Stabilizing Partial Dentures Using Small-Diameter Implants

The innovative use of dental implants is opening doors to many different types of treatments. However, at the same time, criticism is surfacing that the sometimes prohibitive cost of a traditional implant procedure, the stringent candidacy requirements, and general dentists’ apparent reluctance to offer the procedure are combining to inhibit the potential of this treatment. Dr. Gordon Christensen recently highlighted the challenges presented by traditional implant protocols, pointing out that bone grafting, which is often suggested to enable patients with inadequate bone to receive implants, adds additional time and expense to the treatment. The cost of the implant procedure alone may be perceived as high for many patients, and the need for bone grafting may exceed the patient’s budget for this treatment modality.
An appealing solution for many of these issues can be found in the increased use of small-diameter implants (also referred to as mini-implants), which are gaining favor among patients and dental implant practitioners. As a long-time proponent of small-diameter implants, I have seen firsthand how this treatment protocol can be used to overcome patients’ financial and anatomical limitations, providing them with a timely and functional solution that can make an immediate difference in their lives.
While small-diameter implants are most frequently used in lower denture stabilization procedures, there are additional applications for these implants beyond that popular technique. As an instructor on the small-diameter implant technique, I present a series of courses on the types of treatments that can be achieved with small-diameter implant certification. While the basic technique for mandibular denture stabilization can be taught in a one- or 2-day seminar, further opportunities are available to dentists who would like to more fully develop their small-diameter implant capabilities. This article will demonstrate one of those techniques—use of small-diameter implants to stabilize partial dentures.

BACKGROUND: IMPLANT STABLIZATION OF PARTIAL DENTURES
Partial dentures, much like full dentures, can often shift and rock as the patient masticates, speaks, coughs, sneezes, etc, which can be a nuisance in the best conditions, and an embarrassing handicap in others. To overcome these problems, small-diameter implants can be utilized with partial dentures in both the maxilla and mandible. The use of small-diameter implants to retain partial dentures helps reduce movement of the partial denture, thereby increasing the overall function of the prosthesis, as well as the patient’s security and social confidence. The advantages to using small-diameter implants in conjunction with partial dentures are very similar to the benefits of the treatment for patients wearing full dentures. The technique for placing the small-diameter implants is less invasive, less costly, and can be completed in a shorter amount of time when compared to the protocol for regular diameter implants. Furthermore, the candidacy requirements for patients are not as stringent for small-diameter implants as they are for traditional implants, making them a more viable option for the edentulous and partially edentulous population.
The diameter of small-diameter implants ranges from 1.8 to 2.9 mm, and the placement and denture adaptation procedure can be performed in about one hour. An important distinction of small-diameter implants is their ability to be immediately loaded in the mandible, making them a convenient option for patients who are seeking an immediate solution for denture stabilization. Finally, small-diameter implants are a practical service that can be offered in a general dental practice setting. With proper training, the technique can be incorporated with a minimal investment in equipment and materials, and this service appeals to a large patient population.

CASE EXAMPLES
Small-Diameter Implants for Upper Partial Dentures
The patient, an elderly man, had an existing partial upper denture that used clasps to help secure it to teeth Nos. 6 and 12. The patient was not fully satisfied with the aesthetics, function, or retention of the partial denture. Therefore, we discussed the option of creating a new partial denture that would be stabilized with small-diameter implants instead of traditional partial denture clasps. The patient agreed to explore this treatment plan, and we proceeded with a diagnostic workup. Unlike the diagnostic procedure for lower denture stabilization, a lateral film is not usually necessary for placement of small-diameter implants in the upper arch. The diagnostic workup is completed with a panoramic radiograph and bone sounding to determine the bone width, or a computed tomography scan can be utilized (Figure 1). Anatomical considerations during the diagnostic steps include location of the maxillary sinuses and nasal sinuses.

Figure 1. A panoramic radiograph was taken to locate maxillary sinuses and nasal sinuses.	Figure 2. Due to periodontal involvement, the upper right first bicuspid was extracted. A tooth was then added to the patient’s existing partial denture.

