Fracture properties of aged and post-processed dental composites

Logistic Regression Analysis of LC-MS/MS Data of Monomers Eluted from Aged Dental Composites: A Supervised Machine-Learning Approach

Compound identification by database searching that matches experimental with library mass spectra is commonly used in mass spectrometric (MS) data analysis. Vendor software often outputs scores that represent the quality of each spectral match for the identified compounds. However, software-generated identification results can differ drastically depending on the initial search parameters. Machine learning is applied here to provide a statistical evaluation of software-generated compound identification results from experimental tandem MS data. This task was accomplished using the logistic regression algorithm to assign an identification probability value to each identified compound. Logistic regression is usually used for classification, but here it is used to generate identification probabilities without setting a threshold for classification. Liquid chromatography coupled with quadrupole-time-of-flight tandem MS was used to analyze the organic monomers leached from resin-based dental composites in a simulated oral environment. The collected tandem MS data were processed with vendor software, followed by statistical evaluation of these results using logistic regression. The assigned identification probability to each compound provides more confidence in identification beyond solely by database matching. A total of 21 distinct monomers were identified among all samples, including five intact monomers and chemical degradation products of bisphenol A glycidyl methacrylate (BisGMA), oligomers of bisphenol-A ethoxylate methacrylate (BisEMA), triethylene glycol dimethacrylate (TEGDMA), and urethane dimethacrylate (UDMA). The logistic regression model can be used to evaluate any database-matched liquid chromatography-tandem MS result by training a new model using analytical standards of compounds present in a chosen database and then generating identification probabilities for candidates from unknown data using the new model.

Comparative Evaluation of Fixed Functional Cantilever Space Maintainer and Fixed Nonfunctional Space Maintainer: A Randomized Controlled Trial

Background and objectives

Effective way to prevent mesial drift after the early loss of primary first molars is by inserting a durable space maintainer. Several space maintainers are available; fixed nonfunctional (FNF) space maintainer (crown and loop) is commonly used when abutment teeth need full-coronal restoration. Disadvantages of crown and loop space maintainer are nonfunctional, nonesthetic, and fracture of solder loop. To overcome this drawback, new design of fixed functional cantilever (FFC) space maintainer (crown and pontic) using bis-acrly composite resin. The study evaluated the longevity and acceptance of an FFC and compared it with a FNF space maintainer.

Materials and methods

A total of 20 healthy children, aged 6-9 years, were selected having bilateral premature loss of lower deciduous first molars. FFC space maintainer in one quadrant and FNF space maintainer in the other was cemented. The subject's acceptance of treatment was checked using a visual analog scale after the treatment completion. Criteria for complication leading to the failure was assessed in both the designs in the 3rd, 6th, and 9th month. Cumulative success longevity was obtained at a 9 month evaluation.

Results

Patient acceptability was greater in group I (FFC) in comparison to group II (FNF). In group I, fracture of the crown and pontic was the common complication leading to failure, followed by attrition of the crown and loss of material due to abrasion. In group II, fracture of the solder joint was the common complication leading to failure, followed by slippage of the loop gingivally and cement loss. The longevity of groups I and II were 70 and 85%, respectively.

Conclusion

FFC can be considered a viable alternative to conventional FNF space maintainers.

How to cite this article

Sathyaprasad S, Krishnareddy MG, Vinod V, et al. Comparative Evaluation of Fixed Functional Cantilever Space Maintainer and Fixed Nonfunctional Space Maintainer: A Randomized Controlled Trial. Int J Clin Pediatr Dent 2022;15(6):750-760.

Physical and Mechanical Properties of Bulk-Fill, Conventional, and Flowable Resin Composites Stored Dry and Wet

Surface degradation, margin, and bulk fracture are common reasons that necessitate replacement of resin composite restorations. The purpose of this study was to determine filler weight (FW), fracture toughness (FT), Vickers hardness (VHN), sorption/solubility (S/S), and colour change (ΔE) of four resin composites in dry and wet conditions. Four resin composites of shade A2 were investigated: Aura bulk-fill (AB) (SDI), Tetric Evoceram (TE) (Ivoclar), G-ænial Universal Flo (GUF) (GC), and GC Kalore (GCK) (GC). For FT, VHN, and ΔE, the specimens were prepared, divided into 2 groups, and stored dry or immersed in distilled water. The specimens were subdivided into three subgroups and stored for 1, 7, and 60 days and then subjected to the relevant tests. Six fractured remnants were weighed for each material to measure FW%. To test S/S, ISO 4049 was used. The data were analysed using ANOVA and Tukey's test. There was an inverse correlation between FW and FT. A significantly higher FT was found for GUF. There were no significant differences between conditions in materials except for AB. The highest VHN was found for GCK and AB. After 1 and 7 days, a significant difference was observed in S/S between all materials with the highest values for GUF. There was a correlation between sorption and solubility. The material, the media, and aging have an influence on the properties of resin composites. It is important to emphasise that each material should be used for a specific clinical need based on their properties.

