Forty‐nine patients were randomized to receive 6‐mm implants (test group) and 46 patients to receive 11‐mm implants (control group). The baseline characteristic of the patients is depicted in Table 1. A flow‐diagram from enrollment to 5‐year follow‐up can be found in Figure 3. A total of 209 implants were inserted: 108 implants in the 6‐mm group and 101 implants in the 11‐mm group. During the 5‐year follow‐up, three patients (with 8 implants) were lost to follow‐up in the 6‐mm group (one patient had not enough bone to place implants, one patient lost both implants, and one patient moved without leaving address).

In the 11‐mm group, seven patients (with 14 implants) were lost to follow‐up (one patient died, six patients moved without leaving address). Remaining patients could all be evaluated at the 5‐year evaluation visit. In the 6‐mm group, three subjects lost a total of four implants (three prior to loading and one after 15 months in function). In the 11‐mm group, one implant was lost (after 2 months in function). This led to a 5‐year implant survival rate of 96.0% and 98.9% for the 6‐mm and 11‐mm group respectively, with a p‐value = .376 indicating no difference between the groups.

From loading to the 5‐year follow‐up, a mean marginal bone level change of 0.01 ± 0.45 mm (bone gain) in the 6‐mm group and −0.12 ± 0.93 mm (bone loss) in the 11‐mm group was found (Table 2), without a significant difference between the groups (p = .767). At the 5‐year evaluation, the radiographs of three implants in the 6‐mm group and six implants in the 11‐mm group were not of sufficient diagnostic quality to perform a secure analysis. It was decided not to include these implants in the statistical analysis. p‐values indicated no differences between the groups concerning presence of plaque, bleeding on probing and pocket probing depth (Table 3). However, the 6‐mm group tended to have higher proportion of bleeding than the 11‐mm group.

Prevalence of peri‐implant mucositis at time of the 5‐year follow‐up was 44% of the implants in the 6‐mm group and 33% of the implants in the 11‐mm group (p = .131). Prevalence of peri‐implantitis at time of the 5‐year follow‐up was 6% in the 6‐mm group and 7% in the 11‐mm group (p = 1.000).

The reported technical complications were equally divided between the groups, only loosening of bridge screws occurred twice as often in the 11‐mm group and was also the most common complication both groups (Table 4).