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1.  [No title available] 
PMCID: PMC3899825  PMID: 24252652
2.  [No title available] 
PMCID: PMC3999475  PMID: 24332989
3.  Therapeutic polymers for dental adhesives: Loading resins with bio-active components 
Objectives
Many recent adhesives on the market exhibit reasonable clinical performance. Future innovations in adhesive materials should therefore seek out novel properties rather than simply modifying existing technologies. It is proposed that adhesive materials that are “bio-active” could contribute to better prognosis of restorative treatments.
Methods
This review examines the recent approaches used to achieve therapeutic polymers for dental adhesives by incorporating bio-active components. A strategy to maintain adhesive restorations is the focus of this paper.
Results
Major trials on therapeutic dental adhesives have looked at adding antibacterial activities or remineralization effects. Applications of antibacterial resin monomers based on quaternary ammonium compounds have received much research attention, and the loading of nano-sized bioactive particles or multiple ion-releasing glass fillers have been perceived as advantageous since they are not expected to influence the mechanical properties of the carrier polymer.
Significance
The therapeutic polymer approaches described here have the potential to provide clinical benefits. However, not many technological applications in this category have been successfully commercialized. Clinical evidence as well as further advancement of these technologies can be a driving force to make these new types of materials clinically available.
doi:10.1016/j.dental.2013.06.003
PMCID: PMC4312699  PMID: 23899387
Adhesives; Dental polymers; Bio-active; Antibacterial; Remineralization; QAC; Nano-particle
4.  Dentin Biomodification: Strategies, Renewable Resources and Clinical Applications 
Objectives
The biomodification of dentin is a biomimetic approach, mediated by bioactive agents, to enhance and reinforce the dentin by locally altering the biochemistry and biomechanical properties. This review provides an overview of key dentin matrix components, targeting effects of biomodification strategies, the chemistry of renewable natural sources, and current research on their potential clinical applications.
Methods
The PubMed database and collected literature were used as a resource for peer-reviewed articles to highlight the topics of dentin hierarchical structure, biomodification agents, and laboratorial investigations of their clinical applications. In addition, new data is presented on laboratorial methods for the standardization of proanthocyanidin-rich preparations as a renewable source of plant-derived biomodification agents.
Results
Biomodification agents can be categorized as physical methods and chemical agents. Synthetic and naturally occurring chemical strategies present distinctive mechanism of interaction with the tissue. Initially thought to be driven only by inter- or intra-molecular collagen induced non-enzymatic collagen cross-linking, multiple interactions with other dentin components are fundamental for the long-term biomechanics and biostability of the tissue. Oligomeric proanthocyanidins show promising bioactivity, and their chemical complexity requires systematic evaluation of the active compounds to produce a fully standardized intervention material from renewable resource, prior to their detailed clinical evaluation.
Significance
Understanding the hierarchical structure of dentin and the targeting effect of the bioactive compounds will establish their use in both dentin-biomaterials interface and caries management.
doi:10.1016/j.dental.2013.10.012
PMCID: PMC3972923  PMID: 24309436
5.  Biomimetic remineralization of dentin 
Objectives
Remineralization of demineralized dentin is important for improving dentin bonding stability and controlling primary and secondary caries. Nevertheless, conventional dentin remineralization strategy is not suitable for remineralizing completely-demineralized dentin within hybrid layers created by etch-and-rinse and moderately aggressive self-etch adhesive systems, or the superficial part of a caries-affected dentin lesion left behind after minimally invasive caries removal. Biomimetic remineralization represents a different approach to this problem by attempting to backfill the demineralized dentin collagen with liquid-like amorphous calcium phosphate nanoprecursor particles that are stabilized by biomimetic analogs of noncollagenous proteins.
Methods
This paper reviewed the changing concepts in calcium phosphate mineralization of fibrillar collagen, including the recently discovered, non-classical particle-based crystallization concept, formation of polymer-induced liquid- precursors (PILP), experimental collagen models for mineralization, and the need for using phosphate-containing biomimetic analogs for biomimetic mineralization of collagen. Published work on the remineralization of resin-dentin bonds and artificial caries-like lesions by various research groups was then reviewed. Finally, the problems and progress associated with the translation of a scientifically-sound concept into a clinically-applicable approach are discussed.
Results and Significance
The particle-based biomimetic remineralization strategy based on the PILP process demonstrates great potential in remineralizing faulty hybrid layers or caries-like dentin. Based on this concept, research in the development of more clinically feasible dentin remineralization strategy, such as incorporating poly(anionic) acid-stabilized amorphous calcium phosphate nanoprecursor-containing mesoporous silica nanofillers in dentin adhesives, may provide a promising strategy for increasing of the durability of resin-dentin bonding and remineralizing caries-affected dentin.
doi:10.1016/j.dental.2013.07.013
PMCID: PMC3867526  PMID: 23927881
Biomimetic; Mineralization; Dentin
6.  Edge chipping and flexural resistance of monolithic ceramics☆ 
Objective
Test the hypothesis that monolithic ceramics can be developed with combined esthetics and superior fracture resistance to circumvent processing and performance drawbacks of traditional all-ceramic crowns and fixed-dental-prostheses consisting of a hard and strong core with an esthetic porcelain veneer. Specifically, to demonstrate that monolithic prostheses can be produced with a much reduced susceptibility to fracture.
