Dental materials: official publication of the Academy of Dental Materials

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To evaluate the effect of different surface treatments on the bond strength between polyetheretherketone (PEEK) composite materials and each of two different luting cements. One hundred specimens were randomly divided into five groups (n=20/group) as follows: (A) no treatment, (B) 98% sulfuric acid, (C) 9.5% hydrofluoric acid, (D) argon plasma treatment, and (E) sandblast with 50μm Al2O3 particles. Each group was divided into two subgroups of different cements: RelyX™ Unicem and SE Bond/Clearfil AP-X™. The cements were bonded onto the specimens. All specimens were stored in distilled water at 37° for 24h. Bond strength was measured in a shear test, and failure modes were assessed by stereomicroscopy. The surfaces were observed by SEM after the different pretreatments. Etching with 98% sulfuric acid and argon plasma treatment can significantly enforce the bond strength of RelyX™ Unicem or SE Bond/Clearfil AP-X™ to PEEK composite materials in comparison to the group of no treatment, hydrofluoric acid or sandblasting (p<0.05). No adhesion was established on the groups of no treatment and hydrofluoric acid when RelyX™ Unicem was used. Applying the SE Bond/Clearfil AP-X™ system, no statistical differences were found whether hydrofluoric acid was applied or not (p>0.05). The shear bond strength value of using SE Bond/Clearfil AP-X™ was higher than that of using RelyX™ Unicem with the same surface conditioning method (p<0.05). The use of SE Bond/Clearfil AP-X™ after the surface of PEEK composite material treated with sulfuric acid or argon plasma can be recommended as an effective bonding method.
 
The major concern associated with the use of polysiloxanes as polymer matrices in dental restorative materials, is the generally modest mechanical properties of the polymers. However, it has long been demonstrated that thermal stability, and mechanical properties of polysiloxanes can be substantially modified by incorporation of bulkier substituents such as phenyl groups or more polar groups in the chains. The purpose of this research was to evaluate visible light activated dental composites based on the high molecular weight siloxane monomer 1,3-bis[(p-acryloxymethyl) phenethyl] tetramethyldisiloxane (BAPD). Hardness, diametral tensile strength (DTS), degree of conversion (DC), water sorption (WS) and polymerization shrinkage of BAPD-based composites and bis-GMA-based composites were determined and compared. Composites based on BAPD exhibited low WS, high DC, low polymerization shrinkage, and had hardness and DTS values that were not significantly lower than those of dental composites based on bis-GMA. BAPD is a high molecular weight monomer (MW = 511) with a low viscosity. It did not require the use of low molecular weight diluent monomers in formulating composite resins. The DC of BAPD was high, ranging from 86 to 94%. Although the DC of BAPD was significantly higher than the conventional difunctional dental monomers, the polymerization shrinkage of the siloxane composites (1.70 - 1.81 vol%) was comparable to several composites based on bis-GMA.
 
The purpose of this study was to evaluate the fit of metal ceramic crowns cast in Au-1.6 wt% Ti alloy and investigate the effect of abutment finish line curvature on the fit of crowns. Three types of finish line curvature abutments were prepared (1, 3 and 5mm-curvature). For each type of abutment, five metal ceramic crowns of the facial veneered type were fabricated, which were cast in Au-1.6 wt% Ti alloy. Used as controls, another fifteen specimens were made from a commercially available gold alloy. The fit was measured in the as-cast and after porcelain application. In the as-cast specimens, the greater the finish line curvature was, the larger the gaps exhibited at the mesial and distal margins of copings, compared with labial and lingual margins. The distal margin of copings for 5mm-curvature abutments showed the largest gap (35 (7) microm). After porcelain application, the greater was the finish line curvature, the larger the labial marginal gap became (mean 44, 34, 25 microm, respectively, for 5, 3, 1mm-curvature). However, there was no significant difference on marginal gaps between specimens of Au-1.6 wt% Ti alloy and control gold alloy. This study indicated that the metal ceramic crowns cast in Au-1.6 wt% Ti alloy had equivalent accuracy to those that cast in control gold alloy, and the abutment finish line curvature had a significant effect on the marginal fit of metal ceramic crowns.
 
The influence of Be content on the corrosion behavior and strength of dental alloys was examined using experimental Ni-25Cr-10Mo-xBe alloys with graduated Be contents of 0, 0.6, 1.1, 1.6, and 2.1 wt.%. It became evident that the corrosion resistance is reduced even by a 0.6 wt.% Be content. Strength increases by 51% with increasing Be content, while ductility is reduced by 84%. The results revealed that, from the stand-point of corrosion resistance, Be-free Ni-Cr-Mo alloys should be preferred in clinical use.
 
The first commercial high-copper amalgam was developed in the mid-1960's. In 1975, a study to evaluate in vivo/in vitro performance of nine of these new alloys was initiated at Indiana University. These nine high-copper amalgams plus a traditional amalgam were tested for four laboratory properties and their gamma-2 content, and were clinically assessed for fracture at the margins. Originally, 60 restorations of each material were placed in patients and then recalled at six, 12, and 24 months. Recently, 13 years post-operatively, approximately one-third of the original patients were located. These patients were given a clinical exam, and photographs were taken of their restorations. From these recall data, the mean loss of all restorations at 13 years was 11.3%. The alloys Cupralloy, Tytin, and Dispersalloy had the lowest loss rates. The evaluation of the fracture at the margins (ridit means) indicates that there are five groups of alloys with some overlap between groups. The alloys Cupralloy, Indiloy, Dispersalloy, and Phasealloy exhibited the least fracture at the margins. The gamma-2-containing alloys--Optaloy II, Micro II, Velvalloy, and Aristaloy CR--showed the greatest rate of fracture at the margins. A correlation matrix of the ridit means at different years, the loss of restorations at 13 years, and the mechanical properties indicate that the early (one- and two-year) fracture at the margins predicts the 13-year results. Mechanical properties, however, do not predict the clinical performance of the materials at 13 years.
 
To evaluate zirconia-based fixed partial dentures (FPDs) after more than 8 years in clinical service. Patients treated between 2000 and 2004 with zirconia FPDs were identified from the records of a manufacturer of FPD substructures. Of the 45 patients who met the inclusion criteria 30 attended the appointment and 33 FPDs were evaluated using modified California Dental Association (CDA) criteria. In addition, plaque and the bleeding index were registered. Patient satisfaction with the restorations was evaluated using a 10-point visual analog scale (VAS). All the FPDs were made using CAD/CAM and hot isostatic pressed yttria-tetragonal zirconia polycrystal (HIPed Y-TZP) ceramic (Denzir) and were placed within general practices. The mean observation period was 9.6±1.6 years (range 3.0-13.1 years). The CDA rating was 90% satisfactory for the surface. Corresponding figures for anatomic form, color and margin integrity were 94%, 100% and 94%, respectively. Regarding surface three (9.7%) FPDs exhibited veneer chipping and were rated 'not acceptable'. For margin integrity two (6.5%) were rated 'not acceptable' because of caries. For anatomic form two (6.1%) were rated 'not acceptable' due to two lost FPDs. No significant differences were seen between the FPDs and controls for plaque and bleeding. The Kaplan-Meier survival rate (still in clinical function) was 94%, the success rate (technical events accounted for) 91% and (biological events accounted for) 73%. Based on the VAS the mean value for patient satisfaction was 9.3±1.2. Ninety-four percent of the FPDs were still in clinical function. HIPed Y-TZP could serve as an alternative for FPD treatments similar to those in the current study. Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
 
The aim of this study was to evaluate the clinical long-term retention to dentin of seven adhesive systems. A total of 337 Class V restorations of three three-step etch-and-rinse, one two-step etch-and-rinse and three self-etch adhesive systems were placed in non-carious cervical lesions without intentional enamel involvement. The restorations were evaluated at baseline and then every 6 months during a 13 years follow-up. Dentin bonding efficiency was determined by the percentage of lost restorations. During the 13 years, 275 restorations could be evaluated. The cumulative loss rate at 13 years was 60.3%, with significant different failures rates for the different systems varying between 26.3 and 94.7%. Three materials fulfilled the ADA 18 months full acceptance criteria. Three systems showed already at 18 months or earlier catastrophical debonding rates. The annual failure rates for the three-step etch-and-rinse systems were: Allbond 2 4.1%, Clearfil LB 2.0% and Denthesive 7.3%. For the two-step etch-and-rinse Gluma 2000 6.5%, and for the self-etch systems ART 3.2%, Denthesive 2 5.7% and PUB 3 4.5% A continuous degradation of the resin-dentin bond was observed for all bonding systems during the follow-up expressed by the increasing loss rates. A wide variation of dentin bonding effectiveness was seen between the systems independent to adhesion strategy.
 
