A rabbit model for experimental alveolar cleft grafting

Fabrication of a transforming growth factor β1 functionalized silk sericin hydrogel through genetical engineering to repair alveolar bone defects in rabbit

Cleft palate is one of the most prevalent congenital craniofacial birth defects in human congenital facial anomaly. Severe cleft palate is usually accompanied by alveolar bone defects (ABDs). Growth factors (GFs) are considered as desirable opportunity to promote the craniofacial healing post the surgery. However, limited resource, susceptibility to degradation, and lack of appropriate delivery systems greatly hinder the clinic application of GFs in the ABDs repair. In this study, a transforming growth factor β1 variant (eTGF-β1) with enhanced extracellular matrix (ECM) binding efficiency was engineered to generate transgenic silkworm using the silk gland biosynthesizing system for cost effective and massive bio-synthesis of the eTGF-β1 functionalized silk fibers. The eTGF-β1 achieved a highly-efficient expression in the middle silk gland (MSG) cells of transgenic silkworm, and secretion and distribution in the sericin layer of silk fiber which accounted for approximately 5.57 ± 0.72 % of the cocoon shell weight. The eTGF-β1 functionalized silk sericin hydrogel (eTGF-β1 SH) was then fabricated with excellent mechanical and processing properties, injectability, biocompatibility, biodegradability, sustained release of eTGF-β1, and capability to promote cell proliferation, which significantly accelerated the bone defect repair particularly the osteoblast maturation and new bone formation through regulating the expressions of the bone formation-related genes in a rabbit alveolar process cleft model. This study provides a valuable strategy for future the treatments of ABDs in rabbit with cleft palate using the genetically engineered eTGF-β1 silk sericin hydrogel.

Histomorphometric and CBCT comparison of osseointegration around orthodontic titanium miniscrews coated with different nanoparticles: An in-vivo animal study

BACKGROUND

Temporarily installed titanium orthodontic miniscrews are usually used for many orthodontic applications, especially those cases that need high force, such as skeletally anchored orthodontic appliance cases. Surface modification of titanium miniscrews has proved success in preventing failure and overcoming their limitations.

OBJECTIVE

The present study aims at the assessment of the quality of osseointegration of surface modified titanium miniscrews installed in the maxilla of albino rabbits with cone-beam computed tomography (CBCT) imaging as well as histomorphometric investigations.

MATERIAL AND METHODS

The orthodontic titanium miniscrews (TMSs) were coated with silver/hydroxyapatite (Ag/HA) nanoparticles (NPs) or zinc oxide (ZnO) NPs via electrochemical deposition. The coating nanomaterials were then characterized with X-ray diffractometry (XRD) and scanning electron microscopy (SEM) imaging. Moreover, the antimicrobial activity of the coated titanium miniscrews were evaluated in the rabbits' oral cavity to investigate their ability to prevent biofilm formation.

RESULTS

It was found that the Ag/HA-coated TMSs demonstrated the highest antimicrobial activity and bone area fill, followed by the ZnO NPs-coated TMSs when compared to their uncoated counterparts. In the anterior area surrounding the installed TMSs, the highest osseointegration was demonstrated by ZnO NPs-coated TMSs. However, Ag/HA-coated TMSs showed the highest osseointegration values in the posterior peri-implant area.

CONCLUSIONS

Ag/HA- and ZnO NPs-coated TMSs may provide a promising solution to overcome the 30% probable failure in temporarily installed orthodontic miniscrews, as they can enhance the osseointegration process and prevent biofilm formation.

