4.1 Effect of threshold selection on reported prevalence of peri‐implantitis

The choice of appropriate threshold in assessing prevalence of peri‐implantitis is challenging, as evidenced by the range of reported estimates for peri‐implantitis from 1% to 47%, with a 2012 EAO consensus reporting prevalence to be on the order of 10% of implants and 20% of patients. Prevalence is typically determined by cross‐tabulating bleeding‐on‐probing scores (BOP) with MBL, thus it is important to consider how each is determined.

BOP scores are typically recorded as either bleeding is present or absent and are used as an indicator for mucositis. Most studies, according to the EAO consensus of 2012, used this simple binary BOP score plus suppuration, while others used a binary BOP with no reference to suppuration while only one study used the ordinal sulcus bleeding index (SBI). Dental implants, however, tend to bleed upon probing more frequently and at lower thresholds of probing force than teeth. Indeed in this current cohort, BOP was never below 35% at the implant level and it was ≥ 45% at the patient level over all time points. Therefore an ordinal scale may offer more specific information about the peri‐implant soft tissue and in this study a modification of the Sulcus Bleeding Index (SBI) which included suppuration, termed the Implant Mucosal Index (IMI), was used. The IMI has previously been shown to be a useful method to assess inflammation and, further, to relate each increase in IMI score with a doubling of MBL.