Sterilization beneath rings on dental instruments.

This study determined the effectiveness of standard methods of instrument sterilization beneath instrument rings. Sets of three types of dental instruments were contaminated with known amounts of bacterial spores (Bacillus stearothermophilus or Bacillus subtilis). Instrument rings were placed over the contamination and the instruments processed through standard cycles in a steam autoclave, an unsaturated chemical vapor sterilizer, a standard dry heat sterilizer, an ethylene oxide gas sterilizer or a 2.0% alkaline glutaraldehyde solution. Controls consisted of spore-contaminated instruments without rings that were not processed through any sterilizing method and that were processed through each sterilizing method. All instruments and their associated rings were cultured for the presence of live spores. The results indicate that the reliability of sterilization beneath the instrument rings used is greatest if the ringed instruments are processed through a steam autoclave or an unsaturated chemical vapor sterilizer.     

Steam sterilization of air turbine dental handpieces

The efficacy of autoclaving high-speed dental handpieces was tested in two types of downward displacement steam sterilizers (instrument autoclaves), commonly used in the dentist's office. Eight series of experiments were performed with various sterilization schedules. Lubrication oils with or without antimicrobial agent were used in four of the series. Each handpiece was inoculated with 1 ml of a suspension containing equal amounts of saliva and spores of Bacillus stearothermophilus (approx. 10(6) spores/ml). Neither sterilization at 120-124 degrees C for 20 min nor at 134-136 degrees C for 10 min resulted in complete inactivation of the spores in series in which the instruments were tested without oil or with oil containing no antimicrobial agent. However, when the handpieces were lubricated with oil containing isopropanol and formaldehyde and the schedule 134-136 degrees C/10 min was used, no growth was observed. The results indicate that instrument autoclaves with built-in programs of 120-124 degrees C/20 min and 134-136 degrees C/10 min could have insufficient capacity to sterilize lubricated or unlubricated dental handpieces. The use of oils containing an antimicrobial agent can overcome this problem.     

不同灭菌法对齿科高速裂钻腐蚀的初步研究

目的研究齿科常用的灭菌方法：干热灭菌法、湿热灭菌法、化学浸泡灭菌法对高速裂钻腐蚀的影响。方法将100根全新高速裂钻随机分为10组,每组10根。第1组为对照组,不予以任何处理;另9组为实验组,分别用湿热灭菌法、干热灭菌法、化学浸泡法处理5、10、15次。采用称重法、扫描电镜观察及成分分析、表面显微硬度测量法对高速裂钻的腐蚀情况进行研究。结果湿热法处理5、10、15次组,干热法处理10、15次组以及化学浸泡法处理15次组与对照组相比,其重量增加均有统计学意义（ P<0.05）。电镜图片显示：湿热组形貌改变最为显著,出现明显腐蚀外观并与灭菌次数呈正相关;干热组最轻微。表面成分分析显示高速裂钻中的主要成分钨、铬、铁、钴、镍在灭菌处理前后其相对体积分数有所改变,其中钨以对照组、干热组、化学浸泡组、湿热组顺序依次增多;铁则以此顺序依次降低。与对照组相比,三种灭菌法均降低裂钻表面硬度（ P<0.05）,其中湿热组影响最大;干热组和化学浸泡组次之。随着灭菌次数的增加,湿热组和化学浸泡组裂钻表面硬度差异具有统计学意义（ P<0.05）,干热组硬度差异无统计学意义（ P>0.05）。结论不同灭菌处理对高速裂钻均产生一定的腐蚀,以湿热法最为明显。温度和湿度对高速裂钻的腐蚀有协同作用,干热灭菌对裂钻的腐蚀作用较轻。     

