How different curing methods affect mechanical properties of composites for inlays when tested in dry and wet conditions

Water absorption in artificial composites: Curse or blessing?

OBJECTIVES

This study evaluated the impact of mutable water uptake on the durability of mechanical properties and the long-term reliability of artificial composites.

METHODS

Three resin-based CAD/CAM restorative materials (CRMs) were investigated in three-point bending tests to calculate flexural strength (FS), modulus of elasticity (ME), modulus of resilience (MR), modulus of toughness (MT), and elastic recovery (ER). All specimens (n = 180) were stored under the same conditions and tested in four subsets (n = 15 per material) that were respectively withdrawn after repeated thermocycling (5000 cycles; 5-55 °C, H2O) and repetitive drying (7 d; 37 °C, air). For every specimen, weight differences were determined per storage condition. Likewise, loss tangent data were separately recorded via dynamic mechanical analysis to reliably assess damping characteristics.

RESULTS

Repeated thermocycling always induced weight increase and a concurrent significant loss in all mechanical properties except for MT and ER of a polymethylmethacrylate-based CRM. Drying consistently provoked weight loss and raised mechanical properties to initial values. Weight increase, however, enhanced loss tangent values and accordingly distinct damping characteristics, whereas weight decrease markedly lowered damping properties.

SIGNIFICANCE

Water uptake repeatedly induced a decrease in common mechanical properties but concurrently increased damping behavior. Invertible equilibrium processes were found with no evidence for permanent material degradation.

Viscoelastic stability of pre-cured resin-composite CAD/CAM structures

OBJECTIVES

To study the effect of water storage (3 months) on the creep deformation and recovery of CAD/CAM composite materials to determine their viscoelastic stability.

MATERIALS AND METHODS

Five CAD/CAM composite blocks, with increasing filler loading, and one polymer-infiltrated ceramic network (PICN) were studied. Six specimens of each material were separated into two groups (n=3) according to their storage conditions (24 h dry storage at 23°C versus 3 months storage in 37°C distilled water). A constant static compressive stress of 20 MPa was applied on each specimen via a loading pin for 2 h followed by unloading and monitoring strain recovery for a further period of 2 h. The maximum creep-strain (%) and permanent set (%) were recorded. Data were analysed via two-way ANOVA followed by one-way ANOVA and Bonferroni post hoc tests (<0.05) for comparisons between the materials. Homogeneity of variance was calculated via Levene's statistics.

RESULTS

The maximum creep strain after 24 h dry ranged from 0.45% to 1.09% and increased after 3-month storage in distilled water to between 0.71% and 1.85%. The permanent set after 24 h dry storage ranged from 0.033% to 0.15% and increased after 3-month water storage to between 0.087% and 0.18%. The maximum creep strain also reduced with increasing filler loading.

SIGNIFICANCE

The PICN material exhibited superior dimensional stability to all of the pre-cured resin composite blocks in both storage conditions with deformation being predominantly elastic rather than viscoelastic. Notwithstanding, two of the resin-matrix composite blocks approached the PICN performance, when dry, but less so after water storage.

Comparison of immediate and delayed light-curing on nano-indentation creep and contraction stress of dual-cured resin cements

STATEMENT OF PROBLEM

Polymerization protocol of dual-cured resin cements plays a great role in the success of restorations. Knowledge about the effect of light-curing protocol on the contraction stress value and the mechanical properties would assist in the development, selection and handling of the resin cement material.

PURPOSE

This study was undertaken to assess the effects of two different light-curing protocols on the polymerization shrinkage stress and nano-creep of two current dual-cured resin cements.

MATERIALS AND METHODS

Twenty-four soda-lime glass disks, measuring 1mm in thickness, with a perforation in their center that measured 3mm in diameter, received four Vickers indentations at a distance of 500µ from the margin. The indent cracks were measured before and at 15-, 30- and 60-min intervals after restoration of the cavity with either CLEARFIL™ SA or RelyX™ Ultimate cement. Twelve specimens were prepared from each resin cement and divided into two groups according to the curing protocol used: immediate and delayed light-curing. Stresses at the indent impression were calculated by considering glass fracture toughness and the increase in crack length. Stress at the bonded interface was calculated using the Lame equation for thick-walled cylinder under an internal pressure. Nano-indentation hardness, modulus of elasticity and creep of each cement were measured under a 10-mN load for 20s holding time. The specimens were stored in distilled water at 37°C for 24h before the nano-indentation tests. Data were analyzed with two-way and repeated-measures ANOVA (α≤0.05).

