Effect of Prion Decontamination Protocols on Nickel-Titanium Rotary Surfaces

Impact of endodontic irrigants on surface roughness of various nickel-titanium rotary endodontic instruments

BACKGROUND

The aim of the current study is to assess the surface roughness of several recent nickel-titanium (Ni-Ti) rotary endodontic instruments, namely: Protaper next (PTN); Hyflex CM (CM); Hyflex EDM (EDM); WaveOne gold (WOG); and trunatomy (TN), before and after application of 5.25% sodium hypochlorite (NaOCl) irrigant solution.

METHODS

In this in vitro study, five recently introduced rotary endodontic instruments of different metallurgical properties and designs were subjected to Atomic Force Microscopy (AFM) analysis, and then each file was rotated in 5.25% NaOCl for 15 min., with speed and torque according to manufacturer's instructions. The instruments were then subjected to AFM analysis again. The surface roughness average (Sa) parameter was calculated. Data were analyzed by Paired T test, One-way ANOVA and Tukey tests.

RESULTS

There was a statistically significant decrease in the surface roughness of all rotary endodontic instruments after immersion in irrigants (P ≤ 0.05).

CONCLUSION

The new TN and PTN instruments showed the least surface roughness. All tested Ni-Ti rotary endodontic instruments after irrigants exposure showed a varying increase in surface roughness.

An in vitro comparison of alterations in surface topographies of three different rotary files after root canal preparation with different irrigating solutions: Atomic force microscopic study

Objectives

The objective of the study was to evaluate and compare the surface topographies of WaveOne Gold (WOG), FlexiCON X1, and EdgeOne Fire (EOF) reciprocating files before and after root canal instrumentation using different irrigating solutions.

Materials and Methods

Forty-eight extracted mandibular molars were selected and randomly assigned into three groups (n = 16) based on the file system used and each group was divided into two subgroups based on the irrigants used during root canal treatment. (Group-1: WOG; Group-2: FlexiCON X1; Group-3: EOF; Subgroup-A: 3% sodium hypochlorite [NaOCl] +17% ethylenediaminetetraacetic acid [EDTA]; Subgroup-B: Citra wash as irrigating solutions). The surface topography of the files was analyzed using atomic force microscope before and after instrumentation. Average roughness and root mean square roughness were calculated. Independent and paired t-tests and one-way analysis of variance with Tukey's post hoc were used for statistical analysis.

Results

Atomic force microscopy results showed an increase in surface roughness after instrumentation, EOF showing the highest roughness. Citra wash showed more roughness compared to NaOCl and EDTA together. However, the surface roughness between the experimental groups WOG and EOF are statistically insignificant and this insignificance was also seen among subgroups (P>0.05).

Conclusion

Instrumentation with various irrigating solutions affected the surface topography of EOF, WOG, and FlexiCON X1 reciprocating files.

Effect of phosphoric acid and sodium hydroxide on cleaning and bonding of saliva-contaminated feldspar porcelain

Purpose Hydrofluoric acid has been used to remove salivary contamination in dental glass-ceramics before bonding treatment. However, alternative methods are required because hydrofluoric acid is harmful. This study examined the cleaning effects of phosphoric acid and sodium hydroxide on glass-ceramics for bonding pre-treatment.Methods Feldspar porcelain was divided into four groups: (C) cleaned porcelain without any contamination, (S) porcelain contaminated with saliva, (SPA) porcelain cleaned with 37% phosphoric acid after saliva contamination, and (SSH) porcelain cleaned with 10% sodium hydroxide after saliva contamination. Each sample was bonded to the resin cement using a silane-containing primer. They were then subjected to a shear bond strength (SBS) test. Each surface was analyzed by scanning electron microscopy (SEM), contact angle measurements, and Fourier transform infrared spectroscopy (FT-IR).Results The SBS of group SSH was comparable to that of group C but significantly higher than that of groups S and SPA. SEM observations showed that saliva-like structures remained on the samples of groups S and SPA, but not on the SSH group. The contact angles of groups C and SSH were comparable and significantly smaller than those of groups S and SPA, respectively. FT-IR analysis also revealed saliva in groups S and SPA, which was absent in the SSH group.Conclusions The saliva remained on the porcelain even after cleaning with phosphoric acid, and SBS was not restored to the same level as before the contamination. In contrast, sodium hydroxide eliminated saliva and restored SBS to the same level as before contamination.

