Rahmat A. Barkhordar

Effect of metal collars on resistance of endodontically treated teeth to root fracture

Fractures of restored pulpless teeth without reinforcement are a familiar dilemma to the dentist. This study examined the effect of a metal collar with approximate 3 degrees of taper on the resistance of endodontically treated roots to fracture. Teeth without copings failed at a load of 49.6 kg whereas teeth with metal collars failed at a load of 65.29 kg. Our findings indicated that reinforcement with a metal collar is necessary to enhance resistance to root fracture.

Removal of intracanal smear by doxycycline in vitro

UNLABELLED Cleansing and shaping result in a smear layer on the instrumented canal wall surfaces. The smear layer may inhibit close contact between sealers and dentin, and inhibits diffusion of medicaments. OBJECTIVE This study assessed the effect of doxycycline hydrochloride (DH) on smear layer on intracanal walls. STUDY DESIGN Scanning electron microscopy was used to evaluate the remaining smear layer using different concentrations of DH. Single-canal palatal roots of extracted maxillary molars were irrigated with saline-15% EDTA; saline-25 mg/ml DH; saline-50 mg/ml DH; saline-100 mg/ml DH; NaOCl-15% EDTA; NaOCl-25 mg/ml DH; NaOCl-50 mg/ml DH; and NaOCl-100 mg/ml DH. The roots were fractured into halves and the amount of smear layer assessed in the middle and apical third. RESULTS Doxycycline-HCl of 100 mg/ml was the most effective in removing smear layer. In the saline group, 100 mg/ml of DH was more effective than EDTA. In the hypochlorite group, 50 mg/ml and 100 mg/ml of DH were more effective than EDTA (p < 0.05). CONCLUSION Doxycycline solution may be an effective irrigant.

Detection of interleukin-1 beta in human periapical lesions

Interleukins are involved in modulating bone cell activity. Interleukin-1 (IL-1) has been shown to be potent stimuli of bone resorption in organ culture. This hormone-peptide is produced primarily by monocytes and macrophages. Diverse inflammatory cell types are clearly present in periapical lesions. The purpose of this study was to detect IL-1 beta activity in human periapical lesions. Eight human periapical lesions were examined for the presence of IL-1 beta. Pulp tissue of clinically impacted teeth were used as controls. Each specimen was quick-frozen and stored in liquid nitrogen. IL-1 beta activity was measured with, an IL-1 beta enzyme-linked immunosorbent assay that used monoclonal antibodies specific for IL-1 beta. Periapical samples exhibited significant activity of IL-1 beta (mean 604.4 +/- 563.0 pg/mg protein), whereas normal pulp had no activity. These results demonstrate that IL-1 beta is produced and released locally in inflammatory periapical lesions to mediate bone resorption.

Interleukin-1β Activity and Collagen Synthesis in Human Dental Pulp Fibroblasts

Immunopathologic reactions play a significant role in inflammatory diseases of dental pulp. Interleukin-1beta (IL-1beta) is recognized as a key player in mediating cellular immune response. In this study, we measured the content of IL-1beta and its effect on collagen synthesis in cultures of fibroblasts derived from healthy and diseased dental pulps. We found that diseased pulp fibroblasts contain 2.5-fold greater amounts of IL-1beta and synthesized 80% greater amounts of collagen compared with healthy pulp fibroblasts. However, exogenous IL-1beta failed to stimulate collagen synthesis by diseased fibroblasts, whereas collagen synthesis by healthy pulp fibroblasts was stimulated by more than 2-fold. These observations imply that pulp disease induces abnormalities associated with fibroblast response toward IL-1beta.

Use of glass ionomers as retrofilling materials

Many materials have been used as retrofillings. Because of the bonding property of glass ionomer cement, this study was conducted to evaluate its possible use as a retrofilling material. Seventy human maxillary anterior teeth were chosen. The root canal systems were cleansed and shaped, and the teeth were assigned to six groups of 10 each. The root canals were obturated with gutta-percha and Grossman sealer, and the apical 2 mm of each root was resected. In all groups a retrofilling preparation was made to a depth of a number 331 bur. The apical preparations were filled in the following manner: silver amalgam (group I), silver amalgam plus two layers of varnish (group II), Ketac-Silver plus two layers of varnish (group III), Ketac-Silver without varnish (group IV), Ketac-Fil plus two layers of varnish (group V), Ketac-Fil without varnish (group VI), and Ketac-Bond (group VII). All the root surfaces with the exception of 2 mm from the resected line were coated with two layers of clear varnish. All the teeth were immersed in methylene blue for 24 hours. After vertical sectioning, dye penetration was measured under a dissecting microscope. The mean apical leakage (in millimeters) was as follows: I = 0.57, II = 0.39, III = 0.22, IV = 0.54, V = 0.11, VI = 0.46, and VII = 0.17. One-way analysis of variance performed on the group means indicated that Ketac-Fil with varnish (group V) and Ketac-Bond (group VII) had significantly less leakage than other groups (p less than 0.05). This study indicates that Ketac-Fil and Ketac-Bond may have potential as retrofilling materials.

