Understanding Lab Putty

Lab putty is the dental material's version of baseball’s utility player. In the lab, it can be used for a variety of applications like restorative space analysis, as a matrix for provisional fabrication or as a guide for the fabrication of definitive restorations. The usefulness extends into clinical applications as well – for instance, chairside space analysis and as a matrix for direct restorations.

What is Lab Putty?

Lab putty is a silicone impression material and falls into the more general category of elastomeric impression materials. Lab putties may be differentiated by their chemistry:

Condensation reaction silicones irreversibly cure leaving ethyl alcohol as a by-product and aren’t meant to polymerize intra-orally. The reaction and the by-product can lead to polymerization shrinkage, so this kind of material is generally packaged with a highly filled putty base and a lower viscosity catalyst activator. The highly filled putty base has less polymer and results in less polymerization shrinkage. Examples of this type of lab putty are Sil-Tech (Ivoclar Vivadent) and Lab-Putty (Coltene/Whaledent). Some users report skin irritation from the catalyst and recommend using gloves while mixing this type of lab-putty. Latex gloves have been implicated in interference of the setting reaction so a different glove material is suggested.

Addition reaction silicones are familiar to restorative dentists as cartridge dispensed polyvinylsiloxane (PVS) impression materials. When used as lab putty, this type of material is packaged as two high viscosity putties. The base and the catalyst are differentiated by color and the two are mixed by hand until a homogenous, streak free mass is achieved. As with condensation reaction silicone, sulfur contamination from natural latex gloves can inhibit the setting reaction of addition reaction silicones and alternatives should be used if desired. Examples of addition reaction lab putty are Flexitime (Heraeus-Kulzer) and Matrix Form (Anaxdent North America).

Lab Putty: Are They All the Same?

Yes and no. Every kind of lab putty can be stretched or compressed slightly while maintaining the ability to rebound without permanent deformation. All lab putties have a reasonable setting time, are dimensionally very stable and highly accurate in detail reproduction.

There are some differences in handling, due mostly to differences in tear strength and resistance to abrasion, but one of the main differences between lab putties is the difference as measured by Shore hardness. Hardness refers to an elastomer's resistance to permanent indentation and is usually measured with a device called a durometer.  Lab putty with a lower Shore hardness may feel softer or spongier to the hand. As an example, imagine the difference between a rubber band and a car tire. In this scenario the rubber band would have a lower Shore hardness than the car tire. Lab putty with lower Shore hardness will demonstrate lower stiffness. As a result, less force is required to remove the material from undercuts. This can be especially helpful around delicate diagnostic wax-ups or trial dentures.

Unfortunately, decreased stiffness may allow the lab putty to be easily deformed while used as a provisional matrix. One solution is to use low Shore hardness putty around the wax up and higher Shore putty to reinforce the matrix. Remember: not all lab putties are compatible with each other. If you want to combine different layers of putty its recommended to stay within one manufacturer’s product family.

References:

1. Anusavice, K. (2003). Phillips' Science of Dental Materials, 11th ed. St. Louis: Elsevier.
2. Finger, W., & Komatsu, M. (1985). Elastic and plastic properties of elastic dental impression materials. Dental Materials , 1 (4), 129-134.