Maxillary Small-Diameter Implant-Retained Overdentures

INTRODUCTION
When considering the use of dental implants in the maxillary arch to retain an overdenture, a great amount of consideration must be given to anatomy, physiology, biomechanics, and to the opposing dentition. Although many articles and studies have been conducted, there is quite a controversy on the use of unsplinted dental implants in the maxillary arch to retain an overdenture. My personal philosophy is to place an implant with a diameter that can comfortably fit in the volume of bone present. If a small-diameter implant (SDI) is selected, then it may be prudent to offset the decrease in diameter by increasing the number of implant fixtures.
The SDI does have its place for use in the resorbed edentulous upper arch. General practitioners continue to commonly see ill-fitting upper dentures. Most of these patients have simply learned how to tolerate their less-than-ideal prostheses. When given the option to have additional bone added, our efforts fall short with a miserable 3% of the general public having this treatment. The promising news is that SDIs, with a history of more than 10 years of clinical use, can provide an alternative option. Originally de­signed for use in the lower arch and for immediate load under certain criteria, the SDI has shown great promise in the maxillary arch when following sound guidelines.1 The guidelines include: narrow atrophic residual ridges to allow for bicortical stabilization, an opposing denture to minimize occlusal forces, 12 mm vertical ridge height to increase bone to implant contact, 4 mm buccal-lingual width, and a minimum of 30 Ncm of initial stability.
Small-diameter implants continue the trend of minimally invasive dentistry that embodies the philosophy to consider all solutions prior to committing the patient to the scalpel. When additional surgery is contraindicated to rehabilitate the atrophic maxilla, SDIs should be considered if all other guidelines have been met. With the use of a minimum of 6 SDIs, a maxillary overdenture has been shown to be effective. Great care should be exercised to place the implants as parallel as possible. In addition, no more than 20° of divergence should be allowed, as this will prevent off axis loads, premature o-ring wear, and difficulties in seating the overdenture for the patient. As wide of an anterior-posterior (AP) spread between the implants as is possible should be planned. This will reduce the force placed on each individual implant.2 Also important, a final overdenture impression should capture the maxillary tuberosity so a proper posterior stop can be placed in the denture.

CASE REPORT
Diagnosis and Treatment Planning

A 58-year-old fully edentulous male presented to our office with upper and lower dentures that he had been wearing for more than 22 years. The existing prostheses were extremely worn. Clinically, the residual ridge appeared to have adequate width to consider implant therapy (Figure 1).
During the initial consultation, the patient expressed his frustration with both his upper and lower dentures, complaining that he had to constantly “glue” them in place. Surprisingly, his upper was more of an annoyance than his lower, often falling down when speaking or smiling.

Figure 1. Pre-op maxillary arch.
Figure 2a. Seven small-diameter implants (SDIs) (Inclusive Tooth Replacement Solution [Glidewell Laboratories]) placed in the maxillary arch using a flapless approach. Figure 2b. Post-op panoramic radiograph.

Bone sounding was done with the use of a bone caliper to determine the bone anatomy on both arches and revealed thick maxillary tissue with around 4 mm of bone in the buccal-lingual dimension. It was decided to consider the use of SDIs in both arches to minimize surgery and reduce cost, and to preserve as much of the residual ridge as possible. With more implant fixtures, additional areas of bone would be stimulated. This would allow for more of the residual alveolar ridge to stay intact over time. The positions of the most posterior implants would be in the second premolar regions bilaterally, with additional implants being placed in the premaxilla; this approach would produce the widest AP spread and keep the SDIs as parallel as possible.

Clinical Protocol
One hour prior to implant placement, the patient was prescribed 2 g of amoxicillin, and a chlorhexidine gluconate rinse (GUM Chlorhexidine Gluconate Oral Rinse [Sunstar Amer­icas]) was done immediately before surgery. Using the study cast and bone-sounding data, the case was planned for 7 SDIs (Inclusive Tooth Replacement Solu­tion [Glidewell Laboratories]) via a flapless approach. Note: An alternative to bone sounding to visualize the bony ridge would have been to obtain a computed tomography scan. A surgical marking pen was used to transfer the selected sites to the maxilla. Next, local anesthesia was administered (2% Xylocaine Dental with Epineph­rine [DENTSPLY North America]). Then, a 1.7 mm pilot bit (in an implant handpiece with copious irrigation) was used to perforate the cortical plate, but not allowed to go to full depth. The initial osteotomies were then assessed with a blunt-ended endodontic explorer to allow tactile perception of bone quality. As expected, the bone was of a spongy nature and deemed to be of D3 quality; thus the osteotomies were only taken to one half the length of the SDIs. Two different sizes of SDI (2.5 mm and 3.0 mm) were selected, based of the width of the residual ridge. This would ensure that the implant would be encased and supported bicortically with dense bone with a minimum of one mm circumferentially. One by one, each SDI was removed from the sterile vial and placed via a implant handpiece (Aseptico AEU 7000) at 40 rmp. I prefer to place SDIs via a handpiece instead of a hand wrench in order to minimize off-axis tipping forces. The resulting placement of all 7 SDIs replicated our diagnostic treatment plan with a wide AP spread and parallel implants to minimize off-axis forces and o-ring wear (Figure 2a). All 7 SDIs had over 40 Ncm of initial stability and were ready to be put into function. A postoperative panoramic radiograph was taken (Figure 2b).

