Correlation between degree of conversion,resin–dentin bond strength and nanoleakage of simplified etch-and-rinse adhesives

Objectives

The aim of this study was to correlate the degree of conversion measured inside the hybrid layer (DC) with the microtensile resin–dentin bond strength (μTBS) and silver nitrate uptake or nanoleakage (SNU) for five simplified etch-and-rinse adhesive systems.

Methods

Fifty-five caries free extracted molars were used in this study. Thirty teeth were used for μTBS/SNU [n = 6] and 25 teeth for DC [n = 5]. The dentin surfaces were bonded with the following adhesives: Adper Single Bond 2 (SB), Ambar (AB), XP Bond (XP), Tetric N-Bond (TE) and Stae (ST) followed by composite resin build-ups. For μTBS and SNU test, bonded teeth were sectioned in order to obtain stick-shaped specimens (0.8 mm²), which were tested under tensile stress (0.5 mm/min). Three bonded sticks, from each tooth, were not tested in tensile stress and they were immersed in 50% silver nitrate, photo-developed and analyzed by scanning electron microscopy. Longitudinal 1-mm thick sections were prepared for the teeth assigned for DC measurement and evaluated by micro-Raman spectroscopy.

Results

ST showed lowest DC, μTBS, and higher SNU (p < 0.05). All other adhesives showed similar DC, μTBS, and SNU (p > 0.05), except for TE which showed an intermediate SNU level. The DC was positively correlated with μTBS and negatively correlated with SNU (p < 0.05). SNU was also negatively correlated with μTBS (p < 0.05).

Significance

The measurement of DC inside the hybrid layer can provide some information about bonding performance of adhesive systems since this property showed a good correlation with resin–dentin bond strength and SNU values.     

Effect of sonic application mode on the resin–dentin bond strength and nanoleakage of simplified self-etch adhesive

Objectives

This study aims to evaluate the effect of different application modes on the immediate and 6-month resin–dentin bond strength (μTBS) and nanoleakage in the hybrid and adhesive layers.

Materials and methods

Three 1-step self-etch adhesives (One Coat 7.0 (OC), Clearfil S³ Bond (CS), and FuturaBond NR (FB)) were applied on a flat superficial dentin surface of 30 human molars under manual mode or sonic vibration at a frequency of 170 Hz (SV). Composite build-ups were constructed incrementally; specimens were sectioned to obtain resin–dentin sticks with cross-sectional area of 0.8 mm² and tested in tension (0.5 mm/min) immediately (IM) or after 6 months (6M) of water storage. Two bonded sticks, from each tooth at each storage time, were immersed in a silver nitrate solution, photo-developed, and analyzed under scanning electron microscopy. The amount of nanoleakage was measured using the ImageTool 3.0 software. Data, from each adhesive, were analyzed by two-way ANOVA and Tukey’s test (α?=?0.05).

Results

OC and CS showed higher μTBS and lower nanoleakage in the IM period when applied with SV groups. For FB, no significant difference was observed between the two modes of application. All materials showed lower nanoleakage in the SV groups. Higher nanoleakage was observed after 6M for OC and FB.

Conclusions

The sonic application mode at an oscillating frequency of 170 Hz can improve the resin–dentin μTBS, reduce the nanoleakage, and retard the degradation of the resin–dentin μTBS of Clearfil S³ Bond and One Coat 7.0 adhesives.

Clinical significance

Sonic application mode at an oscillating frequency of 170 Hz can be helpful and easy to use in dental practice to guaranty long-lasting restorations.     

