Hygroscopic expansion of a compomer and a composite on artificial gap reduction

Long-term hydrolytic stability of CAD/CAM composite blocks

This study aimed to assess water sorption and solubility of CAD/CAM composite blocks compared to CAD/CAM ceramic after 8 months storage in water and artificial saliva. Eight CAD/CAM blocks were investigated: Five resin-composite blocks (RCBs), one polymer-infiltrated ceramic network (PICN) block, one ceramic-filled polyetheretherketone (PEEK) block, and one feldspathic ceramic block. One hundred and twelve specimens were prepared comprising 14 specimens of each of the eight materials. From each group of specimens, seven randomly selected specimens were immersed in 10 mL of water, while the other seven specimens were immersed in artificial saliva. All specimens were stored at 37°C and weighed at various time intervals. The data were analysed via repeat measures ANOVA, one-way ANOVA and Tukey's post hoc test (α = 0.05 for all tests). Sorption values (mean [SD]) in water were within the range -1.21 (0.4) to 39.3 (2.1) μg/mm³ and in artificial saliva between -0.7 (0.2) and 41.6 (1.3) μg/mm³ . Solubility values in water were between -0.43 (0.08) and 0.34 (0.18) μg/mm³ and in artificial saliva between -0.53 (0.07) μg/mm³ and 0.33 (0.2) μg/mm³ . CAD/CAM composite blocks were hydrolytically stable under long-term storage (according to ISO 4949:2009), although not as stable as ceramic. Water sorption of CAD/CAM composite blocks was dependent on the resin-matrix and was influenced by the filler weight %.

Effect of flowable composites on the clinical performance of non-carious cervical lesions: A systematic review and meta-analysis

OBJECTIVES

To answer the following PICO question (participant, intervention, comparator and outcome): Does flowable resin composite restorations compared with regular resin composites improve the marginal adaptation, marginal discoloration and retention rates of restorations placed in non-carious cervical lesions [NCCLs] of adults?, through a systematic review and meta-analysis.

SOURCE

MEDLINE, Scopus, Web of Science, LILACS, BBO, Cochrane Library and SIGLE were searched without restrictions, as well as the abstracts of the IADR, clinical trials registries, dissertations and theses in May 2016 (updated in April 2017).

STUDY SELECTION

We included randomized clinical trials (RCTs) that answered the PICO question. RCTs were excluded if cavities other than NCCLs were treated; indirect restorations; polyacid-based resins instead of composite resins were employed, restorations in primary teeth and restorations were placed in carious cervical lesions. The risk of bias tool of the Cochrane Collaboration was applied in the eligible studies and the GRADE tool was used to assess the quality of the evidence.

DATA

After duplicates removal, 5137 articles were identified. After abstract and title screening, 8 studies remained. Six were at "unclear" risk of bias. The study follow-ups ranged from 1 to 3 years. No significant difference was observed between groups for loss of retention and marginal discoloration in all follow-ups. Better marginal adaptation was observed for restorations performed with flowable composites. At 1-year (risk ratio=0.27 [0.10 to 0.70]) and 3-year (risk ratio=0.34 [0.17 to 0.71]) follow-ups, flowable composites showed a risk 73% and 66% lower than regular composites for lack of adaptation, respectively. The evidence was graded as moderate quality for loss or retention at 3 years due to risk of bias and low and very low for all other outcomes due to risk of bias, imprecision and inconsistency.

CONCLUSIONS

We have moderate confidence that the resin composite viscosity does not influence the retention rates at 3 years. Similar marginal discoloration and better marginal adaptation was observed for flowable composites but the quality of evidence is doubtful. (PROSPERO CRD42015019560).

Influence of water immersion on the mechanical properties of fiber posts

PURPOSE

The purpose of this study was to evaluate the influence of water immersion on the mechanical properties of three kinds of glass fiber posts and the fracture resistance of structures using resin composites with glass fiber posts.

METHODS

Each post was divided into three groups; a control group and two water immersion groups (30 and 90 days). Flexural strength was determined by three-point bending test. Each structure was divided into two groups; a control group and a water immersion group for 30 days. The fracture strength of structures was determined by a static loading test.

RESULTS

In the flexural strength, two kinds of post in water immersion groups showed lower values than control groups. In the fracture strength, two kinds of structures in water immersion group showed lower values than control groups.

CONCLUSION

The prefabricated glass fiber posts and structures using resin composites with glass fiber posts were affected by water immersion.

