High-level microwave disinfection of dental gypsum casts

PURPOSE: To test whether microwave oven irradiation can disinfect gypsum casts in compliance with current disinfection requirements, and to determine whether this procedure would be as effective as a validated method of chemical disinfection of impressions. MATERIALS AND METHODS: In 2 in vitro experiments, samples of 5 irreversible hydrocolloid impressions of a disinfected acrylic resin model were contaminated with suspensions of recommended test organisms Staphylococcus aureus and Pseudomonas aeruginosa, respectively. In 1 in vivo experiment, 10 impressions were made of 10 subjects. All impressions were poured and the resulting casts cut in 2 halves. One half of each cast was exposed to 5 minutes of irradiation in a microwave oven at 2,450 MHz and 900 W. The other halves were left untreated as controls. In a second in vivo experiment, 10 impressions were disinfected by immersion in a 0.07% solution of NaOCl at pH of about 10 for 3 minutes, and then poured. All casts were incubated aerobically in Bacto tryptic soy broth at 37 degrees C for 6 hours and assessed for bacterial growth by counting colony-forming units per milliliter (cfu/mL) of the culture. The results were analyzed using the Wilcoxon signed-rank test. RESULTS: Untreated gypsum casts showed cfu/mL counts with a median log value of 6, while microwave-irradiated ones had median cfu/mL counts of 0. Casts poured from chemically disinfected impressions demonstrated cfu/mL counts with a median log value of 4. CONCLUSION: Under the described conditions, microwave-irradiated gypsum casts satisfy current disinfection requirements, but gypsum casts poured from chemically disinfected impressions do not.     

5种消毒方法对染菌口腔印模消毒效果的比较

目的：评价２％戊二醛浸泡、喷涂,５％艾力克浸泡、喷涂,臭氧柜处理对口腔印模和石膏模型上的表皮葡萄球菌、血液链球菌和枯草杆菌芽孢的消毒效果。方法：将无菌的印模和石膏模型平均分成３组,每组印模和石膏模型表面分别涂表皮葡萄球菌悬液、血液链球菌悬液和枯草杆菌芽孢菌悬液,并设立同期空白对照组。采用２％戊二醛浸泡、喷涂与５％艾力克浸泡、喷涂分别对染菌印模进行消毒处理。臭氧柜对石膏模型进行消毒处理。其后的不同时     

Efficacy of high-level microwave disinfection of dental gypsum casts: the effects of number and weight of casts

The aim of this study was to determine if the bactericidal effect of microwaving gypsum casts is maintained at maximum capacity of the oven (16 casts). Batches of 8 and 16 gypsum casts made from in vivo impressions were divided in half. One half of each cast was microwaved at 900 W for 5 minutes. The remaining halves were left untreated. When assessed for bacteriological growth, the median cfu/mL of the untreated casts was between 10(5) and 10(6) [corrected] while the microwaved casts showed a cfu/mL of 0, indicating that microwaving as described will disinfect gypsum casts even at maximum capacity of the oven.     

Disinfection procedures: their efficacy and effect on dimensional accuracy and surface quality of an irreversible hydrocolloid impression material

Objectives

This study investigated the antibacterial efficacy and effect of 0.55% ortho-phthalaldehyde (Cidex OPA^®) and 0.5% sodium hypochlorite (NaOCl) on the dimensional accuracy and surface quality of gypsum casts retrieved from an irreversible hydrocolloid impression material.

Methods

A simulated clinical cast and technique was developed to compare the dimensional accuracy and surface quality changes of the test gypsum casts with controls. Dimensional accuracy measurements were completed between fixed points using a travelling microscope under low angle illumination at a magnification of ×3. Surface quality changes of “smooth” and “rough” areas on the cast were evaluated by means of optical profilometry. The efficacy of the disinfection procedures against Pseudomonas aeruginosa was evaluated by determining the number of colony forming units (cfu) recovered after disinfection of alginate discs inoculated with 1 × 10⁶ cfu for defined intervals.

