Dimitris Papadogiannis

Setting characteristics and cavity adaptation of low-shrinking resin composites

OBJECTIVES The aim of this study was to evaluate the setting characteristics of low-shrinking resin composites and examine the possible interactions with curing efficiency and marginal adaptation in dentin cavities. METHODS The materials tested were Ceram X Mono/CM, Premise/PR, Clearfil Majesty/CM, ELS/EL, and Filtek Silorane/FS. Polymerization shrinkage strain (%S), strain rate (%S(r)) and time at maximum strain rate (t(max)) were measured using the bonded disk method. Curing efficiency was measured on the top and bottom surfaces of composites with ATR-FTIR spectroscopy. Marginal adaptation was measured in unbonded (%VVF) and bonded (%XVF) specimens by computerized X-ray microtomography (micro-XCT). The % linear length of the interfacial gaps along the cavity margins (%LD) and the maximum gap width (WD(max)) were calculated under optical microscopy on sectioned specimens. Statistical analysis was performed with one- and two-way ANOVA, Bonferronis post hoc test and Pearsons correlation coefficient. RESULTS The %S values ranged from 1.34% (FS) to 2.29% (CX), while %S(r) ranged from 0.06%s(-1) (FS) to 0.15%s(-1) (CX). %VVF values extended from 1.9% (FS) to 5.3% (CX) and for %XVF from 1.98% (FS) to 3.35% (CX). The values for %LD ranged from 36.52% (FS) to 81.28% (CX). Linear regression showed strong positive correlation for %S(r) and t(max) with %VVF (r(2)=0.884 and r(2)=0.927) and also for %S(r) and t(max) with %LD (r(2)=0.823 and r(2)=0.869). SIGNIFICANCE %S(r) and t(max) are more representative than %S in determining the setting pattern of the materials and are strongly correlated to marginal adaptation. The silorane material showed better behavior than the dimethacrylate materials in setting shrinkage and marginal adaptation.

Assessment of differences between repeated pulse wave velocity measurements in terms of ‘bias’ in the extrapolated cardiovascular risk and the classification of aortic stiffness: Is a single PWV measurement enough?

Currently, there is no recommendation regarding the minimum number of pulse wave velocity (PWV) measurements to optimize individuals cardiovascular risk (CVR) stratification. The aim of this study was to examine differences between three single consecutive and averaged PWV measurements in terms of the extrapolated CVR and the classification of aortic stiffness as normal. In 60 subjects who referred for CVR assessment, three repeated measurements of blood pressure (BP), heart rate and PWV were performed. The reproducibility was evaluated by the intraclass correlation coefficient (ICC) and mean±s.d. of differences. The absolute differences between single and averaged PWV measurements were classified as: ⩽0.25, 0.26–0.49, 0.50–0.99 and ⩾1 m s−1. A difference ⩾0.5 m s−1 (corresponding to 7.5% change in CVR, meta-analysis data from >12 000 subjects) was considered as clinically meaningful; PWV values (single or averaged) were classified as normal according to respective age-corrected normal values (European Network data). Kappa statistic was used to evaluate the agreement between classifications. PWV for the first, second and third measurement was 7.0±1.9, 6.9±1.9, 6.9±2.0 m s−1, respectively (P=0.319); BP and heart rate did not vary significantly. A good reproducibility between single measurements was observed (ICC>0.94, s.d. ranged between 0.43 and 0.64 m s−1). A high percent with difference ⩾0.5 m s−1 was observed between: any pair of the three single PWV measurements (26.6–38.3%); the first or second single measurement and the average of the first and second (18.3%); any single measurement and the average of three measurements (10–20%). In only up to 5% a difference ⩾0.5 m s−1 was observed between the average of three and the average of any two PWV measurements. There was no significant agreement regarding PWV classification as normal between: the first or second measurement and the averaged PWV values. There was significant agreement in classification made by the average of the first two and the average of three PWV measurements (κ=0.85, P<0.001). Even when high reproducibility in PWV measurement is succeeded single measurements provide quite variable results in terms of the extrapolated CVR and the classification of aortic stiffness as normal. The average of two PWV measurements provides similar results with the average of three.