RESULTS

Curing protocol had a significant effect on both resin cements; higher stress values were recorded with the immediate curing mode (P=0.033). Curing mode did not exert a significant effect on the modulus of elasticity (P=0.595) and hardness (P=0.454) of resin cements. However, in relation to creep, it exhibited significant effects (P<0.0001).

CONCLUSIONS

Immediate light-curing resulted in higher polymerization stress and lower nano-creep values compared to the delayed protocol with the resin cements assessed.

Fracture Resistance of Cuspal Coverage of Endodontically Treated Maxillary Premolars with Combined Composite-Amalgam Compared to Other Techniques

Combined composite-amalgam for cuspal coverage of endodontically treated premolars was similar to direct composite coverage in strengthening restored teeth; however, composite onlay had the highest fracture resistance.

Influence of DPSS laser on polymerization shrinkage and mass change of resin composites

OBJECTIVES

This study evaluated the effectiveness of the diode-pumped solid state (DPSS) laser as a light source for light-curing dental resin composites.

BACKGROUND DATA

A DPSS laser of 473  nm may be useful because of its match with the absorption peak of camphorquinone (CQ), the photoinitiator.

MATERIALS AND METHODS

A DPSS laser (LAS) of 473  nm and a quartz-tungsten-halogen (QTH) light-curing unit (OP) were used as the light sources for light curing six different resin composites (four nanocomposites and two hybrid composites). Polymerization shrinkage and mass change (water sorption and solubility) were measured during and after light curing to determine the degree of polymerization. Mass change was evaluated by following the ISO 4049 standard.

RESULTS

According to the evaluation, the specimens light cured using LAS showed similar maximum polymerization shrinkage (12.3∼18.1  μm for LAS; 13.2∼16.2  μm for OP) and water sorption (11.4∼24.1  μg/mm(3) for LAS; 11.3∼22.8  μg/ mm(3) for OP) to the cases light cured using OP. The specimens light cured using LAS showed a significantly higher solubility than the cases light cured using OP (2.4∼6.6  μg/ mm(3) for LAS; 0.8∼1.6  μg/ mm(3) for OP). However, the maximum water sorption and solubility obtained from the specimens were lower than the values permitted by the ISO 4049 standard.

CONCLUSIONS

The results may suggest that the DPSS laser with an emission wavelength of 473  nm can be used as a light source for light-curing dental resin composites.

Fracture strength of temporary fixed partial dentures: CAD/CAM versus directly fabricated restorations

OBJECTIVES

This study aimed at investigating the influence of fabrication method, storage condition and material on the fracture strength of temporary 3-unit fixed partial dentures (FPDs).

METHODS

A CrCo-alloy master model with a 3-unit FPD (abutment teeth 25 and 27) was manufactured. The master model was scanned and the data set transferred to a CAD/CAM unit (Cercon Brain Expert, Degudent, Hanau, Germany). Temporary 3-unit bridges were produced either by milling from pre-fabricated blanks (Trim, Luxatemp AM Plus, Cercon Base PMMA) or by direct fabrication (Trim, Luxatemp AM Plus). 10 FPDs per experimental group were subjected either to water storage at 37 °C for 24h and 3 months, respectively, or thermocycled (TC, 5000×, 5-55 °C, 1 week). Maximum force at fracture (Fmax) was determined in a 3-point bending test at 200 mm/min. Data was analyzed using parametric statistics (α = 5%).

RESULTS

Fmax values ranged from 138.5 to 1115.5N. FPDs, which were CAD/CAM fabricated, showed a significant higher Fmax compared to the directly fabricated bridges (p < 0.05). TC significantly affected Fmax for Luxatemp (p < 0.05) but not for the PMMA based materials (p > 0.05). CAD/CAM milled FPDs made of Luxatemp showed significantly higher Fmax values compared to Trim and Cercon Base PMMA (p < 0.05).

