INTRODUCTION:

Aerosols are potential hazards to dentists in the workplace. These airborne particles are composed of debris and micro organisms propelled into the air from the oral cavities of the patients treated in the clinic throughout the day. These particles range from relatively harmless to highly infectious. These small particles remain suspended in air relatively for many hours after the completion of treatment (1-6).These particles when inhaled, their small size allows penetration into the alveoli of the lower respiratory tract, where infectivity is greatly increased (7-8). Dentists use high energy equipments such as handpieces, scalers in presence of bodily fluids like saliva, blood and dental plaque. This combination has been shown to generate aerosols of micro organisms and blood (9).The micro organisms transported in the aerosols can contaminate the skin, mucous membrane of the mouth , respiratory passages and eyes of dentists (10-14).

Aerosol and Splatter:

Dentist’s working handpieces are supplied with water through a system of thin plastic tubes which constitute dental unit waterlines (DUWL). Water cools the burs and scaler tips (an additional handpiece used to remove dental deposits) and rinses tissues during preparation.

A stream of water and/or air produced by an air-water syringe is used during other therapeutic procedures. Two types of water circulation in dental unit waterlines may be distinguished by the water supply: 1) an open system where the source of water is a municipal water system, and 2) a closed system in which water is drawn from a container (reservoir) belonging to a unit. Dental handpieces produces aerosols which is a mixture of air coming from handpiece, water from DUWL and patient’s saliva and is always accompanied by splatter. Due to this, dental professionals are exposed to wide range of micro organisms causing diseases like common cold, pneumonia, tuberculosis , hepatitis B and acquired immuno deficiency syndrome (AIDS) (15,16).

Aerosols are liquid or solid particles, 50 μm or less in diameter, suspended in air. They can remain in air for a long time and be transported with air flows at long distances. They are capable of penetrating deep into the respiratory system, reaching as far as pulmonary alveoli(17,18). Splatter is usually described as a mixture of air, water and/or solid substances, such as fragments of dental fillings, carious tissues, sandblasting powder, etc. Water droplets in splatter are from 50 μm to several millimetres in diameter and are visible to the naked eye. They have sufficient mass and kinetic energy to move ballistically and quickly settle on objects due to the action of gravitation forces. Splatter shows limited penetration into the respiratory system. Splatter particles, moving along trajectories, can come into contact with the mucosa of nostrils, open mouth, eyes and skin. They are deposited on hair, clothes and in the immediate surroundings of the splatter source. The range of splatter is from 15 to 120 cm from a patient’s oral cavity. Thus, splatter can easily reach a doctor and an assistant (19,16). Aerosol composition varies from patient to patient, depends on the site and type of procedure in the oral cavity (tooth preparation, polishing, dental deposits removal) (20). The most intensive aerosol and splatter emission occurs during the work of an ultrasonic scaler tip and of a bur on a high-speed handpiece (21,12,14).

Microbes in aerosol and splatter:

The microflora of DUWL water and that of a patient’s oral cavity exerts a decisive influence on the microbiological composition of dental aerosol produced by unit handpieces(22,23,24). During conservative treatment and professional oral hygiene procedures, the sites showing the highest microbiological contamination due to aerosol and splatter are (in descending order): dentist’s masks, a unit lamp, surfaces close to spittoons, and mobile instrument material tables. On the contaminated surfaces the following bacteria were found: bacteria of the Streptococcus genus, which constitute 42% of total bacteria, Staphylococcus – 41%, and Gram-negative bacteria – 17%. The differences in contamination between a dentist’s mask and a table are significant for the first two genera (25). Factors forming the dental aerosol plays a major role in composition of surgery microflora(26). With the use of handpieces, there is increase in the concentration of microflora during work and immediately after treatment (27). The microflora of air in a dental surgery contains Staphylococcus epidermidis – 37.1% of total bacteria, Micrococcus spp. – 32.6%, nondiphterial corynebacteria – 28.2%, Staphylococcus aureus – 0.6%, Pseudomonas spp.– 0.6%, and fungi – 0.9%. The presence of opportunistic microorganims (Staphylococcus epidermidis, non-diphterial corynebacteria, Pseudomonas spp.) is significant (28).

