Live Webinar: Prosthetic Implant Complications: Causes, Prevention and Management

In the FOR Webinar on Implant Prosthetic Complications, Dr. Todd Schoenbaum shares some strategies, understanding and techniques on what to expect for implant complications, related to the prosthetic side. He provides us with information on how to manage them when they appear and how to prevent them from occurring in the future.

Dr. Schoenbaum opens the webinar with the statement that most of the restorative dentistry done in our practices today is replacing old dentistry. Implant rehabilitations do not last forever and with time going by, and more and more implants being done, a much greater portion of our practices will be taking care of revision, repair and replacement of those rehabilitations. He believes that a strong team is needed in order to solve complex problems in a clinical setting. That includes a surgeon, a prosthodontist and a lab technician. 

Looking at the complications, Dr. Schoenbaum presents 4 categories:

1. Peri-implant problems
2. Contact problems
3. Prosthetic screw problems
4. Prosthetic problems

The first classification, peri-implant problems is related to the bone and soft tissue around the implants. Usually this is the domain of the surgeon, but much of what a prosthodontist does in the rehabilitation of implants can lead to this type of problems. Sometimes, when implants are restored, an environment can be caused or produced that is more susceptible to peri-implant problems, like peri-implant mucositis, inflammation recession, and peri-implantitis, meaning bone loss and implant loss. At the benign end of the spectrum is recession around implants. Dr. Schoenbaum shares a clinical case of a patient with a maxillary right lateral incisor that has been in place for 5 years and is now showing the cement margin and the zirconia abutment that was not visible before. This is now producing an aesthetic complication for the patient as she shows a high smile line because of the recession related to that implant. Taking a closer look, Dr. Schoenbaum points out that when an abutment is received from the lab and inserted, the tissue will blanch. That blanching should be a yellow flag for us. According to Dr. Schoenbaum, if the tissue blanches, the body is trying to tell us that the tissue will recede in the future. We must evaluate the clinical impact this could have with each case. Maybe a molar site a small recession is a minor consequence, while in the aesthetic zone a recession may produce an aesthetic challenge as with the shown case. This can result in something that we need to revise or replace the rehabilitation or the abutment. In the shown case, he investigated the restoration to look for a non-surgical solution and proceeded with the production of a temporary abutment with a gross under-contouring of the areas of concern. Here it is the papilla areas in the mid-facial aspect on the palatal side. In most of the cases there is no need for any over-contour or emergence on the palatal or lingual side. In the presented case, we can see that the abutment at the time of delivery probably produced a fair amount of blanching. That blanching was a warning sign for the clinician that it would lead to recession. Just at a 2-dimensional photo we can observe the over-contouring of the abutment in both the horizontal and the vertical direction. He exchanged this abutment against an under-contoured provisional and allowed the tissue to migrate into a more favorable position over 6 weeks. He shows the deconstruction of the case, highlighting that Guttapercha should not be used to close screw holes. Teflon can be considered the standard to seal the screw access or a cotton, but Guttapercha is very difficult to remove in case of a revision as it can lead to a stripped screw and increase the complexity even more. He continues to show the next steps of the process, including the placement of the titanium abutments, which have been grossly under-contoured on the mid-facial aspect to allow space for the papilla to migrate as much as possible. The soft tissue around the implant is not to be forced, it needs to be protected and given room to migrate to the most favorable position, Dr. Schoenbaum reminds us. The patient will wear the provisional for at least 6 weeks, she can wear it up to 1 year. She returns after 4 months and we can see that a correction of about 90% of the distal papilla was achieved, and about 85% correction of the mesial and about 80-85% of the mid-gingival zenith. At this point, Dr. Schoenbaum contacts the lab technician to fabricate a custom zirconia abutment with the margins nearly equi-gingival, maybe minus 0.5. Even with the patient having recession before, it is important to not put the margins too deep, he emphasizes. The custom zirconia abutment with a titanium base is produced, here it is important to ensure that no zirconia is going inside the implant. The connection needs to be metal. The custom-milled zirconia abutment has the margin nearly equi-gingival, as it is imperative to have access to the cement. If the margin is too deep, we cannot access the cement. He concludes the case with a follow-up image, pointing out that there should be a follow-up after the delivery of the prosthetics. This follow-up visit is also important in regards to evaluating soft tissue health, that patient hygiene is appropriate and adequate, as is the occlusal scheme which should be appropriate given the loads of the system. When looking at cement in detail, Dr. Schoenbaum mentions, that cement has a long legacy of causing problems around implants. He proposes to us that it is not necessarily the cement causing the problems, as he demonstrates in a moment. The next case is a patient with a 4-unit bridge that he needed to remove from 2 implants, as they had a poorly cemented PFM bridge with open margins and lots of excess cement around it . The patient presented at UCLA’s Center for Aesthetic Dentistry, at the time lead by Ed McLaren, for a consultation of the implants that were placed 2 years prior. She was a young patient, 26-27 years, with a high smile line and high aesthetic desires and expectations. Only after 1 year the implants showed profound recession and the tissue was very inflamed and undergoing