0033 Competition Between Acid-base and Polymerization Reactions in a Resin-modified Glass-ionomer
S. ABEY1, D.W. BERZINS1, and H.W. ROBERTS2, 1Marquette University, Milwaukee, WI, USA, 2USAF Dental Evaluation and Consultation Service, Great Lakes, IL, USA

Resin-modified glass-ionomers (RMGI) set by at least two mechanisms and each is dependent upon reactant diffusion prior to gelation.  The kinetics and extent of each setting reaction/mechanism may rely on and/or compete with the other.  Objectives: To investigate possible RMGI setting reaction interactions using differential scanning calorimetry (DSC) by varying visible light activation (VLC) initiation times after mixing. Methods:  GC Fuji II LC was mixed per manufacturer's instructions, placed in an aluminum crucible, and transferred to a DSC at 37oC with VLC (20 seconds) occurring immediately or at 5 or 10 minutes after mixing.  Another group (Dark cure) was evaluated without VLC.  The VLC polymerization and/or acid-base reaction exotherms were monitored for 30 minutes followed by a forward and reverse DSC dynamic scan between 37 and 240oC.  The scan produced an endotherm that served as a relative indicator of glass-ionomer/resin material character.  Finally, a 15 minute 37oC isothermal was conducted to determine VLC thermal energy input.  Results were analyzed with ANOVA/Scheffe (a=.05). Results:   The mean and standard deviation for each group/parameter are listed (n=10).  Within each parameter, different letters denote significant (p<0.05) differences exist.

 

Group

VLC Reaction

Exotherm (J/g)

Acid-Base Reaction Exotherm (J/g)

Dynamic Scan Endotherm (J/g)

Peak Temp During Endotherm (oC)

Immediate VLC

43.7±8.1 A

Not Detected

-19.8±3.5 AB

199.4±15.9 A

5 min VLC delay

32.8±7.5 B

4.8±1.8 A

-24.7±8.9 BC

157.4±5.7 B

10 min VLC delay

19.6±9.1 C

5.8±2.3 A

-32.1±5.6 CD

146.8±3.3 B

Dark Cure

N/A

6.4±1.5 A

-36.1±9.4 D

148.6±4.4 B

As time allowed for the acid-base components to react increased, the extent of VLC reaction exotherm decreased.  Conversely, dynamic DSC data suggest earlier beginning times of light polymerization may limit the acid-base reaction. Conclusion:   Results indicate RMGI acid-base and light polymerization reactions compete and possibly inhibit one another during early RMGI development.

Seq #12 - Glass Ionomers, New Resins and Composites, Photocuring
2:30 PM-4:00 PM, Wednesday, March 21, 2007 Ernest N. Morial Convention Center 391

Back to the Dental Materials: V - Polymer Materials-Chemistry Program
Back to the IADR/AADR/CADR 85th General Session and Exhibition (March 21-24, 2007)

Top Level Search