Structural changes and biological responsiveness of an injectable and mouldable monetite bone graft generated by a facile synthetic method.

Brushite (dicalcium phosphate dihydrate) and monetite (dicalcium phosphate anhydrous) are of considerable interest in bone augmentation owing to their metastable nature in physiological fluids. The anhydrous form of brushite, namely monetite, has a finer microstructure with higher surface area, strength and bioresorbability, which does not transform to the poorly resorbable hydroxyapatite, thus making it a viable alternative for use as a scaffold for engineering of bone tissue. We recently reported the formation of monetite cements by a simple processing route without the need of hydrothermal treatment by using a high concentration of sodium chloride in the reaction mix of ß-tricalcium phosphate and monocalcium phosphate monohydrate. In this paper, we report the biological responsiveness of monetite formed by this method. The in vitro behaviour of monetite after interaction and ageing both in an acellular and cellular environment showed that the crystalline phase of monetite was retained over three weeks as evidenced from X-ray diffraction measurements. The crystal size and morphology also remained unaltered after ageing in different media. Human osteoblast cells seeded on monetite showed the ability of the cells to proliferate and express genes associated with osteoblast maturation and mineralization. Furthermore, the results showed that monetite could stimulate osteoblasts to undergo osteogenesis and accelerate osteoblast maturation earlier than cells cultured on hydroxyapatite scaffolds of similar porosity. Osteoblasts cultured on monetite cement also showed higher expression of osteocalcin, which is an indicator of the maturation stages of osteoblastogenesis and is associated with matrix mineralization and bone forming activity of osteoblasts. Thus, this new method of fabricating porous monetite can be safely used for generating three-dimensional bone graft constructs.

Stress analysis of different post-luting systems: a three-dimensional finite element analysis.

BACKGROUND: The longevity of endodontically treated teeth is usually determined by the adequacy of root canal treatments, coronal seal and favourable stress distribution within the remaining tooth tissues. The aim of this study was to investigate the influence of post material and luting cement on the biomechanics of endodontically treated teeth using three-dimensional finite element analysis (3-D FEA). METHODS: A 3 mm section of endodontically treated canine tooth was scanned and reconstructed for 3-D modelling and FE analyses. A metal post (MP) and a glass fibre post (GFP) were tested individually with four luting cements [zinc phosphate (ZPH), glass ionomer (GI), resin modified glass ionomer (RMGI) and resin based cements (RC)]. A push-out test was conducted by subjecting all models to 100 N perpendicular loading at the post. RESULTS: The maximum stresses generated along the MP-cement interface were significantly higher than corresponding stresses in the GFP-cement interface regardless of the cement type. GFP generated seven times higher stresses within the root dentine than metal posts when ZPH and GI were used, and three times higher when RMGI and RC were used. The displacement of GFP was double (50 µ) the displacement of MP (20 µ) in all groups. CONCLUSIONS: The low elastic modulus of GFP generated lower stresses along its interface and higher stresses within the root dentine, therefore the probability of debonding and root fracture in the GFP group was lower.

A novel method of forming micro- and macroporous monetite cements.

Second to autologous bone grafts are the calcium phosphate cements (CPCs) used as synthetic bone substitutes due to their chemical similarity to the mineral component of bone. Their ability to conform to complex bone defects and excellent osteoconductivity also render them excellent scaffolds for bone tissue engineering, although they do have their own limitations. Calcium phosphates can be divided into two main categories, namely apatite and brushite. Apatites exhibit low solubility, whereas, calcium phosphates that set to form brushite, are metastable, which degrade rapidly, but do subsequently form hydroxyapatite that retards the rate. In contrast dicalcium phosphate anhydrous (monetite) has a higher solubility than octacalcium phosphate and does not transform to an apatite; thus, it is able to continue to degrade with time. Herein, a new method was used via the addition of sodium chloride to ß-tricalcium phosphate and monocalcium phosphate monohydrate to form micro- and macroporous monetite (DCPA). The X-ray diffraction and FTIR spectra confirmed the formation of monetite in the presence of both, 6.2 M NaCl solution or 60% of solid sodium chloride. The maximum compressive strength (σc = 12.3 ± 1.8 MPa) and the Young's modulus (E = 1.0 ± 0.1 GPa) of the monetite cements obtained were comparable to the upper limits of the values reported for cancellous bone and also higher than that reported by other routes used to form monetite. The porous cements analysed by microCT revealed an interconnected porosity with the preliminary in vitro biological evaluation indicating favourable osteoblast cell attachment and growth.

