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 »  Home  »  Endodontic Articles 1  »  A comparative study of root canal preparation using ProFile .04 and Lightspeed rotary Ni–Ti instruments
A comparative study of root canal preparation using ProFile .04 and Lightspeed rotary Ni–Ti instruments
Introduction - Materials and methods



Introduction.
The main parameters included in the evaluation of any technique or device for root canal preparation should be the ability to clean the root canal walls and to shape the root canal without straightening. In addition, a prerequisite for the use of any instrument or technique is that it is safe. It has been shown in numerous investigations that preparation of curved root canals with stainless steel instruments frequently results in undesirable aberrations such as elbows, zips and danger zones, as well as loss of working length, perforations or instrument fractures (Weine et al . 1975, 1976, Abou-Rass et al . 1980, Bolanos et al . 1988, Al-Omari et al . 1992a,b, Hülsmann & Stryga 1993, Hülsmann et al . 1998, 1999a, Hülsmann 2000). Many studies have also reported that large amounts of debris and smear layer often remain after manual or automated preparation with endodontic handpieces (Hülsmann & Stryga 1993, Hülsmann et al . 1998, 1999a, Hülsmann 2000). During the last decade, several new nickel–titanium instruments for manual root canal preparation as well as for use in a rotary endodontic handpiece have been developed in order to facilitate the difficult and time consuming process of cleaning and shaping the root canal system and to improve the final quality of root canal preparation.
In the past few years advanced instrument designs including non-cutting tips, radial lands and varying tapers have been developed to improve the safety of preparation, to shorten working time, and to create a greater flare of preparations. Due to these new instrument designs, advanced preparation concepts have been developed: most Ni–Ti systems with increased instrument tapers are used in a crown-down sequence.
Numerous studies have shown the ability of several new rotary nickel–titanium systems to maintain original canal curvature and to produce a well tapered root canal form sufficient for obturation. Nevertheless, serious concern has been expressed about the safety of such systems, largely because of the high incidence of instrument fractures (Kavanagh & Lumley 1998, Barthel et al . 1998, Schäfer & Fritzenschaft 1999, Baumann & Roth 1999).
Few studies have been published investigating the cleaning ability of these new rotary nickel–titanium files (Peters et al . 1997, Peters et al . 1998, Kochis et al . 1998, Bertrand et al . 1999, Medioni et al . 1999, Hülsmann et al . 2001).
The aim of the present study was to evaluate several parameters of automated root canal preparation using Profile .04 (Dentsply Maillefer, Ballaigues, Switzerland) and Lightspeed (Lightspeed Inc., San Antonio, TX, USA) Ni–Ti instruments. The parameters evaluated were: straightening of curved root canals, postoperative root canal diameter, root canal cleanliness, incidence of procedural errors such as file 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, Hülsmann et al . 1999b) was used to evaluate simultaneously the cleaning ability as well as preparation form (longitudinal and cross-sectional), safety issues, and working time on extracted teeth under conditions comparable to the clinical situation. A muffle-block was constructed, consisting of a u-formed middle section and two lateral walls which are fixed together with three screws. Grooves in the walls of the muffle-block allowed removal and exact repositioning of the complete toothblock or sectioned parts of the tooth. A modification of a radiographic platform, as described by Southard et al . (1987) and Sydney et al . (1991) could be adjusted to the outsides of the middle part of the muffle. This allowed the exposure of radiographs under standardized conditions and geometric relationship in order to allow the superimposition of views taken before, during and after root canal preparation. Two metallic reference objects inserted into the film holder facilitated exact superimposition of the radiographs. The system and the evaluation technique have been described previously (Hülsmann et al . 1999b).
Fifty extracted mandibular molars with two curved mesial root canals were opened and controlled for apical patency with a size 10 reamer. All teeth were shortened to a length of 19 mm. The teeth were mounted in the mould with acrylic resin and isolated with rubber dam and a clamp, simulating the clinical situation and ensuring the operator could gain access to the root canal only from the mesial direction. Root canal curvatures were measured as described by Schneider (1971) from preoperative radiographs after insertion of a size 15 reamer. The teeth were randomly divided into two groups. By exchanging a few single teeth a similar mean degree of curvature was achieved for both groups. Twenty-five teeth with 50 curved mesial root canals were prepared with the Profile .04 Ni–Ti system (Dentsply Maillefer), and 25 teeth were prepared with Lightspeed Ni–Ti rotary instruments (Lightspeed Inc.).

Instruments and preparation techniques.
Profile .04
 In the present study root canal preparation was performed in the following crown-down-sequence: Profile .04 size 25: 14 mm, size 30: 14 mm, size 20: 16 mm, size 15: working length (18 mm), sizes 20–45: working length (18 mm). The total number of instruments used was 10.

