In vitro evaluation of the marginal degradation of dental composites under simulated occlusal loading

Performance of low shrinkage Bis-EFMA based bulk-fill dental resin composites

OBJECTIVES

The purpose of this study was evaluating the performance of new Bis-EFMA based bulk-fill composites with common methacrylate based composites and commercial dental composites.

METHODS

The Bis-EFMA monomer was synthesized and the novel Bis-EFMA based bulk-fill composites were prepared. The resin composite samples were co-cultured with human gingival epithelial cells and human dental pulp stem cells to test the biocompatibility. The edge adaptation was observed under a combination of stereoscope and scanning electron microscope. The internal hardness was measured using a Vickers microhardness tester after one-time filling of cavities prepared in extracted teeth. After friction and wear test on the surface of the resin composites, the surface morphology and volume wear of each group were measured by the optical profilometer. The color stability was measured by a colorimeter.

RESULTS

Direct contact with human gingival epithelial cells and human dental pulp stem cells did not cause significant changes in their growth density and morphology, indicating good biocompatibility of Bis-EFMA group (p > 0.05). The continuous margin proportion of the Bis-EFMA group was as good as commercial bulk-fill composites (p > 0.05). The sectional microhardness results showed that the Bis-EFMA group had the highest microhardness. After the friction and wear test, the volume wear of the Bis-EFMA group was minimal, indicating its good wear resistance and mechanical strength. Color changes in all resin groups after 28 days of immersion were within the clinically acceptable range.

SIGNIFICANCE

The addition of Bis-EFMA demonstrated excellent biocompatibility, edge adaptation and color stability comparable to commonly used clinical bulk-fill composites, along with preferable mechanical strength, friction and wear resistance. Bis-EFMA based bulk-fill composites have the potential to be employed as a bulk filling material in commercial dental composite applications.

An In Vitro Comparison of Shear Bond Strength for Heated Composite Resin With Three Conventional Luting Cements

Background: This research set out to collate and contrast three popular luting agents-heated composite resin, resin-modified glass ionomer cement (RMGIC), and resin cement, and light-cure resin cement by measuring their shear bond strengths. Shear bond strength was measured between lithium disilicate discs (IPS E-max) and specimens luted with heated composite resin (Tetric N-Ceram, Ivoclar Vivadent), self-adhesive resin cement (3M ESPE Rely X U200), light-activated resin cement (Rely X Veneer cement), and resin-modified glass ionomer cement (Fuji Plus, GC America). A comparison was made between the shear bond strength of standard luting cement and heated composite resin on lithium disilicate discs.

MATERIALS AND METHODS

Forty-eight lithium disilicate disc samples are collected and put on acrylic blocks for this investigation. To improve luting cement adhesion, the discs are etched with 5% hydrofluoric acid (HF) gel. For easier handling and lower viscosity during luting, the composite resin is heated to between 55 and 68°C on a digital wax melter. Shear bond strength tests were executed with the universal testing device after the following luting cement was applied in the center of the test specimen (lithium disilicate discs). Statistics software was used for the calculations and analysis.

RESULTS

In accordance with the findings of the tests, shear bond strengths ranged from 2.2851 ± 0.5901 for nanohybrid composite resin to 7.3740 ± 0.6969 for self-adhesive resin cement and 4.4647 ± 0.9774 for light-activated resin cement. A statistically significant (p≤0.001) difference between the groups was found. Mean shear bond strength was significantly highest in the self-adhesive resin cement group, followed by the light-activated resin cement group, resin-modified GIC, and least with the nanohybrid composite resin group.

CONCLUSION

Composite resins; in fixation of indirect restorations can have their viscosity reduced by preheating in a device, but they must be employed as soon as possible after removal. Standardizing the methods of heating composite resins for cementation is necessary to achieve desirable outcomes and direct the physician in their application. Although preheating composite resins for luting operations can be utilized to decrease the material's viscosity and enhance the restoration setting; it may not increase bond strength.

Evaluation of flexible three-dimensionally printed occlusal splint materials: An in vitro study

OBJECTIVE

To evaluate and compare the mechanical properties, water sorption, water solubility, and degree of double bond conversion of three different commercially available three-dimensional (3D) printing resins used for the fabrication of flexible occlusal splints.

METHODS

A digital printer was used to generate specimens from the evaluated splint materials (KeySplint Soft, IMPRIMO LC Splint flex, and V-Print splint comfort). The specimens were equally divided and tested either dry or after water storage at 37 °C for 30 days. A three-point bending test was used to assess flexural strength, elastic modulus, and fracture toughness. A two-body wear test was performed using a dual-axis chewing simulator. Water sorption and water solubility were measured after 30 days. The degree of double bond conversion was determined by FTIR-spectrometry. All data for the evaluated properties were collected and statistically analyzed.

RESULTS

Both material and storage conditions had a significant effect on the flexural strength (P < 0.001), elastic modulus (P < 0.001), fracture toughness (P < 0.001), and wear (P < 0.001). The highest water sorption was noticed with IMPRIMO LC Splint flex (1.9 ± 0.0 %), while V-Print splint comfort displayed the lowest water solubility (0.2 ± 0.0 %). For the degree of conversion, it was statistically non-significant among the different materials (P = 0.087).

SIGNIFICANCE

Different flexible 3D-printed splints available in the market displayed variations in the evaluated properties and clinicians should consider these differences when choosing occlusal device materials. Among the tested flexible splint materials, KeySplint Soft had the greatest flexural strength, elastic modulus, fracture toughness, wear resistance, and degree of conversion. It also showed the lowest water sorption.

Wear behavior at margins of direct composite with CAD/CAM composite and enamel

OBJECTIVES

The aim was to investigate the two-body wear at the marginal area between direct filling composites and substrate of CAD/CAM composites or enamel.

