Influence of two different cement space settings and three different cement types on the fit of polymer-infiltrated ceramic network material crowns manufactured using a complete digital workflow.

OBJECTIVES: The study evaluates the influence of two spacer settings and three resin luting materials on the marginal and internal fit of polymer-infiltrated ceramic network (PICN) material crowns manufactured using a complete digital workflow. METHODS: Optical impressions of fifty identical dies were performed using the 3M scanner (software version 5.0.2). Twenty crowns were designed using Ceramill Mind (version 3.4.10.1163), from which ten with spacer setting of 50 µm (G1) and ten with 80 µm (G2). Thirty crowns (spacer setting of 50 µm) were divided into three groups corresponding to the resin materials used as follows: RelyX Unicem (RX), Variolink Esthetic (VLE), and Nexus 3 (NX3). All crowns were milled from Vita Enamic blocks. After micro-CT scanning, absolute marginal discrepancy (AMD), internal gap (IG), total cement space volume (TCV), and marginal porosities (VP) were measured. RESULTS: Significant difference was detected on the VP between the RX and NX3 group (p = 0.033). The mean values of all parameters were the following: AMD (µm): G1 182.6, G2 253.7, RX 210.8, VLE 195.5, NX3 186.6; IG (µm): G1 215.6, G2 173.1, RX 171.1, VLE 198.6, NX3 203; TCV (mm3): G1 22.9, G2 20.49, RX 17.57, VLE 17.49, NX3 20.59; VP (mm3): G1 0.26, G2 0.34, RX 0.32, VLE 0.46, NX3 0.54. CONCLUSIONS: Fit of PICN material crowns was not significantly influenced by increasing the spacer settings and cementation with different resin materials. Additionally, RelyX Unicem showed significantly less porosities as compared with Nexus3. CLINICAL RELEVANCE: Both 50 µm and 80 µm virtual spacer settings can be suggested for the manufacture of PICN crowns when Ceramill Mind (version 3.4.10.1163) is used. Furthermore, a self-adhesive system can be recommended for the cementation.

Do strength of zirconia-abutment-interfaces depend on cement, zirconia type and titanium abutment dimensions?

OBJECTIVES: Part 1 of this study investigates the influence of zirconia types, chimney heights, and gingival heights on the strength of the zirconia-abutment-interface. Part 2 extends the analysis to include adhesive brands and macro-retentions. METHODS: In Part 1, the study utilized three zirconia types (700 MPa, 1000 MPa, 1200 MPa) to fabricate 234 screw-retained zirconia crowns with varying chimney heights (3.5 mm, 4.1 mm, 5 mm) and gingival heights (0.65 mm, 1.2 mm, 3 mm) of the titanium abutments. All adherend surfaces underwent sandblasting with aluminum oxide before cementation with a specific resin cement. In Part 2, the investigation of 240 screw-retained zirconia crowns focused on a single zirconia type (1000 MPa) with chimney heights of 3.5 mm and 5 mm and a gingival height of 0.65 mm of the titanium abutments, cemented with three different resin cements. All adherent surfaces underwent sandblasting with aluminum oxide before cementation, whereas 120 out of 240 abutments received additional macro retentions. Storage in water at 37 °C for 24 h preceded the tensile test. RESULTS: The study revealed a substantial impact of chimney height and zirconia type on the bond strength of the zirconia-abutment-interface. Neither adhesive brands nor macro retentions significantly impacted the bond strength. Fracture incidence was significantly influenced by gingival height and zirconia type in part 1, whereas in part 2 smaller chimney heights correlated with a higher fracture incidence. SIGNIFICANCE: This study contributes insights into the complex interplay of factors influencing the zirconia-abutment-interface. The results provide a foundation for refining clinical approaches, emphasizing the importance of chimney height and zirconia type in achieving successful anterior gap implant restorations.

Clinical and Radiographic Outcomes of Single Implant-Supported Zirconia Crowns Following a Digital and Conventional Workflow: Four-Year Follow-Up of a Randomized Controlled Clinical Trial.

