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J Am Dent Assoc, Vol 131, No 6, 786-792.
© 2000 American Dental Association |
TRENDS |
OF U.S. DENTAL LABORATORIES
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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Methods. Four hundred dental laboratory directors were selected in a blinded and random manner. To create a geographically representative sample, an equal number of laboratory directors from the East, Midwest and West were interviewed. A survey consisting of 16 open-ended questions was conducted by trained interviewers via 10- to 15-minute telephone interviews. All dental laboratory directors stated that they were thoroughly familiar with their laboratory’s disinfection protocol.
Results. The survey documented that the majority of impressions were made of polyvinyl (57 percent) or polyether (27 percent) materials. Only 44 percent of the respondents stated that they knew if the impressions they received had been disinfected. Twenty-three percent of the laboratory directors did not know the method of disinfection used, and 47 percent did not know the length of time involved. Forty-five percent of the respondents reported that they receive inadequate instruction in regard to disinfection techniques. No one class of impression materials was found to be more problematic than others by the laboratory directors.
Conclusions. The results indicate a significant and problematic lack of communication between these team members. The responses also suggested that laboratory-perceived problems with impressions were not linked to any particular type of material, but more to the disinfection technique used.
Practice Implications. Lack of communication between dentists, staff members and dental laboratory personnel, along with poor training of laboratory personnel in disinfection techniques, may have a direct effect on the prosthetic results achieved in dental practices.
Dental laboratory technicians are particularly vulnerable to microbial cross-contamination from the elastomeric impressions they receive from dental offices.1,2 Casts poured from impressions can also harbor infectious microorganisms that can be distributed throughout the laboratory when the casts or dies are trimmed.3
To address these cross-contamination concerns, the American Dental Association issued guidelines for disinfecting impressions in 1988, 1991 and 1996.4–6 These guidelines recommend using an ADA-accepted spray or immersion disinfectant, depending on the material, for the duration suggested by the product manufacturer.4–6 Other disinfection protocols also have been developed to prevent the transmission of infectious diseases such as hepatitis B, tuberculosis, herpes and AIDS.7–9
Although much is known about how to effectively kill these microbes, eliminating microbial contamination from an impression poses a special problem. The disinfection process should be adequate but should not adversely affect the dimensional accuracy or surface detail of the impression. Several variables can affect impression materials, including the composition and concentration of the disinfectant, the exposure time and the compatibility of various disinfectants with specific impression materials. Many studies have described how disinfecting agents and methods affect impression materials, but there has been little consensus and frequent contradictions among these studies. For instance, Toh and colleagues10 found that polyvinyl siloxane exhibited dimensional changes after a 30-minute soak in iodophor or glutaraldehyde, but Merchant and colleagues11 noted no changes in their study.
How to best disinfect polyether materials without adversely affecting the impression’s accuracy and stability is a controversial issue. Some studies have shown that immersion disinfection has no clinically relevant effect on polyethers12; however, other studies have suggested that the dimensional stability of these hydrophilic materials is affected adversely by immersion.13 It is commonly understood that this effect is attributed to solution absorption.
In a 1997 study, Lepe and Johnson14 found that overnight immersion (18 hours) of polyether or addition silicone impressions in 2 percent glutaraldehyde significantly affected their occlusogingival dimensions, as well as the mesiodistal dimensions of the addition silicone.14 They concluded that overnight disinfection of these impressions would be suitable when making conventional removable partial dentures, but would not be advised for implants, attachments, crowns and fixed partial dentures.
This lack of consensus explains in part why dental clinicians and laboratory personnel seem to vary widely in the methods and materials they use for impression disinfection. In fact, although there are an estimated 10,000 dental laboratories operating in the United States (National Association of Dental Laboratories, oral communication, September 1997), little is known about the disinfection protocol in the laboratories and/or habits of dental clinicians and staff members.
In this article, we report the results of a survey distributed to 400 randomly selected U.S. dental laboratories. The survey was designed to determine how well dentists are communicating with laboratory personnel about impression disinfection, and, in turn, what laboratory technicians are doing to protect themselves against microbial cross-contamination from impressions they receive. Although laboratory staff members clearly lack the necessary information to scientifically determine which impression problems can be linked to the disinfection process, the survey queried them about any perceived problems with specific materials and possible steps to take to improve the outcomes of the cases they manage.
