Study In Minipigs Research Articles

Circulation: Clinical Summaries

<i>Circulation:</i> Clinical Summaries

Microcomputed Tomographic and Histologic Analysis of Animal Experimental Degree II Furcation Defects Treated With Porous Titanium Granules or Deproteinized Bovine Bone

Titanium is an interesting material for osseous reconstruction given its thrombogenic properties. The aim of this study is to compare the potential of porous titanium granules (PTGs) with sham and deproteinized bovine bone mineral (DBBM) in the reconstructive treatment of surgically created buccal, degree II furcation defects in mini-pigs. Buccal degree II furcation defects were surgically created in maxillary premolar teeth in adult, female, mini-pigs and filled with PTG or DBBM or were left empty (sham). After 6 weeks of healing, pigs were euthanized. Teeth with defects were excised en bloc and analyzed by microcomputed tomography (microCT) and histology. The histologic analysis showed significantly more vertical bone formation in both PTG and sham groups compared to DBBM-treated defects (P <0.01). The microCT analysis showed significantly more bucco-palatal bone formation in furcations treated with PTG compared to the DBBM and sham (P <0.05). Bucco-palatal cylindrical microCT cores demonstrated a median defect fill of 96.8% for PTG-implanted defects, which was significantly greater than sham (72.2%) and DBBM (62.0%) (P <0.001) treatments. Significantly more regenerated periodontal ligament was seen for sham than DBBM-treated defects (P <0.05). Root resorption lacunae were small and infrequent and did not differ among groups. The results of this study in mini-pigs suggest that PTG may integrate well in alveolar bone and supports osseous regrowth in degree II furcation defects. Moreover, PTG seems safe to use in close proximity to root surfaces. Clinical studies will be necessary to further explore these experimental animal findings.

Stability of the miniplate osteosynthesis used for sagittal split osteotomy for closing an anterior open bite: an experimental study in mini-pigs

Bilateral sagittal split osteotomy of the mandible with counterclockwise rotation of the occlusal plane alone has traditionally been considered the least stable treatment method. Two miniplates on each side of the osteotomy may resolve this problem. The authors compared early vertical and transverse stability of a simple mandibular advancement (group A), mandibular advancement with counterclockwise rotation (CCW) stabilized with one miniplate (group B), and two miniplates (group C) on mini-pig mandibles mounted on a custom-made loading unit. Two miniplates markedly increased the resistance to vertical bite forces. On a 100-N load, a median of dislocation of 0.53mm, 0.46mm, and 0.23mm was achieved in groups A, B, and C, respectively. The difference was statistically significant between groups A and B in comparison with group C. The results of transverse displacement were not statistically significant. The use of two miniplates in larger shifts, as well as in CCW cases, increases stability in the vertical direction.

Volumetric changes of the graft after maxillary sinus floor augmentation with Bio-Oss and autogenous bone in different ratios: a radiographic study in minipigs

The objective of the present study was to learn about the volumetric changes of the graft after maxillary sinus floor augmentation with Bio-Oss and autogenous bone from the iliac crest or the mandible in different ratios in minipigs. Bilateral maxillary sinus floor augmentation was performed in 40 minipigs with: (A) 100% autogenous bone, (B) 75% autogenous bone and 25% Bio-Oss, (C) 50% autogenous bone and 50% Bio-Oss, (D) 25% autogenous bone and 75% Bio-Oss, and (E) 100% Bio-Oss. The autogenous bone graft was harvested from the iliac crest or the mandible and the graft composition was selected at random and placed concomitant with implant placement. Computed tomographies of the maxillary sinuses were obtained preoperatively, immediately postoperatively, and at euthanasia after 12 weeks. The volumetric changes of the graft were estimated using the Cavalieri principle and expressed as mean percentage with a 95% confidence interval (CI). The mean volume of the graft was reduced by (A) 65% (95% CI: 60-70%), (B) 38% (95% CI: 35-41%), (C) 23% (95% CI: 21-25%), (D) 16% (95% CI: 12-21%), and (E) 6% (95% CI: 4-8%). The volumetric reduction was significantly influenced by the ratio of Bio-Oss and autogenous bone (P<0.001), but not by the origin of the autogenous bone graft (P=0.2). The volume of autogenous bone grafts from the iliac crest and the mandible is reduced significantly after maxillary sinus floor augmentation in minipigs. The graft volume is better preserved after the addition of Bio-Oss and the volumetric reduction is significantly influenced by the ratio of Bio-Oss and autogenous bone. However, further studies are needed addressing the amount of new bone formation and bone-to-implant contact before the final conclusion can be made about the optimal ratio of Bio-Oss and autogenous bone.

