Implant and Abutment Surfaces

In the first part of our FOR exclusive series of expert lectures, we are joining Dr. Glen Liddelow on the evolutionary journey of implant and abutment surfaces to improve the long term implant longevity outcomes.

Dr. Liddelow starts his journey at the time when the ground rules for what is happening during the process of osseointegration were first defined. The factors that control osseointegration are things like material biocompatibility, the implant macrostructure, the implant microstructure, the status of the implant bed – meaning the patient, the surgical trauma, and the prosthetic loading. The biocompatibility of titanium, Zirconia and ceramics are important to get this osseointegration, this is known according to Dr. Liddelow. And titanium would be the single biggest material that has the longest research, so it is known that it works over a long period of time.

He continues his lecture by presenting the various types of titanium with their different grades, different strengths and different alloys and alloy mixtures. What is the macrostructure of the implant? Is this a screw or is it a nail? Interestingly, nail type of implants still exist to this day, but the vast majority of implants that are used are a screw type of implant. And they might be at tissue level, they might be at bone level, and they have different thread pitches and thread designs and all sorts of things that fit into that. Next is the titanium oxide complex. There is the titanium material, but it forms a titanium oxide within a few nanoseconds of exposure and then it can be treated in different ways. This means there can be the surface after milling or machine-fabricating the implant and there can be additions or subtractions to the surface that can create a certain level of surface roughness. In pioneering studies by Ann Wennerberg back in the ’90s the ideal surface roughness that is ideal for an implant is usually around 1- 1.5 microns of SA value. 

Dr. Liddelow is moving to the implant systems. Implants and the history have been incredibly successful over a long period of time. He states that he will have a look at the history and science and try to decipher some of that as opposed to some of the marketing hype that goes on. He shows a patient with an implant, placed 40 years ago. This implant is a machined or turned implant, a Brånemark MKII with a CeraOne abutment on top. The situation shows good tissue, and good bone, and it has survived incredibly well. With a bit of extra work, restoring mainly the teeth around it and maybe restoring the implant, a very nice-looking result can be achieved, even 40 years after placement. He continues with another case, which he did in the era when immediate placement and immediate loading became popular. The implant was restored with a Zirconia abutment and a Zirconia crown. He shows the 5-year, 10-year and 25-year follow-up of this case. The soft tissue and the appearance of the implant looks very good. Due to the aging of the patient, there was some differential growth and movement of the anterior maxilla. For further information on the impact of aging, Dr. Liddelow recommends the work of Oded Bahat and his co-workers. The bone levels of the implant are very favorable. He concludes that what we've been doing and using all these times can work and work very well.

Dr. Liddelow shares that his practice is a referral-based practice and that he sees the majority of his referrals coming in as problems with implants. He observes that vast majority of the problems that he sees are still iatrogenic and have less to do with the implant or implant system that has been used, but more to do with how it's been done and those sorts of factors. The reason for this is not only a surgical reason, and not only a prosthetic reason but a combination of the two and they probably pay equal parts in the outcome of an implant restorations.

If the procedure is done properly a good integration for a long period of time and generally favorable aesthetic outcomes can be achieved. But what if you want to achieve excellence? The boundaries are pushed more and more. At this point in time implant treatment is a lot more sophisticated, the excitement about the osseointegration process is replaced by the fact that is needs to look amazing, too. Social Media is playing a big part and one needs to be able to share results on Instagram and get 1 million likes. But what really dictates aesthetic success, Dr. Liddelow asks. Is it the implant, the abutment, the system, the soft tissue thickness, the platform shifting surfaces, the ceramics? According to Dr. Liddelow all of these things are important, but the most important thing is the position of the implant. It is known that the positioning of the implant should be 3 to 4 millimeters apical to the desired free gingival margin. It should be slightly palatal to allow for screw access and some tissue thickness in the labial aspects of that implant. Studies have also shown that the buccal shoulder position of the implant forward of a line drawn between the adjacent free gingival margins, there will be three times as much recession than if that implant has been placed a little bit more palataly. Interestingly, the tissue biotype is not significant in that calculation. Dr. Liddelow illustrates this with a case with an implant being placed forward of that line between the two free gingival margins, which leads to recession and loss of tissue thickness. The result will be a reasonably well integrated and functioning implant, but an esthetic disaster. The reason for most of the issues he sees everyday are problems with the implant position. The implant position needs to be prosthetically driven to get the optimal result. He has been using digital planning and guided surgery for around 20 years and it has become a standard of care. 

Dr. Liddelow moves on to the topic of abutments and starts to discuss cement- and screw-retained abutments. A main cause for peri-implant problems nowadays is the use of cement-retained abutments, based on his experience. There could be a thin layer of cement causing bone loss or cases where the excess cement was not even removed, as in the presented case. When cleaning out the massive excess and repositioning the abutment, a bit of bone gain could be observed after three months. As it has been well shown that almost all cemented crowns on flat abutments have some residual excess cement, Dr. Liddelow urges us to screw-retain a restoration. A literature review also shows that most of the complications happened with cement-retained compared to screw-retained restorations. An implant that cannot be restored by 25 degrees or more with a angulated screw channel, should be taken out and a new treatment should be started. 

