Development of dual-curing type experimental composite resin cement for orthodontic bonding -effect of additional amount of accelerators on the mechanical properties-.

In this study, a dual-curing type composite resin cement that included a photo-initiator and two accelerators was designed. In particular, special emphasis was made on addressing questions on the effects from different amounts of additional accelerators on the flexural strength of the designed experimental composite resin cement, as well as on the tensile bond strength of the bracket bonded onto the enamel surface by the experimental composite resin cement. When 0.25 mass% of the p-tolydiethanolamine and sodium p-toluenesulfinate were added, the maximum flexural strength was obtained for the chemical-cured and dual-cured experimental composite resin cement. The dual-cured experimental composite resin cement's flexural strength value was in the mid-range of the values exhibited from the commercial resin cements. However, the dual-cured experimental composite resin cement exhibited noticeably high tensile bond strength when compared with the results obtained with the commercial resin cements.

Characterization of sintered TCP sheets with various contents of binder prepared by tape-casting technique.

OBJECTIVES: The purpose of this study was to investigate the effect of binder content on the characterization of sintered tricalcium phosphate (TCP) sheets prepared by the tape-casting technique. METHODS: Poly(acrylic acid)-based binder was added at four contents: 5, 10, 15, or 30 mass%, to a beta-TCP aqueous slurry. The TCP green sheets were fabricated with the prepared TCP slurry by the tape-casting technique, and were sintered at 1200 degrees C for 2h. The sintered TCP sheets were characterized by field-emission scanning electron microscope (FE-SEM) observation, X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectrometry. Apatite precipitation on the sintered TCP sheet surface in Hanks' balanced salt (HBS) solution at pH 7.4 was monitored over 14 days at 37 degrees C. RESULTS: A TCP green sheet with 5 mass% binder content had insufficient flexibility before sintering, and that with 30 mass% binder content had a problem in controlling the viscosity of slurry. FE-SEM observation showed that no differences in grain size existed in the various sintered TCP sheets. Measurement of XRD and FT-IR showed the presence of alpha-TCP phase in the various sintered TCP sheets, and same crystallographic structure was observed among various sintered TCP sheets. After 14 days immersion in HBS solution, the surfaces of sintered TCP sheets were completely covered with precipitated apatite crystals. SIGNIFICANCE: The binder content of 10 or 15 mass% is suitable for sintering TCP sheets. The sintered TCP sheet prepared by the tape-casting technique is a promising material as bone substitute.

NMR study on the adhesion efficacy of experimental phosphonic acid monomers.

Three experimental self-etching primers - consisting of N-methacryloyl-omega-aminoalkyl phosphonic acid (NMomegaP) with different methylene chain lengths and N-methacryloyl glycine (NMGly) - were formulated. The influence of methylene chain length in NMomegaP derivatives on the chemical nature of calcium salts was examined following their application to tooth components. Bond strengths of experimental self-etching primers created with these monomers to enamel and dentin were also investigated. Nuclear magnetic resonance spectroscopy showed that NMomegaPs decalcified tooth components with formation of calcium salts, which changed from calcium hydrogen phosphonate to calcium phosphonate with increase in methylene chain length within the NMomegaP structure. Disparity in calcium salt formation was related to increases in bond strength to enamel from 18 to 24 MPa. However, bond strength to dentin remained unchanged (22 MPa). The relative dependency of bond strength on monomer methylene chain length was probably attributable to the sites where these NMomegaP calcium salts had deposited on the bonding substrates.

Characterization and bioactivity of tape-cast and sintered TCP sheets.