Preclinical Evaluation of Local JAK1 and JAK2 Inhibition in Cutaneous Inflammation

JAKs are required for signaling initiated by several cytokines (e.g., IL-4, IL-12, IL-23, thymic stromal lymphopoietin (TSLP), and IFNγ) implicated in the pathogenesis of inflammatory skin diseases such as psoriasis and atopic dermatitis (AD). Direct antagonism of cytokines, such as IL-12 and IL-23 using ustekinumab, has proven effective in randomized studies in psoriasis patients. We hypothesized that local inhibition of cytokine signaling using topical administration of INCB018424, a small molecule inhibitor of JAK1 and JAK2, would provide benefit similar to systemic cytokine neutralization. In cellular assays, INCB018424 inhibits cytokine-induced JAK/signal transducers and activators of transcription (STAT) signaling and the resultant production of inflammatory proteins (e.g., IL-17, monocyte chemotactic protein-1, and IL-22) in lymphocytes and monocytes, with half-maximal inhibitory concentration values <100 nM. In vivo, topical application of INCB018424 resulted in suppression of STAT3 phosphorylation, edema, lymphocyte infiltration, and keratinocyte proliferation in a murine contact hypersensitivity model and inhibited tissue inflammation induced by either intradermal IL-23 or TSLP. Topical INCB018424 was also well tolerated in a 28-day safety study in Gottingen minipigs. These results suggest that localized JAK1/JAK2 inhibition may be therapeutic in a range of inflammatory skin disorders such as psoriasis and AD. Clinical evaluation of topical INCB018424 is ongoing.

Effect of Enamel Matrix Derivative and Parathyroid Hormone on Bone Formation in Standardized Osseous Defects: An Experimental Study in Minipigs

Previous experimental studies have indicated that locally administered enamel matrix derivative (EMD) and parathyroid hormone (PTH) may have a stimulatory effect on bone formation. However, it is not clear if the positive effect of EMD is related to its effect on the periodontium as a whole or directly on the bone-forming cells. In addition, it is not known if the presentation of PTH by adding the amino acid sequence Arg-Gly-Asp (RGD) is essential for its osteopromotive effect. Local delivery of a bioactive substance at the right time and in the right concentration often constitutes a major challenge. Polyethylene glycol-based hydrogel (PEG) is a degradable vehicle developed for delivery of bioactive proteins. To enhance the mechanical stability of the PEG-bioactive substance complex, an osteoconductive bone substitute material is often needed. Three standard diameter monocortical bone defects were prepared bilaterally in the mandibles of 18 Göttingen minipigs. The six defects of each animal were grafted with 1) autogenous bone chips, 2) biphasic calcium phosphate bone substitute (BCP), 3) PEG + BCP, 4) EMD + PEG + BCP, 5) PTH + PEG + BCP, or 6) PTH-RGD + PEG + BCP. A non-resorbable barrier membrane was used to cover the defects. Three groups of six animals healed for 2, 4, and 8 weeks, respectively. There was no statistically significant effect of EMD, PTH, and PTH + RGD on bone formation compared to BCP and BCP + PEG. Particulated autografts showed the highest amount of new bone formation at all observation periods. The present study fails to demonstrate any stimulatory effect of EMD, PTH, or PTH + RGD in combination with an experimental PEG hydrogel and BCP on bone formation.

