Disinfection of Dental Impressions: A Survey of Private Practices and Dental Universities in Karachi, Pakistan

Disinfection of Dental Impressions: A Survey of Private Practices and Dental Universities in Karachi, Pakistan
Irfan Qamruddin*, Adel Z Siddiqui**, Sidra Butt***

* Assistant Professor & Head Department of Orthodontics, Baqai Dental College/ Baqai Medical University, Karachi.
** Assistant Professor, Department of Dental Material, Baqai Dental College / Baqai Medical University, Karachi.
*** Demonstrator, Department of Orthodontics, Baqai Dental College / Baqai Medical University, Karachi.
Correspondance :“Dr. Irfan Qamruddin”

How to CITE:

J Pak Dent Assoc.2011; 20 (1): 19-22


To assess the compliance of dental practitioners towards disinfection of dental impressions and to notify the reasons if they do not follow the general guidelines of impressions disinfection.


A questionnaire that comprised of 10 questions was distributed to the general dental practitioners doing private clinics and to various dental colleges and universities of Karachi, Pakistan. Questionnaires were recollected after a period of 3 weeks.


A response rate of 74.6% was achieved. 58.5% of practitioners don not disinfect and 15.6% do not even rinse their dental impressions after they are made. Shortage of disinfectant solutions in clinical practices and lack of awareness of the importance of the issue, were among the most common reasons of their negligence.


The response from the dentists indicates that the dental colleges in Karachi should incorporate the impression disinfection protocol in their curriculum.


Dental Impressions; Disinfection.


All members of dental professionals are exposed to a wide variety of microorganisms during everyday practice. 1, 2 Dental professionals are at least at three times greater risk to get infections and developing the carrier state.3Dental impressions are often heavily contaminated with microorganisms from saliva, plaque and blood. If casts are poured from contaminated impressions, microorganisms are transferred to gypsum models and subsequently to the laboratory personnel.1-3Dental health care personnel can be exposed to various viral diseases like Hepatitis B, Hepatitis C, Acquired immunodeficiency syndrome, Herpes simplex, Mycobacteriumtuberculosis , Streptococci , Staphylococci and other bacteria that colonizes oral cavity.2, 4

Sterilization of dental impressions is not possible, because of the high temperature and time required therefore disinfection is the method of choice. World Health Organization (WHO) recommends immersion in 2% glutaraldehyde or 1% sodium hypochlorite solution for 60- minutes.5 Because of dimensional instability of alginate impression material in response to prolonged immersion, American Dental Association (ADA) recommends a ten-minute immersion in a 1:10 dilution (0.525%) of sodium hypochlorite solution or spray disinfecting technique.6 Thirty minutes immersion in gluteraldehyde is recommended by ADA for polysulphide, condensation and addition silicone impression material and chlorine spray disinfecting method for polyether impression material.7 In spite of the recommendations for impression disinfections by dental organizations worldwide, few dental personnel have adhered to these procedures in their clinical practices.8

Studies have shown that large numbers of dental impressions are sent to the laboratory, contaminated with blood and food debris.9

The reasons for this poor compliance by dental practitioners may include: extra efforts and time required; loss of surface detail and dimensional accuracy of the impression.10,11,12,13,14 most of the disinfectants are irritants which may present health risks to the dental team; and toxic disinfectants may also cause corrosion of metal trays and dislodgement of the impression from tray.15

The purpose of this study was to assess compliance of dental practitioners of Karachi, Pakistan towards disinfection of dental impressions and to notify the reasons if they do not follow the general guidelines of impressions disinfection


A questionnaire that comprised of 10 questions was designed to assess the attitude of practitioners towards the disinfection of dental impressions and the methods and materials they use to rinse and disinfect the various types of impression materials. The questionnaires were sent to the general dental practitioners doing private clinics in the city of Karachi and were also sent to different dental colleges and universities of all the districts of Karachi, Pakistan. The researchers personally contacted all the dentist and faculty members of colleges to elaborate the study purpose and the questionnaires were handed out personally. Most of the questionnaires were recollected personally after a period of 3 weeks and few were received via postal mail. The questionnaires addressed the following topics: rinsing of the impressions; disinfection of the impressions; type of disinfectant solution used for alginates and elastomeric impression materials; disinfection technique (spray, immersion or intermediate) used for alginates and elastomeric impression materials; and the reasons for not complying with impression disinfection procedure.

The answers were recorded and processed using the statistics package for social sciences (SPSS) for Windows version 14.