Titanium alloys are considered the material of choice when used as endosteal part of implants. However, they are not able to bond directly to bone. The objective of this study was to suggest a chemical surface treatment for Ti-13Nb-13Zr to initiate the formation of hydroxy carbonated apatite (HCA) during in vitro bioactivity tests in simulated body fluid (SBF). Titanium, niobium, and zirconium hydride powders were blended, compacted and sintered. Sintered Ti-13Nb-13Zr samples were etched in HCl, H(3)PO(4), and in a mixture of HF+HNO(3), respectively, and subsequently pretreated in NaOH. The influence of acid etching conditions on the microstructure of the Ti-13Nb-13Zr alloys as well as on the rate of HCA formation was evaluated using SEM-EDS, FTIR, and gravimetric analyses. Sintered Ti-13Nb-13Zr alloys consist of a Widmannstätten (alpha+beta) microstructure. Exposure of chemically etched and NaOH activated samples to SBF for 1 week leads to the formation of a HCA layer on the surface of HCl as well as H(3)PO(4) treated samples. No HCA formation was found on HNO(3) treated samples. After 2 weeks in SBF the mass increase, that can be correlated to the HCA formation rate, was the highest for HCl pretreated samples (2.4 mg/cm(2)) followed by H(3)PO(4) (0.8 mg/cm(2)) and HNO(3) pretreated ones (0.2 mg/cm(2)). Since the in vitro HCA formation from SBF is generally accepted as a typical feature for bioactive materials, it is supposed that HCl etching with subsequent NaOH treatment might enhance the in vivo bone-bonding ability of Ti-13Nb-13Zr.
 
The purpose of the present investigation was to trace the fate of bisphenol A injected into pregnant mice, focusing on its potential accumulation in the fetus and the brain, critical targets of hormonal chemicals, using whole-body autoradiography. Pregnant mice were injected intraperitoneally with 0.46MBq of (14)C-BPA and then killed at 1h or 1, 3, or 5 days after injection. Sections for autoradiography were prepared in a cryomicrotome and the exposed imaging plate was processed using a fluorescent/radioisotope image analyzer. Intraperitoneally injected (14)C-BPA was distributed throughout the body, including the fetus and the brain, within 1h. Radioactivity faded gradually from the whole body by the fifth day, and no accumulation in any specific organ was found. However, although (14)C was detected in the fetuses immediately after injection, the transfer of BPA from mother to newborn was not observed. The routes of rapid BPA discharge were confirmed, and BPA neither accumulated in the body nor was it transferred to newborn mice. No evidence was observed to suggest the existence of a blood-placenta or blood-brain barrier for BPA. This information should be taken into consideration when assessing the risks of using dental materials that contain BPA.
 
The fate of the dimethylpolysiloxane (silicone oil) component of the root canal filling material “Vitapex”, consisting of calcium hydroxide and iodoform with the addition of silicone oil, was investigated by whole-body, light microscopic, and electron microscopic autoradiography of the 14C-labelled compound. These studies suggest that some of the dimethylpolysiloxane component passed into the digestive tract. Furthermore, the data indicate that the dimethylpolysiloxane plays some part in the calcification caused by the embedded paste.
 
The Portland Composites Symposium (POCOS) was held from June 17-19, 2004 at Oregon Health & Science university, Portland, Oregon. The current status and challenges ahead for the dental posterior restorative composites was discussed in the symposium considering the clinical, chemical and physical behavior of the composites. It is pointed out that there is a need to understand the change in the properties of resin composites with time, post-curing behavior of resins after restoration and degradation mechanisms of the resins. The need to develop standardized test methods and controls in addition to identifying appropriate time scales for the tests is also recommended.
 
The aim of this study was to determine the influence of particle size, particle material and morphology on the sliding wear of 19 light curing, commercially available composites (Durafill VS, Metafil CX, Heliomolar RO, Solitaire, Arabesk, Artglass, Charisma F, Pertac II, Charisma, Degufill Ultra, TPH Spectrum, Z100, Tetric classic, Pertac Hybrid, Estilux Hybrid, Dyract AP, Compoglass F, Compoglass and Hytac). The materials were applied to an aluminum sample holder (7.5 mm diameter, 2 mm depth) in one layer and polymerized in a Dentacolor XS light curing unit for 180 s. The surface was ground flat (#1000) to remove any matrix rich surface layer. Then samples were stored in Ringer's solution for 24 h at 37 degrees C. Occlusal contact wear was simulated in a sliding wear tester (Munich Artificial Mouth). Eight specimens of each material were tested in a pin-on-block design with oscillating sliding of a Degussit antagonist (5 mm diameter) at a vertical load of 50 N. The horizontal excursion of the antagonist was 8 mm. Wear was quantified by a replica technique every 6000, 10,000, 30,000 and 50,000 cycles using a 3D-laser scanner. The materials were compared by their mean wear after 50,000 cycles. Comparisons of different composites and compomers were performed using analysis of variance and t-tests including the Bonferroni correction. The microfiller composites (Durafill VS, Metafil CX, Heliomolar RO) revealed the lowest, and the compomers (Dyract AP, Compoglass F, Compoglass and Hytac) showed the highest contact wear (p < 0.05). The wear of the hybrid composite (Estilux Hybrid) and the micro hybrid composites (Solitaire, Arabesk, Artglass, Charisma F, Pertac II, Charisma, Degufill Ultra, TPH Spectrum, Z100, Tetric classic, Pertac Hybrid) was higher than that of the microfiller composites (p < 0.05). The results showed additional significant differences within the three groups of composites. The coefficient of determination between loss of height and maximum particle size was r2 = 0.41. Both particle size and morphology have a high influence on the wear properties concerning the two-body wear in the occlusal contact area.
 
Methacrylate-based (co)monomers released from dental composites can be, metabolized in vivo to methacrylic acid (MA). MA can be further oxidized to the toxic 2,3-epoxymethacrylic acid (2,3-EMA) by cytochrome P450 (CYP450) enzymes. The subform CYP450-2E1, can metabolize xenobiotics with low-molecular weight to epoxides. Oral cells are highly exposed to (co)monomers released from composites. Therefore in this study the, expression of CYP450-2E1 in human oral (and other) cells was investigated as well as the formation of 2,3-EMA in cells exposed to MA. Following human oral cells were used: human gingiva fibroblasts (HGF), human pulp fibroblasts (HPF), and human tumor buccal keratinocytes (SqCC/Y1). As negative control V79 cells without CYP450-2E1 expression were used. As positive controls V79 cells with CYP450-2E1 expression (V79-CYP450-2E1) and pooled human liver microsomes were used. The expression of CYP450-2E1 in cells was analyzed with the real-time polymerase chain reaction (RT-PCR). 2,3-EMA was quantified by the use of the method of gas chromatography/mass spectrometry (GC/MS). The highest expression of CYP450-2E1 was found in human liver microsomes, followed by SqCC/Y1 cells, V79-CYP450-2E1 cells, HGF, and HPF. The highest amount of 2,3-EMA (μmol/L; mean±SEM, n=3) was found in human liver microsomes (5.0±1.0), followed by SqCC/Y1 cells (2.5±0.8), V79-CYP450-2E1 cells (1.5±0.6), HPF (0.3±0.3), and HGF (0.2±0.2). It is concluded that the formation of the toxic epoxide 2,3-EMA, as intermediate in the metabolism of dental materials, can occur also in human oral cells which can express the CYP450-2E1 enzyme system.
 
