Bond strengths, degree of conversion of the cement and molecular structure of the adhesive-dentine joint in fibre post restorations

The resin-matrix cement layer thickness resultant from the intracanal fitting of teeth root canal posts: an integrative review

OBJECTIVE

The aim of this study was to perform an integrative review on the layer thickness and microstructure of resin-matrix cements around custom-made or standard teeth root intracanal posts.

MATERIALS AND METHODS

An electronic search was conducted on the PubMed using a combination of the following scientific terms: intraradicular post, root intracanal post, resin cement, thickness, adaptation, endodontic post, layer thickness, fit, shape, and endodontic core. The literature selection criteria accepted articles published in the English language, up to May 2021, involving in vitro analyses, meta-analyses, randomized controlled trials, and prospective cohort studies.

RESULTS

The search identified 154 studies, of which 24 were considered relevant to this study. The selected studies provided important data considering cement layer thickness, tooth preparation, endodontic post, and type of resin-matrix cement. The anatomical variability of root canal systems, such as the oval- or C-shaped, represents a challenge in dental restoration with tooth root intracanal posts. The fitting of intracanal posts to different root regions is variable resulting in thick and irregular layers of resin-matrix cement. Defects like pores, micro-cracks, and micro-gaps were detected in the resin-matrix cement microstructure and represent spots of stress concentration and fracture. Custom-made tooth root intracanal posts provide a proper fitting and decrease the layer thickness of resin-matrix cement.

CONCLUSIONS

In fact, the layer thickness of resin-matrix cements depends on the fitting of endodontic posts to tooth root canals. An increase of resin cement thickness causes the appearance of defects like pores, micro-cracks, and micro-gaps that can induce stress concentration and fractures at interfaces.

CLINICAL RELEVANCE

The fitting of the endodontic post into the teeth root canal determine the layer thickness of the resin-matrix cement to establish an adequate retention. However, the increase in the thickness of the resin-matrix cement layer can lead to a high number of defects like pores or cracks and therefore decrease the strength of the interface.

Evaluation of various methods of methylene blue removal from the post space after photodynamic therapy on the bonding interface using different resin cementation systems

BACKGROUND

To evaluate the effects of three protocols for removing 0.01 % methylene blue from the post space after photodynamic therapy on bond strength and tag formation in the dentin of the fiber post space, using a conventional cementation system with an etch-and-rinse or universal adhesive system.

METHODS

Sixty human canines were endodontically treated for fiber post cementation. The specimens were randomized into 6 groups (n = 10): G1, G2, G3, G4, G5, and G6. The G1, G2, and G3 groups were irrigated with saline solution, 2.5 % sodium hypochlorite (NaOCl), and 2.5 % NaOCl, agitated by passive ultrasonic irrigation (PUI), respectively. In these groups, a conventional cementation system with etch-and-rinse adhesive was used. The G4, G5, and G6 groups were irrigated with the respective solutions mentioned above and cemented using a conventional cementation system with universal adhesive. Tag formation in the dentin was evaluated by confocal laser scanning microscopy. The push-out bond strength test was performed on three thirds of the specimens.

RESULTS

In the cervical and middle thirds, the greatest extent of dentin tag formation occurred in the G1 (p = 0.023 and p = 0.033, respectively). In the apical third, G1, G2, and G3 demonstrated similar tag formation between themselves (p = 0.089). In the cervical and middle thirds, G4 demonstrated the highest bond strength when compared to the other groups (p < 0.05).

CONCLUSION

The protocols for removing 0.01 % methylene blue with NaOCl, irrespective of the involvement of passive ultrasonic irrigation, negatively effects the bond strength and tag formation in the dentin of the post space.

Application of a Novel Modification of the Microbond Test for Evaluation of Adhesive Bond Strength Between Fiber Posts and Dual-Cure Dental Resin Cement

Background

While several tests can be used in the laboratory evaluation of composite resin-based cement materials, the push-out test remains the most prevalent. Due to difficulties in sample preparation, as well as a highly complex procedure, we attempted to develop an alternative method for testing the bond strength of dental resin cement materials.

Material/Methods

Ninety-six experimental samples of 2 dual-cure resin cements and 1 fiber post system were prepared for the 2 testing procedures: the push-out test and the modified Microbond test. The degree of monomer conversion was measured by Fourier-transform infrared spectroscopy.