Studies shows that 85-90% of the bacteria in dental surgery atmosphere is streptococcus sp typical of oral cavity(29). This is one of the dangerous contamination in dentist environment. The contamination is from inhalation of infectious particles , they are suspended in air, settled on surfaces and are reaspirated(28, 20,27).

Significance of bacterial aerosols:

Dental procedures mainly produce aerosols predominantly of streptococcus and staphylococcus sp.Other infective bacteria include M. tuberculosis has been found in particles generated by high speed hand pieces during treatment on active tuberculosis patients(30). Micik et al. demonstrated that dental procedures incorporating the use of water sprays or rotary instruments generated aerosols with significantly greater numbers of bacteria(31).Grenier demonstrated dental treatment in general significantly increased the level of bacteria air contamination and ultrasonic scaling produced three times contamination than operative dental treatment(32). Bentley et al. also found higher aerosolized bacterial counts of alpha hemolytic streptococci during ultrasonic scaling therapy than during tooth preparation(33).

Measuring bacterial aerosols:

The methods used to collect air samples are SAS (Automated Surface Air System) sampler (34), RODAC plates (35), TSA (Trypticase Soy Agar) (36), TYC agar (Tryptone Yeast extract Cysteine), Casella slit sampler , Columbia blood agar, Aderson sampler (29), Vacuum Air Sampling device with Filters and Reynier’s slit sampler(37).The concentration of bacterial aerosols can be measured quantitatively by using the slit-to-agar air sampler, the technique of vacuum aspiration impaction, which can quantitatively estimate the number of bacteria in a certain volume of air, usually expressed as colony forming units (CFU) per m3. Agar plates are attached containing different agar media, which can measure total bacteria count and specific bacterial organisms(14). Single air sampling has limitations as the environment may change from time-to-time; however bacterial aerosols can be serially monitored and should be undertaken in consistent manner within the breathing zone of the dental staff or the patients or both, depending on what the target group is. Many previous studies were limited by the small sample size or by employing procedures which did not allow accurate quantification of bacteria. Some also used an experimental design, which may not have represented the real situation in most dental clinics(14). Blood agar plate is a general purpose, non-selective, enriched medium that promotes the growth of micro-organisms(20). According to Legnani et al, plate method gives a precise indication of the possible contamination over time by measuring dental particulate and aerosol precipitation on different exposed surfaces in the operatory room(27). Cochran et al. (38) and Bentley et al.(16)observed the larger salivary droplets generated during dental procedures settle rapidly from the air with heavy contamination on the patient’s chest.

Protective measures against bacterial aerosols:

Modern dental clinics are closed systems with air conditioning which needs regular monitoring. Bacterial aerosols can be minimised by using air filters and ultraviolet (UV) light. The use of UV lamps or portable filters for particle removal may increase equivalent room air changes, but does not satisfy fresh air requirements. Laminar air flow may further reduce exposure. Reseachers prove the importance of routine monitoring of micorbiological contamination of dental surgeries – the surface of instruments and devices, air and dental unit water, and – in the case of their contamination – the need for sterilization and disinfection.

A large volume of literature has demonstrated the effectiveness of certain antiseptic mouth rinses in helping to reduce development of gingivitis and periodontitis(39). Use of an antiseptic mouthwash by the patient prior to ultrasonic scaling has also been shown to be effective in reducing bacterial aerosols during treatment(40). Chlorhexidine gluconate has been found to be more effective than other solutions in reducing bacterial aerosols(41).

Suction and preoperative oral hygiene procedures may not be effective in reducing contamination from bacterial splatters(18). High-volume evacuation may however reduce bacterial aerosols and splatter during dental procedures, such as with the use of ultrasonic scaling(12).

King et al. suggested the use of aerosol reduction device as an effective method in reducing the number of microorganisms generated during ultrasonic scaling, therefore reducing the risk of disease transmission(20).