Establishment of the epithelial attachment and connective tissue adaptation to implants installed under the concept of “platform switching”: a histologic study in minipigs

To validate the "platform switching" concept at oral implants with respect to the preservation of the alveolar crestal bone levels in an animal model. Five minipigs received three implants each with a 0.25 mm implant/abutment mismatch and were placed flush (T(0)), 1 mm below (T(1)) and 1 mm above (T(+1)) the alveolar bony crest, and as a control, one conventionally restored implant placed at the bone level. The implants were randomly inserted flapless into the mandible. Four months after implant insertion, the animals were sacrificed, and undecalcified block sections were obtained and used for histological analyses. The mean values for peri-implant bone resorption were 1.09 ± 0.59 mm (Control), 0.51 (± 0.27 mm, T(0)), 0.50 (± 0.46 mm, T(+1)) and 1.30 (± 0.21 mm, T(-1)), respectively. Statistically significant differences (P<0.05) were found among the test (T(0), T(-1)) and the control sites. Control implants presented an average biologic width length of 3.20 mm (± 0.33), with a connective tissue adaptation compartment of 1.29 mm (± 0.53) and an epithelial attachment of 1.91 mm (± 0.71). T(0), T(+1) and T(-1) implants presented with a mean biologic width of 1.97 mm (± 1.20), 2.70 mm (± 1.36) and 2.84 mm (± 0.90), respectively, with a connective tissue adaptation compartment of 1.21 mm (± 0.97), 1.21 mm (± 0.65) and 1.50 mm (± 0.70) and an epithelial attachment of 0.84 mm (± 0.93), 1.66 mm (± 0.88) and 1.35 mm (± 0.44), respectively. Differences between the configurations were mainly associated with the length of the epithelial attachment. The epithelial attachment was significantly longer in the C sites than in T(0) (P=0.014). However, no other differences between configurations were detected. If the implants are positioned at the level of the alveolar bony crest, the platform-switching concept may have a minor impact on the length of the epithelial attachment (0.84 vs. 1.91 mm), while the connective tissue adaptation compartment remains relatively unaffected. Moreover, platform switching resulted in less resorption of the alveolar crest (0.58 mm).

Comparison of zirconia and titanium implants after a short healing period. A pilot study in minipigs

The aim of this animal study was to investigate and compare the osseointegration of zirconia and titanium dental implants. 14 one-piece zirconia implants and 7 titanium implants were inserted into the mandibles of 7 minipigs. The zirconia implants were alternately placed submerged and non-submerged. To enable submerged healing, the supraosseous part was removed, using a diamond saw. The titanium implants were all placed submerged. After a healing period of 4 weeks, a histological analysis of the soft and hard tissue and a histomorphometric analysis of the bone-implant contact (BIC) and relative peri-implant bone-volume density (rBVD; relation to bone-volume density of the host bone) was performed. Two zirconia implants were found to be loose. All other implants were available for evaluation. For submerged zirconia and titanium implants, the implant surface showed an intimate connection to the neighbouring bone, with both types achieving a BIC of 53%. For the non-submerged zirconia implants, some crestal epithelial downgrowth could be detected, with a resultant BIC of 48%. Highest rBVD values were found for submerged zirconia (80%), followed by titanium (74%) and non-submerged zirconia (63%). The results suggest that unloaded zirconia and titanium implants osseointegrate comparably, within the healing period studied.

Bioactive nucleic-acid coatings for implants as an innovative approach for difficult bone conditions—an experimental study in minipigs

Particularly in difficult bone situations, dental implants are able to expand their indications by osteoinductive coatings. The transfer of nucleic acids enables strengthening the bodýs own cell production of particular or combined cytokines like bone morphogenetic protein-2 (BMP-2) and transforming growth factor-beta or insulin-like growth factor without the drawbacks of direct applications of recombinant proteins. Until now, central issue of bioactive surfaces has been stability and release behaviour.

Effect of Mesenchymal Stem Cells and Platelet-Rich Plasma on the Healing of Standardized Bone Defects in the Alveolar Ridge: A Comparative Histomorphometric Study in Minipigs

