Bonding glass-ionomer cements to chemomechanically-prepared dentin

Comparative evaluation of microshear bond strength of the caries-affected dentinal surface treated with conventional method and chemomechanical method (papain)

Background:

There is a growing interest in chemomechanical excavation (papain) in permanent molar teeth. There are several studies dealing with primary molar teeth.

Aim:

The aim of this study was to evaluate the influence of conventional method and Carie-care (chemomechanical method) on the microshear bond strength (μSBS) and the type of failure of an adhesive system to caries-affected dentin of permanent molar teeth.

Materials and Methods:

Twenty permanent molar teeth with carious lesions extending into the dentin were selected. Through the center of the carious lesion, teeth were sectioned mesiodistally and divided into two groups based on the method of caries excavation (conventional and chemomechanical method). The time required for the completion of excavation procedure was noted. Samples were again divided into two subgroups in each according to the method of restoration (Ketac N100 and Filtek Z350 composite). The bonded interface was subjected to μSBS testing in a universal testing machine. Fractured surfaces were examined under a stereomicroscope, and representative specimens were examined under scanning electron microscope for the type of failure.

Statistical Analysis:

It was achieved with unpaired t-test and Kruskal-Wallis H-test at 5% level of significance.

Results:

The μSBS values of Carie-care groups were similar to that of the conventional method. The μSBSs of resin composite were significantly (P < 0.001) more than that of resin glass ionomer bonded irrespective of the method of caries excavation.

Conclusion:

A papain-based chemomechanical agent can be used safely as a method for caries removal when employing conventional adhesive systems.

pH gradient and distribution of streptococci, lactobacilli, prevotellae, and fusobacteria in carious dentine

OBJECTIVES

Caries process comprises acidogenic and aciduric bacteria that are responsible for lowering the pH and subsequent destruction of hydroxyapatite matrix in enamel and dentine. The aim of this study was to identify the correlation between the pH gradient of a carious lesion and proportion and distribution of four bacterial genera; lactobacilli, streptococci, prevotellae, and fusobacteria with regard to total load of bacteria.

MATERIALS AND METHODS

A total of 25 teeth with extensive dentinal caries were sampled in sequential layers. Using quantitative real-time PCR of 16S rRNA gene, we quantified the total load of bacteria as well as the proportion of the above-mentioned genera following pH measurement of each sample with a fine microelectrode.

RESULTS

We demonstrated the presence of a pH gradient across the lesion with a strong association between the quantity of lactobacilli and the lowest pH range (pH 4.5-5.0; p = 0.003). Streptococci had a tendency to occupy the most superficial aspect of the carious lesion but showed no correlation to any pH value. Prevotellae showed clear preference for the pH range 5.5-6.0 (p = 0.042). The total representation of these four genera did not reach more than one quarter of the total bacterial load in most carious samples.

CONCLUSION

We revealed differential colonization behavior of bacteria with respect to pH gradient and a lower than expected abundance of lactobacilli and streptococci in established carious lesions. The data indicate the numerical importance of relatively unexplored taxa within the lesion of dentinal caries.

CLINICAL RELEVANCE

The gradient nature of pH in the lesion as well as colonization difference of examined bacterial taxa with reference to pH provides a new insight in regard to conservative caries management.

Bonding of contemporary glass ionomer cements to dentin

OBJECTIVE

The objective of this study was to investigate the microtensile bond strength (microTBS) of contemporary glass ionomer cements (GIC) to sound coronal dentin.

METHODS

Three specimen teeth were prepared for each material tested: Fuji IX GP (GC), ChemFlex (Dentsply) and Ketac-Molar Aplicap (ESPE). GIC buildups were made according to the manufacturers' instructions. After being stored at 37 degrees C, 100% humidity for 24h, the teeth were vertically sectioned into 1x1mm beams for microTBS evaluation. Representative fractured beams were prepared for scanning (SEM) and transmission electron microscopic (TEM) examination.

