INTRODUCTION
Our modern endosseous dental implants osseointegrate into the available hard tissue and serve as a foundation for fixed and fixed-detachable prostheses.1
Many advances in dental implant prosthetics are available, including full-arch, implant-retained prostheses and implant-retained overdentures. Conventional dentures serve a viable function for many individuals. Today, quality-of-life issues and improved chewing function, as well as aesthetic concerns, are in the spotlight. Many of our patients present to our practices wishing to consider options that may improve their overall health and self-confidence. Dentures give some function and facial support, but the gagging reflex caused by full-palatal coverage of the maxilla and diminished chewing efficiency steers some to something better. Mandibular full-arch dentures have significant negative effects as they tend to be unstable.
CASE REPORT
Our patient was a 75-year-old female with no negative medical conditions that could affect the integration of dental implants. She had been edentulous for a major portion of her adult life. Figure 1 illustrates the preoperative panoramic radiograph and CBCT evaluation of the minimal mandibular and maxillary anterior hard tissue.
Figure 1. Preoperative panoramic and CBCT evaluation on minimal available mandibular and maxillary anterior hard tissue.
There are 2 basic criteria for patients who would like restorations over implants. First, there must be relative health with no significant issues that could affect healing, such as uncontrolled diabetes, uncontrolled hypertension, or immuno-suppressive diseases. The second issue that must be considered is the amount of vertical and horizontal available bone. Certain protocols are followed to allow for ideal integration of the fixtures. Ideally, a minimum of 1 to 2 mm of facial and palatal/lingual bone would be present. The length of implants chosen is dictated by the existing vertical volume that presents. The engineering principles of crown-to-root ratio and spacing need to be respected, as physical forces of mastication over time could result in the breakdown of the supporting structures. Implants need to be spaced along the arches to prevent rocking and instability. Implant-retained overdentures are a cost-effective clinical treatment modality that helps improve chewing function and creates retention and stability. The removable appliance is easily maintained, even for individuals with manual dexterity issues or poor oral hygiene capabilities. The critical factor with these overdentures is that the implants need to be strategically placed. According to Misch,2 stability is achieved by placing the implants around the arch with as much spread as the available anatomy will allow. The limiting factors include loss of vertical and horizontal bone and collapse of the posterior anatomy, resulting in potential trauma to the mandibular and mental nerves. Implant-retained prostheses can predictably cantilever up to 1.5 times the distance between a line drawn through the most anterior implants and a line drawn through the most posterior implants. This is referred to as the anterior-posterior (A-P) spread. Remember that implant-retained overdentures are usually both implant- and soft-tissue-supported, so proper spacing of the retentive devices is important.
LOCATOR (Zest Dental Solutions) attachments are an efficient and cost-effective means to achieve retention. The system is designed for use with overdentures or partial dentures. They provide a low vertical height and a self-locating design that allows the patient to easily seat the appliance. The dual-retention innovation provides a significant surface area. Inside and outside retention ensures a long-lasting wear factor. The retentive nylon attachment remains in contact with the abutment socket, while the titanium denture cap has a full range of rotational movement over the male. They can be used with non-parallel implants. The system can restore an implant with up to 10° of divergence or 20° between 2 implants. There is even an extended-range replacement attachment that can accommodate a divergent implant between 10° and 20°, or 40° between implants.3-5
Fixed, full-arch implant prostheses may be the preferred choice for many patients in this fast-paced world. However, the amount of available bone and financial budgets may not allow for that form of therapy. Other options exist that are equally life-altering, allowing for stability while dramatically increasing chewing efficiency, aesthetics, and improvement in self-confidence. Implant-retained overdentures are an excellent alternative to conventional dentures and the more expensive fixed prostheses. Implant overdentures are designed in 2 distinct ways: freestanding implants and implants connected with a cast or, most recently, milled bars. Freestanding implants have retentive devices, such as the LOCATOR, that attach to matching retentive devices in the denture base. This appliance is implant- and tissue-supported. Implants need to be strategically positioned to minimize rocking, though retention is dramatically improved over a conventional denture. A bar-overdenture, as described in this case presentation, has attachments that are placed on the bar itself. The milled bar connects the implants together and provides for better distribution of functional forces among the implants connected by the bar. The prosthesis has greater implant support and less support from the surrounding tissue.
