Surgery

Implants (SLA® (sandblasted and acid-etched, internal connection system), Straumann AG, Basel, Switzerland, or Branemark® System Mk-III (TiUnite, external connection system), Nobel Biocare, Gothenburg, Sweden) were used depending on the patient’s clinical characteristics. The operating surgeon was blinded to the bone analysis results and was unaware of the bone density measurements at the implant sites. Seventeen SLA® implants were placed in nine patients and eighteen Branemark® System Mk-III implants in nine patients. The prosthetic rehabilitation phase was started after a healing period of 2–4 weeks. Implant surgery and prosthetic rehabilitation were performed by experienced prosthodontists.

Measurement of marginal bone loss

During the follow-up observation period, at least the final restoration was repaired and the marginal bone loss (MBL) was measured on dental radiography using Image J software (National Institutes of Health, Bethesda, MD, USA). The reference points for the measurements included the implant platform (the horizontal interface between the implant and the abutment), the implant tip, and the first bone-implant contact (FBIC). The length from the implant platform to the FBIC was defined as the marginal bone level. The marginal bone level was measured in mm using the ratio of the real implant length and the length from the implant platform to the tip on the images.

MBL values were measured as the difference in the marginal bone level at the follow-up period and at the baseline. The mean MBL value of mesial and distal sides was used for the study. This method is diagrammatically represented in Fig. 2.

Statistical analysis

Mann–Whitney test was used to determine the differences in the bone density values [HU] between the normal and abnormal group. A value of P < 0.05 was considered significant, and the effect size r was subsequently shown.