The purpose of this study was to investigate the influence of sintering temperature on in vivo and in vitro bioactivities of sintered tricalcium phosphate (TCP) sheets prepared by the tape casting technique. Green sheets of beta-TCP prepared by tape casting were sintered for 2 h in a furnace at atmospheric pressure, at five different sintering temperatures: 900, 1000, 1100, 1150, and 1200 degrees C. Measurement of X-ray diffraction and Fourier transform infrared spectrometry showed the presence of alpha-tricalcium phosphate phase in the TCP sheet sintered at 1200 degrees C, in addition to beta-TCP phase. As compared with the other sintered TCP sheet, the TCP sheet sintered at 1200 degrees C demonstrated a lower dissolution rate in phosphate buffered saline solution at 37 degrees C and pH 7.4 over 24 weeks, and more amount of apatite formation in Hanks' balanced salt solution with pH 7.4 was observed. After 4 weeks' implantation of sintered TCP sheets into tibial diaphyses of rabbits, the bone-sheet contact of the TCP sheet sintered at 1200 degrees C was significantly higher than that of the TCP sheet sintered at 900 degrees C. These results indicate that a flat sintered TCP sheet prepared by tape casting is a promising material for a bone substitute.

Trabecular bone response to titanium implants with a thin carbonate-containing apatite coating applied using the molecular precursor method.

PURPOSE: The influence of thin carbonate-containing apatite (CA) coating on the trabecular bone response to titanium implants was investigated. MATERIALS AND METHODS: Thin CA coatings were deposited by a new method known as the molecular precursor method. Using a precursor solution composed of an EDTA-calcium complex, a CA film was deposited on the titanium surfaces. Uncoated and CA-coated titanium were placed in the trabecular bone of the left and right femoral condyles of 16 rabbits. After implantation periods of 2, 4, 8, and 12 weeks, the bone-implant interface was evaluated histologically and histomorphometrically. RESULTS: Histologic evaluation revealed new bone formation around the uncoated and CA-coated implant surfaces after only 4 weeks of implantation. After 12 weeks, mature trabecular bone surrounded all implants. At 4 and 8 weeks of implantation, no difference existed in bone contact between uncoated and CA-coated implants. After 12 weeks of implantation, the CA-coated implant group showed a significantly higher percentage of bone contact than the uncoated implant group. DISCUSSION AND CONCLUSION: The present study demonstrated that thin CA coatings applied using the molecular precursor method showed greater bone-to-implant contact during the healing phase than uncoated controls. The results were similar to those observed with implants with calcium phosphate coatings deposited with a physical vapor deposition technique.

Dynamic viscoelastic behavior of dental composites measured by Split Hopkinson pressure bar.

The present study evaluated the dynamic viscoelastic behavior of commercially available dental composites by a Split Hopkinson pressure bar (SHPB) test machine. Five commercially available composite resins--namely, two conventional hybrid composites (Filtek Z100, Z100; Filtek Z250, Z250), a packable composite (Filtek P60, P60), a flowable composite (Filtek Flow, FL), and a nanofill composite (Filtek Supreme, SU)--were evaluated. By means of SHPB technique, the dynamic stress-strain curve, storage modulus, and loss tangent of the five dental composites were calculated. All specimens exhibited a nonlinear stress-strain curve in the loading process, which resulted not only from the viscoelasticity--but also from the plasticity--of matrix. In terms of storage modulus, no significant differences were exhibited among the five dental composites (p > 0.05). In terms of loss tangent, Z100 showed a significantly higher value than P60, FL, and SU (p < 0.05). Within the limitations of this investigation using SHPB, it was indicated that the loss tangent increased with increasing filler content.

Mode superposition transient dynamic analysis for dental implants with stress-absorbing elements: a finite element analysis.

The purpose of this study was to analyze the dynamic behavior of a dental implant with a stress-absorbing element, using dynamic analysis. Two model types, stress-absorbing model with a resilient stress absorber made of polyoxymethylene and non-stress-absorbing model with rigid titanium, were employed. In both model types, the implant was 4.0 mm in diameter and 13.0 mm in length and placed in the mandibular first molar region. Shapes of the finite element implant and implant-bone were modeled using computer-aided design. All calculations for the dynamic analysis were performed using the finite element method. It was found that the stress-absorbing model had a lower natural frequency than the non-stress-absorbing model. In addition, the stress-absorbing model had a higher damping effect than the non-stress-absorbing model. It was concluded that mode superposition transient dynamic analysis is a useful technique for determining dynamic behavior around dental implants.

