Julie L P Jessop

University of Iowa, Iowa City, Iowa, United States

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Publications (19)29.66 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Purpose: To directly test the effectiveness of ethanol-wet bonding (EW) in improving monomer infiltration into demineralized dentin through quantitative measurement of bis-GMA and TEG-DMA molar concentrations within hybrid layers, and to comprehensively evaluate the effect of EW and chlorhexidine on durability of resin-dentin bonds compared to conventional water-wet bonding (WW). Materials and Methods: A three-step etch-and-rinse adhesive (70% bis-GMA/28.75%TEG-DMA) was applied to coronal dentin using a clinically relevant ethanol-wet bonding protocol (EW) or the conventional water-wet bonding (WW) technique. Bis-GMA and TEG-DMA molar concentrations at various positions across the resin/dentin interfaces formed by EW and WW were measured using micro-Raman spectroscopy. The experiment was repeated at the same positions after 7-month storage in phosphate buffer solution containing 0.1% sodium azide. The μTBS and hybrid layer morphology (TEM) of bonding groups with and without chlorhexidine application were compared immediately and after 1-year storage in terms of nanoleakage, collagen fibril diameter, collagen interfibrillar width, and hybrid layer thickness. Results: Specimens bonded with EW showed significantly higher monomer molar concentrations and μTBS throughout the hybrid layer immediately and after storage, providing direct evidence of superior infiltration of hydrophobic monomers in EW compared to WW. Microscopically, EW maintained interfibrillar width and hybrid layer thickness for resin infiltration and retention. The application of chlorhexidine further preserved collagen integrity and limited the degree of nanoleakage in EW after 1-year storage. Conclusion: EW enhances infiltration of hydrophobic monomers into demineralized dentin. The results suggest that a more durable resin-dentin bond may be achieved with combined usage of a clinically relevant EW and chlorhexidine.
    The journal of adhesive dentistry 09/2014; · 0.91 Impact Factor
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    ABSTRACT: Objective: To assess the effects of ceramic opacity and thickness on delivered irradiance and energy density and degree of conversion and microhardness of the light-cured resin cement. Method: IPS e-Max ceramic discs (Ivoclar Vivadent) were fabricated in 3 thicknesses (0.5, 1.0, and 1.5mm) and 4 opacities (HT, LT, MO, HO) (n=3/per group). Light-cured resin cement (Variolink Veneer Luting Cement – shade MVO, Ivoclar Vivadent) 50µm thick was cured through these ceramics disks using a halogen curing light unit (Optilux 501, Kerr) with its energy density and irradiance measured by MARC from a fixed distance (1.5mm). Knoop hardness and Raman microscopy were used to evaluate the bottom degree of cure. Descriptive statistics were conducted. One- and two-way ANOVA with post-hoc Tukey’s HSD test and Pearson correlation test were used for the statistical analyses (alpha=0.05). Result: Significant interaction was found between ceramic thickness and opacity on resin cement degree of conversion (p<0.0001), irradiance (p=0.0062), and energy density (p=0.0078). Subsequent analyses demonstrated that there was a significant simple effect for opacity and for thickness on conversion, irradiance and energy density under different conditions of thickness and opacity. Although the curing unit used has relatively good beam homogeneity, no significant correlation was found between hardness and degree of conversion (r=0.03; p=0.8859) unless data collection locations of Raman and Knoop Hardness were taken in close proximity (R2= 0.9, p=0.0006). The calibration curve representing this correlation will be used in the final data collection. Conclusion: Ceramic opacity and thickness affect the polymerization of light-cured resin cements and need to be considered and compensated for when bonding indirect restorations. Based upon the findings of this preliminary study, the final study is ongoing.