MATERIALS AND METHODS

Flat specimens were prepared from CAD/CAM composites (CERASMART 270 and SFRC CAD) and bovine enamel. A box-shaped cavity cut into CAD/CAM composites and enamel surfaces was made. The prepared cavity in CAD/CAM composites was treated with a primer, while in enamel, the cavity was treated with an adhesive. Three conventional composites (Universal Injectable, G-aenial A'Chord, and Filtek Bulk Fill) and one short fiber composite (everX Flow) were placed and cured in the prepared cavities. A two-body wear test was conducted with 15,000 chewing cycles using a dual-axis chewing simulator. The specimens (n = 5/per group) were positioned to produce wear (load = 20 N) across the marginal area between filling composites and substrates. The wear depth was analyzed using a 3D optical profilometer. SEM was used to evaluate the wear behavior and margins between the filling and substrate materials.

RESULTS

All composites used displayed different wear behavior (20-39 µm) (p < 0.05). The highest wear values were recorded for A'Chord and Filtek, while the lowest values were for Injectable and CERASMART 270. The data analysis showed that the wear behavior of substrate materials depends on the filling materials used at margins (p < 0.05). The marginal breakdown was seen only between bovine enamel and filling composites.

CONCLUSIONS

The use of the two-body wear simulation method revealed important information about the behavior of the filling composites at the marginal area with CAD/CAM composites or bovine enamel substrates.

CLINICAL RELEVANCE

The marginal breakdown related to the material combination at the bonding region.

The Effect of Occlusal Loading on Gingival Microleakage of Bulk Fill Composites Compared with a Conventional Composite

Statement of the Problem:

Bulk fill composites have been introduced over the recent years in order to accelerate the process of tooth restoration by inserting composite in bulk up to 4mm thickness. Occlusal loading may influence the gingival microleakage of this composite.

Purpose:

This in vitro study aims to evaluate the effect of occlusal loading on the gingival microleakage of bulk fill composites compared with a conventional composite.

Materials and Method:

In this experimental study, box only class II cavities with gingival margins placed 1mm below the cemento-enamel junction were prepared on the mesial and distal surfaces of 36 maxillary premolars (72 cavities). The samples were divided into three groups and restored as follows: Group 1 (Tetric N-Ceram, incremental filling), Group 2 (X-tra fill, bulk filling), Group 3 (Tetric N-Ceram Bulk Fill, bulk filling). All restorations were thermocycled for 2000 cycles (5-50̊C) and then half of the samples were subjected to 200,000 cycles of loading. All the specimens were immersed in 0.5% basic fuchsin for 48 hours, then, sectioned, and evaluated for microleakage with a stereomicroscope. Data were analyzed using Kruskal-Wallis and Mann-Whitney U-tests. p< 0.05 was considered significant.

Results:

There were no significant differences among the gingival microleakage of three composites in both unloaded and loaded groups. In addition, no statistically significant difference was found between the microleakage of unloaded and loaded groups in all materials.

Conclusion:

Occlusal loading did not affect the gingival microleakage of bulk fill composites, and the microleakage of class II cavities restored with the bulk filling technique was similar to that of restored with the incremental technique.

The effect of aging methods on the fracture toughness and physical stability of an oxirane/acrylate, ormocer, and Bis-GMA-based resin composites

PURPOSE

To determine the effect of aging methods on the fracture toughness of a conventional Bis-GMA-based resin composite (Filtek Supreme), an ormocer-based resin composite (Admira), and an experimental hydrophobic oxirane/acrylate interpenetrating network resin system (OASys)-based composite.

METHODS

A 25 × 5 × 2.8-mm stainless-steel mold with 2.5 mm single-edge center notch, following ASTM standards [E399-90], was used to fabricate 135 specimens (n = 15) of the composite materials and randomly distributed into groups. For the baseline group, specimens were fabricated and then tested after 24-h storage in water. For the biofilm challenge, specimens were randomly placed in a six-well tissue culture plate and kept at 37 °C with bacterial growth media (Brain Heart Infusion (BHI); Streptococcus mutans) changed daily for 15 days. For the water storage challenge, specimens were kept in 5 ml of deionized distilled autoclaved water for 30 days at 37 °C. μCT evaluation by scanning the specimens was performed before and after the proposed challenge. Fracture toughness (K_Ic) testing was carried out following the challenges.

RESULTS

μCT surface area and volume analyses showed no significant changes regardless of the materials tested or the challenge. Filtek and Admira fracture toughness was significantly lower after the biofilm and water storage challenges. OASys mean fracture toughness values after water aging were significantly higher than that of baseline. Toughness values for OASys composites after biofilm aging were not statistically different when compared to either water or baseline values.

CONCLUSION

The fracture toughness of Bis-GMA and ormocer-based dental resin composites significantly decreased under water and bacterial biofilm assault. However, such degradation in fracture toughness was not visible in OASys-based composites.

CLINICAL SIGNIFICANCE

Current commercial dental composites are affected by the oral environment, which might contribute to the long-term performance of these materials.

Wear and damage at the bonded interface between tooth enamel and resin composite

OBJECTIVE

To investigate the wear mechanisms and evolution of damage in tooth enamel-resin composite bonded interfaces caused by sliding contact, and to develop an understanding of interface degradation from a tribological viewpoint that supports clinical recommendations for improving interface integrity.

METHODS

Reciprocating wear tests were performed on bonded interface samples involving commercial resin composite (Tetric N Ceram Bulk Fill), resin cement (Rely X U200) and tooth enamel using the ball-on-flat configuration. The bonded samples were subjected up to 5 × 10⁴ cycles of sliding contact, and the wear depth and wear track morphology were characterized after increments using white light interferometry and scanning electron microscopy, respectively. Optical microscopy was also used to evaluate cracks and their propagation in the samples.

RESULTS

In the early stages of sliding contact, wear evolved most rapidly at the interface, followed by the enamel and the resin composite. Gradually, the difference between the wear depth at the interface and other areas decreased. Furthermore, cracks and brittle fracture appeared in the enamel during the early stages of wear, adjacent to the interface. With continuing cyclic loading, enamel wear manifested primarily as ploughs, with discontinuous pits and peeled material. Cracking decreased to only a few cracks extending to the inner enamel and parallel to the interface.

CONCLUSIONS

Cracking and damage occurred in the enamel during the early stages of sliding contact and accelerated by poor margin finishing. Cracks caused by wear under sliding contact could be one of the reasons for secondary caries and tooth discoloration.

