María Piedad Ramírez-Fernández

Histomorphometric and mineral degradation study of Ossceram®: a novel biphasic B-tricalcium phosphate, in critical size defects in rabbits

OBJECTIVE To carry out a histomorphometric analysis of a new highly porous (95%) biphasic calcium phosphate (hydroxyapatite 60%/B-tricalcium phosphate 40%), used to fill critical size defects in rabbit tibiae, supplementing histomorphometric findings with radiographic thermal imaging, EDX analysis and Ca/P ratio mapping at different time stages. MATERIALS AND METHODS Two critical size defects of 6 mm diameter were created in both tibiae of 21 New Zealand rabbits, test group (Ossceram) and control group. Histomorphometric, radiographic thermal imaging, EDX and element mapping analysis were performed at 15, 30 and 60 days after graft insertion. RESULTS Histomorphometric analysis at 30 days showed more new bone formation in defects filled with Ossceram 4.41 ± 0.23 mm than the test group 1.94 ± 0. 28 mm (P<0.05). Element analysis revealed higher percentages of Ca (42.33 ± 2.8%) and P (1.3 ± 0.8%) in the test group than in the control group (P<0.05). Element mapping showed that Ca and P were concentrated in medullar and cortical zones in the test group but were concentrated only in cortical zones in the control group. Test group histomorphometry at 60 days showed complete closure of the cortical defect 5.37 ± 0.32 mm more than the control group 2.3 ± 0.54 mm. There was no cortical defect closure or medullar bone formation in the control group (P<0.05). Element analysis revealed higher percentages of Ca (32.26 ± 21.7%) and P (1.5 ± 0.3%) in the test group than in the control group (P<0.05). CONCLUSION Defects of a critical size in a rabbit tibia model can be sealed using a highly porous biphasic calcium phosphate; this supports new bone formation, creates a bridge between borders and facilitates bone ingrowth. Furthermore, this study observed partial dissolution of the mineral phase of the graft material and its incorporation into the surrounding bone. Radiographic thermal imaging may be used to supplement histological and chemical analyses.

Melatonin stimulates the growth of new bone around implants in the tibia of rabbits

Abstract:  This study evaluated the effect of the topical application of melatonin in accelerating bone formation associated with implants 2 months after their application to the tibiae of rabbits. Twenty New Zealand rabbits were used. Twenty implants treated with melatonin and 20 control implants without melatonin were placed in the proximal metaphyseal area of each tibia. Studies of new bone formation were subsequently made at 15, 30, 45 and 60 days. Cortical width and cortical length of new bone formation were measured. Following implantation, an anteroposterior and lateral radiologic study was carried out. Collected samples were sectioned at 5 μm and stained using hematoxylin–eosin, Masson’s trichromic and Gordon‐Switt reticulin stains. After a 60 day treatment period, melatonin increased the length of cortical bone (95.13 ± 0.42%) versus that around control implants (62.91 ± 1.45%). Related to the perimeter of cortical bone of the tibiae, melatonin induced new bone 88.35 ± 1.56% versus 60.20 ± 1.67% in the control implants. Melatonin regenerated the width and length of cortical bone around implants in tibiae of rabbits more quickly than around control implants without the addition of melatonin.

Effects of growth hormone on initial bone formation around dental implants: a dog study