Bone Tissue Engineering Strategies for Alveolar Cleft: Review of Preclinical Results and Guidelines for Future Studies

The current standard of care for an alveolar cleft defect is an autogenous bone graft, typically from the iliac crest. Given the limitations of alveolar bone graft surgery, such as limited supply, donor site morbidity, graft failure, and need for secondary surgery, there has been growing interest in regenerative medicine strategies to supplement and replace traditional alveolar bone grafts. Though there have been preliminary clinical studies investigating bone tissue engineering methods in human subjects, lack of consistent results as well as limitations in study design make it difficult to determine the efficacy of these interventions. As the field of bone tissue engineering is rapidly advancing, reconstructive surgeons should be aware of the preclinical studies informing these regenerative strategies. We review preclinical studies investigating bone tissue engineering strategies in large animal maxillary or mandibular defects and provide an overview of scaffolds, stem cells, and osteogenic agents applicable to tissue engineering of the alveolar cleft. An electronic search conducted in the PubMed database up to December 2021 resulted in 35 studies for inclusion in our review. Most studies showed increased bone growth with a tissue engineering construct compared to negative control. However, heterogeneity in the length of follow up, method of bone growth analysis, and inconsistent use of positive control groups make comparisons across studies difficult. Future studies should incorporate a pediatric study model specific to alveolar cleft with long-term follow up to fully characterize volumetric defect filling, cellular ingrowth, bone strength, tooth movement, and implant support.

A novel pilot animal model for bone augmentation using osseous shell technique for preclinical in vivo studies

OBJECTIVES

Bone grafting is commonly used to reconstruct skeletal defects in the craniofacial region. Several bone augmentation models have been developed to evaluate bone formation using novel bone substitute materials. The aim of this study was to evaluate a surgical animal model for establishing a three-dimensional (3D) grafting environment in the animal's mandibular ramus for bone augmentation using the osseous shell technique, as in humans.

MATERIALS AND METHODS

Osteological survey of New Zealand white (NZW) rabbit skull (Oryctolagus cuniculus): Initial osteological and imaging surveys were performed on a postmortem skull for a feasibility assessment of the surgical procedure. Postmortem pilot surgery and cone beam computed tomography imaging: a 3D osseous defect was created in the mandibular ramus through a submandibular incision. The osseous shell plates were stabilized with osteosynthesis fixation screws, and defects were filled with particular bone grafting material. In vivo surgical procedure: surgeries were conducted in four 8-week-old NZW rabbits utilizing two osseous shell materials: xenogeneic human cortical plates and autogenous rabbit cortical plates. The created 3D defects were filled using xenograft and allograft bone grafting materials. The healed defects were evaluated for bone formation after 12 weeks using histological and cone beam computed tomography imaging analysis.

RESULTS

Clinical analysis 12 weeks after surgery revealed the stability of the 3D grafted bone augmentation defects using the osseous shell technique. Imaging and histological analyses confirmed the effectiveness of this model in assessing bone formation.

CONCLUSIONS

The proposed animal model is a promising model with the potential to study various bone grafting materials for augmentation in the mandibular ramus using the osseous shell technique without compromising the health of the animal. The filled defects could be analyzed for osteogenesis, quantification of bone formation, and healing potential using histomorphometric analysis, in addition to 3D morphologic evaluation using radiation imaging.

Development of root resorption during orthodontic tooth movement after cleft repair using different grafting materials in rats

OBJECTIVE

The aim of the present study was to investigate the influence of three grafting materials for cleft repair on orthodontic tooth movement in rats.

MATERIALS AND METHODS

Artificial alveolar clefts were created in 21 Wistar rats and were repaired 4 weeks later using autografts, human xenografts and synthetic bone substitute (beta-tricalcium phosphate/hydroxyapatite [β-TCP/HA]). A further 4 weeks later, the first molar was moved into the reconstructed maxilla. Microfocus computed tomography (μCT) was performed six times (T0-T5) to assess the tooth movement and root resorption. After 8 weeks, the affected reconstructed jaw was resected for histopathological investigation.

