Dental materials: official publication of the Academy of Dental Materials

Publications in this journal

• Article: Osteoblast and bone tissue response to surface modified zirconia and titanium implant materials.

  Ralf J Kohal, Maria Bächle, Wael Att, Saad Chaar, Brigitte Altmann, Alexander Renz, Frank Butz
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  ABSTRACT: OBJECTIVE: This study examined the in vitro and in vivo response of osteoblasts to a novel, acid-etched and sandblasted zirconia surface. METHODS: Osteoblastic hFOB 1.19 cells were cultured either on electrochemically anodized titanium (TiUnite(®)), machined titanium (Ti-m), sandblasted and acid-etched zirconia (TZP-proc), and machined zirconia (TZP-A-m). The surface topography of the various substrates was analyzed by 3D laserscan measurements and scanning electron microscopy. At culture days 1, 3, 7, 14, 21, and 28, cell proliferation was determined. Gene expression was analyzed using RT-PCR. Histologic analysis and biomechanical testing was performed on miniature implants placed in the rat femur. RESULTS: During the first 7 days, a retarded cell proliferation was observed on the TiUnite(®) surface. After 28 days of cultivation, cell proliferation reached similar levels on all surfaces. An up-regulation of bone and extracellular matrix specific genes could be seen for TZP-proc at day 21. The mean bone-implant contact rate after a healing period of 14 and 28 days, respectively, was higher for TiUnite(®) than for TZP-proc. At 28 day, the biomechanical test showed significantly higher values for TiUnite(®) than for all other surfaces. SIGNIFICANCE: The novel, rough zirconia surface was accepted by hFOB 1.19 cells and integrates into rat bone tissue. However, osseointegration seemed to proceed more slowly and to a lesser extent compared to a moderately roughened titanium surface.
  Dental materials: official publication of the Academy of Dental Materials 05/2013;
• Article: Self-adhesive restoratives as pit and fissure sealants: A comparative laboratory study.

  Anna Eliades, Eleftheria Birpou, Theodore Eliades, George Eliades
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  ABSTRACT: OBJECTIVES: To evaluate the properties of self-adhesive restorative materials used as sealants in comparison with sealants with hydrophobic or hydrophilic monomers. METHODS: The self-adhesive materials tested were Fusio (FS) and Vertise-Flow (VF) and the sealants Embrace Wetbond (EM/hydrophilic) and Helioseal-F (HS/hydrophobic). The properties tested were: (a) degree of cure (%DC, n: 5, ATR-FTIR), (b) extent of oxygen inhibition (n: 5, transmission optical microscopy), (c) flow (n: 5, ASTM D-4242 method), (d) hardness (VH0.2kp/10s dry/1w in water), (e) adaptation, microleakage and fissure penetration (n: 10, 1% fuschin dye, reflection optical microscopy and ESEM). Statistical analysis was performed by one-way ANOVA plus Tukey test (a-d), Fisher's exact and Kruskal-Wallis plus Tukey tests (e) at a 95% confidence level. RESULTS: VF showed the highest %DC(76.1) followed by HS(68.7) and EM(61.3), FS(59.2). HS demonstrated the highest extent of oxygen inhibition (23μm vs. 13-10μm of the rest). EM and HS exhibited the greatest flow, followed by FS and VM. The VHN(0.2kp/10s) ranking before and after 1week water exposure was FS≥VF>EM≥HS. Water storage increased VF and reduced HS values. The lowest adaptation and microleakage scores were found in HS. FS and VF after alumina sandblasting showed the worst adaptation and leakage scores, that were improved after acid-etching. Improved fissure penetration was found in HS, EM and FS, VF after acid-etching. SIGNIFICANCE: Although the self-adhesive materials presented improved setting characteristics, their low flow affected fissure penetration capacity. When combined with enamel acid-etching, adaptation and microleakage scoring were substantially improved in comparison with enamel sandblasting. The sealant with the hydrophobic monomers demonstrated the best sealing characteristics.
  Dental materials: official publication of the Academy of Dental Materials 05/2013;
• Article: Let there be light!

  David C Watts
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: A characterization of the mechanical behavior of resin-infiltrated dentin using nanoscopic Dynamic Mechanical Analysis.

