FROM the ARCHIVES Laboratory Procedure How To Process a Mach-2 Laminar Impression ® Bonding agents for the befuddled, the confused, the technique-challenged, and everyone else – By Rod Kurthy, D.M.D., and Paula Kim, C.D.T. O Introduction (Dr. Kurthy) ver the past two years I’ve authored several articles concerning the Laminar Impression Technique. In a nutshell … Before tooth preparation, I take a preliminary impression using Super-Fast BluMousse® in a sideless double-arch tray. After the teeth have been prepped, 2 holes are drilled one mesial and one distal to each prep. The impression is reseated and a flowable wash is injected into the holes. I learned about the Laminar Impression from its creator, Dr. Gary Schoenrock (Perrysburg, OH). At first I was highly skeptical. I couldn’t believe any technique that used disposable double-arch trays could produce 1st-class crowns. Boy, was I ever mistaken! Not only was the fit as good or better than I’d previously been getting, but the time required to impress a typical patient dropped substantially. My contribution to the Laminar Technique was the use of a very flowable, extremely hard-setting material (Mach-2® “die silicone”) for the injection-step. When intercuspation is good, much of the side-to-side strength of an impression comes from the wash material - not the Blu-Mousse. In my judgment, a traditional light-body wash produces an impression that’s too flexible. It’s prone to distortion either from “snap-back” when removed from the mouth or from mishandling at the lab. When I switched to Mach-2 for the injection wash, the crown adjustments went from “rare” ... to “nonexistent”, and the margins became so good I couldn’t even feel them with a hand instrument.* For more info about the Mach-2 variation of the Laminar Technique, see Parkell Special Report #28 or visit Parkell’s website (www.parkell.com). Almost as gratifying as the improvement in my crowns is the feedback I’ve received from other dentists who’ve read my articles. They’re reporting exactly the same results I’ve experienced. (And this from a technique that slashes 10 minutes or more off the typical impression procedure!) However, a few dentists have reported some initial resistance from their laboratory. Sometimes the technician has been burned by other double-arch techniques. Even experienced laminar technicians can be perplexed by that super-stiff wash, because it requires a number of changes to the traditional laminar lab technique. So I thought it might be helpful if I asked Paula Kim, CDT (owner - Aspen Dental Laboratory), to describe how she and her crew fabricate a crown using one of our impressions. This article follows a single case from impression, through fabrication and the postinsertion radiograph ... documenting each step of the process. We’re not proposing that this is the only way to handle a Mach-2 laminar impression ... but it’s a technique that works consistently well for us. Incidentally, here in California, qualified Extended-Functions RDAs (or “EFRDA”s) can legally take impressions. So this laminar impression was taken by my very-talented assistant, Manuela “Nellie” Vargas. She did everything from packing the cord to injecting the Mach-2. As I’ve mentioned in prior articles, I always make a small 3-unit trayless impression as a backup. I hardly ever need it, but it’s good insurance in case something horrible happens at the lab. Besides, since the tissue is already retracted, the backup adds only a minute to the total procedure. (If you’re interested in the back-up technique, ask for Parkell Impression Newsletter #14 or see the step-by-step illustrated (Fig. 1) Here’s what Dr. Kurthy sends to the lab: A standard workorder ... the laminar working impression ... plus the trayless backup. technique at Parkell’s website – (www.parkell.com) The Laboratory Technique (Paula Kim, C.D.T.) Traditional Laminar Impressions are extremely accurate, but they share one thing with other double-arch techniques. They must be handled with kid gloves in the laboratory to avoid distortion (See sidebar page 3). From the technician’s point of view, one of the nice things about the Mach-2 modification to the laminar technique is the increased strength. Dr. Kurthy’s Laminar impressions are substantially more robust than most impressions taken with a conventional flexible wash. This permits us to process the model more like a traditional quadrant impression. IMPORTANT: Careful trimming of both the impression and the excess stone is critical to processing a Mach-2 Laminar Impression. Some technicians have difficulty creating multiple pours from a * To learn more about the Laminar Technique in general see Dr. Schoenrock’s Video. MDEG 6920 Springvalley Dr. Suite 103, Holland OH 43528, 419866-1238, FAX 419-866-1907. Or go to the “Tech Articles” section of www.parkell.com © 2011 Parkell, Inc. • Toll Free: 1-800-243-7446 • Visit www.parkell.com • Email: [email protected] 