Dimensional changes of resin/ionomer restoratives in aqueous and neutral media.
OBJECTIVE
The aim was to study dimensional time-dependence of resin/ionomer formulations from 5 min age to one month and to separate out the intrinsic setting shrinkage and hygroscopic expansion effects, by using non-aqueous and aqueous storage media, respectively.


METHODS
Materials studied included: A: resin-, B: metal- and C: polyphosphonate-modified glass-ionomer cements [GICs]; and controls of D: poly-acid modified composite [compomer]; and E: resin-composite. Separate specimen groups (n = 5) were stored in different storage-media: (i) silicone fluid; (ii) de-ionized water. Experiments were repeated at 23 and 37 degrees C. Volumetric changes of specimens (4 mm diameter x 6 mm height) were obtained via accurate mass measurements (to 10(-4) g), using Archimedes principle, with silicone or water also used as the Archimedean fluid. These measurements were made periodically over a 30 day period, post fabrication.


RESULTS
In silicone at 23 degrees C, all materials underwent further gradual intrinsic shrinkage (after 5 min from mix). This was highly significant (p < 0.05) for the RM-GIC (A). At 37 degrees C, however the RM-GIC expanded, indicating that its cure is temperature-sensitive. In water, at 23 and 37 degrees C, the shrinkage was either partially offset (materials C, D, E), or replaced by appreciable expansions (materials A and B). Differences between RM-GIC (A) and MM-GIC (B) were significant (p < 0.05).


CONCLUSIONS
The deployment of dual storage media made an important contribution to the separate analysis of the volumetric changes due to the on-going setting chemistry in these systems and the time-dependent effects of an aqueous environment.
Watts
D C
DC
University of Manchester Dental School, Higher Cambridge Street, Manchester M15 6FH, UK. david.watts@man.ac.uk
Kisumbi
B K
BK
Toworfe
G K
GK
D000704:Analysis of Variance; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D020770:Compomers / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D003793:Dental Restoration, Permanent; D005899:Glass Ionomer Cements / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008422:Materials Testing; D008670:Metals / Q000737:chemistry; D008689:Methacrylates / Q000737:chemistry; D010755:Organophosphates / Q000737:chemistry; D009943:Organophosphorus Compounds / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D012117:Resins, Synthetic / Q000737:chemistry; D017640:Silicates / Q000737:chemistry; D012822:Silicon Dioxide; D012828:Silicones / Q000737:chemistry; D013223:Statistics as Topic; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry; D015040:Zirconium
D020770:Compomers; D003188:Composite Resins; C088486:Dyract; C079765:Fuji II LC cement; D005899:Glass Ionomer Cements; C106661:Hi-Dense; D008670:Metals; D008689:Methacrylates; D010755:Organophosphates; D009943:Organophosphorus Compounds; D019279:Resin Cements; D012117:Resins, Synthetic; D017640:Silicates; D012828:Silicones; C083568:Z100 composite resin; C119822:glass poly(vinylphosphate)cement; D014867:Water; C020477:polyphosphonate; D012822:Silicon Dioxide; D015040:Zirconium