Show Your Work: Guided Implant Surgery (Part 1) by Dr Alif Moosajee

Introduction
There was a debate for a long time about whether implants are best restored with crowns that are screw-retained or cement-retained. I think it’s now universally acknowledged that screw retention is preferable because although there are a similar number of complications, the type of complications one gets with screw-retained is normally far less damaging to the implant prosthesis complex, and it is normally easier and more predictable to rectify.

Although it can be relatively simple to angle a single implant in a bounded saddle for screw retention, I find it very challenging to freehand-place multiple implants (especially in the anterior region) in a position that guarantees that the prosthesis will be screw-retained. It is for this reason that I like to assess the patient, then digitally plan where the restoration is going to go before working out the ideal position for the implant(s).

A guide can be created that ensures replication of this position.

It is my intent to convey in this two-part article how much simpler, quicker and more predictable the surgical placement is using this method. In Part 2, I will discuss in more depth how I use Cerec and CBCT to fabricate the guide.

Case
The patient attended complaining of anterior teeth that had been missing for many years. He previously had a denture but was unable to tolerate it and wanted a fixed solution.

The patient initially attended with periodontal disease and mobility in the teeth adjacent to the gaps, so the option of bridge treatment was actively discouraged.

We discussed the option of implant treatment but it was made very clear that it would be a long road because we would first have to remove teeth that had failed. We also had to ensure that we were able to successfully treat the periodontal disease and that this would be monitored for some time after treatment to ensure that this was stable.

It was noted upon radiographic exposure that there was a retained upper right canine which was palatally positioned. A CT scan was taken to determine the exact position of the canine (#13) and whether it was going to impinge upon implant placement (Fig.?1). It was noted that this would indeed be the case and so it was arranged for the patient to be seen at the local maxillofacial unit. The canine was removed under general anaesthetic.

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  Fig. 1

The initial phase of treatment was commenced. This included extraction of teeth with poor prognosis along with initial cleaning. Pocket charting before root surface debridement (RSD) was completed and then repeated two months after healing.

There was favourable resolution of the periodontal condition with no bleeding and resolution of pockets all to 4mm or less.

At this stage it was felt that we could proceed with implant placement as all active disease had been managed.

The ideal position of the front five teeth that were missing and then the position of the implants to best support those teeth were decided. Sites were chosen where the bone was deemed best.

It is important to note that when placing bridges on implants, the rules many people would use to govern how to design bridges on teeth are not necessarily the same; hence, it is worth reviewing the literature before committing to implant bridge design.

In this case it was elected to place three implants which would support two separate bridges.

On the right, there was to be a double abutting three-unit bridge restoring #11–13 with two implants in the 13 and 12 positions.

On the left there was to be a two-unit cantilever bridge restoring 21 and 22 which was supported by single implant in the 22 position.

Once I had globally selected the sites for the implants, the decision was made on how best to position and angle the implants so that we could obtain screw retention.

Once a digital wax-up has been done with the tooth positions set, these teeth can be superimposed onto the CBCT scan and then the implants virtually placed in their ideal positions to provide retention (Fig. 2).

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  Fig. 2

This process will be explained in far greater detail in Part 2 of this article.

Once the implant position has been designed upon them, the implant guide can be made which when secured to the teeth will ensure that the operator will drill the osteotomy in exactly the correct place.

The drill guide helps to control the angle of the drill in terms of buccolingual angulation, mesiodistal angulation and also the depth of the osteotomy and hence determine the final implant position.

Figures 3 and 4 and Figures 5 and 6 show the patient before surgery but after initial extractions and periodontal therapy.

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  Fig. 3

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  Fig. 4

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  Fig. 5

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  Fig. 6

After anaesthetising the patient, I tried in the drill guide (Fig. 7) and pushed a bur through the guide hole (Fig. 8) to mark the mucosa (Fig. 9). This helps to position the primary incision (Fig. 10) because if able to join those dots, then a flap can be raised in the position that helps to see the maximum amount of ridge. The site of the proposed osteotomy will be right in the middle of where that flap has been raised.

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  Fig. 7

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  Fig. 9

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  Fig. 10

I’ve also found that if I introduce local anaesthetic (under high pressure) directly onto the ridge, I find it much easier and quicker to raise the flap, because the liquid helps to separate the periosteum from the bone (Fig. 11).

The guide was placed and the implant pilot drill was used through the guide holes, allowing the guide to control where the bone was drilled (Fig. 12).

Three osteotomy pilot holes were prepared (Fig. 13). This initial step used to take me a long time because I would be agonising over the correct position to start the osteotomies.

Now this step takes me about two minutes because I am allowing the guide to control where I’m going. All the planning has been done before. As can be seen in Figure 14, the positioning is very good.

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  Fig. 11

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  Fig. 12

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  Fig. 13

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  Fig. 14

I then proceeded freehand to increase the size of the osteotomies working through the drill sequence as normal (using Astra EV).

Once the positioning, angulation and depth of the osteotomies have been worked out using the guide I am happy to widen the osteotomies freehand (Figs. 15 and 16). I feel like at this point the hard work has already been done!

When the osteotomies are prepared, the implants can be placed (Fig. 17) and the healing caps placed (Fig. 18).

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  Fig. 15

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  Fig. 16

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  Fig. 17

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  Fig. 18

Final positioning and all healing caps on (Fig. 19) before sutures were placed.

Note that the decision was made to raise two separate small flaps, rather than one large flap across the midline. This was done to be as minimally invasive as possible while still maintaining adequate access for visualisation.

Please note that when this approach is taken, suturing is far easier at the end of the surgery (Fig. 20).

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  Fig. 19

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  Fig. 20

Eight weeks later, impressions were taken and two screw-retained restorations were fabricated (Figs. 21 and 22). These were inserted in the normal fashion and the screw holes covered with PTFE and composite. The patient was delighted with the final result—as was I (Figs. 23–25). 

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  Fig. 21

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  Fig. 22

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  Fig. 23

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  Fig. 24

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  Fig. 25