     The patient in this case was considered a good candidate for the procedure due to the quality and quantity of bone, and he consented to proceed with the small-diameter implant treatment plan. Due to periodontal involvement, the upper right first bicuspid was extracted and a tooth was added to the patient’s existing partial denture. The site was allowed to heal for 4 months before the small-diameter implants were placed (Figure 2).
Following the healing period, rests and guide planes were prepared. Then, a polyether impression was taken for construction of the new partial denture. A dental laboratory prescription was prepared requesting a closed oval major connector, with no mesh in areas where the small-diameter implants were to be placed. While it is possible in some maxillary partial denture cases to adapt an existing denture for use with implants (as is often done in the mandible), fabricating a new custom metal framework allows for better small-diameter implant location and provides additional room for the female metal housing pickup without damaging the framework.
Using the bone topography measurements obtained in the diagnostic workup, the precise locations for each of the 4 implants were determined. Classic MDI Implants with a MAX Thread Design (2.4 mm diameter) were placed in the upper right first bicuspid, upper right central incisor, upper left central incisor and upper left canine regions. There are several reasons that I prefer this type and size of small-diameter implant for maxillary use. One reason is that the thread pattern is designed for greater engagement with the softer bone in the upper jaw. Additionally, the slightly larger size of the implant allows for greater surface area to integrate with the bone.

Figure 3. A pilot hole was drilled through the gingiva to penetrate the cortical plate.	Figure 4. The small-diameter implant was inserted and rotated clockwise until resistance was felt.
Figure 5. A winged thumb wrench was used to further thread the implant into place.	Figure 6. The 4 maxillary implants in place.

     The procedure for placing small-diameter implants in the upper arch is similar to that for the lower. The patient rinsed with a mouthwash containing chlorhexadine (Peridex [3M ESPE]) and local infiltration anesthesia was administered. The locations for each of the 4 implants were marked with an indelible ink pen on the inside of the patient’s new partial denture, which was then briefly seated in the patient’s mouth in order to transfer the ink marks to the gingiva. The implants were placed one at a time by first drilling a pilot hole through the gingiva and penetrating the cortical plate (Figure 3), after which the implant was inserted and rotated clockwise until resistance could be felt (Figure 4). A series of wrenches was then used to further thread the implant into place until the desired level of torque, 35 Ncm, was obtained (Figure 5). In cases such as this one, because upper partial dentures often have less room to accommodate the female housings for the implants, it is helpful to place the prosthetic platform of the MDI slightly deeper than the traditional placement level in the mandible (Figure 6).
To fit the partial denture with the female metal housings for the implants, the ink marks previously made on the denture were used as guides to relieve the area for drilling. The partial denture was hollowed out, until a passive fit was obtained over the implants. The MH-2 metal housings (30% smaller than MH-1 metal housings) were selected and snapped on to the implants (Figure 7). In this case, due to the implants’ prosthetic portion being deeper in the gingiva, it was not necessary to place block-out shims over the implants prior to placement of the metal housings. The metal housings were already flush with the gingiva and there was no risk of acrylic flowing underneath the housings and causing denture lock-on. However, in other cases, block-out shims are often still necessary.

Figure 7. The metal housings were snapped on to the implants.	Figure 8. Pick-up material was placed in the relieved areas of the partial denture.
Figure 9. The denture was removed after the metal housings cured in place, then a final polish was performed.	Figure 10. The completed partial was snapped onto the implants.

     Adhesive for the pick-up material was applied to the denture in the areas that had been relieved, and SECURE Hard Pick-Up Material (3M ESPE) was placed onto the metal housings and in the relieved areas (Figure 8). The denture was seated in the patient’s mouth, and the patient was instructed to apply normal bite pressure for 7 to 9 minutes while the material set. The denture was then removed and checked for voids, and a final polish was performed (Figure 9). Next, the occlusion was evaluated and adjusted.
Finally, postoperative instructions were given as follows: The patient was instructed to not remove the denture for 24 hours and was informed that some bruising and swelling may occur. He was advised to eat a soft diet for 2 weeks, and an appointment was made for the patient to return the next day for a postoperative checkup.
The following day, the patient was examined for denture sore spots and was shown the path of insertion to remove and insert his new clasp-less partial denture (Figure 10).