bond Strength Test Methods: A Review of Literature

Background

The rapid developments in the field of adhesive dental materials have led to improvements in many aspects of clinical dentistry. Adhesive bond strength plays an important role in determining the clinical performance and longevity of dental restorations. Nevertheless, bond strength tests have never been well-standardized, although a number of important recommendations have been made.

Objective

The aim of this paper is to critically review the validity of different bond strength testing methods for assessment of bonding effectiveness of adhesive materials to tooth structure and discuss factors that may affect bond strength measurement.

Data Collection

Relevant literature published between 1983 and 2018 was collected and reviewed from the PubMed database and Google scholar resources.

Review Results

Results of the current bond testing methods should be used to compare materials tested under the same laboratory settings, but they shouldn't be used to make direct inferences on their clinical behaviour. Shear and micro-shear tests, result in non-uniform stress distribution, stress concentration at the substrate area, and predominantly tensile stresses rather than shear stresses. Micro-tensile bond tests provide many advantages over the shear tests, although these methods are technique sensitive and labour intensive.

Conclusion

Bond strength testing methods should be well-standardized, but there are many factors that cannot be fully controlled which leads to variation and misinterpretation of the data about the bonding abilities of adhesives.

Clinical Significance

New adhesive materials should be subjected to a combination of testing protocols to properly assess their bonding effectiveness.

Effect of surface treatment of prefabricated teeth on shear bond strength of orthodontic brackets

Objective:

The aim of this in vitro study was to evaluate and compare the effects of grinding, drilling, sandblasting, and ageing prefabricated teeth (PfT) on the shear bond strength (SBS) of orthodontic brackets, as well as the effects of surface treatments on the adhesive remnant index (ARI).

Methods:

One-hundred-ninety-two PfT were divided into four groups (n = 48): Group 1, no surface treatment was done; Group 2, grinding was performed with a cylindrical diamond bur; Group 3, two drillings were done with a spherical diamond bur; Group 4, sandblasting was performed with 50-µm aluminum oxide. Before the experiment, half of the samples stayed immersed in distilled water at 37^oC for 90 days. Brackets were bonded with Transbond XT and shear strength tests were carried out using a universal testing machine. SBS were compared by surface treatment and by ageing with two-way ANOVA, followed by Tukey’s test. ARI scores were compared between surface treatments with Kruskal-Wallis test followed by Dunn’s test.

Results:

Surface treatments on PfT enhanced SBS of brackets (p< 0.01), result not observed with ageing (p= 0.45). Groups II, III, and IV showed higher SBS and greater ARI than the Group 1 (p< 0.05). SBS was greater in the groups 3 and 4 (drilling, sandblasting) than in the Group 2 (grinding) (p< 0.05). SBS and ARI showed a positive correlation (Spearman’s R²= 0.57; p< 0.05).

Conclusion:

Surface treatment on PfT enhanced SBS of brackets, however ageing did not show any relevance. Sandblasting and drilling showed greater SBS than grinding. There was a positive correlation between SBS and ARI.

Wear measurement of dental tissues and materials in clinical studies: A systematic review

OBJECTIVES

This study aims to systematically review the different methods used for wear measurement of dental tissues and materials in clinical studies, their relevance and reliability in terms of accuracy and precision, and the performance of the different steps of the workflow taken independently.

METHODS

An exhaustive search of clinical studies related to wear of dental tissues and materials reporting a quantitative measurement method was conducted. MedLine, Embase, Scopus, Cochrane Library and Web of Science databases were used. Prospective studies, pilot studies and case series (>10 patients), as long as they contained a description of wear measurement methodology. Only studies published after 1995 were considered.

RESULTS

After duplicates' removal, 495 studies were identified, and 41 remained for quantitative analysis. Thirty-four described wear-measurement protocols, using digital profilometry and superimposition, whereas 7 used alternative protocols. A specific form was designed to analyze the risk of bias. The methods were described in terms of material analyzed; study design; device used for surface acquisition; matching software details and settings; type of analysis (vertical height-loss measurement vs volume loss measurement); type of area investigated (entire occlusal area or selective areas); and results.

SINIFICANCE

There is a need of standardization of clinical wear measurement. Current methods exhibit accuracy, which is not sufficient to monitor wear of restorative materials and tooth tissues. Their performance could be improved, notably limiting the use of replicas, using standardized calibration procedures and positive controls, optimizing the settings of scanners and matching softwares, and taking into account unusable data.

Effect of adhesive layers on microshear bond strength of nanocomposite resin to dentin

Background

Bond strength of adhesive layer can absorb unwanted stresses of polymerization shrinkage in composite resin restorations; increased microshear bond strength can prevent failure of restoration materials, the purpose of this study was to evaluate the effect of adhesive layers on microshear bond strength of nanocomposite resin to dentin.

