UCSF

Introduction and Objectives:

Mineral trioxide aggregate (MTA), a hydraulic Portland-cement based dental restorative material, is commonly used in various endodontic and restorative procedures. Numerous methods have been proposed for clinical placement of MTA due to its difficult handling and placement in its paste form. A clear relationship between porosity and compressive strength of hydraulic cements has been established in previous reports. In this study, we used gas adsorption porosimetry to quantify specific pore characteristics of Portland cement samples prepared by two different placement methods. A correlation was made between specific pore characteristics to compressive strength in general.

Methods:

Portland cement paste was placed in cylindrical moulds using either compaction alone (Group 1) or compaction along with indirect ultrasonic agitation (Group 2) of the paste. Visible differences in porosity on surface and in cross sections of specimens were evaluated using a stereomicroscope. Specific pore characteristics and compressive strength were quantified using a gas adsorption porosimeter and an Instron universal testing machine, respectively. Student's t-test was used for statistical evaluation. A regression and correlation analysis was done to compare specific pore characteristics against compressive strength in general.

Results:

Gas adsorption porosimetry provided quantitative values for specific pore characteristics of the set specimens. Microscopic evaluation revealed visibly larger pores both on the surface and in cross-sections of specimens prepared by the indirect ultrasonic activation method. This group also displayed weakened demarcation lines between aliquots of cement paste in each specimen. Based on the limited preliminary data (n=8) no significant difference in mean values of specific pore characteristics or compressive strength of specimens may be reported. Regression/ correlation analyses do not show a statistically significant relationship between compressive strength and any specific pore characteristic.

Conclusions:

1. Gas adsorption porosimetry may be used to quantify specific pore characteristics of hydraulic cement based dental restorative materials

2. Ultrasonic agitation of the cement may separate the liquid from the solid component of each aliquot of cement, producing weakened areas at the interface between aliquots of paste placed on top of each other

3. Larger scale studies are needed to evaluate the superiority of one method of placement over the other.