On marginal bone resorption around oral implants

Abstract

The etiology of marginal bone loss (MBL) around osseointegrated implants remains controversial. Despite extensive research, the initiating causes of MBL are unclear. Long-term clinical studies challenge the notion that peri-implantitis, an infectious condition resulting in accelerating MBL over time, is the primary driver, as most implant failures occur early and decline over time. This thesis investigates alternative etiological factors for MBL, focusing on immune-mediated and iatrogenic causes. Study I systematically reviewed animal models for peri-implantitis, resulting in a qualitative synthesis of 133 studies and a meta-analysis of 35 studies. Plaque accumulation alone did not induce relevant MBL after up to 1.5 years. When artificial ligatures were added, as in 119 studies, MBL varied significantly depending on ligature materials and ligature application methods. The possibility that the ligature itself, due to its provocation of the immune system, could induce MBL, although refuted by some authors, was not tested in any of the reviewed ligature studies. Studies II and III examined possible immune-mediated MBL from aseptic ligatures in rabbit femurs and tibia using histology and qPCR, comparing silk and cotton ligatures to controls over 8 weeks (silk and cotton) and 12 weeks (silk). The studies confirmed significant MBL from ligatures at 8 weeks (p=0.007), with partial recovery at 12 weeks. At both time points, inflammatory infiltrates dominated by macrophages and foreign body giant cells surrounded all ligatures and were separated from resorbed bone surfaces by fibrous enclosure. M2 macrophages balanced inflammatory responses. Study IV compared chair-side cement-fitted (CR) and screw-fitted (SR) implant restorations over 1 year in 24 patients in a cross-over RCT design divided into three periods (P) of 16 + 16 + 20 weeks. Patients were randomly assigned to SR (group 1) or CR (group 2) at baseline. Restoration type was then swapped during P2, and during P3, both groups had SR. Radiographic MBL and clinical peri-implant indices were measured at baseline, 16, 32, and 52 weeks. The immunological response was assessed by qPCR on peri-implant soft tissue biopsies at 32 weeks. MBL was observed during periods with CR in both groups, and bone gain was observed during periods with SR. Differences in MBL were significant between groups during P1 (p = 0.006) and P2 (p < 0.001) and within group 2 during P1 (p = 0.002). Further, a 7-fold upregulation of IL-6 was found from CR after P2. Excess cement was found in 75% of all CR cases upon removal. In summary, this thesis demonstrates that immune-material interactions beyond the presence or absence of infection regulate MBL. Further, MBL recovery may occur after removing iatrogenic factors such as excess cement.