Prions and the Oral Cavity

Microbial Culture and Scanning Electron Microscopic Evaluation of Endodontic Hand Files: An In Vitro Study

Background

Endodontic hand files are used during root canal treatment in the cleaning and shaping step of the procedure. Whether endodontic instruments should be single-use or reusable is a topic of debate. This in vitro study aimed to analyze the bioburden on used and new sterilized endodontic hand files.

Methodology

A total of 30 K-files (15 used, 15 new) and 30 H-files (15 used, 15 new) were studied. After clinical use, the used and new files were subjected to phloxine B staining, scanning electron microscope (SEM) analysis, and microbial culture. We used a Fisher’s exact test to investigate the significant difference in contamination and bioburden between new and used endodontic files.

Results

The chi-square test showed no statistically significant difference between new and used groups in staining. In the used group, 20% of the H-files and 6.7% of the K-files were positive for bioburden (p > 0.05). The SEM analysis showed that all used files (100%) were contaminated with biological debris. All new files and most of the used files (86.7%) were negative for bacterial culture.

Conclusions

Used K-files and H-files (sizes 25 and below) had greater contamination and bioburden than new files. Our results highlight the inadequacy of cleaning methods (mechanical/ultrasonication pre-cleaning and heat sterilization) employed between re-usage of files in this study. Appropriate decision-making on either adapting an evidence-based and effective reprocessing strategy or single-use files can be considered by dentists.

Implications for Creutzfeldt-Jakob Disease (CJD) in Dentistry: a Review of Current Knowledge

This review explores our current understanding of the risks of (variant) Creutzfeldt-Jakob disease transmission via dental practice, and whether they merit the rigorous enforcement of improved standards of instrument cleaning and decontamination. The recognition of prions as novel infectious agents in humans has caused significant concern among the public and medical professionals alike. Creutzfeldt-Jakob disease (CJD) in humans has been shown to be transmissible via several routes, including transplantation, contaminated medical products, and via neurosurgery. While the likelihood of transmission via dentistry is undoubtedly very low, this may be amplified considerably by unknown risk factors, such as disease prevalence (particularly in the UK), altered tissue distribution of vCJD, and the failure of decontamination processes to address the inactivation of prions adequately. Since current diagnostic techniques are unable to detect PrPSc in human dental tissues, there is limited evidence for the presence of infectivity. Given these uncertainties, the control of risk by reinforced and improved decontamination practices seems the most appropriate response.

Implications of prion diseases for dentistry: an update

Prions are normal proteins present in all mammals, especially in the central nervous system (CNS) and lymphoreticular tissue. Their transformation into a highly infectious molecule gives rise to a group of diseases known as transmissible spongiform encephalopathies (TSEs), which cause vacuolar degeneration of gray matter and produce a fatal neurodegenerative disorder. Prion diseases have attracted considerable attention in recent years, and this review of the literature was designed to determine their implications for dentistry, studying the possibility of cross-transmission in the dental office and describing their oral manifestations. The main oral manifestations are dysphagia, dysarthria, paresthesias, dysesthesias, and dysgeusia. The most frequently involved oral tissues are the trigeminal ganglion, posterior third of the tongue, tonsils, and, much less commonly, alveolar nerves, gingiva, and salivary glands. Although no contagion has been reported in the dental setting to date, prions resist the usual dental sterilization systems and transmission of this type of disease remains a potential risk. It is therefore important for dentists to be aware of these diseases, to identify high-risk patients by obtaining an adequate clinical history, and to know the appropriate procedures to be followed.

Effect of Prion Decontamination Protocols on Nickel-Titanium Rotary Surfaces

Decontamination of instruments is a prerequisite for their potential reuse but may affect surface integrity. Hence, the effect of prion removal protocols on 7 brands of nickel-titanium files was investigated. Baseline debris scores were determined under magnification after staining with van Gieson's solution. After shaping root canals in vitro, rotaries were mechanically and ultrasonically cleaned followed by immersion for 24 hours in 2 M sodium hydroxide (NaOH), 6 M CH(5)N(3), or 3% sodium hypochlorite (NaOCl); control files were stored dry. After sterilization, files were again stained and evaluated. Two of seven file brands demonstrated significantly higher baseline debris scores compared to final scores. Uniformly, debris could not be completely removed; there were no significant differences among groups. After immersion in NaOCl, 27.8% of instruments showed corrosion; however, no deterioration after immersion in the other solutions was found in the other groups. Regarding corrosion, no significant difference was found between brands. Based on these findings, single use of nickel-titanium rotaries appears beneficial.

Comparison of ultrasonic cleaning schemes: a pilot study

OBJECTIVE

Ultrasonic cleaning is an effective method for cleaning dental instruments prior to sterilisation. However, there are few studies that directly compare precleaning and ultrasonic cleaning solutions. This study evaluated the efficacy of different ultrasonic cleaning schemes.

