Introduction

Furthermore, due to the pattern of bone resorption and the presence of the alveolar nerve, prosthetic rehabilitation of resorbed edentulous mandible is difficult. ²

Several studies have shown that implant-supported overdentures in the mandible are a successful therapeutic technique, particularly in individuals with substantial residual bone loss, where retention and stability need to be improved. ^3,4

The following case report describes the use of the ø2.4 mm Straumann® Mini Implant in a patient with limited bone availability in the lower jaw. The Straumann® Mini Implant System, made of Roxolid® with the SLA® surface, offers one-piece Tissue Level implants with an Optiloc® prosthetic connection.

Initial situation

A systemically healthy, non-smoking 64-year-old female came to our clinic requesting a solution to improve her smile esthetics and masticatory function. She stated: “I am looking for a non-invasive solution for my mouth. I no longer tolerate the adhesive glue to hold the lower denture in place, and continuous direct and indirect relines have been unsuccessful.” She reported wearing full-arch dentures in the upper jaw for 15 years and in the lower jaw for 40 years.

The extraoral examination showed a lack of support for the lips, and this was reflected in the patient's profile.

The intraoral examination revealed fully edentulous maxillary and mandibular arches. In the lower jaw, the shape of the alveolar processes in the anterior zone was round and adequate in height and width (Class III, Cawood and Howell Classification). On the other hand, in the posterior zone, a knife-edged ridge form was encountered, adequate in height and inadequate in width (Class IV, Cawood and Howell Classification). In addition, the width of keratinized mucosa was minimal (Fig. 1).

The radiographic examination showed generalized vertical bone resorption with very limited bone availability in the posterior area of the lower jaw (Fig. 2).

The width of the alveolar ridge was measured using computed tomography (CT) scan images. The assessment depicted bone availability for the implantation of Straumann® Mini Implants for a full-arch rehabilitation (Figs. 3,4).

The SAC classification was used to evaluate the degree of difficulty of the patient's implant-related rehabilitation. In terms of surgical and prosthodontic categorization, the patient was considered complex (Fig. 5).

Treatment planning

The prosthetic options with advantages and disadvantages were presented after the clinical examination and radiographic analysis. The treatment plan for this patient was considered a challenge due to anatomical limitations and the desire of the patient for a non-invasive treatment. Nevertheless, a customized treatment plan was prepared to meet our patient’s expectations.

The treatment workflow included:

1. Conventional open-flap surgical procedure to enable a complete view of the available anatomy.
2. Insertion of four Straumann® Mini Implants with Optiloc® in the following regions: #34 (10 mm), #32 (12 mm), #42 (12 mm), and #44 (10 mm). 
3. Given the morphology of the anterior cortex and the risk of high post-insertion fracture, an immediate loading approach was avoided by opting for a 6-week healing phase before loading the implants with the prostheses.

Surgical procedure

One hour before surgery, the patient was given amoxicillin 2000 mg for antibiotic prophylaxis. The surgery was performed under local anesthesia (Ubistesin forte: articaine 4% and epinephrine 1:100,000, 3M ESPE). A full-thickness mucoperiosteal flap was raised, beginning with a supracrestal and midline releasing incision with a size 15 scalpel blade along the mandibular ridge. This strategy of bone exposure was chosen due to the limited quantity of bone available and for better visibility for the implant bed preparation to ensure a safe distance from the mental nerve (Fig. 6).

To prepare the alveolar ridge, bone pliers were used to remove the serrated sections of the cortex, and a milling cutter was used to smooth the bone surface while preserving as much of the cortical lamina as possible (Figs. 7,8).

The Straumann® Modular Cassette was used to prepare the implant bed following the pilot drilling protocol. First, a 1.6 mm needle drill was used, followed by the 2.2 mm BLT Pilot Drill with a maximum speed of 800 rpm. The drilling speed was determined by the density of the bone. Then the paralleling posts were placed to evaluate the implant's proper three-dimensional position. The parallel posts were left as a reference for the next implant bed preparation in order to align them with the other implants and to respect the minimum distance between them of 5 mm (Figs. 9,10).

Straumann® Mini Implants were delivered in a sterile vial and mounted on the vial cap, which acted as the initial insertion instrument (Fig. 11). The vial cap served as a finger driver, and the ratchet was used to rotate the implant clockwise into its final position. Four Straumann® Mini Implants with Optiloc® were inserted with a torque of 35 Ncm in regions #34 (10 mm), #32 (12 mm), #42 (12 mm), and #44 (10 mm).

The operative wound was closed with individual cross-stitched sutures (Fig. 12). The postoperative X-ray showed four parallel implants adequately distributed and at a safe distance from the mental nerve. (Fig. 13).

The prosthesis was delivered the same day to the patient, modifying the existing well-fitting denture, and creating space in the location of the corresponding Optiloc® abutments.

Prosthetic procedure

The patient returned six weeks after the surgery. The healing was uneventful, and an impression was taken (Fig. 14). First, the impression caps were positioned on the Mini Implants, and the existing prosthesis was used as a tray to take the mucodynamic impression in centric occlusion with vinyl polysiloxane material (Fig. 15). The impression was then sent to the laboratory, where the Optiloc® Model Analogs were inserted into the Optiloc® Impression Coping and the master cast was made in type IV dental stone (Fig. 16). The Straumann® Optiloc® Retentive System for removable overdentures has a carbon-based prosthetic connection coating (ADLC1) with outstanding wear resistance capable of resisting implant convergences or divergences up to 40°. This system enables a less invasive treatment strategy that results in faster healing and reduced post-operative discomfort.

The matrix housing and a retention insert were placed onto the Optiloc®. Next, white collars were put on each Optiloc® Model Analog. The overdenture was processed in the lab according to the standard procedures and returned to the clinic. Chairside, the appropriate Optiloc® Retention Insert was selected and placed. The Optiloc® Retention Inserts were then exchanged for the Matrix Housing, and the overdenture was delivered.

After one year, the patient reported no complications, presented healthy soft tissues, and the overdenture was in good condition (Figs. 17,18).

The radiographic follow-up showed stable implants (Fig. 19).

On clinical evaluation at the 3.5-year follow-up, the implants were osseointegrated, with good functional conditions and no clinical evidence of biological complications (Figs. 20-22).

No abnormal evidence of remodeling around implants was identified on the control radiograph (Fig. 23).

Treatment outcomes

The patient was pleased with the outcome, which exceeded her expectations. She had gained more confidence with the use of her stable overdenture. Her quality of life improved while keeping her upper removable prosthesis.

With the Mini Implant System we have been able to avoid a bone augmentation in a patient with reduced horizontal and vertical bone availability. The small diameter of the implants provides a new possibility for implant placement while obtaining good osseointegration and stability.

Author’s testimonial

Our patient had severe bone loss in both vertical and horizontal dimensions. By choosing the Straumann® Mini-implant system, we could improve her quality of life, avoiding any complex surgery for augmenting or harvesting the bone. Although this treatment solution has short-term scientific evidence, with the SLActive® surface and the Roxolid® material we can have predictable and stable results over time.