The effect of esterase enzyme on aging dental composites

We measured the push-out and diametral tensile strength of dental restorative composites following aging under environmental conditions relevant to the oral cavity; air (A), artificial saliva (AS), acidified (50 mM CH₃ COOH, pH = 4.7) artificial saliva (AS + HAc), and AS with esterase enzyme (AS + ENZ). Cylindrical test specimens (6.3 mm diameter by 5.1 mm long) were prepared by placing 0.3 g of nanofilled composite in an epoxy ring and cured. Twenty samples were aged in each environment for 163-186 days at 37°C. The push-out strengths (mean ± standard error of the mean [SEM], in MPa) for specimens were: A-2.4 ± 0.2, AS-7.3 ± 0.5, AS + HAc-7.2 ± 0.9, and AS + ENZ-6.0 ± 0.6. Following the push-out test, the diametral tensile strength and elasticity were immediately determined. The diametral tensile strengths (mean ± SEM, in MPa) for specimens were: A-54.0 ± 1.6, AS-31.4 ± 1.3, AS + HAc-34.3 ± 1.2, and AS + ENZ-22.5 ± 0.7. The push-out strength was lowest for the A environment due to shrinkage of the composite. The push-out strength increased significantly as water diffused into the specimens (AS and AS + HAc) but decreased significantly in the enzyme environment (AS + ENZ). The diametral tensile strength was highest for specimens in the A environment, which was significantly higher than both the AS and AS + HAc specimens and > 2× higher than the AS + ENZ specimens. The results indicated that a water environment (with or without acid) caused a significant decrease in the mechanical properties of this composite, but the greatest decrease was seen in water with esterase. This is the first study to demonstrate that esterase enzymes affect the bulk strength of a commonly used commercial dental composite. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2178-2184, 2019.

Effect of cusp coverage and water storage on compressive strength of composite restorations of premolars

Background

The aim of this study was to assess the effect of cusp coverage and water storage on compressive strength of composite restorations.

Material and Methods

This in vitro experimental study was conducted on 40 extracted human maxillary premolar teeth, which were randomly divided into four groups of 10. Mesio-occluso-distal (MOD) cavities were prepared in all teeth. The thickness of composite for cusp coverage was 1.5 mm in groups 1 and 3 and 2.5 mm in groups 2 and 4. Compressive strength (CS) was measured after 24 hours in groups 1 and 2 and after six months of water storage in groups 3 and 4. Two-way ANOVA was used to statistically analyze the data.

Results

The mean and standard error (SE) of compressive strength was 795.23 ± 35.18N in Group 1, 1232.52 ± 78.01N in Group 2, 617.18 ± 40.19N in Group 3 and 963.22 ± 50.05N in Group 4.

Conclusions

Statistical analysis showed a significant difference in compressive strength measured after 24 hours (groups 1 and 3) and after six months of water storage (groups 2 and 4). The compressive strength of groups with 2.5 mm cusp coverage was significantly greater than that of groups with 1.5 mm cusp coverage.

Key words:Fracture strength, cusp coverage, water absorption, composite resin, compressive strength.

Influence of Water Storage and Bonding Material on Bond Strength of Metallic Brackets to Ceramic

This study investigated the influence of water storage (24 h and 6 months), and Transbond XT and Fuji Ortho LC bonding materials on the bond strength of metallic brackets bonded to feldspathic ceramic. Four cylinders of feldspathic ceramic were etched with 10% hydrofluoric acid for 60 s. Each cylinder received two layers of silane. Metallic brackets were bonded to the cylinders using Transbond XT or Fuji Ortho LC. Light-activation was carried out with 40 s total exposure time using Bluephase G2. Half the specimens for each bonding materials (n=20) were stored in distilled water at 37 °C for 24 h and the other half for 6 months. Shear bond strength testing was performed after storage times at a crosshead speed of 1 mm/min. The adhesive remnant index (ARI) was used to evaluate the amount of adhesive remaining on the ceramic surface at ×8 magnification. Data were subjected to two-way ANOVA and Tukey's test (p<0.05). Transbond XT showed significantly higher bond strength (p<0.05) than Fuji Ortho LC. Significant differences in bond strength (p<0.05) were found when 24 h and 6 months storage times were compared between materials. ARI showed a predominance of score 0 for all groups, and higher scores at 1, 2 and 3 for 24 h storage time. In conclusion, storage time and bonding materials showed significant influence on the bond strength of brackets to ceramic.

Surface and bulk properties of dental resin- composites after solvent storage

OBJECTIVES

To investigate the surface micro-hardness and the diametral tensile strength (DTS) of bulk-fill and conventional resin-composites after storage in food simulating solvents.

METHODS

Eight materials were investigated. For the micro-hardness measurement, Teflon mould with an internal dimensions of 10mm and 2mm (n=15). For the DTS measurement, Split stainless steel moulds were used to make disk-shaped specimens of 6mm diameter and 2mm thickness (n=15). Materials were subdivided in to three groups (water, 75% ethanol/water and MEK). Micro-hardness measurements were made under a load of 300gm with a dwell time of 15s at 7, 30, and 90ds after storage. DTS was measured after 30ds at a cross head speed of 0.5mm/min.