SIGNIFICANCE

CAD/CAM fabricated FPDs exhibit a higher mechanical strength compared to directly fabricated FPDs, when manufactured of the same material. Composite based materials seem to offer clear advantages versus PMMA based materials and should, therefore, be considered for CAD/CAM fabricated temporary restorations.

Acrylic bone cements: influence of time and environment on physical properties

Acrylic bone cements are in extensive use in joint replacement surgery. They are weight bearing and load transferring in the bone-cement-prosthesis complex and therefore, inter alia, their mechanical properties are deemed to be crucial for the overall outcome. In spite of adequate preclinical test results according to the current specifications (ISO, ASTM), cements with inferior clinical results have appeared on the market. The aim of this study was to investigate whether it is possible to predict the long term clinical performance of acrylic bone cement on the basis of mechanical in vitro testing. We performed in vitro quasistatic testing of cement after aging in different media and at different temperatures for up to 5 years. Dynamic creep testing and testing of retrieved cement were also performed. Testing under dry conditions, as required in current standards, always gave higher values for mechanical properties than did storage and testing under more physiological conditions. We could demonstrate a continuous increase in mechanical properties when testing in air, while testing in water resulted in a slight decrease in mechanical properties after 1 week and then levelled out. Palacos bone cement showed a higher creep than CMW3G and the retrieved Boneloc specimens showed a higher creep than retrieved Palacos. The strength of a bone cement develops more slowly than the apparent high initial setting rate indicates and there are changes in mechanical properties over a period of five years. The effect of water absorption is important for the physical properties but the mechanical changes caused by physical aging are still present after immersion in water. The established standards are in need of more clinically relevant test methods and their associated requirements need better definition. We recommend that testing of bone cements should be performed after extended aging under simulated physiological conditions. Simple quasistatic and dynamic creep tests seem unable to predict clinical performance of acrylic bone cements when the products under test are chemically very similar. However, such testing might be clinically relevant if the cements exhibit substantial differences.

Physical properties of self-, dual-, and light-cured direct core materials

The objective of this study is to evaluate flexural strength, flexural modulus, compressive strength, curing temperature, curing depth, volumetric shrinkage, water sorption, and hygroscopic expansion of two self-, three dual-, and three light-curing resin-based core materials. Flexural strength and water sorption were measured according to ISO 4049, flexural modulus, compressive strength, curing temperature, and curing depth according to well-proven, literature-known methods, and the volumetric behavior was determined by the Archimedes' principle. ANOVA was calculated to find differences between the materials' properties, and correlation of water sorption and hygroscopic expansion was analysed according to Pearson (p < 0.05). Clearfil Photo Core demonstrated the highest flexural strength (125 ± 12 MPa) and curing depth (15.2 ± 0.1 mm) and had the highest flexural modulus (≈12.6 ± 1.2 GPa) concertedly with Multicore HB. The best compressive strength was measured for Voco Rebilda SC and Clearfil DC Core Auto (≈260 ± 10 MPa). Encore SuperCure Contrast had the lowest water sorption (11.8 ± 3.3 µg mm(-3)) and hygroscopic expansion (0.0 ± 0.2 vol.%). Clearfil Photo Core and Encore SuperCure Contrast demonstrated the lowest shrinkage (≈2.1 ± 0.1 vol.%). Water sorption and hygroscopic expansion had a very strong positive correlation. The investigated core materials significantly differed in the tested properties. The performance of the materials depended on their formulation, as well as on the respective curing process.

Is it the end of the road for dental amalgam? A critical review

The longevity of dental restorations is dependent on many factors, including those related to materials, the dentist, and the patient. Dental amalgams have successfully served the profession for over a century. The main reasons for restoration failure are secondary caries, fracture of the bulk of the restoration or of the tooth, and marginal deficiencies and wear. The importance of direct-placement, aesthetic, tooth-colored restorative materials is still increasing. Amalgam restorations are being replaced because of alleged adverse health effects and inferior aesthetic appearance. All alternative restorative materials and procedures, however, have certain limitations. This article will attempt to critically analyse both amalgams and resin based composites, through an evaluation of scientific literature.