The public has become aware of the treatment modality involving dental implants that replace missing or unhealthy dentition with implant-retained prostheses. These “permanent” restorations are cemented to place over custom-milled abutments or are screw-retained. These appliances have a tooth-colored component and gingival-shaded material when needed for lip support to make the tooth design appear natural. These implant-retained devices are aesthetic, increase chewing efficiency, eliminate the necessity of palatal coverage, and have outstanding wear characteristics. They are strong and resistant to chipping and fracture. The zirconia materials used are precisely milled as a solid piece to achieve proper form. The solid zirconia construction maintains periodontal and peri-implant health because plaque and debris do not easily adhere to the material.6,7 CBCT provides 3D diagnosis and planning in evaluating the amount of hard tissue available for our implants and any vital anatomic concerns. The ability to virtually position our implants in appropriate sites is critical to managing engineering principles. In some situations, the final design of the prosthesis is visualized prior to any surgical intervention. Complications can be determined, and solutions can be evaluated. To determine which type of prosthesis is possible for the individual situation, a treatment map is formulated. Maxillary and mandibular anatomic restrictions are evaluated. These include the maxillary sinuses in the posterior maxilla and the mandibular and mental nerves, as well as lingual concavities in the lower arch. In this case, a screw-retained zirconia bridge (BruxZir [Glidewell]) was planned for the maxillary arch, and a removable implant overdenture over a milled bar was planned for the mandible. Since angulation of the implants in the available bone compromises the emergence of the access holes to accommodate the seating screws, multi-unit angled abutments were used to allow these access holes to be ideally positioned in the cingulum or occlusal surfaces of the final restoration.
Following Hahn Tapered Implant System (Glidewell) surgical protocols, a 2.4-mm-diameter pilot bur was used at 800 to 1,000 rpm to establish angulation, length, and proper position facial-palatally/lingually to support the desired prostheses. Maxillary implants were precisely positioned in the available bone anterior to the maxillary sinuses, thus eliminating invasive sinus augmentation procedures. (Figure 2).
Figure 2. Maxillary implants precisely positioned in available bone anterior to the maxillary sinuses.
Full-arch solid zirconia implant prosthetics are a durable alternative to acrylic, screw-retained hybrid dentures.8 They are very aesthetic and resistant to the staining and chipping that often occurs with acrylic appliances, and their flexural strength is ideal. The 5-visit appointment time for fabrication provides for an accurate and stress-free process that allows the patient to be a part of the communicative process and approve final-to-final production. Following 4 months of integration, the maxillary implants were uncovered, and open-tray impression copings were used to fabricate the initial cast. Vinylpolysiloxane (VPS) material was used (Panasil [Kettenbach LP]) (Figure 3). Figure 4 shows the impression made of the 3 Hahn mandibular implants precisely positioned in the symphysis. Following this uncovering of the implants, 3-mm-tall healing abutments were torqued to 25 Ncm, and the tissue reflection was closed using Vicryl sutures (REDISORB PRO 3-0 [Newport Biologics]) (Figure 5).
Figure 3. Following 4 months of integration, the maxillary implants were uncovered, and open-tray impression posts were used to fabricate the initial cast.
Figure 4. Impression made of 3 Hahn mandibular implants (Glidewell) precisely positioned in the symphysis.
Figure 5. Following uncovering, healing abutments were torqued to place the tissue reflection closed with Vicryl sutures.
