Bending, buckling and torsional resistance of rotary and reciprocating glide path instruments.

AIM: To evaluate the bending, buckling and torsional resistance of ProGlider (PG) (Dentsply Sirona, Ballaigues, Switzerland), R-Pilot (RP) (VDW, Munich, Germany) and WaveOne Gold Glider (WOGG) (Dentsply Sirona). METHODOLOGY: Ninety instruments were used: 30 PG (size 0.16, .02v taper), 30 RP (size 0.125, .04 taper) and 30 WOGG (size 0.15, .02v taper). The bending resistance test was performed on 10 randomly selected instruments of each system according to ISO 3630-1 specifications. For the buckling resistance test, a loading was applied in the axial direction of each instrument using a universal test machine, with a 20 N cell and 15 mm min-1 speed, in the axial direction. When a lateral elastic displacement of 1 mm occurred, the force was registered. The torsional resistance test was performed according to ISO 3630-1 specifications. Statistical analysis was performed using one-way anova and post hoc Student-Newman-Keuls test (P < 0.05). RESULTS: WOGG had the lowest bending resistance, whilst RP had the highest bending resistance (P < 0.05). RP also had the highest buckling resistance, and WOGG had the lowest (P < 0.05). PG had intermediate results regarding bending and buckling resistance, with significant differences to RP and WOGG (P < 0.05). RP had the highest torsional strength and the lowest angular deflection when compared to PG and WOGG (P < 0.05). No differences in the torsional strength and angular deflection were observed between WOGG and PG (P> 0.05). CONCLUSION: The glide path instruments had different behaviours in term of bending, buckling and torsional resistance.

Extended cyclic fatigue life of F2 ProTaper instruments used in reciprocating movement.

AIM: To evaluate the cyclic fatigue fracture resistance of engine-driven F2 ProTaper instruments under reciprocating movement. METHODOLOGY: A sample of 30 NiTi ProTaper F2 instruments was used. An artificial canal was made from a stainless steel tube, allowing the instruments to rotate freely. During mechanical testing, different movement kinematics and speeds were used, which resulted in three experimental groups (n = 10). The instruments from the first group (G1) were rotated at a nominal speed of 250 rpm until fracture, whilst the instruments from the second group (G2) were rotated at 400 rpm. In the third instrument group (G3), the files were driven under reciprocating movement. The time of fracture for each instrument was measured, and statistical analysis was performed using parametric methods. RESULTS: Reciprocating movement resulted in a significantly longer cyclic fatigue life (P < 0.05). Moreover, operating rpm was a significant factor affecting cyclic fatigue life (P < 0.05); instruments used at a rotational speed of 400 rpm (approximately 95 s) failed more rapidly than those used at 250 rpm (approximately 25 s). CONCLUSIONS: Movement kinematics is amongst the factors determining the resistance of rotary NiTi instruments to cyclic fracture. Moreover, the reciprocating movement promoted an extended cyclic fatigue life of the F2 ProTaper instrument in comparison with conventional rotation.

Bacteria on the apical root surfaces of untreated teeth with periradicular lesions: a scanning electron microscopy study.

AIM: The purpose of this study was to examine the presence of bacteria on the apical root surfaces of untreated teeth associated with chronic periradicular lesions. METHODOLOGY: Twenty-seven extracted teeth with extensive carious lesions, radiolucent lesions of varying sizes and attached periradicular lesions after extraction, were selected for study. Following fixation, lesions were removed and the apical 5-mm portion of each root was sectioned. Root tips were dehydrated, sputter-coated with gold, and then examined for the occurrence of bacteria on the apical root surfaces using a scanning electron microscope. RESULTS: Bacterial cells were usually observed close to the apical foramen, but restricted to the root canal. Morphologically, these bacteria consisted of cocci and rods. A dense bacterial aggregate composed mainly of rods was observed within the root canal and surrounding the apical foramen of one specimen. Beyond the apical foramen, other bacterial morphological types were recognized, including coaggregations of cocci and filaments, characterizing a fully developed 'corn cob'. CONCLUSIONS: Extraradicular bacteria were observed in one tooth out of 27 (4% of the cases).

