Improving Denture Retention with Freestanding Attachments
Denture stabilization has become a common clinical treatment option for patients presenting with decreased removable prosthesis stability during function. Although they are not new, the design of implants and attachments to removable prostheses has undergone steady improvement. Mini and narrow-diameter implants are being used with increasing frequency for these applications. Selection of the implant diameter should be dependent upon the available bone width at the site to receive the implant, however; it should not be focused on use of less expensive fixtures (mini implants) as the sole implant for treatment of these cases. With this in mind, treatment may require use of different-diameter implants in the same arch to achieve the best load handling based on bone availability.
The surgical armamentarium used for placement of implants has typically required separate kits for placement of either mini implants or standard-diameter fixtures. Most manufacturers offering mini implants (1.8 to 2.9 mm in diameter) include in their product line implants in the 2.2- to 2.8-mm range. Practitioners who desire a wider diameter implant—either one with a small diameter (3.0 to 3.5 mm) or a standard diameter (3.75 to 5.0 mm)—must invest in two separate surgical kits to place the range of implants that may be needed when offering overdenture approaches with freestanding attachments.
An Alternative to Ball Attachments
Multiple manufacturers offer mini implants with a ball attachment as a one-piece implant. The limitations to a ball attachment include a greater inter-arch space requirement due to the taller supragingival attachment portion of the implant. One-piece implants with lower profile attachments like the ERA®, allow less required interarch space and additionally permit a greater thickness of denture material over the attachment for improved strength. This also means the implants need a greater degree of parallelism to avoid a difficult seating of the prosthesis as well as lateral loads placed on the implants when the prosthesis was seated.1
As an alternative, Sterngold reduced the size of their widely used ERA® attachment, creating a micro ERA® that is 20% smaller than the standard ERA®. This is offered as a mini implant in a 2.2-mm diameter in either a one-piece implant or as a two-piece implant—where the attachment can be placed either immediately or with a delayed approach—and as a 3.25-mm two-piece implant.
Implant selection should maximize the available bone at the site to provide better load handling and long-term prognosis. With this in mind, Sterngold also offers the Stern IC implant, a Straumann-compatible single-stage implant available in both 3.3- and 4.1-mm diameters. The IC implant has a conical connector with an internal octagon at the depth of the conical connector to offer anti-rotational capabilities with the prosthetic abutment should a fixed approach be desired for a single unit. When the IC implant is to be used for a freestanding overdenture, ERA® attachments are available for both the 3.3- and 4.1-mm diameters (Figure 1).
When using the 2.2- and 3.25-mm implants, divergence of the individual fixtures can be corrected using different angulations of the micro ERA® attachment. The micro ERA® is offered in 0-, 5-, 11-,17-, 23-, and 30-degree angulation options to allow the practitioner to correct implant placement that has been dictated by the angulation of available bone (Figure 2). This overcomes a common issue observed with ball-attachment mini implants, in which lateral loading results when the implants are divergent and stresses are placed on the implants both during insertion and while the prosthesis sits intraorally on the arch. In addition, the “all-in-one” surgical kit from Sterngold provides these in a single kit to minimize the number of kits needed for a wide range of clinical applications (Figure 3), thereby giving practitioners flexibility when treatment planning.
Placement of four to six well-spaced implants in the mandible as freestanding fixtures with micro ERA® attachments greatly improves patients’ denture satisfaction, providing better stability and retention2 (Figure 4 and Figure 5).
Selecting the correct implant for the site is based on anatomical considerations, which include the length as well as width of the ridge present. Implant selection thus needs to maximize the available width of the ridge at the site selected. This may require that implants in the mini, small-diameter, and standard-diameter ranges be selected and mixed in a particular case.
As resorptive patterns are dependent on the condition (periodontal and endodontic) that leads to loss of the tooth as well as the patient’s individual resorptive potential, some sites may not accommodate an implant wider than a mini or small-diameter implant. In that case, adjacent sites may be able to accommodate a standard-diameter implant, necessitating mixing of different diameters within the arch (Figure 6).
For patients who desire to improve the stability of their overdenture by moving either to a bar overdenture approach or fixed prosthesis, there are 3.3- and 4.1-mm, IC implants offering that capability. There is also the SFI-Bar®, which combines Cendres+Métaux’s innovative bar solution for removable dentures and Sterngold Dental’s extensive knowledge of implant abutment connections. Sterngold manufactures abutments for most popular implant platforms, which makes possible a prefabricated bar system that is easily modified intraorally to be placed on the IC implants. Once the bar system is assembled and attached to the implants, the retentive sleeve is placed on the bar segments and picked up in the prefabricated denture with a resin like ERA Pickup® resin, converting the freestanding implant overdenture to a bar overdenture prosthesis. If a fixed approach is desired, there are stock cementable abutments available, or custom CAD/CAM abutments can be fabricated for either a cementable or screw-retained fixed prosthesis.
Patients who present with the complaint of denture instability can be assisted by the placement of individual implants with overdenture attachments spread over the arch to prevent prosthesis lift off the ridge. Those patients who have minimal ridge width that cannot accommodate standard diameter implants can be treated with mini implants. The available angulations of attachments allow the practitioner to align the attachments irrespective of the placement angle to have a better path of insertion of the prosthesis limiting wear of the attachment over time. Those patients who are not candidates for freestanding overdenture attachments can be accommodated with the SFI-Bar®, a prefabricated bar system that offers expandability should the need arise to add additional implants at a later date.
Dr. Kurtzman has been compensated as a lecturer by Sterngold.
1. Schneider AL, Kurtzman GM. Restoration of divergent free-standing implants in the maxilla. J Oral Implantol. 2002;28(3):113-116.
2. Kurtzman GM, Dompkowski D. Maximizing denture stability and retention. Dent Today. 2009;28(7):92, 94-6.
For more information, contact:
Sterngold Dental, LLC
About the Author
Gregori M. Kurtzman, DDS, MAGD, FACD, DICOI
Silver Spring, Maryland