Fluid movement across the resin-dentin interface during and after bonding

Immediate Dentin Sealing for Adhesive Cementation of Indirect Restorations: A Systematic Review and Meta-Analysis

Immediate dentin sealing (IDS) involves applying an adhesive system to dentin directly after tooth preparation, before impression. This was considered an alternate to delayed dentin sealing (DDS), a technique in which hybridization is performed following the provisional phase and just before the indirect restoration luting procedure. This study aimed to compare the bond strength of restorations to dentin of the IDS and the DDS techniques throughout a systematic review and meta-analysis. The following PICOS framework was used: population, indirect restorations; intervention, IDS; control, DDS; outcomes, bond strength; and study design, in vitro studies. PubMed (MedLine), The Cochrane Library, ISI Web of Science, Scielo, Scopus, and Embase were screened up to January 2022 by two reviewers (L.H. and R.B.). In vitro papers studying the bond strength to human dentin of the IDS technique compared to the DDS technique were considered. Meta-analyses were carried out by using a software program (Review Manager v5.4.1; The Cochrane Collaboration). Comparisons were made by considering the adhesive used for bonding (two-step etch-and-rinse, three step etch-and-rinse, one-step self-etch, two-step self-etch, and universal adhesives). A total of 3717 papers were retrieved in all databases. After full-text assessment, 22 potentially eligible studies were examined for qualitative analysis, leaving a total of 21 articles for the meta-analysis. For the immediate bond strength, regardless of the adhesive strategy used, the IDS technique improved the bond strength of restorations to the dentin (p < 0.001). Taking into account the subgroup analysis, it seems that the use of the IDS technique with a two-step etch-and-rinse or a one-step self-etch adhesive system does not represent any advantage over the DDS technique (p = 0.07, p = 0.15). On the other hand, for the aged bond strength, regardless of the adhesive strategy used, the IDS technique improved the bond strength of restorations to the dentin (p = 0.001). The subgroups analysis shows that this improvement is observed only when a three-step etch-and-rinse adhesive system (p < 0.001) or when a combination of an adhesive system plus a layer of flowable resin (p = 0.01) is used. The in vitro evidence suggests that the use of the IDS technique improves the bond strength of dentin to resin-based restorations regardless of the adhesive strategy used. The use of a three-step etch-and-rinse adhesive system or the combination of an adhesive system plus a layer of flowable resin seems to considerably enhance the bond strength in the long term.

Evaluation of shear bond strength of various adhesives under Simulated intrapulpal pressure: An in vitro study

Introduction:

The presence of pulpal fluid can influence dentin bonding. This study aimed to evaluate the shear bond strength of universal dental adhesives under simulated intrapulpal pressure.

Materials and Methods:

Forty intact maxillary premolars were distributed into four groups (Group 1 – 3M ESPE Adper Single Bond 2 total etch adhesive, Group 2 – 3M ESPE Single Bond Universal, Group 3 – Prime and Bond universal adhesive, and Group 4 – Ivoclar Tetric N Bond Universal). Adhesive restorative procedures were carried under intrapulpal pressure simulation following which it was subjected to a shear load of 0.5 mm/min. Fracture mode analysis was performed using a stereomicroscope. The data obtained were subjected to ANOVA and Tukey post hoc test with a P < 0.05.

Results:

Highest bond strength was exhibited by Group 3 (7.01 ± 2.02 MPa) and least by Group 1 (5.36 ± 3.03 MPa). However, there were no statistical differences among the groups. Group 1 and 2 showed mostly cohesive failure, whereas Group 3 and 4 showed mixed failure.

Conclusion:

The results demonstrated that the experimental universal adhesive agents exhibited comparative shear bond strength when subjected to pulpal pressure. Pulpal pressure has a significant effect on bond strength.

Comparing the Ability of Various Resin-Based Composites and Techniques to Seal Margins in Class-II Cavities

Background: Resin-based composites (RBCs) provide excellent esthetics but the marginal micro-leakage in the proximal cavities remains a major concern. The aim of the present study was to assess the ability of various dental RBCs and techniques utilized for sealing deep dentin margin in class-II cavities. Methods: Box-cavities (class-II) on the distal and mesial surfaces of extracted (premolar) teeth were prepared with a gingival margin placed 1mm apical to the cemento-enamel junction. Teeth with prepared class II cavities were randomly divided into four study groups according to the type of restorative materials (conventional RBC; bulk-fill RBC; conventional RBC lined with flowable RBC and conventional RBC lined with resin-modified glass-ionomer-cement (GIC) as open sandwich-technique). Each group was further subdivided into a total-etch subgroup in which a separate etching step was performed before applying the bonding agent and a self-etch subgroup in which a self-etch adhesive system was used (n = 10). For each group, cavities were restored using the respective restorative materials and techniques, subjected to 1000 thermocycles, and placed in the methylene-blue dye. The specimen teeth were sectioned for further microscopic examination for micro-leakage. Results: The least dye penetration values were reported for group 4 (GIC) followed by the group Bulk-fill using the self-etch adhesive system (group 2b). The highest dye penetration was reported for the group Bulk-fill using the total-etch adhesive system (2a), followed by the group conventional RBC using the total-etch adhesive system). The total-etch adhesive system had significantly greater micro-leakage compared to the self-etch adhesive system (1a) (p = 0.026). Conclusions: The self-etch adhesive system significantly reduced the micro-leakage compared to the total-etch system. Bulk-fill RBC when bonded with the self-etch adhesive provided good marginal sealing ability comparable to open sandwich-technique using GIC.

Development of dental inspection method: Nondestructive evaluation of an adhesive interface by ACTIVE acoustic emission

PURPOSE

This study aims to confirm the usefulness of active acoustic emission (Active AE) for reproducible and non-invasive generation of physical external force which is required for conventional AE.

METHODS

Experiment 1: A root dentin-resin adhesive interface was observed. The post space was filled with a dual-cure resin composite core material with and without adhesive. The vibration characteristics of the data obtained from the time-frequency analysis were evaluated. Experiment 2: A crown-abutment tooth adhesive interface was observed. Adhesive resin cement was used for luting the crown and adhesion states in the same specimen over time were analyzed with three measurements: at trial-fitting, immediately after luting, and 2 weeks after luting. Data were subjected to time-frequency analysis and relationships between amplitude (indicating loudness) and frequency (indicating the sound component) were analyzed.

RESULTS

Experiment 1: Time-frequency analysis confirmed multiple peak frequencies for each specimen without adhesive and monomodal peak frequency in all specimens using adhesive. Experiment 2: Two weeks after luting, all specimens showed a single major peak except one which showed multiple weak peaks.The three-dimensional visualization of time-frequency analysis revealed one specimen with multiple weak peaks while all others displayed a single, low-amplitude band at 2 weeks after luting.

CONCLUSIONS

The state of the adhesive interface can be evaluated using active AE. This basic technique may prove useful to evaluate changes in the adhesive interface of prostheses over time.