Viscoelastic properties, creep behavior and degree of conversion of bulk fill composite resins

OBJECTIVES The aim of this study was to investigate the viscoelastic properties and creep behavior of bulk fill composites under different conditions and evaluate their degree of conversion. METHODS Seven bulk fill composites were examined: everX Posterior (EV), SDR (SD), SonicFill (SF), Tetric EvoCeram Bulk Fill (TE), Venus Bulk Fill (VE), x-tra base (XB) and x-tra fil (XF). Each material was tested at 21°C, 37°C and 50°C under dry and wet conditions by applying a constant torque for static and creep testing and dynamic torsional loading for dynamic testing. Degree of conversion (%DC) was measured on the top and bottom surfaces of composites with ATR-FTIR spectroscopy. Statistical analysis was performed with two-way ANOVA, Bonferronis post hoc test and Pearsons correlation coefficient. RESULTS Shear modulus G ranged from 2.17GPa (VE) to 8.03GPa (XF) and flexural modulus E from 6.16GPa (VE) to 23GPa (XF) when the materials were tested dry at 21°C. The increase of temperature and the presence of water lead to a decline of these properties. Flowable materials used as base composites in restorations showed significantly lower values (p<0.05) than non-base composites, while being more prone to creep deformation. %DC ranged from 47.25% (XF) to 66.67% (SD) at the top material surface and 36.06% (XF) to 63.20% (SD) at the bottom. SIGNIFICANCE Bulk fill composites exhibited significant differences between them with base flowable materials showing in most cases inferior mechanical properties and higher degree of conversion than restorative bulk fill materials.

Blood pressure variability: a confounder and a cardiovascular risk factor

High blood pressure (BP) is a leading cause of cardiovascular (CV) disease. Although the diagnosis of high BP appears to be straightforward, in clinical practice, misdiagnosis is not rare, and even after many years of research there are still several unresolved issues regarding optimal BP classification.1 For example, the phenomena of isolated office hypertension (that is, high BP when at the doctors office despite a normal BP out of the office) and masked hypertension (that is, normal BP in the doctors office and high BP out of the office) lead to frequent over- and under-diagnosis of BP-associated CV risk. One of the main causes of the misdiagnosis of hypertension is the variability of BP.

Mechanical viscoelastic behavior of dental adhesives

OBJECTIVES The purpose of the study was to evaluate the mechanical properties of dental adhesive materials at different testing temperatures after dry and wet storage. METHODS Specimens (d=1 mm, l=18 mm) from six materials were tested: Silorane Adhesive System (SL), Heliobond (HE), One-Step Plus (OS), Optibond Solo Plus (OP), cmf Adhesive System (CF) and Protobond (PR). Static and creep testing was performed by applying a constant torque below the proportional limit of the materials, while dynamic testing consisted of dynamic torsional loading. Experiments were performed after 24h of dry and wet storage under temperatures from 21°C to 50°C and various viscoelastic parameters were calculated. RESULTS Shear modulus ranged from 0.19 to 1.99 GPa, while flexural modulus from 0.67 to 5.69 GPa. Most of the materials were affected by the presence of water and increase of temperature. OP showed the highest recovery after creep, while SL exhibited the highest permanent deformation. SIGNIFICANCE Contact with water after polymerization and increase of temperature resulted in a decline of the mechanical properties, especially for the HEMA-containing adhesives.

Experimental and numerical determination of the mechanical response of teeth with reinforced posts

The aim of this study was to evaluate the mechanical behavior of endodontically treated teeth restored with fiber reinforced composite posts versus titanium posts, by both experimental testing and numerical simulation (finite element analysis (FEA)). Forty maxillary central incisors were endodontically treated to a size 45 file and then obturated using gutta-percha points and sealer with the lateral condensation technique. The teeth were divided into four groups of ten teeth each. All the posts were of similar dimensions. The first group was restored using carbon fiber reinforced posts (CB), the second and third groups were restored using glass fiber reinforced posts (DP and FW, respectively), and the fourth group (control group) was restored using conventional titanium posts (PP). Half of the specimens of every group were submitted to hydrothermal cycling (2000 cycles, at 5 °C and 55 °C, respectively). All specimens were loaded until failure at a 45° angle with respect to the longitudinal axis at a cross head speed of 0.5 mm min(-1). A two-dimensional finite element model was designed in order to simulate the experimentally obtained results. Mechanical testing revealed that teeth restored with titanium posts exhibited the highest fracture strength. Debonding of the core was the main failure mode observed in glass fiber posts, whereas vertical root fractures were observed in the titanium posts. FEA revealed that the maximum stresses were developed at the interface between the post, dentin and the composite core critical regions in all three cases. Hydrothermal cycling had no significant effect on the fracture behavior of fiber reinforced composite posts.

