There are several things to keep in mind when removing existing restorations. A successful procedure requires great preparation, focus, and precision. With 3 decades in the dental profession, Dr Robert Lowe has the experience and a wealth of knowledge regarding this topic. Below Dr Lowe answers questions posed by several dentists who attended his virtual event, “Three Keys to Removing Existing Restorations.”Dental Student: For a single tooth crown prep, do you parallel your contacts, that is, take a disk to the interproximal surfaces of the adjacent teeth to achieve a broader contact to make delivery easier and more hygienic?
Dr Lowe: I worked with a guy who took a disk to a tooth once. He ended up cutting a tongue in half during the procedure. I never take a disk to a tooth. I’m not going to broaden the contact. Contacts in the posterior should be elliptical, located to the buccal of the central groove. So, the answer is no; I don’t make contacts larger and broader. It does not make seating easier; it makes cleanability more difficult. Stick to your anatomy and what you learned.
Dental Student: That’s incredibly important. If you don’t have enough incisal gingival height for a prep, how do you handle it?
Dr Lowe: One way to handle this is by crown lengthening. Take a look at your x-ray. How much tooth is above and how much is below the gum? I always say that once you get past that minimum incisal height of 3 mm, you’re compromising the resistance and retention form of any restoration. There is no cement that we can bond to a flat stump. If you have a short cervical incisal prep, first see how much tooth is under the tissue. Then consider a surgical approach to reposition the tissue and gain more height of the tooth to prepare, or make the contact real tight and tell the patient gravity will affect it if it’s an upper.
Dental Student: Do you remove an existing restoration like that amalgam before or after crown prep?
Dr Lowe: The answer is yes. When I’ve got an old amalgam that I know I’ve cleaned out, and now years later for whatever reason, tooth fracture or what have you, I’m not quick to take it out immediately. I’ll prep it, and if the margins are clean, I may elect to leave it if it’s still a sound, marginally competent core. If someone else does the procedure with evidence of decay and the margins are incompetent due to poor fit, I’ll take it out and build the core immediately. It’s case dependent. You can’t go wrong by removing any old core and replacing it.
Dental Student: Completely understandable. Is there a certain measurement that you go by in order to determine if you want to close an anterior contact with a veneer or a crown if you are deciding between those two?
Dr Lowe: It’s not really a measurement. It has to do with the contour of the existing tooth, relative to both the facial and lingual surfaces. I’ve seen too many people try to be conservative and just do a facial veneer, and then have patients end up with class III composite restorations in the lingual because of crowding, poor contours, or places where it’s difficult to maintain effective home care. It’s not just the number of microns of enamel you conserve; the patient must be able to maintain what you do. Many teeth are sacrificed on the altar of false conservatism. It’s not conservative to shortcut your prep and have a long-term difficulty with maintenance and function. Cut your loss at the beginning, create upper thicknesses and proper contours in whatever you do that first time. You’ll have a much better chance for long-term success.
Dental Student: Very helpful, indeed. We touched on zirconia crowns earlier in the lecture. What is your approach regarding instrumentation? What’s your handpiece selection when cutting into the dense material?
Dr Lowe: I use an electric handpiece, but it has to have constant torque. How much do you want to spend on handpiece repair? If you beat the heck out of an air turbine trying to get these things off day after day, it will really damage your handpiece. If you don’t have an electric handpiece, consider purchasing one. I have an electric and an air rotor on every delivery unit. Because the electric handpiece has constant torque, it is less damaging to the instrument when removing something as dense and difficult as zirconia.
Dental Student: Interesting! Do you vary your approach at all if you have a patient who has a high lip line when you’re working in the anterior? Does that influence your margin selection at all?
