Less Invasive Surgical Procedures Using Narrow-Diameter Implants: A Prospective Study in 20 Consecutive Patients
Narrow-diameter implants (NDIs) are increasingly produced and used in implant dentistry, especially since the introduction of new, more resistant materials. The objective of the present study was to evaluate the clinical performance of NDIs (3.3 mm) placed in thin alveolar crests. Twenty consecutive patients needing implant-supported fixed partial dentures and presenting an alveolar thickness ≤6 mm were treated with 1 or several NDIs. The surgical protocol was chosen according to the clinical situation: (1) flapless, (2) mini-cervical flap, (3) wide flap, (4) wide flap + guided bone regeneration (GBR). Implants were immediately loaded if the primary stability was higher than 20 Ncm. Implant survival and success, prosthodontic success rates, and patient-centered outcomes were evaluated after a follow-up period of 1 year. A total of 39 implants were placed in 20 patients, 12 and 27 implants in the anterior regions and in the posterior mandible, respectively. All but 1 implant reached an insertion torque higher than 20 Ncm and were loaded within 48 hours. The implant survival and success rates both reached 94.7%. The need for GBR was avoided in 60% of the implant sites. The mean peri-implant bone remodeling after a follow-up period of 1 year was −0.35 mm at the implant level. Peri-implant bone remodeling was higher in the posterior region, when the alveolar crest was thinner than 4 mm and GBR was required in addition. In conclusion, use of NDIs to restore partial edentation in sites with limited horizontal thickness seems to be an effective treatment option that prevented GBR in the majority of the present cases. Immediate provisionalization of NDIs does not seem to impair the results.
Figure 1. (a) Preoperative computerized tomography (CT) scan. This patient presented a bilateral knife-edge bone resorption in the posterior mandible. (b) Postoperative CT scan. After bone regeneration, the CT scan shows that the available bone quantity could be noticeably augmented but was still limiting for implant placement. (c) Horizontal thickness was measured (5 mm) on the CT scan (orange arrow), perpendicular to the planned implant axis (blue arrow), and 2 mm below the cervical edge of the alveolar crest. Figure 2. Description of the different flap design and surgical techniques. (a) Flapless. (b) Mini split-thickness flap. (c) Full thickness flap. (d) Full thickness flap + guided bone regeneration. Figure 3. The surgical procedure of the same case whose CT scans were shown in Figure 1. Five NDIs were placed using a minimal flap in split thickness to avoid exposure of the regenerated bone.
Figure 4. Description of the loading protocol. (a) Immediately after the surgery, an impression of the implant positions was taken. (b) The provisional resin bridges were produced in the laboratory on the selected final titanium abutments. Figure 5. (a) Height and transgingival height of the titanium abutment were selected in the lab once the working models were inserted in the articulator and according to the clinical situation. (b) Replicas of the final abutments were performed as well as the corresponding resin copings (blue cap). The copings were used directly on the titanium abutment for the final impression to allow a seamless procedure. The replicas of the final abutments were used on the master model for the realization of the final prostheses.
Figure 6. (a) Within 48 hours after surgery, the selected and adjusted final titanium abutments were placed and torqued by hand. (b) The provisional bridges, realized in the lab, were cemented using temporary cement. Care was taken to avoid cement spreading under the flap. The occlusion was fine-tuned to reduce occlusal contacts as much as possible. Figure 7. The final prosthesis, consisting of ceramic-fused-to-metal frameworks, were placed after 6 months. (a) Intra-oral radiographs after the 1-year follow-up period. Note the stable bone level, despite the very demanding initial clinical situation. (b) Clinical pictures of the final bridges after 1 year. Note the gingival health.
Figure 8. Factors influencing peri-implant bone remodeling: (a) Posterior (molars/premolars) vs anterior (canines, incisors) teeth: Higher mean bone loss was found in implants placed in the posterior mandible (0.46 mm ± 0.44 mm vs 0.14 mm ± 0.17 mm, P = .026). The standard deviation was high, pointing toward substantial bone loss occurring in a limited number of implants. (b) When the initial bone thickness was ≤4 mm, the results showed a tendency for increased bone remodeling (P = .08). (c) Significantly higher bone remodeling was associated with full thickness flaps and GBR compared to the other surgical approaches (P = .015). The residual bone thickness and the need for GBR correlated. Implant sites displaying substantial bone loss often combined the 3 risk factors: Implants placed in the posterior mandible in sites with a residual bone thickness <4 mm and the need for simultaneous GBR. Figure 9. Evaluation of the patient-centered outcomes before treatment (baseline), 1 month after the provisional restoration (provisional delivery), and after 1 year (final delivery) for the 4 assessed parameters: (a) Phonation. (b) Eating function. (c) Esthetics. (d) Confidence. All outcomes significantly improved after placement of the provisional prostheses.
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