Reza B. Kazemi

Dimensional changes of endodontic sealers

The purpose of this study was a long-term comparison of the dimensional changes of endodontic sealers of diverse properties. The sealers were injected as thin layers on the internal walls of glass pipettes 1 mm in diameter. The pipettes were filled with deionized water, and the water meniscus levels were recorded periodically up to 180 days. The water was removed from the pipettes, samples were allowed to dry, and the mass and the volume of the sealers were measured. AH26 and Endo-Fill had an initial expansion followed by a volumetric loss. The two zinc oxide eugenol-based sealers studied started to shrink within hours after mixing; the first volumetric loss for AH26 was recorded during the first 30 days and for Endo-Fill after 30 days. The least dimensional change at any time was observed for Endo-Fill. It was concluded that a significant dimensional change and continued volume loss can occur in some endodontic sealers.

Effect of Fatigue Testing on Core Integrity and Post Microleakage of Teeth Restored with Different Post Systems

The purpose of this study was to evaluate a new nondestructive test system, which could test concurrently fatigue and microleakage. Fifty, single-rooted teeth were restored with one of the following posts systems and a composite core: titanium ParaPost cemented with zinc phosphate cement; CosmoPost; C-Post; Esthetic C-Post; and FibreKor post, all cemented with resin cement. Samples were embedded and placed in a positioning jig. They were impacted at 45 degrees to the long axis of the tooth with a force of 55 N at a frequency of 3 Hz for a total of 100,000 impacts. After 60,000 impacts, samples were thermocycled. Core integrity and post microleakage were evaluated periodically throughout the 100,000 impacts. Samples showed no detectable displacement of any of the cores, but the metallic group showed a statistically significant increase in microleakage (p < 0.05) at the conclusion of the study compared with the nonmetallic groups.

Smear layer production by 3 rotary reamers with different cutting blade designs in straight root canals: a scanning electron microscopic study☆

OBJECTIVES The design of the cutting blade of rotary instruments may affect the outcome of root canal instrumentation in terms of cleanliness. The aim of this scanning electron microscopic study was to compare the quality and amount of smear layer generated in the apical third of straight root canals by 2 rotary nickel-titanium reamers and 1 rotary steel reamer with different cutting blade designs. STUDY DESIGN Seventy intact, single-rooted human mandibular premolars with straight, fully developed roots were selected for this study. Before instrumentation, the cervical portion of all teeth was removed by using a microtome (Isomet), leaving 13-mm-long roots. Automated preparation was performed with ProFile (n = 20) and Hero 642 (n = 20) reamers by using the crown-down technique and with a stainless steel engine reamer (Mani; n = 20) by using a reaming motion. All root canals were instrumented to No. 40. A control group (pulp extirpation with barbed broaches; n = 10) was also included. Irrigation with 3 mL of a 1% sodium hypochlorite (NaOCl) solution was performed after each instrumentation. After the instrumentation, each root was split longitudinally, and a scanning electron microscope was used to examine the selected areas of the canal walls at the apical third from 2 different perspectives. A 4-category scoring system for smear layer was used, and the resulting scores were statistically analyzed. RESULTS The least smear layer remained in the Hero 642 group at the selected apical third of straight root canals (P < .05). However, all instruments left a smear layer. The surface texture of the smear layer, in addition to the depth and the frequency of packed materials into the dentinal tubules, varied with instrument type. CONCLUSION These data revealed that the design of the cutting blade of rotary instruments can affect root canal cleanliness in straight root canals. This information may be useful in the selection of nickel-titanium rotary reamers.

Machining efficiency and wear resistance of nickel-titanium endodontic files

OBJECTIVE Nickel-titanium endodontic files are more flexible than stainless steel. Little information is reported concerning machining efficiency and wear resistance of nickel titanium. This study assessed the dentin-machining ability and wear resistance of nickel titanium endodontic files in vitro. STUDY DESIGN The method described earlier to assess machining efficiency and wear resistance of stainless steel files was used. Eight different types and brands of nickel titanium files were studied: Ultra-Flex Hedström, Ultra-Flex K, Mity Hedstrom, Mity K, Mity Turbo, Hedstrom Naviflex NT, NiTiFlex, and Hyflex X-file. Thirty files of each brand were evaluated. One-way ANOVA and t tests were performed to analyze the data. RESULTS Considerable variation was found in matching efficiency and wear. The best initial machining ability of all nickel titanium instruments was recorded for the Hyflex-X file (0.60 +/- 0.16 mm2); the poorest performance was for the Mity Turbo file, which machined less than one third of the best performing instrument (0.19 +/- 0.12 mm2). CONCLUSIONS We compared our results with results of a previous study of stainless steel endodontic files and concluded that nickel titanium instruments are as aggressive as or better than stainless steel instruments in removing dentin. They are also more durable than their stainless steel counterparts.

