Minimally invasive blocks
No second surgery, perfect fit, simple procedure – the advantages of patient-specific allogenic bone blocks are convincing more and more implantologists and patients. The autologous bone is now losing its image in Germany too. Is there a new gold standard??
Case 1: Initial situation of upper jaw tooth area on the right, augmentation alio loco with autologous bone, dehiscence and total loss of the block © Back / Blume
Patient-specific allogenic bone blocks are clearly gaining in acceptance. When are they indexed?
Smeets: That depends on different factors. Soft tissue thickness, soft tissue mobilization, postoperative care and clinical risk factors such as smoking play a crucial role. In addition there are the accuracy of fit, the defect localization as well as biological and clinical limitations.
What does that mean in practice??
Buchbinder: Let’s start with the accuracy of fit: each individual planning is only as good as the data on which it is based. The prerequisite for this is a clear delineation of hard and soft tissue and a uniform defect surface. Difficulty of fitting is therefore to be expected with relatively fresh defects with tissue in healing (low degree of mineralization) and fissured defect surfaces. Also, the bone block needs a vital and stable recipient bed, so that in particular in the maxilla larger perforations lead to the maxillary sinus to difficulties.
Now for the clinical and biological limitations: The experience of the treating surgeon plays an important role in the expected dimensional changes of the alveolar ridge. While 5-6 mm widening on the horizontal is usually more than enough to gain a sufficient implant site, vertical defects require a lot of sensitivity: most users can control up to 3 mm vertically in a relatively predictable manner. In addition, as Prof. Smeet’s previously mentioned soft tissue thickness and its mobilization, postoperative care and risk factors such as smoking play a crucial role.
I understand that correctly: A vital receiver bed is a must?
Buchbinder: A vital receiver bed makes much easier, but it is not always possible to realize. Depending on the manufacturer, less perfused recipient sites are either a contraindication in accordance with the product and product information, or the need for careful consideration of the surgeon’s use is noted.
Smeets: My concept is to drill the bone monocortically for freshening up. Although this is not clearly documented in the literature, it is extremely successful in practice.
This applies to autologous and allogenic bones?
Smeets: There are currently no applicable studies.
Buchbinder: In both variants, there are advocates of the perforation of the recipient site and opponents. But especially in the posterior mandible with very thick cortical bone, I see no disadvantage, while in the upper jaw it could be largely dispensed with.
Dr. Flower, Dr. Back, you have been using augmentations with allogeneic prefabricated bone blocks in your practice for five years. Why?
Flower: The majority of our patients now reject their own bones and wish for the elucidation of all alternatives prefabricated allogeneic blocks. That they fit perfectly into the bone defect – like a key in a keyhole – convinced. There is no more dead space, no gap between transplanted and localized bone. The operating time is short, the surgical trauma is low and the volume stability extremely high. On the other hand, self-bones can not be precisely milled; there are simply no surgical procedures available.
How do you proceed concretely??
Back: We work with our own DVT device. We record the bone defect, discuss the situation with the patient, and discuss all treatment alternatives – from allogenic bone block to osteoplastic procedures such as bone splitting. If the patient chooses to augment CAD / CAM-fabricated allogenic blocks, we will send the DICOM data we generate to the company that provides the technology, in our case, the Botiss or Zimmer Dental. There, the three-dimensional bone block is designed.
How long does it take?
Flower: About seven days. After receiving the data, we check the fitting accuracy together with the patient and then order the allogeneic, individually manufactured block, which reaches our practice after four to six weeks. Only from this point on it will be paid for the patient.
What are the main indications?
Flower: We focus on more complicated indications: anterior tooth, difficult posterior region of the upper jaw, difficult posterior region of the lower jaw.
What is the biggest challenge?
Back: Still the cut. In the first year we had some dehiscences, probably due to the huge increase in volume from the transplant. We have therefore changed from the typical incision, which runs along the alveolar crest, to a cut with two vertical incisions into the vestibule, which is then connected via a horizontal incision located far in the vestibule.
