Retrospective Cohort Study of 4,591 Straumann Implants Placed in 2,060 Patients in Private Practice with up to 10-Year Follow-up: The Relationship Between Crestal Bone Level and Soft Tissue Condition.

PURPOSE: The purpose of this report is to describe the crestal bone level (CBL) around implants of various designs, describe the peri-implant soft tissue condition, and evaluate the relationship between the two over time. MATERIALS AND METHODS: This retrospective cohort study reports on 2,060 patients with 4,591 implants evaluated after 3 months; 1, 3, 5, and 7 years; and up to 10 years. Periapical radiographs were used to evaluate changes in CBL. The peri-implant soft tissue was evaluated using a modified Bleeding Index termed the Implant Mucosal Index (IMI) where: 0 = no bleeding; 1 = minimal, single-point bleeding; 2 = moderate, multipoint bleeding; 3 = profuse, multipoint bleeding; and 4 = suppuration. RESULTS: At 3 months, the mean CBL was 0.06 +/- 0.22 mm; by 8 to 10 years, it had increased to 0.44 +/- 0.81 mm. The median CBL remained stable throughout the study at < 0.1 mm. At 8 to 10 years, 15% of implants exhibited a CBL > 1.02 mm, and 5% exhibited a CBL > 2.28 mm. More than 50% of patients experienced some bleeding, as seen by an IMI >/= 1 during follow-up. A positive correlation was found between IMI and CBL, as shown by a mean CBL after 4 years of 0.33 mm, 0.71 mm, and 1.52 mm for IMI = 2, 3, and 4, respectively. One exception was between IMI = 0 and IMI = 1, where no significant difference was found and bone loss was minimal. CONCLUSION: Bone loss, as measured by changes in CBL during the first 10 years of implant life spans, was minimal for most implants. Nevertheless, it is not unusual to observe implants with advanced bone loss. The soft tissue condition is a good indicator of bone loss. Time alone and minimal bleeding did not correlate with bone loss, but care should be taken for implants with profuse bleeding or suppuration.