Material and Methods

Two different types of adhesive systems: universal adhesive (ExciTE) and newly developed adhesive (Nano-Bond), and one type of light-cured resin restorative material (Nanocomposite resin) were used in this study. The occlusal surfaces of extracted human molar teeth were ground perpendicular to the long axis of each tooth to expose a flat dentin surface. The adhesives were applied on dentin surfaces (single application or double application). Nanocomposite resin was then placed and light cured for 40 seconds. After 24 hours of immersion in water at 37°C, then subjected to thermocycling before testing, a microshear bond test was carried out. The data were analyzed by a two-way ANOVA. For comparison between groups, Tukey’s post-hoc test was used.

Results

The mean bond strengths of ExciTE and Nano-Bond adhesives with a single application were 8.8 and 16.6 MPa, respectively. The mean bond strengths of ExciTE and Nano-Bond adhesives with double application were 13.2 and 21.8MPa, respectively. There were no statistically significant differences in microshear bond strengths between the single application of Nano-Bond and the double application of ExciTE adhesives.

Conclusions

Microshear bond strength increased significantly as the applied adhesive layer was doubled.

Key words:Adhesive, microshear, bond, strength, nanocomposite.

A Critical Review of the Durability of Adhesion to Tooth Tissue: Methods and Results

The immediate bonding effectiveness of contemporary adhesives is quite favorable, regardless of the approach used. In the long term, the bonding effectiveness of some adhesives drops dramatically, whereas the bond strengths of other adhesives are more stable. This review examines the fundamental processes that cause the adhesion of biomaterials to enamel and dentin to degrade with time. Non-carious class V clinical trials remain the ultimate test method for the assessment of bonding effectiveness, but in addition to being high-cost, they are time- and labor-consuming, and they provide little information on the true cause of clinical failure. Therefore, several laboratory protocols were developed to predict bond durability. This paper critically appraises methodologies that focus on chemical degradation patterns of hydrolysis and elution of interface components, as well as mechanically oriented test set-ups, such as fatigue and fracture toughness measurements. A correlation of in vitro and in vivo data revealed that, currently, the most validated method to assess adhesion durability involves aging of micro-specimens of biomaterials bonded to either enamel or dentin. After about 3 months, all classes of adhesives exhibited mechanical and morphological evidence of degradation that resembles in vivo aging effects. A comparison of contemporary adhesives revealed that the three-step etch-and-rinse adhesives remain the ‘gold standard’ in terms of durability. Any kind of simplification in the clinical application procedure results in loss of bonding effectiveness. Only the two-step self-etch adhesives approach the gold standard and do have some additional clinical benefits.

Shear bond strength between alumina substrate and prosthodontic resin composites with various adhesive resin systems

Background

With the increase in demand for cosmetics and esthetics, resin composite restorations and all-ceramic restorations have become an important treatment alternative. Taking into consideration the large number of prosthodontic and adhesive resins currently available, the strength and durability of these materials needs to be evaluated. This laboratory study presents the shear bond strengths of a range of veneering resin composites bonded to all-ceramic core material using different adhesive resins.

Methods

Alumina ceramic specimens (Techceram Ltd, Shipley, UK) were assigned to three groups. Three types of commercially available prosthodontic resin composites [BelleGlass®, (BG, Kerr, CA, USA), Sinfony® (SF, 3 M ESPE, Dental Products, Germany), and GC Gradia® (GCG, GC Corp, Tokyo, Japan)] were bonded to the alumina substrate using four different adhesive resins. Half the specimens per group (N = 40) were stored dry for 24 hours, the remaining were stored for 30 days in water. The bonding strength, so-called shear bond strengths between composite resin and alumina substrate were measured. Data were analysed statistically and variations in bond strength within each group were additionally evaluated by calculating the Weibull modulus.

Results

Bond strengths were influenced by the brand of prosthodontic resin composites. Shear bond strengths of material combinations varied from 24.17 ± 3.72–10.15 ± 3.69 MPa and 21.20 ± 4.64–7.50 ± 4.22 at 24 h and 30 days, respectively. BG resin composite compared with the other resin composites provided the strongest bond with alumina substrate (p < 0.01). SF resin composite was found to have a lower bond strength than the other composites. The Weibull moduli were highest for BG, which was bonded by using Optibond Solo Plus adhesive resin at 24 h and 30 days. There was no effect of storage time and adhesive brand on bond strength.

Conclusion

Within the limitations of this study, the shear bond strengths of composite resins to alumina substrate are related to the composite resins.

Influence of ceramic thickness and type on micromechanical properties of light-cured adhesive bonding agents

OBJECTIVE

The aim of this study was to evaluate the micromechanical properties of different adhesive bonding agents when polymerized through ceramics.

MATERIALS AND METHODS

Sixty sound extracted human third molars were selected and the crowns were sectioned perpendicular to the long axis in order to obtain dentin slices to be bonded with one of the following adhesives: Syntac/Heliobond (Ivoclar-Vivadent) or Adper-Scotchbond-1XT (3M-ESPE). The adhesives were cured by using a LED-unit (Bluephase®, Ivoclar Vivadent) with three different curing times (10 s, 20 s and 30 s) under two ceramics (IPS-e.max-Press, Ivoclar-Vivadent; IPS-Empress®CAD, Ivoclar-Vivadent) of different thicknesses (0 mm, 0.75 mm, 2 mm). Thirty groups were included, each containing 60 measurements. Micromechanical properties (Hardness, HV; indentation modulus, E; and creep, Cr) of the adhesives were measured with an automatic microhardness indenter (Fisherscope H100C, Germany). Data were statistically analyzed by using one-way ANOVA and Tukey's post-hoc test, as well as a multivariate analysis to test the influence of the study parameters (SPSS 18.0).