  Heonjune Ryou, David H Pashley, Franklin R Tay, Dwayne Arola
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  ABSTRACT: This study explored the spatial variations in mechanical behavior of resin-infiltrated dentin using nanoscopic Dynamic Mechanical Analysis (DMA). OBJECTIVE: The objectives were to: (1) evaluate the mechanical behavior of resin-infiltrated dentin using a scanning-based approach to nanoindentation, (2) identify contributions of the collagen matrix to time-dependent deformation of the hybrid layer, and (3) assess the importance of specimen hydration on the nanoDMA response. METHODS: Specimens of completely demineralized dentin infiltrated with commercial resin adhesive and control samples of resin adhesive were evaluated using a nanoindenter in scanning mode. The load and displacement responses were used to perform DMA and to estimate the complex (E*), storage (E') and loss (E″) moduli over selected regions of evaluation. The importance of hydration on the mechanical behavior was also examined from a comparison of responses in the hydrated and dehydrated conditions. RESULTS: In the hydrated state the apparent complex, storage and loss moduli for the resin-infiltrated dentin samples were 3.5±0.3GPa, 3.4±0.2GPa and 0.9±0.3GPa, respectively. Those values for the resin adhesive control were 2.7±0.3GPa, 2.7±0.3GPa and 0.2±0.02GPa, respectively. Viscoelastic deformation of the resin-infiltrated collagen exceeded that occurring in regions of uniform resin adhesive. Though dehydration resulted in a significant increase in both the complex and storage moduli of the macro hybrid layer, the largest changes occurred to the resin adhesive. SIGNIFICANCE: The microstructure and hydration play critical roles on the mechanical behavior of the hybrid layer and nanoDMA provides a potent measurement tool for identifying the spatial variations.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Comparison of an absolute and surrogate measure of relative translucency in dental ceramics.

  Lisa S Spink, Patchanee Rungruanganut, Spiro Megremis, J Robert Kelly
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  ABSTRACT: PURPOSE: The objective was to compare absolute translucency with a frequently used surrogate measure of relative translucency (contrast ratio) from 14 all-ceramic materials having a wide range of translucencies. MATERIALS AND METHODS: Standardized disks were fabricated from fourteen ceramics, varying both thickness (0.3mm, 0.5mm, 1.0mm, and 1.5mm) and chroma (high and low). Absolute translucency (percent transmission) was measured using a spectroradiometer with an integrating sphere. Relative translucency was measured using a spectrophotometer as contrast ratio (contrast ratio; ratio of L* values recorded on black and white backgrounds). Non-linear regression was used to compare measurements of absolute versus relative values for each of the spectrophotometers. RESULTS: Contrast ratio was not able to characterize translucency across the range of materials studied and became less sensitive with increasing opacity. A non-linear correlation was found between percent transmission and contrast ratio down to 50% transmission (r(2)=0.97) and contrast ratio was insensitive to transmission differences below 50% transmission. CONCLUSION: Contrast ratio is not a direct measure of translucency and cannot be used below 50% transmission.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Light curing in orthodontics; Should we be concerned?

  Neil McCusker, Siu Man Lee, Stephen Robinson, Naresh Patel, Jonathan R Sandy, Anthony J Ireland
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  ABSTRACT: OBJECTIVES: Light cured materials are increasingly used in orthodontic clinical practice and concurrent with developments in materials have been developments in light curing unit technology. In recent years the irradiances of these units have increased. The aim of this study was to determine the safe exposure times to both direct and reflected light. METHODS: The weighted irradiance and safe exposure times of 11 dental curing lights (1 plasma arc, 2 halogen and 8 LED lights) were determined at 6 distances (2-60cm) from the light guide tip using a spectroradiometer. In addition, using the single most powerful light, the same two parameters were determined for reflected light. This was done at a distance of 10cm from the reflected light, but during simulated bonding of 8 different orthodontic brackets of three material types, namely stainless steel, ceramic and composite. RESULTS: The results indicate that the LED Fusion lamp had the highest weighted irradiance and the shortest safe exposure time. With this light the maximum safe exposure time without additional eye protection for the patient (at 10cm), the operator (at 30cm) and the assistant (at 60cm) ranged from 2.5min, 22.1min and 88.8min respectively. This indicates a relatively low short term risk during normal operation of dental curing lights. For reflected light at a distance of 10cm the risk was even lower, but was affected by the material and shape of the orthodontic bracket under test. SIGNIFICANCE: The short term risks associated with the use of dental curing lights, halogen, LED or plasma, appear to be low, particularly if as is the case adequate safety precautions are employed. The same is true for reflected light from orthodontic brackets during bonding. What is still unclear is the potential long term ocular effects of prolonged exposure to the blue light generated from dental curing lights.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Fracture strength of minimally prepared all-ceramic CEREC crowns after simulating 5 years of service.