    AADR Annual Meeting & Exhibition 2014; 03/2014
  • Brian Dillman, Julie L. P. Jessop
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    ABSTRACT: The effects of chain transfer agents (CTA) on cationic ring-opening polymerization of 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate (EEC) were explored. EEC was polymerized in the presence of various CTAs, and epoxide conversions monitored via Raman spectroscopy. Polymer films were prepared and analyzed by dynamic mechanical analysis. Many of the organic alcohols studied greatly enhanced epoxide polymerization rates and conversion levels. The gel fraction of polymer specimens decreased rapidly with increasing amounts of octanol (gel fraction >90% up to 0.3 equiv OH) but remained high with increasing amounts of 1,2-propanediol (gel fraction >90% up to 0.6 equiv OH). Increasing the size of primary alcohols had little effect on the polymerization rates and conversions. The polymerization rate decreased with increasing alcohol substitution (1°>2°>3°). Acidic alcohols had very low impact on conversion and polymerization rates relative to the neat epoxy resin. The glass transition temperature was inversely related to the size and amount of CTA. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
    Journal of Polymer Science Part A Polymer Chemistry 05/2013; 51(9):2058-2067. · 3.54 Impact Factor
  • Brian F. Dillman, Na Yeon Kang, Julie L.P. Jessop
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    ABSTRACT: A simple, low environmental impact procedure for preparing acrylated castor oil (ACO) was developed using a hybrid acrylate isocyanate monomer. The photopolymerization of neat ACO and the co-polymerization of ACO with common low molecular weight acrylate monomers were rapid and reached high conversions, as monitored by real-time FT-IR spectroscopy. The mechanical properties of the ACO polymers and copolymers were determined by dynamic mechanical analysis of the thin polymer films. The resulting copolymers ranged from highly flexible, low glass transition materials to rigid, high glass transition materials depending on the functionality and secondary functional groups of the commercial monomers used. The ACO oligomer was compatible with a variety of acrylate monomers and produced transparent films regardless of co-monomer used. The glass transition temperatures of the copolymers can be coarsely estimated a priori using the Fox correlation. ACO-based materials provide a promising route to introduce renewable materials in many acrylate-based coating applications.
    Polymer. 03/2013; 54(7):1768–1774.
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    ABSTRACT: Ethanol-wet bonding (EW) was proposed to increase the strength and durability of the resin-dentin bond by producing a more hydrolytic resistant hybrid layer (HL) via increased infiltration of hydrophobic monomers into the acid-etched dentin. Objectives: The aim of this study is to evaluate effect of EW on same-day and 7-month molar concentration (MC) of BisGMA and TEGDMA in HL. Methods: Experimental co-monomers were prepared to construct calibration curves for MC calculation in resin-dentin bond specimens. Eight sound human molars were randomly and systematically rotated for EW and water-wet bonding (WW) treated surfaces. All teeth were flattened with a carbide bur in the CNC Specimen Former (University of Iowa) to expose coronal dentin. Sticky wax was used to build 2-mm wall on top of the midline cut to separate each tooth into 2-halves treated with EW and WW. For EW, the etched and water rinsed dentin was subsequently rinsed with absolute ethanol for 15s X 3 before primer (50%resin/50%ethanol) application. After solvent removal, pure adhesive (71%Bis-GMA/28%TEGDMA) was applied and 2-mm resin-based composite (Z100, 3M ESPE) built-up. Two 1-mm-thick resin-dentin slabs were formed per tooth and polished using a series of diamond suspensions. On each side of slabs, two locations with 3μm-thick HL were randomly selected on EW and WW treated surfaces. At each location, Raman spectra were obtained at 5 positions across the resin-dentin interface (n=64) through 100x objective lens using 8-11mW from 785 nm laser (1.5μm spot size) for 60s (micro-Raman Spectroscopy, Kaiser Optical System, Inc.). Peak area at 605 and 1610 cm-1 were used for MC calculation. Resin-dentin slabs were stored for 7-month at 37C in PBS before re-collecting the data at the same positions. Results: Positions Short-term BisGMA MC(mol/L) Short-term TEGDMA MC(mol/L) EW Mean(±SD) WW Mean(±SD) EW Mean(±SD) WW Mean(±SD) Adhesive layer 1.69A* 1.69A* 1.19(±0.62)A 1.43(±0.90)A* Adhesive-HL interface (AHI) 1.17(±0.34)A* 1.00(±0.40)B* 0.97(±0.62)A* 0.81(±0.57)A HL (1μm below AHI) 0.82(±0.30)A 0.59(±0.35)B* 0.67(±0.49)A* 0.57(±0.47)A HL (2μm below AHI) 0.56(±0.32)A* 0.33(±0.24)B* 0.42(±0.26)A* 0.39(±0.45)A* HL-tooth interface 0.35(±0.25)A* 0.20(±0.23)B* 0.30(±0.42)A* 0.17(±0.22)B* Means with the same letters showed no significant difference of BisGMA or TEGDMA MC between EW and WW (p>0.05). (*) indicates significant reduction of the mean BisGMA or TEGDMA MC after 7-month at each position within each bonding group (p<0.05). Conclusion: EW enhances infiltration (increased MC) of hydrophobic monomers into demineralized dentin.
