Does the contact time of alginate with plaster cast influence its properties?

Abstract

The aim of this study was to verify the influence of the time of contact between alginate and gypsum after the modeling procedure on the properties of the plaster cast, such as surface detail, dimensional stability and microhardness. Thirty cylindrical specimens of orthodontic gypsum Type III were made by means of impressions of a stainless steel master model which had five reference lines in the upper surface. The samples were divided into two groups: Group 1 (G1) -with time of contact of 1 hour; and Group 2 (G2) -12 hours of contact. All the specimens were stored up to 48 hours until they underwent laboratory testing. Surface detail and dimensional stability were tested by one calibrated examiner using a visual analysis and a profilometer (Profile Projector Nikon model 6C, Nikon Corporation, Tokyo, Japan), respectively, to evaluate the quality of reproduction of the lines and the distances between them. The microhardness was determined for each sample by making six indentations with a Vickers diamond pyramid indenter (Buehler, Lake Bluff, USA) under a load of 100 gF for 15 s. The results showed significant difference (P ≤ 0.05) between groups in two of the three properties examined: surface detail and microhardness, which decreased as the time of contact rose. The 12-hour time of contact between alginate and the plaster cast is not recommended because it influences the quality of the plaster cast.

Do Ca2+-chelating polysaccharides reduce calcium ion release from gypsum-based biomaterials?

“…For this reason, calcium sulphate dihydrate is usually used in alginate/gypsum-based dental impression mixtures as this enables slower calcium ion release and a controlled alginate setting time. On the other hand, it is also known [37,38] that alginate belongs to the gypsum setting time retarders, similarly as blood, saliva and agaragar, and reduces the number of crystallisation nuclei for the dihydrate particles. Therefore, it is not surprising that the setting time of the samples containing 5% alginate was extended by 5 minutes in comparison with the compositions without alginate.…”

Effect of Contact Time Between Silicone Impression Materials and Stone on Dimensional Stability of Resultant Cast

“…Therefore, we need to discuss this issue with caution, and further studies are needed in this regard. The only similar study was done by Marquezan et al who investigated the effect of contact time (1 and 12 hours) between stone and alginate impression material, and it was found that increasing the contact time did not have any effect on the dimensional stability of the casts (8). Concerning the reasons for the difference in results between the latter and the present study can be attributed to the differences in the type of impression material used and the contact time between the stone and the impression (which were lower than the times tested in our study).…”

“…In order to make each prosthesis with good adaptation, it is important to have an accurate impression combined with a cast which has high dimensional stability (1,8). As previously mentioned, several factors are effective in producing dimensional accuracy of impressions and resultant casts.…”

Assessment of Influence of Contact Time between Alginate and Type III Dental Stone on Properties of Cast Model: An in vitro Study

“…From the results, they concluded that by expansion of the contact time between the above-said two dental materials, enhancement of hardness was achieved. The impact of the contact time between alginate and gypsum was assessed by Marquezan et al, 17 who demonstrated the techniques which affected the properties of cast models. They used 30 cylindrical stainless steel models which were used for making Type III gypsum.…”