  Nikoleta Skouridou, Sarah Pollington, Martin Rosentritt, Effrosyni Tsitrou
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  ABSTRACT: OBJECTIVES: To examine the strength and mode of fracture of traditionally and minimally prepared all-ceramic resin bonded CAD/CAM crowns after fatigue loading. METHODS: Thirty human maxillary molars were used and divided in three groups namely; traditional crown preparation group (I), minimal crown preparation group (II) and occlusal veneer preparation group (III). A leucite reinforced glass ceramic (IPS Empress CAD) was used for fabricating the crowns. The CEREC InEOS system (v3.10) was used for scanning, designing and milling. Five years of clinical service were simulated and the fracture strength of the crowns was measured. One-way ANOVA and Kruskal-Wallis test were used for data analysis (α=0.05). RESULTS: The mean fracture strength and SD in Group I was 1070N (±181) and in Group II 1110N (±222). One-way ANOVA analysis showed no statistically significant difference between the two groups (p>0.05). In Group III all restorations developed cracks during TCML and were not subjected to fracture loading. Three of the traditionally designed crowns (Group I) and 4 of the minimally designed crowns (Group II) developed surface cracks during TCML. SIGNIFICANCE: Minimal all-ceramic resin-bonded crowns can potentially form a viable restorative option as they demonstrated comparable strength to traditional all-ceramic crowns. However, this should be interpreted with caution as a number of crowns showed cracks after 5 years of simulated service. All the occlusal veneers developed cracks during simulation and further investigation is needed for this to be considered a viable option.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Fractographic analyses of all-ceramic crowns: A study of 27 clinically fractured crowns.

  Marit Oilo, Nils Roar Gjerdet
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  ABSTRACT: OBJECTIVES: The use of all-ceramic restorations has been steadily increasing in the decades since the introduction of high-strength core ceramics as an alternative to metal cores. Even with high-strength ceramic cores, the crowns are susceptible to fractures during clinical function, probably the major concern associated with all-ceramic restorations. The aim of this study was to analyze fracture features of clinically fractured crowns in order to determine crack initiation sites and crack propagation paths. METHODS: Fractographic methods were used to analyze 27 all-ceramic full coverage crowns with alumina cores and feldspatic veneering ceramic. The fractured crowns were supplied by dentists in private and public practices with information of type of cement and time in function if available. RESULTS: The fractured crowns comprised 13 incisors, 3 premolars and 11 molars. The results revealed that all fractures initiated in the cervical margin of the crowns and usually from the approximal area close to the most coronally placed curvature of the margin. There was no statistically significant association between the cement used and time in function. SIGNIFICANCE: Fractography of clinically failed all-ceramic crowns can provide information on the fracture modes and design considerations. The findings are in contrast to fracture modes from in vitro tests. The results suggest that more clinically relevant in vitro test methods to study the durability of ceramic crowns should be developed.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Effects of curing mode and moisture on nanoindentation mechanical properties and bonding of a self-adhesive resin cement to pulp chamber floor.

  Horieh Moosavi, Ilnaz Hariri, Alireza Sadr, Suppason Thitthaweerat, Junji Tagami
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  ABSTRACT: OBJECTIVE: This study aimed to investigate the effect of dentin surface moisture and curing mode on microtensile bond strength (MTBS) and nanoindentation characteristics of a self-adhesive resin cement. METHODS: Forty-four extracted human molars were distributed into four groups according to dentin surface moisture (dry or wet) and curing mode of the resin cement (light or chemical). Clearfil SA Cement (Kuraray Noritake Dental, Japan) was used for cementation of composite cores to the pulp chamber dentin. The specimens were sectioned into beams for MTBS test at the pulpal floor. Nanoindentation hardness and creep of the cement layer were measured under 100mN load with 30s hold segment. Data were statistically analyzed using two-way ANOVA and Weibull distribution of MTBS (α=0.05). RESULTS: Moisture, curing mode or their interaction did not significantly affect mean MTBS values that ranged 17.6-22.6MPa (p>0.05); however, the lowest characteristic strength was found in moist chemically cured group. Hardness ranged 437-512MPa, and was not affected by the experimental factors (p>0.05). Nanoindentation creep ranged 9.3-10.9% with the chemically cured groups showing the highest values, indicating lower cross-linking and deformation resistance of their polymer network. SIGNIFICANCE: Additional moisture on dentin surface did not contribute to adhesion of the anhydrous self-adhesive resin cement to dentin. Light-curing, despite attenuation through the composite core, was beneficial and improved nanoindentation creep resistance of the cement. The difference was not, however, reflected in the mean bond strength or hardness values.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Controlled release of metronidazole from composite poly-ε-caprolactone/alginate (PCL/alginate) rings for dental implants.