The purpose of this study was to test the effect of the combination of mesenchymal stem cells (MSCs) and platelet-rich plasma (PRP) incorporated into a fluorohydroxyapatite (FHA) scaffold on bone regeneration in cylindrical defects in the edentulous mandibular ridge of minipigs. Two mandibular premolar teeth were extracted bilaterally in 8 adult minipigs. After 2 months, 4 standardized defects of 3.5 mm diameter and 8 mm depth were created in each root site. The defects were randomly grafted with autogenous mandibular bone, FHA alone, PRP-FHA, or MSCs-PRP-FHA. A resorbable collagen membrane was placed over the defect area and the flaps were sutured. The animals were sacrificed 3 months later and biopsy samples were taken from the defect sites for histologic and histomorphometric assessment. There was no evidence of inflammation or adverse tissue reaction with either treatment. MSCs-PRP-FHA-treated sites showed new vital bone between residual grafting particles. PRP-FHA- and FHA-treated sites showed residual particles in a background of marrow soft tissue with a moderate quantity of newly formed bone. Autogenous bone (46.97%) and MSCs-PRP-FHA (45.28%) produced a significantly higher amount of vital bone than PRP-FHA (37.95%), or FHA alone (36.03%). Further, the MSCs-PRP-FHA-treated defects showed a significantly higher percentage of contact between graft particles and newly formed bone compared with PRP-FHA and FHA group (59.23% vs 48.37% and 46.43%, respectively). Our results suggest that, in this animal model, the addition of MSCs to PRP-FHA enhances bone formation after 3 months.

Histologic and tomographic analyses of the temporomandibular joint after mandibular advancement surgery: study in minipigs

The aim was to elucidate the changes occurring in temporomandibular joint (TMJ) after surgical mandibular advancement with different fixation materials: bicortical screws and miniplates. Eighteen minipigs were randomly divided into 3 groups: group I (control), nonoperated animals; group II, animals submitted to surgical advancement surgery and osteosynthesis by bicortical screws; and group III, animals submitted to surgical advancement surgery and osteosynthesis by miniplates. Four months after the surgeries, TMJs were collected and histologically prepared after computerized tomography (CT) scanning for the blind detection of erosion, flattening, and osteophyte. The CT analysis revealed significant alterations in the shape of the condyles (erosion: P = .0010; flattening: P < .0001) for group II compared with groups I and III. Descriptive histologic analysis was compatible with the CT findings. The results indicated that bicortical screw fixation resulted in more pronounced condylar alterations in the shape of the condyles than miniplate osteosynthesis. However, further clinical studies are necessary to confirm these data.

Comparative study of biphasic calcium phosphates with different HA/TCP ratios in mandibular bone defects. A long‐term histomorphometric study in minipigs

Three biphasic calcium phosphate (BCP) bone substitute materials with hydroxyapatite (HA)/tricalcium phosphate (TCP) ratios of 20/80, 60/40, and 80/20 were compared to coagulum, particulated autogenous bone, and deproteinized bovine bone mineral (DBBM) in membrane-protected bone defects. The defects were prepared in the mandibles of 24 minipigs that were divided into four groups of six with healing times of 4, 13, 26, and 52 weeks, respectively. The histologic and histomorphometric evaluation focused on differences in amount and pattern of bone formation, filler degradation, and the interface between bone and filler. Collapse of the expanded polytetrafluoroethylene barrier membrane into the coagulum defects underlined the necessity of a filler material to maintain the augmented volume. Quantitatively, BCP 20/80 showed bone formation and degradation of the filler material similar to autografts, whereas BCP 60/40 and BCP 80/20 rather equaled DBBM. Among the three BCP's, the amount of bone formation and degradation of filler material seemed to be inversely proportional to the HA/TCP ratio. The fraction of filler surface covered with bone was highest for autografts at all time points and was higher for DBBM than BCP 80/20 and 60/40 at the early healing phase. TRAP-positive multinucleated cells were identified on BCP and DBBM surfaces without showing typical signs of resorption lacunae.

Histological and molecular temporomandibular joint analyses after mandibular advancement surgery: study in minipigs

The objective of this study was to elucidate the changes occurring in the temporomandibular joint (TMJ) after surgical mandibular advancement with different fixation techniques: bicortical screws (rigid fixation) and miniplates (semi-rigid fixation). Eighteen minipigs were equally and randomly divided into 3 groups: Group I (control), nonoperated animals; Group II, animals submitted to surgical advancement surgery and osteosynthesis by bicortical screws; and Group III, animals submitted to surgical advancement surgery and osteosynthesis by miniplates. Four months after the surgeries, the presence of interleukin (IL)-6 and IL-10 in synovial fluid samples was assessed in ELISA experiments. TMJs were histologically prepared. Higher levels of IL-10 (P = .0436) were found for Group II. Descriptive histological analysis was compatible with the ELISA findings. Rigid fixation evokes more pronounced signs of bone remodeling in the TMJ, whereas malleable fixation promotes a more intense inflammatory activity. Therefore, rigid fixation seems to transmit a higher impact of postoperative masticatory forces to the TMJ.

