LITERATURE REVIEW

Literature Review

Literature Review

In the past, the most biologically contaminated item to leave the dental surgery for further handling was the dental impression on its way to the dental laboratory. Dental impressions become contaminated with the patient's saliva, bacterial plaques, and blood. This offers a significant cross-infection vehicle for dangerous pathogens such as the human immunodeficiency virus and hepatitis-B virus among others. It is now a requirement of standard cross-infection protocols that impressions are delivered to the laboratory after disinfection.

Dental Gypsum is a calcium salt that is utilized for various reasons most importantly in dentistry as an impression material. It exists in various forms and states of hydration. Micro-organisms can survive on, or even inside, the impressions . Even though their number decreases rapidly after impression making and rinsing with water further eliminates them [perhaps to a practically harmless level ], it has been shown that measurable bacterial load remains on impressions and can be transferred to casts .

Therefore, the effort to eliminate as many potential risks as possible seems logical and the application of a disinfection treatment on impressions is considered mandatory. Although alternative methods are being proposed, such as ethylene oxide , autoclave , microwave , ultraviolet radiation , or even immediate pour and disinfection of the casts , chemical disinfection, preferably by immersion, seems to be the most reliable and practical method, provided that it does not adversely affect the dimensional integrity of the impressions.

Dimensional stability of disinfected impressions is therefore critical and a considerable number of articles were found reporting on it. The investigations showed a remarkable variation of important experimental attributes; the differences can be briefly summarized as follows:

Various combinations of impression materials/disinfecting solutions were encountered. Addition silicone was the most frequently used impression material, followed by polyether, irreversible hydrocolloid, polysulphide, condensation silicone, and reversible hydrocolloid; the so-called 'rigid' materials - zinc oxide-eugenol paste, modelling plastic impression compound, and impression plaster - were considerably less investigated. Glutaraldehyde seemed to be the preferred disinfectant, but chlorine compounds, iodophors, phenolic and alcohol compounds were also tested.

The specimens were usually immersed in the disinfectant or control solution, but spraying as an application technique was also investigated. The time of contact between the impression material and disinfecting solution was, in most cases, limited to <60 min and selected according providers' instructions and relevant guidelines. However, 12 investigations studied the effect of long-time contact, several hours or even days.

Control specimens were left either in water - usually distilled or deionized - or in air; in nine studies the control sample consisted of impression specimens poured immediately. Nine studies used both water and air as control environments. The experimental specimens consisted of either impressions or the casts poured on them. Two articles measured dimensions of both impressions and their casts.

The usual method to estimate dimensional changes involves measurement of distances between selected points on the experimental/control specimens and comparison with analogous distances on the recorded object - a master arch model or a standardized metal ...