Managing Temporomandibular Joint Osteoarthritis by Dental Stem Cell Secretome

The potential therapeutic role of the Dental Pulp Stem Cells Secretome (SECR) in a rat model of experimentally induced Temporomandibular Joint (TMJ) Osteoarthritis (OA) was evaluated. Proteomic profiling of the human SECR under specific oxygen tension (5% O2) and stimulation with Tumor Necrosis Factor-alpha (TNF-α) was performed. SECR and respective cell lysates (CL) samples were collected and subjected to SDS-PAGE, followed by LC-MS/MS analysis. The identified proteins were analyzed with Bioinformatic tools. The anti-inflammatory properties of SECR were assessed via an in vitro murine macrophages model, and were further validated in vivo, in a rat model of chemically-induced TMJ-OA by weekly recording of the head withdrawal threshold, the food intake, and the weight change, and radiographically and histologically at 4- and 8-weeks post-treatment. SECR analysis revealed the presence of 50 proteins that were enriched and/or statistically significantly upregulated compared to CL, while many of those proteins were involved in pathways related to "extracellular matrix organization" and "immune system". SECR application in vitro led to a significant downregulation on the expression of pro-inflammatory genes (MMP-13, MMP-9, MMP-3 and MCP-1), while maintaining an increased expression of IL-10 and IL-6. SECR application in vivo had a significant positive effect on all the clinical parameters, resulting in improved food intake, weight, and pain suppression. Radiographically, SECR application had a significant positive effect on trabecular bone thickness and bone density compared to the saline-treated group. Histological analysis indicated that SECR administration reduced inflammation, enhanced ECM and subchondral bone repair and regeneration, thus alleviating TMJ degeneration.

Effectiveness of conservative therapeutic modalities for temporomandibular disorders-related pain: a systematic review

PURPOSE

The aim of this systematic review was to evaluate the effectiveness of conservative different therapeutic modalities for temporomandibular disorders (TMD) pain.

MATERIALS AND METHODS

An electronic systematic search was conducted in the MEDLINE (PubMed) database to identify the randomized clinical trials (RCTs) published between 2001 and 2021. The following, simple or multiple conjunctions, search keywords were selected: TMD pain, TMD management or conservative treatment or treatment strategies and TMD pain, therapeutic modalities or interventions and TMD. Studies included must have patients older than 18 years, with painful TMD, which diagnosis was performed by Research Diagnostic Criteria for TMD or Diagnostic Criteria for TMD. Outcome variables were pain relief and post treatment pain intensity reduction. Data were analysed with non-parametric tests and the level of significance was set at p<.05.

RESULTS

Out of 1599 articles obtained, 28 RCTs fulfilled all selection criteria and were included. The results of this study show that there was a significant decrease in short-term post-treatment TMD pain with the use of occlusal splint alone or in combination with other therapeutic modalities when compared with the control group. Statistically significant differences were also detected between laser and photobiomodulation group and the control, in short-term treatment TMD-related pain.

CONCLUSIONS

The primary findings of the present systematic review showed that the occlusal splint alone or combined with other therapeutic intervention presented positive effect on short-term TMD pain reduction. Secondary outcome suggests that laser and photobiomodulation therapy had, also, a significant role in short term pain relief.

Effect of different zirconia surface pretreatments on the flexural strength of veneered Y-TZP ceramic before and after in vitro aging

PURPOSE

The investigation of zirconia core surface pretreatments on the flexural strength of bilayered zirconia ceramics before and after artificial accelerating aging.

METHODS

Ninety bar-shaped specimens were manufactured from Yttria Stabilized Tetragonal Zirconia Polycrystal (Y-TZP) and divided in three groups depending on zirconia surface pretreatment before veneering: layering with liner, pretreatment with silane-containing gas flame (SGF) with the Silano-Pen device and alumina air-abrasion. Half of the veneered specimens in each group (n=15) underwent artificial accelerating aging. A 4-point bending test was performed to determine flexural strength. Three specimens from each group were further analyzed using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) before veneering and after fracture (aged and non-aged subgroups).

RESULTS

Alumina air-abrasion was correlated to increased phase transformation from tetragonal to monoclinic zirconia phase. Qualitative analysis revealed that with the majority of the specimens pretreated with the silane-containing gas flame, areas of the veneering material remained firmly attached to the zirconia core after flexural strength testing. There was no statistically significant difference on the flexural strength among the groups before or after aging. Artificial accelerating aging resulted in statistically significant higher flexural strength of the specimens after aging.

CONCLUSION

SGF pretreatment can be an acceptable and feasible alternative method before the veneering of Y-TZP zirconia as it presented slightly higher bond strength compared with alumina air-abrasion which was associated with higher tetragonal to monoclinic (t→m) phase transformation. Accelerating aging leads to an increase of the mechanical properties under in vitro conditions.

Screwmentable implant-supported prostheses: A systematic review

STATEMENT OF PROBLEM

Screwmentable prostheses were developed to combine the benefits of screw retention and cement retention. However, data are limited on the clinical performance of this type of prosthesis.

PURPOSE

The purpose of this systematic review was to collect scientific evidence on screwmentable prostheses and evaluate their long-term clinical behavior.

MATERIAL AND METHODS

An electronic search was conducted by 2 independent reviewers for articles published in scientific dental journals in English from 2004 to April 2020. The search strategy followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Inclusion criteria were scientific studies concerning the screwmentable type of prosthesis.

RESULTS

The search provided 494 records. Of these, 24 studies fulfilled the inclusion criteria and were included in the review. The included articles presented significant heterogeneity concerning the manufacturing process and the materials used. One randomized clinical trial, 2 prospective clinical studies, 14 in vitro studies, 3 protocol descriptions, 1 case series, and 3 case reports were included.

CONCLUSIONS

Based on the systematic search of the literature, it is concluded that the screwmentable prosthesis combines advantages of both cement-retained and screw-retained restorations, including passive fit, retrievability, excess cement control, tissue-friendly emergence profile, and improved esthetics. Nevertheless, data from well-designed clinical trials are limited, and further research is required to provide evidence on their long-term clinical behavior.

Mapping the Secretome of Dental Pulp Stem Cells Under Variable Microenvironmental Conditions

There is substantial evidence supporting the anti-inflammatory and regenerative potential of dental pulp stem cells (DPSCs) through direct cell transplantation or paracrine action. However, DPSC secretome profile remains inadequately studied. This study provides proteomic profiling of the human DPSC secretome by comparatively analysising cell lysates and respective culture supernatants (i.e. conditioned media-CM) under variable oxygen tension conditions (normoxia-20% O₂/CM_Norm vs. hypoxia 2% O₂/CM_Hyp) and/or stimulation with Tumor Necrosis Factor alpha (TNF-α). DPSC-CM samples and respective crude lysates (DPSC-CL) were collected and subjected to SDS-PAGE, followed by LC-MS/MS analysis. The identified proteins were analyzed by Gene Ontology, Reactome, and String databases. The anti-inflammatory properties of DPSC-CMs were validated via an in vitro RAW_246.7 murine macrophages model through evaluation of the expression of pro-and anti-inflammatory markers by real-time PCR. Results showed a total of 2413 proteins identified in CM_Norm, 2479 in CM_Norm+TNF-α, 1642 in CM_Hyp, and 2002 in CM_Hyp + TNF-α samples. CM_Norm contained 122 proteins statistically significantly upregulated compared to the CM_Hyp and involved in pathways related to "ECM organization", "cellular response to hypoxia", and "IL signaling". Functional network analysis showed that TGFβ1, TIMP1 and TIMP2 were key nodes among proteins significantly upregulated in the CM_Norm compared to the CM_Hyp, interacting with more than 10 proteins, each. DPSC-CM application in the in vitro RAW_246.7 model decreased the expression of pro-inflammatory markers (MMP-3, MMP-9, MMP-13, MCP-1), while increasing anti-inflammatory markers (IL-10). Overall, DPSC-CM collected under normoxic conditions is enriched with anti-inflammatory, tissue repair and regenerative factors, which prompts further investigation on its therapeutic applications.

Effect of in vitro aging and acidic storage on color, translucency, and contrast ratio of monolithic zirconia and lithium disilicate ceramics

STATEMENT OF PROBLEM

How the translucency and color of ceramic restorations are affected by surface changes from the corrosive environment in the oral cavity and aging of materials is unclear.

