The application of magnetic resonance microimaging to the visible light curing of dental resins. 3. Stray-field nuclear magnetic resonance imaging (STRAFI).
OBJECTIVE
To investigate the application of stray-field nuclear magnetic resonance imaging (STRAFI) to the visible light curing of dental restorative materials. STRAFI can overcome peak broadening associated with the conventional magnetic resonance microimaging (MRM) of glassy polymers, and has the potential to image dental restorative resins at both low and high degrees of conversion.


METHODS
Cylindrical composite specimens were light-cured from one end to produce some that were fully cured throughout their length and others that were fully cured at one end and uncured at the other. A one-dimensional probe was used to measure the magnetisation in 40 microm thick slices at 100 microm intervals along the length of the specimen. A quadrature pulse sequence was applied and the magnetisation decay recorded in a train of eight echoes.


RESULTS
A value for T(2) could be obtained only for the polymer (59+/-16 microms), therefore the echoes were summed to give an approximate indication of the degree of conversion. The echo sum for the monomer was significantly higher than that for the polymer. Differences in composite shade and cure time produced changes in the cure profiles.


CONCLUSIONS
STRAFI produced measurements for both monomer and polymer in all stages of conversion that allowed cure profiles to be produced. Summing the decay echoes produced a qualitative measure of the condition of the material in the selected slice. The same data can be used to calculate T(2), a quantitative parameter. This first investigation has demonstrated that STRAFI is well suited to polymerisation studies.
Lloyd
C H
CH
Dundee Dental School, University of Dundee, Dundee DD1 4HN, Scotland, UK. c.h.lloyd@dundee.ac.uk
Scrimgeour
S N
SN
Lane
D M
DM
Hunter
G
G
McDonald
P J
PJ
D000465:Algorithms; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003116:Color; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D006244:Hardness; D006801:Humans; D006859:Hydrogen; D008027:Light; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation / Q000379:methods*; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011138:Polytetrafluoroethylene; D013997:Time Factors; D014520:Urethane / Q000737:chemistry / Q000528:radiation effects
D003188:Composite Resins; D003764:Dental Materials; D011108:Polymers; C056413:Occlusin; D014520:Urethane; D006859:Hydrogen; D011138:Polytetrafluoroethylene