Glass bead sterilization of orthodontic bands

The purpose of this study was threefold: to determine if bead sterilization is capable of sterilizing orthodontic bands, if so, to establish a minimal time for sterilization when bands are inoculated with bacteria and spores, and to compare bead sterilization to other methods of cleansing and disinfecting orthodontic bands used in the office setting. Ten bands per time trial inoculated with either Bacillus subtilis spores or Staphylococcus albus bacteria were used along with ten controls (inoculated but not placed in the bead sterilizer). The bands were placed one at a time into a 226 degrees C bead sterilizer for 15, 30, 45, and 60 seconds, transferred to a test tube with BHI broth, and incubated at 37 degrees C for 3 days. The results indicated that 15 seconds is required to sterilize bacteria and 45 seconds required for spores. If five bands were placed in the bead sterilizer simultaneously, twice the time was required for sterilization. Other techniques for disinfecting bands, such as a 5-second tap water rinse, 10-second soap scrub, 30-minute immersion in alcohol, and alcohol flame, were ineffective in killing bacteria or spores with one exception--the alcohol flame was capable of preventing growth on bands inoculated with Staphylococcus albus.     

Monitoring dental sterilizers' effectiveness using biological indicators

The purpose of this study was to evaluate the effectiveness of dental office sterilizers as measured by their ability to kill bacterial spores present on biological indicator strips. The biological indicators used in this study contained two different spores, Bacillus stearothermophilus and Bacillus subtilis (Spordi, AMSCO/Medical Products). Ten spore test strips were sent to 87 dental offices; 51 sterilizers were tested. Office personnel were instructed to place four strips in the center of a normal sterilization load and process the load. The procedure was repeated on a second day. The processed strips, along with two unprocessed control strips, were returned by mail for laboratory culturing. The results indicated the overall failure rate (positive test) of sterlizers tested for both days was 51% at the culturing temperature of 37 degrees C and 33.3% at 55 degrees C. McNemar's test indicated a significant difference (p less than .03) in sterilization failures associated with the type and number of microorganisms present on the test strips. This study also showed that the more times a sterilizer was tested, the more likely a failure would occur. Overall, an alarming number of sterilizers (64.7%) were not effective in killing all the spores present on the indicator strips. When office personnel were given information for improving sterilizer performance, there was a noticeable reduction in sterilization failures following retesting.     

Viable spore counts in biological controls pre-sterilization

The aim of the present study was to evaluate the total count of viable spores in standardized inoculated carriers pre-sterilization. Samples of "Bacterial Spore Sterilization Strip" (R Biological Laboratories) (well before their expiry date) were divided into Group A (B. subtilis) and Group B (B. stearothermophylus). Twenty-four strips were tested per group. The strips were minced in groups of three, placed in chilled sterile water and vortexed for 5 minutes to obtain a homogenous suspension. Ten ml of the homogenous suspension were transferred to two sterile jars, i.e. one jar per group. The samples were then heated in a water bath at 95 degrees C (Group A) or 80 degrees C (Group B) for 15 minutes and cooled rapidly in an ice bath at 0- 4 degrees C during 15 minutes. Successive dilutions were performed until a final aliquot of 30 to 300 colony-forming units (CFU) was obtained. The inoculums were placed in Petri dishes with culture medium (soy extract, casein agar adapted for spores, melted and cooled to 45-50 degrees C) and incubated at 55 degrees C or 37 degrees C. Statistical analysis of the data was performed. A larger number of spores were found at 48 hours than at 24 hours. However, this finding did not hold true for all the groups. The present results show that monitoring viable spores pre-sterilization would guarantee the accuracy of the data. Total spore counts must be within 50 and 300% of the number of spores indicated in the biological control. The procedure is essential to guarantee the efficacy of the biological control.     