METHOD AND MATERIALS

Twenty representative dental instruments, five of which were soiled with a mixture of blood and hydroxyapatite, were used in a series of cleaning runs. Cleaning employed a presoaking agent, ultrasonic cleaning, or a combination of both. Two presoaking agents (Non-ionic Ultrasonic Cleaning Solution and ProEZ Foaming Enzymatic Spray) plus five ultrasonic cleaners (UltraDose, General Purpose Cleaner, Co-enzyme Concentrate, Enzol Enzymatic Detergent, and Non-ionic Ultrasonic Cleaning Solution) were compared, with tap water serving as a control. There were two cleaning times: seven and 15 minutes. After rinsing, the working ends of the instruments underwent scrubbing for 20 seconds using a dental polishing brush held in a haemostat. After scrubbing, the brush and instrument were placed in a tube containing sterile saline. Vortexing of the tube lasted 30 seconds. Testing for the post-cleaning presence of blood involved Hemastix dipsticks. These sticks measure minute amounts of blood in urine and can detect as few as 35 red blood cells per ml. Comparisons of colour change were made to a standard scale followed by assignment of numeric values.

RESULTS

Tap water was the poorest cleaning solution, while UltraDose was the most effective. Blood removal improved when cleaning time was increased from seven to 15 minutes. The combined effect of a presoak immersion followed by ultrasonic cleaning was the most effective cleaning scheme overall. Cleaning by either ultrasound or presoaking only was less effective. Some instruments were more difficult to clean than others.

CONCLUSION

Within the constraints of the small number of test runs performed, it was concluded that application of a presoak agent before ultrasonic cleaning produced the most effective instrument-cleaning regimen.

Endodontic complications after plastic restorations in general practice

AIM

To test the hypothesis that dentine and pulp protection by conditioning-and-sealing is no less effective than using a conventional calcium hydroxide lining.

METHODOLOGY

A cohort of healthy adults requiring a new or replacement restoration in a posterior tooth was recruited in six general practices. All procedures received local Ethics Committee approval. Exclusion criteria included signs and symptoms of pulp necrosis or inflammation, and patients unable to commit to a long-term trial. Cavity preparations were randomized to receive a calcium hydroxide lining or conditioning-and-sealing with a smear-removing bonding system. Choice of bulk restorative material (composite resin or amalgam) was at the discretion of the dentist. The key outcome measure was evidence of pulpal breakdown identified at unscheduled (emergency) or scheduled recall examinations. Postoperative sensitivity was recorded on 100 mm VAS at 24 h, 4 days and 7 days. Pulp status was assessed at 6, 12, 24 and 36 month recall, and at any emergency recall appointment. The relationship between pre-treatment and treatment variables and pulp breakdown was assessed by logistic regression (P = 0.05).

RESULTS

A total of 602 teeth were recruited, with comparable numbers of cavities lined (288, 47.8%) or conditioned and sealed (314, 52.2%). The majority (492, 81.7%) were replacement restorations, and amalgam was the most common bulk restorative material (377, 62.6%). A total of 390 (64.8%) restored teeth were reviewed at 6 months, 307 (51%) at 12 months, 363 (60.3%) at 24 months, and 279 (46.3%) at 36 months post-restoration. Sixteen cases of pulp breakdown were identified within 36 months of restoration placement, 11 presenting as emergencies and five detected at routine recall examination. Logistic regression showed that preoperative pain, cavity treatment by lining or conditioning-and-sealing and the use of rubber dam isolation had no association with pulp breakdown. Pulp breakdown was associated with deep or pulpally exposed cavities (P < 0.001, odds ratio 7.8) and with composite rather than amalgam restorations (P = 0.001, odds ratio 2.13). Re-coding to identify teeth with pulp exposures revealed that pulpal exposure was the key determinant of adverse pulp outcomes (P < 0.0001, odds ratio 28.4) and that composite resin restorations were again more likely to be associated with pulp breakdown than amalgam (P = 0.017, odds ratio 3.92).

CONCLUSIONS

Considered within the context of routine primary dental care: Dentists can be confident that pulps will be equally well protected from post-restorative breakdown up to 36 months by calcium hydroxide lining and conditioning-and-sealing with adhesive resins. Residual dentine thickness appears to be a key determinant of pulp responses after restorative dental treatment. In deep and pulpally exposed cavities in posterior teeth, composites were associated with more pulpal breakdown than amalgams.

A SEM evaluation of debris removal from endodontic files after cleaning and steam sterilization procedures

BACKGROUND

In recent times, it has been proposed to classify endodontic files as single-use items due to a perceived inability to adequately clean the instruments. The purpose of the present study was to quantify the surface debris on files removed from the manufacturer's packaging, and after cleaning using an ultrasonic bath or a thermal disinfector.

METHODS

Stainless steel and rotary nickel-titanium files were examined after removal from the manufacturer's packaging, after instrumentation in broth-contaminated human teeth, and after various cleaning procedures. The cleaning procedures consisted of either a thermal disinfector cycle, ultrasonication with the files placed in a perforated container or ultrasonication with the files loosely placed in a beaker. The presence of manufacturing debris and biological debris was evaluated using scanning electron microscopy and quantified using image analysis software.

RESULTS

The effectiveness of cleaning was not affected by variation in the size or taper of the files when an effective cleaning procedure was used. Cleaning the files in a thermal disinfector or by ultrasonication within a container did not consistently achieve complete removal of biological debris. Placing the files loosely in the ultrasonic bath achieved the most effective cleaning, an average of 98.33 per cent of the file surface area was freed of any biological debris.

CONCLUSIONS

A conventional cleaning method is capable of effectively removing biological debris from endodontic files. The efficacy of ultrasonic cleaning was impaired when the files were placed within a perforated container.