Conversion degree of indirect resin composites and effect of thermocycling on their physical properties

PURPOSE

This study evaluated the degree of conversion (DC) of four indirect resin composites (IRCs) with various compositions processed in different polymerization units and investigated the effect of thermal aging on the flexural strength and Vicker's microhardness.

MATERIALS AND METHODS

Specimens were prepared from four IRC materials, namely Gr 1: Resilab (Wilcos); Gr2: Sinfony (3M ESPE); Gr3: VITA VMLC (VITA Zahnfabrik); Gr4: VITA Zeta (VITA Zahnfabrik) using special molds for flexural strength test (N = 80, n = 10 per group) (25 x 2 x 2 mm(3), ISO 4049), for Vicker's microhardness test (N = 80, n = 10 per group) (5 x 4 mm(2)) and for DC (N = 10) using FT-Raman Spectroscopy. For both flexural strength and microhardness tests, half of the specimens were randomly stored in distilled water at 37 degrees C for 24 hours (Groups 1 to 4), and the other half (Groups 5 to 8) were subjected to thermocycling (5000 cycles, 5 to 55 +/- 1 degree C, dwell time: 30 seconds). Flexural strength was measured in a universal testing machine (crosshead speed: 0.8 mm/min). Microhardness test was performed at 50 g. The data were analyzed using one-way and two-way ANOVA and Tukey's test (alpha= 0.05). The correlation between flexural strength and microhardness was evaluated with Pearson's correlation test (alpha= 0.05).

RESULTS

A significant effect for the type of IRC and thermocycling was found (p= 0.001, p= 0.001) on the flexural strength results, but thermocycling did not significantly affect the microhardness results (p= 0.078). The interaction factors were significant for both flexural strength and microhardness parameters (p= 0.001 and 0.002, respectively). Thermocycling decreased the flexural strength of the three IRCs tested significantly (p < 0.05), except for VITA Zeta (106.3 +/- 9.1 to 97.2 +/- 14 MPa) (p > 0.05) when compared with nonthermocycled groups. Microhardness results of only Sinfony were significantly affected by thermocycling (25.1 +/- 2.1 to 31 +/- 3.3 Kg/mm(2)). DC values ranged between 63% and 81%, and were not significantly different between the IRCs (p > 0.05). While a positive correlation was found between flexural strength and microhardness without (r = 0.309) and with thermocycling (r = 0.100) for VITA VMLC, negative correlations were found for Resilab under the same conditions (r =-0.190 and -0.305, respectively) (Pearson's correlation coefficient).

CONCLUSION

Although all four IRCs presented nonsignificant DC values, flexural strength and microhardness values varied between materials with and without thermocycling.

Opalescence and fluorescence properties of indirect and direct resin materials

OBJECTIVE

To measure the opalescence and fluorescence properties of indirect and direct resin materials before and after polymerization, and to determine the influence of the material and shade group combination on these properties.

MATERIAL AND METHODS

BelleGlass NG (BG, indirect resin) and Estelite Sigma (ES, direct resin), each composed in 3 shade groups (EN, OD and TL for BG; BS, AS and OP for ES) out of a total of 16 shades were investigated. Resin material was packed into a mold (the BEC condition) and polymerized with a light-polymerization unit (CWL). Secondary polymerization (CIC) was performed for BG. Color was measured in the BEC, CWL, and CIC conditions, and the opalescence parameter (OP) and fluorescence parameter (FL) were calculated.

RESULTS

For the OP, the mean for BG material was 24.3 before polymerization, which changed to 19.9 after polymerization (CIC). In the case of ES, the mean OP before polymerization was 25.6, which changed to 12.4 after polymerization (CWL). For the FL, the mean FL for BG was 2.5 before polymerization, which changed to 0.7 after polymerization. In the case of ES, the mean FL before polymerization was 1.2, which did not change after polymerization. Material and shade group combination influenced the OP and FL values (p<0.05).