remodeling. As we can see with the deconstruction, a main point is the cement. Dr. Schoenbaum proposes to look closely at the deep margins of the abutments, particularly the interproximal areas, as the real problem is the depth of the margins. With deep margins, cement will get left behind and then cause inflammation, followed by bone loss, possibly leading to implant loss for the patient. Illustrating on an image, he points out that the margins are far to deep to clinically remove the cement without opening a flap, leaving cement behind. The case was done using custom abutments, meaning the design of the abutments was prescribed. Either the clinician or the technician put the margins too deep subgingivally, guaranteeing the cement being left behind. In non-aesthetic areas or with patients with minor aesthetic concern, it can be done with very minimal change of retained cement, with the caveat that the margins are placed nearly equi-gingival. In some cases, we might think about placing them super-gingival. The prescription is very easy, according to Dr. Schoenbaum, it will be for a custom-milled titanium abutment. Ideally, the production of the abutment is done by the manufacturer of the implant. Additionally, the prescription will add 0.5 or even 1 mm. If there is sufficient retention and in a non-aesthetic area, we can put the margins were they are not an issue. According to Thomas Linkevicius from Valenius, Lithuania, who did early in-vitro and in-vivo studies on the effect of margin depth on cement retention, we know that the deeper the margin has been placed, the greater the chance and volume of retained cement are. With margins placed super-gingivally, it would be very easy to address cement if it was not detected in the first place. He continues with a that presented regarding mild sensitivity, pain on palpation, and occasional pimples above the implant at the maxillary left central incisor position. He points out the remnant about 4 mm above the crown, at the area where typically the implant abutment junction would be. Looking a radiographic close-up, we can see some atypical bone loss. The radiograph only without any clinical signs or symptoms, could lead to the assumption that the implant was placed not deep enough or that there was perhaps bone remodeling. With the clinical signs and symptoms, this might be an active, ongoing and progressive problem that needs to be resolved before it leads to the loss of the implant. On the clinical image we can see that the soft tissue completely fills both papilla spaces. Looking at the radiograph, we can see that from the contact point down to where this changing contour happens, where the cement margin is that we're approximately five millimeters deep sub -gingival for where the cement will be expressed. We can see that currently the patient is probing about 8-10mm circumferentially around that implant crown suggesting that we do have some active bone loss. Following this we see the deconstruction with some of the cement. A sad case with the margins of a custom abutment being placed simply far too deep sub-gingivally. The problem with this case was that the clinician or lab technician were unaware or decided to place the margins too deep. The margins are the issue, if the margins were not too deep, the patient would not face this problem. As a take-home message, Dr. Schoenbaum reminds us that if a cement-retained restoration is indicated, we should place the margins where we can see them. This might require a custom-milled abutment, ideally produced by a milling center belonging to the implant manufacturer. Most major implant companies have a milling center for their abutments and the margins need to be specifically prescribed no deeper than 1mm. Some people want to know what will happen in 5, 10 or 20 years when we have a recession. If the margin should become visible and if it is an aesthetic concern for the patient, a new abutment can be purchased, again not deeper than 1mm sub-gingivally. He mentions that although he is on Team “screw-retained”, he comfortably cements restorations when the indications ask for it. In general, he would opt for a screw-retained restoration. With cemented restorations, the margins are the key factor for minimizing the incidence of peri-implantitis. Another point to look out for is occlusion, according to Dr. Schoenbaum, as implants can handle occlusion, but it needs to be appropriate and reasonable and ideally along the implant axis. We need to make sure to torque the screws correctly, and all parts need to fit as ideally as possible. This means all parts should be made by the manufacturer of the implant. This applies to all implant systems. He also addresses the topic of angled screw channels, which have been around for over 40 years. Referring to a publication in 1987, showing their use in some of the old PFM restorations. In the current form as offered by the manufacturers, they are relatively new, he says. In general, they allow us to move a screw channel to a non-aesthetic area up to 20 or 25 degrees. He shares a new case of a patient seeking consultation for implants that have already osseointegrated, and the angulation of the central incisor could be brought back to the palatal with an angled screw system. For the lateral incisor that angulation is probably actually too severe for correction with most angled screw channel systems, so this would typically lead to a cemented solution. We can see a variety of offerings of angled screw channel system from different manufacturers. We should remember that we require a different driver for this solution. The driver for an angled screw channel abutment is unique to the manufacturer and not interchangeable. The first versions of these abutments had very short Ti bases which work fine in an axial load environment but typically we use them in the anterior maxilla and here much of the force is vectoring out to the facial as non-axial forces, which results in quite a bit of debonding. Developed from these original designs, now we can see 3rd generation angled screw channel systems, offering a custom milled abutment with enhanced retention for full support of the crown and minimizing debonding, with more idealized emergence profiles, customized to the site and angulated screw channel. 