  Shih-Feng Lan, Timilehin Kehinde, Xiangming Zhang, Sharukh Khajotia, David W Schmidtke, Binil Starly
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  ABSTRACT: OBJECTIVE: Dental implants provide support for dental crowns and bridges by serving as abutments for the replacement of missing teeth. To prevent bacterial accumulation and growth at the site of implantation, solutions such as systemic antibiotics and localized delivery of bactericidal agents are often employed. The objective of this study was to demonstrate a novel method of controlled localized delivery of antibacterial agents to an implant site using a biodegradable custom fabricated ring. METHODS: The study involved incorporating a model antibacterial agent (metronidazole) into custom designed poly-ε-caprolactone/alginate (PCL/alginate) composite rings to produce the intended controlled release profile. The rings can be designed to fit around the body of any root form dental implants of various diameters, shapes and sizes. RESULTS: In vitro release studies indicate that pure (100%) alginate rings exhibited an expected burst release of metronidazole in the first few hours, whereas Alginate/PCL composite rings produced a medium burst release followed by a sustained release for a period greater than 4 weeks. By varying the PCL/alginate weight ratios, we have shown that we can control the amount of antibacterial agents released to provide the minimal inhibitory concentration (MIC) needed for adequate protection. The fabricated composite rings have achieved a 50% antibacterial agent release profile over the first 48h and the remaining amount slowly released over the remainder of the study period. The PCL/alginate agent release characteristic fits the Ritger-Peppas model indicating a diffusion-based mechanism during the 30-day study period. SIGNIFICANCE: The developed system demonstrates a controllable drug release profile and the potential for the ring to inhibit bacterial biofilm growth for the prevention of diseases such as peri-implantitis resulting from bacterial infection at the implant site.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Mechanical viscoelastic behavior of dental adhesives.

  D Papadogiannis, R S Lakes, Y Papadogiannis, K Tolidis
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  ABSTRACT: OBJECTIVES: The purpose of the study was to evaluate the mechanical properties of dental adhesive materials at different testing temperatures after dry and wet storage. METHODS: Specimens (d=1mm, l=18mm) from six materials were tested: Silorane Adhesive System (SL), Heliobond (HE), One-Step Plus (OS), Optibond Solo Plus (OP), cmf Adhesive System (CF) and Protobond (PR). Static and creep testing was performed by applying a constant torque below the proportional limit of the materials, while dynamic testing consisted of dynamic torsional loading. Experiments were performed after 24h of dry and wet storage under temperatures from 21°C to 50°C and various viscoelastic parameters were calculated. RESULTS: Shear modulus ranged from 0.19 to 1.99GPa, while flexural modulus from 0.67 to 5.69GPa. Most of the materials were affected by the presence of water and increase of temperature. OP showed the highest recovery after creep, while SL exhibited the highest permanent deformation. SIGNIFICANCE: Contact with water after polymerization and increase of temperature resulted in a decline of the mechanical properties, especially for the HEMA-containing adhesives.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Endodontic access cavity simulation in ceramic dental crowns.