In previous studies it could be demonstrated that methacrylic acid (MA) is an intermediate in the metabolism of unpolymerized dental comonomers, released from dental restorative materials. This study was performed to identify the possible dental material intermediate 2,3-epoxymethacrylic acid (2,3-EMA) from MA in human liver microsomes. Most epoxy compounds are regarded as highly toxic substances. The formation and hydrolysis were studied in defined systems containing only MA and human liver microsomes at 37 degrees C. Hydrolysis was inhibited by cyclohexene oxide, a competitive inhibitor of epoxide hydrolase. The reaction product 2,3-EMA was analyzed by the headspace gas chromatography-mass spectrometry. After 5, 30, and 60 min samples were taken and analyzed. For the reaction of MA to 2,3-EMA the average conversion rate was about 5% within 1h. It was found that without cyclohexene oxide the rate constant of enzymatic hydrolysis at pH 7.4 was about 10 times higher than the rate constant of the formation from MA in combination with cyclohexene oxide (k=8.3 versus 0.83 micromol/l min), indicating an instability and thus a high reactivity of 2,3-EMA. The formation of the MA intermediate 2,3-EMA was not observed when heat-inactivated liver microsomes were used (controls). It could be clearly demonstrated that 2,3-EMA is a product of dental material metabolisms in biological systems. Therefore, increased toxicity might occur on dental restorative materials which are able to release (co)monomers which can be metabolized to MA.
 
The purpose of this study was to evaluate the effect of two additives, propionaldehyde/aldehyde or 2,3-butanedione/diketone, on mechanical properties of Bis-GMA-based composites containing TEGDMA, propoxylated Bis-GMA (CH(3)Bis-GMA) or propoxylated fluorinated Bis-GMA (CF(3)Bis-GMA). Three control composites, Bis-GMA/diluent monomer (25/75 mol%), and six test composites, Bis-GMA/diluent monomer/aldehyde or diketone (17/51/32 mol%) were prepared. All composites contained hybrid treated filler (barium aluminosilicate glass/pyrogenic silica; 60 wt%), and 0.2 wt% each of camphorquinone and N,N-dimethyl-p-toluidine. Degree of conversion (DC%), flexural strength (FS), modulus of elasticity (E), modulus of resilience (R) and diametral tensile strength (DTS) were determined. DC% (n=3) was investigated by FT-IR. For FS and E, beam-shaped specimens (25mm x 2mm x 2mm) were prepared (n=6), stored for 7 days in 37 degrees C deionized water and tested on an Instron utilizing a three-point loading jig (0.5mm/min). The R-values were obtained from the following equation: R=(FS)(2)/2E. For DTS, cylindrical specimens (4mm x 8mm) were prepared (n=6), stored for 7 days in 37 degrees C deionized water and diametrically loaded on an Instron (0.5mm/min). Data were analyzed by one-way ANOVA and Tukey's test (alpha=0.05). Incorporation of additives led to an increase in DC%, FS and E for Bis-GMA/TEGDMA and Bis-GMA/CH(3)Bis-GMA systems. R-values for all systems were unaffected by addition of additives. They had no significant effect on DC% or mechanical properties of Bis-GMA/CF(3)Bis-GMA. The findings correlate with the ability of additives to improve degree of conversion of some composite systems thereby enhancing mechanical properties.
 
The purpose of this laboratory study was to evaluate the influence of different cleaning methods after saliva contamination and after using a silicone disclosing medium on the resin bond strength to zirconia ceramic. The hypothesis was that the resin-ceramic bond strength and its durability are related to the ceramic surface condition. Plexiglas tubes filled with composite resin were bonded to air-abraded zirconia ceramic disks using a phosphate monomer containing composite resin. Four surface cleaning methods were used after contaminating the ceramic surface: air abrasion with 50 mum Al(2)O(3) at 2.5 bar pressure for 15s, cleaning with 37% phosphoric acid for 60s once or for 30s twice, or cleaning in 96% isopropanol for 15s. The specimens of the control group were not cleaned after using the silicone disclosing medium. For each combination 16 specimens were bonded in an alignment apparatus. Subgroups of eight bonded specimens were tested for tensile bond strength (TBS) after storage for either 3 or 150 days combined with 37,500 thermal cycles. The statistical analyses were performed with the Kruskal-Wallis test, followed by multiple pair-wise comparisons using the Wilcoxon rank sum test. The mean TBS ranged from 6.6 to 49.9 MPa after 3 days and from 0 to 19.8 MPa after 150 days. Air abrasion of the ceramic surface provided statistically significantly higher bond strengths than the other cleaning methods after 3 and 150 days. Alcohol cleaning of the ceramic did not provide durable bond strengths over time. Ceramic cleaning methods after try-in procedures have a significant influence on the resin-ceramic bond strength. Air abrasion of contaminated zirconia ceramic is the most effective.
 
Although nitric acid is a component in some new bonding systems, the action of nitric acid as an etchant for the improvement of adhesion of bonding systems for resin composites to dentin and enamel has not been reported. A determination of the extent of etching on both dentin and enamel using 2.5% HNO3 solution at various application time periods was the purpose of this study. Extracted human molars were cleaned and sectioned so that flat samples of dentin and enamel would be produced. Surfaces were abraded with 320-grit aluminum-oxide paper, washed with distilled water for 10 s, and blown with air for 10 s. Duplicate samples of dentin and enamel were treated with a drop of 2.5% HNO3. Application periods varied by 10-second intervals, from 10 s up to 60 s. After being rinsed with distilled water and dried, the sections were routinely processed for observation by SEM. The micrographs of the treated surfaces showed various degrees of etching and erosion proportional to the length of application time. The 30-second application revealed a well-etched surface with minimal erosion.
 
The literature demonstrates that conventional luting of metal-based restorations using zinc phosphate cements is clinically successful over 20 years. This study compared the clinical outcomes of metal-based fixed partial dentures luted conventionally with zinc phosphate and self-adhesive resin cement. Forty-nine patients (mean age 54+/-13 years) received 49 metal-based fixed partial dentures randomly luted using zinc phosphate (Richter & Hoffmann, Berlin, Germany) or self-adhesive resin cement (RelyX Unicem Aplicap, 3M ESPE, Germany) at the University Medical Center Regensburg. The core build-up material was highly viscous glass ionomer; the finishing line was in dentin. The study included 42 posterior, 5 anterior crowns and two onlays. Forty-seven restorations were made of precious alloys, 2 of non-precious alloys. The restorations were clinically examined every year. The clinical performance was checked for plaque (0-5; PI, Quigley-Hein), bleeding (0-4; PBI; Mühlemann) and attachment scores. The examination included pulp vitality and percussion tests. Means of scores, standard deviation, cumulative survival and complication rates were calculated using life tables. The mean observation time was 3.16+/-0.6 years (min: 2.0; max: 4.5 years). During that time no restoration was lost, no recementation became necessary. One endodontic treatment was performed in the self-adhesive composite group after 2.9 years. At study end bleeding (1.44 RelyX Unicem vs. 1.25 zinc phosphate) and plaque (1.64 RelyX Unicem vs. 1.0 zinc phosphate) scores showed no statistically significant difference. The self-adhesive resin cement performed clinically as well and can be used as easily as zinc phosphate cement to retain metal-based restorations over a 38-month observation period.
 
Boxplot graphs of log-transformed wear raw data for each test method. 1 = Empress, 2 = belleGlass, 3 = SureFil, 4 = Estenia, 6 = Amalcap, 7 = Targis, 8 = Heliomolar, 9 = Tetric Ceram, 10 = Chromasit. Note: Material no. 5 (Targis cured at 130 • C) has been excluded for the analysis of the present study.
Agreement between laboratory methods measured by relative ranks 1-9 (y-axis).
The purpose of the present study was to submit the same materials that were tested in the round robin wear test of 2002/2003 to the Alabama wear method. Nine restorative materials, seven composites (belleGlass, Chromasit, Estenia, Heliomolar, SureFil, Targis, Tetric Ceram) an amalgam (Amalcap) and a ceramic (IPS Empress) have been submitted to the Alabama wear method for localized and generalized wear. The test centre did not know which brand they were testing. Both volumetric and vertical loss had been determined with an optical sensor. After completion of the wear test, the raw data were sent to IVOCLAR for further analysis. The statistical analysis of the data included logarithmic transformation of the data, the calculation of relative ranks of each material within each test centre, measures of agreement between methods, the discrimination power and coefficient of variation of each method as well as measures of the consistency and global performance for each material. Relative ranks of the materials varied tremendously between the test centres. When all materials were taken into account and the test methods compared with each other, only ACTA agreed reasonably well with two other methods, i.e. OHSU and ZURICH. On the other hand, MUNICH did not agree with the other methods at all. The ZURICH method showed the lowest discrimination power, ACTA, IVOCLAR and ALABAMA localized the highest. Material-wise, the best global performance was achieved by the leucite reinforced ceramic material Empress, which was clearly ahead of belleGlass, SureFil and Estenia. In contrast, Heliomolar, Tetric Ceram and especially Chromasit demonstrated a poor global performance. The best consistency was achieved by SureFil, Tetric Ceram and Chromasit, whereas the consistency of Amalcap and Heliomolar was poor. When comparing the laboratory data with clinical data, a significant agreement was found for the IVOCLAR and ALABAMA generalized wear method. As the different wear simulator settings measure different wear mechanisms, it seems reasonable to combine at least two different wear settings to assess the wear resistance of a new material.
 
