Marginal Fit, Mechanical Properties, and Esthetic Outcomes of CAD/CAM Interim Fixed Dental Prostheses (FDPs): A Systematic Review.

This systematic review aimed to study the outcomes of CAD-CAM (milled and 3D-printed) interim dental prostheses when compared to conventional ones. The focused question of "In natural teeth, what are the outcomes of CAD-CAM interim FDPs compared to the conventionally-manufactured ones regarding marginal fit, mechanical properties, esthetics, and color stability" was formulated. The systematic search was conducted electronically in the PubMed/MEDLINE, CENTRAL, EMBASE, Web of Science, New York Academy of Medicine Grey Literature Report, and Google Scholar databases by using the MeSH keywords and keywords associated with the focused question and limiting articles to those published between 2000 and 2022. A manual search was conducted in selected dental journals. The results were analyzed qualitatively and are presented in table format. Of the included studies, 18 studies were in vitro and 1 was a randomized clinical trial. Of the eight studies analyzing the mechanical properties, five studies favored the milled interim restorations, one study favored both 3D-printed and milled interim restorations, and two studies reported better mechanical properties in conventional interim restorations. Among four studies evaluating the marginal discrepancies, two studies favored the marginal fit in milled interim restorations, one study reported a better marginal fit in both milled and 3D-printed interim restorations, and one study found conventional interim restorations have a better marginal fit and smaller marginal discrepancy when compared to both milled and 3D-printed restorations. Among five studies that evaluated both the mechanical properties and marginal fit, 1 study favored 3D-printed interim restorations and four studies favored milled interim restorations over the conventional ones. Two studies analyzing the esthetics outcomes demonstrated better results with milled interim restorations compared to conventional and 3D-printed interim restorations in terms of their color stabilities. The risk of bias was low for all the studies reviewed. The high level of heterogeneity within the studies excluded meta-analysis. Most of the studies favored the milled interim restorations over the 3D-printed and conventional restorations. The results suggested that milled interim restorations offer a better marginal fit, higher mechanical properties, and better esthetic outcomes in terms of color stabilities.

Validation of the modified radiographic union score for tibia fractures (mRUST) in murine femoral fractures.

Bony union is a primary predictor of outcome after surgical fixation of long bone fractures. Murine models offer many advantages in assessing bony healing due to their low costs and small size. However, current fracture recovery investigations in mice frequently rely on animal sacrifice and costly analyses. The modified Radiographic Union Score for Tibia fractures (mRUST) scoring system is a validated metric for evaluating bony healing in humans utilizing plain radiographs, which are relatively inexpensive and do not require animal sacrifice. However, its use has not been well established in murine models. The aim of this study was to characterize the longitudinal course of mRUST and compare mRUST to other conventional murine fracture analyses. 158 mice underwent surgically created midshaft femur fractures. Mice were evaluated after fracture creation and at 7, 10, 14, 17, 21, 24, 28, 35, and 42 days post-injury. mRUST scoring of plain radiographs was performed by three orthopaedic surgeons in a randomized, blinded fashion. Interrater correlations were calculated. Micro-computed tomography (µCT) was analyzed for tissue mineral density (TMD), total callus volume (TV), bone volume (BV), trabecular thickness, trabecular number, and trabecular separation. Histomorphometry measures of total callus area, cartilage area, fibrous tissue area, and bone area were performed in a blinded fashion. Ultimate torque, stiffness, toughness, and twist to failure were calculated from torque-twist curves. A sigmoidal log-logistic curve fit was generated for mRUST scores over time which shows mRUST scores of 4 to 6 at 7 days post-injury that improve to plateaus of 14 to 16 by 24 days post-injury. mRUST interrater correlations at each timepoint ranged from 0.51 to 0.86, indicating substantial agreement. mRUST scores correlated well with biomechanical, histomorphometry, and µCT parameters, such as ultimate torque (r=0.46, p<0.0001), manual stiffness (r=0.51, p<0.0001), bone percentage based on histomorphometry (r=0.86, p<0.0001), cartilage percentage (r=-0.87, p<0.0001), tissue mineral density (r=0.83, p<0.0001), BV/TV based on µCT (r=0.65, p<0.0001), and trabecular thickness (r=0.78, p<0.0001), among others. These data demonstrate that mRUST is reliable, trends temporally, and correlates to standard measures of murine fracture healing. Compared to other measures, mRUST is more cost-effective and non-terminal. The mRUST log-logistic curve could be used to characterize differences in fracture healing trajectory between experimental groups, enabling high-throughput analysis.