RESULTS

Significant differences were observed between the micromechanical properties of the adhesives (p < 0.05). The ceramic type showed the highest effect on HV (Partial-eta squared (η(2)) = 0.109) of the tested adhesives, while E (η(2) = 0.275) and Cr (η(2) = 0.194) were stronger influenced by the adhesive type. Ceramic thickness showed no effect on the E and Cr of the adhesives.

CONCLUSIONS

The adhesive bonding agents used in this study performed well by curing through different thicknesses of ceramics. The micromechanical properties of the adhesives were determined by the adhesive type and were less influenced by ceramic type and curing time.

Shear bond strength of self-adhering flowable composite on dentin with and without application of an adhesive system

PURPOSE

The aim of this study was to evaluate the shear bond strength (SBS) of conventional and self-adhering flowable resin composites on the dentin surfaces of primary and permanent teeth and to evaluate the effect of the application of an adhesive system under self-adhering flowable resin composite on SBS.

METHODS

Prepared permanent and primary tooth dentin surfaces were randomly distributed into 3 groups according to application protocols as follows: group 1: Vertise Flow; group 2: OptiBond + Filtek Ultimate; and group 3: OptiBond + Vertise Flow. A universal testing machine was used to measure SBS of prepared specimens, and data were analyzed using 1-way ANOVA and Tukey test.

RESULTS

Statistically significant differences were observed among all groups for primary and permanent teeth (P<0.05). The highest values were observed in group 2, followed by group 3, in both permanent and primary teeth. SBSs of all groups were significantly higher for permanent teeth than for primary teeth (P<0.05).

CONCLUSION

Although SBS values of Vertise Flow groups were lower than those for conventional flowable resin composite groups, with further developments in material technology, self-adhering materials could be promising materials especially for pediatric dentistry.

Influence of intermediate resin on the bond strength of light-curing composite resin to polymer substrate

OBJECTIVES

The aim of this study was to examine the effect of intermediate resin (IMR) of different monomer compositions and viscosities on the shear bond strength between polymer substrate and light-curing composite.

METHODS

The substrate used in the study was an autopolymerizing polymethyl methacrylate (PMMA) based polymer. The substrate was treated with the IMR for 3 min before application of light polymerizable particulate filler composite resin. The monomers of the IMR were either bisphenol-A-glycidyl dimethacrylate (BisGMA) and triethyleneglycol dimethacrylate (TEGDMA) or BisGMA and methyl methacrylate (MMA). The shear bond strength of the IMR treated substrate to the particulate filler composite was evaluated after storing the specimens dry and after thermocycling the specimens in water. Light microscope examination was accomplished to determine the swelled layer of the substrate.

RESULTS

Significant differences were found between the shear bond strength values of the IMRs (p < 0.001). The bond strengths were generally higher in the BisGMA-MMA groups than in the BisGMA-TEGDMA groups. Two-way ANOVA revealed significant effects of type of IMR (p < 0.001) and thermocycling (p = 0.017) on the shear bond strength. No interaction was found between these variables (p > 0.05).

CONCLUSIONS

The results suggest that the monomer composition and ratio of the IMRs used in the study influence the shear bond strength of the polymer substrate to the new resin.

Effect of surface area and air-drying distance on shear bond strength of etch-and-rinse adhesive

We evaluated the effects of air-drying distance and bond surface area on the shear bond strength of a 2-step etch-and-rinse adhesive. A total of 120 bovine anterior teeth were equally divided into 6 main groups based on bonding surface area. The main groups were divided into sub-groups (n = 5) according to air-drying distance. The shear strength was determined using a universal testing machine at a crosshead speed of 0.5 mm/min. The averaged results were subjected to two-way ANOVA and Tukey's test (α = 0.05). Two-way ANOVA testing identified no significant cross-product interactions (p > 0.05), but the main factors of area (p < 0.0001) and air-drying distance (p < 0.00001) significantly affected the mean bond strength. Shorter air-drying distances improved bond strength, and increased surface area decreased the bond strength.

Factors affecting the bond strength of self-etch adhesives: A meta-analysis of literature

Aim:

The purpose of this study is to critically evaluate the factors that affect the bond strength of one-step and two-step self-etch adhesives by using meta-analysis.

Materials and Methods:

Potential papers that were selected according to inclusion and exclusion criteria from articles were published in 13 peer-reviewed journals using “PubMed data base”. From each report, means and standard deviations of bond strengths were extracted and tabulated with corresponding experimental conditions.

Results:

All the studied parameters showed no significant difference, except for dentin origin/site and bonding area. In addition, statistical analysis done with ANOVA showed statistical significance between the one-step and two-step self-etch adhesives.

Conclusions:

Our analysis has showed that two-step self-etch adhesive system showed a superior in vitro performance in comparison to one-step self-etch system. Nevertheless, certain factors such as dentin origin, site and area of bonding affect the bond strength of adhesives.