PURPOSE

The purpose of this in vitro study was to compare the impact of acidic exposure and aging on the color and translucency of monolithic zirconia and lithium disilicate ceramics.

MATERIAL AND METHODS

Twenty computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic zirconia specimens and 20 pressed lithium disilicate specimens were fabricated. Half of the specimens of each group were aged in an autoclave (7.5 hours, 134 °C, 0.2 MPa), and the rest were immersed in hydrochloric acid to simulate the acidic conditions in the oral cavity from gastric reflux. The color coordinates L∗, a∗, and b∗ were measured with an ultraviolet spectrophotometer before and after aging or acidic storage. The translucency parameters and contrast ratios were calculated, and the CIEDE2000 color difference formula was used to determine color differences before and after each treatment. ANOVA and ANCOVA test models were used for data analysis (α=.05), while differences of color parameters in respect to acceptability and perceptibility thresholds were evaluated with the 1-sample t test (α=.05).

RESULTS

Lithium disilicate presented a significantly higher translucency parameter and lower contrast ratio at baseline compared with monolithic zirconia specimens (P<.001). Acidic storage significantly impacted all parameters compared with aging, especially for the lithium disilicate group. Color differences were above the acceptability ΔΕ₀₀ threshold for lithium disilicate after acidic storage (P=.001) and below for monolithic zirconia after acidic storage (P=.003).

CONCLUSIONS

The performance of lithium disilicate was slightly inferior compared with that of monolithic zirconia specimens, as they presented significant and clinically observable differences for the translucency parameter and ΔΕ₀₀ after acidic storage and aging.

Fracture strength of endodontically treated premolars restored with different post systems and metal-ceramic or monolithic zirconia crowns

The purpose of this study was to investigate the fracture strength of endodontically treated human maxillary premolars (ETP) restored with posts and metal ceramic (MC) or monolithic zirconia (MZ) crowns. Sixty ETP were randomly divided into 3 groups. Teeth in control group (C) received a resin filling. ETP in the MC group were restored with prefabricated metal posts, composite cores and MC crowns while in the MZ group with glass-fiber posts, composite cores and MZ crowns. Half of the specimens were loaded at a 135° angle and half under axial loading until fracture. The fracture modes were divided in repairable and irreparable using optical microscopy. Mean fracture strength was significantly higher for MC than for MZ crowns and control group only under axial loading. The distribution of repairable and irreparable failures presented no significant differences. Crown placement significantly improved the fracture strength of ETP irrespectively of post and crown type.

Hybrid chitosan/gelatin/nanohydroxyapatite scaffolds promote odontogenic differentiation of dental pulp stem cells and in vitro biomineralization

OBJECTIVE

Hybrid chitosan/gelatin/nanohydroxyapatite (CS/Gel/nHA) scaffolds have attracted considerable interest in tissue engineering (TE) of mineralized tissues. The present study aimed to investigate the potential of CS/Gel/nHA scaffolds loaded with dental pulp stem cells (DPSCs) to induce odontogenic differentiation and in vitro biomineralization.

METHODS

CS/Gel/nHA scaffolds were synthesized by freeze-drying, seeded with DPSCs, and characterized with flow cytometry. Scanning Electron Microscopy (SEM), live/dead staining, and MTT assays were used to evaluate cell morphology and viability; real-time PCR for odontogenesis-related gene expression analysis; SEM-EDS (Energy Dispersive X-ray spectroscopy), and X-ray Diffraction analysis (XRD) for structural and chemical characterization of the mineralized constructs, respectively.

RESULTS

CS/Gel/nHA scaffolds supported viability and proliferation of DPSCs over 14 days in culture. Gene expression patterns indicated pronounced odontogenic shift of DPSCs, evidenced by upregulation of DSPP, BMP-2, ALP, and the transcription factors RunX2 and Osterix. SEM-EDS showed the production of a nanocrystalline mineralized matrix inside the cell-based and - to a lesser extent - the cell-free constructs, with a time-dependent production of net-like nanocrystals (appr. 25-30nm in diameter). XRD analysis gave the crystallite size (D=50nm) but could not distinguish between the initially incorporated and the biologically produced nHA.

SIGNIFICANCE

This is the first study validating the potential of CS/Gel/nHA scaffolds to support viability and proliferation of DPSCs, and to provide a biomimetic microenvironment favoring odontogenic differentiation and in vitro biomineralization without the addition of any inductive factors, including dexamethasone and/or growth/morphogenetic factors. These results reveal a promising strategy towards TE of mineralized dental tissues.

Advanced in Vitro Experimental Models for Tissue Engineering-based Reconstruction of a 3D Dentin/pulp Complex: a Literature Review

OBJECTIVE

Experimental procedures have been used to monitor cellular responses at the dentin/pulp interface. Aiming to divert from in vivo studies and oversimplified two-dimensional assays, three-dimensional (3D) models have been developed. This review provides an overview of existing literature, regarding 3D in vitro dentin/pulp reconstruction.

MATERIAL & METHODS

PubMed, Scopus, Cochrane Library and Web of Science- were systematically searched for attributes between 1998 and 2020. The search focused on articles on the development of three-dimensional tools for the reconstruction of a dentin/pulp complex under in vitro conditions, which were then screened and qualitatively assessed. Article grouping according to mode of implementation, resulted in five categories: the customised cell perfusion chamber (CPC) (n = 8), the tooth bud model (TBM) (n = 3), the 3D dentin/pulp complex manufactured by tissue engineering (DPC) (n = 6), the entire tooth culture (ETC) (n = 4) and the tooth slice culture model (TSC) (n = 5).

RESULTS

A total of 26 publications, applying nine and eight substances for pulp and dentin representation respectively, were included. Natural materials and dentin components were the most widely utilized. The most diverse category was the DPC, while the CPC group was the test with the highest longevity. The most consistent categories were the ETC and TSC models, while the TBM presented as the most complete de novo approach.

CONCLUSIONS

All studies presented with experimental protocols with potential upgrades. Solving the limitations of each category will provide a complete in vitro testing and monitoring tool of dental responses to exogenous inputs.

CLINICAL RELEVANCE

The 3D dentin/pulp complexes are valid supplementary tools for in vivo studies and clinical testing. Graphical Abstract.

The effect of different aging protocols on the flexural strength and phase transformations of two monolithic zirconia ceramics

Introduction:

The aim of the present study was to investigate how different aging protocols can affect the flexural strength and phase transformations of yttrium-stabilized zirconia ceramics (Y-TZP) for monolithic restorations.

Materials and methods:

Bar-shaped specimens from two zirconia ceramics bars were divided into three groups: a. no treatment (c), b. aging in an autoclave (a), and c. thermal cycling (t). The flexural strength was determined by the 3-point bending test and statistical analysis was performed to determine significant differences ( p< 0.05). Weibull statistics was used to analyze the dispersion of strength values while surface microstructural analysis was performed through X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).

Results:

Aging did not significantly affect the flexural strength but differences were recorded between the two groups, with group A presenting higher strength values and m-phase percentages.

Conclusions:

The observed differences between the two ceramics could be attributed to variations in composition and processing.

Variables affecting the fit of zirconia fixed partial dentures: A systematic review

STATEMENT OF PROBLEM

Different parameters affect the marginal and internal fit of zirconia fixed partial dentures (FPDs) on natural teeth. Determining a way to optimize these restorations is essential.

PURPOSE

The purpose of this systematic review was to determine the variables affecting the marginal fit and internal accuracy of zirconia FPDs on natural teeth.

MATERIAL AND METHODS

An electronic search was conducted by 2 independent reviewers by using the MEDLINE, Cochrane, Web of Science, and Scopus databases, as well as Google Scholar, for studies published up to July 2018, and a manual search was conducted from the reference lists of related articles. Eligibility criteria included articles in English published in peer-reviewed journals that assessed the marginal and/or internal adaptation of zirconia FPDs on teeth with 3 or more units, with at least 1 of the experimental groups being frameworks or FPDs fabricated from zirconia. Risk of bias was assessed with the aid of the Cochrane Handbook for Systematic Reviews of Interventions.

