Effect of cooling rate during oxidation treatment on the hardness change by post firing heat treatment of a Pd-Cu-Ga-Zn alloy after simulated porcelain firing / 대한치과재료학회지

Effect of cooling rate during oxidation treatment on the hardness change by post firing heat treatment of a Pd-Cu-Ga-Zn alloy after simulated porcelain firing was investigated and the following results were obtained. In the firing simulated specimens after quenching during the oxidation treatment, the hardness did not increase by post-firing heat treatment. However, in the firing simulated specimens after slow cooling during the oxidation treatment, post-firing heat treatment for 25 minutes was effective in increasing the hardness (p < 0.05). In the firing simulated specimens after quenching during the oxidation treatment, the significant decrease in hardness during the post-firing heat treatment was attributed to the coarsening of fine precipitates formed in the matrix and plate-like precipitates. In the firing simulated specimens after slow cooling during the oxidation treatment, the increase in hardness during the post-firing heat treatment for 25 minutes was due to precipitation hardening. From these results, it was found that the cooling rate during the oxidation treatment affected the change of hardness by the post-firing heat treatment after the simulated firing. From these results, post-firing heat treatment increased the hardness of the Pd-Cu-Ga-Zn alloy only when the cooling rate during the oxidation treatment was slow.

The effect of different cooling rates and coping thicknesses on the failure load of zirconia-ceramic crowns after fatigue loading

PURPOSE: The purpose of this study was to evaluate the influence of different coping thicknesses and veneer ceramic cooling rates on the failure load of zirconia-ceramic crowns. MATERIALS AND METHODS: Zirconia copings of two different thicknesses (0.5 mm or 1.5 mm; n=20 each) were fabricated from scanning 40 identical abutment models using a dental computer-aided design and computer-aided manufacturing system. Zirconia-ceramic crowns were completed by veneering feldspathic ceramics under different cooling rates (conventional or slow, n=20 each), resulting in 4 different groups (CONV05, SLOW05, CONV15, SLOW15; n=10 per group). Each crown was cemented on the abutment. 300,000 cycles of a 50-N load and thermocycling were applied on the crown, and then, a monotonic load was applied on each crown until failure. The mean failure loads were evaluated with two-way analysis of variance (P=.05). RESULTS: No cohesive or adhesive failure was observed after fatigue loading with thermocycling. Among the 4 groups, SLOW15 group (slow cooling and 1.5 mm chipping thickness) resulted in a significantly greater mean failure load than the other groups (P<.001). Coping fractures were only observed in SLOW15 group. CONCLUSION: The failure load of zirconia-ceramic crowns was significantly influenced by cooling rate as well as coping thickness. Under conventional cooling conditions, the mean failure load was not influenced by the coping thickness; however, under slow cooling conditions, the mean failure load was significantly influenced by the coping thickness.

The effet of cooling rate on the residual stresses in the veneer ceramics of zirconia-ceramic restorations: a literature review / 대한치과보철학회지

Nowadays, dental zirconia is widely used as a framework material for a fixed dental prosthesis as well as a single restoration. However, clinical studies have reported high incidence of veneer chipping of zirconia-ceramic restorations compared to that of metal-ceramics. Several factors were raised as the possible causes of veneer ceramic chipping, however, it is still in debate. Recently, residual stresses in the veneer ceramics after cooling process gathers attention as one possible cause of chipping and many studies reported that the rate of cooling significantly influenced the types and the amount of residual stress. The purpose of current review was to briefly describe the effect of cooling rate on the residual stress in zirconia-ceramics. It was also described that the different behavior of residual stress between zirconia-ceramics and metal-ceramics following different cooling rate.