PURPOSE: This study aimed to compare the clinical and radiographic outcomes of single posterior screw-retained monolithic implant crowns following a digital and conventional workflow and to report on the survival/complication rate after a mean 4-year follow-up. MATERIALS AND METHODS: Thirty patients with a single posterior tooth missing were rehabilitated with a bone-level implant. After a healing period of ≥3 months, they were subjected to both a digital and conventional workflow to fabricate two screw-retained monolithic implant crowns. The quantitative clinical adjustments to both crowns (intrasubject comparison) and a questionnaire were recorded at try-in. Thereafter, a crown of the digital and conventional workflows was randomly inserted. At the last follow-up, the marginal bone level (MBL), peri-implant health-related parameters (bleeding on probing (BoP), plaque, pocket probing depth (PPD)), and functional implant prosthodontic score (FIPS) were assessed. Furthermore, the implant survival and success rates and technical complications were evaluated. RESULTS: A total of 27 patients were followed for a mean period of 4.23 ± 1.10 years. There was no significant difference between the digital and conventional workflows regarding clinical adjustments and questionnaire outcomes. More than twice as many participants recommended digital (n = 16) compared to conventional impressions (n = 7) to friends. The implant survival and success rate were 100% and 96.3%, respectively. Furthermore, two de-cementations and one fracture of the ti-base abutment occurred. There were no significant differences in BoP, plaque, and PPD metrics between the two groups. The changes in the MBL between implant crown insertion (baseline) and the last follow-up were 0.07 ± 0.19 mm and 0.34 ± 0.62 mm in the digital and conventional groups, respectively (p = 0.195). The mean overall FIPS score was 8.11 ± 1.37 (range: 5-10). CONCLUSIONS: The clinical and radiographic outcomes of single screw-retained monolithic implant crowns were similar between both workflows after a mean of 4 years of service. The patients did not clearly prefer an impression technique for their restoration, although they would recommend the digital impression more often to friends. Thus, decision regarding clinical workflows may be based on the patient's and/or clinician's preference.

The impact of print orientation and graphene nanoplatelets on biaxial flexural strength and cytotoxicity of a 3D printable resin for occlusal splints.

OBJECTIVES: 3D printing found its way into various medical applications and could be particularly beneficial for dentistry. Currently, materials for 3D printing of occlusal splints lack mechanical strength compared to polymethyl methacrylate (PMMA) used for standard milling of occlusal splints. It is known that print orientation and graphene nanoplatelets (GNP) can increase biaxial strength in a variety of materials. Thus, the aim of this study was to assess if adjustment of print orientation and addition of GNP improve biaxial strength and if they affect cytotoxicity of a 3D printable resin for occlusal splints. METHODS: Specimens were printed vertically and horizontally with a stereolithography (SLA) printer and multilayered GNP powder was added to the resin at different concentrations. Printed specimens were characterized by Raman spectroscopy, optical profilometer analysis and scanning electron microscopy. Biaxial strength was evaluated by biaxial flexural testing. Cytotoxicity of specimens on L929 and gingival stromal cells (GSC) was assessed by the toxdent test, the resazurin-based toxicity assay and live-dead staining. RESULTS: Horizontally printed specimens showed significantly higher biaxial strength and lower deformation. GNP did not improve biaxial strength and material deformation of 3D-printed resins. None of the specimens were cytotoxic to L929 cells or GSC. SIGNIFICANCE: Print orientation in SLA printing has a significant impact on biaxial strength and material deformation. 3D printable materials can reach comparable or even improved biaxial strength compared to PMMA when using the optimal print orientation while GNP has no beneficial effects on the biaxial strength of resins for 3D printing of occlusal splints.

Comparison of Virtual Intersection and Occlusal Contacts between Intraoral and Laboratory Scans: An In-Vivo Study.