Results

The push-out test results indicated that the bond strength of dual-cure resin cement differs depending on the tooth root region to which it is applied (p<0.05), In addition, our findings show that Variolink II exhibits a much lower bond strength relative to RelyX ARC. These findings were confirmed by the modified Microbond test results. The monomer conversion rate results indicate average conversion rates of 85.81% and 61.35% for RelyX ARC and Variolnik II, respectively.

Conclusions

Our study confirms the practical utility of the modified Microbond test in the assessment of bond strength of dental cement resin-based materials. The proposed test method is particularly useful given that, relative to the push-out test, it requires a much smaller number of preparation and execution steps, thus reducing the potential for introducing errors, while increasing the reliability of the obtained findings.

Physical and mechanical properties of dual functional cements-an in vitro study

OBJECTIVES

The aim of this study was to evaluate the physical and mechanical properties of different dual functional cements.

MATERIALS AND METHODS

Three dual functional cements (Allcem Core (FGM), Rebilda DC (VOCO), and LuxaCore Z (DMG)), a luting resin cement (Rely X ARC (3 M ESPE)), and a Core Buildup composite resin GrandioSo (VOCO) were used. Flexural strength (n = 10) and film thickness (n = 6) were evaluated according to ISO 4049:2009. Flow (n = 6) was evaluated according to ISO 6876:2001. Degree of conversion (DC) was assessed immediately and 24 h after polymerization (n = 5). For resistance to dislodgment (RD) analysis, bovine teeth were prepared to receive fiber glass posts, and a push-out test (n = 12) was used.

RESULTS

Luxacore Z presented lower flexural strength when compared to GrandioSo (p < 0.001). No statistical difference was found between cements for film thickness (p = 0.66). Reduced flow values were found for Allcem Core (p = 0.006). No statistical difference was found for immediate DC for different cements (p > 0.05). After 24 h, DC increased for all groups, except for Luxacore Z (p = 0.054). The RD did not differ from the control Rely X ARC, regardless of the root third (p > 0.05). Luxacore Z showed lower mean values in the apical third compared to the coronal third (p = 0.046).

CONCLUSIONS

The dual functional cements (Allcem Core and Rebilda DC) possessed similar physical and mechanical properties of luting resin cement (RelyX ARC) and Core Buildup composite resin (GrandioSo). Hence, they could be used for one-stage post and core buildup restorations.

CLINICAL RELEVANCE

The dual functional cements could be used for one-stage post and core buildup restorations since they possess similar physical and mechanical properties of luting resin cements and Core Buildup composite resin.

Influence of an iodonium salt on the properties of dual-polymerizing self-adhesive resin cements

STATEMENT OF PROBLEM

Dual-polymerizing self-adhesive resin cements present mechanical properties that may adversely affect the clinical performance of luted fiber-reinforced posts.

PURPOSE

The purpose of this in vitro study was to evaluate the properties of dual-polymerizing self-adhesive resin cements after the addition of an onium salt.

MATERIAL AND METHODS

The experimental groups were set according to the molar concentration of diphenyliodonium hexafluorphosphate (DPIHFP) (0.5, 1, and 2 mol%). The resin cements were submitted to a push-out bond strength test and assessed for flexural strength (ISO 4049/2009), degree of conversion (Fourier-transformed infrared spectroscopy), depth of polymerization, swelling coefficient, and degradation in solvent. The data were statistically analyzed by ANOVA, Tukey test, Kruskal-Wallis test, Dunn multiple comparison, and paired Student t test (α=.05).

RESULTS

All the RelyX U100 groups with onium salt showed the highest degree of conversion after 24 hours and 7 days (P<.001). However, no statistical difference was found among the BisCem groups (P=.054). The addition of 0.5 mol% DPIHFP increased the push-out bond strength and microhardness of RelyX U100 and promoted less degradation after immersion in solvent. The BisCem control group did not present a statistical difference from the experimental groups in terms of bond strength; the control group and the 0.5 mol% group showed no degradation in solvent. For swelling coefficient and flexural strength, no difference was found between the BisCem groups (P=.067 and P=.173), and the RelyX U100 2 mol% group presented the lower value (P<.001 and P=.048). Depth of polymerization was not statistically different in the experimental groups for either resin cement (P=.999).

CONCLUSIONS

The addition of 0.5 mol% DPIHFP improved the physical properties of dual-polymerizing self-adhesive resin cements.