Estudio comparativo de dos hidroxiapatitos biológicos utilizados en procesos de elevación de senos maxilares

Resumen

Several factors will influence the results of grafting the floor of the maxillary sinus, especially surgical techniques and selection of graft material. Although the surgical techniques of sinus lift are well described, researchers have not come to an agreement about which material is the most suitable to sinus augmentation. Hydroxyapatite is the major inorganic component of natural bone and has been applied widely in medical field as bone repair material because of its excellent bioactive and biocompatibility properties. Biomaterials that mimic the structure and composition of bone tissues are important for the development of bone tissue engineering applications. Synthetic hidroxyapatites are the most frequently used but they do not completely match the chemical composition of human bone. Fortunately bones from other species possess a tissue structure similar to that of human bones. During the last decade there has now been a move back to natural hydroxiapatites and has been used as reference material in this PhD thesis. Deproteinization is an indispensable process for the elimination of antigenicity in xenograft bones. The sintering temperature is seen as important factors that could alter the HA ́s characteristics. The most important parameters that can affect the properties of HA are the temperature of heat treatment. All aspects of a substitute material must be studied. Part of biological response produced by a biomaterial, is conditioned by their physical and chemical properties. The work reported in this PhD thesis indicates the great importance of full characterization of the materials being used. The large number of alternatives available in contrast with the few comparative studies leaves the choice of the grafting material to the surgeon ́s preferences, no always scientifically based. Based on these data, the present PhD thesis developed a protocol for characterization the xenograft. The objetive of this study was to characterize the physicochemical properties of two xenografts deproteinized at different temperature and how the physicochemical properties influence the material performance in vivo. Two commercial bone grafts used in dentistry in the form of granules a non-sintered PBM, OsteoBiol ® mp3 a natural hydroxyapatite of porcine origin, deproteinized at low temperature (130°C) and a sintered BBM, Endobon® a natural hydroxyapatite of bovine origin, deproteinized at high temperature (1200°C) were characterized before being used in sinus lift procedures. Both materials were characterized in terms of crystallinity, morphology, particle size distribution, porosity and pore size, specific surface area, density, and ratio calcium/phosphate in the composition. The hidroxiapatites were characterized thorough powder X-ray diffraction XDR analyses, Fourier transforms infrared spectroscopy FTIR, gas pycnometry, mercury intrusion and scanning electron microscopy SEM. Quantitative analyses were made by an Electronic Dispersive X-ray Spectroscopy (EDX) system. Ten patients were selected who required bilateral sinus augmentation. The study was performed in two surgical phases. In the first phase, the basic surgical procedure was represented in all patients by maxillary sinus floor elevation via a lateral approach, one material was placed in the right sinus and the other in the left sinus, as determined by randomized choice in a split mouth design. The patients were followed up clinical and radiologicaly. All patients underwent CBCT after 6 month of surgery as a routine diagnostic approach. The images obtained were processed by Image J software and color thermal graduation was used to observe the changes in radiopacity in the grafted area. In the second surgical phase the functional implants were placed on each side. Each side received three implants 3i T3® Implante Certain® Tapered placed 6 months after augmentation. A trephine bone core was harvested from the previously elevated maxillary sinus at the moment of implant insertion, 60 bone samples were retrieved and sent for histomorphometric analysis. The specimens were processed for observation under a scanning electron microscope with backscattered electron imaging (SEM-BSE). Histomorphometric analysis was performed on the bone core samples to determine the vital bone, connective tissue, and residual graft material content. In addition the chemistry of the interphases and the chemical degradation process of the xenograft biomaterials were analyzed using X-ray elemental maps in scanning mode. Additional information was obtained from line scans and elemental maps. Analysis was carried out at a selection of different points, taking different points of interest from the middle and from the periphery of the samples to detect changes in Ca/P ratios. Data were then collected from deliberately targeted sites of interest within the residual biomaterial (RB), close to and distal from new bone (NB) and at the bone–implant interface if present. A total of more than 900-point analyses were carried out on the sixty biopsies. After dental implant insertion, the resonance frequency evaluation was performed using the OstellTM Mentor for measure the primary stability of the implant. The RF value is represented by a quantitative parameter called ISQ. The ISQ values were measured during the surgical procedure (T1- baseline), at 3 months (T2) after surgery and at 