Morphological confocal laser scanning microscope evaluation of four different “etch and rinse^|^quot; adhesives in post endodontic restoration

The effect of etching techniques on cement penetration into dentinal tubules on fiber post cementation

Objective

A combination of self-etch and additional etch techniques as pre-cementation procedures for fiber post restoration was reported able to increase the bonding of adhesive material. This research aimed to determine the effects of different etching techniques on resin cement penetration into dentinal tubules.

Materials and methods

Thirty-two endodontic treated premolars were prepared for 10 mm fiber posts and were divided into two groups (n = 16). Group one was treated with self-etch only, and the second was treated with a combination of self-etch and additional etching. The fiber posts were cemented using fluorescent rhodamine B 0.1%-colored resin cement. The samples were cut to a 2 mm thickness in the middle third of the root and were evaluated with confocal laser scanning microscopy (CLSM). Statistical analysis measurements were analyzed by an independent t-test and Pearson correlation test.

Results

There were statistically different in densities hybrid layer and resin tag penetration lengths. Statistically strong linear positive correlations between the hybrid layer density and resin tag penetration length in both groups were also observed. Hybrid layer density (9.68 μm), resin tag penetration depth (32.51 μm) in the self-etch group with additional etching were higher than in the other group. The Pearson correlation test results between hybrid bond density and resin tag penetration depth in the self-etch treatment group showed a value of r = 0.634 and p-value = 0.008 and in the etching group self-treatment with additional etching a value of r = 0.516 and p-value = 0.041 (p ≤ 0.05).

Conclusion

There is a statistically significant positive correlation or linear relationship between hybrid bond density and the penetration depth of resin tags in both treatment groups: the thicker the hybrid layer density, the deeper the penetration of the resin tags. This phenomenon may increase mechanical strength regarding stronger binding of resin cement to a tooth’s substrate.

Comparative Evaluation of Resin Dentin Interface using Universal and Total- Etch Adhesive Systems on Sound and Eroded Dentin: In Vitro Study

Objective This study aimed to compare the resin-dentin interface of sound and eroded dentin using universal and total-etch adhesive systems.

Materials and Methods Forty caries-free extracted human premolars were collected, and the occlusal surfaces were ground by using slow speed diamond disc with copious water supply until a flat superficial dentin was exposed. The test group underwent erosive cycle (n = 20), and another group (n = 20) was reserved for control group. Erosive protocol consisted of immersion in 1.23% citric acid for 1 minute every 12 hours and stored in artificial saliva. Both the control and eroded teeth were further subdivided (n = 10) for composite restoration by using either self-etch or total-etch systems. Then the tooth samples were sectioned longitudinally and observed under confocal laser scanning microscope at ×10 magnification to evaluate resin tag length and hybrid layer thickness.

Statistical Analysis The data obtained were analyzed by using independent t-test.

Results The highest mean value of the resin tag length and thickness of hybrid layer was observed with total-etch system in sound dentin group compared with other groups (p < 0.001).

Conclusion The resin-dentin interface of sound dentin was found to be better than eroded dentin by using total-etch system. The resin-dentin interface of eroded dentin was superior to sound dentin by using self-etch adhesive system.

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.

Analysis of the bond interface between self-adhesive resin cement to eroded dentin in vitro

The purpose of this study was to evaluate the bonding interface between a self-adhesive resin cement to in vitro eroded dentin. Seventy-two third molars were used and divided into two groups: sound dentin and in vitro eroded dentin. The in vitro erosion was performed following a demineralization protocol, in which the specimens were immersed in a demineralizing solution for 2 minutes per cycle and remineralizing solution for 10 minutes per cycle for 9 days. Both groups were submitted to four dentin surface treatments: control group (without any treatment), 2% chlorhexidine, 20% polyacrylic acid, and 0.1 M EDTA (n = 9). Blocks of resin-based composite were bonded with RelyX U200 self-adhesive resin cement applied on the pretreated dentin surfaces. The teeth were sectioned into beams (1mm²) and submitted to microtensile bond strength testing to evaluate the bond strength of self-adhesive resin cement to dentin after 24 hours and 8 months of immersion in artificial saliva. Three specimens of each group were longitudinally cut and evaluated using confocal laser scanning microscopy to analyze the dentin/cement interface. Eroded dentin showed higher bond strength values when compared to sound dentin for the 2% chlorhexidine group (p = 0.03), 24 hours after adhesion. When considering eroded dentin, the 0.1M EDTA group showed higher bond strength values with a statistically significant difference only for the control group (p = 0.002). After 8 months of storage, the present results showed that there was no statistically significant difference between the two substrates for all experimental groups (p>0.05). Analysis of the microscopy confocal showed different types of treatments performed on dentin generally increased tags formation when compared to the control group. The eroded dentin showed a significant increase in density and depth of resinous tags when compared to sound dentin. The storage of samples for 8 months seems to have not caused significant degradation of the adhesive interface.