BACKGROUND: The inaccurate maxillomandibular relationship of virtual casts following alignment by the vestibular scan may result in intersection (intermesh penetration) between opposing dental arch surfaces. Intersection occurs at short interocclusal distances in the occlusal contact area (OCA) and may result in infra-occluded definitive restorations. The purpose of this clinical study was to compare initial (by the proprietary scanner software) and new alignments (by a standalone 3D software) of virtual casts regarding OCA and intersection failure. New alignments aimed to rectify intersections by refinement of occlusal contacts. MATERIAL AND METHODS: The virtual casts of 30 patients following digital and conventional impression-taking were analyzed, which were acquired for single implant restoration in the posterior site. Digital impressions were performed by both IOS 1 (3M True Definition) and IOS 2 (TRIOS 3), either as complete- or partial-arch scans, respectively. Mounted gypsum casts were digitized as complete-arch by a laboratory scanner (LS) in enabled and disabled mode to avoid intersection [LS (+)/LS (-)]. All virtual casts were newly aligned by a 3D software. The difference of the OCA and the area of intersection were calculated for initial and new alignments, using interocclusal distance ranges of 0-100 µm, 0-10 µm or <0 µm (=intersection). The difference of the OCA was compared using a linear mixed model. The distribution of occlusal contact points per modality and alignment was assessed independently by three observers and estimated by inter- and intraclass correlation (ICC) coefficients. RESULTS: Virtual casts following initial alignment demonstrated intersections irrespective of the modality. The mean area of the intersection was most for IOS 2 (79.23 mm2), followed by IOS 1 (48.28 mm2), LS (-) (2.77 mm2), and LS (+) (2.01 mm2) in partial-arch scans. Complete-arch scans demonstrated an area of intersection of 70.63 mm2 for IOS 1 followed by 65.52 mm2 (IOS 2), 6.13 mm2 [LS (-)] and 2.76 mm2 [LS (+)]. Newly aligned scans showed no intersections. The overall distribution of occlusal contact points demonstrated moderate reliability (ICC 0.63). Good reliability could be observed (ICC 0.9) for LS (-) scans. CONCLUSIONS: Intersections in the area of occlusal contact points are a phenomenon restricted to virtual casts, which should be considered in CAD/CAM. Initial alignments of LS are less affected by this virtual phenomenon, and contact points may be more distinct according to their anatomic region compared to IOS. Furthermore, intersections can be rectified in a 3D software by adjustment of the maxillomandibular relationship.

3D printed indirect bonding trays: Transfer accuracy of hard versus soft resin material in a prospective, randomized, single-blinded clinical study.

OBJECTIVES: This prospective clinical study aimed to compare transfer accuracy and immediate loss rate of hard versus soft transfer trays utilizing a CAD/CAM workflow. METHODS: We performed virtual bracket placement on intraoral scans of adolescent patients to create individual indirect bonding trays. Orthodontic software (Appliance Designer, 3Shape, Copenhagen, Denmark) was used to design the trays, which were then produced using 3D printing technology. Patients were randomly assigned to the hard or soft resin groups with a 1:1 allocation. Subgroups were determined based on the Little's Irregularity Index and distributed equally. RESULTS: 552 brackets were bonded onto adolescent patients using 46 CAD/CAM indirect bonding trays. The linear mean transfer errors ranged from -0.011 mm (soft) to -0.162 mm (hard) and angularly -0.255° (hard) and -0.243° (soft). No statistically significant differences were found between the subgroups or soft and hard resin groups. However, the transfer accuracy of molar brackets was significantly lower in the transversal and horizontal directions. All mean transfer errors were within the limits of clinical acceptability. The loss rate was 2.4 % in the hard resin group and 2.3 % in the soft resin group. The Intra Observer Correlation was excellent. SIGNIFICANCE: CAD/CAM technology for indirect bracket bonding has been proven reliable in a randomized clinical trial. Both hard and soft resin showed a low rate of immediate loss compared to the current literature. Soft resin was more favorable than hard resin in terms of accuracy and usability. However, the indirect bonding of molar brackets is significantly less accurate than incisor brackets.

CAD/CAM indirect bonding trays using hard versus soft resin material: a single-blinded in vitro study.

OBJECTIVES: The present in vitro study aimed to evaluate the accuracy of three-dimensional (3D) printed indirect bonding trays consisting of hard or soft resin materials produced using computer-aided design and manufacturing (CAD/CAM). METHODS: Forty-eight dental casts were 3D printed. Four groups based on frontal crowding were defined and divided into hard- and soft-resin groups. After virtual bracket positioning on the digital models, the transfer trays were 3D printed. To evaluate the accuracy of the procedure, measurements were performed using a digital overlay of the virtual (target) bracket position and a post-bonding scan. The horizontal, transverse, and vertical deviations and angular discrepancies were analyzed. The loss rate was evaluated descriptively as a percentage. RESULTS: A total of 553 brackets were bonded using 24 soft and 24 resilient indirect bonding trays. The mean deviations were of 0.05 mm (transversal), 0.05 mm (horizontal), 0.09 mm (vertical), 0.13° (angulation) in the resilient resin group and of 0.01 mm (transversal), 0.08 mm (horizontal), 0.08 mm (vertical), 0.37° (angular) in the soft resin group. The loss rate was 6.9% and 0.7% in the hard and soft resin groups, respectively. Angular deviations were significantly higher in the soft resin group (P = 0.009), whereas the loss rate was considerably higher in the hard resin group (P < 0.001). SIGNIFICANCE: The findings indicate that indirect bonding using CAD/CAM is an accurate procedure in the laboratory setting. Soft resins are considered favorable for loss rate and useability.