RESULTS

The storage time and type of solvent had a significant influence on the micro-hardness. MEK showed more drastic reduction in the material micro-hardness with an exception of G-aenial universal flo (GA-F) which showed similar results in water/ethanol and MEK. DTS values of materials stored in water ranged from 48.7MPa for the GA-F and 30.6MPa for Ever X posterior (EXP). Generally, the results are observed to decrease with increasing solvent power, except for GA-F.

SIGNIFICANCE

Bulk-fill materials showed no superior results compared with the other materials. For the bulk-fill materials that are designed to be used as a base, their penetration by the solvents may be shielded and thus the changes observed in this study may not be of clinical importance.

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.

Investigation of mechanical properties of modern dental composites after artificial aging for one year

This in vitro study investigated the aging behavior of dental composites with regard to surface roughness (SR), Vickers hardness (VH) and flexural strength (FS), and the study elucidated the impact of artificial aging parameters. One hundred and sixty-five rectangular specimens were prepared from five composites (Filtek Supreme XT, Filtek Silorane, CeramX, Quixfil, experimental ormocer) and subjected to various artificial aging protocols (storage in distilled water/ethanol/artificial saliva for 7, 90 and 365 days; thermal cycling, 2 x 3000 cycles 5/55 degrees C). SR, VH and FS were determined at baseline and after each aging treatment. Means and standard deviations were calculated; statistical analysis was performed using three-way ANOVA and the Tukey-Kramer multiple comparison test (alpha=.05). The results showed a significant influence in the composite and aging duration on mechanical parameters; the aging medium did not have a significant influence on VH and FS, but there was a significant influence on SR. The highest overall VH was found for theexperimental ormocer; Filtek Silorane yielded the lowest values. For FS, the significantly highest values were found for Filtek Silorane, and the lowest values were found for the experimental ormocer. Prolonged aging periods (90 or 365 days) or thermal cycling led to significant decreases in both VH and FS and significant increases in SR. The findings of the current study indicate that composites differ significantly for SR and its mechanical properties with regard to FS and VH, as well as in aging behavior. Generally, artificial aging leads to a significant decrease in mechanical properties, which underlines the relevance of continuous improvement of dental composites.

Fracture toughness of cross-linked and non-cross-linked temporary crown and fixed partial denture materials

OBJECTIVES

Temporary crowns and fixed partial dentures are exposed to considerable functional loading, which places severe demands on the biomaterials used for their fabrication (= temporary crown & bridge materials, t-c&b). As the longevity of biopolymers is influenced by the ability to withstand a crack propagation, the aim of this study was to investigate the fracture toughness of cross-linked and non-cross-linked t-c&bs.

METHODS

Four different t-c&bs (Luxatemp AM Plus, Protemp 3 Garant, Structur Premium, Trim) were used to fabricate bar shaped specimens (2mmx5mmx25mm, ISO 13586). A notch (depth 2.47mm) was placed in the center of the specimen using a diamond cutting disc and a sharp pre-crack was added using a razor blade. 60 specimens per material were subjected to different storage conditions (dry and water 37 degrees C: 30min, 60min, 4h, 24h, 168h; thermocycling 5-55 degrees C: 168h) prior to fracture (3-point bending setup). The fracture sites were inspected using SEM analysis. Data was subjected to parametric statistics (p=0.05).

RESULTS

The K(IC) values varied between 0.4 and 1.3MPam(0.5) depending on the material and storage time. Highest K(IC) were observed for Protemp 3 Garant. Fracture toughness was significantly affected by thermocycling for all dimethacrylates (p<0.05) except for Structur Premium. All dimethacrylates showed a linear-elastic fracture mechanism, whereas the monomethacrylate showed an elasto-plastic fracture mechanism.

SIGNIFICANCE

Dimethacrylates exhibit a low resistance against crack propagation immediately after curing. In contrast, monomethacrylates may compensate for crack propagation due to plastic deformation. However, K(IC) is compromised with increasing storage time.

Degradation, fatigue, and failure of resin dental composite materials

The intent of this article is to review the numerous factors that affect the mechanical properties of particle- or fiber-filler-containing indirect dental resin composite materials. The focus will be on the effects of degradation due to aging in different media, mainly water and water and ethanol, cyclic loading, and mixed-mode loading on flexure strength and fracture toughness. Several selected papers will be examined in detail with respect to mixed and cyclic loading, and 3D tomography with multi-axial compression specimens. The main cause of failure, for most dental resin composites, is the breakdown of the resin matrix and/or the interface between the filler and the resin matrix. In clinical studies, it appears that failure in the first 5 years is a restoration issue (technique or material selection); after that time period, failure most often results from secondary decay.

