Why do shear bond tests pull out dentin?

Effect of cross-head speed on the bond strength of dental resin to tooth structure - A review and re-analysis

OBJECTIVE

To review the published evidence for the role of cross-head speed on the apparent mechanical properties and bond strength of filled resins to tooth structure in order to identify the causes of inconsistency and contradictory results.

METHOD

The data for all available mechanical test results for studies involving dental resins at more than one strain rate was collected from 22 papers. Statistical reanalysis using linear regression was used to test the hypothesis that cross-head speed was correlated with the outcome, with the implication of causality, in each case.

RESULTS

In many cases the expected trend was found, in others not. However, it was apparent that the quality of data was often less than can be achieved, and that known interferences have not been recognized.

SIGNIFICANCE

Experimental work for the effect of cross-head speed on bond strength and other properties for dental resin-based materials has often failed to reach the standard which is required for useful data and thus better comprehension of behaviour. Other relevant conditions, such as temperature and water saturation, are in need of attention in this context.

Silane and acid etch cross contamination of dentin and composite reduced µ-tensile bond strength

Objectives

To investigate whether acid etch contamination of silane-treated composite influenced repair bond strength and whether silane contamination on dentin influenced composite bond strength to dentin.

Materials and methods

Forty composite blocks stored in water for 4 weeks were divided into four groups. Specimens in groups 1-3 were coated with Bis-Silane and contaminated with acid etch + water spray (group 1) or water spray (group 2). Group 3 was not contaminated. Group 4 was untreated. The occlusal third of 60 third molars was cut off, ground flat, and divided into three groups. After etching, the surfaces in groups A and B were contaminated with Bis-silane. The contaminated surfaces in group A were re-etched.Each composite repair group and composite-dentin group was divided into two subgroups receiving Adper Scotchbond 1 XT or Clearfil SE Bond 2 adhesives followed by a composite build up. After ageing for 3 months, specimens were sectioned into 1.1 mm × 1.1 mm rods for tensile testing and strength calculated at fracture. The fracture was examined using microscope.

Results

Bis-Silane surface treatment increased the repair bond strength. Contamination with acid reduced the strength of the repair bond. Similar results were obtained for both adhesives. Tooth surface contamination with silane reduced the bond strength between dentin and composite. Additional acid etching or water spray on silane contaminated dentin did not influence the weakened bond strength. Most fractures were adhesive type.

Conclusions

Silane contamination on etched dentin and acid etch contamination on silanized composite surfaces significantly reduced tensile bond strength.

Enhancing dentin bonding through new adhesives formulations with natural polyphenols, tricalcium phosphate and chitosan

OBJECTIVES

The aim of the study was to develop new adhesive formulations that include natural polyphenols extracted from green tea (GTE), tricalcium phosphate (TCP) and chitosan to improve dentin bonding characteristics and cytotoxicity.

METHODS

Four experimental adhesives were formulated under laboratory conditions. The groups differed in the integration of either GTE and/or TCP + chitosan. The four experimental and one clinically proven reference adhesive underwent shear bond testing after 24 h and 6 months of aging (n = 200) with subsequent fractographic analysis. Bond morphology was analyzed under a scanning electron microscope. The presence of phenolic compounds was validated by high performance liquid chromatography. Cytotoxicity was assessed by the WST-1 colorimetric assay on eluates up to 6 months. Statistical analysis was performed by one- and three-way ANOVA, Games-Howell and Tukey's post-hoc test as well as multiple students t-tests (α = 0.05). Weibull analysis was further conducted.

RESULTS

The addition of GTE into the bonding agent did show immediate (p = 0.023, p = 0.013) and long-term (p < 0.001) effects on bond strength. After 24 h, GTE doped groups performed equal to the reference (p = 0.501, p = 0.270) and TCP and chitosan displayed improvements in reliability (m=4.0, m=4.3). Bond strength is retained after aging by adding GTE (p = 0.983). The additional presence of TCP and chitosan reduces it (p = 0.026). Excluding cohesive and mixed failures, the reference adhesive performed statistically equal to three of the four experimental groups. No long-term cytotoxic effects were shown.

SIGNIFICANCE

The integration of GTE can enhance bond strength and a calcium source helps to improve immediate bond reliability.

Application and limitations of configuration factor (C-factor) in stress analysis of dental restorations

OBJECTIVE

The configuration factor (C-factor) is an index used to evaluate the relationship between cavity configuration and the development of polymerization shrinkage stress in dental restorations. Although C-factor has been widely researched, its correlation with stress analysis in dental restorations remains controversial. This review aims to discuss the application and limitations of C-factor and define the restricted conditions under which the C-factor "rule of thumb" is applicable.

METHODS

A thorough literature review was conducted on the application and limitations of C-factor in stress analysis of dental restorations. This was principally based on MEDLINE/PubMed and Web of Science databases and a review of the relevant studies and publications in scientific papers in international peer-reviewed journals for the specific topic of C-factor and polymerization shrinkage.

RESULTS

The C-factor alone cannot provide an accurate prediction of the shrinkage stress of restorations and the mechanical behavior of material-tooth interfaces. C-factor is only applicable under one condition not typically seen in clinical practice: low, near-rigid compliance.

SIGNIFICANCE

Conditions for the application of C-factor have been explicitly defined. A more accurate and precise understanding and utilization of the C-factor is of benefit as it contributes to better understanding of polymerization shrinkage behavior of restorations.

Pushout Bond Strength in Coronal Dentin: A Standardization Approach in Comparison to Shear Bond Strength

To find an alternative that is closer to clinical reality in terms of cavity geometry and configuration factor, this study investigated the pushout test on in vitro adhesive testing to coronal dentin when compared to the established shear test, both in a standardized approach. For a feasible comparison between both tests, the pushout specimen was adjusted in thickness (1.03 ± 0.05 mm) and cavity diameter (1.42 ± 0.03 mm) to receive a bonding area (4.63 ± 0.26 mm2) that matches that of the shear test (4.57 ± 0.13 mm2). Though, the configuration factor between both tests differs largely (pushout 1.5 ± 0.08; shear bond 0.20 ± 0.01). The bond strength of five different adhesives (n = 20) was investigated for both tests. The pushout test registered a high number of invalid measurements (30%) due to concomitant dentin fracture during testing. In contrast to the shear test, the pushout test failed to discriminate between different adhesives (p = 0.367). Both tests differed largely from each other when comparing adhesive groups. When solely looking at the valid specimens, Weibull modulus reached higher values in the pushout approach. Conclusively, the pushout test in this specific setup does not distinguish as precisely as the shear bond test between different adhesives and needs adaption to be routinely applied in adhesive dentistry.