Assessment of marginal stability and permeability of an interim restorative endodontic material

The purpose of this study was to assess the marginal stability and permeability of a new interim restorative endodontic material, Tempit (Centrix Inc., Milford, Conn.), and to compare the findings with the results of two commonly used restorative endodontic materials, Cavit (Premier Dental Products Co., Philadelphia, Pa.) and IRM (Intermediate Restorative Material Capsules, The Caulk Co., Division of Dentsply International Inc., Milford, Del.) This study was performed in several steps. First, the endodontic access cavities were prepared and restored on 80 extracted mandibular molars. The samples were exposed to methylene blue dye solution for 6 days, thermocycled, and sectioned; the dye penetration and diffusion were measured along the margins and into the body of the materials. The second experiment was a special study performed in standardized glass tubes to better evaluate the marginal and body dye penetration into the materials by increasing the length of the fillings. To eliminate the possibility of hygroscopic setting mechanisms of materials, samples were first allowed to set under water before dye was introduced. Cavit and Tempit showed a substantial amount of dye diffusion into the body of the materials. Cavit exhibited the best sealing ability at all times. The marginal and body dye penetration were significantly different for the Tempit material in all experiments than Cavit (p < 0.001). IRM demonstrated the least body penetration of all three materials (p < 0.001) but had a substantial marginal leakage not significantly different from the results of the Tempit material (p = 0.6 and p = 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)

The endodontic file is a disposable instrument

Most cutting and machining tools wear when properly operated on intended substrates. Little is known about endodontic files when machining on human dentin. It was shown earlier that the efficiency of files was very variable when evaluated on Plexiglas substrates. The present study of seven different brands and types of files was undertaken to understand their wear better when machining human dentin. It was shown that all files evaluated rapidly deteriorated when machining dentin. This decline in efficiency was significant but different within, as well as, among brands. It was suggested that endodontic files be disposable.

Morphologic effects on L929 fibroblasts of titanium tetrafluoride application

OBJECTIVE The aim of this study was to investigate the effect of titanium tetrafluoride solution on L929 fibroblasts by scanning electron microscopy. Titanium tetrafluoride was then compared with sodium fluoride and acidulated phosphate fluoride. STUDY DESIGN Cells were treated with fluoride solutions for 1 minute either directly, through a filter membrane with a pore size of 0.4-micron, or indirectly, through dentin disks; they were then investigated at an electron microscopic level. RESULTS Fluoride application on smeared dentin disks showed fewer cytotoxic effects on fibroblasts than application on nonsmeared dentin disks. Acidulated phosphate fluoride and titanium tetrafluoride appeared to be more cytotoxic than sodium fluoride. Because all fluoride solutions used in this study contained the same fluoride concentration, pH was considered to be the main factor causing the higher toxicity. CONCLUSION Because these solutions demonstrated toxicity in vitro, they must be further evaluated under in vivo conditions to ascertain their clinical safety.

Permeability changes of dentine treated with titanium tetrafluoride

OBJECTIVES The aim of this research was to evaluate the effect of titanium tetrafluoride on dentine permeability in comparison with sodium fluoride and acidulated phosphate fluoride to determine their contribution to acid resistance of dentine. METHODS Thirty-two dentine discs were prepared from extracted mandibular molars. The hydraulic conductance of all discs was measured before and after the formation of smear layer. The discs were then randomly divided into five experimental and one-control groups. Coronal surfaces of dentine discs were treated with either fluoride solutions of NaF, APF, 1% TiF4, 0.5% TiF4 and 0.1% TiF4 or de-ionised water. Following the measurement of hydraulic conductance, treated surfaces were subjected to 25% citric acid application. Then, final permeability measurements were made. The data were statistically analysed using ANOVA and Tukeys HSD multiple comparisons. RESULTS While smear layer formation considerably reduced dentinal permeability of dentine discs, fluoride or de-ionised water application to smeared surfaces did not cause any significant change in hydraulic conductance (p > 0.05). After citric acid application, control and NaF groups showed higher permeability values than 1%, 0.5% and 0.1% TiF4 and APF groups (p < 0.01). CONCLUSION Clinical use of acidic solutions of titanium tetrafluoride in dentine cavities may be considered since smeared dentine surfaces are modified to a stabile and acid-resistant state.

Effect of reduced air pressure on dye penetration in standardized voids

OBJECTIVE This study determined the correlation between the degree of dye penetration in standardized voids to various reduced pressures. STUDY DESIGN Standardized voids of 0.50 and 0.22 mm in diameter were created in 60 human roots; specimens were divided into five groups. Four groups were subjected to a 2% filtered aqueous methylene blue dye solution under different conditions of atmospheric pressure for 7 days and reduced pressures of a 10 torr, a 260 torr, and a 510 torr for 30 minutes. The conditions for the fifth group were similar to the last group except that ethyl alcohol was substituted for water in the dye. RESULTS All positive control specimens showed complete dye penetration. The least linear dye penetration was observed in passively immersed specimens. The results were significantly different from those when reduced pressure had been used (p < 0.001). There were no significant differences among the groups with reduced pressure. No significant difference was found at any pressure level between the means of dye diffusion in the 0.50 and the 0.22 mm voids. The smallest standard deviations were observed for the most reduced air pressure of 10 torr, followed by the group of the least reduced pressure of 510 torr, with the use of the tincture dye solution. CONCLUSIONS A 10-torr reduced pressure and an application of the tincture dye solution would provide an improved method for microleakage studies.

Polypeptide-catalyzed Biosilicification of Dentin Surfaces

In situ formation of mineral particles by biocatalysis would be advantageous for occluding dentin tubules to reduce permeability or for sealing of material-tooth interfaces. One approach would require that the peptide-catalyst remain functional on the dentin surface. Based on recent observations of retained activity on other surfaces, we hypothesized that poly(L-lysine) (PLL), an analog of the protein catalyst responsible for silica formation in primitive marine species, would remain functional on dentin. PLL was applied to dentin discs along with a pre-hydrolyzed silica precursor, tetramethyl orthosilicate (TMOS). Discs were analyzed microscopically (scanning electron microscopy, SEM) and chemically (x-ray photoelectron spectroscopy, XPS). The treated discs, but not the negative controls, exhibited partial distinct coating whose XPS survey was consistent with that of silica, demonstrating that the polypeptide was required and retained its mediating activity. Peptide-catalysts that mediate mineral formation can retain functionality on dentin, suggesting a wide range of preventive and treatment strategies.