Direct comparison of the bond strength results of the different test methods: a critical literature review

OBJECTIVE

The goal of this paper is to undertake a literature search collecting all dentin bond strength data obtained for six adhesives with four tests (shear, microshear, tensile and microtensile) and to critically analyze the results with respect to average bond strength, coefficient of variation, mode of failure and product ranking.

METHOD

A PubMed search was carried out for the years between 1998 and 2009 identifying publications on bond strength measurements of resin composite to dentin using four tests: shear, tensile, microshear and microtensile. The six adhesive resins were selected covering three step systems (OptiBond FL, Scotch Bond Multi-Purpose Plus), two-step (Prime & Bond NT, Single Bond, Clearfil SE Bond) and one step (Adper Prompt L Pop).

RESULTS

Pooling results from 147 references showed an ongoing high scatter in the bond strength data regardless which adhesive and which bond test was used. Coefficients of variation remained high (20-50%) even with the microbond test. The reported modes of failure for all tests still included high number of cohesive failures. The ranking seemed to be dependant on the test used.

SIGNIFICANCE

The scatter in dentin bond strength data remains regardless which test is used confirming Finite Element Analysis predicting non-uniform stress distributions due to a number of geometrical, loading, material properties and specimens preparation variables. This reopens the question whether, an interfacial fracture mechanics approach to analyze the dentin-adhesive bond is not more appropriate for obtaining better agreement among dentin bond related papers.

Shear bond strength of orthodontic brackets bonded to provisional crown materials utilizing two different adhesives

OBJECTIVE

To test the hypothesis that there is no difference in the shear bond strength of brackets bonded to provisional crown materials (PCMs) using two adhesive agents.

MATERIALS AND METHODS

Four PCMs were tested: Integrity, Jet, Protemp, and Snap. Forty cylindrical specimens of 10 mm diameter x 5 mm were prepared for each PCM. Ten specimens from each group were bonded to one of the two brackets, Clarity or Victory, using one of the two adhesives, Fuji Ortho LC or Ortho Bracket Adhesive. The brackets were debonded in shear at a cross-head speed of 5 mm/min, and the shear bond strength (SBS) was calculated. The type of failure was visually determined. The numeric data were analyzed using three-way analysis of variance and Tukey multiple range test at alpha = .05.

RESULTS

The mean SBSs ranged from 2.81 MPa to 9.65 MPa. There was a significant difference between Snap and the other three materials (P < .0001). There was no significant difference between the two brackets or the two adhesives (P > .05). The bond failure for all the specimens was of the adhesive type between the PCM and the adhesive resin.

CONCLUSIONS

The PCM Snap yielded a significantly lower mean SBS value compared to the other three materials. No significant differences were found between the brackets or the adhesives. The bond failure was of the adhesive type.

Bond strength test: role of operator skill

BACKGROUND

Test method, substrate material and operator variability are factors known to affect bond strength test outcomes. The aim of this study was to determine if, with increasing experience, individual operator skill in material handling influenced microshear bond strength outcomes.

METHODS

This retrospective study used data collected from six preliminary tests carried out successively on enamel microshear bond strength for two adhesives: Clearfil SE Bond (Kuraray) and Adper Single Bond 2 (3M ESPE) by one operator. Mean and median microshear bond strength values, standard deviations and coefficients of variation for each adhesive test group were calculated and assessed.

RESULTS

A gradual increase in mean microshear bond strengths, a decrease in standard deviations and coefficients of variation over time for both adhesives and a progressively more uniform distribution of microshear bond strength results recorded in individual test sets was observed. The results suggest an improvement in bonding reliability as experience is gained.

CONCLUSIONS

Operator skill in material handling appears to play a critical role in determining the outcome of bond strength testing. This same skill is probably relevant when using an adhesive for the first time clinically. It is important that clinicians become familiar with new adhesives in order to achieve optimal outcomes.

Shear versus micro-shear bond strength test: A finite element stress analysis

OBJECTIVES

This study aimed at comparing the stress distribution in shear and micro-shear test set-ups using finite element analysis, and suggesting some parameter standardization that might have important influence on the results.

METHODS

Two-dimensional plane strain finite element analysis was performed using MSCPatran and MSCMarc softwares. Model configurations were based on published experimental shear and micro-shear test set-ups and material properties were assumed to be isotropic, homogeneous and linear-elastic. Typical values of elastic modulus and Poisson's ratios were assigned to composite, dentin and adhesive. Loading conditions considered a single-node concentrated load at different distances from the dentin-adhesive interface, and proportional geometry (1:5 scale, but fixed adhesive layer thickness in 50microm) with similar calculated nominal strength. The maximum tensile and shear stresses, and stress distribution along dentin-adhesive interfacial nodes were analyzed.

RESULTS

Stress distribution was always non-uniform and greatly differed between shear and micro-shear models. A pronounced stress concentration was observed at the interfacial edges due to the geometric change: stress values farther exceeded the nominal strength and tensile stresses were much higher than shear stresses. For micro-shear test, the relatively thicker adhesive layer and use of low modulus composites may lead to relevant stress intensification. An appropriate loading distance was established for each test (1mm for shear and 0.1mm for micro-shear) in which stress concentration would be minimal, and should be standardized for experimental assays.