    IADR/AADR/CADR General Session and Exhibition 2013; 03/2013
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    ABSTRACT: Adequate degree of conversion (DC) of resin adhesives is critical to resin-dentin bond strength and clinical durability. Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) is a promising alternative photoinitiator compared to redox initiators based on camphorquinone for resin adhesives. Photoinitiator combinations may provide broader light absorptivity and more reactive radicals with the potential to enhance polymerization. Objectives: Evaluate effect of five photoinitiator systems on DC and resin/composite-dentin shear bond strength (SBS). Methods: DCs of hydrophilic (PMGDM/HEMA) and hydrophobic (BisGMA/TEGDMA) resins containing 5 photoinitiator systems; BAPO, BAPO/benzoyl peroxide (BAPO/BPO), camphorquinone/ethyl-4-dimethylaminobenzoate (CQ/4E), CQ/BAPO, and CQ/BPO were measured at 24-hour by FTIR using Near-infrared (NIR; 1.8mm-thick resins) for both resins and Mid-infrared (Mid-IR;25 micron-thick resins) for BisGMA/TEGDMA (n=5). 50 sound molars were randomly divided into 5 groups by photoinitiator system. All teeth were flattened and ground with #320-grit SiC papers to completely remove coronal enamel before application of a 3-step etch-and-water rinse, primer and bonding resin adhesive (35% phosphoric acid etchant, PMGDM/HEMA/50%acetone primers, and BisGMA/TEGDMA bonding resins) and a commercial resin-based composite (TPH3, Dentsply). SBS (knife-edge chisel-on-iris) was evaluated at 24-hour followed by fracture mode evaluation under a light microscope. Results: Photoinitiators DC at 24h (%) by NIR Mean SBS at 24h (MPa) Bis-GMA/TEGDMA7:3 by mass PMGDM/HEMA 3.3:1 by mass. BAPO (1%) 81.37(±0.52)A,a 76.58(±0.46)B,b 35.31(±6.87)A BAPO (1%) BPO (1%) 81.97(±0.78)A,a 79.20(±0.53)A,b 35.58(±7.56)A CQ (0.25%) 4E (1%) 76.61(±1.08)B,a 67.53(±0.55)C,b 27.22(±9.04)B CQ (0.25%) BAPO (1%) 80.06(±1.84)A,a 76.70(±1.61)B,b 21.17(±5.92)B CQ (0.25%) BPO (1%) 74.35(±0.72)C,a 58.68(±0.78)D,b 14.28(±2.35)C Groups with same upper case letters within columns and same lower case letters within rows are not significantly different (p > 0.05). NIR measured significantly higher DC of BisGMA/TEGDMA resin at 24-hour compared to Mid-IR; BAPO=59(1.6)%, BAPO/BPO=61(1.6)%, CQ/4E=54(1.5)%, CQ/BAPO=62(1.6)%, CQ/BPO=59(0.5)%. No cohesive failures were observed. Groups with lower SBS had a higher percentage of joint failures; while groups with higher SBS had a higher percentage of mixed failure. Conclusion: The use of BAPO alone and in combination with BPO and CQ increased DC of both hydrophobic and hydrophilic resins over resins containing CQ/4E. Only BAPO and BAPO/BPO demonstrated significantly higher SBS over resins containing CQ/4E. Supported by NIST, NIDCR Interagency agreement (Y1-DE-7005), ADAF PRC, and University of Iowa.