Another aspect to look at is platform shifting. As literature shows platform shifting provides less crestal bone loss, improved soft tissue support, a greater thickness of soft tissue around the coronal aspect in that submergence area which should lead to longer term success. One of our goals in implant treatment is to have at least around 2 millimeters of attached keratinized tissue, so there will be less plaque, less mucositis, less recession, less early implant failure, less peri- implantitis type of events. Studies have shown 5x less crestal bone loss and less mucosal recession with a soft tissue thickness of greater than 2 millimeters on the coronal aspect of the implant.

What about the abutment surface? Dr. Liddelow moves on to the microstructure with a look at the surface. A new surface treatment (Xeal) was released by Nobel Biocare including an anodization process. The surface is smooth with an SA value of 0.2. But what are the benefits of this surface? Compared to machined surfaces, this surface allows for a faster and increased amount of epithelial growth on the abutment surface, as well as a better attachment of keratinocytes and a greater amount of soft tissue attachment. From a clinical point of view this is relevant as a denser soft contact to the abutment can act as a protective barrier for the underlying bone. If the bone is protected, less inflammatory response around the abutment occurs and the chance of getting a dissolution of the attachment to the abutment is lower. It was found in a randomized controlled study, that compared to machined surfaced implants, the Xeal surfaced implants showed less bacteria, less inflammatory response, and a larger amount of keratinized mucosa. A different study, conducted by Giacomo Fabbri and coworkers, showed a greater marginal bone height while using an On1 abutment with a Xeal surface, a larger amount of keratinized tissue, and even a larger amount of marginal tissue height, and marginal tissue gain around those.

Next, Dr. Liddelow looks at the implant surface and reminds us that a moderate rough implant surface of 11.5 helps with the formation of a blood clot. With the modern implant surfaces we moved from distance osteogenesis (bone growing towards the implant surface) to contact osteogenesis (bone growing on the implant surface), this helps to have a better performance of the implants and an improved success and survival rates. It also reduces early failures resulting in stronger and faster bone growth which supports the immediate function approach. The main question now is, does this work? A group at the Brånemark Clinic in Gothenburg, Sweden, compared their statistics on maxilla and mandible in full arch restorations, and compared machined implants versus TiUnite implants when they were introduced. These implants had a modified implant surface and in particular the success of maxillary implants improved dramatically. This study is most likely one of the largest meta-analyses of prospective studies at the highest clinical level. Besides implant surface, the implant chemistry is another relevant part of the scenario. With the application of anodization on the implant surface, hydroxyl groups are created, which create an adhesion point for proteins and cells. But what happens if the implant gets exposed? Ideally, a soft tissue cuff is created which reduces the likelihood of this, but there will be patients who will experience this anyways. Some patients are more prone to having such problems, may have mucosal issues, may have a lack of oral hygiene, or may have some underlying medical issues. If the surface gets exposed, a rougher surface is obviously going to attract more plaque and bacteria. There has to be a balance between integration in the first place and cleanability, according to Dr. Liddelow. Using a Xeal abutment and a TiUltra implant creates a multi-zone implant system with a minimally rough, non-porous but enhanced surface chemistry to get better soft tissue integration on the abutment level. On the implant level, TiUltra is also non-porous and just slightly rougher than the abutment, so an exposure does not attract as much plaque and is easier to clean. Moving down to the implant apex, it becomes a rougher surface, which helps with osseointegration. Another positive characteristic of the implant is its hydrophilicity, supporting earlier osseointegration and a higher bone-to-implant contact even in the early stages of healing, as some pre-clinical studies showed. He shares an early study, conducted by Fabbri and coworkers, which showed that with a TiUltra implant and a Xeal abutment they had high success rates and got bone gain in most cases. Another important thing to mention is the fact that very little inflammatory response was observed. 98.1% of the cases had no inflammation around the implant at all. All cases showed increased keratinized mucosa height which very interesting regarding the soft tissue goals of a restoration. A similar result was observed in an All-on-4 study, run by Ana Ferro and coworkers, which had a 100% success rate and marginal bone gain in many cases, but very little over a 2-year period. One of the biggest studies that is ever been undertaken and set in a real-world scenario, 1000 patients are treated with almost 1,400 implants placed, and a 99% success rate up to almost two years. 93% of the implants did not show any inflammatory response at all. This study nicely shows that the theory and the evolutionary process is working well, says Dr. Liddelow. Illustrating with a clinical case, he shares that also after 4 years the bone levels around the implant are good and no inflammatory response was noted. The evolution of implants may not be super revolutionary but also small steps can make a big difference when ideally combined. According to Dr. Liddelow a multi-zone implant makes especially sense for patients who are susceptible to peri-implant disease, as cleanability is improved should the implant become exposed. The abutments help to promote a better soft tissue barrier, reducing the foreign body response to plaque induced inflammation, which helps to prevent future bone loss. With this summary, Dr. Liddelow closes his lecture.