Scanning Electron Microscope Analysis of Internal Adaptation of Materials Used for Pulp Protection under Composite Resin Restorations

Effect of different chelating agents on the shear bond strength of calcium silicate-based cements to coronal dentin

We evaluated the shear bond strength (SBS) of mineral trioxide aggregate (MTA) and Biodentine (BD) to coronal dentin after treatment with ethylenediaminetetraacetic acid (EDTA), phytic acid (IP6), or etidronic acid (HEDP). Sodium hypochlorite-treated dentin surfaces were randomly divided into four groups according to conditioning protocol namely, 17% EDTA, 2.5% IP6, 9% HEDP, or distilled water (DS). Specimens were further divided according to the type of cement placed on conditioned dentin and SBS was tested. The results showed that DS/MTA and IP6/MTA groups had the highest values, and there was no significant difference between these two groups. IP6/BD group showed a lower SBS value compared to IP6/MTA; however, this did not reach the level of significance. The BS to dentin was influenced by the type of calcium silicate material and chelating agent. IP6 either improved or maintained the bonding while EDTA and HEDP showed a negative or no influence effect.

Evaluation of Shear Bond Strength of Resin-Based Composites to Biodentine with Three Types of Seventh-Generation Bonding Agents: An In Vitro Study

Background and Aim. Biodentine refers to a bioactive material commonly applied for dental restoration in clinical practice, but poor adhesion of the Biodentine to the restorative materials could affect the quality and long-term integrity of the final restoration. The study aimed to assess shear bond strength (SBS) of two resin-based composites to Biodentine using three commercially available 7th generation bonding agents. Methods. Forty-eight acrylic blocks having central holes with a nominal diameter of 4 mm and a depth of 2 mm were prepared. The holes of the acrylic blocks were filled with Biodentine, which was prepared following the guidelines provided by the manufacturer. Then, the specimens were divided into six groups (n = 8). Groups 1, 2, and 3, Tetric N-Ceram composite bonded to Biodentine with Tetric N-bond, Xeno V+, Bond Force bond, respectively. Group 4, 5, and 6, Filtek Z350 bonded to Biodentine with the same three adhesives. The specimens were placed in distilled water for 24 hours and tested for the SBS in a universal testing machine at a crosshead speed of 1 mm/min. The test data were listed in a table and independent samples t-test and analysis of variance (ANOVA) were conducted as a part of the statistical analysis. Results. The Tetric N bonding agent achieved the highest SBS followed by Bond Force, and Xeno V and highly significant difference was found. On the other hand, an overall increase in the SBS values of the Tetric N-Ceram resin was noticed in comparison with the Filtek Z350 and the differences was statistically significant. Although the specimens failed in adhesive, cohesive and mixed fracture modes but the cohesive was found to be the dominant failure mode in all groups. Conclusion. Among the tested bonding agents and resin composites, the Tetric N-Ceram composite bonded by Tetric N-bond self-etch adhesive with the Biodentine showed the highest SBS compared to the other combinations.

Evaluating the Failure of Resin-based Materials on the Proximal Cervical Dentin

Background:

Resin-based materials are the popular restorative material in dentistry. The majority of these materials are light cured with a major disadvantage: marginal leakage.

Objective:

To evaluate the gap width of different resin-based materials at the cervical dentin when achieved mechanical force.

Methods:

Class II cavities were prepared on extracted premolar teeth with the gingival margin 1 mm below the Cementoenamel Junction (CEJ). In the first three experimental groups, three different lining materials (flowable resin composite, bulk-fill flowable resin composite, and resin-modified glass ionomer cement) were placed at the cervical dentin with a thickness of 1 mm. The rest of the cavities were restored with conventional resin composite. The other two groups were restored with conventional resin composite (control) or high viscosity bulk-fill resin composite, respectively. All groups were thermocycled and underwent vacuum pressure 2.6 KPa for 30 min in a Scanning Electron Microscope (SEM).