  Mitchell Cuddihy, Catherine M Gorman, Francis M Burke, Noel J Ray, Denis Kelliher
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  ABSTRACT: OBJECTIVES: It is proposed that a non-uniform rational B-spline (NURBS) based solid geometric model of a ceramic crown would be a flexible and quick approach to virtually simulate root canal access cavities. The computation of strain components orthogonal to surface flaws generated during the drilling would be an appropriate way of comparing different access cavity configurations. METHODS: A μCT scan is used to develop a full 3D NURBS geometric solid model of a ceramic crown. Three different access cavity configurations are created virtually in the geometric model and there are then imported into proprietary finite element software. A linear analysis of the each crown is carried out under appropriate in vivo loading and the results are post-processed to carry out a quantitative comparison of the three configurations RESULTS: The geometric model is shown to be a flexible and quick way of simulation access cavities. Preliminary indications are that post processed strain results from the finite element analysis are good comparators of competing access cavity configurations. SIGNIFICANCE: The generation of geometric solid models of dental crowns from μCT scans is a flexible and efficient methodology to simulate a number of access cavity configurations. Furthermore, advanced post-processing of the primary finite element analysis results is worthwhile as preliminary results indicate that improved quantitative comparisons between different access cavity configurations are possible.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Riboflavin-ultraviolet-A-induced collagen cross-linking treatments in improving dentin bonding.

  Yung-Show Chiang, Yuh-Ling Chen, Shu-Fen Chuang, Ching-Ming Wu, Pal-Jen Wei, Chang-Fu Han, Jui-Che Lin, Hsiao-Tzu Chang
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  ABSTRACT: OBJECTIVES: To evaluate the collagen cross-linkers, riboflavin-ultraviolet-A (RF/UVA) and glutaraldehyde, with regard to their efficacy in cross-linking the dentinal collagen and improving dentin bonding. METHODS: Glutaraldehyde and different RF/UVA protocols (0.1%RF/1-minUV, 0.1%RF/2-minUV, and 1%RF/1-minUV) were first evaluated by gel electrophoresis to determine their abilities of collagen cross-linking. The mechanical properties of acid-etched dentin receiving these cross-linking treatments were examined in either dry or wet condition by a nanoindentation test. Fifteen teeth with exposed occlusal dentin received the microtensile bond strength (μTBS) test. The teeth were primed either with RF/UVA or glutaraldehyde, followed by adhesive treatment and composite restorations, and then cut into resin-dentin microbeams. Half of the microbeams received the μTBS test after 24h, and the other half received test after 5000 thermocycles. Nanoleakage at the bond interface was examined under TEM. The alignments of collagen fibrils in the hybrid layers were also defined by an image analysis. RESULTS: Gel electrophoresis showed that glutaraldehyde induced strong collagen gelation, while RF/UVA generated milder collagen cross-linking. Glutaraldehyde, 0.1%RF/2-min-UVA, and 1%RF/1-minUV showed higher stiffness compared to untreated and 0.1%RF/1-minUV in wet condition. All the crosslinking treatments improved early μTBS, but 0.1%RF/2-minUVA treatment maintained high μTBS after theromocycles. Under TEM, glutaraldehyde-treated dentin showed dense and enclosed collagen network on the adhesive interface. 0.1%RF/2-minUVA showed the least nanoleakage, and this could be associated with the suspended collagen fibrils in the hybrid layer. SIGNIFICANCE: 0.1%RF/2-minUVA treatment enhanced resin-dentin bond possibly through enhancing the stiffness and maintaining the expanding collagen matrix in the hybrid layer.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Electrically induced transport of macromolecules through oral buccal mucosa.

  Mangala P Patel, Svetla T Churchman, Alan T Cruchley, Michael Braden, David M Williams
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  ABSTRACT: OBJECTIVE: To investigate the feasibility of iontophoretic delivery of large molecules across buccal mucosa, and to establish its potential for enhanced drug delivery. METHODS: Qualitative (6h) and quantitative (8 and 36h) assessment of porcine buccal mucosa, using a diffusion cell in vitro model, was carried out by fluorescent microscopy and UV/Vis spectroscopy respectively, with four fluorescently-labeled model species (3 and 10kDa dextrans, 12kDa parvalbumin and 66kDa bovine serum albumin, BSA). Passive and iontophoresis parameters were obtained. The experimental iontophoresis data were compared with theoretical predictions. RESULTS: The two dextrans and parvalbumin showed enhanced permeation through buccal mucosa after anodal iontophoresis (1-6h). Passive diffusion and cathodal iontophoresis resulted in minimal permeation. BSA could not be measured by either mode. Iontophoretic delivery profiles compared to passive delivery, had reduced time lags (30-50 versus ~270min) and increased flux (~37 times faster). Time lag factor/enhancement ratio (TLF/ER) data confirmed that iontophoresis significantly enhanced permeation. The diffusion coefficients (D, passive) for dextrans were significantly higher than for parvalbumin, with the converse obtained for solubility (C0); permeability coefficients (P) were similar for all three species. Potential differences (V) for the two higher kDa species were significantly higher than for the lowest kDa species. Experimental and theoretical data were in reasonable agreement. SIGNIFICANCE: The experimental and theoretical data, confirming enhanced delivery of the model species via iontophoresis, gave a suitable basis for its potential application in the mouth, in a clinical setting and opens pathways to further research for delivering precious drugs topically and systemically.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Fracture toughness versus micro-tensile bond strength testing of adhesive-dentin interfaces.