MATERIALS AND METHODS
TOP
ABSTRACT
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSION
REFERENCES
We selected 400 U.S. dental laboratory directors in a blind and random manner from a pool of National Association of Dental Laboratories members who provided services for making crowns, bridges and implants. The study was conducted in January 1998. To create a geographically representative sample, we selected an equal number of laboratory directors from the East, Midwest and West. In conjunction with market research experts, we developed a survey with 16 open-ended questions, as listed in the box
("The Survey Instrument"). Trained interviewers from Focus Data Inc. conducted the survey via 10- to 15-minute telephone interviews. All of the 400 dental laboratory directors stated that they were thoroughly familiar with their laboratory’s disinfection protocol. We conducted statistical analyses of the sample data according to the three major U.S. geographical areas (East, Midwest and West). Analysis by region yielded no significant differences.
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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The survey results showed that dentists and laboratory personnel do not communicate well about the disinfection procedures they follow.
Impression materials. A mean of 57 percent of all the impressions received by the surveyed laboratories are made of polyvinyl materials, a mean of 27 percent are made of polyethers, a mean of 7 percent are made of reversible hydrocolloid and a mean of 9 percent are made of other materials. The types of materials most frequently seen did not vary significantly according to geographical location.
The survey results showed that dentists and laboratory personnel do not communicate well about the disinfection procedures they follow. Only 175 (44 percent) of the surveyed laboratory directors said they knew if the impressions they received from dentists had been disinfected at the dental office. Among those who did get regular confirmation, nearly half (48 percent) obtained this information through oral communication with the dental office, while others received some written verification of disinfection, such as stickers or notations on the laboratory order form.
Disinfection methods. According to the survey results, when the laboratories do receive information from dentists about whether they disinfect the impressions, specific information about the solution and technique used is often lacking. Among the laboratory directors who reported having knowledge of disinfection procedures, 34 percent said immersion typically is used, 46 percent said spray disinfection typically is used, 23 percent admitted they did not know which method is typically used (some respondents gave more than one answer) and 47 percent did not know for how long the impressions had been disinfected. In addition, about 20 percent of respondents said that they usually received impressions in plastic bags containing disinfectant solution.
Solutions used. Because of these uncertainties about the impressions they receive and the lack of standard disinfection protocol in the dental profession, 351 (94 percent) of 373 laboratories surveyed routinely take the extra precaution of disinfecting all impressions they receive, regardless of whether they have been treated at the dental office. About one-third of 373 respondents reported that they use glutaraldehyde (116 repondents [31 percent]) or iodophor solutions (93 respondents [25 percent]). Two hundred one respondents (54 percent) use bleach or solutions not specifically recommended by the ADA or impression manufacturers. (The preceding numbers total more than 373 because respondents could give more than one answer.)
Duration. Twenty-seven percent of the respondents reported that their laboratories disinfect impressions for 10 minutes to an hour, while 15 percent disinfect for less than 10 minutes. Twelve percent of respondents reported that they disinfect for one to 24 hours. About 45 percent of the dental laboratory directors reported that they feel laboratory personnel receive inadequate instruction about appropriate disinfection techniques for various impression materials.
Problems encountered.
Although dental laboratory directors cannot scientifically judge whether any problems they encounter with impressions are the result of variables in the disinfection process, we sought to determine whether laboratories perceive any regular noteworthy problems with impressions in general. When asked to consider all of the impression materials used in their laboratories, 116 (29 percent) of respondents said they did find noteworthy problems. The most commonly reported problems are ranked in the table, along with the materials corresponding to them. The laboratory directors also noted that a mean of 5 percent (± SD = 8 percent) of the impressions must be remade. The most commonly reported reasons for remaking impressions are delineated in Figure 1. We found it interesting that no particular type of impression material was considered to be more problematic than other materials.
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With regard to which disinfection techniques and solutions are best suited to individual impression materials, 184 (46 percent) of the 400 respondents reported that the instructions available from manufacturers were inadequate, 144 (36 percent) labeled them adequate, 60 (15 percent) said they were sometimes adequate and 12 (3 percent) were unsure.
To indirectly assess whether laboratory directors detected a need for better communication with dentists regarding disinfection and other impression-related matters, we asked an open-ended question about the advice they would offer to ensure total satisfaction with the crowns and bridges they deliver to dentists. These results are shown in Figure 2.
