Influence of revascularization process on onlay bone graft remodeling: a histometric, immunohistochemical and tomographic study in rabbits: Part II - Calvaria

Abstract

The knowledge behind integration, survival and volume maintenance of onlay bone grafts are still controversial. Despite some existing consensus that the revascularization process is important to ensure graft survival, there is no scientific evidence about the role and timing of revascularization influencing graft maintenance in the long term. Moreover, the biomolecular aspects that take part in the bone graft remodeling process are not fully understood and the literature available on the relationship between revascularization and the changes of onlay grafts morphology over time is rather fragmented. Actually, this issue has not been approached in a multidisciplinary way and important information like chronology of the revascularization process and molecular events that leads to bone deposition and resorption as well as the effects of a combination of the two on the bone graft long-term survival, have not been yet gathered in a sole study.Recently, our group carried out an experimental investigation aimed at the assessment of iliac crest (i.e. endochondral origin) graft placed onlay on the mandible's body. The methodological tools used for graft evaluations comprised histological, histometric, tomographic and immunohistochemical analysis. The first outcomes of the study showed a negative correlation between timing of graft revascularization and the amount of bone volume and density (ongoing Fapesp 04/01113-4 funding grant). While this latter study is an important contribution towards a better understanding of grafts integration, it is still required a comparison with bone grafts from other sources in order to establish the influence of bone origin and architecture upon graft maintenance. In this respect the calvarial bone - intramembranous origin – has gained enormous scientific interest on the clinical evidence of good amount of bone tissue delivered at the donor site, low local morbidity following bone harvesting and the perception of excellence in terms of graft maintenance. Differently from iliac crest bone the calvaria exhibits two strictly cortical plates (internal and external) separated by a layer of cancellous bone. The hypothesis that bone micro-architecture plays a crucial role in bone volume maintenance has been raised in many studies. Thus, a comparison between grafts of distinct embryologic origins and internal architecture, using identical and multidisciplinary experimental designs is highly recommended to determine the influence of revascularization on grafts volume maintenance.Sixty adult male New Zealand White rabbits weighing between 3.5 and 4.0 Kg will be used in this study. All animals will be submitted to unilateral surgery in the mandible’s body. One bony block taken from the parietal skull bone will be onlay transplanted onto the mandible. The receptor bed in thirty animals will be perforated in a standardized way before graft fixation, whereas in the remaining the receptor bed will be kept intact. Six rabbits in each group will be sacrificed at 5, 7, 10, 20 e 60 days following surgery, respectively. Samples of the experimental sites will be processed for: 1) histological analysis; 2) immunohistochemistry (VEGF, PECAM, Osteocalcin, Osteopontin and Type I Colagen anti bodies) in order to recognise the biomolecular events (i.e. angiogenesis and osteogenesis) occurring in both the graft itself and the graft-bed interface; 3) tomography for graft volume and density detection, taken at the moment of grafting and animals sacrifice. (AU)