Dr Lowe: Sometimes. I’ve seen patients with a high lip line who have root recession. Some do not care that they have yellow roots showing and teeth above them. For some patients, I don’t necessarily cover everything that is above the pink. If their aesthetic outcome is such that you are doing something with a higher lip line and they don’t like that, then you may need a combined approach with the periodontist to do some gingival surgery to level things out. Maybe shorten the teeth and cover the roots to the existing height of the tissue. My best advice is to talk with your patient and find out if it really matters.
Dental Student: Great advice! What’s your preferred temporary material for a crown? What’s your current temporization technique?
Dr Lowe: We have a lot of good temporary provisional materials out there. Most of them are visicryls, light composites that have been improved over time. The knock on early visicryls was their brittleness. Some people still use laboratory-process . One company makes a rubberized urethane, which is not a visicryl, and it’s more impact resistant, so that’s another selection for long-term temporization. Some of the newer provisional materials are now using nanofiller because people are realizing that you should make the temporary look good due to patient demand. I don’t have one provisional material I prefer; I have about 3 or 4 depending upon the shade and whether it’s aesthetics or long-term I’m going for, and the technique is pretty much the same. It’s an indirect technique; I either have a preoperative wax-up or a mock-up made with composite on a model that’s adjusted so that I can make a putty stent or a suck down from that. Once I prepare the teeth by lubricating them, I fill the space for the crown with the provisional material; the lubrication allows for easier removal. Afterward, I place the stent over the teeth for the appropriate time, remove and carve it, and finally finish the margins and cement it.
Dental Student: Your practice has exposure to CAD/CAM crowns and you’ve also used the phrase “smoothing and polishing your prep.” Do you make any other adjustments to your prep technique or specifically the CAD/CAM crowns?
Dr Lowe: First, I don’t use chairside, however, I’m not against it. I think it’s one good option for indirect technique. I still use a laboratory process for most of my restorations, although some of them are made from traditional impressions, as well as hammers or optical impressions. Remember when you make an optical impression, it’s still a picture. It’s 2D, which is why I think the preparation design is even more critical. Irregularities are even more of a problem. So, if you are using today’s scanners, make sure your preparations are smooth and the margins are very distinct with no irregularities. If you follow this, you’ll have a better result because of the technique by which they’re made, which is optical information. They literally can be made without a dye.
Dental Student: What’s the best way to remove existing composite without sacrificing tooth structure?
Dr Lowe: If you’re working without magnification, get that fixed right now. If you’re using 2.5 loupes, you’ll learn that they do not magnify enough. I’ve used 4.0 since I was a dental student. If you want to effectively take out a composite differentiated between , use magnification and you will not have a problem. The same applies to cutting off a tooth-colored crown.
Dental Student: This is the last question for you, Dr Lowe. For a full zirconia crown in the posterior (you’re going to take a traditional impression and send it to the lab for fabrication), in your world would that be a heavy chamfer or a shoulder margin that is dictating your choice here?
Dr Lowe: There’s still a little bit of controversy on whether you can prepare zirconia like gold or whether you should prepare it of porcelain. The answer to your question regarding zirconia crowns is yes, but the bigger question is this: Most teeth that I prepare for zirconia are not virgin teeth. Most of them have had existing restorations. What is the number one thing that determines what your margin will be? Well, what was there to begin with? If there was already a big wide shoulder, you cannot make it smaller. A lot of these back teeth that I’m finding going to zirconia have had either previous crowns on them that have broken, or have had large fillings on them. There’s no cut-and-dry answer. We’re not preparing virgin teeth here. You need to look at what you’re facing. What is core? What is old filling? What is healthy tooth? How much is above and below the gums? Do you have ferrule? A 2-mm ferrule effect is required for retention. If you don’t have 2 mm of tooth structure above the finish line, you don’t ferrule effect, and that could adversely affect retention and the ability of the crown to stay solid.
Thank you, Dr Lowe, for taking the time to share your extensive knowledge with our user community! Click here to watch other videos from THE NEXTDDS regarding Topics in Dexterity, Hand Skills, and Instrumentation.