Effect of pre-heating methods and devices on the mechanical properties, post-gel shrinkage, and shrinkage stress of bulk-fill materials

This study evaluated the effect of using two different pre-heating methods on the three resin-based composite (RBCs). Three paste viscosity bulk-fill RBCs (VisCalor Bulk [VC]; VOCO; x-tra fil Caps [XF], VOCO; Filtek One Bulk Fill [FO], 3 M) were pre-heated using either a VisCalor Dispenser (VOCO) to 65 °C, or the Caps Warmer (VOCO) to 37 °C, 54 °C, or 68 °C. The temperature inside the capsules and cavity was monitored before and after insertion into the matrix. Within 30 s of inserting the RBC, they were light-activated using a VALO (Ultradent) curing light for 20 s. The post-gel shrinkage (Shr - %), Flexural Strength (FS - MPa), Elastic Modulus (E - MPa), degree of conversion (DC - %), Knoop Hardness (KH - N/mm²), diametral tensile strength (DTS - MPa), and compressive strength (CS - MPa) of the RBCs were measured (10 specimens per group). The shrinkage stress was calculated using three-dimensional finite element analysis. Data were analyzed using one-way, two-way ANOVA and Tukey's test (α = 0.05). The temperature fell rapidly after the RBC was inserted into the cavity. Pre-heating the RBCs did not affect the mechanical properties. FO had the lowest E, DC, and KH values, VC had intermediate values, and XF achieved the highest values. The DTS and CS values were not affected by the various pre-heating methods, the temperature, or RBC. Pre-heating methods at 37 °C produced higher shrinkage for all RBCs. VC pre-heated to 65 °C produced the lowest stress when measured at 10 min after light activation.

Adhesion to a CAD/CAM Composite: Causal Factors for a Reliable Long-Term Bond

Computer aided design/manufacturing (CAD/CAM) technology has become an increasingly popular part of dentistry, which today also includes CAD/CAM resin-based composite (RBC) applications. Because CAD/CAM RBCs are much more difficult to bond, many methods and attachment materials are still being proposed, while the best application method is still a matter of debate. The present study therefore evaluates causal factors for a reliable long-term bond, which includes the surface preparation of the CAD/CAM RBC, aging and the type of luting material. The reliability of the bond was calculated, and supplemented by fractography to identify fracture mechanisms. Five categories of luting materials were used: (1) temporary zinc phosphate cement, (2) glass ionomer cement (GIC), (3) resin-modified GIC, (4) conventional adhesive resin cement (ARC), and (5) self-adhesive RC. Half of the CAD/CAM RBC surfaces (n = 200) were sandblasted (SB) with 50 µm aluminum oxide, while the other half remained untreated. Bond strength measurements of the 400 resulting specimens were carried out after 24 h (n = 200) or after additional aging (10,000 thermo-cycles between 5 and 55 °C) (n = 200). The data were statistically analyzed using one- and three-way ANOVA followed by Games-Howell post-hoc test (α = 0.05) and Weibull analysis. Aging resulted in a significant decrease in bond strength primarily for the conventional cements. The highest bond strengths and reliabilities were recorded for both ARCs. SB caused a significant increase in bond strength for most luting materials, but also caused microcracks in the CAD/CAM RBC. These microcracks might compromise the long-term reliability of the bond in vivo.

Effect of firing temperature on the interface between 3Y-TZP zirconia and porcelain

PURPOSE

The purpose of this study is to clarify the porcelain firing temperature conditions that give strongest bonding strength of porcelain to zirconia to manufacture all-ceramic fixed dental prostheses (FDPs) with excellent long-term stability.

METHODS

Opaque porcelain samples (8.0 × 3.0 × 1.2 mm) were placed in the center of zirconia plates (25.0 × 3.0 × 0.5 mm) and fired at temperatures of 950°C, 1,050°C, 1,100°C, and 1,150°C. Schwickerath crack initiation tests, elemental analyses, and morphological changes of the samples were compared.

RESULTS

There was no difference in the bonding strength among all the groups of porcelain fired at different temperatures. Elemental analysis of Si and O₂ at the interface between the zirconia and porcelain were observed in the 950°C, 1,050°C, and 1,100°C groups. No silicon was found in the 1,150°C group by elemental analysis, and the zirconia plate where the porcelain sample was placed had irregular shape changes.

CONCLUSION

It is suggested that silicon is also involved in chemical bonds due to firing at high temperatures.

Effect of adhesive application method on repair bond strength of composite

Objectives

This study aimed to evaluate the effect of the application method of universal adhesives on the shear bond strength (SBS) of repaired composites, applied with different thicknesses.

Materials and Methods

The 84 specimens (Filtek Z350 XT) were prepared, stored in distilled water for a week and thermocycled (5,000 cycles, 5°C to 55°C). They were roughened using 400-grit sandpapers and etched with phosphoric acid. Then, specimens were equally divided into 2 groups; Single Bond Universal (SU) and Prime&Bond Universal (PB). Each group was subdivided into 3 subgroups according to application methods (n = 14); UC: 1 coat + uncuring, 1C: 1 coat + curing, 3C: 3 coats + curing. After storage of the repaired composite for 24 hours, specimens were subjected to the SBS test and the data were statistically analyzed by 2-way analysis of variance and independent t-tests. Specimens were examined with a stereomicroscope to analyze fracture mode and a scanning electron microscope to observe the interface.

Results

Adhesive material was a significant factor (p = 0.001). Bond strengths with SU were higher than PB. The highest strength was obtained from the 1C group with SU. Bonding in multiple layers increased adhesive thicknesses, but there was no significant difference in SBS values (p = 0.255). Failure mode was predominantly cohesive in old composites.

Conclusions

The application of an adequate bonding system plays an important role in repairing composite resin. SU showed higher SBS than PB and the additional layers increased the adhesive thickness without affecting SBS.

The salivary pellicle on dental biomaterials

The salivary pellicle, an adlayer formed by adsorption of salivary components on teeth and dental biomaterials, has direct consequences on basic outcomes of dentistry. Here, we provide an overview of salivary pellicle formation processes with a critical focus on dental biomaterials. We describe and critique the array of salivary pellicle measurement techniques. We also discuss factors that may affect salivary pellicle formation and the heterogeneity of the published literature describing salivary pellicle formation on dental biomaterials. Finally, we survey the many effects salivary pellicles have on dental biomaterials and highlight its implications on design criteria for dental biomaterials. Future investigations may lead to rationally designed dental biomaterials to control the salivary pellicle and enhance material function and patient outcomes.

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.

Influence of ceramic veneer thickness and antagonist on impact stresses during dental trauma with and without a mouthguard assessed with finite element analysis

BACKGROUND/AIM

Little is known about the effect of dental trauma and mouthguards (MG) on teeth with ceramic laminate veneers (CLV). The aim was to evaluate the influence of CLV thickness and the presence of a MG with and without antagonist tooth contact on impact stresses during dental trauma.

