Denture Stabilization With Small-Diameter Implants

PDF | Print | E-mail

There are calls across the profession for dentists to offer more functional solutions to edentulous patients. The drawbacks of standard dentures are well known—too often, they lack the stability that patients require, leaving them unable to enjoy normal foods and uncomfortable in social situations.
As an alternative, the mandibular 2-implant overdenture has been gaining favor, and has been recommended as a first treatment option in a consensus statement released by McGill University.1 However, while this solution certainly addresses the stability problem posed by traditional dentures, the procedure comes with its own set of drawbacks. The process of placing regular-diameter endosseous dental implants is lengthy, invasive, and costly for patients. Additionally, many edentulous patients are not good candidates for traditional implants, due to a lack of sufficient bone to anchor the implant.

THE SMALL-DIAMETER IMPLANT ALTERNATIVE
Over the past decade, an alternative to traditional diameter endosseous implants (at least 3.5 mm in diameter) has been increasing in popularity. Small-diameter implants (SDIs) (also referred to as mini-implants) which vary in diameter from 1.8 mm to 2.9 mm offer dentists a solution for denture stabilization that avoids many of the drawbacks of regular endosseous diameter implants. SDIs can be placed in a one-hour, minimally invasive (MI) procedure and are able to be immediately loaded, meaning patients can instantly experience the benefits of the added stability. The small size of these implants makes them suitable for many patients who do not qualify for traditional diameter implants, due to lack of sufficient bone width, and the request not to undergo extensive bone grafting procedures. Furthermore, the cost of the procedure is more affordable for patients.2
While the number of general dentists who offer this service to their patients is growing, I believe that there is far more potential for its continued expansion. The cause of many dentists’ hesitancy to adopt this service may simply be that they are unfamiliar with the technique for placing SDIs. Furthermore, some may not feel comfortable with the idea of incorporating dental implantology into their practices. However, one of the key virtues of SDIs is their simple-to-learn technique. I know from both my own experience and from the experience of others, as well as in teaching these techniques, that a general dentist’s skill set is quite sufficient to successfully begin implementing these services. Unlike the complicated technique required for traditional diameter implants, the MI procedure for SDIs makes it a valuable service to offer in a general practice setting.
Although a number of procedures can be performed with SDIs, the standard utilization and the basic technique taught at introductory courses is placing 4 implants in the anterior mandible to help stabilize a complete lower denture. This is an ideal procedure to begin offering in general practice, and in my 10 years of experience performing this technique, I have seen it make a dramatic difference in the lives of many patients.

DIAGNOSIS AND TREATMENT PLANNING
The procedure for placing 4 SDIs in the mandible can be completed in 2 visits—one for the diagnostic workup, and one for the MI surgery. At a patient’s initial visit, his or her candidacy for the procedure is assessed, and the patient’s current denture is examined. The occlusion of the denture, the degree of wear, and the size of the lower denture are analyzed to determine if the existing denture can be adapted to accommodate the metal housings needed for the implant system. In the event that a denture is too worn, or there is lack of thickness of acrylic to insert the metal housings, the possibility of fabricating a new denture is discussed with the patient.

Figure 1. Panoramic radiograph with radiopaque foil showing relationship of second bicuspids and the mental foramina.

Figure 2. Lateral view showing outline of denture resting on anterior mandible.

Also importantly, the patient’s medical history and dental health are assessed. Keratinized gum tissue is preferred for implant placement,3 so the health of the gums needs to be examined. Next, the patient’s bone is evaluated, both with a brief tactile examination and also with a caliper to measure the bone thickness. Panoramic- and lateral-view radiographs are taken to more accurately determine the dimensions of the bone and to locate the mental foramen, an important step in the diagnostic workup. (A No. 4 large-sized radiographic film can be used to capture the lateral views, or a lateral cephalometric radiograph can be used.) To assist with the panoramic view, I place 2 small pieces of radiographic foil on the inside of the lower denture in each of the second bicuspid regions. These dots show on the panoramic film (Figure 1), giving me reference points to locate the mental foramina in relation to the denture. The distal-most implants will be placed 5 to 6 mm ahead of the mental foramen to avoid the possibility of an anterior loop of the inferior alveolar nerve being present.
The existing dentures are worn for the lateral film as well. For this view, I wrap a thin strip of radiographic foil around the front of the lower denture, extending completely around the outline of the denture. The film then shows the bony ridge in the anterior of the mandible, as well as the outline of the denture and how it sits on the crest of the ridge (Figure 2). Like the panoramic view, this also helps in determining the ideal length of the SDIs. Additionally, it assists with determining the proper angulation of the mini dental implants in order for the female housings to be incorporated inside the lower denture. Alternatively, a computed tomography scan can be taken.
Once the measurements and radiographs have been examined and the medical history has been reviewed, we can determine whether the patient is a good candidate for SDIs. Patients who are in reasonably good health, with at least 10 mm of bone height in the anterior mandible and a bone thickness of at least 4 mm, are considered to be suitable candidates. After discussing the cost of the procedure with the patient and obtaining informed consent, we are able to move forward and schedule the procedure.