Methods
Protocols were applied for quantifying resistance to chipping as well as resistance to flexural failure in two classes of dental ceramic, microstructurally-modified zirconias and lithium disilicate glass–ceramics. A sharp indenter was used to induce chips near the edges of flat-layer specimens, and the results compared with predictions from a critical load equation. The critical loads required to produce cementation surface failure in monolithic specimens bonded to dentin were computed from established flexural strength relations and the predictions validated with experimental data.
Results
Monolithic zirconias have superior chipping and flexural fracture resistance relative to their veneered counterparts. While they have superior esthetics, glass–ceramics exhibit lower strength but higher chip fracture resistance relative to porcelain-veneered zirconias.
Significance
The study suggests a promising future for new and improved monolithic ceramic restorations, with combined durability and acceptable esthetics.
doi:10.1016/j.dental.2013.09.004
PMCID: PMC4000448  PMID: 24139756
Edge chipping; Flexural fracture; Monolithic restorations; Zirconia-based ceramic; Glass–ceramic; Graded glass–zirconia
7.  Fatigue loading and R-curve behavior of a dental glass-ceramic with multiple flaw distributions 
Objectives
To determine the effects of surface finish and mechanical loading on the rising toughness curve (R-curve) behavior of a fluorapatite glass-ceramic (IPS e.max ZirPress) and to determine a statistical model for fitting fatigue lifetime data with multiple flaw distributions.
Materials and Methods
Rectangular beam specimens were fabricated by pressing. Two groups of specimens (n=30) with polished (15 μm) or air abraded surface were tested under rapid monotonic loading in oil. Additional polished specimens were subjected to cyclic loading at 2 Hz (n=44) and 10 Hz (n=36). All fatigue tests were performed using a fully articulated four-point flexure fixture in 37°C water. Fractography was used to determine the critical flaw size and estimate fracture toughness. To prove the presence of R-curve behavior, non-linear regression was used. Forward stepwise regression was performed to determine the effects on fracture toughness of different variables, such as initial flaw type, critical flaw size, critical flaw eccentricity, cycling frequency, peak load, and number of cycles. Fatigue lifetime data were fit to an exclusive flaw model.
Results
There was an increase in fracture toughness values with increasing critical flaw size for both loading methods (rapid monotonic loading and fatigue). The values for the fracture toughness ranged from 0.75 to 1.1 MPa·m1/2 reaching a plateau at different critical flaw sizes based on loading method.
Significance
Cyclic loading had a significant effect on the R-curve behavior. The fatigue lifetime distribution was dependent on the flaw distribution, and it fit well to an exclusive flaw model.
doi:10.1016/j.dental.2013.08.208
PMCID: PMC3818533  PMID: 24034441
Dental ceramic; pressable ceramic; fractography; exclusive flaw model
8.  Time-dependent fracture probability of bilayer, lithium-disilicate-based glass-ceramic molar crowns as a function of core/veneer thickness ratio and load orientation 
Recent reports on bilayer ceramic crown prostheses suggest that fractures of the veneering ceramic represent the most common reason for prosthesis failure.
Objective
The aims of this study were to test the hypotheses that: (1) an increase in core ceramic/veneer ceramic thickness ratio for a crown thickness of 1.6 mm reduces the time-dependent fracture probability (Pf) of bilayer crowns with a lithium-disilicate-based glass-ceramic core, and (2) oblique loading, within the central fossa, increases Pf for 1.6-mm-thick crowns compared with vertical loading.
Materials and methods
Time-dependent fracture probabilities were calculated for 1.6-mm-thick, veneered lithium-disilicate-based glass-ceramic molar crowns as a function of core/veneer thickness ratio and load orientation in the central fossa area. Time-dependent fracture probability analyses were computed by CARES/Life software and finite element analysis, using dynamic fatigue strength data for monolithic discs of a lithium-disilicate glass-ceramic core (Empress 2), and ceramic veneer (Empress 2 Veneer Ceramic).
Results
Predicted fracture probabilities (Pf) for centrally-loaded 1,6-mm-thick bilayer crowns over periods of 1, 5, and 10 years are 1.2%, 2.7%, and 3.5%, respectively, for a core/veneer thickness ratio of 1.0 (0.8 mm/0.8 mm), and 2.5%, 5.1%, and 7.0%, respectively, for a core/veneer thickness ratio of 0.33 (0.4 mm/1.2 mm).
Conclusion
CARES/Life results support the proposed crown design and load orientation hypotheses.
Significance
The application of dynamic fatigue data, finite element stress analysis, and CARES/Life analysis represent an optimal approach to optimize fixed dental prosthesis designs produced from dental ceramics and to predict time-dependent fracture probabilities of ceramic-based fixed dental prostheses that can minimize the risk for clinical failures.
doi:10.1016/j.dental.2013.08.206
PMCID: PMC3855228  PMID: 24060349
Core ceramic; Veneering ceramic; Lithium disilicate; Glass-ceramic; Load orientation; Prosthesis design; Thickness ratio; Dynamic fatigue; Finite element analysis; Stress; CARES/Life; Fracture probability
9.  Property evolution during vitrification of dimethacrylate photopolymer networks 
Objectives
This study seeks to correlate the interrelated properties of conversion, shrinkage, modulus and stress as dimethacrylate networks transition from rubbery to glassy states during photopolymerization.