不同灭菌法对齿科高速裂钻力学性能的影响

目的研究齿科常用的3种灭菌方法（干热法、湿热法、化学浸泡法）对牙科高速裂钻力学性能的影响。方法将200根全新的钨钢高速裂钻随机分为10组。分别通过弯曲实验和扭转实验观察高速裂钻在不同灭菌方法处理后弯曲强度、弹性模量和扭转强度等力学指标的改变。结果干热灭菌法、化学浸泡法和湿热灭菌法对裂钻的力学性能均有影响,随着灭菌次数的增加,裂钻的弯曲强度、弹性模量和扭转强度均相应减弱。3种灭菌方法比较发现,湿热处理引起裂钻的力学性能降低最明显,而化学浸泡和干热处理引起的变化相似,且较小。结论不同灭菌方法对高速裂钻产生一定的作用,影响大小排列依次为：湿热法、化学浸泡法、干热法。鉴于干热灭菌腐蚀作用最弱,建议齿科常用的小型器械可使用干热灭菌法进行灭菌。     

Dynamic ultraviolet sterilization of different implant types

This paper investigates the use of the dynamic ultraviolet sterilization process with various dental implants, stainless steel orthopedic cortical bone screws, and polysulfone polymer healing caps. These biomaterials were inoculated with the spores of Bacillus subtilis and Bacillus stearothermophilus. They were then exposed to dynamic ultraviolet radiation in the chamber of a BUD Ultraviolet Device. Samples were incubated in trypticase soy broth at 37 degrees C and 56 degrees C, and they were subcultured onto an enriched agar medium. Results indicate that 16 seconds of dynamic ultraviolet radiation is effective in sterilizing these materials. This is significantly less time than other sterilization techniques presently used.     

The effect of clinical use and sterilization on selected orthodontic arch wires.

The effect of clinical use and various sterilization/disinfection protocols on three types of nickel-titanium, and one type each of beta-titanium and stainless steel arch wire was evaluated. The sterilization/disinfection procedures included disinfection alone or in concert with steam autoclave, dry heat, or cold solution sterilization. No clinically significant differences were found between new and used arch wires. The direction of load application to the arch wire and the particular segment of arch wire tested was found to cause substantial differences in generated loads for certain arch wire types.     

Influence of sterilization on mechanical properties and fatigue resistance of nickel-titanium rotary endodontic instruments

AIM: To evaluate the effect of repeated sterilization cycles in dry oven or autoclave, on the mechanical behaviour and fatigue resistance of rotary endodontic Ni-Ti instruments. METHODOLOGY: New Ni-Ti instruments were subjected to five consecutive sterilization cycles in a dry oven or steam autoclave. Microhardness was measured in the nonmachined parts of the shanks of instruments using a Vickers indenter. Specimens of Ni-Ti wires were submitted to the same sterilization protocol and tensile tested until rupture. A group of instruments were fatigued to one half of their average fatigue life and then sterilized. New and sterilized instruments were fatigue tested until rupture. anova tests at alpha = 0.05 were used for statistical analysis. RESULTS: Sterilization procedures resulted in no significant changes in Vickers microhardness, nor in the parameters describing the mechanical behaviour of the wires. However, the number of cycles to failure was statistically higher for all instruments after dry heat or autoclave sterilization cycles. In the instruments previously fatigued to one half of their fatigue life, autoclave sterilization gave rise to an increase of 39% in the remaining number of cycles to failure. CONCLUSIONS: Changes in the mechanical properties of Ni-Ti endodontic instruments after five cycles of commonly used sterilization procedures were insignificant. The sterilization procedures are safe as they produced a significant increase in the fatigue resistance of the instruments.     

Effect of steam versus dry-heat sterilization on the wear of orthodontic ligature-cutting pliers.