Lightspeed
Preparation with Lightspeed instruments was performed using a step-back technique (Wildey & Senia 1989, Wildey et al . 1992). The sequence of instruments used in the present study was the one proposed by the manufacturer: Hand instrument size 15: working length (18 mm), Lightspeed instruments sizes 20–45: working length (18 mm), sizes 47–70: step-back with each instrument used 1 mm shorter than the preceeding one. The total number of instruments (incl. size 15 hand-file) used was 20.
All root canals were prepared with a dental handpiece in a low-speed motor with torque-control (TCM 3000, Nouvag, Konstanz, Germany). Preparation speed was 350 r.p.m. for Profile .04 and 1300 r.p.m. for Lightspeed. Irrigation was performed with 2 mL NaOCl (3%) after each instrument size in the ProFile group and after each second instrument in the Lightspeed group with a final irrigation of 5 mL NaOCl (3%) in both groups. RC-Prep (Premier, Philadelphia, USA) was used as a chelating agent with each instrument. In both groups instruments were discarded after preparation of 10 root canals.

Assessment of preparation.
First the mesio-buccal root canal was instrumented in the unsectioned teeth. Maintenance of root canal curvature, safety issues (loss of working length, apical blockage, instrument fracture, lateral perforation), and working time were evaluated at this time. Before preparation a radiograph with a size 15 stainless steel reamer in situ was taken and the initial root canal curvature was determined using the technique proposed by Schneider (1971). Following preparation to size 45 a further radiograph was taken with a size 40 stainless steel reamer. The outlines of the inserted instruments, the root outlines and the metallic reference objects in the film holder were superimposed under an X-ray viewer with a 10 magnification and the degree of straightening was evaluated by measuring the angle between the two instrument tips. The reference objects allowed control of exact superimposition of the radiographs.
The teeth were sectioned horizontally at 3, 6 and 9 mm from the apex and the preoperative root canal diameters were photographed under standardized conditions. The horizontal segments were remounted into the mould which was facilitated by the horizontal grooves and the mesio-lingual root canals were prepared to size 45 as described above. Again procedural accidents were recorded and straightening of the root canal curvature was measured using the radiographic platform. At the end of preparation the cross-section of the disto-lingual root canal was photographed again. According to Loushine et al . (1989) the postoperative cross-sections were classified as round, oval or irregular using reference photographs. Only irregular cross sections were regarded as unacceptable preparation results, since an oval cross section may be due to the cutting angle during the sectioning procedure. The divergence of pre- and postoperative root canal diameter was evaluated by superimposing pre- and postoperative canal outlines.
Following this the segments were removed from the mould and the three root segments were freed from the resin and split vertically. For the SEM investigation the mesiobuccal root canals, prepared before sectioning the teeth, were selected since irregular hydrodynamics in the sectioned roots could have influenced the degree of cleanliness. The buccal half of the split root canal segments was prepared for SEM investigation. The roots were coded and mixed so that the type of instrument used for preparation could not be identified during the SEM investigation.
Separate evaluations were undertaken for debris and smear layer with a five score system for each using the same set of reference photographs as in previous investigations (Hülsmann et al . 1997, 1998, 1999a, Hülsmann 2000, Hülsmann et al . 2001).
Debris was defined as dentine chips, pulp remnants and particles loosely attached to the root canal wall:

  • Score 1: Clean root canal wall, only few small debris particles
  • Score 2: Few small isles of debris
  • Score 3: Many accumulations of debris covering less than 50% of the root canal wall
  • Score 4: More than 50% of the root canal wall covered by debris
  • Score 5: Complete or nearly complete root canal wall covered by debris.

Scoring of debris was performed using 200 magnification.
Smear layer was defined as proposed by the American Association of Endodontists’ (1994) glossary Contemporary Terminology for Endodontics : A surface film of debris retained on dentine or other surfaces after instrumentation with either rotary instruments or endodontic files; consists of dentine particles, remnants of vital or necrotic pulp tissue, bacterial components and retained irrigant.

  • Score 1: No smear layer, dentinal tubules open
  • Score 2: Small amount of smear layer, some dentinal tubules open
  • Score 3: Homogeneous smear layer covering the root canal wall, only few dentinal tubules open
  • Score 4: Complete root canal wall covered by a homogeneous smear layer, no open dentinal tubules
  • Score 5: Heavy, inhomogeneous smear layer covering the complete root canal wall.

Smear layer was scored under 1000 magnification.
After the central beam of the SEM had been directed to the centre of the object by the SEM-operator (F.S.) under 10 magnification, the magnification was increased to 200 and 1000 , respectively, and the canal wall region appearing on the screen was scored. The scoring procedure was performed by a second operator (M.H.) who could not identify the coded specimens nor the device used for root canal preparation. This operator had been trained in the scoring procedure, resulting in a sufficient intraobserver reproducibility (Hülsmann et al . 1997).
The incidence of procedural accidents was assessed during preparation of both the unsectioned and sectioned root canals. Apical patency was controlled using an ISO 10 reamer extending 1 mm beyond working length.

Statistical analysis.
Statistical analysis was performed using the following tests: for straightening Wilcoxon’s test was used ( P < 0.05); for comparison of the cross-sections and root canal cleanliness Fisher’s exact-test ( P < 0.05) was taken. The Mann–Whitney test ( P < 0.05) was used for comparison of working time.