Physical property investigation of contemporary glass ionomer and resin-modified glass ionomer restorative materials

OBJECTIVES

The objective of this study was to investigate selected physical properties of nine contemporary and recently marketed glass ionomer cement (GIC) and four resin-modified glass ionomer cement (RMGI) dental restorative materials.

MATERIALS AND METHODS

Specimens (n = 12) were fabricated for fracture toughness and flexure strength using standardized, stainless steel molds. Testing was completed on a universal testing machine until failure. Knoop hardness was obtained using failed fracture toughness specimens on a microhardness tester, while both flexural modulus and flexural toughness was obtained by analysis of the flexure strength results data. Testing was completed at 1 h, 24 h, 1 week, and then at 1, 3, 6, and 12 months. Mean data was analyzed with Kruskal-Wallis and Mann-Whitney (p = 0.05).

RESULTS

Physical properties results were material dependent. Physical properties of the GIC and RMGI products were inferior at 1 h compared to that at 24 h. Some improvement in selected physical properties were noted over time, but development processes were basically concluded by 24 h. A few materials demonstrated improved physical properties over the course of the evaluation.

CONCLUSIONS

Under the conditions of this study: 1. GIC and RMGI physical property performance over time was material dependent; 2. Polyalkenoate maturation processes are essentially complete by 24 h; 3. Although differences in GIC physical properties were noted, the small magnitude of the divergences may render such to be unlikely of clinical significance; 4. Modest increases in some GIC physical properties were noted especially flexural modulus and hardness, which lends support to reports of a maturing hydrogel matrix; 5. Overall, GIC product physical properties were more stable than RMGI; 6. A similar modulus reduction at 6 months for both RMGI and GIC produced may suggest a polyalkenoate matrix change; and 7. Globally, RMGI products demonstrated higher values of flexure strength, flexural toughness, and fracture toughness than GIC materials.

CLINICAL RELEVANCE

As compared to RMGI materials, conventional glass ionomer restorative materials demonstrate more stability in physical properties.

Effect of Different Composite Restorations on the Cuspal Deflection of Premolars Restored with Different Insertion Techniques- An In vitro Study

INTRODUCTION

This study was conducted to assess the effect of different composite materials on the cuspal deflection of premolars restored with bulk placement of resin composite in comparison to horizontal incremental placement and modified tangential incremental placement.

AIM

The aim of this study was to evaluate the cuspal deflection caused by different composite materials when different insertion techniques were used.

MATERIALS AND METHODS

Two different composite materials were used that is Tetric N Ceram (Ivoclar Vivadent marketing, India) and SonicFill^TM (Kerr Sybron Dental). Forty standardized Mesio-Occluso-Distal (MOD) preparations were prepared on maxillary first premolars. Each group was divided according to composite insertion technique (n=10), as follows: Group I - bulk insertion using Tetric N Ceram, Group II - Horizontal incremental insertion technique using Tetric N Ceram, Group III- Modified tangential incremental technique using Tetric N Ceram, and Group IV- bulk insertion using SonicFill^TM. Preparations were acid-etched, and bonded with adhesive resin to provide micro mechanical attachment before restoration using a uniform etching and bonding protocol in all the groups. All groups received the same total photo-polymerization time. Cuspal deflection was measured during the restorative procedure using customized digital micrometer assembly. One-way ANOVA test was applied for the analysis of significant difference between the groups, p-value less than 0.05 was considered statistically significant.

RESULTS

The average cuspal deflections for the different groups were as follows: Group I 0.045±0.018, Group II 0.029±0.009, Group III 0.018±0.005 and Group IV 0.017±0.004. The intergroup comparison revealed statistically significant difference.

CONCLUSION

A measurable amount of cuspal deflection was present in all the four studied groups. In general, bulkfill restoration technique with conventional composite showed significantly highest cusp deflection. There were no significant differences in cuspal deflection among sonicFill^TM and modified tangential incremental insertion techniques.

Academy of Dental Materials guidance-Resin composites: Part I-Mechanical properties

OBJECTIVE

The objective of this project, which was initiated from the Academy of Dental Materials, was to review and critically appraise methods to determine fracture, deformation and wear resistance of dental resin composites, in an attempt to provide guidance for investigators endeavoring to study these properties for these materials.

METHODS

Test methods have been ranked in the priority of the specific property being tested, as well as of the specific test methods for evaluating that property. Focus was placed on the tests that are considered to be of the highest priority in terms of being the most useful, applicable, supported by the literature, and which show a correlation with clinical findings. Others are mentioned briefly for the purpose of being inclusive. When a standard test method exists, including those used in other fields, these have been identified in the beginning of each section. Also, some examples from the resin composite literature are included for each test method.

RESULTS

The properties for evaluating resin composites were ranked in the priority of measurement as following: (1) Strength, Elastic Modulus, Fracture toughness, Fatigue, Indentation Hardness, Wear-abrasion (third body) and Wear-attrition (contact/two body), (2) Toughness, Edge strength (chipping) and (3) Wear determined by toothbrush.

SIGNIFICANCE

The following guidance is meant to aid the researcher in choosing the proper method to assess key properties of dental resin composites with regard to their fracture, deformation and wear resistance.

Selected physical properties of new resin-modified glass ionomer luting cements

STATEMENT OF PROBLEM

Two resin-modified glass ionomer (RMGI)-based luting agents have been recently marketed without independent reports of their physical properties.

PURPOSE

The purpose of this in vitro study was to evaluate selected physical properties of 2 newly marketed RMGI luting agents and compare the findings with traditional materials.

MATERIAL AND METHODS

Specimens (N=12) of Nexus RMGI, UltraCem, GC Fuji Cem 2, and RelyX Luting Plus were fabricated using standardized molds for flexural strength and fracture toughness according to manufacturer recommendations and stored in physiologic phosphate-buffered saline solution at 37°C until testing. Specimens were tested at 1 and 24 hours, 1 week, and 1 month. Mean values for flexural strength, flexural modulus, flexural toughness, and fracture toughness were determined. Additionally, film thickness (N=12) for each material was determined following Amerian National Standards Association/American Dental Association (ANSI/ADA) specifications. Mean results were analyzed with Kruskal-Wallis and Mann-Whitney U tests (α=.05).

