Water absorption in artificial composites: Curse or blessing?

OBJECTIVES

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

METHODS

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(n = 180) were stored under the same conditions and tested in four subsets (n = 15 per material) that were respectively withdrawn after repeated thermocycling (5000 cycles; 5-55 °C, H2O) and repetitive drying (7 d; 37 °C, air).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

RESULTS

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

SIGNIFICANCE

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

Residual stresses in glass crowns generated by polymerization and water sorption of resin cements

This study investigated residual stresses in glass crowns cemented with resin cements. Glass caps were cemented to cylindrical cores using a conventional resin composite cement, a self-adhesive resin cement, or a methyl methacrylate (MMA)-based cement in dual-cure or self-cure mode. The cemented caps were stored in 37°C water for 28 days, and stresses on the cap surface were repeatedly measured. The water sorption, water solubility, and elastic modulus of the cements were also measured. Polymerization of the cements initially generated compressive stresses on the surfaces. Dual-curing or a greater modulus yielded greater initial stress. The stresses gradually decreased over time and lingered on the surfaces at 28 days with all the cements. Greater sorption tended to lead to greater stress reduction; however, the MMA-based cement exhibited less stress reduction despite exhibiting the greatest sorption. The use of a resin composite cement or dual-curing is recommended to reinforce crown restorations.

Flexural Strength of Conventional or Bulk-fill Resin Composite Repaired with High- or Low-viscosity Restorative Materials

OBJECTIVE

To evaluate the flexural strength of two types of high-viscosity resin composites (conventional or bulk-fill) that were repaired with either high-viscosity composites (conventional or bulk-fill) or low-viscosity composites (conventional or bulk-fill) of the same manufacturer (3M Oral Care, St Paul, MN, USA).

METHODS AND MATERIALS

Specimens (25 mm × 2 mm × 2 mm) of both conventional nanofilled resin (Filtek Z350XT), and bulk-fill nanofilled resin (Filtek One Bulk Fill) were prepared. After fracture of the specimens in the 3-point bending test (initial), half of the specimens were repaired immediately afterwards (24 hours), and the other half were repaired after 6 months of storage in distilled water. Repairs were performed with (n=15) high-viscosity resin composites (Filtek Z350XT, Filtek One Bulk Fill), or their low-viscosity versions (Filtek Supreme XT Flow, Filtek Bulk Fill Flowable Restorative). The repair was performed by roughening the surface and applying phosphoric acid, silane, and adhesive. The bending test (results reported in MPa) was performed in a universal testing machine, and the fracture pattern was determined. Data were evaluated by generalized linear models, chi-square test and the Fisher exact test (α=0.05).

RESULTS

There was no significant difference between the former pair of high-viscosity resins in terms of initial flexural strength (p=0.42). The repairs performed with low-viscosity resin composites after 24 hours or 6 months obtained higher MPa values compared with those using high-viscosity composites (p=0.0006). There was a significant decrease in MPa values when the repair was performed after 24 hours and an increase after 6 months, regardless of the material (p<0.0001). After 6 months, fractures involving the old (conventional) resin were more frequent in the repair performed with bulk-fill resin composites compared with the conventional composites (p=0.02).

CONCLUSIONS

Considering the tested products, the material to be repaired did not influence the flexural strength of the repair composite; however, the use of the low-viscosity resin composites resulted in greater flexural strength of the repaired material. The repair of the aged composite resulted in an increase in its flexural strength, regardless of the material repaired or used to perform the repair.

Self-adhesive flowable composite resins and flowable composite resins in permanent teeth with occlusal cavities: A systematic review and meta-analysis

OBJECTIVES

To compare the clinical performance (retention, secondary caries, marginal adaptation, marginal discoloration, and postoperative hypersensitivity) of self-adhesive flowable composite resins (SAFCs) and flowable composite resins (FCs) in permanent teeth with occlusal cavities.

