What is Shore Hardness and what does it mean in dentistry?
Shore Hardness is a method of rating the hardness of a metal or of a plastic or rubber material. It measures penetration of a blunt indenter into a soft or elastic material and is useful for soft materials such as elastomeric materials. A lower hardness is less stiff and will feel softer or spongier to the hand, so a rubber band has a lower shore hardness than a car tire.
There are different shore hardness categories.
This is the confusing part; we use Shore A to test soft elastomers and we use Shore D to test hard elastomers.
Why is Shored Hardness important in dentistry? When do we discuss it?
Nearly all materials we use have a specific hardness that help determine when and why we use that material. A great dental example is an impression of a wax up for veneer temps or additive trial smile. I really love the trial smile and it’s incredibly helpful for patients so if you are not aware of it or utilizing it I highly recommend checking out the link about it. In the impression for the trail smile fabrication you or the lab take two impressions of the wax up. The first impression is with a higher shore hardness material and the second inner layer is a lower hardness level. The outer stiffer layer with a higher shore hardness maintains the shape and the inner layer with a lower shore hardness allows for removal despite the existence of undercuts.
We use the same idea for all PVS and PE dental impressions if you use two viscosity materials. We also consider shore hardness when looking at bite registration materials, lab putties, and night guard or mouth guard materials. Quick reminder when doing a bite registration to only place the bite registration material on the tooth preps, this assumes cast hand articulate.
The Futar line of products seem to be big on sharing their shore harness numbers.
- Futar D (pink): 30 sec. work time, 90 sec. set time, Shore D 43 hardness, Non-brittle
- Futar (green): 90 sec. work time, 90 sec. set time, Shore A 87 hardness
- Vanilla Bite: 55 sec. set time, mousse-like consistency and a Shore A Hardness of 90, medium viscosity VPS bite registration material ideal for 1-2 unit cases, vanilla scent