    IADR General Session 2011; 03/2011
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    Yuan Zou, Julie L P Jessop, Steven R Armstrong
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    ABSTRACT: Penetration of adhesives into the demineralized dentin surface and their subsequent conversion are critically important to longevity of the adhesive resin (AR)-dentin bond. The durability of the resin-dentin bond is investigated by monitoring the change of adhesive concentration within the hybrid layer (HL) of aged specimens using Raman spectroscopy. Absolute molar concentrations of Bis-GMA and HEMA were measured across the HL of resin-dentin specimens 24 h after photopolymerization and after 24-week storage in one of three media: artificial saliva (SAL), SAL containing cholesterol esterase to attack resin (EST), and SAL containing bacterial collagenase to attack collagen (COL). No significant difference among these groups for both Bis-GMA and HEMA molar concentrations at 24-h storage was found; however, concentrations decreased from the AR to the middle of the HL. Concentrations remained unchanged at any resin-dentin position after aging in SAL. In the HL, concentrations significantly decreased with aging in COL and tended to decrease in EST. While showing potential enzymatic biodegradative effects of endogenous matrix metalloproteinases and salivary esterases, this methodology may also prove to be a valuable assessment of new chemistries and future approaches to improve resin-dentin bond performance. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.
    Journal of Biomedical Materials Research Part A 07/2010; 94(1):187-92. · 2.83 Impact Factor
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    Yuan Zou, Steven R Armstrong, Julie L P Jessop
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    ABSTRACT: The objective was to determine absolute molar concentration of adhesive resin components in the hybrid layer by establishing methods based on Raman spectroscopy fundamentals. The hybrid layer was treated as a three-component system consisting of collagen and an adhesive resin containing two monomers. Adhesive standard specimens and Raman peak area ratios obtained with a 785 nm excitation wavelength were used to construct separate calibration curves for comonomer relative molar concentration and Bis-GMA absolute molar concentration. As collagen and water had no measurable peaks in the fingerprint region, a dilution coefficient K(j) was defined to describe their impact on Raman peak area and to calculate HEMA absolute molar concentration. Methodology was validated using an analogous system containing acetone/ethanol/water. The absolute molar concentration of Bis-GMA and HEMA decreased 87% and 83%, respectively, from the top quarter to the middle of the hybrid layer. Additionally, less Bis-GMA penetrated the hybrid layer than HEMA, as indicated by the approximately 20% decrease in comonomer molar concentration ratio between the adhesive resin layer and the top half of the hybrid layer. Lack of complete monomer infiltration will further challenge dentin-adhesive bond longevity. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.
    Journal of Biomedical Materials Research Part A 02/2010; 94(1):288-97. · 2.83 Impact Factor
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    ABSTRACT: To examine the degree of conversion (DC) of the adhesive interfaces created by Filtek Silorane Adhesive and Clearfil SE Bond using micro-Raman spectroscopy. The adhesives were applied on human dentin in accordance with manufacturer's instructions. Specimens were cut to expose the bonded interfaces to the micro-Raman beam (Ranishaw InVia; laser wl 785 nm). Raman spectra were collected along the dentin/self-etching primer/adhesive interface at 1 microm intervals. The relative intensities of bands associated with mineral (P-O functional group at 960 cm(-1)) and adhesive (C-C-O group at 605 cm(-1)) components within the bonded interface were used to detect monomer penetration into the dentin matrix and to calculate the degree of conversion (C=C at 1640 cm(-1) as reaction peak, C-C-O at 605 cm(-1) as reference peak). Data were statistically analyzed with two-way ANOVA. DC of Filtek Silorane Adhesive was 69+/-7% in the adhesive layer, increasing (p<0.05) to 93+/-5% in the primer and 92+/-9% in the hybrid layer. Clearfil SE Bond showed a DC of 83+/-3% in the hybrid and 85+/-3% in the adhesive layer. Thus, Filtek Silorane Adhesive showed a higher DC than Clearfil SE Bond in the hybrid layer (p<0.05), but a lower DC in the adhesive (p<0.05). As high DC is a fundamental pre-requisite for the stability of the bond over time, this study supports the hypothesis that optimal stability of Filtek Silorane Adhesive can be obtained. However, further research is needed to investigate the mechanical properties of the hybrid layer created by Filtek Silorane Adhesive and its long-term stability.