This retrospective longitudinal study investigated the longevity of posterior restorations placed in a single general practice using 2 different composites in filler characteristics and material properties: P-50 APC (3M ESPE) with 70vol.% inorganic filler loading (midfilled) and Herculite XR (Kerr) with 55vol.% filler loading (minifilled). Patient records were used for collecting data. Patients with at least 2 posterior composite restorations placed between 1986 and 1990, and still in the practice for regular check-up visits, were selected. 61 patients (20 male, 41 female, age 31.2-65.1) presenting 362 restorations (121 Class I, 241 Class II) placed using a closed sandwich technique were evaluated by 2 operators using the FDI criteria. Data were analyzed with Fisher's exact test, Kaplan-Meier statistics, and Cox regression analysis (p<0.05). 110 failures were detected. Similar survival rates for both composites were observed considering the full period of observation; better performance for the midfilled was detected considering the last 12 years. There was higher probability of failure in molars and for multi-surface restorations. Both evaluated composites showed good clinical performance over 22 years with 1.5% (midfilled) and 2.2% (minifilled) annual failure rate. Superior longevity for the higher filler loaded composite (midfilled) was observed in the second part of the observation period with constant annual failure rate between 10 years and 20 years, whereas the minifilled material showed an increase in annual failure rate between 10 years and 20 years, suggesting that physical properties of the composite may have some impact on restoration longevity.
 
Evaluate the cytotoxic effect of the three dental adhesive systems. The immortalized mouse odontoblast cell line (MDPC-23) was plated (30,000 cell/cm2) in 24 well dishes, allowed to grow for 72 h, and counted under inverted light microscopy. Uncured fresh adhesives were added to culture medium to simulate effects of unset adhesive. Three adhesives systems were applied for 120 min to cells in six wells for each group: Group 1) Single Bond (3M), Group 2) Prime & Bond 2.1 (Dentsply), and Group 3) Syntac Sprint (Vivadent). In the control group, PBS was added to fresh medium. The cell number was counted again and the cell morphology was assessed under SEM. In addition, the adhesive systems were applied to circles of filter paper, light-cured for 20 s, and placed in the bottom of 24 wells (six wells for each experimental materials and control group). MDPC-23 cells were plated (30,000 cell/cm2) in the wells and allowed to incubate for 72 h. The zone of inhibition around the filter papers was measured under inverted light microscopy; cell morphology was evaluated under SEM; and the MTT assay was performed for mitochondrial respiration. The fresh adhesives exhibited more toxic (cytopathic effects) to MDPC-23 cells than polymerized adhesives on filter papers, and as compared to the control group. The cytopathic effect of the adhesive systems occurred in the inhibition zone around the filter papers, which was confirmed by the MTT assay and statistical analysis (ANOVA) combined with Fisher's PLSD test. In the control group, MDPC-23 cells were dense on the plastic substrate and were in contact with the filter paper. In the experimental groups, when acid in the adhesive systems was removed by changing the culture medium, or when the adhesives were light-cured, some cells grew in the wells in spite of the persistent cytotoxic effect. All dentin adhesive systems were cytotoxic odontoblast-like cells. Both acidity and non-acidic components of these systems were responsible for the high cytopathic effect of those dental materials.
 
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.
 
The main objective is the characterization of the setting reaction in glass ionomer cements (GICs) based on experimental glasses using the (27)Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy in order to understand the crosslinking process during the setting reaction. Three types of GICs which are based on fluoro-alumino-silicate glasses (LG125, ART10, and LG26Sr) were studied using (27)Al MAS-NMR to monitor the setting reaction of the cements. The result showed clearly the formation of six coordinate, aluminium Al(VI), that crosslink the carboxyl groups in the PAA. The deconvolution study was performed to quantify the amount of each Al species in the cements. The finding showed that composition of original glass has a substantial effect on the setting behavior of the cements. Our data demonstrate that the setting reaction of GICs can be followed by (27)Al MAS-NMR spectroscopy discovering the conversion of Al(IV) to Al(VI). Considerable amount of the five coordinate aluminium, Al(V), species was found in the cements aged up to one year. The presence of phosphorus has a strong influence on the setting reaction. The formation of Al-O-P species was postulated to be present in the cement.
 
– X-ray diffraction patterns of nanocrystalline 304ss and microcrystalline 304ss samples at room temperature.  
– (a) Open circuit potentials (OCP) and (b) potentiodynamic polarization curves of microcrystalline 304ss and nanocrystalline 304ss in artificial saliva.  
– Metallic ions release till 63 days immersion: (a) Ni in artificial saliva and (b) Cr in artificial saliva (*significant difference in the measurement when compared to the two pairs at P ≤ 0.05).  
– XPS spectra of 14 days immersion of (a) nanocrystalline 304ss and (b) microcrystalline 304ss in artificial saliva.  
– Cell viability expressed as a percentage of the viability of cells in the control after 1, 2 and 4 days of culture in microcrystalline 304ss and nanocrystalline 304ss extraction mediums: (a) NIH3T3 cell line; (b) L-929 cell line; (c) ECV304 cell line and (d) MG63 cell line (*significant against cell proliferation on control group at P ≤ 0.05).  
SUS 304 stainless steels have been widely used in orthodontics and implants such as archwires, brackets, and screws. The purpose of present study was to investigate the biocompatibility of both the commercial microcrystalline biomedical 304 stainless steel (microcrystalline 304ss) and novel-fabricated nanocrystalline 304 stainless steel (nanocrystalline 304ss). Bulk nanocrystalline 304ss sheets had been successfully prepared by microcrystalline 304ss plates using severe rolling technique. The electrochemical corrosion and ion release behavior immersion in artificial saliva were measured to evaluate the property of biocorrosion in oral environment. The cell lines of murine and human cell lines from oral and endothelial environment were co-cultured with extracts to evaluate the cytotoxicity and provide referential evidence in vivo. The polarization resistance trials indicated that nanocrystalline 304ss is more corrosion resistant than the microcrystalline 304ss in oral-like environment with higher corrosion potential, and the amount of toxic ions released into solution after immersion is lower than that of the microcrystalline 304ss and the daily dietary intake level. The cytotoxicity results also elucidated that nanocrystalline 304ss is biologically compatible in vitro, even better than that of microcrystalline 304ss. Based on the much higher mechanical and physical performances, nanocrystalline 304ss with enhanced biocorrosion property, well-behaved in vitro cytocompatibility can be a promising alternative in orthodontics and fixation fields in oral cavity.
 
The polishing and coating of ceramic surfaces is recommended in order to improve the physical properties of dental ceramics. Conventional methods for the surface treatment of dental ceramic materials are not capable of creating a smooth surface without microcracks. The special radiation characteristics of XeCl excimer laser light indicate that it must be possible to treat ceramic surfaces in order to produce a polished finish. The aim of this study was to investigate the efficacy of XeCl excimer laser radiation for the polishing and coating of dental ceramics. Samples (n = 64) of four different dental ceramic materials were irradiated with 308 nm XeCl excimer laser radiation at varying energy densities per laser pulse of 1.57, 3.14, and 6.28 J cm-2. In detail, the subjects for irradiation were samples of Ivoclar-Empress (leucite-reinforced feldspathic ceramic), In-Ceram Spinell (double crystalline spinell ceramic), In-Ceram Alumina (alumina oxide; continous interpenetrating phase composite ceramic) and Vita-Mark II (feldspathic ceramic). The roughness (Ra) of the laser-treated ceramic surfaces was measured using a profilometer. In addition, SEM and AFM investigations of the changes in surface structure were conducted. The changes in surface roughness due to laser treatment were analyzed for their statistical significance using ANOVA with the Scheffé test at a level of significance of 0.05% (p < 0.05). Depending on the type of ceramic material and the energy density of the radiation, varying reductions of the surface roughness were obtained. In general, minimum values of the roughness were measured on samples irradiated with maximum energy density of radiation. The lowest roughness value was obtained for the specimen of In-Ceram Spinell: 1.30 (+/- 0.19) microns. The mean value for minimal roughness of Ivoclar-Empress was 1.92 (+/- 0.35) microns, that for In-Ceram Alumina was 2.04 (+/- 0.49) microns, and that for Vita-Mark II was 2.72 (+/- 0.40) microns. Ultrastructural examination of laser-treated ceramics in part demonstrated both extensive fusion and inhomogeneous surfaces with blistering and the formation of microcracks. It is concluded that the physical roughness of dental ceramic surfaces can be significantly reduced by 308 nm excimer laser irradiation. Nevertheless, the laser-treated surface was in no case completely fused and the formation of microcracks and blistering was observed. Therefore, after using an XeCl excimer laser for finishing dental ceramic alloys, further polishing of the laser-treated ceramic surfaces will be needed.
 