Effects of air polishing on the resin composite–dentin interface

The aim of this study was to examine defect depths and volumes at the resin composite–dentin (R/D) interface after air polishing with different particles and spray angles. Samples were 54 dentin specimens that were formed in saucer-shaped cavities filled with resin composite. Each specimen was air polished with either sodium bicarbonate (NaHCO₃) or one of two glycine (Gly) powders. The air polisher was set at angles of 90° to the interface and at 45° to the interface from both the dentin and resin composite sides. Air polishing with Gly powder produced defects with less depth and volume than NaHCO₃ powder (p < 0.05). Air polishing with a spray angle of 45° to the interface from the resin composite side produced fewer defects (p < 0.05) than polishing from the dentin side. Air polishing to the R/D interface from the resin composite side produced fewer defects to the interface because the hardness of the resin composite was higher than that of dentin.     

Load cycling enhances bioactivity at the resin–dentin interface

Objectives

The purpose of this study was to evaluate if mechanical loading promotes bioactivity at the resin interface after bonding with three different adhesive approaches.

Methods

Dentin surfaces were subjected to three different treatments: demineralisation by (1) 37% phosphoric acid (PA) followed by application of an etch-and-rinse dentin adhesive Single Bond (SB) (PA + SB), (2) by 0.5 M ethylenediaminetetraacetic acid (EDTA) followed by SB (EDTA + SB), (3) application of a self-etch dentin adhesive: Clearfil SE Bond (SEB). Bonded interfaces were stored in simulated body fluid during 24 h or 3 w. One half of each tooth was submitted to mechanical loading. Remineralisation of the bonded interfaces was assessed by AFM imaging/nano-indentation, Raman spectroscopy/cluster analysis, dye assisted confocal microscopy evaluation (CLSM) and Masson's trichrome staining.

Results

Loading cycling for 3 w promoted an increase of mechanical properties at the resin–dentin interface. Cluster analysis demonstrated an augmentation of the mineral–matrix ratio in SB-loaded specimens. CLSM showed an absent micropermeability and nanoleakage after loading EDTA + SB and SEB specimens. Trichrome staining reflected a narrow demineralised dentin matrix after loading, almost not observable in EDTA + SB and SEB.

Significance

In vitro mechanical loading promoted mineralization in the resin–dentin interfaces, at 24 h and 3 w of storage.     

Do blood contamination and haemostatic agents affect microtensile bond strength of dual cured resin cement to dentin?

Objective:

The purpose of this study was to evaluate the effects of blood contamination and haemostatic agents such as Ankaferd Blood Stopper (ABS) and hydrogen peroxide (H₂O₂) on the microtensile bond strength between dual cured resin cement-dentin interface.

Material and Methods:

Twelve pressed lithium disilicate glass ceramics were luted to flat occlusal dentin surfaces with Panavia F under the following conditions: Control Group: no contamination, Group Blood: blood contamination, Group ABS: ABS contamination Group H₂O₂: H₂O₂ contamination. The specimens were sectioned to the beams and microtensile testing was carried out. Failure modes were classified under stereomicroscope. Two specimens were randomly selected from each group, and SEM analyses were performed.

Results:

There were significant differences in microtensile bond strengths (µTBS) between the control and blood-contaminated groups (p<0.05), whereas there were no significant differences found between the control and the other groups (p>0.05).

Conclusions:

Contamination by blood of dentin surface prior to bonding reduced the bond strength between resin cement and the dentin. Ankaferd Blood Stoper and H₂O₂ could be used safely as blood stopping agents during cementation of all-ceramics to dentin to prevent bond failure due to blood contamination.     

Effect of different surface treatments on the composite–composite repair bond strength

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

Do intact collagen fibers increase dentin bond strength?