Flower: The cut reminds of the pedestal of a pillar and we called it Pillar Incision. The whole flap in the upper jaw is then prepared for palatal. In the lower jaw, the incision is somewhat different, but also very paramarginal. Important: The local teeth should not be touched, because then dehiscences threaten. Since we developed these two incisions, the dehiscence problem in our practice is almost off the table.
What should you pay particular attention to when using allogeneic materials? What’s different than with autologous bone?
Buchbinder: In the case of augmentations beyond the limits mentioned above, a risk assessment should always be carried out and possibly autologous bone should be preferred. A key factor is the use of barrier membranes. Acellular allografts and other bone replacement materials must be screened during the initial healing phase of rapidly proliferating fibroblasts to prevent connective tissue deposition of the materials. (Scientific opinion DGZMK).
And that’s not the case with my own bones?
Buchbinder: No, with autologous transplants, some of the cells are transplanted live and need to be supplied with nutrients as quickly as possible by newly formed blood vessels – neoangiogenesis. A barrier membrane would be more of a hindrance.
What other distinguishing features are there?
Flower: Due to the different pretreatments – dehydrated, degreased, decellularized – the allogenic bone block has hardly any real bone constituents, only calcium, phosphorus and collagen. The advantage: fat cells are not present and thus can not be infected.
This lacks the allogenic bone block but also of biological value.
Flower: In comparison to autologous bone already. But the biological value of allogeneic materials is still significantly higher than the xenogeneic or synthetic materials.
Buchbinder: Allografts can be replaced by normal remodeling processes in the long term by the body’s own living bones, while bovine and xenogeneous materials create ceramo-osseous regeneration complexes that remain stable over the long term even without mechanical stress. If it is foreseeable that the augmented area will not be subject to mechanical stress, preference should be given to bovine materials, since these are not subject to resorptive processes and thus ensure very good long-term stability (Riachi et al., 2012 / Lorean et al.
Flower: Many bone substitutes, not just the bovines, but all the way to algae, are not only dehydrated, degreased, decellularized, as allografts, but additionally thermally treated, so fired in a blast furnace at up to 1350 ° C. And only then does a calcium phosphate scaffold emerge from the original bovine bone.
A hydroxylapatide …
Flower: … exactly, and that is hardly absorbed.
So in principle it remains as a foreign body?
Flower: That’s how you could put it. The allogeneic bone block, on the other hand, is completely rebuilt into its own bone. There is a reorganization and no incorporation, yet the allogenic bone block maintains a very stable volume in the healing phase.
The volume preservation afford almost all bone replacement materials but also.
Flower: But allogenic bone blocks are not granules. And that is a decisive advantage, especially in the regions where we absolutely want to maintain the vertical height, such as in the upper jaw front. Particulate materials can also collapse in addition to the resorptions and thereby lose volume.
This concerns, for example, BioOss?
Flower: Ultimately, this holds true for all particulate materials, whether hydroxyapatite or tricalcium phosphate.
Under autograft, favor autologous or allogeneic blocks?
Smeets: Allogene, mainly due to the mechanical properties. The moldings do not break easily and can be adjusted more easily. This makes it possible to produce a wide variety of geometries, either chairside or already in the tissue bank, which can be used in the patient without a greater risk of fractures.
Wound dehiscences with no bone regeneration often lead to the loss of the augmentation – even in allogenic bone blocks?
Flower: In our experience, augmentation with allogeneic blocks results in wound healing disorders, but it is a complication – the exposed bone is infected and becomes necrotic – but the unexposed bone, the bone that is still covered by the mucous membrane, is mostly preserved. It is nourished, comes to life and you can almost always implant when you re-suck something. If, on the other hand, an autologous bone block is dehiscent, you lose everything – not just the bone that is exposed.
Can protect shell technology from that?
Smeets: Quite: I am a fan of the shell technique according to Prof. Dr. med. Fouad Khoury, which represents the lateral and vertical boundary of the defect and thus defines the limits of augmentation. Professor Khoury showed us early that augmentation using shell technique is better built than an autologous bone block. The principle of the shell technique is based on creating a biological container, which gives sufficient space for the complete incorporation of the particulate KEM.