Ex vivo Detection of Amyloid-β in Naturally Formed Oral Biofilm

Background

Oral infection has been implicated in the possible etiology of Alzheimer's disease.

Objective

To detect amyloid-β (Aβ) within microbial biofilms.

Methods

Freshly extracted teeth (N = 87) with periodontal disease were separated into Group A (N = 11), with primary root canal infection and Group B (N = 21) with failed endodontic treatment identified by the presence of, gutta percha root filling. Biofilm characteristics were observed by scanning electron microscopy (SEM). Demineralized paraffin wax embedded tooth sections and mineralized calculus biofilm were immunostained with the anti-Aβ antibody. The gutta perchas were processed either for on-section acrylic resin tissue immunocolloidal gold silver staining (IGSS) using the anti-Aβ antibody or in Araldite resin for ultrastructure.

Results

SEM demonstrated calculus and gutta percha in situ harboring a polymicrobial biofilm featuring extracellular polymeric substance (EPS) and water channels. Immunohistochemistry on rehydrated paraffin wax tooth sections from Group A, demonstrated Aβ staining on external (calculus and plaque) and all intracanal infected regions. In Group B, the gutta percha biofilm IGSS gave an inconclusive result for Aβ. Transmission electron microscopy of selected teeth with infected intra-canals (Group A) and 20% of gutta percha biofilm (Group B) EPS contained electron dense fibrils of variable sizes, some of which were typical of human Aβ fibrils.

Conclusion

This study detected both soluble and insoluble Aβ fibrils within the EPS of periodontal and endodontic natural biofilm, strongly suggesting its role as an antimicrobial peptide in combatting local infection, with potential risk for cross-seeding into the brain for AD development.

Assessment of the Sterility of New Endodontic Files Received From the Manufacturer Using Microbial Culture and Scanning Electron Microscopic Analysis: An In Vitro Study

Background

As endodontic hand files are essential tools for root canal instrumentation and treatment, these instruments have been a constant source of debate regarding whether to reuse them or use them just once. The aim of this in vitro study is to evaluate the sterility of five brands’ new endodontic files received from manufacturers without sterilization before clinical use via microbial culture (bacteria and fungi) and bioburden using scanning electron microscopic (SEM) analysis.

Methodology

This study included 25 K-type hand files with equal numbers from five brand groups (n=5; groups 1 to 5), named Tia Dent, Prevalent, Mani, Thomas, and Dentsply, respectively. The new files were exposed to microbial culture prior to clinical use and SEM analyses. A Fisher’s exact test was performed to compare the differences in contamination among the five tested groups.

Results

In the SEM, all the five brand groups showed one contaminated file out of five files (20%). Fisher's exact test findings revealed statistically significant variations between the five brand groups, as nine out of 25 (36%) files of the tested groups had positive contamination in the microbial culture experiment. Bacterial contamination was present in three (60%) of the five Tia Dent group files, four (80%) in the Prevalent group files, and two (40%) in the Mani group files. Those with fungal contamination were one (33%) in the Tia Dent group and one (25%) in the Prevalent group (P=0.027). The bacterial culture showed that 100% of the new K-files tested negative in both the Thomas and Dentsply groups.

Conclusions

This study concluded that there was a bioburden on new endodontic K-type hand files of different brand groups before sterilization or when immediately used.

Evaluation of Curved Canal Transportation Using the Neoniti Rotary System with Reciprocal Motion: A Comparative Study