Universal adhesive: the effect of different simulated pulpal pressure fluids and bonding modes to dentin

The aim of this study was to evaluate the effect of SPP with either fetal bovine serum (FBS) or deionized water (DW) on the bond strength (μTBS) of a Universal adhesive to dentin, in both etch-and-rinse (ER) and self-etch (SE) modes. The kinematic viscosity (cSt) of FBS and DW was measured at 25 °C ± 0.1 ºC. Seventy-two sound human molars were sectioned and randomly divided into three groups according to the SPP conditions: (1) Control (0 cm H₂O), (2) SPP (15 cm H₂O) with FBS, (3) SPP (15 cm H₂O) with DW. Each group was subdivided (n = 10) based on the bonding modes: ER (37% phosphoric acid + ScothBond Universal Adhesive) or SE (ScothBond Universal Adhesive). Samples were then submitted to μTBS. Data were analyzed by Student's t test, two-way ANOVA and Tukey tests (p < 0.05). The cSt results showed that DW (23.59 ± 0.39) had significantly higher values than FBS (22.33 ± 0.06). With regard to SPP, the control group (36.1 MPa) had significantly higher values of μTBS when compared to the SPP using FBS (31.06 MPa) and SPP with DW (26.55 MPa). According to ANOVA, the bonding modes and the interaction of simulated pulpal pressure (SPP) did not statistically influence the results (p < 0.05). The presence of SPP reduced the bond strength of Universal adhesive to dentin. DW during SPP had significantly reduced bonding values when compared to FBS. Bonding strategies were not affected by SPP when evaluated in a short period of time (24 h).

Development of dental inspection method: nondestructive evaluation of a dentin-adhesive interface by acoustic emission

PURPOSE

The state of adhesion between root dentin and a resin composite core material was inspected using acoustic emission (AE).

METHODS

A total of 14 human incisors and premolars were used to prepare "no-adhesive group" and "adhesive group" specimens. For "adhesive group" specimens, a bonding agent was applied to root canal dentin. The entire post space was subsequently filled with a resin composite for both specimen groups. The prepared specimens were fixed onto a jig on which an AE sensor was installed. A zirconia ball was used for the impact test, and a vibration wave generated by the collision was measured by the system using an AE sensor. The obtained data were subjected to time-frequency analysis using analysis software (LabVIEW), and the relationship between the amplitude indicating the loudness and the frequency indicating the sound component was analyzed.

RESULTS

Zirconia-ball collision tests using AE revealed differences between the groups with respect to the waveform of vibration waves transmitted to the root dentin through the root dentin-resin interface. The time-frequency analysis of the obtained data confirmed that multiple peaks were observed for each specimen in the no-adhesive group, whereas a single characteristic vibration peak was observed for all specimens in the adhesive group.

CONCLUSIONS

The state of the adhesive interface was successfully evaluated by AE. This demonstration is expected to lead to the development of a device that can detect problems at the bonding interface between the prostheses and tooth substances.

Dentin Permeability and Nanoleakage of Universal Adhesives in Etch-and-rinse vs Self-etch Modes

PURPOSE

This study evaluates the reduction in dentin permeability (P) and the expression of nanoleakage in resin-dentin interfaces made with universal adhesives, comparing the self-etch mode of application with the etch-and-rinse mode of application.

METHODS AND MATERIALS

To measure dentin P at the baseline and after adhesive polymerization, 80 extracted noncarious human third molars (N=80) were sectioned to obtain 0.7-mm-thick midcoronal dentin disks. The specimens were randomly assigned to 8 groups according to the different adhesive systems and application modes used: Scotchbond Universal (SBU; etch-and-rinse [ER] mode vs self-etch [SE] mode), OptiBond XTR (OPT; etch-and-rinse mode vs self-etch mode), Clearfil Universal Bond Quick (CL; etch-and-rinse mode vs self-etch mode), and Adhese Universal (ADH; etch-and-rinse mode vs self-etch mode). A two-way analysis of variance with interaction was used to evaluate the P reduction differences among the groups (α=0.05). Sixteen additional 0.7-mm-thick dentin disks were similarly prepared and treated, immersed in 50 wt% ammoniacal silver nitrate, and then processed according to conventional methods for analysis under transmission electron microscopy.

RESULTS

The differences in P reduction among the adhesives were significant (p=0.029). For OPT and ADH (p=0.0304 and p=0.0120, respectively), the P reduction was higher in the ER mode than in the SE mode. For CL and SBU, no differences in P reduction was observed between the two application modes (p>0.05). All the groups showed some pattern of nanoleakage.

CONCLUSIONS

No adhesive system completely reduced dentin P. Dentin sealing was higher for OPT and ADH in the ER mode, while for SBU and CL, there was no difference between the two modes. All the adhesive systems showed nanoleakage.

Physicochemical characterization, water sorption and solubility of adhesive systems incorporated with titanium tetrafluoride, and its influence on dentin permeability

Titanium tetrafluoride (TiF₄) in an aqueous solution can decrease dentin permeability, but some effects of its incorporation into adhesive systems are not yet known. Therefore, the aim of this study was to characterize the physicochemical, water sorption (WS) and solubility (SL) properties of two adhesive systems (Clearfil SE Bond/C and Scotchbond Universal/S) incorporated with 0.0% (T0), 2.5% (T2) and 4.0% (T4) titanium tetrafluoride (TiF₄), and determine dentin permeability (L) after application of these adhesive systems both immediately afterwards (baseline) and after 6 months of storage. The physicochemical analyses of the incorporated solutions were performed based on evaluating particle size (PS), polydispersity index (PDI) by dynamic light scattering, and zeta potential (ZP) by electrophoresis. WS and SL tests followed ISO 4049 standards, and used a 7-day water storage period. The L test was performed by analyzing human dentin discs before and after adhesive system application, and after storage. PS and PDI were higher for CT0 and ST4 (p < 0.0001; ANOVA, Tukey). ZP was lower for CT4, ST2 and ST4 (p < 0.0001; ANOVA, Tukey). A 4.0% TiF₄ incorporation showed higher WS (p < 0.05; Mann Whitney, Kruskal Wallis, Dunn). Higher SL was observed for CT0 and ST4 (p < 0.05; Mann Whitney, Kruskal Wallis, Dunn). The L value at baseline was lower for ST4, but was not different from the CT4 groups after storage (p < 0.05; Mann Whitney, Kruskal Wallis, Dunn). It can be concluded that TiF₄ affected the colloidal stability of Scotchbond, but did not alter the other properties. The 2.5% TiF₄ did not affect the PDI, WS or L of the Clearfil, and can be considered an alternative for reducing hybrid layer degradation.

Impact of biomineralization on resin/biomineralized dentin bond longevity in a minimally invasive approach: An "in vitro" 18-month follow-up

OBJECTIVES

To determine the impact of treating caries-affected dentin (CAD) with: 0.2% sodium fluoride (NaF), casein phosphopeptide-amorphous calcium phosphate (CPP-ACP/MI Paste™) or peptide P₁₁-4 (Curodont™ Repair) on the longevity of resin/CAD interface at storage times of 24 -h, 6- and 18-month.

METHODS

255 caries-free third molars were used, and CAD was produced by a biological method. The teeth were randomly distributed into: G1- Sound dentin (SD); G2- CAD; G3- CAD + 0.2% NaF (CAD/NaF); G4- CAD + CPP-ACP (CAD/ACP); G5- CAD + Curodont™ Repair (CAD/P₁₁-4). The Filtek Z350 composite resin block was bonded to dentin using Adper™ Single 2 (4 mm/height). Resin/dentin blocks were stored in a solution of Simulated Body Fluid at 37 °C, pressures were modified to simulate natural pulpal pressures. Specimens were investigated by microtensile bond strength (μTBS) (n = 8), Scanning Electron Microscopy (to assess the failure mode) (n = 8), nanoinfiltration (to assess the interface sealing) (n = 3), in situ zymography (to assess the gelatinolytic activity) (n = 3) and micro-computed microtomography (μ-CT) (to assess the mineralization) (n = 3). Data from μTBS, μ-CT and, nanoinfiltration and hybrid layer formation/degradation were submitted to two-way ANOVA and Tukey tests, and failure patterns and in situ zymography to Kruskal-Wallis and Dunn tests (α = 5%).

