Delivery of a Mini Implant-Retained Mandibular Overdenture
The placement of small-diameter "mini" implants in the edentulous mandible is designed to allow for the immediate loading of an implant-retained overdenture, provided primary stability is achieved. If the patient's existing denture presents an acceptable fit with proper extensions and balanced occlusion, it may be used as the final prosthesis following a hard reline performed chairside to pick up the O-ring implant attachments. If the existing denture needs to be replaced, however, the accepted protocol is to perform a soft reline and use it as a provisional prosthesis only, while the attachments are incorporated into the new, lab-fabricated overdenture.1 In this follow-up to a clinical case report documenting the placement of 3.0 mm diameter mini implants (Inclusive, Vol. 2, Issue 2), we detail the process of delivering a new mandibular overdenture to a patient following osseointegration.
Case Planning and Surgical Review
Seeking to improve the function and stability of her traditional mandibular denture, the fully edentulous patient in this case underwent the minimally invasive placement of four Inclusive® Mini Implants (Glidewell Laboratories) in the anterior mandible utilizing a digital treatment plan and guided surgery.2,3 The virtual planning process helped to confirm adequate bone width and quality, identify vital structures, and determine the ideal location and angle of insertion (Fig. 1). With the resulting surgical guide helping to ensure accuracy and parallelism during physical placement, there was no need for soft tissue reflection, thereby minimizing patient trauma, required healing time and the duration of the procedure (Fig. 2, Fig. 3).
Although primary stability of the implants was achieved, the patient's existing denture had been heavily modified with deep extensions of the lingual flanges (Fig. 4).4 It was therefore determined that she would be better served with a new prosthesis. After doubling as a radiographic guide in the digital planning phase, the patient's existing denture was relieved and soft-relined at the time of surgery for a passive fit over the implant heads. The patient was thus able to wear her modified existing denture as a provisional prosthesis while the final Inclusive Mini Implant Overdenture was fabricated. With consideration given to the elderly patient's bone quality, a timeline of two months was established to ensure full osseointegration prior to her first prosthetic appointment.
First Prosthetic Appointment: Preliminary Impressions
Approximately two months after guided surgical placement of the four mini implants, the patient returned to the office for an inspection of the implant sites. A sore spot was noted, due to a slight overextension of the denture border in the anterior section, but overall tissue health and implant stability was deemed acceptable for proceeding with the fabrication of a permanent prosthesis incorporating the O-ring attachments.
For the purpose of making custom trays, an initial impression was made of the lower arch using irreversible hydrocolloid (alginate) material in a stock tray (Fig. 5). This impression revealed the location of the O-ball abutments. To avoid potential inaccuracies, the patient was instructed to close slightly, allowing the muscles of mastication to relax. Upon removal, the first impression revealed a minor imperfection caused by tongue placement during insertion of the stock tray. Rather than risk future complications, the impression was remade.
Following a satisfactory lower impression, an initial impression was made of the upper denture for the opposing cast, to be saved for teeth-in-wax placement (Fig. 6). Both mandibular and maxillary impressions were poured up immediately with improved gypsum stone.
The soft liner of the provisional prosthesis was adjusted slightly in the lingual flange area due to the patient's sore spot (Fig. 7). The denture was then cleaned, and bilateral balancing occlusion was confirmed.
Second Prosthetic Appointment: Final Impression
With a custom tray fabricated by the laboratory from the preliminary mandibular impression, the patient returned to have border-molded impressions made that would be used to create the master cast.
The Inclusive Mini Implants were inspected and found to be clean. Because Inclusive Mini Implants have a one-piece design, there is no abutment-to-implant interface, eliminating any gap problems or microleakage associated with standard, two-piece implant designs. Mini Implant Impression Copings, another component of the Inclusive Mini Implant System, were snapped into place atop each O-ball abutment (Fig. 8). Using a mouth mirror to help guide insertion, the custom tray was tried in to ensure ample room for the impression copings.
Border molding was performed by filling first one side of the custom tray with Adaptol® impression material (J.F. Jelenko & Co.; New York, N.Y.) that had been heated in a warm water bath at 120 to 125 degrees Fahrenheit (Fig. 9). The patient was guided through a series of movements that exercised the muscles of mastication to create a highly accurate natural border along that half-arch (Fig. 10). The border mold on that side was cooled in ice water for approximately one minute and then dried with compressed air. Heated Adaptol was then placed in the other side of the tray, and the border molding process repeated for that half of the arch (Fig. 11). Minor adjustments were made as needed by warming one side at a time, keeping the other side cool to avoid unwanted movement. Border molding is a key step toward ensuring proper fit and function of the prosthesis itself, which will maximize patient comfort and reduce stress on the implants.