The ideal root canal preparation is where the original canal morphology is maintained during the biomechanical preparation. Preparation of curved canals has always been a challenge to clinicians. Better results have been suggested for a single NiTi instrument with reciprocating motion than the conventional continuous rotation method in the preparation of curved root canals. Although the Neoniti rotary system is not suggested to be used with reciprocal motion, running a pilot study, we found that it could be possible. The present study aimed to investigate if shaping curved canals using the Neoniti rotary system with reciprocal motion leads to better results in terms of root canal transportation. One hundred acrylic j-shape canal simulator endoblocks were used in this study. Five preparation sequences were applied: GPS followed by A1#20 (GPS + A1#20), GPS followed by A1#20 and then A1#25 (GPS + A1#20 + A1#25), GPS followed by A1#25 (GPS + A1#25), hand file followed by A1#20 (hand file + A1#20), and GPS followed by A1#20 (with reciprocal motion) (GPS + A1#20(reciprocal)). Pictures were taken from blocks once before and once after preparation from two dimensions. Before-and-after pictures were superimposed in Photoshop software. Measurements were performed in Digimizer. The number of autoreverses and pecking motions was recorded after reviewing the recorded videos. Data were analyzed in SPSS, version 26. A p value of less than 0.05 was considered statistically significant. The group GPS + A1#20 + A1#25 had more transportation compared with the others, at apical, middle, and coronal thirds not only in the frontal view but also in the lateral view. Other groups were not significantly different. The number of peckings and autoreverses was significantly less when A1#25 was used after GPS and A1#20. When A1#20 was used with reciprocal motion, it had less peckings compared with the same file with continuous rotation, and no autoreverses were observed in that group. Using Neoniti files with reciprocal motion might result in less instrument fatigue and favorable results, with respect to canal anatomy preservation. Using A1#20 before A1#25 also will decrease the stress on the instrument during preparation. However, this may lead to significantly more canal transportation.

Scanning electron microscopy analysis of conventional and controlled-memory nickel titanium files before and after multi-uses in root canals

The current study aimed to examine changes in the physical properties of conventional and CM nickel-titanium instruments after repeated clinical use, disinfection-sterilization processes, using scanning electron microscopy (SEM). Sixty extracted mandibular molar mesial roots were used in this ex vivo study. The 60 teeth underwent final apical shaping (#25/.06) by the Revo-S SU (Revo-S Group: #25/.06; Micromega; n = 10) and Hyflex CM (Hyflex CM group: #25/.06; Coltene-Whaledent; n = 10) groups. One instrument of each group was used to shape six different teeth (Revo-S SU in 3 MB and 3 ML canals, and Hyflex CM in 3 MB and 3 ML canals), sequentially. The physical changes evident on the surfaces of the files after sequential use and sterilization processes were analyzed by SEM after the first, third, and sixth use. The first SEM examination was performed immediately after removal from the packages. Following first SEM examination, the files were sterilized before the first use as would be customary in practice. Qualitative evaluations were made by two evaluators, according to the following criteria: tip deformation, cutting edge deformation, debris, and microfracture. Revo-S showed a significant difference in cutting edge deformation, tip deformation, and microcrack formation, as compared to Hyflex CM. There was no significant difference between the groups in debris with the increasing number of uses. In this study, Hyflex CM (CM nickel-titanium) files showed better performance in terms of deformation and microcrack formation as the number of uses increased than did Revo-S (conventional nickel-titanium) files.

Topographic changes in NiTi rotary instruments after the clinical use

Surface alterations of instruments were investigated after single and multiple uses in the root canals. XP-endo Shaper (n = 5) and WaveOne GOLD (n = 5) files were used until the separation of the instruments occurred. The apical 3-mm and separated fragments were analysed by SEM to determine the changes in the instruments and the cross-sections of the separated fragments. Each group was divided into five subgroups: control, first, second, third and fourth molar. The results were reported descriptively for each group. In the XP-endo Shaper group, microcracks started to appear after the second use, and pitting and galvanic corrosion occurred after the third use. During the fourth use, microcracks propagated, resulting in ductile fracture while it happened after the third use in the second group. The single use of XP-endo Shaper and WaveOne GOLD was safe without any major changes on their surfaces. Reciprocating motion was not necessarily superior to full rotation motion.

Current Trends in Use and Reuse of Nickel-Titanium Engine-driven Instruments: A Survey of Endodontists in the United States

INTRODUCTION

Information is scarce regarding current usage practices of nickel-titanium (NiTi) engine-driven instruments in clinical practice. Therefore, the specific purpose of this survey was to assess trends among endodontists regarding the use and reuse of NiTi instruments.

METHODS

A 16-question survey was sent by e-mail to about 4000 active members of the American Association of Endodontists. Data were collected over a 6-month period and compared using chi-square tests.

