The influence of absolute humidity on shear bond adhesion

Objectives: The purpose of this study was to investigate the relationship between dentine shear bond strength, using data from experiments performed according to a standard protocol, and the absolute humidity for a new, fourth generation dentine adhesive system.

Methods: Results of seven recently performed adhesion experiments using the same protocol and product were analysed. Groups of 10 human molars were each bonded in a humidity chamber. The temperature and relative humidity conditions varied from 23 to 37 °C and 30 to 95%. After bonding of the composite resin a shear bond test at a crosshead speed of 2.0 mm/min was performed.

Results: The bond strength levels of the dentine adhesive system were influenced significantly by extreme temperature and humidity differences. Adhesion levels varied from 27.8 (SD 8.5) MPA to 12.8 (SD 1.4) MPA. Isobond strength curves are a good method to gain insight into the humidity sensitivity of adhesive systems.

Conclusions: Results of in vitro adhesive bonding procedures for a dentine adhesive can be significantly influenced by the absolute humidity levels at which the procedures are performed. Consequently “Materials and Methods” sections of publications should refer to absolute humidity or temperature and relative humidity levels as a relevant parameter.     

An experimental study of the stability of irradiated teeth in the region of the dentinoenamel junction

Abstract In this in vitro study we investigated the influence of ionizing gamma rays on the stability in the region of the dentinoenamel junction. We removed the enamel on the labial surface of 30 incisors of bovines up to the dentinoenamel junction, so that a circular area of enamel with a diameter of 2.0 ± 0.1 mm was left and an enamel cylinder was created. 15 teeth were irradiated by a cobalt-60-source (energy dose 70 Gy). The other 15 teeth were used as controls. Using a material testing apparatus the shear bond strengths were measured by breaking off the enamel cylinders. Furthermore, the breaking modes were investigated in SEM. Comparing the results of the shear bond strength experiments, it was obvious that the stability in the region of the dentinoenamel junction was significantly less among the irradiated teeth than among the non-irradiated teeth. The median value of the gamma ray treated teeth was x?= 19.1 MPa and that of the non-ray-treated teeth was x?= 37.4 MPa. The non-irradiated teeth showed fractured surfaces only in dentin in 10 cases and in 5 cases in both dentin and enamel. In contrast to that, the irradiated teeth had fractured surfaces in 12 cases exclusively in dentin and only in 3 cases the enamel was also fractured. These results lead us to conclude that changes of biophysical property of teeth can be caused by the influence of ionizing rays.     

Application of the Periodic Bond Chain (PBC) Theory and Attachment Energy Consideration to Derive the Crystal Morphology of Hexamethylmelamine

The habit (external morphology) of a crystal is controlled by both the external (environmental) conditions of crystallization and the internal (structural) factors of the crystal. In order to separate the effects of the crystal structure and of the solvent and other external factors on the experimentally observed growth habit, the theoretical habit can be derived from the crystal structure using the periodic bond chain (PBC) theory and attachment energy considerations. According to the PBC theory the crystal habit is governed by a set of uninterrupted chains of strong bonds formed in the crystal lattice. In addition, the attachment energy (E _att) is defined as the energy released per mole when a new layer is deposited on a crystal face. Since the habit of a crystal is determined by the relative growth rate (R) of the various faces, by taking R proportional to E _att, the theoretical habit can thus be derived from E _att. Using this approach, we obtained the theoretical crystal habit of an antitumor drug, hexamethylmelamine (HMM). The possible effect of solvents on the habit modification of HMM is discussed. This technique, based purely on the knowledge of the crystal structure, is directly applicable to other pharmaceuticals in deriving their theoretical crystal habit.     

大鼠心房肽Ⅲ及其小分子类似物的合成与生物活性

以逐步合成法固相合成了大鼠心房肽Ⅲ(APⅢ)及22肽的小分子类似物。用无水氟化氢将肽从树脂上切下,同时脱除所有侧链保护基。还原产物在30%乙酸高度稀释下用碘作氧化剂,使分子内2个半胱氨酸氧化形成二硫键。经SephadexG-l5柱层析、透析和高效液相层析分离纯化,获得在反相高效液相层析(分析柱)为单一峰的高纯度产物。酸水解后氨基酸组成分析证实与理论值相符,生物活性测定表明,合成的APⅢ有强利尿、利尿钠、降血压和舒张血管乎滑肌作用。化学修饰后的小分子APⅢ类似物有APⅢ的全部生物活性,且作用时间延长。     

Perceived and observed mother–child interaction at time of hospitalization and release in postpartum depression and psychosis

Summary Introduction: A pilot study was conducted which compared perceived mother–infant bonding in women admitted with postpartum depression or psychosis, with observations of mother–infant interaction by the nursing staff at both the time of hospitalization and that of release. Method: 25 mother–infant pairs admitted to a psychiatric unit were included in this study. The Postpartum Bonding Questionnaire was used to assess the perceived mother–infant bond and the observation of mother–infant interaction was assessed with the Bethlem Mother–Infant Interaction Scale. Results: At the time of both hospitalization and release postpartum depressed women experienced the bond with their child significantly more negative than women with postpartum psychosis. In contrast to women with postpartum psychosis, the experience of postpartum depressed women was significantly correlated with the observations of the nursing staff at time of release. Conclusion: Treatment that focuses on a mother’s experience of the bond with her child could be especially beneficial for mothers with postpartum depression. Correspondence: Mijke P. van den Berg, MA, MD, PhD, Department of Psychiatry, Erasmus Medical Centre, PO Box 2040, 3000 CA Rotterdam, The Netherlands     

