Stable Implant Overdentures

Fabrication of a stable mandibular denture begins with careful diagnosis and case planning. Listening to the patient’s concerns and desires will make the final prosthesis acceptable.
This article will describe a case involving a 67-year-old female who was being treated with oral medications for osteoporosis and who admitted being anxious. She had undergone breast cancer treatment without radiation or chemotherapy and was a half-pack-per-day smoker. Her chief complaint was that her dental prostheses did not fit properly, and she was told that she had a serious caries problem. She was unhappy with the aesthetics of the preoperative, conventional complete denture, feeling that too much pink gingiva was showing. There was also a chronic need for adhesive. The patient wanted her teeth to look more natural and fit better, in that order.

CASE REPORT

The patient presented with an ill-fitting conventional maxillary complete denture and a mandibular removable partial denture over atrophic posterior mandibular bone. Splinted crowns from right to left mandibular cuspid retained the partial denture. Unfortunately, decay had progressed, making the abutment crowns mobile, resulting in less stability of the mandibular appliance. The prognosis of these teeth was poor. The patient was concerned with her ability to maintain the existing teeth and keep up good oral hygiene.
Several options were discussed with the patient, including root canal therapy, crown lengthening, post and core fabrication, and splinted crowns, in the attempt to maintain the mandibular abutment teeth as support for a precision mandibular partial denture. After deliberation, it was determined that the remaining root structures were not adequate to act as strong abutments.
Because of the severe atrophy in the posterior mandible and the limited amount of height and width of bone in the symphysis area, it was decided to restore the patient’s mandibular arch using the Straumann Dental Implant System (Straumann). The first Straumann implant was introduced in 1974. It provides an 8º Morse Taper internal connection. The flared-neck implant design used here is ideal for soft-tissue contouring.

Figure 1. Unaesthetic maxillary complete denture opposing faulty anterior crowns acting as abutments for a conventional removable partial denture.

Figures 1 to 4 illustrate the closed vertical dimension of occlusion, resulting in improper lip support and a poor frontal and lateral aesthetic profile. The patient’s decrease in function may be due to the poor tooth position and plane of occlusion. Without posterior support her quality of life was dramatically reduced. Figure 5 shows the remaining abutment teeth, which had decayed dramatically. The splinted crowns were easily removed, leaving root structures (Figure 6) with a poor prognosis.
To achieve the best functional and aesthetic result and increase stability of any prosthesis, it was decided simply to extract the remaining root structures and immediately surgically place 3 Straumann dental implants in the Nos. 22, 24, and 26 areas. The mental foramen area was evaluated, and the implants were placed anteriorly in the symphysis to avoid potential paresthesia of the atrophic bone.

Figure 5. Poor plane of occlusion results in instability of the appliances.	Figure 6. Gross decay of the remaining natural abutments made these teeth unrestorable.

An initial marking of the implant site, following the extractions, was done with a 3.0-mm round bur. A simple surgical stent was fabricated using a cast of the patient’s original prosthesis to help guide the bur to the proper angulation and position. It was imperative that the implants be placed parallel to each other along the long axis of the bone. Retraction of soft tissue revealed adequate ridge height in the symphysis area and width for placement of 3 Straumann Standard Plus Regular Neck 3.3-mm x 10-mm implants.
Prior to any surgical intervention, the main risks were discussed in detail with the patient. These included potential for nerve damage or paresthesia. Reasons for implant failure were also discussed, including her smoking habit during initial integration of the implants, neglect, denture adhesive use, and stresses on the surgical site as the result of any transitional appliance fabrication.
Temporization would prove to be a challenge in this case. It was determined that the forces of a denture would need to be reduced during the healing phase. The patient’s original partial denture was relined and the existing splinted crowns added to the RPD, creating a denture with little or no contact with the anterior tissue. A resilient soft liner COE-SOFT (GC America) was used in the anterior area under the splinted crowns attached to the patient’s old removable appliance.
The preparation of the osteotomy began with a 2.2-mm pilot drill. The initial drill depth was 10 mm. Implant site preparation continued with a 2.8-mm pilot drill to the 10-mm depth. A bone tap was used to create the thread pattern of the implant into the bone. The bone in this area can be dense and difficult to drill into. Each preparation was made parallel to the next using guiding pins. Straumann Standard Plus 3.3-mm x 10-mm implants with sand-blasted large-grit acid-etch surfaces were placed and ratcheted into position. The shoulder of the implant was left slightly coronal to the crestal bone to allow for easy access; 1.5-mm tall closure screws were placed into each implant, and the area was sutured using Vicryl (Ethicon).
Following 3 months of integration and periodic changing of the resilient liner, a closed custom-tray impression of the implants was made using the Straumann impression cap and synOcta positioning cylinders. A master impression was sent to the lab to have the proper analogs placed into the impression for a master model pour. The master cast was poured, duplicating all peripheral borders. A bite registration was used to position the casts. Teeth were positioned to aesthetics and function.