RESULTS

All luting agents exhibited a similar film thickness that met ANSI/ADA requirements for aqueous-based luting agents. Nexus RMGI surprisingly demonstrated significantly greater flexural strength and fracture toughness at 1 hour, which decreased significantly at 24 hours, making it similar to the other materials evaluated. All materials had similar flexural strength values at 7 days.

CONCLUSIONS

Physical property performance was material dependent. Nexus RMGI demonstrated greater early physical properties that were significantly less at 24 hours. UltraCem, GC Fuji Cem 2, and RelyX Luting Plus demonstrated the increasing physical property development that is normally associated with polyalkenoate-based systems.

Effect of cyclic loading on microleakage of silorane based composite compared with low shrinkage methacrylate-based composites

Background:

There are many concerns regarding the marginal seal of composite restorations, especially when composite restorations are subjected to cyclic loading. The aim of this study was to evaluate the effect of cyclic loading on the microleakage of silorane based composite compared with low shrinkage methacrylate-based composites in class V cavities.

Materials and Methods:

In this in vitro study, class V cavities were prepared on the facial and lingual surfaces of 48 human premolars (96 cavities). The teeth were randomly divided into four groups of 12 teeth (24 cavities) each and restored as follows: Group 1 (Siloran System Adhesive + Filtek P90), Group 2 (All Bond SE + Aelite LS Posterior), Group 3 (Futurabond NR + Grandio), and Group 4 (G-Bond + Kalore-GC). All the specimens were thermocycled for 2000 cycles (5-55°C) and then half of the specimens from each group, were Load cycled. All teeth were immersed in 0.5% basic fuchsine dye, sectioned, and observed under a stereomicroscope. Data were analyzed using Wilcoxon test, Kruskal–Wallis, and Mann–Whitney U-tests. P < 0.05 was considered as significant.

Results:

In both unloaded and loaded groups, no statistically significant differences were observed among four composites at the occlusal margin, but a significant difference in gingival microleakage was found between Aelite and silorane. Occlusal and gingival microleakage was not affected by cyclic loading in none of the four restorative materials.

Conclusion:

Silorane did not provide better marginal seal than the low shrinkage methacrylate-based composites (except Aelite). In addition, cyclic loading did not affect the marginal microleakage of evaluated composite restorations.

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.

Resin-based composites show similar kinetic profiles for dimensional change and recovery with solvent storage

OBJECTIVES

To investigate the sorption, solubility, mass change and hygroscopic expansion (solvent swelling) of resin-composites after long term storage in different solvents.

METHODS

Eight materials were studied: two bulk-fill flowable materials (SDR and Venus bulk fill, V-BF), a packable bulk-fill material (Tetric Evoceram bulk-fill, TET-BF), a fiber reinforced material (Ever X posterior, EVX), a nano-hybrid conventional material (Tetric Evoceram, TET) and micro-hybrid conventional materials (G-aenial anterior, GA-P and posterior, GA-A). Three groups of disk shaped specimens were prepared using split stainless steel molds. Each group was stored, respectively, in: water, 75% ethanol/water and methyl ethyl ketone (MEK). The total storage time was 180 d plus a reconditioning time of 120 d. A non-contact laser scanning micrometer was used to measure the diametral changes.

RESULTS

Significant differences were found in the sorption and solubility of the materials. Generally, MEK stored specimens had the highest values followed by 75% ethanol/water then water. A similar trend was found with the mass and volume changes (except for EVX). V-BF showed the highest sorption (98.1μg/mm(3)) and solubility (10μg/mm(3)) after MEK storage. Mass and volume changes showed near-linear correlation, with high Pearson coefficients (0.86-0.99).

SIGNIFICANCE

Generally the materials were most greatly affected by MEK storage compared to the other two solvents. The glass-fiber-reinforced EVX, however, was most affected by water immersion. The pattern of change/recovery behavior of the materials, during solvent challenge, was similar to the pattern of viscoelastic creep/recovery behavior of resin-composite materials.

Polymerization stress--is it clinically meaningful?

OBJECTIVES

The objective of this article is to discuss the evidence for polymerization shrinkage and shrinkage stress of dental composite restoratives in terms of its potential relevance to the clinical situation

METHODS

Articles relating to the issue of polymerization contraction stress generation in dental composite materials, and the factors that influence it, were reviewed and included. Particular attention was paid to evidence derived from clinical studies. Articles were identified through PubMed and through the bibliographies of other articles.

RESULTS

There is extensive evidence for the presence of polymerization contraction stress in dental composites, as well as evidence for its deleterious effects, which include marginal leakage, gap formation, cuspal deflection, tooth cracking, reduced bond strength and lowered mechanical properties of the restorative. There is little, if any, direct evidence for the clinical effect of these contraction stresses. No study has directly established a link between these stresses and enhanced postoperative sensitivity or recurrent caries, for example. However, the concern over these stresses and the manner in which they influence the placement of current composite materials demonstrates that they are considered to be very important.

CONCLUSION

Though no direct evidence exists to prove that the generation of contraction stress in dental composite restorations causes reduced clinical longevity, the indirect evidence from numerous in vitro studies and the concern over controlling their effects proves that they are clinically relevant.

Retrospective evaluation of posterior direct composite restorations: 10-year findings

OBJECTIVES

This 10-year retrospective study investigated the differences in the changes and the longevity of Class II restorations using 4 similar microhybrid resin composites (Filtek Z250, Herculite XR, Gradia Direct Posterior, Renew).

METHODS

Data were collected from patient records. Those patients who received posterior restoration between 2001 and 2003, and who still visited the clinical practice for regular check-up visits were selected. A total of 225 adult patients (86 males, 139 females) with 701 restorations were evaluated by 2 operators using the USPHS criteria. Data were analyzed with Fisher's Exact Test, Pearson's Chi-Square Test and Kaplan-Meier analysis (p<0.05).

