This case study presents the immediate full arch rehabilitation of a partially dentate patient. The system used has
several novel features that permit provision of a prefabricated PMMA provisional bridge. A second article will cover the permanent restoration and provide more detail on the techniques used.
The patient was a 58 year old male who had been wearing a partial upper cobalt chrome prosthesis and wanted a permanent restoration. Function rather than appearance was his main priority. A CBCT scan showed very limited bone volume. The options were between large scale ridge augmentation, an overdenture, or accepting a compromised appearance with long clinical crowns, but a fixed restoration. This was made feasible by a low lip line concealing the mucosa in normal function The prognosis for the remaining teeth was poor and it was agreed to remove these and immediately restore with a full arch provisional.
Placing implants and immediately restoring them with a screw retained denture is a widely used protocol but often results in a bulky, difficult to maintain restoration. The objective was to restore the implants using a pre milled PMMA bridge on permanent milled abutments, which would be much better tolerated by the patient.
Technique
Firstly a silicone impression was taken in a tray modified by the addition of a Lego brick (fig 3). The Lego brick is an established fiduciary marker used to allow each of the scans taken in the process to be accurately aligned.
A CBCT scan was taken with the impression in the patient’s mouth. If a CBCT with a small FOV is used, as here, then care is required to ensure the volume includes the Lego brick. If the patient is referred to a CT centre then it is a good idea to trim any interproximal tags of impression material. This will ensure the impression can easily be reinserted by the radiographer.
The impression was then sent directly to the laboratory for a model to be poured. The model is mounted onto a Lego plate along with three other Lego brick markers prior to the impression being removed.
This was then scanned with a white light scanner to produce an STL file. The impression can then be removed from the model and the model rescanned, again on the Lego plate. The use of the three Lego bricks permits accurate alignment between the two scans. The model was removed from the plate, a diagnostic wax-up is produced and scanned.
The DICOM file is uploaded to the server of the planning software along with the STL files from the lab scans. There is the facility to share a case with a colleague. Using the Lego bricks all the scans are aligned. The implants can then be placed virtually, choosing from a library of systems in the software. In this case Dentium SuperLine and NR Line were used. The abutment can also be selected and working back from the diagnostic wax-up scan the optimal implant position can be found. The software includes a safety margin and rings to show the required drilling space. It is also possible to plan the position of the retaining screws.
Once the plan is finalised the file is saved and sent to be formatted and printed. The guide itself is made from printed titanium in the form of a lightweight lattice which can be either supported on the teeth or onto the mucosa. For tooth borne guides, the ability to produce fine rests from the titanium makes for a much more positive and accurate fit compared with acrylic guides covering the whole occlusal surface. In edentulou cases the guide is secured with three retaining screws, as used here. Minimal local anaesthetic is used for placement of the securing screws to avoid swelling of the tissue. Once the guide is secured the rest of the LA can be given.
The guide was refitted to the model and used to create osteotomies in the model into which implant analogues were then fitted. Permanent titanium abutments were milled and fitted to the model which was then scanned and a full arch bridge milled from PMMA and stained. The bridge was made loose fitting to be further modified at the fit.
The 2Ingis guide works in a different way to conventional tube guides. A modified handpiece has a pair of legs, which come in different lengths to stabilise the head of the handpiece. By inserting the legs into the tubes in the drill guide the orientation and depth of the drill procedure is closely controlled.
Not having the tube offers multiple advantages, one of the most obvious is that you can see what is going on even though, in theory, with guided surgery that is not necessary
Another advantage is being able to use zirconia drills. Zirconia drills can be made very sharp so they cut very well, but are brittle and prone to fracture. The drills are modified to be driven by a hex on the shank rather than the latch on the end. Using zirconia drills in tubes can lead to ‘chatter’ and increased risk of fracture. Stabilising the handpiece head with two remote legs prevents chatter. Bottenburg showed that using zirconia drills with irrigation heated bone significantly less.
The teeth were extracted and the surgical guide secured with three screws. Instead of a flap a tissue punch was used to remove a disc of mucosa. Like most alveolar ridges this one was not flat and it was levelled using the Zirconflat drill. This bulky drill does not flex and has three blades on the tip. Depth is controlled by the guide. The osteotomies were then prepared using zirconia drills specific to the implant system according to the surgical guide.
Drilling lengths can be varied by the use of spacers. There is also the option of using ridge expanders in the guide. Finally the implants were inserted using the guide with the handpiece set in excess of 40Ncm of torque, the exception being site 15 which achieved only 20Ncm.
The guide was then removed and the pre-prepared abutments fitted to the implants. The PMMA bridge was tried in with a thin plastic pull down used to locate the correct occlusal position. The bridge was made loosely fitting, after the addition of flowable composite to refine the fit it was cemented temporarily. With greater experience in future cases we anticipate being able to refine the appearance further. A final check on the occlusion and the patient was
given instruction in maintenance, emphasising the need for a soft diet for a month.
At review one week later the patient reported no post operative discomfort or complications. Initial healing was good. There is evidence that it may be possible to maintain gingival tissue better with such a technique. The patient was very happy with the appearance at a normal smile. This is consistent with the findings of Youk et al who concluded that patients treated with guided surgery felt less pain and higher satisfaction.
Part 2 of this article will show the definitive restoration.
References available o request.