The differences between impression materials, as outlined above, are the materials themselves and the purpose they are used for. Each of the materials has advantages and disadvantages, but they are each used for a different purpose and are effective and commonly used products in dentistry today. Objective: Oral rehabilitation success is enhanced by an accurate and reproducible final impression. The purpose of this study is to evaluate the dimensional changes of a polyether and addition silicone subjected to disinfection and/or sterilization after a long storage period. Fenske C. The influence of five impression techniques on the dimensional accuracy of master models. Braz Dent J. 2000;11:19-27. Ideally, the impression material should flow freely and wet the tissue as it is being injected to achieve adaptation, and then resist flow away from the intended surface areas. The same procedure will facilitate spreading of heavy-body material on the impression tray and retain it in the tray. This phenomenon is called shear thinning ( Chapter 3). Essentially, a stress-thinning material becomes less viscous when stressed as during injection and then recovers its viscosity when it rests on the tissue or or in the tray. All elastomeric impression materials exhibit shear-thinning characteristics before setting.

Recently, variations of these putty/wash techniques suggest that they can be successfully utilized to obtain impressions without the use of retraction cords. The concept is that the wash material can hydrostatically be forced into the gingival sulcus when the set putty impression is reseated in the mouth, thereby capturing the impression of the margins without having to place retraction cords or remove gingival tissue with a laser or electrosurgically. Some techniques further suggest that this technique can hydrostatically displace crevicular fluids as well as tissue. The most effective way of recording a putty wash impression is to use the one-stage technique in a rigid metal tray. The most difficult aspect of a crown preparation is the interproximal margin. Therefore it makes sense to reduce the amount of preparation required in the area.Horowitz RA, Leventis MD, Rohrer MD, Prasad HS. Bone grafting: history, rationale, and selection of materials and techniques. Compend Contin Educ Dent. 2014;35(4 Suppl):1-6. The Oraseal Caulking and Putty Kit effectivley adhears to wet dental dam, wet gingival and mucosal tissue, wet teeth and metal, even under water or in saliva. This is further complicated by the fact that many commercial laboratories employ plastic, disposable articulators to use in the fabrication process, adding to the inaccuracies that can occur. Evaluation of the 6 most popular plastic, disposable articulator systems used with dual-arch impressions found that with all systems, it was virtually impossible to maintain and repeat a centric occlusal position stop. The conclusion was that they should only be used for single units, not when the terminal unit in the arch is being prepared. 1

Evaluation of the efficacy of bioactive synthetic graft material in the treatment of intrabony periodontal defects. Grover V, Kapoor A, Malhotra R, Uppal RS, J Indian Soc Periodontol. Jan-Feb 2013; 17(1): 104-110. Margins should be smooth and continuous with no steps. This is difficult to achieve. I find that a fine grit bur (yellow or white) is very helpful in refining the margins. Panichuttra R et al. Hydrophilic poly(vinyl siloxane) impression materials: dimensional accuracy, wettability, and effect on gypsum hardness. Int J Prosthodont 1991; 4: 240–248. Final impressions: Final impressions are sent to a dental laboratory for the fabrication of dental restorations or appliances. These may include crowns, bridges, dentures, retainers and more. A-type silicones – also known as VPS impression materials – are hydrophobic (i.e. water-resistant). By the addition of surfactants (wetting agents), it is possible to increase the material’s hydrophilicity even in the unset state. In addition, there are great variations of the flow behavior during the working time offered by different materials with a flow reduction seen especially towards the end of the working time. General advantages of VPS are their superior elastic recovery, high dimensional stability over time, and neutral taste.

Figures

Typically, dental materials require a reduction of between -0.7mm and 2mm for a crown. Correct taper