RESULTS

The highest mineral density change by μ-CT, smallest silver nitrate infiltration and proteolytic activity in the adhesive layer were obtained significantly for the groups SD, CAD/ACP and CAD/P₁₁-4, with most mixed fractures at 18-month (p < 0.001). CAD/NaF showed significantly similar values to CAD, CAD and CAD/NaF which presented a high percentage of adhesive fracture (p < 0.001) at all time periods.

SIGNIFICANCE

Treating caries-affected dentin with remineralizing agents CPP-ACP and Curodont™ Repair, has the potential to be a clinically relevant treatment protocol to increase the longevity of adhesive restorations.

Significance of immediate dentin sealing and flowable resin coating reinforcement for unfilled/lightly filled adhesive systems

BACKGROUND

Immediate dentin sealing implies applying an adhesive system to dentin directly after tooth preparation, before impression. The technique is universal (inlays, onlays, veneers, crowns) and well documented clinically and experimentally. Different types of dentin bonding agents (DBAs) are available on the market. Major differences lie in the thickness of the hybrid layer and overlaying adhesive resin (filled vs. unfilled/lightly filled adhesives).

OBJECTIVE

The objective of this work is to provide precise clinical instructions and present new experimental data about the bond strength of five DBAs (Optibond FL, Scotchbond MP, Single Bond Plus, Clearfil SE Bond, and Scotchbond Universal) used conventionally (dentin sealed at the time of restoration delivery) or with immediate dentin sealing, as well as with an additional flowable resin coating.

METHODS

Seventy-five human molars were selected, restored/tested according the microtensile bond strength method. Fifteen groups (n=5) were obtained from the combination of the five DBAs and three application modes: delayed dentin sealing, immediate dentin sealing and immediate dentin sealing with flowable resin coating.

RESULTS

It appears that immediate dentin sealing was confirmed to significantly improve the bond strength of all tested adhesives. The use of a flowable resin coating reinforcement after immediate dentin sealing increased the microtensile bond strength of all unfilled/lightly filled adhesives (from 233% of increase for ScotchBond MP, up to 560% for Clearfil SE Bond) and maintained the performance of the 3-step golden standard adhesive. Optibond FL used with (52.51 MPa) or without (54.75 MPa) additional flowable resin coating and Clearfil SE Bond (45.64 MPa) used with flowable resin coating provided the best results.

CLINICAL SIGNIFICANCE

The original immediate dentin sealing (IDS) technique implies the use of a filled DBA. With unfilled/lightly filled adhesives, it is suggested to reinforce IDS with an additional flowable resin coating. This seems especially paramount to the performance of simplified adhesive systems to protect the thin bonding interface from oxygen inhibition and preserve IDS layer during predelivery cleaning of the preparation. The clinical reinforcement of unfilled/lightly filled IDS with flowable resin composite is encouraged for more predictable bonding.

Shear bond strength of the adhesive/dentin interface after different etching protocols

Background:

Aim:

Materials and Methods:

Results:

Conclusion:

Thermal and bioactive optimization of a unidose 3-step etch-and-rinse dentin adhesive

STATEMENT OF PROBLEM

The limited durability of resin-dentin bonds is considered a major disadvantage of adhesive restorations. Therefore, clinical strategies have been developed to improve hybrid layer stability over time. These strategies require testing.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of preheating and the inclusion of a bioactive glass in a unidose 3-step etch-and-rinse adhesive system on the adhesion of direct composite resin restorations.

MATERIAL AND METHODS

Dentin disks from 80 molars were assigned to 8 groups (n=10): CG-T1/CG-T2: control group; PG-T1/PG-T2: adhesive preheated to 68 °C; BG-T1/BG-T2: 0.05 mg of Bioglass 45S5 (BAG) (particle size: 3 μm) added to primer; PBG-T1/PBG-T2: adhesive and BAG-modified primer preheated to 68 °C. Sticks were fabricated for microtensile bond strength (μTBS) testing and were tested at 1 week (T1) and after 6 months (T2) of storage. μTBS data were analyzed by using 2-way ANOVA and the Tukey-Kramer post hoc test (α=.05). Scanning electron microscopy was used to analyze the failure mode. Attenuated total reflection Fourier transform infrared spectroscopy was used to quantitatively analyze the modifications to the chemical structure of the adhesive system from preheating and BAG inclusion.

RESULTS

The mean bond strength values at 1 week were statistically different, with PG-T1 (69.8 ±7.8 MPa) superior to all other groups. CG-T1 (58.2 ±6.7 MPa), BG-T1 (60.7 ±4.4 MPa), and PBG-T1 (61.0 ±4.6 MPa) were not statistically different (P>.05). PG-T2 maintained the highest bond strength at 6 months (68.3 ±3.7 MPa), with no decrease in μTBS observed over time. Failure modes were mostly adhesive. Attenuated total reflection Fourier transform infrared spectroscopy analysis reported that primer preheating caused solvent evaporation and revealed that preheating the bonding agent promoted the condensation reaction between the silane and adhesive fillers.

CONCLUSIONS

No decrease in μTBS was observed for any group after 6 months. Preheating the adhesive system (primer and bonding resin) significantly increased the 1-week and 6-month μTBS. Inclusion of BAG did not affect the bond strength.

Effect of thermo-mechanical cycling and chlorhexidine on the bond strength of universal adhesive system to dentin

OBJECTIVES

This study evaluated the influence of thermo-mechanical cycling (TMC) on the bond strength (BS) of a universal adhesive system (UAS - Adper Single Bond Universal, 3M ESPE) to dentin treated or not with 0.2% chlorhexidine (CHX).

METHODS

Eighty human molars were flattened until reach the dentin and separated into 4 groups according to the bonding protocol: ENR Group: 37% phosphoric acid + 3-step etch-and-rinse adhesive system (ENR); UAS Group: UAS in self-etch mode; ENR + CHX Group: 37% phosphoric acid + CHX + ENR; UAS + CHX Group: CHX + UAS in self-etch mode. After treatments, teeth were restored (Filtek Z350, 3M ESPE). Samples (n = 10) were submitted to aging process: stored in distilled water at 37°C/30 days or TMC (ERIOS - 98N/1.6Hz + thermal cycling 5/37/55 °C - 1,200,000 cycles). Specimens were sectioned into sticks (1.0 mm2) and submitted to the microtensile test (Mechanical Test Machine - 0.5 mm/min). Fracture patterns and hybrid layer integrity were analyzed under Stereomicroscope and Scanning Electron Microscopy (SEM).

RESULTS

The BS results (3-way ANOVA, Bonferroni's test, α = 5%) showed that groups treated with CHX presented higher BS values than control groups; significant in all cases (p < .05), except for ENR submitted to TMC (p > .05). When CHX was applied and samples were cycled, UAS revealed higher BS (p < .05) than ENR. After TMC, cohesive fractures increased for UAS, regardless of CHX application. SEM analysis demonstrated different hybridization patterns for the adhesive systems tested.

CONCLUSION

The performance of the universal adhesive system used in self-etch mode was better than that of the 3-step etch-and-rinse adhesive system.

CLINICAL SIGNIFICANCE

Universal adhesive systems have been developed in order to simplify the dentin hybridization protocol. It is important to determine the longevity of the adhesive interface using these bonding materials after chewing.