Methods
An unfilled BisGMA/TEGDMA resin was photocured for various irradiation intervals (7–600 s) to provide controlled levels of immediate conversion, which was monitored continuously for 10 min. Fiber optic near-infrared spectroscopy permitted coupling of real-time conversion measurement with dynamic polymerization shrinkage (linometer), modulus (dynamic mechanical analyzer) and stress (tensometer) development profiles.
Results
The varied irradiation conditions produced final conversion ranging from 6 % to more than 60 %. Post-irradiation conversion (dark cure) was quite limited when photopolymerization was interrupted either at very low or very high levels of conversion while significant dark cure contributions were possible for photocuring reactions suspended within the post-gel, rubbery regime. Analysis of conversion-based property evolution during and subsequent to photocuring demonstrated that the shrinkage rate increased significantly at about 40 % conversion followed by late-stage suppression in the conversion-dependent shrinkage rate that begins at about 45–50 % conversion. The gradual vitrification process over this conversion range is evident based on the broad but well-defined inflection in the modulus versus conversion data. As limiting conversion is approached, modulus and, to a somewhat lesser extent, stress rise precipitously as a result of vitrification with the stress profile showing little if any late-stage suppression as seen with shrinkage.
Significance
Near the limiting conversion for this model resin, the volumetric polymerization shrinkage rate slows while an exponential rise in modulus promotes the vitrification process that appears to largely dictate stress development.
doi:10.1016/j.dental.2013.09.002
PMCID: PMC3862026  PMID: 24080378
dental materials; dimethacrylate; polymers; shrinkage; stress; modulus; vitrification; dark cure
10.  Mechanical performance of novel bioactive glass containing dental restorative composites 
Objectives
Bioactive glass (BAG) is known to possess antimicrobial properties and release ions needed for remineralization of tooth tissue, and therefore may be a strategic additive for dental restorative materials. The objective of this study was to develop BAG containing dental restorative composites with adequate mechanical properties comparable to successful commercially available composites, and to confirm the stability of these materials when exposed to a biologically challenging environment.
Methods
Composites with 72 wt.% total filler content were prepared while substituting 0–15% of the filler with ground BAG. Flexural strength, fracture toughness, and fatigue crack growth tests were performed after several different soaking treatments: 24 hours in DI water (all experiments), two months in brain-heart infusion (BHI) media+S. mutans bacteria (all experiments) and two months in BHI media (only for flexural strength). Mechanical properties of new BAG composites were compared along with the commercial composite Heliomolar by two-way ANOVA and Tukey’s multiple comparison test (p≤0.05).
Results
Flexural strength, fracture toughness, and fatigue crack growth resistance for the BAG containing composites were unaffected by increasing BAG content up to 15% and were superior to Heliomolar after all post cure treatments. The flexural strength of the BAG composites was unaffected by two months exposure to aqueous media and a bacterial challenge, while some decreases in fracture toughness and fatigue resistance were observed. The favorable mechanical properties compared to Heliomolar were attributed to higher filler content and a microstructure morphology that better promoted the toughening mechanisms of crack deflection and bridging.
Significance
Overall, the BAG containing composites developed in this study demonstrated adequate and stable mechanical properties relative to successful commercial composites.
doi:10.1016/j.dental.2013.08.207
PMCID: PMC3868470  PMID: 24050766
Resin Composite; Bioactive Glass; Strength; Fracture Toughness; Fatigue; Bacteria; Hydration
11.  Shrinkage stress development in dental composites—An analytical treatment 
Objectives
The aim of this paper is to develop a comprehensive mathematical model for shrinkage stress development in dental composites that can account for the combined effect of material properties, specimen geometry and external constraints.
Methods
A viscoelastic model that includes the composite’s elastic, creep and shrinkage strains, and their interaction with the sample’s dimensions and the external constraint is developed. The model contains two dimensionless parameters. The first one represents the compliance of the external constraint relative to that of the composite sample, and the second controls the rate of shrinkage stress decay through creep. The resulting differential equation is solved for two special cases: zero compliance and zero creep. Predictions for shrinkage stress measurements are then made using the analytical solutions for instruments with different compliances, samples with different thicknesses and composites with different filler fractions.
Results
The model correctly predicts how shrinkage stress increases with time, its dependence on the interaction between the entire system’s compliance and the material properties, and the effect of the filler fraction on its maximum value. Comparisons with reported shrinkage stress measurements have provided very good agreement between theory and experiments.
Significance
The results provided by the model can help to resolve most, if not all, of the seemingly conflicting experimental observations reported in the literature. They can also provide some useful guidelines for optimizing the mechanical performance of dental composite restorations. The compliance ratio, a new parameter derived from the model, represents a fuller description of the constraints of the system.
doi:10.1016/j.dental.2013.08.198
PMCID: PMC3887224  PMID: 24029101
Dental composites; Shrinkage stress; Compliance; Filler fraction; Mathematical model
12.  Inhibition of endogenous human dentin MMPs by Gluma 
Objective
The objective of this study was to determine if Gluma dentin desensitizer (5.0% glutaraldehyde and 35% HEMA in water) can inhibit the endogenous MMPs of dentin matrices in 60 sec. and to evaluate its effect on dentin matrix stiffness and dry mass weight.