Effect of hydrogel-based antibiotic intracanal medicaments on crown discoloration.

OBJECTIVES: This study evaluated the effects of low and moderate concentrations of triple antibiotic paste (TAP) and double antibiotic paste (DAP) loaded into a hydrogel system on crown discoloration and explored whether application of an adhesive bonding agent prevented crown discoloration. MATERIALS AND METHODS: Intact human molars (n = 160) were horizontally sectioned 1 mm apical to the cementoenamel junction. The crowns were randomized into 8 experimental groups (calcium hydroxide, Ca[OH]2; 1, 10, and 1,000 mg/mL TAP and DAP; and no medicament. The pulp chambers in half of the samples were coated with an adhesive bonding agent before receiving the intracanal medicament. Color changes (ΔE) were detected by spectrophotometry after 1 day, 1 week, and 4 weeks, and after 5,000 thermal cycles, with ΔE = 3.7 as a perceptible threshold. The 1-sample t-test was used to determine the significance of color changes relative to 3.7. Analysis of variance was used to evaluate the effects of treatment, adhesive, and time on color change, and the level of significance was p < 0.05. RESULTS: Ca(OH)2 and 1 and 10 mg/mL DAP did not cause clinically perceivable tooth discoloration. Adhesive agent use significantly decreased tooth discoloration in the 1,000 mg/mL TAP group up to 4 weeks. However, adhesive use did not significantly improve coronal discoloration after thermocycling when 1,000 mg/mL TAP was used. CONCLUSIONS: Ca(OH)2 and 1 and 10 mg/mL DAP showed no clinical discoloration. Using an adhesive significantly improved coronal discoloration up to 4 weeks with 1,000 mg/mL TAP.

Internal Fixation Construct and Defect Size Affect Healing of a Translational Porcine Diaphyseal Tibial Segmental Bone Defect.

BACKGROUND AND OBJECTIVE: Porcine translational models have become the gold-standard translational tool to study the effects of major injury and hemorrhagic shock because of their similarity to the human immunologic response to trauma. Segmental bone defects (SBDs) typically occur in warfighters with associated severe limb trauma. The purpose of this study was to develop a translational porcine diaphyseal SBD model in Yucatan minipigs (YMPs), which could be used in bone healing investigations that simulate injury-relevant conditions. We were specifically working toward developing a critical sized defect (CSD). METHODS: We used an adaptive experimental design in which both 25.0 mm and 40.0 mm SBDs were created in the tibial mid-diaphysis in skeletally mature YMPs. Initially, eight YMPs were subjected to a 25.0 mm SBD and treated with intramedullary nailing (intramedullary nail [IMN] 25mm). Due to unanticipated wound problems, we subsequently treated four specimens with identical 25.0 mm defect with dual plating (open reduction with internal fixation [ORIF] 25mm). Finally, a third group of four YMPs with 40.0 mm defects were treated with dual plating (ORIF 40mm). Monthly radiographs were made until sacrifice. Modified Radiographic Union Score for Tibia fractures (mRUST) measurements were made by three trauma-trained orthopedic surgeons. CT scans of the tibias were used to verify the union results. RESULTS: At 4 months post-surgery, mean mRUST scores were 11.7 (SD ± 1.8) in the ORIF 25mm YMPs vs. 8.5 (SD ± 1.4) in the IMN 25mm YMPs (P < .0001). All four ORIF 25mm YMPs were clinically healed. In contrast, none of the IMN 25mm YMPs were clinically healed and seven of eight IMN 25mm YMPs developed delayed wound breakdown. All four of the ORIF 40mm YMPs had flail nonunions with complete hardware failure by 3 months after surgery and were sacrificed early. CT scanning confirmed that none of the IMN 25mm YMPs, none of the ORIF 40mm YMPs, and two of four ORIF 25mm YMPs were healed. A third ORIF 25mm specimen was nearly healed on CT scanning. Inter-rater and intra-rater reliability interclass coefficients using the mRUST scale were 0.81 and 0.80, respectively. CONCLUSIONS: YMPs that had a 40 mm segment of bone removed from their tibia and were treated with dual plating did not heal and could be used to investigate interventions that accelerate bone healing. In contrast, a 25 mm SBD treated with dual plating demonstrated delayed but successful healing, indicating it can potentially be used to investigate bone healing adjuncts or conversely how concomitant injuries may impair bone healing. Pigs treated with IMN failed to heal and developed consistent delayed wound breakdown presumably secondary to chronic limb instability. The porcine YMP SBD model has the potential to be an effective translational tool to investigate bone healing under physiologically relevant injury conditions.