MATERIALS AND METHODS

Twelve 2D-finite element models of a head with maxillary structures and upper incisors, six with and six without antagonist tooth, were created in three CLV conditions: sound incisor (no CLV), 0.3 mm CLV, and 1.0 mm CLV. These were evaluated with and without a 4.0-mm ethylene-vinyl acetate MG, with and without an antagonist tooth. An impact analysis was performed in which the head frontally hits a rigid surface at a speed of 1 m/s (3.6 km/h). The results were analyzed using Critical modified von Mises (MPa). The mean of the 10% highest modified von Mises stresses in each structure was collected.

RESULTS

MG presence substantially reduced impact stresses in the CLV and tooth structures. The contact of the antagonist tooth promoted better stress distribution and reduced the stress levels in the traumatized tooth. Critical stress areas were found in the palatal enamel, incisal enamel, labial cervical area, and enamel under the CLV for all models without MG. In the models with MG, the stresses reduced significantly. Critical modified von Mises stress showed that sound or prepared enamel experienced more critical impact stresses than 0.3 or 1.0-mm thick CLV.

CONCLUSIONS

The use of 4.0 mm EVA mouthguard reduced the impact stress levels in models with 0.3-mm CLV and 1.0-mm CLV, similar to a sound tooth. The contact of an antagonist tooth and the MG better distributed the stresses and reduced the impact stress in the traumatized tooth.

Biomechanical evaluation of anterior implants associated with titanium and zirconia abutments and monotype zirconia implants

PURPOSE

The present in silico study evaluated the behavior of titanium dental implants associated with abutments in zirconia and monotype zirconia implant using finite element analysis (FEA).

METHODS

A partial image of the anterior region of the maxilla was obtained by computed tomography. Three models of finite element were made using 3D modeling software (SolidWorks): Ti-Ti (control): implant morse cone (3.75 x 11mm; NobelActive) and titanium abutment (Esthetic Abutment); Ti-Zr: cone morse implant in titanium (3.75 x 11mm; NobelActive) and zirconia abutment (Procera Esthetic Abutment #9); Zr: monotype zirconia implant (4.1 x 12mm; Straumann Pure Ceramic). Computerized crowns of element 11 in lithium disilicate (IPS e.max Press, Ivoclar Vivadent) cemented in all groups were created. A load of 100N (45º) was applied simulating the excursion movement of the incisal guide. The von Mises, modified von Mises, maximum (tensile) and minimum (compression) principal stresses were obtained, compared and used for the quantitative and qualitative evaluation of the groups.

RESULTS

The Zr presented the lowest values of maximum, minimum, and von Mises tensions than the two pieces systems (Ti-Ti and Ti-Zr). Ti-Zr group had the highest values of tensions evaluated in this study.

CONCLUSIONS

The type of material as well as the geometry of implant influenc ed the tension values evaluated.

Effect of luting materials, presence of tooth preparation, and functional loading on stress distribution on ceramic laminate veneers: A finite element analysis

STATEMENT OF PROBLEM

How the polymerization shrinkage, loading, and mechanical properties of luting materials affect the shrinkage and functional stresses in ceramic laminate veneers (CLVs) with and without tooth preparation is unclear.

PURPOSE

The purpose of this finite element analysis (FEA) study was to evaluate the effect of the polymerization shrinkage, functional loading, and mechanical properties of different luting materials on the stresses in ultrathin 0.3-mm CLVs with and without tooth preparation.

MATERIAL AND METHODS

Three resin cements, RelyX Veneer (RV), Allcem Veneer APS (AV), Variolink Esthetic LC (VE), and 1 flowable composite resin, Tetric N-Flow (TF), were tested for post-gel shrinkage (Shr), Knoop hardness (KHN), elastic modulus (E), compressive strength (CS), and diametral tensile strength (DTS). IPS e.max CAD disks of 0.3-mm thickness were made for simulating the effects of light attenuation. Eight 2-dimensional finite element models (Marc-Mentat) of a maxillary central incisor were generated to evaluate the polymerization shrinkage stress of different materials for luting 0.3-mm CLVs with or without tooth preparation and the stress during functional loading by using a modified von Mises criterion (mvm). Collected data from Shr, KHN, and E were submitted to 2-way ANOVA and the Tukey HSD test (α=.05).

RESULTS

Light attenuation by the 0.3-mm ceramic disk did not significantly affect the E values, but Shr was significantly lower in VE (26%) and TF (35%). TF had lower volumetric Shr (%) when interposing a ceramic disk (0.31%). Both tested tooth preparation options showed similar stress distributions from polymerization shrinkage or functional loading, with higher stress concentration on the incisal edge and also on the cervical surface. The model featuring tooth preparation and RV resin cement had the highest and VE the lowest stress levels.

CONCLUSIONS

The flowable composite resin had similar mechanical properties as the resin cements. The stress distribution from shrinkage and functional loading was similar for both techniques with or without tooth preparation.

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.

HF etching of CAD/CAM materials: influence of HF concentration and etching time on shear bond strength

Background

The required pretreatment of CAD/CAM ceramic materials before resin composite cement application varies among studies. The aim of the present study was to evaluate the effect of hydrofluoric acid concentration and etching time on the shear bond strength (SBS) of two adhesive and two self-adhesive resin composite cements to different CAD/CAM ceramic materials.

Methods

SBS of two adhesive (Panavia V5, Kuraray, [PV5]; Vita Adiva F-Cem, Vita Zahnfabrik, [VAF]) and two self-adhesive (RelyX Unicem 2 Automix, 3 M Espe, [RUN]; Vita Adiva S-Cem, Vita, [VAS]) cements to four different CAD/CAM materials (Vitablocs Mark II, Vita, [VM]; Vita Enamic, Vita, [VE]; e.max CAD, Ivoclar Vivadent, [EC]; Vita Suprinity PC, Vita, [VS]) was measured. The effect of the surface pretreatment by using two different hydrofluoric acid products (HF5% Vita Ceramics Etch, Vita and HF9% buffered, Ultradent Porcelain Etch, Ultradent Products) were assessed at etching times of 0 s, 5 s, 15 s, 30s and 60s for each cement and restorative material combination (n = 10 per group, total n = 1440).

Results

Significant effects were found for the etching time and cement for all materials with highest shear bond strength for etching times of 60s = 30s = 15 s ≥ 5 s > 0 s and for RUN>PV5 = VAF > VAS (p < 0.05). Etching with HF5% for 5 s to 15 s resulted in higher SBS values, while no differences were observed between HF5% and HF9% buffered when the substrates were etched for 30s to 60s (p < 0.05).

