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 ß-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.

Molecular toxicology of substances released from resin-based dental restorative materials.

Resin-based dental restorative materials are extensively used today in dentistry. However, significant concerns still remain regarding their biocompatibility. For this reason, significant scientific effort has been focused on the determination of the molecular toxicology of substances released by these biomaterials, using several tools for risk assessment, including exposure assessment, hazard identification and dose-response analysis. These studies have shown that substances released by these materials can cause significant cytotoxic and genotoxic effects, leading to irreversible disturbance of basic cellular functions. The aim of this article is to review current knowledge related to dental composites' molecular toxicology and to give implications for possible improvements concerning their biocompatibility.

Abutment screw loosening in single-implant restorations: a systematic review.

PURPOSE: The purpose of this study was to systematically review clinical studies on the incidence of abutment screw loosening in single-implant restorations with different implant-abutment connection geometries. MATERIALS AND METHODS: The literature search was conducted using several electronic databases. Specific terms were used for the database search, which spanned the years 1990 to 2006. The search was augmented by using the option of "related articles" as well as hand searching of references and relevant journals. Relevant studies were selected according to predetermined inclusion and exclusion criteria. Agreement between reviewers was determined by using Cohen's kappa coefficients. Three-year complication-free rates (survival proportions) were calculated with the aid of a survival function, assuming constant failure rates. Summary estimates per group for complication-free rate after 3 years (M-estimator) were calculated using Tukey's biweight estimator. RESULTS: The initial database search yielded 1,526 relevant titles. After the subsequent filtering process, 27 studies were finally selected. Interexaminer agreement ranged from good to perfect. The external-connection group comprised 12 studies following 586 single-implant restorations for a mean follow-up time that ranged from 3 to 5 years. The estimated percent of complication-free single-implant restorations after 3 years was 97.3% (95% CI: 95.6-98.3). The internal connection group comprised 15 studies following 1,113 single-implant restorations for a mean follow-up time that ranged from 3 to 10 years. The estimated percentage of complication-free single-implant restorations after 3 years was 97.6% (95% CI: 96.5-98.3). CONCLUSION: The results show that abutment screw loosening is a rare event in single-implant restorations regardless of the geometry of implant-abutment connection, provided that proper antirotational features and torque are employed.

The effect of thermal cycling and air abrasion on cement failure loads of 4 provisional luting agents used for the cementation of implant-supported fixed partial dentures.

PURPOSE: To investigate the effects of thermal cycling and surface roughness of metal implant abutments and the intaglio surface of the copings on the retentive properties of 4 provisional luting agents commonly used in the cementation of implant-retained fixed partial dentures (FPDs). MATERIALS AND METHODS: A 2-unit implant-retained FPD and a 4-unit implant-retained FPD were fabricated using gold-palladium alloy. The abutments used were 5 mm in height. The FPDs were cemented with 4 commonly used provisional luting agents and thermocycled for 700 cycles from 5 degrees C to 36 degrees C to 55 degrees C and were then subjected to tensile strength testing. After thermal cycling, the intaglio surfaces of the same FPDs and the abutments were air-abraded with 50 microm Al2O3 particles. FPDs were cemented using the same provisional cements, and after 24 hours of storage in 100% humidity, tensile strength tests were performed. Descriptive statistics, 2-way analysis of variance, Friedman's 2-way ANOVA, and Tukey's HSD test (alpha = .05) were performed. RESULTS: Both thermal cycling and air abrasion had a significant effect (P < .001) on the retentive values of all cements tested. A noneugenol provisional cement (Nogenol) exhibited the lowest mean retentive value after both thermal cycling and air abrasion for both the 2- and 4-unit FPD models. The urethane resin provisional cement (Improv) exhibited the highest mean retentive strength for both the 2- and 4-unit FPDs after thermal cycling and air abrasion treatments. CONCLUSIONS: Thermal cycling had a detrimental effect on the retentive properties of all cements tested. Air abrasion significantly improved the cement failure loads of the provisional luting agents used in the study and seems to be an effective way of increasing the retention of implant-retained FPDs.