RESULTS

A total of 957 surveys were collected (response rate = 23%). Of the respondents, 40.2% worked in solo practices; among them, there were significantly fewer recent graduates (<10 years) compared with those who graduated more than 10 years ago. Furthermore, 41.7% were in a group practice, 4.3% in corporate practice, 10.7% in university settings, and 3% in the military. Overall, 98.3% of respondents reported using NiTi instruments. Respondents who graduated less than 25 years ago use NiTi instruments significantly more (99%) than those who graduated more than 25 years ago (92.6%). Although 22.9% of respondents buy presterilized instruments, 41.6% sterilize them before use, and 35.5% do not sterilize new instruments before use; dental officers in the military reported that they use sterile new instruments in 100% of cases. NiTi instruments were reused by 74% of respondents. The 2 largest segments of the specialist endodontic instrument market belonged to Dentsply (York, PA; 56.9%) and EdgeEndo (Albuquerque, NM; 28.8%).

CONCLUSIONS

There are significant differences in the use of NiTi instruments among types of practice and years since graduation. There were noticeable changes compared with findings reported about 10 years ago.

Is the re-use of sterilized implant abutments safe enough? (Implant abutment safety)

Background: The reuse of implant healing abutments is common in dental practice. Effective elimination of bacteria and viruses is accomplished by conventional sterilization. The aim of this work was to explore the eventual survival of microorganisms on sterilized healing abutments and to rule out the presence of transmissible organic material after standard procedures. Material and Methods: A total of 55 healing abutments previously used in patients will be washed and sterilized in a steam autoclave at 121ºC for 15 min. Each healing abutment will be cultured in Brain Heart Infusion broth (BHI) under strict aseptic conditions. Besides, two control groups will be included: one of 3 unused healing abutments, and the other of just medium. After 10 days at 37°C under a 5% CO2 100 µl of the broth will be plated on solid media (Brain Infusion Agar, BHIA) and Columbia Blood agar to test for sterility. The remaining volume will be centrifuged, the sediment fixed, and a Gram stain performed to discard the presence of non-cultivable microorganisms. Moreover, to determine the presence of remaining organic material after the cleaning and sterilizing treatments, the bioburden will be determined by measuring total organic carbon (TOC) in another 10 previously used healing abutments, cleaned and sterilized, that will be submerged in Milli-Q water and sonicated. Results: No bacterial growth was detected on any of the 58 cultured abutments, indicating that the sterilization was completely satisfactory in terms of removal of live bacteria or spores. Nevertheless, significant amounts of organic carbon may still be recovered (up to 125,31 µg/abutment) after they have been sterilized. Conclusions: Significant amounts of the bioburden remained adhered to the surfaces in spite of the cleaning and sterilization procedures. Taking into account our results and data from other authors, the presence of infectious particles on the reused healing abutments such as prions cannot be ruled out.

Key words:Healing abutment, abutment surface, peri-implantitis, mucositis, sterilization.

Rotary Versus Reciprocation Root Canal Preparation: Initial Clinical Quality Assessment in a Novice Clinician Cohort

INTRODUCTION

Reports comparing clinical outcomes using nickel-titanium (NiTi) reciprocating instruments with other instrumentation modalities are scarce. This study examined initial shaping outcomes after an instrumentation change of root canal instrumentation technique in a doctor of dental surgery educational program. Student characteristics, faculty/student ratio, facility, and overall endodontic treatment guidelines remained unchanged.

METHODS

A total of 200 nonsurgical initial molar root canal treatments completed by third-year dental students were evaluated. The cases were examined regarding the number of treatment appointments, access cavity preparation, canal taper, canal transportation, perforations, missed canals, presence of ledges, fractured instruments, obturation length, obturation quality, and sealer extrusion. Two independent evaluators determined the number of appointments per case; 4 independent and blinded evaluators analyzed radiographs at 4 treatment stages: preoperative situation, working length, cone fit, and obturation.

RESULTS

The following factors were significantly different between the 2 cohorts: the number of appointments, preparation length, taper, and occurrence of ledges. The WaveOne (Dentsply Sirona, York, PA) cohort had a significantly reduced treatment time compared with hand/GT rotary instrumentation (Dentsply Tulsa Dental, Tulsa, OK) (average of 3.3 vs 4.3 appointments). Appropriate length control and adequate taper were significantly more frequent in the WaveOne group. The frequency of ledges was significantly larger in the hybrid group. Other variables, such as access cavity preparation, canal transportation, perforations, missed canals, fractured instruments, obturation quality, and sealer extrusion, were statistically similar between the 2 groups.

CONCLUSIONS

NiTi reciprocation instrumentation was superior to hybrid hand/NiTi rotary instrumentation in reducing both patient appointments and the incidence of ledging and in improving obturation length and taper in a dental student clinic setting.