Effect of Hydrogel-Based Antibiotic Intracanal Medicaments on Push-Out Bond Strength.

OBJECTIVE: This study aimed to evaluate the effects of typical clinical concentration (1,000 mg/mL), low concentration (1 mg/mL) triple antibiotic pastes (TAP), and double antibiotic pastes (DAP) on the bond strength between various root cements and radicular dentin. MATERIALS AND METHODS: Intact single-rooted human teeth (n = 144) were horizontally decoronated and canals instrumented. The roots were treated for 4 weeks with Ca(OH)2, 1,000 mg/mL of TAP or DAP, and 1 mg/mL of TAP or DAP. Untreated roots served as a control. After treatment, the medicaments were irrigated and each group was divided into three subgroups receiving MTA, Biodentine, or Endosequence putty cement. After 2 weeks, coronal and middle root cylinders were obtained from each root. Push-out bond strength test and failure analysis were performed for all root cylinders. STATISTICAL ANALYSIS: Three-way ANOVA, pairwise comparisons and logistic regression were used for statistical analyses. A significance level of 5% was used. RESULTS: For MTA applied in the coronal part of the roots, 1 mg/mL DAP and TAP and Ca(OH)2 demonstrated significantly higher bond strength compared with the typical clinical concentration and the control groups. For Biodentine applied coronally in the roots, 1 mg/mL of DAP resulted in significantly higher bond strength than all other groups. For Endosequence putty cement applied coronally in the roots, 1 mg/mL of DAP offered significantly higher bond strength than all groups except for Ca(OH)2. CONCLUSION: The use of 1 mg/mL DAP resulted in significantly higher push-out bond strength compared with the typical clinical concentration of TAP and DAP regardless of the type of the root cement used.

Scaffold-free bioprinting of mesenchymal stem cells using the Regenova printer: Spheroid characterization and osteogenic differentiation.

Limitations in scaffold material properties, such as sub-optimal degradation time, highlight the need for alternative approaches to engineer de novo tissues. One emerging solution for fabricating tissue constructs is scaffold-free tissue engineering. To facilitate this approach, three-dimensional (3D) bioprinting technology (Regenova Bio 3D Printer) has been developed to construct complex geometric shapes from discrete cellular spheroids without exogenous scaffolds. Optimizing spheroid fabrication and characterizing cellular behavior in the spheroid environment are important first steps prior to printing larger constructs. Here, we characterized spheroids of immortalized mouse bone marrow stromal cells (BMSCs) that were differentiated to the osteogenic lineage. Immortalized BMSCs were seeded in low attachment 96-well plates in various numbers to generate self-aggregated spheroids either under the force of gravity or centrifugation. Cells were cultured in control or osteogenic media for up to 28 days. Spheroid diameter, roundness and smoothness were measured. Cell viability, DNA content and alkaline phosphatase activity were assessed at multiple time points. Additionally, expression of osteogenic markers was determined using real time qPCR. Spheroids formed under gravity with 20 K, 30 K and 40 K cells had average diameters of 498.5 ± 8.3 µm, 580.0 ± 32.9 µm and 639.2 ± 54.0 µm, respectively, while those formed under 300G centrifugation with the same numbers of cells had average diameters of 362.3 ± 3.5 µm, 433.1 ± 6.4 µm and 491.2 ± 8.0 µm. Spheroids formed via centrifugation were superior to those formed by gravity, as evidenced by better roundness and smoothness and double the retention of DNA (cellular) content. Cells in spheroids exhibited a robust osteogenic response to the differentiation medium, including higher mRNA expression of alkaline phosphatase, collagen type I, and osteocalcin than those cultured in control medium, as well as greater alkaline phosphatase activity. The optimal spheroid fabrication technique from this study was to aggregate 40K cells under 150-300G centrifugation. In future investigations, these spheroids will be 3D printed into larger tissue constructs.