SIGNIFICANCE

The elastic modulus of bonded composites, relative adhesive layer thickness and load application distance are important parameters to be standardized, once they influence stress concentration.

Adhesion between dental ceramic and bonding resin: quantitative evaluation by Vickers indenter methodology

OBJECTIVES

The purpose of this study was to evaluate the adhesion to dental ceramic by Vickers indenter methodology. This technique allows the creation of adhesive fractures and determines the influence of the surface treatment on adhesive capacities.

METHODS

A single bond adhesive system (One Step Bisco) was applied to ceramic Vitapan 3D Master CE 0124 samples. Ceramic samples were polished with 500 or 4000-grit paper, sandblasted or not (Sa/NSa), treated with fluorhydric acid or not (A/NA) and silane or not (Si/NSi). The experimental groups (Gr) were: (Gr 1) 4000; (Gr 2) 4000+Si; (Gr 3) 4000+Sa+A; (Gr 4) 4000+Sa+A+Si; (Gr 5) 500+Sa+A+Si. Each sample was indented with the diamond Vickers indenter Leitz Durimet 2 (Wetzlar, Germany) using a load of 20N for 30s. The surfaces of the debonded areas were observed in an optical microscope providing a digital image of the debonded surface. The adhesion bond strength was calculated according to the formula of Engel and Roshon [Engel PA, Roshon DD. Indentation-debonding of an adhered surface layer. J Adhesion 1979;10(33): 237-53]. The statistical analysis was conducted using Student's t test (p<0.05).

RESULTS

The values obtained for each group were: (Gr 1) 32MPa; (Gr 2) 52MPa; (Gr 3) 112MPa; (Gr 4) 131MPa; (Gr 5) 265MPa. There is a significant improvement in bond strength with the silane application on the 4000 polished surface (Gr 2). However, there is no significant difference when silane is applied or not on a sanded and etched ceramic (Gr 4). Bond strengths were higher with 500 grit polished, sanded, etched with silane application on the surface (Gr 5).

SIGNIFICANCE

The Vickers indenter methodology is able to discriminate between the influences of different surface treatments on the adhesion of an adhesive layer on a feldspathic ceramic.

Effect of Storage Duration/Solution on Microshear Bond Strength of Composite to Enamel

The aim of this study was to determine the effect of three storage solutions and two storage durations on microshear bond strength (microSBS) of a resin composite. Sixty non-carious human permanent molars were stored in three storage solutions (0.1% thymol, 10% formalin, and distilled water). Each tooth was separated mesio-distally into two parts. Specimens of the first part were stored for 24 hours, while specimens of the second part were stored for two months in the solutions. After each storage period, the enamel surface was covered with a composite resin in combination with an etch-rinse adhesive system. Specimens were then serially sectioned into sticks of 1 mm' bond area and subjected to microSBS test. There were no statistically significant differences between the two storage periods for each solution (p>0.05). The thymol solution group showed lower microSBS values than those of distilled water for both storage periods (p<0.05). As for the formalin group, its microSBS values were not statistically different from those of distilled water and thymol groups at each storage period (p>0.05). In conclusion, the thymol solution caused the microSBS of the resin composite to decrease when compared to both formalin and distilled water after 24 hours and two months. However, the microSBS of the resin composite was not affected by storage duration.

Comparison of microshear bond strengths of four self-etching bonding systems to enamel using two test methods

BACKGROUND

Recent advances in enamel and dentine adhesive technology have resulted in the emergence of many new adhesive systems. Self-etching bonding systems do not require a separate etching step and the newest systems are the "all-in-one" systems which combine etching, priming and bonding into a single application. This study reports laboratory enamel microshear bond strengths of a self-etching priming and three all-in-one systems and also evaluates two different microshear bond test methods.

METHODS

One hundred and nineteen enamel specimens were bonded (0.8 mm diameter) with either Clearfil Protect Bond (Kuraray), Xeno III (Dentsply), G Bond (GC) or One-Up Bond F (Tokuyama) using Palfique Estelite resin composite and stored in 37 degrees Celsius water for seven days. The microshear bond test method used either a blade or wire to apply the shear stress. Results were analysed with one-way ANOVA and post hoc (Tukey) multiple comparison analysis.

RESULTS

Clearfil Protect Bond demonstrated higher and more consistent bond strengths than Xeno III, G Bond or One-Up Bond F. The wire method showed much greater reliability in results, with a coefficient of variation half that of the blade method.

CONCLUSIONS

All-in-one adhesives seem to be less reliable than the two-step self-etching priming adhesive when bonding to enamel. Test method can significantly affect results in the microshear bond test method.

In vitro microleakage of adhesive-sealed dentin with lactic acid and saliva exposure: a radio-isotope analysis

OBJECTIVES

The aim of this study was to evaluate the dentin-protective potential of two dentin-bonding systems (Syntac and Clearfil SE Bond) on artificial saliva and lactic acid exposure.