To use (31)P solid-state MAS-NMR to determine which compounds form in phosphate-bonded dental casting investment material during setting, when the ambient temperature is altered. To determine whether they differ in material originating at the center of the mix from material that adheres to the mixing bowl wall. (1)H high powered decoupled (HPDC) and (1)H cross polarized (CP) (31)P solid-state MAS-NMR spectroscopy were used at a resonance frequency of 121.4MHz to determine molecular structure. Four commercial products were examined. Manufacturer's instructions were followed and special liquid used without dilution. Ambient temperature was between 18 and 37 degrees C. Molecular structures change with ambient temperature and product. Amorphous Mg(3)(PO(4))(2) or struvite dominate with newberyite, cattiite, amorphous Mg(2)P(2)O(7) and amorphous MgHPO(4) present as minor phases. Exceptionally, amorphous MgHPO(4) dominates. Differences in structure were found in material taken from the center of the mix compared with that scraped from the bowl wall, but the incidence may be specific to the product/mixer combination and not a general effect. The formation of compounds in phosphate-bonded investment can be affected by ambient temperature. This effect and the use of material adhering to the bowl wall (instead of that from the center of the mix) are possible causes for the unpredictability of setting expansion measurements between laboratories. There is variation between products. When phosphate-bonded investment is required for casting, a consistent ambient temperature must be used and it would be wise to mix sufficient material to avoid scraping the bowl.
 
To use (31)P solid-state MAS-NMR to determine the phosphorus compounds that occur in dental casting investment material: (a) as-received, (b) after setting and (c) after burn-out and discover whether such compounds are the same in each material across a product range. [(1)H] High powered decoupling (HPDC) and [(1)H] cross-polarization (CP) (31)P solid-state MAS-NMR spectroscopy at a resonance frequency of 121.4 MHz were used. Six commercial products were examined. Manufacturer's instructions were followed and a special liquid was used without dilution. All products contain ammonium dihydrogen phosphate as the acid phosphate required for the setting reaction. All set by the formation of struvite and significant amounts of amorphous magnesium orthophosphate. In three products, lesser amounts of newberyite were present and in another the equivalent amorphous compound was formed. When burnt-out, magnesium metaphosphate or pyrophosphate was the dominant matrix compound. A higher burn-out temperature favoured pyrophosphate formation. Farringtonite was present to a lesser extent with the metaphosphate. Compounds that were not detected in earlier X-ray powder diffraction spectroscopy studies were detected by NMR, notably amorphous and glassy compounds (magnesium orthophosphate in set investment and magnesium metaphosphate in burnt-out material). The variation between products was significant and far greater than expected from the published scientific literature. Since the formation of compounds is affected by technical procedure and ambient conditions, these findings could offer some insight into the cause of the unpredictability of expansion measurements between laboratories. Further research is being undertaken.
 
The structure and function of P in P-based dental adhesives have not been defined properly. The purpose of this study was to evaluate these parameters in some currently available materials. Five dental adhesives were selected: Bondlite, Clearfil New Bond, J&J Dental Adhesive, Prisma Universal Bond, and Scotchbond. High-resolution 31P-NMR spectroscopy was used to identify the phases of the incorporated P and the kinetics of monomer-bonded P in an aqueous environment. Areas of 5 mm diameter located on polished sound dentin were subjected to the corresponding adhesive treatments and covered with translucent molds of the same diameter, which were filled up to 1 mm length with a visible-light-cured hybrid composite. Following 60 sec of light exposure from lateral directions, the specimens were embedded in fast-setting resin, cross-sectioned, and analyzed in an electron probe microanalyzer. The elemental profiles of Ca, P, and Cl were determined from area and line scans. Great differences in the 31P resonance shifts were obtained from the tested adhesives, indicating the presence of monomer-bonded and free P. A rapid hydrolysis of the resin-bonded P in the presence of water was identified. The x-ray images revealed dentin demineralization, with distinct differences in the P distribution pattern and the P/Cl ratio.
 
Previous temperature-modulated differential scanning calorimetry (TMDSC) study of nickel-titanium orthodontic wires revealed a large exothermic low-temperature peak that was attributed to transformation within martensitic NiTi. The purpose of this study was to use transmission electron microscopy (TEM) to verify this phase transformation in a clinically popular nickel-titanium wire, identify its mechanism and confirm other phase transformations found by TMDSC, and to provide detailed information about the microstructure of this wire. The 35 degrees C Copper nickel-titanium wire (Ormco) with cross-section dimensions of 0.016 in. x 0.022 in. used in the earlier TMDSC investigation was selected. Foils were prepared for TEM analyses by mechanical grinding, polishing, dimpling, ion milling and plasma cleaning. Standard bright-field and dark-field TEM images were obtained, along with convergent-beam electron diffraction patterns. A cryo-stage with the electron microscope (Phillips CM 200) permitted the specimen to be observed at -187, -45, and 50 degrees C, as well as at room temperature. Microstructures were also observed with an optical microscope and a scanning electron microscope. Room temperature microstructures had randomly oriented, elongated grains that were twinned. Electron diffraction patterns confirmed that phase transformations took place over temperature ranges previously found by TMDSC. TEM observations revealed a high dislocation density and fine-scale oxide particles, and that twinning is the mechanism for the low-temperature transformation in martensitic NiTi. TEM confirmed the low-temperature peak and other phase transformations observed by TMDSC, and revealed that twinning in martensite is the mechanism for the low-temperature peak. The high dislocation density and fine-scale oxide particles in the microstructure are the result of the wire manufacturing process.
 
This study investigated the wavelength-dependent photosensitivity of eleven resin composites (Admira A2, Heliomolar A2, Herculite XRV A2, Pyramid Dentin A2, Solitaire 2 A2, Z250 A2, AElite LS A2, Vit-l-escence A2, Tetric Ceram Bleach XL, Tetric Ceram A2, Pyramid Enamel Neutral). Resin composites 1.6mm thick were exposed to narrow bandwidths of light at the following peak wavelengths: 394, 400, 405, 410, 415, 420, 430, 436, 442, 450, 455, 458, 467, 470, 480, 486, 493, 500, 505, and 515+/-5nm. A spectroradiometer was used to ensure that the same irradiance (mW/cm(2)) and total energy density (J/cm(2)) was delivered through each filter. For each resin composite, three specimens were exposed through each filter. The Knoop micro-hardness at the top and bottom of the composites was then measured. The wavelength-dependent photosensitivity of each resin composite was analyzed by plotting the mean hardness achieved at each wavelength. The composites responded variably when they received light through the narrow bandpass filters. Six resin composites had a single peak of wavelength-dependent photosensitivity at approximately 470nm. Four resin composites had two peaks of wavelength-dependent photosensitivity at approximately 470 and approximately 405nm. One resin composite had a single peak of wavelength-dependent photosensitivity at approximately 405nm and was only sensitive to light below 436nm. Using light delivered through narrow bandpass filters is a convenient method to determine the wavelength-dependent photosensitivity of resins and can be used to predict the performance of dental curing lights.
 
To evaluate the effects of silica (SiO(2)) (0.5 wt%) and zinc oxide (ZnO) (0.25 wt%) dopants on the mechanical and biological properties of tricalcium phosphate (TCP) scaffolds with three dimensionally (3D) interconnected pores. Scaffolds were created with a commercial 3D printer. Post sintering phase analysis was determined by X-ray diffraction. Surface morphology of the scaffolds was examined by field emission scanning electron microscopy (FESEM). Mechanical strength was evaluated with a screw driven universal testing machine. MTT assay was used for cellular proliferation characteristics and cellular morphology was examined by FESEM. Addition of dopants into TCP increased the average density of pure TCP from 90.8 ± 0.8% to 94.1 ± 1.6% and retarded the β to α phase transformation at high sintering temperatures, which resulted in up to 2.5 fold increase in compressive strength. In vitro cell-materials interaction studies, carried out using hFOB cells, confirmed that the addition of SiO(2) and ZnO to the scaffolds facilitated faster cell proliferation when compared to pure TCP scaffolds. Addition of SiO(2) and ZnO dopants to the TCP scaffolds showed increased mechanical strength as well as increased cellular proliferation.
 