Analysis of the degradation of a model dental composite

Dental composites undergo material property changes during exposure to the oral environment and may release compounds of potential toxicity, such as bisphenol A. Degradation of dental composites was studied in a simplified overlayer model in which bisphenol A diglycidyl methacrylate (BisGMA) was covalently bound to a porous silicon oxide surface. It was hypothesized that the chemical structure of this overlayer would allow release of bisphenol A, BisGMA, and the decomposition products thereof, upon exposure to water for an extended period. Liquid chromatography mass spectrometry found leaching of intact BisGMA and several degradation products that contained the bisphenol A moiety from the overlayer into distilled water after 2 wks of aging. The absence of bisphenol A release from the overlayer reduces concerns regarding its potential health risk in dental composites. Nevertheless, health concerns might arise with respect to BisGMA and the leached degradation products, since they all contain the bisphenol A moiety.

ABBREVIATIONS

BisGMA, bisphenol A diglycidyl methacrylate; HPLC, high-performance liquid chromatography; LCMS, liquid chromatography mass spectrometry; MA, methacrylic acid; MPS, 3-(trimethoxysilyl) propyl methacrylate; m/z, mass-to-charge ratio; and TIC, total ion chromatogram.

Compressive fatigue behavior of dental restorative composites

The purpose of this study was to investigate the compressive fatigue behavior of five dental composites. Cylindrical specimens of 8 mm length and 4 mm diameter were made according to manufacturers' recommendations and stored for two weeks in distilled water at 37 degrees C. Compressive fracture strength was measured, and subsequently fatigue tests at 10 Hz frequency were carried out in distilled water. Compressive fatigue strength was thereby obtained using the staircase method for 10(5) cycles (n = 17) under sinusoidal loading. Acquired data for compressive fracture strength were analyzed using ANOVA and Weibull statistics. Among the dental composites examined, Filtek Z250 exhibited the highest fatigue strength. This seemed to be due to the superior matrix properties coupled with a specific filler type at the highest weight%/volume% ratio. In addition, fracture mechanisms of the composites were examined.

Effect of water storage and surface treatments on the tensile bond strength of IPS Empress 2 ceramic

PURPOSE

The aim of this study was to evaluate the effect of water storage (24 hours and 1 year) on the tensile bond strength between the IPS Empress 2 ceramic and Variolink II resin cement under different superficial treatments.

MATERIALS AND METHODS

One hundred and eighty disks with diameters of 5.3 mm at the top and 7.0 mm at the bottom, and a thickness of 2.5 mm were made, embedded in resin, and randomly divided into six groups: Groups 1 and 4 = 10% hydrofluoric acid for 20 seconds; Groups 2 and 5 = sandblasting for 5 seconds with 50 microm aluminum oxide; and Groups 3 and 6 = sandblasting for 5 seconds with 100 microm aluminum oxide. Silane was applied on the treated ceramic surfaces, and the disks were bonded into pairs with adhesive resin cement. The samples of Groups 1 to 3 were stored in distilled water at 37 degrees C for 24 hours, and Groups 4 to 6 were stored for 1 year. The samples were subjected to a tensile strength test in an Instron universal testing machine at a crosshead speed of 1.0 mm/min, until failure. The data were submitted to analysis of variance and Tukey's test (5%).

RESULTS

The means of the tensile bond strength of Groups 1, 2, and 3 (15.54 +/- 4.53, 10.60 +/- 3.32, and 7.87 +/- 2.26 MPa) for 24-hour storage time were significantly higher than those observed for the 1-year storage (Groups 4, 5, and 6: 10.10 +/- 3.17, 6.34 +/- 1.06, and 2.60 +/- 0.41 MPa). The surface treatments with 10% hydrofluoric acid (15.54 +/- 4.53 and 10.10 +/- 3.17 MPa) showed statistically higher tensile bond strengths compared with sandblasting with 50 microm(10.60 +/- 3.32 and 6.34 +/- 1.06 MPa) and 100 microm (7.87 +/- 2.26 and 2.60 +/- 0.41 MPa) aluminum oxide for the storage time 24 hours and 1 year.

CONCLUSIONS

Storage time significantly decreased the tensile bond strength for both ceramic surface treatments. The application of 10% hydrofluoric acid resulted in stronger tensile bond strength values than those achieved with aluminum oxide.

Flexure strength evaluation of a laboratory-processed fiber-reinforced composite resin

STATEMENT OF PROBLEM

A fiber-reinforced composite resin system has been introduced for posterior restorations; however, little information is known regarding possible degradation of its flexure strength with respect to aging and cyclic loading.

PURPOSE

The aim of this in vitro study was to determine whether the fiber reinforcement improved the flexure strength of an indirect composite resin aged in air and water for 3 months and then subjected to static and cyclic loading.

