Effect of adhesion to cavity walls on the mechanical properties of resin composites.
OBJECTIVE
To evaluate the regional mechanical properties of resin composite under free and constrained conditions during polymerization.


METHODS
Forty cavities (8mm diameter and 5mm depth) were fabricated in resin blocks. Half of the cavities were bonded and the other half left un-bonded. The cavities were bulk-filled with one of the following composites: flowable composite (Palfique Estelite LV, Unifil Lo Flo), and Universal composites (Clearfil AP-X, Palfique Estelite Sigma), followed by photo-curing for 30s. After 24h storage, each specimen was sliced parallel to the long axis to harvest three slabs. The middle slab was serially sliced to harvest five sticks, which were trimmed to an hour-glass shape for measurement of regional ultimate tensile strength (UTS). The remaining semi-circular slabs were polished for microhardness measurement (KHN). Data were analyzed using three-way ANOVA followed by Tukey's HSD test and t-test (alpha=.05).


RESULTS
The KHNs of all the resin composites were not significantly different between the bonded and unbonded groups at each cavity depth (p>0.05). The Ucapital TE, CyrillicS of the bonded group of flowable composites was significantly lower than those of the un-bonded group at the upper regions (p<0.05), while for universal composites, there were no significant differences in UTS between the bonded and un-bonded groups (p>0.05), although Clearfil AP-X had a trend toward lower UTS under the constrained condition at the upper regions.


CONCLUSIONS
The UTS of resin composite decreases due to polymerization shrinkage stress when polymerized under a constrained condition, however, these effects were dependent upon regions in the cavity and the resin materials.
Nayif
Ma'an M
MM
Cariology and Operative Dentistry, Department of Restorative Science, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-Ku, Tokyo 113-8549, Japan. nayif.ope@tmd.ac.jp
Nakajima
Masatoshi
M
Aksornmuang
Juthatip
J
Ikeda
Masaomi
M
Tagami
Junji
J
D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects; D001840:Dental Bonding; D003737:Dental Cavity Preparation; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis; D006244:Hardness; D008027:Light; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D044367:Phase Transition; D011109:Polymethacrylic Acids / Q000737:chemistry / Q000528:radiation effects; D019279:Resin Cements; D013314:Stress, Mechanical; D013718:Tensile Strength; D000267:Tissue Adhesions
C112828:Clearfil AP-X; D003188:Composite Resins; D008689:Methacrylates; D011109:Polymethacrylic Acids; D019279:Resin Cements; C501418:Unifil LoFlo Plus; C086113:palfique estelite