Non-linear finite element analysis of the failure progression of fiber-reinforced ceramics produced by tape casting technique.

The purpose of this study was to investigate the failure progression process of fiber-reinforced ceramic by finite element (FE) analysis. The three-dimensional FE model for three-point bending simulation was 40 mm long, 4 mm wide, 3 mm thick, and with a span length of 30 mm. Nodal force with load increment of 20 N was applied at the center of the upper surface of the beam. To evaluate matrix fracture and fiber fracture, von Mises criterion and Tsai-Hill criterion were used respectively. Consequently, the stress-deflection curve obtained from FE simulation agreed with that obtained from the experimental testing. Differences in flexural strength and modulus between the analytical and experimental results were 1.3 and -2.9% respectively--demonstrating a close agreement between both results. In conclusion, the FE model applied in the present study was shown to be valid for predicting the failure progression of fiber-reinforced ceramics.

[Effectiveness of methacrylamide monomer for dentin bonding].

PURPOSE: In this study, we investigated the conditioning efficacy of a self-etching primer consisting of methacrylamide, N-methacryloyl-omega-amino acid (M omega A) derivatives for enhancing the bond strength of resin to crown and root dentins. METHODS: A series of four M omega A derivatives, with different methylene chain numbers, were synthesized, as follows. 1: N-methacrylole glycine (Gly); 2: N-methacrylole-beta-alanine (beta Ala); 3: N-methacrylole-4-aminobutyric acid (Bu); 4: N-methacrylole-5-aminovaleric acid (Va). The dissociation equilibrium pH (pKa) of carboxylic acid in each of the M omega A derivatives was determined. The shear bond strengths of resin to the crown and root dentins, primed with the Gly solution were measured for various conditioning times. We also measured the bond strength to both the dentins following application of the M omega A adhesives with different pKa values for 30 seconds. RESULTS: For the Gly primer, the bond strength of resin to both dentins increased with the conditioning time until 30 seconds, leveled off thereafter by increase in the methylene chain number. The effects of conditioning time on the bond strength to the crown and the root dentin were the same. Furthermore, the bond strengths to the dentins, conditioned with each of the four M omega A derivatives for 30 seconds, were the same, even though the decalcified amounts of the dentin apatite noted following conditioning with Bu and Va were lower than that noted following conditioning with Gly. This was attributed to the pKa value of the acidic groups in the acidic monomer directly relating to the decalcified amount of dentin apatite. CONCLUSIONS: Application of the M omega A solutions, resulted in an increase in the bond strength of resin to both crown and root dentins. In particular, the Bu and Va primers were very useful as primers promoting the bond of resin to dentin, since the etching potential was very low.

The effect of hydrophilic adhesive monomers on the stability of type I collagen.