RESULTS

Total distances reached ranged from 0.82 ± 0.72 mm (β-TCP/HA) to 0.67 ± 0.27 mm (autograft). The resorption was particularly determined at the mesiobuccal root. Descriptive tooth movement slowed and root resorption increased slightly. However, neither the radiological changes during tooth movement (µCT T1 vs. µCT T5: autograft 1.85 ± 0.39 mm³ vs. 2.38 ± 0.35 mm³, p = 0.30; human xenograft 1.75 ± 0.45 mm³ vs. 2.17 ± 0.26 mm³, p = 0.54; β-TCP/HA: 1.52 ± 0.42 mm³ vs. 1.88 ± 0.41 mm³, p = 0.60) nor the histological differences after tooth movement (human xenograft: 0.078 ± 0.05 mm²; β-TCP/HA: 0.067 ± 0.049 mm²; autograft: 0.048 ± 0.015 mm²) were statistically significant.

CONCLUSION

The autografts, human xenografts or synthetic bone substitute used for cleft repair seem to have a similar effect on the subsequent orthodontic tooth movement and the associated root resorptions.

CLINICAL RELEVANCE

Development of root resorptions seems to have a secondary role in choosing a suitable grafting material for cleft repair.

The effect of biphasic calcium phosphate and demineralized bone matrix on tooth eruption in mongrel dogs

BACKGROUND

Bone grafts can provide an optimal environment for permanent tooth to erupt and enhance the stability of the alveolar maxilla. Although autologous bone is an optimal source for osteogenesis, its inevitable donor site morbidity has led to active research on bone substitutes. This study was designed to evaluate the safety and feasibility of using biphasic calcium phosphate (BCP; Osteon) as a bone substitute in dogs.

METHODS

Bilateral third and fourth premolars of four 15-week-old mongrel dogs were used. All teeth were extracted except the third premolar of the right mandible, which was used as a control. After extraction of the premolars, each dog was administered BCP (Osteon), demineralized bone matrix (DBM; DBX), and no graft in the hollow sockets of the right fourth premolar, left fourth premolar, and left third premolar, respectively. Radiographs were taken at 2-week intervals to check for tooth eruption. After 8 weeks, each dog was sacrificed, and tooth and bone biopsies were performed to check for the presence of tooth and bone substitute particle remnants.

RESULTS

Four weeks after the operation, permanent tooth eruptions had started at all the extraction sites in each dog. Eight weeks after the operation, all teeth had normally erupted, and histological examination revealed BCP particles at the right fourth premolar.

CONCLUSION

In all four dogs, no delay in the eruption of the teeth or shape disfigurement of permanent teeth was observed on gross inspection and radiologic evaluation. On histological examination, most of the BCP and DBM were replaced by new bone. Bone substitutes can be used as graft materials in patients with alveolar clefts.

Evaluation of different grafting materials for alveolar cleft repair in the context of orthodontic tooth movement in rats

To minimize the postoperative risks posed by grafting autologous transplants for cleft repair, efforts are being made to improve grafting materials for use as potential alternatives. The aim of this study was to compare the bone graft quality of different bone substitutes including the gold standard autografts during the healing processes after cleft repair in the context of orthodontic treatment. In 21 Wistar rats, a complete, continuity-interrupting cleft was created. After 4 weeks, cleft repair was performed using autografts from the hips’ ischial tuberosity, human xenografts, or synthetic bone substitutes [beta-tricalcium phosphate (β-TCP)/hydroxyapatite (HA)]. After another 4 weeks, the first molar movement was initiated in the reconstructed jaw for 8 weeks. The bone remodeling was analyzed in vivo using micro-computed tomography (bone mineral density and bone volume fraction) and histology (new bone formation). All the grafting materials were statistically different in bone morphology, which changed during the treatment period. The β-TCP/HA substitute demonstrated less resorption compared to the autologous and xenogeneic/human bone, and the autografts led to a stronger reaction in the surrounding bone. Histologically, the highest level of new bone formation was found in the human xenografts, and the lowest was found in the β-TCP/HA substitute. The differences between the two bone groups and the synthetic materials were statistically significant. Autografts were confirmed to be the gold standard in cleft repair with regard to graft integration. However, parts of the human xenograft seemed comparable to the autografts. Thus, this substitute could perhaps be used as an alternative after additional tissue-engineered modification.