Results

The dimensional accuracy of the gypsum casts was not significantly affected by the disinfection protocols. Neither disinfectant solution nor immersion time had an effect on the surface roughness of the “smooth” area on the cast, however, a significant increase in surface roughness was observed with increasing immersion time for the “rough” surface. Complete elimination of viable Pseudomonas aeruginosa cells from alginate discs was obtained after 30 and 120 s immersion in Cidex OPA^® and NaOCl, respectively.

Conclusions

Immersion of irreversible hydrocolloid impressions in Cidex OPA^® for 30 s was proved to be the most effective disinfection procedure.     

A study on the effect on surface detail reproduction of alginate impressions disinfected with sodium hypochlorite and ultraviolet light — An In Vitro study

Objectives of the study

To evaluate the surface detail reproduction of dental casts with impressions made using commercially available alginate impression materials after disinfecting with chemical disinfectant sodium hypochlorite and physical means of disinfection using ultraviolet radiation.

Materials and methods

A stainless steel die was used to make impression according to ADA/ANSI specification No. 18 having 25, 50 and 75 µm lines. Totally 70 impressions were made and divided in to 7 groups. The impressions in the first group were only rinsed with 250 ml of water. The 2nd, 3rd and 4th groups were disinfected by immersing in sodium hypochlorite for 1, 5 and 10 minutes, respectively. Fifth, 6th and 7th group samples were disinfected by placing them in ultraviolet chamber for 6, 12 and 18 minutes, respectively. All the impressions were poured immediately using type III gypsum. The casts were recovered and subjected for evaluation of the 75 µm lines using stereomicroscope.

Results

There was no statistically significant change in the surface detail reproduction when disinfected with sodium hypochlorite or ultraviolet radiation.

Conclusion

Alginate impressions subjected to immersion disinfection using sodium hypochlorite for 1, 5 and 10 minutes and subjected to ultraviolet disinfection for 6, 12 and 18 minutes exhibited no statistically significant differences for surface detail reproduction compared to control groups.     

Disinfection procedures: their effect on the dimensional accuracy and surface quality of irreversible hydrocolloid impression materials and gypsum casts.

OBJECTIVES: This study primarily investigated the effect of disinfection procedures (Perform and sodium hypochlorite) on the dimensional accuracy and surface quality of four irreversible hydrocolloid impression materials and the resultant gypsum casts. The antibacterial efficacy of the procedures was also studied. METHODS: Dimensional accuracy was determined from the mean percentage deviation of six measurements taken from casts made from disinfected impressions compared with corresponding measurements from the master model and controls. Statistical analysis of data was determined by analysis of variance. Surface quality was determined using a stainless steel test block in accordance with ISO 1563. RESULTS: The dimensional accuracy of the impression materials tested were of a comparable standard following disinfection. The surface quality of casts taken from Blueprint Cremix impressions were unaffected by the disinfection procedures. The remaining impression materials studied showed greater surface deterioration on casts following disinfection with sodium hypochlorite than immersion in Perform. All disinfection procedures selected proved appropriate for antibacterial purposes. SIGNIFICANCE: Individual analysis of impression materials is required to determine their suitability to a given disinfection protocol.     