Human pulp response to conventional and resin-modified glass ionomer cements applied in very deep cavities

OBJECTIVES

This study assessed the human pulp response after adhesive restoration of cavities by indirect pulp capping with a conventional or a resin-modified glass ionomer cement.

MATERIALS AND METHODS

Deep cavities prepared in 26 human premolars were lined with Riva Light Cure (Riva LC), Riva Self Cure (Riva SC), or Dycal, and then restored with composite resin. Four teeth were used as intact control. After time intervals of 7 or 30 days, the teeth were extracted, processed for histological evaluation of the pulp, and the remaining dentin thickness (RDT) between the cavity floor and the pulp was measured.

RESULTS

At 7 days, a slight pulp inflammation associated with discrete tissue disorganization was observed in most of t the teeth lined with Riva LC and Riva SC. Moderate pulp inflammation occurred in one tooth lined with Riva LC. Bacteria were identified in one specimen of the same group that exhibited no pulp damage. At 30 days, slight pulp inflammation and discrete tissue disorganization persisted in two specimens treated with Riva LC, in which a thin layer of tertiary dentin was deposited. Mean RDTs ranged from 383.0 to 447.8 μm.

CONCLUSIONS

Riva LC produced more damage to the pulp than Riva SC. However, the initial pulp damage decreased over time and after 30 days both GICs were labeled as biocompatible.

CLINICAL RELEVANCE

In this study conducted with human teeth, the conventional and the resin-modified glass ionomer cements investigated were shown not to cause post-operative sensitivity or persistent pulp damage when applied as liners in very deep cavities, thereby indicating their biocompatibility.

Effect of erosive and abrasive stress on sealing ability of different desensitizers: In-vitro study

This in vitro study examined the sealing ability of different desensitizing agents under a chemo-mechanical stress condition. For the study, a total of 144 extracted, caries-free human third molars were used to produce 1 mm-thick dentin discs. The specimens were divided randomly into four groups: Superseal (SS), Gluma (GL), Gluma Self-etch (GS), and Tooth Coat (TC). For each group, the permeability was measured before and after applying the desensitizer, after being exposed to Coca Cola for 5 minutes, and after 3150 strokes of a brushing abrasion. The decrease in permeability after the erosive and abrasive stress was analyzed by ANOVA and Tukey post hoc test. As a result, the dentin permeability decreased significantly for all desensitizers immediately after application (p < 0.05). SS and GS showed a significant difference in permeability reduction observed immediately after application and after acid action with Coca Cola (p < 0.05). After brushing abrasion, the permeability reduction decreased significantly for all desensitizers tested in this study (p < 0.05). TC showed the largest decrease in dentinal permeability compared to that of the other desensitizers and the differences were significant after brushing abrasion (p < 0.05). All tested desensitizers were effective in reducing dentin permeability. The behavioral characteristics under erosive and abrasive stress varied according to the products used. TC exhibited excellent sealing ability among the other desensitizers.

The Role of Transient Receptor Potential (TRP) Channels in the Transduction of Dental Pain

Dental pain is a common health problem that negatively impacts the activities of daily living. Dentine hypersensitivity and pulpitis-associated pain are among the most common types of dental pain. Patients with these conditions feel pain upon exposure of the affected tooth to various external stimuli. However, the molecular mechanisms underlying dental pain, especially the transduction of external stimuli to electrical signals in the nerve, remain unclear. Numerous ion channels and receptors localized in the dental primary afferent neurons (DPAs) and odontoblasts have been implicated in the transduction of dental pain, and functional expression of various polymodal transient receptor potential (TRP) channels has been detected in DPAs and odontoblasts. External stimuli-induced dentinal tubular fluid movement can activate TRP channels on DPAs and odontoblasts. The odontoblasts can in turn activate the DPAs by paracrine signaling through ATP and glutamate release. In pulpitis, inflammatory mediators may sensitize the DPAs. They could also induce post-translational modifications of TRP channels, increase trafficking of these channels to nerve terminals, and increase the sensitivity of these channels to stimuli. Additionally, in caries-induced pulpitis, bacterial products can directly activate TRP channels on DPAs. In this review, we provide an overview of the TRP channels expressed in the various tooth structures, and we discuss their involvement in the development of dental pain.

Effects of different resin adhesives on the microleakage in a new model with simulated subgingival condition and pulpal pressure

Resin adhesive restorations are susceptible to oral fluid contamination and greatly influenced by dentinal tubule fluid because of pulpal pressure, especially when the restorative cavities are near gingival tissues. This study designed a novel model to evaluate the microleakage of self-adhesive flowable composite and traditional resin adhesives under simulated subgingival cavity preparations and pulpal pressure. We applied three different adhesive systems, include Vertise Flow, Optibond all-in-one, and Optibond S, on premolars with V-shaped cavity. All samples exhibited good marginal sealing at resin-enamel interfaces. At resin-dentin interfaces, microleakage in control group was similar among different adhesive systems. Microleakage in group pulpal pressure was greater than that in control group for all adhesive systems except Vertise Flow. All adhesive systems in pulpal pressure and simulated subgingival group exhibited significantly greater microleakage. In total, Vertise Flow exhibited better marginal sealing under pulpal pressure than other traditional adhesives.

Effect of self-etch adhesives on the internal adaptation of composite restoration: a CP-OCT Study

Despite improvements in dental adhesive materials, internal adaptation remains a challenge in bonded restorations. The aim of this study was to compare microgaps and internal floor adaptation between two different self-etch adhesives in class-V cavities using cross-polarization optical coherence tomography (CP-OCT). In this in vitro study, standardized round class-V cavities were prepared in 20 non-carious human upper central incisor teeth. They were randomly divided into two groups, TN and SE, with each group receiving a different dental adhesive. In TN group, the adhesive used was all-in-one Tetric N-Bond Self-Etch (TN; Ivoclar/Vivadent, Liechtenstein), while SE group was bonded with two-step self-etch Clearfil SE Bond 2 adhesive (SE; Kuraray Noritake Dental Inc, Japan). The prepared cavities were restored with flowable composite and then stored in distilled water for 24 h. Next, they were immersed in silver nitrate, followed by immersion in a photo-developing solution. Optical comparison was carried out by CP-OCT to assess microgaps and composite adaptation at the cavity floor. A Mann-Whitney test was applied to the data, which showed a statistically significant difference in composite adaptation among the two groups (p < 0.001) with the SE group showing superior adaptation. CP-OCT is a reliable tool for non-invasive imaging that gives an insight into composite performance. Better adaptation was found with the two-step self-adhesive for the composite used in this study.

Application of Calcium Silicate Materials After Acid Etching May Preserve Resin-Dentin Bonds

INTRODUCTION

The aim of the present study was to evaluate the effect of the application of calcium silicate materials (CSMs), after acid etching, on the longevity of the hybrid layer and marginal adaptation of composite restorations.