The adsorption effects of adhesive monomers on the structural stability of type I collagen were studied at an acid pH condition for two monomers: 2-hydroxyethyl methacrylate (HEMA), a neutral monomer and N-methacryloyl glycine (NMGly), an acidic monomer. Differential scanning calorimetry (DSC) measurements were done to assess the denaturation temperature (Td), which is a measure of the structural stability of the proteins, including the bovine tendon collagen (BTC). While HEMA lowered the Td of the BTC linearly with HEMA concentrations, NMGly exhibited a two-step decrease of the Td. The rate of decrease in the Td by the NMGly was by far greater than the rate of decrease with the HEMA. The first step had a larger slope than the second step in the Td vs. CNMGly plot. The degree of adsorption of these two monomers to the BTC was estimated from infrared absorption measurements on the monomer solutions of various concentrations, before and after the immersion of the BTC. Both the adsorption of HEMA to the BTC and the Td of the BTC were linearly dependent on HEMA concentrations. Conversely, NMGly was adsorbed to the BTC, again, in a two-step decrease similar to the Td vs. CNMGLy profile. An enhanced adsorption of NMGly, which might be attributed to a strong electrostatic interaction, was observed below 0.013 mol%. Circular dichroism measurements of the collagen of the same type as the BTC, in the absence and in the presence of the monomers, revealed that the native collagen helix structure was scarcely affected by the monomers. From these observations, it was concluded that (1) both of the monomers were adsorbed onto the BTC, which thus destabilized the triple helical collagen structure, and that (2) the effect was higher for NMGly in which the electrostatic attraction with the oppositely charged collagen might be effective at a pH of 3. If compared to HEMA, an acidic NMGly is a potential monomer that binds strongly to collagen and one that is hardly hydrolyzed.

Efficacy of varying the NMEP concentrations in the NMGly-NMEP self-etching primer on the resin-tooth bonding.

It is well understood that the application of a self-etching primer enhances the bonding at the resin-teeth interface. In this study, we designed a self-etching primer consisting of N-methacryloyl glycine (NMGly) and N-methacryloyl-2-aminoethyl phosphonic acid (NMEP). The demineralization effects on the hydroxyapatite or dentin by the carboxylic acid in the NMGly and by the phosphonic acid in the NMEP and their effects on the bond strength of the resin to the tooth were examined. The application of the NMGly-NMEP solution to the enamel resulted in an increase in the bond strength when additional amounts of NMEP were added to the NMGly aqueous solution. This increase was due to the phosphonic acid in the NMEP demineralizing the enamel. Conversely, the addition of the NMEP to the NMGly solution resulted in a decrease in the bond strength to the dentin. The optimal concentration of the NMEP in the NMGly-NMEP solution resulted in bond strengths of over 20 MPa for both the enamel and dentin.

Tape-casting technique can prepare beta-TCP sheets with uniform thickness and flexibility.

The objective of this study is to propose a new fabrication technology for bone substitutes. In this study, a tape-casting method was used to prepare flexible beta-tricalcium phosphate (beta-TCP) sheets. A beta-TCP slurry containing a binder and plasticizer was used in a doctor blade system. The beta-TCP sheet obtained by this tape-casting method was highly flexible, enabling twisting and free-form shaping. The beta-TCP sheet was approximately 0.21 mm thick. X-ray diffraction and Fourier transform infrared spectrometry revealed that the structure of the beta-TCP component in the sheet is the same as that of the original beta-TCP powder. Observation by field-emission scanning electron microscopy showed that the beta-TCP sheet had a flat, microgranular surface. During the early stages, the tensile stress-strain curves of the beta-TCP sheet showed a nonlinear behavior until reaching the point of final fracture. This result was derived from the ductile property of the prepared beta-TCP sheet. In conclusion, a flexible beta-TCP sheet was easily prepared using a tape-casting technique. Fabrication using tape casting offers the advantages of enabling the preparation of ceramic sheets with precise thickness and not requiring expensive fabrication facilities.

Analysis of photopolymerization behavior of UDMA/TEGDMA resin mixture and its composite by differential scanning calorimetry.

The aim of this study was to investigate the extent of polymerization (Ep) in terms of polymerization rate of UDMA/TEGDMA resin mixtures and its composite resin, by using a differential scanning calorimeter (DSC) technique employing a photopolymerization apparatus. The resin mixtures used in this study consisted of urethane dimethacrylate (UDMA) as a base monomer and triethyleneglycol dimethacrylate (TEGDMA) as a low viscosity monomer. The concentration of TEGDMA in the mixed monomer was varied to 0, 20, 40, 60, 80, and 100 mol %. Additionally, using a base monomer consisting of 60 mol % UDMA and 40 mol % TEGDMA, four kinds of composites with silica filler of 0, 20, 40, 60, and 70 wt %, were prepared in this study. The general reaction profile and Ep values were obtained from the DSC curves. Increasing the concentration of TEGDMA resulted in a decrease in the viscosity of the UDMA/TEGDMA mixture, a delay in the time to maximum polymerization rate, and an increase in the Ep values of the resin mixtures. Furthermore, Ep values decreased with increasing filler content between 0 and 60 wt % but did not decrease further between 60 and 70 wt %.