DATA

Randomized controlled trials (RCTs) of SAFCs versus FCs with a follow-up length of at least one year. No restrictions were placed on language or publication date.

SOURCES

Five databases, including PubMed, Embase, Web of Science, Scopus, and the Cochrane Central Register of Controlled Trials, were searched manually by browsing ten related journals. On 14 June 2023, all electronic and manual searches were updated.

STUDY SELECTION

Five RCTs with 138 participants were included. Cochrane's risk of bias tool (2.0) was implemented in selected studies, and the GRADE tool was utilised to evaluate the evidence quality. To summarize the effects of the treatments and pool the data, a random-effects model was used.

CONCLUSIONS

According to the modified United States Public Health Service Evaluation (USPHS) criteria, there was no discernible difference between the groups during the two-year follow-up period (maximum follow-up time). Nevertheless, FCs applied with the etch-and-rinse mode demonstrated superior marginal adaptation and marginal discoloration at the two-year follow-up (relative risk = 3.21 [1.50 to 6.83], 3.40 [1.10, 10.48]). The evidence for marginal discoloration at any recall time and marginal adaptation at the one-year follow-up was graded as moderate quality due to inconsistency. Moreover, low-quality evidence for marginal adaptation at two-year follow-up was due to imprecision and inconsistency.

CLINICAL SIGNIFICANCE

SAFCs exhibited clinical performance comparable to that of FCs in occlusal cavities. Further high-quality clinical trials are needed to provide solid evidence to support the clinical application of SAFCs.

REGISTRATION

PROSPERO (CRD42022374983).

Bonding performance of experimental HEMA-free two-step universal adhesives to low C-factor flat dentin

OBJECTIVES

Experimental two-step universal adhesives (2-UAs) providing a particle-filled hydrophobic adhesive resin with a significant film thickness to hydrophobically seal the adhesive interface were designed and synthesized. This study aimed to characterize their interfacial interaction with dentin, to determine whether the 2-UA formulations achieve durable bonding to low C-factor flat dentin and to measure their water sorption.

METHODS

Bonding effectiveness of 2-UAs that combine a 10-MDP-based primer with hydrophobic adhesive resins differing only for filler (BZF-21, BZF-29, and BZF-29_hv) were comparatively investigated with the commercial adhesive Clearfil SE Bond 2 (C-SE2, Kuraray Noritake). Adhesive-dentin interfaces were characterized with TEM. Adhesive-resin disks were immersed in distilled water at 37 °C for 1 week, 6 months and 1 year to measure water sorption and solubility. 'Immediate' and 'aged' micro-tensile bond strength (μTBS) of the adhesives applied in etch-and-rinse (E&R) and self-etch (SE) bonding mode to low C-factor flat dentin were measured. Statistical analyses involved linear mixed-effects (LME) modelling and Kruskal-Wallis testing (p < 0.05).

RESULTS

TEM revealed that E&R hybrid layers were more sensitive to aging than SE hybrid layers. Lower water sorption was recorded for all UAs compared with C-SE2. The immediate μTBS of BZF-21 and BZF-29 was not significantly different from that of C-SE2. The 1-year aged μTBS of all 2-UAs was significantly lower than that of C-SE2, except for BZF-29 applied in E&R mode. A significant reduction in μTBS upon 1-year aging was recorded for BZF-21 and BZF-29 applied in E&R mode. A significant difference in μTBS between E&R and SE bonding modes was recorded for all adhesives except BZF-21.

SIGNIFICANCE

Experimental 2-UAs with a hydrophobic adhesive-resin design produced± 20-μm thick adhesive-resin layers, absorbed less water and resulted in bonding performance that was more aging-resistant when applied in SE than in E&R bonding mode. The silica-filled BZF-29 2-UA revealed the most comparable bonding performance with C-SE2 in a low C-factor condition (flat dentin).