    Dental materials: official publication of the Academy of Dental Materials 07/2009; 25(9):1178-85. · 2.88 Impact Factor
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    ABSTRACT: Nanoleakage and ultrastructure study suggest that inadequately infiltrated collagen leads to hydrolytic degradation and long-term resin-dentin bond failure. Ethanol-wet bonding as a bonding technique to effectively infiltrate hydrophobic monomers into acid-etched dentin and chlorhexidine as collagen preservation has been proposed to maintain bond integrity. Objectives: To evaluate effect of ethanol-wet bonding (EW) and CHX on same-day and 1 year nanoleakage and collagen morphology. Methods: 6 sound molars were randomly divided into water-wet (WW) and EW groups. All teeth were flattened with a carbide bur to expose coronal dentin. For EW, the etched and water rinsed dentin was subsequently rinsed with absolute ethanol for 15 s X 3 before primer (50% Bis-GMA/TEGDMA/50% ethanol) application. For both EW and WW groups 2% CHX was applied to of the tooth before priming. After solvent removal, pure adhesive (Bis-GMA/TEGDMA) was applied and cured followed by 0.5-mm-thick flowable resin-based composite (Heliomolar, Ivoclar Vivadent). Four 0.5 x 0.5 mm2 resin-dentin beams from each half of each tooth were formed. Then one-half of the beams were placed in Karnovsky's fixative for short-term study with the remainder in PBS for long-term study (1 year). The fixed specimens were further processed for nanoleakage evaluation by pre-section staining with ammoniacal silver nitrate or collagen morphology evaluation by post-section staining in 1% phosphotungstic acid and 5% uranyl acetate. Five grids containing 90-nm-thick sections were created per specimen for TEM (JEOL 1230). Results: In short-term, WW group showed more specimen separation during TEM sectioning and a greater amount of silver uptake in reticular form. No water tree formation was observed in either group. Collagen banding and interfibrillar spaces were more distinct in EW group. Conclusion: In short-term, the ethanol-wet bonding technique showed less nanoleakage and more distinct collagen morphology in agreement with previous TBS results. (Resin provided by Bisco.)
    IADR General Session 2009; 04/2009
  • Ying Cai, Julie L.P. Jessop
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    ABSTRACT: Photopolymerization systems based on hybrid monomer 3,4-epoxy-cyclohexylmethyl methacrylate (METHB) were studied to investigate water effects on conversion and polymer coating properties. METHB contains epoxide and methacrylate moieties, which undergo cationic and free-radical photopolymerization, respectively. The conversion of both groups was obtained by Raman spectroscopy in real time and depth. Water concentration and initiator system compositions were varied and shown to affect reaction kinetics and depth profile. With increasing water concentration, the epoxide induction period increased when only cationic initiator was present; however, the induction period disappeared when using the dual-initiator system. In addition, epoxide groups continued reacting after light was shuttered and reached a higher and more homogeneous conversion. Hybrid systems were shown to be less sensitive to water at low or intermediate concentrations. With high water concentrations, hybrid monomer systems manifested increased ring opening during illumination due to chain transfer and decreased physical properties due to loss of cross-linking.Graphical abstract
    Polymer. 01/2009; 50(23):5406-5413.
  • Chris M. Comer, Julie L. P. Jessop
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    ABSTRACT: Starch-g-poly(methyl methacrylate) (PMMA) was prepared by emulsion photopolymerization without photoinitiator. Grafting efficiency was determined for two types of starch (high-amylose and amylopectin) and at several illumination times. Since clogging of the graft copolymer prevented vacuum filtration and Soxhlet extraction was too time-consuming, a new method to separate the PMMA homopolymer from the graft copolymer was developed. Back-flush filtration uses an intermittent pressure pulse to clean the filter as the homopolymer is separated from the graft copolymer. Back-flush filtration was shown to be more efficient by reducing the separation time and solvent use, and the grafting efficiencies obtained with back-flush filtration compare favorably with those from Soxhlet extraction for the starch-g-PMMA copolymer systems studied. More accurate grafting efficiencies could be obtained by applying a nonstick coating to the inside chamber of the back-flush filtration unit.
