Chiara Navarra

Degree of conversion of Filtek Silorane Adhesive System and Clearfil SE Bond within the hybrid and adhesive layer: An in situ Raman analysis

OBJECTIVESnTo examine the degree of conversion (DC) of the adhesive interfaces created by Filtek Silorane Adhesive and Clearfil SE Bond using micro-Raman spectroscopy.nnnMETHODSnThe adhesives were applied on human dentin in accordance with manufacturers 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.nnnRESULTSnDC 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).nnnSIGNIFICANCEnAs 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.

Degree of conversion and interfacial nanoleakage expression of three one-step self-etch adhesives.

Suboptimally polymerized monomers may be responsible for the reduced material properties of simplified adhesives and their inherent bonded interface instability. This study was performed to determine the degree of cure within the hybrid layers produced by three one-step self-etch adhesives in situ using Raman microspectroscopy and to investigate nanoleakage expression. Dentin disks were bonded with AdheSE One, Adper Prompt L-Pop, or iBond. Composite layers of 2-mm thickness were built up in bulk on the polymerized adhesive surfaces and then the adhesive-dentin interfaces were exposed to a micro-Raman beam. Adhesive penetration was calculated using the relative intensities of bands associated with mineral and adhesive, and the degree of conversion (DC) was evaluated. Interfacial nanoleakage expression was evaluated on the same specimens. The DC values for the tested adhesives were found to increase in the following order: AdheSE One (48 +/- 16%) < Adper Prompt L-Pop (83 +/- 2%) = iBond (90 +/- 6%; P < 0.05). AdheSE One showed greater nanoleakage expression than iBond or Adper Prompt L-Pop. Increased nanoleakage expression was associated with AdheSE One that showed the lowest DC. This suggests that a low DC may affect the quality and the long-term stability of the adhesive interface owing to the elution of unreacted monomers forming a porous and highly permeable hybrid layer.

Degree of conversion of resin blends in relation to ethanol content and hydrophilicity

OBJECTIVESnTo evaluate the degree of conversion of five experimental adhesive systems in relation to their hydrophilicity. The resin blends ranged from hydrophobic to hydrophilic and were tested as neat bonding agents, or solvated with increasing percentages of ethanol. The hypothesis tested was that extent of polymerization of resin blends is affected by resin hydrophilicity, solvent concentrations or time of polymerization.nnnMETHODSnFive light-curing versions of neat experimental resin blends were submitted to investigation: (1) 70% E-BisADM, 28.75% TEGDMA; (2) 70% BisGMA, 28.7% TEGDMA; (3) 70% BisGMA, 28.7% HEMA; (4) 40% BisGMA, 30% TCDM, and 28.75% TEGDMA; (5) 40% BisGMA, 30% BisMP, and 28.75% HEMA. All blends included 1% EDMAB and 0.25% CQ. Ethanol in different weight percentages (A: 0%, B: 30%, C: 50%, D: 70% and E: 90%) was added to these resin blends simulating different formulation of adhesives. A differential scanning calorimeter was used to measure the degree of conversion of resin blends as a function of resin hydrophilicity, solvent concentration and time of curing. Data were analyzed with three-way ANOVA and Tukeys post hoc test.nnnRESULTSnExotherms showed that degree of conversion was influenced by the hydrophilicity of the blends resin (p<.05), percentage of ethanol dilution (p<.05) and time of curing (p<.05). 30% ethanol dilution increased degree of conversion compared to neat compounds irrespective to resin type and curing time, showing the highest degree of conversion values of the study design.nnnSIGNIFICANCEnThis study supports the hypothesis that high ethanol percentages (>50mass%) may compromise extent of polymerization kinetics of dental adhesives.

Kinetics of polymerization and contraction stress development in self-adhesive resin cements.