Effective Expansion: Balance between Shrinkage and Hygroscopic Expansion

The purpose of this study was to investigate the relationship between hygroscopic expansion and polymerization shrinkage for compensation of polymerization shrinkage stresses in a restored tooth. One resin-modified glass-ionomer (RMGI) (Ketac Nano, 3M ESPE), 2 compomers (Dyract, Dentsply; Compoglass, Ivoclar), and a universal resin-based composite (Esthet•X HD, Dentsply) were tested. Volumetric change after polymerization ("total shrinkage") and during 4 wk of water storage at 37°C was measured using an optical method (n= 10). Post-gel shrinkage was measured during polymerization using a strain gauge method (n= 10). Extracted human molars with large mesio-occluso-distal slot preparations were restored with the tested restorative materials. Tooth surfaces at baseline (preparation), after restoration, and during 4 wk of 37°C water storage were scanned with an optical scanner to determine cuspal flexure (n= 8). Occlusal interface integrity was measured using dye penetration. Data were analyzed using analysis of variance and post hoc tests (significance level 0.05). All tested materials shrunk after polymerization. RMGI had the highest total shrinkage (4.65%) but lowest post-gel shrinkage (0.35%). Shrinkage values dropped significantly during storage in water but had not completely compensated polymerization shrinkage after 4 wk. All restored teeth initially exhibited inward (negative) cuspal flexure due to polymerization shrinkage. Cuspal flexure with the RMGI restoration was significantly less (-6.4 µm) than with the other materials (-12.1 to -14.1 µm). After 1 d, cuspal flexure reversed to +5.0 µm cuspal expansion with the RMGI and increased to +9.3 µm at 4 wk. After 4 wk, hygroscopic expansion compensated cuspal flexure in a compomer (Compoglass) and reduced flexure with Dyract and resin-based composite. Marginal integrity (93.7% intact restoration wall) was best for the Compoglass restorations and lowest (73.1%) for the RMGI restorations. Hygroscopic expansion was more effective in compensating shrinkage stress than would be assumed based on total shrinkage, because only post-gel shrinkage needed compensation. Effective expansion is therefore hygroscopic expansion minus post-gel shrinkage.

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.

Bioactive polymeric composites for tooth mineral regeneration: physicochemical and cellular aspects

Our studies of amorphous calcium phosphate (ACP)-based dental materials are focused on the design of bioactive, non-degradable, biocompatible, polymeric composites derived from acrylic monomer systems and ACP by photochemical or chemically activated polymerization. Their intended uses include remineralizing bases/liners, orthodontic adhesives and/or endodontic sealers. The bioactivity of these materials originates from the propensity of ACP, once exposed to oral fluids, to release Ca and PO₄ ions (building blocks of tooth and bone mineral) in a sustained manner while spontaneously converting to thermodynamically stable apatite. As a result of ACP's bioactivity, local Ca- and PO₄-enriched environments are created with supersaturation conditions favorable for the regeneration of tooth mineral lost to decay or wear. Besides its applicative purpose, our research also seeks to expand the fundamental knowledge base of structure-composition-property relationships existing in these complex systems and identify the mechanisms that govern filler/polymer and composite/tooth interfacial phenomena. In addition to an extensive physicochemical evaluation, we also assess the leachability of the unreacted monomers and in vitro cellular responses to these types of dental materials. The systematic physicochemical and cellular assessments presented in this study typically provide model materials suitable for further animal and/or clinical testing. In addition to their potential dental clinical value, these studies suggest the future development of calcium phosphate-based biomaterials based on composite materials derived from biodegradable polymers and ACP, and designed primarily for general bone tissue regeneration.

A comparison of resin-modified glass-ionomer and resin composite polymerisation shrinkage stress in a wet environment

OBJECTIVE

The aim of this study was to investigate the polymerisation shrinkage stress under water of four resin-modified glass-ionomers and three resin composite materials.

METHODS

Transparent acrylic rods (5mm diameter×30mm) were prepared and secured into drill chucks connected to a universal testing machine. A plastics cup was placed around the lower rod and a distance of 1.00mm was established between the prepared surfaces which provided a C-factor of 2.5. For composite only, an adhesive layer (Scotchbond Universal Adhesive) was placed on the rod ends and cured to achieve a bond with the rod end. Materials were placed between the rods and a strain gauge extensometer was installed. Materials were light cured for 40s and the plastics cup was filled with ambient temperature water. To determine polymerisation shrinkage stress (σpol) three specimens of each material were tested for a 6-h period to determine mean maximum σpol (MPa), σpol rate (MPa/s) and final σpol (MPa). ANOVA and post hoc Tukey tests were used to determine significant differences between means.