OBJECTIVE The aim of this study was to evaluate the effects of topical application of growth hormone (GH) on the osteointegration of dental implants in dogs at 5 and 8 weeks after surgery. MATERIALS AND METHODS Mandibular premolars and molars were extracted from 12 Beagle dogs. Four screw implants were placed in each mandible. Before implant placement, 4 IU of GH were applied to the test sites (TS); no treatment was applied to control sites (CS). Morphometric parameters, bone-to-implant contact (BIC), peri-implant connective tissue, interthread bone and newly formed bone were measured. The Students t-test for was used for statistical analysis of data obtained. RESULTS After 5 weeks of treatment, BIC values varied slightly between 34.33 ± 2.35% (CS) and 35.76 ± 2.96% (TS). Interthread bone tissue was 64.08 ± 8.68 at CS and 72.86 ± 2.93 at TS, with statistical significance (P<0.05). Bone neoformation was 72.53 ± 4.54 at the CS and 80.74 ± 1.65 for the GH group, these being statistically significant differences (P<0.05). After 8 weeks, BIC had slightly increased for the GH group (36.47 ± 3.09 vs. 39.61 ± 2.34). Interthread bone was 80.57 ± 2.28 at the CS and 82.58 ± 2.44 at the GH site, which was statistically significant. Bone neoformation was 88.09 ± 1.38 at CS and 91.01 ± 1.52 at TS, showing statistical significance (P<0.05). CONCLUSION Topical application of 4 IU of GH like a biomimetic agent at the moment of implant placement has no significant effects on the BIC at 5 and 8 weeks, although bone neoformation and inter-thread bone values did increase significantly.

Porous titanium granules in critical size defects of rabbit tibia with or without membranes

Recently, porous titanium granules (PTGs) have been indicated for the preservation of the dimensions of post-extraction sockets, as a filler in sinus lift procedures and for the treatment of peri-implant and periodontal defects, based on the osteoconductivity and dimensional stability of the titanium granules. However, there is a lack of information regarding the use of this material in larger defects and in conjunction with membranes. The objective of this study is to test the behavior of PTGs used to fill critical size defects in rabbit tibiae, with and without membranes. Critical defects were created in both tibiae of rabbits, divided randomly into three groups: Group A (defect filled with PTG), Group B (defect filled with PTG+collagen membrane) and a control group (empty defect). After six weeks, histomorphometric analysis was performed. The results showed more defect closures at the cortical area (87.37%±2.2%) and more bone formation at the marrow area (57.6%±1.3%) in Group B, in comparison with the other groups (P<0.05); the use of membranes improved the material stability expressed as more percentages of the original material when membranes were used (P<0.05). Finally, inflammatory reactions were observed when the granules were not protected by membranes. In spite of the limitations of this animal study, it may be concluded that PTG particles are osteoconductive and allow bone growth. The PTG particles must be covered by a membrane, especially when grafting larger defects, in order to control particle migration, promote clot stabilization and separate the PTG graft from undesired soft tissue cells.

Histologic and histomorphometric behavior of microgrooved zirconia dental implants with immediate loading.

PURPOSE The study aims to assess the total soft tissue (ST) width, crestal bone level (CBL), bone-to-implant contact (BIC), and bone density (BD) for zirconia implants textured with microgrooved surfaces and immediately loaded. MATERIALS AND METHODS This study included 51 implants; one implant from each study group was retained for surface characterization. The 48 remaining implants were inserted randomly in premolar areas of both sides of the healed edentulous lower jaws of foxhound dogs. They were divided into three groups of 16: control (titanium); test A (zirconia), and test B (microgrooved zirconia). The implants were splinted and covered with an acrylic bridge. A split-mouth design was used and immediate occlusal loading was applied on one side, while the other side did not have occlusal contact. ST, CBL, BIC, and BD were evaluated after 3 months. The effects of immediate loading on these parameters were analyzed. RESULTS All the implants were osseointegrated. ST was established at 3 months with mean values of 2.9 ± 0.4 mm for all groups. No differences were appreciated between loaded and unloaded sides regarding ST (p > .05). CBL showed a mean of 1.2 ± 0.3 mm for all groups without differences between loaded and unloaded sides (p > .05). BIC percentages were significantly higher for loaded all-microgrooved implants (p < .05). BD percentages were higher in areas close to all-microgrooved implants (p < .05) and significantly higher for loaded implants than unloaded. CONCLUSIONS Within the limitations of the present study, it may be concluded that for zirconia dental implants with microgrooved surfaces and immediate loading, the thickness of STs remains stable resulting in 3 mm mean biologic width, that crestal bone preservation is related to insertion depth, and that higher BIC percentages and increased BD around implants microgrooved over the entire intraosseous area may be expected at 3 months following implant insertion and immediate loading.