CONCLUSIONS

The opalescence and fluorescence properties of resin materials varied depending on the material, shade group, and polymerization. Clinically, these properties should be considered when neighboring teeth are restored with different types of material.

Time-dependent visco-elastic creep and recovery of flowable composites

Creep behaviour of flowable composites was evaluated in relation to their filler fraction and the postcure period. Solid cylindrical specimens were prepared (4 x 6 mm) using steel moulds, with thorough light curing from multiple directions at 600 mW cm(-2). The specimens were divided into two groups (n=3/material) as follows: group I, loaded 5 min after preparation; and group II, loaded after storage for 1 month in water at 37+/-1 degrees C. A constant compressive stress of 36 MPa was applied to each specimen for 2 h followed by removal of the weight for 2 h of strain recovery. Axial strain measurements were obtained continuously over the total analysis time of 4 h. The maximum creep strain ranged from 2.04 to 7.69% and from 1.03 to 6.12% for groups I and II, respectively. Flowables that had the highest percentage of filler produced the lowest creep strain. The creep response decreased with 1 month of preload storage. Clinically, the finding of this study suggests that flowable composites are unsuitable for stress-bearing areas.

The effects of thermocycling on the flexural strength and flexural modulus of modern resin-based filling materials

OBJECTIVE

Evaluation of flexural strengths and flexural moduli of hybrids, packables, ormocers, compomers and flowables prior to, and after, thermocycling.

MATERIALS AND METHODS

Twenty specimens, size (25 +/- 2) mm x (2 +/- 0.1) mm x (2+/-0.1) mm, of Herculite (HE), Point 4 (P4), TetricCeram (TC), Miris (MI), TetricCeram HB, (HB), Solitaire 2 (SO), Surefil A (SU), Definte (DE), Admira (AD), Dyract AP (DY), Compoglass (CO) and TetricFlow (TF) were made according to ISO 4049. A three-point-bending test was carried out for the first 10 specimens after 24 h water storage at 37 degrees C and for the second 10 specimens after 30-day water storage at 37 degrees C, followed by 5000 thermocycles between +5 and +55 degrees C. For each test series flexural strengths and flexural moduli were calculated. Statistical significance was p < 0.05.

RESULTS

Flexural strengths of DY and CO missed the 80 MPa limit of ISO 4049 for occlusal fillings prior to and after thermocycling. AD missed it after thermocycling. HE, P4, TC, MI, HB, SO, SU, DE and TF did not significantly differ prior to and after thermocycling. Flexural strength of SO and AD significantly decreased after thermocycling. No change of the flexural moduli could be observed for any of the test materials. Only SU exceeded 10,000 MPa prior to and after thermocycling.

SIGNIFICANCE

Only DY and CO missed the flexural strength limit of ISO 4049 for occlusal fillings. Only SU exceeded a flexural modulus of 10,000 MPa prior to and after thermocycling.

Clinical Evaluation of Direct Cuspal Coverage with Posterior Composite Resin Restorations

BACKGROUND

Composite resins have esthetic properties; they join the ability to preserve and reinforce sound tooth structure. Conservation is becoming popular for both small to medium defects and more compromised teeth.

PURPOSE

This study aimed to evaluate the clinical performance of Class II cuspal coverage direct composite restorations.

MATERIALS AND METHODS

Twenty patients, 18 years or older, were included in this clinical trial restoring 25 vital molar teeth with one or two missing cusps. Criteria for inclusion are two or three surface restorations, replacement of composite and amalgam fillings (secondary decay, fracture of either filling material or tooth structure, aesthetic considerations), or virgin teeth with decay undermining a cusp. Teeth with residual cavity walls less than 1 mm or with complete loss of the clinical crown were excluded. Teeth were restored using a combination of Ultra-Etch 35% phosphoric acid, PQ1 adhesive system, and Vit-l-escence microhybrid composite resin (Ultradent Products, Inc., South Jordan, UT, USA). The enamel peripheral skeleton of the restoration was built up first, followed by dentin and enamel occlusal surface stratification. Wedge-shaped increments of composite resin were placed and cured using the variable intensity polimerizer (VIP) light (Bisco Inc., Schaumburg, IL, USA) through a combination of a pulse and progressive curing technique.

