Prosthetics: impression materials

The following articles on impression materials are of interest. Items 2 and 3 are included in Table 2 in previous posting.

2008

1. Effect of temperature on rheological properties of dental interocclusal recording material. Pae A, Lee H, Kim H-S. Korea–Australia Rheology Journal 2008 20:4 221-226

This study used parallel plate geometry with gap size 0.5mm in oscillating mode. Storage modulus and tan delta were recorded at 21 C and 33 C, n=5.
Values of storage modulus were higher at 33 C than at 21C. There were significant differences in G and tan delta recorded for polyether and polyvinylsiloxene materials.



2. Determining the complex modulus of alginate irreversible hydrocolloid dental material. Dental Materials, Volume 24, Issue 11, November 2008, Pages 1545-1548. Shalinie King, Howard See, Graham Thomas, Michael Swain

A Micro-Fourier Rheometer using parallel plates with varying gap size to produce a squeeze effect gave values for loss and storage moduli at 23C. Because of the squeeze mechanism, the MFR can record moduli longer than the controlled stress rheometer beyond the clinical working timeand until the alginate is completely set.

Blogger comment : The material will be setting at mouth temperature clinically so do the results have clinical relevance?

3. Surface detail reproduction of elastomeric impression materials related to
rheological properties. Dent Mater. 2008 Jul;24(7):951-6. Epub 2007 Dec 27.
German MJ, Carrick TE, McCabe JF.

A controlled stress rheometer with cone and plate geometry, gap size 0.7mm measured viscosity and tan delta of materials at 23C every 30s until the amount of set at working time allowed no further measurements(n=5). Flow of the material was also recorded using a shark’s fin test. Hydrophilicity was tested in moist gypsum casts.
Tan delta most accurately reflected flow of materials, the higher tan delta giving most accurate impressions of large detail. For smaller detail, hydrophilicty has better effect on accuracy.

2007

Working time of elastomeric impression materials: relevance of rheological tests. Am J Dent. 2007 Dec;20(6):347-52. Balkenhol M, Kanehira M, Finger WJ, Wastmann B.

Phase angle and storage modulus measured and working time determined according to ISO 4823. Dimensional accuracy was measured at 30s intervals.
For most materials, impression accuracy was constant within the manufacturers' recommended working time whereas phase angle and storage modulus changed
significantly. When determined according to ISO 4823, working
time was longer than operator-assessed working time for all materials investigated.