Influence of implant/abutment joint designs on abutment screw loosening in a dental implant system.

The objective of this study was to investigate the influence of implant/abutment joint designs on abutment screw loosening in a dental implant system, using nonlinear dynamic analysis of the finite element method (FEM). This finite element simulation study used two dental implant systems: the Ankylos implant system (Degusa Dental, Hanau, German) with a taper joint (taper joint-type model), and the Bränemark implant system (Nobel Biocare, Gothenburg, Sweden) with an external hex joint (external hex joint-type model). The nonlinear dynamic analysis was performed using three-dimensional finite element analysis. In comparing the movement of the taper type-joint model and external hex type-joint model, it was found that the external hex type-joint model had greater movement than the taper type-joint model. The external hex joint-type model showed rotation movement, whereas the movement of the taper joint-type model showed no rotation. It was concluded that the nonlinear dynamic analysis used in this study clearly demonstrated the differences in rotation of components in dental implant systems with taper or external hex joints.

Efficacy of water-soluble photoinitiator on the adhesion of composite resin to bovine teeth in all-in-one bonding system.

The self-etching primer adhesives examined in the present study were aqueous mixtures of 30 wt% 2-methacryloyloxyethyl phenyl hydrogen phosphate, 35 wt% 2-hydroxyethyl methacrylate, and photoinitiator. For the photoinitiator, camphorquinone (CQ) or 2-hydroxyl-3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N,N,N-trimethyl-1-propanaminium chloride (QTX) was used--where QTX is a unique water-soluble photoinitiator. The self-etching primer adhesive was applied directly to polished bovine dentin or enamel. Tensile bond strength of flowable composite resin to bovine teeth was measured after one-day immersion in water at 37 degrees C. The addition of QTX tended to increase tensile bond strength to dentin, whereby addition of 3 wt% of QTX produced the highest mean bond strength of approximately 10 MPa. CQ, on the other hand, did not show any efficacy in improving bond strength. For enamel bonding, there were no significant differences in bond strength between CQ and QTX. In conclusion, QTX was effective in improving the bond strength of composite resin to dentin in an all-in-one bonding system.

Influence of cortical bone quality on stress distribution in bone around dental implant.

Using finite element method (FEM), this study sought to investigate how the thickness and Young's modulus of cortical bone influenced stress distribution in bone surrounding a dental implant. The finite element implant-bone model consisted of a titanium abutment, a titanium fixture, a gold alloy retaining screw, cancellous bone, and cortical bone. The results showed that von Mises equivalent stress was at its maximum in the cortical bone surrounding dental implant. Upon investigation, it was found that maximum von Mises equivalent stress in bone decreased as cortical bone thickness increased. On the other hand, maximum von Mises equivalent stress in bone increased as Young's modulus of cortical bone increased. In conclusion, it was confirmed that von Mises equivalent stress was sensitive to the thickness and Young's modulus of cortical bone.

Effect of base monomer's refractive index on curing depth and polymerization conversion of photo-cured resin composites.

In this study, we examined the effect of the transmitted amount of visible light through a resin composite on the curing depth and polymerization conversion. Transmitted amount of visible light was strongly dependent on the magnitude of refractive index difference that existed between the resin and silica filler. More specifically, the differences arose from the type of base monomer used. The transmitted amount of visible light exhibited a good correlation with the curing depth and Knoop hardness ratio of the bottom surface against the top surface of the resin composite. To improve the polymerization conversion of the cavity floor, it is important to reduce the refractive index difference that exists between the base resin and silica filler.