Specialisation and specialist education in prosthetic dentistry in Europe.

This presentation reports on the results of a meeting of prosthodontists from selected European countries. The aim of the meeting was to analyse and promote specialisation and specialist education in Prosthetic Dentistry in Europe. Representatives for Europe were selected from the European Prosthodontic Association (EPA) board, the Education and Research Committee of International College of Prosthodontists (ICP), countries with a legally recognised speciality, countries without a recognised speciality but organised training programmes and countries with neither of these situations. Data about specialisation and specialist training in Prosthodontics in Europe was scrutinised and discussed. The programmes for countries with specialist training had relatively similar content, mostly of three years duration. There was strong agreement that a recognised speciality raises the level of care within the discipline for both specialists and non-specialists. In several of the countries where a speciality had been introduced it had been initiated by pressure from public health planning authorities. The conclusions are that from a professional viewpoint an advancement of the speciality over Europe would develop the discipline, improve oral health planning and quality of patient care. A working group for harmonisation was recommended.

Cement-retained versus screw-retained implant restorations: a critical review.

This article presents a comparison of screw-retained and cement-retained implant prostheses based on the literature. The advantages, disadvantages, and limitations of the 2 different types of restorations are discussed, because it is important to understand the influence of the attachment mechanism on many clinical aspects of implant dentistry. Several factors essential to the long-term success of any implant prosthesis were reviewed with regard to both methods of fixation. These factors include: (1) ease of fabrication and cost, (2) passivity of the framework, (3) retention, (4) occlusion, (5) esthetics, (6) delivery, and (7) retrievability. (More than 50 references).

A meta-analysis of prosthodontic complication rates of implant-supported fixed dental prostheses in edentulous patients after an observation period of at least 5 years.

PURPOSE: To systematically review clinical studies on prosthodontic complication rates of implant fixed dental prostheses in edentulous patients after an observation period of at least 5 years. MATERIALS AND METHODS: A literature search was conducted using different electronic databases. Specific terms were used for the database search, which spanned the years 1990 to 2008. The search was augmented by using the option of "related articles" as well as by hand searching of references and relevant journals. Relevant studies were selected according to predetermined inclusion and exclusion criteria. Agreement between reviewers was determined by using Cohen kappa coefficients. RESULTS: The initial database search yielded 8,216 relevant titles. Following the filtering process, 19 studies were finally selected. No study directly compared the incidence of prosthodontic complications of complete implant-supported metal-ceramic versus metal-acrylic resin fixed prostheses in the completely edentulous patient. Studies of metal-ceramic prostheses were scarce and short term. CONCLUSION: Metal-acrylic resin complete implant fixed prostheses presented with various prosthodontic complications after long-term function. The most frequent complications were veneer fracture and material wear.

Effects of HEMA and TEDGMA on the in vitro odontogenic differentiation potential of human pulp stem/progenitor cells derived from deciduous teeth.

OBJECTIVES: The aim of this study was to investigate the effects of HEMA and TEGDMA on the odontogenic differentiation potential of dental pulp stem/progenitor cells. METHODS: Dental stem/progenitor cell cultures were established from pulp biopsies of human deciduous teeth of 1-3 year-old children (Deciduous Teeth Stem Cells-DTSCs). Cultures were characterized for stem cell markers, including STRO-1, CD146, CD34, CD45 using flow cytometry. Cytotoxicity was evaluated with the MTT assay. DTSCs were then induced for osteo/odontogenic differentiation by media containing dexamethasone, KH(2)PO(4),ß-glycerophosphate and L-ascorbic acid phosphate in the presence of nontoxic concentrations of HEMA (0.05-0.5mM) and TEGDMA (0.05-0.25mM) for 3 weeks. Additionally, the effects of a single exposure (72 h) to higher concentrations of HEMA (2mM) and TEGDMA (1mM) were also evaluated. RESULTS: DTSCs cultures were positive for STRO-1 (7.53±2.5%), CD146 (91.79±5.41%), CD34 (11.87±3.02%) and negative for CD45. In the absence of monomers cell migration, differentiation and production of mineralized dentin-like structures could be observed. Cells also progressively expressed differentiation markers, including dentin sialophosphoprotein-DSPP, bone sialoprotein-BSP, osteocalcin-OCN and alkaline phosphatase-ALP. On the contrary, long-term exposure to nontoxic concentrations of HEMA and TEGDMA significantly delayed the differentiation and mineralization processes of DTSCs, whereas, one time exposure to higher concentrations of these monomers almost completed inhibited mineral nodule formation. BSP, OCN, ALP and DSPP expression were also significantly down-regulated. SIGNIFICANCE: These findings suggest that HEMA and TEGDMA can severely disturb the odontogenic differentiation potential of pulp stem/progenitor cells, which might have significant consequences for pulp tissue homeostasis and repair.