Ultrastructural study by backscattered electron imaging and elemental microanalysis of biomaterial-to-bone interface and mineral degradation of bovine xenografts in maxillary sinus floor elevation.

OBJECTIVES The aim of this study was to perform an ultrastructural study of the bone-to-biomaterial interface and biomaterial mineral degradation in retrieved bone biopsies following maxillary sinus augmentation using bovine xenografts (Endobon(®)) in 15 clinical cases. MATERIALS AND METHODS Nine months after sinus lifting, bone cores were harvested from the maxillary sinus. The specimens were processed for observation under a scanning electron microscope with backscattered electron imaging (SEM-BSE). In addition, chemical analysis and elemental mapping of the mineral composition were generated using a microanalytical system based on energy-dispersive X-ray spectrometry (EDX). RESULTS No clinical complications occurred during surgery. Scanning electron microscopy revealed that newly formed bone was closely attached to the xenograft. Elemental analysis showed a significantly high Ca/P ratio in the residual biomaterials (3.031 ± 0.104) compared with the interface (2.908 ± 0.115) and new bone (2.889 ± 0.113), which suggests that there may be a gradual diffusion of Ca ions from the biomaterial into the newly forming bone at the interface as part of the biomaterials resorption process. EDX analysis of the residual bovine biomaterial showed particle categories with different mean Ca/P ratios according to size, pointing to different stages of the resorption process. CONCLUSIONS The biomaterial proved to be biocompatible and osteoconductive when used as a bone substitute for maxillary sinus elevation. The grafting material used is not a completely resorbable material over the time period covered by this study.

Different configuration of socket shield technique in peri-implant bone preservation: An experimental study in dog mandible

The aim of this study was to evaluate the influence of the residual root and peri implant bone dimensions on the clinical success of the socket shield technique. Thirty-six dental implants were installed in 6 dogs. The clinical crowns of teeth P3, P4 and M1 were beheaded. Afterwards, the roots were worn down 2-3mm in apical direction until they were located at crestal level. Posterior implant beds were prepared in the center of the roots passing by 3mm apically forming 6 groups in accordance to the remaining root thickness. Radiography of the crestal bone level was performed on day 0 and after 12 weeks. Histomorphometric analyses of the specimens were carried out to measure the crestal bone level, the bone to implant contact and the buccal and lingual bone thickness at the implant shoulder portion. Correlations between groups were analyzed through nonparametric Friedman test, statistical significance was set as p<0.05. All 36 implants were osseointegrated, but 3 samples showed a clinical inflammatory reaction and some radicular fragments presented a small resorption process. On the buccal and lingual side, the radicular fragment was attached to the buccal bone plate by a physiologic periodontal ligament. In the areas where there was space between the implant and the fragment, newly formed bone was demonstrated directly on the implant surface. Within the limitations of an animal pilot study, root-T belt technique may be beneficial in preserving and protecting the bundle bone and preservation of soft tissues. If the thickness of the buccal bone is 3mm, and the thickness of the remaining root fragment is 2mm, the socket shield technique is more predictable and the bone contours can be maintained.

