Purpose: To monitor the volume changes that take place in gutta-percha as a function of temperature.
Volumetric changes were measured using two techniques of heating
1- Slow cycle series: dilatometer was heated in room temperature water bath and then the temperature was gradually increased to 80 C and decreased gradually to 37 C and remained constant for 24 hours. Mercury height was measured before and after and in between.
2- Plunge cycle series: 2 temperatures were chosen 80 C for the bulk of the GP and 45 C for the apical 2 mm of GP alternating from 37 C temperature (37 (precycle) to 45 or 80 C to 37 to 45 or 80 C. to 37 C) This alternate plunging was performed to simulate the thermal cycle of GP at various locations within the root canal during clinical usage.
- Beta crystalline structure of GP transforms to alpha structure at 46-52 C and from 56-62 C it transforms to alpha amorphous melt which semi crystalize in to beta structure at 42-40 C
- Slow cycle: >5% volume increase at 80 C. Shrinkage is noted after cooling to 37 C but does not reach to the room temperature level (it has a higher volume).
- 45 C Plunge cycle series: there is a net increase in volume of GP at 45 C (after heating at 45 C and cooling to 37 C, the GP retained 1.3% of volume.
- 80 C Plunge cycle series : 1.4% volume loss at 37 C after the application of 80 C compared to the volume at the precycle 37 C
There is a small volume reduction upon cooling to 37 C. Thus, condensation is advocated to compensate for volumetric changes and the apical part of the GP undergoes minimal volumetric changes because the lower the temperature the less volumetric changes.