Results:

There was no gap formation at the cervical dentin on the external surface when restored with high-viscosity bulk fill resin composite. Almost all gaps occurred at the interface between restorative materials and the hybrid layer. The flowable bulk fill resin composite showed a significantly smaller gap width on both the external and internal surfaces compared to the other groups (p< 0.05). The resin-modified glass ionomer cement showed the largest gaps in the cervical dentin (p < 0.05).

Conclusion:

The different types of resin-based materials demonstrated a different failure of gap width under mechanical force. It clearly occurred at the restorative material-hybrid layer interface.

Cavity Bases Revisited

OBJECTIVE

The aim of this paper was to review the current literature on cavity bases while focusing on the role of zinc oxide eugenol (ZOE) and resin-modified glass ionomers (RMGI) as cavity bases.

MATERIALS AND METHODS

A thorough literature search between 1970 and 2020 was done using Scopus, PubMed, and Google Scholar databases. The keywords of the search strategy were as below: cavity liners and bases, pulp protection, zinc oxide eugenol, and resin-modified glass ionomer. No specific inclusion or exclusion criteria were applied as to what articles would be included in this review.

CONCLUSION

This review emphasizes that the available literature provides very little evidence to support the routine use of a base under amalgam or composite restorations. This review favors the adoption of "no more lining or bases" in shallow and moderate cavity preparations. However, an exception might be a "protective base" of RMGI following the application of calcium hydroxide (CH) liners in deep cavities. Bonded RMGIs are suitable cavity base materials and should always replace zinc oxide eugenol bases in daily practice.

Microtensile bond strength of resin cement primer containing nanoparticles of silver (NAg) and amorphous calcium phosphate (NACP) to human dentin

PURPOSE

The purpose of the current study was to evaluate the effect of incorporating nanoparticles of silver (NAg) and amorphous calcium phosphate (NACP) into a self-etching primer of a resin cement on the microtensile bond strength of dentin, regarding the proven antibacterial feature of NAg and remineralizing effect of NACP.

MATERIALS AND METHODS

Flat, mid-coronal dentin from 20 intact extracted human third molars were prepared for cementation using Panavia F2.0 cement. The teeth were randomly divided into the four test groups (n=5) according to the experimental cement primer composition: cement primer without change (control group), primer with 1% (wt) of NACP, primer with 1% (wt) of physical mixture of NACP+Nag, and primer with 1% (wt) of chemical mixture of NACP+Nag. The resin cement was used according to the manufacturer's instructions. After storage in distilled water at 37℃ for 24 h, the bonded samples were sectioned longitudinally to produce 1.0 × 1.0 mm beams for micro-tensile bond strength testing in a universal testing machine. Failure modes at the dentin-resin interface were observed using a stereomicroscope. The data were analyzed by one-way ANOVA and Tukey's post-hoc tests and the level of significance was set at 0.05.

RESULTS

The lowest mean microtensile bond strength was obtained for the NACP group. Tukey's test showed that the bond strength of the control group was significantly higher than those of the other experimental groups, except for group 4 (chemical mixture of NACP and NAg; P=.67).

CONCLUSION

Novel chemical incorporation of NAg-NACP into the self-etching primer of resin cement does not compromise the dentin bond strength.

The Relationship of Surface Characteristics and Antimicrobial Performance of Pulp Capping Materials

INTRODUCTION

Pulp capping materials need to be able to protect the pulp but also bond to the overlying restorative materials. Light-curable pulp capping materials bond better to restorative materials and are easier to place than most water-based cements. The aim of this study was to characterize new light-curable tricalcium silicate-based pulp capping materials and compare their surface and antimicrobial properties with clinically available Theracal (Bisco, Schaumburg, IL) and Biodentine (Septodont, Saint-Maur-des-Fossés, France).

METHODS

The surface characteristics of 3 light-curable pulp capping materials based on a resin and filled with tricalcium silicate and tantalum oxide radiopacifier and Theracal and Biodentine were assessed by scanning electron microscopy, X-ray diffraction, and contact angle measurement. The radiopacity was measured following ISO 6876 standards. The antimicrobial activity was determined by the direct contact test and the antibiofilm activity by the adenosine triphosphate assay and the confocal laser scanning Live/Dead assay (Invitrogen, Eugene, OR) using a polymicrobial culture.

