The rheology of gutta percha
Michaelian, Marshall S.
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Gutta percha is the natural form of trans 1,4 polyisoprene. It has been used in dentistry for over 125 years, as a mixture with zinc oxide, barium sulfate, waxes and resins. Specifically, gutta percha has been the filling material of choice for endodontic therapy for over 15 years. This study was directed toward the investigation of the rheological behavior of dental gutta percha. Rheology is that branch of material science defined as the study of deformation and flow. Its primary applications over the past twenty years include the rubber, petroleum, chemical, food and medical industries. The current study is the first application of rheological principles to the flow characteristics of gutta precha during its vertical compaction into a root canal system. After receiving gutta percha samples from Mynol, Hygienic, Union Broach, and Premier, the rheological properties were measured using the latest rheological instrumentation available today - namely the Visco-Elastic Tester by Rheometrics Inc. The samples were evaluated for "flowability" over a wide temperature range (20-85 degrees C) and over 3 decades of frequency or rate of deformation. The results show that(1) all commercially available dental gutta percha are not the same; (2) rheological parameters can differentiate between the various manufacturers; (3) there is a significant decrease in flow resistance with each degree rise in temperature; and (4) of the samples tested Premier showed the greatest ease for "flow", Union Broach was the most resistant to flow, and Mynol and Hygienic behaved almost identically. A second experiment designed to test the results of the rheological measurements involved compacting gutta percha into simulated root canals within plastic blocks at various temperatures. Each block has five apicies of increasing diameter. The force needed to mold the gutta percha to the apex was measured for each sized canal. The results of the simulated root canal packings are in direct correlation to the measured rheological properties. Union Broach gutta percha required the greatest force to move the gutta percha, and requiring tempretures exceeding 47 degress C. Conversely, Premier gutta percha molded into the apex with minimal forces at temperatures as low as 41 degrees C and Hygienic showed nearly identical results. Normal forces flowed the gutta percha into the various apical sizes at temperatures as low as 43 degrees C. In addition to this confirmatory data, this experiment showed that (1) at the same force, it takes more heat (i.e. a higher temperature) or at the same temperature it takes more force to mold the gutta percha into smaller apices, (2) with the exception of Union Broach's sample, all gutta percha flowed into apical sizes at temperatures ranging from 5-7 degrees above body temperature. This study demonstrates the application of the latest rheological measuring devices to the flow of dental gutta percha. Additional studies such as aging and compositional effects on flow are natural spinoffs from this project.
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact email@example.com.Colored photographs included.Thesis (M.Sc.D.)--Boston University, Henry M. Goldman School of Graduate Dentistry, 1979 (Endodontics)Bibliography : leaves 212-221.
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