Treatment of Necrotic Teeth Using Two Engine-Driven Systems and Patient's Postoperative Pain: A Double-Blind Clinical Trial

INTRODUCTION

One of the most important reasons for postoperative pain is the extrusion of debris from the apical foramen during preparation and shaping of root canals. The aim of this clinical trial was to evaluate the severity of postoperative pain with the use of two different engine-driven NiTi systems.

METHODS AND MATERIALS

Ninety mandibular molars were randomly divided into two groups (n=45), and root canal cleaning and shaping was done using either RaCe or Reciproc instruments. The severity of postoperative pain was determined with visual analogue scale (VAS) at 4-, 12-, 24-, 48- and 72 h and 1-week intervals and postoperative pain was compared between the two groups. The chi-squared test and repeated-measures analysis were used to compare the data between the two groups.

RESULTS

Based on the results of the statistical analyses, the two groups were matched regarding the age and gender, with no significant differences. In addition, except for 4- and 24-h and 1-week intervals, postoperative pain was significantly less in the RaCe group compared to the Reciproc group (P<0.001).

CONCLUSION

Based on the results of the present study, use of RaCe files for cleaning and shaping of root canals in necrotic mandibular molars resulted in less severe postoperative pain compared to Reciproc files.

Sterilization of rotary NiTi instruments within endodontic sponges

AIM

To determine whether the following can be sterilized by autoclaving - endodontic sponges, rotary nickel-titanium (NiTi) instruments within endodontic sponges, and rotary NiTi instruments with rubber stoppers.

METHODOLOGY

Sixty-four samples of eight different endodontic sponges (n = 512) were placed into brain heart infusion broth (BHI) for 72 h. An aliquot of this was then spread onto horse blood agar and cultured aerobically and anaerobically to test sterility at purchase. Bacterial suspensions of Enterococcus faecalis, Porphyromonas gingivalis and Geobacillus stearothermophilus in BHI were used to contaminate sterile sponges and rotary NiTi instruments (with and without rubber stoppers) inserted into sponges. The various samples were autoclaved and then cultured aerobically and anaerobically. Success of sterilization was measured qualitatively as no growth. The experiment was repeated with clinically used rotary NiTi instruments (n = 512). All experiments were conducted in quadruplicate.

RESULTS

No sponges on purchase had microbial growth when anaerobically cultured but some did when aerobically cultured. All autoclaved sponges and instruments (within or without sponges, and with or without rubber stoppers) were associated with no microbial growth. All nonautoclaved positive control samples showed microbial growth.

CONCLUSIONS

Autoclaving was effective in the sterilization of sponges and endodontic instruments. Endodontic sponges should be autoclaved before clinical use. For clinical efficiency and cost-effectiveness, rotary NiTi instruments can be sterilized in endodontic sponges without removal of rubber stoppers.

The effect of multiple autoclave cycles on the surface of rotary nickel-titanium endodontic files: An in vitro atomic force microscopy investigation

Aims:

To observe and study the effect of multiple autoclave sterilization cycles, on the surface of nickel-titanium (NiTi) files.

Materials and Methods:

The file used for this study was the M_two file (VDW) and ProTaper (Dentsply). The apical 5 mm of the files were attached to a silicon wafer and subjected to autoclave cycles under standardized conditions. They were scanned with an AFM after 1, 5, and 10 cycles. The unsterilized files were used as control, before start of the study. Three vertical topographic parameters namely maximum height (MH), root mean square (RMS) of surface roughness, and arithmetic mean roughness (AMR)were measured with the atomic force microscope (AFM). Analysis of variance along with Tukey's test was used to test the differences.

Results:

The vertical topographic parameters were higher for both the files, right after the first cycle, when compared with the control (P < 0.01). The surface roughness increased sharply for M_two when compared to ProTaper, though ProTaper had a rougher surface initially.

Conclusions:

The study confirmed that the irregularities present on the surface of the file became more prominent with multiple autoclave cycles, a fact that should be kept in mind during their reuse.

Comparison of different cleaning procedures of implant drills using TC99

PURPOSE

This study was carried out to evaluate implant drills' cleaning protocols efficiency as tested by the use of nuclear medicine.

