Know Your Implant Options
Understanding the implications of various strategies helps inform optimal treatment plans
More than 5 million dental implants are placed each year by dentists in the United States,1 and the number has been increasing: A 2018 study found the increase in dental implant prevalence among adults missing any teeth was 5.7% from 2015 to 2016, up from 0.7% from 1999 to 2000.2 The global dental implant market has been forecast to nearly double from 2018 ($3.9 billion) to 2027 ($7.4 billion).3 Meanwhile, laboratory fees for dental implants have risen from an average of $288 in 2012 to $335 for screw-retained and $313 for cement-retained in 2020, with more than 60% of laboratories offering these services.4,5 Much of that growth has been attributed to improved technology and materials, but leaders in the field caution against relying too heavily on these new developments; a strong understanding of the various considerations that go into implant treatment plans is critical for all members of the restorative team, including the dental laboratory technician.
"Technicians should not be afraid to provide input on treatment plans," says Joe Abad Santos, Owner of Virtual Axis 109 Dental Design in Phoenix, Arizona. "As the ones fabricating the restorations, we are expected to have that knowledge. If the implants fail, then we will be blamed."
Various strategies exist for dental implants. They can be retained via either screws or cement. They can utilize either an overdenture or an all-on-X prosthetic. They can be splinted, and they can be immediately loaded. They can be crafted from zirconia, PMMA, or other materials. There is often more than one acceptable solution, but developing those solutions requires a strong grasp of the components and options involved.
"So much goes into it, and we as laboratories need to ensure that we understand everything correctly, because clinicians are asking us for help more and more," says Lars Hansson, CDT, Owner of LH Dental Design Solutions in Virginia Beach, Virginia, and Clinical Faculty at Virginia Commonwealth University. "Digital dentistry and implants have brought us closer to surgery, but just having the software does not mean you understand implant dentistry biologically."
Retention: Screws vs Cement
One of the primary questions at the start of any implant case is whether to utilize screw retention or cement. An Inside Dentistry survey of clinical readership found that 64% of dentists utilize screw-retained implant restorations and 53% utilize cement.6 The current popularity of screw retention is primarily attributed to its retrievability and the risk of peri-implantitis when cement is retained in the sulcus.
"Screw-retained is generally preferable, but the question is: Can you physically do it?" Hansson says, adding that the involvement of surgical guides, if they are being utilized in the design, can allow the laboratory to help ensure that screw retention is possible. "With screw-retained implants, we can repair them more easily when necessary. Making a proper emergence profile is easier, as is following the proper biological width."
Cement retention can be necessary if the angle of the implant makes a screw impracticable for functional and/or esthetic reasons, but certain conditions must be present in order to make cement retention viable. The laboratory's involvement in the planning stages of a case is preferable in order to ensure these determinations are made correctly.
"When I receive a fixture-level impression, I look for the angulation of the implants and parallelism," says Steven Pigliacelli, MDT, CDT, Vice President and Director of Education for Marotta Dental Studio in East Farmingdale, New York. "Based on the implant placement, the screw access channel could be problematic and could present esthetic and functional risks to the restoration. In those situations, cementing the crown onto a custom abutment is the preferable solution. I also analyze the interocclusal space; if the space is not adequate for cementation, then the better option is to screw retain. Additionally, in some cases, creating the tooth form becomes more challenging because of the amount of buccal, lingual, mesial, and distal corridor that needs to be filled; set screws could be required, and based on the implant interface and emergence profile, creating ridge lap structures should be avoided because hygiene and cleansability become more difficult."
Angled screw access channels are one solution that has been provided by manufacturers. Of course, with a proper understanding of all the options and implications, technicians sometimes can get creative. One hybrid solution incorporates both screws and cement.
"If the implant is subgingival but we want to make it screw-retained, stock Ti bases typically are not long enough, and all of the forces are on the teeth, which are supragingival," Abad Santos says. "I fabricate a custom abutment, rescan it, and use it as my preparation, putting an access hole on the occlusal surface for the crown so that the crown itself has an access hole also. When the dentist gets it, it is already cemented and they need only to screw it in."
