Delayed linear expansion of improved dental stone

Area of Science:

• Dental Materials Science
• Biomaterials Engineering

Background:

• American Dental Association (ADA) Specification 25 mandates final setting expansion measurements for dental stones at 2 hours.
• Pilot studies indicated that some dental stones exhibit delayed expansion or early contraction for up to 120 hours.

Purpose of the Study:

• To measure the linear setting expansion of six ADA type IV and V dental stones up to 120 hours.
• To compare the 2-hour expansion values against ADA Specification 25.
• To characterize the expansion changes over extended periods.

Main Methods:

• Six dental stones (Die-Keen, Jade Stone, Vel-Mix, ResinRock, Fuji Rock, Silky Rock) were mixed using standardized techniques.
• Setting expansion was continuously measured using an electronic device for 120 hours.
• Data were analyzed using 2-way repeated-measures multivariate analysis of variance.

Main Results:

• All tested dental stones showed increased linear expansion at 120 hours compared to 2 hours.
• Expansion was largely complete by 96 hours for most stones, excluding ResinRock.
• Die-Keen had the highest total mean expansion (0.35%), while Silky Rock had the lowest (0.14%) at 120 hours.
• Significant interactions between stone type and time were observed (P<.0001).

Conclusions:

• Dental stones continue to expand during setting beyond the initial 2-hour measurement period.
• The proportion of expansion occurring after 2 hours ranged from 22% to 71% across different materials.
• Die-Keen showed the highest overall expansion but the least expansion after 2 hours, stabilizing by 72 hours, similar to Silky Rock.