FOUR SMALL-DIAMETER IMPLANTS IN ONE HOUR
The Technique

At the implant placement appointment, patients are first instructed to rinse with a chlorhexidine mouthwash (Peridex [3M ESPE Dental Products]). Local infiltration anesthesia (articaine hydrochloride 4% with 1:100,000 epinepherine) is then administered buccally and lingually from the mental foramina forward. While the anesthetic takes effect, the location of the 4 implants is marked on the inside of the patient’s lower denture with an indelible ink pen (Figure 3). The posterior-most location on both sides is marked 5 to 6 mm in front of the mental foramen, and the 2 anterior sites are marked approximately 10 mm ahead of the distal sites. Once these 4 sites are marked inside the denture, it is placed back inside the patient’s mouth and he or she is asked to bite gently against the maxillary denture. This transfers the ink marks from the inside of the denture to the patient’s ridge. The upper and lower dentures are then removed.

Figure 3. Location of small-diameter implants (SDIs) marked inside patient’s lower denture.

Figure 4. A pilot drill was used to create an undersized osteotomy.

Figure 5. A winged thumb wrench was placed on the implant to provide more torque for inserting the implant.

Figure 6. A ratchet was used for the final stages of insertion.

Figure 7. The implants, postinsertion.

Figure 8. A cold-cure acrylic was applied to the denture.

The first implant is placed at the site in the patient’s ridge with the least amount of bone. This is done in order to allow for alignment and the angulation of the next 3 implants. A tissue punch can be used to remove a small amount of gingiva where the SDI is to be inserted. To place the implant, a pilot drill under sterile saline irrigation is used to penetrate the cortical plate, which provides a path for the self-tapping SDI to follow (Figure 4). Next, while maintaining a dry field, the implant is transferred from the sterile vial on a carrier and is inserted into the pilot opening. The carrier is rotated clockwise until the implant becomes stable. The carrier cap is then removed and a finger driver is placed on the o-ball head and rotated clockwise while downward pressure is exerted. The implant is rotated until noticeable bony resistance is encountered. The finger driver is then removed and a winged thumb wrench is placed on the implant to provide more torque for inserting the SDI (Figure 5). After the winged thumb wrench becomes difficult to turn, a ratchet or adjustable torque wrench is used for the final stages of insertion (Figure 6). Carefully controlled turns are made with the adjustable torque wrench set at 45 Ncm to avoid placing excessive torquing forces on the implant. The implant is placed so that all etched threads are engaged in bone. The implant is then tested for stability by placing the adjustable torque wrench at a setting of 30 Ncm, which should cause the break-arm to release. This is the minimal level of resistance required to allow for immediate loading of the implants.
The implants are placed individually, with each successive implant used to parallel the pilot drill for the next site. After all 4 implants are placed (Figure 7), the denture is then retrofitted with the female housings for the implants. If the implant placement corresponds to the 4 ink marks on the denture, those marks can then serve as a guide to initiate relieving the denture. A portion of the denture is drilled out in each of the 4 sites, and occlusal spray is then applied inside the holes. The denture is then gently seated on the implants, then removed and checked for transfer of the spray to the implant. Additional relief is done until a passive fit is obtained on top of the implants.
Three different sizes of metal housings are available to customize the retentiveness of the denture, ranging from the largest and least retentive, MH-1, to smallest and most retentive, MH-3. The patient’s level of dexterity, the size of the patient’s denture, and the angulation of the implants are all factors for clinicians to consider when selecting the metal housing size. For instance, a 90-year-old patient with arthritic hands will likely require a less retentive fit than a younger, healthier patient, thus making an MH-1 more suitable. In cases where an MH-1 would be most appropriate, but the patient’s denture is not large enough to accommodate the size, the smaller MH-2 can be provided with a less retentive o-ring which allows the lower denture to be easier to remove.

Figure 9. The blockout shims were removed and the denture polished.

Figure 10. The denture was seated securely back in the patient’s mouth.