Dr. Schoenbaum moves on to the next topic, contact problems. He presents one of his own patients, one year after having an implant crown on the maxillary first premolar and a replacement crown placed on the canine on an adjacent, natural tooth. On the 1-year follow-up we can see that the contact present is no longer appropriate. It is fully to the palatal side and all the way gingival. Some time between the delivery of the restoration and the follow-up, this non-ideal contact was developed, probably because of some sort of occlusal contact on the canine that either Dr. Schoenbaum underestimated or overlooked, as he shares. When opening the flap a fair amount of bone loss around the implant is visible. For the mesial contact, the ceramic material appears to be chipped or broken, or the adjacent tooth migrated mesial, leading to an open contact, food impaction, and now to a fairly extensive bone loss around the implant. The restoration is a screw-retained restoration. Often times cement is the only thing blamed for peri-implantitis and obviously with a screw-retained restoration, it is not part of the issue. He explains, open contacts are slightly more common in the mandible, and slightly more common on the mesial side of the teeth, and slightly more common in smaller-sized teeth, like the premolars. Over time the teeth are migrating towards the midline. Thinking about older patients, we see many of them with crowded mandibular anteriors, where they did not necessarily have that at a younger age. With the shrinkage of the interdental periodontal ligament, all teeth generally drift to the midline, leaving an implant behind. Illustrating this with clinical images, Dr. Schoenbaum shows a case with lateral incisors restored with implants and 10 or 20 years later, the rest of the dentition has continued its natural physiologic drifting. With the patient not wearing nightguards or retainers, the lateral incisors end up looking rather short. What can we do to minimize the incidence of open contacts in our patients? One thing is to emphasize the need for some sort of rigid occlusal guard, preferably on the treated arch for single implants, otherwise on the arch based on our clinical discretion or preference. Traditional orthodontic work, bonded wires, Hawley appliances, invisible liners, can help to slow down the development of open contacts. With patient compliance, open contacts are an easy thing to prevent. If the patient is not compliant, there are also quite expensive things to fix, typically requiring repair or replacement of the implant restoration. 

The next topic, Dr. Schoenbaum is discussing, is screw problems, including loose, broken, and stripped screws. He shows a clinical case of a patient seeking consultation for an implant bridge that was replaced 6 weeks prior and is already loose. As we are facing a new restoration, documentation should be of importance. Radiographs of the case do not provide documentation of loose restorations, demonstrated in the shown case as the radiograph looked fine. When we need to repair, remove, or restore something that has been loose for a while, it is important to clean the inside of the implant. His favorite tool is chlorhexidine, but also a more neutral solution like sterile saline would work. A proxy brush can be used to clean the interior of the implant, a monojet syringe, proxy brush, lots of flushing, rotating, and scrubbing is required. Before we put a new restoration on to the implant, it needs to be clean. Dr. Schoenbaum continues with a new case, where the clinical screws were sent in the cast where they are not supposed to be. Clinical screws should be delivered in a separate bag, unopened, untouched, and unused and the shown screws look very worn. If we would try to torque them down, they would probably strip out at about 10-15 Ncm. The cause is that probably the drivers that were used in the lab were either the wrong drivers or worn-out drivers. 

