Clinical Case Report: 3.0 mm Diameter Mini Implants for Retention of a Mandibular Overdenture

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Preoperative Work-Up Photos
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Surgical Procedure
Before starting the surgical procedure, a surgical guide was fabricated for the 1.7 mm drill by exporting a manufacturing file from the implant treatment planning software, and then printing the appliance with UV-cured acrylic.

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Surgical Procedure Photos
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Prosthetic Procedure at the Time of Surgery
While adequate primary stability was obtained during the surgical procedure, the decision was made to relieve the patient's existing denture for a soft reline. A new denture incorporating the O-ring housings will be fabricated for placement in approximately three to four months. A cast framework will be incorporated into the new denture to provide strength to the prosthesis and support to the housings.

Prosthetic Procedure Photos
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While the placement of minis may appear to be relatively straightforward – potentially consisting of the use of a single drill before each implant is placed – their positions must be precisely planned. The anatomical locations of the mandibular canal, including the possibility of an anterior loop, and the mental foramina must be identified. This should be done utilizing proper radiography. To maximize denture stability, the four implants should be placed with as wide an anterior-posterior spread as possible. The tops of the polished collars should be slightly above the crest of the soft tissue over the ridge. This will help discourage mucosa from growing over the collar rim, where it may be pinched between the implant and the denture.

Primary stability of the implants is critical because they will be immediately loaded. The drilling protocol should be based on the quality of the bone. In denser bone, such as Type II bone, the drill that matches the minor diameter of the threaded section of the implant should be utilized. In bone that is less dense, a smaller diameter drill can be used and the implant allowed to self-tap during placement. If good primary stability is not achieved, the next wider diameter implant may be an option, provided there is adequate bone. With smaller diameter mini implants, such as 2.2 mm and 2.5 mm, it is recommended that a single drill be utilized to prepare the osteotomy to a depth of approximately one-half the length of the threaded portion of the implant, taking into account any additional depth such as soft tissue and surgical template thickness. The 3.0 mm diameter falls between the smaller diameters and conventional-sized implants. Ideally, one drill should be used here as well. Another option, as illustrated with this case, is to start with a smaller diameter drill to get a clinical feel for the bone quality and then adjust your protocol as needed.

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From a prosthetic perspective, the vertical and horizontal space also must be taken into account. For example, each O-ring housing provided with the Inclusive Mini Implant System is 3.5 mm in height and 4.75 mm in diameter. The housings must be completely encased in acrylic, and there should be at least 3 mm of acrylic above the top of each housing to provide adequate strength. If vertical space is limited, a cast framework incorporated into the prosthesis may be required. While the O-ring housings can be rotated to correct for up to 30 degrees of divergence between implants when they are processed into the denture, all efforts should be made to make the implants and housings as parallel as possible. This will also extend the life of the O-rings within the housings.

Conclusion
When using small-diameter implants, the clinician should be aware of the indications and the contraindications of this type of implant. In appropriate cases and with proper selection, planning and execution of surgical and prosthetic procedures, smaller diameter implants can provide an excellent solution to denture instability.

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