Figure 11a. A postoperative radiograph was taken to confirm proper placement of the implants.

Figure 11b. Five-year follow up radiograph demonstrating maintenance of bone levels and osseointegration of the small-diameter implants (SDIs).

Additionally, each metal housing size can accommodate a different degree of divergence among the 4 implants, allowing practitioners to customize combinations of housings if necessary. While the MH-1 housing can allow the denture to seat with the SDIs up to 30º divergent (included), the MH-2 fits included angles up to 15º off. Therefore, in a case in which the practitioner would ordinarily fit the denture with 4 MH-2 housings, but one implant is 20º off, an MH-1 can be used for that individual site while the other three are fitted with MH-2s as planned.
Once the metal housings are selected, blockout shims are trimmed to size and placed on each implant. The metal housings are then snapped on to the top of the implants and checked for a passive fit over the blockout shims. The denture is drilled again to fit over the female housings. IMTEC (a 3M Company) SECURE Adhesive is applied to the holes in the denture, and then followed with SECURE Hard Pick-Up material, IMTEC’s cold-cure acrylic for dentures (Figure 8). The denture is seated back in the patient’s mouth, and the upper denture is inserted as well. The patient bites in a functional bite gently for approximately 10 minutes while the material sets.
After the material has set, both the upper and lower dentures are removed, and the lower is checked for voids. In the event of voids, an additional application of SECURE Hard Pick-Up material can be applied to the deficient areas and allowed to set again. The denture is polished and delivered back to the patient (Figures 9 and 10), and an additional panoramic radiograph is captured to confirm proper placement of the implants before the patient leaves the office (Figures 11a and 11b).

Patient Instructions
Patients are instructed not to remove the lower denture for at least 48 hours immediately following the procedure, in order to prevent the tissues from swelling, and also because some patients may have difficulty reinserting the denture initially. Furthermore, I believe that minimizing the movement of the denture in the first 24 hours helps prevent additional discomfort. Recall procedures may vary, but I instruct my patients to return to the office the following day, at which point the lower denture is removed and the gums are examined for any sore spots where the denture may be rubbing. Also at this visit, patients are instructed in the proper way to insert and remove the denture, and an assistant helps them practice taking it in and out until they are comfortable with the denture’s path of insertion.
Patients are instructed to eat a soft diet for 2 weeks and are informed that minor bruising and swelling is normal. Cleaning instructions are given, with patients told to remove the denture for cleaning after meals. We request that patients return 5 days after their first recall, at which point we perform any necessary light adjustments. After an additional 5 days, we see patients once more to ensure they are satisfied with their stabilized lower denture.

CLOSING COMMENTS
SDIs can quickly and affordably restore a level of function that many denture patients have missed for years. Patients’ reactions to the procedure are dramatic and very rewarding to witness. In my experience, the benefits that SDIs offer to patients—added function, minimal invasiveness, and an affordable price—make them a good solution for many patients. A study is currently underway at McGill University comparing the efficacy and success rate of this treatment versus standard implants in stabilizing dentures.4
I encourage you to explore the possibility of becoming certified and offering SDIs to your patients when appropriate. After only a one- or 2-day seminar, it is possible to begin performing this technique and witnessing the difference that it makes in your patients’ lives. Additionally, once you are comfortable with the basic procedure for placing the implants, the technique can be adapted for other clinical applications.
(A future article in Dentistry Today will explore additional uses for this versatile technology.)


References

  1. Feine JS, Carlsson GE, Awad MA. The McGill consensus statement on overdentures. Mandibular two-implant overdentures as first choice standard of care for edentulous patients. Montreal, Quebec, May 24-25, 2002. Int J Oral Maxillofac Implants. 2002;17:601-602.
  2. Christensen GJ. The ‘mini’-implant has arrived. J Am Dent Assoc. 2006;137:387-390.
  3. Bouri A Jr, Bissasa N, Al-Zahrani MS, et al. Width of keratinized gingiva and the health status of the supporting tissues around dental implants. Int J Oral Maxillofac Implants. 2008;23:323-326.
  4. McGill University. International projects (Asia/ Australia). mcgill.ca/international/projects/asia/. Accessed May 4, 2010.

Dr. Erwood received his DDS degree from the University of Western Ontario in Canada. He is a Fellow of the Academy of General Dentistry and the International Congress of Oral Implantologists. He can be reached via e-mail at irwe@aol.com.

Disclosure: Dr. Erwood is a lecturer for IMTEC, a 3M Company. He receives compensation for lectures but has not received compensation for writing this article.

Banner