METHODS AND MATERIALS

Eighty human permanent molars received an intrapulpal pressure of 15 cm H₂O. Sixty teeth received a mesial proximal slot preparation with the gingival margin extending 1 mm below the cemento-enamel junction. The samples were divided into two groups. Group 1 received restorations using two types of etch-and-rinse adhesives: ethanol based (Single Bond, 3M ESPE, St Paul, MN, USA) and acetone based (Prime & Bond NT, Dentsply, DeTrey GmbH, Germany). In group 2 samples, a commercially available CSM (ProRoot MTA) was allowed to set before grinding and placing into a distilled water solution. This solution was applied on the cavity floor after acid etching. The surface was washed after 30 seconds followed by application of adhesives and restorations as in group 1. The samples were stored in phosphate-buffered saline for six months, maintaining the intrapulpal pressure. An epoxy replica was made, and the marginal adaptation was evaluated using scanning electron microscopy. The percentage of continuous margin (CM) was recorded for each group. Another 20 samples were used for hybrid layer evaluation. The crowns were ground to expose dentin. Intrapulpal pressure was applied. The samples were divided into two groups and restored similar to samples restored for marginal adaptation evaluation. The samples were longitudinally cut in 1-mm slices. The slices were stored under 15 cm of phosphate-buffered saline to simulate the pulpal pressure. After six months, the adhesive interface was evaluated using a scanning electron microscope. Statistical analysis was done with two-way analysis of variance with Holm-Sidak's correction for multiple comparisons.

RESULTS

Application of CSMs improved the marginal adaptation values in both adhesive groups. In group 1, there were areas of incomplete penetration of resins along with evidence of partial degradation of resin tags. Samples receiving CSM application after acid etching demonstrated long and regular resin tags with very few signs of degradation.

CONCLUSIONS

Application of CSMs after acid etching can be a potential avenue in preserving the resin-dentin bonds.

Water-associated attributes in the contemporary dentin bonding milieu

OBJECTIVES

The water-associated attributes of resin-dentin interfaces created by contemporary adhesives are important determinants of bond integrity and stability. In the present work, these attributes were estimated from the perspectives of causality, to examine the behavior of the first and most-recently launched versions of universal adhesives when applied in either the etch-and-rinse mode or the self-etch mode.

METHODS

The immediate cause of interfacial permeability and the time-dependent cause of water sorption were investigated in conjunction with the intermediate effect of interface degradation and the more long-term effect of loss of mechanical strength, before and after thermomechanical cycling. The results were compared with control etch-and-rinse and self-etch adhesives.

RESULTS

Although the introduction of this new class of universal adhesives has brought forth significant changes to the dental adhesion arena, including more application options, reduced bonding armamentarium and increased user friendliness, the water-associated attributes that are critical for making resin-dentin bonds more durable to environmental challenges and less susceptible to degradation have remained unchanged at large, when compared with benchmarks established by former classes of adhesives.

CONCLUSION

It appears that the current trend of adhesive development has brought forth significant changes but lacks the vigor that demarcates progress and technological sublimity.

CLINICAL SIGNIFICANCE

The advent of the user friendly universal adhesives has brought forth significant changes to the dental adhesion arena. However, the elements that are critical for making resin-dentin bonds more durable to environmental challenges and less susceptible to degradation have remained unchanged at large.

In Vitro Evaluation of Onlay Restorations on Primary Teeth

Purpose

Many novel materials have been developed such as composite resin, ceramic, zircon or metal-supported ceramic for use in aesthetic restoration of primary teeth and permanent teeth with extensive crown damage. The aim of the present study was to compare microtensile bond strengths on materials using the microtensile bond strength test.

Materials and methods

The microtensile bond strength on the primary tooth dentin was measured on extracted primary teeth using an indirect method and fracture patterns were evaluated.

Results

The analysis of bond strengths using the Mann-Whitney U-test did not show significant difference between the rank averages of the compomer and composite resin (p = 0.741). The dentin sections, from which test samples were obtained, contributed to the bond strength; dentin samples obtained just above the pulp had lower bond strength, and the difference was statistically significant (p = 0.005). The adhesive type fracture was the most prevalent fracture type for both materials.

Conclusions

When the chemical, physiological, and micromorphological differences between primary and permanent teeth are taken into consideration, the success of the materials used for restorations can be different between primary and permanent teeth. Therefore, materials used in the dentistry must be evaluated separately for primary teeth.

Effect of Dentin Wetness on the Bond Strength of Universal Adhesives

The effects of dentin wetness on the bond strength and adhesive interface morphology of universal adhesives have been investigated using micro-tensile bond strength (μTBS) testing and confocal laser scanning microscopy (CLSM). Seventy-two human third molars were wet ground to expose flat dentin surfaces. They were divided into three groups according to the air-drying time of the dentin surfaces: 0 (without air drying), 5, and 10 s. The dentin surfaces were then treated with three universal adhesives: G-Premio Bond, Single Bond Universal, and All-Bond Universal in self-etch or etch-and-rinse mode. After composite build up, a μTBS test was performed. One additional tooth was prepared for each group by staining the adhesives with 0.01 wt % of Rhodamine B fluorescent dye for CLSM analysis. The data were analyzed statistically using ANOVA and Tukey's post hoc tests (α = 0.05). Two-way ANOVA showed significant differences among the adhesive systems and dentin moisture conditions. An interaction effect was also observed (p < 0.05). One-way ANOVA showed that All-Bond Universal was the only material influenced by the wetness of the dentin surfaces. Wetness of the dentin surface is a factor influencing the micro-tensile bond strength of universal adhesives.

Classification review of dental adhesive systems: from the IV generation to the universal type

Adhesive dentistry has undergone great progress in the last decades. In light of minimal-invasive dentistry, this new approach promotes a more conservative cavity design, which relies on the effectiveness of current enamel-dentine adhesives. Adhesive dentistry began in 1955 by Buonocore on the benefits of acid etching. With changing technologies, dental adhesives have evolved from no-etch to total-etch (4^th and 5^th generation) to self-etch (6^th, 7^th and 8^th generation) systems. Currently, bonding to dental substrates is based on three different strategies: 1) etch-and-rinse, 2) self-etch and 3) resin-modified glass-ionomer approach as possessing the unique properties of self-adherence to the tooth tissue. More recently, a new family of dentin adhesives has been introduced (universal or multi-mode adhesives), which may be used either as etch-and-rinse or as self-etch adhesives. The purpose of this article is to review the literature on the current knowledge for each adhesive system according to their classification that have been advocated by many authorities in most operative/restorative procedures. As noted by several valuable studies that have contributed to understanding of bonding to various substrates helps clinicians to choose the appropriate dentin bonding agents for optimal clinical outcomes.

No-waiting dentine self-etch concept-Merit or hype

OBJECTIVE

A recently-launched universal adhesive, G-Premio Bond, provides clinicians with the alternative to use the self-etch technique for bonding to dentine without waiting for the adhesive to interact with the bonding substrate (no-waiting self-etch; Japanese brochure), or after leaving the adhesive undisturbed for 10s (10-s self-etch; international brochure). The present study was performed to examine in vitro performance of this new universal adhesive bonded to human coronal dentine using the two alternative self-etch modes.

METHODS

One hundred and ten specimens were bonded using two self-etch application modes and examined with or without thermomechanical cycling (10,000 thermal cycles and 240,000 mechanical cycles) to simulate one year of intraoral functioning. The bonded specimens were sectioned for microtensile bond testing, ultrastructural and nanoleakage examination using transmission electron microscopy. Changes in the composition of mineralised dentine after adhesive application were examined using Fourier transform infrared spectroscopy.

RESULTS

Both reduced application time and thermomechanical cycling resulted in significantly lower bond strengths, thinner hybrid layers, and significantly more extensive nanoleakage after thermomechanical cycling. Using the conventional 10-s application time improved bonding performance when compared with the no-waiting self-etch technique. Nevertheless, nanoleakage was generally extensive under all testing parameters employed for examining the adhesive.

