Elastomeric impression materials

The preceding research on the model maxillofacial material was followed by TMDSC study of several representative elastomeric impression materials, which are extensively used in dentistry for the accurate fabrication of inlays and crowns from dental alloys, metal-ceramic restorations, and fixed and removable partial dentures [1-3]. There have been numerous studies reporting the clinically relevant properties of these impression materials (viscosity before setting by polymerization, strain in compression after setting, permanent deformation for simulated in vivo removal of the impressions, and tear strength of the thin impressions). However, only minimal research has been reported [44] on some thermal properties of impression materials obtained by conventional DSC. Our pioneering TMDSC study [45] was designed to obtain fundamental information about impression materials and seek correlations with their relevant properties. 

Additional TMDSC study of other vinyl polysiloxane, polyether and polysulfide impression materials is important to verify if the polymer transitions shown in Figures 16 to 19 generally exist in different products and to investigate the effects of other temperature modulation conditions. Complementary research on correlations with clinically relevant mechanical properties of the elastomeric impression materials is needed to verify if these thermal analyses have useful predictive power. Interestingly, when compared at apparently similar viscosities, the reported values of the elastic modulus [3] are highest for the vinyl polysiloxane silicone impression materials, intermediate for the polyether impression materials, and lowest for the polysulfide impression materials, in reverse order to the relative values of Tg fovind in our thermal analyses [45]. Our X-ray diffraction and scanning electron microscopic study [47] of these impression materials has shown that they contain substantial amounts of crystalline filler particles in the micron size range, which are incorporated by manufacturers to achieve the clinically desired viscosity levels. Tliese filler particles should have considerable influence on the mechanical properties of the impression materials. 

The objective of this investigation was to find a suitable comonomer for the development of a new elastomeric impression material for dental application using a bis-triazolinedione as a chain extending or cross-linking agent. Eugenol is a naturally occurring material which has been... 

Silicone liners are similar in composition to the previously described elastomeric impression materials, which are produced by condensation pol5mieriza-tion. Systems for the relining application may be either a one-component system, which cures in the presence of moisture or heat, or a two-component system, containing base and catalyst. Both types generally have poor adhesion to the denture surface, and can readily support bacterial growth. 

Figure 18. Elastomeric impression material showing packaging and mixing of the base and catalyst pastes.

Current elastomeric impression materials are based on the oxidative polymerization of polysulfides, the condensation of hydroxyl-terminated poly(siloxanes) with alkyl orthosilicates, addition reactions of vinyl poly(siloxane), or the cationic polymerization of ethylenimine-terminated intermediates often referred to as "polyethers . 

Elastomer Impression Materials. Dentistry requires impression materials that are easily handled and accurately register or reproduce the dimensions, surface details, and interrelationship of hard and soft oral tissues. Elexible, elastomeric materials are especially needed to register intraoral tooth stmctures that have undercuts. The flexibility of these elastomers allows their facile removal from undercut areas while their elasticity restores them to their original shape and size. 

To improve the rheological properties and extend the very short working time, a simple polyester is kicluded as thinner. Mixing is easy, and dimensional change ki ak is less than 0.1% over several hours. Elastic recovery and reproduction of detail are exceUent. The elastomeric cycHc imine impression materials have a higher modulus of elasticity than the condensation siHcone or polysulfide mbbers, and are more difficult to remove from the mouth. The materials have relatively low tear strength and an equUibrium water sorption of 14% thus, polyether impression materials tear readily. Because of thek poor dimensional stabUity ki water, they should be stored ki a dry environment. 

The exceptionally rapid reaction of triazolinediones with a variety of organic molecules prompted us to investigate these compounds as chain extenders or crosslinking agents for potential use in elastomeric dental impression materials. This topic has been discussed at length in the... 

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