It must be kept in mind how surgical decisions directly affect prosthetic results. Examples of this are correct spacing of implants, achieving adequate alevoloplasty for prosthetic thickness, and providing the correct implant angulations; all of these surgical steps directly affect prosthetic success and choices.
This month’s Implants Today topic is “Dental Implants: Prosthetic Options.” This is a very broad topic and yet an important one that relates to all aspects of implant treatment. Although I will be focusing on the many choices of prosthetic options for dental implants, it must be kept in mind how surgical decisions directly affect prosthetic results. Examples of this are correct spacing of implants, achieving adequate alevoloplasty for prosthetic thickness, and providing the correct implant angulations; all of these surgical steps directly affect prosthetic success and choices. Implant dentistry is truly a prosthetic discipline with a surgical base.
The various prosthetic options are also related to treatment planning. In my opinion, treatment planning is about knowing your patient and making a decision with that individual, after he or she is educated on all options in conjunction with a diagnostic exam. The decision of a prosthetic choice with the patient is related to his or her lifestyle, age, and health; the length of treatment; the financial costs; and more. While some patients put aesthetics as a priority, other patients just want to be able to eat without pain or discomfort. It is only through an interview process with the patient that the right decision can be made.
I would like to say a few words about the prosthetic options when treatment planning for both a quadrant of dentistry with one or more implants as well as the full-arch tooth replacement options for a patient.
When you are treatment planning a quadrant of implant-supported prosthetics, there are various options to consider as an implant dentist. The first consideration is whether the crown will be screw- or cement-retained. Screw-retained crowns offer the advantage of predictable retrievability. One consideration of screw-retained prosthetics, especially in the anterior region, is the location of the screw hole. This is directly related to the surgically placed angle of the implant. Another consideration with screw-retained prosthetics is the material of which the crown is being made. PFM crowns tend to have less aesthetic access hole openings than zirconia crowns. Zirconia crowns with a screw access hole also tend to be less susceptible to chipping. When considering screw-retained crowns in the posterior region, the issue of accessibility can sometimes come into play for patients with a limited occlusal opening.
Cement-retained crowns offer the advantage, from an aesthetic standpoint, of not having a screw hole. There is also increased strength of a nonscrew-retained implant crown due to the lack of a screw hole. An issue of concern with cement-retained crowns or bridges is the risk of cement getting into the sulcus, causing peri-implant issues. There are various published methods to avoid this cement issue in the sulcus from happening. Retrievability of cement-retained crowns and bridges can be controlled by the type and amount of cement used, but this is often not predictable. The best way to control retention in cemented implant crowns and bridges is to use custom abutments that have adequate retention and a retentive path of draw. Custom abutments can also allow for corrected angulation when implants are placed in angled root areas. Another consideration, with respect to abutments, is whether to use a zirconia abutment in the aesthetic zone or a titanium abutment. My preference in the anterior region is to use a milled zirconia custom abutment with a titanium base inside for the connection.
When full-arch tooth replacement is being treatment planned for implant-supported prosthetics, there are additional considerations regarding quadrant treatment planning. There are 5 prosthetic options available to restore an entire arch of teeth, each one with advantages and disadvantages; they are as follows: implant-supported overdentures, cement-retained PFM bridges, acrylic hybrid bridges, screw-retained PFM bridges, and screw-retained zirconia bridges.
Implant-supported overdentures offer the most stability when supported by a bar versus being tissue-supported. Overdentures have the advantage of offering more occlusion with fewer implants and less grafting than other fixed options. The disadvantages of overdentures are that they are removable and are less natural-feeling for a patient than fixed alternative options. In addition, since they are acrylic, they will wear down and need replacement in the long term. In general, there are also maintenance issues with overdentures that require replacement of retentive parts. This maintenance of parts requires time and must take into account the associated financial considerations from a practice management standpoint.
From a functional and aesthetic standpoint, cement-retained PFM bridges offer the closest approximation to natural teeth. The same retrievability issues and cement peri-implant issues as with quadrant implant prosthetics exist. If porcelain were to chip, it could be due to the retrievability issues. This choice is one of the most demanding of all the full-arch options, due to the frequent need for extensive grafting and/or sinus grafting. A distal cantilever with a cement-retained bridge is not an ideal situation, because if that cantilever becomes loose, it can be a difficult issue to deal with prosthetically. One advantage of a full-arch cement-retained PFM bridge is that the cement can negate some of the casting distortions inherent in a long-span cast bridge.
Acrylic hybrid bridges are the most problematic prosthetic option of all full-arch choices. The difference between an acrylic overdenture and a hybrid bridge is that the hybrid bridge does not move, thus all the stress is taken up by acrylic teeth that will often chip and break off over time. Acrylic is porous, causing the material to pick up stains, also creating a higher potential for peri-implant issues. Another disadvantage of acrylic hybrid bridges are the screw holes, which are susceptible to chipping. Furthermore, the screw holes are not aesthetic when a composite is placed in them due to the show-through of the underlying metal framework.
Screw-retained PFM bridges can offer an excellent option for full-arch tooth replacement, featuring the advantages of a cement-retained PFM bridge with increased retrievability. Implants Today advisory board member Dr. Jack Piermatti has an exceptional example of this in his article. He clearly explains the prosthetic and dental laboratory steps for success. One key to success with this prosthetic option is to reduce any casting distortion so that stress is not put on the implants.
Screw-retained zirconia bridges have the advantage of being CAD-milled with no casting distortion issues. One reality when treatment planning this zirconia option is that it’s most predictable, from a prosthetic success standpoint, when the zirconia screw-retained bridge has adequate prosthetic thickness. This often mandates that the prosthesis be what Misch calls FP2 or FP3, with a pink gingival area present. This requires either surgical alveoloplasty or natural alveoloplasty from periodontal disease. Another advantage is that zirconia is resistant to chipping when presented without porcelain on the facial aspects of the teeth as a full-contour option. The aesthetics of zirconia allow for a full-contour option in most clinical cases.
While I have spelled out the basic advantages and disadvantages of both quadrant and full-arch prosthetic options, there are many other prosthetic considerations involved to ensure that any of these choices work out successfully. Dental implant prosthetics is a multidisciplinary combination of parts, pieces, and clinical steps that must come together in a coordinated manner.
By : Michael Tischler, DDS
source : dentistrytoday.com