Recent studies have suggested that external constraint produced by adhesion may affect the magnitude of polymerization shrinkage of composites measured with certain testing modalities.  Objectives: The purpose of this study was to compare the volumetric polymerization contraction of commercial and experimental dental composites of varying filler concentration using different surface treatments to alter adhesion to the glass support in a mercury dilatometer.

Methods: The volumetric contraction of two commercial (A110 and Z100; 3MESPE) and three experimental composites (60, 70 and 80 wt% Sr glass/OX50 silica combination), all based on light-cured Bis-GMA/TEGDMA matrices, was evaluated in a mercury dilatometer (ADA Health Foundation).  Adhesion of the composite (~0.1g) to the cleaned (acetone) glass slide support was varied by treating the glass as follows: 1) air abrade/silane, 2) silane only, 3) no prep, 4) hi-vacuum grease.   Specimens were light-cured for 60 seconds (~400 mW/cm²) and contraction was monitored for 20 minutes (n=5).  Volumetric contraction (mean % ± s.d.) was compared with 2-way ANOVA/Tukey's (p≤0.05).

Results: 

	A110	Z100	80% filler	70% filler	60% filler
Air/Silane	2.32±0.04a	3.00±0.14a	3.69±0.15a	4.39±0.10a	4.98±0.16a
Silane	1.94±0.20b	3.03±0.14a	3.59±0.14ab	4.25±0.14a	4.86±0.08ab
No Prep	1.95±0.12b	2.84±0.11a	3.41±0.35ab	4.14±0.20a	4.63±0.09b
Grease	1.82±0.06b	2.07±0.09b	3.33±0.46b	3.69±0.12b	4.63±0.17b

Comparing composite shrinkage for each treatment, the order was A110<Z100<80%<70%<60% (all significantly different), verifying that volumetric contraction was inversely correlated with filler content.  The lowest shrinkage of the microfill A110 was due to the presence of pre-polymerized resin fillers.  Greased surfaces always produced lower shrinkage than Air/Silane.  Silane was equal to No Prep and Air/Silane (except for A110).  Partial debonding of the composite was evident for many of the specimens in the Grease and No Prep surface conditions.  Conclusions:  Surface treatments that improve adhesion to the glass may result in higher volumetric contractions for composites when testing in the mercury dilatometer.

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