The purpose of the present study was to evaluate surface morphology and shear bond strength of All Bond 2 bonded to dentin surfaces, that were treated progressively to remove collagen fibers. For the study of surface morphology, fifteen teeth were divided in to five groups. Dentin surfaces in groups 1-4 were etched either with 24% EDTA for 30 seconds or 32% phosphoric acid for 15 seconds with and without subsequent treatment with 10% NaOCl for 60 seconds. Group 5 received no treatment and served as control. Evaluation was performed using scanning electron microscopy. Thirty teeth were used for the shear bond strength test. Two experimental surfaces were prepared on each tooth and cylindrical copper matrixes were attached to the surfaces. Experimental surfaces were divided into four groups and treated in the same way as group 1-4 in the morphology part of the study. Dentin was bonded with All Bond 2, after which a flowable composite was inserted and light cured. Shear strength test was performed at a crosshead speed of 1 mm/minute until the composite debonded. Results showed that etching followed by treatment with NaOCl removed all collagen fibers from the dentin surfaces, while treatment with EDTA alone denuded the fiber structures. Shear strength was significantly decreased when surfaces were treated with NaOCl. The highest shear strength values were obtained in the EDTA etched group. The results from the present study indicate that exposed dentin associated collagen fibers increases adhesion of All Bond 2 to dentin.     

Chemical,microbial, and host-related factors: effects on the integrity of dentin and the dentin–biomaterial interface

Dentin is the largest substrate available whenever restorative procedures are implemented on the exposed crown or root of teeth. In endodontics, restorative/obturating procedures are practically restricted to dentin. It is well recognized that the incidence of fracture in endodontically treated teeth is intrinsically related to the amount of remaining dentin. Ideally, it is expected that a gap-free, solid interface can be formed between the restorative/obturating materials and root dentin, providing an impervious seal and, simultaneously, fracture resistance to root-filled teeth. Over the past years, a number of new obturating biomaterials have been launched in the market, bringing to endodontists the expectation of achieving consistent sealing/reinforcing of the root canal system. However, the successful sealing of root dentin remains one of the greatest challenges in restorative dentistry. This article will focus on reviewing some factors that affect the formation and integrity of dentin–biomaterial interfaces from the perspective of the dentin substrate. Because other articles in preceding issues of Endodontic Topics have already covered dentin structure and composition, the objective here is not to review these aspects. Specific attention is given, however, to depicting how chemical treatments affect existing root filling/restorative mechanisms and how some microbial and host-related aspects can compromise the interaction of dentin with new biomaterials.     

Effect of tin–chloride pretreatment on bond strength of two adhesive systems to dentin

Objectives

To determine the effect on resin composite-to-dentin bond strength of incorporation of an acidic tin–chloride pretreatment in two adhesive systems.

Materials and methods

Human molars were ground to expose mid-coronal dentin. For microtensile bond strength (μTBS) testing, dentin was treated with Optibond FL or Clearfil SE according to one of six protocols (n?=?22/group). Group 1: Phosphoric acid etching, Optibond FL Prime, Optibond FL Adhesive (manufacturer’s instructions; control); Group 2: Tin–chloride pretreatment, Optibond FL Prime, Optibond FL Adhesive; Group 3: Phosphoric acid etching, tin–chloride pretreatment, Optibond FL Prime, Optibond FL Adhesive; Group 4: Clearfil SE Primer, Clearfil SE Bond (manufacturer’s instructions; control); Group 5: Phosphoric acid etching, Clearfil SE Primer, Clearfil SE Bond; and Group 6: Tin–chloride pretreatment, Clearfil SE Primer, Clearfil SE Bond. The molars were then built up with resin composite (Clearfil Majesty Esthetic). After storage (1 week, 100  % humidity, 37 °C) the μTBS was measured and failure mode was determined. Additionally, pretreated dentin surfaces were evaluated using SEM and EDX. The μTBS results were analyzed statistically by a Welch Two Sample t-test and a Kruskal–Wallis test followed by exact Wilcoxon rank sum tests with Bonferroni–Holm adjustment for multiple testing (α?=?0.05).

Results

When Optibond FL was used, partial or total replacement of phosphoric acid with tin–chloride decreased μTBS significantly. In contrast, when Clearfil SE was used, inclusion of a tin–chloride pretreatment in the adhesive procedure increased μTBS significantly.

Conclusions

Tin–chloride pretreatment had a beneficial influence on the bond promoting capacity of the MDP-containing adhesive system Clearfil SE.     