RESULTS

The highest mean maximum σpol of (5.4±0.5) MPa was recorded for RMGIC and (4.8±1.0) MPa for composite. The lowest mean final σpol of (0.8±0.4) MPa was recorded for RMGIC. For mean maximum σpol,σpol rate and final σpol there were significant differences between materials within groups, although no significant difference (p>0.05) was observed when comparing the RMGIC group to the composite group.

CONCLUSION

When comparing mean σpol, maximum σpol, and σpol rates between individual RMGIC and composite materials significant differences (p<0.05) were observed. However when comparing the group RMGIC to composite no significant differences (p>0.05) were observed. The null hypothesis that there is no difference in the short term σpol of RMGIC materials when compared to composite materials is only partly rejected.

RELEVANCE

Limited information is available on the comparison of RMGIC and resin composite σpol levels. This study provides information on the short term levels in a wet environment and will assist in understanding the initial σpol rates RMGIC place in cavities.

Evaluation of the effect of water on three different light cured composite restorative materials stored in water: an in vitro study

Objectives. The objective of this in vitro study was to investigate whether weight gain or loss in the three different composites occurs due to water absorption when they are stored in water. Methods. The composite restorative materials selected for this study included a microfine hybrid (Synergy) and two nanofilled composite restorative materials (Ceram X and Filtek Supreme Ultra). Twenty specimens of each material were fabricated of each composite material. Group A: Filtek Supreme Ultra, Group B: Synergy, Group C: Ceram X. Then all the specimens were stored in 10 ml Distilled water containing test tubes and placed in incubator at 37°C for six weeks. The weight changes of these specimens were measured daily for the first week and later once a week for next five weeks by using an electrical analytical balance. Results. The data was analyzed by one-way analysis of variance and Student's t test. All groups showed maximum amount of water absorption in the first week than gradual decrease in the water absorption from the second to the sixth week, as compared to the first week and there is no statistically significant difference between the groups tested. Conclusion. All the composite restorative material absorbs some amount of water. The water absorption of the composite may decrease the physical and mechanical properties of the composites; hence it is necessary to consider the type of the material before starting the treatment.

Effect of conventional and resin-modified glass-ionomer liner on dentin adhesive interface of Class I cavity walls after thermocycling

OBJECTIVE

The aim of this in vitro study was to analyze the effect of glass-ionomer cement as a liner on the dentin/resin adhesive interface of lateral walls of occlusal restorations after thermocycling.

MATERIALS AND METHODS

Occlusal cavities were prepared in 60 human molars, divided into six groups: no liner (1 and 4); glass-ionomer cement (GIC, Ketac Molar Easymix, 3M ESPE) (2 and 5); and resin-modified glass-ionomer cement (RMGIC, Vitrebond, 3M ESPE) (3 and 6). Resin composite (Filtek Z250, 3M ESPE) was placed after application of an adhesive system (Adper Single Bond 2, 3M ESPE) that was mixed with a fluorescent reagent (Rhodamine B) to allow confocal microscopy analysis. Specimens of groups 4, 5 and 6 were thermocycled (5°C-55°C) with a dwell time of 30 seconds for 5000 cycles. After this period, teeth were sectioned in approximately 0.8-mm slices. One slice of each tooth was randomly selected for confocal microscopy analysis. The other slices were sectioned into 0.8 mm × 0.8 mm beams, which were submitted to microtensile testing (MPa). Data were analyzed using two-way ANOVA and Tukey test (p<0.05).

RESULTS

There was no detectedstatistical difference on bond strength among groups (α<0.05). Confocal microscopy analysis showed a higher mean gap size in group 4 (12.5 μm) and a higher percentage of marginal gaps in the thermocycled groups. The RMGIC liner groups showed the lowest percentage of marginal gaps.

CONCLUSIONS

Lining with RMGIC resulted in less gap formation at the dentin/resin adhesive interface after artificial aging. RMGIC or GIC liners did not alter the microtensile bond strength of adhesive system/resin composite to dentin on the lateral walls of Class I restorations.