Methods
Dentin beams of 2×1×6 mm were obtained from extracted human third molars coronal dentin. To measure the influence of Gluma treatment time on total MMP activity of dentin, beams were dipped in 37% phosphoric acid (PA) for 15 sec. and rinsed in water. The acid-etched beams were then dipped in Gluma for 5, 15, 30 or 60 sec., rinsed in water and incubated into SensoLyte generic MMP substrate (AnaSpec, Inc.) for 60 min. Controls were dipped in water for 60 sec. Additional beams of 1×1×6 mm were completely demineralized in 37% PA for 18 h, rinsed and used to evaluate changes on the dry weight and modulus of elasticity (E) after 60 sec. of Gluma treatment followed by incubation in simulated body fluid buffer for zero, one or four weeks. E was measured by 3-pt flexure.
Results
Gluma treatment inhibited total MMP activity of acid-etched dentin by 44, 50, 84, 86 % after 5, 15, 30 or 60 sec. of exposure, respectively. All completely demineralized dentin beams lost stiffness after one and four weeks, with no significant differences between the control and Gluma-treated dentin. Gluma treatment for 60 sec. yielded significantly less dry mass loss than the control after four weeks.
Significance
The use of Gluma may contribute to the preservation of adhesive interfaces by its cross-linking and inhibitory properties of endogenous dentin MMPs.
doi:10.1016/j.dental.2014.04.006
PMCID: PMC4159091  PMID: 24846803
Degradation; dentin collagen; glutaraldehyde; matrix metalloproteinase; mechanical properties; proteolytic activity
13.  Can 1% chlorhexidine diacetate and ethanol stabilize resin-dentin bonds? 
Objectives
To examine the effects of the combined use of chlorhexidine and ethanol on the durability of resin-dentin bonds.
Methods
Forty-eight flat dentin surfaces were etched (32% phosphoric acid), rinsed (15 s) and kept wet until bonding procedures. Dentin surfaces were blot-dried with absorbent paper and re-wetted with water (Water, control), 1% chlorhexidine diacetate in water (CHD/Water), 100% ethanol (Ethanol), or 1% chlorhexidine diacetate in ethanol (CHD/Ethanol) solutions for 30 s. They were then bonded with All Bond 3 (AB3, Bisco) or Excite (EX, Ivoclar-Vivadent) using a smooth, continuous rubbing application (10 s), followed by 15 s gentle air stream to evaporate solvents. The adhesives were light-cured (20 s) and resin composite build-ups constructed for the microtensile method. Bonded beams were obtained and tested after 24-hours, 6-months and 15-months of water storage at 37°C. Storage water was changed every month. Effects of treatment and testing periods were analyzed (ANOVA, Holm-Sidak, p<0.05) for each adhesive.
Results
There were no interactions between factors for both etch-and-rinse adhesives. AB3 was significantly affected only by storage (p = 0.003). Excite was significantly affected only by treatments (p = 0.048). AB3 treated either with ethanol or CHD/ethanol resulted in reduced bond strengths after 15 months. The use of CHD/ethanol resulted in higher bond strengths values for Excite.
Conclusions
Combined use of ethanol/1% chlorhexidine diacetate did not stabilize bond strengths after 15 months.
doi:10.1016/j.dental.2014.04.003
PMCID: PMC4151321  PMID: 24815823
ethanol-wet bonding; chlorhexidine; dentin; bonding; stability
14.  Step-stress analysis for predicting dental ceramic reliability 
Objective
To test the hypothesis that step-stress analysis is effective to predict the reliability of an alumina-based dental ceramic (VITA In-Ceram AL blocks) subjected to a mechanical aging test.
Methods
Bar-shaped ceramic specimens were fabricated, polished to 1µm finish and divided into 3 groups (n=10): (1) step-stress accelerating test; (2) flexural strength- control; (3) flexural strength- mechanical aging. Specimens from group 1 were tested in an electromagnetic actuator (MTS Evolution) using a three-point flexure fixture (frequency: 2Hz; R=0.1) in 37°C water bath. Each specimen was subjected to an individual stress profile, and the number of cycles to failure was recorded. A cumulative damage model with an inverse power law lifetime-stress relation and Weibull lifetime distribution were used to fit the fatigue data. The data were used to predict the stress level and number of cycles for mechanical aging (group 3). Groups 2 and 3 were tested for three-point flexural strength (σ) in a universal testing machine with 1.0 s in 37°C water. Data were statistically analyzed using Mann-Whitney Rank Sum test.
Results
Step-stress data analysis showed that the profile most likely to weaken the specimens without causing fracture during aging (95% CI: 0–14% failures) was: 80 MPa stress amplitude and 105 cycles. The median σ values (MPa) for groups 2 (493±54) and 3 (423±103) were statistically different (p=0.009).