Creep and dynamic viscoelastic behavior of endodontic fiber-reinforced composite posts

PURPOSE Fiber-reinforced composite (FRC) posts have gained much interest recently and understanding of their viscoelastic properties is important as they can be used in stress-bearing posterior restorations. The aim of this study was to evaluate the creep behavior and the viscoelastic properties of four commercial FRC posts under different temperatures and different storage conditions. METHODS The FRC posts tested were Glassix, C-Post, Carbonite and Snowlight. For the creep measurements a constant load below the proportional limit of the posts was applied and the angular deformation of the specimens was recorded. The viscoelastic parameters were determined by using dynamic torsional loading under four different conditions. RESULTS All materials were susceptible to creep and exhibited linear viscoelastic behavior. Residual strain was observed in all FRC posts. The viscoelastic properties were affected by the increase of temperature and water storage (p<0.001) resulting in their decline. Carbon fiber posts exhibited better performance than glass fiber posts. CONCLUSIONS FRC posts exhibit permanent strains under regular masticatory stresses that can be generated in the oral cavity. Their properties are susceptible to changes in temperature, while direct contact with water also affects them deleteriously.

Viscoelastic Properties of Orthodontic Adhesives Used for Lingual Fixed Retainer Bonding

OBJECTIVE To evaluate the viscoelastic properties of two experimental BPA-free and one BisGMA-based orthodontic resin composite adhesives for bonding fixed retainers. METHODS A commercially available BisGMA-based (TXA: Transbond LR) and two bisphenol A-free experimental adhesives (EXA and EXB) were included in the study. The viscoelastic behavior of the adhesives was evaluated under static and dynamic conditions at dry and wet states and at various temperatures (21, 37, 50°C). The parameters determined were shear modulus (G), Youngs modulus (E) under static testing and storage modulus (G1), loss tangent (tanδ) and dynamic viscosity (n*) under dynamic testing. Statistical analysis was performed by 2-way ANOVA and Bonferroni post-hoc tests (α=0.05). RESULTS For static testing, a significant difference was found within material and storage condition variables and a significant interaction between the two independent variables (p<0.001 for G and E). EXA demonstrated the highest G and E values at 21°C/dry group. Dry specimens showed the highest G and E values, but with no significant difference from 21°C/wet specimens, except EXA in G. Wet storage at higher temperatures (37°C and 50°C) adversely affected all the materials to a degree ranging from 40 to 60% (p<0.001). For dynamic testing, a significant difference was also found in material and testing condition groups, with a significant interaction between the two independent variables (p<0.001 for G1 and n*, p<0.01 for tanδ). Reduction in G1, and n* values, and increase in tanδ values were encountered at increased water temperatures. SIGNIFICANCE The apparent detrimental effect of high temperature on the reduction of properties of adhesives may contribute to the loss of stiffness of the fixed retainer configuration under ordinary clinical conditions with unfavorable effects on tooth position and stability of the orthodontic treatment result.

Setting characteristics and mechanical properties of self-adhesive resin luting agents

OBJECTIVE To evaluate the degree of conversion (DC%), salt yield and mechanical properties of self-adhesive luting agents (SAA) set under dual-cure (E) and self-cure (NE) modes. METHODS Three SAA (GC LinkAce/GCLA, MaxCem Elite/MXEL, Rely-X Unicem 2/RXUN) and an adhesive resin luting agent (Rely-X Ultimate/RXUL-control) were used. The properties tested under E and NE modes were a) DC% and phosphate salt yield after 10min, 1h (h) and 3 weeks (w) storage, by infrared spectroscopy; and b) the mechanical properties of 3w-stored specimens by instrumented indentation testing (Martens hardness/HM, Elastic modulus/EIT, Elastic index/ηIT) and microscopic Vickers hardness/VH. Statistical analysis was performed by 3-way ANOVA (DC%), 2-way ANOVA (salt yield) and 1-way ANOVA (mechanical properties) at an a=0.05. RESULTS Significantly higher DC% was found in E, except from the 3w groups of GCLA and MXEL. Within E, no significant differences were found, but within NE, there were differences in the 3 w groups of GCLA (vs 10 min) and MXEL (vs 1h). All materials demonstrated increased salt yield in NE, with the highest values found in RXUL and RXUN. GCLA, RXUL showed the lowest HM in E and MXEL the highest in NE. The rankings of the significant differences in EIT were MXEL>GCLA,RXUN,RXUL (E) and RXUL,MXEL>GCLA,RXUN (NE), whereas for ηIT RXUL,RXUN>GCLA,MXEL (E) and GCLA>RXUL>MXEL,RXUN (NE). The results of VH measurements showed an overestimation ranging from 13% up to 38% in comparison with HM. SIGNIFICANCE There are significant differences in the properties tested, which may anticipate variations in the chemical, mechanical and biological performance of the products.