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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Although the ADA and dental literature provide guidance about how specific impression materials should best be disinfected to balance the goals of safety and accuracy, they cannot offer definitive answers to the problems at hand because there is no faultless universal disinfectant. The lack of communication between clinicians and laboratory staff members may be detrimental in light of what we do know—or at least strongly suspect—regarding the lack of standardized disinfection procedures by dental offices.
Duration of disinfection. One concern, supported by the results of this study, is that dentists and laboratories disinfect impressions for longer-than-recommended durations. For instance, it is well-known that polyethers and newer hydrophilic materials tend to absorb liquid, and some authors have noted distorted characteristics after these materials are disinfected for prolonged periods.7,15,16 In addition, many studies on the effect of various disinfection variables on specific impression materials have used immersion durations of as brief as five to 10 minutes and as long as 30 to 60 minutes, with good results in terms of such factors as accuracy and surface detail.17–20 The ADA recommends the use of ADA-accepted disinfectants that require no more than 30 minutes for disinfection.5
The results of our survey indicate that, in actual practice, impressions may be undergoing disinfection for longer periods than those used in the studies above. According to the laboratory directors, 11 percent of the clinicians with whom they work indicate that they have disinfected impressions for periods ranging from one hour to more than 24 hours—much longer than any disinfectant manufacturer recommends. The actual percentage may be higher in light of the fact that nearly half of the respondents said they never know for how long the impressions have been disinfected before they receive them. In addition, 94 percent of the laboratory directors indicated that they also routinely disinfect impressions—for mean durations of 10 to 60 minutes—even if they know that the impressions have already been disinfected at the dental office.
Need for standardized practices.
Disinfection for long periods may be responsible, at least in part, for margin inaccuracy and distortions of impressions, which were the most frequent problems reported by respondents (Table). However, studies must be undertaken to specifically address this possibility. In the meantime, it may be helpful for dental offices to initiate a standardized tagging system for all impressions to be sent to the laboratory. Dental staff members can place a sticker, label or notation on the laboratory report indicating how the impression was disinfected. Although oral confirmation of disinfection of some sort is most commonly used, this may be inadequate to inform all laboratory technicians who are involved with the particular case. In addition, unless the impression will be transferred to the laboratory immediately, dentists should rethink the need to package or store impressions in disinfectant for lengthy intervals. Finally, it may be useful for laboratories to notify their dentist clients in writing of how they routinely handle disinfection in the laboratory so that their efforts can be coordinated to some degree.
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It may be helpful for dental offices to initiate a standardized tagging system for all impressions to be sent to the laboratory.
Another concern raised by this survey is that at least some laboratories disinfect impressions with high levels of bleach (that is, higher than the 1:10 ratio of bleach-to-water recommended by manufacturers [oral communication, Dentsply, May 2000]), which can cause deterioration of certain impression materials, and some use other solutions not recommended in the guidelines of the impression material manufacturers or the ADA. How these procedures may affect various brands of impression material, particularly those that have been exposed to these other solutions, has not been pinpointed, and this, too, is an area of research that must be pursued.
Again, communication between clinicians and their dental laboratories about specific disinfection practices could eliminate a potential problem. In addition, manufacturers of impression materials should provide specific advice about disinfectant solutions and techniques that are compatible with their products. Where no such guidance exists, laboratories and clinicians should follow the ADA recommendations.4–6
In regard to choosing one impression material over another to improve the outcome, the results of this survey suggest that any perceived problems with impressions were more likely linked to disinfection technique than to material type. Although 116 (29 percent) of the 400 laboratory directors reported that they had seen noteworthy problems with the impression materials used, no particular type of material was singled out as especially problematic.
It is clear that more research using standardized test methods is needed to provide useful information about how disinfection variables affect impression materials and to develop and implement universal disinfection guidelines. We hope that, in the near future, manufacturers of impression materials will routinely provide such science-based guidance on the best use of their products.
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CONCLUSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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FOOTNOTES |
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REFERENCES |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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This article has been cited by other articles:
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  Z. N. Al-Dwairi Infection Control Procedures in Commercial Dental Laboratories in Jordan J Dent Educ., September 1, 2007; 71(9): 1223 - 1227. [Abstract] [Full Text] [PDF]
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