A novel surgical model for the preclinical assessment of the osseointegration of dental implants: a surgical protocol and pilot study results

BACKGROUND

Dental implants are considered the gold standard replacement for missing natural teeth. The successful clinical performance of dental implants is due to their ability to osseointegrate with the surrounding bone. Most dental implants are manufactured from Titanium and it alloys. Titanium does however have some shortcomings so alternative materials are frequently being investigated. Effective preclinical studies are essential to transfer the innovations from the benchtop to the patients. Many preclinical studies are carried out in the extra-oral bones of small animal models to assess the osseointegration of the newly developed materials. This does not simulate the oral environment where the dental implants are subjected to several factors that influence osseointegration; therefore, they can have limited clinical value.

AIM

This study aimed to develop an appropriate in-vivo model for dental implant research that mimic the clinical setting. The study evaluated the applicability of the new model and investigated the impact of the surgical procedure on animal welfare.

MATERIALS AND METHODS

The model was developed in male New Zealand white rabbits. The implants were inserted in the extraction sockets of the secondary incisors in the maxilla. The model allows a split-mouth comparative analysis. The implants' osseointegration was assessed clinically, radiographically using micro-computed tomography (µ-CT), and histologically. A randomised, controlled split-mouth design was conducted in 6 rabbits. A total of twelve implants were inserted. In each rabbit, two implants; one experimental implant on one side, and one control implant on the other side were applied. Screw-shaped implants were used with a length of 8 mm and a diameter of 2 mm.

RESULTS

All the rabbits tolerated the surgical procedure well. The osseointegration was confirmed clinically, histologically and radiographically. Quantitative assessment of bone volume and mineral density was measured in the peri-implant bone tissues. The findings suggest that the new preclinical model is excellent, facilitating a comprehensive evaluation of osseointegration of dental implants in translational research pertaining to the human application.

CONCLUSION

The presented model proved to be safe, reproducible and required basic surgical skills to perform.

Predifferentiated Gingival Stem Cell-Induced Bone Regeneration in Rat Alveolar Bone Defect Model

Cleft alveolus, a common birth defect of the maxillary bone, affects one in 700 live births every year. This defect is traditionally restored by autogenous bone grafts or allografts, which may possibly cause complications. Cell-based therapies using the mesenchymal stem cells (MSCs) derived from human gingiva (gingiva-derived mesenchymal stem cells [GMSCs]) is attracting the research interest due to their highly proliferative and multilineage differentiation capacity. Undifferentiated GMSCs expressed high level of MSC-distinctive surface antigens, including CD73, CD105, CD90, and CD166. Importantly, GMSCs induced with osteogenic medium for a week increased the surface markers of osteogenic phenotypes, such as CD10, CD92, and CD140b, indicating their osteogenic potential. The objective of this study was to assess the bone regenerative efficacy of predifferentiated GMSCs (dGMSCs) toward an osteogenic lineage in combination with a self-assembling hydrogel scaffold PuraMatrix™ (PM) and/or bone morphogenetic protein 2 (BMP2), on a rodent model of maxillary alveolar bone defect. A critical size maxillary alveolar defect of 7 mm × 1 mm × 1 mm was surgically created in athymic nude rats. The defect was filled with either PM/BMP2 or PM/dGMSCs or the combination of three (PM/dGMSCs/BMP2) and the bone regeneration was evaluated at 4 and 8 weeks postsurgery. New bone formation was evaluated by microcomputed tomography and histology using Hematoxylin and Eosin staining. The results demonstrated the absence of spontaneous bone healing, either at 4 or 8 weeks postsurgery in the defect group. However, the PM/dGMSCs/BMP2 group showed significant enhancement in bone regeneration at 4 and 8 weeks postsurgery, compared with the transplantation of individual material/cells alone. Apart from developing the smallest critical size defect, results showed that PM/dGMSCs/BMP2 could serve as a promising option for the regeneration of bone in the cranio/maxillofacial region in humans.

