Spontaneous early exposure and marginal bone loss around conventionally and early-placed submerged implants: A double-blind study

Purpose: The aim of this retrospective study was to compare the frequency of spontaneous early exposure of cover screws and marginal bone resorption in conventionally and early-placed submerged implants before second-stage surgery.Materials and methods: A total of 103 Nobel Biocare Branemark implants were conventionally (Group 1), or early-placed (Group 2) in 46 consecutive patients following the two-stage surgical protocol. Patients in both groups received oral hygiene training in self-performed plaque control measures, including exposure of cover screws during healing. Spontaneous cover screw exposure (CSE) of each implant was recorded for both groups and scored from Class 0 (no perforation) to Class 4 (complete exposure). Plaque index scores were recorded and marginal bone-level (MBL) changes were measured in radiographs before second-stage surgery in a blind manner.Results: MBL in Group 2 was higher than Group 1 in patients with or without interim prosthesis (P<0.05). The use of interim prosthesis did not increase MBL in Group 1, but led to higher MBL in Group 2. The percentage of non-exposed implants in Group 1 was higher than Group 2 (P=0.007, odds ratio=7). Group 1 implants had 11.5 times greater plaque index score 0 than those in Group 2 (P=0.031, odds ratio=11.5). The differences between MBL with regard to CSE scores 0 and 1-4 was significant for both sides in Group 2 and the mesial side in Group 1 (P<0.05). The difference between MBL with regard to plaque index scores 1-3 was similar in both groups (P>0.05).Conclusions: There is a direct relation between spontaneous early cover screw perforations with early crestal bone loss. Early-placed implants experienced more spontaneous perforations and associated bone loss in comparison with conventionally placed submerged implants. The use of interim dentures may lead to more CSE and consequent MBL in the early-placement protocol.