Pejman Parsa

Date of Graduation

2015

Document Type

Thesis

Degree Type

MS

College

School of Dentistry

Department

Orthodontics

Committee Chair

Takashi Komabayashi

Committee Co-Chair

Michael Bagby

Committee Member

Anthony T Borgia

Abstract

Introduction.;Preventing apical periodontitis has been the cornerstone of endodontic therapy. For decades, clinicians have been challenged by the microorganisms present in the root canal system to help host defenses heal the apical tissues. Root canals that have been biomechanically cleaned, shaped and disinfected by instrumentation, irrigation and medication are in need of obturation. To the experienced practitioner it is prudent that a three-dimensional obturation that is fluid tight be placed in order to prevent oral and apical micro leakage. Many different techniques and materials are advocated to achieve this type of fill. The most commonly used material with the longest history of use is gutta percha. The natural chemical form is trans 1,4-poly-isoprene. This material, when heated, will flow and upon cooling it will shrink slightly. Different components are present in dental gutta percha. Namely zinc oxide, heavy metal salts, and other waxes and resins, with only about one fifth of the chemical constituent being actual gutta percha.;Traditionally gutta-percha used in obturation comes as pre-shaped cones that can be placed into canals, which creates the clinical problem of adequately filling canals that are not inherently circular in cross section with pre-shaped circular gutta percha cones. To better address this problem, warm and heated gutta-percha, with its flowable properties, has been used in combination with traditional cones to provide a fluid tight seal. Some clinicians have even used warm gutta-percha to entirely fill a canal. Using thermoplasticized gutta-percha as the sole obturation material has advantages in that a better obturation in three dimensions can be achieved. In this method, controlling the apical extent of the gutta-percha may be an unreliable and unpredictable procedure.;Materials and Methods.;One hundred and forty maxillary and mandibular incisors were selected. Conventional endodontic accesses were prepared in all these teeth after their crowns were sectioned off at the cementoenamel junction. The total teeth were divided into 5 groups, with each group being comprised of 7 teeth from each particular tooth number (#8, #9,#24, #25). All teeth were prepared with 4 percent taper. Five groups of preparation sizes were used as follows: 20, 25, 30, 25, and 40. The patency of the apical foramen was tested using a #10 K file. Thereafter, the canal was negotiated with a # 15 file until it was visible at the portal of exit, with the working length being determined by subtracting 1 mm from this measurement. At this measurement, the first file to bind (FFTB) was determined for each tooth. After determination of the FFTB, a glide path equal to size 20 handfile was created. The canals were shaped according to their respective groups using NiTi rotary instrumentations in a crown down manner using copious 2.5% NaOCl irrigation. The dentinal smear layer was removed using 17% EDTA and a 2.5% NaOCL. The canals were dried with 70% alcohol and paper points and a thin layer of Roth's root canal cement was placed. Excess cemented was wicked out with paper points. Thermoplastic obturation was carried out with the Calamus DUALRTM obturation systems by holding the extruder tip 3-5 mm away from the working length.;After backward selection, the final logistic regression model included FFTB, File Size Group and the interaction between these two variables, while adjustments are made to block the variability of tooth number. This means that the other variable (extruder distance from WL) does not add any additional information to our understanding of extrusion probability beyond FFTB and file size group. Since the statistical interaction between FFTB and file size group is statistically significant, all interpretations of the model were conducted jointly. So, for examples when the FFTB was a size 20, the odds of extrusion decrease 82% (1-0.18 x 100%) for each additional increase in file size used (from 20 to 25, 30, 35, 40).;Conclusions.;The results of this study indicate that the FFTB and File Size group play a more significant role than the extruder distance from working length. While keeping the file size group constant, if the FFTB were to increase, an increase in the rate of extrusion would be seen. Therefore, the larger the difference between the original size of the canal and the final preparation of the canal, extrusion becomes less likely. This is invariably due to the larger apical stop (platform) created. This platform serves as a matrix and barrier for materials to discontinue their flow. Keeping these measurements in mind, the clinician can make mindful decisions during his procedure to prevent overextension and procedural mishaps. (Abstract shortened by UMI.).

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