Bone ingrowth for Sinus lift augmentation with Micro Macroporous Biphasic Calcium

The development of implantology requires enough bone support, sufficient bone architecture. The use of autograft remains the gold standard; however the surgeons use cortical bone coming from mandibular part or craniofacial site, involving severe anaesthetic bone loss. The strategy of bone substitutes in place of autograft can be an efficient method. Several patients having a sinus lift augmentation using MBCP, and BioOss have been performed in human, and bone biopsies were realized during the preparation of the site for dental implantation. Biopsies were analyzed in classical histology without decalcification and by 3D reconstruction using micro CT. Both techniques revealed bone ingrowth and MBCP resorption. For BioOss, no bone ingrtowth and resorption process were observed in spite of stability of the implant and clinical efficiency. These case reports confirm the performance of bone substitutes for Sinus Lift augmentation. Introduction Among the available materials used for pre-implant bone reconstruction, autologous bone is currently the gold-standard because it is a source of osseous matrix, cells, and growth modulating molecules [1]. However, it requires the graft to be harvested at a distance from the operation site, which makes the initial operation more complicated. To overcome the autograft limits, many substitution biomaterials have been proposed. Materials of human and animal origin have the disadvantages of limited supply and potential risk of cross contamination.[5,6]. Consequently, synthetic products were developed.[4]; generally Biphasic calcium phosphate (BCP), an intimate mixture of hydroxyapatite (HA) and ß-tricalcium phosphate (ß-TCP) [5] or pure B-TCP was proposed in dentistry as reference for synthetic materials. However xenograft as BioOss® derived from bovine bone was largely used in dentistry in spite of animal origin material. BCP offers the potential for bone reconstruction since it has a chemical composition close to biologic bone apatites, and has already proven its efficacy as a bone substitute material in many human clinical applications.[6,13]. The concept of HA and β-TCP mixture (BCP) with varying HA/β-TCP, demonstrated the bioactivity of these bioceramics. Subsequently, focussed studies on BCP led to the significant increase in manufacture and use of BCP as bone substitute materials for dental and orthopaedic applications and for matrices for tissue engineering. However scare human clinical studies for bone reconstruction to support further dental implantation have been published to compare synthetic Bioceramics and bone substitute of animal origin. Materials and Methods The micro macroporous biphasic calcium phosphate (MBCP ®) is an intimate mixture of HA and TCP with a ratio of 60/40. The granules size was 0.5 to 1mm. The total porosity is 70% constituted of 30 % micropores and 70% macropores over 300μm. and BioOss® (no micro and macroporosity) were used in the same Sinus Lift augmentation procedure in humans. Fig.1 : 3mm in diameter bone biopsy before titanium implantation Patients were treated under local anesthesia by para apical and palatin infiltration. Crestal incision, followed by vertical discharge were associated to the displacement of all the total thickness mucosa. The bone window was created by drilling using a diamond bur, then, the Schneider membrane was displaced slightly. Using classical techniques for sinus lift, 1 to 2 cc of 0.5 to 1mm of granules were used. After wetting the granules into sterile water the granules were gently packed under the mucosa taking care of mucosa lesion. Amoxicilline 2g/d were realized during 8 days and Ibuprofène 1200mg/d during 4 days. Before dental implantation, under local anesthesia biopsies were performed using a cylindrical trocard and irrigation, 3mm in diameter (fig.1) (2 for MBCP, and 1 BioOss®), bone biopsies were harvested. The biopsies were fixed in a formalin solution, dehydrated with graded alcohol and embedded in GMMA for histological analyses. Before sectioning process using diamond saw and a hard tissue microtome, the blocks were analysed with microCT (Skyscann 1072). On thicker sections (100μm), SEM observations using backscattering electron (BSE) combined to Image analysis were used for bone ingrowth and bioceramic resorption evaluation. Light microscopy was performed on 7 μm thick section (Movat’s pentachrome staining) and polarized light microscopy on thick section of 100μm without staining. Results and discussion In all patients, radiograph revealed newly formed bone with higher density, indicating after 6 to 8 months residual unresorbed grains of bioceramics (MBCP or β-TCP), while for BioOss®, X-Ray was unable to differentiate the material from the natural bone. During drilling, bone density was high without interference with residual granules (fig.2). Fig.2 : Sinus Lift augmentation using MBCP, 6 months Fig.3 : Micro CT MBCP, Fig.4 : Polarized microscopy MBCP, Dental implants have good mechanical stability according classical test performed after the surgery. Micro CT demonstrates 3D bone ingrowth, and radiodensity changes of the unresorb granules for MBCP (fig. 3). The residual granules look different in density and structure than granules before implantation. This observation confirms the physicochemical modification of the mineral synthetic phases of HA and b-TCP into Biological apatite. Over 30% granules resorption was observed in one patient and over 80% on the second. In SEM and light microscopy, organized and well mineralized bone ingrowth is observed. in some part of the biopsy total resorption of the MBCP® were observed and replaced by bone trabeculae (fig.4). This data confirm the resorbability on time of MBCP® and the scaffold effect of the HA content and high osteoconduction property. These two properties involved a balance resorption and bone ingrowth at the expense of the micro macroporous Bioceramics. This achieved an architectured bone regeneration required for physiological bone reconstruction. For BioOss, no newly formed bone can be observed between the granules (fig. 5). A fibrous tissue as observed between the granules without any osteoid or newly formed bone. No resorption process can be evidenced. (fig. 6).. In human, these results are in contradiction with the biofonctionality of the implanted area in regard to the implant stability. It was necessary to have additional human biopsies, larger representative, to understand why without granules resorption and bone ingrowth at the expense of BioOss®, clinical efficacy was reported by the surgeons during theirs clinical practices.