The first results of this longitudinal study include data from 9 patients with an average age of 57 years (range from 44 to 80) in whom 30 implants were inserted (maxilla n = 15, mandible n = 15). All 30 implants in the 9 patients could be inserted without intraoperative problems. Based on intraoperative and radiological findings, the bone quality was assessed as follows: D1 in n = 2, D2 in n = 3, D3 in n = 2 and D4 in n = 2 cases. The employed implant dimensions were as follows: 4.1 × 5 mm (n = 2), 4.1 × 6 mm (n = 1), 4.1 × 7 mm (n = 10) and 3.75 × 7 mm (n = 17). The expansion process could successfully be performed in every case. The healing period was uneventful. Patients were rehabilitated with fixed dentures in 5 cases and with removable dentures in 4 cases. Basic clinical characteristics are summarised in detail in Table 4.

Over the 3-year follow-up period, the overall cumulative implant success rate in these patients was 28/30 (93.3%). Two implants were lost in the posterior maxilla. The two affected patients had highly atrophic posterior maxillae (Cawood et Howell IV–V) and a bone quality of D3–D4 (Table 4). The male patient was a smoker and suffered from a squamous cell carcinoma of mouth floor. In both cases, the manufactured removable denture was successfully relined and no technical complications were observed to date.

The Kaplan-Meyer analysis of implant survival for both jaws is visualised in Fig. 2 (log rank test, p = 0.173): 1-year survival 96.7% and 2-year survival 93.3%. The 3-year follow-up has not yet been completed by all patients (Table 4).

Measurements of implant stability by resonance frequency analysis (RFA) displayed the following ISQ values: primary stability 69.7 ± 10.3 95% CI (65.9; 73.6) ISQ units and secondary stability 69.8 ± 10.2 95% CI (65.8; 73.5) ISQ units (Fig. 3a-b). The differences were not statistically significant (p = 0.780; paired t test). In detail, the ISQ values for primary stability displayed in the maxilla 66.9 ± 8.9 95% CI (61.9; 71.8), and in the mandible 72.5 ± 11.1 95% CI (66.4; 78.7). The differences were not statistically significant (p = 0.134; independent t test). According to the measurement of secondary implant stability, we observed comparable ISQ values in the maxilla 66.4 ± 10.0 95% CI (60.9; 71.9) and higher ISQ values in the mandible 73.0 ± 9.7 95% CI (67.6; 78.4). The differences were as well not statistically significant (p = 0.780; independent t test).

Over the follow-up period, the mean crestal bone changes after loading were as follows (each compared to the baseline): in the first year, 1.0 ± 0.9 mm 95% CI (0.5; 1.5) in the maxilla and 0.7 ± 0.4 mm 95% CI (0.5; 1.0) in the mandible (p = 0.011; independent t test), and in the second year, 1.3 ± 0.8 mm 95% CI (0.8; 1.7) in the maxilla and 1.0 ± 0.7 mm 95% CI (0.6; 1.4) in the mandible (p = 0.644; independent t test). Clinical and radiological investigations did not reveal any inflammatory signs or radiolucency in the periapical region for all inserted implants.

A representative case of a rehabilitated female patient is visualised in Fig. 4a-h and Fig 5a-d (radiograms).