Sinus Floor Augmentation Comparing an In Situ Hardening Biphasic Calcium Phosphate (Hydroxyapatite/β-Tricalcium Phosphate) Bone Graft Substitute with a Particulate Biphasic Calcium Phosphate (Hydroxyapatite/β-Tricalcium Phosphate) Bone Graft Substitute: An Experimental Study in Sheep

Comparison of Particulate, Block and Putty Forms of β-tricalcium Phosphate-Based Synthetic Bone Grafts on Rat Calvarium Model

Purpose

Bone augmentation is a necessity for atrophied alveolar ridge prior to dental implant placement. Various bone graft types and forms with different characteristics are available in the market for alveolar augmentation. Beta tricalcium phosphate (β-TCP) is a synthetic biomaterial known as the oldest type of calcium phosphate. Studies comparing particulate, block or putty grafts are very limited. The aim of this study was to compare the particulate, block and putty forms of the same β-TCP bone graft and analyze the efficiency in critical size calvarium defects.

Material and Methods

Twenty male Wistar-Albino rats were employed for the study. Four bicortical bone defects with 5 mm diameter were created on each rat calvarium, and three defects were filled with particulate, block or putty β-TCP graft and one defect was left empty. The animals were killed after 8 weeks. New bone formation, residual graft, loose connective tissue, condensed mesenchyme, alkaline phosphatase, proliferating cell nuclear antigen, osteocalcin were measured on the specimens.

Results

Compared to block and putty forms, significantly higher new bone formation and least residual graft were observed in the particulate graft group. The residual graft was significantly higher in the block graft group than both the particulate and the putty groups. The cellular immunoreactivity of the samples in the particulate graft group was significantly higher. There was no significant difference between putty and block graft groups.

Conclusion

Bone regeneration is significantly affected by the form of β-TCP bone graft, and the particulate form was the most successful in our study.

Development of a new critical size defect model in the paranasal sinus and first approach for defect reconstruction-An in vivo maxillary bone defect study in sheep

Fractures of the paranasal sinuses often require surgical intervention. Persisting bone defects lead to permanent visible deformities of the facial contours. Bone substitutes for reconstruction of defects with simultaneous induction of new bone formation are not commercially available for the paranasal sinus. New materials are urgently needed and have to be tested in their future area of application. For this purpose critical size defect models for the paranasal sinus have to be developed. A ≥2.4 cm large bilateral circular defect was created in the anterior wall of the maxillary sinus in six sheep via an extraoral approach. The defect was filled with two types of an osteoconductive titanium scaffold (empty scaffold vs. scaffold filled with a calcium phosphate bone cement paste) or covered with a titanium mesh either. Sheep were euthanized after four months. All animals performed well, no postoperative complications occured. Meshes and scaffolds were safely covered with soft tissue at the end of the study. The initial defect size of ≥2.4 cm only shrunk minimally during the investigation period confirming a critical size defect. No ingrowth of bone into any of the scaffolds was observed. The anterior wall of the maxillary sinus is a region with low complication rate for performing critical size defect experiments in sheep. We recommend this region for experiments with future scaffold materials whose intended use is not only limited to the paranasal sinus, as the defect is challenging even for bone graft substitutes with proven osteoconductivity. Graphical abstract.

A fully ingrowing implant for cranial reconstruction: Results in critical size defects in sheep using 3D-printed titanium scaffold

Current alloplastic materials such as PMMA, titanium or PEEK don't show relevant bone ingrowth into the implant when used for cranioplasty, ceramic implants have the drawback being brittle. New materials and implant designs are urgently needed being biocompatible, stable enough for cranioplasty and stimulating bone formation. In an in vivo critical size sheep model circular cranial defects (>2.4 cm) were covered with three different types of a 3D-printed porous titanium scaffolds with multidirectional, stochastically distributed architecture (uncoated scaffold, hydroxyapatite-coated scaffold, uncoated scaffold filled with a calcium phosphate bone cement paste containing β-TCP granules). An empty titanium mesh served as control. Among the different investigated setups the hydroxyapatite-coated scaffolds showed a surprisingly favourable performance. Push-out tests revealed a 2.9 fold higher force needed in the hydroxyapatite-coated scaffolds compared to the mesh group. Mean CT density at five different points inside the scaffold was 2385HU in the hydroxyapatite-coated group compared to 1978HU in the uncoated scaffold at nine months. Average lateral bone ingrowth after four months in the hydroxyapatite-coated scaffold group was up to the implant center, 12.1 mm on average, compared to 2.8 mm in the control group covered with mesh only. These properties make the investigated scaffold with multidirectional, stochastically distributed structure superior to all products currently on the market. The study gives a good idea of what future materials for cranioplasty might look like.

Stiffness Regulates the Morphology, Adhesion, Proliferation, and Osteogenic Differentiation of Maxillary Schneiderian Sinus Membrane-Derived Stem Cells

Recent studies, which aim to optimize maxillary sinus augmentation, have paid significant attention exploring osteogenic potential of maxillary Schneiderian sinus membrane-derived cells (MSSM-derived cells). However, it remains unclear that how MSSM-derived cells could respond to niche's biomechanical properties. Herein, this study investigated the possible effects of substrate stiffness on rMSSM-derived stem cell fate. Initially, rMSSM-derived stem cells with multiple differentiation potential were successfully obtained. We then fabricated polyacrylamide substrates with varied stiffness ranging from 13 to 68 kPa to modulate the mechanical environment of rMSSM-derived stem cells. A larger cell spreading area and increased proliferation of rMSSM-derived stem cells were found on the stiffer substrates. Similarly, cells became more adhesive as their stiffness increased. Furthermore, the higher stiffness facilitated osteogenic differentiation of rMSSM-derived stem cells. Overall, our results indicated that increase in stiffness could mediate behaviors of rMSSM-derived stem cells, which may serve as a guide in future research to design novel biomaterials for maxillary sinus augmentation.