The surgeons among us know that after placing a certain number of implants, the osteotomy drills get dull, will overheat the bone, and need to be replaced. Instruments for prosthetic use also wear out. Our implant drivers wear out over time, and we can see on an image Dr. Schoenbaum shows, a driver that has been misused and abused. This driver will not be able to create any torque. He reminds us to train the team members to check the drivers. A simple test is to attach a healing abutment to the driver, give it a little wiggle and if it falls off, the driver needs to be replaced. Another item to look after is the torque wrench. Most of the torque wrenches should be disassembled for autoclaving and sterilization, and we should know which way is which when we use it to tighten a screw. Dr. Schoenbaum mentions the direction as it can get confusing working in the maxilla of a supine positioned patient to identify the correct direction for tightening and loosening of a screw. A very common mistake, as he points out, is to put the thumb on the little bar when using the torque wrench. We should avoid touching the bar at all, as this will alter the torque that we want to achieve. 

While removing and replacing a cemented crown to correct or replace a loose screw is relatively easy, it may not be that easy to remove a screw-retained crown, for example in the posterior. We need to drill a hole through the top, trying to find the screw access cylinder, remove the Teflon tape or cotton and then remove and replace the screws as needed. With stripped screw, we might have to replace a crown or take an abutment off, that is not ours. We have to identify the implant, have the right drivers, need to access, and find a stripped screw. According to Dr. Schoenbaum there are different ways to remove stripped screws. The “classic” way is to use a slot driver, which needs to be order prior. If we restore many implants, he recommends us to add this driver to our tooling assortment. To remove a screw with a slot driver, we need to cut a slot across the stripped-out screw connection, by for example using a 169l or a round bur. The slot driver will then engage in that newly created slot, and we should be able to remove the screw. This works with all screw systems. When we face a broken screw, the manufacturers are providing us with so-called rescue or revision or service kits, of which many include a broken screw retrieval drill, which is a like a little claw drill. This needs to be run counterclockwise and at slow speed with the handpiece or a hand driver to unwind that last bit of a broken screw. We need to drill a hole through the middle of the screw and then, like a corkscrew the drill gets forced and threaded into the screw piece, and hopefully can get retrieved. They are also offered by some of the manufacturers. 