Methacrylate Polymers With “Flipped External” Ester Groups: A Review

Current resin composites have favorable handling and upon polymerization initial physical properties that allow for efficient material replacement of removed carious tooth structure. Dental resin composites have long term durability limitations due to the hydrolysis of ester bonds within the methacrylate based polymer matrix. This article outlines the importance of ester bonds positioned internal to the carbon-carbon double bond in current methacrylate monomers. Water and promiscuous salivary/bacterial esterase activity can initiate ester bond hydrolysis that can sever the polymer backbone throughout the material. Recent studies have custom synthesized, with the latest advances in modern organic chemical synthesis, a novel molecule named ethylene glycol bis (ethyl methacrylate) (EGEMA). EGEMA was designed to retain the reactive acrylate units. Upon intermolecular polymerization of vinyl groups, EGEMA ester groups are positioned outside the backbone of the polymer chain. This review highlights investigation into the degradation resistance of EGEMA using buffer, esterase, and microbial storage assays. Material samples of EGEMA had superior final physical and mechanical properties than traditional ethylene glycol dimethacrylate (EGDMA) in all degradation assays. Integrating bioinformatics-based biodegradation predictions to the experimental results of storage media analyzed by LC/GC-MS revealed that hydrolysis of EGEMA generated small amounts of ethanol while preserving the strength bearing polymer backbone. Prior studies support investigation into additional custom synthesized methacrylate polymers with “flipped external” ester groups. The long term goal is to improve clinical durability compared to current methacrylates while retaining inherent advantages of acrylic based chemistry, which may ease implementation of these novel methacrylates into clinical practice.

Coulometric titration of water content and uptake in CAD/CAM chairside composites

OBJECTIVES

This study aimed to evaluate the water content and uptake of CAD/CAM chairside composites over 60 days using coulometric Karl Fischer (KF) titration.

METHODS

Rectangular plates (10 ×10×1 mm³ of thickness) were cut from the blocks of composites Cerasmart 270 (CS), Katana Avencia (KA), Grandio Blocs (GB), and Lava Ultimate (LU). Specimens were stored in distilled water for up to 60 days at 37 °C, and non-stored specimens were used as a control (n = 5). Specimens were isothermally heated at 200 °C, and the water content was evaporated and transferred to the titration cell throughout a nitrogen gas flow. The KF coulometer determined the percentage of water in each specimen. Data were analyzed by 2-way ANOVA and Tukey`s test (α = 0.05).

RESULTS

The water content of non-stored specimens ranged from 0.29 to 1.66 wt% (6.9-32.9 μg/mm³) for GB and LU, respectively. The water content increased underwater storage (0.82-2.96 wt% after 60 days). The extend of water sorption (11.9-26.1 μg/mm³) among the materials was directly related to their base water content. No additional water content increase was observed after 7 (LU and KA) or 21 (GB and CS) days. Measuring the water content in wt% or μg/mm³ affected the ranking of materials when KA and CS were analyzed.

SIGNIFICANCE

Composites with higher base water content also presented higher water sorption. KF titrationshowed to be a reliable method to measure the water sorption of composites, including their base water content.

The effect of functionalized titanium dioxide nanotube reinforcement on the water sorption and water solubility properties of flowable bulk-fill composite resins

The aim of this study was to investigate the effects of titanium dioxide nanotube addition on the water sorption and water solubility values of different composite resins. Titanium dioxide nanotubes were synthesized from titanium dioxide powder in anatase form and in 13 nm diameter by hydrothermal process and then functionalized with methacrylic acid. Characterization of the nanotubes was performed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. A flowable composite resin (Filtek Ultimate Flowable) and four flowable bulk-fill composite resins (Filtek Bulk Fill Flowable, SDR Bulk Fill Flowable, Venus Bulk Fill, X-tra Base) were tested. Two groups of each composite resin were prepared: groups of the resins without nanotubes; groups of the resins reinforced with 1.0 wt% functionalized titanium dioxide nanotube. Sorption and solubility in water were assessed according to ISO 4049 standards after 1, 7, 14, 21 days immersion periods. Data were analyzed using Mann-Whitney U and Kruskal-Wallis H tests (p  <  0.05). Long cylindrical tubular structures with a diameter of 41.09-72.49 nm were observed in electron microscopy analysis. The band at 1636 cm^- 1 showed the existence of the vinyl (C=C) bond of methacrylic acid coordinated to the nanotubes in Fourier transform infrared spectroscopy analysis. None of the materials tested in this study exceeded the maximum sorption and solubility values established by ISO. Regarding the water solubility, negative values were obtained. TiO₂ nanotube reinforcement decreased the water sorption and solubility values significantly at different evaluation periods in all composite resins except for Venus (p < 0.05).