RESULTS

The search provided 418 records, with 41 fulfilling the inclusion criteria. The selected studies showed considerable heterogeneity regarding materials, state of sintering, manufacturer and computer-aided design and computer-aided manufacturing (CAD-CAM) system, experimental methodology, sample size, and span length. Of the included articles, 36 were in vitro studies and 5 were clinical studies, most of which exhibited high-performance and detection biases. CAD-CAM systems provided more precise marginal and internal fit than CAM systems. An increase of framework span length to 6 or more units decreased both marginal and internal fit. The reported marginal gap tended to increase after the veneering process. The introduction of a conventional impression into an otherwise digital workflow seems to have a negative effect on the marginal fit.

CONCLUSIONS

The accuracy of zirconia FPDs or frameworks is considerably influenced by the processing procedure used and the choice of CAD-CAM system.

Color alterations of a PMMA resin for fixed interim prostheses reinforced with silica nanoparticles

PURPOSE

The aim of the present study was to evaluate the color changes of an autopolymerizing PMMA resin used for interim fixed restorations, reinforced with SiO₂ nanoparticles.

MATERIALS AND METHODS

Silica nanoparticles were blended with the PMMA resin powder through high-energy ball milling. Four shades of PMMA resin were used (A3, B3, C3, D3) and total color differences were calculated through the equations ΔE_ab= [(ΔL^*)² + (Δa^*)² + (Δb^*)²]^½ and ΔE00=[ΔL′KLSL2+ΔC′KCSC2+ΔH′KHSH2+RTΔC′KCSCΔH′KHSH]1/2. Statistically significant differences between ΔE_ab and the clinically acceptable values of 3.3 and 2.7 and those between ΔE₀₀ and the clinically acceptable value of 1.8 were evaluated with one sample t-test (P<.05). Differences among the different shades were assessed through One-Way ANOVA and Bonferroni multiple comparison tests.

RESULTS

Significantly lower values were detected for all groups concerning ΔE_ab compared to the intraorally clinical acceptable values of 3.3 and 2.7. Significantly lower mean values were detected for groups B3, C3, and D3, concerning ΔE₀₀ compared to the intraorally clinical acceptant value of 1.8. Color pigments in red-brown (A3) and red-grey (D3) shades affect the total color change to a greater extent after the reinforcement with SiO₂ nanoparticles compared to the red-yellow (B3) shade.

CONCLUSION

Within the limitations of this in vitro study, it can be suggested that reinforcing PMMA with SiO₂ nanoparticles at 0.25 wt% slightly affects the optical properties of the PMMA resin without being clinically perceivable.

In vitro evaluation of the shear bond strength and bioactivity of a bioceramic cement for bonding monolithic zirconia

STATEMENT OF PROBLEM

Adhesive cementation is the most common bonding strategy for zirconia restorations. Although cementation with a bioactive luting agent has been proposed as an alternative, how the bond strength compares is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate shear bond strength after cementing a monolithic zirconia ceramic to human dentin with a bioceramic cement, compare it with a traditional cement, and evaluate its bioactive properties.

MATERIAL AND METHODS

A total of 120 dentin specimens and 120 yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) (BruxZir) cylindrical specimens were used. Zirconia and dentin specimens were randomly divided into 8 study groups (n=15) based on 2 luting cement types (a bioceramic cement or glass ionomer cement as control), 2 airborne-particle abrasion protocols (50 μm or 110 μm), and 2 water storage durations (24 hours or 30 days). After the shear bond strength test using a universal machine at a crosshead speed of 1 mm/min, fracture patterns were evaluated under a stereomicroscope and a scanning electron microscope. Strength values were statistically analyzed with a 3-factor ANOVA model (α=.05). Bioactivity was evaluated in simulated body fluid (SBF).

RESULTS

The control glass ionomer cement achieved significantly greater shear bond strength compared with the tested bioceramic cement. Mean bond strength values ranged from 2.52 MPa to 5.23 MPa for the bioceramic cement tested and from 4.20 MPa to 6.61 MPa for the control cement. The duration of water storage played a significant role in the bond strength, with groups stored for 30 days reaching higher bond strength values, whereas the particle size of airborne-particle abrasion did not have a significant effect. Failure types were primarily mixed. No apatite formation was recorded on the surface of the specimens even after 30 days of immersion in SBF.

CONCLUSIONS

The evaluated cement did not develop apatite in SBF, and its bond strength values were below the control glass ionomer cement.

Effect of Immediate Dentin Sealing on the Bond Strength of Monolithic Zirconia to Human Dentin

Objective:

This study evaluated the shear bond strength (SBS) of pretreated monolithic zirconia surfaces bonded to human dentin following immediate dentin sealing (IDS) using two different self-adhesive resin luting agents.

Methods and Materials:

Sixty intact human third molars were collected, stored, sectioned appropriately, and molded according to ISO 29022:2013, resulting in 120 dentin specimens. Ceramic cylindrical specimens were fabricated using CAD/CAM technology and sintered as recommended (final bonding area A=2.56 mm2). Specimens were randomly assigned to eight groups (15≥n≥14) depending on dentin conditioning method (IDS or delayed dentin sealing [DDS]), zirconia surface pretreatment (airborne particle abrasion [APA] with 50 μm Al2O3 particles at 3 bar for 10 seconds or tribochemical silica coating [TBC] with 30 μm CoJet particles at 2.8 bar for 10 seconds), and adhesive luting agent type (Panavia F2.0 [PAN] or PermaCem Dual Smartmix [PER]). Bonded specimens were water-stored (37°C, 24 hours) and subjected to SBS testing (50-kgF load cell, 1 mm/min). Fracture type was evaluated with stereomicroscopy. Data (MPa) were statistically analyzed using three-way analysis of variance (α=0.05).

Results:

All factors significantly affected SBS values (p&lt;0.001). Dentin conditioning method presented the greatest effect. Mean SBS values ranged from 12.603 MPa (PER-APA-DDS) to 40.704 MPa (PER-TBC-IDS). Based on the fracture type, adhesive failures at the luting agent–zirconia interface were the least common.

Conclusion:

Bonding strategies for monolithic zirconia restorations could potentially benefit from IDS, regardless of the adhesive luting agent system used.

Evaluation of the biological behaviour of various dental implant abutment materials on attachment and viability of human gingival fibroblasts

OBJECTIVE

This study aimed to investigate the biological effects of yttria-stabilized zirconia (Y-TZP) compared to other dental implant abutment materials, i.e. lithium disilicate (LS2) and titanium alloy (Ti), as well as the effects of aging of Y-TZP on viability/proliferation and attachment properties of Human Gingival Fibroblasts (HGFs).

METHODS

Cylindrical specimens of each material were prepared as per manufacturer's instructions. Y-TZP specimens were divided into three groups: 1. no aging (Zr0), 2. aging for 5 h, 134 °C, 2 bars, 100% humidity (Zr5), 3. aging for 10 h under the same conditions (Zr10). Surface roughness was evaluated by optical profilometry; cell metabolic activity/viability by MTT assay, morphological changes by Scanning Electron Microscopy (SEM) and ratio of live/dead cells by confocal microscopy.

RESULTS

Results showed statistically significant reduction of HGF metabolic activity/viability in contact with Y-TZP after aging. Nevertheless, non-aged zirconia showed no significant differences compared with LS2, Ti and control cultures. In contrast, significant stimulation of cell metabolic activity/viability was observed in HGFs exposed to LS2 eluates. Differential morphological patterns were observed for HGF in contact with different materials/treatments, with obviously increased number of dead cells and sparser distribution of HGFs cultured on Zr10 specimens. These effects were not correlated with surface topography, since Y-TZP aging did not alter surface micro-roughness.

SIGNIFICANCE

These findings indicate that Y-TZP shows comparable biological properties to Ti and LS2 as implant abutment material. Nevertheless, Y-TZP aging might influence gingival cell attachment and proliferation properties, providing an alert to a potentially negative effect on the long-term maintenance of gingival architecture.

Dental pulp stem cells in chitosan/gelatin scaffolds for enhanced orofacial bone regeneration

OBJECTIVE

Biomimetic chitosan/gelatin (CS/Gel) scaffolds have attracted great interest in tissue engineering of several tissues. However, limited information exists regarding the potential of combining CS/Gel scaffolds with oral cells, such as dental pulp stem cells (DPSCs), to produce customized constructs targeting alveolar/orofacial bone reconstruction, which has been the aim of the present study.

