IMPLANT ABCs

1. Implant Market Expected to Grow Rapidly. Inside Dental Technology. 2017;8(1);10.

PETER PIZZI: Do you prefer fixed or removable solutions when treating an edentulous maxilla? And how key are cleansability and hygiene?

MAMALY RESHAD: As a fixed prosthodontist, I prefer fixed restorations, adhering to the philosophy that we want to achieve a nature-driven restorative solution that avoids tissue contact as much as possible. Thus, we try to replicate natural dentition as much as we can. In some cases we have no choice but to prescribe a removable prosthetic, typically because of the lack of lip support. Lip support is a defining factor on whether you need a fixed or removable prosthesis. The majority of the time we can avoid the flange or the vestibule to create that lip support, so it makes sense to go for a fixed prosthesis. A great deal of the evidence shows that fixed is a much lower maintenance solution and one that is easier to handle.

In terms of hygiene and cleansability, our philosophy, generally speaking, is that no prosthesis should be delivered if it is not cleansable. A fixed restoration should be as cleansable as a removable one that you take out and visually clean. There is no evidence in the literature to show one is better than the other in terms of hygiene or avoiding issues such as peri-implantitis.

DANIEL ALTER: What determines the number of implants placed, their locations, the angulation, and how you can clinically marry them restoratively to achieve the best results for the patient?

WESAM SALHA: Today, it is standard that all treatment be prosthetically driven. The implant position always follows the prosthetic design, which follows function and esthetics, and that’s how we guide the entire case. When determining the location/position for implant placement, buccal-lingual, mesio-distal, coronal-incisal, and vertical dimensions all play a big role. Years ago, we thought short implants were a big no-no. We now know there are many scenarios in which shorter-length implants are viable, allowing us to decrease the amount of surgery necessary. The same is true for angulated implants. But we try at least to plan for the angulation instead of making a surgical mistake for which we need to compromise the prosthetic outcome later. The same determinations apply for hybrid cases where you need to plan the interocclusal space ad distribution of implants.

VICTOR CASTRO: For us the diagnostic wax-up drives the whole case; knowing where the teeth have to be makes it easier to plan and place the implants to optimize the case. Sometimes we need to compromise on certain aspects because rarely do we have the perfect case. Oftentimes the dentist or surgeon performing the surgery will call or text about deviations he found. Sometimes I have to tell them that I cannot create the implant prosthetic the way they need it, but if I customize it with CAD/CAM or with a UCLA abutment, we can make the case work. Frequently, 80% of the cases go as planned, and for the remaining 20% we have to improvise.

PIZZI: From a retrievability point of view, once you decide on a fixed restoration, are you concerned with the size of the restoration? Are you segmenting the restorations? Are you looking for access should repair or changes be needed?

RESHAD: These are the types of questions that keep Domenico and me awake at night. We chat every morning. It’s an interesting evolution that we have gone through over the 15 years we’ve worked together. Our whole fixed design has changed. We started with a combination prosthesis, which we invented. We had a bar and individually cemented restorations over that bar. Then we realized that the prosthesis was not as retrievable as we would like. We want our full-mouth restorations removable once a year for cleaning and to inspect the condition of the implants. That’s much harder with individually cemented restorations. What we wanted to achieve is a hygiene appointment that is similar to a Formula One car pit stop. The patient arrives to the pit stop and you have about 15 seconds to do everything. We realized that the way we need to design the prosthesis was with four screw access holes, which will allow us to unscrew them, remove the prosthesis, and properly service it. Sometimes it is not possible to deliver a one-piece monolithic restoration because of difficult angles. But even with an angled correction, it’s impossible to get a prosthesis that is not going to have issues.

DOMENICO CASCIONE: We often use the Diamart Implant Solution. The solution utilizes a substructure-titanium bar that we can design to remedy angulation challenges with the implants, and then we create a zirconia suprastructure that we screw on top of this bar. There is no cement used for retention, so it is 100% retrievable by the dentists. We also have the advantage of supporting a long cantilever. Until recently, I was creating each of the parts myself. I milled the acrylic prototype, scanned it for a copy mill in titanium, which was sent to the milling center. Once the milled titanium bar returned, I scanned it again and made the zirconia suprastructure to fit over the bar.