Hygroscopic dimensional changes of self-adhering and new resin-matrix composites during water sorption/desorption cycles

OBJECTIVES

To study hygroscopic dimensional changes in new resin-matrix composites during water sorption/desorption cycles.

METHODS

Five materials were examined: a self-adhering flowable composite: Vertise® Flow (VF), a universal composite: GC Kalore (GCK), two micro-fine hybrid composites: GC Gradia Direct Anterior (GDA) and GC Gradia Direct Posterior (GDP), and a posterior restorative composite: Filtek® Silorane (FS). Five disk-shaped specimens of each material were prepared (15 mm diameter × 2 mm thickness) according to ISO 4049. The mean diameter of each specimen was measured by a custom-built laser micrometer (to a resolution of 200 nm) periodically over 150d water immersion and 40d recondition periods at (37 ± 1)°C. Perspex controls were used. Data analysis was performed by repeated measures ANOVA, one-way ANOVA and Tukey's post hoc test (p<0.05).

RESULTS

Differences in hygroscopic expansion were found for all test materials during sorption, ranging from 0.74% (± 0.05) for FS to 4.82% (± 0.13) for VF. The differences were significant for all materials (p<0.001), except between GCK and GDA. The mathematical relationship between diametral expansion and square root of time was non-linear. VF exhibited significant dehydration shrinkage.

SIGNIFICANCE

The silorane composite FS had the lowest hygroscopic expansion. The extent of compensation of polymerization shrinkage by hygroscopic expansion depends on materials, specimen dimensions and time-scale. So the clinical situation must be taken into consideration in the application of these findings.

Effect of pre-heated composites and flowable liners on Class II gingival margin gap formation

PURPOSE

To evaluate the effect of preheated composites (PHC) and flowable liners (FL) on the gingival margin gap formation of Class II composite restorations compared to the placement of room temperature composites (RTC).

MATERIALS AND METHODS

Class II composite restorations were prepared on 40 extracted mandibular third molars, with the gingival margin located 1 mm below the CEJ in dentin. Optibond FL (Kerr), microhybrid Filtek Z-250 (3M ESPE) and Flow-It (Jeneric Pentron) were used to evaluate five study groups: 1) PHC, 130 degrees F/54.4 degrees C; 2) PHC, 155 degrees F/68.3 degrees C; 3) FL cured prior to the first increment composite; 4) FL cured simultaneously with the first increment composite and 5) RTC (Control). Impressions were taken with quick set polyvinyl siloxane impression material, and epoxy resin replicas were evaluated under SEM (200x). Gingival margin adaptation was quantitatively evaluated in terms of percentage of gap formation according to a modified ordinal scoring criteria. All margins were evaluated twice for reliability assessment. A non-parametric Kruskal-Wallis test was used to determine whether significant differences in gap formation existed among the study groups.

RESULTS

A high level of agreement was observed between duplicate measurements of the percentage of gap formation (intra-class correlation = 0.956, p < 0.0001). There was no evidence of a difference among groups defined by placement technique (p = 0.82). Overall, the mean gap-percentage for the 40 margins evaluated was 6.3 (Median = 1.1; SD = 14.8).

CONCLUSIONS

Gingival margin adaptation was not improved relative to the control by any of the placement techniques tested. No significant differences in gap formation were found among the study groups. A high degree of intra-examiner reliability was confirmed.

Fine-Tuning of Polymeric Resins and Their Interfaces with Amorphous Calcium Phosphate. A Strategy for Designing Effective Remineralizing Dental Composites

For over a decade our group has been designing, preparing and evaluating bioactive, remineralizing composites based on amorphous calcium phosphate (ACP) fillers embedded in polymerized methacrylate resin matrices. In these studies a major focus has been on exploring structure-property relationships of the matrix phase of these composites on their anti-cariogenic potential. The main challenges were to gain a better understanding of polymer matrix/filler interfacial properties through controlling the surface properties of the fillers or through fine-tuning of the resin matrix. In this work, we describe the effect of chemical structure and composition of the resin matrices on some of the critical physicochemical properties of the copolymers and their ACP composites. Such structure-property studies are essential in formulating clinically effective products, and this knowledge base is likely to have strong impact on the future design of therapeutic materials, appropriate for mineral restoration in defective tooth structures.

