The accuracy of different dental impression techniques for implant-supported dental prostheses: A systematic review and meta-analysis

Aim: This systematic review and meta-analysis were conducted to assess and compare the accuracy of conventional and digital implant impressions. The review was registered on the PROSPERO register (registration number: CRD42016050730). Material and Methods: A systematic literature search was conducted adhering to PRISMA guidelines to identify studies on implant impressions published between 2012 and 2017. Experimental and clinical studies at all levels of evidence published in peer-reviewed journals were included, excluding expert opinions. Data extraction was performed along defined parameters for studied specimens, digital and conventional impression specifications and outcome assessment. Results: Seventy-nine studies were included for the systematic review, thereof 77 experimental studies, one RCT and one retrospective study. The study setting was in vitro for most of the included studies (75 studies) and in vivo for four studies. Accuracy of conventional impressions was examined in 59 studies, whereas digital impressions were examined in 11 studies. Nine studies compared the accuracy of conventional and digital implant impressions. Reported measurements for the accuracy include the following: (a) linear and angular deviations between reference models and test models fabricated with each impression technique; (b) three-dimensional deviations between impression posts and scan bodies respectively; and (c) fit of implant-supported frameworks, assessed by measuring marginal discrepancy along implant abutments.) Meta-analysis was performed of 62 studies. The results of conventional and digital implant impressions exhibited high values for heterogeneity. Conclusions: The available data for accuracy of digital and conventional implant impressions have a low evidence level and do not include sufficient data on in vivo application to derive clinical recommendations

Molecular and cellularf unctions of CTLA-4

Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) is an inhibitory receptor belonging to the CD28 immunoglobulin subfamily, expressed primarily by T-cells. Its ligands, CD80 and CD86, are typically found on the surface of antigen-presenting cells and can either bind CD28 or CTLA-4, resulting in a costimulatory or a co-inhibitory response, respectively. Because of its dampening effect, CTLA-4 is a crucial regulator of T-cell homeostasis and self-tolerance. The mechanisms by which CTLA-4 exerts its inhibitory function can be categorized as either cell-intrinsic (affects the CTLA-4 expressing T-cell) or cell-extrinsic (affects secondary cells). Research from the last decade has shown that CTLA-4 mainly acts in a cell-extrinsic manner via its competitionwith CD28, CTLA-4-mediated trans-endocytosis of CD80 and CD86, and its direct tolerogenic effects on the interacting cell. Nonetheless, intrinsic CTLA-4 signaling has been implicated in T-cell motility and the regulation of CTLA-4 its subcellular localization amongst others. CTLA-4 is well recognized as a key immune checkpoint and has gained significant momentum as a therapeutic target in the field of autoimmunity and cancer. In this chapter, we describe the role of costimulation in immune response induction as well as the main mechanisms by which CTLA-4 can inhibit this process