Three-Dimensional Treatment Planning with Surgical Guides and Mini Implant-Retained Dentures

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Mini implants have been used successfully to improve the retention of dentures.1 With the average age of our population increasing as people continue to live longer, the need to improve patients' lives with secure full dentures is growing.2 Many edentulous patients present with inadequate bone width for the placement of traditional implants, which can require 6 mm of bone or more in the buccal-lingual dimension. To reach the necessary bone width, these patients would have to undergo expensive, time-consuming bone grafting procedures. Even if grafting is not required, many elderly patients are dissuaded by the cost and trauma associated with implant surgery. A mini implant, however, can be placed in as little as 3 mm of buccal-lingual bone width. The single-stage placement protocol is simpler and less traumatic.

Fewer office visits are required because mini implants allow for immediate loading in the presence of primary stability,

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CASE REPORT
The patient in this case, a 55-year-old female, had had all her remaining maxillary and mandibular teeth extracted 11 months prior (Fig. 2a, Fig. 2b). At that time, she had received conventional maxillary and mandibular dentures. Her chief complaint was that these dentures were nonretentive and nonfunctional, becoming dislodged or falling out whenever she ate or spoke. Although the extractions were recent and she was not a denture wearer for a considerable amount of time, there was already excessive resorption noted in the mandible. Radiographically, bilateral pneumatization of the maxillary sinus was also noted (Fig. 3).

Prior to obtaining a CT scan, reline impressions were taken with Impregum™ brand impression material (3M ESPE; St. Paul, Minn.), and the dentures were sent to Glidewell Laboratories (Newport Beach, Calif.) (Fig. 4a, Fig. 4b). From that set of impressions, upper and lower dual-scan appliances were fabricated (Fig. 5a, Fig. 5b). It is important to note here that the accuracy of each surgical guide depends greatly on the accuracy of the impression taken for each scan appliance. Any reduction in movement of the surgical guide will increase the accuracy and likely success of the final implant placement. Using the GXCB-500™ powered by i-CAT® (Gendex Dental Systems; Des Plaines, Ill.), three CT scans were taken – one of the patient with the scan appliances in the mouth, and one of each scan appliance by itself. From these scans, the Inclusive® Mini Implants (Glidewell Laboratories) selected for this procedure could be virtually placed utilizing Blue Sky Plan® software (Blue Sky Bio; Grayslake, Ill.).

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For the retention of a maxillary overdenture, it is recommended that six mini implants be placed in the premaxillary region. To retain a mandibular overdenture, no fewer than four mini implants should be placed anterior to the mental foramina.4 The smaller number of implants required in the mandible is due to the increased bone density compared to that found in the maxilla. In this case, it was decided that 1.5 mm diameter guide sleeves would be used for the 2.2 mm diameter Inclusive Mini Implants to be placed in the mandible. Due to the softer bone of the maxilla, it was decided that 1.5 mm sleeves would also be used for the thicker, 2.5 mm diameter Inclusive Mini Implants placed there. In denser bone, I would have asked for 1.7 mm diameter sleeves for use in the maxilla.

Even though the placement of mini dental implants is relatively simple and straightforward, a common argument against placing them is that the surgery is performed "blind."5 Critics contend that by not raising a flap, as is the recommended protocol when placing mini implants, the doctor cannot accurately gauge the proper insertion path. With a CT scan, however, all of the patient's anatomy and soft tissue anomalies can be factored into the digital treatment plan. This digital treatment plan is not merely a "best guess"; rather, it provides a true representation of the anticipated clinical outcome. The surgical guide used to translate the virtual outcome to a physical outcome is precisely fabricated by a computer-controlled milling station, and the guide sleeves are placed to tight tolerances. As a result, the opportunity for error during placement is significantly reduced.

The patient was draped, and a clean operating environment was established.

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The drilling process was conducted at 1250 RPM under copious irrigation using the MD 20 Dual Motor System (Nouvag USA; Lake Hughes, Calif.). For the best chance of long-term implant success, it is important to minimize tissue damage and thermal trauma to the bone.6 Because Inclusive Mini Implants are self-tapping, only a single pilot drill is required; no additional finishing bits or bone formers are needed. The implant will follow the path created by the pilot drill and compress and condense the bone to help achieve immediate primary stability. In certain cases, it is possible to engage both cortical plates for even greater stability. All six pilot holes were made following the same process, and the surgical guide was removed. A periodontal probe was used to confirm that all pilot holes in the cortical bone did not perforate in the buccal-lingual dimension.

One at a time, the Inclusive Mini Implants were removed from their sterile packs and glass vials and hand-tightened with the attached carrier until they were difficult to turn (Fig. 8).

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The same process was repeated for the mandible using the lower surgical guide (Fig. 10). In this case, the Inclusive Mini Implants were 13 mm in length, so the pilot drill was taken to a depth of approximately 18 mm, or almost to the hub. The overall length of the pilot drill from cutting tip to shank is approximately 20 mm. Once again, final seating was verified at 35 Ncm to ensure primary stability (Fig. 11).

Following successful placement of all mini implants, Blu-Bite HP bite registration material (Henry Schein; Melville, N.Y.) was injected onto the intaglio surface of the dentures to help indicate where the dentures would need to be relieved to allow for passive fit over the mini implant heads (Fig. 12a, Fig. 12b). An NTI® Universal Cutter pear-shaped bur (Axis Dental; Coppell, Texas) was used to help create the appropriate-shaped spaces (Fig. 13a, Fig. 13b, Fig. 13c, Fig. 13d). The acrylic bur is 2.9 mm wide and cuts a hole that is just the right size for the O-ball head of the mini implant. With a few circular strokes, you can easily widen the hole to accommodate the full O-ring Housing, which is approximately 3.5 mm tall and 4.75 mm wide.

Once the majority of acrylic was removed, Dr. Thompson's Color Transfer Applicators (Great Plains Dental Products; Kingman, Kan.) were used to mark the tops of the O-balls. Any marks that transferred to the dentures indicated additional acrylic that had to be removed to ensure a completely passive fit (Fig. 14a, Fig. 14b).

A soft reline was performed chairside using COE-SOFT™ reline material (GC America; Alsip, Ill.) to stabilize the existing denture during the healing phase. This gives the mini implants a chance to osseointegrate fully before more stressful loads are placed upon them.

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A postoperative CT scan was then taken. The cross-sectional slices demonstrate the implants in almost the exact positions proposed by our digital treatment plan. They confirm our preoperative goals of taking full advantage of the available bone while keeping the implants as parallel as possible (Fig. 15). Had we attempted this case without the use of a digitally milled surgical guide, these goals would have been far more difficult to achieve.

CONCLUSION
The Inclusive Mini Implant System, particularly when used in concert with Digital Treatment Planning services, represents an ideal opportunity for general practitioners to become involved in implant dentistry. In today's repressed economy, offering this kind of valuable, inexpensive treatment enables cost-conscious patients to enjoy the many benefits of secure, retentive dentures. The use of CBCT, digital planning and surgical guides helps to reduce clinician stress, save chairtime and ensure a predictable outcome. The flapless technique allows for minimal patient discomfort and a greater chance for immediate loading – aspects that improve overall client satisfaction. These simplified protocols and conservative procedures are made possible by integrating advanced technology and new materials into everyday implant dentistry.