The purpose of this study was to compare the wear of orthodontic ligature-cutting pliers after multiple cycles of cutting stainless steel ligature wire (.025 mm) and sterilizing with dry heat or steam autoclave. Fifty ligature-cutting pliers with stainless steel inserts were randomly divided into 2 equal groups to be sterilized in either dry heat or steam autoclave. Each plier was subjected to a series of ligature wire cuts followed by the assigned sterilization method. The amount of wear at the tip of each plier in both groups was measured with a stereo microscope system and digital photomicrography. Wear was defined as the difference in initial length from a marked reference line to the tip of the plier minus the length after 6 and 12 cycles of use and sterilization. There was no significant difference in the mean wear at the tip of the pliers between the 2 groups. It appears that there is no need to maintain both sterilization systems, dry heat and steam autoclave, in the orthodontic office. Steam autoclave sterilization can be used with no deleterious effects on the pliers if they are manufactured with stainless steel inserts.     

Effect of three sterilization techniques on finger pluggers.

The effects of different sterilization methods on the fatigue life of finger pluggers were investigated. Ninety finger pluggers for each of four sizes (A, B, C, and D) were subdivided into subgroups of 10. Each subgroup was subjected to 1, 8, or 15 cycles of steam autoclave, dry heat, or bead sterilization. Ten control pluggers for each size were not sterilized. After sterilization, experimental and control finger pluggers were subjected to cyclic bending until fracture. Only the A finger pluggers autoclaved for eight cycles had a significantly lower number of cycles to failure compared with that of the controls. Nine subgroups had significantly greater number of cycles before failure than did the control. Because all but one sterilized group had fatigue lifetimes statistically equal to or greater than nonsterilized controls, clinicians generally can use any of the three sterilization methods without fear of plugger failure.     

Effectiveness of microwave irradiation on the disinfection of complete dentures

PURPOSE: The purpose of this study was to evaluate the effectiveness of microwave irradiation on the disinfection of simulated complete dentures. MATERIALS AND METHODS: Eighty dentures were fabricated in a standardized procedure and subjected to ethylene oxide sterilization. The dentures were individually inoculated (10(7) cfu/mL) with tryptic soy broth (TSB) media containing one of the tested microorganisms (Candida albicans, Streptoccus aureus, Bacillus subtilis, and Pseudomonas aeruginosa). After 48 hours of incubation at 37 degrees C, 40 dentures were individually immersed in 200 mL of water and submitted to microwave irradiation at 650 W for 6 minutes. Forty nonirradiated dentures were used as positive controls. Replicate aliquots (25 microL) of suspensions were plated at dilutions of 10(-3) to 10(-6) on plates of selective media appropriate for each organism. All plates were incubated at 37 degrees C for 48 hours. TSB beakers with the microwaved dentures were incubated at 37 degrees C for 7 more days. After incubation, the number of colony-forming units was counted and the data were statistically analyzed by Kruskal-Wallis test (alpha = .05). RESULTS: No evidence of growth was observed at 48 hours for S. aureus, B. subtilis, and C. albicans. Dentures contaminated with P. aeruginosa showed small growth on 2 plates. After 7 days incubation at 37 degrees C, no growth was visible in the TSB beakers of S. aureus and C. albicans. Turbidity was observed in 3 broth beakers, 2 from P. aeruginosa and 1 from B. subtilis. CONCLUSION: Microwave irradiation for 6 minutes at 650 W produced sterilization of complete dentures contaminated with S. aureus and C. albicans and disinfection of those contaminated with P. aeruginosa and B. subtilis.     

Biological monitoring of sterilizers and sterilization failures in Norwegian dental offices in 1985 and 1996.