Changes of residual stresses on the surface of leucite-reinforced ceramic restoration luted with resin composite cements during aging in water

The objective of this study was to compare the changes in the residual stresses present on the surface of leucite-reinforced dental ceramic restorations luted with a self-adhesive and a conventional resin composite cement during aging in water. Ring specimens made of a leucite-reinforced ceramics were luted to ceramic cylinders using a self-adhesive (Panavia SA Luting Plus) or a conventional resin composite cement (Panavia V5) in dual-cure or self-cure mode. Residual stresses on the ring surface were measured using indentation fracture method at 1 h, 1, 3, 7, 14 and 28 days of the 37 °C water immersion. Water sorption, water solubility and elastic modulus of the cements were also measured. Compressive stress was generated on the surface of the ceramic rings by the polymerization of the resin composite cements, and the stresses appeared to decrease over time by water sorption of the cements. The dual-cured conventional resin composite cement remained compressive stresses on the ceramic surface, while only the self-cured self-adhesive cement, which demonstrated the greatest water sorption, generated tensile stresses during the four weeks of aging in water. The elastic moduli of cements did not significantly change through the immersion, suggesting that the stresses were less affected by the modulus. To prevent the generation of tensile stresses on the leucite-reinforced ceramic restoration, self-adhesive cements exhibiting small water sorption should be clinically selected.

Clinical Evaluation of a Self-Adhering Flowable Resin Composite in Minimally Invasive Class I Cavities: 5-year Results of a Double Blind Randomized, Controlled Clinical Trial

OBJECTIVE

The aim of this study was to evaluate the long-term clinical performance of a self-adhering flowable resin composite compared to a conventional flowable resin composite used with an etch&rinse adhesive system in minimally invasive Class I cavities.

MATERIALS AND METHODS

Twenty-five patients received at least one pair of Class I restorations (n=65). After class I cavities had been prepared, they were randomly restored either with a self-adhering flowable resin composite (VertiseFlow/Kerr-VR) [Group-1 (n=33)], or with a flowable resin composite (Luxaflow/DMG-LX) in combination with an etch&rinse adhesive (Teco/DMG) [Group-2 (n=32)] according to the manufacturers' instructions. The restorations were evaluated at baseline and yearly during 5 years according to the FDI criteria by two evaluators. A statistical analysis was carried out using the Pearson Chi-Square test and the Cochran Q-test followed by the Mc Nemar's test (p=0.05).

RESULTS

After 5 years a total of 47 restorations were evaluated with a recall rate of 68%. At 4-year, 3 (11.5%) VR and 2 LX (7.6%) restorations exhibited a cumulative retention loss. Seventeen (73.9%) VR and 14 LX (58.3%) restorations exhibited clinically acceptable (2) scores for marginal adaptation. At 5-year evaluations VR and LX showed similar results regarding all evaluated criteria (p > 0.05). The cumulative retention loss rates of VR and LX were 15.3% and 7.6%, respectively. None of the restorations demonstrated a recurrence of caries and post operative sensitivity. Both materials showed significant changes at 4 and 5 years regarding marginal staining when compared to baseline (p<0.001). Furthermore, significant changes were observed for VR and LX at 1, 2, 3, 4 and 5 years for marginal adaptation according to baseline (p<0.001).