Retention of cast endodontic posts: Comparison of cementing agents

Zinc phosphate, glass-ionomer, and polycarboxylate cements were compared with a composite for ability to retain cast gold posts in prepared root canals of extracted teeth. Zinc phosphate and glass-ionomer cements were found to be more retentive than polycarboxylate cement and composite.

Sealing ability of intermediate restorations and cavity design used in endodontics

Temporary filling materials are used in endodontics to prevent contamination of the root canal system during intertreatment visits. Recently, a new composition resin (TERM) has been introduced as an interim restoration in endodontics. The purpose of this investigation was to evaluate the efficacy of this resin as an interim restoration and possible effect of access cavity design with respect to its sealing ability compared with other temporary restorative materials. Sixty human teeth were divided into two categories, and two types of access cavities were prepared, namely tapered access with walls divergent toward the occlusal surface and straight access with parallel walls. The prepared teeth from each category were divided into three subgroups of ten each to receive Cavit (group I), IRM (group II), or TERM (group III). After the fillings were placed, the teeth were transferred into a humidor where they stayed for 24 hours. The teeth were then thermocycled. Each group was thermocycled for 2 hours at 1 minute intervals at 60 degrees C and 4 degrees C. Then the teeth were sealed with a compound and coated with two layers of clear varnish, with the exception of cavity margins. Each occlusal surface was immersed in a vial containing silver nitrate. The teeth were sectioned longitudinally, and the degree of dye penetration was evaluated under a dissection microscope according to set criteria. Our findings demonstrated that design of cavity preparation was not a functional parameter in leakage pattern. Results indicated that Cavit had the best sealing ability whereas IRM showed the maximum dye penetration.

Technical note: Antimicrobial action of glass-ionomer lining cement on S. sanguis and S. mutans

There are a number of glass-ionomer lining cements available to the profession. It is generally agreed that the glass-ionomer cements demonstrate reasonably good biocompatibility. The purpose of this study was to evaluate the antimicrobial activity of six glass-ionomer cements on S. sanguis and S. mutans. Forty-eight plates of TSA-SRBC (10%), each with 3.0-mm-diam. wells, were divided into two groups (1 and 2) of 24 each. Group 1 was inoculated with S. sanguis (10558) and Group 2 with S. mutans (6715-13 w.t.). Each well was filled with 4.0 mg of one of the following liners: Glassic (A), Shofu lining cement (B), GC lining cement (C), Ever Bond (D), Gingiva Seal (E), and Ketac Bond (F); the empty wells served as control. Plates were incubated under microaerophilic conditions at 37 degrees C, and checked daily over seven days for inhibition zones. Average inhibition zones (mm) at 7 days were as follows: Group 1-1A = 10.00, 1B = 7.83, 1C = 18.50, 1D = 13.00, 1E = 8.67, and 1F = 9.33; Group 2-2A = 3.08, 2B = 10.25, 2C = 12.75, 2D = 15.58, 2E = 8.83, and 2F = 3.20. All control wells were 0.0 GC liner and Ever Bond showed significantly greater overall inhibition of microbial growth than did other tested liners (p less than 0.5). A one-way ANOVA and SNK test showed that all tested liners were significantly more toxic toward S. sanguis than toward S. mutans (p less than 0.05).

Cyanoacrylate as a retrofilling material.

The sealing ability of cyanoacrylate as a retrograde root canal filling material was evaluated in vitro. Fifty roots were cleansed, shaped, and assigned to five groups of ten roots each. The root canals were obturated with gutta-percha and Grossmans sealer. The apical 2 mm of each root in the five groups was resected. In groups I, II, and III, retrofilling preparation was made and filled with amalgam, varnish and then amalgam, and cyanoacrylate, respectively. In group IV, a hot instrument was used to seal the gutta-percha, and in group V, a cold burnisher was used for the same purpose. All of the teeth were immersed in 1% methylene blue dye for 24 hours and sectional longitudinally; dye penetration was then measured. One-way analysis of variance performed on the means of the groups indicated that group III had the least amount of leakage (p less than 0.05). This study indicates that cyanocrylate may have potential as a retrograde filling material.

Evaluation of antimicrobial activity in vitro of ten root canal sealers on Streptococcus sanguis and Streptococcus mutans

The antimicrobial activity of ten root canal sealers was studied on Streptococcus sanguis and Streptococcus mutans. One hundred plates of trypticase soy agar-sheep red blood cell (10%), each with four distinct 3 mm diameter wells, were divided into two groups of 50 by means of the Lawn technique; one group was inoculated with S. sanguis and the other with S. mutans. Four milligrams of each root canal sealer was placed in each of three wells in 10 plates (five plates of each inoculant); the fourth well was left empty as a control site. Plates were incubated at 37 degrees C and checked after 2, 7, and 14 days. All root canal sealers inhibited growth of both organisms. The inhibitory zones for S. sanguis were larger than inhibitory zones for S. mutans for all tested sealers, except Diaket. Dentinol, Kerr, and Tubliseal had significantly more inhibitory effect on S. sanguis than did other tested sealers (p less than 0.05). Diaket had superior inhibition on S. mutans.