Medical 3D printing with polyjet technology: effect of material type and printing orientation on printability, surface structure and cytotoxicity.

Due to its high printing resolution and ability to print multiple materials simultaneously, inkjet technology has found wide application in medicine. However, the biological safety of 3D-printed objects is not always guaranteed due to residues of uncured resins or support materials and must therefore be verified. The aim of this study was to evaluate the quality of standard assessment methods for determining the quality and properties of polyjet-printed scaffolds in terms of their dimensional accuracy, surface topography, and cytotoxic potential.Standardized 3D-printed samples were produced in two printing orientations (horizontal or vertical). Printing accuracy and surface roughness was assessed by size measurements, VR-5200 3D optical profilometer dimensional analysis, and scanning electron microscopy. Cytotoxicity tests were performed with a representative cell line (L929) in a comparative laboratory study. Individual experiments were performed with primary cells from clinically relevant tissues and with a Toxdent cytotoxicity assay.Dimensional measurements of printed discs indicated high print accuracy and reproducibility. Print accuracy was highest when specimens were printed in horizontal direction. In all cytotoxicity tests, the estimated mean cell viability was well above 70% (p < 0.0001) regardless of material and printing direction, confirming the low cytotoxicity of the final 3D-printed objects.

Biomechanical finite element analysis of short-implant-supported, 3-unit, fixed CAD/CAM prostheses in the posterior mandible.

OBJECTIVE: To assess the biomechanical effects of different prosthetic/implant configurations and load directions on 3-unit fixed prostheses supported by short dental implants in the posterior mandible using validated 3-D finite element (FE) models. METHODS: Models represented an atrophic mandible, missing the 2nd premolar, 1st and 2nd molars, and rehabilitated with either two short implants (implant length-IL = 8 mm and 4 mm) supporting a 3-unit dental bridge or three short implants (IL = 8 mm, 6 mm and 4 mm) supporting zirconia prosthesis in splinted or single crowns design. Load simulations were performed in ABAQUS (Dassault Systèmes, France) under axial and oblique (30°) force of 100 N to assess the global stiffness and forces within the implant prosthesis. Local stresses within implant/prosthesis system and strain energy density (SED) within surrounding bone were determined and compared between configurations. RESULTS: The global stiffness was around 1.5 times higher in splinted configurations vs. single crowns, whereby off-axis loading lead to a decrease of 39%. Splinted prostheses exhibited a better stress distribution than single crowns. Local stresses were larger and distributed over a larger area under oblique loads compared to axial load direction. The forces on each implant in the 2-implant-splinted configurations increased by 25% compared to splinted crowns on 3 implants. Loading of un-splinted configurations resulted in increased local SED magnitude. CONCLUSION: Splinting of adjacent short implants in posterior mandible by the prosthetic restoration has a profound effect on the magnitude and distribution of the local stress peaks in peri-implant regions. Replacing each missing tooth with an implant is recommended, whenever bone supply and costs permit.

Experimental validation of a micro-CT finite element model of a human cadaveric mandible rehabilitated with short-implant-supported partial dentures.

PURPOSE: This study aimed to address the predictive value of a micro-computed tomography (µCT)-based finite element (µFE) model of a human cadaveric edentulous posterior mandible, rehabilitated by short dental implants. Hereby, three different prosthetic/implant configurations of fixed partial dentures ("Sp"-3 splinted crowns on 3 implants, "Br" - Bridge: 3 splinted crowns on 2 implants, and "Si"- 3 single crowns) were analysed by comparing the computational predictions of the global stiffness with experimental data. METHODS: Experimental displacement of the bone/implant/prosthesis system was measured under axial and oblique loads of 100 N using an optical deformation system (GOM Aramis) and the overall movement of the testing machine (Zwick Z030). Together with the measured machine force, an "Aramis" (optical markers) and "Zwick" (test machine) stiffness were calculated. FE models were created based on µCT-scans of the cadaveric mandible sample (n = 1) before and after implantation and using stl-files of the crowns. The same load tests and boundary conditions were simulated on the models and the µFE-results were compared to experimental data using linear regression analysis. RESULTS: The regression line through a plot of pooled stiffness values (N/mm) for the optical displacement recording (true local displacement) and the test machine (machine compliance included) had a slope of 0.57 and a correlation coefficient R2 of 0.82. The average pooled correlation of global stiffness between the experiment and FE-analysis (FEA) showed a R2 of 0.80, but the FEA-stiffness was 7.2 times higher. The factor was highly dependent on the test configuration. Sp-configuration showed the largest stiffness followed by Br-configuration (17% difference in experiment and 21% in FEA). CONCLUSIONS: The current study showed good qualitative agreement between the experimental and predicted global stiffness of different short implant configurations. It could be deduced that 1:1 splinting of the short implants by the crowns is most favorable for the stiffness of the implant/prosthesis system. However, in the clinical context, the absolute in silico readings must be interpreted cautiously, as the FEA showed a considerable overestimation of the values.