OBJECTIVESnThe aim of the study was to evaluate the contraction stress, microhardness and polymerization kinetics of three self-adhesive cements vs. conventional dual-cure resin cement.nnnMETHODSnCements tested were: RelyX Unicem (3M ESPE, St. Paul, MN, USA), MaxCem Elite (Kerr, Orange, CA, USA), Clearfil SA Cement (Kuraray, Tokyo, Japan) and Duolink (Bisco Inc., Schaumburg, IL, USA). Cements were irradiated with a LED-curing unit (bluephase, IvoclarVivadent) for 20 or 40 s and the contraction forces (N) generated during polymerization were continuously recorded for 6 h with a universal testing machine. Polymerization kinetics were monitored using micro-Raman spectroscopy and degree of conversion was calculated. Vickers microhardness was also recorded. All measurements were performed at 10 min and 6h. Data were statistically analyzed by three-way ANOVA with repeated measures and Tukeys post hoc test (α=0.05).nnnRESULTSnIrrespective of exposure time, stress analysis ranked in the following order: Clearfil SA Cement<MaxCem<RelyX Unicem≤Duolink (p<0.05). Stress was correlated with microhardness values (p<0.05). Kinetic curves showed that maximum degree of conversion was attained more quickly than maximum stress after light activation.nnnSIGNIFICANCEnThe conventional resin-based cement showed higher stress values than the self-adhesive cements. The results were material-dependent and probably correlated to the composition of each material.

Contraction stress, elastic modulus, and degree of conversion of three flowable composites

The aim of this study was to measure the contraction stress of three flowable resin composites and to correlate the stress with the elastic modulus and the degree of conversion. One low-shrinkage (Venus Diamond Flow) and two conventional (Tetric EvoFlow and X-Flow) flowable composites were polymerized for 40s with a light-emitting diode (LED) curing unit. Contraction force was continuously recorded for 300s using a stress-analyser, and stress values were calculated at 40s and at 300s. The maximum stress rate was also calculated for each specimen. The elastic modulus of each composite was assayed using a biaxial flexural test, and degree of conversion was analysed with Raman spectroscopy. X-Flow exhibited higher stress values than the other tested materials. Venus Diamond Flow showed the lowest stress values at 40s and at 300s, and the lowest maximum stress rate. Stress values were correlated with elastic modulus but not with degree of conversion, which was comparable among all tested materials.

The effects of two 10% carbamide peroxide nightguard bleaching agents, with and without desensitizer, on enamel and sensitivity: an in vivo study

OBJECTIVESnThis study aimed to compare the effects of two 10% carbamide peroxide (CP) agents with or without desensitizers on tooth sensitivity, colour and enamel morphological changes.nnnMETHODSnTwenty subjects used a 10% carbamide peroxide gel with or without fluoride and potassium nitrate for 2xa0weeks. Sensitivity, spectrophotometric evaluation of colour and morphological analyses of replicas with scanning electron microscope (SEM) were performed before and after treatment. All data were analysed statistically.nnnRESULTSnBoth bleaching agents induced sensitivity; however, the 10% CP bleaching agent with fluoride and potassium nitrate produced significantly lower sensitivity (Pxa0<xa00.05) than the bleaching product without desensitizing agents. In spectrophotometric evaluation, no difference in bleaching effectiveness was found between the tested bleaching gels, and the SEM analysis confirmed the absence of relevant alterations of the enamel surface in both groups.nnnCONCLUSIONnThe use of 10% carbamide peroxide gel with fluoride and potassium nitrate reduced the incidence of sensitivity during the bleaching treatment compared to a bleaching agent that did not contain desensitizing agents. The bleaching effectiveness of the tested products was comparable.

Degree of conversion of two-step etch-and-rinse adhesives: In situ micro-Raman analysis.

OBJECTIVESnDC of three commercial two-step etch-and-rinse adhesives across the dentine-adhesive interface was investigated using micro-Raman spectroscopy. The hypothesis tested was that no difference in DC would exist among the adhesives tested.nnnMETHODSnAdper Scotchbond 1XT (3M ESPE), Prime&Bond NT (Dentsply DeTrey), and Ambar (FGM) were applied on human dentine disks (n=9). Composite increments of 2mm were then applied on the adhesive surface. Raman spectra were collected along the dentine-adhesive interface. The relative intensities of the peaks associated with the mineral (PO(4)(3-) at 960cm(-1)) and the adhesive (CC at 1640cm(-1); phenyl CC at 1610cm(-1)) were used to identify the adhesive within the hybrid layer and calculate its DC.nnnRESULTSnAdper Scotchbond 1XT and Ambar showed similar DC (79±7% and 77±7%, respectively), while a lower DC was found for Prime&Bond NT (70±7%; p<0.05).nnnCONCLUSIONSnThe hypothesis tested was rejected because differences were found among the adhesives tested. The difference in DC among the three adhesive systems can be attributed to different monomer compositions and solvents. Further studies are needed to correlate DC with other mechanical properties of these adhesives.nnnCLINICAL SIGNIFICANCEnInsufficient polymerization of an adhesive can result in a weak hybrid layer, and the presence of unreacted monomers may result in degradation of the polymeric network, decreasing the strength and longevity of the bond. In the present study, Adper Scotchbond 1XT and Ambar performed significantly better than Prime&Bond NT.