Development of self-etching primer adhesive in all-in-one bonding system.

The self-etching primer adhesives examined in the present study were aqueous mixtures of 5 wt% MDP, 35 wt% HEMA, 3 wt% 2-hydroxyl-3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N,N,N-trimethyl-1-propanaminium chloride (QTX), 0.5 wt% ethyl-p-(N,N-dimethylamino)benzoate (EDM), and 30 wt% water-soluble dimethacrylate (i.e., 2,2-bis(4-methacryloxy polyethoxypheny)propane (BPE), Glycerol dimethacrylate (GMR), or Glycerol methacrylate acrylate (GAM)). Self-etching primer adhesive was directly applied to polished bovine teeth. Tensile bond strength of composite resin to bovine teeth was measured after one-day immersion in water at 37 degrees C. Differences in water-soluble dimethacrylate monomer did not produce any significant differences in tensile bond strength to dentin or enamel. The use of N-phenyliminodiacetic acid (PIDAA) instead of EDM showed significantly higher bond strength to dentin and enamel. In conclusion, GMR and GAM were useful as water-soluble dimethacrylates while the combination of PIDAA and QTX was effective in improving the bond strength of composite resin to teeth in an all-in-one bonding system.

Effect of acidic primers on bonding three magnetic steel alloys with tri-n-butylborane initiated methacrylic resin.

The purpose of this study was to evaluate the effect of acidic primers on bonding magnetic steel alloys. Three alloys (XM27, 447J1, and AUM20) were primed with one of the following materials: Acryl Bond, Estenia Opaque Primer, Eye Sight Opaque Primer, M. L. Primer, or Super-Bond liquid. The specimens were bonded with a tri-n-butylborane initiated resin, and bond strength was determined both before and after thermocycling in water. Unprimed specimen was considered as the control. Average bond strength varied from 0 to 45.3 MPa for the XM27 alloy, 0.3 to 43.6 MPa for the 447J1 alloy, and 0.5 to 41.1 MPa for the AUM20 alloy. Of the five primers, Estenia Opaque Primer exhibited better adhesive performance than the other materials regardless of the type of steel alloy. It can be concluded that the use of the Estenia Opaque Primer, which contains an adhesive monomer (10-methacryloyloxydecyl dihydrogen phosphate; MDP), is recommended for bonding the three magnetic steel alloys with TBB-initiated resin.

Characterization and protein-adsorption behavior of deposited organic thin film onto titanium by plasma polymerization with hexamethyldisiloxane.

Plasma polymerized hexamethyldisiloxane (HMDSO) thin film was deposited onto titanium using a radio-frequency apparatus for the surface modification of titanium. A titanium disk was first polished using colloidal silica at pH=9.8. Plasma-polymerized HMDSO films were firmly attached to the titanium by heating the titanium to a temperature of approximately 250 degrees C. The thickness of the deposited film was 0.07-0.35mum after 10-60min of plasma polymerization. The contact angle with respect to double distilled water significantly increased after HMDSO coating. X-ray photoelectron spectroscopy revealed that the deposited thin film consisted of Si, C, and O atoms. No Ti peaks were observed on the deposited surface. The deposited HMDSO film was stable during 2-weeks immersion in phosphate buffer saline solution. Fourier transform reflection-absorption spectroscopy showed the formation of Si-H, Si-C, C-H, and Cz.dbnd6;O bonds in addition to Si-O-Si bonds. Quartz crystal microbalance-dissipation measurement demonstrated that the deposition of HMDSO thin films on titanium has a benefit for fibronectin adsorption at the early stage. In conclusion, plasma polymerization is a promising technique for the surface modification of titanium. HMDSO-coated titanium has potential application as a dental implant material.