    Starch - Starke 07/2008; 60(7):335 - 339. · 1.22 Impact Factor
  • Yuan Zou, Julie L P Jessop, Steven R Armstrong
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    ABSTRACT: Penetration and conversion of adhesives into the hybrid layer (HL) is important to the quality and longevity of the adhesive resin (AR)-dentin bond. In this study, a methodology is developed to examine the degree of conversion and relative HEMA concentration with respect to Bis-GMA using Raman spectroscopy. This methodology will be used in the future reports related to this topic. Conversion in the AR of water-stored resin-dentin samples (84% +/- 3%) agreed well with that measured in commercial adhesive (Comm Adh) resin samples after 24-h water storage (80% +/- 2% from Part 1) and was significantly higher than Comm Adh without water storage (58% +/- 3% from Part 1) (p = 0.0005). Adhesive conversion was not significantly different (p = 0.5036) through the middle of the HL, with a mean of 83% +/- 6%. HEMA mole fraction, relative to Bis-GMA, was significantly higher (p = 0.0028) in the top half of the HL (0.67 +/- 0.03), when compared to HEMA in the AR (0.60 +/- 0.01). HEMA and EDMAB were identified through GC/MS as leachable components in the aqueous 24-h storage media. The effect of this elution explains the change in conversion measurements observed between dry and water-stored conditions, which is more appropriately described as the "apparent" conversion.
    Journal of Biomedical Materials Research Part A 05/2008; 89(2):355-62. · 2.83 Impact Factor
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    ABSTRACT: To measure the denaturation temperature (Td) of demineralised dentine matrix as a function of infiltration with water vs. polar solvents vs. adhesive resins. Small discs of normal dentine were completely demineralised in 0.5M EDTA. Dried demineralised specimens were placed in water, methanol, ethanol, acetone, eta-butanol or HEMA. Additional specimens were infiltrated with Prime&Bond NT and polymerised. All specimens sealed in high-pressure pans and scanned using differential scanning calorimetry (DSC). Demineralised dentine saturated with water showed a Td of 65.6 degrees C that increased with saturation by methanol, ethanol, acetone, eta-butanol or HEMA to 148.5 degrees C. These increases in Td were inversely related to the molar concentration of the solvents and to their Hoy's solubility parameter for hydrogen bonding (delta h, p<0.01), as well as directly related to the cube root of their molecular weights (p<0.001). The presence of adhesive resins also increased the Td of demineralised matrices to even higher values depending if the resin bonded dentine was measured after 24h of water storage (166.8 degrees C) or dry (172.7 degrees C) storage. Solvents and monomers with low delta(h) values (i.e., 100% HEMA) increase the Td of demineralised dentine above that produced by solvents with higher delta h values such as methanol and water.
    Journal of Dentistry 01/2008; 36(1):8-14. · 3.20 Impact Factor
  • Yuan Zou, Steven R Armstrong, Julie L P Jessop
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    ABSTRACT: Monomer conversion of adhesives in the hybrid layer is important to the quality and longevity of the dentin bond. In this study, degree of conversion and relative co-monomer concentrations of both experimental and commercial adhesive resins were determined using Raman spectroscopy. The objectives were to identify stable Raman scattering peaks to use as internal references and to determine the effect of water storage on measured conversion and co-monomer concentrations. The peak at 605 cm(-1) did not change throughout polymerization and is associated with monomers in both adhesives. This peak was used as an internal reference for conversion and composition calculations before and after water storage. Conversion of the adhesive resins immediately after photopolymerization was approximately 20% lower than that measured after 24-h water storage. HEMA concentration (relative to bis-GMA) in the adhesive resins immediately after photopolymerization was at least 5 wt % higher than that measured after 24-h water storage. Elution of unreacted HEMA provides a reasonable explanation for the "supposed" change in conversion measurements, which is more appropriately described as apparent conversion. This apparent conversion will impact interpretation of physical properties and structure of the polymer, as well as increase the probability of water penetration and its reaction within the hybrid layer.
    Journal of Biomedical Materials Research Part A 12/2007; 86(4):883-91. · 2.83 Impact Factor
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    ABSTRACT: The denaturation temperature (T(d)) of dentin collagen in mineralized versus demineralized teeth was examined as a function of dentin age and the extent of dehydration. Using differential scanning calorimetry, T(d) of mineralized dentin was shown to be between 160 degrees C to 186 degrees C, depending on whether it was from young or old dentin that was hydrated or dehydrated, respectively. Demineralized dentin exhibited a T(d) of 65.6 degrees C that increased with dehydration to 176 degrees C. The presence of apatite crystallites or interpeptide bonding increased the T(d) of demineralized matrices. Interpeptide hydrogen bonding seems to stabilize collagen to thermal challenge. Water breaks interpeptide hydrogen bonds making collagen more susceptible to thermal denaturation. Rises in intracanal temperature are unlikely to cause extensive denaturation of mineralized root dentin walls. However, hydrated or partially dehydrated root canal walls that have been partially demineralized with chelating agents or mild acids may be susceptible to thermal denaturation.