The use of biodegradable scaffold as an alternative to silicone implant arthroplasty for small joint reconstruction: An experimental study in minipigs

Biodegradable poly- l/ d-lactide (P( l/d)LA) 96/4 joint scaffold arthroplasty is a recently clinically introduced concept in the reconstruction of small joints, however its histology and function in vivo is unknown. In this experimental study on 11 minipigs the fifth metacarpophalangeal joints were reconstructed using a P( l/d)LA 96/4 joint scaffold or Swanson silicone implant. They were evaluated until 3 years. The P( l/d)LA 96/4 joint scaffold formed a porous interposition spacer, which maintained the arthroplasty space and induced fibrous tissue in-growth in situ. No differences were found in the range of motion or arthroplasty space width between the study groups. The P( l/d)LA 96/4 joint scaffold was initially filled with vascular, loose connective tissue. Along with degradation of the scaffold, the in-grown connective tissue matured and condensed turning into dense fibrous connective tissue. After 3 years, the P( l/d)LA 96/4 joint scaffold had almost completely degraded and been replaced by dense fibrous connective tissue. These findings indicate that P( l/d)LA 96/4 joint scaffold arthroplasty leads to the formation of a functional fibrous joint. The avoidance of permanent foreign material makes the biodegradable joint scaffold an attractive alternative for small joint arthroplasty.

Comparative Study of Biphasic Calcium Phosphates with Different HA/TCP Ratios in Mandibular Bone Defects. Long-Term Histomorphometric Study in Minipigs

Comparative Study of Biphasic Calcium Phosphates with Different HA/TCP Ratios in Mandibular Bone Defects. Long-Term Histomorphometric Study in Minipigs

Evaluation of bone height and bone density after tooth extraction: an experimental study in minipigs

The objective of this study was to radiographically quantify bone density and bone height preservation in tooth extraction alveolus filled with xenograft. The maxillary and mandibular fourth deciduous molars and fourth premolars of 6 minipigs were removed. Randomly, in 3 animals the right side was used as the test side and in the other 3 animals the left side was the test side. Intraoral radiographs were performed to compare the condition at the initial time and 3 months later. Measurements of bone height and bone density were performed using KS300 (Zeiss) software. After 3 months, there was a statistically significant smaller bone height loss for the test group. The test group presented a statistically greater bone density immediately after tooth extraction. However, after 3 months there was no statistically significant difference between the groups. The results suggest that treatment of postextraction alveolus with xenograft can preserve bone height initially but differences in bone density compared to when no xenograft is used are not sustained.

Cytokines and Growth Factors Involved in the Osseointegration of Oral Titanium Implants Positioned Using Piezoelectric Bone Surgery Versus a Drill Technique: A Pilot Study in Minipigs

Most dental implants are positioned using a drilling surgery technique. However, dentistry recently experienced the implementation of piezoelectric surgery. This technique was introduced to overcome some of the limitations involving rotating instruments in bone surgery. This study used biomolecular and histologic analyses to compare the osseointegration of porous implants positioned using traditional drills versus the piezoelectric bone surgery technique. Porous titanium implants were inserted into minipig tibias. Histomorphology and levels of bone morphogenetic protein (BMP)-4, transforming growth factor (TGF)-beta2, tumor necrosis factor-alpha, and interleukin-1beta and -10 were evaluated in the peri-implant osseous samples. Histomorphological analyses demonstrated that more inflammatory cells were present in samples from drilled sites. Also, neo-osteogenesis was consistently more active in bone samples from the implant sites that were prepared using piezoelectric bone surgery. Moreover, bone around the implants treated with the piezoelectric bone surgery technique showed an earlier increase in BMP-4 and TGF-beta2 proteins as well as a reduction in proinflammatory cytokines. Piezoelectric bone surgery appears to be more efficient in the first phases of bone healing; it induced an earlier increase in BMPs, controlled the inflammatory process better, and stimulated bone remodeling as early as 56 days post-treatment.

