Ergonomics of hygiene-asepsis for implant-supported prostheses

The hygiene-asepsis procedures to be adopted for implant-supported prostheses must be as rigorous as those for traditional prostheses. The essential objective is to follow a chain of asepsis that assures protection during these therapeutic procedures. In order to master it, it is necessary to establish a course of action that means being vigilant as well as observing a strict attention to detail. Practitioners must take care to achieve a consistency of action, appropriate to the level of risk of the procedure involved, such as the construction of an implant-supported prosthesis.

Indeed, according to the American Dental Association, all instruments, impression materials, wax models, etc. that are carried between the surgery and the laboratory and that have been in contact with blood or saliva are potential vectors of contamination (^{Merchant and Molinari, 1989}). It has been demonstrated that viruses, such as those of herpes and hepatitis B, may be present in saliva (^{Scully and Bagg, 1992}).

The implant-supported prosthesis requires the use of many special instruments specific for every implant system. The multiplicity of these items obliges the practitioner to think how to establish a strict, ergonomic way of working that is appropriate for this procedure.

First of all, it is necessary to organise simple and precise storage for the various pieces of reusable equipment to be used for constructing implant-supported prostheses. These instruments must follow the chain of sterilisation.

Some practitioners (^{Yen-Chen and Yu-Fu Shen, 2001}) recommend the adaptation of medical pill boxes (small plastic boxes containing several compartments) in which to arrange and to decontaminate the various instruments before sterilisation.

In the same way, it is possible to have a cupboard with racks or drawers that permit an ergonomic arrangement for these sets of instruments. This will facilitate preparation for the various clinical sessions.

The risks of cross-contamination are very high during prosthetic treatments because of the need for multiple manipulations and the, sometimes, prolonged length of the appointments.

It is essential to programme sessions for prosthetic treatment perfectly. All necessary items must be prepared before the appointment so that, ideally, drawers or boxes do not have to be opened during treatment. In order to do this, it is necessary to systematise the standard procedures and even to write a card for each procedure, noting the hand instruments normally used, the necessary materials, the handpiece, the contra-angle, the diamond-tipped instruments, the essential specific instruments required for the implant-supported prosthesis, etc. Before every procedure, one or several trays will be put in place, with all the necessary materials.

The appointment for impression-taking

Before seating the patient, the assistant places the materials necessary for this type of procedure on two or three trays :

- tray n° 1 is usually placed on the bracket table and contains the small instruments on a sterile surface (mirrors, probes, tweezers, spatulas, etc.) and all the specific instruments required for the implant-supported prosthesis (implant carriers, titanium forceps, screwdriver) (^{fig. 1}) ;

- note : a specific kit containing all the necessary instruments is suggested for some systems of implant-supported prosthesis (screwdriver, torque wrench, etc.) (^{fig. 2}) ;

- tray n° 2 contains all the non-sterile instruments : the items required for impression-taking (impression tray, silicone, putty, light, bite plate, alginate, bowl, spatula, water…) (^{fig. 3}) ;

- tray n° 3 includes a pot containing chlorhexidine, pledgets, one or more radiographic films, and it provides a place to put the healing abutments that are removed whilst impressions are being taken (^{fig. 4} and ⁵).

The impressions, once taken, will be put on this last tray and should quickly undergo decontamination treatment before being sent to the prosthetic laboratory. This treatment of the impressions is often forgotten by practitioners and by technicians, whereas it requires a specific protocol (^{fig. 6}).

Decontamination of the impressions

Both practitioners and laboratory technicians often misunderstand the principles of decontamination, cleaning and disinfection of impressions and, above all, seldom apply them. The risk of affecting dimensional stability and the condition of the surface often leads to the absence of any treatment, either in the surgery or in the laboratory. Yet, the risk of cross-infection remains since there is, whatever the impression material used, a transfer of microorganisms from one to the other (^{Gerhard and Sydiskis, 1991}).

Whatever the technique and the material used, one can never expect to achieve a total elimination of the bacteria and viruses, amounting to sterilisation. One is content therefore, for the impressions to be clean and to be decontaminated.

This decontamination is achieved in two stages : cleaning and effective decontamination (^{Missika and Drouhet, 2001}).

Cleaning or rinsing

Rinsing of the impressions is the essential stage. Whatever the material used, this must be done on removal from the oral cavity, under running water, until there are no signs of blood, saliva or other organic material. This simple rinsing is considered to be the most important action because it reduces contamination by 90 % in 15 seconds.

Cleaning must follow certain rules. It must be done :

- immediately after removal from the mouth ;

- preferably in the same room to avoid any transfer of bacteria ;

- with gloves, mask and eye protection ;

- under a current of cold water for 15 seconds.

All surfaces of the impression and impression tray must be rinsed.

Rinsing must always be completed with vigorous shaking of the impression or by drying it lightly, in order to eliminate excess water that would dilute the subsequently-applied disinfectant.

Decontamination

This involves simple decontamination and not full disinfection ; the latter would take too long to achieve and would involve chemical solutions that are too concentrated to allow impression materials to maintain their properties.