Effects of various combinations of cryoprotectants and cooling speed on the survival and further development of mouse oocytes after vitrification / 대한생식의학회지

OBJECTIVE: The objectives of this study were to analyze efficacy of immature and mature mouse oocytes after vitrification and warming by applying various combinations of cryoprotectants (CPAs) and/or super-rapid cooling using slush nitrogen (SN2). METHODS: Four-week old ICR female mice were superovulated for GV- and MII-stage oocytes. Experimental groups were divided into two groups. Ethylene glycol (EG) only group: pre-equilibrated with 1.5 M EG for 2.5 minutes and then equilibrated with 5.5 M EG and 1.0 M sucrose for 20 seconds. EG+dimethylsulfoxide (DMSO) group: pre-equilibrated with 1.3 M EG+1.1 M DMSO for 2.5 minutes and equilibrated with 2.7 M EG+2.1 M DMSO+0.5 M sucrose for 20 seconds. The oocytes were loaded onto grids and plunged into SN2 or liquid nitrogen (LN2). Stored oocytes were warmed by a five-step method, and then their survival, maturation, cleavage, and developmental rates were observed. RESULTS: The EG only and EG+DMSO groups showed no significant difference in survival of immature oocytes vitrified after warming. However, maturation and cleavage rates after conventional insemination were greater in the EG only group than in the EG+DMSO group. In mature oocytes, survival, cleavage, and blastocyst formation rates after warming showed no significant difference when EG only or EG+DMSO was applied. Furthermore, cleavage and blastocyst formation rates of MII oocytes vitrified using SN2 were increased in both the EG only and EG+DMSO groups. CONCLUSION: A combination of CPAs in oocyte cryopreservation could be formulated according to the oocyte stage. In addition, SN2 may improve the efficiency of vitrification by reducing cryoinjury.

Effect on Survival and Developmental Competence of Vitrified Mouse Embryos Using Various Cryoprotectants and Cooling Speeds / 대한불임학회지

OBJECTIVE: Vitrification requires a high concentration of cyroprotectant (CPA) and an elevated cooling speed to avoid ice crystal formation. We have evaluated the effect of different combinations of cooling rate and CPA on embryonic integrity (developmental competence) in order to increase the efficiency of vitrification without impairing embryo viability. We hypothesized that the combination of CPA or the increase of cooling rates can reduce the concentration of toxic CPA for vitrification. As consequently, we performed experiments to evaluate the effect of various composition of CPA or slush nitrogen (SN2) on the mouse embryonic development following vitrification using low CPA concentration. METHODS: Vitrification of mouse embryos was performed with EM grid using liquid nitrogen (LN2) or SN2 and different composition of CPAs, ethylene glycol (EG) and dimethylsulfoxide (DMSO). After vitrification-warming process, their survival and blastocyst formation rates were examined. For analyzing long-term effect, these blastocysts were transferred into the uterus of foster mothers. RESULTS: Survival and blastocyst formation rates of vitrified embryos were higher in EG+DMSO group than those in EG only. Furthermore, the group using SN2 with a lower CPA concentration showed a higher survival of embryos and developmental rates than group using LN2. CONCLUSION: The combination of EG and DMSO as CPAs may enhance the survival of mouse embryos and further embryonic development after vitrification. SN2 can generate high survival and developmental rate of vitrified/warmed mouse embryos when a lower concentration of CPA was applied. Therefore, these systems may contribute in the improvement of cryopreservation for fertility preservation.

Imersão em água fria para o manejo da hipertermia severa / Cold water immersion to the control of exertional heat illness

A incapacidade de dissipar o calor gerado pela atividade muscular prejudica o desempenho e aumenta a predisposição a lesões do organismo. A hipertermia severa induzida pelo esforço físico (HTE) prejudica a saúde e está associada à morbidade e mortalidade de indivíduos em diferentes atividades ocupacionais e atléticas. Estudos sobre a eficiência de métodos de resfriamento corporal têm recomendado a imersão em água fria para o tratamento da HTE. Sua utilização nos minutos iniciais pós-hipertemia parece a melhor recomendação por reduzir o tempo no qual a temperatura central permanece elevada. A manutenção de infraestrutura necessária para a realização desse procedimento deve ser considerada em atividades físicas e condições ambientais nas quais os indivíduos estão mais suscetíveis ao acometimento da HTE. As taxas de resfriamento observadas através da imersão em água a diferentes temperaturas podem servir de referência para o controle da duração do procedimento. Esta revisão analisa a recomendação da imersão em água fria como procedimento de resfriamento corporal para o manejo da HTE.