Scaffold-free Bioprinting of Mesenchymal Stem Cells with the Regenova Printer: Optimization of Printing Parameters.

The Kenzan bioprinting method provides a high-resolution biofabrication process by facilitating the fusion of submillimeter cell aggregates (spheroids) into larger tissue constructs on a needle array that is removed upon spheroid fusion. Although the method is relatively straightforward in principle, Kenzan method bioprinting relies on a complex 3D bioprinter (Regenova Bio 3D Printer, Cyfuse, K.K., Japan) implementing an advanced vision system to verify the microscopic spheroids' geometry and high-precision mechatronics to aseptically manipulate the spheroids into position. Due to the complexity of the operation, the need for aseptic conditions, and the size of the spheroids, proficiency with the Regenova Bio 3D Printer and the Kenzan method requires development of best practices and troubleshooting techniques to ensure a robust print and minimize the use of resources. In addition, managing the construct post-bioprinting both in culture and for surgical implantation requires careful consideration and workflow design. Here, we describe methods for generating a competent tissue construct and optimizing the bioprinting process. Optimization resulted in a 4-fold reduction in print times, a 20-fold reduction in the use of bioprinting nozzles, and more robust constructs. The results and procedures described herein will have potential applications for tissue engineering, research, and clinical uses in the future.

A Pyk2 inhibitor incorporated into a PEGDA-gelatin hydrogel promotes osteoblast activity and mineral deposition.

Pyk2 is a non-receptor tyrosine kinase that belongs to the family of focal adhesion kinases. Studies from our laboratory and others demonstrated that mice lacking the Pyk2 gene (Ptk2B) have high bone mass, which was due to increased osteoblast activity, as well as decreased osteoclast activity. It was previously reported that a chemical inhibitor that targets both Pyk2 and its homolog FAK, led to increased bone formation in ovariectomized rats. In the current study, we developed a hydrogel containing poly(ethylene glycol) diacrylate (PEGDA) and gelatin which was curable by visible-light and was suitable for the delivery of small molecules, including a Pyk2-targeted chemical inhibitor. We characterized several critical properties of the hydrogel, including viscosity, gelation time, swelling, degradation, and drug release behavior. We found that a hydrogel composed of PEGDA1000 plus 10% gelatin (P1000:G10) exhibited Bingham fluid behavior that can resist free flowing before in situ polymerization, making it suitable for use as an injectable carrier in open wound applications. The P1000:G10 hydrogel was cytocompatible and displayed a more delayed drug release behavior than other hydrogels we tested. Importantly, the Pyk2-inhibitor-hydrogel retained its inhibitory activity against the Pyk2 tyrosine kinase, and promoted osteoblast activity and mineral deposition in vitro. Overall, our findings suggest that a Pyk2-inhibitor based hydrogel may be suitable for the treatment of craniofacial and appendicular skeletal defects and targeted bone regeneration.

Should Live Patient Licensing Examinations in Dentistry Be Discontinued? Two Viewpoints: Viewpoint 1: Alternative Assessment Models Are Not Yet Viable Replacements for Live Patients in Clinical Licensure Exams and Viewpoint 2: Ethical and Patient Care Concerns About Live Patient Exams Require Full Acceptance of Justifiable Alternatives.

This Point/Counterpoint article addresses a long-standing but still-unresolved debate on the advantages and disadvantages of using live patients in dental licensure exams. Two contrasting viewpoints are presented. Viewpoint 1 supports the traditional use of live patients, arguing that other assessment models have not yet been demonstrated to be viable alternatives to the actual treatment of patients in the clinical licensure process. This viewpoint also contends that the use of live patients and inherent variances in live patient treatment represent the realities of daily private practice. Viewpoint 2 argues that the use of live patients in licensure exams needs to be discontinued considering those exams' ethical dilemmas of exposing patients to potential harm, as well as their lack of reliability and validity and limited scope. According to this viewpoint, the current presence of viable alternatives means that the risk of harm inherent in live patient exams can finally be eliminated and those exams replaced with other means to confirm that candidates are qualified for licensure to practice.