CONCLUSION

Although sufficient bond strength to dentine may be achieved using the present universal adhesive in the no-waiting self-etch mode that does not require clinicians to wait prior to polymerisation of the adhesive, this self-etch concept requires further technological refinement before it can be recommended as a clinical technique.

CLINICAL SIGNIFICANCE

Although the surge for cutting application time to increase user friendliness remains the most frequently sought conduit for advancement of dentine bonding technology, the use of the present universal adhesive in the no-waiting self-etch mode may not represent the best use of the adhesive.

Minimizing Dentinal Fluid Flow Associated with Gap Formation

The relationship between gap formation and outward fluid flow and procedures to minimize both phenomena were investigated in extracted human premolars restored in vitro with MOD composite restorations. We hypothesized that either glass-ionomer cement (GIC) liners or low-shrinkage composite could reduce fluid flow related to gap formation. Two groups restored with bonding agents with either high- or low-shrinkage resin composites, and 2 groups restored by either conventional or light-cured GIC liner plus resin composite were compared (8 teeth/group). Fluid flow was measured with an automated apparatus. Baseline fluid flow was low and unchanged after bonding, but increased sharply (though transiently) after teeth were lined with GIC. Outward flow was significantly greater with conventional than with light-cured GIC. Inward fluid flow occurred during light-curing, followed by extensive, prolonged outward flow after curing. Low-shrinkage composite or GIC liners reduced gap formation and limited outward fluid flow. GIC liners promoted outward fluid flow during their setting reactions. Abbreviations: GIC, glass-ionomer cement; CEJ, cemento-enamel junction; MOD, mesio-occluso-distal; SEM, scanning electron microscopy.

Contraction Stress in Dentin Adhesives Bonded to Dentin

Adhesives cured under constrained conditions develop contraction stresses. We hypothesized that, with dentin as a bonding substrate, the stress would reach a maximum, followed by a continuous decline. Stress development was determined with a tensilometer for two total-etch systems and two systems with self-etching primers. The adhesives were placed in a thin layer between a glass plate and a flat dentin surface pretreated with phosphoric acid or self-etching primer. After an initial maximum shortly after light-curing, the stress decreased dramatically for the total-etch systems (70%) and, to a lesser extent, for the adhesives with self-etching primers (30%). The greater stress decrease for the total-etch systems was ascribed to water and/or solvents released into the adhesives from the fully opened dentinal tubules by the pulling/sucking action of the contraction stress. This happened less with the adhesives with self-etching primers, where the tubules remained mainly closed.

Effects of Dentin Characteristics on Interfacial Nanoleakage

Water emanating from dentinal tubules during air-drying and light-curing of adhesives leads to entrapment of droplets at the resin-dentin interface and contributes to nanoleakage. This study tested the null hypothesis that characteristics of substrate dentin and type of adhesive used for bonding would not affect the occurrence of nanoleakage. Three self-etch adhesives were used to bond to 4 types of dentin with different characteristics in 12 groups. After silver challenge, nanoleakage percentage was measured within the hybrid layer of each sample. The deep dentin cut perpendicular to tubules always showed a significantly higher nanoleakage percentage compared with that of the other 3 types of dentin. The percentages of nanoleakage within the hybrid layers were not statistically different among adhesives. However, when bonding to deep perpendicular dentin, both all-in-one adhesives revealed more distinct nanoleakage within the adhesive layer compared with that achieved with Clearfil SE Bond, a two-step self-etch adhesive. The results did not support the null hypothesis.

Tubular Occlusion Prevents Water-treeing and Through-and-Through Fluid Movement in a Single-bottle, One-step Self-etch Adhesive Model

Water entrapment occurs at resin-dentin interfaces of one-step self-etch adhesives. We hypothesized that by preventing water fluxes from dentin, any water entrapment would be attributed to incomplete removal of adhesive solvents. We tested this hypothesis by bonding to transparent carious dentin containing occluded dentinal tubules. An experimental single-bottle, one-step self-etch adhesive was applied to flat surfaces of caries-affected dentin surrounded by sound dentin, with or without pulpal pressure. Resin-dentin interfaces were examined with TEM after silver-impregnation. Although caries-affected dentin was highly porous, adhesive layers were devoid of silver deposits when tubules were occluded. Conversely, variable extents of water-treeing and water-droplets were identified from adhesive layers in bonded sound dentin. Water-treeing and water-droplet formation, being manifestations of evaporative and convective water fluxes, can be eliminated during bonding to occluded transparent carious dentin. However, the highly porous nature of this clinically relevant substrate after bonding may lead to potentially undesirable consequences.

Marginal integrity of low-shrinkage and methacrylate-based composite resins: Effect of three different hemostatic agents

Background

Moisture control is very important in restorative procedures in dentistry. Use of hemostatic agents helps control moisture; however, they might result in changes on enamel and dentin surfaces, affecting composite resin bond quality. The aim of this in vitro study was to evaluate the marginal microleakage of two different composite resins with the use of three different hemostatic agents.

Material and Methods

Standardized Class V cavities were prepared on the buccal and lingual surfaces of 48 premolars with cervical margins 1 mm apical to the cementoenamel junction (CEJ). The samples were randomly divided into 8 groups. In groups 1 to 4, an etch-and-rinse adhesive (Adper Single Bond) was applied as the bonding system, followed by exposure to different hemostatic agent: group 1: no hemostatic agent (control); group 2: ViscoStat; group 3: ViscoStat Clear; and group 4: trichloracetic acid, as hemostatic agents. The cavities were restored with Z-250 composite resin. In group 5 to 8 Silorane System Adhesive (Filtek P90 Adhesive) was applied as a bonding agent, followed by exposure to different hemostatic agents in a manner similar to that in groups 1to 4. The cavities were restored with Filtek P90, a low-shrinkage composite resin. The samples in each group were evaluated for dye penetration under a stereomicroscope at ×36 after 24 hours and a 500-round thermocycling procedure at enamel and dentin margins. Statistical analysis was carried out using Kruskal-Wallis and Mann-Whitney tests (α=0.05).

Results

Z-250 composite resin exhibited significantly higher dentin microleakage scores compared to Filtek P90 (P = 0.004). Trichloracetic acid increased dentin microleakage with Filtek P90 (P=0.033).

Conclusions

Under the limitations of this in vitro study, application of hemostatic agents did not affect microleakage of the two tested composite resins except for trichloracetic acid that increased marginal microleakage when used with Filtek P90.

Key words:Composite resin, dental leakage, hemostatics, silorane system adhesive.

The influence of intrinsic water permeation on different dentin bonded interfaces formation

OBJECTIVES

To determine the effects of intrinsic wetness on the formation of dentin bonding interfaces of four resin cement systems bonded to dentin under different pulpal pressures.

METHODS

Thirty-six freshly extracted third molars were selected and processed for dentin μTBS. The teeth were randomly assigned into 12 experimental groups, according to the adhesive luting system [Adper Single Bond Plus (3M ESPE) combined with two luting agents RelyX ARC (3M ESPE) and heated Filtek Z250 Universal Restorative (3M ESPE), Clearfil CD Bond (Kuraray) combined with Clearfil Esthetic Cement (Kuraray), and RelyX Unicem 2 Automix (3M ESPE)] and pulpal pressure (0, 5, and 20 cm of simulated pulpal pressure). Leucite-reinforced glass-ceramic slabs (IPS Empress CAD, Ivoclar Vivadent) of 3mm thickness were bonded to dentin. The samples were stored in distilled water for 24h and then sectioned in X/Y directions across the adhesive interface to obtain specimens with a cross section of 0.8 ± 0.2mm(2). All sticks were fractured by tension at a crosshead speed of 1.0mm/min and the data were submitted to Kruskal-Wallis and Mann-Whitney Tests (α=0.05). Ultrastructural analysis of the interfaces was performed using Confocal Laser Scanning Microscopy (CLSM) and Scanning Electron Microscopy (SEM).