What you have to pay particular attention to the shell technique?
Smeets: That the cortical shell is never too close to the implant. Sharp edges should also be carefully rounded, for example with a diamond ball. Furthermore, it is important to achieve an absolutely tension-free and saliva-tight wound closure. Under no circumstances may the cloth “rub” on the screws. As dehiscence protection, I recommend a pericardial membrane, which should be fixed, so sewed or fixed with pins. Because even micro-movements attract resorptions.
But you do not work like Khoury with autologous plates …
Smeets: No, we use prefabricated bone plates from donor bone. The procedure, ie the technique, is identical, but the invasive removal surgery is eliminated. Since we also observed cases in which this cortex was not fully integrated, over-augmentation occurs around the width of the cortical bone. After attachment with at least two osteosynthesis screws, the gap in the middle is filled up with allogeneic granules. The procedure is relatively simple and withdrawal morbidity is completely eliminated.
Still rely on xenogeneic or autologous material?
Smeets: Of course, every material has its indication. It is naïve to believe that you can treat any defect with a material. Neither xenogenic nor autologous nor allogenic. You have to decide individually, which is better. The respective indication always depends on many factors:
- How much vertical distance do I have in the sinus lift? How much residual bone is there?
- If I have 7 to 10 mm, I do not do a sinus lift but put short implants, I have 3 to 6, then I opt for the external sinus lift and a simultaneous implantation.
- If there are only 3 mm residual bone, I advocate an external sinus lift and a secondary implantation. Not only the choice of my material, but also the concept and the technology are multifactorial.
Package can not answer that?
Smeets: No, a review of 136 studies on sinus floor elevations using autologous, allogeneic, xenogeneic and synthetic KEM by Danesh-Sani from the year 2017 shows that the comprehensive literature review showed:
- After less than 4.5 months of healing, autologous bone produces the most new bone,
- Between 4.5 and nine months, there are no differences,
- After more than nine months, allogeneic KEM scores the most newly formed bone.
When would you argue for example for Titanmeshes? What role does defect size play??
Back: For example, we only use prefabricated titanium meshes for manageable vertical defects. So far, we have operated twelve cases with prefabricated titanium nickels. The meshes are cheaper than allogenic blocks, but can not be changed after production. That may be a disadvantage.
What is the problem?
Back: If resorption already occurs in the healing phase, this can not be corrected. So far, however, we have not been able to observe this problem. When introducing allogenic bone blocks, a possible resorption can be better planned by over-augmentation, which is corrected.
How does it work exactly??
Back: We calculate expected resorptions in the design of the allogenic bone block and model the augmentation during the insertion intraoperatively. That’s not possible with the Titanmesh. You have to use it the way you get it. With nondestructive healing, everything runs smoothly, the volume under the titanium grid is maintained and creates a good implant bed. For larger defects, we prefer the allogenic bone block. The fact that titanium mesh can not be modeled, is quite a disadvantage.
Smeets: Also difficult is the soft tissue handling. I urge you to put a collagen membrane over the titanium mesh.
Buchbinder: However, with inhomogeneous and difficult-to-differentiate bone conditions, meshes have clear advantages over abutment sculptures, since meshes are constructed based on the desired jaw contour, regardless of the surface condition of the defect. This simplifies planning considerably. However, the necessity of removal and the high rate of exposure reported by various sources averaging 30 percent are to be considered negative.
An exposure rate of 30 percent, that’s huge. How come? And: Is that also true for the prefabricated ones??
Smeets: Yes, and the exposure rates also occur in experienced surgeons. In my opinion, this is due to the material, the foreign body, the soft tissue covering the often large area is problematic. We are currently testing lattices of magnesium to make meshes absorbable and unrecoverable.
Let’s get to the allogeneic bone rings: The charming thing about this technique is that the patient gets the implant delivered immediately …
Back: … and that brings a lot of risk. At any rate, we have not had much experience with it so far. I favor a succession: first the structure, then the implantation. If the bone ring fails – in our case – you lose the entire implant.
