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6 mCME Dental Tribune Middle East & Africa Edition | 2/2017 Treatment options for the edentulous arch CAPP designates this activity for 1 CE Credits mCME articles in Dental Tribune have been approved by: HAAD as having educational content for 1 CME Credit Hours DHA awarded this program for 1 CPD Credit Points By Marc Montana Introduction Historically, when a patient’s dental condition reached a state of total tooth loss, treatment was limited to a complete denture with no hope of improving that status. The greatest challenge, particularly when work- ing with a lower jaw was providing a denture with reasonable stability and retention. Success was greatly dependent upon the skill of the practitioner but also on the neu- romuscular ability of the patient, their supporting structures and a philosophical attitude toward their condition. Treatment for patients suffering complete edentulism has been revolutionized by the ongoing success of dental implants such that the standard of care for the mandible is an implant overdenture. The spectrum of prosthetic modali- ties developed since the acceptance of endosseous implants to the dental market ranges from the very simple to the astoundingly complex. As this fi eld of study once directed by spe- cialists has evolved into a mainstay of the general practice, favor of ex- peditious and reproducible methods has gained dominance over complex therapies. Implant overdentures and fi xed hybrid prostheses are choices typically offered by the dentist based upon a patient’s fi nancial ability. While both are generally successful, the overdenture and the hybrid prosthesis are not without pitfalls. The implant-retained overdenture The implant-retained overdenture is described as a prosthesis that covers, and is supported by, the natural tis- sues retained by the dental implant; the design is considered implant- assisted rather than supported. Placement of two to fi ve implants is commonly found for the edentulous mandible with emphasis on creating a large anteroposterior spread be- tween the endosseous pillars. If more than two implants are clustered in a small AP range, the prosthesis can- not move freely about a single axis of rotation and the denture may dis- lodge during function. By creating the fulcrum on the most posterior overdenture abutments, the denture will pivot in function resulting in disengagement from the attachment mechanism and cause premature wear of the retentive components. Therefore, an increase in the number of implants beyond two does not necessarily provide a linear increase in retention and sta- bility. In fact, the opposite may be true. Because support is provided by the mandible itself, resorption of the supporting structure will result in increased tipping of the denture during function, resulting in dislodg- ment. Therefore, the dentist and pa- tient must be cognizant of the need for relining of the prosthesis periodi- cally to assure optimal performance. is, Recommendation therefore, placement of two implants in the anterior mandible to allow one axis of rotation. These implants should also be positioned such that future implants may be considered should the patient wish for an implant-sup- ported alternative. The hybrid prosthesis The screw-retained hybrid prosthesis is a fully implant-supported struc- ture and, therefore, is not affected by incremental resorption of the resid- ual ridges. It has gained in popularity as the technically diffi cult and costly gold frameworks have been replaced by CAD/CAM titanium structures and by proven success of angled im- plant placement to increase the AP spread. Because the restoration has a metal substructure, it is possible to cantilever posterior to the terminal abutment, increasing the length of the functional arch. However, the esthetic component of the restoration, namely the denture teeth and acrylic resin matrix, are inherently weak materials originally intended for use in complete and partial dentures where functional load is comparatively low. If insuffi - cient inter-arch space is available, the risk of fracture or displacement of denture teeth or resin base is high as the materials will be too thinned to withstand forces generated during function and especially parafunc- tion. Unfortunately, this is an increasingly common occurrence, especially in restoration of the maxilla with a fi xed hybrid prosthesis. Inconven- ient screw-access holes may further weaken the prosthetic teeth. Repair of a fractured or lost tooth requires removal of the hybrid prosthesis and correction in the dental labora- tory. The dentist must be prepared to remove the structure and later re- seat it once the repair is completed. The patient must accept they will be without “teeth” for the length of time required for the technician to fi x the problem. Attempts to prevent frac- turing by increasing the thickness of the resin is limited by the space available to do so. If inadequate inter- arch