MATERIAL AND METHODS

The materials tested in this study, non-fiber-reinforced composite resin (n=160) (Tescera Dentin) and fiber-reinforced composite resin (n=160) (Tescera U-beam and Rod), were fabricated as bars, 25.0 x 4.5 x 4.5 mm, and polished with 120- to 320-grit silicon carbide grinding paper. The static (n=15) and cyclical (n=25) flexure strengths (MPa) of specimens were tested initially and after 3 months' aging in air and water. The specimens were tested in 3-point loading in their respective aging media at a loading rate of 2 mm/min. Cyclic testing followed the staircase approach of either 1000 cycles or until specimen fracture. Statistical analysis for the static-loaded specimens consisted of a 3-way analysis of variance (media, aging, and fiber-reinforced versus unreinforced) (alpha=.05), whereas the cyclic-loaded specimens used confidence levels of .95 for the respective variables (media, aging, and fiber-reinforced versus unreinforced) and to compare static versus cyclic loading.

RESULTS

The statistical analysis of the static specimens showed no significant difference between control (unaged) groups and aged groups and aging media, but a significant difference (P<.001) between reinforced versus unreinforced specimens. For the cyclic-loaded specimens, the confidence levels at .95 showed no difference between control (unaged) groups and aged groups and aging media (air or water), but a difference between reinforced versus unreinforced specimens, and static-loaded versus cyclic-loaded specimens. During testing, the specimens separated into several pieces when the fiber reinforcement was on the compressive side, whereas the specimen remained intact when the fiber reinforcement was on the tensile side.

CONCLUSIONS

When compared to indirect composite resin without fiber reinforcement, the addition of fibers is an effective method to improve the flexure strength of indirect composite resin for the materials tested.

Contact versus flexure fatigue of a fiber-filled composite

OBJECTIVE

The intent of this project was to examine the effect of two different modes of fatigue loading, contact and flexure, on the flexure strength of a dental composite.

METHODS

The composite was Restolux (a fiber-filled composite) formed as bars 3 mm x 3 mm x 25 mm in size. The cyclic loading ranges were 30-50, 60-80, and 90-110 N for contact loading and 20-40 and 40-60 N for the flexure loading. Number of cycles completed was 1, 1000 or 100,000 in four different media: air, water, artificial saliva, and a 50/50 mixture of water and ethanol. Specimens were aged in sealed polyethylene containers in their respective media for 4 months at 37 degrees C.

RESULTS

Statistical analysis indicated a significantly lower flexure strength for the specimens flexure loaded versus contact loaded. For the flexure loaded specimens, the number of cycles had no significant effect, but the aging, load, and the media were all significant. For the contact loaded specimens, a significant effect was observed for the media, aging, and cycles completed, but no effect for the different cycling loads.

SIGNIFICANCE

In summary, the decrease in flexure strength from flexure loading was mainly affected by the aging media, whereas, the decrease from contact loading was attributed mainly to the number of cycles.

Evidence-based decision making: Guide to reading the dental materials literature

Although potential links between materials data and clinical behavior are often implied, the status of such linkage is often left obscure. This paper provides clinicians a context within which to view materials information as evidence for clinical indications and to broaden readers' appreciation for the subject. Hierarchies of both clinical and nonclinical data are presented and discussed from the point of view of their predictive potential regarding clinical performance. Excellent sources of information are identified for the clinician making treatment decisions, and perspectives are offered on the value of other published materials data.

Mechanical stability of resin-dentin bond components

OBJECTIVES

To evaluate the effects of long-term storage on the mechanical properties of the components of resin-dentin bonds, that is, resin composite, adhesive system, demineralized and mineralized dentin.

METHODS

Specimens of resin composite (Z250) and adhesive systems (Single Bond-SB; One-Step-OS and Clearfil Liner Bond 2V-CL) were cast in molds. Dentin specimens were prepared from dentin discs obtained from the crowns of extracted human molars. Specimens of demineralized dentin were obtained by immersion of dentin discs for 6 days in 0.5 mol/l EDTA (pH 7.0). Both dentin and resin-based substrates were shaped to hourglass or I-beam specimens that were used to determine the true stress (TS) or apparent modulus of elasticity (E), respectively. Control specimens were subjected to tensile testing at 0.6 mm/min after 24 h of immersion in distilled water. Experimental specimens were stored at 37 degrees C in either distilled water or mineral oil and tested after 12 months. The data of each group were individually analyzed by ANOVA and Tukey's test.

RESULTS

Both TS and E of the resin-based materials decreased significantly after 12 months of storage in water (p < 0.05) except the TS of SB (p > 0.05). No changes were observed for specimens of mineralized dentin, regardless of storage condition (p > 0.05). Storage of demineralized dentin in water did not cause any significant effect in either TS or E (p > 0.05), however, significant reductions of TS and E of demineralized dentin occurred after storage in oil for 1 year (p < 0.05).

SIGNIFICANCE

Storage time and medium may be deleterious to the mechanical properties of the resin-dentin bond components, which ultimately could compromise the durability of resin-dentin bonds.