Optimizing the fitting-surface preparation of zirconia restorations for bonding to dentin.

OBJECTIVES: The aim of this study was to identify the relative strengths and weaknesses of different interfaces within the multilayer structure of a zirconia crown restoration when applying different surface pretreatments. These include the influence on shear strengths of different air abrasion protocols, glaze-on techniques, zirconia primers and self-adhesive cements for either the complex structure: zirconia / self adhesive resin composite cement (RCC) / bovine dentin substrate (part 1) or the RCC / zirconia substrate (part 2). METHODS: In Part 1, zirconia discs, pretreated by either glaze-on techniques or air abrasion using Rocatec™ Soft, were bonded to bovine dentin substrates with different self-adhesive RCCs. In Part 2, steel-cylinders were bonded to zirconia cuboid substrates, pretreated by either different protocols for air-abrasion or a glaze-on-technique, with different self-adhesive RCCs. Shear bond strengths (SBS) were measured for all interfacial combinations. RESULTS: In part 1, application of air abrasion using Rocatec™ Soft significantly increased the SBS of zirconia to dentin compared to control specimens without pretreatment, while glaze-on techniques did not increase the SBS. Pretreatment of zirconia surfaces with two primers (either Clearfil Ceramic Primer, or Monobond S) showed significantly higher SBS than the controls. Cementations with RelyX Unicem 2 Automix showed significantly higher SBS than with MaxCem Elite. In Part 2, all air abrasion protocols increased the SBS, but there was no significant difference between these protocols. Again the glaze-on technique did not increase SBS. A significant difference between the two RCCs was again observed. When zirconia substrates were air abraded, regardless of which protocol was applied, the highest SBS were obtained by Calibra with P&B active followed by Panavia with or without Clearfil Ceramic Primer Plus. Calibra applied without P&B active exhibited the lowest SBS. SIGNIFICANCE: Pretreatment of zirconia substrates using air abrasion and/or ceramic primers increased the SBS of the zirconia cement interface. For all tested glaze-on treatments, in our experimental setting no effect was observed.

The proliferation and differentiation of osteoblasts in co-culture with human umbilical vein endothelial cells: An improved analysis using fluorescence-activated cell sorting.

The interaction of osteoblasts and endothelial cells plays a pivotal role in osteogenesis. This interaction has been extensively studied using their direct co-culture in vitro. However, co-culture experiments require clear discrimination between the two different cell types in the mixture, but this was rarely achieved. This study is the first to use fluorescence-activated cell sorting (FACS) for the separation and quantitative analysis of the proliferation and differentiation of MG-63 cells grown in direct co-culture with human umbilical vein endothelial cells (HUVECs). The cells of the MG-63 cell line have properties consistent with the characteristics of normal osteoblasts. We labeled HUVECs with fluorescent antibody against CD31 and used FACS to measure the proportions of each cell type and to separate them based on their different fluorescence intensities. The rate of proliferation of the MG-63 cells was estimated based on a count of the total viable cells and the proportion of MG-63 cells in the mixture. The mRNA expression levels of the osteoblast differentiation markers alkaline phosphatase (ALP), collagen type 1 (Coll-1) and osteocalcin (OC) in the MG-63 cells were measured via real-time PCR after the separation via FACS. We found that HUVECs stimulated the proliferation of the MG-63 cells after 72 h of co-culture, and inhibited it after 120 h of co-culture. The mRNA expression levels of ALP and Coll-1 significantly increased, whereas that of OC significantly decreased in MG-63 after co-culture with HUVECs. Using FACS for the quantitative analysis of the proliferation and differentiation of osteoblasts directly interacting with endothelial cells could have merit for further co-culture research.

Limited reciprocity in curing efficiency of bulk-fill resin-composites.