印模消毒后石膏模型的尺寸变化研究

目的 研究不同方式印模消毒后石膏模型的尺寸变化。 方法 对一标准模型制取藻酸盐印模54个,分别采用冲洗（对照组）、1〖JP20〗∶〖JP〗100含氯消毒液或2%戊二醛消毒液消毒后,用普通石膏、硬石膏和超硬石膏灌模,共灌注模型54个。对石膏模型特定位置的尺寸进行测量,并与标准模型对应尺寸进行比较,数据行双因素方差检验和Tukey HSD分析。 结果 经过消毒处理后,无论使用何种石膏材料灌模,尺寸均较标准模型减小;普通石膏组尺寸大小与标准模型更为接近。同一种消毒处理方式下,戊二醛组中的超硬石膏尺寸（17.80±0.13） mm大于硬石膏（17.79±0.26） mm,对照组及含氯消毒液组尺寸均为普通石膏>硬石膏>超硬石膏。统计分析显示,不同消毒处理方式对模型尺寸的影响不存在显著性差异（P=0.843）,不同石膏材料对模型尺寸的影响存在显著性差异（P=0.001）。此外,石膏模型最大尺寸变化为-0.71 mm。 结论 含氯消毒液和戊二醛消毒液处理印模对石膏模型的尺寸影响不大。     

The accuracy and efficacy of disinfection by spray atomization on elastomeric impressions

Five disinfectants applied by spray atomization were examined for possible dimensional distortion of elastomeric impression materials, polyether, polysulfide, and addition silicone, and the associated improved, type IV gypsum casts. The disinfectants did not affect, in a clinically significant manner, the three dimensions measured with an instrument accurate to 1 micron on improved gypsum casts that reproduced a stainless steel standard. The master cast represented two teeth of a fixed partial denture prepared for complete veneer retainers. The use of control casts from elastomeric impressions that were not treated with the disinfectants further supported previous investigations reporting the accuracy of dental casts as the function of the impression material. The use of a spray disinfectant will not appreciably alter the dimensional accuracy of improved stone casts made within elastomeric impressions. The most accurate stone cast system was produced by addition silicone impressions disinfected by a surface spray. It was also shown that four of the disinfectants applied by spray atomization were effective in disinfecting the surface of an elastomeric impression material contaminated with selected test organisms.     

Effect of disinfectant agents on dimensional stability of elastomeric impression materials

STATEMENT OF PROBLEM: Difficulties in sterilizing impressions by traditional methods have led to chemical disinfection as an alternative, and some studies have shown that disinfectants may adversely affect impressions. PURPOSE: This study investigated the effect of disinfection methods on the dimensional stability of 6 elastomeric materials. MATERIAL AND METHODS: Impression materials were submitted to the following treatments: immersion in 5.25% sodium hypochlorite solution for 10 minutes, immersion in 2% glutaraldehyde solution for 30 minutes, and no immersion (control). After treatments, impressions were poured, and respective stone casts were measured with a Nikon Profile projector and compared with the master model. RESULTS: The elastomeric materials had different reproduction capacities, and the disinfecting treatments did not differ from the control.     

Accuracy and stability of impression materials subjected to chemical disinfection – a literature review

Summary  Disinfection of impressions by immersion or spraying with disinfecting solutions is considered nowadays mandatory for effective infection control. The purpose of this review was to examine existing evidence on the effects that chemical disinfection may have on critical qualities of impressions, namely dimensional accuracy and stability over time. A PubMed search was conducted to include original laboratory research articles written in English, published between 1980 and 2005 in peer-reviewed journals and investigating the effect of chemical disinfection, by immersion or spraying, on the dimensional changes that the impression materials experience after setting. Studies were also sought manually, by tracing the references cited in the retrieved articles. The reports on dimensional changes of disinfected impression materials, although rather numerous, are difficult to compare and analyze because of variations of the experimental design. The investigations broadly agree that the disinfection process does not generally affect the dimensional integrity of the impressions, in spite of the statistically significant differences occasionally found. However, the immersion in the disinfecting solution encourages water absorption phenomena in the case of the so-called hydrophilic impression materials, especially after the long-term immersion. Chemical interactions between impressions and disinfectants may occur, but they do not appear to influence the dimensional behaviour of the former. The overall effect of the disinfection is influenced not only by the changes experienced by the impression per se , but also by the alterations of the acrylic tray containing the impression and of the gypsum product poured in it.     

