![]() ![]() A knowledge of these structures and the chemistry is essential in order to make an intelligent selection. Again, compromise is necessary to balance the various beneficial and detrimental properties.įlexible impression materials play a crucial role in the fabrication of many dental devices, from full dentures to inlays, from orthodontic appliances to implanted prostheses. The many sources of permanent deformation after exposure to a stress mean that perfection is unattainable in practice. These two types are sensitive to water gain and loss. Two polysaccharide materials, agar and alginate, are strongly dependent on hydrogen bonding for network formation alginate relies on a chelation mechanism as well. Polysulphide, polyether and silicone impression materials all give covalently-bonded networks when set, although each has its own particular dimensional stability problems arising from their chemistry. The properties are also dependent on the nature of the filler. However, the large strains that these materials must endure may result in a structural breakdown called strain-softening. The good as well as the bad points of each must be taken into account in the selection of the type of product and its manipulation for the task in hand.Īll flexible mould materials are polymeric and must be cross-linked to be rubber-like, that is, three-dimensional random networks, and they are markedly non-Hookean in their deformation behaviour this can be traced to features of their structure.įillers are again often important in order to obtain adequate viscosity in the unset material, and appropriate stiffness when it is set. This chapter describes a range of common types of dental impression material and how they meet – or fail to meet – those demands. ![]() No perfect solution has been found, although many attempts have been made. It includes severe requirements for flow, setting in a reasonable time and perfect elasticity as well as absence of dimensional changes on setting and after. ![]() The problem of designing a mould material for making dental models is formidable. ![]()
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