Shear bond strength of a light-cured veneering composite to fiber-reinforced composite substrates.

PURPOSE: The aim of this study was to compare the shear bond strength of a veneering composite to 2 differently treated fiber-reinforced composite (FRC) substrates and to a base metal alloy. MATERIALS AND METHODS: A veneering composite (SR Adoro) was bonded to the following substrates: (1) a nickel-chromium base metal alloy (control, group A), (2) an FRC substructure (Vectris) with a flat surface (group B), and (3) an FRC substructure (Vectris) with retentive rods 0.5 x 0.5 mm in cross section and 10 mm in length, positioned parallel to each other at a distance of 0.5 mm (group C). Thirty-nine specimens were fabricated and divided into 3 groups of equal size. All specimens were thermocycled for 5,000 cycles at 5 degrees C and 55 degrees C with dwell time of 30 seconds in each bath. Evaluation of shear bond strength was performed at a constant crosshead speed of 0.5 mm/min according to ISO 10477. RESULTS: The mean values for the shear bond strength were 19.29 MPa for the control group (group A), 16.66 MPa for group B, and 16.74 MPa for group C. Despite a tendency to higher bond strength of group A specimens, no statistically significant difference was recorded between the groups (P > .05). CONCLUSIONS: No statistically significant difference was found between the metal and FRC substructures. Retentive rods on the FRO substructure do not seem to increase the bond strength significantly.

Pre- and post-set hydrophilicity of elastomeric impression materials.

PURPOSE: To evaluate the hydrophilicity of one polyether, four poly(vinyl siloxanes), and one condensation silicone before and after setting under simulated clinical conditions, and to correlate the findings to the contact angle values of these materials. MATERIALS AND METHODS: The hydrophilicity before and after setting, as well as the contact angle values of the elastomeric impression materials were evaluated. Part I: A freshly extracted tooth, which was prepared for a full coverage restoration, was kept in saliva for 15 minutes and was then rinsed for 10 seconds. Impressions were taken without any drying of the tooth. A total of ten samples were taken for each material. The specimens were evaluated at a 10x magnification for defects. Part II: After the evaluation, the impressions were poured with a type IV dental stone and were left for 1 hour before separation. The stone specimens were then evaluated at a 10x magnification for negative voids. A total of 60 specimens were tested. Part III: Sixty identical 10 x 10 x 4 mm(2) plastic molds were used for the fabrication of the impression material specimens. Contact angle measurements of each specimen were made 1 hour after separation from the plastic mold. A calibrated pipette was used to place a drop (0.05 ml) of saturated calcium sulfate dehydrate onto each specimen. Digital images were taken for each specimen, and contact angle values were measured with appropriate software. RESULTS: Part I: One-way ANOVA revealed significant differences among the materials (F = 15.526, p < 0.0005). Polyether had the fewest voids. The poly(vinyl siloxanes) did not present any significant differences among them, according to Tukey's HSD test (p < 0.05). Part II: One-way ANOVA revealed significant differences among the materials (F = 46.164, p < 0.0005). Polyether (Impregum) was the material which produced stone specimens with the fewest voids. Part III: One-way ANOVA indicated significant differences among the elastomeric impression materials (F = 494.918, p < 0.0005). Polyether displayed the smallest contact angle values. CONCLUSIONS: Polyether was the most hydrophilic of all materials tested.

