Effects of Skin Contact on Two Impression Materials

Objectives: Dental impression materials used in the analysis of bite marks are required to maintain their dimensional stability for extended periods of time. It has been observed that certain impressions taken of skin lose their dimensional stability with time, becoming tacky and unusable as evidence. The objective of this study was to investigate the onset of “tackiness” of two commonly used dental impression materials when brought into contact with skin. Methods: The two dental impression materials tested, were Impregum, and low viscosity President. The materials were mixed according to the manufacturers' instructions, and syringed into glass rings positioned on the shoulders of 28 volunteers. This brought the impression material into contact with skin. An additional seven glass rings of Impregum and seven glass rings of President, which did not come into contact with skin, were used as controls. The impressions where stored at a constant temperature of 21º centigrade. Changes in tackiness were monitored at monthly intervals over a four-month period using a Zwick Z010. A specially designed 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. Results: Over a period of four months, 12 of the 28 rings of Impregum became tacky and changed colour from purple to turquoise. Sixteen Impregum samples which came into contact with skin remained unchanged. All control samples of Impregum and all the President samples also remained unchanged. Conclusion: The results of this study show that certain factors present in skin or in products applied to the skin in the form of creams or oils are responsible for the loss of dimensional stability of Impregum. The factors responsible for these changes have not as yet been determined.