METHODS

Two scaffold types, designated as CS/Gel-0.1 and CS/Gel-1, were fabricated using 0.1 and 1% (v/v) respectively of the crosslinker glutaraldehyde (GTA). Scaffolds (n=240) were seeded with DPSCs with/without pre-exposure to recombinant human BMP-2. In vitro assessment included DPSCs characterization (flow cytometry), evaluation of viability/proliferation (live/dead staining, metabolic-based tests), osteo/odontogenic gene expression analysis (qRT-PCR) and structural/chemical characterization (scanning electron microscopy, SEM; energy dispersive X-ray spectroscopy, EDX; X-ray powder diffraction, XRD; thermogravimetry, TG). In vivo assessment included implantation of DPSC-seeded scaffolds in immunocompromised mice, followed by histology and SEM-EDX. Statistical analysis employed one/two-way ANOVA and Tukey's post-hoc tests (significance for p<0.05).

RESULTS

Both scaffolds supported cell viability/proliferation over 14 days in culture, showing extensive formation of a hydroxyapatite-rich nanocrystalline calcium phosphate phase. Differential expression patterns indicated GTA concentration to significantly affect the expression of osteo/odontogenic genes, with CS/Gel-0.1 scaffolds being more effective in upregulating DSPP, IBSP and Osterix. In vivo analysis demonstrated time-dependent production of a nanocrystalline, mineralized matrix at 6, 8 and 10 weeks, being more prominent in constructs bearing rhBMP-2 pre-treated cells. The latter showed higher amounts of osteoid and fully mineralized bone, as well as empty space reduction.

SIGNIFICANCE

These results reveal a promising strategy for orofacial bone tissue engineering.

Evaluation of the micro-mechanical and bioactive properties of bioactive glass-dental porcelain composite

The aim of this study was to evaluate microhardness and elastic modulus of a novel sol-gel derived dental ceramic - 58S bioactive glass composite (BP67: Bioactive Glass:33.3%, Dental Ceramic:66.7%) BP67¹ material by micro-indentation and to investigate its microstructure and bioactivity. The research hypotheses were that the values of microhardness (1) and elastic modulus (2) of the novel bioceramic composite and the commercial dental ceramic will be of the same order. The experimental sol-gel derived ceramics showed similar microstructural characteristics to a commercial feldspathic porcelain, and presence of additional calcium phosphate phases, which contributed its bioactivity. The formation of an apatite-like layer on the materials' surface observed by Fourier Transform Infrared (FTIR)² spectroscopy, X-ray Diffraction (XRD)³ and Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS)⁴ techniques after 12 days of maintenance in Conventional Simulated Body Fluid (cSBF)⁵ solution. The BP67 exhibited values of microhardness and modulus of elasticity which were not statistically significant different compared to dental ceramic, indicating the adequate mechanical integrity of the material. The results of this study suggest that the novel bioactive composite could be potentially applied in prosthetic dentistry, while its thermal and optical properties should be investigated in future studies.

Fibro/chondrogenic differentiation of dental stem cells into chitosan/alginate scaffolds towards temporomandibular joint disc regeneration

Tissue engineering (TE) may provide effective alternative treatment for challenging temporomandibular joint (TMJ) pathologies associated with disc malpositioning or degeneration and leading to severe masticatory dysfunction. Aim of this study was to evaluate the potential of chitosan/alginate (Ch/Alg) scaffolds to promote fibro/chondrogenic differentiation of dental pulp stem cells (DPSCs) and production of fibrocartilage tissue, serving as a replacement of the natural TMJ disc. Ch/Alg scaffolds were fabricated by crosslinking with CaCl2 combined or not with glutaraldehyde, resulting in two scaffold types that were physicochemically characterized, seeded with DPSCs or human nucleus pulposus cells (hNPCs) used as control and evaluated for cell attachment, viability, and proliferation. The DPSCs/scaffold constructs were incubated for up to 8 weeks and assessed for extracellular matrix production by means of histology, immunofluorescence, and thermomechanical analysis. Both Ch/Alg scaffold types with a mass ratio of 1:1 presented a gel-like structure with interconnected pores. Scaffolds supported cell adhesion and long-term viability/proliferation of DPSCs and hNPCs. DPSCs cultured into Ch/Alg scaffolds demonstrated a significant increase of gene expression of fibrocartilaginous markers (COLI, COL X, SOX9, COM, ACAN) after up to 3 weeks in culture. Dynamic thermomechanical analysis revealed that scaffolds loaded with DPSCs significantly increased storage modulus and elastic response compared to cell-free scaffolds, obtaining values similar to those of native TMJ disc. Histological data and immunochemical staining for aggrecan after 4 to 8 weeks indicated that the scaffolds support abundant fibrocartilaginous tissue formation, thus providing a promising strategy for TMJ disc TE-based replacement.

Isolation and prolonged expansion of oral mesenchymal stem cells under clinical-grade, GMP-compliant conditions differentially affects "stemness" properties

Background

Development of clinical-grade cell preparations is central to meeting the regulatory requirements for cellular therapies under good manufacturing practice-compliant (cGMP) conditions. Since addition of animal serum in culture media may compromise safe and efficient expansion of mesenchymal stem cells (MSCs) for clinical use, this study aimed to investigate the potential of two serum/xeno-free, cGMP culture systems to maintain long-term “stemness” of oral MSCs (dental pulp stem cells (DPSCs) and alveolar bone marrow MSCs (aBMMSCs)), compared to conventional serum-based expansion.

Methods

DPSC and aBMMSC cultures (n = 6/cell type) were established from pulp and alveolar osseous biopsies respectively. Three culture systems were used: StemPro_MSC/SFM_XenoFree (Life Technologies); StemMacs_MSC/XF (Miltenyi Biotek); and α-MEM (Life Technologies) with 15% fetal bovine serum. Growth (population doublings (PDs)), immunophenotypic (flow cytometric analysis of MSC markers) and senescence (β-galactosidase (SA-β-gal) activity; telomere length) characteristics were determined during prolonged expansion. Gene expression patterns of osteogenic (ALP, BMP-2), adipogenic (LPL, PPAR-γ) and chondrogenic (ACAN, SOX-9) markers and maintenance of multilineage differentiation potential were determined by real-time PCR.

Results

Similar isolation efficiency and stable growth dynamics up to passage 10 were observed for DPSCs under all expansion conditions. aBMMSCs showed lower cumulative PDs compared to DPSCs, and when StemMacs was used substantial delays in cell proliferation were noted after passages 6–7. Serum/xeno-free expansion produced cultures with homogeneous spindle-shaped phenotypes, while serum-based expansion preserved differential heterogeneous characteristics of each MSC population. Prolonged expansion of both MSC types but in particular the serum/xeno-free-expanded aBMMSCs was associated with downregulation of CD146, CD105, Stro-1, SSEA-1 and SSEA-4, but not CD90, CD73 and CD49f, in parallel with an increase of SA-gal-positive cells, cell size and granularity and a decrease in telomere length. Expansion under both serum-free systems resulted in “osteogenic pre-disposition”, evidenced by upregulation of osteogenic markers and elimination of chondrogenic and adipogenic markers, while serum-based expansion produced only minor changes. DPSCs retained a diminishing (CCM, StemPro) or increasing (StemMacs) mineralization potential with passaging, while aBMMSCs lost this potential after passages 6–7 under all expansion conditions.

Conclusions

These findings indicate there is still a vacant role for development of qualified protocols for clinical-grade expansion of oral MSCs; a key milestone achievement for translation of research from the bench to clinics.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0705-0) contains supplementary material, which is available to authorized users.

Platelet-rich plasma for the therapeutic management of temporomandibular joint disorders: a systematic review

This systematic review aimed to investigate whether intra-articular injections of platelet-rich plasma (PRP) are beneficial for the treatment of degenerative temporomandibular disorders, such as temporomandibular joint osteoarthritis (TMJ-OA) and disc displacement with osteoarthritic lesions, when compared to other treatments, such as injections of hyaluronic acid (HA) or saline. An electronic search of the MEDLINE and Scopus databases was performed using combinations of the terms "temporomandibular" and "platelet rich plasma", to identify studies reported in English and published up until May 2017. A hand-search of relevant journals and the reference lists of selected articles was also performed. The initial screening identified 153 records, of which only six fulfilled the inclusion criteria and were included in this review. Of these studies, three compared PRP with HA, while three compared PRP with Ringer's lactate or saline. Four of the studies found PRP injections to be superior in terms of improvements in mandibular range of motion and pain intensity up to 12 months after treatment, while the remaining two studies found similar results for the different treatments. There is slight evidence for the potential benefits of intra-articular injections of PRP in patients with TMJ-OA. However, a standardized protocol for PRP preparation and application needs to be established.