Optical and mechanical factors in the temporal development of tooth–composite bond

ObjectivesTo obtain an accurate picture of the temporal development of bond strength between resin composites and tooth structures during cure for assessing debonding at the tooth–composite interface.MethodsAn assembly of uncured composite sandwiched between a glass block and a dentin slab with a layer of pre-cured adhesive was used in this study. A conventional composite was compared against a bulk-fill composite. The rate of bond formation was determined by measuring the tensile bond strength of specimens of different thicknesses at different time points during cure. The changing light irradiance exiting the composite as it cured was also recorded. Mode of fracture was analyzed by examining the fracture surfaces.ResultsPhoto-bleaching occurred in both resin composites. The development of the dentin–composite bond strength was initially dictated by the developing cohesive strength of the resin composite, and its final value was capped by the strength of the preformed dentin–adhesive bond. The higher interfacial irradiance in the bulk-fill composite did not lead to faster development of the overall bond strength. This was caused by its slower rate of cohesive strength development as reflected in the longer time for its interfacial irradiance to plateau and the greater proportion of cohesive failure seen in the initial stage of polymerization. The law of reciprocity did not hold for the development of dentin bond strength.SignificanceThe results from this study, when compared with the development of shrinkage stress, can be used as a basis for ensuring the integrity of the dentin–composite interface during cure.     

Effect of conditioning and 1 year aging on the bond strength and interfacial morphology of glass-ionomer cement bonded to dentin

ObjectiveThe purpose of this study was to determine the bond stability and the change in interfacial ultra-structure of a conventional glass-ionomer cement bonded to dentin, with and without pre-treatment using a polyalkenoic acid conditioner.MethodsThe occlusal dentin surfaces of six teeth were ground flat. Glass-ionomer cement was bonded to the surfaces either with or without polyalkenoic acid conditioning. The teeth were sectioned into 1-mm² stick-shaped specimens. The specimens obtained were randomly assigned to two groups with different periods of storage in water: 1 week and 1 year. The micro-tensile bond strength (μTBS) was determined for each storage time. Additional specimens were prepared for Transmission Electron Microscopy (TEM); they were produced with or without prior polyalkenoic acid conditioning in the same way as in the μTBS test.ResultsThere was no significant difference in μTBS to conditioned dentin and non-conditioned dentin (p > 0.05). The failures appeared to be of a mixed nature, although aging caused more areas of cohesive than adhesive failure in both groups. The TEM observation showed an intermediate layer, a matrix-rich layer and a partially demineralized layer in the polyalkenoic acid conditioned group.SignificanceAging did not reduce the bond strength of the conventional glass-ionomer cement to dentin with or without the use of a polyalkenoic acid conditioner.     

Does the thickness of the resin cement affect the bond strength of a fiber post to the root dentin?

This study aimed to evaluate the influence of cement thickness on the bond strength of a fiber-reinforced composite (FRC) post system to the root dentin. Eighteen single-rooted human teeth were decoronated (length: 16 mm), the canals were prepared, and the specimens were randomly allocated to 2 groups (n = 9): group 1 (low cement thickness), in which size 3 FRC posts were cemented using adhesive plus resin cement; and group 2 (high cement thickness), in which size 1 FRC posts were cemented as in group 1. Specimens were sectioned, producing 5 samples (thickness: 1.5 mm). For cement thickness evaluation, photographs of the samples were taken using an optical microscope, and the images were analyzed. Each sample was tested in push-out, and data were statistically analyzed. Bond strengths of groups 1 and 2 did not show significant differences (P = .558), but the cement thicknesses for these groups were significantly different (P < .0001). The increase in cement thickness did not significantly affect the bond strength (r2 = 0.1389, P= .936). Increased cement thickness surrounding the FRC post did not impair the bond strength.     

Do the origins of primary teeth affect the bond strength of a self-etching adhesive system to dentin?

