M. De Luca, G. Gambarini, G. Pongione, M. Bossu
Università degli Studi di Roma, "La Sapienza", Facoltà di Medicina e Chirurgia, Cattedra di Clinica Odontoiatrica, Titolare:Prof.M.De Luca

Smear layer removal using profile .04 and .06 tapers rotary instrumentation: a SEM study.

Abstract
The purpose of this study was to evaluate smear layer removal using Profile .04 and .06 Tapers crown-dowm instrumentation technique. Twenty-two freshly extracted roots were selected for the study.Ten canals were instrumentated (Fig.1) and irrigated with 17% EDTA and 5% NaOCl (group A). Two canals served as control (noninstrumented), while the remaining ones (group B) were irrigated only with sterile saline solutions. All specimens were prepared for scanning electron microscopic evaluation, and scored for the presence or absence of smear layer in the coronal,middle and apical thirds.Results showed good canal cleanliness only for group A. Nevertheless a significant difference between the coronal two-thirds (fig.2) and apical third was found. Ni-Ti rotary instrumentation was significantly faster, thus allowing limited time for tissue-chemical contact.This might have affected the solvent efficacy of the irrigants in narrow,apical space,where contact is minimal. Debridement of group B specimens was less satisfactory ( statistically significant differences were found at the three levels), due to the complete lack of chemical action of the irrigating solution.

Fig.1. Root canal preparation

Fig.2. Root canal debridement

Introduction
The main objective of root canal debridement is to completely remove the vital tissues, necrotic debris and microorganisms in order to eliminate any irritant or bacterial substrate.Unfortunately root canals are irregular,complicated system that are difficult to clean and shape.Sodium hypochlorite has proven to be more effctive than other irrigants, even if many studies (3,10) have shown that traditional chemio-mechanical methods were not able to entirely clean the endodontic space.Moreover,NaOCl has not been shown to effectively remove the smear layer.These problems have resulted in a wide search for new materials and irrigation techniques to obtain a clean,debris-free canal for obturation.To date, the most effective method to remove organic debris and smear layer is to irrigate the root canals using EDTA in combination with NaOCl (4).

Traditional instrumentation with stainless steel files has been shown to produce undesiderable results in canals,regardless of the technique or file type used (5,16).Recently Ni-Ti rotary instruments,which are more flexible and resistant to torsional fracture, have been introduced to overcome these problems. Several studies ( 6-9 ) demonstrated that they can efficiently create a smooth funnelform shape with minimal risk of ledging or transporting the canals,in less time than it takes with traditional techiniques. Their unique design has been specificaly developped to minimize iatrogenic errors,while enhancing cutting and debridement capability.

It may be speculated that ihese new rotary instruments could cut dentin and remove deris more efficiently than traditional hand-filing, leading to a better debridement of the endodontic space.At time being,however, the ability of Ni-Ti rotary instrumentation to effectively debride the root canal system has not been evaluated thoroughly.The purpose of this in vitro study was to evaluate the degree of smear layer removal with ProFile .04 and .06 Tapers Ni-Ti rotary instruments (Maillefer, Baillagues,Switzerland) using two different irrigating solutions.

Materials and methods
Twenty-two freshly extracted human roots were selected for this study.Teeth had been extracted for periodontal purpose and stored in refrigerated physiological solution for a maximum of 3 days. No formalin was used at this stage,to avoid any possible " fixing " effect on pulp or dentin that might alter the result of canal preparation. None of these teeth had received endodontic therapy before extraction. Crown were cut off with a separating disk, so all roots were approximately 10-12 mm. long. Canals which could not be negotiated with a n.10 K-files were discarded. Deep longitudinal grooves,which did not penetrate into the canal,were made in the mesial and distal surfaces of the roots,to facilitate their fracture. After having chosen the two control roots,the remaining ones were randomly divided into two groups. The working lenght was estabilished by the insertion of an endodontic instrument into the canal until its tip was visible at the apical foramen and then by a subtraction of 0,5 mm.The two experimental groups,each containing 10 roots,were prepared as follows:

The bulk of the pulp was extirpated using a small barbed broach. ProFile.04 and .06 Tapers were used in high-torque,low speed handpiece, with a speed range between 150-200 rpm. A coronal-apical instrumentation technique was used, following manufacturer's instructions. Th coronal half of the canal was initially,sequentially enlarged with ProFile .06 n.25 and n.20 used passively to a depth of 1/2 to 2/3 down the canal. Next,a n.25 and a n.20 ProFile were selected and used to a depth of 2/3 to 3/4 of the way down the canal,to assist opening of the apical area.After having determined working length with proper hand instruments,the smallest ProFile .04 Taper instrument necessary ( usually n.15) was selected to reach full working length. The apical area was then sequentially enlarged to the extent deemed necessary, completing an .04 tapered funnelform preparation from the orifice to the apex. A ProFile .04 Taper n.30 was used as a MAF for both groups.

Irrigation of Group A consisted of 2 ml of solution injected through a 27-gauge endodontic needle. 5% sodium hypochlorite (Niclor,Ogna,Milan,Italy) and 17% EDTA ( Ogna,Milan,Italy) were alternatively used after each instrument. A final flushing of 0,9% physiological solution was performed to terminate any chemical activity of irrigants. Group B specimens were irrigated with 2 ml. of sterile saline solutions after each instrument. Two control roots were not instrumented and irrigated.

After canal preparation,all teeth were dried with paper points,fractured into halves and immediately immersed in neutral-buffered 10% formalin solution until SEM preparation. Teeth were then dehydrated using a graded series of alcohol, coated with gold-palladium,and their surfaces examined by scanning electron microscopy (Stereoscan 240,Cambrigge Instrument,Cambridge,UK).

A standardized series of 6 photomicrographs for each root canal ( 2 in the coronal third,2 in the middle third and 2 in the apical third) was taken for comparative purpose.Blind evaluation was performed by two trained observers and scores were compiled separately.Cleanliness of the canals was scored as follows, according to the rating system developped by Rome et al (12):

0 = no or minimal smear layer; most tubules are totally clean and open.

1 =little to moderate smear layer,some tubules are not open or contain debris plug.

2 = moderate to heavy smear layer, minimal to no tubule visibility or patency.

Values obtained were tabulated and statistical analyses were carried out using the Kruskal-Wallis test.

Second part >