The following describes a modified technique for obtaining tool mark impressions utilizing polyvinylsiloxane impression material. Advantages of the polyvinylsiloxane materials include ease of use, accuracy, and dimensional stability over time.
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- Obtain general, midrange, and closeup photographs without and with scale as necessary of the tool mark and its associated location (Figure 2).
- Place a soft orthodontic wax rope as a border around the tool mark to control the flow of excess impression material and block out any undercuts that could interfere with smooth removal of the impression from the surface (Figure 3).
- Place a small hole in the center of the fingerprint card (Figure 1).
- Lightly mist the tool mark area with Mizzy silicone emulsion spray (Figure 3).
- Place an AccuTrans cartridge in the automix dispenser and inject material into the tool mark (Figure 4).
- Place the fingerprint card over the tool impression and depress it into the impression material until it contacts and lightly adheres to the orthodontic wax (excess impression material will extrude from the hole in the fingerprint card). Note: polyvinylsiloxane material flows more effectively into surface details when a slight force is applied to it (Figure 5).
- Check for complete “set” of the material by periodically placing a fingernail into the material that has extruded from the hole in the fingerprint card. The material is completely “set” once the fingernail indentation in the material rebounds to normal contour immediately after removal of the fingernail from the material.
- Place case number, orientation marks, date, and a sketch of the location (door, window, etc.) on the card prior to its removal from the surface (Figure 6).
- Remove the impression from the surface and remove the wax rope from the impression for possible re-use on another impression (Figure 7).
- Pour the impression in dental stone or acrylic if necessary for further evaluation.
From: Tool Mark Impressions by Steven L. Petersen, CCSI, and Shawn L. Naccarato, DDS/CCSA