The effects of 3D bioactive glass scaffolds and BMP-2 on bone formation in rat femoral critical size defects and adjacent bones.

Reconstruction of critical size defects in the load-bearing area has long been a challenge in orthopaedics. In the past, we have demonstrated the feasibility of using a biodegradable load-sharing scaffold fabricated from poly(propylene fumarate)/tricalcium phosphate (PPF/TCP) loaded with bone morphogenetic protein-2 (BMP-2) to successfully induce healing in those defects. However, there is limited osteoconduction observed with the PPF/TCP scaffold itself. For this reason, 13-93 bioactive glass scaffolds with local BMP-2 delivery were investigated in this study for inducing segmental defect repairs in a load-bearing region. Furthermore, a recent review on BMP-2 revealed greater risks in radiculitis, ectopic bone formation, osteolysis and poor global outcome in association with the use of BMP-2 for spinal fusion. We also evaluated the potential side effects of locally delivered BMP-2 on the structures of adjacent bones. Therefore, cylindrical 13-93 glass scaffolds were fabricated by indirect selective laser sintering with side holes on the cylinder filled with dicalcium phosphate dehydrate as a BMP-2 carrier. The scaffolds were implanted into critical size defects created in rat femurs with and without 10 µg of BMP-2. The x-ray and micro-CT results showed that a bridging callus was found as soon as three weeks and progressed gradually in the BMP group while minimal bone formation was observed in the control group. Degradation of the scaffolds was noted in both groups. Stiffness, peak load and energy to break of the BMP group were all higher than the control group. There was no statistical difference in bone mineral density, bone area and bone mineral content in the tibiae and contralateral femurs of the control and BMP groups. In conclusion, a 13-93 bioactive glass scaffold with local BMP-2 delivery has been demonstrated for its potential application in treating large bone defects.

The impact of hydrofluoric acid etching followed by unfilled resin on the biaxial strength of a glass-ceramic.

OBJECTIVES: To evaluate the null hypotheses that hydrofluoric (HF) acid etching time would neither decrease the biaxial flexural strength of a glass-based veneering ceramic nor enhance it after silane and unfilled resin (UR) applications. METHODS: Disc-shaped IPS e.max ZirPress specimens were allocated into 12 groups: G1-control (no-etching), G2-30 s, G3-60 s, G4-90 s, G5-120 s, G6-60 s+60 s. Groups (G7-G12) were treated in the same fashion as G1-G6, but followed by silane and UR applications. Surface morphology and roughness (Ra and Rq) of the ceramics were assessed by means of scanning electron microscopy (SEM) and profilometry, respectively. Flexural strength was determined by biaxial testing. Data were analyzed by two-way ANOVA and the Sidak test (α=0.05). Weibull statistics were estimated and finite element analysis (FEA) was carried out to verify the stress concentration end areas of fracture. RESULTS: The interaction (etching time vs. surface treatment) was significant for Ra (p=0.008) and Rq (0.0075). Resin-treated groups presented significantly lower Ra and Rq than non-treated groups, except for the 60s group (p<0.005). SEM revealed that etching affected the ceramic microstructure and that the UR was able to penetrate into the irregularities. A significant effect of etching time (p=0.029) on flexural strength was seen. G7-G12 presented higher strength than G1-G6 (p<0.0001). None of experimental groups failed to show 95% confidence intervals of σ0 and m overlapped. FEA showed lower stress concentration after resin treatment. SIGNIFICANCE: HF acid etching time did not show a damaging effect on the ceramic flexural strength. Moreover, the flexural strength could be enhanced after UR treatment.

Effects of DCPD cement chemistry on degradation properties and cytocompatibility: comparison of MCPM/ß-TCP and MCPM/HA formulations.