Conclusions

Within the limitations of this study the recommended surface pretreatment of silicate ceramics is HF etching with concentrations of 5% or 9% for 15 s to 60s to achieve highest shear bond strength while the glassy matrix is sufficiently dissolved. The tested resin composite cements can be applied with all tested materials and suggested for clinical application.

Effect of Immediate Dentin Sealing on the Bond Strength of Monolithic Zirconia to Human Dentin

Objective:

This study evaluated the shear bond strength (SBS) of pretreated monolithic zirconia surfaces bonded to human dentin following immediate dentin sealing (IDS) using two different self-adhesive resin luting agents.

Methods and Materials:

Sixty intact human third molars were collected, stored, sectioned appropriately, and molded according to ISO 29022:2013, resulting in 120 dentin specimens. Ceramic cylindrical specimens were fabricated using CAD/CAM technology and sintered as recommended (final bonding area A=2.56 mm2). Specimens were randomly assigned to eight groups (15≥n≥14) depending on dentin conditioning method (IDS or delayed dentin sealing [DDS]), zirconia surface pretreatment (airborne particle abrasion [APA] with 50 μm Al2O3 particles at 3 bar for 10 seconds or tribochemical silica coating [TBC] with 30 μm CoJet particles at 2.8 bar for 10 seconds), and adhesive luting agent type (Panavia F2.0 [PAN] or PermaCem Dual Smartmix [PER]). Bonded specimens were water-stored (37°C, 24 hours) and subjected to SBS testing (50-kgF load cell, 1 mm/min). Fracture type was evaluated with stereomicroscopy. Data (MPa) were statistically analyzed using three-way analysis of variance (α=0.05).

Results:

All factors significantly affected SBS values (p&lt;0.001). Dentin conditioning method presented the greatest effect. Mean SBS values ranged from 12.603 MPa (PER-APA-DDS) to 40.704 MPa (PER-TBC-IDS). Based on the fracture type, adhesive failures at the luting agent–zirconia interface were the least common.

Conclusion:

Bonding strategies for monolithic zirconia restorations could potentially benefit from IDS, regardless of the adhesive luting agent system used.

Dry-bonding to dentin using alternative conditioners based on iron-containing solutions or nitric acid

OBJECTIVES

To evaluate the effect of experimental conditioners (10-3 solution - 10-3, 6.8% ferric oxalate - FOX, and 1.4% nitric acid - NI) on dentin elastic modulus, flexural strength, bond strength, failure mode, and adhesive interface morphology of two etch-and-rinse adhesives (XP Bond, Dentsply or One-Step, Bisco) applied on etched dry dentin.

METHODS

Sound human third molars were used for the microtensile bond strength test (n = 8), performed at 24 h and after one year of water storage. Failure modes were evaluated by scanning electron microscopy. Dentin bonding interface was analyzed by confocal laser scanning microscopy (n = 3). Adhesive systems were applied on phosphoric acid-etched, wet (positive control) and dry (negative control) dentin, and on etched and dry dentin previously treated with 10-3 (15s), FOX (60s), or NI (15s). Bovine dentin bars (n = 15) were immersed into the conditioning solutions and subjected to a three-point bending test.

RESULTS

XP Bond + 10-3 or NI resulted in lower bond strength than phosphoric acid. One-Step + 10-3 or NI resulted in bond strengths equivalent to the positive control. Experimental conditioners presented no bond strength reduction after one year, regardless of the bonding agent tested. One-Step resulted in more adhesive failures than XP Bond at 24 h, and mixed failures increased after storage. All experimental conditioners promoted hybridization and resin tags formation, except FOX. Dentin elastic modulus was not affected by the conditioners, whereas flexural strength was significantly reduced by FOX.

CONCLUSIONS

Adequate and stable dentin bonds were achieved when the bonding agents were applied on 10-3 or NI-treated dentin. None of the experimental conditioners reduced dentin elastic modulus, but dentin flexural strength was significantly reduced by FOX-conditioning.

Influence of elastic modulus mismatch between dentin and post-and-core on sequential bonding failure

PURPOSE

Clinical failures of teeth restored with post-and-core are critical issues for the survival of teeth and maintenance of oral functions. A tooth with post-and-core restoration is a complex structure. Cement adhesion is believed to be the weakest component, and breakage in this component leads to changes in stress distribution in the complex structure. The tested hypothesis was that cement breaking processes of prosthetic treated teeth were affected by elastic properties of post-and-cores.

METHODS

Finite element analysis focused on sequential adhesion failure between the dentin and cement; the penalty function method was used to analyze stress during each stage of bonding conditions. Failure patterns of adhesion and stress distribution within dentin under load of different materials of post-and-core was observed.

RESULTS

Although, an initial failure of cement was observed at the palatal crown margin regardless of the material. Different patterns of adhesion failure between dentin and post-and-cores were observed by different elastic properties of post-and-cores. Stress concentration was observed at the corresponding areas of interface between adhesion failure and continued elements using both post-and-cores.

CONCLUSIONS

Using failure criteria for cement adhesion, sequential changes of adhesion failure between dentin and post-and-cores were observed. Local stress concentrations leading to severe destruction of dentin were caused by not only materials of post-and-cores but their adhesive conditions to dentin. Nonlinear finite element analysis (FEA) using complex structure model which deals with alterations of interfacial condition between components could provide the simulation for the clinical failure of teeth restored with post-and-cores.

Cuspal Flexure and Stress in Restored Teeth Caused by Amalgam Expansion

Objective:

Cracks in amalgam-filled teeth may be related to amalgam expansion. This study measured cuspal flexure and used finite element analysis to assess associated stress levels in amalgam-filled teeth.

Methods and Materials:

External surfaces of 18 extracted molars were scanned in three dimensions. Nine molars were restored with mesio-occluso-distal amalgam fillings; the other teeth were left intact as controls. All teeth were stored in saline and scanned after two, four, and eight weeks. Cuspal flexure and restoration expansion were determined by calculating the difference between scanned surfaces. Stresses in a flexed tooth were calculated using finite element analysis.

Results:

Cusps of amalgam-filled teeth flexed outward approximately 3 μm, and restoration surfaces expanded 4 to 8 μm during storage. Cuspal flexure was significantly higher in the amalgam group (multivariate tests, p&lt;0.05), but storage time had no significant effect (repeated measures, p&gt;0.05). Expansion caused stress concentrations at the cavity line angles. These stress concentrations increased stresses due to mastication 44% to 178%.

Conclusions:

Amalgam expansion pushed cavity walls outward, which created stress concentrations at the cavity line angles. Expansion stresses can raise stresses in amalgam-filled teeth and contribute to incidentally observed cracks.