It is essential that dental office sterilizers be regularly challenged with biological indicators (BIs) in order to prove that the test spores are being killed during sterilization. The aims of the study were to biologically monitor Norwegian dental office sterilizers and to identify factors contributing to sterilization failure. In 1985, participants received a packet containing: (i) 4 BI units; (ii) a set of instructions; (iii) a questionnaire concerning operation (including biological monitoring) of the office sterilizer(s), and (iv) a return-address envelope. In 1996, offices were sent (i) a survey which included demographic questions and inquiries concerning instrument sterilization processes; (ii) 2 sets of 3 BI units with instructions for their use on 2 different days; (iii) 1 control BI unit that was not to be processed, and (iv) a return-address envelope. Both private and public offices participated. Response rate to the 1996 study was 60%, which was 9.1% of all dental offices in Norway. Testing results indicated a 6.3% overall sterilization failure rate. Three out of 163 steam autoclaves (SAs) (1.8% of total) and 14 out of 109 dry heat (DH) ovens (12.8% of total) failed. DH ovens were over 7 times more likely to fail BI testing than were SAs (chi2, P < 0.01). Demographic or hygiene procedural factors could not be correlated to sterilization performance (chi2, P > 0.05). The failure rate for SAs (n = 216) in 1985 was almost 5 times greater than in 1996 (8.8% vs 1.8%). Improvement in sterilizer performance during the decade may be related to issuance in 1986 of Norway's 1st infection control guidelines for dentistry and greater awareness of infection control practices and/or to increases over the previous 10 years in the number of postgraduate courses offered in infection control. The current Norwegian guidelines on infection control practices in public health services, including dentistry, recommend regular biological monitoring of sterilizers without specifying how often. There is a lack of information among Norwegian dentists as to how frequently dental office sterilizers should be regularly monitored by BI.     

The effectiveness of two sterilization methods when different precleaning techniques are employed

The effectiveness was investigated of methods for the preparation of dental handpieces prior to sterilization procedures utilizing ethylene oxide (ETO) gas. The handpieces were cleaned using either a forced-air purging unit (group 1) or by flushing with air and water from the dental unit (group 2). They were inoculated with either Bacillus subtilis or Streptococcus mutans. After exposure to either steam or ETO gas, the handpieces were flushed with saline and the viability of recovered bacteria assessed. No viable bacteria were recovered from group 1 handpieces treated with either ETO gas or steam. However, viable S. mutans were recovered from group 2 handpieces following exposure to ETO gas. Thus, the use of a high-pressure forced-air purging unit may be required for the reliable sterilization of dental handpieces by ETO gas, as viable S. mutans could be recovered from untreated handpieces exposed to ETO gas.     

Biological monitoring of sterilizers and sterilization failures in Norwegian dental offices in 1985 and 1996

It is essential that dental office sterilizers be regularly challenged with biological indicators (BIs) in order to prove that the test spores are being killed during sterilization. The aims of the study were to biologically monitor Norwegian dental office sterilizers and to identify factors contributing to sterilization failure. In 1985, participants received a packet containing: (i) 4 BI units; (ii) a set of instructions; (iii) a questionnaire concerning operation (including biological monitoring) of the office sterilizer(s), and (iv) a return-address envelope. In 1996, offices were sent (i) a survey which included demographic questions and inquiries concerning instrument sterilization processes; (ii) 2 sets of 3 BI units with instructions for their use on 2 different days; (iii) 1 control BI unit that was not to be processed, and (iv) a return-address envelope. Both private and public offices participated. Response rate to the 1996 study was 60%, which was 9.1% of all dental offices in Norway. Testing results indicated a 6.3% overall sterilization failure rate. Three out of 163 steam autoclaves (SAs) (1.8% of total) and 14 out of 109 dry heat (DH) ovens (12.8% of total) failed. DH ovens were over 7 times more likely to fail BI testing than were SAs (χ², P < 0.01). Demographic or hygiene procedural factors could not be correlated to sterilization performance (χ², P > 0.05). The failure rate for SAs (n = 216) in 1985 was almost 5 times greater than in 1996 (8.8% vs 1.8%). Improvement in sterilizer performance during the decade may be related to issuance in 1986 of Norway's 1st infection control guidelines for dentistry and greater awareness of infection control practices and/or to increases over the previous 10 years in the number of postgraduate courses offered in infection control. The current Norwegian guidelines on infection control practices in public health services, including dentistry, recommend regular biological monitoring of sterilizers without specifying how often. There is a lack of information among Norwegian dentists as to how frequently dental office sterilizers should be regularly monitored by BI.