RESULTS

All 25 restorations were evaluated at 6-month intervals during the 30-month period using a modified US Public Health Service (USPHS) criteria by two independent evaluators precalibrated at 85% reliability. No failures were reported and alpha scores were recorded for all parameters. Statistical analysis was performed using a Chi-square test (chi(2)) and the Fisher's exact test. Sixteen of the 25 samples (64%) exhibited preoperative sensitivity to air (chi(2)=10.6; p=0.001). A significant difference in tooth sensitivity was reported after completion of the restorations. No teeth exhibited sensitivity both at the 2-week recall and the 30-month follow-up (chi(2)=23.5; p < 0.0001).

CONCLUSION

Microhybrid composite resin demonstrated excellent clinical performance in direct cuspal coverage at completion of a 30-month evaluation. CLINICAL SIGNIFICANCE In selected clinical situations, cuspal coverage direct posterior composite restorations may represent a valid alternative to conventional indirect restorations.

Direct cuspal-coverage posterior resin composite restorations: A case report

The clinical success of direct composite restorations is the result of the correct use and performance of adhesive systems, resin composites and light curing systems. Total-etch adhesive systems and microhybrid resin composites have seen continuous improvement; various clinical techniques have been introduced to address polymerization shrinkage. Manufacturers have introduced sophisticated light-curing devices with the hope of improving performance. Direct resin bonded composites (RBCs) are becoming the first choice in many clinical situations. This article presents an experimental clinical technique that outlines the reconstruction of severely damaged posterior teeth missing multiple cusps; particular attention to incremental and curing techniques is adopted to complete each restoration.

Effect of metal halide light source on hardness, water sorption and solubility of indirect composite material

This study evaluates the effects of a metal halide light source on the post-polymerization properties of the Sinfony indirect composite material. Two polymerization systems were employed: the Hyper LII system, comprising a metal halide polymerization unit, and the Visio system, comprising two proprietary units designed for polymerizing the Sinfony composite. The composite material was polymerized for 60, 120 or 180 s with the LII system. As a control, the composite was polymerized for 15 min with the Visio system. Knoop hardness, water sorption and solubility were determined. The results were analyzed by Dunnett's T3 multiple comparison test (P<0.05). Knoop hardness was greater for polymerization with the LII unit than for that with the Visio system. Water sorption was greater for polymerization with the Visio system than that with the LII unit. For polymerization with the LII unit for 180 s, solubility was significantly reduced as compared with the Visio system. Within the limitations of the current experiment, it can be concluded that the metal halide unit exhibited better polymerizing performance for the composite material than the proprietary units.

Compressive creep and recovery of light-cured packable composite resins

OBJECTIVE

The purpose of this investigation was to study the time-dependent creep and recovery behavior of some packable composites resins compared to a typical dispersion-phase amalgam alloy.

METHODS

Three packable posterior composite resins (ALERT, SureFil, Solitaire) were used as experimental groups and a high copper admixed amalgam alloy (Dispersalloy) was chosen as a control material. Cylindrical specimens (4 mm x 8 mm) were fabricated and stored in artificial saliva for 1 week at 37 degrees C. A custom-made creep testing machine was used to test the compressive creep of each of the materials under specified conditions of stress and temperature (155.5 MPa and 37 degrees C, 155.5 MPa and 55 degrees C; 36 MPa and 37 degrees C; 36 MPa and 55 degrees C) for 24 h, after which the strain recovery was recorded over a period of 24 h.

RESULTS

One-way ANOVA and Fisher's test showed no significant differences in creep and recovery strain behaviors between ALERT and SureFil for each test condition (P > 0.05). However, for residual strain, there was a highly significant difference between Dispersalloy and each of the packable composites (P < 0.01), but no significant differences between the composites themselves (P > 0.05). ALERT and SureFil had the lowest creep strain (1.91 +/- 0.59% and 1.96 +/- 0.36%, respectively) while Solitaire showed 6.09 +/- 0.26% creep strain at 155.5 MPa and 37 degrees C.