  Jan De Munck, Anne-Katrin Luehrs, André Poitevin, Annelies Van Ende, Bart Van Meerbeek
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  ABSTRACT: OBJECTIVE: To assess interfacial fracture toughness of different adhesive approaches and compare to a standard micro-tensile bond-strength (μTBS) test. METHODS: Chevron-notched beam fracture toughness (CNB) was measured following a modified ISO 24370 standard. Composite bars with dimensions of 3.0×4.0×25mm were prepared, with the adhesive-dentin interface in the middle. At the adhesive-dentin interface, a chevron notch was prepared using a 0.15mm thin diamond blade mounted in a water-cooled diamond saw. Each specimen was loaded until failure in a 4-point bend test setup and the fracture toughness was calculated according to the ISO specifications. Similarly, adhesive-dentin micro-specimens (1.0×1.0×8-10mm) were stressed in tensile until failure to determine the μTBS. RESULTS: A positive correlation (r(2)=0.64) was observed between CNB and μTBS, which however was only nearly statistically significant, mainly due to the dissimilar outcome of Scotchbond Universal (3M ESPE). While few μTBS specimens failed at the adhesive-dentin interface, almost all CNB specimens failed interfacially at the notch tip. Weibull moduli for interfacial fracture toughness were much higher than for μTBS (3.8-11.5 versus 2.7-4.8, respectively), especially relevant with regard to early failures. SIGNIFICANCE: Although the ranking of the adhesives on their bonding effectiveness tested using CNB and μTBS corresponded well, the outcome of CNB appeared more reliable and less variable. Fracture toughness measurement is however more laborious and requires specific equipment. The μTBS nevertheless appeared to remain a valid method to assess bonding effectiveness in a versatile way.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Cyanoacrylate-POSS nanocomposites: Novel adhesives with improved properties for dental applications.

  Parastoo Fadaie, Mohammad Atai, Mohammad Imani, Akbar Karkhaneh, Samaneh Ghasaban
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  ABSTRACT: OBJECTIVES: This study evaluates the effect of incorporation of an acrylate polyhedral oligomeric silsesquioxane nanostructure (APOSS) on the physical and mechanical properties and hydrolytic stability of octyl cyanoacrylate (CA) adhesives. MATERIALS AND METHODS: CA was photopolymerized under irradiation of visible light using 1-phenyle-1,2-propandione (PPD), and 2,3-botanedione (BD) as photoinitiators. Following the polymerization shrinkage kinetics of the adhesives, the initiator concentration was optimized. Mechanical properties of the bulk CA-APOSS nanocomposites, including flexural strength and modulus, were investigated. Miroshear bond strength of dental composite bonded to human dentin applying the CA-APOSS adhesives was also determined. The effect of APOSS on the stability of CA adhesive against hydrolysis studied performing solubility, water uptake, and aging tests. RESULTS: The results revealed higher efficiency of BD in comparison to PPD. A 3% (mol/mol) of BD was obtained as the optimum photoinitiator concentration. The incorporation of APOSS increased the polymerization shrinkage rate of the CA adhesives. The flexural strength of CA adhesive was significantly improved incorporating less than 20wt.% APOSS while an increasing trend was observed in the flexural modulus with the nanostructures loading. The microshear bond strength to dentin was also enhanced using 10wt.% APOSS as reinforcing/crosslinking nanofillers. A decrease in the solubility and water sorption was the result of incorporation of APOSS in CA adhesives. Degradation due to the hydrolysis in water was diminished in the specimens containing APOSS nanostructures, revealed after aging in water at 37°C. SIGNIFICANCE: CA adhesives are good soft tissue adhesives which their low mechanical properties and lack of hydrolytic stability has made them less interesting in the applications deal with hard tissues. The study shows that the incorporation of POSS nanostructures into CA could reduce the drawbacks.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Quantification of elutable substances from methacrylate based sealers and their cytotoxicity effect on with human gingival fibroblasts.