All-on-X vs Overdentures
Another early decision in treatment planning involves whether to fabricate an overdenture or an all-on-X prosthesis. An Inside Dentistry survey of clinical readership found that 34% of dentists provide overdentures to patients, while 16% offer all-on-X.
"As technicians, part of our challenge is to be educated enough to help manage our clinical partners in the restorative process," Hansson says. "Most laboratories today want to specialize. Being involved clinically helps them better understand the clinical and restorative challenges, and makes them better partners for dentists. So many complexities are involved in the choice between removable and fixed."
Hansson says the first step is determining where the teeth will go, assisted by an understanding the patient's facial anatomy.
"Understanding the bone anatomy and tissue anatomy leads to lip support, which is necessary with removables but a complicated issue unto itself," he says. "We can put four implants in and fabricate a locator overdenture, but if there is too much resorption in the maxilla, how will you ever get them to be parallel enough for a path of draw? Every patient is different.
"With fixed, you need to deal with a transition zone between the ridge and the intaglio surface of the prosthesis. Then, we need to consider the vertical dimension of occlusion (VDO). What type of bony architecture has the patient lost, and what are we replacing?"
Abad Santos says he looks first at two factors: the patient's bone structure and their existing dentition or denture. Worn-down teeth are often an indicator of bruxism, which could make an overdenture less desirable because it is less repairable.
"I recommend utilizing a bar—whether overdenture or screw-retained—for all my patients because it is nice to have all those implants splinted together, and implant failure is less likely," Abad Santos says. "Our patients are provisionalized as a blueprint for the final restorative options, which helps us make decisions on materials and other considerations. Still, I always make a night guard, so when the patient clenches or moves their teeth sideways, we are not jeopardizing both the implant and the opposing dentition."
Similarly, Pigliacelli prefers to make a bar and two dentures for certain patients.
"So many think full-arch zirconia is the answer to all of our problems," Pigliacelli says, "but for certain patients, wear is inevitable, and I would rather create a situation where we can easily retrieve and repair the prosthetic. People forget that if you put this rigid rock on this monster bite, something has to give. If the patient has broken their teeth previously, the force is still there, so they will break restorations. With an easily repairable solution, they can simply wear the second prosthetic while the first is being repaired. That is an agreement made with the patient: In order to preserve your bite, there will be a maintenance requirement. I have had success with that strategy many times."
Implant manufacturers have developed various innovative components to address some of the challenges involved in these treatment strategies, but Hansson notes that adding more components creates more flexibility and movement.
"This is a very broad field, and it must be discussed in detail not only with the clinician looking at the treatment plan but also with the patient," Hansson says. "Do they all want fixed? No. Can we always do fixed? No. Can we always do removable? No. We can create esthetically beautiful restorations, but if our planning of the implants and the various choices involved are not well informed, we are not necessarily helping the patient long-term because we might be creating new problems."
Zirconia on Zirconia?
One significant choice in any implant case involves material selection, and one of the most controversial questions is whether to use zirconia on zirconia. The material obviously is strong, but some cite clanking sounds in the mouth as a reason to use softer materials.
"People talk about softer materials being like a cushion for the implant, but that is not really how it works," Hansson says. "The softer the material, the more wear you will have. The more material that you cannot high-polish and high-shine—not glaze—the more porosity and infiltration of bacteria you will have. When you start to layer materials such as nanocomposites and high-performance polymers, you are using multiple materials that do not 100% bond to each other, which requires cementing between them. These materials are then placed in an environment with constant movement and heat change. These patients did not become edentulous without biological or parafunctional problems. I do not see many articles or photographs of these nanocomposite layered restorations after 3 to 5 years in the mouth. They are beautiful materials to work with at the bench, but when it comes to long-term intraoral durability, they start to break down over time in the more hostile environment. Zirconia will break down over time too, but not the same way."
Hansson and Abad Santos both say the clanking issue with zirconia is a result of improper design, rather than a flaw with the material.