Failure of anti-retraction valves and the procedure for between patient flushing: a rationale for chemical control of dental unit waterline contamination

PURPOSE: To evaluate the efficacy of anti-retraction valves; and to compare between-patient flushing with water and with using a chemical treatment to control patient-to-patient contamination through dental unit waterlines (DUWL). METHODS: For the first aim, nine new antiretraction valves from three different manufacturers were utilized. Each valve was installed along the water line connecting the high-speed handpiece to the dental unit. The handpieces were made to run and stop in a container filled with a solution of about 7 log10/mL of Bacillus subtilis spores (used as a marker) and retraction of spores was measured. Subsequently, all nine valves were installed in dental units in use in private offices, and all tests repeated after 15, 30 and 60 working days. For the second aim, the efficacy of mechanical flushing (30 seconds for each instrument) was compared with that of mechanical flushing in combination with pressurized air and of a between-patient disinfecting procedure (2 minutes contact with TAED and persalt utilizing an "autosteril" system). Before each test (10 tests for each procedure), known concentrations of Pseudomonas aeruginosa (ATCC 27853) suspension (4 to 7 log10cfu/mL) was loaded in the DUWL and let sit for 20 minutes. RESULTS: In the anti-retraction valve experiment, at baseline only one anti-retraction valve showed a failure in opposing fluid retraction. After 15 days, three valves, after 30 days, six valves, and after 60 days, eight valves showed failure. In the flushing experiment, a highly significant linear correlation (r =.9178) was found between values before and after mechanical flushing. Post flush log10cfu/mL values showed the removal of about only 1 log10cfu/mL of the microorganisms (only about 10% in absolute counts). On the other hand, no cfu/mL was detected in waterlines after the "autosteril" disinfecting cycles.     

Accuracy of stereolithography additive casts used in a digital workflow

Statement of problem

Despite the increasing demand for a digital workflow in the fabrication of indirect restorations, information on the accuracy of the resulting definitive casts is limited.

2％酸性戊二醛对藻酸盐印模浸泡消毒的效果评价

目的评价2％酸性戊二醛浸泡消毒对藻酸盐印模表面的变形链球菌“C”、白色念珠菌、大肠杆菌、金黄色葡萄球菌和枯草杆菌黑色变种芽孢的消毒效果。方法制作5cm×5cm大小无菌印模试件,分成5组,分别用变形链球菌“C”、白色念珠菌、大肠杆菌、金黄色葡萄球菌和枯草杆菌黑色变种芽孢5种菌液污染。采用2％酸性戊二醛对染菌印模进行浸泡消毒处理,以蒸馏水浸泡作为对照组。其后不同时间在印模试件表面取样、接种、培养,并进行CFU计数,计算抑菌率。根据抑菌率大小评价消毒效果。结果2％酸性戊二醛浸泡消毒10min,可对藻酸盐印模表面的变形链球菌“C”、白色念珠菌、大肠杆菌和金黄色葡萄球菌达到有效消毒,在实验限定的作用时间内对枯草杆菌黑色变种芽孢消毒无效。结论2％酸性戊二醛浸泡为有效的印模消毒方法,但不能达到高水平的消毒。     

The dimensional stability of self-disinfecting alginate impressions compared to various immersion regimes

Alginate impressions of a master acrylic study model pair were made in order to assess the effect of various disinfection techniques on dimensional stability. Impressions were made using self-disinfecting alginate, traditional alginate which had been dipped or soaked in a disinfecting solution, and included was a control group which was not disinfected. Inter- and intra-arch linear measurements of the resultant study casts were made using a Reflex Metrograph. The small differences found for the variables measured were not statistically significant.     