The last category of complication, Dr. Schoenbaum is addressing, is prosthetic problems. This is related to abutments, frameworks, non-passive frameworks commonly, and/or the ceramic overlying them. The causes of prosthetic complications, such as breakages, things coming apart can happen over time after a normal treatment. There will be some wear and tear over time, even with zirconia and titanium. One of the issues that can occur is occlusion. When looking at single unit implant restorations, there are some guidelines that it should drag shimstock under moderate occlusal pressure and hold under firm occlusal pressure. Generally speaking, he reminds us to make sure our implant restorations are not too high, are not the first thing touching. And to the extent possible, the forces should be directed in axial direction. Another point is to make sure the frameworks are passive. An easy test for passivity is to tighten the screws, and they should go in easily until they hit the bottom and then torque to full specs within about half a turn. If the screws are going and getting tighter and tighter and are still turning, that should be warning sign for us that something is being compressed or stretched or bent – which could be the framework. He shows images of a clinical case, a patient of his, with an implant crown at the left lateral position. The patient is 65 years old and shows very little signs of wear on the central incisors. 5 years later, Dr. Schoenbaum is contacted by colleague, who sent him an image of the patient with the abutment broken off. A patient with little occlusal demands, snapped an abutment in half after 5 years. Looking at it in retrospective, he points out that the titanium abutments are too small, and the zirconia walls are too thin, which he didn’t notice at the time. He also highlights another possible reason for this: the mandibular teeth may have got crowded over time, for example the canine or the lateral incisor, leading to a traumatic occlusal scheme and then overloading the inferior, weakly designed abutment. On the radiograph of this case, we can see something strange inside the implant. The little ring is actually zirconia that has broken off inside the implant. This trend has largely stopped, according to Dr. Schoenbaum, but there was a time, when zirconia was invincible, and we were putting it inside an implant. Zirconia is not invincible, and the forces and the thicknesses demanded inside the implant a far too weak of a material generally to hold up in most environments. The patient had a screw-retained 3-unit implant bridge, that is zirconia on Ti abutments. He points out that both Ti abutments are engaging, and the implants are not perfectly 0.001 degree parallel. An implant bridge on both of those abutments cannot be engaging. In the presented case, the implants were quite parallel, but when the screws were tightened, they were tightening and kept on turning, not reaching the full spec leading to zirconia experiencing spring forces, resulting in the patient returning after 1 week with the bridge looking like on the images. At the time of the delivery of the restoration, the manufacturer did not offer non-engaging abutments. Many of us are familiar with screw-retained zirconia restorations, sometimes referred to “screw-mentable” – with different meanings for different people. One of the most common restorations today, is a zirconia crown cemented onto a stock Ti component, called a Ti base. So, this a small titanium abutment that is cemented into a zirconia crown, the crown is then screw-retained into the site. This procedure is relatively affordable lab bills, it is very robust, and can be made quite aesthetic. The downside is that the little Ti base needs to be cemented into the zirconia crown, which makes them insufficient for high load scenarios. Dr. Schoenbaum shares, that from his perspective, high load scenarios in the mouth are anywhere that is not a premolar or lateral incisor. Central incisors, canines and molars need something more robust than this solution, in his personal opinion. Another clinical case shows a patient 1 week in with a mandibular first molar implant rehabilitation. We can see a gray ring that is a broken part of the abutment still stuck inside the crown. The walls are insufficiently thick in most of the these to support molar restorations. The patient came to the clinic, reporting a “clicking” sound of her restoration, and the radiograph reveals a gap between the abutment and the PFM bridge, where either it was not cemented fully, or the cement had debonded. When taking the bridge off, he could see that the abutments were poorly designed for holding cement. The lab needs to cement the crowns onto the abutments. The abutments are about 3mm tall, completely smooth, and devoid of any profound retentive features. The superior option for anything that is not a premolar or lateral incisors today would be zirconia, perhaps lithium disilicate would suffice in some scenarios, layered or not layered, stained or not stained, and made by the manufacturer of the implant. The margins on this can be placed as deep as needed, because the lab will typically be cementing those together, or if we prefer, we can cement them intraorally, then remove the restoration, cleaning up the cement, and then re-screw it like a regular screw-retained restoration. In the aesthetic zone we can do something similar, we can have the margins quite deep, and the zirconia superstructure cemented on the custom titanium abutment, but the entire emergence area is made of zirconia to minimize aby graying of the soft tissue. Summarizing things, we can do to prevent problems with our implant restorations: ensure everything is passive, patients are wearing an occlusal guard to slow down migration of teeth and protect the materials from trauma and occlusion at night. Everything should be as accurate as possible, is it when scanning, using photogrammetry or traditional impression materials. And we need to collaborate with a high-quality lab, as there is a lot that goes on at the lab side that can lead to complications. The technicians need to understand the need for manufacturer brand and componentry, if and when possible. Providing clinical images, Dr. Schoenbaum shows a patient that presented with a sort of provisional restoration where a part seemed to be made from PMMA, even a papilla. Prosthetic materials should not be wrapped around natural teeth that they are not glued to, he emphasizes. In the shown case, when the papilla filled up, it created a concave surface and a food trap around the lateral incisor, which unfortunately had to be extracted. The site was disinfected through a full flap decontamination and a GBR procedure to maintain the implant. On the lab side, the technician needs to understand the importance of making sure on the aesthetic zone that the entire palatal contour is supported with zirconia and not unsupported feldspathic porcelain. The new restoration provides a relatively normal smile line, and the defect is mostly camouflaged. The loss of the mesial papilla did not bother the patient. If it would bother the patient, it could be closed with the implant restoration and some composite or a mini veneer on the adjacent natural teeth. In these cantilever scenarios it is important to make sure that the occlusion is also on the implant-supported tooth and not on the cantilever pontic tooth. With the reminder that the patient also needs to wear their occlusal guard again and understands not to function excessively on that cantilever, Dr. Schoenbaum concludes his presentation.