Introduction - Materials and methods.
S. K. Kim & Y. O. Kim Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu, Republic of Korea.Introduction.
Effective cleaning and shaping is the foundation of successful root-canal treatment. However, because of the complexity of root-canal systems, complete cleaning and shaping with presently available irrigants and instruments is difficult. When sufficient bacteria remain within the system, they can proliferate and reinfect the root-canal space (Bystrom & Sundqvist 1981).
Intracanal medication has been advocated to further reduce the number of microorganisms between appointments. A wide range of chemicals have been used to disinfect the root-canal system including formocresol, cresatin, phenolic compounds, aldehydes, antibiotics, steroids, and calcium hydroxide.
Calcium hydroxide has been widely used as an intracanal medicament. Calcium hydroxide should be removed before root-canal filling, however, its complete removal is problematic, and some calcium hydroxide may be retained in the apical area (Guignes et al. 1991, Margelos et al.1997, Lambrianidis et al.1999).
Recently, Margelos et al. (1997) reported a possible problem caused by the interaction between calciumhydroxide and zinc oxide-eugenol sealers. There is a concern that, at the time of root-canal filling, the retention of calciumhydroxide on the canal wall might affect the quality of the seal and influence the prognosis of treatment. A few studies have reported on this problem with inconsistent findings. An apical leakage study (Porkaew et al. 1990) in teeth filled using lateral condensation demonstrated that teeth dressed with calcium hydroxide had significantly less leakage than those not medicated. A further study (Holland et al.1995) supported this finding. However, these studies also noted that when calcium hydroxide dressing was retained in the canal, apical leakage increased with time. Recently, other studies (Kontakiotis et al. 1997, Wu et al. 1998) have described the possibility of false positive results occurring with previous dye-leakage studies using methylene blue dye, because it may loose its colour in contact with calcium hydroxide.
The purpose of this study was to determine the influence of calcium hydroxide intracanal medication, and various techniques for its removal on the apical sealing ability of gutta-percha root fillings when a zinc oxide- eugenol sealer was used. Materials and methods.Preparation of specimens.
Eighty extracted multi-rooted human mandibular molars were used. Calculus and soft tissue debris was removed with scalers and each tooth was sectioned vertically with a disc to separate each root. After access cavity preparation, size 10-20 K-files were introduced to determine working lengths and apical foramen sizes.
Three separate roots with similar canal configuration were matched in a set, and 25 sets of roots were selected from 80 teeth; the remaining roots were discarded. The roots in each set were randomly divided into three groups A, B, and C of 25 roots each, so that the three groups had a similar root-canal configuration (Table 1). An additional six roots were used for negative and positive leakage controls.
All the root canals were prepared by one operator. Working lengths were established1mmshort of the apical foramen, and size 10-20 K-files were used as initial apical files (IAF). The coronal one-third was flared with size 4-2 Gates Glidden burs and the apical two-thirds of the canals were instrumented sequentially with size 40-25, 0.06 ProFiles (Dentsply Maillefer, Ballaigues, Switzerland) at a constant speed of 300 r.p.m. in a crown-down manner. The apical region was then enlarged with size 20-30, 0.06 ProFiles until the master apical file (MAF) size was three sizes larger than the size of the IAF. Root canals were irrigated after each instrument, and 5 mL of15% EDTA and 5 mL of 2.5% sodium hypochlorite (NaOCl) solutions were used alternately with a 25-gauge needle.
Table 1. Root-canal configurations of specimens in each group.
Calcium hydroxide paste was made by mixing D.S.P. GR reagent grade calciumhydroxide (Duksan Pure Chemical Co. Ltd., Ansan, Korea) with distifilled water at a powder to liquid ratio of1:1.25. After canals were dried with paper points, calcium hydroxide paste was placed in the canal with the use of a lentulo spiral filler in groups A and B; no medication was introduced in group C. The access cavities of all the roots were temporarily sealed with gutta-percha and CavitW (Espe, Seefeld, Germany). All the roots were stored at 37 8Cat100%relativehumidity for 7 days.
After removing the temporary coronal restoration, two different techniques were used to remove the calcium hydroxide. In group A, after irrigation with 2.5 mL of 2.5%NaOCland 5.0 mL of15%EDTAsolutions, canals were cleaned to the working length with a K-file one size larger than the MAF size with reaming motion, and step-back preparation was completed up to four sizes larger than the first file (Holland et al.1995). Canals were irrigated again with 2.5 mL of 2.5% NaOCl. In group B, after irrigation with 2.5 mL of 2.5% NaOCl and 5.0 mL of distifilled water, canals were instrumented to the working length with a K-file of MAF size (Margelos et al. 1997). Canals were irrigated again with 2.5 mL of 2.5% NaOCl. In group C, no irrigation or filing was completed.
After the canals were dried with paper points, a zinc oxide-eugenol sealer, Tubli-seal (Kerr, Romulus, MI, USA) was applied and the canals obturated by lateral condensation of gutta-percha (DiaDent1 gutta-percha points, DiaDent Group International Inc., Chongju, Korea) with the exception of three positive leakage controls. Buccolingual and mesiodistal radiographs were taken in order to confirm the root-canal fillings were at length and were dense. Dye-leakage test.
The access cavity of each root was filled with a lightcuring composite resin (Metafil CX, Sun Medical Co. Ltd., Moriyama, Japan). All the specimens, except the negative leakage controls, were coated with nail varnish on all but a 1-mm area around the apex. Three roots of the negative leakage controls were completely coated with nail varnish. All the roots were suspended on base-plate wax and the apical 3 mm of each was dipped in India ink (Winsor & Newton Ink, London, UK) and incubated at 37 8C and100% humidity for14 days. Evaluation of apical leakage.
All the specimens were sectioned horizontally at 1,2,3,4, and 5 mm from the root apex with a microtome (Isomet, Buehler, Lake Bluff, IL, USA).
Linear measurements of apical leakage were recorded with a stereomicroscope (SZ40, Olympus Optical Co. Ltd., Tokyo, Japan) to evaluate the dye-penetration depth. The number of specimens with leakage was counted at each section level. Statistical analysis
Fisher’s exact test was used to determine the difference of the number of specimens at each leakage level amongst the three groups. Duncan’s multiple range test was also adapted for a post hoc test. Correspofinding P-values less than 0.05 were considered significant.