Purpose: Poor alveolar bone quality and quantity may cause low insertion torque during implant placement; therefore, a delicate occlusal design is important for the immediate loading procedure. This retrospective clinical study aimed to investigate (1) the proportion of implants with a low insertion torque between the maxilla and mandible, (2) factors affecting implants with a low insertion torque, and (3) survival rates of implants with a low insertion torque value (< 35 Ncm) using different occlusal designs with full-arch fixed prostheses supported by immediately loaded implants.
Materials and methods: Between 2013 and 2017, patients who received full-arch reconstructions were treated with immediately loaded one-piece fixed prostheses supported by four to six implants. Full-arch fixed prostheses with at least one immediately loaded regular implant with a low insertion torque value were included in this study. The fixed provisional acrylic prosthesis with a rigid framework was delivered within 3 to 5 days after surgery. According to the distribution of implants with low insertion torque, provisional prostheses were divided into three groups with different occlusal schemes. Definitive prostheses were fabricated after 3 months of loading.
Results: A total of 144 patients were treated; 608 and 304 regular implants were inserted in 118 maxillae and 76 mandibles, respectively. Moreover, 42 patients (11 men and 31 women) with 39 maxillae and 4 mandibles were included in this study. The proportion of implants with low insertion torque values in the maxilla was significantly greater than that in the mandible (10.5% vs 1.6%, respectively, P < .001). Implant length and low insertion torque value had no significant correlation (P = .948). Implants with a 3.3-mm diameter (narrow platform) had a greater proportion of low insertion torque values than 4-mm-wide implants (P = .002). Implants placed in a fresh socket had a greater proportion of insertion torque values ≥ 35 Ncm (P = .023). The overall cumulative implant survival rate was 98.6%. Groups 1, 2, and 3 had 14, 23, and 6 provisional prostheses, respectively. The survival rates for implants with insertion torque values < 35 Ncm and ≥ 35 Ncm were 98.4% and 98.7%, respectively, and were not significantly different (P = .866). All prostheses were still functioning during the mean follow-up of 3.7 ± 1.2 years.
Conclusion: The high cumulative implant survival rate indicated that implants with a low insertion torque in immediately loaded full-arch provisional prostheses did not jeopardize the outcomes after a corresponding occlusal scheme was used.