For years, the working group has been Bernhard Giesenhagen strong for the bone ring technique, now also allograft rings are offered from the pack. The technique is considered less invasive and has quite a lot of followers. Is it really practicable??
Smeets: Not in principle. The technique has its indications, and those who control it can achieve great results, but that requires intensive training. Because as simple as it seems, the method is not. In order to be able to apply the bone ring technique, certain conditions regarding the design of the local bone bed are required. Most importantly, studies and data on complication rates and indications are lacking. And as with all augmentation procedures, soft tissue management is often the problem.
Dr. Buchbinder, botiss offers the allogeneic bone rings. Are you a “storekeeper”??
Buchbinder: Not at all. In certain situations, the technique is great, for example in the case of purely vertical defects in a single tooth gap or one-stage sinus floor elevations with minimal bone supply (1-3 mm). Also after explantation of peri-implant compromised implants that need to be removed by Trepan and subsequent decontamination of the area allogeneic bone rings interesting treatment options.
Less invasive than all augmentations is the avoidance of bone build-up. This is possible with short and reduced-diameter implants. Is that an option for you??
Smeets: Of course: The implant dimensions should always be discussed. Above all, we are opening up new indications with reduced-diameter and short implants. For example, a 2.9mm diameter implant is an elegant solution for aplasia of 22. Reduced implant dimensions make a complex but never a simple case …
Flower: … and they do not always allow augmentation avoidance. Example: Short implants – less than 6 mm – are clearly contraindicated in the anterior region. If the vertical height is missing, longer crowns are needed – a no-go in the aesthetic area. But: The patient must always be informed about all alternatives to augmentation.
Buchbinder: The understanding of optimal implant to crown length has changed significantly in recent years. Especially with large vertical defects, however, at some point for functional or aesthetic reasons, a limit is reached, which can be overcome without augmentation. Naturally, not only the primary stability should be taken into account for the reduced-diameter implants, but also the age-related dimensional changes of the alveolar bone should always be considered. To stabilize the thin alveolar ridge, for example, after insertion of thin implants, contouring with resorption-stable bovine KEM could provide long-term stability.
In contrast to short and diameter-reduced implants, the stool for the application of allografts is quite thin. At the same time, there are many prejudices. How do you deal with that?
Flower: There are already a lot of studies on allografts, but with regard to the CAD / CAM-made ones, it still looks pretty bad. We have introduced nearly 70 bone blocks over the past five years and are surprised at how stable the volume of the allogenic blocks has remained, especially in terms of vertical height. And that’s one of the main arguments for us why we recommend this augmentation method. Such constancy in the vertical do not offer other bone replacement materials.
So not the own bone?
Smeets: Unfortunately, the data is thin. But, for example, the study by Monje and colleagues from 2014 on bone augmentation prior to implantation in the atrophic maxilla in 15 works with 361 bone blocks (follow up 4-9 mo post-op) shows that allografts are a reliable alternative to autologous bone with lower hoof defect morbidity and surgery Time. Nissan and colleagues showed in 2011 that allografts are also a safe and reliable alternative to autologous bone when it comes to bone formation prior to implantation in the atrophic mandible.
And in contrast to the self-bone, the protocol is extremely practical and almost simple. The DICOM record of the defect is generated and sent to the manufacturer, who mills the allogenic bone blocks as desired and sends them to the practice. If the resident colleague observes the guidelines – no sharp edges, the correct distance to the neighboring teeth, countersunk screws, so that the non-scrubbing of soft tissue, applying the cloth correctly, working with membranes – hardly anything can go wrong. It is also important to use a collagen membrane to cover it and, to conclude, the fibrin membrane (PRF). Please implant after four months at the earliest. The bigger the defect (from 3-5 mm vertically in the UK six months!), The longer I wait (is also dependent on the AZ: in smokers and diabetics I wait longer).
Are there any other studies on the way??
Flower: At least I have not noticed yet. At any rate, we work intensively on the preparation of our cases. We also have promising histologies in the meantime.
Dr. Buchbinder, why is the study situation incomplete?