OBJECTIVE: The aim of the study was to identify experimental limits of the general reciprocity hypothesis that the same photo-cure outcomes will result from applying essentially constant energy densities, despite reciprocal variations in the irradiance and irradiation time-period, for a representative set of bulk fill (BF) and non-BF resin composites. METHODS: Six BF and two non-BF resin-composites were selected. The unset pastes were inserted into white acetal molds (5mm id) with (n=6) depths (1, 2, 3, 4, 5 and 6mm). Three light curing units (LCUs) of increasing radiant emittance capability: 1200, 2000 and 3200mW/cm2 were used. Composite specimen groups (n=3, per depth, per LCU) were irradiated on the upper surface only. For each specific composite, the irradiation times for each LCU were reduced reciprocally, as the LCU irradiance increased, to deliver a constant energy density (J/cm2) to that composite. However, the required energy density for a given composite differed in accordance with each composite manufacturer recommendations. After storing for 24h at 37°C, light transmission measurements were made through each specimen and re-expressed as Apparent Absorbance (A'). Vickers hardness (HV) measurements (n=10) were made on both top and bottom surfaces, for each specimen, and HVversus "depth" profile plots created. From the top-surface data, a Depth-of-Cure parameter could be derived. Data were statistically evaluated for differences between top and bottom HV values and for other predefined variables of interest. RESULTS: Irradiation with the LCU of 1200mW/cm2 generally gave the highest HV/depth for most materials tested compared to the other curing lights with higher power output, regardless of top and bottom measurements (p<0.001). However, this difference was material-dependent. With one BF composite, 1200 and 2000mW/cm2 irradiance did not show a significant difference between top and bottom HV. Composites with higher translucency showed reduced differences in top/bottom HV than more opaque composites. SIGNIFICANCE: Reciprocity was found to be limited with most materials examined, such that irradiance periods of 10s, gave generally better HV outcomes than by using LCUs of superior radiant emittance while reciprocally reducing irradiance time to maintain constant dose of energy density.

Micro-CT evaluation of marginal and internal fit of cemented polymer infiltrated ceramic network material crowns manufactured after conventional and digital impressions.

PURPOSE: Purpose of this study was to evaluate the accuracy of fit of cemented polymer infiltrated ceramic network (PICN) material crowns manufactured after digital and conventional impression techniques using micro computed tomography (CT). Furthermore to determine the cement space volume and porosities in the cement layer. METHODS: A molar typodont tooth was prepared for PICN material crowns and replicated thirty times. The dies were randomly divided into three groups of 10 specimens each according to the impression technique: 3M True Definition Scanner (TDS), cara TRIOS (Trios) and Impregum Penta Soft (Impregum). PICN material crowns were milled for each specimen from Vita Enamic blocks and cemented on their respective dies. The absolute marginal discrepancy (AMD), internal fit (IG), total cement space volume (TVC) and marginal porosities (VP) were measured using Micro-CT. RESULTS: Mean and standard deviations values in µm for the AMD were: TDS 140.1 (28.4); Trios 253.7 (56.8); Impregum 220.2 (101.1). IG values in µm: TDS 173.1 (27.7); Trios 222.2 (22.4); Impregum 211.6 (55.9). TVC in mm3: TDS 19.82 (2.9); Trios 23.67 (2.01); Impregum 23.77 (5.09). VP in mm3: TDS 0.38 (0.09); Trios 0.36 (0.10); Impregum 0.51 (0.31). CONCLUSIONS: TDS group showed significantly better marginal and internal fit than the Trios group. No difference of the parameters was detected between the Impregum and both digital groups which implies that the digital impression technique is suitable in the manufacturing process of PICN material crowns.

Comparison of Bleaching Products With Up to 6% and With More Than 6% Hydrogen Peroxide: Whitening Efficacy Using BI and WI D and Side Effects - An in vitro Study.

The aim of this study was to evaluate the effect of bleaching agents containing different concentrations of hydrogen peroxide (HP) on color-change and on enamel-surface in bovine teeth. Furthermore the influence on cell viability and proliferation was investigated. Two hundred and forty teeth were randomly assigned into four groups (home bleaching ≤6%, in-office bleaching ≤6%, in-office bleaching > 6% HP, and control group). Bleaching was performed after artificial staining and the bleached index (BI) as well as the whiteness index (WI D ) was measured at several time points. Chemical analysis for HP concentrations and the pH of the bleaching products was done. Furthermore, enamel surfaces of randomly selected specimens were analyzed using scanning electron microscopy (SEM) and cytotoxicity of the tested bleaching products was evaluated in vitro using dental pulp cells (DPCs) and L929 cells. A statistically significant whitening effect was observed in almost all products. As expected all investigated products resulted in decreased cell viability, however, with different values of LC50 (median lethal concentration). SEM analysis showed an analog of enamel alterations with decreasing pH, increasing exposure time, and increasing HP concentration. Bleaching agents containing a low HP concentration are considered to be effective and to have less damaging effects on enamel and tested cells.

