It is unfortunate that I often have to relearn that paying attention to the small details at the beginning of a case helps to prevent big messes towards the end of that case. The details are like compound interest: it doesn’t seem like much when you make your first deposit in a 401K, but leave it alone and see how large it can get!
This is a case that I recently completed. It is a full upper-arch zirconia implant-supported hybrid prosthesis against a full lower arch of crowns and veneers and a couple of implants Not the kind of case I do regularly, but they come along once in a while. They are usually a lot of fun to figure out and plan.
The patient had worn an implant-supported, bar-retained overdenture for about 10 years and was tired of something that felt bulky and that he had to remove on a regular basis.
The sequence for this case was to first create a trial denture that would be used as a scan denture in order to treatment plan the placement of the implants. Then I would sequentially remove the old implants and graft so that new implants could be placed in such a way that they could support the desired prosthesis.
The scan denture is fabricated just as a conventional denture would be, with a bite rim and try-in appointments.
I marked the bite rim as I always do with the appropriate landmarks so that when the teeth were set, the technician would know the correct place to set the anteriors.
The red line is where the bite rim is marked; it lines up perfectly with the midline of the lower incisors. The yellow line is the anatomic midline. I have no explanation for why I marked it the way I did and prefer to blame my advanced age.
Notice the lab dutifully placed the teeth in the position where I marked the bite rim.
Now, this may seem like no big deal – just move the teeth a little to fix it. It is important to remember that this denture is going to be the template for the final prosthesis. And that template will determine where the implants are placed.
This scan denture is processed with glass beads embedded in the palate to serve as radiographic markers for planning the case.
It will later be converted into a clear acrylic scan denture for additional scans that will also be used to determine final implant placement.
The tooth position in this denture determines final implant position.
In this image, you can see the planned implant position for the centrals and canines. The exit in a perfect position for a screw-retained prosthesis, just palatal to the incisal edge.
The implants were placed using guided surgery and at healing appeared to be in a perfect position. Final impressions were made and the case sent to my ceramist for design and fabrication.
We decided to use a milled PMMA (polymethyl methacylate) provisional in order to confirm final tooth position, lip support and passive fit before fabricating the final prosthesis.
During that design process, Matt, my ceramist, innocently asked if I would like to correct the midline discrepancy.
As he showed me his design, it suddenly became obvious that I had missed that detail from the very beginning. The right thing to do was ask the patient, and I assumed that since he nor his wife had noticed that it wouldn’t be a big deal to leave it alone. I was wrong; his wife wanted it corrected.
Now, think about this. All the planning had been based on the tooth position of the trial denture and the implant was now placed. Moving the midline to his left meant shifting the access openings by as much as half a tooth. Not only did it affect the access openings of the centrals but of every other implant access in the arch.
Almost every access opening is in a less favorable position and no longer perfectly placed.
In this case, I got lucky. The case is full-arch zirconia with cutbacks for porcelain layering on the facial. And because of the strength of zirconia, even though the access on the left canine and first premolar are closer to the facial than I would like, they likely will be OK.
Had the midline been another half millimeter to the left, I would have been on the cusp tips of those teeth and then been in a real pickle.
The case is in, the patient is happy and if something goes wrong because of my error, I will make it right. And if that happens, it will be a very expensive and very painful lesson.
I think it is important to not get caught in the trap I let myself fall into. I have always used checklists in the past, much like a pilot does every time she flies. It ensures that things like this don’t happen. I got sloppy with my lists and thought I had my sequence down. I’d like to say it won’t happen again. I guess we’ll see.
(Click this link for more dentistry articles by Dr. Steve Ratcliff.)
Steve Ratcliff, D.D.S., M.S., Spear Faculty and Contributing Author