After cooling and drying, excess Adaptol material was trimmed away from the intaglio surface of the border mold with a very sharp Bard-Parker™ surgical blade (Aspen Surgical Products; Grand Rapids, Mich.) (Fig. 12). Duller blades may chip the border mold and should be avoided. The finished mold was cooled and dried again, prior to the application of adhesive on the intaglio surface of the custom tray and the Adaptol border, to ensure adhesion of the polyvinyl siloxane (PVS) impression material to both the border and tray (Fig. 13). This adhesive was allowed to set for seven minutes. Light-bodied PVS impression material was then placed around the implants, making sure not to place any of the material over the undercut areas of the impression copings (Fig. 14). The impression was allowed to set in the mouth for four minutes, picking up the four impression copings upon removal (Fig. 15). The overall quality of the impression was deemed excellent, having captured all of the borders and necessary anatomical landmarks. The impression was then sent to the lab for the insertion of Inclusive Mini Implant Analogs and pouring of the master cast.
Third Prosthetic Appointment: Wax Rim Try-in
With a mandibular wax occlusion rim (also known as a bite block) and master cast of her lower arch (complete with silicone-based soft tissue insert) (Fig. 16), the patient returned for jaw relation records, including vertical dimension of occlusion (VDO), centric relation and centric registration. The wax rim contained a pair of attachments to snap onto the patient's distal implants, for stability during the relation processes (Fig. 17). The patient's existing treatment dentures were used as a baseline measurement.
A dot was placed on the patient's nose and chin with an indelible marker. The patient was asked to lick her lips, swallow, and then close her jaw, teeth biting together gently. The distance between the two dots was measured, and the process repeated, to verify that the measured VDO was consistent (Fig. 18). The process was repeated yet again, but this time the patient was asked to relax her jaw, keeping her teeth apart, in order to measure the vertical dimension at rest (VDR). Spoken "s" sounds (i.e., "Mississippi" and "sixty-six") revealed a 1 to 2 mm freeway space, or rest position. It is important not to coerce or guide the patient too much, as this can result in unnatural movements and inaccurate measurements. The locked guide was set aside to save the measurement.
The treatment denture was removed and the wax occlusion rim inserted over the implants. A vertical opening of 5 mm was observed. A heated wax spatula was then used to decrease the height of the occlusal wax rim, maintaining the accuracy of the occlusal plane in reference to the existing maxillary denture (Fig. 19). The wax was removed gradually, with multiple try-ins, to avoid having to go back and add wax, which is much more difficult than wax removal. When the proper vertical height was established, a Bard-Parker surgical blade was used to notch the occlusion rim, and PVS occlusal registration material injected (Fig. 20, Fig. 21). The mandible was relaxed by mandibular manipulation to ensure a repeatable centric position. The PVS material was allowed to set for two minutes, resulting in a proper bite registration with the teeth in place at the correct VDO (Fig. 22).
A natural tooth shade was selected and verified, using the teeth set in the treatment denture as a guide (Fig. 23). The desired tooth mould was then selected, again using the existing denture as a reference. A Boley gauge was used to measure the posterior area to help decide the number of teeth to be used (Fig. 24). In this case, four teeth were chosen for the distal progression in order to cover the retromolar pads and provide a nice permanent stop in the posterior, matching the design of the maxillary prosthesis.
Fourth Prosthetic Appointment: Wax Denture Try-in
Using the relation records and tooth selections (shade and mould) from the wax try-in, the lab fabricated and delivered a trial denture with teeth set in wax, mounted on an adjustable articulator. Before authorizing final processing of the denture in acrylic, the patient returned to the office for a try-in of the trial setup for evaluation of esthetics, phonetics, centric relation, VDO, tooth shade and arrangement.
It was quickly discovered that the teeth were arranged in a standard, Class I occlusion. However, it was decided to recreate the patient's existing Class II occlusion, in deference to the moderate bone loss that gave her jaw a mildly distended appearance. Keeping the Class I arrangement, with the teeth too far facial, would result in a pouty lower lip, sometimes referred to as the "George Washington" look (as seen on a U.S. one-dollar bill). Speaking function was also deemed better served by the desired Class II, with the teeth positioned more lingually.