Patterns of cell death and cell cycle profiles of cultured WEHI 13 var fibroblasts exposed to eluates of composite resins used for direct and indirect restorations.

Previous studies have shown that in vitro exposure to single compounds released from composite resins may induce cell death. In the present study the effects of eluates from commercially available composite resins used for direct or indirect restorations were evaluated on the cell cycle progression and type of cell death of cultured WEHI 13 var fibroblasts. Cells exposed to eluates of the materials were assessed for cytotoxicity by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for cell death, for cell cycle profiles by flow cytometry, for caspase-3 biochemically and by immunocytochemistry, and for morphological changes by fluorescence microscopy with acridine orange. The direct composite resin eluates induced extensive apoptosis, followed by secondary necrosis. This was accompanied by cell enlargement, micromultinucleation, chromatin disintegration, cell cycle arrest at different phases, and caspase-3 activation. The composites for indirect restorations were much less cytotoxic at all biological end-points investigated. The findings suggest that composite resins used for direct and indirect dental restorations differ in their cytotoxic potential and their ability to affect basic cellular functions. This underlines the impact of improved polymerization with respect to their biologic behavior.

Bonding indirect resin composites to metal: part 2. Effect of alloy surface treatment on elemental composition of alloy and bond strength.

PURPOSE: This laboratory study compared the effect of different surface treatments of a medium-gold, high-noble alloy on the shear bond strength of an indirect, highly filled resin composite to the alloy and on the elemental composition of the alloy surface. MATERIALS AND METHODS: Ninety disks, cast in a medium-gold, high-noble porcelain-fused-to-metal alloy (V-Deltaloy), received three different surface treatments: sandblasting with 50-microm Al2O3 (group 1) or 250-microm Al2O3 (group 2) and chemical agents, or with 250-microm Al2O3 without chemical agents (group 3) prior to bonding of an indirect resin composite (Artglass, and chemical agents Siloc-pre and Siloc-bond). The specimens were tested in shear, half of them after 24-hour dry storage at room temperature and the rest after 10-day storage in normal saline solution at 37 degrees C and thermocycling (2,500 cycles between 5 and 55 degrees C). Morphologic and qualitative changes on the alloy surface after sandblasting with 50- or 250-microm Al2O3 were examined by SEM using EDS analysis and compared with polished specimens. Statistical analysis was performed using two-factor ANOVA. RESULTS: The mean shear bond strengths (in MPa) after dry or wet storage and thermocycling were 29 and 24 for group 1, 21 and 18 for group 2, and 17 and 12 for group 3, respectively; there was a statistically significant difference among the groups. Sandblasting of the alloy surface led to statistically significant changes in elemental composition. These changes were of greater magnitude when 50-microm Al2O3 particles were used. CONCLUSION: The particle size used for sandblasting influences the shear bond strength between a high-noble alloy and a highly filled indirect resin composite, as well as the elemental composition of the alloy surface.

A survey of the use of mandibular implant overdentures in 10 countries.

PURPOSE: This preliminary international survey compared provision of implant-retained overdentures to fixed implant-supported prostheses for edentulous mandibles. MATERIALS AND METHODS: Questionnaires based on a 2001 Swedish study were sent to prosthodontists and specialist clinics in nine additional countries. RESULTS: Response rate varied from 53% to 100% in 10 national surveys and should allow careful comparison of results. The relationship between implant overdentures and fixed implant-supported prostheses in treatment of edentulous mandibles varied much; in Sweden, the proportion of overdentures was 12%, whereas it was 93% in The Netherlands. In all countries, the most common reason for choice of the overdenture was reduced cost. In all but two countries, the majority of respondents thought that patients with implant overdentures were equally or more satisfied with overdentures as those with fixed implant-supported prostheses. CONCLUSION: There were great differences among the 10 countries in choice of implant treatment of the edentulous mandible. The relative proportion of mandibular overdentures to fixed prostheses was low in Sweden and Greece and varied from one to two thirds in the other countries, except The Netherlands.