RESULTS

A failure rate of 2.1% was detected. The reasons of failures included restoration fracture, secondary caries and endodontic treatment. Similar survival rates for Gradia Direct Posterior (91.25%) and Renew (92.19%) were observed; better performance was observed with the Filtek Z250 (99.1%) and Herculite XR (98.64%). There was a higher probability of failure in 3 surface (n=10) than in 2 surface (n=5) restorations (p<0.001), and this rate was similar when molars (n=8) and premolars (n=7) were compared. The most frequent but clinically acceptable deficiency was the marginal discoloration.

SIGNIFICANCE

All four microhybrid resin composites showed acceptable clinical durability in Class II restorations during the 10-year follow-up period, with an overall survival rate of >97.8%. Higher rates of failures and deficiencies were observed with the Renew (fracture) and Gradia Direct Posterior (color match), respectively.

Size-dependent strength of dental adhesive systems

OBJECTIVE

The aim of this study is to explain the influence of peripheral interface stress singularities on the testing of tensile bond strength. The relationships between these theoretically predicted singularities and the effect of specimen size on the measured bond strength are evaluated.

METHODS

Finite element method (FEM) and boundary element method (BEM) analyses of microtensile bond strength test specimens were performed and the presence of localized high stress concentrations and singularities was analyzed. The specimen size effect predicted by the models was compared to previously published experimental data.

RESULTS

FEM analysis of single-material trimmed hour-glass versus cast cylindrical specimens showed different theoretical stress distributions, with the dumbbell or cylindrical specimens showing a more homogeneous distribution of the stress on the critical symmetry plane. For multi-material specimens, mathematical singularities at the free edge of the bonded interface posed a computational challenge that resulted in mesh-dependence in the standard FEM analysis. A specialized weighted-traction BEM analysis, designed to eliminate mesh-dependence by capturing the effect of the singularity, predicted a specimen size effect that corresponds to that published previously in the literature.

SIGNIFICANCE

The results presented here further support the attention to specimen dimensions that has already broadened the empirical use of the microtensile test methods. FEM and BEM analyses that identify stress concentrations and especially marginal stress singularities must be accounted for in reliable bonding strength assessments. Size-dependent strength variations generally attributed to the effects of flaw distributions throughout the interfacial region are not as relevant as the presence of singularities at bonded joint boundaries - as revealed by both FEM and BEM analyses, when interpreted from a generalized fracture mechanics perspective. Furthermore, this size-dependence must be considered when evaluating or designing dental adhesive systems.

Effect of light polymerization time, mode, and thermal and mechanical load cycling on microleakage in resin composite restorations

This study evaluated the effect of polymerization mode and time and thermal and mechanical loading cycling (TMC) on microleakage in composite resin restorations. One hundred and eighty cavities were prepared and randomly divided according to the light curing time (20, 40, or 60 s), modes (quartz-tungsten-halogen (QTH)-420 mW/cm(2), LED 2 (2nd degree generation)-1,100 mW/cm(2), or LED 3 (3rd degree generation)-700 mW/cm(2)), and TMC. Following standard restorative procedures, the samples were prepared for analysis in an absorbance spectrophotometer. All results were statistically analyzed using the three-way ANOVA and Tukey test (p ≤ 0.05). The results revealed that the groups QTH and LED 3 submitted to TMC showed higher microleakage than those that were not submitted to TMC. Only for LED 3, 60 s showed higher microleakage than 20 s. For LED 2 and QTH, there were no differences between the times. QTH showed lower microleakage means than LED 2, when photoactivated for 20 s, without TMC. When photoactivated for 60 s, QTH showed lower microleakage means than LED 3, for the groups with or without TMC. It was concluded that TMC, the increase in polymerization time, and the irradiance were factors that may increase the marginal microleakage of class II cavities.

Resin-based composite performance: are there some things we can't predict?

OBJECTIVE

The objective of this manuscript is to address the following questions: Why do direct dental composite restorative materials fail clinically? What tests may be appropriate for predicting clinical performance? Does in vitro testing correlate with clinical performance?

METHODS

The literature relating to the clinical and laboratory performance of dental composite restorative materials was reviewed. The main reasons for failure and replacement of dental composite restorations provided the guidance for identifying specific material's properties that were likely to have the greatest impact on clinical outcomes.

RESULTS

There are few examples of studies showing correlation between laboratory tests of physical or mechanical properties and clinical performance of dental composites. Evidence does exist to relate clinical wear to flexure strength, fracture toughness and degree of conversion of the polymer matrix. There is evidence relating marginal breakdown to fracture toughness. Despite the fact that little confirmatory evidence exists, there is the expectation that clinical fracture and wear relates to resistance to fatigue. Only minimal evidence exists to correlate marginal quality and bond strength in the laboratory with clinical performance of bonded dental composites.

SIGNIFICANCE

The use of clinical trials to evaluate new dental composite formulations for their performance is expensive and time consuming, and it would be ideal to be able to predict clinical outcomes based on a single or multiple laboratory tests. However, though certain correlations exist, the overall clinical success of dental composites is multi-factorial and therefore is unlikely to be predicted accurately by even a battery of in vitro test methods.

Quantitative evaluation by glucose diffusion of microleakage in aged calcium silicate-based open-sandwich restorations

This study compared the in vitro marginal integrity of open-sandwich restorations based on aged calcium silicate cement versus resin-modified glass ionomer cement. Class II cavities were prepared on 30 extracted human third molars. These teeth were randomly assigned to two groups (n = 10) to compare a new hydraulic calcium silicate cement designed for restorative dentistry (Biodentine, Septodont, Saint Maur des Fossés, France) with a resin-modified glass ionomer cement (Ionolux, Voco, Cuxhaven, Germany) in open-sandwich restorations covered with a light-cured composite. Positive (n = 5) and negative (n = 5) controls were included. The teeth simultaneously underwent thermocycling and mechanocycling using a fatigue cycling machine (1,440 cycles, 5-55°C; 86,400 cycles, 50 N/cm(2)). The specimens were then stored in phosphate-buffered saline to simulate aging. After 1 year, the teeth were submitted to glucose diffusion, and the resulting data were analyzed with a nonparametric Mann-Whitney test. The Biodentine group and the Ionolux group presented glucose concentrations of 0.074 ± 0.035 g/L and 0.080 ± 0.032 g/L, respectively. No statistically significant differences were detected between the two groups. Therefore, the calcium silicate-based material performs as well as the resin-modified glass ionomer cement in open-sandwich restorations.