The anterior teeth needed to be pushed back at least 2 mm, especially on the left side. A chairside adjustment with Bunsen burner and spatula would necessitate keeping the patient in the chair for an hour or more, so the decision was made to send the case back to the lab. To transmit the desired information, a new bite registration was taken, demonstrating desired centric relation (Fig. 25). With this and the cast of the existing prosthesis, the laboratory technician can mount the information on an articulator and precisely determine the changes to be made (Fig. 26).
The follow-up try-in appointment revealed a prosthesis with excellent occlusion, phonetics and esthetics (Fig. 27). By properly providing the lab technician with the necessary information (i.e., cast, centric relation record and detailed prescription) upon the first try-in, further try-in appointments were avoided.
Final delivery of the lab-fabricated Inclusive Mini Implant Overdenture commenced with a demonstration of the connection between the implant analogs seated on the cast and the O-ring attachments housed within the prosthesis, so that the patient could hear the snapping sound indicating a proper, retentive fit.
The patient's existing denture was then removed for a side-by-side comparison (Fig. 28). The new overdenture exhibited a much cleaner look, without the transitional soft liner. Of particular note in the new prosthesis was the reduced size of the lingual flange extensions. While the patient had a lateral throat form conducive to such extensions, they were no longer needed because the retention provided by the O-ring attachments is far greater than that provided by any traditional denture modification.
The patient's implants were examined for cleanliness, which is critical to ensuring a proper, retentive fit (Fig. 29). Minor amounts of plaque and calculus were removed with a plastic scaling instrument. The patient was then shown how to fit the prosthesis in her mouth, sliding it gently into position, with the attachments aligned over the implant abutments. Once in position, two fingers were used to apply downward pressure upon the anterior laterals of the prosthesis. A patient should never "bite" the overdenture into place, as this can cause unnecessary wear on the O-rings.
With the overdenture fully seated, the borders were inspected for proper alignment. Phonetics and occlusion were also evaluated (Fig. 30), using excursive movements to ensure bilateral balancing occlusion (Fig. 31). Centric relation marks were very close, with heavy marks on the posteriors and light marks on the four anteriors. While it is important not to overload the implants with pressure on the anteriors, there should be sufficient support to permit proper function. Excessive pressure on the patient's upper denture in the anterior section could result in "combination syndrome," marked by premaxillary resorption.
The patient was asked to wait 10 minutes to allow for the manifestation of any sore spots. Two areas of tissue irritation were noted. The affected areas were marked for transfer to the prosthesis (Fig. 32). Relief of the marked areas was performed chairside with a carbide bur (Fig. 33), trimming away just enough acrylic to relieve the sore spot, after which the overdenture was cleaned and placed back in the mouth. The patient was encouraged to remove and reinsert the prosthesis herself. She did so without any pain or discomfort.
Occlusion and phonetics were checked anew, as relieving the denture will cause it to settle a little bit in those areas that were previously too high. Both were deemed satisfactory. Esthetics were similarly pleasing, consisting of a nice maxillary overlap so that the lower teeth did not look too bulky, avoiding the unsightly "bulldog" or "George Washington" look.
Figure 34 and Figure 35 illustrate the desired surgical outcome and final prosthetic outcome. The patient was asked to return the next day for a follow-up to check for any new sore spots. She was further asked to limit herself, initially, to softer, easy-to-chew foods while acclimating to her new prosthetic reality. Though accustomed to cutting up her food, the patient was told she should no longer have to do so, due to the superior retention provided by the implant attachments. She was encouraged to keep her old, soft-lined denture as a backup prosthesis. A home care cleaning kit and instructions were provided for use with both the primary and backup dentures. In-office visits for ultrasonic cleaning of the prostheses were recommended every three months. When provided with a denture adhesive for use with her traditional maxillary denture, she was quite happy to receive confirmation that traditional adhesive would no longer be needed for her mandibular overdenture.
Traditional dentures have long been a source of frustration and discomfort for users, particularly in the edentulous mandible, where even simple, everyday oral movements may dislodge the prosthesis. Implant-retained overdentures can offer dramatic improvement in form and function, and small-diameter implants can prove an ideal treatment option when conventional implants are contraindicated due to medical, anatomical or financial reasons. The ultimate solution, however, is still highly dependent upon proper delivery and adjustment of the final prosthesis. Whether utilizing the patient's existing denture or providing a new one, establishing ideal fit, balance, occlusion, and overall patient comfort will help to maximize the short- and long-term success of any implant-retained removable solution.