CONCLUSION

The use of both materials for the restoration of Class-I cavities demonstrated clinically acceptable performance at the end of 5-year. The self-adhering flowable composite exhibited a clinical performance similar to the conventional flowable applied with an etch&rinse adhesive.

Hygroscopic expansion of self-adhesive resin cements and the integrity of all-ceramic crowns

OBJECTIVE

Low pH neutralization and subsequent remnant hydrophilicity can lead to hygroscopic expansion of self-adhesive resin cements (SARCs) after water storage. The aim of this in vitro study was to investigate the effects of hygroscopic expansion of SARCs, used as luting and partial core build-up material, on integrity and cement gap thickness increase of all-ceramic CAD/CAM crowns.

METHODS

Human third molars (n=48) were prepared and anatomical all-ceramic CAD/CAM crowns were manufactured (VITABLOCS Mark II, VITA Zahnfabrik). Crowns internal surfaces were HF etched and silanized. The prepared teeth with their respective crowns were divided into 6 groups (n=8). In groups 1, 3 and 5 the coronal dentin was removed to simulate a partial core build-up. Groups 1 and 2 were luted with iCEM (Heraeus Kulzer), 3 and 4 with RelyX Unicem 2 Automix (3M), 5 and 6 with Variolink Esthetic DC (Ivoclar Vivadent). All specimens were dual cured and stored in distilled water at 37°C. Crown integrity was controlled at baseline and in regular intervals until 180 days. Cement gap thickness was measured using an optical 3D scanner (ATOS Triple scan, GOM) at baseline and after 180 days. Crown integrity was statistically analysed using Kaplan-Meier survival analysis and cement gap thickness increase using two-way ANOVA (α=0.05).

RESULTS

After 180 days storage, crack formation was observed in all specimens of group 1 (mean survival time of 85.5 days), in one specimen of group 2 and in two specimens of group 4. Two-way ANOVA analysis revealed a statistically significant interaction between material type and build-up on cement gap size increase for iCEM.

SIGNIFICANCE

Within the limits of this study, the application of SARCs with low pH neutralization as partial build-up material under CAD/CAM crowns is not recommended for clinical use.

In vitro aging behavior of dental composites considering the influence of filler content, storage media and incubation time

Objective

Over time dental composites age due to mechanical impacts such as chewing and chemical impacts such as saliva enzymes and food ingredients. For this research, the focus was placed on chemical degradation. The objective of this study was to simulate hydrolysis by using different food simulating liquids and to assess their impact on the mechanical parameter Vickers microhardness (MHV) and the physicochemical parameter contact angle (CA).

Methods

Specimen of three composites (d = 6 mm, h = 2 mm; n = 435) classified with respect to their filler content (wt%), namely low-filled, medium-filled and highly-filled, were stored for 0, 14, 30, 90 and 180 days in artificial saliva (pH 7), citric acid (pH 3; pH 5), lactic acid (pH 3; pH 5) and ethanol (40%vol; 60%vol) and assessed regarding to MHV and CA. Statistics: Kruskal-Wallis test, stepwise linear regression, bivariate Spearman Rank Correlation (p < 0.05).

Results

While stored in artificial saliva, acid and ethanol the CA decreased especially for the low- and medium-filled composites. It was shown that rising the filler content caused less surface changes in the CA. Storage in ethanol led to a significant decrease of MHV of all composites. Regression analysis showed that the effect of in vitro aging on MHV was mainly influenced by the composite material and therefore by filler content (R² = 0.67; p < 0.05). In contrast, the CA is more influenced by incubation time and filler content (R² = 0.2; p < 0.05) leading to a higher risk of plaque accumulation over time. Significance: In vitro aging showed significant changes on the mechanical and physicochemical properties of dental composites which may shorten their long-term functionality. In conclusion, it can be stated, that the type of composite material, especially rising filler content seems to improve the materials’ resistance against the processes of chemical degradation.

