Influence of light-curing sources on polymerization reaction kinetics of a restorative system.
OBJECTIVE
To determine the effect of using a variety of commercial light-curing units on polymerization of a dentin-bonding agent (Adper Single Bond) and of a resin composite (Filtek Z250).


METHODS
Infrared (IR) spectra were obtained kinetically at one scan/second at 2 cm(-1) resolution for a period of 5 minutes and were analyzed for: maximum conversion rate (%/s), time into exposure when maximum rate occurred (seconds), conversion at maximum rate (%), and total conversion (%) at 300 seconds by comparison of aliphatic-to-aromatic absorption IR peak ratios, before and after polymerization. Light units used were: QTH 540 mW/cm2 (XL3000); LED 750 mW/cm2 (Elipar FreeLight 2); PAC 2,130 mW/cm2 (ARC II). Exposure followed manufacturers' recommendations: dentin bonding agent for 10 seconds, RC for 20 seconds (QTH), and 10 seconds (LED and PAC). Polymerization kinetics was evaluated at the bottom surface (2.5 mm thick) for the resin composite and as a thin film for the dentin bonding agent on the diamond surface of an attenuated total reflectance accessory in the IR spectrometer. Values (n = 5) were compared using ANOVA and Tukey's pairwise post-hoc test: pre-set alpha 0.05.


RESULTS
PAC produced the highest total conversion and conversion rate for the resin composite (P < 0.05). Total conversion was lower for dentin bonding adhesive using PAC than with LED or QTH (P < 0.05). LED provided the highest proportion of conversion at the maximum rate with respect to conversion at 300 seconds for both materials. QTH demonstrated the lowest maximum rate value that occurred at a longer time into exposure (P < 0.05). Polymerization kinetic parameters varied greatly between the restorative materials as well as among light-curing unit types when compared to values observed when using a QTH light as control.
D'Alpino
Paulo H P
PH
Department of Operative Dentistry, Endodontics and Dental Materials, Hospital de Reabilitação de Anomalias Craniofaciais, Bauru Dental School, University of São Paulo, Brazil.
Svizero
Nádia R
NR
Pereira
José C
JC
Rueggeberg
Frederick A
FA
Carvalho
Ricardo M
RM
Pashley
David H
DH
D000042:Absorption; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D017220:Dentin-Bonding Agents / Q000737:chemistry* / Q000528:radiation effects; D006801:Humans; D008029:Lighting / Q000295:instrumentation*; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D013055:Spectrophotometry, Infrared; D013997:Time Factors
D003188:Composite Resins; D003764:Dental Materials; D017220:Dentin-Bonding Agents; C444701:Filtek Z250; D011108:Polymers; C115612:single bond; D017438:Bisphenol A-Glycidyl Methacrylate