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DT U.S. Edition, Nov./Dec. 2010, Vol. 5, No. 23

Industry News DENTAL TRIBUNE | Nov./Dec. 201026A dentists do not want to adjust occlu- sion, so just leave it out of contact altogether. The flaw with both of these tech- niques is there is no way to gauge how much to leave the crown out of occlu- sion so it is correct in the mouth. These techniques can never be exactly correct, and they both cre- ate problems for proximal contacts because they raise the proximal con- tact up, which makes the proximal contact shy at the delivery appoint- ment. This also creates an unstable situ- ation because that tooth can now drift either mesially or distally, creating possible occlusal interferences. The only way to have predictable, adjustment-free delivery appoint- ments is to correctly equilibrate the accurately mounted working casts. This will take a trained technician approximately five to six minutes per case. This technique should be used for all restorations whether Emax, Empress, LAVA, Cristobal+, Belle- Glass, Implants, PFM, etc. It can also be used on all partial denture cases. Anything involving nat- ural teeth, from full-arch impressions or double bite trays — this technique should be employed, always! An example of model equilibration for a #30 Centric equilibration 1) Opposing model and working models are both poured in liquid/pow- der ratio measured die stone. (Cru- cial!) 2) After mounting accurately, verify the mounting. Bite should not be taken with base plate wax but with a polyvi- nyl bite material that can be trimmed to allow only cusp tip show through. Use double-sided, Exacta-film red/ black of 19-micron thickness, use black for centric, tap models together. Notice not all teeth are in contact. 3) Initial incline contacts should be removed. Do not ever remove cusp tips. Remove only inclines, as would be done for intraoral equilibration. 3a) A black dot stable holding con- tact should be found in the fossa of adjacent teeth; #31 and #29 in this example. 3b) There should be no con- tacts found on inclines, only on cusp tips and fossa. These hold- ing contacts are found on all teeth. You can now proceed to the ante- rior guidance equilibration process. Lateral equilibration 4) There should be no change in vertical dimension of the equilibrated models in centric because this rep- licates a “power clinch” of all teeth. (Periodontal ligaments are fully depressed.) 4a) With the red side of Exacta-film, move models laterally and remove all red marks except those on canines, without removing black holding con- tacts on posterior teeth. The goal is to have black dots on all posterior teeth and red marks on the anterior teeth. 4b) At Williams Dental Laboratory, we go one step further to absolutely ensure no posterior interferences. We know all healthy teeth intrude into their periodontal ligament and move laterally. In this example, imagine the canine will move laterally 56 to 75 microns in a clinching lateral force. 4c) We safely remove approxi- mately 5 degrees off of canine disclu- sion to further “shallow” the guidance to ensure no posterior interferences. Posterior interferences must then be rechecked. Remember: the key is that lateral equilibration will not change the vertical dimension, only shallow the disclusion, further ensuring no posterior interferences. Now, and not until now, are the models ready to be utilized as an accu- rate portrayal of the mouth. This system, along with the use of a solid proximal contact model and soft- tissue model, should be employed on all cases in the laboratory regardless of material choice. DT About the author Bob Clark, CDT, LVIM, is the first and only lab technician in the world to receive mastership status with LVI. He is co-owner of Williams Dental Laboratory, a small family-operated, full- service lab located in Gilroy, Calif. He and his team have been working and training with LVI dentists for many years. Clark may be reached at (800) 713- 5390 or bob@williamsdentallab. com. AD f DT page 25A