6 months (T3) after surgery. The values were recorded for the bucco-lingual (B-L) direction and mesio-distal (M-D) direction. The results of Characterization of Deproteinized Hydroxyapatite Materials show that X- ray diffraction analysis revealed typical structure of hydroxylapatite for both materials. Both xenograft are porous and exhibit intraparticle pores. Strong differences were observed in term of porosity, cristallinity, density, surface area, and ratio calcium/phosphate composition. PBM has the greatest porosity (59.90%); however, about forty per cent (38.11%) of this porosity corresponds to submicron pore entrances. BBM porosity was (49,13%) but this exhibit a much smaller proportion of submicron pores, only (3.66%). In term of crystallinity the PBM granules exhibit low crystallinity, crystal size is 325 nm, while BBM structure consisted of a highly crystallinity and the crystal size is 732 nm. Higher density was measured for BBM (2.98 g/cm3) respect (2.85 g/cm3) for the PBM. More surface área were observed for the PBM (97.84) (m2/g) compare to the BBM (2.77 m2/g). Statistically significant difference was found between PBM (2.22± 0.08) and BBM (2.31±0.09) ratio calcium/phosphate composition. Although radiopacity of the augmented volume increased with time for both xenograft materials, the control sites receiving showed a higher density of radiopacity compared with the PBM. Scanning electron microscopy revealed that newly formed bone had become closely attached to both HAs. Histomorphometric measurements on the bone biopsies showed statistically significant differences. For the PBM, the newly formed bone represented (25.92 ± 1.61%), residual graft material (24.64 ± 0.86%) and connective tissue (49.42 ± 1.62%), while for the BBM newly formed bone (26.83 ± 1.42%), residual graft material (30.80 ± 0.88%) and non-mineralized connective tissue (42.79 ± 2.88%). In all cases, EDX analysis found a significant a decrease in the percentage of Ca/P ratio was found in the residual biomaterial, with respect to the initial composition while a gradual increase in the percentages of Ca/P ratio was found at the interface, suggesting an increase in the osteoinductive capacity of the materials and replacement by new bone at its periphery. The PBM showed numerous regions of resorptions, and presented an average Ca/P rate of 1.08±0.32 with respect to the average Ca/P rate 1.85±0.34 of BBM. Statistically significant differences were found too in the interface and in the new bone between the groups. Ca/P ratio in the interface was 1.93 ± 0.18 for the PBMwith respect the 2.14 ± 0.08 of the BBM, and the ratio in the new bone was 1.84 ± 0.14 for the PBM with respect the 2.00 ± 0.08 of the BBM. Line Scan show an increase in the porosity inside the material and a faster degradation of PBM in relation with BBM can be observed, fact that it is related with the crystallinity of the material. BSE image showing the resorbed PBM graft in relation to surrounding bone, granular residual material consisting of areas of very few and smaller particles. These indicated the almost complete resorption of the PBM similarly in the middle, and at the periphery of the samples. According to the elemental X-ray maps and SEM images of the interface between the BBM and PBM implants and the natural bone, the reaction zone was composed of Ca and P phase as well as a short distance away from the reaction zone. There were no obvious morphological differences between the newly formed bone and the old bone into which the implants were inserted. ISQ (Baseline) averaged values were 63.8±2.97 for a sintered BBM, and 62.6±2.11 for a non-sintered PBM. ISQ (Stage 2) average values were 73.5±4.21 for BBM and 67±4.99 for PBM. ISQ (Stage 3) average values were 74.65±2.93 for BBM and, 72.9±2.63 for PBM; differences were statistically significant in all of stages studied. As a general conclusion of the work done in this Doctoral Thesis we can say that the data from this study show the effect of sintering temperature on the physico-chemical properties of Natural HAs and the influence in the biological behavior. The differences found in the physic-chemical characteristics of both xenografts justify this distinct in vivo performance. The HAs assessed in the study were shown to be biocompatible and osteoconductive when used for maxillary sinus elevation. A significant difference in resorption time and in the stability of the implants was found in both groups. The PBM non-sintered hydroxiapatite with high porosity, low cristallinity, low density, high surface area and low calcium/phosphate ratio presents high resorption rate but might not withstand the sinus pressure leading to a repneumatization of the sinus. Whereas the BBM sintered hydroxiapaite with low porosity, high cristallinity, high density, low surface area and high calcium/phosphate ratio presents a slow resorption rate that inhibit the resorption of the newly formed bone, tents the sinus lining, maintains the space, and stablies augmented the maxillary sinus floor increased the early implant stability. Detailed information about graft material characteristics is crucial to evaluate their clinical outcomes. The influence of physic-chemical properties of the bone graft materials on osseointegration has translated to shorter healing times from implant placement to restoration. A sound understanding of various aspects of biomaterial properties and their relation and influence towards bone healing is of utmost importance.