Objectives: Tubules dominate the microstructure of dentin, and in crowns of human teeth they are surrounded by thick mineralized peritubular cuffs of high stiffness. Here we examine the three-dimensional (3D) arrangement of tubules in relation to enamel on the buccal and lingual aspects of intact premolars and molars. Specifically we investigate the angular orientation of tubules relative to the plane of the junction of dentin with enamel (DEJ) by means of wet, non-destructive and high-resolution phase-contrast (coherent) tomography. Methods: Enamel capped dentin samples (n=16), cut from the buccal and lingual surfaces of upper and lower premolar and molar teeth, were imaged in water by high-resolution synchrotron-based phase-contrast X-ray radiography. Reconstructed 3D virtual images were co-aligned with respect to the DEJ plane. The average tubule orientation was determined at increasing distances from the DEJ, based on integrated projections onto orthogonal virtual planes. The angle and curl of the tubules were determined every 100 microm to a depth of 1.4mm beneath the DEJ. Results: Most tubules do not extend at right angles from the DEJ. Even when they do, tubules always change their orientations substantially within the first half-millimeter zone beneath the DEJ, both on the buccal and lingual aspects of premolar and molar teeth. Tubules also tend to curl and twist within this zone. Student t-tests indicate that lower teeth seem to have greater tilts in the tubule orientations relative to the DEJ normal with an average angle of 42 degrees (+/-2.0 degrees), whereas upper teeth exhibit a smaller change of orientation, with an average of 32 degrees (+/-2.1 degrees). Significance: Tubules are a central characteristic of dentin, with important implications on how it is arranged and what the properties are. Knowing about the path that tubules follow is important for various reasons, ranging form improving control over restorative procedures to understanding or simulating the mechanical properties of teeth. At increasing depths of dentin beneath enamel, tubules are significantly tilted relative to the DEJ norm, which may be important to understand clinical challenges such as sensitivity, effectiveness of bonding techniques or prediction of possible paths for bacterial invasion. Our data show dissimilar average tubule angles of upper versus lower teeth with respect to the DEJ which presumably contributes to different shear responses of the tissue under function. The degree to which this may warrant improved restoratives or new adhesive techniques to enhance adhesive restorations merits further investigation.
 
This project studies the effect of high-performance polyethylene (HPPE) fibers on stress distributions in a maxillary denture and the influence of fiber position on improving denture performance. A denture was scanned with a 3D Advanced Topometric Sensor digitizing system. The measuring system converted the images into a 3D digital model. A 3D reverse engineering technology then produced a numerical model which was then refined with Rapidform software. The underlying mucosa and bone were constructed using a freeform system integrated with a PHANTOM haptic device. A fiber lamella reinforcement was incorporated into the denture at different positions (fitting side, mid-palatal plane, polished side) with SolidWorks software. Boundary conditions were constrained at the top of the basal bone while bite force of 230 N was applied to the posterior teeth on both sides. The denture models were analyzed with ABAQUS software. Stress concentrations were found at the incisal notch and at the anterior and posterior palatal surfaces of the unreinforced denture. The incorporated reinforcement effectively reduced the stress concentrations at these surfaces. Placement of the fibers at polished side was the best position in reducing stress concentrations. 3D FEM usefully provides a non-laboratory means to reveal the weak areas in the maxillary complete denture, and exhibit the effectiveness of HPPE reinforcement together with fiber positions on enhancement of denture strength.
 
The purpose of this study was to investigate the effect of differences in the resin-cement elastic modulus on stress-transmission to ceramic or resin-based composite inlay-restored Class II MOD cavities during vertical occlusal loading. Three finite-element (FE) models of Class II MOD cavity restorations in an upper premolar were produced. Model A represented a glass-ceramic inlay in combination with an adhesive and a high Young's modulus resin-cement. Model B represented the same glass-ceramic inlay in combination with the same adhesive and a low Young's modulus resin-cement. Model C represented a heat-cured resin-composite inlay in combination with the same adhesive and the same low Young's modulus resin cement. Occlusal vertical loading of 400 N was simulated on the FE models of the restored teeth. Ansys FE software was used to compute the local von Mises stresses for each of the models and to compare the observed maximum intensities and distributions. Experimental validation of the FE models was conducted. Complex biomechanical behavior of the restored teeth became apparent, arising from the effects of the axial and lateral components of the constant occlusal vertical loading. In the ceramic-inlay models, the greatest von Mises stress was observed on the lateral walls, vestibular and lingual, of the cavity. Indirect resin-composite inlays performed better in terms of stress dissipation. Glass-ceramic inlays transferred stresses to the dental walls and, depending on its rigidity, to the resin-cement and the adhesive layers. For high cement layer modulus values, the ceramic restorations were not able to redistribute the stresses properly into the cavity. However, stress-redistribution did occur with the resin-composite inlays. Application of low modulus luting and restorative materials do partially absorb deformations under loading and limit the stress intensity, transmitted to the remaining tooth structures.
 
The present study aimed at providing 3D-FEA engineering tools for the understanding of the influence of tooth preparation design on the stress distribution and localization of critical sites in maxillary central incisors restored by means of alumina porcelain veneers under functional loading. A 3D-FEM model of a maxillary central incisor is presented. An arbitrary chewing static force of 10 N was applied with an angulation of 60 and 125 degrees to the tooth longitudinal axis at the palatal surface of the crown. The model was considered to be restored by means of alumina porcelain veneers with different tooth preparation designs. The differences in occlusal load transfer ability of the two restorative systems are discussed. The maximum Von Mises equivalent stress values were observed in the window restorative system for both 125 and 60 degrees load angulations. When the chamfer with palatal overlap preparation was simulated, the stress distributed uniformly in the cement layer, whereas in the window preparation the stress mainly occurred in the incisal area of the cement layer. When restoring a tooth by means of porcelain veneers, the chamfer with palatal overlap preparation better restores the natural stress distribution under load than the window technique.
 
In restored teeth, stresses at the tooth-restoration interface during masticatory processes may fracture the teeth or the restoration and cracks may grow and propagate. The aim was to apply numerical methodologies to simulate the behavior of a restored tooth and to evaluate fatigue lifetimes before crack failure. Using a CAD-FEM procedure and fatigue mechanic laws, the fatigue damage of a restored molar was numerically estimated. Tessellated surfaces of enamel and dentin were extracted by applying segmentation and classification algorithms, to sets of 2D image data. A user-friendly GUI, which enables selection and visualization of 3D tessellated surfaces, was developed in a MatLab(®) environment. The tooth-boundary surfaces of enamel and dentin were then created by sweeping operations through cross-sections. A class II MOD cavity preparation was then added into the 3D model and tetrahedral mesh elements were generated. Fatigue simulation was performed by combining a preliminary static FEA simulation with classical fatigue mechanical laws. Regions with the shortest fatigue-life were located around the fillets of the class II MOD cavity, where the static stress was highest. The described method can be successfully adopted to generate detailed 3D-FE models of molar teeth, with different cavities and restorative materials. This method could be quickly implemented for other dental or biomechanical applications.
 
The aim of this study was to develop a method to experimentally determine and visualize the direction and amount of polymerization shrinkage. We modified a composite to include 1.5 wt% traceable glass beads. A cylindrical cavity (6mm diameter, 3mm height) was restored with this traceable composite, with and without dentin adhesive, and digitized with high-resolution micro-computed tomography (microCT). Image segmentation was performed to extract the glass beads from the acquired 3D microCT images (uncured and cured). Afterwards, each glass bead was subjected to local rigid registration. The resulting displacement vectors were used to examine and calculate the changes. In unbonded restorations, the displacement vectors were oriented inwards to the center of mass, although not perfectly. Bonded restorations exhibited two contraction patterns: either toward one side of the cavity or toward the top-surface of the restoration. The displacement vector length values (mean/SD) for the bonded group (46.8 microm/10.0 microm) was significantly higher (p<0.01) than unbonded group (31.3 microm/8.5 microm), and the histogram curve was flatter (skew/kurtosis: 0.10/-0.56) as compared to the unbonded group (skew/kurtosis: 0.03/-0.26). The proposed method can visualize real 3D displacement vectors generated by polymerization shrinkage. The bonding quality and cavity geometry are critical for the direction of polymerization contraction. This method has the potential to validate current models concerning the amount and orientation of shrinkage vectors.
 