Aging of 3Y-TZP dental zirconia and yttrium depletion

OBJECTIVE

Yttrium-stabilized zirconia is susceptible to low temperature degradation after interaction with water. Various mechanisms by which water molecules destabilize the tetragonal phase have been proposed, while the concept of yttrium depletion by the incorporation of hydroxyl ions in the crystalline structure either through the formation of YOH/ZrOH bonds or small α-Y(OH)₃ crystallites, is prevailing. The present study was performed to investigate the surface alterations on a 3Y-TZP dental ceramic during the process of in-vitro aging and to further explore the yttrium depletion mechanism that occurs upon interaction with water.

METHODS

Surface structural changes of zirconia specimens where investigated before and after in-vitro aging with X-ray diffraction analysis, Fourier-transformed infrared spectroscopy, X-ray photoelectron spectroscopy, fluorescence microscopy and scanning electron microscopy.

RESULTS

High luminescence generated from the non-aged specimen was explained by the high amount of oxygen vacancies. The phase transformation from the t-ZrO₂ to the m-ZrO₂ phase after aging was accompanied by a significant loss of yttrium, a clear decrease of oxygen vacancies and a profound decrease of luminescence. Surface oxygen vacancies either migrated into the inner of the specimens or/and/engaged oxygen from the ZrO₂ and formed the metallic phase of Y₂O₃ on the surface after aging.

SIGNIFICANCE

An "ideal" amount of oxygen vacancies that could stabilize the tetragonal phase in Y-TZP zirconia ceramics, without compromising esthetics and LTD resistance, is still a matter of further research and different susceptibilities to LTD among various dental zirconia ceramics are based on the amount of oxygen vacancies that can be annihilated by water molecules.

Psychopathologic Profiles of TMD Patients with Different Pain Locations

PURPOSE

The aim of this study was to examine whether psychopathologic profile is related to the location of pain in temporomandibular disorder (TMD) patients with myofascial and/or temporomandibular joint pain.

MATERIALS AND METHODS

A total of 75 painful TMD patients (39 women and 36 men) participated in the study. Participants were divided into three groups (myogenous, arthrogenous, and mixed) using the Research Diagnostic Criteria for TMD (RDC/TMD) Axis I guidelines for assessment of TMD signs and symptoms. Three psychometric instruments were used to assess the psychopathologic profile of the TMD subgroups. Patients' state and trait anxiety were assessed using the State-Trait Anxiety Inventory (STAI-S, STAI-T), depression was measured with the Center for Epidemiological Studies Depression Scale (CES-D), and psychosocial functioning was evaluated using the Global Disability Scale (Glo.Di.S). The three TMD groups were compared with Kruskal-Wallis test followed by pairwise Mann-Whitney tests relative to the psychometric scores. Statistical analyses were performed with SPSS 15.0 software.

RESULTS

No significant differences were detected among the different TMD groups in the three psychometric scales; STAI-T, CES-D, Glo.Di.S (P > .05). When the psychometric scale of state anxiety (STAI-S) was considered, significant differences were revealed between the myogenous and the arthrogenous pain groups (P = .008) and also between the mixed and the arthrogenous groups (P < .001).

CONCLUSION

These findings suggest that the psychopathologic profile is not related to the location of pain in TMD patients. However, anxiety was found to be higher in TMD patients with myogenous pain alone or combined with arthrogenous pain compared to those with only arthrogenous pain.

Evaluation of color stability of preshaded and liquid-shaded monolithic zirconia

STATEMENT OF PROBLEM

The effect of thermal aging on the color stability of monolithic zirconia has not been thoroughly investigated.

PURPOSE

The purpose of this in vitro study was to evaluate the color stability before and after thermocycling of monolithic zirconia specimens, which were either preshaded or characterized in the laboratory through the assessment of color parameters L*, a*, and b*.

MATERIAL AND METHODS

A total of 80 specimens (10×10×15 mm) were prepared from zirconia disks (BruxZir) and divided into 2 groups. The first group consisted of preshaded specimens from disks 100, 200, 300, and 400, and the second group consisted of white specimens characterized before the sintering stage with coloring liquids in shades A2, B2, C2, and D2. Ten specimens of each shade were used. A double-beam ultraviolet-visible light recording spectrophotometer was used to assess the color parameters L*, a*, and b* before and after thermocycling. The color difference ΔE was calculated based on ΔΕ=[(ΔL*)²+(Δa*)²+(Δb*)²]^½. The reliability of the examiner was investigated by MedCalc v12.5 software, and the tests of normality, homogeneity of variances, and 1-way ANOVA statistical analysis of variance were performed by IBM Statistics SPSS v20.0 software (α=.05).

RESULTS

No statistically significant ΔΕ (P>.05) was observed among the different groups after thermocycling. All ΔΕ values were below the limit of the 3.7 that an untrained observer can perceive. Only for the specimens in shades 200 and 400 was ΔΕ above 1, revealing a visible color difference, which, however, was still clinically acceptable. The L*, a*, and b* values for both liquid-shaded and preshaded zirconia specimens were not significantly affected by thermocycling. A higher color stability for laboratory-characterized compared with preshaded monolithic zirconia was observed irrespective of the color shade.

CONCLUSIONS

Within the limitations of this in vitro study, monolithic zirconia specimens of any shade, either preshaded or characterized in the laboratory, can be considered as color-stable materials after thermocycling.

Oculo-Dento-Digital Dysplasia (ODDD) Due to a GJA1 Mutation: Report of a Case with Emphasis on Dental Manifestations

Oculo-dento-digital dysplasia (ODDD) is a congenital disorder manifesting with multiple phenotypic abnormalities involving the face, eyes, teeth, and limbs in addition to neurologic symptomatology. This report aims to present a female patient with ODDD who was referred due to extensive oral restorative needs. The presence of hypoplastic enamel triggered further evaluation. Characteristic facies with hypoplastic alae nasi and syndactyly offered greater insight into the phenotype of the syndrome. Clinical suspicion was confirmed by genetic sequencing revealing heterozygous mutation in GJA1. It is important to be aware of genetic disorders associated with characteristic dental malformations to offer appropriate counseling and treatment.

An experimental bioactive dental ceramic for metal-ceramic restorations: Textural characteristics and investigation of the mechanical properties

The aim of this study was the evaluation of the textural characteristics of an experimental sol-gel derived feldspathic dental ceramic, which has already been proven bioactive and the investigation of its flexural strength through Weibull Statistical Analysis. The null hypothesis was that the flexural strength of the experimental and the commercial dental ceramic would be of the same order, resulting in a dental ceramic with apatite forming ability and adequate mechanical integrity. Although the flexural strength of the experimental ceramics was not statistically significant different compared to the commercial one, the amount of blind pores due to processing was greater. The textural characteristics of the experimental ceramic were in accordance with the standard low porosity levels reported for dental ceramics used for fixed prosthetic restorations. Feldspathic dental ceramics with typical textural characteristics and advanced mechanical properties as well as enhanced apatite forming ability can be synthesized through the sol-gel method.

Inducing bioactivity of dental ceramic/bioactive glass composites by Nd:YAG laser

OBJECTIVES

Aims of this study were to investigate the optimal conditions of laser irradiation of a novel Bioactive Glass/Dental Ceramic-BP67 composite for acceleration of hydroxyapatite-HA formation and to assess cellular responses on the precipitated HA region.

METHODS

BP67 (Bioactive Glass: 33.3%, Dental Ceramic: 66.7%) was fabricated by the sol-gel method. A laser assisted biomimetic-LAB process was applied to BP67 sintered specimens immersed in 1.5-times concentrated simulated body fluid-1.5×-SBF. The effect of various energy densities of pulsed nanosecond Nd-YAG (1064nm) laser and irradiation exposure times (30min, 1 and 3h) were evaluated for HA precipitation. The HA film was characterized by FTIR, XRD, SEM and micro Raman techniques. ICP-AES was used for revealing changes in chemical composition of the 1.5×-SBF during irradiation. Cell viability and morphological characteristics of periodontal ligament fibroblasts-PDLFs, human gingival fibroblasts-HGFs and SAOS-2 osteoblasts on the HA surface were evaluated by MTT assays and SEM.