The Locator (Zest Anchors) attachments are intended to act as retentive devices for overdentures. Because of their design, the patient is able to align and seat the overdentures easily. It is important, however, that the implants be placed in a parallel position to each other to simplify the prosthetic construction (Figures 7 and 8). According to the manufacturer, the attachments resist wear and maintain satisfactory retention for up to 56,000 cycles of function. It is a nice system to use where occlusal clearance is a problem, since it is only 3.17 mm in total height. The male portions can be easily changed chairside, with minimal inconvenience to the patient. The Locators come in a variety of retentions from extra light (blue) to heavy (clear). In this case the average-retention orange attachment was used (Figures 9 and 10).

Figure 11. Panoramic radiographs of Straumann implants in position. Note the excessive atrophy of the posterior mandibular bone.

This type of prosthesis allowed for excellent retention and stability for this patient. The Locator attachments were positioned extracoronally to allow for good tissue adaptation and easy maintenance with a simple toothbrush or endtuft brush. If manual dexterity becomes a concern, the implants can be maintained at home using a wash rag or cotton applicators. Follow-up care includes clinical assessment for abutment stability, mobility of the implants, and plaque accumulation. Since the perimucosal seal is vital to protect the underlying connective tissue, probing a healthy implant is not advised.
Radiographs are taken annually to determine bone position and contour (Figure 11). Metal scalers and ultrasonic instruments may scar and pit the titanium abutment surface; therefore, plastic, gold, or graphite scalers should be used as necessary.

CONCLUSION

This patient exhibited a positive end result because of her understanding of the limiting factors involved in this case and the final prosthesis (Figures 12 to 15). She is, however, able to chew more efficiently and speak clearly without worry of the prosthesis loosening or any of the abutments decaying.

Dr. Kosinski is an adjunct assistant professor at the University of Detroit Mercy School of Dentistry and maintains a private practice devoted to comprehensive and implant dentistry. He serves on the editorial review board of REALITY, and is a Diplomat 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, American and International Colleges of Dentists, and Academy of Dentistry International, and received his Mastership in the AGD. He is a member of Omicron Kappa Upsilon and the Pierre Fauchard Academy. He has published more than 45 articles on the surgical and prosthetic phases of implant dentistry and was a contributor to the textbook Principles and Practice of Implant Dentistry. He can be reached at (248) 646-8651 or drkosin@aol.com.

Dr. Owen graduated from the University of Detroit School of Dentistry in 1985. He has been involved in aesthetic and implant dentistry since that time. He completed an implant mini-residency through the American Academy of Implant dentistry and is currently credentialed as an Associate Fellow. Dr. Owen is a Fellow of the AGD, is an award-winning editor and president of the Michigan AGD, and currently serves on the Board of Trustees of the Michigan AGD. He is also a Fellow of the Pierre Fauchard Academy. He can be reached at (248) 646-8651.