The aim of this investigation was to determine the influence of a variety of parameters on the effectiveness of hard substance ablation and the thermal side effects when using Er:YAG laser (Key I and II, KaVo) and Nd:YAG laser (SunLase 800, Sunrise Technologies/Orbis). For this study, ablation and temperature measurements were carried out on 170 dentin slices and 170 extracted teeth via computer-controlled cavity preparation. The Er:YAG laser settings varied from 250-400 mJ/pulse, 3-15 pps and 20-180 s processing time, and in the case of the Nd:YAG laser from 83-100 mJ/pulse, 10-20 pps, and 20-260 s processing time. The ablation rate was measured volumetrically via a 3D sensor. Temperatures were measured for each setting both on the dentin slice and in the pulp of the extracted teeth. The results were analyzed using a t-test for independent samples and a one-way ANOVA (Bonferroni). Also a liner regression analysis was done using Pearson's coefficient. The results show that with the Er:YAG laser, in combination with water-spray cooling, an effective 3D ablation rate (up to 0.017 mm3/pulse = 50 microns linear) can be achieved without raising the temperature of the surrounding tissue. In the case of the Nd:YAG laser, no measurable ablation rate was evident without conditioning of the dentin surface and, in the case of conditioning with black ink, a low ablation rate (0.00004 mm3/pulse = linear 0.2 micron/pulse) was found. In contrast to the Er:YAG laser, it is apparent, that with the Nd:YAG laser from a total energy of 80 J onwards, the rise in temperature in the pulp is above 8 degrees C. For that reason, the use of the Nd:YAG laser at higher total energies is not recommended. The temperature rise with the Nd:YAG laser is dependent on the direction of the dentin tubuli. Dentin tubuli running parallel to the surface prevent significant heat penetration, whereas those running in a transverse direction to the surface (= parallel to the laser beam) support the penetration of heat. This finding supports the light-propagating theory for spreading effects of laser beams in dentin.
 
To comparatively evaluate the 3D-marginal adaptation to dentine versus shrinkage strain of two light-cured microhybrid resin composites. Dentine cavities (Ø: 2 mm; h: 1 mm; n=2x4) were prepared, filled with a single layer of EsthetX and Premise resin composites, respectively, without any adhesive cavity pre-treatment, and light-cured for 40s at 750 mW/cm2. All the specimens were imaged by computerized X-ray microtomography. Sequential sections (n=11) at 8.09 pixel size were taken at top, middle and bottom sites of each restoration relative to the axial wall and the interfacial micro-void volume fraction (%VF) was calculated. Shrinkage strain (%S) and strain rate (%SR) of the composites were measured by the bonded-disc method (n=4). The results of %VF per material and restoration site were subjected to statistical analysis by 2-way ANOVA and Tukey's test, whereas the results of %S and %SR were analysed by t-test (p=0.05). Regression analysis was performed to determine correlations between %PF and %S, %S(R). The results of %VF at top (t), middle (m) and bottom (b) restoration sites were (%, mean+/-S.D.): EsthetX 0.84+/-0.11 (t), 0.80+/-0.32 (m), 6.74+/-5.12 (b), Premise 0.99+/-0.24 (t), 0.92+/-0.38 (m), 1.72+/-0.97 (b). The results of %S were (%, mean+/-S.D.): EsthetX 2.60+/-0.29, Premise 1.91+/-0.10 and of %SR were (%, mean+/-S.D.): EsthetX 1.47+/-0.04, Premise 1.18+/-0.02. %VF(b) of EsthetX showed the highest values within and between the testing groups (p<0.05). %S and %S(R) values of EsthetX were significantly higher from Premise (p<0.05). Strong positive correlations were documented between %VF(b)-%S (r=0.843) and %VF(b)-%SR (r=0.943). The results confirmed a positive correlation between setting shrinkage and interfacial gap volume at bottom sites of light-cured microhybrid composite restoration due to differential shrinkage. Shrinkage strain rate seems to be a more sensitive factor in determining percentage volume of interfacial porosity at bottom restoration sites.
 
The aim was to evaluate the stress distribution, comparing an anterior sound tooth with post-endodontic restored teeth under mechanical loading. A three-dimensional finite element analysis was performed based on micro-CT scan images of a maxillary canine. Twelve models with different crown properties and post-configurations were simulated. The model of the maxillary sound canine was also created and investigated. A load of 50N was applied at a 63° angle with respect to the longitudinal axis of the tooth on the palatal surface of the crown. Principal stresses were registered. Numerical FEA results were statistically analyzed to show the influence of post shape and crown materials. All analyzed models (M1-M12) exhibited a high stress gradient, due to different material stiffnesses present at the various interfaces. The most uniform mechanical behavior of the investigated models, very similar to sound tooth, was the combination of a composite crown and a cylindrical or conical fiber-glass post. The results of this study facilitate informed clinical choice between possible material combinations in restorative procedures of endodontically treated anterior teeth.
 
The objectives of this study were to assess demineralized dentin porosity and quantify the different porous features distribution within the material using mercury intrusion porosimetry (MIP) technique. We compared hexamethyldisilazane (HMDS) drying and lyophilization (LYO) (freeze-drying) in sample preparation. Fifty-six dentin discs were assigned into three groups. The control (CTR) group discs were superficially acid-etched (15s 37% H(3)PO(4)) to remove the smear layer and then freeze-dried whereas LYO and HMDS groups samples were first totally demineralized using EDTA 0.5M and then freeze-dried and HMDS-dried respectively. MIP was used to determine open porosity and pore size distribution of each pair of samples. Field emission scanning electron microscopy (FESEM) was used to illustrate the results. The results showed two types of pores corresponding either to tubules and micro-branches or to inter-fibrillar spaces created by demineralization. Global porosity varied from 59% (HMDS-dried samples) to 70% (freeze-dried samples). Lyophilization drying technique seems to lead to less shrinkage than HMDS drying. FESEM revealed that collagen fibers of demineralized lyophilized samples are less melted together than in the HMDS-dried samples. Demineralized dentin porosity is a key parameter in dentin bonding that will influence the hybrid layer quality. Its characterization could be helpful to improve the monomers infiltration.
 
The present study aimed at evaluating different restoring configurations of a crownless maxillary central incisor, in order to compare the biomechanical behavior of the restored tooth with that of a sound tooth. A 3D FE model of a maxillary central incisor is presented. An arbitrary static force of 10 N was applied with an angulation of 125 degrees to the tooth longitudinal axis at level of the palatal surface of the crown. Different material configurations were tested: composite, syntered alumina, feldspathic ceramic endocrowns and glass post resorations with syntered alumina and feldspathic ceramic crown. High modulus materials used for the restoration strongly alter the natural biomechanical behavior of the tooth. Critical areas of high stress concentration are the restoration-cement-dentin interface both in the root canal and on the buccal and lingual aspects of the tooth-restoration interface. Materials with mechanical properties underposable to that of dentin or enamel improve the biomechanical behavior of the restored tooth reducing the areas of high stress concentration. The use of endocrown restorations present the advantage of reducing the interfaces of the restorative system. The choice of the restorative materials should be carefully evaluated. Materials with mechanical properties similar to those of sound teeth improve the reliability of the restoartive system.
 
Teeth, adhesively restored with resin-based materials, were modeled by 3D-finite elements analysis that showed a premature failure during polymerization shrinkage and occlusal loading. Simulation of Class II MOD composite restorations with a resin bonding system revealed a complex biomechanical behavior arising from the simultaneous effects of polymerization shrinkage, composite stiffness and adhesive interface strain. Due to a polymerization contraction, shrinkage stress increases with the rigidity of the composites utilised in the restoration, while the cusp movements under occlusal loading are inversely proportional to the rigidity of the composites. The adhesive layer's strain also plays a relevant role in the attenuation of the polymerization and occlusal loading stresses. The choice of an appropriately compliant adhesive layer, able to partially absorb the composite deformation, limits the intensity of the stress transmitted to the remaining natural tooth tissues. For adhesives and composites of different rigidities, FEM analysis allows the determination of the optimal adhesive layer thickness leading to maximum stress release while preserving the interface integrity. Application of a thin layer of a more flexible adhesive (lower elastic modulus) leads to the same stress relief as thick layers of less flexible adhesive (higher elastic modulus).
 
