Force Required to Displace Pastes and Gels for Gingival Retraction

Objectives: Retraction pastes and gels are used to displace gingival tissues prior to making an impression. If pastes or gels are used without retraction cord, they must be able to effectively deflect the gingival tissue around the margin of the prepared tooth in order to ensure an accurate impression.  The better the paste or gel resists displacement, the better the gingival retraction. However, a suitable method to evaluate this displacement does not yet exist. In this study, a new in-vitro method to measure and compare the force that is required to displace retraction pastes and gels was used.

Methods: A Zwick Z020 (Zwick Roell Comp., Germany) with a brass mold (diameter 8.0mm, depth 5.6mm) and a piston (diameter 6.0mm) from brass was used as the test equipment. The mold was completely filled with paste. Then the piston was moved into the mold (drive speed 0.25mm/sec.) displacing the paste. At a penetration depth of 4.0mm the force was recorded.

The investigated materials were: Retraction Capsule (RC, #AWT-008, 3M ESPE), Expasyl (Ex, #3416, Acteon), Traxodent (Tr, #5834HMD, Premier), Hemostasyl (He, #3581, Acteon), Racegel (Ra, #B00852AC, Septodont), Gel Cord (GC, #L080122, Pascal), ViscoStat Clear (VC, #B5LLD, Ultradent).

Results: Mean values and corresponding standard deviations are shown (n=6). Data was analyzed using One-way ANOVA (p<0.05). Values with the same letters in the superscript are not significantly different.

Material	Force [N]
RC	16.7 (0.8)b
Ex	28.6 (1.7)a
Tr	3.1 (0.3)c
He	<1d
Ra	<1d
GC	<1d
VC	<1d

Conclusions: This new measurement method distinguishes between the flow resistance of various retraction pastes and gels.  He, Ra, GC, VC were too flowable to show any resistance. The resistance of Tr was slight while RC and EX showed substantial flow resistance.
In a clinical setting, only materials that are highly resistant to flow should be considered when used without retraction cord.  Low flow resistant materials should be used in combination with cord(s) to ensure adequate retraction.