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Diagnostics and planning

How to plan bone reconstructions

Anyone planning bone regeneration should never just follow a rigid decision tree, but focus instead on the most important connections and factors.

Dr. Grunder, in what kinds of cases would you plan for a bone augmentation as a two-stage procedure?

Dr. Grunder: On the one hand, it depends on the remaining volume of bone – is there enough to anchor the implant for primary stability? While, on the other hand, the defect and its environment must allow a risk-free placement of a dimensionally stable membrane, which I can use for larger-scale bone augmentations. If one of these two conditions is not present, then I’d prefer to take a two-stage approach.


What planning criteria play a role?

Dr. Grunder: First of all, one should be aware of what’s required for the final result. What level of outlay is or should be required? In the esthetic field a higher level of outlay is generally justified. The reason being that you need to assess the bone defect both horizontally and vertically, and – what’s especially important – you have to make a judgment about the attachment level of the neighboring teeth. An accurate perio score is vital for this.


Do you routinely take CBCT images to assess the bone?

Dr. Grunder: No, in only about 10 percent of cases. For example, if I have to explain to a patient why I am going to use a one- or two-stage procedure. But the bone situation is best judged after surgically exposing the site.


What’s your basic approach when planning an augmentation?

Dr. Grunder: The most important thing is the prosthetic planning. It is critical for where the implant will eventually be placed and, from an esthetic point of view, where the bone and soft tissue have to be. A surgical template can be useful for planning. It should determine not only the position and orientation of the implant but in the esthetic zone it should also take into consideration the desired soft-tissue development for crowns. This is known as the emergence profile. It lets you plan how much bone must be augmented vertically and horizontally, so that from an esthetic viewpoint you will have sufficient volume in the end.

In the case of several implants next to each other, the prosthetic plan must also include information about the required contact point between two neighboring implant crowns. This will help to clarify to what extent the bone must be built up vertically, so that in the end a papilla will fill the interproximal space properly.


For bone augmentation, what determines your selection of materials?

Dr. Grunder: It depends on the answers to two key questions: how much volume stability is needed? And how long will it take for the bone to regenerate?


And on what does volume stability depend?

Dr. Grunder: How much volume stability the material has to have depends on whether I’m only filling in a defect, which is surrounded by existing bone, or if I’m creating new bone in the sense that it’s a de novo construction of bone. If it only involves filling in a defect surrounded by bone, you can use materials which are not volume-stable, because in these cases the bony environment already provides the necessary stability. In such cases I use bone replacement material in granular form, for instance, and a resorbable collagen membrane. In the case of de novo bone formation – for example, for larger horizontal and vertical defects – the filling material or membrane must be volume-stable, but at the same time easily adaptable, as this is the only way to build up a perfect contour.


And on what does the second factor, the speed of bone regeneration, depend?

Dr. Grunder: If it is a four-wall defect, for example, the regenerative capacity comes from the existing four bony walls. This allows a relatively rapid formation of new bone, and it is enough if the membrane inhibits ingrowth of soft tissue for just a few weeks. Single-walled defects, on the other hand, regenerate slowly. You can either accelerate this process by mixing autologous bone chips in with the bone replacement material, or you can use a membrane with a long-lasting barrier function. Such membranes are frequently not resorbable, however, and they have to be removed later on.


What materials do you select if you are reconstructing large bone defects, and you need a dimensionally stable material?

Dr. Grunder: I don’t like using autologous bone blocks because they resorb. But if volume stability is required, I choose a dimensionally stable, non-resorbable, titanium-reinforced membrane, and under it I use either a mixture of Geistlich Bio-Oss® and autologous bone chips, or, more frequently, just Geistlich Bio-Oss® Collagen.


Do you have a decision tree for bone regenerations that you always use?

Dr. Grunder: I take a very critical view of decision trees. A decision tree gives users the feeling of being able to reach the right decision based on simple criteria, while in actual fact, numerous factors come into play. A rigid decision tree can mean you miss certain details and select the wrong procedure. I would advise that you always keep your focus on which factors play what roles and understand these relationships. Using a decision tree in no way insures that you have really understood all the issues involved.

Interview by Verena Vermeulen

Illustration Header: Geistlich

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