METHODS

Radiochemical analysis in combination with polarization-microscopy was used in the current study. Different applications in MOD preparations in irradiated human molars were compared. Untreated cavities and cavities covered with flowable resin served as controls. Forty-eight specimens were immersed in artificial saliva (pH 7.5), 48 in lactic acid (pH 4). Activity of (32)P was measured between days 1 and 21 and loss of mineralized tissue was estimated.

RESULTS

In lactic acid, cavities sealed with single bond, double bond or bond plus cavity sealer application resulted in significantly lower mineralized tissue loss compared to negative controls (p < 0.05). Upon both saliva and lactic acid exposure, bonding plus sealer application proved to be the most protective treatment (p < 0.05).

CONCLUSIONS

Based on these in vitro findings it may be advisable to use a filled cavity sealer or a flowable resin to protect dentin from demineralization. The radiochemical analysis appeared to be valuable in evaluating the protective potential of bonding agents against dentin demineralization.

Bond failure at dentin-composite interfaces with 'single-bottle' adhesives

OBJECTIVES

Significant differences in interfacial fracture toughness (intK(1c)) among six dentinal adhesives have been reported. Resulting fractured test specimens were examined under SEM to determine differences in micromorphology, which might account for the respective intK(1c) results.

METHODS

Interfacial fracture toughness specimens were assembled from bovine dentin and P50 resin composite under moist conditions, using one of five 'single-bottle' adhesives; either Single Bond, One Step, Optibond Solo, Prime & Bond 2.1, Bond 1 or a resin-modified glass ionomer, Fuji Bond LC. After fracture toughness testing, four fractured specimens from each group were sectioned transversely, critical-point dried and examined under SEM.

RESULTS

Most bond failures occurred at the interface between adhesive resin and the top of the hybrid layer. Single Bond and One Step gave the highest intK(1c) results and showed good resin infiltration at this interface. Average film thickness of unfilled adhesives was 30 microm. When this intermediate adhesive layer was too thin, resin infiltration was poor and associated with low fracture toughness. Filled adhesives, Optibond Solo and Fuji Bond LC, formed thick films varying from 60 to 250 microm which failed cohesively, effectively sealing the dentin surface despite moderate fracture toughness results.

CONCLUSIONS

Most bond failures occurred between the adhesive and hybrid layers. Good resin infiltration at the top of the hybrid layer combined with an intermediate adhesive layer of adequate width produced a fracture-resistant interface. Filled adhesives failed cohesively, providing a good dentin seal, despite material fracture.

Fracture toughness and microhardness of a composite: do they correlate?

OBJECTIVES

Chipping and bulk fracture are major contributors in clinical failures of composite restorations. Fracture toughness (K(Ic)) quantifies susceptibility for fracture, but experimental determination is complicated. It would be beneficial for the dental community if a relatively simple experiment, such as microhardness (HK), could be used to screen composites for fracture resistance. This study explores a possible correlation between K(Ic) and HK.

METHODS

Composite cylinders (4mm diameter and approximately 7 mm long) were cured for five combinations of light intensity (I, microm W/cm(2)) and curing time (T, s) to achieve a range of different total light energy densities (I x T=100 x 10, 100 x 20, 300 x 20, 300 x 40, and 700 x 60 microm W s/cm(2)). A chevron-notch was cut in the median plane of the cylinders for the fracture toughness test, which was executed in a displacement control mode at 6 micro m/s cross-head speed (sample size 4). Knoop hardness was determined at the median plane of the cylinders (sample size 6). The tests were performed 15 min and 24h after curing.

RESULTS

Both the K(Ic) and HK increased with increased light energy density and storage time. Linear regression analysis indicated a strong correlation between HK and K(Ic) tested at the same time period (R(2)=0.97 and 0.90 for 15 min and 24h, respectively). The correlation became weaker between the different storage times (R(2)=0.71), indicating a change in fracture toughness and/or microhardness mechanisms.

CONCLUSION

Fracture toughness of a composite cannot be simply extrapolated from microhardness.

Fracture mechanics analysis of the dentine-luting cement interface

The objectives of this study were to determine the fracture toughness of adhesive interfaces between dentine and clinically relevant, thin layers of dental luting cements. Cements tested included a conventional glass-ionomer, F (Fuji 1), a resin-modified glass-ionomer, FP (Fuji Plus) and a compomer cement, D (DyractCem). Ten miniature short-bar chevron notch specimens were manufactured for each cement, each comprising a 40 microm thick chevron of lute, between two 1.5 mm thick blocks of bovine dentine, encased in resin composite. The interfacial K(IC) results (MN/m3/2) were median (range): F; 0.152 (0.14-0.16), FP; 0.306 (0.27-0.37), D; 0.351 (0.31-0.37). Non-parametric statistical analysis showed that the fracture toughness of F was significantly lower (p <0.05) than those of FP or D, and all were significantly lower than values for monolithic cement specimens. Scanning electron microscopy of the specimens suggested crack propagation along the interface. However, energy dispersive X-ray analysis indicated that failure was cohesive within the cement. It is concluded that the fracture toughness of luting cement was lowered by cement-dentine interactions.