In vivo degradation of resin-dentin bonds produced by a self-etch vs. a total-etch adhesive system

The purpose of this study was to evaluate the long-term durability of in vivo bond strengths and the morphological changes of interfaces between dentin and two adhesive systems. Class V preparations were prepared on the facial surfaces of 14 intact teeth of two monkeys and restored with a combination of Unifil Bond/Z250 or Single Bond/Z250. One year later, 10 additional teeth were restored with the same materials and the monkeys were killed after 24 h. All of the restored teeth were subjected to microtensile bond strength ( micro TBS) testing. The debonded surfaces of the dentin sides were morphologically observed using Fe-scanning electron microscopy (SEM), as were the polished cross-sections of resin-dentin interfaces. For both Unifil Bond and Single Bond, the micro TBS at 24 h was significantly higher than that at 1 yr. Fe-SEM observations of polished cross-sectioned and fractured surfaces showed that porosity within the hybrid layers produced by Single Bond increased over time. However, the interface produced by Unifil Bond revealed no noticeable changes in morphology between 24-h and 1-yr specimens. It is concluded that even though the bond strengths of both adhesive systems declined over time, the bonding interface using self-etching primers was relatively stable over time compared to the wet bonding system.

Comparison of fracture tests of denture base materials

STATEMENT OF PROBLEM

Clinical studies have shown midline fracture to be a common problem in dentures. In order to evaluate the resistance of denture base resins against fracture, not only impact strength measurements but also fracture toughness tests should be performed.

PURPOSE

The aim of this study was to determine the fracture toughness of denture base resins and to compare the results with impact strength measurements.

MATERIALS AND METHODS

Seven heat-polymerized denture base resins were chosen for the study: 5 high impact (GC Luxon, Injectall IPF HI-I, Ivocap Plus, Lucitone 199, and Trevalon HI) and 2 conventional (Major Base 2 and Probase Hot). Three series of 12 specimens were used for the Charpy impact test (specimen dimensions: 80 x 10 x 4 mm, notch depth: 2 mm) and 2 Izod impact tests (specimen dimensions: 50 x 6 x 4 mm; notch depth: 1.2 mm for the first series, 3.4 mm for the second series). The maximum stress intensity factor (K(I,max)) (MPa.m(1/2)) and the work of fracture (WOF) (kJ/m2) were measured for 8 specimens in a fracture toughness test (specimen dimensions: 40 x 8 x 4; notch depth: 3.2 to 3.3 mm). A 1-way ANOVA with a post-hoc Tukey-Kramer test (alpha=.05) was used to compare the data.

RESULTS

The results achieved by the different materials and the rankings varied, depending on which parameter was considered. For example, the 1.2-mm Izod impact strength of Ivocap Plus (2.49 +/- 0.24 kJ/m2) was not significantly different from GC Luxon (2.64 +/- 0.15 kJ/m2) and significantly higher than Major Base 2 (1.99 +/- 0.23 kJ/m2) and Probase Hot (1.79 +/- 0.20 kJ/m2) (P<.001). On the other hand, the Charpy impact strength of Ivocap Plus (1.47 +/- 0.16 kJ/m2) was almost half the value of GC Luxon (2.85 +/- 0.05 kJ/m2) and not significantly different from Major Base 2 (1.36 +/- 0.03 kJ/m2) and Probase Hot (1.36 +/- 0.09 kJ/m2). In the fracture toughness test, the K(I,max) values of GC Luxon (2.63 +/- 0.09 MPa.m(1/2)), Lucitone 199 (2.53 +/- 0.08 MPa.m(1/2)), Trevalon HI (2.56 +/- 0.13 MPa.m(1/2)), and Ivocap Plus (2.41 +/- 0.04 MPa.m(1/2)) were not significantly different. Among all parameters, the WOF value appeared to be the test that allowed a clear differentiation between the products, placing Probase Hot (0.27 +/- 0.03 kJ/m2) and Major Base 2 (0.38 +/- 0.03 kJ/m2) on a low level, Injectall IPF HI-I (0.63 +/- 0.17 kJ/m2) on an intermediate level, Ivocap Plus (1.12 +/- 0.06 kJ/m2) on a medium-high level, and Lucitone 199 (1.41 +/- 0.06 kJ/m2), GC Luxon (1.50 +/- 0.17 kJ/m2), and Trevalon HI (1.58 +/- 0.07 kJ/m2) on a high level.

CONCLUSION

Specimen geometry and testing configuration influenced the impact strength measurements. The fracture toughness method seems to be more suitable than impact strength measurements to demonstrate the effects of resin modifications. The differences between conventional and so-called "high-impact" denture base resins are more clearly demonstrated with fracture toughness measurements.

Leaching and mechanical properties characterization of dental composites

The objective of this study was to determine the leaching of Ba, Si, and Sr from four dental composites: Restolux (RX), Micronew (M), Renew (RW), and Choice (C) and to correlate the effects of such leaching with flexure strength and modulus of elasticity. The specimens were 3 x 3 x 25-mm bars, polished with 120- and 240-grit SiC paper, and were aged for 4, 6, and 8 months in artificial saliva, distilled water, and a 50/50 mixture of ethanol and distilled water. Inductively coupled plasma with mass spectroscopy (ICP/MS) was used to determine the ion concentrations after aging. The greatest release of Ba and Sr occurred after aging in 50/50 volume fraction mixture of ethanol/water and for Si in artificial saliva. The 50/50 solution caused a breakdown of the resin and glass matrix, resulting in an increase of Ba and Sr, whereas aging in artificial saliva resulted in an ion charge balance, which allowed an elevated and continuous release of Si. The flexure strength and the elastic modulus showed a gradual decrease over time, with the greatest decreases occurring following aging in the 50/50 water/ethanol solution, but little correlation with the leaching of the filler ions.