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

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

Selected physicochemical properties of the experimental endodontic sealer

This study explores water sorption, hygroscopic expansion, mechanical strength and ion release from the experimental amorphous calcium phosphate (ACP) composites formulated for application as endodontic sealers. Light-cure (LC) and dual-cure (DC; combined light and chemical cure) resins comprised urethane dimethacrylate (UDMA), 2-hydroxyethyl methacrylate (HEMA), methacryloyloxyethyl phthalate (MEP) and a high molecular mass oligomeric co-monomer, poly(ethyleneglycol)-extended UDMA (PEG-U) (designated UPHM resin). To fabricate composites, a mass fraction of 60% UPHM resin was blended with a mass fraction of 40% as-made (am-) or ground (g-) ACP. Glass-filled composites were used as controls. Both DC and LC ACP UPHM composites exhibited relatively high levels of water sorption accompanied by a significant hygroscopic expansion. The latter may potentially be useful to offset high polymerization stresses that develop in these materials. Ion release profiles of the experimental materials confirmed their potential for regeneration of mineral-deficient tooth structures. Their moderate to low mechanical strength after 3 months of aqueous immersion did not diminish the enthusiasm for the proposed use as endodontic sealers. For that application, DC g-ACP composites appear to be the most adequate, but micro-leakage and quantitative leachability studies are needed to fully establish their suitability.

A 36-month Clinical Evaluation of Ethanol/Water and Acetone-based Etch-and-Rinse Adhesives in Non-carious Cervical Lesions

Based on the findings of this clinical trial, one may conclude that non-carious cervical lesions should be restored with the ethanol/water-based two-step etch-and-rinse adhesive Single Bond, instead of the acetone-based One Step, as the latter presents a high number of debonded restorations after short- and long-term recalls. However, other literature findings should also be taken into account before reaching a clinical decision.

Effect of different surface treatments on the composite-composite repair bond strength

The aim of this study was to investigate the effect of different mechanical and adhesive treatments on the bond strength between pre-existing composite and repair composite using two aging times of the composite to be repaired. Standardized cylinders were made of a microhybrid composite (Spectrum TPH) and stored in saline at 37 degrees C for 24 h (n = 140) or 6 months (n = 140). Three types of mechanical roughening were selected: diamond-coated bur followed by phosphoric acid etching, mini sandblaster with 50-microm aluminum oxide powder, and 30-microm silica-coated aluminum oxide powder (CoJet Sand), respectively. Adhesive treatment was performed with the components of a multi-step bonding system (OptiBond FL) or with a one-bottle primer-adhesive (Excite). In the CoJet Sand group, the effect of a silane coupling agent (Monobond-S) was also investigated. The repair composite (Spectrum TPH) was applied into a mould in three layers of 1 mm, each separately light-cured for 40 s. Repair tensile bond strengths were determined after 24-h storage. Mechanical and adhesive treatment had significant effects on repair bond strength (P < 0.001). The age of the pre-existing composite had no significant effect (P = 0.955). With one exception (CoJet Sand/OptiBond FL Adhesive), adhesive treatments significantly increased repair bond strengths to 6-month-old composite when compared to the controls without adhesive. Adhesive treatment of the mechanically roughened composite is essential for achieving acceptable repair bond strengths. The more complicated use of silica-coated particles for sandblasting followed by a silane coupling agent had no advantage over common bonding systems.

Evaluation of weight change in three different light cured composite restorative materials stored in water: An in vitro study

AIMS AND OBJECTIVES

The objective of this in vitro study was to investigate whether weight gain in three different composites occurs due to water absorption, when stored in water.

MATERIALS AND METHODS

The composite restorative materials selected for this study included a micro-fine hybrid (Synergy) and two nano-filled composites (CERAM X duo and FILTEK Z 350). Twenty specimens of each material were fabricated with each composite material.- Group A: Filtek Z 350, Group B: Synergy, and Group C: CERAM X Duo. Then all the specimens were stored in 10 ml distilled water in test tubes, and then placed in an incubator at 37oC for six weeks. The weight changes of these specimens were measured daily for the first week, and, later, once a week, for the next five weeks, by using an electrical analytical balance.

RESULTS

The data were analyzed using one-way analysis of variance and Student 't' test. There was a tendency for the weight of the specimens to increase with the passage of time, when stored in water. All the groups showed maximum amount of water absorption in the first week; then there was a gradual decrease in the water absorption, from the second to the sixth week. Synergy showed the maximum amount of water absorption in the first week, as compared to FILTEK Z 350 and Ceram X Duo. However, FILTEK Z 350 showed the maximum amount of water absorption from the second week to the sixth week, as compared to Ceram X Duo and Synergy.