Significance
The aging profile determined by step-stress analysis was effective to reduce alumina ceramic strength as predicted by the reliability estimate, confirming the study hypothesis.
doi:10.1016/j.dental.2013.05.009
PMCID: PMC3756882  PMID: 23827018
ceramics; aging; fatigue
15.  Synthesis of new antibacterial quaternary ammonium monomer for incorporation into CaP nanocomposite 
Objectives
Composites are the principal material for tooth cavity restorations due to their esthetics and direct-filling capabilities. However, composites accumulate biofilms in vivo, and secondary caries due to biofilm acids is the main cause of restoration failure. The objectives of this study were to: (1) synthesize new antibacterial monomers; and (2) develop nanocomposite containing nanoparticles of amorphous calcium phosphate (NACP) and antibacterial monomer.
Methods
Two new antibacterial monomers were synthesized: dimethylaminohexane methacrylate (DMAHM) with a carbon chain length of 6, and dimethylaminododecyl methacrylate (DMADDM) with a chain length of 12. A spray-drying technique was used to make NACP. DMADDM was incorporated into NACP nanocomposite at mass fractions of 0%, 0.75%, 1.5%, 2.25% and 3%. A flexural test was used to measure composite strength and elastic modulus. A dental plaque microcosm biofilm model with human saliva as inoculum was used to measure viability, metabolic activity, and lactic acid production of biofilms on composites.
Results
The new DMAHM was more potent than a previous quaternary ammonium dimethacrylate (QADM). DMADDM was much more strongly antibacterial than DMAHM. The new DMADDM-NACP nanocomposite had strength similar to that of composite control (p > 0.1). At 3% DMADDM in the composite, the metabolic activity of adherent biofilms was reduced to 5% of that on composite control. Lactic acid production by biofilms on composite containing 3% DMADDM was reduced to only 1% of that on composite control. Biofilm colony-forming unit (CFU) counts on composite with 3% DMADDM were reduced by 2-3 orders of magnitude.
Significance
New antibacterial monomers were synthesized, and the carbon chain length had a strong effect on antibacterial efficacy. The new DMADDM-NACP nanocomposite possessed potent anti-biofilm activity without compromising load-bearing properties, and is promising for antibacterial and remineralizing dental restorations to inhibit secondary caries.
doi:10.1016/j.dental.2013.05.005
PMCID: PMC3845440  PMID: 23768794
Antibacterial nanocomposite; calcium phosphate nanoparticles; quaternary ammonium; human saliva microcosm biofilm; mechanical properties; caries inhibition
16.  Surface modification of several dental substrates by non-thermal, atmospheric plasma brush 
Objective
The purpose of this study was to reveal the effectiveness of non-thermal atmospheric plasma brush in surface wettability and modification of four dental substrates.
Methods
Specimens of dental substrates including dentin, enamel, and two composites Filtek Z250, Filtek LS Silorane were prepared (~2 mm thick, ~10 mm diameter). The prepared surfaces were treated for 5–45 s with a non-thermal atmospheric plasma brush working at temperatures from 36 to 38 °C. The plasma-treatment effects on these surfaces were studied with contact-angle measurement, X-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM).
Results
The non-thermal atmospheric argon plasma brush was very efficient in improving the surface hydrophilicity of four substrates studied. The results indicated that water contact angle values decreased considerably after only 5 s plasma treatment of all these substrates. After 30 s treatment, the values were further reduced to <5°, which was close to a value for super hydrophilic surfaces. XPS analysis indicated that the percent of elements associated with mineral in dentin/enamel or fillers in the composites increased. In addition, the percent of carbon (%C) decreased while %O increased for all four substrates. As a result, the O/C ratio increased dramatically, suggesting that new oxygen-containing polar moieties were formed on the surfaces after plasma treatment. SEM surface images indicated that no significant morphology change was induced on these dental substrates after exposure to plasmas.
Significance
Without affecting the bulk properties, a super-hydrophilic surface could be easily achieved by the plasma brush treatment regardless of original hydrophilicity/hydrophobicity of dental substrates tested.
doi:10.1016/j.dental.2013.05.002
PMCID: PMC3730850  PMID: 23755823
non-thermal plasmas; contact angle; wettability; dental surfaces; composites
17.  Fracture toughness improvements of dental ceramic through use of yttria-stabilized zirconia (YSZ) thin-film coatings 
Objectives
The aim of this study was to evaluate strengthening mechanisms of yttria-stabilized zirconia (YSZ) thin film coatings as a viable method for improving fracture toughness of all-ceramic dental restorations.
Methods
Bars (2×2×15mm, n=12) were cut from porcelain (ProCAD, Ivoclar-Vivadent) blocks and wet-polished through 1200-grit using SiC abrasive. A Vickers indenter was used to induce flaws with controlled size and geometry. Depositions were performed via radio frequency magnetron sputtering (5mT, 25ºC, 30:1 Ar/O2 gas ratio) with varying powers of substrate bias. Film and flaw properties were characterized by optical microscopy, scanning electron microscopy (SEM), and x-ray diffraction (XRD). Flexural strength was determined by three-point bending. Fracture toughness values were calculated from flaw size and fracture strength.
Results
Data show improvements in fracture strength of up to 57% over unmodified specimens. XRD analysis shows that films deposited with higher substrate bias displayed a high %monoclinic volume fraction (19%) compared to non-biased deposited films (87%), and resulted in increased film stresses and modified YSZ microstructures. SEM analysis shows critical flaw sizes of 67±1μm leading to fracture toughness improvements of 55% over unmodified specimens.