SIGNIFICANCE

The low creep and residual strain values of ALERT and SureFil compared to Dispersalloy amalgam suggest that these packable composite resins are suitable for restoring stress-bearing areas because of their ability to withstand viscoelastic deformation better than amalgam, over extended time periods, even under high load and temperature.

Effect of drying time of 3-methacryloxypropyltrimethoxysilane on the shear bond strength of a composite resin to silica-coated base/noble alloys

OBJECTIVES

In this in vitro study, the effect of various drying (surface reaction) times of a commercial silane, other than that recommended by the manufacturer (at least 5 min), on the bond strength between the resin composite and silica coated base and noble alloys was evaluated.

METHODS

A total of 112 disc specimens (9 mm diameter and 0.5 mm thickness) were cast out of two types of alloy designed for ceramic firing, one of which was a noble (Degunorm) (gold-silver-platinum) and the other a base alloy (Wiron 99) (nickel-chromium-molybdenum). The specimens were assigned to two main groups according to each alloy type. These two main groups were further divided into seven subgroups, having eight specimens each. The specimens of both alloy types were air-abraded with 30 microm silica (SiO2) coated alumina (Al2O3) (CoJet-Sand, ESPE, Seefeld, Germany). The conditioned surfaces were coated with 3-methacryloxypropyltrimethoxysilane (MPS) and were allowed to react and dry for 1, 2, 3, 4, 5, 6, and 7 min, respectively, before the opaquer was applied. Immediately after the waiting periods for the silane to dry, first opaquer and then resin composite were applied. After storage in water for 30 days at 37 degrees C and thermocycling (5000 cycles, 5-55 degrees C), shear tests were performed using the universal testing machine at a crosshead speed of 0.5 mm/min.

RESULTS

Analysis of data showed no significant difference in bond strength for any silane drying and reaction period for both base and noble alloys between 1 and 7 min (ANOVA, P = 0.05) (Degunorm: 5.8 - 7.4 MPa and Wiron 99: 7.2 - 10.2 MPa, respectively). Bond strengths of resin composite to base alloys were significantly higher than those to noble alloys at 2, 3 and 5 min (P = 0.0045, P = 0.05, P = 0.002, respectively).

SIGNIFICANCE

In order to optimize the flow of laboratory work, the silane solution drying time might be reduced to 1 min for both base and noble alloys.

Separation of ethoxylated bisphenol A dimethacrylates in dental composite after derivatisation to ionisable amines by capillary zone electrophoresis

Bisphenol A ethoxylate dimethacrylates (Bis-EMA) are transformed into ionisable amines by derivatisation in order to make the analytes applicable to capillary electrophoresis. For this goal, piperidine was added onto the C=C double bond of the alpha,beta-unsaturated ester group forming a tertiary amine with pKa values between 9 and 10. Formation of the derivatives was confirmed by electrospray ionisation MS. Commercial Bis-EMA is a mixture of homologues with different number of ethoxy groups; it is characterised by the average number of the ethoxy groups in the chains. These homologues were resolved by capillary zone electrophoresis at pH 4. It is shown for the product with an average of four ethoxy groups per Bis-EMA molecule that about seven homologues can be baseline separated when differing by only one ethoxy group. For Bis-EMA with 30 ethoxy groups in average, about 23 homologues could be differentiated. The high resolution power of capillary zone electrophoresis enables characterisation of commercial dental composite material concerning the Bis-EMA constituents.

Influence of pH and storage time on the sorption and solubility behaviour of three composite resin materials

OBJECTIVES

The aim of this study was to determine whether pH and time has any influence on the sorption and solubility behaviour of composite resin materials stored in a buffer solution.

METHODS

Three hybrid composite restorative resin materials (Spectrum, Z-100 and ArtGlass) with different matrix structure and filler composition were studied. One hundred and twenty specimens of each material were produced according to ISO 4049. The materials were stored in McIlvain's buffer solution at different pH (4, 6 and 8) at 1, 7, 60 and 180 days. pH measurements were carried out before and after completed storage.