Monomer conversion, dimensional stability, strength, modulus, surface apatite precipitation and wear of novel, reactive calcium phosphate and polylysine-containing dental composites

Purpose

The aim was to assess monomer conversion, dimensional stability, flexural strength / modulus, surface apatite precipitation and wear of mono / tri calcium phosphate (CaP) and polylysine (PLS)—containing dental composites. These were formulated using a new, high molecular weight, fluid monomer phase that requires no polymerisation activator.

Materials and methods

Urethane and Polypropylene Glycol Dimethacrylates were combined with low levels of an adhesion promoting monomer and a light activated initiator. This liquid was mixed with a hybrid glass containing either 10 wt% CaP and 1 wt% PLS (F1) or 20 wt% CaP and 2 wt% PLS (F2). Powder to liquid mass ratio was 5:1. Commercial controls included Gradia Direct Posterior (GD) and Filtek Z250 (FZ). Monomer conversion and polymerisation shrinkage were calculated using Fourier Transform Infrared (FTIR). Subsequent volume increases in water over 7 weeks were determined using gravimetric studies. Biaxial flexural strength (BFS) / modulus (BFM) reduction and surface apatite precipitation upon 1 and 4 weeks immersion in water versus simulated body fluid (SBF) were assessed using a mechanical testing frame and scanning electron microscope (SEM). Mass / volume loss and surface roughness (R_a) following 7 weeks water immersion and subsequent accelerated tooth-brush abrasion were examined using gravimetric studies and profilometer.

Results

F1 and F2 exhibited much higher monomer conversion (72%) than FZ (54%) and low calculated polymerization shrinkage (2.2 vol%). Final hygroscopic expansions decreased in the order; F2 (3.5 vol%) > F1 (1.8 vol%) ~ Z250 (1.6 vol%) > Gradia (1.0 vol%). BFS and BFM were unaffected by storage medium type. Average BFS / BFM upon 4 weeks immersion reduced from 144 MPa / 8 GPa to 107 MPa / 5 GPa for F1 and 105 MPa / 6 GPa to 82 MPa / 4 GPa for F2. Much of this change was observed in the first week of immersion when water sorption rate was high. Surface apatite layers were incomplete at 1 week, but around 2 and 15 micron thick for F1 and F2 respectively following 4 weeks in SBF. Mass and volume loss following wear were equal. Average results for F1 (0.5%), F2 (0.7%), and FZ (0.5%) were comparable but lower than that of GD (1%). R_a, however, decreased in the order; F1 (15 μm) > F2 (11 μm) > GD (9 μm) > FZ (5 μm).

Conclusions

High monomer conversion in combination with large monomer size and lack of amine activator should improve cytocompatibility of the new composites. High monomer molecular weight and powder content enables low polymerisation shrinkage despite high conversion. Increasing active filler provides enhanced swelling to balance shrinkage, which, in combination with greater surface apatite precipitation, may help seal gaps and reduce bacterial microleakage. High monomer conversion also ensures competitive mechanical / wear characteristics despite enhanced water sorption. Furthermore, increased active filler could help reduce surface roughness upon wear.

The Influence of Water Sorption of Dental Light-Cured Composites on Shrinkage Stress

The contraction stress generated during the photopolymerization of resin dental composites is the major disadvantage. The water sorption in the oral environment should counteract the contraction stress. The purpose was to evaluate the influence of the water sorption of composite materials on polymerization shrinkage stress generated at the restoration-tooth interface. The following materials were tested: Filtek Ultimate, Gradia Direct LoFlo, Heliomolar Flow, Tetric EvoCeram, Tetric EvoCeram Bulk Fill, Tetric EvoFlow, Tetric EvoFlow Bulk Fill, X-tra Base, Venus BulkFil, and Ceram.X One. The shrinkage stress was measured immediately after curing and after: 0.5 h, 24 h, 72 h, 96 h, 168 h, 240 h, 336 h, 504 h, 672 h, and 1344 h by means of photoelastic study. Moreover, water sorption and solubility were evaluated. Material samples were weighted on scale in time intervals to measure the water absorbency and the dynamic of this process. The tested materials during polymerization generated shrinkage stresses ranging from 6.3 MPa to 12.5 MPa. Upon water conditioning (56 days), the decrease in shrinkage strain (not less than 48%) was observed. The decrease in value stress in time is material-dependent.