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 (Fig. 2) The first step is to carefully inspect the impression to be certain that Dr. Kuthy didn’t screw up (Kidding). Notice there is virtually no Mach-2 wash outside the prep area. This is important. If a film of wash covers the proximal teeth, don’t even bother pouring the model. That film indicates that the pressure of laminar injection caused the bite to open slightly and the patient did not return to centric before the Mach-2 set. A crown made using that impression will be high. (Fig. 3) We then carefully trim the impression. This makes it easier to handle. But more important, after the excess Blu-Mousse is trimmed, the model will be much easier to remove without damaging either model or impression (Fig. 4 & 5) We box the impression and pour. When the stone has partially set, we use a lab knife to remove the overpour. We do this for the same reason we trimmed the excess BluMousse: to prevent lock-on. Remember, in the Mach-2 laminar technique the impression is almost as hard as the stone. (If it locks on, you’re going to have to cut the impression off to avoid breaking teeth.) (Fig. 6) After the stone has completely set, we carefully remove the model. Despite this care, the rigid Mach-2 may tear in the thin proximal areas. Don’t worry. This won’t pose a problem. This is our working model. (Fig. 7) The working model base is trimmed, drilled and pinned. Fig. 8 Fig. 9 Fig. 10 Fig. 11 Fig. 12 Fig. 13 (Fig. 8) The opposing side of the impression is poured in exactly the same fashion. (The excess stone is trimmed when partially set, etc., etc.) (Fig. 9) The bases of the upper and lower working models are poured ... (Fig. 10) The models trimmed ... (Fig. 11) … and the die separated and ditched. (Fig. 12) We can use either the working model or the solid model for articulation. In this case we used the pinned working model. (Fig. 13) We apply a moderate coat of die spacer (Kerr), taking care to keep it short of the margin. Fig. 14 Fig. 15 Fig. 16 (Fig. 14) The models are carefully placed back into the impression for articulation ... and mounted using the laminar impression for registration. (At this stage it may be necessary to trim interproximally to facilitate reseating.) The type of articulator we use isn’t determined by the impression technique, so that’s the dentist’s call. (Fig. 15) The pattern is waxed ... (Fig. 16) …cast ...and the coping is fitted to the die. 2 Enjoy this article? Visit our article archive to download other free technique articles. And what if the dentist uses a flexible wash? by Paula Kim, CDT Here’s how to process a laminar impression if the dentist doesn’t use Mach-2 for the injection. Except for the meticulous care we take during trimming, our lab technique for a Mach-2 Laminar Impression is almost identical to our standard model procedure. However, if a conventional light-body material is substituted for the Mach-2 injection step, the impression will be more prone to distortion during pouring and handling.* Here the lab should use a different technique. Most of these hints were first printed by Dr. Schoenrock in the Interface Newsletter (May/June ‘94).** • Pour the counter side of the impression first. The stone reinforces the impression so the die-side can be manipulated with less chance of distortion. (Fig. 17 & 18) Our ceramist builds and fires the porcelain. (Fig. 19) We seat the crown on our proximal check model to confirm the contacts ... and on the model from the back-up impression to confirm the margins (shown here). If the crown fabricated from one impression fits the model from another impression – we can pretty much guarantee that it will fit in the mouth. The crown plus all the models are sent to Dr. Kurthy. (The articulated models are always still mounted on the articulator.) (Fig. 20) At the cementation appointment, the crown slides home without adjustment. (Fig. 21) The post cementation radiograph shows the kind of marginal fit that’s typical with this Mach-2 Laminar technique. • Pour both sides of the impression and articulate before removing the models from the impression. This is recommended procedure for most double-arch impressions ... and it’s the rule most frequently ignored by labs. That’s because it means setting their pin heads in unset stone using the old “bobby-pin” technique. If you simply MUST drill dowel pin holes, pour your working model - VERY carefully remove it - then pour a second model which you leave in the impression for articulation. There are two downsides to this approach. (1) You may distort the flexible impression when removing the first impression. (2) Your working model won’t be articulated. As a result, during fabrication you’ll have to repeatedly switch back and forth between the working model and the articulated model. Dr. Schoenrock makes other good recommendations which don’t specifically apply to the laminar technique (e.g. Trim dies carefully and harden them with cyanoacrylate, never alter casts, always return cases mounted on the articulator, etc.) * And if the dentist ever sends a laminar impression with the primary impression taken using conventional heavy-body PVS (NOT Blu-Mousse or something approaching it), SEND IT BACK. Or at least make it clear that you will not assume responsibility for the fit. ** Midwest Dental Evaluation Group. INTERFACE. 