An analysis of the persistent presence of opportunistic pathogens on patient-derived dental impressions and gypsum casts

PURPOSE: This study aimed to assess the persistent presence of microorganisms on patient-derived dental impressions and gypsum casts, while highlighting important human pathogens such as Candida, methicillin-resistant Staphylococcus aureus (MRSA), and Pseudomonas aeruginosa. MATERIALS AND METHODS: The practices and opinions regarding cross-infection control from 59 general dentists in Japan were obtained via a questionnaire. Alginate impressions were made from 56 patients. Using a brain heart infusion agar medium, impression and imprint cultures were carried out to visualize the microbial contamination on the surfaces of the impressions and gypsum casts, respectively. The colonies on the surfaces of the 30 impression cultures and 26 imprint cultures were collected by swabbing and then inoculated onto selective agar plates to detect streptococci, staphylococci, Candida, MRSA, and P aeruginosa. RESULTS: The questionnaire showed that only 54% of general dentists had a cross-infection policy in their dental clinics, and only 30% to 40% were aware of the possible persistence of MRSA or P aeruginosa on impressions and gypsum casts. The impression/imprint cultures grew a large number of visible bacterial colonies on all of impression/gypsum cast samples investigated. Selective agar cultures demonstrated the presence of streptococci (100, 100%), staphylococci (56.7, 65.4%), Candida (30, 46.2%), MRSA (26.7, 15.4%), and P aeruginosa (6.7, 7.7%) on the impressions and the gypsum casts, respectively. CONCLUSIONS: This investigation showed that patient-derived dental impressions and gypsum casts are contaminated with numerous microbes, including Candida, MRSA, and P aeruginosa, which are known pathogens responsible for nosocomial and/or life-threatening infection in the immunocompromised host.     

Effect of disinfecting solutions on surface texture of alginate and elastomeric impressions

The effect of immersion in six disinfecting solutions on the surface texture of 10 impression materials was investigated. Assessment of the surface texture was based on measurement of the ability to reproduce fine detail. Impressions were taken of a roughness standard, i.e. a steel block with known roughness. After setting, the impressions were either stored at room temperature for 24 h, for control, or immediately immersed in a disinfecting agent for 60 min (in one case 10 min), and after 24 h poured with gypsum. After another 24 h, the roughness of the dies was recorded with a profilometer. Three addition-curing silicones were left unaltered by disinfection. For the remaining seven materials, the ability of detail reproduction was changed for some of the combinations of impression material and disinfecting solution. In general, this meant a reduction of detail reproduction, but occasionally an improvement of the surface texture resulted from disinfection. Changes in surface texture were most often brought about by a solution of chlorinated trisodium phosphate. It was concluded that elastomeric impression materials reproduced fine detail better than did alginates and that both types of impression material may be immersed in specific disinfecting solutions for as long as 1 h without the surface texture being impaired.     

The effect of immersion disinfection of elastomeric impressions on the surface detail reproduction of improved gypsum casts

This investigation examined improved gypsum casts for surface roughness and line-detail reproduction after the immersion disinfection of elastomeric impression materials in an acid glutaraldehyde, an alkaline glutaraldehyde, and a phenol. Impressions were made of a surface roughness standard (Ra = 3.08 microns) that was custom made to include engraved grooves following American Dental Association specification No. 19. Mean surface roughness (Ra) values for all casts of all combinations of disinfectant treatments, impression materials, and improved gypsum stones were obtained with a surface analyzer. Untreated impressions served as controls. Data examined by an analysis of variance indicated that the addition silicone and polyether impression materials provided a surface roughness similar to the precision displacement specimen standard. The acid glutaraldehyde disinfectant demonstrated enhanced line-detail reproduction compared with the standard. Addition silicone and polyether impression materials combined with the acid glutaraldehyde provided the model system closest to the mean surface roughness of the reference standard. These combinations revealed differences in the surface roughness reproduction among the represented improved dental stones.     