Dicalcium phosphate dihydrate (DCPD) cements are attractive biomaterials for bone repair, and a number of different DCPD cement formulations have been proposed in the literature. In this study, we have specifically compared monocalcium phosphate monohydrate (MCPM)/hydroxyapatite (HA) and MCPM/ß-tricalcium phosphate (ß-TCP) formulations to test the hypothesis that DCPD cement chemistry affects the degradation properties and cytocompatibility of the cement. Using simple in vitro models we found that MCPM/ß-TCP formulations degraded primarily by DCPD dissolution, which was associated with a slight pH drop and relatively low mass loss. Cytocompatibility testing of cement conditioned culture media revealed no significant change in cell viability relative to the negative control for all of the MCPM/ß-TCP formulations. In contrast, the MCPM/HA formulations were prone to undergo rapid conversion of DCPD to HA, resulting in a sharp pH drop and extensive mass loss. A stoichiometric excess of HA in the cement was found to accelerate the conversion process, and significant cytotoxicity was observed for the MCPM/HA formulations containing excess HA. Collectively, these results show that, although the product of the setting reaction is the same, DCPD cements produced with MCPM/HA and MCPM/ß-TCP formulations differ significantly in their degradation properties and cytocompatibility. These differences may have important implications for the selection of a DCPD cement formulation for clinical application.

Absence of exposed bone following dental extraction in beagle dogs treated with 9 months of high-dose zoledronic acid combined with dexamethasone.

PURPOSE: Factors contributing to osteonecrosis of the jaw with anti-remodeling drug treatment are unclear. Epidemiologic and experimental studies have suggested the combination of bisphosphonates and dexamethasone results in osteonecrosis of the jaw more often than either agent alone. The goal of this study was to assess the combination of these 2 drugs in a large animal model previously shown to be susceptible to exposed bone in the oral cavity when treated with bisphosphonates. MATERIALS AND METHODS: Skeletally mature beagle dogs were untreated controls or treated with zoledronic acid (ZOL), dexamethasone (DEX), or ZOL plus DEX. ZOL and DEX were given at doses based on those used in humans. All animals underwent single molar extraction at 7 and 8 months after the start of the study. Extraction sites were obtained at month 9 for assessment of osseous healing using micro-computed tomography and histology. RESULTS: No animals were observed to have exposed bone after dental extraction, yet 1 animal treated with ZOL and 1 treated with ZOL plus DEX had severely disrupted extraction sites as viewed by computed tomography and histology. These 2 animals had an intense periosteal reaction that was less obvious but still present in all ZOL-treated animals and absent from untreated animals. There was no significant difference in bone volume within the socket among groups at 4 or 8 weeks after healing, yet the ratio of surface to volume was significantly higher in animals treated with ZOL plus DEX at 8 weeks compared with control animals. CONCLUSIONS: These findings suggest a more complex pathophysiology to osteonecrosis of the jaw than is implied by previous epidemiologic studies and those in rodents and raise questions about the potential role of DEX in its etiology.

Recent advances in the development of GTR/GBR membranes for periodontal regeneration--a materials perspective.

UNLABELLED: Periodontitis is a major chronic inflammatory disorder that can lead to the destruction of the periodontal tissues and, ultimately, tooth loss. To date, flap debridement and/or flap curettage and periodontal regenerative therapy with membranes and bone grafting materials have been employed with distinct levels of clinical success. Current resorbable and non-resorbable membranes act as a physical barrier to avoid connective and epithelial tissue down-growth into the defect, favoring the regeneration of periodontal tissues. These conventional membranes possess many structural, mechanical, and bio-functional limitations and the "ideal" membrane for use in periodontal regenerative therapy has yet to be developed. Based on a graded-biomaterials approach, we have hypothesized that the next-generation of guided tissue and guided bone regeneration (GTR/GBR) membranes for periodontal tissue engineering will be a biologically active, spatially designed and functionally graded nanofibrous biomaterial that closely mimics the native extra-cellular matrix (ECM). OBJECTIVE: This review is presented in three major parts, including (1) a brief overview of the periodontium and its pathological conditions, (2) currently employed therapeutics used to regenerate the distinct periodontal tissues, and (3) a review of commercially available GTR/GBR membranes as well as the recent advances on the processing and characterization of GTR/GBR membranes from a materials perspective. SIGNIFICANCE: Studies of spatially designed and functionally graded membranes (FGM) and in vitro antibacterial/cell-related research are addressed. Finally, as a future outlook, the use of hydrogels in combination with scaffold materials is highlighted as a promising approach for periodontal tissue engineering.

