Notes on the Mixing & Handling of MTA
All current formulations of MTA (grey and white, ProRoot and Angelus) are presented as a powder and liquid for manual mixing.
Generally, the sachets and vials contain more powder than needed for a single case, and because the powder will deteriorate on contact with moist air, it is wise to dispense the contents of sachets which cannot be re-sealed into a small air tight vessel.
Mixing:
In common with other Portland cements, the setting process is a complex hydration reaction, requiring that all of the particles are thoroughly mixed with water before application. This must be balanced with the need to produce a mix which is easy to carry and pack into the repair-site.
- Always shake the powder well before dispensing to ensure an even distribution of powder particles and correct handling behaviour.
- After assessing the size of the repair, dispense an appropriate volume of powder into a dappens dish or onto a mixing slab. A drop of sterile water is then gradually incorporated into the powder with a spatula, ensuring full wetting of the powder particles. Thorough wetting can take 30s.
- A clay-like consistency is usually the most straightforward to carry and pack. If the mix is too dry, add a little more water; if it is too wet, remove excess water by 'tapping' the surface of the mixed material with an absorbent cotton role or tissue, trying to avoid fibre incorporation.
- The material is highly prone to drying and becomes crumbly as water is lost by evaporation. This is especially true if the material is mixed on a slab. Evaporation can be minimised by overlaying the mixed material with a moist gauze, but if the material does dry, simply add more water and manipulate as before to get the correct stiffness for the task in hand.
| John Whiteworth PhD, BChD, FDS RCS Ed, FDS RCS (Rest Dent) Senior Lecturer / Consultant in Restorative Dentistry (Endodontics) |