Effect of disinfecting solutions on surface texture of alginate and elastomeric impressions

Abstract – The effect of immersion in six disinfecting solutions on the surface texture of 10 impression materials was investigated. Assessment of the surface texture was based on measurement of the ability to reproduce fine detail. Impressions were taken of a roughness standard, i.e. a steel block with known roughness. After setting, the impressions were either stored at room temperature for 24 h, for control, or immediately immersed in a disinfecting agent for 60 min (in one case 10 min), and after 24 h poured with gypsum. After another 24 h, the roughness of the dies was recorded with a profilometer. Three addition-curing silicones were left unaltered by disinfection. For the remaining seven materials, the ability of detail reproduction was changed for some of the combinations of impression material and disinfecting solution. In general, this meant a reduction of detail reproduction, but occasionally an improvement of the surface texture resulted from disinfection. Changes in surface texture were most often brought about by a solution of chlorinated trisodium phosphate. It was concluded that elastomeric impression materials reproduced fine detail better than did alginates and that both types of impression material may be immersed in specific disinfecting solutions for as long as 1 h without the surface texture being impaired.     

Effects of disinfection of combined agar/alginate impressions on the dimensional accuracy of stone casts

This study investigated the effects of disinfection of combined agar/alginate impressions on the dimensional accuracy of resultant stone casts. Impressions of a master cast designed to simulate an abutment tooth were prepared by combining each of two brands of cartridge-form agar impression materials with an alginate impression material. The impressions were immersed in 1% sodium hypochlorite for 10 minutes or 2% glutaraldehyde for 30 minutes. The remaining impressions were sprayed with these two disinfectants and then stored in sealed bags for 10, 30, 60, and 120 minutes. Stone casts obtained from the non-disinfected impressions were also prepared as control. Changes in diameter of the stone casts were then measured. Results indicated that storage for 10 minutes after spraying with 1% sodium hypochlorite was an appropriate disinfection method for combined agar/alginate impressions, as well as immersion in 1% sodium hypochlorite for 10 minutes.     

Optimisation of the long-term efficacy of dental chair waterline disinfection by the identification and rectification of factors associated with waterline disinfection failure

Although many studies have highlighted the problem of biofilm growth in dental chair unit waterlines (DUWs), no long-term studies on the efficacy of DUW disinfection using a large number of dental chair units (DCUs) have been reported. OBJECTIVES: To investigate the long-term (21 months) efficacy of the Planmeca Waterline Cleaning System (WCS) to maintain the quality of DUW output water below the American Dental Association (ADA) recommended standard of < or =200cfu/mL of aerobic heterotrophic bacteria using once weekly disinfection with the hydrogen peroxide-and silver ion-containing disinfectant Planosil. METHODS: Microbiological quality of DUW output water was monitored by culture on R2A agar for 10 DCUs fitted with the WCS. The presence of biofilm in DUWs was examined by electron microscopy. RESULTS: During the first 9 months a high prevalence (28/300 disinfection cycles; 9.3%) of intermittent DUW disinfection failure occurred in 8/10 DCUs due to operator omission to disinfect all DUWs (10/28 failed cycles), incorrect compressed air pressure failing to distribute the disinfectant properly (4/28 failed cycles) and physical blockage of disinfectant intake valves due to corrosion effects of Planosil (14/28 failed cycles). On rectification of these faults through engineering redesign and procedural changes, no further cases of intermittent DUW disinfection failure were observed. Independently of these factors, a rapid and consistent decline in efficacy of DUW disinfection occurred in 4/10 DCUs following the initial 9 months of once weekly disinfection. There was a highly significant difference (P<0.0001) in the prevalence of strongly catalase-positive Novosphingobium and Sphingomonas bacterial species (mean average prevalence of 37.1%) in DUW output water from these 4 DCUs compared to the other 6 DCUs and DCU supply water (prevalence <1%), which correlated with biofilm presence in the DUWs and indicated selective pressure for maintenance of these species by prolonged disinfectant usage. Planosil was reformulated to a more concentrated form (Planosil Forte) and when used once weekly was found to maintain bacterial density in output water below the ADA standard for all 10 DCUs. CONCLUSIONS: A variety of factors can contribute to failure of DUW disinfection in the long-term, including human error, disinfectant corrosion of equipment and natural selection of naturally disinfectant-tolerant bacterial species.