Connective Tissue Characteristics around Healing Abutments of Different Geometries: New Methodological Technique under Circularly Polarized Light

PURPOSE To describe contact, thickness, density, and orientation of connective tissue fibers around healing abutments of different geometries by means of a new method using coordinates. MATERIALS AND METHODS Following the bilateral extraction of mandibular premolars (P2, P3, and P4) from six fox hound dogs and a 2-month healing period, 36 titanium implants were inserted, onto which two groups of healing abutments of different geometry were screwed: Group A (concave abutments) and Group B (wider healing abutment). After 3 months the animals were sacrificed and samples extracted containing each implant and surrounding soft and hard tissues. Histological analysis was performed without decalcifying the samples by means of circularly polarized light under optical microscope and a system of vertical and horizontal coordinates across all the connective tissue in an area delimited by the implant/abutment, epithelium, and bone tissue. RESULTS In no case had the connective tissue formed a connection to the healing abutment/implant in the internal zone; a space of 35 ± 10 μm separated the connective tissue fibers from the healing abutment surface. The total thickness of connective tissue in the horizontal direction was significantly greater in the medial zone in Group B than in Group A (p < .05). The orientation of the fibers varied according to the coordinate area so that internal coordinates showed a higher percentage of parallel fibers in Group A (p < .05) and a higher percentage of oblique fibers in Group B (p < .05); medial coordinates showed more oblique fibers (p < .05); and the area of external coordinates showed the highest percentage of perpendicular fibers (p < .05). The fiber density was higher in the basal and medial areas (p < .05). CONCLUSIONS Abutment geometry influences the orientation of collagen fibers; therefore, an abutment with a profile wider than the implant platform favors oblique and perpendicular orientation of collagen fibers and greater connective tissue thickness.

Enhanced bone regeneration with a novel synthetic bone substitute in combination with a new natural cross‐linked collagen membrane: radiographic and histomorphometric study

OBJECTIVES 4Bone is a fully synthetic bioactive bone substitute composed of 60% hydroxyapatite (HA) and 40% beta-tricalcium phosphate (ß-TCP). This study aimed to investigate the effect of resorbable collagen membranes (RCM) on critical size defects in rabbit tibiae filled with this novel biphasic calcium phosphate at 15, 30, 45, and 60 days by radiological and histomorphometric analysis. MATERIAL AND METHODS Three critical size defects of 6 mm diameter were created in both tibiae of 20 New Zealand rabbits and divided into three groups according to the filling material: Group A (4Bone), Group B (4Bone plus RCM), and Group C (unfilled control group). At each of the four study periods, five rabbits were sacrificed. Anteroposterior and lateral radiographs were taken. Samples were processed for observation under light microscopy. RESULTS At the end of treatment, radiological analysis found that cortical defect closure was greater in Group B than Group A, and radiopacity was clearly lower and more heterogeneous in Group A cortical defects than in Group B. There was no cortical defect closure in Group C. Histomorphometric evaluation showed significant differences in newly formed bone and cortical closure in Group B compared with Groups A and C, with the presence of higher density newly formed bone in cortical and medullar zones. CONCLUSIONS Biphasic calcium phosphate functioned well as a scaffolding material allowing bone ingrowth and mineralization. The addition of absorbable collagen membranes enhanced bone gain compared with non-membrane-treated sites. This rabbit study provides radiological and histological evidence confirming the suitability of this new material for guided tissue regeneration of critical defects.

Peri-implant tissue behavior around non-titanium material: Experimental study in dogs.

The aim of this study is to assess the effectiveness of using non-titanium abutments for better establishment of peri-implant biological width and to assess the stability of the soft tissue. Forty-eight tapered dental titanium implants with internal connection of 3.5mm in diameter and 10mm length were implanted in post extraction alveoli of 6 dogs. Twenty-four abutments made in a reinforced polyetheretherketone (PEEK) formed the test group, and 24 titanium abutments, the control group. The groups were randomized. Histological, histomorphometric, ISQ and radiological analyses were performed. Greatest differences (control group vs. test group) were found at PM-Lc (Mucosa to lingual bone contact) (2.91±0.03 vs. 3.71±0.18), and to PM Lingual-IS (2.65±0.43 vs. 3.57±0.38). Reinforced PEEK constitutes an effective alternative to conventional titanium abutments, given its high rate of biocompatibility, preservation of bone height and soft tissue stability.