Degree of conversion of dual-cured resin cement light-cured through three fibre posts within human root canals: an ex vivo study

Aim  To evaluate the degree of conversion of one dual-cured resin cement light-cured through three fibre posts within extracted human teeth.
Methodology  Fifteen mandibular premolars were root filled and then divided into three groups. Variolink II was light-cured through the posts (LP, D.T. Light-Post; PP, FRC Postec Plus; SP, Snowpost) within the root canal. The degree of conversion was obtained at 1 mm intervals in 9 mm-deep longitudinally sectioned root canals using an optical microscope connected to an FTIR spectrophotometer ( n  =   10). The light transmission of each post tested was also examined using UV–Vis spectroscopy. Data were analysed using anova and Tukey's test ( α  = 0.05).
Results  The LP and PP posts revealed a light transmission of 10.2% and 7.7%, respectively, whereas the SP post exhibited a significantly lower value of 0.5%. The degree of conversion mean value ranged from 32.78% to 69.73% depending on the depth and type of post. For all the groups, there were significant decreases in the degree of conversion values for the middle region when compared with those for the cervical region ( P  <   0.05). Except at a depth of 1 mm, the SP group consistently exhibited significantly lower degree of conversion values than the other groups ( P  <   0.05). The linear regression analysis revealed a strong correlation between the light transmission of the posts and the overall degree of conversion value for each group ( R ² = 0.9888).
Conclusions  The decrease in the degree of conversion for Variolink II relative to the depth was dependent on the light transmission capacity of the posts tested.     

Effect of halogen light irradiation on hydrogen peroxide bleaching: an in vitro study

Background: The aim of this study was to evaluate the effect of halogen light irradiation on hydrogen peroxide (HP) bleaching by assessing HP concentrations, tooth whitening efficacy, and temperature variations in bleaching agents and pulp chambers. Methods: Sixteen premolars were randomly divided into two groups: Group BL (bleaching agent with halogen light irradiation for 3 × 10 minutes) and Group B (bleaching agent alone). HP concentrations were tested before and after treatment. CIE L*a*b* values of specimens were obtained using a spectrophotometer. Temperatures of bleaching gels and pulpal chambers were recorded by a digital multimeter with K‐type thermocouple. Data were analysed using ANOVA and paired t‐test. Results: After treatment, HP concentration in group BL was slightly higher than that in group B. Paired t‐tests revealed significant differences of ΔE between groups BL and B in all time intervals except at day 35. The temperature rise of bleaching gels and pulpal chambers in group BL was significantly higher than that in group B. Conclusions: In‐office bleaching was effective for tooth whitening. The involvement of halogen light was beneficial for the immediate whitening effect but had little impact on the long‐term whitening effect.     

Microshear bond strength of dual-cure resin cement in zirconia after different cleaning techniques: an in vitro study

PURPOSEThis study aimed to compare the microshear bond strength (µSBS) of dual-cure resin cement in CAD-CAM zirconia after different cleaning techniques.MATERIALS AND METHODSFifty discs of zirconia-based ceramic from Ivoclar Vivadent were embedded in acrylic resin. The discs were divided into five groups according to the cleaning methods used: Group 1: drying with spraying + sandblasting with Al₂O₃; Group 2: washed with water and dried with spraying + sandblasting with Al₂O₃; Group 3: washed with distilled water and dried with spraying + sandblasting with Al₂O₃ + zirconium oxide (Ivoclean); Group 4: washed with distilled water and dried with spraying + sandblasting with Al₂O₃ + potassium hydroxide (Zirclean); and Group 5: washed with distilled water and dried with spraying + sandblasting with Al₂O₃ + 1% NaClO. All of the groups were contaminated with artificial saliva for 1 minute and then cleaned. Statistical analyses were performed using ANOVA and Tukey''s tests. RESULTSThere were statistically significant differences among all groups for µSBS (P < .05). The group treated with zirconium oxide (Group 3) showed the highest µSBS (18.75 ± 0.23 MPa).CONCLUSIONWhen applied to zirconia, the cleaning methods affected the bonding with resin cement differently.     

