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At least 55 records · Page 3Linked to original sources
PubMed2006

A pilot study to determine the effects of skin contact on two commonly used dental impression materials.

Impression materials used in the analysis of bite marks are required to maintain their stability and integrity for extended periods. It has been observed that certain impressions taken of skin lose their properties with time, becoming sticky and unusable as evidence. The objective of this study was to investigate the onset of "stickiness" in two commonly used dental impression materials when brought into contact with skin. The two materials tested were Impregum and President. They were syringed into glass rings positioned on the upper arms of 28 volunteers. Changes in stickiness were monitored over a four-month period using a tensile testing machine. A metal plunger was lowered onto the impression material and then retracted measuring the adhesive force of the material to the lower surface of the plunger. Over the research period 17 of the 28 rings of Impregum became sticky and changed colour from purple to turquoise. The remaining 11 Impregum samples, all the President samples and all control samples remained unchanged over the 120 day period. The results of this study show that certain factors present in or on skin are responsible for the loss of surface integrity of Impregum. The factors responsible for these changes have not been established.

Adhesiveness↗
PubMed1989

Measurement of pressure ulcer volume using dental impression materials: suggestion from the field.

Understanding of the healing rates of deep pressure ulcers may be enhanced in future studies by relating changes in wound volume to changes in WSA. In this report, a type of dental impression material, vinyl polysiloxane, was used to produce a model of the internal topography of a pressure ulcer. This model was used to obtain volumetric measurements of the wound cavity. A permanent replica (cast) of the wound was also fabricated. Further clinical trials investigating the reliability of this method for measuring the volume of deep pressure ulcers are indicated.

Dental Impression Technique↗
PubMed1994

Comparison of physical properties of light-curing and self-curing dental impression materials.

A light-curing polyether urethane dimethacrylate impression material was recently developed. Its polymerization reaction is activated by intensified visible light; therefore, the on-demand set allows operators to work at their own pace. Furthermore, its constant viscosity provides a constant flow rate at the critical stages of taking impressions. The purposes of this study were to evaluate the physical properties and accuracy of this light-curing impression material and to compare it with those of self-curing impression materials currently used in our dental clinic. Physical properties such as strain in compression, compression set, dimensional stability, and tear strength of the impression materials were measured according to test methods stipulated in ADA Specification No. 19 for elastomeric impression materials. The template-coping method developed by Lewinstein and Craig was used to evaluate the accuracy of the impression materials. It was found that the strain in compression of the polyether urethane dimethacrylate was higher than that of the condensation silicones, but lower than that of the addition silicones. The compression set of the condensation silicones was more than that of the polyether urethane dimethacrylate, but much less than that of the polysulfides. The dimensional stability showed that all of the impression materials, except the polyether urethane dimethacrylate, had a negative dimensional change 24 hours after mixing. The sequence is: polysulfide < condensation silicone < addition silicone. The expansion rate of the light-curing material was measured under 0.07% one day after curing. The polyether urethane dimethacrylate had extraordinary tear resistance compared to the other impression materials.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗
PubMed2006

Assessing the effects of three dental impression materials on the isolated sciatic nerve of rat and frog.

The effects on nerve tissue of three dental impression pastes were compared in this study. Two of the impression pastes, Examix and Express 3M, contained vinyl polysiloxane while the other, Xanthopren, did not. An in vitro model based on the isolated sciatic nerve of the frog and rat was used. As an indication of the proper functioning of the fibres in the nerve, the amplitude of evoked compound action potential (CAP) was monitored continuously. The results clearly showed that the number of active nerve fibres in the isolated sciatic nerves of either rat or frog exposed directly to impression pastes containing vinyl polysiloxane, decreased much faster than those of the nerves in contact to impression material without vinyl polysiloxane. When the nerve of the frog was exposed to Xanthopren there was a decrease in the CAP to 50% of the control values within 56.87+/-2.42 h (n=6). This value was called inhibition time to 50%, IT(50) and for Examix it was found to be 9.97+/-1.53 h. When the nerve of the rat was exposed to Xanthopren, the IT(50) was 15.34+/-2.97 h (n=6) for the Xanthopren and only 2.86+/-1.20 h for Examix and 2.76+/-0.48 h for Express 3M (n=6). There was no significant difference between the action of the last two compounds (P=0.85). This fast nerve fibre inactivation could be caused either by the chemical used for the synthesis of the two impression pastes, Examix and Express 3M, or by the unusual constriction of the nerve when it is embedded in the materials with vinyl polysiloxane. There is strong evidence to support the first case, since the incubation of the nerve in the presence of Examix, Express 3M and Xantopren in a way so the nerve was not in contact with the impression pastes, shows a much faster decrease of the CAP in the presence of the first two pastes. The decrease is caused by the death of nerve fibres, since there is no recovery in the CAP after the removal of Examix from the incubating saline.

Action Potentials↗
PubMed1979

Replication techniques with new dental impression materials in combination with different negative impression materials.

New materials and new techniques have enabled the fabrication of more reliable and more accurate replicas. Not only is the reproduction of detail of importance, but the expertise required from the operator and the time involved to produce a replica are considered key factors. For various reasons a reliable and reproducible replication technique for scanning electron microscopy offers many advantages. Recently a new dental precision impression material has been introduced, which in combination with low viscosity resins has produced superior results over other techniques. This combination processed by means of a centrifugal casting machine has produced replicas which could easily be compared to a standard test die at magnifications up to 3000 X. More in depth testing will have to be performed to establish whether these materials can be universally applied to a broad spectrum of replication problems. The combination Reprosil/Spurr low viscosity imbedding medium yielded replicas of high quality which can be made with simple equipment and without possessing special skills. Centrifugation of the positive replication material into the negative impression virtually eliminated the entrapment of airbubbles.

Dental Impression Materials↗