Reducing crestal bone loss (CBL) around implants allows for soft tissue stability and long-term

success. The aim of the present study was to evaluate the extent of CBL in implants placed with

the implant shoulder at the equi-crestal level and 2 mm below the alveolar ridge at 2, 12, 36, and

60 months. A split-mouth randomized controlled clinical trial was conducted by selecting

subjects with Kennedy Class IV partial edentulism of the lower jaw. Two implants were inserted,

of equal length and diameter, one equi-crestal and the other sub-crestal, in the site corresponding

to the lateral incisor. Intraoral periapical radiographs with Rinn centering devices were

performed at the time of implant insertion (T0), at 2 (T1), 12 (T2), 36 (T3), and 60 months (T4).

Descriptive statistics and the T-test were used, setting the significance to P⩽ 0.05. Twenty-five

subjects were recruited, with a mean age of 65 years (SD 9.88, range 42-82). No subject dropped

out. A total of 50 implants were inserted, 25 at crestal and 25 sub-crest level. At the 60-month

follow-up, no implant or prosthetic failure was recorded. An average loss of -0.81 mm was

recorded in the crestal implant group (n.25; SD: 0.40; max-min: -1.6 – -0.1) while in the implants

positioned below the crest the average CBL was -0.87mm (n.25; SD: 0.41; max-min: -2 – -0.2);

however, the higher CBL in the sub-crestal implant group was not statistically significant

(P=0.65). Comparing the mean CBL values of the two groups at the various follow-ups, a greater

crestal bone resorption was recorded in sub-crest implants between T0 and T1 (-0.25 vs -0.1) and

between T1 and T2 (-0.39 vs -0.23), while in subsequent follow-ups a greater, statistically

significant (P=0.01), crestal bone loss was recorded in ridge implants between T3 and T4 (-0.05

vs -0.18). Over time, therefore, the extent of CBL seems to be reduced in implants placed below

the crest, with bone retention above the implant shoulder. Ultimately, although the position of

the implant shoulder relative to the crestal ridge doesn’t affect the CBL, sub-crestal placement is

recommended in order to reduce the risk of exposure of the rough surface of the implant.