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 »  Home  »  Endodontic Articles 11  »  The effects of dentine pretreatment on the adhesion of root-canal sealers
The effects of dentine pretreatment on the adhesion of root-canal sealers
Introduction - Materials and methods.



I.M. Saleh, I.E. Ruyter, M. Haapasalo & D. Orstavik
NIOM, Scandinavian Institute of Dental Materials.
Department of Endodontics, Institute of Clinical Dentistry, University of Oslo, Norway.


Introduction.
The standard method of obturation of the root-canal system uses a core material in combination with a rootcanal sealer. Despite ongoing research and recent developments in endodontic materials, complete sealing of the root-canal system with currently accepted materials and obturation techniques is not a predictable procedure. Microleakage, whether from an apical (Dow&Ingle 1955, Strindberg 1956) or a coronal direction (Madison &Wilcox1988), remains a clinical problem and a possible source of failure (Saunders&Saunders1994). Adesirable property of a root-canal sealer, therefore, is to have good sealing ability (Branstetter & von Fraunhofer 1982). In addition, a good sealer must have adhesive strength, both to the dentine and to the core material, which usually is gutta-percha (SpDngberg 1998). The sealer must also have cohesive strength to hold the obturation together. Although good adhesion of the sealer might be expected to improve the sealing ability, such a relationship has not yet been proven.
The sealing ability of endodontic sealers has traditionally been evaluated by leakage tests. Dye leakage (Stewart1958, Ainley1970), bacterial leakage (Goldman et al. 1980) and liquid pressure techniques (Wu et al. 1993) are amongst the most frequently used methods. Endodontic leakage tests may be difficult to standardize (Al-Ghamdi & Wennberg 1994) and the results are difficult to reproduce and compare (Wu & Wesselink 1993).
Only a few studies have attempted to evaluate the adhesive properties of root-canal sealers by measuring their bond strengths (Wennberg & Irstavik 1990, Gettleman et al. 1991, De Gee et al. 1994, Fidel et al. 1994, Lalh et al. 1999a, Pecora et al. 2001, Timpawat et al. 2001). These studies have investigated the effect of smear layer removal on sealer adhesion with controversial results. It has been suggested that the endodontic smear layer acts as a physical barrier interfering with adhesion and penetration of sealers into dentinal tubules, which may affect the sealing efficacy of rootcanal obturation (Sen et al.1995). The majority of these studies used the same dentine pretreatment for different sealers, irrespective of the chemical composition of the sealer. Sealers available to the profession today are zinc oxide-eugenol based, calciumhydroxide based, resin based, glass ionomer based or silicone based. The mechanism of adhesion amongst this wide range of chemical compositions cannot be expected to be exactly the same.
The purpose of this investigation was therefore to study the adhesion of root-canal sealers of different chemical composition to dentine and gutta-percha by tensile bond strength measurements. The effect on adhesion of various dentine pretreatments and the effect of an experimental primer on the adhesion of a silicone-based sealer were also investigated. Another aim was to describe the type of bond failure at the dentine-sealer and the sealer-gutta-percha interfaces for the debonded surfaces.

Materials and methods.
The technique for testing adhesion of the root-canal sealers to dentine and gutta-percha was a modification of a previously described method (Wennberg & Irstavik 1990).
A total of 104 extracted human single-rooted teeth were used in this study. The teeth were stored in 0.01% NaOCl at 4 8C. Before performing the experiments, the teeth were thoroughly rinsed with distilled water. Root dentine cylinders, 4 mm in diameter, were cut in a bucco-lingual direction at a right angle to the tooth’s long axis, using a water-cooled carbide trephine bur. The cylinders were mounted in brass holders using zinc phosphate cement. After setting, the dentine surfaces were ground flat against 500-grit silicone carbide abrasive paper (Struers, Copenhagen, Denmark) under running water. A Planopol grinding machine (Struers, Copenhagen, Denmark) was used to control the angle of the ground surface. The prepared specimens were stored in distilled water at 4 8C. Gutta-percha cylinders of 4 mm diameter were prepared from heat-softened gutta-percha (Roeko, Langenau, Germany).The cylinders were mounted in brass holders and secured mechanically by holes in the holders. Their end surfaces were ground flat in a similar manner to the dentine cylinders.
The dentine specimens were randomly divided into four equal groups and their surfaces conditioned with either 37% H3PO4 for 30 s, 25% citric acid for 30 s, 17% disodium ethylene diamine tetraacetic acid (EDTA) for 5 minor10 mL distilled water (control).The conditioned dentine surfaces were then rinsed with 10 mL distilled water and dried with an air stream for 5 s. The surfaces thus produced were further characterized by scanning electron microscopy. Each group of conditioned specimens was further divided into six equal subgroups (n = 4) according to the type of sealer used.
Five sealers of different chemical compositions were tested (Table 1). An experimental primer supplied with RoekoSeal Automix (RS) was also investigated. The sealers were mixed according to the manufacturer’s instructions. The dentine and gutta-percha surfaces were coated with a thin layer of the freshly mixed sealer and the cylinders were immediately pressed together by means of a spring. To ensure alignment of the dentine and gutta-percha surfaces during the setting of the sealer, the two brass holders with their respective dentine and gutta-percha cylinders were placed in a special device consisting of a plastic block with a semicircular groove of the same diameter as the brass holders (Fig.1). Excess sealer was carefully removed with a cotton pellet. The brass holders were then fixed in that position with a clamp.
The test specimens were kept in an incubator at 37 8C and a relative humidity of 90 _5%. The sealers were allowed to set for1.5 times the manufacturer’s stated setting time. The test specimen, still fixed to the plastic block, was then mounted in a universal testing machine (Instron, Instron Limited, Bucks, UK). After mounting, the plastic block was removed and the test specimen was subjected to a tensile load at a constant cross-head speed of 1mm min_1 (Fig. 2). The force (N) required to rupture the bond was recorded and used to calculate the bond strength (MPa).
After adhesion testing, the fractured surfaces were examined under a stereomicroscope at x25 magnification to describe the nature of bond failure: cohesive within the sealer, adhesive at the sealer-gutta-percha interface and/or adhesive at the sealer-dentine interface (Fig. 3).
Statistical analysis was performed using one-way anova followed by the Bonferroni test for multiple comparisons to compare the mean tensile bond strength of the six sealers at the different dentine pretreatment conditions. Significance was established at the 5% level.

Table 1. Root-canal sealers tested.

Root-canal sealers tested

Figure 1. A test specimen with gutta-percha (left), sealer (middle) and dentine (right) in plastic holder.

A test specimen with gutta-percha, sealer and dentine in plastic holder

Figure 2. A test specimen mounted in the testing machine.

A test specimen mounted in the testing machine