Impression procedure for problem mandibular complete dentures.

One of the most critical problems related to hand mixing of an elastomeric impression material is air entrapment during spatulation. This leads the formation of both surface and subsurface bubbles which in turn may result in inaccurate dental impressions and/or jeopardize their physical properties. In the present study the influence of the mixing technique has been determined by evaluating the surface area and the number of voids in two polyether materials (Permadyne and Impregum, Espe, Seefeld, Germany). The techniques tested were the stropping technique as hand-mixing and the Pentamix device (Espe) as mechanical mixing. Eighty special trays (10 mm x20 mm x43mm) featuring 10 transverse slots were fabricated and divided into four groups of twenty units. Groups 1 and 2 received the hand-mixed materials Permadyne high viscosity and Impregum F, respectively. Groups 3 and 4 (Pentamix group) received the mechanically mixed materials Permadyne Penta H and Impregum Penta, respectively. After polymerization, 10 slices of material were obtained for each tray by sectioning through the tray slots with a surgical blade. The slices were glued on a card and black and white photographs were taken. Subsequently, the negative films were placed on a viewing box and digitized with a video camera. A special software program allowed to identify and calculate the total surface area and the number of voids. Significant differences between the "stropping" groups (groups 1 and 2) and "Pentamix" groups (groups 3 and 4) were found. The mechanical mixing (Pentamix) generated the smallest number and total surface area of voids, while no significant differences were detected between Permadyne Penta H and Impregum Penta. Clearly, mechanical mixing represents a marked improvement over the traditional hand-mixing methods.

Dental Impression Materials↗

PubMed2001

Dimensional changes of dental impression materials by thermal changes.

Dental impression materials for prosthodontic treatment must be easy to use, precisely replicate of oral tissue, be dimensionally stable, and be compatible with gypsum materials. The dimensional accuracy of all materials is affected by thermal changes; impression materials shrink during cooling from mouth temperature (37 degrees C) to room temperature (23 degrees C). Five kinds of light body addition-reaction silicone impression materials [Contrast (CT), Voco Co., Germany; Examix (EM), GC Co., Japan; Extrude (EX), Kerr Co., USA; Imprint II (IM), 3M Co., USA; Perfect (PF), Handae Chemical, Korea] were tested by making cylindrical specimens (6 mm diameter and 12 mm height). The thermal expansion of the impression materials was measured with a thermomechanical analyzer (TMA 2940, TA Instruments, USA) between 23-37 degrees C. Data were analyzed via the Mann-Whitney Usage Test. To simulate actual dental impressions, tooth and tray shapes were modeled to measure the linear shrinkage of impression materials at anterior and posterior locations. The thermal expansion of impression materials tested decreased as follows: CT >or= PF >or= EM >or= EX >or= IM (p < 0.05). The anterior region changed more than the posterior region for the same impression materials. The dimensional changes averaged more than 40 microm in the anterior region, but less than 40 microm in the posterior region for all materials. Thermal expansion coefficients of some impression materials were significantly different from each other (p < 0.05), and the anterior region had more dimensional change than the posterior region for the same impression materials.

Dental Impression Materials↗

PubMed2001

How to obtain uniformity of occlusal detail.

At a recent Primary Dental Care Editorial Board meeting it was suggested that a series of short articles providing practical advice on clinical procedures might well be appreciated by our readers. This, then, is an invitation to our readers to submit material of this type, for publication. The text may be kept brief by the use of illustrations. The following example is the type of communication that we have in mind, but any information of a practical nature about the use of dental products would be carefully considered. We are grateful to the publishers of Fenestra (3M Dental Products) and the authors for permission to republish this piece first published in 1999.

Dental Impression Materials↗