Rheological properties of elastomeric impression materials for selective pressure impression technique.
OBJECTIVE
The selective impression technique is recommended for removable prosthodontics. However, the viscoelastic rheological properties of impression materials, particularly the time-dependent viscoelastic changes in impression material immediately after tray seating, are unknown. The objective of this study is to clarify the viscoelastic rheological properties of impression materials by focusing on tray seating.


METHODS
In this study, eight types of polyvinylsiloxane (PVS), two types of polyether, and two types of alginate impression materials were used. The storage modulus (G'; degree of stiffness) and loss tangent (tanδ; degree of hardening) were determined as functions of time from 0 to 360 s, commencing immediately after the completion of mixing, using a stress control-type rheometer. Thus, G' and tanδ at 0s and 20 s were compared.


RESULTS
Stiffness was found to be widely distributed (4.49-0.26 × 10(4)Pa) among PVS-types, even immediately after mixing the impression material. There was also variation among polyethers (1.55-0.5 × 10(4)Pa) and among alginates (0.64-0.21 × 10(4)Pa). The hardening of all impression materials progresses beyond 20 s after the completion of mixing.


CONCLUSIONS
The G' values varied with each impression material, even immediately after mixing, and the accurate impression-taking time was determined from the results of tanδ. These results provide unique insight into the selective impression technique.
Department of Oral Function and Rehabilitation, Nihon University School of Dentistry at Matsudo, Japan. Electronic address: kawara.misao@nihon-u.ac.jp.
Misao
M
Kawara
Nihon University Graduate School of Dentistry at Matsudo, Japan.
Masatoshi
M
Iwasaki
Nihon University Graduate School of Dentistry at Matsudo, Japan.
Yoshihiro
Y
Iwata
Nihon University Graduate School of Dentistry at Matsudo, Japan.
Yoshihiro
Y
Komoda
Nihon University Graduate School of Dentistry at Matsudo, Japan.
Sayumi
S
Inoue
Department of Oral Function and Rehabilitation, Nihon University School of Dentistry at Matsudo, Japan.
Osamu
O
Komiyama
Department of Oral Function and Rehabilitation, Nihon University School of Dentistry at Matsudo, Japan.
Hiroshi
H
Suzuki
Department of Oral Function and Rehabilitation, Nihon University School of Dentistry at Matsudo, Japan.
Toshikazu
T
Kuroki
Laboratory of Physical Chemistry, School of Pharmacy, Nihon University, Japan.
Kaname
K
Hashizaki
D000464:Alginates; D003760:Dental Impression Materials; D003761:Dental Impression Technique; D004548:Elasticity; D004987:Ethers; D008422:Materials Testing; D012212:Rheology; D012826:Silicone Elastomers; D013997:Time Factors; D014783:Viscosity
D000464:Alginates; D003760:Dental Impression Materials; D004987:Ethers; D012826:Silicone Elastomers
Dynamic viscoelasticity; Impression materials; Removable denture; Rheological properties; Selective pressure impression