Poly(propylene fumarate) reinforced dicalcium phosphate dihydrate cement composites for bone tissue engineering.

Calcium phosphate cements have many desirable properties for bone tissue engineering, including osteoconductivity, resorbability, and amenability to rapid prototyping-based methods for scaffold fabrication. In this study, we show that dicalcium phosphate dihydrate (DCPD) cements, which are highly resorbable but also inherently weak and brittle, can be reinforced with poly(propylene fumarate) (PPF) to produce strong composites with mechanical properties suitable for bone tissue engineering. Characterization of DCPD-PPF composites revealed significant improvements in mechanical properties for cements with a 1.0 powder to liquid ratio. Compared with nonreinforced controls, flexural strength improved from 1.80 ± 0.19 MPa to 16.14 ± 1.70 MPa, flexural modulus increased from 1073.01 ± 158.40 MPa to 1303.91 ± 110.41 MPa, maximum displacement during testing increased from 0.11 ± 0.04 mm to 0.51 ± 0.09 mm, and work of fracture improved from 2.74 ± 0.78 J/m(2) to 249.21 ± 81.64 J/m(2) . To demonstrate the utility of our approach for scaffold fabrication, 3D macroporous scaffolds were prepared with rapid prototyping technology. Compressive testing revealed that PPF reinforcement increased scaffold strength from 0.31 ± 0.06 MPa to 7.48 ± 0.77 MPa. Finally, 3D PPF-DCPD scaffolds were implanted into calvarial defects in rabbits for 6 weeks. Although the addition of mesenchymal stem cells to the scaffolds did not significantly improve the extent of regeneration, numerous bone nodules with active osteoblasts were observed within the scaffold pores, especially in the peripheral regions. Overall, the results of this study suggest that PPF-DCPD composites may be promising scaffold materials for bone tissue engineering.

In vitro degradation and cytocompatibility of dicalcium phosphate dihydrate cements prepared using the monocalcium phosphate monohydrate/hydroxyapatite system reveals rapid conversion to HA as a key mechanism.

We previously showed that dicalcium phosphate dihydrate (DCPD) cements can be prepared using monocalcium phosphate monohydrate (MCPM) and hydroxyapatite (HA). In this study, we have characterized the degradation properties and biocompatibility of these novel cements. To study the degradation properties, cements were prepared using MCPM:HA molar ratios of 4:1, 2:1, 2:3, and 2:5. Degradation was evaluated in vitro by static soaking in PBS, and changes in pH, mass, compressive strength, and composition were monitored. Conversion of DCPD to HA was noted in the 4:1 group, which initially consisted of pure DCPD. However, the 2:1 group, which initially consisted of DCPD and an intermediate amount of unreacted HA, underwent rapid conversion to HA associated with significantly greater pH drop and mass loss as well as a complete loss of mechanical integrity. On the basis of these results, we directly compared the cytocompatibility of 2:1 MCPM:HA cements to DCPD cements prepared with an equivalent percent molar excess of ß-tricalcium phosphate (ß-TCP) using an in vitro cell viability assay. Viability of cells co-cultured with 2:1 MCPM:HA cements was significantly reduced after just 48 h, while viability of cells cultured with the ß-TCP-based cements was no different from control cells. In conclusion, this study demonstrates that conversion to HA plays an important role in the degradation of DCPD cements prepared with the MCPM/HA system, affecting both physical properties and cytocompatibility. These results could have important clinical implications for MCPM/HA cements.

Additive concentration effects on dicalcium phosphate dihydrate cements prepared using monocalcium phosphate monohydrate and hydroxyapatite.