RESULTS

The surface characteristics of the materials varied with the unfilled resin and Biodentine exhibiting a hydrophobic surface. Biodentine showed significantly higher antimicrobial properties in the direct contact test, but this property was absent in the antibiofilm activity tests. The resins filled with tricalcium silicate and Theracal showed higher antimicrobial activity than Biodentine in the adenosine triphosphate and live/dead assays.

CONCLUSIONS

The surface characteristics of a material affect its antimicrobial properties. The experimental resin-modified materials exhibited comparable antimicrobial properties with other light-curable pulp capping agents. Further long-term studies on the materials' antimicrobial activity are required to assess whether they can result in better clinical outcomes.

An end to linings under posterior composites?

BACKGROUND AND OVERVIEW

There is an uncertainty among dentists as to whether to place a lining under a direct posterior composite restoration and, if so, what material or combination of materials to use. In this article, the authors consider the evidence for the placement of a lining under posterior composites of different depths, including indications and contraindications for different lining materials.

CONCLUSIONS

The available evidence does not support the use of linings under direct, bonded posterior composites, unless being placed in deep cavities for therapeutic reasons.

PRACTICAL IMPLICATIONS

The best available evidence indicates that dentists can place posterior composites without linings, except for therapeutic purposes, with no adverse effect on postoperative complications, with possible improvements in performance in clinical service, and with efficiency savings in chairside time.

Effect of resin-modified glass-ionomer cement lining and composite layering technique on the adhesive interface of lateral wall

Interface integrity can be maintained by setting the composite in a layering technique and using liners.

Polymerization shrinkage of different types of composite resins and microleakage with and without liner in class II cavities

AIM

To determine the volumetric polymerization shrinkage of four different types of composite resin and to evaluate microleakage of these materials in class II (MOD) cavities with and without a resin-modified glass ionomer cement (RMGIC) liner, in vitro.

MATERIALS AND METHODS

One hundred twenty-eight extracted human upper premolar teeth were used. After the teeth were divided into eight groups (n=16), standardized MOD cavities were prepared. Then the teeth were restored with different resin composites (Filtek Supreme XT, Filtek P 60, Filtek Silorane, Filtek Z 250) with and without a RMGIC liner (Vitrebond). The restorations were finished and polished after 24 hours. Following thermocycling, the teeth were immersed in 0.5% basic fuchsin for 24 hours, then midsagitally sectioned in a mesiodistal plane and examined for microleakage using a stereomicroscope. The volumetric polymerization shrinkage of materials was measured using a video imaging device (Acuvol, Bisco, Inc). Data were statistically analyzed with Kruskal-Wallis and Mann-Whitney U-tests.

RESULTS

All teeth showed microleakage, but placement of RMGIC liner reduced microleakage. No statistically significant differences were found in microleakage between the teeth restored without RMGIC liner (p>0.05). Filtek Silorane showed significantly less volumetric polymerization shrinkage than the methacrylate-based composite resins (p<0.05).

CONCLUSION

The use of RMGIC liner with both silorane- and methacrylate-based composite resin restorations resulted in reduced microleakage. The volumetric polymerization shrinkage was least with the silorane-based composite.

Comparison of quaternary ammonium-containing with nano-silver-containing adhesive in antibacterial properties and cytotoxicity

OBJECTIVE

Antibacterial primer and adhesive are promising to help combat biofilms and recurrent caries. The objectives of this study were to compare novel bonding agent containing quaternary ammonium dimethacrylate (QADM) with bonding agent containing nanoparticles of silver (NAg) in antibacterial activity, contact-inhibition vs. long-distance inhibition, glucosyltransferases (gtf) gene expressions, and cytotoxicity for the first time.

METHODS

QADM and NAg were incorporated into Scotchbond Multi-Purpose adhesive and primer. Microtensile dentin bond strength was measured. Streptococcus mutans (S. mutans) biofilm on resin surface (contact-inhibition) as well as S. mutans in culture medium away from the resin surface (long-distance inhibition) were tested for metabolic activity, colony-forming units (CFUs), lactic acid production, and gtf gene expressions. Eluents from cured primer/adhesive samples were used to examine cytotoxicity against human gingival fibroblasts.