  S Furche, R Hickel, F X Reichl, K van Landuyt, M Shehata, J Durner
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  ABSTRACT: OBJECTIVES: Previous studies have shown that resin composites may cause persistent inflammation of oral or pulpal tissues as well as cell death through eluted substances. The aim of this study was to investigate the leaching of ingredients from commercial dental fissure sealers as well as their cytotoxic effects on human gingival fibroblast (HGF). METHODS: The sealers tested were: Helioseal(®) F, Helioseal(®) Refill, Fissurit(®) F, Grandio(®) Seal, Ultraseal XT(®) plus and Delton(®) FS. Ten discs of each sealer were respectively immersed in methanol or water and incubated at 37°C. The eluates were analysed by gas chromatography/mass spectrometry at day 1, 3 and 7. In the XTT-test, eight discs of each fissure sealer were immersed into medium. The eluates of the respective sealer were mixed and used undiluted and diluted with medium. HGF were incubated with the dilutions at 37°C for 24h. Then XTT-salt was added and the XTT-formazan formation was quantified. RESULTS: In eluates from polymerized sealers, comonomers (triethylene glycol dimethacrylate (TEGDMA)) and additives were found (e.g. camphorquinone (CQ), butylated hydroxytoluene, triphenylstibane). 7 d after the beginning of the experiments the highest amount of TEGDMA was found in the aqueous eluate from Grandio(®) Seal (9944.31 (2250.56)μmol/l). The most cytotoxic eluate found in the XTT-test was from Fissurit(®) F (EC50 value at 27.13 (7.04)%; (mean(SD)). SIGNIFICANCE: Because of the use of sealers in preventative dental medicine it should be taken into account that substances like TEGDMA or CQ, that are often causing allergic reactions, are elutable. Before using the sealers patients should be asked for allergic reactions to these substances.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;
• Article: Full-contour Y-TZP ceramic surface roughness effect on synthetic hydroxyapatite wear.

  Alaa H A Sabrah, N Blaine Cook, Palika Luangruangrong, Anderson T Hara, Marco C Bottino
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  ABSTRACT: OBJECTIVE: To investigate the effects of polishing techniques on the surface roughness of Y-TZP ceramic and on the wear behavior of synthetic hydroxyapatite (HA). METHODS: Thirty-two full-contour Y-TZP (Diazir(®)) sliders (φ=2mm×1.5mm in height) were manufactured using CAD/CAM, embedded in acrylic resin using brass holders, and randomly allocated into four groups (n=8): according to the finishing/polishing procedure: G1-as-machined, G2-glazed, G3-diamond bur finishing and G4-G3+OptraFine(®) polishing kit. Thirty-two sintered HA disks (φ=13mm×2.9mm in height) were similarly mounted in brass holders. Y-TZP sliders baseline surface roughness values (Ra and Rq, in μm) were recorded using a non-contact profilometer (Proscan 2000). A two-body pin-on-disc wear test was performed. HA height (μm) and volume (mm(3)) losses were measured. Y-TZP height loss was measured using a digital micrometer. One-way ANOVA was used to determine the effect of the polishing techniques on the surface roughness. Comparisons between groups for differences in antagonist height loss/volume, and slider height loss were performed using one-way ANOVA. Statistical significance was set at α=0.05. RESULTS: Roughness measurements showed significant differences (p=0.0001) among the surface treatments with G1 (Ra=0.84, Rq=1.13μm) and G3 (Ra=0.89, Rq=1.2μm) being the roughest, and G2 (Ra=0.42, Rq=0.63μm) the smoothest (p=0.0001). Y-TZP slider height loss was highest for the glazed group (35.39μm), and was lowest for the polished group (6.61μm) (p=0.0001). Antagonist volume and height losses for groups (G1-G3) were similar, while the polished group (1.3mm(3), 14.7μm) showed significant lower values (p=0.0001). SIGNIFICANCE: Although glazed zirconia provides an initially smooth surface, significantly increased antagonist wear was observed compared to the polished Y-TZP zirconia surface.
  Dental materials: official publication of the Academy of Dental Materials 04/2013;