Bond strength test: role of operator skill

BACKGROUND: Test method, substrate material and operator variability are factors known to affect bond strength test outcomes. The aim of this study was to determine if, with increasing experience, individual operator skill in material handling influenced microshear bond strength outcomes. METHODS: This retrospective study used data collected from six preliminary tests carried out successively on enamel microshear bond strength for two adhesives: Clearfil SE Bond (Kuraray) and Adper Single Bond 2 (3M ESPE) by one operator. Mean and median microshear bond strength values, standard deviations and coefficients of variation for each adhesive test group were calculated and assessed. RESULTS: A gradual increase in mean microshear bond strengths, a decrease in standard deviations and coefficients of variation over time for both adhesives and a progressively more uniform distribution of microshear bond strength results recorded in individual test sets was observed. The results suggest an improvement in bonding reliability as experience is gained. CONCLUSIONS: Operator skill in material handling appears to play a critical role in determining the outcome of bond strength testing. This same skill is probably relevant when using an adhesive for the first time clinically. It is important that clinicians become familiar with new adhesives in order to achieve optimal outcomes.     

Bonding of brackets using a caries-protective adhesive patch

OBJECTIVES: The purpose of this study was to assess the shear bond strength (SBS) of metal brackets when placed with a caries protective adhesive patch. METHODS: Forty stainless steel brackets (Ormco) were bonded to 40 bovine enamel samples according to the following conditioning/bonding procedures using a resin-based orthodontic luting material (Heliosit Orthodontic, N=10 per group): (A) 35% phosphoric acid (30s), rinse and dry; (B) as in A but additional placement of a prototype adhesive patch (Ivoclar Vivadent) using a bonding agent (Heliobond); (C) application of a two-step self-etch adhesive (AdheSE); (D) as in C but additional patch placement. Samples were stored at 37 degrees C for 24h. SBS was measured with a universal testing machine with a crosshead speed of 0.5mm/min and the adhesive remnant index (ARI) was determined under a stereomicroscope (16x). RESULTS: Mean SBS (standard deviation) values were as follows: (A) 16.6 (6.4)MPa; (B) 12.2 (5.8); (C) 12.9 (5.0); and (D) 10.5 (4.7). Analysis of variance followed by Bonferroni correction revealed no statistically significant differences. In 2 (B) and 4 (D) specimens, complete retention of the adhesive patch was observed. CONCLUSIONS: All treatment groups showed adequate bond strength values. The adhesive patch could therefore be applied in combination with orthodontic brackets and seal the enamel adjacent to the bracket.     

Effect of surface treatments on the tensile bond strength of repaired water-aged anterior restorative micro-fine hybrid resin composite

OBJECTIVES: The purpose of this study was to characterize changes in surface topography associated with different surface treatments and their effect on tensile bond strength (TBS) of repaired water-aged anterior restorative micro-fine hybrid resin composite. METHODS: The TBS of repaired resin-based composite slabs either non-treated or exposed to different mechanical and/or chemical surface treatment procedures were measured. The cohesive tensile strength of non-repaired intact slabs was used as a control group. The topographical effects of acid etching, grinding, and grinding followed by acid etching were characterized by AFM and SEM. RESULTS: All repaired groups showed significantly lower TBS than the control group. The TBS of repaired groups was ranged from 15% to 59% of the cohesive tensile strength of the control group (18.8+/-4.5MPa). The surface roughness of the non-treated aged specimens was significantly higher than other treated specimens. Specimens treated by acid etching showed significant increase in surface area compared to the non-treated and treated specimens. CONCLUSIONS: Aging process resulted in the formation of degradable surface layer which adversely affects the repair bond strength. The use of silane primer prior to the application of the adhesive after mechanical grinding, with or without the use of 37% phosphoric acid etching; improves the repair bond strength.     

Chemical speciation by selective heteronuclear single-quantum coherence spectroscopy: determination of double-bond quantity in unsaturated fatty acid compounds

A method for identifying fatty acid species based on the number of double bonds contained in a lipid molecule is presented. Common to all polyunsaturated fatty acids are two signature resonances at approximately 5.3 and 2.8 ppm in the proton chemical-shift spectrum of NMR. These resonances are from the vinyl and bis-allyl protons, respectively, and, although they can be readily observed by NMR from lipid extracts of biological samples, direct speciation has never been demonstrated by NMR. By modifying a conventional HSQC pulse sequence with a J-pulse on the spin system of the vinyl group (generalized as an IS spin system) at the beginning of the initial polarization transfer period and selectively inverting the 13C (I) spins with a narrowband sech/tanh inversion pulse, the collection of data in both dimensions can be restricted to a narrow slice of the chemical-shift range. The resolution is subsequently determined by digitizer efficiency, and spectra can be collected optimally from within a very narrow 1 x 6 ppm window of the respective proton and carbon chemical-shift ranges. With this modification it is possible to distinguish at least one resonance each from the multiple shifts expected from the indirectly detected nuclei of the fatty acid species, oleic acid, linoleic acid, linolenic acid and arachidonic acid, which contain one, two, three and four double bonds, respectively. This and similar methods of applied selectivity are of potential interest in characterizing speciation in biological samples where mixtures are often encountered and chemical shifts of the same structural group of similar molecules give rise to complicated overlapping resonances but are important for diagnosis of disease processes such as cancer.