Evaluation of mold-enclosed shear bond strength between zirconia core and porcelain veneer

This study aimed to evaluate the mold-enclosed shear bond strength (ME-SBS) of zirconia to veneering porcelain with different surface treatments. Colored or uncolored zirconia coupons were either highly polished or airborne-particle abraded. The specimens were divided into groups with/without application of liner. Veneering porcelain was fired into an alumina ring mold on the zirconia coupons. The assembled specimens were subjected to the ME-SBS test. The mean ME-SBS for groups ranged from 7-10 MPa with no significant difference (p>0.05). A three-way ANOVA showed that coloring and surface roughening of the zirconia specimen had no significant influence on the ME-SBS value, but liner application exhibited a significant effect with a minor decrease in the MESBS (p=0.049). Surface treatments (coloring, airborne-particle abrasion, and liner application) were found to not cause a significant increase to the zirconia-porcelain bond strength. The application of zirconia liner had a slight negative influence on the ME-SBS results.

Relationship between mechanical properties and bond durability of short fiber-reinforced resin composite with universal adhesive

The purpose of this study was to determine the relationship between mechanical properties and bond durability of short fiber-reinforced resin composite with universal adhesive. As controls, micro-hybrid and nano-hybrid resin composites were tested. The universal adhesives used were Scotchbond Universal, Adhese Universal, and G-Premio Bond. The fracture toughness and flexural properties of resin composites, and shear bond strength and shear fatigue strength of universal adhesive with resin composite using both total-etch and self-etch modes were determined. In the results, short fiber-reinforced resin composite showed significantly higher fracture toughness than did micro-hybrid and nano-hybrid resin composites. The flexural strength and modulus of short fiber-reinforced and nano-hybrid resin composites were significantly lower than were those of micro-hybrid resin composites. Regardless of etching mode, the shear bond strength of universal adhesives with short fiber-reinforced resin composite did not show any significant differences from micro-hybrid and nano-hybrid resin composites. The shear fatigue strength of universal adhesives with short fiber-reinforced resin composite and micro-hybrid resin composites were significantly higher than that of nano-hybrid resin composites. The results of this study suggest that the mechanical properties of short fiber-reinforced resin composite improve their bond durability with universal adhesive.

Comparison of the Shear Bond Strength of Silorane-Based Composite Resin and Methacrylate Based Composite Resin to MTA

Background. Mineral trioxide aggregate (MTA) is a material that has recently gained popularity in the application of the vital pulp therapy. Along with the increasing use of MTA to this end, the permanent restoration material to be placed on MTA has become a significant issue. The aim of this in vitro study was to investigate the bond strength of the novel low-shrinkage silorane-based composite resin (SBC) to MTA.

Methods. Twenty acrylic blocks filled with MTA were prepared for this study. SBC was the test group and methacrylate-based composite resin (MBC) was used as the control group. Shear bond strength test was performed to determine the bond strength. The surfaces of broken samples were evaluated under a stereomicroscope and grouped as adhesive, cohesive and mixed. Data were examined by statistical analysis.

Results. Statistical analysis revealed that SBC exhibited higher shear bond strength than the control group. It was observed that most of the failures in the test group were of cohesive type within MTA.

Conclusion. Based on the results, SBC showed higher shear bond strength than the control group; however, clinical follow-up is needed to evaluate the clinical success.

Microshear bond strength of self-adhesive composite to ceramic after mechanical, chemical and laser surface treatments

Objectives

This study aimed to assess the microshear bond strength of a repairing self-adhesive flowable composite to ceramic after mechanical, chemical and laser treatment of the ceramic surface.

Materials and Methods

Forty zirconia and forty feldspathic ceramic blocks measuring 8 x 8 x 2 mm were fabricated. Feldspathic blocks were divided into four groups of control (1), laser (2780 nm) (2), sandblasting + hydrofluoric (HF) acid + silane (3) and laser (2780 nm) + HF acid + silane (4). Zirconia blocks were also divided into four groups of control (1), laser (2780 nm) (2), sandblasting + Z-Prime Plus (3) and laser (2780 nm) + Z-Prime Plus (4). Vertise Flow composite was bonded to treated ceramic surfaces as a repairing material, then the samples were subjected to 1000 thermal cycles. Repair bond strength was measured by Instron machine and data were analyzed using one-way ANOVA and post hoc test (P < 0.05).

Results

Maximum and minimum bond strength values were observed in zirconia-control (22.57 ± 4.76 MPa) and feldspathic-control (8.65 ± 6.41 MPa) groups, respectively. There was no significant differences between subgroups within the zirconia or feldspathic groups (P > 0.05), however the bond strength of zirconia subgroups was significantly higher than that of feldspathic subgroups.

Conclusion

Vertise Flow provides relatively good bond strength to ceramic even with no surface treatment.

Effect of thermocycling and surface treatment on repair bond strength of composite

Background

Repair of composite restorations is a conservative method that can increase the longevity and durability of restorations while preserving the tooth structure. Achieving a suitable bond between the old and new composite is difficult. To overcome this problem, some methods have been recommended to increase the repair bond strength of composite.This study aimed to assess the effect of aging by thermocycling (5,000 and 10,000 cycles) and mechanical surface treatments (Er,Cr:YSGG laser and bur) on repair shear bond strength of composite resin.

Material and Methods

Totally, 120 composite blocks measuring 6x4x4 mm were fabricated of Filtek Z250 composite and were randomly divided into three groups (n=40) based on initial aging protocol: (a) no aging: storage in distilled water at 37°C for 24 hours, (b) 5,000 thermal cycles, (c) 10,000 thermal cycles. Each group was then randomly divided into two subgroups (n=20) based on mechanical surface treatment (laser and bur). The laser and bur-prepared surfaces were silanized and Adper Single Bond 2 was then applied. The repair composite was bonded to surfaces. Half of the samples in each subgroup (n=10) were subjected to 5,000 thermal cycles to assess durability of bond. The remaining half were stored in distilled water at 37°C for 24 hours and all samples were then subjected to shear bond strength testing in a universal testing machine with a crosshead speed of 1mm/min. Data (in megapascals) were subjected to one-way ANOVA and Tukey’s test (P=0.05). Mode of failure was determined under a stereomicroscope.

Results

Bur preparation significantly improved the bond strength compared to laser (P<0.001). Aging by 10,000 thermal cycles significantly decreased the repair bond strength of composite (P<0.001). No significant difference was noted in this regard between distilled water and 5,000 thermal cycles groups (P=0.699). Primary bond strength and bond strength after 5,000 thermal cycles in the same subgroups were not significantly different either (P=0.342).

Conclusions

Aging by 10,000 thermal cycles significantly decreases the repair bond strength of composite and surface preparation by bur provides a higher bond strength compared to laser.

Key words:Thermocycling, Composite, Repair, Laser.