In the past 6 months, Panthera Dental has bought the exclusive rights to produce this product. Now, Panthera Dental uses the original prototype in acrylic, sent by the laboratory, to create the titanium substructure and the zirconia suprastructure, and sends both sections to the laboratory so that the technician would only need to overlay porcelain or stain the zirconia. A big advantage to this solution is that a technician can also make three-segmented sections of zirconia on top of this bar, which will produce three screw-retained zirconia bridges to fit on top of the titanium bar. Because everything is screw-retained, they are completely retrievable. Between the bar and the zirconia, we always suggest using antibacterial cement and silicone cement as a temporary cement, so it can be removed when the patient returns in 1 year. We are just finishing a study at UCLA on streoptococcus mutans suspension that was placed directly on the cements; also, bacterial growth was evaluated by a temperature-controlled microplate spectrophotometer.

ALTER: What is the current clinical thinking on when to place four versus six or more implants for full-arch cases?

SALHA: All-on-4 is a great solution for full-arch restorations, with more than 20 years of published data indicating very reasonable success and survival rates. However, the literature also indicates the procedure has limitations in terms of its most successful treatment. When the process of providing a patient with a fixed complete denture involves such significant amounts of time, effort, finances, and morbidity, I believe it is prudent to place more than four implants if possible. This way, if, for whatever reason, a patient loses an implant a few years later, the same prosthesis can be utilized without compromising the entire case. Typically, we place six implants in the maxilla and five in the mandible. The only circumstances where I have used four implants for a full-arch fixed full denture case is where there was a shortened dental arch, for example, or where there was compromised anatomy.

CASTRO: Using six implants can also increase the chances of survival for each individual implant, because the mastication forces are distributed over six rather than four, putting less loading forces on each implant. Even if one implant should fail, the full-arch restoration can be saved because a five implant-supported prosthesis is still viable. However, a full-arch prosthesis supported by only four implants can be completely compromised by the loss of one of those four implants. When situations such as these happen, it is merely an aggravation for periodontists and laboratories, but for the general dentist, going from four implants to three is devastating because of lost time and money since the case would need to be started from the beginning.

ALTER: When would you opt for a full-arch fixed restoration over a removable implant-supported prosthesis? For instance, a bar overdenture or a zirconia implant-supported hybrid?

SALHA: I think today most patients want a fixed solution, which is understandable. It’s more stable in the mouth, it can be more esthetic, and it makes them feel and function more naturally. Achieving these outcomes is not always easy. That’s where we need to look at the costs and benefits of one treatment versus the other. Can we achieve something esthetic, functional, and cleansable, within a reasonable amount of time and number of surgeries, or can we do something removable that also gives the patient the function and esthetics desired? Each scenario has a certain cost in terms of time, surgeries, morbidities, and actual cost to the patient. Other important considerations when deciding the best restorative treatment are lip support and the amount of gingiva the patient displays. The quality and quantity of hard and soft tissue also plays a big role in the decision, as well as the class of interarch relationship, the number and length of surgeries, and esthetic considerations. All factor in when making a decision on which restorative option is best for the patient.

CASTRO: For me, the most important evaluation is the amount of lip support. Dr. Salha and I have this discussion frequently. If the patient is a Class III, then the restorative solution needs to be detachable; that is the only way we can create a ridge lap of more than 6 to 7 mm for a proper overbite. We try to do the most we can, whenever we can, in ceramic for hygienic purposes, but sometimes we have to go with these new techniques like BDT¹ to create something that can be removable by the patient.

PIZZI: As great as the technology is, and being able to produce this titanium subframe and either zirconia or secondary frames, what is your key to still creating a lifelike restoration, regardless of the CAD system that you’re using?

CASCIONE: We need to have high esthetics. We have to layer porcelain on top of zirconia. What’s important is not only the layering, but the kind of porcelain that we use. It’s important to have a zirconia material that gives you enough translucency. When we do a full-mouth rehabilitation, we cannot use a 600- or 700-MPa zirconia because it is not strong enough. We have to go to a 1200- or 1300-MPa zirconia, and most of these zirconias on the market are not translucent enough. However, I found a few zirconias that are really, really nice. With minimal layering, with a good technique, internal stains in the green stage, we can get a very good result, and we can preserve the strength of the prosthetic.

ALTER: When choosing materials, do you consider the opposing dentition, the AP spread,* where the implant placements are, etc?

CASTRO: In my opinion, the materials do not make the case; the space makes the case. We have so many materials that are all good, but my favorite is ceramics or zirconia for their esthetics and longevity. To achieve success with any material, we must plan on functional esthetics and not just esthetics. The AP spread dictates if we need to do a removable or fixed prosthesis. If the AP spread allows me to go just to the second bicuspid and we need to create first molar occlusion or second molar occlusion for the chewing surface, then the case has to be a removable prosthesis. The AP spread must be right or otherwise the prosthesis can fail. It’s pure physics. If you go over the limits of the physics, something is going to break.