RESULTS

At optimal energy fluence of 1.52J/cm² and irradiation time for 3h followed by immersion in 1.5×-SBF at 60°C, a dense HA layer was formed on laser-irradiated BP67 within 7 days. The resulting HA film was tightly bonded to the underlying substrate and had mineral composition similar to cementum. MTT assay showed a consistent reduction of cell proliferation on the HA layer in comparison to conventional control ceramic and BP67 for all 3 cell lines studied.

SIGNIFICANCE

These findings suggest LAB is an effective method for acceleration of HA formation on materials with low bioactivity, while cellular responses need further investigation.

Angiogenic Potential and Secretome of Human Apical Papilla Mesenchymal Stem Cells in Various Stress Microenvironments

Stem cells from the apical papilla (SCAP) of human adult teeth are considered an accessible source of cells with angiogenic properties. The aims of this study were to investigate the endothelial transdifferentiation of SCAP, the secretion of pro- and antiangiogenic factors from SCAP, and the paracrine effects of SCAP when exposed to environmental stress to stimulate tissue damage. SCAP were exposed to serum deprivation (SD), glucose deprivation (GD), and oxygen deprivation/hypoxia (OD) conditions, individually or in combination. Endothelial transdifferentiation was evaluated by in vitro capillary-like formation assays, real-time polymerase chain reaction, western blot, and flow cytometric analyses of angiogenesis-related markers; secretome by antibody arrays and enzyme-linked immunosorbent assays (ELISA); and paracrine impact on human umbilical vein endothelial cells (HUVECs) by in vitro transwell migration and capillary-like formation assays. The short-term exposure of SCAP to glucose/oxygen deprivation (GOD) in the presence, but mainly in deprivation, of serum (SGOD) elicited a proangiogenesis effect indicated by expression of angiogenesis-related genes involved in vascular endothelial growth factor (VEGF)/VEGFR and angiopoietins/Tie pathways. This effect was unachievable under SD in normoxia, suggesting that the critical microenvironmental condition inducing rapid endothelial shift of SCAP is the combination of SGOD. Interestingly, SCAP showed high adaptability to these adverse conditions, retaining cell viability and acquiring a capillary-forming phenotype. SCAP secreted higher numbers and amounts of pro- (angiogenin, IGFBP-3, VEGF) and lower amounts of antiangiogenic factors (serpin-E1, TIMP-1, TSP-1) under SGOD compared with SOD or SD alone. Finally, secretome obtained under SGOD was most effective in inducing migration and capillary-like formation by HUVECs. These data provide new evidence on the microenvironmental factors favoring endothelial transdifferentiation of SCAP, uncovering the molecular mechanisms regulating their fate. They also validate the angiogenic properties of their secretome giving insights into preconditioning strategies enhancing their therapeutic potential.

Effective Cell Growth Potential of Mg-Based Bioceramic Scaffolds towards Targeted Dentin Regeneration

New emerging approaches in tissue engineering include incorporation of metal ions involved in various metabolic processes, such as Cu, Zn, Si into bioceramic scaffolds for enhanced cell growth and differentiation of specific cell types. The aim of the present work was to investigate the attachment, morphology, growth and mineralized tissue formation potential of Dental Pulp Stem Cells (DPSCs) seeded into Mg-based glassceramic scaffolds with incorporated Zn and Cu ions. Bioceramic scaffolds containing Si 60%, Ca 30%, Mg 7.5% and either Zn or Cu 2.5%, sintered at different temperatures were synthesized by the foam replica technique and seeded with DPSCs for up to 21 days. Scanning Electron Microscopy with associated Energy Dispersive Spectroscopy (SEM-EDS) was used to evaluate their ability to support the DPSCs’s attachment and proliferation, while the structure of the seeded scaffolds was investigated by X-Ray Diffraction Analysis (XRD). Zn-doped bioceramic scaffolds promoted the attachment and growth of human DPSCs, while identically fabricated scaffolds doped with Cu showed a cytotoxic behaviour, irrespective of the sintering temperature. A mineralized tissue with apatite-like structure was formed on both Cu-doped scaffolds and only on those Zn-doped scaffolds heat-treated at lower temperatures. Sol-gel derived Zn-doped scaffolds sintered at 890oC support DPSC growth and apatite-like tissue formation, which renders them as promising candidates towards dental tissue regeneration.

Wnt/β-catenin signaling regulates Dental Pulp Stem Cells' responses to pulp injury by resinous monomers

OBJECTIVES

Aim of this study was to investigate whether Dental Pulp Stem Cells-DPSCs responses to pulp injury caused by resinous monomers is be mediated through activation of Wnt/β-catenin signaling.

METHODS

DPSCs cultures were established from third molars of healthy donors and characterized for stem cell markers with flow cytometry. Cells were exposed to TEGDMA (T: 0.5-2mM) with or without presence of the Wnt-1 ligand (W:25-100ng/ml) or the GSK3β inhibitor Lithium (L:1-10mM), used both as activators of Wnt/β-catenin signaling. Cell viability was evaluated by MTT assay, cell cycle profiles by flow cytometry and expression of key molecules of Wnt/β-catenin signaling by Real-time PCR and Western Blot.

RESULTS

DPSC exposure to TEGDMA caused a concentration-dependent cytotoxicity, accompanied by G1 arrest at lower and G2/M arrest at higher concentrations or after prolonged exposure. Lithium caused a dual effect, by stimulating/inhibiting cell proliferation at lower/higher concentrations respectively and causing a G2/M arrest in a concentration-dependent manner. Wnt signaling could be activated in DPSCs after Lithium or Wnt-1 treatment, as shown by accumulation of β-catenin, its translocation into the nucleus and enhanced expression of key pathway players, like LEF1 and Cyclin D1. Importantly, exposure to TEGDMA caused a more pronounced activation of the pathway, whereas cumulative effects were observed after T/L or T/W co-treatment, indicating a very strong activation of Wnt signaling after treatment of already "activated" (by Lithium or Wnt-1) cells with TEGDMA.

SIGNIFICANCE

These findings highlight the important role of Wnt canonical signaling in pulp repair responses to common injuries.

Effect of in vitro aging on the flexural strength and probability to fracture of Y-TZP zirconia ceramics for all-ceramic restorations

OBJECTIVES

Dental zirconia restorations should present long-term clinical survival and be in service within the oral environment for many years. However, low temperature degradation could affect their mechanical properties and survival. The aim of this study was to investigate the effect of in vitro aging on the flexural strength of yttrium-stabilized (Y-TZP) zirconia ceramics for ceramic restorations.

METHODS

One hundred twenty bar-shaped specimens were prepared from two ceramics (ZENO Zr (WI) and IPS e.max(®) ZirCAD (IV)), and loaded until fracture according to ISO 6872. The specimens from each ceramic (nx=60) were divided in three groups (control, aged for 5h, aged for 10h). One-way ANOVA was used to assess statistically significant differences among flexural strength values (P<0.05). The variability of the flexural strength values was analyzed using the two-parameter Weibull distribution function, which was applied for the estimation of Weibull modulus (m) and characteristic strength (σ0). The crystalline phase polymorphs of the materials (tetragonal, t, and monoclinic, m, zirconia) were investigated by X-ray diffraction (XRD) analysis, Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy.

RESULTS

A slight increase of the flexural strength after 5h, and a decrease after 10h of aging, was recorded for both ceramics, however statistically significant was for the WI group (P<0.05). Both ceramics presented a t→m phase transformation, with the m-phase increasing from 4 to 5% at 5h to around 15% after 10h.

SIGNIFICANCE

The significant reduction of the flexural strength after 10h of in vitro aging, suggests high fracture probability for one of the zirconia ceramics tested.

The effect of type of restoration on the stress field developed in terminal abutments with severely reduced periodontal support and coronal structure

STATEMENT OF PROBLEM

Periodontally compromised teeth (PCT) that serve as terminal abutments (TAs) are often challenging depending on the post-and-core treatment, the type of partial fixed dental prosthesis (PFDP), and the periodontal support.