"Usually, the reason for clanking is that the vertical dimension of occlusion (VDO) is too open," Abad Santos says. "When you talk and eat, you are not supposed to touch your teeth. Only when you close your bite should you touch your teeth. If a person is talking and they start clanking, it means the VDO needs to be closed down. When I do zirconia over zirconia, I tell the dentist to always look at the VDO and check the way the patient speaks. Take a video and pictures. I want to see how much I need to open or close the bite. If the case is done correctly, there should not be clanking."
Another way to strengthen implants is by splinting them—an issue with extensive literature regarding when to do it and when not to.
When considering whether to splint implant to implant, Hansson recommends considering the stability/mobility of the rest of the dentition, as implants are an ankylosed component, whereas teeth have periodontal ligaments.
"Splinting adds strength to a restoration," Hansson says. "Location in the arch form matters. The highest bite force is in the posterior. Meanwhile, the mandible has stronger bone than the maxilla. The anterior-posterior spread also is a factor in splinting."
Splinting with natural teeth is more complicated. In some situations, it is absolutely necessary. In others, such as when two implants surround one natural tooth, it can work well. For the most part, though, many recommend avoiding it.
"The implant crown is ankylosed, so when it is cemented to a natural tooth with a periodontal ligament, flexure is created in the prosthesis, which compresses the tooth and leads the cement seal to break," Hansson says. "When that seal breaks, the frame leaves a gap, and food or bacteria fill it. We have tried using telescopic copings on the natural teeth and cementing a bridge to the coping, but the same scenario occurred. Then, we thought switching to screw retention would help, but we experienced screw breakage."
A popular option for delivery of all-on-X prostheses is immediate loading. This strategy offers obvious benefits to the patient, but it must be done with care.
"There is a lot of literature to support immediate loading, and it works," Pigliacelli says. "However, if you do not understand the principles and you do not know how to do it correctly, that can lead to failure. Incorrect planning and loading can lead to the prosthesis not being adequately screwed down, or gaps being created. For example, in some cases only three of the four implants are engaged, so the other side is up, and every time the patient chews, they rip out two of the implants. Now they only have two left and the bone has been destroyed, so they end up needing an overdenture. You can do real damage; this is not something where you can take a weekend course, have a guide fabricated, and place an immediate load. Training and experience are important."
Abad Santos prefers a next-day strategy that provides some immediacy to the patient but a more predictable outcome. He designs the prosthesis prior to the surgery but then fabricates a titanium bar to deliver the next day with a PMMA overlay that gets cemented over the bar.
"It is thinner, more natural looking, and more comfortable for the patient," Abad Santos says. "Yes, the patient leaves the first day with no teeth; but they come back the following day, wide awake, not sedated, and they can actually evaluate their new teeth with a clear head and test their speech with the prosthesis in the mouth. The bulky, thick same-day conversions take more time for everyone, they are not comfortable enough, and over time, they get worn down."
Whether simply offering input on strategy or developing innovative new options, the key for laboratories is education. When you know the "why" behind the various questions, you are equipped to develop and select solutions.
Abad Santos recommends taking as many seminars and webinars as possible, including clinical ones.
"We need to be able to tell our dentists the pros and cons of the various options," Abad Santos says. "When we can do that, we earn their respect."
In addition to tradeshows, institutes such as the Dawson Academy, the Kois Center, the Pankey Institute, and Spear Education offer courses on implants. Online resources are available, as are books; for instance, Hansson recommends the book Cementation in Dental Implantology: An Evidence-Based Guide, by Chandur Wadhwani, DDS, MSD.
Of course, real-world experience is critical. Soliciting as much feedback as possible from dentists is the best way to learn what works and what does not.
"If you are running any business, you always want to be aware of what succeeded and what had issues," Pigliacelli says. "Sometimes it is not even a matter of a case failing. We were using a pour resin for hybrid cases at one time, and a year later, it looked terrible in the mouth. I would have never known. Relationships and ongoing learning are what allow us to do exceptional work."