METHODS

Eighty-one new drills of 2 different implant systems (Nobel Biocare and BioMet 3i) were selected as study samples. Six of these drills were used as positive control group, and the rest were contaminated with TC-labeled blood. The instruments were divided randomly into 5 groups (negative control group; group 1: immersion and brushing; group 2: immersion and brushing and then evaluation under magnifier; group 3: immersion and brushing and then ultrasonic cleaning for 15 minutes; and group 4: immersion and brushing and then ultrasonic cleaning for 30 minutes) so that every group contained equal number of each implant drills brand. Then the emitted γ rays were counted by means of a gamma counter.

RESULTS

Statistically significant differences were observed between the full cleaning protocol and ultrasonication group (P < 0.009). Immersion and brushing, and ultrasonic cleaning for 30 minutes before sterilization, were the most effective methods to remove contamination.

CONCLUSIONS

Complete removal of biologic debris was not attained with any of the cleaning techniques used. It is recommended to use ultrasonic cleaner for 30 minutes after immersion and brushing to achieve the best results.

Effect of altering the reciprocation range on the fatigue life and the shaping ability of WaveOne nickel-titanium instruments

INTRODUCTION

The purpose of this study was to investigate the effect of altering the reciprocation range of the WaveOne instrument (Dentsply Maillefer, Ballaigues, Switzerland) on its fatigue life and shaping ability regarding tendency for canal transportation, the canal centering ratio, and preparation time.

METHODS

Thirty primary WaveOne instruments were divided into 3 equal groups according to the reciprocation range used: G1: 150 counterclockwise (CCW)-30 clockwise (CW), G2: 120 CCW-30 CW, and G3: 90 CCW-45 CW. They were activated in a cyclic fatigue testing device until fracture. The time to fracture and the length of the fractured tip were recorded and registered. To assess the shaping ability, 30 mesiobuccal canals of mandibular molars were prepared using the same reciprocation ranges. Canals were scanned using cone-beam computed tomography scanning before and after preparation to evaluate root canal transportation and the canal centering ratio at 1, 4, and 7 mm from the apex. The time taken to complete canal preparation was also recorded. The mean ± standard deviation values were analyzed using analysis of variance and the Tukey post hoc test. The significance level was set at P < .05.

RESULTS

The time to fracture recorded increased as the reciprocation range decreased, and this was significant for the 90 CCW-45 CW group (P < .05). Regarding preparation time, it increased significantly as the reciprocation range was decreased (P < .05). Results for canal transportation and the canal centering ratio showed that at 1 mm from the apex there were no significant differences between the experimental groups. For the other studied levels, the 150 CCW-30 CW group had the highest mean for canal transportation and the lowest mean for the canal centering ratio, which was statistically significant in comparison with the other experimental groups (P < .05).

CONCLUSIONS

Decreasing the reciprocation range of WaveOne instruments resulted in an increased cyclic fatigue resistance with less canal transportation and more centered preparations but with longer preparation times.

Alteration in the inherent metallic and surface properties of nickel-titanium root canal instruments to enhance performance, durability and safety: a focused review

The expanded use of nickel-titanium (NiTi) rotary instruments in root canal procedures has led to the development of a wide variety of shapes, designs and applications. Root canal anatomy has not changed, however, and the same challenges exist in both initial treatment and the revision of unacceptable treatment. These challenges include application with high levels of achievement and low to no levels of adverse effects, such as instrument fracture, root canal wall ledging, dentine wall perforation and so forth. To that end, many manufacturers have been seeking ways to alter the presently available and wide range of root canal instrument designs, with a focus on altering the surface of the alloy or altering the alloy microstructure with post-machining or post-twisting heat treatment. This focused review will address the impact that these modifications have had on instrument flexibility, resistance to cyclic fatigue and cutting efficiency.

Defects in nickel-titanium instruments after clinical use. Part 5: single use from endodontic specialty practices

INTRODUCTION

Single use of endodontic nickel-titanium (NiTi) instruments has been recommended to reduce instrument fatigue and the possibility of cross-contamination. The purpose of this study was to evaluate the defects of three NiTi rotary systems (ProFile series 29 [Dentsply Tulsa Dental Products, Tulsa, OK], ProFile [Dentsply Tulsa Dental Products], and ProTaper [Dentsply Maillefer, Ballaigues, Switzerland]) that were discarded after single use by two endodontic clinics.