A total of 448 dental practitioners out of 600, which included 297 males and 151 females responded the questionnaire representing a response rate of 74.6%. Not all the respondents answered every question. The data collection was done anonymously so the results from the study could not be analyzed with regard to the name and qualification of individual dentist. Regarding rinsing of the dental impressions, 84.4% responded that they do rinse the impressions after they are made. Majority of the dentists rinse their impressions in running tap water (82.14%) whereas few of them use cold water for rinsing their impressions (5.8%). 1.3% of dentist prefer luke warm water, 1.8% use liquid detergent and 2.6% scrub dental impressions gently before they wash them. 15.6% of dental practitioners do not rinse the impressions at all. Concerning the time duration of rinsing the impressions 67.9% dentists rinse the impressions until the removal of any debris or trace of blood while 25.4% rinse for few seconds. With regard to disinfection of impressions 58.5% of dental practitioners do not use any disinfectant to decontaminate their dental impression after they are made, while 29% disinfect the dental impressions. 4.9% dentist disinfect the impressions only those which are soiled by debris or blood whereas 4.9% of them use disinfectant for decontamination of impressions of known high risk patients. Some 15.1% of dentist responded that they use chlorine compound for disinfection while 11.2% used 2% glutaraldehyde. 9.3% mentioned use of branded products but they were not aware of the constituents of that brand. Use of 0.5% chlorhexidine was preferred by 6.3% of practitioners. Few of the dentists also used iodophor, synthetic phenols and peroxygenated compound. Majority of dentists mentioned sodium hypochlorite as their material of choice to disinfect elastomeric impression materials. Considering the preferred method and duration of disinfecting impressions most of the dentists preferred spray method followed by wrapping in a disinfection soaked bag for 10 min. 23.2% of dentists also rinse the impression after disinfecting them with chemical disinfectants.

With regard to the reason for not complying with disinfection protocol of dental impressions majority (14.7%) of dental practitioners consider it time consuming and unnecessary procedure. 9.9% of practitioners believe that disinfection of impression is not needed as it has to be poured and sent to the laboratory ultimately. 13.4% of the dentists do not want to spend additional money for the disinfectants as they are expensive. Many of the dental practitioners (13.5%) were also concerned about the loss of precision and dimensional instability of the dental impression material. Very few dentists also supposed that the use of disinfectant may cause corrosion of metallic trays. Large number of dentists (17.4%) does not use the disinfectant due to unavailability of the chemical disinfectant at their clinics.


Infection control is an important part of all health care professional and is one of the most costbeneficial medical interventions,16 which is also considered as a core element of dental practices.17 This is the first study conducted to

evaluate the compliance of dental practitioners working in private clinics as well as dental universities in Karachi, Pakistan with impression disinfection protocols to control cross infection. In this research we studied impression disinfection procedures carried out in dental colleges and universities because these academic institutes are supposed to provide basic infection control guidelines for the imminent dental practitioners. The response rate to the questionnaire in this study was 74.6% which was comparable to the previous studies.18

The result of this survey was worrisome as majority of dentists do not follow the recommended guidelines of impression disinfection and impressions are sent to the laboratory without proper disinfection.

Based on the guidelines provided by Centers for Disease Control and Prevention (CDC) and American Dental Association (ADA) all the dental prostheses, impressions, orthodontic appliances, and other prosthodontic materials (e.g., occlusal rims, temporary prostheses or wax bite registrations) should be thoroughly cleaned, disinfected with an EPA-registered hospital disinfectant and thoroughly rinsed before being handled in the in-office laboratory or sent to an off-site laboratory.19,20,21

Furthermore they have emphasized that the best time to clean and disinfect impressions is as soon as possible after removal from the patient’s mouth before drying of blood or other contaminants can occur.

In this research it was observed that 15.6% of the dental practitioners do not rinse dental impressions at all and 4.9% rinse only those impressions contaminated with blood and debris. Rinsing an impression under running water should be a routine procedure to remove saliva, blood and food debris. This removes 90% of the microorganisms from the impression surface.22 Available literature shows that only washing the impression in running water is inadequate from the microbiological perspective. This highlights the importance of disinfectants to decontaminate the dental impressions.23, 24

The result of the present study reveals that 58.5% do not use any disinfectant to decontaminate the dental impressions. Few of the dentists follow the protocol just for high risk patients or when impressions are soiled with debris and blood. This finding was close to the result obtained in a survey conducted in Brazilian dental school where 70% of the students did not follow the impression disinfection guidelines.8 Marya et al in her research conducted in Indian dental colleges, also reported that 24% students disinfect the dental impressions properly.25

Our survey was also designed to explore the reasons why dentists do not disinfect the impressions. The responses indicate that a high percentage of the dentists do not know the importance of the impression disinfection procedures and they take it as a time consuming and a costly practice. They consider it as needless procedure because impressions are poured and ultimately sent to the laboratory. Many of the respondents reasoned unavailability of the disinfectants for their negligence to the impression disinfection protocol. Similar was the reason for non compliance in Indian dental college survey where out of 54 departments, chemical disinfectants were available in 36 departments.25

Several dentists do not disinfect the impression due to the concerns with the dimensional stability of the material and loss of precision. This reason was also reported in a survey where 35.4% of the dental professionals did not accomplish any type of disinfection of impressions because they thought that such procedure could cause dimensional changes in the materials.26 Very few dentists were also concerned about the corrosion of metallic impression tray which may be caused by chemical disinfectants.


This survey shows that most dental practitioners in their private practices and dental colleges do not disinfect dental impressions routinely and just wash them in running water which is inadequate from a microbiological perspective. Majority of them are unaware of the importance of the issue. Therefore dental colleges in Karachi should incorporate the impression disinfection protocol in their curriculum for students, dental technicians and other dental auxiliary personnel immediately


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