Can long-term dentine bonding created in real life be forecasted by parameters established in the laboratory?

Tooth-coloured plastic dental fillings secured by adhesives to tooth structures are widely used to fix decayed teeth. Whereas laboratory tests demonstrate rapid deterioration of the ability of the adhesives to stick to dentine, clinical studies show that these fillings are relatively durable. This discrepancy suggests that the parameters used for simulating bond degradation in the laboratory setting do not correlate well with clinical outcomes. The present study examined the long-term tensile bond strength of resin composite fillings performed in real life and under different laboratory-simulated bonding conditions to identify parameters that may be used to forecast the durability of adhesive bonds created in dentine. Fillings placed in vivo were subjected to different periods of intraoral function. In vitro specimens were bonded based on whether simulated pulpal pressure (SPP) or thermomechanical cycling was implemented, and how long the completed fillings were stored in water. Thermomechanical cycling used in combination with long-term water ageing are useful in forecasting the decline in strength of resin-dentine bonds created in vivo. These parameters should be adopted for future evaluations. Conversely, the use of SPP does not appear to be a significant parameter in the simulation of long-term clinical deterioration of bond integrity.

Dental Composites with Calcium / Strontium Phosphates and Polylysine

Purpose

This study developed light cured dental composites with added monocalcium phosphate monohydrate (MCPM), tristrontium phosphate (TSrP) and antimicrobial polylysine (PLS). The aim was to produce composites that have enhanced water sorption induced expansion, can promote apatite precipitation and release polylysine.

Materials and Methods

Experimental composite formulations consisted of light activated dimethacrylate monomers combined with 80 wt% powder. The powder phase contained a dental glass with and without PLS (2.5 wt%) and/or reactive phosphate fillers (15 wt% TSrP and 10 wt% MCPM). The commercial composite, Z250, was used as a control. Monomer conversion and calculated polymerization shrinkage were assessed using FTIR. Subsequent mass or volume changes in water versus simulated body fluid (SBF) were quantified using gravimetric studies. These were used, along with Raman and SEM, to assess apatite precipitation on the composite surface. PLS release was determined using UV spectroscopy. Furthermore, biaxial flexural strengths after 24 hours of SBF immersion were obtained.

Results

Monomer conversion of the composites decreased upon the addition of phosphate fillers (from 76 to 64%) but was always higher than that of Z250 (54%). Phosphate addition increased water sorption induced expansion from 2 to 4% helping to balance the calculated polymerization shrinkage of ~ 3.4%. Phosphate addition promoted apatite precipitation from SBF. Polylysine increased the apatite layer thickness from ~ 10 to 20 μm after 4 weeks. The novel composites showed a burst release of PLS (3.7%) followed by diffusion-controlled release irrespective of phosphate addition. PLS and phosphates decreased strength from 154 MPa on average by 17% and 18%, respectively. All formulations, however, had greater strength than the ISO 4049 requirement of > 80 MPa.

Conclusion

The addition of MCPM with TSrP promoted hygroscopic expansion, and apatite formation. These properties are expected to help compensate polymerization shrinkage and help remineralize demineralized dentin. Polylysine can be released from the composites at early time. This may kill residual bacteria.

Self-adhesive resin cements: pH-neutralization, hydrophilicity, and hygroscopic expansion stress

OBJECTIVES

The objective of the study was to investigate the relationship between pH-neutralization, hydrophilicity, and free hygroscopic expansion stress of self-adhesive resin cements (SARCs) after storage in artificial saliva.