RESULTS

Time had a significant influence on the sorption and solubility behaviour of the composite resin materials tested. One of the materials Z-100 showed a significant mass increase and/or decrease depending on the pH of the solution. The material Spectrum was significantly influenced by pH, resulting in different sorption depending on the pH of the solution.

CONCLUSIONS

Time of storage was important for the sorption and solubility behaviour of the composite resin materials tested. Comparison of solubility for one of the materials showed twice as high values in the present study as previously reported when distilled water was used as storage medium. pH in the solution seems to have an influence on the sorption and solubility behaviour of composite resin materials. The sensitivity of the sorption and solubility behaviour to time and pH of the materials tested seems to be related to the hydrophilicity of the matrix and the chemical composition of the filler.

The effect of postcuring on quantity of remaining double bonds, mechanical properties, and in vitro wear of two resin composites

OBJECTIVES

To determine the effect of different postcuring methods on degree of conversion, mechanical properties, and in vitro wear of two resin composites (Z100 and Charisma). The postcuring methods involved devices for inlay curing as well as devices present for other purposes in many dental laboratories or dental offices.

METHODS

Specimens of the resin composites were initially light cured and then postcured according to one of the following methods: Translux EC handheld curing unit (10min), Translux EC light box (10min), Triad II (10min), 40 degrees C (10min), 70 or 110 degrees C for 10min, 1, 6, or 24h. The properties were determined following storage of the specimens for 1week in water at 37 degrees C. The degree of conversion was determined using transmission IR. The mechanical properties tested were diametral tensile strength, flexural strength, and flexural modulus. In vitro wear was induced by a three-body wear simulator.

RESULTS

Most postcuring methods increased degree of conversion of both materials. Postcuring increased the mechanical properties and in vitro wear resistance of Charisma, whereas no effect of postcuring was found on these properties of Z100.

CONCLUSION

Postcuring with the use of devices readily available in the dental laboratory and dental office increased the degree of conversion of Z100 and Charisma as well as the mechanical properties and in vitro wear resistance of Charisma. A heat treatment at 110 degrees C for 10-60min was found to be the most promising postcuring method.

Direct resin composite inlays/onlays: an 11 year follow-up

OBJECTIVES

The aim of this study was to present an 11-year assessment of direct resin composite inlays/onlays.

METHODS

One-hundred Class II direct resin composite inlays and 34 direct resin composite restorations were placed in 40 patients. The restorations were evaluated clinically, according to modified USPHS criteria, annually over a 11-year period.

RESULTS

Of the 96 inlays/onlays and 33 direct restorations evaluated at 11 years, 17. 7% in the inlay/onlay group and 27.3% in the direct restorations group were assessed as unacceptable. The differences in longevity were not statistically significant. The main reasons for failure for the inlays/onlays and direct restorations were fracture (8.3 and 12. 1%, respectively), occlusal wear in contact areas (4.2 and 6.1%, respectively) and secondary caries (4.2 and 9.1%, respectively). Eight of the non-acceptable inlays/onlays and five of the direct restorations were replaced, while the other ones were repaired with resin composite. Unacceptable wear was observed in occlusal contact areas of six restorations, in patients who were severe bruxers. For the other restorations occlusal wear was not found to be a clinical problem and no difference was observed between the inlays/onlays and direct composite restorations. The marginal adaptation of the inlays/onlays was still good at the end of the study. Ditching was only observed in a few inlays. A higher failure rate was observed in molar teeth than in premolar teeth.

CONCLUSIONS

Good durability was observed for the direct resin composite inlay/onlay technique. Excellent marginal adaptation and low frequency of secondary caries in patients with high caries risk were shown. No apparent improvement of mechanical properties was obtained by the secondary heat treatment of the inlays. Also, the difference in failure rate between the resin composite direct technique and the inlay technique was not large, indicating that the more time-consuming and expensive inlay technique may not be justified. The direct inlay/onlay technique is recommended to be used in Class II cavities of high caries risk patients with cervical marginal placed in dentin.