The effect of milling on nanmetric synthesis, setting time and apical microleakage of white mineral trioxide aggregate as a root-end filling material

Abstract

Mineral trioxide aggregate (MTA) is a cement type material that was advocated to be used for many situations in endodontics. One disadvantage of MTA is its extended setting time. The purpose of this study was to evaluate the effect of ball milling on setting time and its effect on apical microleakage of MTA as a root-end filling material and probability of nanometric MTA production within the appartus sensivity. Methods: WMTA was milled in a planetary ball mill for 120, 240, 360, 480, 600 and 720 seconds.The high power field mode of the flow particle image analyzer was used for particles size measurement. The setting time of the samples was measured by the Gilmore needle test. Microleakage was compared among groups by evaluating bovine serum albumin (BSA) microleakage using spectrophotometry. 70 single rooted teeth were divided into seven groups, instrumented, obturated and apices were resected. Root end cavities were filled with non milled MTA and milled MTA for 120, 240, 360, 480, 600 and 720 seconds. Results: The size of WMTA particles was 500nm to 30 ?m before ball milling and most of them were between 1 to 3 ?m. After ball milling for 120, 240, 360, 480, 600 and 720 seconds most of the particles size were 1 to 3?m , 600nm to 3?m , 700nm to 3?m ,600nm to 2?m , 600nm to 2?m and 600nm to 2?m respectively. The initial setting time standard error in non milled WMTA group and ball milled WMTA groups for 120, 240, 360, 480, 600, 720 seconds were 41.6 0.93,42.90.76, 32.20.51,53.8 1.73, 86.24.02, 110.32.57 and 148.16.07 minutes respectively. The differences between non milled WMTA and ball milled WMTA for 480, 600 and 720 seconds were statistically significant (p<0.001). The amount of microleakage standard error in non milled WMTA group and ball milled WMTA groups for 120, 240, 360, 480, 600, 720 seconds were 2.3 0.11,2.10.77, 2.10.12,1.5 0.14, 17.13.19, 21.82.93 and 28.52.66 ng respectively. The differences between non milled WMTA and ball milled WMTA for 480, 600 and 720 seconds were statistically significant (p<0.001). conclusion: Ball milling of the particles up to 480 second led to increase the amount of smaller particles, however ball milling more than 480 second could not be able to produce smaller particles in the range of the apparatus sensitivity and significantly increased the setting time and apical microleakage of WMTA.