Volumetric Polymerization Shrinkage Characteristics of Provisional Crown & Bridge Materials

Different test methods exist to measure polymerization shrinkage of dental filling materials. However, determination of total polymerization shrinkage for chemically cured materials, which must be mixed together, is challenging since the initial starting volume cannot be determined with absolute accuracy. Objectives: The objective of this study was to use the Archimedes method in order to evaluate the volumetric polymerization shrinkage characteristics for nine chemically cured provisional crown & bridge materials. Methods: The Archimedes principal was used to evaluate the clinically relevant shrinkage (starting from the approximate end of the working or mixing time) and the theoretical (calculated) polymerization shrinkage. Six paste: paste (P:P) and three powder: liquid (P:L) products were tested. One percent of sodium lauryl sulphate was used as the buoyancy medium. The density of the mixed base and catalyst was measured at one minute after the start of the mix. The theoretical shrinkage could only be determined for the paste-type base and catalyst materials. The densities of the polymerized pastes were measured at 24 hours after mixing. Six specimens (n=6) of each material were tested. Results: The clinical and theoretical shrinkage of all tested materials are summarized in the table below. One-Way ANOVA (p<0.05) was performed to determine statistical significance.

Material	Manufacturer	% Clinical Shrinkage	% Theoretical Shrinkage	Shrinkage Ratio (Theoretical/Clinical)
Temphase (P:P)	Kerr	4.11 ± 0.18 a	4.76 ± 0.08 d	1.16
Protemp Plus (P:P)	3MESPE	4.59 ± 0.16 b	4.83 ± 0.31 d	1.05
Turbo Temp 2 (P:P)	Danville	4.79 ± 0.23 b	6.69 ± 0.27 e	1.40
CB Temp (P:P)	J.Morita	4.81 ± 0.15 b	5.65 ± 0.10 f	1.17
Luxatemp (P:P)	DMG	4.88 ± 0.22 b	5.64 ± 0.22 f	1.10
Integrity (P:P)	Dentsply	4.93 ± 0.18 b	5.49 ± 0.26 f	1.11
Jet Tooth (P:L)	Lang	5.40 ± 0.23 c	N/A	N/A
Alike (P:L)	GC Inc.	5.70 ± 0.26 c	N/A	N/A
Snap (P:L)	Parkell	5.83 ± 0.29 c	N/A	N/A

Values with the same superscripts are not statistically different (n=6).

Conclusions: This study showed the difference between theoretical (calculated) and clinical shrinkage, which was less for all the materials tested. Shrinkage ratios between the clinical and theoretical values were fairly consistent for the materials tested.