Mrazek Prosthodontics, Ltd Naperville, IL 60563 (630) 416-9876 MPLTD4@aol.com
I think it's safe to say that we all would like to find ways to make the dentist/den-tal laboratory relationship and restora-tive results as predictable as possible. Sometimes a slight adjustment in technique or a simple timesaving tip can make a big difference in day-to-day routines. Here are a few technical tips and clinical considerations used in our laboratory that I recommend to dentists to guarantee consistent and predictable results.
Dentist Data Sheets Each of the dentists with whom our laboratory works is asked to fill out a Dentist Data Sheet (DDS) that we provide for them. The purpose of the DDS is to inform our labo-ratory of standard prescription requests for every case. Those requests include preferred alloy choice, use of occlusal stains, porcelain butt margins on all cases/anteriors only/or as requested, broad or point contacts, light or tight occlusion, and anything else the dentist requires on every case. The purpose of the sheet is to minimize the amount of information written on the prescription. Every prescription should still include essential information (the dentist's name, license number, signature, date prescription was written, due date, shade, tooth/teeth numbers, and type of restoration). If your laboratory does not provide this type of form, send your lab a list of your standard requirements with your signature for their records. It will save both you and your laboratory time, and will eliminate phone questions in the long run.
Preparation Shade Metal-free restorations are being requested with increasing frequency. When they are, it is imperative that a prep shade be included on the prescription as well as the final shade. The color of the preparation can have a direct effect upon the final hue, chroma, and value of the final restoration, especially porcelain laminate veneers. The laboratory needs to make adjustments in the shade of the restoration to compensate for dark underlying prep colors when a patient requests lighter and brighter results in the final restoration. The preparation shade can be taken with conventional shade guides or specially designed preparation shade tabs, such as Ivoclar's Stumpfa shade guide.
Posterior Quadrant Bite Registrations When restoring an entire posterior quadrant, the final restorations often require occlusal adjustments. A bite registration is generally taken after all of the teeth have been prepared. Unfortunately, the patient may over-close during the bite registration process because all of the posterior stops have been removed.
To help eliminate or at least minimize this problem, Donald Chinlund, DDS, of Crystal Lake, Illinois, and I developed a very successful technique. Before preparing any of the posterior teeth, place a strip of articulating paper in the posterior region and ask the patient to bite into centric occlusion. Locate the most posterior occlusal marking and re-mark that contact area with a permanent marker. The permanent marker will prevent the mark from washing off while irrigating during the preparation process. Prepare all of the teeth as usual, but leave that most posterior contact untouched. The contact may be a cusp tip or central fossa island. Then take a bite registration. The remaining posterior occlusal contact will prevent the patient from over-closing. If the patient did bite down in centric occlusion, there should be a hole in the bite registration material where the contact still remains. If there is no hole, the patient did not bite down correctly, and a new bite should be taken.
To verify that the hole was created by the proper centric contact and not created by an excursive contact during closing, remove the bite registration material and place a piece of articulating paper over the remaining contact point. Have the patient slowly bite down in centric occlusion once again. Remove the articulating paper and verify that a mark was made on the opposing tooth in the centric contact. Place the bite registration back on the opposing teeth. If the articulating paper mark is lined up with the hole in the bite registration, it is an accurate registration.
Once the bite registration appears correct, reduce the remaining occlusal tooth structure and take the impression. If preparing both quadrants on the same arch at the same appointment, use the same technique on the opposite side. Send the registration(s) with the impressions to the laboratory for mounting.
Packaging Bite Registrations Unfortunately, it is not an uncommon occurrence for laboratories to open a box containing a new case to find the bite registration broken into pieces, especially if it was taken with wax. A simple way to prevent this is to purchase small snack-sized zip-lock bags (half the size of the sandwich size) at the grocery store. Place the bite registration in the bag and zip it closed except for a small opening. Insert the tip of your air syringe into the bag and inflate it. Remove the air syringe and quickly zip the bag shut. The bite is now protected within its own bubble.
Packaging Face-Bows Another unfortunate occurrence is finding a face-bow for a case with its set screws loosened to fit it into a box. The ramifications of this practice are obvious. The best way to prevent this, simply package the face-bow in a separate box and pack it with Styrofoam popcorn packing material. If it is absolutely necessary to loosen the screws to fit it into a box (which should only be done as a last resort), use a fine point permanent marker to draw reference lines at the points where the face-bow rods meet. The technician needs only to realign the marker lines and tighten the set screws before mounting the maxillary cast.
A word about study casts—the word is "Yes!" Please send your laboratory study casts whenever possible, especially with anterior cases. A study cast provides a wealth of information about occlusion, contours, and incisal edge placement, and serves as a basis for any changes the patient may be requesting. A study cast of anterior provisional restorations is even more helpful when teeth are being aligned differently than the original arrangement. Oh, one more word: "bubble-wrap!"
Last but not least, I would like to bring your attention to a product that we use in the laboratory when duplicating models of diagnostic wax-ups with alginate impressions—The Alginator from Dux Dentalb. The Alginator enables us to mix the alginate to a smooth, bubble-free consistency every time. The resultant casts are clean and accurate in every detail.
In conclusion, I invite any technical tips, clinical considerations, or questions that you may have for future columns. Please submit suggestions or questions to MPLTD4@aol.com
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