PURPOSE

The purpose of this study was to investigate the biomechanical impact of 3 types of PFDP supported by cast post-and-cores on PCT serving as terminal abutments.

MATERIAL AND METHODS

A 3-dimensional (3D) model of a human mandible was fabricated by using computed tomography (CT) images and parameterized in a computer-aided design (CAD) environment as follows: Right premolar preparation geometries were designed. The second premolar was assembled with 7-mm or 10-mm cast post-and-core models. Both premolar-models were designed to support single, splinted, or 1-unit cantilever splinted crowns. In each situation, their periodontium geometries were designed to be reduced by 10%, 50%, and 70%. All models were imported into a 3D finite element analysis (FEA) environment and loaded; von Mises stress values and distribution patterns were evaluated.

RESULTS

Insertion of the post primarily affected the apical areas of both the root and post; the type of PFDP and periodontal support mainly affected stress distribution. In patients with a normal periodontium, splinting the teeth did not contribute to their stress relief. By extending the post length, a stressful area close to the apex of the post was developed. Splinting mitigated the stress field of the coronal part of the 50% PCT (up to 98.9%); the 30% PCT experienced a substantial decrease (up to 215.9%) in stress in the radical part as well. The increase in the length of the post produced negligible stress-related differences in the apical part of the 50% PCT (0.2% to 2.6%). The use of the 7-mm post effectively relieved the radical part of the splinted 30% PCT. The magnitude of the stress on the radical part of post-restored PCT was considerably increased in the presence of a cantilever.

CONCLUSIONS

Splinted crowns supported by a 7-mm cast post-and-core are a favorable biomechanical approach for the restoration of PCT with severe loss of coronal structure. The use of a cantilever greatly aggravates the biomechanical response, especially of post-restored PCT.

A FEM based endosteal implant simulation to determine the effect of peri-implant bone resorption on stress induced implant failure

Although dental implants exhibit only limited failure rates, their fracture is associated to major modifications of the prosthetic treatment and complex surgery for the removal of the remaining embedded implant part. This investigation aims to assess the developing stress fields in the bone-implant interface during mastication and asses the failure modes of oral implants.In order to achieve this, a FEM model of an implant was reverse engineered and virtually loaded at the top of the crown for a force spectrum ranging from 75-225 N in a vertical, horizontal and oblique occlusal direction. The calculated stress fields were compared with clinically retrieved fractured implants with identical geometrical characteristics and the fracture modes of both cases were correlated. The developing stress patterns facilitated the interpretation of the implant failure as the maximum stresses, indicated critical values in both, lingual and buccal sides of the implant-bone interface at a certain critical level of bone resorption, in which failure occurs.

Comparative characterization of STRO-1(neg)/CD146(pos) and STRO-1(pos)/CD146(pos) apical papilla stem cells enriched with flow cytometry

OBJECTIVE

Stem Cells residing in the Apical Papilla (SCAP) of human permanent teeth represent a promising cell source for dental tissue regeneration. Therefore, the functional and molecular properties of specific subpopulations existing within heterogeneous cultures should be further investigated to give insight whether their selection could be beneficial for targeted therapeutic applications.

DESIGN

In this study we extensively characterized SCAP cultures established from 10 healthy subjects, as well as their STRO-1(pos/)CD146(pos) and STRO-1(neg/)CD146(pos) subpopulations isolated with fluorescence-activated cell sorting. SCAP were analyzed for embryonic (Nanog, Oct3/4, SSEA-3, TRA-1-60), mesenchymal (STRO-1, CD146/MUC18, CD105/endoglin, CD24, CD90/Thy-1, CD81-TAPA, CD34, CD49f/a6-integrin), neural (CD271/NGFR, nestin) and hematopoietic (CD117/c-kit, CD45) stem cell (SC) markers using flow cytometry. Multipotentiality was evaluated with culture specific staining (Alizarin-Red-S, Oil- Red-O) and RT-PCR analysis for osteo/odontogenic (DSPP, BSP, ALP, osteocalcin, osteonectin, BMP-2, Runx2), adipogenic (lipoprotein-lipase-LPL) and neurogenic (Neurofilament/NFL-L, nestin, β-tubulin-III, NCAM) markers.

RESULTS

Our results showed that the STRO-1(pos)/CD146(pos) subpopulation demonstrated higher CFU efficiency and much higher expression of several embryonic and mesenchymal SC markers compared to the non-sorted SCAP. They also showed enhanced odontogenic differentiation potential, as evidenced by higher mineralization capacity and expression of osteo/odontogenic markers. By contrast, absence of STRO-1 in the STRO-1(neg)/CD146(pos) subpopulation yielded the opposite results and was associated with significant downgrading of the above-mentioned properties.

CONCLUSIONS

These results suggest that STRO-1(pos)/CD146(pos) SCAP cells represent a very promising adult MSCs source with enhanced multipotent SC properties that could be easily isolated with simple flow cytometric methods to be used for tissue engineering applications.

Development of new sol-gel derived Ag-doped biomaterials for dental applications

The aim of this work was to develop a new Ag-doped bioactive material with antibacterial behavior, optimizing the properties of the new fabricated composite material in the system SiO2 58.6 -P2O5 7.2 -Al2O3 4.2 -CaO 24.9 -Na2O 2.1 -K2O 3 (wt%). Two systems with different concentrations in Ag2O (Ba with 2.1 and Bb with 4.2 wt%) were prepared by the sol-gel method and compared to the respective silver-free control composite (CONTROL). The microstructural characteristics of the developed compositions were characterized by different techniques as UV/VIS spectroscopy, X-ray diffraction analysis (XRD) and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS). The antibacterial properties of the Ag-doped glass-ceramics were tested against the bacterial colony Staphylococcus aureus (S. aureus) which is very characteristic oral bacteria and the material-cell interaction was monitored in a primary culture of Human Gingival Fibroblasts (HGFs). Our study shows the successful incorporation of the silver ions in the ceramic structure and the preparation of new Ag-doped composite materials with cell-proliferation-inductive, as well as antibacterial properties indicating their potential application dental tissue restoration strategies.

Survival of ceramic veneers made of different materials after a minimum follow-up period of five years: a systematic review and meta-analysis

PURPOSE

The purpose of this systematic review was to compare the survival and complication rates of ceramic veneers produced with different techniques and materials after a minimum follow-up time of 5 years.

MATERIALS AND METHODS

A literature search was conducted, using electronic databases, relevant references, citations and journal researching, for clinical studies reporting on the survival of ceramic veneers fabricated with different techniques and materials with a mean followup time of at least 5 years. The search period spanned from January 1980 up to October 2010. Event rates were calculated for the following complications associated with ceramic veneers: fracture, debonding, marginal discoloration, marginal integrity, and caries. Summary estimates, and 5-year event rates were reported. Comparison between subgroups of different materials, as well as statistical significance, was calculated using a mixed effects model.

RESULTS

Nine studies were selected for final analysis over an initial yield of 409 titles. No study directly compared the incidence of complications between ceramic veneers fabricated from different materials. Four of the included studies reported on the survival of ceramic veneers made out of feldspathic ceramics; four studies were on glass-ceramic veneers and one study included veneers fabricated from both materials. The mean observation time ranged between 5 and 10 years. Overall, the 5-year complication rates were low, with the exception of studies reporting on extended ceramic veneers. The most frequent complication reported was marginal discoloration (9% at 5 years), followed by marginal integrity (3.9-7.7% at 5 years). There was no statistically significant difference in the event rates between the subgroups of different materials (feldspathic vs. glass-ceramic).

CONCLUSION

The results of this systematic review showed that ceramic veneers fabricated from feldspathic or glass-ceramics have an adequate clinical survival for at least 5 years of clinical service, with very low complication rates.