22-Year clinical evaluation of the performance of two posterior composites with different filler characteristics

OBJECTIVES

This retrospective longitudinal study investigated the longevity of posterior restorations placed in a single general practice using 2 different composites in filler characteristics and material properties: P-50 APC (3M ESPE) with 70vol.% inorganic filler loading (midfilled) and Herculite XR (Kerr) with 55vol.% filler loading (minifilled).

METHODS

Patient records were used for collecting data. Patients with at least 2 posterior composite restorations placed between 1986 and 1990, and still in the practice for regular check-up visits, were selected. 61 patients (20 male, 41 female, age 31.2-65.1) presenting 362 restorations (121 Class I, 241 Class II) placed using a closed sandwich technique were evaluated by 2 operators using the FDI criteria. Data were analyzed with Fisher's exact test, Kaplan-Meier statistics, and Cox regression analysis (p<0.05).

RESULTS

110 failures were detected. Similar survival rates for both composites were observed considering the full period of observation; better performance for the midfilled was detected considering the last 12 years. There was higher probability of failure in molars and for multi-surface restorations.

SIGNIFICANCE

Both evaluated composites showed good clinical performance over 22 years with 1.5% (midfilled) and 2.2% (minifilled) annual failure rate. Superior longevity for the higher filler loaded composite (midfilled) was observed in the second part of the observation period with constant annual failure rate between 10 years and 20 years, whereas the minifilled material showed an increase in annual failure rate between 10 years and 20 years, suggesting that physical properties of the composite may have some impact on restoration longevity.

Effect of preheating resin composite and light-curing units on the microleakage of Class II restorations submitted to thermocycling

This in vitro study evaluated microleakage in Class II cavities restored with dental composite and varying light-curing units and the temperature of the composite when subjected to a thermocycling test. Ninety cavities were prepared on the proximal surfaces of bovine teeth and randomly divided according to the light-curing mode (QTH-420 mW/cm2, LED 2nd generation-1100 mW/cm2, or LED 3rd generation-700 mW/cm2) and temperature of the resin composite (23°C, 54°C and 60°C). Following the restorative procedures and thermocycling, the samples were immersed in methylene blue for 12 hours. The samples were ground and the powder prepared for analysis in an absorbance spectrophotometer. All the results were statistically analyzed using the nonparametric tests of Kruskal-Wallis and Dunn (p ≤ 0.05). The results showed that there was no statistical difference between the light-curing modes at a temperature of 23°C. For 54°C, QTH showed a microleakage mean that was significantly lower than those of the LED groups, and for 60°C, QTH had a microleakage mean significantly lower than that of the LED 2nd generation group. There was no statistical difference between the temperatures of the resin composite when LEDs were used. For QTH, 54°C showed statistically lower microleakage than 23°C. The group preheated to 60°C showed no difference when compared to the group heated to 23°C. Preheating the resin composite (54°C and 60°C) did not improve the microleakage means when high-irradiance LED was used; however, it decreased the microleakage means when a QTH with low irradiance was used.

Effect of Dual Cure Composite as Dentin Substitute on the Marginal Integrity of Class II Open-Sandwich Restorations

Dual-curing composites may present a good alternative to RMGIC in open-sandwich restorations and act as a dentin substitute. However, this study showed that RMGIC remains the best intermediate material when open-sandwich restorations are indicated.

Edge strength of indirect restorative materials

OBJECTIVES

To evaluate the edge strength and fracture patterns of different all-ceramic and indirect composite materials used in prosthodontic applications.

METHODS

Fourteen rectangular-shaped samples (2-2.5 mm thick) were prepared of each of the following materials: BelleGlass NG (Kerr) (BG), fibre-reinforced BelleGlass/EverStick (Kerr/Stick Tech Ltd.) (BGES), Vita Mark II (Vita Zahnfabrik) (VMII), bilayered IPS e.max Ceram/CAD (Ivoclar-Vivadent) (Ceram/CAD), bilayered IPS e.max Ceram/ZirCAD (Ivoclar-Vivadent) (Ceram/ZirCAD) and unilayered IPS e.max CADLT (Ivoclar-Vivadent) (CADLT). Each group was further subdivided into seven subgroups (n=2) corresponding to different edge distances at which samples were loaded. Samples were tested with an edge strength machine (CK10, Engineering Systems, Nottingham, UK) using a diamond Vickers indenter. The force-to-failure (N) was recorded and four readings were obtained per sample. The mode of failure was analysed microscopically. One-way ANOVA was used to detect differences in edge strength among the groups and correlation and regression analyses were used to detect the correlation between distance of loading and failure force.

RESULTS

The mean values of edge strength (N) were 94.1 (11.2) for BG, 134.4 (10.9) for BGES, 50.5 (8.9) for VMII, 54.4 (7.5) for Ceram/CAD, 53.2 (8.4) for Ceram/ZirCAD and 69.1 (9.1) for CADLT. Significant (p<0.05) strong positive linear correlations were found between the force-to-failure and edge distance among all groups. Three patterns of failure were identified: surface indentation without visible cracking, surface indentation with visible cracking and chipping.

CONCLUSIONS

Indirect composite materials had better edge fracture behaviour than all-ceramic materials. The addition of fibres enhanced the performance of the resin-composite material. Fracture strength increased as the distance from the edge increased. Edge fracture was restricted to the veneer material in bilayared systems and therefore a stronger veneer material is recommended.

Bis-GMA co-polymerizations: influence on conversion, flexural properties, fracture toughness and susceptibility to ethanol degradation of experimental composites

OBJECTIVES

The aim of this study was to evaluate the influence of monomer content on fracture toughness (K(Ic)) before and after ethanol solution storage, flexural properties and degree of conversion (DC) of bisphenol A glycidyl methacrylate (Bis-GMA) co-polymers.