RESULTS

The statistical analyses showed that pulpal pressure decreased μTBS for all groups. Significantly higher μTBS values were obtained in heated Z250 group restored without any pulpal pressure. CLSM showed that the uptake of water through the dentin tubuli and their anastomosis of lateral branches during the adhesive luting procedures prevented adequate formation of the dentin bonding interfaces. SEM showed that the luting film created is material- dependent and all adhesive failure occurred at the resin-dentin interface.

CONCLUSION

The constant intrinsic wetness replenishment prevents adequate formation of the hybrid layer.

CLINICAL SIGNIFICANCE

Intrinsic moisture during adhesive luting procedures significantly affects the interaction between luting materials and dentin subtract and decreases the quality and bonding strength of the resin-dentin bond.

Effects of Immediate Dentin Sealing and Pulpal Pressure on Resin Cement Bond Strength and Nanoleakage

Objective: The object of this study was to evaluate the simulated pulpal pressure (SPP) and immediate dentin sealing technique (IDS) effects on the microtensile bond strength (μTBS) and nanoleakage of interfaces produced by different luting agents.

Methods and Materials: Two self-adhesive luting agents (RelyX Unicem [UC] and Clearfil SA Luting [SA]) and two conventional luting agents (Rely X ARC [RX] and Panavia F [PF]) were evaluated. Eighty human molars were divided in four groups according to luting agents. Each group was subdivided according to SPP (with or without) and dentin sealing (immediate or delayed) using Clearfil SE Bond (n=5). After IDS was performed, specimens were stored in water for seven days before luting procedures. Composite blocks were luted according to the manufacturers' instructions. One half of the specimens were subjected to 15 cm H2O of hydrostatic pressure for 24 hours before cementation procedures and continued for 24 hours afterward. Then, restored teeth were sectioned into beams and tested in tension. Two additional teeth per group were prepared for nanoleakage evaluation with scanning electron microscopy. Bond strength data were statistically analyzed by three-way analysis of variance and Tukey test.

Results: μTBS of RX decreased when it was subjected to SPP without IDS. However, in the same conditions, μTBS of UC increased. The IDS prevented negative influence of SPP on μTBS of RX and PF; however, a decrease in μTBS of SA and UC was observed. Except for RX, IDS increased μTBS for all resin cements.

Conclusion: Independent of SPP, the IDS technique obtained higher μTBS for PF, SA, and UC and did not influence RX μTBS.

Effect of Carbodiimide on Bonding Durability of Adhesive-cemented Fiber Posts in Root Canals

This study was undertaken to investigate whether using a protein cross-linker, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), improves bonding stability of fiber posts to root dentin using three resin cements. Sixty human maxillary central incisor roots were randomly divided into six groups after endodontic treatment, according to the cements used with and without EDC pretreatment. In the etch-and-rinse group, 0.3 M EDC aqueous solution was applied on acid-etched root dentin prior to Excite DSC/Variolink II for post cementation. In the self-etch and self-adhesive groups, EDC was used on EDTA-conditioned root space prior to application of ED Primer II/Panavia F2.0 and Clearfil SA, respectively. After microslicing the root dentin, a push-out bond strength (BS) test was performed immediately or after one-year of water storage for each group. Data were analyzed using three-way analysis of variance and Tukey tests (α=0.05). A significant effect of cement type, time, EDC, and Time × Cement and Time × EDC interactions were observed (p≤0.001). EDC pretreatment did not affect immediate bonding of the three cements (p>0.05). Aging significantly reduced the BS in all the groups (p≤0.001), but EDC groups exhibited a higher BS compared with the respective control groups (p<0.001). Despite the significant effect of aging on decreasing the BS of fiber post to radicular dentin, EDC could diminish this effect for the three tested cements.

One-year Adhesive Bond Durability to Coronal and Radicular Dentin Under Intrapulpal Pressure Simulation

OBJECTIVE

To evaluate the microtensile bond strength (μTBS) of different adhesives to coronal vs radicular dentin after one year of storage in artificial saliva and under intrapulpal pressure (IPP) simulation.

METHODS AND MATERIALS

Roots of 36 freshly extracted premolars were sectioned 5 mm apical to the cemento-enamel junction and pulp tissue was removed. Buccal enamel and cementum were trimmed to obtain standardized flat dentin surfaces. Specimens were divided into three groups (n=12/group) according to the adhesive strategies utilized: a two-step etch-and-rinse adhesive; a two-step self-etch adhesive; and a single-step self-etch adhesive. Adhesives and resin composite were applied to coronal and radicular dentin while the specimens were subjected to IPP simulation. After curing, specimens were stored in artificial saliva at 37°C in a specially constructed incubator while the IPP was maintained for either 24 hours or one year prior to testing. Bonded specimens were sectioned into sticks with a cross section of 0.8 ± 0.01 mm(2) and subjected to μTBS testing. Data were statistically analyzed using multi-way analysis of variance (ANOVA) with repeated measures; one-way ANOVA tests; and Bonferroni post hoc test (p<0.05). Failure modes were determined using a scanning electron microscope at 100× magnification.

RESULTS

ANOVA results revealed a statistically significant effect for the adhesive strategy (p<0.001) and storage period (p<0.001) as well as for their interaction (p=0.024) on the μTBS. However, dentin substrate and its interactions revealed no significant effects. For both dentin substrates, the two-step self-etch adhesive revealed statistically significantly higher μTBS values than did the other two adhesives after 24 hours and one year of storage. After one-year storage, a significant decrease in bond strength values of all tested adhesives occurred with both dentin substrates. Modes of failure were mainly adhesive and mixed.

CONCLUSIONS

Adhesives were not sensitive to structural differences between coronal and radicular dentin even after one year of storage under IPP simulation. However, all tested adhesive systems strategies were sensitive to storage.

Preheating impact on the degree of conversion and water sorption/solubility of selected single-bottle adhesive systems

OBJECTIVE

This study evaluated the degree of conversion (DC) and the water sorption/solubility of preheated single-bottle adhesive systems.

METHODS AND MATERIALS

Five adhesive systems were tested: Adper Easy One and Adper Single Bond 2 (3M ESPE), Excite and Tetric N-Bond (Ivoclar/Vivadent), and XP Bond (Dentsply/Caulk). After storage for two hours at 25°C or 60°C, 50 samples (n=5) were prepared for all adhesive systems and stored dry in lightproof containers at 37°C for 24 hours. Fourier transform infrared/attenuated total reflectance spectroscopy was used to evaluate the DC, and water sorption/solubility was measured by means of mass loss and gain after water storage. The data were analyzed by two-way analysis of variance followed by Tukey's test (p<0.05).

RESULTS

Preheated adhesive systems showed statistically significantly higher DC than those kept at 25°C. Except for XP Bond, preheated adhesive systems presented statistically significantly lower water sorption/solubility means.

CONCLUSIONS

Preheating improved the DC for all tested adhesive systems. Also, it promoted a decrease of water sorption/solubility, except for the XP Bond adhesive system.

