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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 7  »  Effects of rotary instruments and ultrasonic irrigation on debris and smear layer scores: a scanning electron microscopic study
Effects of rotary instruments and ultrasonic irrigation on debris and smear layer scores: a scanning electron microscopic study
Introduction - Materials and methods.



B. E. Mayer, O. A. Peters & F. Barbakow
Department of Preventive Dentistry, Cariology and Periodontology, University of Zurich, Switzerland.

Introduction.
Irrigation during the cleaning and shaping of root canal systems is a critical component of endodontic therapy. Traditionally, irrigants are delivered by syringe and needle, with larger preparations facilitating their insertion. However, irrigants can only progress 1 mm further than the tip of the needle (Ram 1977). Larger apical canal shapes also improve debridement and disinfection of canals (Abou-Rass & Piccinino 1982). However, thorough cleaning of the most apical part of any preparation remains difficult (Wu & Wesselink 1995).
Procedural errors such as zipping or ledging are likely to occur when canals are shaped using manual techniques, but the introduction of engine driven nickel– titanium instruments such as Lightspeed (Lightspeed Inc, San Antonio, TX, USA), ProFile (Dentsply Maillefer, Ballaigues, Switzerland) and Quantec (NT Company, Chattanooga, TN, USA) have minimized the incidence of such procedural errors. Preparations are better centred, working length is rarely lost and larger sized apical stops can be achieved (Thompson & Dummer 1997a, 1997b, Bryant et al. 1998a, 1998b). However, common to all types of cutting instruments, residual debris and smear layer is found on root canal walls after rotary preparation (Peters & Barbakow 2000).
The use of ultrasonic files to shape canals was accompanied by improved debridement (Cunningham & Martin 1982). However, ultrasonically activated stainless steel files tended to ledge and perforate canal walls (Sundqvist & Figdor 1998). Initial studies indicated that ultrasonic files produced significantly cleaner canal walls than specimens without the use of ultrasonic energy (Cunningham & Martin 1982). Furthermore, Krell et al. (1988) showed that freely oscillating files transported irrigants in vitro into the apical parts of the preparation.
In contrast, other experiments reported little or no difference in root canal debridement when using ultrasonic energy. This finding was particularly prevalent in curved and irregular canals in which remnants of pulp tissue, debris and smear layer were detected (Langeland et al. 1985, Lev et al. 1987, Cheung & Stock 1993, Heard & Walton 1997). However, these studies were carried out using different procedures and different techniques to evaluate debris and smear layer quantities.
The aim of this study was to evaluate whether the material and the geometric design of ultrasonic tips affected the debridement of root canals in vitro during irrigation. In addition, the influence of two engine-driven rotary preparation techniques on canal surface morphology was also examined.

Materials and methods.
Forty-two single-rooted extracted human premolars and canines, each with one single root canal, were selected from the Department’s pool of extracted teeth. The specimens were stored in 0.1% thymol solution throughout the experiment. The teeth were randomly numbered and equally divided into four test and two control groups. Access cavities were prepared using diamond burs (Intensiv, Bioggio, Switzerland) while Gates-Glidden burs (Dentsply Maillefer, Ballaigues, Switzerland) were used for the step-down preparation. Patency of apical foramina was standardized using size 08 or 10 stainless steel K-Files (Dentsply Maillefer). Working lengths were set by deducting 1 mm from the lengths of the files when they extruded just beyond the apical foramina. Canals were shaped by Lightspeed or ProFile .04 instruments used according to the procedures established in the Department (Peters et al. 1997, Schrader et al. 1999). All preparations were carried out by the principal author. In all canals, apical stops were prepared to size 45 and irrigants were delivered using a 27-gauge needle (Braun, Melsungen, Germany) which was inserted as far into the prepared root as possible without binding.
Specimens in groups 1, 2 and 3 were prepared using ProFile instruments, while those in groups 4, 5, and 6 were prepared using Lightspeed instruments (Table 1). Canals in all groups were irrigated using 2 mL of a 5.25% NaOCl solution and 2 mL of a 17% EDTA solution, alternatingly, after each instrument. Groups 1 and 4 served as controls in which the irrigants were not ultrasonically activated. Final aliquots of EDTA and NaOCl were left in situ for 1 min before being flushed with NaOCl. In groups 2 and 5, aliquots of EDTA and NaOCl were left in situ for 1 min and were ultrasonically activated using a size 15 stainless steel K-file (Endosonore, Dentsply Maillefer, Fig. 1). A final flush with NaOCl concluded the preparation.