Antimicrobial activity and flow rate of newer and established root canal sealers.

Endodontic sealers that possess both optimum flow ability and antimicrobial properties may theoretically assist in the elimination of microorganisms located in confined areas of the root canal system. The antimicrobial effects and the flow rate of the following sealers were investigated and compared: Kerr Pulp Canal Sealer EWT, Grossman's Sealer, ThermaSeal, Sealer 26, AH Plus, and Sealer Plus. The agar diffusion test was used to assess the antimicrobial activity of the sealers. In the flow assay, the sealers were placed between two glass slabs and a weight of 500 g was placed on the top of the glass. The diameters of the formed discs were recorded. All root canal sealers tested showed some antimicrobial activity against most of the microorganisms. There were no significant differences between the materials tested (p > 0.05). All root canal sealers also flowed under the conditions of this study. Statistical analysis of the results revealed that AH Plus and Kerr Pulp Canal Sealer EWT had flow values significantly superior to the other sealers tested (p > 0.05). Taken together, these findings suggest that these sealers have the potential to help in the microbial control in the root canal system.

Scanning electron microscopic investigation of the surface of gutta-percha cones after cutting.

The surface of auxiliary gutta-percha cones after cutting with different methods was evaluated. The tips of gutta-percha cones size fine were cut off using scissors, a razor blade against a glass slab, a razor blade combined with a calibrator, or a razor blade/calibrator followed by a further cutting with a razor blade against a glass slab. Samples were examined under scanning electron microscopy. Cutting with scissors and razor blade/calibrator produced significant irregularities in the cone surface. Cutting with razor blades against a glass slab, with or without previous use of a calibrator, allowed the development of a smooth gutta-percha cone surface.

Mechanisms of antimicrobial activity of calcium hydroxide: a critical review.

Literature review The primary function of calcium hydroxide as a routine intracanal medicament is to provide antimicrobial activity. However, the mechanisms of antimicrobial activity of calcium hydroxide are not well known. Physicochemical properties of this substance may limit its effectiveness in disinfecting the entire root canal system. In addition, calcium hydroxide is not effective against all bacterial species found in root canal infections. Association with other medicaments may enhance the efficacy of the intracanal medication in eliminating residual bacteria in the root canal system.

Mechanical reduction of the bacterial population in the root canal by three instrumentation techniques.

The in vitro reduction of the bacterial population in the root canal by the mechanical action of instrumentation and irrigation was evaluated. Root canals inoculated with a Enterococcus faecalis suspension were instrumented using hand Nitiflex files, Greater Taper (GT) files, and Profile 0.06 taper Series 29 rotary instruments. Irrigation was performed using sterile saline solution. Root canals were sampled before and after instrumentation. In the group of the Nitiflex files, samples were also taken after each file size. After serial dilution, samples were plated onto Mitis-Salivarius agar, and the colony forming units grown were counted. All techniques and instruments tested were able to reduce significantly the number of bacterial cells in the root canal. Instrumentation to a Nitiflex #30 was significantly more effective than GT files. There were no significant differences when comparing the effects of the Profile instrument #5 with either the GT files or the Nitiflex #30. Enlargement to a Nitiflex #40 was significantly more effective in eliminating bacteria when compared with the other techniques and instruments tested (p < 0.05). The results of this study showed that the instrumentation and irrigation can mechanically remove more than 90% of bacterial cells from the root canal.

Coronal leakage of two root canal sealers containing calcium hydroxide after exposure to human saliva.

This in vitro study evaluated the coronal leakage of human saliva into root canals filled by lateral condensation of gutta-percha using two root canal sealers containing calcium hydroxide. Obturated canals with gutta-percha and either Sealapex of Sealer 26 were mounted in an apparatus and then exposed to saliva. The number of days required for total recontamination of the root canal was recorded. Evaluation was conducted for 60 days. Thirty-five percent of the specimens of the Sealer 26 group showed entire recontamination at 60 days. Eighty percent of the root canals obturated with Sealapex showed complete recontamination at 60 days. Sealer 26 presented significantly less leakage than Sealapex (p < 0.01).