METHODS

A total of 1,071 ProFile .04, 432 ProFile series 29 .04, and 1,895 ProTaper rotary instruments were collected over 12 months and analyzed. These discarded files were ultrasonically cleaned and autoclaved. The lateral view of the deformed instruments and fracture surface of the separated instruments were examined by scanning electron microscopy. Qualitative X-ray energy-dispersive spectrophotometric (EDS) spot analyses were performed on particles adherent to the surface and those apparently wedged in surface microcracks.

RESULTS

There were no fractures or deformations in the ProFile Series 29. The overall prevalence of deformation was 2.9% in ProTaper and 0.75% in ProFile. The incidence of instrument separation was 0.26% in ProTaper, whereas no fractures occurred in ProFile instruments. The majority of instrument defects occurred in size 25 (6/8) for ProFile and in Sx for ProTaper (22/60). The separated ProTaper instruments failed mostly because of shear stress. Some surface deposits and microcracks were found in single-use NiTi instruments. EDS indicated that surface deposits may be dentin.

CONCLUSION

The risk of NiTi rotary instrument fracture in the canal is low when a new instrument is used by experienced endodontists. The most common cause of failure, albeit rare, was shear failure.

Rapid chairside sterilization of endodontic files using 6% sodium hypochlorite

INTRODUCTION

The purpose of this study was to assess the percentage of new endodontic files (taken directly from the manufacturers' packages) that were contaminated with viable microorganisms and to determine the amount of time new files needed to be immersed in 6% sodium hypochlorite to achieve sterility.

METHODS

Endodontic files from four manufacturers were placed either immediately in thioglycolate broth or immersed in 6% sodium hypochlorite for 1, 2, or 5 minutes before placement in the broth. The files were aerobically incubated for 72 hours and sterility determined by the absence of broth turbidity, as determined by a blinded examiner. The data were analyzed using the Cochran-Q test followed by the McNemar test for pair-wise comparisons. The level of statistical significance was set at alpha = 0.05.

RESULTS

When pooling all manufacturers' files, no significant differences were found between groups.

CONCLUSION

New files demonstrated a 6% contamination rate and none of the immersion times in NaOCl achieved file sterility.

Resistance of bovine spongiform encephalopathy (BSE) prions to inactivation

Distinct prion strains often exhibit different incubation periods and patterns of neuropathological lesions. Strain characteristics are generally retained upon intraspecies transmission, but may change on transmission to another species. We investigated the inactivation of two related prions strains: BSE prions from cattle and mouse-passaged BSE prions, termed 301V. Inactivation was manipulated by exposure to sodium dodecyl sulfate (SDS), variations in pH, and different temperatures. Infectivity was measured using transgenic mouse lines that are highly susceptible to either BSE or 301V prions. Bioassays demonstrated that BSE prions are up to 1,000-fold more resistant to inactivation than 301V prions while Western immunoblotting showed that short acidic SDS treatments reduced protease-resistant PrP(Sc) from BSE prions and 301V prions at similar rates. Our findings argue that despite being derived from BSE prions, mouse 301V prions are not necessarily a reliable model for cattle BSE prions. Extending these comparisons to human sporadic Creutzfeldt-Jakob disease and hamster Sc237 prions, we found that BSE prions were 10- and 10(6)-fold more resistant to inactivation, respectively. Our studies contend that any prion inactivation procedures must be validated by bioassay against the prion strain for which they are intended to be used.

Effect of Immersion in Sodium Hypochlorite on Torque and Fatigue Resistance of Nickel-Titanium Instruments

This study investigated the effect of immersion in sodium hypochlorite (NaOCl) on torque and fatigue resistance of two nickel-titanium files. Size 25 .04 ProFile and RaCe files were immersed in 5.25% NaOCl for 1 or 2 hours at temperatures of 21 degrees C and 60 degrees C. Torque and angle at failure were measured according to ISO 3630-1. Resistance to cyclic fatigue was determined by counting rotations to breakage in a 90 degrees curve with a 5-mm radius. Data were analyzed by 2-way analysis of variance. Torsional resistance of both rotaries was not significantly affected by immersion in NaOCl, except after 2 hours of immersion at 60 degrees C. Resistance to cyclic fatigue decreased significantly for ProFile and RaCe instruments after immersion in NaOCl. Spontaneous fractures occurred in 28 of 160 files during immersion in NaOCl. In conclusion, nickel-titanium rotaries have reduced resistance to cyclic fatigue after contact with heated NaOCl and may then be considered single-use instruments.