Figure 3. Fit check material (QuickUP [VOCO America]) was placed on the internal aspect of the denture, then seated over the SDIs and allowed to set. Figure 4. Relief wells for housings.
Figure 5. Small-diameter implant impression caps. Figure 6. Putty matrix was utilized for denture duplication.
Figure 7. Custom impression inside the duplicated denture. Figure 8. The maxillary denture was then relined at the chair with a soft reline material (Ufi Gel SC [VOCO America]).
Figure 9. Master cast with SDI analogs. Figure 10. Postoperative smile.
Figure 11. Final maxillary SDI-retained overdenture. Figure 12. Cast-metal frame with housings.

The current denture would be replaced with a new overdenture; however, it would be necessary to provide relief in the interim. Fit check material (QuickUP [VOCO America]) was placed on the internal aspect of the denture, then seated over the SDIs and allowed to set (Figure 3). All areas of show-through acrylic in the denture were removed to allow for passive seating over the SDIs (Figure 4). Snap caps were placed over the 7 SDIs (Figure 5) and a full-arch polyether impression (Impregum Soft [3M ESPE]) was taken inside a lab putty (Capture [Glidewell Laboratories]) duplicated copy of the patient’s existing denture (Figures 6 and 7). The existing upper denture was relined with a soft chairside reline material (Ufi Gel SC [VOCO America]) to help retention (Figure 8). A final stone model with lab analogs was created by our dental laboratory team (Figure 9).
Because the final impression was taken in the duplicated denture, a tooth set-up in wax was returned to verify fit, aesthetics, occlusion, phonetics, and comfort (Figure 10). All criteria were approved by the patient and doctor, and the wax set-up was sent back for final processing. The final overdenture (Glidewell Labora­tories) was created with a metal substructure and lab processed o-ring housings (Figures 11 and 12). The use of a metal substructure would allow for partial palatal coverage and some additional cross-arch support.
At delivery, the new overdenture only needed slight relief in the buccal-flange area and around one of the housings. This was done utilizing a ceramic E-cutter style lab bur that generates very little heat (Ceramic Cutter [Komet USA]).

Postoperative Follow-up
The patient was followed at one-, 3-, 6-, and 9-month intervals; no complications were encountered or reported by the patient. All 7 implants demonstrated no marginal bone loss (intraoral periapicals were ta­ken at 9 months); all were without mobility and all had probing depths circumferentially of less than 4 mm. Overall, the patient was pleased with the stability and improved function that the SDI-retained overdenture provided.

IN CLOSING
Several design features may have contributed to the initial success of this case, in­cluding: undersized osteot­omies to compress and condense the Type III bone; self-tapping aggressively threaded SDIs; a flapless approach to minimize disruption of blood flow; an opposing full removable denture; approximately 2 SDIs to replace each standard-body implant; a wide AP spread; the cast-metal frame overdenture; and an SDI length of greater than 10 mm.
This case study demonstrates the potential successful use of freestanding SDIs in the maxillary arch to retain a palate-free overdenture.


References

  1. Flanagan D, Mascolo A.The mini dental implant in fixed and removable prosthetics: a review. J Oral Implantol. 2011;37(Spec No 1):123-132.
  2. Krämer A, Weber H, Benzing U. Implant and prosthetic treatment of the edentulous maxilla using a bar-supported prosthesis. Int J Oral Maxillofac Implants. 1992;7:251-255.

Dr. Patel is a graduate of University of North Carolina at Chapel Hill School of Dentistry and the Medical College of Georgia/American Acad­emy of Implant Dentistry Maxi Course. He is the co-founder of the American Academy of Small Diameter Implants and is a clinical in­structor at the Reconstructive Dentistry In­sti­tute. Dr. Patel has placed more than 2,500 mini-implants and has worked as a lecturer and clinical consultant on mini-implants for various companies. He can be reached at pareshpateldds2@gmail.com or at the Web site dentalminiimplant.com.

Disclosure: Dr. Patel reports no disclosures.



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