ZEST ANCHORS

Retrofit conversion of an implant-attachment/ bar-retained overdenture using the Locator attachment

By Dr. Allen L. Schneider, FAGD, DICOI. Information provided by Zest Anchors.

Following are step-by-step procedures for a retrofit conversion of an implant attachment/bar-retained overdenture using the Locator attachment.

The 55-year-old male patient presented with a maxillary implant-supported bar on the right side and a single free-standing implant attachment on the left side (Fig. 1). The bar was retained by two implants in teeth 3 and 5, and had stud-type attachment extensions on both the anterior and distal. A third clip-type attachment was positioned along the cast bar between the implants. The patient's chief complaint was the lack of retention provided by the single implant attachment on the left side, which would then cause the right side to become loose.

Fig. 1 Maxillary implant-supported bar and single free-standing implant attachment (mirror image).

The treatment plan provided for a retrofit conversion of both extension attachments on the bar and replacement of the single implant attachment with Locator attachments. Although the cast bar had a very narrow middle section for retention of the clip attachment that would still be used, the two extension ends had more than the minimum 4-mm width required for use of the Locator attachment (Fig. 2).

Fig. 2 Cast bar with very narrow middle section.

1. After removing the bar, drill straight through the attachment using a contra-angle twist drill provided by the manufacturer (Fig. 3).

Fig. 3 Drill straight through the attachment.

Note: The resulting preparation is an exact-sized hole for passively cementing the Locator attachment's 1.8-mm-diameter post.

2. Use the special diamond sizing bur to create a tapered seat for the attachment (Fig. 4).

Fig. 4 Create a tapered seat for the Locator attachment.

3. Insert the 6-mm-long posts of the attachments through the prepared holes in the bar (Fig. 5); then, using a disk, shorten the posts to the same height as the bar.

Fig. 5 Insert the 6-mm-long post through the prepared hole.

4. Cement the attachments into place using a strong metal-to-metal cement (Fig. 6).

Fig. 6 Cement the attachments into place.

5. Secure the retrofitted bar back into place on the patient's maxillary implants.

6. Use a Locator attachment with a tissue-cuff height that matches the surrounding gingival level to replace the patient's existing attachment in the implant on the opposite side of the ridge (Fig. 7).

Fig. 7 The Locator attachment replaces the existing attachment in the implant.

(A direct chairside pickup of the new denture cap components was possible because of the good overall fit of the patient's existing prosthesis.)

7. Remove all the old denture attachments from the overdenture except for the metal clip, which remains as an additional retentive element for the bar.

Note: The clip also aids in proper orientation of the prosthesis while the other three attachments are being added.

8. Etch the superior surface of the attachment male's metal housing to create better adhesion texture. The Macro Cab micro-etching unit (Danville Engineering) was used in this case.

9. Paint Metalprimer II primer material (GC America) onto the etched metal attachment housing for extra strength in bonding denture resin to metal.

10. Using either self-curing or light-curing acrylic resin, pick up the black Locator Processing Cap Male in a passive condition without compressing the soft tissue.

11. Cure the Locator Processing Cap Males into place; then remove the black processing liners and replace them with the final nylon retentive liners.

Note: In this case, because four attachments were used, the pink light-retention nylon males (with a retention of 3 pounds) were chosen to reduce the overall retention of the prosthesis (Fig. 8).

Fig. 8 The completed conversion.

The patient was immediately impressed with the strong retention the attachments added to his denture. He also commented that the insertion of his appliance was easier with the self-aligning ability of the new attachments. nDPR