METHODS

Five formulations were tested, containing Bis-GMA (B) combined with TEGDMA (T), UDMA (U) or Bis-EMA (E), as follows (in mol%): 30B:70T; 30B:35T:35U; 30B:70U; 30B:35T:35E; 30B:70E. Bimodal filler was introduced at 80 wt%. Single-edge notched beams for fracture toughness (FT, 25 mm x 5 mm x 2.5 mm, a/w=0.5, n=20) and 10 mm x 2 mm x 1 mm beams for flexural strength (FS) and modulus (FM) determination (10 mm x 2 mm x 1 mm, n=10) were built and then stored in distilled water for 24 h at 37 degrees C. All FS/FM beams and half of the FT specimens were immediately submitted to three-point bending test. The remaining FT specimens were stored in a 75%ethanol/25%water (v/v) solution for 3 months prior to testing. DC was determined with FT-Raman spectroscopy in fragments of both FT and FS/FM specimens at 24 h. Data were submitted to one-way ANOVA/Tukey test (alpha=5%).

RESULTS

The 30B:70T composite presented the highest K(Ic) value (in MPa m(1/2)) at 24 h (1.3+/-0.4), statistically similar to 30B:35T:35U and 30B:70U, while 30B:70E presented the lowest value (0.5+/-0.1). After ethanol storage, reductions in K(Ic) ranged from 33 to 72%. The 30B:70E material presented the lowest reduction in FT and 30B:70U, the highest. DC was similar among groups (69-73%), except for 30B:70U (52+/-4%, p<0.001). 30B:70U and 30B:35T:35U presented the highest FS (125+/-21 and 122+/-14 MPa, respectively), statistically different from 30B:70T or 30B:70E (92+/-20 and 94+/-16 MPa, respectively). Composites containing UDMA or Bis-EMA associated with Bis-GMA presented similar FM, statistically lower than 30B:35T:35U.

SIGNIFICANCE

Composites formulated with Bis-GMA:TEGDMA:UDMA presented the best compromise between conversion and mechanical properties.

Effect of dual cure composite as dentin substitute on marginal integrity of class II open-sandwich restorations

The current study compared the marginal adaptation of Class II open-sandwich restorations with a RMGIC versus a dual-cure composite as dentin substitute. Class II cavities were prepared on 50 extracted human third molars. The teeth were randomly assigned to two groups of 25 teeth to compare one dual cure composite (MultiCore Flow) with one resin-modified glass-ionomer cement (Fuji II LC) in open-sandwich restorations recovered with a light cure composite. The teeth were thermomechanocycled (2000 cycles, 5 degrees C to 55 degrees C; 100,000 cycles, 50 N/cm2). The specimens were then sealed with a 1 mm window around the cervical margin interface. Samples were immersed in a 50% w/v ammoniacal silver nitrate solution for two hours and exposed to a photo-developing solution for six hours. The specimens were sectioned longitudinally and silver penetration was directly measured using a light microscope. The results were expressed as a score from 0 to 3. The data were analyzed with a non-parametric Kruskal and Wallis test. The degree of leakage significantly increased with MultiCore Flow (median 2) compared to Fuji II LC (median 1). Resin-modified glassionomer cements remain the best intermediate material when open-sandwich restorations are indicated. A comparison of the degradation of these materials over time remains a topic to be investigated by future studies.

Edge strength of resin-composite margins

OBJECTIVES

Marginal integrity is a major clinical problem in restorative dentistry. The aim of this study was to evaluate the applicability of an edge strength measurement device in an in vitro test to determine the force required to fracture flakes of material by a Vickers indentation at progressively increasing distances from an interface edge of bulk material.

METHODS

Five representative resin-composites were investigated. Fourteen disks of specimens (12mm diameter x 2.5mm thick) were prepared for each material. These were divided into seven sub-groups corresponding to different edge-distances (0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0mm). An edge strength measurement device (CK10) (Engineering Systems, Nottingham, UK) was used. The mode of the failure of each specimen was examined under the integral microscope of the CK10.

RESULTS

The force (N)-to-fracture at a distance of 0.5mm from the edge was defined as the edge strength. The highest failure force (edge strength) was observed for Tetric Ceram (174.2N) and the lowest for Filtek Supreme (enamel) (87.0N). Correlations between the failure-forces to fracture materials with edge-distance were regression analyzed giving coefficients (r) ranging from 0.94 (p=0.02) to 0.99 (p=0.01). Two modes of failure were observed: chipping and--generally at greater distances--cracking.

SIGNIFICANCE

Edge strength is a definable and potentially useful parameter to characterize this aspect of clinically related behavior. A standardized distance of 0.5mm from the specimen's edge, when chipping failure prevails, is suitable and convenient as a reference point.

Fracture Toughness Micromechanics by Energy Methods With a Photocure Fiber-Reinforced Composite

A fracture toughness analysis for discontinuous fiber reinforcement was evaluated as a function of fiber volume percent (Vf) using advanced flexural bend tests. Fully articulated fixtures with 40-mm spans were used to examine specimens (2 × 2 × 50 mm3) under conditions of Euler-type bending to reduce shearing effects. Testing for fracture toughness in standardized international units (kJ/m2) using fundamental mechanics-of-materials energy methods by strain energy was then applied for assessment of resilience and work of fracture (WOF). Fracture toughness was also measured as strain energy release (SERIC) for the condition of unstable fracture between peak load and 5% maximum deflection past peak load. Energies were calculated by numerical integration using the trapezoidal rule from the area under the load-deflection curve. Fracture depths were normalized using sample dimensions from microscopy imaging for a combined correlation matrix analysis of all mechanical test data. Vf significantly correlated with resilience, WOF, and SERIC, but negatively correlated with degree of crack depth with p < 0.0000005. All measured interrelated properties also significantly correlated with one another (p < 0.000001). Significant fracture toughness differences between particulate-filled and fiber-reinforced composites began when adding fiber reinforcement at 10.3 Vf for resilience, 5.4 Vf for WOF, and 5.4 Vf for SERIC (p < 0.05).

