A Novel Method for Creating Endodontic Access Preparations Through All-Ceramic Restorations: Air Abrasion and Its Effect Relative to Diamond and Carbide Bur Use Christopher R. Sabourin, DDS, MS, MSD, Brian D. Flinn, PhD, PE, † David L. Pitts, DDS, MSD, Timothy L. Gatten, DDS, and James D. Johnson DDS, MS Abstract Access through porcelain restorations is a technically delicate and stressful procedure. Although this is a common dilemma in endodontics, little research has explored alternatives in cutting through porcelain. The purpose of this study was to compare the use of a carbide bur plus water, diamond bur plus water, and air abrasion to access through porcelain. All-ceramic sam- ples were accessed using the different techniques. Sam- ples were evaluated using two transillumination meth- ods, white light, and fluorescent liquid penetrant described by the American Society for Testing and Materials. Edge chipping, microcracking, and cata- strophic fracture of porcelain caused by the techniques were statistically compared. Fluorescent liquid pene- trant was a more sensitive method for microcrack de- tection. There were significant differences between the preparation techniques. Air abrasion was significantly less destructive, and caused no catastrophic fractures, edge chipping or microcracks. Preparation by air abra- sion took longer to complete. Key Words Air abrasion, access, all-porcelain, microcracks From the Department of Endodontics, † Department of Materials Science and Engineering, University of Washington, Seattle, Washington. Address requests for reprints to Dr. James Johnson, De- partment of Endodontics, Box 357448, D-669 Health Sciences Bldg, University of Washington, Seattle, WA 93195. E-mail address: jamesj2@u.washington.edu. Copyright © 2005 by the American Association of Endodontists T he original method of endodontic access through porcelain crowns recommended using a #2 diamond bur with water to cut through porcelain, followed by a carbide bur to access through dentin (1). Teplitsky and Sutherland (2) accessed through 56 Cerestore porcelain crowns, and evaluated them for cracks using white light transillumination. Twelve samples were examined with scanning electron microscopy (SEM). None of the crowns experienced a catastrophic fracture, where porcelain separated into two or more parts. Chipping and roughness on the external surfaces was evident. One of the 12 samples evaluated by SEM showed a crack. It is assumed that the preparation was done with a diamond, not a carbide bur. A similar study used 42 Dicor crowns (3). Accesses were prepared with either diamond or carbide burs. Crowns were examined using direct vision, stereomicros- copy, transillumination, and SEM. The tungsten carbide burs produced two cata- strophic fractures and six exhibited microcracks (‘crazing’). In comparison, the dia- mond burs produced one crown with microcracks, but no catastrophic fractures. Mandibular incisor crowns suffered the most damage. Both techniques produced chip- ping. Cohen and Wallace evaluated the effect of access on Dicor crowns (4). Prepara- tions were made with diamond burs using water/air spray. While chipping was evident using SEM, microcracks and catastrophic failures were not. Haselton et al. accessed 28 all-ceramic crowns (5). SEM showed edge chipping in 100% of the samples prepared with tungsten carbide fissure or round medium coarse diamond burs. Microcracks were evident in four crowns, three from the carbide burs, and one from the coarse diamond burs. Three catastrophic fractures occurred, two in the diamond group, one in the carbide group. These were not statistically significant differences. They listed definitions for porcelain evaluation following endodontic access (5): • Edge chipping: disruption of the crown surface integrity at the outline form of the access opening as a result of a loss of thin, wedge-shape pieces of porcelain at least 0.1 mm in length • Microcracking: visibly detectable crack in the porcelain beginning at the outline form of the access opening but not resulting in a separation of porcelain • Fracture: crack in the porcelain resulting in separation of the crown into two or more parts A nondestructive method for accessing through porcelain does not appear in the literature. Consequently, patients are advised that endodontics has a high probability of success, but crowns may be damaged during access preparation. The purpose of this study was to compare microcracking, edge chipping, and catastrophic fractures of porcelain from access preparations completed with either diamond or carbide burs plus water, or a new air abrasion technique. Basic Research—Technology 616 Sabourin et al. JOE — Volume 31, Number 8, August 2005