Evaluation of Poly Lactic-co-Glycolic Acid-Coated β-Tricalcium Phosphate Bone Substitute as a Graft Material for Ridge Preservation after Tooth Extraction in Dog Mandible: A Comparative Study with Conventional β-Tricalcium Phosphate Granules

This study aims to evaluate the safety and efficacy of a poly lactic-co-glycolic acid (PLGA)-coated β-tricalcium phosphate (β-TCP) with N-methyl-2-pyrrolidone (NMP) liquid activator (PLGA/β-TCP) on alveolar ridge preservation after tooth extraction in dog mandible. Thirty-two extraction sites were prepared in eight dog mandibles. A distal root of the mandibular premolar was extracted and randomly grafted with one of the following bone substitutes: (1) PLGA/β-TCP, (2) β-TCP, or (3) left empty as a control, and wounds were closed with keratinized mucosa graft. Post-operative wound healing was observed and scored to evaluate safety. After 12 and 24 weeks, the bone regeneration was evaluated with micro-computed tomography (CT) images and histomorphometric analyses. Gingival epithelization progressed over time without complication or infection. Micro-CT images and histological observation revealed that both PLGA/β-TCP and β-TCP granules supported sufficient new bone formation. Although bone formation and substrate resorption were delayed slightly with the PLGA and the NMP-containing plasticizer as compared to those treated with conventional β-TCP, it can be concluded that the PLGA and the NMP-containing plasticizer that facilitated the in situ hardening properties of the material had no negative influence on the biocompatibility of the material.

Sinus floor elevation using particulate PLGA-coated biphasic calcium phosphate bone graft substitutes: A prospective histological and radiological study

BACKGROUND

Poly (lactic-co-glycolic acid) (PLGA) is widely used for the development of delivery systems for drugs and therapeutic biomolecules in tissue engineering applications. Particles of biphasic calcium phosphate can be covered by PLGA to change their manipulating characteristics.

PURPOSE

Aim of this study was to investigate the radiological and histomorphometric results of the use of PLGA-coated biphasic calcium phosphate granules in sinus floor elevation and to analyze the underlying molecular processes by immunohistochemical staining.

MATERIALS AND METHODS

A randomized clinical study was designed to include patients in need of sinus floor elevation. Patients were assigned to receive either PLGA-coated biphasic calcium phosphate particles (group I) or the equivalent but noncoated particles (group II). Cone beam computed tomography (CBCT) scans were performed before and 6 months after the procedure to assess the bone height gain. At the time of implant placement, bone core biopsies were obtained at the site of implant placement. Histological sections were subjected to histomorphometric and immunohistochemical evaluation of differentiation markers (Musashi-1 [MSI1]).

RESULTS

No statistically significant differences were observed between groups for the radiologic parameters. No differences were observed histologically or histomorphometrically. However, PLGA-coated particles (group I) were more colonized by MSI1-positive osteoblast precursors (P = 0.0001, chi-squared test) and were penetrated by more CD34-positive vascular structures (P = 0.001, chi-squared test) than noncoated particles (group II).

CONCLUSIONS

PLGA-coated particles are associated with more MSI11-positive cells and more extensive microvascularization than noncoated particles.

Natural Course of Local Bone Mineralization After Treatment of Benign or Borderline Bone Tumors and Cysts With a Composite Ceramic Bone Graft Substitute

After surgical bone tumor removal, filling of the bone defect is frequently performed using a bone graft or bone graft substitute. During follow-up, precise quantification of changes in bone mineral density, within the treated bone defect, is very difficult using conventional X-ray examinations. The objectives of this study were to characterize the pattern of resorption/biodegradation of a composite calcium sulfate/hydroxyapatite bone graft substitute and to quantify the bone defect healing with repeated dual-energy X-ray absorptiometry (DXA) measurements. Seventeen patients treated for 18 benign bone lesions, with subsequent defect filling using 2 variants of a composite ceramic bone graft substitute (CERAMENT™|BONE VOID FILLER or CERMAMENT™|G, BONESUPPORT AB, Lund, Sweden), were scanned postoperatively and after 2, 6, 12, 26, and 52 wk using DXA. After an initial increase in bone mineral density after implantation of the bone graft substitute, bone mineral density decreased in the bone defect region throughout the 52 wk: rapidly in the first 12 wk and slower in the remaining weeks. Despite this continuous decrease, bone mineral density remained, on average, 25% higher in the operated extremity, compared with the nonoperated extremity, after 52 wk. The observed pattern of reduction in bone mineral density is consistent with the anticipated resorption of calcium sulfate within the bone graft substitute during the first 12 wk after surgery. We believe the DXA technique provides a precise method for quantification of bone graft resorption, but for evaluation of new bone formation, 3-dimensional imaging is needed.