复合树脂高强纤维间隙保持器的抗疲劳强度体外实验

目的：评价复合树脂高强纤维（glass fiber reinforced composite resin ,GFRCR）间隙保持器的抗疲劳强度,比较两种树脂材料制作的GFRCR间隙保持器的抗疲劳强度。方法收集离体磨牙40颗,随机分为A、B两组,每组20颗,分别用树脂Z350和Grengloo制作间隙保持器试件,试件经过温度循环后加载疲劳循环,记录循环次数,分别与标准抗疲劳强度比较,对结果进行统计学分析。结果两组循环次数分别与标准抗疲劳强度比较,差异有统计学意义（P＜0.001）;A、B组间抗疲劳强度差异无统计学意义（P=0.886）。结论 GFRCR制作间隙保持器可获得良好的抗疲劳性能,推荐临床使用;树脂材料Z350和Grengloo制作的高强纤维间隙保持抗疲劳性能无明显差异。     

Experimental polyethylene–hydroxyapatite carrier‐based endodontic system: an in vitro study on dynamic thermomechanical properties,sealing ability,and measurements of micro‐computed tomography voids

The dynamic thermomechanical properties, sealing ability, and voids formation of an experimental obturation hydroxyapatite‐reinforced polyethylene (HA/PE) composite/carrier system were investigated and compared with those of a commercial system [GuttaCore (GC)]. The HA/PE system was specifically designed using a melt‐extrusion process. The viscoelastic properties of HA/PE were determined using a dynamic thermomechanical analyser. Human single‐rooted teeth were endodontically instrumented and obturated using HA/PE or GC systems, and then sealing ability was assessed using a fluid filtration system. In addition, micro‐computed tomography (μCT) was used to quantify apparent voids within the root‐canal space. The data were statistically analysed using one‐way anova and post hoc tests. The HA/PE composite exhibited important modulus and damping changes with an increase of temperature. The HA/PE system was more flexible than GC as the modulus of GC appeared to be significantly higher than that of HA/PE as a result of the high positive glass transition temperature (T_g). However, HA/PE and GC presented similar sealing abilities. In conclusion, because sealing ability and voids formation were comparable between the tested materials, the experimental HA/PE system may be considered a suitable alternative material for root‐canal obturation. Moreover, HA/PE possesses specific viscoelastic behaviour and lower melting points, which may facilitate root‐canal retreatments.     

Effect of CO2 laser on pulpal temperature and surface morphology: an in vitro study

Objectives: The objective of this study was to evaluate the potential effects on underlying dental hard tissues of a high pulse rate carbon dioxide (CO₂) laser that was designed for soft tissue surgery.Methods: Eighteen extracted human teeth were sectioned longitudinally, cleaned, and varnished, leaving nine exposed windows on each: six on the coronal surface (enamel) and three on the root surface (cementum, dentin). The CO₂ irradiation conditions used were: wave length 10.6 μm; 1.2–2.6 J/cm² fluence per pulse; repetition rate 120–1000 Hz; 100–200 ms pulse duration; and cumulative fluences ranging from 14 to 2200 J/cm². Each window was irradiated with a 0.3 mm beam diameter at one of nine power settings for 0.1, 0.5, or 1.0 s. The pulp chamber temperature was measured with a microthermocouple. The irradiated teeth were evaluated by Polarized Light Microscopy (PLM) and Scanning Electron Microscopy (SEM).Results: The pulp chamber temperature rise ranged from 0.5 to 19° C depending on the location of the window and distance to pulp chamber. SEM revealed crystal fusion in both enamel and dentin at all cumulative fluences. At cumulative fluences of 40 J/cm², 200 pulses/second and higher, measurable tissue loss was observed with PLM both in dentin and enamel.Conclusions: These results indicate there are threshold conditions above which pulsed CO₂ laser light used for soft tissue surgery may cause detrimental changes to underlying oral hard tissue and to the pulp.