Comparison of three surgical models of bone tissue defects in cleft palate in rabbits

OBJECTIVE

Cleft palate is one of the most common craniofacial birth defects in the maxillofacial region. There is an urgent need in tissue regeneration research to establish animal models that faithfully mimic human diseases. Here, we compared three surgical models of bone tissue defects in cleft palate in rabbits in order to screen for the biomaterials that induced optimal bone regeneration.

DESIGN

Rabbits were used to establish the models of hard palate cleft, alveolar cleft, and alveolar process cleft. Eight weeks following surgery, bone tissue self-healing capacity was estimated by macroscopic appearance and calculating the area of defective bone tissue. The dimensions of the upper jaw in left and right sides were measured at zero and eight weeks.

RESULTS

Bone defects in three types of cleft palate models were made at the positions of the hard palate, alveoli and alveolar process. After 8 weeks, when the hard palate was partially excised, it underwent self-healing. When the hard palate was completely excised, it underwent partial self-healing. However, in the models of alveolar cleft and alveolar process cleft, there was no significant self-healing in the bone tissues. The dimensions of the upper jaw in left and right sides were no significant differences in three types of cleft palate models.

CONCLUSIONS

Bone defects in the alveolar and alveolar process clefts exhibit a diminished capability for self-healing. This study may provide valuable information for the screening of materials that induce bone regeneration.

Application of Hydroxycholesterols for Alveolar Cleft Osteoplasty in a Rodent Model

BACKGROUND

Bone morphogenetic proteins (BMPs) have played a central role in the regenerative therapies for bone reconstruction, including alveolar cleft and craniofacial surgery. However, the high cost and significant adverse effect of BMPs limit their broad application. Hydroxycholesterols, naturally occurring products of cholesterol oxidation, are a promising alternative to BMPs. The authors studied the osteogenic capability of hydroxycholesterols on human mesenchymal stem cells and the impact of hydroxycholesterols on a rodent alveolar cleft model.

METHODS

Human mesenchymal stem cells were treated with control medium or osteogenic medium with or without hydroxycholesterols. Evaluation of cellular osteogenic activity was performed. A critical-size alveolar cleft was created and one of the following treatment options was assigned randomly to each defect: collagen sponge incorporated with hydroxycholesterols, BMP-2, or no treatment. Bone regeneration was assessed by means of radiologic and histologic analyses and local inflammation in the cleft evaluated. Moreover, the role of the hedgehog signaling pathway in hydroxycholesterol-mediated osteogenesis was examined.

RESULTS

All cellular osteogenic activities were significantly increased on human mesenchymal stem cells treated with hydroxycholesterols relative to others. The alveolar cleft treated with collagen sponge with hydroxycholesterols and BMP-2 demonstrated robust bone regeneration. The hydroxycholesterol group revealed histologically complete bridging of the alveolar defect with architecturally mature new bone. The inflammatory responses were less in the hydroxycholesterol group compared with the BMP-2 group. Induction of hydroxycholesterol-mediated in vitro osteogenesis and in vivo bone regeneration were attenuated by hedgehog signaling inhibitor, implicating involvement of the hedgehog signaling pathway.

CONCLUSION

Hydroxycholesterols may represent a viable alternative to BMP-2 in bone tissue engineering for alveolar cleft.