    Journal of Endodontics 08/2006; 32(7):638-41. · 2.93 Impact Factor
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    ABSTRACT: The purpose of this work was to determine microtensile dentin bond strengths (microTBS) of dentin-resin composite bonds after three-month storage in artificial saliva containing either collagenase (COL) or cholesterol esterase (EST). The null hypothesis tested is that the resin-dentin bond strength is equivalent for each storage medium at the tested storage times. Resin composite was bonded to occlusal dentin, and microTBS specimens were formed and stored in the artificial saliva, COL, EST, or synthetic oil. After 24 h and 12-week storage, microTBS was determined and failure modes were characterized by SEM. The interfacial ultrastructure was evaluated by transmission electron microscopy as unstained and stained sections (phosphotungstic acid/uranyl acetate). Statistical analysis was performed by ANOVA and Weibull survival analyses at the 0.05 level of statistical significance. There were significantly weaker bond strengths after 12 weeks for all experimental storage media (p < 0.001). Artificial saliva containing EST lowered bond strengths to a significantly greater extent than did COL after 12 weeks of storage, while no difference between these groups could be discerned after 24 h. Therefore, the null hypothesis of this experiment is rejected. Exogenous enzymatic challenge to resin-dentin bonds decreased bond durability only with EST. However, when further challenges to ideal infiltration of the comonomers into the hybrid layer were carried out using inadequate removal of solvent, additional alterations in hybrid layer ultrastructure were discerned by TEM that may represent different potential degradative processes. The contribution of endogenous enzymatic challenges to the primary degradative process, ie, hydrolysis, is unknown and deserves continued attention.
    The journal of adhesive dentistry 06/2006; 8(3):151-60. · 0.91 Impact Factor
  • Ying Cai, Julie L.P. Jessop
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    ABSTRACT: Photopolymerization systems based on hybrid monomer 3,4-epoxy-cyclohexylmethyl methacrylate (METHB) were studied to investigate the oxygen inhibition effects on the conversion and polymer properties in films and coatings. METHB contains epoxide and methacrylate functional groups, which undergo cationic and free-radical photopolymerization, respectively. The conversion of both groups was obtained by Raman confocal microscopy as a function of depth. Initiator system compositions were varied and shown to affect the depth profile. The methacrylate group conversion was low at the surface due to oxygen inhibition. When both reactions were present, a cross-linked network formed and reduced oxygen sensitivity. At depths greater than the oxygen-diffusion-affected region, both functional groups' conversions did not show depth dependence. In addition, epoxide groups continued reacting after light was shuttered and reached a higher and more homogeneous conversion. These systems exhibit lower sensitivity to oxygen and offer advantages such as increased cure speed and improved film-forming properties compared to free-radical systems.
    Polymer. 01/2006;
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    ABSTRACT: The use of thick sections of fiber-reinforced polymers (FRPs) is increasing for numerous industrial applications such as wind turbine blades. In situ cure monitoring is very important to directly observe the cure process of FRPs during the manufacturing process. In this work, Raman spectroscopy and dielectric analysis (DEA) are investigated for in situ cure monitoring of an epoxy resin. The cure behavior is first characterized using differential scanning calorimetry (DSC) as a baseline comparison, and the best-fit phenomenological reaction model is determined to describe the cure behavior of the epoxy resin as well as the kinetic parameters. The relationship between Tg and degree of cure is also established. The degree of cure obtained from Raman spectroscopy and DEA under isothermal conditions is compared to that obtained from DSC. A good agreement is observed among the three methods, supporting the potential of these in situ cure monitoring methods during manufacturing. An implementation plan for in-plant monitoring is also discussed.
    Composites Part A Applied Science and Manufacturing 49:100–108. · 2.74 Impact Factor