Table 1. Experimental protocol listing both negative controls and the four test groups. Details of preparation techniques, irrigants used with or without ultrasonics, and the types of ultrasonic tips tested are also given.

Experimental protocol listing both negative controls and the four test groups

Figure 1. SEM micrograph of a size 15 stainless steel K-file used for ultrasonic activation of the irrigation in groups 2 and 5 (original magnification 150x).

SEM micrograph of a size 15 stainless steel K-file used for ultrasonic activation of the irrigation in groups 2 and 5

Figure 2. SEM micrograph of a blunt Ni-Ti-wire, diameter 0.26 mm, used for ultrasonic activation of the irrigation in groups 3 and 6 (original magnification 150x).

SEM micrograph of a blunt Ni-Ti-wire, diameter 0.26 mm, used for ultrasonic activation of the irrigation in groups 3 and 6

In groups 3 and 6, final aliquots of EDTA and NaOCl were left in situ for 1 min during which the irrigant was ultrasonically activated by a specially prepared thin, cylindrical noncutting flexible nickel–titanium (Ni–Ti) wire (ø 0.26 mm, Fig. 2). The Ni–Ti wire used was a shaft of a Lightspeed instrument whose cutting head had been removed. The shaft itself was not further modified except for polishing the cut surface using 1000 grit polishing discs. All ultrasonic tips were placed 1 mm short of the working lengths and no attempt was made to shape the canals with these ultrasonic tips. A final flush with NaOCl concluded the preparation in these groups. Ultrasonic energy was delivered by a standard unit (Piezon Master 400, EMS, Nyon, Switzerland). Power settings were established in pilot experiments so that the outer surface root temperature did not exceed 40 C.
From this point on, all specimens were treated similarly, dried with paper points and temporized with Cavit (Espe, Seefeld, Germany). Root surfaces were grooved to indicate levels 3, 6, and 9 mm from the root apices using separation disks (Intensiv, Bioggio, Switzerland) and the specimens were decoronated. Specimens were immersed in liquid nitrogen and split longitudinally in the buccolingual plane, taking care not to contaminate the canals with debris. Canal halves were secured on metal stubs, desiccated and sputter-coated with gold (500 A, Balzers CSD 030, Balzers, Liechtenstein). Specimens were examined in a SEM (Cambridge Stereoscan 180, Cambridge, UK) at low power (15) and serial photomicrographs were taken of the canal walls at 200x and 400x magnification at the 3-, 6-, and 9 mm levels. These serial photographs were placed adjacent to each other, forming a continuous horizontal examination strip at the three levels. A 200-m square grid was superimposed onto the strip (Fig. 3), from which the debris and smear layer scores were evaluated. The number of ‘assessment units’ varied from 6 to 91, depending on root canal diameters, whereas the height of the examination strips was set at 600 m. Specimens were evaluated for incidence of scratched canal surfaces at low and high power.

Figure 3. SEM micrograph of the 200 lm square grid used to score smear layer and debris (original magnification 200x).

SEM micrograph of the 200 lm square grid used to score smear layer and debris

Amounts of smear layer and debris present in each of the ‘assessment units’ were assessed using a 5-step scale and recorded. The amounts of smear layer present at 200x magnification were graded between 1 and 5. A score of 1 was assigned when all dentinal tubules were open, and no smear layer was present or if uninstrumented calcospherites were noted. A score of 2 was recorded when some dentinal tubules were open and others covered by a thin smear layer. A score of 3 was recorded when a few tubules were open and the rest covered by a thin homogenous smear layer. A score of 4 was recorded when all dentinal tubules were covered by a homogenous smear layer without any open tubules visible. A score of 5 was recorded when a thick homogenous smear layer completely covered the canal walls.
The amounts of debris present at 200x magnification were graded between 1 and 5. A score of 1 was assigned when no debris or only isolated small particles were present. A score of 2 was recorded when minimal debris particles were present in small clumps. A score of 3 was recorded when clumps of debris particles covered less than 50% of the canal wall. A score of 4 was recorded when clumps of debris particles covered more than 50% of the canal wall. A score of 5 was recorded when clumps of debris particles completely covered the canal wall.
For each evaluation strip, average scores for smear layer and debris were calculated from the raw data by dividing the sum of all individual scores by the number of assessment units. Means recorded at the 3, 6 and 9 mm examination levels were statistically analysed for significance (a < 0.05) between and within the groups using the Mann–Whitney U-test and the Kruskal–Wallis test.