Effect of long-term simulated pulpal pressure on the bond strength and nanoleakage of resin-luting agents with different bonding strategies

This study evaluated the effects of simulated hydrostatic pulpal pressure (SPP) on the microtensile bond strength (μTBS) to dentin and nanoleakage patterns produced by self-adhesive luting agents after 12 months. Three self-adhesive luting agents (RelyX Unicem [UN], RelyX U100 [UC], and Clearfil SA Luting [SA]) and three conventional luting agents (Rely X ARC [RX], Panavia F [PF], and a two-step self-etching adhesive system [Clearfil SE Bond] associated with Panavia F [PS]) were evaluated. One hundred twenty-three human molars were abraded to expose occlusal surfaces. Resin cements were used to lute cylindrical composite blocks to the teeth either subjected or not to SPP. Sixty specimens were subjected to 15 cm H2O of SPP for 24 hours before and 24 hours or 12 months after cementation procedures. Afterward, restored teeth were serially sectioned into beams with a cross-sectional area of 1 mm(2) at the bonded interface and were tested in tension (cross-head speed of 1 mm/min). Failure mode was determined using scanning electron microscopy (SEM). Data were statistically analyzed by three-way analysis of variance and post hoc Tukey test (p=0.05). Two additional teeth in each group were serially sectioned into 0.9-mm-thick slabs, which were submitted to a nanoleakage protocol with AgNO3 and analyzed with scanning and transmission electron microscopes. The μTBS values of the etch-and-rinse group (RX) were negatively influenced by SPP and long-term water storage with SPP. After 12 months, UC and SA presented premature failures in all specimens when submitted to SPP. SPP increased silver deposition in most groups in both evaluation times. The hydrostatic pulpal pressure effect was material dependent. The storage time without SPP did not affect bond strength. However, long-term SPP influenced the performance of the etch-and-rinse and self-adhesive cements regarding μTBS and nanoleakage pattern, except to UN.

Multivariate analysis of attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopic data to confirm phase partitioning in methacrylate-based dentin adhesive

Water is ubiquitous in the mouths of healthy individuals and is a major interfering factor in the development of a durable seal between the tooth and composite restoration. Water leads to the formation of a variety of defects in dentin adhesives; these defects undermine the tooth-composite bond. Our group recently analyzed phase partitioning of dentin adhesives using high-performance liquid chromatography (HPLC). The concentration measurements provided by HPLC offered a more thorough representation of current adhesive performance and elucidated directions to be taken for further improvement. The sample preparation and instrument analysis using HPLC are, however, time-consuming and labor-intensive. The objective of this work was to develop a methodology for rapid, reliable, and accurate quantitative analysis of near-equilibrium phase partitioning in adhesives exposed to conditions simulating the wet oral environment. Analysis by Fourier transform infrared (FT-IR) spectroscopy in combination with multivariate statistical methods, including partial least squares (PLS) regression and principal component regression (PCR), were used for multivariate calibration to quantify the compositions in separated phases. Excellent predictions were achieved when either the hydrophobic-rich phase or the hydrophilic-rich phase mixtures were analyzed. These results indicate that FT-IR spectroscopy has excellent potential as a rapid method of detection and quantification of dentin adhesives that experience phase separation under conditions that simulate the wet oral environment.

Strategies to prevent hydrolytic degradation of the hybrid layer-A review

OBJECTIVE

Endogenous dentin collagenolytic enzymes, matrix metalloproteinases (MMPs) and cysteine cathepsins, are responsible for the time-dependent hydrolysis of collagen matrix of hybrid layers. As collagen matrix integrity is essential for the preservation of long-term dentin bond strength, inhibition of endogenous dentin proteases is necessary for durable resin-bonded restorations.

METHODS

Several tentative approaches to prevent enzyme function have been proposed. Some of them have already demonstrated clinical efficacy, while others need to be researched further before clinical protocols can be proposed. This review will examine both the principles and outcomes of techniques to prevent collagen hydrolysis in dentin-resin interfaces.

RESULTS

Chlorhexidine, a general inhibitor of MMPs and cysteine cathepsins, is the most tested method. In general, these experiments have shown that enzyme inhibition is a promising approach to improve hybrid layer preservation and bond strength durability. Other enzyme inhibitors, e.g. enzyme-inhibiting monomers, may be considered promising alternatives that would allow more simple clinical application than chlorhexidine. Cross-linking collagen and/or dentin matrix-bound enzymes could render hybrid layer organic matrices resistant to degradation. Alternatively, complete removal of water from the hybrid layer with ethanol wet bonding or biomimetic remineralization should eliminate hydrolysis of both collagen and resin components.

SIGNIFICANCE

Understanding the function of the enzymes responsible for the hydrolysis of hybrid layer collagen has prompted several innovative approaches to retain hybrid layer integrity and strong dentin bonding. The ultimate goal, prevention of collagen matrix degradation with clinically applicable techniques and commercially available materials may be achievable in several ways.

Influence of solvents and composition of etch-and-rinse and self-etch adhesive systems on the nanoleakage within the hybrid layer

AIM

The goal of this study was to evaluate nanoleakage within the hybrid layer yielded by etch-and-rinse and self-etch adhesive systems, with different solvents and compositions.

MATERIALS AND METHODS

Four adhesives were applied onto 20 human dentin disks: group A: Adper Scotchbond 1XT(™) (3M ESPE), group B: One Coat Bond(®) (Coltène Whaledent), group C: AdheSE(®) (Ivoclar Vivadent) and group D: Xeno-V(®) (Dentsply). The samples were immersed in aqueous ammoniacal silver nitrate for 24 hour, prepared and observed under field-emission scanning electron microscopy with backscattered electrons. Microphotographs were scanned and data were processed. The mean value and standard deviation were calculated. Kruskal- Wallis and Mann-Whitney tests were used (p < 0.05).

RESULTS

All the adhesives showed nanoleakage within the hybrid layer: Adper Scotchbond 1XT(™) (218.5 µm ± 52.6 µm), One Coat Bond(®) (139.6 µm ± 79.0 µm), AdheSE(®) (92.7 µm ± 64.8 µm) and Xeno-V(®) (251.0 µm ± 85.2 µm). AdheSE(®) yielded less nanoleakage than Adper Scotchbond-1XT(™) (p = 0.003) and than Xeno-V(®) (p = 0.007). No other statistically significant differences were detected.

CONCLUSION

Two-step self-etch adhesive system (AdheSE(®)) might contribute for lower nanoleakage deposition and thus better performance in dentin adhesion.

CLINICAL SIGNIFICANCE

The two-step self-etch adhesive system showed the lowest nanoleakage deposition compared with the other adhesive systems evaluated, which seems to indicate a better behavior when a restoration is performed in dentin and possibly can lead to a durable adhesion along time.

Overview of Clinical Alternatives to Minimize the Degradation of the Resin-dentin Bonds

The incorporation of hydrophilic and acidic resin monomers substantially improved the initial bonding of contemporary etch-and-rinse (ER) and self-etch (SE) adhesives to intrinsically wet dental substrates, providing quite favorable immediate results, regardless of the bonding approach used. However, in the long term, the bonding effectiveness of most simplified ER and SE adhesives drop dramatically. This review examines the fundamental processes that are responsible for the aging mechanisms involved in the degradation of the resin-bonded interfaces and some possible clinical approaches that have been effective in minimizing or even preventing the degradation of the adhesive interfaces produced with simplified adhesives. The incorporation of some of the feasible approaches - described in this review - may improve the quality of the adhesive restorations performed in clinical practice, while manufacturers develop bonding materials that are less susceptible to the aging mechanisms present in the oral environment.