In our previous study, we investigated the setting time, mechanical properties and microstructure of dicalcium phosphate dihydrate cements prepared using monocalcium phosphate monohydrate (MCPM) and hydroxyapatite (HA). Despite the use of sodium citrate as a setting regulator, setting occurs rapidly in the MCPM/HA system and further studies on other retardants are needed. In the present study, sodium pyrophosphate and sulfuric acid were tested to evaluate their effectiveness in maintaining workability of the cement paste. MCPM/HA cements at a powder to liquid ratio of 1.0 with sodium pyrophosphate and sulfuric acid at 10, 25, 50, 75 and 100 mM were manufactured and studied based on their setting time, mechanical and porosity properties, phase composition, and microstructure. These measurements were compared to our previous data using sodium citrate. The results showed that the additives have a dose-dependent effect on the setting time. Their order of efficiency is sodium pyrophosphate > sodium citrate > sulfuric acid. However, the sulfuric acid group exhibited the highest compressive strength (CS) compared to the other groups. A lack of correlation between the CS and the porosity of the cements suggested that a mechanism other than porosity reduction was responsible for the CS increase. Since x-ray diffraction analysis did not indicate an effect on composition, explanations based on calcium sulfate dihydrate formation and changes in microstructure were proposed based on scanning electron micrograph observations.

Calcium phosphate cement reinforcement by polymer infiltration and in situ curing: a method for 3D scaffold reinforcement.

This study describes a novel method of calcium phosphate cement reinforcement based on infiltrating a pre-set cement with a reactive polymer and then cross-linking the polymer in situ. This method can be used to reinforce 3D calcium phosphate cement scaffolds, which we demonstrate using poly(ethylene glycol) diacrylate (PEGDA) as a model reinforcing polymer. The compressive strength of a 3D scaffold comprised of orthogonally intersecting beams was increased from 0.31 +/- 0.06 MPa to 1.65 +/- 0.13 MPa using PEGDA 600. In addition, the mechanical properties of reinforced cement were characterized using three PEGDA molecular weights (200, 400, and 600 Da) and three cement powder to liquid (P/L) ratios (0.8, 1.0, and 1.43). Higher molecular weight increased reinforcement efficacy, and P/L controlled cement porosity and determined the extent of polymer incorporation. Although increasing polymer incorporation resulted in a transition from brittle, cement-like behavior to ductile, polymer-like behavior, maximizing polymer incorporation was not advantageous. Polymerization shrinkage produced microcracks in the cement, which reduced the mechanical properties. The most effective reinforcement was achieved with P/L of 1.43 and PEGDA 600. In this group, flexural strength increased from 0.44 +/- 0.12 MPa to 7.04 +/- 0.51 MPa, maximum displacement from 0.05 +/- 0.01 mm to 1.44 +/- 0.17 mm, and work of fracture from 0.64 +/- 0.10 J/m(2) to 677.96 +/- 70.88 J/m(2) compared to non-reinforced controls. These results demonstrate the effectiveness of our novel reinforcement method, as well as its potential for fabricating reinforced 3D calcium phosphate cement scaffolds useful for bone tissue engineering.

Characterization of dicalcium phosphate dihydrate cements prepared using a novel hydroxyapatite-based formulation.

Dicalcium phosphate dihydrate (DCPD) cements are typically prepared using beta-tricalcium phosphate (beta-TCP) as the base component. However, hydroxyapatite (HA) is an interesting alternative because of its potential for reducing cement acidity, as well as modulating cement properties via ionic substitutions. In the present study, we have characterized DCPD cements prepared with a novel formulation based on monocalcium phosphate monohydrate (MCPM) and HA. Cements were prepared using a 4:1 MCPM:HA molar ratio. The reactivity of HA in this system was verified by showing DCPD formation using poorly crystalline HA, as well as highly crystalline HA. Evaluation of cements prepared with poorly crystalline HA revealed that setting occurs rapidly in the MCPM/HA system, and that the use of a setting regulator is necessary to maintain workability of the cement paste. Compressive testing showed that MCPM/HA cements have strengths comparable to what has previously been published for DCPD cements. However, preliminary in vitro analysis of cement degradation revealed that conversion of DCPD to HA may occur much more rapidly in the MCPM/HA system compared to cements prepared with beta-TCP. Future studies should investigate this property further, as it could have important implications for the use of HA-based DCPD cement formulations.