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.

Do condensable composites help to achieve better proximal contacts?

OBJECTIVES

Obtaining acceptable contact areas with adjacent teeth is a significant challenge when placing direct resin composite in Class II preparations. It was the purpose of this laboratory study to evaluate the influence of the type of resin composite ('packable' vs conventional) and of the matrix system on the quality of the proximal contact area in Class II composite restorations.

METHODS

A standardized DO cavity was prepared in 170 frasaco teeth. Two operators each filled 85 teeth in the same frasaco model using four resin composites [Solitaire (S), Surefil (Su), P60, Z100], three matrix systems [Automatrix (A), Palodent (P), Lucifix matrix (L)] and one hand instrument specially designed to achieve better proximal contacts [Belvedere Composite Contact Former (B)]. The teeth were subdivided into 17 groups (Z100/1-A, Z100/1-P, Z100/1-L, S-A, S-P, S-L, Z100/1-A-B, Z100/1-L-B, Su-A, Su-P, Su-L, P60-A, P60-P, P60-L, Z100/2-A, Z100/2-P, Z100/2-L). Each operator made five fillings of each group. The quality of the proximal contacts was assessed by measuring the maximum mesio-distal (M-D) diameter of the restored teeth using a digital micrometer and the tightness of the proximal contact area using standardized metal blades. All data were analyzed using two-way ANOVA and Bonferroni/Dunn's test for multiple comparisons with a significance level of P<0.05.

RESULTS

Regarding the matrix system, a significant larger M-D diameter and a stronger proximal contact area was achieved with the Palodent matrix system. The use of the Belvedere Composite Contact Former together with Lucifix matrix and Automatrix contributed to significantly stronger proximal contact areas. Concerning the type of resin composite, no significant differences were noted for both evaluation criteria when Palodent was used. Using Automatrix or Lucifix matrix, the more condensable resin composite P60 scored slightly better than Surefil and Z100. There was no operator effect. Both operators underwent a learning process. The longer they worked with a specific material/technique, the better proximal contacts they achieved.

SIGNIFICANCE

The best proximal contact areas in Class II composite restorations were obtained using a sectional matrix system. The 'packability' of the resin composite did not help to achieve better proximal contacts.

A morphological and tensile bond strength evaluation of an unfilled adhesive with low-viscosity composites and a filled adhesive in one and two coats

OBJECTIVE

The purpose of this study was to measure the tensile bond strength (TBS) testing of resin composite to dentin of three low-viscosity composites, in association with an unfilled adhesive, and a filled adhesive one and two coats respectively, and to evaluate and compare the SEM morphological observations.

METHODS

The labial surface of 120 bovine lower incisors were ground to obtain a flat dentin surface allowing demarcation of a 4 mm diameter area with adhesive tape. The teeth were randomly divided in six groups of 20 each. The dentin of each ground surface was etched with 35% H(3)PO(4) for 15s, followed by application of the respective adhesive: Single Bond (SB) for Groups 1, 2, 3 and 6; Optibond Solo (OS) for Groups 4 and 5. In Groups 1 and 4, a resin composite rod with a wire loop was luted directly to the adhesive surface with Z100. Group 2 received an intermediate layer of Flow It (FI) composite; Group 3 received an intermediate layer of Protect Liner F (PLF) composite; Group 5 received a second coat of OS; and Group 6 received an intermediate layer of an experimental low-viscosity composite (EM). A resin composite rod was luted to the surface of each specimen with Z100 resin composite. All specimens were stored in distilled water at 37 degrees C for 24h prior to TBS testing. Each specimen was inspected by SEM and classified according to adhesive or cohesive failure mode. One specimen of each group was cut longitudinally, polished and prepared for SEM observation.

RESULTS

The TBS values were: Group 1 (7.86MPa+/-2.28), Group 2 (7.62MPa+/-1.85), Group 3 (7.60MPa+/-2.14), Group 4 (7.96MPa+/-2.36), Group 5 (7.50MPa+/-2.70) and Group 6 (7.18MPa+/-2.40). No significant statistical differences were observed among the groups. However, the analyses of the failure mode presented a considerable variation.

SIGNIFICANCE

The use of a filled adhesive or an unfilled adhesive along with a low-viscosity composite as an intermediate layer may provide a stress absorbing layer, whereby improving the preservation of the bonded interface area.

Conference report. Direct adhesive materials: current perceptions and evidence--future solutions

This paper reports the proceedings, including the consensus views of an Australasian expert group convened to consider current perceptions, evidence and future solutions in the field of direct adhesive materials. This group, in anticipating a trend to preservative dentistry, formed the view that caries risk assessment should increasingly influence the selection of restorative materials. In low caries risk patients, aesthetic demands typically favour the use of resin-based composites. Interactive (biomimetic) materials based on glass-ionomer chemistry have particular application in high caries risk patients. Teaching in dental schools, continuing education programmes and research, both in the laboratory and in the clinical environment should be more attuned to the ever-increasing use of tooth-coloured restorative materials in everyday clinical practice. Linked to this trend are changes in patient--dentist relationships, whereby patients should be encouraged to become more involved in treatment decision-making. Expert group meetings are suggested to be of value in addressing some of the shortfall between the need for good evidence and the relentless challenge of the introduction of new products and concepts in the field of direct adhesive materials.