SALHA: It is very interchangeable as to how materials affect treatment planning. You have to think about the goals you and the patient want to achieve, and techniques and materials you are going to use that suit these goals. Sometimes the goals guide us and make us use certain materials or techniques to give the patient the best treatment, such as an alveoplasty (technique), to create space for pink ceramic (material), to achieve a natural length of teeth and harmonious smile (goal). Nowadays it is very flexible, with many good materials and well-documented techniques available. Regardless of the complexity, if an implant case is planned properly and the implants are placed in the correct positions with proper space and support, and the right materials are used, the outcome usually should be successful.

PIZZI: In the CAD/CAM arena, what solution do you recommend for a case with very limited restorative space?

RESHAD: We have encountered situations where we have limited restorative space. Space, vertically, is typically a problem, especially when the implants have already been poorly placed and the patient arrives with 11 mm of restorative space. Realistically, to restore with a double structure, you would have all these layers resting on top of each other and would need at least 15 mm of vertical space. What do you do? You don’t really want to use porcelain-fused-to-gold because we know the cost issues involved. Our CAD/CAM option today is using milled base-metal alloy. By handling the base metal appropriately—and Domenico is an expert at that—he can layer ceramics over the metal frame and overcome the space issue. One advantage of the base-metal alloy is that it is very strong and we can use it for distal cantilevers. So typically, if you are doing an All-on-4 case, and the anterior wall of the sinus is a problem, you can easily cantilever back one unit to get a molar in that space while maintaining the AP spread. This way, the patient can have a nice smile and not show gaps in the posterior segment of the mouth. Having the cantilever in base alloy makes the prosthesis extremely strong and rigid, alleviating the problems with flexure of the framework or fracture of the ceramic.

PIZZI: When dealing with zirconia cases, you mentioned you use noble metals or you use base metals, depending on the case and, I assume, some titanium frames. Have you noticed any challenges or problems with these full-arch zirconia bridge cases?

RESHAD: If you do enough of anything, you will see problems. Unfortunately, dentistry’s research is based on samples of 10 in the laboratory, so we have low value in terms of editing space. When I speak to engineers in the school of engineering, each of their samples is 5 million in number. When comparing 5 million of each sample, it’s much easier to produce results that have value and may translate to reality. We don’t have the resources to do that, so by the time it gets to the patient’s mouth and works there, our information is derived from clinical observations.

What Domenico and I are finding is that we have seen specific problems. For example, if you torque down on a pure zirconia framework, with no titanium cylinder attaching it to the implant, there is a risk that you can torque down too much and crack the framework. There is a study conducted by Jason Kim that looks into this and other risks. A solution examined was the cemented titanium cylinder in the zirconia framework; it’s a stronger solution than direct zirconia framework. However, when we look at that method more carefully, we see that the bond between the zirconia and the composite cement is basically nonexistent. You cannot bond the two together. It’s simply a matter of mechanical retention, so that can also fail over time. I have seen these debond a few times after 2 to 3 years. Currently, this is the preferred method of treatment. Domenico informs me that there is a new zirconia on the market that you can etch. A new etchable ceramic should help with the bonding issue. Another thing we don’t know is how tall that titanium chimney should be? or how thin or thick the walls should be? We need more research to fully understand and resolve these issues.

ALTER: For fixed complete dentures, how do you handle placing implants in the anterior region?

SALHA: With the angulated abutments that are available on the market today and the improved designs of prostheses, we are able to overcome the phonetic and esthetic problems if implants are placed within the correct parameters. Of course, any time you place too many implants next to each other you could create a problem. Any time you place the implants in the wrong apical-coronal dimension, you are asking for trouble. However, if all the implants are placed within the diagnostic data and parameters, it should be fine. I don’t think esthetically it is as compromising a factor as it was.

CASTRO: For technicians, the most important restorative aspect is the spread of the implants and how that impacts the load of the force over the final prosthesis so that it is more harmonic. Anteriorly, if the implants are well lingualized or palatal, we have enough restorative components today to correct those angulations and bring the access to the lingual aspect or the palatal aspect. We also have angled screws that help significantly. As manufacturers continue to develop new angled abutments, technicians and restorative dentists are becoming more confident using them.