The laboratory then created a stone cast where verification jigs were seated individually, a custom tray, and a stable screw-retained record base with an occlusal rim (Figure 6). The record base and occlusal rim established vertical dimension of occlusion, midlines, and high lip-lines. It is imperative that the final prosthesis be passively seated, so to obtain this goal, inlay resin jigs (DuraLay Inlay Pattern Resin [Reliance Dental Manufacturing]) were created by the laboratory technician and independently threaded into each individual implant (Figure 7). Also, stable screw-retained bite rims began the prosthetic design process during this visit (Figure 8). The jigs were luted together with a pattern resin (Primopattern LC Gel [Primotec USA]) (Figures 9 and 10). A custom open tray was filled with impression material, a medium-body wash was injected around and under the splinted jigs, and a pick-up impression was made. The final impression necessarily needs to be very accurate since it provides the laboratory with the best master cast to continue the process. A very accurate master cast was then poured up using the appropriate laboratory dowels (Figure 11). We now have a basis to artistically create something unique and special for our patients. A conventional denture wax setup gives the patient an opportunity to evaluate tooth size and position. Denture teeth are first used to help determine the proper vertical dimension of occlusion, facial form, and phonetics. This stable, screwed-in palateless denture will not be used by the patient, but rather as a visual guide (Figures 12 to 15). The laboratory will then choose the correct multiunit abutment to adjust any angulation discrepancies resulting from the necessity of angling implants away from vital anatomy or to deal with the natural contours of the arch. Access holes perforating the facial surfaces are not aesthetic. Once the bite relation and final impression are deemed accurate and the wax setup using denture teeth is verified, a polymethymethacrylate (PMMA) appliance is fabricated (Figure 16). This transitional appliance serves as a precursor to the final BruxZir restoration and is easily modified for occlusal discrepancies and aesthetic concerns. The patient may wear this PMMA appliance for 1 to 4 weeks to substantiate his or her expectations prior to the final prosthesis. Once final aesthetic and functional approval is made, the prosthesis is returned to the dental lab.
Figure 6. The technicians at Glidewell lab fabricated a cast and created passive fitting acrylic jigs and custom trays. These were used to establish the final accurate master cast. A stable record base and occlusal rim began prosthetic bite relations and reconstruction.
Figure 7. Splinting the jigs provided for an accurate impression using a custom tray.
Figure 8. Screw-retained bite rims began the prosthetic process.
Figure 9. The jigs were passively threaded to place and splinted together, providing for a very accurate final polyvinylsiloxane impression.
Figure 10. A mandibular cast, passive jigs, a custom tray, and a screw-retained stable record base were fabricated.
Figure 11. The jigs were splinted together, and an accurate final impression was made.
Figure 12. Following master cast fabrication, conventional wax try-ins were made with denture teeth. This established the onset of occlusion, aesthetics, and lip support.
Figure 13. The mandibular wax try-in was completed.
Figures 14 and 15. The maxillary and mandibular wax try-ins were threaded to place and verified.
Figure 16. Due to the necessary surgical position of the mandibular implants, a milled bar was created to extend support posteriorly using 4 LOCATOR (Zest Dental Solutions) attachments. The CAD/CAM-milled LOCATOR bar was connected to the implants. The bar elevated the prosthetic connections, minimizing pressure on the bone and soft tissue in the area of the implants.
Due to the necessary surgical position of the mandibular implants, a milled bar was created to extend support posteriorly using 4 LOCATOR attachments (Zest Dental Solutions). The CAD/CAM-milled LOCATOR bar was connected to the implants. The bar elevated the prosthetic connections, minimizing pressure on the bone and soft tissue in the area of the implants (Figure 17). The mandibular prosthesis is a LOCATOR-attached removable implant overdenture. LOCATOR attachments are easily changed to increase retention for the patient. Black processing caps were removed and replaced with blue retentive caps, which were seated within the LOCATOR housing that were cured into the overdenture during lab fabrication. The housings and nylon caps serve to retain and stabilize the denture when seated over the LOCATOR abutments on the implant bar. The nylon caps come in a number of retentive strengths and are easily replaced when wear occurs over time or when the patient requests greater retention. According to the manufacturer, the retentive caps resist wear during up to 56,000 cycles of function (Figure 18). The fixed maxillary composite, implant-retained bridge was tried in opposing the removable mandibular milled-bar overdenture. Aesthetics and occlusion were verified. The patient was allowed to wear this transitional to evaluate satisfaction prior to final BruxZir fabrication (Figure 19). The final zirconia (BruxZir) implant-retained bridge was threaded to place, and the occlusion was verified with the opposing mandibular overdenture (Figure 20). The access holes of the screw-retained prosthesis were filled with a transitional composite material (Figure 21). The final aesthetic reconstruction was evaluated for function and aesthetics (Figure 22). Our patient was satisfied with the aesthetics and function of her implant-retained prostheses (Figures 23 and 24).
Figure 17. The mandibular prosthesis was a LOCATOR-attached remov- able implant overdenture. LOCATOR attachments were easily changed to increase retention for the patient. Black processing caps were removed and replaced with blue retentive caps, which seated within the LOCATOR housing that were cured into the overdenture during lab fabrication. The housings and nylon caps served to retain and stabilize the denture when seated over the LOCATOR abutments on the implant bar. The nylon caps come in a number of retentive strengths and are easily replaced when wear occurs over time or when the patient requests greater retention. According to the manufacturer, the retentive caps resist wear during up to 56,000 cycles of function.