Effect of material properties of composite restoration on the strength of the restoration-dentine interface due to polymerization shrinkage, thermal and occlusal loading

The purpose of this investigation was to adopt an analytical approach to analyse stresses at the restoration-dentine interface caused by polymerization shrinkage, occlusal and thermal loading with the primary focus on evaluating the effect of the material properties of the composite restoration on the strength of the interface. Some essential simplifications were employed to derive an explicit analytical solution. The results confirm previous findings that interfacial stresses due to polymerization shrinkage are increased with the higher modulus of elasticity of the restoration, while Poisson's ratio of the restorative material has a very small influence on these stresses. Occlusal loading resulted in much lower interfacial stresses when compared to shrinkage and thermal loads. The obtained results were in a good agreement with other numerical and clinical studies. From the modelling analysis it was found that the majority of commercially available composite restorative materials are expected to create significant interfacial stresses when subjected to cold temperatures. In addition, it was shown that there is a considerable potential for interfacial stresses to be minimised by an appropriate selection of thermo-mechanical properties of the restorative material especially with the new finding on the negative temperature variation effect.

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.

Bonding of ceramic insert to a laboratory particle filler composite

The push-out bond strength of cylindrical ceramic inserts (CI) to particulate filler resin composite (VC) was evaluated in this study. Various surface treatments to improve the adhesion of CI to resin composite were tested. Additionally, the effect of fiber-reinforced composite (FRC) laminate encapsulation around CI was tested. Feldspathic porcelain CI with a diameter of 3.1 mm was bonded to VC. Adhesive resin was used for bonding. In group 1, no surface treatment of CI was done. In group 2, CI was encapsulated with a thin layer of woven glass FRC. In group 3, the surface of the CI was tribochemically silica coated and silanized. In group 4, the surface of the CI was grit-blasted with 50 microm aluminum oxide and etched with hydrofluoric acid. In group 5, the grit-blasted CI was encapsulated with a layer of FRC. The specimens (n = 6/group) were either dry stored or thermocycled in water (6000 x 5-55 degrees C). The push-out test was carried out with a universal material testing machine. The highest push-out strength was achieved in group 5 (20.4 MPa) and the lowest in group 2 (11.5 MPa). ANOVA revealed that both surface treatment and storage condition had a significant effect on push-out strength (p < 0.05). We conclude that the additional glass FRC encapsulation can be used to increase the bond strength of insert to composite.

Can a single composite resin serve all purposes?

The consensus view less than a decade ago was that direct posterior composites should be restricted to small restorations, preferably in premolar teeth with little, if any, occlusal function. Major advances in adhesive systems, materials and restorative techniques have combined to allow us to question this view and our increased clinical evidence base makes it appropriate to reconsider this viewpoint.

Discontinuous fiber-reinforced composites above critical length

Micromechanical physics of critical fiber length, describing a minimum filament distance for resin impregnation and stress transfer, has not yet been applied in dental science. As a test of the hypothesis that 9-micron-diameter, 3-mm-long quartz fibers would increase mechanical strength over particulate-filled composites, photocure-resin-pre-impregnated discontinuous reinforcement was incorporated at 35 wt% into 3M Corporation Z100, Kerr Corporation HerculiteXRV, and an experimental photocure paste with increased radiopaque particulate. Fully articulated four-point bend testing per ASTM C 1161-94 for advanced ceramics and Izod impact testing according to a modified unnotched ASTM D 256-00 specification were then performed. All photocure-fiber-reinforced composites demonstrated significant improvements over particulate-filled compounds (p < 0.001) for flexural strength, modulus, work of fracture, strain at maximum load, and Izod toughness, with one exception for the moduli of Z100 and the experimental reinforced paste. The results indicate that inclusion of pre-impregnated fibers above the critical aspect ratio yields major advancements regarding the mechanical properties tested.

The survival and clinical performance of resin-based composite restorations used to treat localised anterior tooth wear

OBJECTIVE

To examine the clinical performance of resin-based composite restorations placed at an increased vertical dimension when used to manage localised anterior tooth wear.

DESIGN

A retrospective analysis of cases treated at a single centre.

SETTING

UK Hospital setting in the year 2000.

SUBJECTS AND METHODS

Two hundred and twenty five restorations placed in 31 subjects were included. Assessment was made following examination of study casts and projected slides. Modified United States Public Health Services criteria were used and data analysed using the software Statistical Programme for Social Sciences (SPSS). Survival analysis was carried out at two levels, major failure only and all types of failure. Kaplan-Meier survival plots were produced against different variables and modes of failure were also noted.

RESULTS

Major failure requiring replacement of the restoration was uncommon within the first five years. Minor failure requiring repair or refinishing presented mainly as wear, marginal discolouration or marginal fracture. Median survival was 4 years 9 months when all types of failure were considered. The restorations have good appearance and are well tolerated.

CONCLUSION

Placement of resin-based composite restorations at an increased vertical dimension to treat localised anterior tooth wear, has good short to medium term survival. The technique is conservative and relatively easy to maintain.

Flexural strength and modulus of a novel ceramic restorative cement intended for posterior restorations as determined by a three-point bending test

The aim of this study was to compare a new restorative cement intended for posterior restorations, Doxadent, with other types of tooth-colored materials as regards flexural strength and flexural modulus. The new restorative material consists mainly of calcium aluminate. Four hybrid resin composites, one polyacid-modified resin composite, one resin-modified glass ionomer cement, one conventional glass ionomer cement, one zinc phosphate cement, and an experimental version as well as the marketed version of Doxadent were investigated. Flexural strength and flexural modulus were tested according to ISO standard 4049 and determined after 1 d, 1 week, and 2 weeks. Together with the zinc phosphate cement, Doxadent had the lowest flexural strengths (13-22 MPa). The strongest materials were the resin composites and the polyacid-modified resin composite (83-136 MPa). The highest flexural modulus was found for Doxadent (17-19 GPa). The flexural strength of Doxadent decreased significantly from 1 week to 2 weeks, while flexural modulus remained unchanged. The other materials reacted in different ways to prolonged water storage. It can be concluded that the restorative cement Doxadent had significantly lower flexural strength and significantly higher flexural modulus than today's materials used for direct posterior restorations.