The objectives of this study were to (1) demonstrate X-ray micro-computed tomography (microCT) as a viable method for determining the polymerization shrinkage and microleakage on the same sample accurately and non-destructively, and (2) investigate the effect of sample geometry (e.g., C-factor and volume) on polymerization shrinkage and microleakage. Composites placed in a series of model cavities of controlled C-factors and volumes were imaged using microCT to determine their precise location and volume before and after photopolymerization. Shrinkage was calculated by comparing the volume of composites before and after polymerization and leakage was predicted based on gap formation between composites and cavity walls as a function of position. Dye penetration experiments were used to validate microCT results. The degree of conversion (DC) of composites measured using FTIR microspectroscopy in reflectance mode was nearly identical for composites filled in all model cavity geometries. The shrinkage of composites calculated based on microCT results was statistically identical regardless of sample geometry. Microleakage, on the other hand, was highly dependent on the C-factor as well as the composite volume, with higher C-factors and larger volumes leading to a greater probability of microleakage. Spatial distribution of microleakage determined by microCT agreed well with results determined by dye penetration. microCT has proven to be a powerful technique in quantifying polymerization shrinkage and corresponding microleakage for clinically relevant cavity geometries.
 
This investigation describes a rapid method for the generation of finite element models of dental structures and restorations. An intact mandibular molar was digitized with a micro-CT scanner. Surface contours of enamel and dentin were fitted following tooth segmentation based on pixel density using an interactive medical image control system. Stereolithography (STL) files of enamel and dentin surfaces were then remeshed to reduce mesh density and imported in a rapid prototyping software, where Boolean operations were used to assure the interfacial mesh congruence (dentinoenamel junction) and simulate different cavity preparations (MO/MOD preparations, endodontic access) and restorations (feldspathic porcelain and composite resin inlays). The different tooth parts were then imported in a finite element software package to create 3D solid models. The potential use of the model was demonstrated using nonlinear contact analysis to simulate occlusal loading. Cuspal deformation was measured at different restorative steps and correlated with existing experimental data for model validation and optimization. Five different models were validated by existing experimental data. Cuspal widening (between mesial cusps) at 100 N load ranged from 0.4 microm for the unrestored tooth, 9-12 microm for MO, MOD cavities, to 12-21 microm for endodontic access cavities. Placement of an MOD adhesive restoration in porcelain resulted in 100% cuspal stiffness recovery (0.4 microm of cuspal widening at 100 N) while the composite resin inlay allowed for a partial recuperation of cusp stabilization (1.3 microm of cuspal widening at 100 N). The described method can generate detailed and valid three dimensional finite element models of a molar tooth with different cavities and restorative materials. This method is rapid and can readily be used for other medical (and dental) applications.
 
The objective was to compare equivalent stresses in molars restored with endocrowns as well as posts and cores during masticatory simulation using finite element analysis. Four three-dimensional models of first mandibular molars were created: A - intact tooth; B - tooth restored by ceramic endocrown; C - tooth with FRC posts, composite core and ceramic crown; D - tooth with cast post and ceramic crown. The study was performed using finite element analysis, with contact elements. The computer simulations of mastication were conducted. The equivalent stresses of modified von Mises failure criterion (mvM) in models were calculated, Tsai-Wu index for FRC post was determinate. Maximal values of the stresses in the ceramic, cement and dentin were compared between models and to strength of the materials. Contact stresses in the cement-tissue adhesive interface around restorations were considered as well. During masticatory simulation, the lowest mvM stresses in dentin arisen in molar restored with endocrown (Model B). Maximal mvM stress values in structures of restored molar were 23% lower than in the intact tooth. The mvM stresses in the endocrown did not exceed the tensile strength of ceramic. In the molar with an FRC posts (Model C), equivalent stress values in dentin increased by 42% versus Model B. In ceramic crown of Model C the stresses were 31% higher and in the resin luting cement were 61% higher than in the tooth with endocrown. Tensile contact stresses in the adhesive cement-dentin interface around FRC posts achieved 4 times higher values than under endocrown and shear stresses increased twice. The contact stress values around the appliances were several time smaller than cement-dentin bond strength. Teeth restored by endocrowns are potentially more resistant to failure than those with FRC posts. Under physiological loads, ceramic endocrowns ideally cemented in molars should not be demaged or debonded.
 
Dentin, a calcareous material sandwiched between the pulp and the enamel in the tooth structure contains highly orientated tubules. As a result of enamel erosion, gum recession, physical trauma or caries the dentin tubules can become patent to the oral cavity. It has been demonstrated in vivo that dentinal fluid flows out of the tubule lumen into the oral cavity and it has been postulated that alterations in fluid flow form the basis of dentin hypersensitivity. In order to better understand the mode of action of desensitising occlusion-based agents the ability to interrogate dentin non-destructively is paramount. Destructive analysis of the tooth structure may yield subtle artifacts leading to erroneous conclusions or inhibit the accurate assessment of the relationship between an occluding agent and the internal dentin morphology. This paper describes the use of a novel and accessible, non-invasive, high-focused X-ray computer tomographic technique for analysis of the dentin substructure. Dentin slices, ca. 300microm3 in size, were taken from the coronal section of unerupted human third molars and etched in citric acid to reveal the open tubule structure. Samples were analyzed, in their dry state, using the Skyscan 2011 nanoCT system. Numerous, homogeneously dispersed elliptical features, distinguished by their contrast and hence low-mineral density, were observed. These features are observed to be approximately 2-5microm in diameter at a density equivalent to 10(6)cm(-2). 2D CT re-slices demonstrate that these circular features form highly orientated cylindrical manifestations extending throughout the sample. Ultra-high-resolution X-ray computed tomography has been shown to be a powerful new technique for interrogating the submicron tubular structure of dentin non-destructively.
 
Objective: The objective of this research was to study the polymerization shrinkage in a dental composite using 3D digital image correlation (DIC). Methods: Using 2 coupled cameras, digital images were taken of bar-shaped composite (Premise Universal Composite; Kerr) specimens before light curing and after for 10 min. Three-dimensional DIC was used to assess in-plane and out-of-plane deformations associated with polymerization shrinkage. Results: The results show the polymerization shrinkage to be highly variable with the peak values occurring 0.6-0.8mm away from the surface. Volumetric shrinkage began to significantly decrease at 3.2mm from the specimen surface and reached a minimum at 4mm within the composite. Approximately 25-30% of the strain registered at 5 min occurred after light-activation. Application of 3D DIC dental applications can be performed without the need for assumptions on the deformation field. Significance: Understanding the local deformations and strain fields from the initial polymerization shrinkage can lead to a better understanding of the composite material and interaction with surrounding tooth structure, aiding in their further development and clinical prognosis.
 
A comparative study on the stress distribution in the dentine and cement layer of an endodontically treated maxillary incisor has been carried out by using Finite Element Analysis (FEA). The role of post and cement rigidity on reliability of endodontic restorations is discussed. A 3D FEM model (13,272 elements and 15,152 nodes) of a central maxillary incisor is presented. A chewing static force of 10 N was applied at 125 degree angle with the tooth longitudinal axis at the palatal surface of the crown. Steel, carbon and glass fiber posts have been considered. The differences in occlusal load transfer ability when steel, carbon and glass posts, fixed to root canal using luting cements of different elastic moduli (7.0 and 18.7 GPa) are discussed. The more stiff systems (steel and carbon posts) have been evaluated to work against the natural function of the tooth. Maximum Von Mises equivalent stress values ranging from 7.5 (steel) to 5.4 and 3.6 MPa (respectively, for carbon posts fixed with high and low cement moduli) and to 2.2 MPa (either for glass posts fixed with high and low cement moduli) have been observed under a static masticatory load of 10 N. A very stiff post works against the natural function of the tooth creating zones of tension and shear both in the dentine and at the interfaces of the luting cement and the post. Stresses in static loading do not reach material (dentine and cement) failure limits, however, they significantly differ leading to different abilities of the restored systems to sustain fatigue loading. The influence of the cement layer elasticity in redistributing the stresses has been observed to be less relevant as the post flexibility is increased.
 
Top-cited authors
Paul Lambrechts
Frank Tay
  • Augusta University
Bart Van Meerbeek
David C Watts
  • The University of Manchester
Albert Feilzer
  • University of Amsterdam