Prevalence and antimicrobial resistance of Listeria monocytogenes isolated in chicken slaughterhouses in Northern Greece

This study was conducted to determine the prevalence and antimicrobial resistance of Listeria monocytogenes recovered from chicken carcasses in slaughterhouses in Northern Greece. A total of 100 poultry samples (300 carcasses) were examined for Listeria spp. The samples were neck skin taken from four different slaughterhouses in Northern Greece. Forty samples were also taken from the environment of the slaughterhouses. Identification of L. monocytogenes was carried out by PCR and fingerprinting of the isolates by random amplified polymorphic DNA. L. monocytogenes strains isolated from chicken carcasses and from the environment of the slaughterhouses were also examined for antibiotic resistance. Fifty-five isolates of L. monocytogenes were tested for susceptibility to 20 antibiotics using the disk diffusion method. Listeria spp. were present in 99 of the poultry samples tested (99%), and 38 yielded L monocytogenes (38%). L. monocytogenes was also isolated in 80% of samples from the environment of a certain slaughterhouse, while the other slaughterhouses were found to be contaminated only with Listeria spp. All isolates were resistant to nalidixic acid and oxolinic acid, the majority of them to clindamycin, and only a few to tetracycline and oxytetracycline, whereas they were found to be susceptible to all other antimicrobials. The results of this study demonstrate a high prevalence of L. monocytogenes contamination in chicken carcasses, and all isolates were found to be sensitive to the antimicrobials most commonly used to treat human listeriosis.

The effect of select pulp cavity conditions on stress field development in distal abutments in two types of fixed dental prostheses

PURPOSE

Insufficient coronal tooth structure may require restoration of endodontically treated (ET) teeth with cast posts and cores (CPCs). The prognosis for these teeth is a matter of scientific debate, especially if they serve as distal abutments in cantilever fixed dental prostheses (FDPs). The purpose of this study was to study stress field development in distal abutments in two types of FDPs with different pulp cavity conditions.

MATERIALS AND METHODS

The methodology involved the development of four digital models in which the right mandibular premolars were splinted via an FDP with: (1) no cantilever and a vital distal abutment, (2) no cantilever and an ET CPC distal abutment, (3) a single-unit cantilever and a vital distal abutment, and (4) a single-unit cantilever with an ET CPC distal abutment. The models were analyzed using a three-dimensional finite element program, and von Mises stress values and patterns were evaluated.

RESULTS

The results revealed that although the stress distribution patterns in dentin were dissimilar, the von Mises stress values registered for the vital and ET CPC distal abutment were not considerably different. However, higher stress values were detected in the dentin area surrounding the post-gutta-percha interface after CPC placement. The addition of the cantilever resulted in a considerable increase in stress on the dental tissue structures.

CONCLUSIONS

CPCs appear to create a risk of potential fracture that is initiated in the dentin at the apex of the post. The type of restoration appears to have a much more serious impact on the stress pattern developed in the distal abutment, and the addition of a cantilever appears to biomechanically compromise both biologic and restorative structures.

Assessment of the impact of two different isolation methods on the osteo/odontogenic differentiation potential of human dental stem cells derived from deciduous teeth

Human deciduous teeth have been proposed as a promising source of mesenchymal stem cells for application in bone and dental tissue engineering. We established cultures of mesenchymal stem cells from the pulp of human deciduous teeth (deciduous teeth stem cells, DTSCs) and analyzed their morphologic, growth, immunophenotypic, and osteo/odontogenic differentiation characteristics using different isolation methods and culturing environments. We compared the biologic behavior of DTSCs isolated either by enzymatic dissociation (DTSCs-ED) or by direct outgrowth from pulp tissue explants (DTSCs-OG). We found that different isolation methods give rise to different populations/lineages of cells with respect to their phenotypic and differentiation characteristics. DTSCs-ED cultures comprised heterogeneous cell populations, whereas DTSCs-OG comprised more homogenous spindle-shaped cells. We have characterized DTSCs as STRO-1(+)/CD146(+)/CD34(+)/CD45(-) cells. However, the percentage of STRO-1(+) and CD34(+) cells was higher in DTSCs-ED (STRO-1, 17.01 ± 5.04%; CD34, 19.79 ± 4.66%) compared to DTSCs-OG cultures (STRO-1, 5.18 ± 2.39%; CD34, 9.94 ± 3.41%), probably as a result of a higher release of stem/progenitor cells from the perivascular niche during enzymatic dissociation. DTSCs isolated using either method displayed an active potential for cellular migration and biomineralization, giving rise to 3D mineralized structures when challenged with dexamethasone, monopotassium phosphate, and β-glycerophosphate. These cellular aggregates progressively expressed differentiation markers of functional odontoblasts, including dentin sialophosphoprotein, bone sialoprotein, osteocalcin, and alkaline phosphatase, having the characteristics of osteodentin. However, in DTSCs-ED, the mineralization rate and the amount of mineralized matrix produced was higher compared to DTSCs-OG cultures. Therefore, DTSCs-ED cells display enhanced biomineralization potential, which might be of advantage for application in clinical therapy.

Comparative analysis of in vitro osteo/odontogenic differentiation potential of human dental pulp stem cells (DPSCs) and stem cells from the apical papilla (SCAP)

OBJECTIVE

The aim of this study was to compare the in vitro osteo/odontogenic differentiation potential of mesenchymal stem cells (MSCs) derived from the dental pulp (dental pulp stem cells - DPSCs) or the apical papilla (stem cells from the apical papilla - SCAP) of permanent developing teeth.

DESIGN

DPSCs and SCAP cultures were established from impacted third molars of young healthy donors at the stage of root development. Cultures were analysed for stem cell markers, including STRO-1, CD146, CD34 and CD45 using flow cytometry. Cells were then induced for osteo/odontogenic differentiation by media containing dexamethasone, KH(2)PO(4) and β-glycerophosphate. Cultures were analysed for morphology, growth characteristics, mineralization potential (Alizarin Red method) and differentiation markers (dentine sialophosphoprotein-DSPP, bone sialoprotein-BSP, osteocalcin-OCN, alkaline phosphatase-ALP), using immunocytochemistry and reverse transcriptase-polymerase chain reaction.

RESULTS

All DPSCs and SCAP cultures were positive for STRO-1, CD146 and CD34, in percentages varying according to cell type and donor, but negative for CD45. Both types of MSCs displayed an active potential for cellular migration, organization and mineralization, producing 3D mineralized structures. These structures progressively expressed differentiation markers, including DSPP, BSP, OCN, ALP, having the characteristics of osteodentin. SCAP, however, showed a significantly higher proliferation rate and mineralization potential, which might be of significance for their use in bone/dental tissue engineering.

CONCLUSIONS

This study provides evidence that different types of dental MSCs can be used in tissue engineering/regeneration protocols as an approachable stem cell source for osteo/odontogenic differentiation and biomineralization that could be further applied for stem cell-based clinical therapies.

Investigation of the influence of gastric acid on the surface roughness of ceramic materials of metal-ceramic restorations. An in vitro study

The rehabilitation of eroded teeth in patients suffering from bulimia nervosa generally includes ceramics. This study compared the roughness of three ceramics before and after exposure to simulated vomit solution (SVS) with a pH of 3.8. Surface roughness parameters Ra, RMS, and AH were calculated using atomic force microscopy before and after exposure to SVS (novel peristaltic pump for 24 hours at 37°C) and were analyzed statistically. Apart from the initial high AH values of the glass-ceramic, none of the parameters evaluated were statistically significantly different after acid exposure. Under the limitations of this in vitro study, the investigated ceramics seem suitable for use in bulimia nervosa patients.

Attitudes of dentists regarding the restoration of root canal treated teeth: a survey in Greece

OBJECTIVES

To investigate attitudes of Greek dentists regarding the restoration of root canal treated (RCT) teeth and to compare them to recommended guidelines. Additionally, to examine relationships between degree of dentists' professional experience or region of practice location and attitudes of restoring RCT teeth.

METHOD

Data were collected from 302 dentists using a structured self-administered questionnaire. For each dentist a score was assigned reflecting the level of compliance with scientific recommendations for restoration of RCT teeth.

RESULTS

89.4% of the respondents reported that not every RCT tooth requires a post while the 46.4% stated that a post reinforces it. 76.2% of the participants believed that the ferrule design provides a reinforcement to RCT teeth. Dentists with 6-20 years of experience showed a higher level of compliance with the principles in the literature than their colleagues with less or more years of practising. No significant difference was detected between dentists practising in urban and rural areas.

CONCLUSIONS

The majority of Greek dentists had knowledge in accordance with recommended guidelines, except the aspect of the reinforcement effect by the post. In contrast to the region of practice location, the degree of professional experience influenced the restoration of root-treated teeth.