Differentiation and cytokine synthesis of human alveolar osteoblasts compared to osteoblast-like cells (MG63) in response to titanium surfaces.

OBJECTIVES: The aim of this study was to investigate the influence of different implant surface topographies and chemistries on the expression of differentiation/proliferation markers on MG63 cells and primary human alveolar osteoblasts. METHODS: Hydrophobic acid-etched (A) and hydrophobic coarse-grit-blasted, acid-etched (SLA) surfaces and hydrophilic acid-etched (modA) and hydrophilic coarse-grit-blasted (modSLA) surfaces were produced. Thereby, modA and modSLA surfaces were rinsed under nitrogen protection and stored in a sealed glass tube containing isotonic NaCl solution at pH 4-6. Tissue culture plates without specimens served as controls. The behavior of MG63 cells and primary human alveolar osteoblasts (AOB) grown on all surfaces was compared through determination of alkaline phosphatase (ALP) activity, cell proliferation ((3)H-thymidin incorporation, MTT colorimetric assay) and expression of osteocalcin (OC), osteoprotegerin (OPG), transforming growth factor-beta1 (TGF-beta(1)) and vascular endothelial growth factor (VEGF), detected with commercial available test kits. RESULTS: Proliferation of MG63 and primary cells was highest on controls, followed by A surfaces, modA and SLA surfaces being almost on the same level and lowest on modSLA surfaces. modSLA surfaces exhibited highest ALP and OC production, followed by SLA, modA and A surfaces. Proliferation and OC production were comparable for MG63 cells and AOB. OPG, TGF-beta(1) and VEGF produced on primary cells showed a slightly different rank order on different surfaces compared to MG63 cells. modSLA still showed the highest production of OPG, TGF-beta(1) and VEGF, but was followed by modA, SLA and A. Statistical significance was checked by ANOVA (p<0.0035). SIGNIFICANCE: MG63 cells and primary human alveolar osteoblasts showed similar proliferation and differentiation characteristics on different titanium surfaces. Only modA surfaces showed enhanced expression of OPG, TGF-beta(1) and VEGF on MG63 cells compared to primary human alveolar osteoblasts. Overall, the lowest proliferation rates and the highest expressions of differentiation markers and growth factor productions were observed on modSLA.

Cytotoxicity and shear bond strength of four orthodontic adhesive systems.

The objective of this study was to compare the cytotoxicity of four orthodontic bonding systems, Light Bond, Enlight, Concise, and Transbond, and to evaluate their shear bond strength (SBS). These orthodontic bonding materials were applied to metal brackets (Mini Diamond). Glass specimens were used as controls in all experiments. Only Concise was a chemically cured system, the other systems were light cured. The specimens were added to L-929 fibroblast cultures immediately after fabrication or after pre-incubation for 7 days. The incubation time was 72 hours and the cells were counted by flow cytometry. One hundred and fifty-seven freshly extracted human third molars were used for testing the SBS in a universal testing machine. Statistical significance was determined using analysis of variance followed by post hoc comparisons for multiple-level alpha control. Pairwise comparisons showed a significant difference only between Light Bond and Concise (P = 0.0126). The highest SBS was obtained with Light Bond (23.23 +/- 1.53 MPa) followed by Transbond (20.39 +/- 1.18 MPa) and Enlight, (20.32 +/- 1.06 MPa). Concise (17.87 +/- 1.04 MPa) showed the lowest SBS. The cytotoxicity of all light-cured systems for fresh specimens was comparable, whereas the chemically cured system, Concise, was significantly more cytotoxic. After 7 days of pre-incubation, all systems were significantly less cyotoxic than fresh specimens (P < 0.001). Brackets alone were not cytotoxic. All bonding systems showed a clinically satisfactory bond strength higher than 10 MPa, with the chemically cured system showing the lowest SBS.

The initial attachment and subsequent behavior regulation of osteoblasts by dental implant surface modification.

