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 »  Home  »  Endodontic Articles 12  »  Quality of preparation of oval distal root canals in mandibular molars using nickel-titanium instruments
Quality of preparation of oval distal root canals in mandibular molars using nickel-titanium instruments
Introduction - Materials and methods.

T. Rodig, M. Hulsmann, M. Muhge & F. Schafers
Department of Operative Dentistry, Preventive Dentistry and Periodontology, University of Gottingen, Robert-Koch-Street 40, 37075 Gottingen, Germany.

The main parameters in evaluation of any technique or device for root canal preparation are the ability to enlarge and clean the root canal sufficiently. Additionally, good working safety should be a main prerequisite for the use of any instrument or technique. Numerous investigations have demonstrated the ability of several new rotary nickel-titanium (NiTi) systems to maintain original curvature of mesial root canals of mandibular molars (Thompson & Dummer 1997a,b,c,d, 1998a,b, Peters et al. 1998, Hulsmann et al. 20 01,Versumer et al. 2002).NiTi instruments have a two to three times higher elastic flexibility (‘superelasticity’ and ‘memory shape’) and a superior resistance to torsional fracture than conventional stainless steel instruments, which makes these instruments useful for the preparation of curved root canals (Walia et al.1988). No data on NiTi preparation of slightly curved but oval root canals could be found in the recent literature. Such cross-sections can often be found in the distal root canals of mandibular molars or in mandibular incisors (Wu et al. 2000). In an investigation of 180te eth of all groups, Wu et al. (2000) detected oval canals in 25% of all sections investigated. Di⁄cult areas for instrumentation and obturation are the buccal and lingual extensions of these irregular canals (Wu et al. 2000). Complete preparation with stainless steel instruments includes a high risk of perforating or significantly weakening the root. On the other hand, it seems questionable whether highly flexible NiTi instruments allow controlled preparation of such extensions. Due to limited efficacy of irrigation in such recesses, debris and smear layer may accumulate and remain on these unprepared root canal walls, decrease the quality of obturation and jeopardize the long-term treatment success.
The aim of the present study was to evaluate several parameters of automated root canal preparation using ProFile .04 (Maillefer, Ballaigues, Switzerland), Quantec SC (Tycom, Irvine, CA, USA) and Lightspeed (Lightspeed Inc., San Antonio, TX, USA) rotary NiTi instruments on oval distal root canals of mandibular molars. The parameters evaluated were: postoperative root canal diameter, root canal cleanliness, incidence of procedural errors such as ¢le fractures and perforations, loss of working length and working time.

Materials and methods.

Preparation of teeth.
A modification of the Bramante technique (Bramante et al. 1987, Hulsmann et al. 1999) was used to evaluate simultaneously the cleaning ability as well as cross-sectional preparation form, safety issues and working time on extracted teeth under conditions comparable to the clinical situation. A muffle block was constructed, consisting of au-shaped middle section and two lateral walls which are fixed together with three screws. Grooves in the walls of the muffle block allowed removal and precise repositioning of the complete tooth block or sectioned parts of the tooth.
Sixty extracted mandibular molars with intact roots and apices were used in this study. Following preparation of standard access cavities, the distal root canals were controlled visually for oval shape at the root canal orifice and with a size10 reamer for apical patency. Only teeth with a bucco-lingual distance twice as long as the mesio-distal distance and root canal curvatures less than 208 were included into the study. All teeth were shortened to a length of 19 mm, mounted into the mould with acrylic resin and isolated with rubber dam and a clamp, simulating the clinical situation and ensuring that the operator could gain access to the root canal only from the mesial direction.
The embedded teeth were sectioned horizontally at 3, 6 and 9 mm from the apex and the preoperative shape of the distal root canals were photographed under standardized conditions and the segments remounted into the mould. The teeth were randomly divided into three groups for preparation with ProFile.04 (Maillefer, Ballaigues, Switzerland), Quantec SC (Tycom, Irvine, CA, USA) and Lightspeed (Lightspeed Inc., San Antonio, TX, USA) NiTi rotary instruments.

Instruments and preparation techniques
ProFile .04
In the present study, root canal preparation was performed in the following step-down sequence: ProFile .04 size 25,14 mm; size 30,14 mm; size 20,16 mm; size 15, working length (18 mm) and sizes 20-45, working length (18 mm). The total number of instruments used was10.

Preparation with Lightspeed instruments was performed using a step-back technique (Wildey & Senia 1989). The sequence of instruments used in this study was the one proposed by the manufacturer: Hand instrument size15, working length(18 mm); Lightspeed instruments sizes 20-45, working length (18 mm) and sizes 47.5-70, step-back with each instrument used 1mm shorter than the last one. The total number of instruments (including size15 handfile) used was 20.

Quantec SC.
Root canal preparation with Quantec SC instruments was performed using a step-down technique: instrument no. 1 (25/.06), 15 mm; no. 2 (15/.02); no. 3 (20/.02); no. 4 (25/.02), working length (18 mm); no. 5-8 (25/.03-.06), working length (18 mm); no.9 (40/.02) and no.10 (45/.02), 17 mm. The total number of instruments used was10.

All root canals were prepared with a dental hand piece in a low-speed, high-torque motor with torque control (TCM 3000, Nouvag, Konstanz, Germany). Preparation speed was 250r .p.m. for ProFile.04, 1300r.p.m. for Lightspeed and 340r .p.m. for Quantec SC as proposed by the manufacturers. The preparation of the oval distal root canals was performed shaping especially the buccal and lingual extensions. Irrigation was performed with 2 mL NaOCl (3%) after each instrument size in the Pro- File .04 and Quantec SC group, and after each second instrument in the Lightspeed group. RC-Prep (Premier, Norristown, PA, USA) was used as a chelating agent with each instrument. Instruments were discarded after preparation of 10 root canals. Apical patency was controlled using an ISO10 reamer extending1mmbeyondworking length following each instrument size.