Figure 18. Following approval of the wax setups, a maxillary, screw-retained PMMA was created. This fixed bridge provided aesthetics and function.
Figure 19. The fixed maxillary composite implant-retained bridge was tried in, opposing the removable mandibular milled-bar overdenture. Aesthetics and occlusion were verified. The patient was allowed to wear this transitional to evaluate satisfaction prior to final BruxZir (Glidewell) fabrication.
Figure 20. The final zirconia (BruxZir) implant-retained bridge was threaded to place, and the occlusion was verified with the opposing mandibular overdenture.
Figure 21. The access holes of the screw-retained prosthesis were filled with a transitional composite material.
Figure 22. The final aesthetic reconstruction was evaluated.
Figures 23 and 24. Our patient was satisfied with the aesthetics and function of her implant-retained prostheses.
Using CAD/CAM technology, the final solid zirconia prosthesis was milled (BruxZir). After seating the final product, the abutment screws were torqued to place using the manufacturer’s guidelines (35 Ncm into an implant itself and 15 Ncm into a multiunit abutment).
CONCLUSION
Communication with our edentulous patients as to what procedures are possible, which are predictable, and which can meet their financial budget is critical to success. Meeting the patient’s expectations is not always simple. Discussing the advantages, disadvantages, and risks of therapy provided will help the patient to be directly involved in the decision process. The more the patient understands, the better the ultimate result. Conventional dentures may be an appropriate therapy for some but a detriment to others. Removable implant-retained overdentures certainly improve chewing efficiency and create stability where bone loss is significant. Understanding the dynamics of ideal implant placement helps the practitioner narrow the options possible. CAD/CAM-designed BruxZir solid zirconia bridges are the most durable and aesthetic. These maxillary prostheses minimize palatal coverage and provide the patient something as close to natural, non-removable teeth as technology allows today. The ultimate limiting factors are the patient’s overall health and healing capabilities and the available bone to surgically align our implants. Psychologically improving the overall quality of life of our patients certainly is a goal.
REFERENCES
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5. Miler AMQP, Correia ARM, Rocha JMC, et al. LOCATOR attachment system for implant overdentures: a systematic review. Stomatologija. 2017;19(4):124–29.
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ABOUT THE AUTHORS
Dr. Kosinski received his DDS degree from the University of Detroit Mercy School of Dentistry (Detroit Mercy Dental) and his mastership in biochemistry from the Wayne State University School of Medicine. He is an affiliated adjunct clinical professor at Detroit Mercy Dental; serves on the editorial review board of REALITY, the information source for aesthetic dentistry; and is the past editor of the Michigan Academy of General Dentistry Update. He is currently the editor of the AGD journals General Dentistry and AGD Impact and is the editor of Implants Today for Dentistry Today. He is a past president of the Michigan AGD. He is a Diplomate of the American Board of Oral Implantology/Implant Dentistry, the International Congress of Oral Implantologists, and the American Society of Osseointegration. He is a Fellow of the American Academy of Implant Dentistry and received his Mastership in the AGD. He can be reached at drkosin@aol.com or via the website smilecreator.net.
Dr. Tilley is a graduate of the University of Alabama School of Dentistry. She is a native of Pensacola, Fla, and has been practicing dentistry in her hometown since 1998. She has done extensive training at the Las Vegas Institute for Advanced Dental Studies and the Engel Institute with Drs. Timothy Kosinski and Todd Engel. Her lectures discuss bone grafting procedures and surgical and prosthetic aspects of implant dentistry. She is a Fellow of the International College of Dentists and most recently was inducted into the American College of Dentists and the Academy of Dentistry International. Dr. Tilley is member of the AGD, the ADA, the Florida Dental Association, the Alabama Dental Association, the Academy of Laser Dentistry, and the Academy of American Facial Esthetics. Dr. Tilley is also a Fellow with the International Congress of Oral Implantologists. She has published extensively on implant dentistry techniques, lasers, and Botox/fillers. She can be reached via email at stephflynntilley@cox.net.
Disclosure: The authors report no disclosures.