The aim of this in vitro study was to evaluate the tensile bond strength of a self-etching adhesive system to three different dentinal substrates. Primary molar teeth that had been recently exfoliated (RE), with unknown time of exfoliation (UT), and extracted due to prolonged retention (PR) were used for this investigation. Ten primary molar teeth of each group were cut in the middle following the mesio-distal direction, creating a total of twenty specimens per group. The specimens were included in acrylic resin and had a flat dentin surface exposed. The self-etching adhesive system was applied to this surface and a 3-millimeter high cone with diameter of 2 mm in the adhesion area was constructed using composite resin. The specimens were stored in distilled water at 37oC for 24 hours. Fifteen specimens of each substrate were used for the tensile bond test (n = 15) and 5 had the interface analyzed by scanning electron microscopy (SEM). The data was examined by one-way ANOVA and presented no significant differences between groups (p = 0.5787). The mean values obtained for RE, UT and PR were 18.39 ± 9.70, 19.41 ± 7.80, and 23.30 ± 9.37 MPa, respectively. Any dentinal substrates of primary teeth studied are safe for tensile bond strength tests with adhesive systems.     

Repair bond strength of restorative resin composite applied to fiber‐reinforced composite substrate

Delamination or fracture of composite veneers can occur as a result of improper design of the fiber‐reinforced composite (FRC) framework. This in vitro study tested the repair bond strength of restorative composite to aged FRC. The substrate was multiphase polymer matrix FRC (everStick) aged by boiling for 8 h and storing at 37°C in water for 6 weeks. The aged substrate surfaces were wet‐ground flat with 1200‐grit silicon carbide paper and subjected randomly to 5 different surface treatments: 1) An adhesion primer (Composite Activator) and resin (CA), 2) Silane (EspeSil) and resin (SIL‐MP), 3) Silane, adhesive primer, and resin (Clearfil Repair) (CF), 4) Air particle‐abrading (CoJet), silane, and resin (CJ‐SIL‐MP), 5) Resin (Scotchbond Multipurpose Resin) only as control (MP). Restorative composite resin (Z250) was added to the substrate in 2 mm layer increments and light‐cured. Subsequently, every surface treatment group was divided into 2 subgroups of 12 specimens each. The specimens were either 48 h water‐stored or thermocycled (6000 x 5–55°C). The shear bond strengths of composite resin to FRC were measured at a crosshead speed of 1.0 mm/min. The data were analyzed by ANOVA for factors ‘treatment type’ and ‘storage condition’; Tukey's post‐hoc tests and Weibull analysis were performed. ANOVA showed a significant difference as a function of surface treatment (P<0.05) and storage condition (P<0.05). The CJ‐SIL‐MP group showed highest bond strength and Weibull modulus after thermocycling. Repair of multiphase polymer matrix FRC may show reliable bond strength when silane treatment is used along with air‐particle abrading.     

Relationship between the canthal–tragus distance and the puncture point in temporomandibular joint arthroscopy

This study investigated whether a relationship exists between the length of the canthal–tragus line and the distance from the tragus at which the puncture point for arthroscope insertion should be made. On one side of 11 cadaver heads, a puncture point was marked 7 mm from the midtragus and 2 mm below the canthal–tragus line. On the other side, the distances were 10 mm and 2 mm, respectively. The arthroscope trocar and cannula were inserted at the marked points. The anatomical location of the arthroscope after insertion was confirmed by open dissection with the arthroscope in place. Following dissection, the canthal–tragus line was measured on each side of the cadaver's head. For measurements >70 mm, puncture points 10 mm from the midtragus led to insertion of the arthroscope inside the upper joint compartment. For measurements ≤70 mm, puncture points 7 mm from the midtragus led to insertion of the arthroscope inside the upper joint compartment. This suggests that for canthal–tragus distances of >70 mm, the arthroscope should be inserted 10 mm from the midtragus and for distances ≤70 mm it should be inserted at 7 mm for the greatest likelihood of entering the upper joint compartment of the TMJ.