Dimensional stability of alginate impression materials measured by a non-pressure direct method.

Abstract

It is well known that the dimensional change occurring in an impression material is an important factor affecting the fitting accuracy of the final restoration. However, no method of directly measuring the dimensional changes in impression materials, from immediately after initial setting, with accuracy and ease has yet been firmly established. In the direct method which necessitates measurement pressure, force may be applied to impression materials which have great plasticity immediately after initial setting, and a flow may thus be created producing dimensional changes. The indirect method is more advantageous in this respect, but its measurement with the passage of time is complicated, and it is difficult to apply under clinical conditions.In the present report, a method divised by the authors for measuring changes in dimension directly, without the application of pressure, is described, and will hereinafter be referred to as the "non-pressure direct method." The method was used to measure dimensional changes in powdered alginate impression materials available on the market at 100% relative humidity and in water. Materials and MethodsThe materials used are shown in Table 1. The last letter "d" in each code means "dust -free ." Although not mentioned in the Table, VA treated with an anti-dust agent and VA with a partially changed filler were prepared. Each material was mixed with water according to the manufacturer's instructions. As for the materials for which no instruction regarding the water-to-powder ratio (g/ml) was given, each powder was weighed with a prepared measuring cup to determine its ratio.Using the pieces of equipment shown in Fig. 1, a 15-mm-tall discshaped specimen with a diameter of 30 mm was made. A steel net frame with a diameter slightly smaller than that of the specimen (Fig. 1-B) was attached to a stainless steel plate with a small piece of magnetic material buried in the center (Fig. 1-A). Over this was placed a ring of a prescribed size (Fig. 1-C), and this ring was then filled with

Effect of immersion disinfection of alginate impressions in sodium hypochlorite solution on the dimensional changes of stone models

“…It was reported that alginate impression materials which underwent small dimensional changes in water also showed small dimensional changes in sodium hypochlorite solution 21) . In our previous study 15) , the dimensional changes of ACZ, AFIII, ALF, and TOA in water were measured using a direct non-pressure method 22) . From the original dimensions of 30 mm diameter and 5 mm thickness, 1 h of immersion in water caused ACZ, AFIII, ALF, and TOA to be expanded by 92, 72, 120, and 91 µm respectively.…”

Avaliação das alterações dimensionais em modelos de gesso para protese total por meio de medição tridimensional em função de materiais e tecnicas de moldagem

“…Em relação à prótese total, foram introduzidos princípios básicos tais como pressão atmosférica, máxima extensão da área basal, equalização da pressão exercida e adaptação da prótese em harmonia com os tecidos adjacentes. Craig et al (1983) Segundo Habu et al (1986), a estabilidade dimensional do material para moldagem era um importante fator na fidelidade de reprodução do modelo de gesso, conseqüentemente, na obtenção de uma prótese bem adaptada e satisfatoriamente duradoura na cavidade bucal.…”