Bonding to Er-YAG-laser-treated Dentin

Er-YAG laser irradiation has been claimed to improve the adhesive properties of dentin. We tested the hypothesis that dentin adhesion is affected by Er-YAG laser conditioning. Superficial or deep dentin from human molars was: (a) acid-etched with 35% H3PO4; (b) irradiated with an Er-YAG laser (KaVo) at 2 Hz and 180 mJ, with water-cooling; and (c) laser- and acid-etched. Single Bond (3M ESPE) and Z100 composite (3M ESPE) were bonded to the prepared surfaces. After storage, specimens were tested in shear to failure. Bonded interfaces were demineralized in EDTA and processed for transmission electron microscopy. Two-way ANOVA revealed that conditioning treatment and interaction between treatment and dentin depth significantly influenced shear bond strength results. Acid-etching alone yielded shear bond strength values that were significantly higher than those achieved with laser ablation alone, or in combination with acid-etching. The Er-YAG laser created a laser-modified layer that adversely affects adhesion to dentin, so it does not constitute an alternative bonding strategy to conventional acid etching.

Microtensile Bond Strength and Failure Modes of Flowable Composites on Primary Dentin with Application of Different Adhesive Strategies

Background:

Resin composite is an option for the restoration of primary teeth, and new materials with simplified procedures are increasingly being suggested.

Aims:

This study aims to evaluate the microtensile bond strengths and fracture modes of flowable composites on primary dentin with application of different adhesive strategies.

Materials and Methods:

Sixty extracted noncaries primary molars were abraded from buccal surfaces to expose dentin surface. The teeth were randomly divided into three groups as follows: Group 1, Vertise™ Flow (Kerr) (self-adhering flowable composite); Group 2, G-aenial Universal Flo^® (GC Europe) (used with one-step self-etch system); Group 3, Tetric^® N-Flow (Ivoclar/Vivadent) (used with two-step total etch system). Then, the flowable composites were applied to buccal dentin surfaces with the help of guide mold. Samples were embedded in acrylic blocks and sectioned to form dentin-composite sticks with a surface area of approximately 1 mm². Finally, a total of 180 sticks were obtained to give each group of 60 sticks. Microtensile bond strengths were measured using a universal testing machine (1 mm/min). Fracture modes were evaluated with scanning electron microscopy.

Statistical Analysis:

Microtensile bond strengths data were analyzed by Kruskal–Wallis nonparametric test.

Results:

The microtensile bond strengths of G-aenial (15.5 megapascals [Mpa]) and Tetric (13.0 MPa) were statistically significant higher than Vertise (2.3 MPa). It was recorded that most of fractures in G-aenial was 40% cohesive, Tetric was 53.3% mixed, and Vertise was 83.3% adhesive.

Conclusions:

The self-adhering flowable composite Vertise™ Flow had the lowest and G-aenial Universal Flo^® had the highest microtensile bond values.

The Influence of Specimen Attachment and Dimension on Microtensile Strength

The higher microtensile bond strength values found for specimens with a smaller cross-sectional area are often explained by the lower occurrence of internal defects and surface flaws. We hypothesized that this aberrant behavior is mainly caused by the lateral way of attachment of the specimens to the testing device, which makes the strength dependent on the thickness. This study showed that composite bars of 1×1×10, 1×2×10, and 1×3×10mm attached at their 1-mm-wide side (situation A) fractured at loads of the same magnitude, as a result of which the microtensile strength (μTS), calculated as F/A (force at fracture/cross-sectional area), significantly increased for specimens with decreasing thickness. Attachment at the 1-, 2-, or 3-mm-wide side (situation B) resulted in equal μTS values (P > 0.05). Finite element analysis showed different stress patterns for situation A, but comparable patterns for situation B. Both situations showed the same maximum stress at fracture.

Effect of surface treatments on shear bond strength of resin composite bonded to CAD/CAM resin-ceramic hybrid materials

PURPOSE

The purpose of this study was to assess the effect of surface treatments on shear bond strength of resin composite bonded to thermocycled and non-thermocycled CAD/CAM resin-ceramic hybrid materials.

MATERIALS AND METHODS

120 specimens (10×10×2 mm) from each material were divided into 12 groups according to different surface treatments in combination with thermal aging procedures. Surface treatment methods were airborne-particle abrasion (abraded with 50 micron alumina particles), dry grinding (grinded with 125 µm grain size bur), and hydrofluoric acid (9%) and silane application. According to the thermocycling procedure, the groups were assigned as non-thermocycled, thermocycled after packing composites, and thermocycled before packing composites. The average surface roughness of the non-thermocycled specimens were measured after surface treatments. After packing composites and thermocycling procedures, shear bond strength (SBS) of the specimens were tested. The results of surface roughness were statistically analyzed by 2-way Analysis of Variance (ANOVA), and SBS results were statistically analyzed by 3-way ANOVA.

RESULTS

Surface roughness of GC were significantly lower than that of LU and VE (P<.05). The highest surface roughness was observed for dry grinding group, followed by airborne particle abraded group (P<.05). Comparing the materials within the same surface treatment method revealed that untreated surfaces generally showed lower SBS values. The values of untreated LU specimens showed significantly different SBS values compared to those of other surface treatment groups (P<.05).

CONCLUSION

SBS was affected by surface treatments. Thermocycling did not have any effect on the SBS of the materials except acid and silane applied GC specimens, which were subjected to thermocycling before packing of the composite resin.

A new concept and finite-element study on dental bond strength tests

OBJECTIVE

Numerous bond strength tests have been performed on dental adhesion experiments. Yet, the validity of these bond strength tests is controversial due to the name (e.g., "shear" or "tensile") may not reflect to the true and complete stress situation, i.e., assumed uniform shear or uniaxial tensile conditions. Thus, the aim of this study was to simulate and compare the stress distribution of and between shear bond strength (SBS), tensile bond strength (TBS), mold-enclosed shear bond strength (ME-SBS) and de novo lever-induced mold-enclosed shear bond strength (LIME-SBS) tests.

METHODS

3-Dimensional finite element method (FEM) was used on the dental resin-bonded surfaces (i.e., titanium alloy, dentine and porcelain) interphased with adhesive layer (thickness 5μm) to simulate the mechanical tests. For ME-SBS, both polycarbonate and stainless steel molds were used. For LIME-SBS, stainless steel levers and molds with lengths of 3mm, 6mm, 12mm, 15mm and 18mm were used. The applied loads on these models were 50N, 100N and 200N.

RESULTS

De novo LIME-SBS test was the most optimal configuration to evaluate "shear" bond strength of adhesive in regards to providing significantly high and uniform shear stress as well as eliminating tensile stress at the interface. The conventional SBS test created very high tensile stress at the load area, whereas the TBS created optimal tensile stress but shear stress indeed co-exist. The ME-SBS test could also eliminate some of the tensile stress. Similar stress distributions pattern appeared on the Ti-adhesive models, the dentine-adhesive models and porcelain-adhesive models.