RESULTS

Bonding agent with QADM greatly reduced CFU and lactic acid of biofilms on the resin surface (p<0.05), while having no effect on S. mutans in culture medium away from the resin surface. In contrast, bonding agent with NAg inhibited not only S. mutans on the resin surface, but also S. mutans in culture medium away from the resin surface. Bonding agent with QADM suppressed gtfB, gtfC and gtfD gene expressions of S. mutans on its surface, but not away from its surface. Bonding agent with NAg suppressed S. mutans gene expressions both on its surface and away from its surface. Bonding agents with QADM and NAg did not adversely affect microtensile bond strength or fibroblast cytotoxicity, compared to control (p>0.1).

SIGNIFICANCE

QADM-containing adhesive had contact-inhibition and inhibited bacteria on its surface, but not away from its surface. NAg-containing adhesive had long-distance killing capability and inhibited bacteria on its surface and away from its surface. The novel antibacterial adhesives are promising for caries-inhibition restorations, and QADM and NAg could be complimentary agents in inhibiting bacteria on resin surface as well as away from resin surface.

Biocompatibility of various dental materials in contemporary dentistry: a narrative insight

In the past few decades, there has been an increase in demand for safety evaluation and control of dental materials used daily in dentistry; however, this task is difficult and cumbersome. Dental materials that are passive and do not react with the oral environment will be more stable and have superior durability. It is expected that dental materials will be universally accepted and will not cause harm or injury to the surrounding structures in the oral cavity. This is an entirely negative approach to the material tolerance and biocompatibility, and hides the possibility that some positive gains can be achieved. Side-effects of dental materials are believed to be rare, and generally, those that have been reported are mild. There are wide varieties of materials used in dentistry, which include liners, irrigants, intracanal filling materials, intracanal medicaments, prosthetic materials, restorative materials, subgingival implants, and mouth rinses. Therefore, in this study, the biocompatibility of various commonly-used clinical materials used in contemporary dentistry was discussed.

Effect of quaternary ammonium and silver nanoparticle-containing adhesives on dentin bond strength and dental plaque microcosm biofilms

OBJECTIVE

Antibacterial bonding agents are promising to hinder the residual and invading bacteria at the tooth-restoration interfaces. The objectives of this study were to develop an antibacterial bonding agent by incorporation of quaternary ammonium dimethacrylate (QADM) and nanoparticles of silver (NAg), and to investigate the effect of QADM-NAg adhesive and primer on dentin bond strength and plaque microcosm biofilm response for the first time.

METHODS

Scotchbond Multi-Purpose adhesive and primer were used as control. Experimental adhesive and primer were made by adding QADM and NAg into control adhesive and primer. Human dentin shear bond strengths were measured (n = 10). A dental plaque microcosm biofilm model with human saliva as inoculum was used to investigate biofilm metabolic activity, colony-forming unit (CFU) counts, lactic acid production, and live/dead staining assay (n = 6).

RESULTS

Adding QADM and NAg into adhesive and primer did not compromise the dentin shear bond strength which ranged from 30 to 35MPa (p>0.1). Scanning electron microscopy (SEM) examinations revealed numerous resin tags, which were similar for the control and the QADM and NAg groups. Adding QADM or NAg markedly reduced the biofilm viability, compared to adhesive control. QADM and NAg together in the adhesive had a much stronger antibacterial effect than using each agent alone (p<0.05). Adding QADM and NAg in both adhesive and primer had the strongest antibacterial activity, reducing metabolic activity, CFU, and lactic acid by an order of magnitude, compared to control.

SIGNIFICANCE

Without compromising dentin bond strength and resin tag formation, the QADM and NAg containing adhesive and primer achieved strong antibacterial effects against microcosm biofilms for the first time. QADM-NAg adhesive and primer are promising to combat residual bacteria in tooth cavity and invading bacteria at the margins, thereby to inhibit secondary caries. QADM and NAg incorporation may have a wide applicability to other dental bonding systems.