Significance
Data supports surface modification of dental ceramics with YSZ thin film coatings to improve fracture toughness. Increase in construct strength was attributed to increase in compressive film stresses and modified YSZ thin film microstructures. It is believed that this surface modification may lead to significant improvements and overall reliability of all-ceramic dental restorations.
doi:10.1016/j.dental.2013.05.003
PMCID: PMC3723696  PMID: 23764025
dental material; fracture toughness; thin film; zirconia; allceramic; failure; stress
18.  Load-bearing properties of minimal-invasive monolithic lithium disilicate and zirconia occlusal onlays: finite element and theoretical analyses 
Objectives
The aim of this study was to test the hypothesis that monolithic lithium disilicate glass-ceramic occlusal onlay can exhibit a load-bearing capacity that approaches monolithic zirconia, due to a smaller elastic modulus mismatch between the lithium disilicate and its supporting tooth structure relative to zirconia.
Methods
Ceramic occlusal onlays of various thicknesses cemented to either enamel or dentin were considered. Occlusal load was applied through an enamel-like deformable indenter or a control rigid indenter. Flexural tensile stress at the ceramic intaglio (cementation) surface—a cause for bulk fracture of occlusal onlays—was rigorously analyzed using finite element analysis and classical plate-on-foundation theory.
Results
When bonded to enamel (supported by dentin), the load-bearing capacity of lithium disilicate can approach 75% of that of zirconia, despite the flexural strength of lithium disilicate (400 MPa) being merely 40% of zirconia (1000 MPa). When bonded to dentin (with the enamel completely removed), the load-bearing capacity of lithium disilicate is about 57% of zirconia, still significantly higher than the anticipated value based on its strength. Both ceramics show slightly higher load-bearing capacity when loaded with a deformable indenter (enamel, glass-ceramic, or porcelain) rather than a rigid indenter.
Significance
When supported by enamel, the load-bearing property of minimally invasive lithium disilicate occlusal onlays (0.6 to 1.4 mm thick) can exceed 70% of that of zircona. Additionally, a relatively weak dependence of fracture load on restoration thickness indicates that a 1.2 mm thin lithium disilicate onlay can be as fracture resistant as its 1.6 mm counterpart.
doi:10.1016/j.dental.2013.04.004
PMCID: PMC3698988  PMID: 23683531
Load-bearing capacity; monolithic ceramic restorations; lithium disilicate; zirconia; flexural fracture
19.  Effect of salivary pellicle on antibacterial activity of novel antibacterial dental adhesives using a dental plaque microcosm biofilm model 
Objectives
Antibacterial primer and adhesive are promising to inhibit biofilms and caries. Since restorations in vivo are exposed to saliva, one concern is the attenuation of antibacterial activity due to salivary pellicles. The objective of this study was to investigate the effects of salivary pellicles on bonding agents containing a new monomer dimethylaminododecyl methacrylate (DMADDM) or nanoparticles of silver (NAg) against biofilms for the first time.
Methods
DMADDM and NAg were synthesized and incorporated into Scotchbond Multi-Purpose adhesive and primer. Specimens were either coated or not coated with salivary pellicles. A microcosm biofilm model was used with mixed saliva from ten donors. Two types of culture medium were used: an artificial saliva medium (McBain), and Brain Heart Infusion (BHI) medium without salivary proteins. Metabolic activity, colony-forming units (CFU), and lactic acid production of plaque microcosm biofilms were measured (n = 6).
Results
Bonding agents containing DMADDM and NAg greatly inhibited biofilm activities, even with salivary pellicles. When using BHI, the pre-coating of salivary pellicles on resin surfaces significantly decreased the antibacterial effect (p < 0.05). When using artificial saliva medium, pre-coating of salivary pellicles on resin did not decrease the antibacterial effect. These results suggest that artificial saliva yielded medium-derived pellicles on resin surfaces, which provided attenuating effects on biofilms similar to salivary pellicles. Compared with the commercial control, the DMADDM-containing bonding agent reduced biofilm CFU by about two orders of magnitude.
Significance
Novel DMADDM- and NAg-containing bonding agents substantially reduced biofilm growth even with salivary pellicle coating on surfaces, indicating a promising usage in saliva-rich environment. DMADDM and NAg may be useful in a wide range of primers, adhesives and other restoratives to achieve antibacterial and anti-caries capabilities.
doi:10.1016/j.dental.2013.11.004
PMCID: PMC4023513  PMID: 24332270
Antibacterial dental adhesive; Quaternary ammonium; Silver nanoparticles; Dental plaque microcosm biofilm; Salivary pellicle
20.  Fatigue of the Resin-Dentin Interface: A New Approach for Evaluating the Durability of Dentin Bonds 
There are concerns regarding the longevity of resin composite restorations and the clinical relevance of in vitro bond strength testing to the durability of dentin bonds in vivo.
Objective
The objectives of this investigation were to: 1) develop a new method of experimental evaluation for quantifying the durability of dentin bonds, 2) apply this method to characterize the interfacial strength of a selected commercial system under both monotonic and cyclic loading, and 3) distinguish mechanisms contributing to the interface degradation and failure.