SIGNIFICANCE

None of the bond strength tests could give purely "shear" or "tensile" bond strength, but LIME-SBS seems to be the best model to evaluate the bond strength under true "shear" mode.

Enamel Wetness Effects on Microshear Bond Strength of Different Bonding Agents (Adhesive Systems): An in vitro Comparative Evaluation Study

AIMS

The purpose of this study was to compare the effect of enamel wetness on microshear bond strength using different adhesive systems.

OBJECTIVES

To evaluate microshear bond strength of three bonding agents on dry enamel; to evaluate microshear bond strength of three bonding agents on wet enamel; and to compare microshear bond strength of three different bonding agents on dry and wet enamel.

MATERIALS AND METHODS

Sixty extracted noncarious human premolars were selected for this study. Flat enamel surfaces of approximately 3 mm were obtained by grinding the buccal surfaces of premolars with water-cooled diamond disks. This study evaluated one etch-and-rinse adhesive system (Single Bond 2) and two self-etching adhesive systems (Clearfil SE Bond and Xeno-V). The specimens were divided into two groups (n = 30). Group I (dry) was air-dried for 30 seconds and in group II (wet) surfaces were blotted with absorbent paper to remove excess water. These groups were further divided into six subgroups (n = 10) according to the adhesives used. The resin composite, Filtek Z 250, was bonded to flat enamel surfaces that had been treated with one of the adhesives, following the manufacturer's instructions. After being stored in water at 37°C for 24 hours, bonded specimens were stressed in universal testing machine (Fig. 3) at a crosshead speed of 1 mm/min. The data were evaluated with one-way and two-way analysis of variance (ANOVA), t-test, and Tukey's Multiple Post hoc tests (a = 0.05).

RESULTS

The two-way ANOVA and Tukey's Multiple Post hoc tests showed significant differences among adhesive systems, but wetness did not influence microshear bond strength (p = 0.1762). The one-way ANOVA and t-test showed that the all-in-one adhesive (Xeno-V) was the only material influenced by the presence of water on the enamel surface. Xeno-V showed significantly higher microshear bond strength when the enamel was kept wet. Single Bond 2 adhesive showed significantly higher microshear bond strength as compared with Xeno-V adhesive but no significant difference when compared with Clearfil SE Bond adhesive in dry enamel. Single Bond 2 adhesive showed no significant difference in microshear bond strength as compared with self-etching adhesive systems (Clearfil SE Bond and Xeno-V), when the enamel was kept wet.

CONCLUSION

From the findings of the results, it was concluded that self-etching adhesives were not negatively affected by the presence of water on the enamel surface.

CLINICAL SIGNIFICANCE

The all-in-one adhesive showed different behavior depending on whether the enamel surface was dry or wet. So the enamel surface should not be desiccated, when self-etching adhesives are used.

Fractography of interface after microtensile bond strength test using swept-source optical coherence tomography

OBJECTIVE

To determine the effect of crosshead speed and placement technique on interfacial crack formation in microtensile bond strength (MTBS) test using swept-source optical coherence tomography (SS-OCT).

MATERIALS AND METHODS

MTBS test beams (0.9×0.9mm(2)) were prepared from flat human dentin disks bonded with self-etch adhesive (Clearfil SE Bond, Kuraray) and universal composite (Clearfil AP-X, Kuraray) with or without flowable composite lining (Estelite Flow Quick, Tokuyama). Each beam was scanned under SS-OCT (Santec, Japan) at 1319nm center wavelength before MTBS test was performed at crosshead speed of either 1 or 10mm/min (n=10). The beams were scanned by SS-OCT again to detect and measure cracks at the debonded interface using digital image analysis software. Representative beams were observed under confocal laser scanning microscope to confirm the fractography findings.

RESULTS

Two-way ANOVA showed that for MTBS the crosshead speed was not a significant factor (p>0.05), while there was a difference between placement techniques (p<0.001), with flowable lining yielding higher mean values. On the other hand, for crack formation, there was a significant difference between crosshead speeds (p<0.01), while the placement technique did not show up as a statistically significant factor (p>0.05). The interaction of factors were not significant (p>0.05).

SIGNIFICANCE

Testing MTBS samples at higher crosshead speeds induced more cracks in dentin. Lining with a flowable composite improved the bonding quality and increased the bond strength. SS-OCT can visualize interfacial cracks after restoration debonding.

Bonding performance and interfacial characteristics of short fiber-reinforced resin composite in comparison with other composite restoratives

The purpose of this study was to investigate the shear bond strength (SBS) and surface free-energy (SFE) of short fiber-reinforced resin composite (SFRC), using different adhesive systems, in comparison with other composite restoratives. The resin composites used were everX Posterior (EP), Clearfil AP-X (CA), and Filtek Supreme Ultra Universal Restorative (FS). The adhesive systems used were Scotchbond Multi-Purpose (SM), Clearfil SE Bond (CS), and G-Premio Bond (GB). Resin composite was bonded to dentin, and SBS was determined after 24 h of storage in distilled water and after 10,000 thermal cycles (TCs). The SFEs of the resin composites and the adhesives were determined by measuring the contact angles of three test liquids. The SFE values and SFE characteristics were not influenced by the type of resin composite, but were influenced by the type of adhesive system. The results of this study suggest that the bonding performance and interfacial characteristics of SFRC are the same as for other composite restoratives, but that these parameters are affected by the type of adhesive system. The bonding performance of SFRC was enhanced by thermal cycling in a manner similar to that for other composite restoratives.

Effect of Restorative Protocol on Cuspal Strain and Residual Stress in Endodontically Treated Molars

Objectives

To evaluate the effect of the restorative protocol on cuspal strain, fracture resistance, residual stress, and mechanical properties of restorative materials in endodontically treated molars.

Methods

Forty-five molars received mesio-occlusal-distal (MOD) Class II preparations and endodontic treatment followed by direct restorations using three restorative protocols: composite resin (CR) only (Filtek Supreme, 3M-ESPE), resin modified glass ionomer cement in combination with CR (Vitremer, 3M-ESPE in pulp chamber and Filtek Supreme in MOD cavity), conventional glass ionomer cement in combination with composite resin (CGI-CR) (Ketac Fil, 3M-ESPE in pulp chamber and Filtek Supreme in MOD cavity). Cuspal strain was measured using strain gauges, and fracture resistance was tested with an occlusal load. Elastic modulus (EM) and Vickers hardness (VH) of the restorative materials were determined at different depths using dynamic microhardness indentation. Curing shrinkage was measured using the strain gauge technique. The restorative protocols were also simulated in finite element analysis (FEA). The shrinkage strain, cuspal strain, EM, VH, and fracture resistance data were statistically analyzed using split-plot analysis of variance and Tukey test (p=0.05). Residual shrinkage stresses were expressed in modified von Mises equivalent stresses.