Effect of carboidiimide on thermal denaturation temperature of dentin collagen

OBJECTIVESn1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) has been shown to cross-link dentin type I collagen. Increased cross-linking usually elevates the glass transition temperature of polymers. The aim of this study was to evaluate the cross-linking reaction promoted by EDC in different aqueous concentrations by measuring the thermal denaturation temperature (Td) of human dentin collagen.nnnMETHODSnThe Td of dehydrated collagen and of insoluble dentin matrix collagen immersed in 0.5M or 1M EDC aqueous solution for different treatment times was obtained using a Differential Scanning Calorimeter (DSC). Specimens were also analyzed by Energy Dispersive X-Ray Spectroscopy.nnnRESULTSnEDC-treated dentin collagen showed a significantly higher Td than the untreated specimens when immersed in either 0.5M EDC or 1M EDC for 10min or longer (p<0.05). EDC-treated dentin collagen showed an increase of sulfur and chloride, not detectable in EDC-untreated dentin specimens. Conversely, the relative amount of carbon, nitrogen and oxygen was not modified by treatments.nnnSIGNIFICANCEnEDC-treated dentin collagen showed a higher Td than the untreated control at all tested concentrations and immersion times. A higher Td can be considered an indirect indicator of a more resistant and highly cross-linked collagen network. More data are needed to confirm these results.

Micromorphometric analysis of bone blocks harvested with eight different ultrasonic and sonic devices for osseous surgery

OBJECTIVESnThe aim of this study was to analyse inxa0vitro the main features of osteotomies performed by means of different ultrasonic and sonic systems for bone surgery.nnnMATERIALS AND METHODSnSix ultrasonic and two sonic devices for osseous surgery were evaluated during block harvesting on bovine bone. After measuring cutting speed, images of the blocks were acquired by light stereo-microscope and E-SEM, in order to measure the osteotomy thickness and to evaluate the presence of intra-trabecular bone debris and signs of thermal injuries on the bone. Roughness evaluation was performed using a profilometer.nnnRESULTSnAll the ultrasonic instruments required a shorter time than sonic systems to perform the block harvesting (pxa0<xa00.05). Piezomed was found to be the most efficient in terms of cutting speed (20.5xa0mm(2)/min), even if not significantly different from most of the devices here tested (pxa0>xa00.05). K-Bisonic and Variosurg 3 showed the smallest percentage variance between tip thickness and osteotomy width. Intra-trabecular debris was found to occur in inverse proportion with the width of the osteotomy: the tighter the track, the higher the amount of debris. Sonicflex Bone, Piezotome 2 and Sonosurgery showed almost no signs of thermal injuries on the osteotomised surfaces.nnnCONCLUSIONSnNo single ultrasonic or sonic device combined all the best features of speed, precision and bone micro-architecture preservation.

The effect of ageing on the elastic modulus and degree of conversion of two multistep adhesive systems

During the curing reaction, the monomers of dentine bonding systems should cross-link sufficiently to strengthen an adhesive so that it is clinically reliable. This study evaluated how different storage conditions (air vs. water storage) affect the elastic modulus (E-modulus) and degree of conversion (DC) of a three-step etch-and-rinse adhesive and a two-step self-etch adhesive. The biaxial flexural test and Raman microscopy were performed on resin disks made from the bonding agents Adper Scotchbond Multi-Purpose (SBMP; 3M ESPE) and Clearfil Protect Bond (CPB; Kuraray). The measurements were repeated after storage in either air or water for 15 and 30 min and for 1, 24, and 72 h. At time 0, the E-modulus was not affected by the adhesive system, whilst the degree of cure of CPB was higher than that of SBMP. Air storage increased the E-modulus at each ageing interval. Storage in water increased the E-modulus until it reached a maximum at 24 h, after which it decreased significantly at 72 h. No linear correlation between the percentage DC and E-modulus of the two adhesives was found when stored in water. The results of this study indicate that the mechanical properties and polymerization kinetics of SBMP and CPB are affected by storage time and medium.