Influence of pH on the Surface Hardness and Microstructure of Mineral Trioxide Aggregate and Biocem: An Invitro Study

The present study was designed to evaluate the surface microhardness of white and grey MTA following exposure to a range of acidic and neutral environments during hydration. In addition, BIOCEM an indigenous MTA like material, has also been studied. EDAX analysis was performed to determine the constituent elements in Biocem. The morphological and microstructural features of the samples were studied using SEM. 99 cylindrical moulds of size 6mm diameter and 10mm length were fabricated and was used in this study. In this seventy two cylindrical moulds were used for microhardness testing and twenty seven cylindrical moulds were used for SEM evaluation. The samples were divided into three groups, Group I – containing 24 samples of GMTA, Group II – 24 samples of WMTA and Group III - 24 samples of BioCem. The three groups were further divided into three sub - groups at pH 5.4, pH 6.4, pH 7.4. Similar grouping was done for SEM evaluation. WMTA, GMTA and BIOCEM was mixed and condensed upto 5mm inside the prepared cylindrical moulds. The material was compacted evenly into the mould using a custom made device under a pressure of 3.22Mpa which was applied for one minute. A wet cotton pellet was placed onto the samples within the polyvinyl tube. The samples were stored at room temperature (20ºC) with in a glass vial for 4 days. The bottom of each vial contained gauze soaked in butyric acid buffered at pH 5.4, 6.4 and 7.4.The opening of the glass vial were covered by moist gauze and covered to ensure the presence of sufficient humidity inside the vials. After four days the samples were removed from the moulds and subjected to microhardness testing and SEM evaluation. The results of the present study were subjected to statistical analysis to interpret the influence of various pH in each group and also between the groups. One-Way ANOVA followed by Tukey HSD test was used for statistical analysis in the present study. CONCLUSION: Within the limitations of this in vitro study, it was concluded that, 1. The surface hardness of all the experimental MTA groups and Biocem were impaired when exposed to acidic environment. 2. The greatest surface hardness values were observed following exposure to pH 7.4(neutral pH) in all the experimental samples. 3. The other interesting findings were that microhardness values decreased following exposure to pH 6.4 and pH 5.4. However there were no statistical difference between the GMTA and WMTA groups and also with the experimental cement Biocem, at the above pH levels. 4. The internal microstructure of all the specimens exposed to butyric acid with pH 7.4 had distinctive crystalline structure embedded within a more uniform matrix partially covered by colloidal gel. As the pH decreased to 6.4, the porosity increased and the pore size diameter was larger when compared to that of 7.4. 5. Specimens exposed to a more acidic environment (pH 5.4) revealed extensive porosity on the surface of the experimental samples. The pore size diameter of the specimens exposed to pH 5.4 was still larger when compared to the specimens exposed to pH 6.4 and pH 7.4. In the new horizon, the advancement in the technological field of biocompatibility testing can predict the property and design the material that can elicit customized biological responses