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Welcome back! This month’s tip involves choosing the proper impression material relative to the desired prosthetic result. Many dentists have asked me how I can justify the high expense of using the same impression material for both the prosthetic and the opposing arches. It is well known that the costs of prosthetic materials are much greater than those of simple alginates for opposing arches that need less accuracy.
In my personal clinical environment, I send all impressions to my prosthetic technician, thus eliminating the need to hurry and pour the opposing model. A survey done by Dental Economics® in 2005 determined that the time it takes to pour a model and clean up all the mess ultimately costs more than sending the impression out to a lab. I have personally tested this theory in my own practice and found it to be true, and it also lessens the chances of getting unwelcome bubbles in places that might make the bite less than desirable.
Most practitioners that I have encountered agree that the convenience of sending all of their impressions to their lab technicians allows their assistants more time for performing patient care. My own assistants seem to function more efficiently (and more willingly) under conditions in which laboratory detail essentials are held to a minimum.
I will now go through the protocol that I adhere to for the selection of the correct impression material in order to achieve the desired prosthetic result, while preventing the costs of materials from getting out of control. A prosthetic restoration involving tooth structure, full or partial edentulous arches that need tissue stability, or functional peripheral perimeters will mandate a material with several viscosities and high hydrophilicity to capture tissue and hard surfaces in full dentures and combination cases (i.e., implant overdentures).
- In the case of the maxillary overdenture, I use a stock thermoplastic tray (the Strong-Massad Denplant® Tray, www.GDIT.US) and heat-mold to the ridge area and implant surfaces. Then, using a rigid viscosity PVS (Aquasil Ultra Rigid, Dentsply Caulk), a small layer is injected into the tray trough and seated (acting as a stop), and then I center the implants within the middle of the tray trough. Following this step, I apply rigid viscosity PVS to the borders, and functional molding is performed.
- Next, a light viscosity PVS is injected around implant fixture level impression copings and placed into the tray, and then the border molding is repeated. The final impression is now ready for casting with the analogs in place. This final cast will have satisfied all of the requirements for the functional, mucostatic, and implant surface definitive cast for optimal accuracy.
- While the hydrophilic, multiviscosity PVS materials are warranted for prosthetic appliance accuracy in many areas, the opposing model generally requires tooth surfaces only. In the case of the fully dentate on the opposing arch, the thermoplastic tray should be heat-shaped to fit the arch, and a small amount of rigid viscosity PVS should be placed in the trough of the tray in order to center the teeth, thus allowing an even amount of material to flow around all surfaces.
- Now, a single medium viscosity PVS (Algin.XTM Ultra Algin, Dentsply Caulk) is injected into the tray and placed back into the mouth until the practitioner can feel the stops. The stops eliminate movement of the tray with the softened PVS until set. No border molding is necessary and the total working set time is only 2½ minutes. The benefits in this case are:
1. a very predictable two-step impression
2. cost is approximately half that of the hydrophilic, multiviscosity, prosthetic PVS.
Same time, easy procedure, no office pour-up … and all this equates to cost savings.
Today, we must provide dentistry in less time, with less effort and frustration, while decreasing the cost of materials, in order to protect our personal overall health while delivering excellent dentistry.
I hope this tip will help you as much as it has me, and that it will increase your pleasure in providing dental care. For a full video step-by-step version, go to www.dentistryiq.com. See you next month. I hope my pleasure in dentistry will also be yours ... Joe Massad.
Dr. Joseph Massad may be reached by phone at (918) 749-5600 or by e-mail at email@example.com.