Methods
A new method for fatigue testing the resin-dentin interface was developed based on a four-point flexure arrangement that includes two identical bonded interfaces. Cyclic loading of specimens comprised of coronal dentin bonded to a commercial resin composite and controls of resin composite was performed to failure within a hydrated environment. Scanning electron microscopy and nanoscopic dynamic mechanical analysis were used to evaluate failure mechanisms.
Results
The fatigue strength of the resin-dentin interface was significantly lower (p≤0.0001) than that of the resin composite and reported for dentin over the entire finite life regime. Defined at 1×107 cycles, the apparent endurance limit of the resin-dentin interface was 13 MPa, in comparison to 48 MPa and 44 MPa for the resin composite and dentin, respectively. The ratio of fully reversed endurance limit to ultimate strength of the interface (0.26) was the lowest of the three materials.
Significance
The proposed approach for characterizing the fatigue strength of resin-dentin bonds may offer new insights concerning durability of the bonded interface.
doi:10.1016/j.dental.2013.01.008
PMCID: PMC3602384  PMID: 23434232
Adhesive Resin; Bonding; Durability; Fatigue; Hybrid Layer; Resin Composite
21.  Enhancement in dentin collagen’s biological stability after proanthocyanidins treatment in clinically relevant time periods 
Objective
To investigate whether proanthocyanidins (PA) is capable of improving dentin collagen’s biological stability through cross-linking within time periods that are clinically relevant.
Materials and methods
Demineralized dentin collagen slabs were treated with 3.75 wt% PA solution for 10 s, 1 min, 30 min, 60 min, 120 min, 360 min, and 720 min, respectively. The resultant cross-linked collagen samples were subject to digestion with 0.1% collagenase at 37 °C for 2 h, 6 h, 12 h, 24 h, 36 h, and 48 h. The percentage of weight loss after digestion was calculated to evaluate PA-treated collagen’s resistance toward enzymatic degradation. Fourier-Transformed Infrared (FTIR) spectroscopy was used to probe evidences of PA-collagen interactions after various periods of PA treatment.
Results
The collagenase digestion assay suggests that PA treatment as short as 10 s can enhance collagen’s resistance toward enzymatic challenge. The FTIR spectroscopy further verifies that PA is indeed incorporated into collagen regardless of treatment time, possibly via a mechanism involving the chemical interactions between PA and collagen.
Significance
This study confirmed that PA can effectively cross-link collagen and improve its biological stability in time periods as short as 10 s. The use of PA as a priming agent is therefore clinically feasible and is a promising approach to improving the durability of current dentin bonding systems.
doi:10.1016/j.dental.2013.01.013
PMCID: PMC3640802  PMID: 23434233
Dentin collagen; Cross-linking; Proanthocyanidins; Biodegradation; FTIR
22.  Novel dental adhesives containing nanoparticles of silver and amorphous calcium phosphate 
Objectives
Secondary caries is the main reason for restoration failure, and replacement of the failed restorations accounts for 50–70% of all restorations. Antibacterial adhesives could inhibit residual bacteria in tooth cavity and invading bacteria along the margins. Calcium (Ca) and phosphate (P) ion release could remineralize the lesions. The objectives of this study were to incorporate nanoparticles of silver (NAg) and nanoparticles of amorphous calcium phosphate (NACP) into adhesive for the first time, and to investigate the effects on dentin bond strength and plaque microcosm biofilms.
Methods
Scotchbond Multi-Purpose adhesive was used as control. NAg were added into primer and adhesive at 0.1% by mass. NACP were mixed into adhesive at 10%, 20%, 30% and 40%. Microcosm biofilms were grown on disks with primer covering the adhesive on a composite. Biofilm metabolic activity, colony-forming units (CFU) and lactic acid were measured.
Results
Human dentin shear bond strengths (n=10) ranged from 26 to 34 MPa; adding NAg and NACP into adhesive did not decrease the bond strength (p > 0.1). SEM examination revealed resin tags from well-filled dentinal tubules. Numerous NACP infiltrated into the dentinal tubules. While NACP had little antibacterial effect, NAg in bonding agents greatly reduced the biofilm viability and metabolic activity, compared to the control (p < 0.05). CFU for total microorganisms, total streptococci, and mutans streptococci on bonding agents with NAg were an order of magnitude less than those of the control. Lactic acid production by biofilms for groups containing NAg was 1/4 of that of the control.
Significance
Dental plaque microcosm biofilm viability and acid production were greatly reduced on bonding agents containing NAg and NACP, without compromising dentin bond strength. The novel method of incorporating dual agents (remineralizing agent NACP and antibacterial agent NAg) may have wide applicability to other dental bonding systems.
doi:10.1016/j.dental.2012.10.005
PMCID: PMC3552134  PMID: 23138046
Antibacterial adhesive; dentin bond strength; silver nanoparticles; calcium phosphate nanoparticles; human saliva microcosm biofilm; caries inhibition
23.  Novel calcium phosphate nanocomposite with caries-inhibition in a human in situ model 
Objectives
Secondary caries at the restoration margins remains the main reason for failure. Although calcium phosphate (CaP) composites are promising for caries inhibition, there has been no report of CaP composite to inhibit caries in situ. The objectives of this study were to investigate the caries-inhibition effect of nanocomposite containing nanoparticles of amorphous calcium phosphate (NACP) in a human in situ model for the first time, and to determine colony-forming units (CFU) and Ca and P ion concentrations of biofilms on the composite restorations.