Water flowing from unit handpieces should meet the conditions for potable water. The quality of water should be monitored with the use of commercial laboratory tests, or sets which can be applied in a dental surgery, in order to determine the number of heterotrophic microflora in potable water (42,43). Various water decontamination methods may be used (44,45,46).

The correct maintenance of handpieces should follow the principle: “Do not disinfect when sterilization is possible”. The principle points to the necessity for routine sterilization. Sterilization of handpieces ensures their internal and external sterility (47,48), eliminating 1) patient-patient infection, and 2) contamination of waterlines with tissue fragments and microorganisms, including viruses, which was confirmed in tests with highly sensitive methods, such as PCR – polymerase chain reaction (49). Because a destructive influence of steam sterilization after every use on the durability of handpieces was reported, disinfection between patients is acceptable (50). However, it is indispensable to sterilize handpieces after a working day. It is strictly necessary to use valves preventing suckback of liquids into DUWL; the valves should be replaced at appropriate intervals (51).

A dental unit should be rinsed at the beginning of a working day, and between patients. The first type of rinsing assures elimination of microflora whose presence is due to the night stagnation. The second type, where 20-30 second rinsing is recommended, is to help reduce the risk of retraction of the oral cavity fluids, and aims at elimination of potential cross infection. At the same time, it should be remembered that rinsing reduces bacteria concentration only temporarily, and exerts no influence on the biofilm. New bacterial contamination, which seems to be a result of bacteria release from the biofilm, was found at different times after rinsing (48, 52, 53).

It is strictly recommended that a dental team should use personal protection measures (clothes, gloves, masks, protective goggles, visor shields). Personal protective measures, such as the use of surgical masks, prescription or safety glasses worn with lateral protection, gowns, and gloves, can decrease the penetration of or reduce contact with bacteria aerosols and splatter(14). Micik et al. studied the efficacy of surgical masks in protecting dental personnel from air borne bacterial particles and tested filtering efficiency of mask varying from14%-99%. Aerosols or airborne particles of less than 1 m can, however, readily penetrate surgical masks although 15-83% of aerosols of 0.06 to 2.5 μm have been shown experimentally to pass through the filter media of various makes of surgical masks(54).

Routine immunizations of dental staff in the dental clinic should be up-to-date according to the relevant national immunization schedule. Many of these immunizations cover bacterial and viral infections which could be transmitted through bacterial aerosols in the dental clinic. Dental staff should also consider Mantoux testing for tuberculosis and BCG immunization, especially for those working in endemic areas(14).

CONCLUSION:

Dental aerosols represent an infection hazard for dental professionals due to their gross contamination with microorganisms and blood. The advent of SARS and its predicted reemergence during the upcoming flu season have brought the dangers of dental aerosols to a higher level. Aerosols are easily controlled with the appropriate precautions. Whenever an ultrasonic scaler or air polisher is used the following steps should be followed: (1) barrier protection (2) high volume evacuation, and (3) pre procedural rinsing. Each of these adds a layer of protection for the operator and others in the dental office. All three steps must be followed for adequate protection. The use of only one or two of the steps will not yield the necessary level of protection adequate for safety. Further, a chapter on aerosols should be mandatory in clinical dentistry text books. The Studies based on aerosol microbial profile, have several methodological variations that affects the aerosol contamination. The operatory measurement is not similar in aerosol studies as the dimension of the room influences the distribution of aerosol; the information regarding the operatory preparation for aerosol study is not mentioned in all the published articles; different air-sampling methods are used; the distance and the location at which the aerosol samples were collected are dissimilar in various studies; the duration of aerosol sampling are different; the position of the operator (mask level) and the treatment area in the oral cavity differs which definitely influences the aerosol contamination. Furthermore, standardized methodology has not been employed and the results have not been reported in a comprehensive form. This has made comparative interpretation of new data difficult and has hampered the further use of aerosol collection measurements in a clinical setting.

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Received on 13.06.2014 Modified on 18.06.2014

Research J. Pharm. and Tech. 7(8): August 2014 Page 938-941