Effects of solvents on the early stage stiffening rate of demineralized dentin matrix.
OBJECTIVE
To monitor the stiffening rate of demineralized dentin matrix at the early stages after exposure to different neat solvents.


METHODS
Dentin beams approximately 0.8x0.7x8.0 mm were obtained from human third molars. After covering their ends with resin composite, the middle exposed length of 4.0mm (gauge-length) was demineralized in 0.5 M EDTA (pH 7.0) for 7 days. The specimens were gripped by a testing machine, pre-loaded to 10 g and cyclically stressed in tension to 5% strain, for 30 repeated cycles (total 20 min) at 0.6 mm/min while immersed in water (control). Then, water was replaced by either 100% acetone, methanol, ethanol, propanol, HEMA or air and the specimens subjected to the same cyclic protocol. The maximum apparent modulus of elasticity (E(Max)) was calculated for every cycle, plotted as a function of time and subjected to regression analysis. Stiffening rate was calculated as changes in E (min). Regression analysis examined the relationship between E and time for each solvent. Data were analyzed by one-way ANOVA and Student-Newman-Keuls test at alpha=0.05.


RESULTS
Regression analysis showed that E increased significantly with time in all water-free solvents (R2=0.8-0.99). Stiffening rate was higher for acetone (0.9 MPa/min) and ethanol (0.8 MPa/min), intermediate for air (0.7 MPa/min), methanol (0.6 MPa/min) and propanol (0.5 MPa/min), lower for HEMA (0.2 MPa/min) and practically none for water (0.07 MPa/min) with p<0.05.


CONCLUSIONS
The solvent-induced stiffening rate of demineralized dentin matrix is both time and solvent-dependent. The ability of solvents to promptly stiffen the demineralized dentin matrix may be important in maintaining the resin-infiltrated matrix expanded during the solvent evaporation stage of resin bonding.
Garcia
Fernanda C P
FC
Department of Operative Dentistry, Endodontics and Dental Materials, Bauru School of Dentistry, University of São Paulo, São Paulo, Brazil.
Otsuki
Masayuki
M
Pashley
David H
DH
Tay
Franklin R
FR
Carvalho
Ricardo M
RM
D000433:1-Propanol / Q000494:pharmacology; D000096:Acetone / Q000494:pharmacology; D000388:Air; D000704:Analysis of Variance; D003094:Collagen / Q000737:chemistry; D003799:Dental Stress Analysis; D003804:Dentin / Q000187:drug effects*; D003808:Dentin Solubility; D004548:Elasticity / Q000187:drug effects; D000431:Ethanol / Q000494:pharmacology; D006801:Humans; D008689:Methacrylates / Q000494:pharmacology; D000432:Methanol / Q000494:pharmacology; D012044:Regression Analysis; D012997:Solvents / Q000494:pharmacology*; D018709:Statistics, Nonparametric; D013718:Tensile Strength / Q000187:drug effects; D013997:Time Factors; D017001:Tooth Demineralization / Q000473:pathology*
D008689:Methacrylates; D012997:Solvents; D000096:Acetone; D000431:Ethanol; C005044:hydroxyethyl methacrylate; D003094:Collagen; D000433:1-Propanol; D000432:Methanol