CONCLUSION

All composite restorative materials absorb some amount of water. The water absorption of the composite may decrease the physical and mechanical properties of the composites; hence, it is necessary to consider the type of the material before starting treatment.

Polymerization shrinkage and hygroscopic expansion of contemporary posterior resin-based filling materials—A comparative study

OBJECTIVES

To investigate the polymerization shrinkage and hygroscopic expansion of contemporary posterior resin-based filling materials.

METHODS

The densities of SureFil (SU), CeramXMono (CM), Clearfil AP-X (CF), Solitaire 2 (SO), TetricEvoCeram (TE), and Filtek P60 (FT) were measured using the Archimedes' principle prior to and 15min after curing for 20, 40 and 60s and after 1h, 24h, 7 d, and 30 d storage at 37 degrees C in water. Volumetric changes (DeltaV) in percent after polymerization and after each storage period in water were calculated from the changes of densities. Water sorption and solubility were determined after 30 d for all specimens and their curing times. Two-way ANOVA was calculated for shrinkage and repeated measures ANOVA was calculated for hygroscopic expansion (p<0.05).

RESULTS

DeltaV depended on filler load but not on curing time (SU approximately -2.0%, CM approximately -2.6%, CF approximately -2.1%, SO approximately -3.3%, TE approximately -1.7%, FT approximately -1.8%). Hygroscopic expansion depended on water sorption and solubility. Except for SU, all materials showed DeltaV approximately +1% after water storage.

CONCLUSION

Polymerization shrinkage depended on the type of resin-based filling material but not on curing time. Shrinkage was not compensated by hygroscopic expansion.

A new in vitro model to study the relationship of gap size and secondary caries

OBJECTIVES

To investigate the relationship of gap size and secondary caries in a newly developed secondary caries microbial model that permits adjustment of the gap between the tooth and a restoration.

METHODS

Tooth-resin-matrix composite specimens were mounted on gap-model stages with a gap size of 50 or 500 microm in experiment 1, and 0, 25, 250, or 1,000 microm in experiment 2. They were attached to plastic Petri plates, gas-sterilized and then incubated in a microbial caries model (with Streptococcus mutans TH16 in 1% sucrose tryptic soy broth for 1 h, 4 times/day, and with a buffer solution for the rest of the day). After 8 days of incubation, tooth specimens were sectioned and stained overnight with a rhodamine B solution. Digital images taken under a confocal microscope were analyzed for lesion size at the outer surface lesion and wall lesion (WL).

RESULTS

Gap size was found to affect the development of dentin WL area in experiment 1 and enamel and dentin WL areas in experiment 2, with bigger lesions being observed in the wider gap group (p < 0.05).

CONCLUSION

The findings of this study suggest that the size of the gap between tooth and restoration affects the development of secondary caries along the cavity wall.

Influence of adhesive systems on interfacial dentin gap formation in vitro

PURPOSE

This study measured: 1) the interfacial dentin gap formation (IGW) of 2 etch & rinse and 3 self-etch systems with different degrees of acidity and determined the correlation between the smear layer thickness and interfacial gap formation after 1 day and 6 months water storage; 2) the hybrid layer thickness (HLT) produced by the adhesives applied under different smear layer thicknesses.

METHODS AND MATERIALS

Three self-etch adhesives, a mild (Clearfil SE Bond; SE), a moderate (Optibond Solo Plus Self-Etch Primer; SO) and a strong (Tyrian Self Priming Etchant + One Step Plus; TY), and 2 etch & rinse systems (Single Bond; SB and Scotchbond Multi-Purpose Plus; SBMP) were studied. After flat grinding of the occlusal surfaces, 30 molars were sectioned longitudinally in 2 halves. Dentin surfaces with thick and thin smear layers were obtained for each tooth after polishing different sections on 60- and 600-grit SiC paper, respectively. A resin composite (Z250) build-up was made on each tooth section after randomized application of the adhesives. After 24-hour storage in water, resin-dentin bonded sticks (0.8 mm2) were prepared and divided for 1-day and 6-month measurements. The IGW was measured in a stereomicroscope under 400x. SEM micrographs were also made in order to measure the HLT provided by each adhesive.