Orthodontic movement in bone defects filled with xenogenic graft: An experimental study in minipigs

In this study, we investigated whether it is possible to orthodontically move a tooth into an adjacent bone defect previously filled with xenogenic grafting material, with emphasis on the reactions of the tooth roots and adjacent tissues. Six minipigs were used. In each animal, 4 defects were created at the mesial aspects of the maxillary and mandibular first permanent molars; the defects on the right were filled with the xenograft (test side), and the opposite defects (control side) were filled with blood clots and allowed to heal spontaneously. Three months later, orthodontic appliances were placed in each quadrant to allow mesial bodily movement of the first permanent molars. When the teeth were moved about halfway into the defect spaces, the animals were killed, and the areas of interest were harvested. The mesial roots of the first molars and adjacent tissues were histologically and morphometrically evaluated. The volume density of bone tissue, the percentage of root resorption, and the bone height were evaluated with image analysis software. Data analysis showed that (1) the percentage of root resorption was smaller (P = .0359) for the test group (4.16%) compared with the control (6.52%); (2) there was no statistically significant differences between groups concerning the volume density of neoformed bone (P >.05); (3) the bovine bone matrix was almost totally replaced by structured bone tissue; (4) the test group had a statistically significant smaller bone height loss (2.18 mm, P = .0018) than the control group (3.26 mm). Based on these results, it was concluded that teeth can be moved into areas of bone defects previously filled with xenograft.

Effects of platelet factors on biodegradation and osteogenesis in metaphyseal defects filled with nanoparticular hydroxyapatite—an experimental study in minipigs

There are no studies on the cellular activity in the early phase of biodegradation and bone healing of bone substitutes loaded with platelet factors (PLF). The purpose of this study was to evaluate the cellular effects of PLF in combination with nanoparticulate hydroxyapatite (HA) on the biodegradation and bone formation after 20 days. Autogenous PLFs were obtained by centrifugation of miniature pig blood samples and subsequent degranulation of platelets by calcium and thrombin. A cylindrical bone defect with a diameter of 8.9 mm was created in the distal femoral condyle of 20 miniature pigs. Four of the defects were left empty, 8 were filled with HA with loading and 8 with HA loaded with PLF. The distal femur was harvested after 20 days and TRAP-staining, cathepsin-K and CD44 staining and scanning electron microscopy were performed for cellular assessment of biodegradation was done. Histomorphometry of new bone formation and of biodegradation of HA material was performed. PLF loading of HA led to statistically significant more TRAP-positive cells with enhanced biodegradation of the nanoparticulate HA but no statistically enhanced new bone formation compared to unloaded HA. Furthermore, there was a higher number of CD44 and cathepsin-K positive cells by PLF-loading. In summary, PLF led to stimulation of the cellular process of the biodegradation of HA.

Biological Factors Involved in the Osseointegration of Oral Titanium Implants With Different Surfaces: A Pilot Study in Minipigs

The stability of titanium implants is determined by the rigid load-bearing connections that are formed by the bone, a process that involves a complex network of cells, pro- and anti-inflammatory mediators, and growth factors. The osseointegration processes at the interfaces of machined and porous implants were studied using molecular and histological techniques. Two machined and two porous titanium implants were inserted into the tibiae of four minipigs. The animals were sacrificed at 15, 30, 60, and 90 days post-implantation. The levels of bone morphogenetic protein (BMP)-4, transforming growth factor (TGF)-beta1, and tumor necrosis factor (TNF)-alpha were quantified in the peri-implant osseous samples. The levels of interleukin (IL)-1beta, IL-6, IL-10, and TNF-alpha in the serum were also assessed. Histomorphological analysis showed evidence of bone ossification around the porous implant at 60 days. Surrounding the machined implants, highly sclerotic fibrous pads started the healing response at 90 days, and the levels of TGF-beta1 and BMP-4 began to increase at 60 days, at which time bone ossification around the porous implants was already evident. TNF-alpha was not present in the bone next to the implants. The serum levels of cytokines IL-1beta, IL-6, and IL-10 were not increased. The serum level of TNF-alpha increased during the healing process. We observed that the levels of BMP-4 and TGF-beta1, which play essential roles in the osteogenesis process, increased earlier around the porous implants than around the machined implants. Similarly, the ossification process was initiated earlier at the surfaces of the porous implants than at the surfaces of the machined implants.