Fracture toughness of nine flowable resin composites

STATEMENT OF PROBLEM

Flowable composite is used in a variety of clinical applications; however, the capacity of these materials to resist crack propagation is not well understood.

PURPOSE

The purpose of this investigation was to compare the resistance to crack propagation of 9 flowable composites as measured by the fracture toughness.

MATERIAL AND METHODS

The composites studied include AeliteFlo, Crystal Essence, Flow-it, FloRestore, Permaflo, Revolution, Tetric Flow, VersaFlo, and Wave. Ten specimens of each composite were formed with a brass mold with a 3-mm preformed notch. The final dimensions of each specimen were 2 x 4.2 x 20 mm. All specimens were light-polymerized to manufacturer specifications and stored in air for 24 hours. The fracture toughness value, K(IC) (MNm(-3/2)), for each specimen was measured by use of a 3-point bending mode and a single-edge notched beam at a crosshead speed of 0.125 mm/min until fracture. The data were analyzed statistically by use of 1-way analysis of variance, t tests (P<.05), and regression analysis.

RESULTS

The flowable composites tested showed a spectrum of fracture toughness values ranging from 1.15 +/- 0.10 MNm(-3/2) for Wave to 1.65 +/- 0.13 MNm(-3/2) for Permaflo (significantly different, P<.05). The remaining materials formed 1 group with intermediate K(IC) values not different from each other (P>.05) but significantly different from Wave and Permaflo. Comparisons of fracture toughness to the filler content by volume of each composite revealed no correlation.

CONCLUSION

This in vitro study concluded that there was no significant difference among 7 of the 9 composites tested in their resistance to fracture. Permaflo showed the greatest resistance to crack propagation. There was no correlation between the filler content by volume and the fracture toughness of these flowable composites.

Influence of fiber type and wetting agent on the flexural properties of an indirect fiber reinforced composite

STATEMENT OF PROBLEM

Different fiber types are available for reinforcing composite restorations. Little information exists regarding optimal fiber type/bonding agent combinations.

PURPOSE

This in vitro study examined the influence of storage time and 2 fiber wetting agents on the flexural properties of an indirect dental composite reinforced by 3 fiber types.

MATERIAL AND METHODS

Three types of fiber (ultra-high molecular weight polyethylene, Kevlar, and Glass fiber) were used to reinforce samples of an indirect composite (Artglass) prepared to test flexural properties. Each fiber type was used to prepare 3 groups of 10 specimens after fiber wetting with an unfilled or a filled resin bonding agent. All fibers were weighed to an accuracy of 0.01 mg to standardize the amount of fiber placed in the base (tensile side) of the specimen preparation mold (2 x 2 x 25 mm). Fiber-reinforced samples wetted with the unfilled resin were stored for 24 hours before flexural testing, whereas separate groups of fiber-reinforced samples wetted with the filled resin were tested after both 24 hours and 6 months storage in water at 37 degrees C. Two additional groups of unreinforced composite control specimens (10 samples per group) were prepared, one for each of the 2 storage times, resulting in 11 groups total. Mean flexural strengths (MPa) and flexural modulus (GPa) values were determined in a 3-point bend test at a crosshead speed of 1 mm/min by use of a universal testing machine. Comparisons between means were performed with 2- and 1-way analysis of variance tests (alpha=.01) to demonstrate the influence of storage time, fiber wetting agent, and fiber type on the flexural properties of the indirect dental composite tested.

RESULTS

Significant increases (124% to 490%) in mean flexural strength (P<.01) were found for all fiber-reinforced groups in comparison to the unreinforced controls at both storage time intervals. The silane containing unfilled bonding agent gave the greatest reinforcing effect (364%) when used with the glass fiber material. After 6 months storage in water, a significant decline (28%) occurred in the mean flexural strength of the glass fiber-reinforced specimens (P<.01) when the filled bonding agent was used.

CONCLUSION

Within the limitations of this study, the choice of fiber type and wetting agent was shown to have a significant positive influence on the flexural properties of the fiber-reinforced composite. When used with the silane containing unfilled bonding agent, the glass fiber increased the mean flexural strength of the unreinforced indirect composite by 364%.

The suitability of packable resin-based composites for posterior restorations

BACKGROUND

Packable composites, promoted for the restoration of stress-bearing posterior teeth, have captured clinicians' interest.