Biomaterials for Cleft Lip and Palate Regeneration

Craniofacial bone defect anomalies affect both soft and hard tissues and can be caused by trauma, bone recessions from tumors and cysts, or even from congenital disorders. On this note, cleft/lip palate is the most prevalent congenital craniofacial defect caused by disturbed embryonic development of soft and hard tissues around the oral cavity and face area, resulting in most cases, of severe limitations with chewing, swallowing, and talking as well as problems of insufficient space for teeth, proper breathing, and self-esteem problems as a consequence of facial appearance. Spectacular advances in regenerative medicine have arrived, giving new hope to patients that can benefit from new tissue engineering therapies based on the supportive action of 3D biomaterials together with the synergic action of osteo-inductive molecules and recruited stem cells that can be driven to the process of bone regeneration. However, few studies have focused on the application of tissue engineering to the regeneration of the cleft/lip and only a few have reported significant advances to offer real clinical solutions. This review provides an updated and deep analysis of the studies that have reported on the use of advanced biomaterials and cell therapies for the regeneration of cleft lip and palate regeneration.

Novel standardized massive bone defect model in rats employing an internal eight-hole stainless steel plate for bone tissue engineering

Massive bone defects are a challenge in orthopaedic research. Defective regeneration leads to bone atrophy, non-union of bone, and physical morbidity. Large animals are important models, however, production costs are high, nursing is complex, and evaluation methods are limited. A suitable laboratory animal model is required to explore the underlying molecular mechanism and cellular process of bone tissue engineering. We designed a stainless steel plate with 8 holes; the middle 2 holes were used as a guide to create a standardized critical size defect in the femur of anaesthetized rats. The plate was fixed to the bone using 6 screws, serving as an inner fixed bracket to secure a tricalcium phosphate implant seeded with green fluorescent protein-positive rat bone marrow mesenchymal stem cells within the defect. In some animals, we also grafted a vessel bundle into the lateral side of the implant, to promote vascularized bone tissue engineering. X-ray, microcomputed tomography, and histological analyses demonstrated the stainless steel plate resulted in a stable large segmental defect model in the rat femur. Vascularization significantly increased bone formation and implant degradation. Moreover, survival and expansion of green fluorescent protein-positive seeded cells could be clearly monitored in vivo at 1, 4, and 8 weeks postoperation via fluorescent microscopy. This standardized large segmental defect model in a small animal may help to advance the study of bone tissue engineering. Furthermore, availability of antibodies and genetically modified rats could help to dissect the precise cellular and molecular mechanisms of bone repair.

Bone regeneration using composite non-demineralized xenogenic dentin with beta-tricalcium phosphate in experimental alveolar cleft repair in a rabbit model

Background

Alveolar cleft repair is performed via bone grafting procedure to restore the dental arch continuity. A suitable bone substitute materials should possess osteoinductive and osteoconductive properties, to promote new bone formation, along with a slowly resorbable scaffold that is subsequently replaced with functionally viable bone. Calcium phosphate biomaterials have long proved their efficacy as bone replacement materials. Dentin in several forms has also demonstrated its possibility to be used as bone graft replacement material in several studies. The purpose of this study was to evaluate bone regeneration pattern and quantify bone formation after grafting pre-established experimental alveolar clefts defects model in rabbits using composite xenogenic dentin and β-TCP in comparison to β-TCP alone.

Methods

Unilateral alveolar cleft defects were created in 16 New Zealand rabbits according to previously described methodology. Alveolar clefts were allowed 8 weeks healing period. 8 defects were filled with β-TCP, whereas 8 defects filled with composite xenogenic dentin with β-TCP. Bone regeneration of the healed defects was compared at the 8 weeks after intervention. Quantification of bone formation was analyzed using micro-computed tomography (µCT) and histomorphometric analysis.

Results

µCT and histomorphometric analysis revealed that defects filled with composite dentin/β-TCP showed statistically higher bone volume fraction, bone mineral density and percentage residual graft volume when compared to β-TCP alone. An improved surgical handling of the composite dentin/β-TCP graft was also noted.

Conclusions

Composite xenogenic dentin/β-TCP putty expresses enhanced bone regeneration compared to β-TCP alone in the reconstruction of rabbit alveolar clefts defects.