Volume contraction in photocured dental resins: the shrinkage-conversion relationship revisited.
Polymerization shrinkage and degree of conversion (DC) of resin composites are closely related manifestations of the same process. Ideal dental composite would show an optimal degree of conversion and minimal polymerization shrinkage. These seem to be antagonistic goals, as increased monomer conversion invariably leads to high polymerization shrinkage values.


OBJECTIVE
This paper aims at accurately determining the polymerization volume contraction of experimental neat resins and to link it to the number of actual vinyl double bonds converted in single ones instead of, as generally done, to the degree of conversion.


METHODS
Different mixtures of Bis-GMA/TEGDMA (traditionally used monomers) were analyzed. Contraction of the polymers was determined by pycnometry and the use of a density column. DC was determined by the use of Raman spectrometry.


RESULTS
An univocal relationship has been found between the volume contraction and the actual number of vinyl double bonds converted into single ones. A contraction value of 20.39 cm3/mole (of converted C=C) was deduced from 27 measurements.


CONCLUSIONS
This relationship helps in finding solutions to the polymerization shrinkage problem. A reduction of the polymerization shrinkage due to the chemical reaction may obviously be expected from the addition of molecules allowing a decrease in the number of double bonds converted per unit volume of resin matrix, while maintaining the degree of conversion (of Bis-GMA and TEGDMA) and thus the mechanical properties. Further research will be directed at this objective.
Dewaele
Magali
M
Ecole de Médecine Dentaire et de Stomatologie, Université catholique de Louvain, Bruxelles, Belgium.
Truffier-Boutry
Delphine
D
Devaux
Jacques
J
Leloup
Gaëtane
G
D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D002244:Carbon / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D006801:Humans; D008027:Light; D008422:Materials Testing; D011092:Polyethylene Glycols / Q000737:chemistry / Q000528:radiation effects; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011109:Polymethacrylic Acids / Q000737:chemistry / Q000528:radiation effects; D013059:Spectrum Analysis, Raman; D013499:Surface Properties; D014753:Vinyl Compounds / Q000737:chemistry / Q000528:radiation effects
D003188:Composite Resins; D003764:Dental Materials; D011108:Polymers; D011109:Polymethacrylic Acids; D014753:Vinyl Compounds; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; D002244:Carbon