METHODS

The authors tested three packable composites (Alert, Jeneric/Pentron; Solitaire, Heraeus Kulzer, Wehrheim, Germany; SureFil, Dentsply De Trey, Konstanz, Germany); a new packable organically modified ceramic, or ormocer (Definite, Degussa AG, Hanau, Germany); a hybrid composite (Tetric Ceram, Ivoclar Vivadent, Schaan, Liechtenstein) and an ion-releasing composite (Ariston pHc, Ivoclar Vivadent, Schaan, Liechtenstein). They determined modulus of elasticity according to EN 24049:1993 of the European Committee for Standardization. They measured Vickers hardness using a 200-gram load for 40 seconds. To determine the materials' depth of cure, they used both a scraping method (International Standards Organization standard CD 4049:1997) and a hardness profiling method.

RESULTS

The authors calculated means and standard deviations from 10 replications of each test and used one-way analysis of variance and post hoc Tukey tests (alpha = .05). The materials had significant differences (P < .001) in all characteristics. Solitaire had the significantly lowest elastic modulus and microhardness; Alert had the highest values for these characteristics. Ariston pHc exhibited the significantly lowest depth of cure. There was a significant correlation between the two methods of measuring depth of cure (r2 = 0.9945; P = .021).

CONCLUSIONS

The material group of packable composites is rather inhomogeneous in terms of mechanical and physical data. Our data suggest that bulk curing of packable composites in deep cavities still is not recommendable.

CLINICAL IMPLICATIONS

The clinician needs to select packable composites carefully, as it seems that not all of these materials quality for stress-loaded posterior restorations.

Mechanical properties of new composite restorative materials

OBJECTIVE

Determination of flexural strength, flexural modulus, fracture toughness, Vickers hardness, and wear resistance of condensable composites (Solitaire, Surefil, Alert) and an ormocer (Definite) in comparison with a hybrid composite (Tetric Ceram) and an ion-releasing composite (Ariston pHc).

METHODS

Flexural strength, flexural modulus, and fracture toughness were determined in 3-point bending. Single-edge notched-bend specimens were used to evaluate fracture toughness. Microhardness was measured with a Vickers indenter. Wear was determined in a pin-on-block-design with a Degusit antagonist at 50 N load and quantified by a replica technique after 6000, 10000, 30000, and 50000 load cycles using a 3D-laser scanner. All results were statistically analyzed with ANOVA and post hoc Tukey HSD tests.

RESULTS

Alert exhibited the highest flexural modulus, K(IC), and hardness, but lowest wear resistance. Solitaire presented the highest wear resistance, but significantly lower flexural strength, flexural modulus, K(IC), and hardness than all other materials. No significant correlation could be detected between hardness and wear of the tested composites with Pearson's correlation coefficient.

SIGNIFICANCE

The condensable composites differed significantly in their mechanical properties. This study suggested that, besides the filler content level and filler size, other factors like matrix-filler interactions highly influence the fracture and wear behavior of the materials.

Mechanical properties and wear behavior of light-cured packable composite resins

OBJECTIVES

Determination of flexural strength, flexural modulus, fracture toughness and wear resistance of three packable composites (Solitaire, Surefil, ALERT) and a packable ormocer (Definite) in comparison with an advanced hybrid composite (Tetric Ceram) and an ion-releasing composite (Ariston pHc).

METHODS

Flexural strength, flexural modulus and fracture toughness of each material were determined in three-point bending (each test n = 10). Single-edge notched-bend specimens were used to evaluate the fracture toughness (K1C). Wear of the materials (n = 8) was determined in a pin-on-block-design with a spherical Degusit antagonist at 50 N vertical load and quantified by a replica technique using a 3D-laser scanner. Replicas were made after 6000, 10,000, 30,000 and 50,000 load cycles. The mean wear rate (MWR (micron 3 cycle-1)) was obtained by a linear regression analysis in the steady-state of the time-wear-curve. All results were statistically analyzed with ANOVA and post hoc Tukey HSD tests (p < 0.05).

RESULTS

ALERT exhibited the highest flexural modulus (12.5 +/- 2.1 GPa) and K1C (2.3 +/- 0.2 MN m-3/2), but the lowest wear resistance (8275 micron 3 cycle-1). Solitaire presented the highest wear resistance (1591 micron 3 cycle-1), but significantly lower flexural strength (81.6 +/- 10.0 MPa), flexural modulus (4.4 +/- 0.3 GPa), and K1C (1.4 +/- 0.2 MN m-3/2) than all other materials. Surefil revealed a significantly higher flexural modulus (9.3 +/- 0.9 GPa) and wear resistance (3028 micron 3 cycle-1) than Tetric Ceram (6.8 +/- 0.5 GPa; 5417 micron 3 cycle-1) and Ariston pHc (7.3 +/- 0.8 GPa; 7194 micron 3 cycle-1).

SIGNIFICANCE

The tested packable composite resins differed significantly in their mechanical properties. This study suggested that fracture and wear behavior of the composite resins are highly influenced by the filler system. Overall, Surefil demonstrated good fracture mechanics parameters and a low wear rate.