Buchbinder: Due to strict regulatory requirements, only a few are available in many countries simultaneously, but often only locally available products. This makes multi-center and large epidemiological studies difficult. On the other hand, due to the high production costs and the small surpluses, the financial resources of the industry are often limited. Tissue banks operate in a nonprofit way anyway and are not able to initiate large studies on their own. In addition, the success of even the more complex operations depends very much on the surgical skills and preferences of the practitioner, so that a comparison of different surgical techniques can never be objective, but is very strongly subjective; Incidentally, this also applies to autologous bone blocks (Motamedian, Khojasteh, Khojasteh, 2016). The excellent results of practicing physicians usually appear only as case studies or case series, as clearly lack the know-how and resources to set up and conduct large-scale studies. In the university area, however, the number of patients or the clinical routine with the techniques are often missing, so that in the future a closer integration of the universities with privately practicing practitioners would be desirable.
Smeets: There are numerous literature on allogeneic blocks, only the prefabricated ones look meager.
Is that also due to the prejudices against donor bones? Is there still a danger today??
Buchbinder: A real threat to patients by the mere use of allografts is long gone, let alone currently proven. Isolated cases of disease transmission may be due to inadequate diagnostic methods and the use of non-sterilized tissues in the past (Hinsenkamp et al., 2012). Thanks to the worldwide monitoring of incidents and the enormous advances in tissue banking, there is now only a theoretical residual risk, for example as a result of diseases not yet described. In fact, there are no confirmed cases of disease transmission worldwide through chemically prepared and gamma-irradiated bone preparations from tested donors, such as those used in Germany. Reports of possible antigenicity and possible complications in subsequent organ transplantation are described as isolated cases for fresh frozen (O’Sullivan, 2016) or cryopreserved bone (Mosconi et al., 2009). In fact, there are now several FDA-registered preparations for use in orthopedics in America, in which processed bone allografts are even combined with isolated allogeneic living osteogenic cells from the same donor (eg, Vivigen, Life Net Health, Virginia Beach) to treat healing fractures.
So the patient does not have to worry about possible disease transmissions today?
Smeets: No, in the 70s, 80s and 90s, people were infected because the investigation methods were not yet so far. Since the introduction of the so-called NAT (Nucleic Acid Test) screening, no incidents have been reported. For example, with more than 250,000 Charité allogeneic transplants set between 1994 and 2015, there was no single infection, no suspicion of viral or bacterial infection. All products have been processed, disinfected and sterilized; that’s the key point. Nevertheless, the patient must be informed about a theoretical residual risk.
Dr. Flower, Dr. Back, how do you clarify in your practice?
Flower: We use Allografts products that are approved in Germany under the German Medicines Act. We can assume that these products have been extensively tested and are safe. I do not question that as a clinician. And that’s what I explain to my patients.
How important are allografts in dentistry in a global comparison??
Buchbinder: Allografts are the most widely used bone replacement material in many countries around the world, not least in the US. Depending on the country, dental allografts account for 35-40 percent of the total market, while synthetic materials account for only about 15-20 percent (Straumann Group 2016 Annual Report). The good handling, the high remodeling potential and the faster bone formation compared to bovine and synthetic materials are valued in allografts (Schmitt et al., 2012)..
Flower: Allografts have today been given a completely different status due to the CAD / CAM prefabrication. Of course, that’s something we can not do with autologous bone. We can not, while the patient is operated on the iliac crest, put the piece right into a milling machine. This currently only works with the allogenic bone block. How attractive that is, we notice, as we get “from all over the world” invitations to talk about it.
Smeets: Allogeneic materials are standard materials in the US. Germany will follow suit, I am convinced of that. More and more case studies show how good the materials are. They have a very good porous surface, they come from the human body, eliminating the removal of morbidity. Allogeneic materials are clearly superior to synthetic ones, that is proven. And: materials of animal origin encounter more and more rejection. Nevertheless, the residual risk must be clarified in detail.
Can own bone in view of the current developments today still be classified as gold standard?
Flower: No, as a gold standard you can not look at your own bone today.
What do you think is the new gold standard??
Flower: The only gold standard that exists is to think again for each patient about the therapy concept and explain the alternatives.
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