Methods
NACP with a mean particle size of 116 nm were synthesized via a spray-drying technique. Two composites were fabricated: NACP nanocomposite, and control composite filled with glass particles. Twenty-five volunteers wore palatal devices containing bovine enamel slabs with cavities restored with NACP or control composite. After 14 days, the adherent biofilms were collected for analyses. Transverse microradiography determined the enamel mineral profiles at the margins, and the enamel mineral loss ! Z was measured.
Results
NACP nanocomposite released Ca and P ions and the release significantly increased at cariogenic low pH (p < 0.05). Biofilms on NACP nanocomposite contained higher Ca (p = 0.007) and P ions (p = 0.005) than those of control (n = 25). There was no significant difference in biofilm CFU between the two composites (p > 0.1). Microradiographs showed typical subsurface lesions in enamel next to control composite, but much less lesion around NACP nanocomposite. Enamel mineral loss ! Z (mean ± sd; n = 25) around NACP nanocomposite was 13.8 ± 9.3 μm, much less than 33.5 ± 19.0 μm of the control (p = 0.001).
Significance
Novel NACP nanocomposite substantially reduced caries formation in a human in situ model for the first time. Enamel mineral loss at the margins around NACP nanocomposite was less than half of the mineral loss around control composite. Therefore, the Ca and P ion-releasing NACP nanocomposite is promising for caries-inhibiting restorations.
doi:10.1016/j.dental.2012.10.010
PMCID: PMC3561736  PMID: 23140916
human in situ model; dental nanocomposite; calcium phosphate nanoparticles; dental biofilms; ion release; secondary caries inhibition
24.  Measurement of micro-strain across resin-dentin interfaces using microscopic moiré interferometry 
Little is known about the mechanical behavior of resin-dentine interfaces during loading. The presence of relatively compliant hybrid and adhesive layers between stiffer dentin and resin composite should deform more during compressive loading.
Objective
The objective of this study was to measure changes in microstrain across bonded dentine interfaces in real time using a recently developed microscope moiré interferometer.
Method
This system used a miniature moiré interferometer, using two CCD cameras for simultaneous recording of longitudinal and transverse deformation fields, a piezotransducer for fringe shifting and use of a microscope objective with magnification up to 600×. Small beams (1 × 2 × 6 mm) of moist resin-bonded dentine covered with a diffraction grating replica were placed in a miniature compression tester to allow controlled loading from 2-37 N while imaging the interference fringe patterns.
Results
Dentine beams bonded with Single Bond/Z100 under compressive loading of resin-dentine interfaces exhibited comparatively large strains across the adhesive-hybrid layer interface. When the wrapped phase maps were unwrapped to permit conversion of fringe order to displacements, the 2-D profiles of strain fields revealed nonuniform strains across the adhesive interface. In the adhesive/hybrid layer zone, the negative strain was larger (i.e. -6000 με) than that seen in the adjacent resin composite or underlying mineralized dentin. The changes were elastic because they disappeared when the load was removed.
Significance
Microscopic moiré interferometry can be very useful in revealing real-time strain of bonded interfaces under load.
doi:10.1016/j.dental.2007.10.005
PMCID: PMC3901046  PMID: 18045678
Composite; Compression; Dentin; Dentin bonding agent; Mechanical properties; Moiré interferometry
25.  Optimizing dentin bond durability: strategies to prevent hydrolytic degradation of the hybrid layer 
Objectives
Endogenous dentin collagenolytic enzymes, matrix metalloproteinases (MMPs) and cysteine cathepsins, are responsible for the time-related hydrolysis of collagen matrix of the hybrid layers. As the integrity of the collagen matrix is essential for the preservation of long-term dentin bond strength, inhibition or inactivation of endogenous dentin proteases is necessary for durable resin-bonded composite resin restorations.
Methods
Dentin contains collagenolytic enzymes, matrix metalloproteinases (MMPs) and cysteine cathepsins, which are responsible for the hydrolytic degradation of collagen matrix in the bonded interface. Several tentative approaches to prevent enzyme function either directly or indirectly have been proposed in the literature.
Results
Chlorhexidine, a general inhibitor of both MMPs and cysteine cathepsins, applied before primer/adhesive application is the most tested method. In general, these experiments have shown that enzyme inhibition is a promising scheme to improve hybrid layer preservation and bond strength durability. Other enzyme inhibitors, e.g. enzyme-inhibiting monomers and antimicrobial compounds, may be considered promising alternatives that would allow more simple clinical application than chlorhexidine. Cross-linking collagen and/or dentin organic matrix-bound enzymes could render hybrid layer organic matrix resistant to degradation, and complete removal of water from the hybrid layer with ethanol wet bonding or biomimetic remineralization should eliminate hydrolysis of both collagen and resin components.
Significance
Identification of the enzymes responsible for the hydrolysis of hybrid layer collagen and understanding their function has prompted several innovative approaches to retain the hybrid layer integrity and strong dentin bonding. The ultimate goal, prevention of collagen matrix degradation with techniques and commercially available materials that are simple and effective in clinical settings may be achievable in several ways, and will likely become reality in the near future.
doi:10.1016/j.dental.2013.07.016
PMCID: PMC3899917  PMID: 23953737

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