The aim of this study was to investigate the influence of hydrophobic acid-etched (A) and coarse-blasted large-grit and acid-etched (SLA) surfaces as well as hydrophilic modified acid-etched (modA) and modified coarse-blasted large-grit and acid-etched (modSLA) surfaces on the behavior of MG63 cells grown on these surfaces through determination of cell attachment and cell proliferation, time-lapse microscopy of fluorescence-labeled cells, and determination of gene expression by reverse transcription-polymerase chain reaction (RT-PCR). No significant difference of cell attachment on various titanium surfaces was found. Increased cell proliferation was observed on the A surface and the SLA surface compared with the modA surface and the modSLA surface. After 2 days of incubation, on modSLA and modA surfaces a tendency of formation of cell clusters has been observed, which was most pronounced on modSLA surface. On the A and the SLA surface, cell cluster formation started after longer incubation periods. The expression level of the bone-associated genes (alkaline phosphatase, osteocalcin, type-I-collagen, osteoprotegerin, and glyceraldehyde-3-phosphate-dehydrogenase) detected by RT-PCR was highest on the modSLA surface. In conclusion it has been demonstrated that the modSLA surface results in an enhanced cluster formation of osteoblasts grown on this surface and in an increased expression of key osteogenic regulatory genes in osteoblasts.

Cytotoxicity of resin composites as a function of interface area.

OBJECTIVES: The standardization protocols for biomaterial cytotoxicity testing require fine tuning for oral biomaterials to obtain international comparability as the basis for risk assessment. The principal aims were specifically to evaluate the effect of (i) relative interface area (ratio of specimen surface to cell layer surface) and (ii) volume of cell culture medium on cytotoxicity as a potential modification of ISO 10993-5. METHODS: ISO 10993-5 was followed with an interface area of 12.5%, as recommended, using primary human gingival fibroblasts and L-929 mouse fibroblasts. In another series of experiments (using L-929 cells) the interface area was varied between 12.5% and 0.71%. For each relative interface area, three conditions for affecting the cure of the resin composite were investigated by using three mould materials: white, transparent and black moulds. In addition, the volume of cell culture medium was varied. Composite specimens (Herculite XRV) were added to the cultures immediately after production or preincubation for 1, 2, 7 days or 6 weeks under cell culture conditions. Specimens were incubated with fibroblasts for 72 h and cell numbers determined by flow cytometry. Glass specimens resembling composite specimens in diameter and height were used as negative controls. RESULTS: Cytotoxicity results with primary gingival fibroblasts were comparable to results with the cell line L-929. An effect from the color/material of the specimen moulds was found. Different ratios of specimen sizes to cell culture parameters (cell layer surface, volume of cell culture medium) produced different results. Three out of four differently designed specimens showed the same behavior in cell culture. SIGNIFICANCE: Cytotoxicity tests should be further standardized in line with existing standards with regard to specimen production protocols to ensure results are internationally comparable to validate these tests as tools for risk assessment.

Proliferation, behavior, and differentiation of osteoblasts on surfaces of different microroughness.

OBJECTIVES: Titanium surface roughness is recognized as an important parameter influencing osseointegration. However, studies concerning the effect of well-defined surface topographies of titanium surfaces on osteoblasts have been limited in scope. In the present study we have investigated how Ti surfaces of different micrometer-scale roughness influence proliferation, migration, and differentiation of osteoblasts in-vitro. METHODS: Titanium replicas with surface roughnesses (Ra) of approximately 0, 1, 2, and 4µm were produced and MG-63 osteoblasts were cultured on these surfaces for up to 5 days. The effect of surface micrometer-scale roughness on proliferation, migration in time-lapse microscopy experiments, as well as the expression of alkaline phosphatase, osteocalcin, vascular-endothelial growth factor (VEGF), osteoprotegerin (OPG), and receptor activator of nuclear factor kappa-B ligand (RANKL) were investigated. RESULTS: Proliferation of MG-63 cells was found to decrease gradually with increasing surface roughness. However, the highest expression of alkaline phosphatase, osteocalcin and VEGF was observed on surfaces with Ra values of approximately 1 and 2µm. Further increase in surface roughness resulted in decreased expression of all investigated parameters. The cell migration speed measured in time-lapse microscopy experiments was significantly lower on surfaces with a Ra value of about 4µm, compared to those with lower roughness. No significant effect of surface roughness on the expression of OPG and RANKL was observed. SIGNIFICANCE: Thus, surfaces with intermediate Ra roughness values of 1-2µm seem to be optimal for osteoblast differentiation. Neither proliferation nor differentiation of osteoblasts appears to be supported by surfaces with higher or lower Ra values.