Study on Rehardening of Demineralized Dentin with Resin-modified Pulp-capping Agents Containing MTA

Abstract

 Purpose: Based on the concept of minimal intervention (MI), temporary indirect pulp capping (IPC) is used to preserve the deep parts of dentin adjacent to the pulp and avoid pulp exposure when caries advances deep into the dentin close to the dental pulp. The purpose of this study was to measure the Knoop hardness of softened dentin applied with cured bodies of resin-modified pulp-capping agents containing MTA at 1 month and 3 months postoperatively.

 Methods: We measured the hardness on the side of the enamel of dentin samples with Cariotester, and used those with enamel side hardness of around 60 KNH as healthy dentin samples. We decalcified the healthy samples according to the method of Matsuda et al., and used those whose hardness decreased to around 20 KNH as softened dentin samples. As pulp-capping agents, we applied TMR-MTA cement (TMR) and NEX MTA cement (NEX), which are conventional MTA cements, and TheraCal LC (TCL) and Super MTA Paste (SMP), which are resin-modified pulp-capping agents containing MTA, on softened dentin samples and coated each with base cement to use them as the pulp-capping samples. We measured the Knoop hardness of the softened dentin after storing the prepared pulp-capping samples in a container at 100% humidity for 1 month and 3 months. We prepared three samples for each condition, and subjected the obtained values to statistical analysis using repeated measure analysis of variance and Tukey’s test (p<0.05).

 Results: After application of pulp-capping agents, the Knoop hardness was 32.8±2.7 KNH after 1 month and 33.2±0.4 KNH after 3 months in the TMR group. The hardness values improved significantly after 1 month and 3 months compared to the softened dentin samples, but were significantly lower than those of the healthy samples. In the NEX group, the hardness was 41.1±2.3 KNH after 1 month and 41.6±4.0 KNH after 3 months. The hardness values improved significantly after 1 month and 3 months compared to the softened dentin samples, but were significantly lower than those of the healthy samples. In the TCL group, the hardness was 20.1±0.5 KNH after 1 month and 27.7±4.4 KNH after 3 months. There was no significant difference in hardness after 1 month or 3 months compared to the softened dentin samples, and the values were significantly lower than those of the healthy samples. In the SMP group, the hardness was 56.5±5.9 KNH after 1 month and 62.0±2.5 KNH after 3 months. The hardness improved significantly after 1 month and 3 months compared to the softened dentin samples. Compared to the healthy samples, hardness improved to a level where there was no significant difference both after 1 month and 3 months. The results of this experiment showed that application of resin-modified pulp-capping agents containing MTA on softened dentin induced recalcification and hardened the softened dentin.

 Conclusion: It was concluded that the application of chemical-cured type resin-modified pulp-capping agents containing MTA improved the hardness of the softened dentin to a level that was not significantly different from that of healthy dentin after 1 month and 3 months.