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 »  Home  »  Endodontic Articles 9  »  The effect of instrument type and preflaring on apical file size determination
The effect of instrument type and preflaring on apical file size determination
Introduction



B. T. Tan & H. H. Messer
Department of Restorative Dentistry, School of Dental Science, University of Melbourne, Melbourne, Australia.

Introduction.
Effective canal debridement relies on the accurate determination of the working length (WL) and adequate apical canal enlargement. The extent of apical enlargement is typically based on anestimate of the initial canal size as determined by the size of hand file that ‘binds’at the WL (Grossman et al. 1988). Both tactile detection of the apical constriction and apical file size determination depend on the assumption that the canal is narrowest in the apical region, with unrestricted passage of the file to that point. Continued dentine formation is responsible for an increased thickness of dentine at the £oor of the pulp chamber and for progressive constriction of the canal space (Philippas 1961). This coronal constriction should be removed by preflaring for accurate WL and file size determination (Leeb 1983, Stabholz et al.1995, Contreras et al. 2001).
In the past, few authors have conducted clinical research on the ability to detect the apical constriction by tactile sensation, and the apical constriction is indeed considered a ‘myth’ by some authors. Seidberg et al. (1975) reported that the apical constriction could be identified accurately in 64% of cases with digital-tactile means as compared with 48% using an (early model) apex locator. Another study (Stabholz et al.1995) showed that determination of the apical constriction by tactile sensation was possible in 75% of cases if the root canal was preflared as compared to only 32.3% of cases if the coronal aspect was not preflared. The most significant finding in that study was that preflaring of the coronal portion of the root canal resulted in more reliable WL determination, implying that coronal constriction affected tactile discrimination in the apical part of the canal.
Leeb (1983) studied the effect of enlarging the rootcanal orifice on biomechanical canal preparation. Using India ink as a marker, he observed that normal dentine apposition caused the cervical region to be the narrowest portion of the root canal. If a Gates-Glidden drill or Peezo reamer was used to enlarge the orifice and to eliminate cervical interference, larger ¢les could be passed more easily to the apical constriction. Recently, Contreras et al. (2001) reported that early coronal flaring resulted in a significantly larger hand file (Flex-R file) fitting to the apex.
Lightspeed1(LS) is a non tapered rotary instrument. It consists of standard and half sizes having a cutting head approximately 1-2-mm long with a non cutting pilot tip. LS instruments have been reported to give a greater apparent apical size than conventionally tapered K-files (Levin et al. 1999, Liu & Jou 1999). A mean difference of 11.03 ISO units was found without preflaring the coronal part of the canal (Liu & Jou 1999). After £flaring, the mean difference was 7.25 ISO units. How ever, no further information was provided regarding the sizes of both instruments and whether only K-files or both instruments increased in sizes after flaring. Liu & Jou (1999) concluded that hand-held LS rotary instruments were better instruments to estimate the size of the apical constricture than K-files.
The above studies have demonstrated the importance of coronal flaring and the effect of different types of instruments on file size and vWL determination. If the Grossman criterion (Grossman et al.1988) of enlarging a root canal to at least three sizes beyond the first file that binds at WL is valid, then one should question whether a standard master apical file size of 25 or 30 would be su⁄cient for the apical preparation of narrow canals, as is routinely recommended by most authors (Grossman et al. 1988, Weine 1989, Ingle et al. 1994, Torabinejad 1994, Walton & Rivera 1996, West & Roane 1998). It may be more accurate to size each canal individually and subsequently determine its master apical file size to ensure that the apical third region is adequately enlarged and debrided prior to obturation.
The aim of this study was to investigate the effect of instrument type (K-files and LS instruments) and preflaring on the determination of initial apical size in a range of different canal types of varying sizes and curvatures. This study focused on posterior teeth only (premolars and molars) because these teeth impose the greatest challenge in root-canal treatment. This information is clinically important, as the extent of apical shaping will rely on the initial assessment of canal size.