Results

Shrinkage strain values (in volume %) were Ketac Fil (0.08±0.01) &lt; Vitremer (0.18±0.01) &lt; Filtek Supreme (0.54±0.03). Cuspal strain was higher and fracture resistance was lower when using CR only compared with the techniques that used glass ionomer. The EM and VH of the materials in the pulp chamber were significantly lower for glass ionomer. The FEA showed that using CR only resulted in higher residual stresses in enamel and root dentin close to the pulp chamber than the combinations with glass ionomers (RMGI-CR and CGI-CR).

Conclusions

The choice of restorative protocol significantly affected the biomechanical behavior of endodontically treated molars. Using glass ionomer to fill the pulp chamber is recommended when endodontically treated molars receive direct composite restorations because it reduces cuspal strain and increases fracture resistance.

Comparison of two test designs for evaluating the shear bond strength of resin composite cements

OBJECTIVE

To compare a shear bond strength test for resin composite cements developed in order to better consider the shrinkage stress (here termed "Swiss shear test") with the shear test design according to ISO 29022.

METHOD

Four restorative materials (VITA Enamic (VE), VITA Suprinity (VS), Vitablocs Mark II (VM) and VITA YZ T (YZ)) served as substrate. VE, VS and VM were polished or etched. YZ was polished, sandblasted or etched. Specimens were either bonded according to the Swiss or the ISO shear test. RelyX Unicem 2 Automix, Maxcem Elite and PermaFlo DC were used as cements. Shear bond strength (SBS) was measured. Failure modes (adhesive, cohesive or mixed) were evaluated by means of SEM.

RESULTS

Mean SBS values obtained with the Swiss shear test were significantly lower than those obtained with the ISO shear test. VE and VM exhibited similar SBS, values of VS were significantly higher. On etched surfaces VM and VE exhibited primarily cohesive failures, VS primarily adhesive failures. On polished substrates significantly lower bond strength values and exclusively adhesive failures were observed. YZ exhibited solely adhesive failures. Compared to polished YZ, SBS significantly increased after sandblasting and even more after etching. Only for adhesively failed specimens mean SBS values of Swiss and ISO shear test were strongly correlated.

SIGNIFICANCE

Both test designs showed the same ranking of test results. When adhesive failure occurred test results were strongly correlated. When cohesive failure was involved, both test designs did not provide reliable results.

Evaluation of shear bond strength of veneering ceramics and zirconia fabricated by the digital veneering method

PURPOSE

The purpose of this study was to evaluate the shear bond strength (SBS) of veneering ceramic and zirconia fabricated by the digital veneering method.

METHODS

A total of 50 specimens were fabricated, i.e., 10 specimens each for the metal-ceramic (control) group and the four zirconia groups. The zirconia groups comprised specimens fabricated by the digital veneering method, the heat pressing method, and hand layering method for two groups, respectively. Furthermore, the shear bond strength was measured with a universal testing machine (Model 3345, Instron, Canton, MA, USA) and statistically analyzed using one-way ANOVA set at a significance level of P<0.05. The corresponding mode of failure was determined from Scanning Electron Microscope (FESEM JSM 6701F, Jeol Ltd., Japan) observations.

RESULTS

One-way analysis of variance (ANOVA) revealed that the metal-ceramic group had the highest SBS (43.62MPa), followed by the digital veneering method (28.29MPa), the heat pressing method (18.89MPa), and the layering method (18.65, 17.21MPa). The samples fabricated by digital veneering had a significantly higher SBS than the other zirconia samples (P<0.05). All of the samples exhibited mixed failure.

CONCLUSIONS

Veneering ceramic with a zirconia core that was fabricated via the digital veneering method is believed to be effective in clinical use since, its shear bond strength is significantly higher than that resulting from the conventional method.

Failure Strengths of Composite Additions and Repairs

Purpose

When adding composite to a cured composite restoration, the intent is to achieve the same failure strength as the original restorative material. This study evaluated the failure strengths of added or repaired composite using various chemical and/or mechanical surface treatments.

Methods

Failure strengths were determined using a four-point bending test. Beam-shaped specimens were fabricated by adding new composite to cured composite (Filtek Supreme Ultra). The cured composites were either fresh or aged seven days (N=10-14). The composite surfaces were left unground or were ground before treatment with various combinations of roughening, acid etching, silane, and dental adhesives (conventional Adper SingleBond Plus or new multimode Scotchbond Universal) and/or tribochemistry (CoJet system). Monolithic composite specimens were the control. Failure strengths were statistically analyzed using one-way analysis of variance and the Fisher protected least significant difference (α=0.05).

Results

Failure strengths (mean ± standard deviation) when composite was added to unground freshly cured composites (111±25 MPa) and aged composites using a new multimode adhesive with (102±22 MPa) or without (98±22 MPa) tribochemical treatment were not significantly lower than the monolithic specimens (122±23 MPa). Grinding the surfaces of freshly cured composite significantly reduced failure strength, either with (81±30 MPa) or without (86±31 MPa) use of conventional adhesive. Failure strengths of aged composites were also significantly lower (51±21 MPa with SingleBond Plus), even after tribochemical treatment (71±29 MPa with SingleBond Plus; 73±35 MPa with Silane-Visiobond).

Conclusions

Using a new multimode adhesive when adding composite to freshly cured or aged composite substrates recovered the failure strength to that of the original monolithic composite.

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.

A critical evaluation of bond strength tests for the assessment of bonding to Y-TZP

OBJECTIVES

To compare three different designs for measuring the bond strength between Y-TZP ceramic and a composite material, before and after ceramic surface treatment, evaluating the influence of the size of the adhesive interface for each design.

METHODS

'Macro' tensile, microtensile, 'macro' shear, microshear, 'macro' push-out, and micropush-out tests were carried out. Two Y-TZP surface treatments were evaluated: silanization (sil) and tribochemical silica coating (30μm silica-modified Al2O3 particles+silanization) (TBS). Failure mode analysis of tested samples was also performed.

RESULTS

Both the surface treatment and the size of the bonded interface significantly affected the results (p=0.00). Regardless of the type of surface treatment, the microtensile and microshear tests had higher values than their equivalent "macro" tests. However, the push-out test showed the highest values for the "macro" test. The tensile tests showed the greatest variability in results. The tribochemical silica coating method significantly increased bond strength for all tests.

SIGNIFICANCE

Different test designs can change the outcome for Y-TZP/cement interfaces, in terms of mean values and reliability (variability). The 'micro' tests expressed higher bond strengths than their equivalent 'macro' tests, with the exception of the push-out test (macro>micro).