The incapacity of dissipating heat generated by muscular activity hampers performance and increases predisposition to physical injuries. Exertional heat illness (HTE) harms health and is associated with morbidity and mortality of individuals in different occupational and athletic activities. Studies on the efficiency of body cooling methods have recommended cold-water immersion for the treatment of HTE. Its use in the initial minutes of post-hyperthermia seems to be the best recommendation to reduce the time central temperature remains high. Maintenance of the infrastructure needed to perform this procedure should be considered in physical activities and environmental conditions in which the individuals are more prone to HTE. The cooling rates observed through water immersion in different water temperatures may serve as reference to the control of HTE procedure duration. This review analyses the recommendation of cold-water immersion as a body cooling procedure for management of HTE.

Cryopreservation of mouse spermatogonial stem cells / 解剖学报

Objective To explore the conditions and methods for cryopreservation and proliferation of mouse spermatogonial stem cells (SSCs). Methods SSCs were isolated from six-day-old Kunming mouse using two-step enzymatic digestion and Percoll discontinuous density gradient centrifugation. Cells were frozen with different freezing medium and cooling rate. After thaw, they were cultured in mimimum essential medium alpha (MEMα) supplemented with 10% fetal calf serum (FCS) and 100μg/L glial cell line-derived neurotrophic factor (GDNF). The survived and proliferating SSCs were examined by WST-8 colorimetric assay. Alkaline phosphatase andreverse transcription-polymerase chain reaction (RT-PCR) were performed to confirm if the cultured 96 hours germ cells were still stem cells. Results The best method to cryopreserve SSCs is using cryoprotector containing 10% dimethyl sulfoxide(DMSO), 10% FCS, 0.07mol/L sucrose and 1℃/min cooling rate, and the viability of cells in this method is more than 84%;Although the cell viability in non-programmed freezing method is less than that in the programmed freezing method, it is a simple and effective cropreservation method for mouse SSCs. What is more, the anchoring time of SSCs in this method is 8-12 hours after thaw, SSCs begin to proliferate 24 hours later, and rapid proliferation appears on the 48 hours, colonies are composed by 20-25 cells in 96 hours, when SSCs proliferated nearly 5 times.Conclusion The culture condition we used is suitable for proliferation of frozen-thawed SSCs.

Effects of cooling rate on the bonding strength of cast titanium to porcelain / 实用口腔医学杂志

Objective:To study effects of the cooling rate on the bonding characteristics of titanium porcelain bonded to cast titanium.Methods:According to ISO 9693,24 cast titanium plates(25 mm?3 mm?0.5 mm)were prepared.The middle of the samples(8 mm?3 mm) were bonded with bonding porcelain,opaque porcelain and dentin porcelain.The specimens from each porcelain-metal combination group were randomly assigned into four experimental cooling rate conditions,namely cooling rate of 15,40,50 and 100 ℃/min.A three-point-flexure-test was used to evaluate the bonding strength of titanium porcelain bonded to cast pure titanium.SEM/EDS were taken to characterize the failed surface of the titanium-porcelain interface.Statistical analyses were made by one-way analysis of variance(ANOVA).Results:The bonding strength of 15 ℃/min group was significantly higher than other groups.There were no significant differences in bond strength between 40 ℃/min and 50 ℃/min groups.SEM/EDS revealed that with an increase cooling rate,the remained porcelains on the titanium side were decreased.Conclusion:The 15 ℃/min cooling rate might be an effective method to improve the titanium-porcelain bonding strength.