RESULTS

The thickness of the smear layer did not influence the mean gap width (p>0.05). The etch & rinse systems showed the lowest mean IGW in the 1-day group. Their IGW remained unchanged after 6 months. The self-etch systems showed wider initial IGW, which diminished after 6 months water storage, to sizes similar to the etch & rinse systems. The hybrid layer was thicker when bonded to #60 SiC-treated dentin; however, this difference was only statistically different for the 3-step etch & rinse system (p=0.001). The thickest hybrid layers were observed for the 2 etch & rinse adhesive systems and the thinnest for the mild self-etch. A negative and strong correlation between IGW and HLT was observed for the self-etching adhesive systems tested (r=80.2, p=0.01).

Effect of Hygroscopic Expansion on the Push-Out Resistance of Glass Ionomer-Based Cements Used for the Luting of Glass Fiber Posts

This study examined the contribution of hygroscopic expansion of glass-ionomer (GIC) and resin modified glass-ionomer (RMGIC) luting cements to the push-out resistance of fiber posts. Glass fiber posts were luted to post spaces using different cements. Experimental specimens were stored in water, while control specimens were desiccated and stored in mineral oil to eliminate water from intraradicular dentinal tubules and/or the external environment that could have contributed to hygroscopic expansion of the cements. Thin slice push-out tests revealed no difference in retention strengths of resin composite cements that were stored in water or oil. Conversely, GIC and RMGIC cements exhibited increased retention strengths after water sorption. As unfavorable cavity geometry is taxing to dentin bond integrity in root canals, a strategy that relies on increasing the frictional resistance to post dislodgement via delayed hygroscopic expansion of glass-ionomer based materials may be a more pragmatic approach to fiber post retention.

Dimensional change of a calcium aluminate cement for posterior restorations in aqueous and dry media

OBJECTIVES

A calcium aluminate cement has recently been developed, with claims of being an alternative to dental amalgam and resin composites in posterior cavities. However, its' mechanical properties are not well evaluated and the aim of the study was therefore, to evaluate its' dimensional stability over time.

METHODS

The dimensional changes of the cement, Doxadent, and two composite resins, Esthet-X and InTen-S, were tested during 360 d. The specimens were stored at 37+/-1 degrees C either in 100% air humidity (dry) or immersed in distilled water (wet), except for the first 24h when all specimens were stored at 100% air humidity and 37+/-1 degrees C.

RESULTS

During the first 24h, Doxadent decreased in volume with 0.04%, while InTen-S and Esthet-X decreased with 1.60 and 1.75%, respectively. From d 1-360, the dry Doxadent specimens increased in volume with 2.0% and in weight with 5.5%, while the corresponding increase for the wet specimens were 4.1 and 6.3%, respectively. The volume of both composites increased 0.8% or less in dry and wet conditions, while the increase in weight for InTen-S was 1.2% for the wet specimens and 0.6% for the dry. The corresponding figures for Esthet-X were 0.7 and 0.2%.

SIGNIFICANCE

Doxadent was less dimensionally stable than the composites tested. Doxadent increased 2 times more in volume immersed in water than in 100% air humidity, while the increase in weight was almost similar. The clinical implications of the results found in the present study are uncertain. A material that continues to absorb water during prolonged periods and continues to react is questionable for clinical use.

Changes in expansion and mechanical strength during water storage of a traditional and three modified resin composites

Four types of resin composites (Dyract AP (DYR), Definite (DEF), Ariston pHc (ARI), and Spectrum TPH (SPE)) were tested after water storage for up to 180 days. The test parameters were flexural strength, flexural modulus, and marginal gaps at fillings in cylindrical cavities. The cavity tests were performed in two ways. One series of filings was finished shortly after curing and the maximal gaps were followed with time during water storage. Another series was finished immediately before gap size measurement and after water storage for various periods. Absence of or reduced gap sizes at 180 days compared to 1 h or 1 day was obsenred for all materials and with both methods. At 180 days, DYR and ARI showed significantly smaller gap sizes than those observed with DEF and SPE. No significant differences in flexural strength were observed when means at 180 days were compared to those observed at 1 day. DEF, ARI, and SPE showed a significant increase in flexural moduli at 180 days compared to 1 day, while DYR showed none. It is concluded that fillings made of Dyract AP or Ariston pHc may show absence of or very small gap sizes between filling and cavity wall after 6 months and with no significant reduction in mechanical strength.