The methods and the disinfectant materials used vary according to the impression material and, sometimes, of the operator. Some recommend soaking, others spraying.

Among the disinfectant solutions (they must, in principle, be bactericidal, fungicidal, virucidal and even sporicidal), one finds two main products : glutaraldehyde and sodium hypochlorite (used in concentrations of 0.5 % to 5 %).

Hydrocolloid impressions

While comparing the advantages and the disadvantages of all the methods proposed, the technique that seems best adapted to this type of impression consists of :

- washing the impression under running water, then shaking it to eliminate excess water (^{fig. 7}) ;

- immersion for several seconds in a 0.5 % solution of sodium hypochlorite so that the whole of the impression and the impression tray are soaked in disinfectant solution ;

- covering the impression with gauze or absorbent paper which, with the aid of a spray, is soaked in the same solution ;

- placing the impression, thus treated, in a tightly closed plastic bag for 30 minutes ;

- finally, rinsing it under cold water in order to eliminate all the disinfecting solution.

This method, described as « halfway », is simple and without any major effect on the qualities of the impression. Nevertheless, it cannot provide perfect decontamination. For that, it would be necessary to use concentrations greater than 5 % and times of immersion of more than 1 hour, which are incompatible with hydrophilic materials.

Silicone impressions

All types of silicone impression material are hydrophobic. This has the effect of retaining fewer micro-organisms. Therefore, their decontamination is more simple and, above all, much less controversial than that for hydrocolloid impressions.

Decontamination by immersion is the method of choice, the technique of spraying having been abandoned by most authors. Immersion can be done with solutions based on glutaraldehyde, sodium hypochlorite, iodine derivatives, etc. According to various studies, the soaking time advised varies from a few minutes to several hours.

Decontamination involves the following stages :

- rinsing the impression under running water for at least 15 seconds (^{fig. 8}) ;

- drying it lightly in order to eliminate excess of water ;

- immersion in a closed bath of 2 % of glutaraldehyde or 0.5 % of sodium hypochlorite solution for 30 minutes ;

- rinsing again under running water ;

- drying.

Return from the laboratory, try-in and fitting

In order to organise these clinical sessions ergonomically, the assistant should put the necessary materials in place and prepare two or three trays, in the same way as the appointment for taking the impression. The trays must assemble the essential instrumentation, according to the requirements of the individual practitioner.

However, there is the problem of the possible contamination of the prosthesis on return from the laboratory. It seems that the only means of contamination possible, at this time, are from airborne sources or by contact (handling). Whether ceramic, metal or resin, these new materials offer little room for contamination, except on their surfaces.

To be precise, a complete or partial removable prosthesis can be immersed in a bath of chlorhexidine prior to try-in or fitting. A fixed prosthesis (metallic or ceramic) can undergo the same treatment followed by rinsing and cleaning in alcohol at 60°, which will afford degreasing of the surfaces prior to cementation. In the case of ceramics, it is necessary to specify that, in the unglazed state, they will not tolerate any disinfectant (^{François and Doukhan, 1997}).

These protocols do not provide true decontamination complying with any standard for hygiene or asepsis, but rather, they follow a general rule of cleanliness. In any case, only the organisation and the manner with which the prosthetic treatment is carried out will be the key to mastery of the chain of asepsis. That is the chain that every practitioner must follow, by a careful and thoughtful consideration if his perception of the risk involved with the procedure.

Finally, if one considers dental prostheses as medical devices, it is necessary to describe them as « non-critical ». Because they are new, « before delivery », the treatment required is low-level disinfection.

Conclusion

The problems of nosocomial contamination are certainly at the heart of the preoccupations of various authorities. Nevertheless, it is necessary that every practitioner assumes his or her responsibilities in respecting the regimes for hygiene that are advised, as well as taking care to maintain a consistency of effort in order to master the chain of asepsis.

In prosthetic and implant treatment, mastery of this chain is the concern of every practitioner, in order to achieve a consistency of action according to the level of risk for every clinical procedure. In order to organise the appointment most efficiently, it is necessary to practice in a methodical, strict and ergonomic way and to act with common sense while anticipating and preparing for the clinical session.

BIBLIOGRAPHIE

• François F, Doukhan JY. Hygiène et asepsie durant les actes prothétiques. Clinic 1997;18:129-139.
• Gerhard DE, Sydiskis RJ. Impression materials and virus. J Am Dent Assoc 1991;122:51-54.
• Merchant VA, Molinari JA. Infection control in prosthodontics : a choice no longer. Gen Dent 1989;37:29-32.
• Missika P, Drouhet G. Hygiène, asepsie, ergonomie. Un défi permanent. Paris : Éditions CdP, 2001.
• Scully C, Bagg J. Viral infections in dentistry. Curr Opin Dent 1992;2:102-115.
• Yen-Chen KU, Yu-Fu Shen. Organized method for ultrasonically cleaning and sterilizing small prosthetic components used in implant therapy. J Prosthet Dent 2001;85:207-208.