Meta-analytical review of factors involved in dentin adherence

Literature data on adherence tests of dentin-bonding systems (DBS) may differ widely, even for the same DBS. The problem of bond testing is that materials are seldom compared with a standard, and experimental conditions often vary. We sought to identify the parameters that influence this variability. Using inclusion and exclusion criteria, we conducted a meta-analytical review of 75 articles, published between 1992 and 1996 in SCI reviews, that give bond strength data for 15 dentin-bonding agents of the so-called third and fourth generations. Seventeen selected parameters were classified into four groups: Group A includes factors related to the dentin substrate (i.e., nature of teeth); group B, composite and bonding area (i.e., composite stiffness); group C, storage conditions of the bonded samples (i.e., thermocycling); and group D, test design (i.e., crosshead speed). For each report, the experimental features, the bond strength means and standard deviations, and the failure mode were extracted and tabulated. Statistical Analysis System software was used to perform Pearson correlation analysis and analysis of variance, with bond strength as the dependent variable and experimental conditions as the independent variables. The meta-analytical review highlighted the significant influence of various parameters in the different groups: origin of dentin, types of teeth, pulpal pressure, tooth storage temperature, maximum storage time of teeth, and dentin depth in group A; type and stiffness of composite and bonding area in group B; storage of bonded samples (medium, temperature, and time) in group C, and testing mode and crosshead speed in group D. A significant positive correlation was observed between the mean bond strength and the rate of cohesive failure. It can be concluded from this study that some of these parameters should be controlled by the use of a standardized protocol. Unfortunately, the substrate-related variables are more difficult to control, even though their influence is consistent.

Mode of failure in the dentin-adhesive resin-resin composite bonded joint as determined by strength-based (muTBS) and fracture-based (CNSB) mechanical testing

OBJECTIVE

To determine the failure mode between dentin-adhesive resin-resin composite bonded joint produced with a chevron-notch short-bar (CNSB) and microtensile test methods.

METHODS

Forty teeth were randomly selected for microtensile and forty for CNSB specimen fabrication and stored in 0.5% chloramine T at 37 degrees C until respective static load to failure testing at 30 and 180days. Failure modes were categorized by SEM and tested with Fisher's exact test. Within respective mechanical testing methods the probability of failure curve distributions being significantly different were analyzed by the Wald chi-square statistic.

RESULTS

The characteristic fracture toughness at 30- and 180-day storage was 0.82 and 0.87MPam(1/2), while the Weibull Modulus (m) for the failure distributions, was 4.60 and 4.56, respectively. No significant difference was demonstrated in the failure distributions between these groups (p=0.45). The characteristic tensile strength (muTBS(o)) at 30- and 180-day storage was 52.53 and 14.71MPa with an m of 3.04 and 1.56, respectively. Failure distributions for muTBS groups were significantly different (p<0.001). K(IvM) failure modes, regardless of storage time, were within the adhesive joint with 30-day debonds primarily through the top region of the hybrid layer (THL) and after 180-days involving the bottom of the hybrid layer (BHL). The 30-day muTBS group demonstrated a propensity to debond in dentin or resin composite substrates but after 180-days storage debonds again involved the BHL.

SIGNIFICANCE

The weak links in the dentin-adhesive resin-resin composite bonded joint may be the interphase regions between the THL and the adhesive resin and the BHL and dentin.

Influence of cross-head speed on resin-dentin shear bond strength

OBJECTIVE

To evaluate the influence of different cross-head speeds on shear bond strength test on the dentin surface.

METHODS

One hundred and twenty extracted bovine incisors were embedded in polystyrene resin. The specimens were prepared by wet grinding with 320-, 400- and 600-grit Al2O3 paper exposing dentin. After the application of the adhesive system Single Bond (3M) to etched dentin, the composite resin Z-100 (3M) was applied and light cured. The specimens were randomly assigned to four groups (n=30). The shear bond strength tests were performed with an EMIC DL 500 universal testing machine at four different cross-head speeds: 0.50 (A); 0.75 (B); 1.00 (C); and 5.00 mm/min (D).

RESULTS

The mean values of shear bond strength in MPa (SD) were: A, 11.78 (3.91); B, 11.82 (4.78); C, 16.32 (6.45); D, 15.46 (5.94). The data were analyzed with one-way ANOVA and Tukey's test (alpha=0.05). The results indicated that A=B<C=D. The fracture pattern was evaluated by visual analysis in a stereomicroscope (25x). The percentage of fractures that occurred at the adhesive interface were: A, 92.5%; B, 91.6%; C, 70.0%; D, 47.0%. The Student's t-test to percentages (alpha=0.05) indicated that there were no significant differences among A, B and C; A and B differed from D, and there was no significant difference between C and D.

SIGNIFICANCE

Different cross-head speeds may influence the shear bond strength and the fracture pattern in dentin substrate. Shear bond strength using cross-head speeds of 0.50 and 0.75 mm/min should be preferred.