The impact of fractured endodontic file removal on vertical root fracture resistance: three-dimensional finite element analysis.

This study investigated by means of finite element analysis the influence of fractured file removal on root fracture resistance in an endodontically-treated canine. A 4mm fragment of an endodontic file was deliberately fractured in the apical third of an upper canine root and removed by ultrasonic tips. Micro-computed tomography scans were carried out before and after fractured file removal on the same tooth. Two 3D-FE models (before and after file removal) were subjected to 100N loading. Results indicate that the fractured file removal increased von Mises stresses by 55%. Peak stresses were located around the root filling/dentine interface prior to file removal. Following file removal, peak stresses were concentrated at the buccal root surface/bone interface that might initiate vertical root fracture buccolingually.

A comparison of 2D and 3D finite element analysis of a restored tooth.

The finite element method is widely used in dental research. The decision to use two-dimensional (2D) or three-dimensional (3D) modelling is dependent on many interrelated factors. The purpose of the present study was to compare and contrast 2D and 3D finite element analysis (FEA) in investigating the mechanical behaviour of a maxillary premolar restored with a full crown under similar conditions of axial and lateral occlusal loading. The 2D analysis required modelling both a buccolingual and mesiodistal section of the restored premolar and for comparison sections of a 3D model were examined. Differences in the results for displacement and maximum principal stress distribution within the component structures and interfaces of the 2D and 3D models were, in general, attributable to differences in geometry represented in the models. Maximum principal stresses tended to be greater under lateral rather than axial occlusal loading. It was concluded that 2D FEA may find application in investigating key aspects of the mechanical behaviour of a dental restoration in a single tooth unit, but that in certain situations combinations of 2D and 3D FEA may offer the best understanding of the biomechanical behaviour of complex dental structures. Sophisticated FE models are required to better understand the mechanical behaviour of restored tooth units.

Finite element analysis of fixed partial denture replacement.

The purpose of this study was to investigate, by means of the finite element method the mechanical behaviour of three designs of fixed partial denture (FPD) for the replacement of the maxillary first premolar in shortened dental arch therapy. Two-dimensional, linear, static finite element analyses were carried out to investigate the biomechanics of the FPDs and their supporting structures under different scenarios of occlusal loading. Displacement and stress distribution for each design of FPD were examined, with particular attention being paid to the stress variations along the retainer-abutment--and the periodontal ligament-bone interfaces. The results indicated that displacement and maximum principal stresses in the fixed-fixed, three-unit FPD were substantially less than those in the two-unit cantilever FPDs. Of the two cantilever FPDs investigated, the distal cantilever design was found to suffer less displacement and stresses than the mesial cantilever design under similar conditions of loading. The highest values for maximum principal stress in the cantilever FPDs were found within the connector between the pontic and the retainer, and within the periodontal ligament and adjacent bone on the aspect of the retainer away from the pontic.

Biomechanics of cantilever fixed partial dentures in shortened dental arch therapy.

PURPOSE: The purpose of the present study was to investigate, by means of 3-dimensional finite element analysis, aspects of the biomechanics of cantilever fixed partial dentures replacing the maxillary canine in shortened dental arch therapy. The null hypothesis was that no differences would be identified by finite element analysis in the mechanical behavior of the 2 designs of cantilever fixed partial denture under different scenarios of occlusal loading. MATERIALS AND METHODS: Single- and double-abutted cantilever fixed partial dentures were modeled and analyzed using the finite element packages PATRAN and ABAQUS. Displacement and maximum principal stresses (magnitude and location) within the fixed partial dentures, supporting structures, and the periodontal ligament/bone and abutment/retainer interfaces were examined under 20 different scenarios of axial and lateral occlusal loading. RESULTS: The results indicate that more displacement occurred in the 2 rather than the 3-unit cantilever fixed partial denture, with the greatest displacement having occurred under lateral loading. The maximum principal stresses observed in the periodontal ligament/bone interfaces were greatest buccocervically, with the highest value being observed in the 2-unit fixed partial denture under lateral loading. The highest maximum principal stresses observed in the retainer/abutment interfaces were located cervically in relation to the distal margin of the retainer of the 2-unit fixed partial denture under axial loading. CONCLUSIONS: It was concluded that in adopting a cantilever fixed partial denture approach for the replacement of a missing maxillary canine in shortened dental arch therapy, there may be merits, in terms of mechanical behavior, in selecting a double-rather than a single-abutment design. Furthermore, prostheses' displacement and functional stresses may be minimized by reducing lateral loading and avoiding pontic only loading.