space is encountered, correction cannot be achieved by adding more material. Rather a change in design to a different and possibly more ex- pensive restoration may be needed. When hybrids are used in the max- illa, confl ict may arise in attempting to improve the esthetic and phonetic result by use of ridge lapping and the limitations such shapes impose on proper oral hygiene. The benefi ts of the fi xed hybrid pros- thesis are clearly improved function and minimal post-treatment com- plications as long as the patient is able to properly clean it and break- age is avoided. Because it is fi xed, the patient cannot remove it to clean away entrapped debris and properly remove plaque. Repair or replace- ment of the resin teeth requires re- moval and re-seating by a dentist. Figure 1. Pre-treatment radiograph showing fi ve implants clus- tered in the anterior mandible Figure 2. Clinical image of patient. Note the wear of the metal abutments due to disengagement of the nylon retention inserts as a result of fulcrum during function. Figure 3. Duplication of an acceptable denture serves as a custom tray. Holes of suffi cient diameter to accommodate impression copings have been prepared. Figure 4. Open tray impression copings seated on the dental implants. One implant is selected for disuse and covered with a transmucosal abutment. Figure 5, 6. Completed fi nal impression using the custom tray and light body and medium body PVS, as well as rigid bite registration material around the impression copings to eliminate any movement of the copings. ATLANTIS Conus concept: the removable implant-support- ed bridge As described above, the tissue-sup- ported overdenture performs best with only two implants placed in the anterior region. When more than two implants are placed, the goal should be to provide a completely implant- supported result. The Atlantis Co- nus concept (DENTSPLY Implants) provides the optimal functioning convenience of a fi xed hybrid but also allows patient retrievability for unobstructed oral hygiene practice, regardless of the degree of ridge lap. It is in effect, a prosthesis that can be removed by the patient, with the sta- bility of a fi xed bridge. The concept centers around patient- specifi c abutments, each milled to a 5 degree convergence, and paral- lel to each other in the dental arch. Recommendation is for at least four implants in the mandible and four to fi ve implants in the maxilla. These uniquely designed, conical abutments are fi tted by correspond- ing metal SynCone caps (DENTSPLY Implants) which are incorporated into the prosthesis. The result is a friction-fi t, stable, retentive and fully implant-supported bridge that remains removable by the patient. No special latches or plunger attach- ments are necessary to retain it. The patient merely slides the bridge in vertically onto the abutments and removes it in the opposite way. Be- cause the abutments are a part of the ATLANTIS (DENTSPLY Implants, Waltham, MA) portfolio, it is avail- able for all major systems. In addition, because each abutment is custom made, correction of angled implant placement is possible up to 30 degrees. Two major require- ments are necessary: the dentist must make an accurate, implant- level impression and a scan must be made of either an approved denture set-up or of a completed denture to be retro-fi tted. The ATLANTIS Conus Abutments are then designed to be positioned optimally within the denture confi nes. The fi xed yet re- movable prosthesis offers the advan- tages of excellent chewing function, improved esthetics and fracture re- sistance (as no screw access holes are present) and optimally facial sup- porting contours, without compro- mising cleaning by the patient. Case Report A 73-year-old woman with a history of 11 years of complete edentulism of the maxilla and mandible, and fi ve endosseous implants in the ante- rior mandible, presented with a chief complaint of a non-retentive and un- stable lower denture. The implants were standard diameter, externally hexed, Branemark fi xtures. She had moderate resorption of both the maxillary and mandibular residual ridges (Fig. 1). The patient had bone loss involving the implant bodies but comparing the radiographic evidence available, documenting her condition through the years, it appears the bone loss oc- curred soon after implant placement and no appreciable change was seen thereafter. During those 11 years, her treatment history included initial restoration of the implants with a complete denture retained by the Locator at- tachment system (Zest Anchors); and the maxilla was restored with a complete denture. She advised that the result was unsatisfactory as the lower denture displaced during function. Her history further reveals that the Locators were replaced with Preci-Clix attachments (Ceka At- tachments) with no demonstrable improvement. The patient was later retreated by the author, with new maxillary and mandibular complete dentures and new Locator attach- ÿPage 7