The thermo-mechanical properties of gutta-percha
Goodman, Alvin Stewart
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Gutta-percha is the natural form of transpolyisoprene and exists in several crystalline states. It has been known to dentistry for about 125 years, gaining greater popularity with its use in the various endodontic techniques. This study was directed toward the investigation and evaluation of the volume-temperature behavior of gutta-percha as it applies to the warm gutta-percha packing procedure in endodontics. Cubical dilatometry was utilized for the purpose of dynamic volume-temperature analysis. Initially it was necessary to determine the temperature range to which the material was subjected within the root canal. This was accomplished by the instrumentation of endodontically prepared teeth with a high response thermocouple assembly and subsequent monitoring of regional temperatures during the warm gutta-percha packing procedure. In order to interpret volume-temperature behavior it was necessary to investigate the transformation temperatures of the various semicrystalline states of the polymer, since these transformations influence the degree of volume reversibility. A differential scanning calorimetric analysis was used to reveal the number of transitions which take place and the temperatures at which they occur. The comparative contributions of compaction and compression to the mechanical phase of the procedure were evaluated by examining gutta-percha under triaxial and uniaxial states of stress. The results indicate that gutta-percha as received in dental compounds exists in a beta form. The beta to alpha transition occurs at 42-49[degrees] C and the alpha to amorphous transition takes place at 53-59[degrees] C, depending on the specific compound. The maximum representative temperature for bulk gutta-percha in the body of the prepared root canal was determined, during the warm gutta-percha packing procedure, to be 80[degrees] C, while the peak temperature experienced in the apical region, 2 mm. from the apex, was 45[degrees] C. Compounded dental gutta-percha subjected to the 80[degrees] C peak experienced an increase in volume of approximately 3 to 5% depending upon the specific compound. Because of the phase transformations which occurred during heating, there resulted, upon cooling to 37[degrees] C, a contraction of the material which continued over a 24 hour holding period to produce a total net loss in volume of 0.03-1.1% relative to original volume at room temperature. Two compounds were exceptions. Repeated cycling from 37[degrees] C to 80[degrees] C to 37[degrees] C produced no further decrease in volume after the first cycle. The compounded dental gutta-percha subjected to a 37[degrees] C to 45[degrees] C to 37[degrees] C plunge cycle, experienced a net post-cycle increase in volume of 1.32% relative to its pre-cycle volume at room temperature. This was due to the fact that the beta to alpha transition point was not exceeded. In a completely sealed (triaxial) system, actual molecular compression of gutta-percha took place only after a stress level of approximately 2000 psi was reached. In an open stress (uniaxial) system, flow occurred long before actual compression levels were reached, preventing the achievement of stress levels sufficient to bring about compression. Compressibility values were determined.
Thesis (M.Sc.D.)--Boston University School of Graduate Dentistry, Dept. of Endodontics, 1973.Includes bibliography.
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