My dentist does CAD/CAM!

Like many people, I don’t particularly like going to the dentist. But I’m lucky: my dentist is excellent and I especially like how he’s always been on the leading edge of whatever is new in oral health. My last checkup showed that I had managed to crack a filling, something not dangerous in itself but that could put the surrounding tooth in jeopardy if the crack widened. It was decided (my dentist does the deciding; I nod) that we would replace the filling with an onlay, a type of filling that is bonded directly onto the tooth using a resin or cement that can increase the strength of a tooth by up to 75%. Onlays last longer and are better in a case like mine, where the old filling had taken up a large part of the original tooth. But swapping out the old filling isn’t simple. In a first appointment, the filling is drilled out and an impression is taken of the now-hollow tooth. That impression is used to make a temporary acrylic onlay that’s put in as a placeholder while a dental lab makes the permanent onlay, using the impression as a guide. At a second visit, the temporary is removed and the permanent onlay is cemented into place. I had no problem with this system, but it has its disadvantages. First, there are the two visits, which is inefficient for both patient and dentist. Then there’s the use of multiple numbing injections, which totally freaks some people out. Making the impression for the lab is also unpleasant to a lot of people. For the dentist, the old way also meant a longer billing cycle. Cut to 2012. Today, my dentist used a hand-held scanner, CAD/CAM software and a relatively small, bench-top milling machine to make the onlay right in his office. It was a one-stop experience that was incredibly cool (and nicely distracting). My dentist first did a scan to capture the “after” state — the finished shape of the top and sides of the onlay as it fits into my mouth. After a bit of prep, he pointed a wand the size of a TV remote at my tooth and took images from a couple of different angles. Once he was happy with the resulting point cloud, we moved on to the unpleasant drilling out of the old filling (can’t escape that) and he scanned the hollow tooth for the bottom side of the onlay. After the two scans, my dentist tweaked the CAD model of the top and bottom sides of the onlay, joining the surfaces when he was satisfied with how it would all fit into the tooth. Some of the muttering was in dentist-speak but “this would go so much faster if I were 14” came through loud and clear — he’s trained in all sorts of things, but not in the lines and arcs that are “home” to a CAD operator. The CAD user interface was decent, however, and he was able to do his fine-tuning with remarkable efficiency. Once he was done, the software took over, creating the tool path and instructing the lab operator to put a specific blank of lavender cementable lithium disilicate into the milling machine. The machine is the size of a large toaster oven, capable of milling to 25 micro-millimeter accuracy; it did my onlay in about 7 minutes. After the milling was complete and the onlay was cleaned, we did a test fit. The dentist shaved off little bits of material here and there, and the blank went off to be cured to the correct tooth-like color. About 45 minutes after starting the milling, the procedure was done with the new onlay cemented in place. Total time from start to finish: a little less than 2 hours. The benefits for the patient are obvious: one trip, fewer jabs, less drilling, nothing temporary. For the dentist, the benefits accrue more slowly: it’s not an inexpensive setup, it takes training to master, the practice needs to keep an inventory of blanks, and a lab tech should be on hand to monitor the milling. My dentist has changed the physical layout of his practice to get maximum use out of the “chairside” unit that does the imaging and CAD, and now schedules patients so that he can overlap the milling/curing stage for one patient with the setup/drilling stage of another. But he sees this as worth it, since it enables him offer better services to his patients and rely less on outside contractors. A quick Google search told me that there are 33,000 of these units currently in use in the world; about 12,000 in the US. The concept isn’t new; it was first proposed back in the 1980s but innovations in materials, curing processes and milling technology didn’t make it economical for a local dental practice until recently. I wasn’t unhappy with the old-fashioned way of doing an onlay, but I can definitely see the benefits of doing the whole thing in one stop, directly in the dentist’s office. New manufacturing techniques enable business changes. At my dentist’s. Who would have guessed? Now, I wonder if he can make a robot in that thing?