     

Effects of the Nd:YAG dental laser on plasma-sprayed and hydroxyapatite-coated titanium dental implants: surface alteration and attempted sterilization.

The Nd:YAG dental laser has been recommended for a number of applications, including the decontamination or sterilization of surfaces of dental implants that are diseased or failing. The effects of laser irradiation in vitro (1) on the surface properties of plasma-sprayed titanium and plasma-sprayed hydroxyapatite-coated titanium dental implants, and (2) on the potential to sterilize those surfaces after contamination with spores of Bacillus subtilis have been examined. Surface effects were examined by scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction after laser irradiation at 0.3, 2.0, and 3.0 W using either contact or noncontact handpieces. Controls received no laser irradiation. Melting, loss of porosity, and other surface alterations were observed on both types of implants, even with the lowest power setting. For the sterilization study, both types of implants were first sterilized by exposure to ethylene oxide and then contaminated with spores of B subtilis. After laser irradiation, the implants were transferred to sterile growth medium and incubated. Laser irradiation did not sterilize either type of implant. The spore-contaminated implants in the control group were successfully sterilized with ethylene oxide.     

过氧乙酸消毒剂对牙胶尖消毒效果的实验研究

目的 初步评价过氧乙酸消毒剂（Peracetic Acid,PAA）对牙胶尖的消毒效果。方法 将800根牙胶尖随机分成5组,分别浸入金黄色葡萄球菌、大肠杆菌、粪肠球菌、枯草杆菌黑色变种芽孢以及白色念珠菌制成的菌悬液进行体外感染,每组160根牙胶尖再分成4小组,分别用0.1%、0.2%、0.5%过氧乙酸溶液和5.25%次氯酸钠溶液（Sodium Hypochlorite,NaOCl）浸泡消毒,在消毒后15s、30s、1min、2min时分别取出10根牙胶尖进行微生物培养,根据培养后有无微生物生长评定消毒效果。结果 0.1%或0.2%过氧乙酸浸泡消毒2min后无法杀灭枯草杆菌黑色变种芽孢;0.5%过氧乙酸或5.25%次氯酸钠浸泡消毒2min后,牙胶尖上5种微生物都被杀灭;对枯草杆菌黑色变种芽孢污染的牙胶尖消毒15s时,0.5%过氧乙酸的消毒效果明显好于5.25%次氯酸钠,但在其它情况下两者的消毒效果无统计学差异。结论 用0.5%过氧乙酸浸泡消毒2min后,能有效杀灭牙胶尖表面微生物,可考虑用于临床上牙胶尖的快速消毒。     

Effect of sterilization on the strength and cutting efficiency of twist drills

Retentive-pin twist drills were subjected to four methods of sterilization and then examined to determine possible effects on resistance to fracture, cutting efficiency, and surface condition. Sterilization methods included steam autoclave, chemical vapor autoclave, dry heat, and immersion in glutaraldehyde. Although the steam and chemical vapor groups had lower mean fracture strengths after sterilization, there was no statistically significant difference among the groups. Only the steam autoclave group showed a statistically significant loss of cutting efficiency. Scanning electron microscopic evaluation revealed that only drills sterilized by steam autoclave showed changes in the surface condition or cutting edges.     

The effects of sterilization techniques on the properties of intracanal instruments.

Three common sterilization techniques, namely, autoclaving (15 and 25 minutes at 250 degrees F.), salt sterilization (5 and 10 seconds at 480 degrees F.), and dry heat (one hour at 340 degrees F.), were used to sterilize 420 root canal reamers and files, both carbon and stainless steel. These intracanal instruments were then tested in tension. An extra eighty-four intracanal instruments were tested without being subjected to any sterilization techniques and served as controls. It was found that carbon steel intracanal instruments were affected more by the different modes of sterilization than were the stainless steel instruments. Time of sterilization did not seem to have an effect on the properties of either instrument.