RESULTS

Results of the microTBS test were: Fuji IX GP (12.4+/-8.6MPa), ChemFlex (15.0+/-9.3MPa) and Ketac-Molar Aplicap (11.4+/-7.7MPa). One-way ANOVA and a multiple comparison test showed that ChemFlex had a statistically higher microTBS (p<0.05). SEM fractographic analysis showed that the predominant failure modes were interfacial and mixed failures. The GIC side of the fractured beams revealed dehydration cracks, a high level of porosity, and voids with an eggshell-like crust. TEM analysis of the demineralized dentin sides of the fractured beams revealed the presence of an intermediate layer along the GIC-dentin interface. This zone was present on the fractured dentin surface in the case of interfacial failure, and beneath GIC remnants in specimens that exhibited a mixed failure mode.

SIGNIFICANCE

The findings suggest that the bonding of GIC to dentin is not weak and that the microTBS values probably represent the weak yield strengths of GICs under tension.

Chemomechanical caries removal: a comprehensive review of the literature

Compared to the past, caries removal has become more efficient, however inherent fundamental drawbacks of the drilling approach have remained: unpleasantness to patients, need for local anesthesia, and potential adverse effects to the pulp due to heat and pressure. Chemomechanical caries removal, introduced almost three decades ago, was claimed to be a non-invasive alternative for the removal of carious dentine. In essence, the technique involved applying a solution onto the decayed dentinal tissue, allowing it to soften it, and, finally, scraping it off with blunt hand instruments. The partially degraded collagen in carious dentine was chlorinated by chemomechanical caries removal solutions. This chlorination affected the secondary and/or quaternary structure of collagen, by disrupting hydrogen bonding. Carious material removal was thus facilitated. The purpose of this paper is to perform a comprehensive review of the literature regarding chemomechanical caries removal, including the most recently available product, the initial reports on which warrant renewed interest in the approach.

Glass polyalkenoate bond strength to dentine after chemomechanical caries removal

The bond strength of a glass polyalkenoate cement after chemomechanical caries removal of dentine with or without the use of a conditioning agent and the mode of bond failure using scanning electron microscopy was examined. Forty extracted carious human teeth were divided into four groups of ten. Conventional caries removal was carried out on two groups and chemomechanical caries removal on the other two groups. Surface conditioner was applied to the dentine in one conventionally treated and one chemomechanically treated group. Glass polyalkenoate cement was applied via a metal holder to the dentine. The samples were stored for 7 days in a moist environment at 37 degrees C. The samples were subjected to a shearing-type stress at a cross-head speed of 0.5 mm min-1. The mean bond strength for each group, in MPa (standard deviation), was: conventional caries removal alone 1.32 (0.51), conventional caries removal and conditioner application 2.43 (0.47), chemomechanical caries removal alone 2.47 (0.99) and chemomechanical caries removal and conditioner application 2.76 (0.96). Mean bond strengths for both the chemomechanically treated groups and the conventionally treated group, coupled with the use of the conditioning agent, were significantly greater than for the conventionally treated groups alone at the 0.05 level. There was no significant difference between the chemomechanically treated groups or the group conventionally treated with conditioner application. SEM examination revealed a combination of cohesive and adhesive bond failure. Different morphologies between the conventionally and chemomechanically treated surfaces were also evident.

Influence of cement layer thickness on the adhesive bond strength of polyalkenoate cements

The fracture toughness and yield stress values of model zinc polycarboxylate and glass polyalkenoate cements have been used to calculate plastic zone sizes. The size of the plastic zone at the crack tip in these materials has been used to predict whether cement layer thickness is likely to influence the adhesive bond strength. In the model zinc polycarboxylate cement studied, the plastic zone size was comparable to the cement layer thickness and had a pronounced influence on the shear bond strengths obtained. In contrast, the plastic zone sizes obtained for the glass polyalkenoate cements were much smaller and the shear bond strengths were found to be much less dependent on cement layer thickness.