MATERIALS AND METHODS

The SARCs RelyX Unicem Automix 2 (RX2, 3 M ESPE), iCEM (iCEM, Heraeus) and Maxcem Elite (MCE, Kerr) were under investigation in this study. Cylinders (height × diameter, 6 × 4mm) were prepared from each material and stored in artificial saliva (7d at 37 °C). Cylinder height was measured at baseline and after 7 days. After storage, the compression modulus was measured to calculate the free hygroscopic expansion stress. For pH-neutralization and hydrophilicity assessment, disks (height × diameter, 1 × 1.5 mm) were prepared, covered with electrolyte, and monitored over 24 h at 37 °C. Hydrophilicity was assessed using the static sessile drop technique at baseline and at different time intervals up to 24 h. Data were analyzed using one-way ANOVA and post hoc Student-Newman-Keuls test (S-N-K, α = 0.05).

RESULTS

After 24 h, RX2 (pH_24h 4.68) had a significantly higher (p < 0.05) pH-value than MCE (pH_24h 4.2) and iCEM (pH_24h 3.23). iCEM showed the significantly highest hydrophilicity (p < 0.05) after 24 h (θ_24h 85.02°), while MCE resulted lower (θ_24h 113.01°) in comparison with RX2 (θ_24h 108.11°). The resulting hygroscopic expansion stress of iCEM (29.15 MPa) was significantly higher (p < 0.05) compared to RX2 (14.5 MPa) and MCE (21.02 MPa).

CONCLUSIONS

The material with lowest pH-neutralization capacity displayed higher hydrophilicity after 24 h and higher hygroscopic expansion stress after 7 days compared to those with high pH-neutralization.

CLINICAL SIGNIFICANCE

Remnant hydrophilicity due to low pH-neutralization of SARCs could lead to cement interface stress build-up and long-term failure of silicate ceramic restorations.

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.

Functional dendritic compounds: potential prospective candidates for dental restorative materials and in situ re-mineralization of human tooth enamel

This review provides a snapshot of recent progress in the synthesis and application of dendritic compounds as potential prospective candidates for dental restorative materials andin siture-mineralization of human tooth enamel.

Two-year Randomized, Controlled Clinical Trial of a Flowable and Conventional Composite in Class I Restorations

OBJECTIVES

This study evaluated the two-year clinical performance and volumetric wear of a flowable resin composite compared to a conventional highly filled composite resin in Class I restorations.

METHODS AND MATERIALS

In this single-center, single-blinded, comparator-controlled clinical study (Institutional Review Board approved), 120 carious teeth distributed in 60 patients were randomly assigned to four calibrated practitioners who placed occlusal restorations (n=60 flowable and n=60 conventional composite). Direct and indirect assessment at baseline, six months, one year, and two years occurred during which the modified Cvar and Ryge criteria were evaluated. Volumetric wear was determined by superimposition of profilometer scans of baseline and two-year casts.

RESULTS

At two years, there was no significant difference in anatomic form (p=0.80), color match (p=0.08), marginal adaptation (p=0.89), marginal discoloration (p=0.79), surface integrity (p=0.18), secondary caries (p=0.66), cold sensitivity (p=0.522), occlusal sensitivity (p=0.818), or volumetric wear (p=0.661) between materials. Both materials showed a decrease in all criteria except secondary caries (p=0.95) over time. Two-year mean volumetric wear was 3.16 ± 2.38 mm(3) for the flowable composite and 3.43 ± 2.50 mm(3) for the conventional composite.

CONCLUSIONS

The flowable and conventional composites used in this study have similar clinical efficacy after two years of service when placed as Class I occlusal restorations having isthmus widths less than one-half the intercuspal distance.

Effects of coronal substrates and water storage on the microhardness of a resin cement used for luting ceramic crowns

Composite resin and metallic posts are the materials most employed for reconstruction of teeth presenting partial or total destruction of crowns. Resin-based cements have been widely used for cementation of ceramic crowns. The success of cementation depends on the achievement of adequate cement curing.