Assessment of the apical transportation of root canals using the method of the curvature radius.

The purpose of this investigation was to evaluate the occurrence of apical transportation after root canal instrumentation using only K-Flexofiles or K-Flexofiles intercalated with K-Flexofile Golden Mediums. For this purpose, the degree (Schneider's method) and the radius of the curvature was recorded before and after instrumentation. The results showed that there was no statistically significant difference between the techniques. The correlation between the degree and the radius of curvature of the root canal was not consistent, nor was there a relationship between the original radius of curvature and the apical transportation. However, determination of curvature by use of its radius has proved to be an effective method.

Effectiveness of four chemical solutions in eliminating Bacillus subtilis spores on gutta-percha cones.

Gutta-percha cones should be free of pathogenic micro-organisms before being used for root canal filling. This study was carried out to evaluate the effectiveness of four chemical agents in eliminating Bacillus subtilis spores from gutta-percha cones. The solutions tested were 5.25% sodium hypochlorite, 2% glutaraldehyde, 2% chlorhexidine digluconate, and 70% ethyl alcohol. The gutta-percha cones coated with spores were placed into contact with the chemical agents for 1, 3, 5 and 10 min. The results showed that 5.25% sodium hypochlorite was effective in destroying the spores after 1 min of contact. Glutaraldehyde, chlorhexidine and ethyl alcohol did not decontaminate the gutta-percha cones even after 10 min of contact.

Recontamination of coronally unsealed root canals medicated with camphorated paramonochlorophenol or calcium hydroxide pastes after saliva challenge.

This in vitro study evaluated the ability of some medications to prevent recontamination of coronally unsealed root canals by bacteria from saliva. The medications tested were camphorated paramonochlorophenol (CPMC) applied in cotton pellets in the pulp chamber; calcium hydroxide/saline solution paste filling the root canal; and calcium hydroxide/CPMC/glycerin paste also filling the root canal. Medicated canals were exposed to saliva, and the number of days required for total recontamination to occur was recorded. Canals medicated with CPMC in cotton pellets were thoroughly recontaminated within an average of 6.9 days. Canals filled with calcium hydroxide/saline solution and calcium hydroxide/CPMC/glycerin showed entire recontamination within an average of 14.7 and 16.5 days, respectively. Calcium hydroxide pastes were significantly more effective than CPMC (p < 0.05).

Evaluation of the effectiveness of sodium hypochlorite used with three irrigation methods in the elimination of Enterococcus faecalis from the root canal, in vitro.

The effectiveness of 4.0% sodium hypochlorite (NaOCl) used with three irrigation methods in the elimination of Enterococcus faecalis from the root canal was tested in vitro. Root canals contaminated with E. faecalis were treated as follows: (i) irrigation with 2 mL of NaOCl solution and agitation with hand files; (ii) irrigation with 2 mL of NaOCl solution and ultrasonic agitation; (iii) irrigation with NaOCl alternated with hydrogen peroxide. Contaminated canals irrigated with sterile saline solution served as the control. Paper points used to sample bacteria from the root canals were transferred to tubes containing 5 mL of brain heart infusion (BHI) broth. Tubes were incubated and the appearance of broth turbidity was indicative of bacteria remaining in the root canal. There were no statistically significant differences between the experimental groups. However, NaOCl applied by the three methods tested, was significantly more effective than the saline solution (control group) in disinfecting the root canal.

Influence of diameter variation of Gates-Glidden drills on torsion resistance.

The aim of this study was to determine the variation of the shaft diameter close to the active cutting region and close to the radius of concordance of 28- and 32-mm Gates-Glidden drills and to analyze the diameter influence on the torsion fracture resistance. Seventy-two stainless steel Maillefer drills were studied. The drill diameter varied along the shaft, the smallest diameter occurring close to the radius of concordance. This variation causes stress concentration which leads to complete fracture of the instrument.