6:33, May/June, 94. Interface $51 per year. MDEG 6920 Springvalley Dr. Suite 103, Holland OH 43528, 419-866-1238, FAX 419-866-1907 Blu-Mousse impression without damaging either the impression or the model. I suspect they’re not adequately trimming. I’m a big fan of Dr. Kurthy’s 3-unit backup impression, and I encourage my other accounts to emulate his technique. Things can happen at even the most careful lab that damage the primary impression. If this occurs, having a small backup impression eliminates the need to contact the dentist and have the patient rescheduled simply to take another impression. As you’ll see, we’ve incorporated the backup impression into our standard technique for Dr. Kurthy’s cases, and it’s improved our fit-checking ability. Ideally, our C&B technique requires three models – at minimum, two models. 1) A working model 2) A solid model to check the proximal contacts, and 3) Another solid model to confirm the marginal fit. © 2011 Parkell, Inc. • Toll Free: 1-800-243-7446 • Visit www.parkell.com • Email: [email protected] In a pinch you can use one model to confirm both the contacts and the margin. Do NOT under any circumstances modify the proximal check model. At the cementation appointment we want the crown to slide home. Any modification of the proximal teeth on the second model will jeopardize the fit. The first two models are poured using the laminar impression. To allow an extra degree of certainty, we pour the third model using Dr. Kurthy’s backup impression. (If a crown fabricated on a model from one impression fits a check-model from another impression, we can be virtually certain it will fit in the mouth.) Because the Mach-2 laminar impression produces such an accurate model, the purpose of this spacer is solely to create space for the cement. It is NOT to compensate for sloppy fit. One coat is sufficient. 3 Note From Dr. Rod: This may upset the congregations of the various Occlusion Churches, but my preference concerning articulators is very simple. If the occlusion is normal (as it was in this case), either a plastic or metal articulator will serve nicely for a single crown. In fact, I actually prefer plastic because it lets me flex the models a bit to detect any high spots. If the occlusion is less-than-ideal, I always insist on metal articulators. Conclusion (Dr Kurthy) And that’s pretty much it. At the cementation appointment, the crown drops home with zero adjustments (Figure 20.) Very, very occasionally I may do some minor tweaking of the occlusion. But in approximately 2000 crowns I’ve impressed using the Mach-2 Laminar Technique, I have NEVER had a redo. Not one. In fact, of those 2000 crowns only 3 (three!) have required any internal adjustment at all in order to persuade them to seat. The seating radiograph (Fig. 21) shows the kind of fit I’m talking about. I’m fortunate. I have a fabulous expanded duty-assistant and a terrific lab. I readily admit that they make my life a lot easier. But I attribute much of my C&B success to the laminar technique I learned from Dr. Gary Schoenrock, plus the super fluid, super hardsetting Mach-2 wash I’m now using. And as I already mentioned, I’m not alone. Other dentists who’ve tried this technique have reported similar success. ABOUT the AUTHORS: Dr. Rod Kurthy Dr. Kurthy maintains a full-time practice in Mission Viejo, CA. He has authored numerous articles concerning clinical dentistry and dental marketing – and recently published a handbook on how to attract only the best kind of new patient – “The No-Coupon Marketable Dentist” (available at www.newpatientsinc.com) Paula Kim, CDT Paula Kim, CDT owns and operates Aspen Dental Laboratory in Anaheim, CA. A graduate of DTI in Orange county California, Ms. Kim has more than 15 years experience in the dental industry. Before opening her own laboratory, Ms. Kim worked in several labs on the East and West Coasts - and served as Manager of High-Tech at Glidewell Laboratories She reportedly has a number of accounts successfully using the laminar impression technique. Ms. Kim can be contacted at Aspen Dental Laboratory, 4081 E. La Palma Ave. - Suite G, Anaheim, CA 92807 714-632-5159, [email protected] Not bad for an impression technique that requires less than 6 minutes start-to-finish. (For detailed information concerning the Mach-2 Laminar Impression Technique - ask for Parkell Special Report #48 or visit the Parkell web site, www.parkell.com.) 4 Enjoy this article? Visit our article archive to download other free technique articles.
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