Comparison between a silorane-based composite and methacrylate-based composites: shrinkage characteristics, thermal properties, gel point and vitrification point.

A silorane-based composite was compared against methacrylate-based composites in terms of shrinkage characteristics, thermal properties, gel point, and vitrification point. Shrinkage strain was measured using a laser triangulation method. Shrinkage stress was measured using a stress analyzer. Heat flow during photopolymerization was measured using photo-DSC. Statistical analysis was performed using one-way ANOVA and Tukey's test (p=0.05). Silorane exhibited significantly lower shrinkage strain than the methacrylate-based composites. It also presented the lowest stress values during light exposure, but the highest maximum stress rate after light exposure. It showed the highest heat flow rate, and it took the longest time to reach gel and vitrification points. Silorane demonstrated improved performance over the methacrylate-based composites with delayed gel and vitrification points as well as reduced shrinkage strain and stress. However, a high quantity of heat was liberated during the curing process, causing silorane to show significantly higher stress rate (p<0.05) than the methacrylate-based composites after light exposure.

[A new dynamic approach to monitoring dental composite curing kinetics].

OBJECTIVE: To employ a laser triangulation method for measuring the dynamic shrinkage of composite resins during polymerization, and to investigate the maximum shrinkage rate (S(max)) and the time at maximum shrinkage rate (t(max)). METHODS: A novel experimental set-up based on laser triangulation was utilized which was capable of real-time shrinkage strain measurements. Uncured composite was condensed into a PTFE mould and irradiated for 40 s. The laser signals obtained from lateral composite surfaces were monitored using a laser triangulation measuring system and were converted into the displacement of the tested surface. The volumetric shrinkage derived from the linear shrinkage was calculated by multiplying 3. Total volumetric shrinkage (%S) of the five restorative materials (AP-X, Charmfill, Charisma, Durafill VS, and Herculite Precis) was measured using three methods (laser triangulation method, Acuvol, and buoyancy method). S(max) and t(max) were measured using the laser triangulation method. Statistical analyses were done using the two-way ANOVA (P<0.05) and post hoc test. RESULTS: The highest shrinkage value was measured by Acuvol, followed by laser method, and the lowest was by buoyancy method. All the three methods of measuring %S generated the same, statistically secured ranking for the five light-cured restorative materials: DurafillVS < AP-X < Herculite Precis < Charisma < Charmfill. %S measured by laser triangulation method varied between 2.06% and 3.37%. S(max) varied between 4.39 µm/s and 29.25 µm/s. t(max) varied between 0.77 s and 1.59 s. Significant differences in S(max) (F=734.87,P<0.01) and t(max) (F=53.24,P< 0.01) for five composite resins were found. CONCLUSION: Laser triangulation method offers several advantages over the conventional methods of measuring polymerization shrinkage. It is simple, compact, non-invasive and suitable for measuring the dynamic polymerization shrinkage in real time without delay. Therefore, it can be used to characterize the shrinkage kinetics in a wide range of visible-light-cure materials.

Polymerization characteristics, flexural modulus and microleakage evaluation of silorane-based and methacrylate-based composites.

PURPOSE: To compare the behavior of a new low-shrinkage silorane-based composite (P90) with two conventional methacrylate-based composites, in terms of polymerization shrinkage, polymerization stress, gel point, flexural modulus and microleakage. METHODS: The materials tested were P90 (3M ESPE), AP-X (Kuraray), Quixfil (Dentsply). Polymerization shrinkage was measured using the Accuvol method. Polymerization stress was assessed using a stress-strain analyzer. Polymerization shrinkage (%) and force (N) were continuously recorded for 300 seconds. Polymerization shrinkage and stress after 300 seconds and gel point were recorded. Flexural modulus was obtained by three-point bending. A laboratory microleakage test was performed. Class V cavities prepared on labial surfaces of 70 freshly extracted human teeth were randomly assigned to the seven groups (N=10): P90/PSA (P90 System Adhesive), AP-X/CBA (Clearfil SE Bond Adhesive), Quixfil/XBA (XP Bond Adhesive), P90/CBA, P90/XBA, AP-X/PSA, Quixfil/PSA. The teeth were immersed in 1% basic fuchsin dye for 24 hours at room temperature. All teeth were cut in a labial-lingual direction and the penetration of dye along the wall of cavities was observed under a stereoscopic light microscope. Statistical analysis was performed with one-way ANOVA, Kruskal-Wallis ANOVA test and post hoc tests (P< 0.05). RESULTS: The low-shrinkage silorane-based composite (P90) exhibited significantly lower polymerization shrinkage, polymerization stress, flexural modulus and a later gel point than the conventional methacrylate-based composites. In the microleakage test, P90/PSA, AP-X/CBA, AP-X/PSA demonstrated the lowest microleakage scores without a significant difference among them (P> 0.05). Quixfil/XPA exhibited the highest microleakage scores.

[Evaluation of laser triangulation method for measurement of post-gel shrinkage and post-vitrification shrinkage in composite resins].

OBJECTIVE: To employ a laser triangulation method for measuring post-gel and post-vitrification polymerization shrinkage of composite resins. METHODS: A novel experimental set-up capable of measuring real-time shrinkage strain was utilized. Total shrinkage of the five composite resins was measured. The measurements of post-gel and post-vitrification linear shrinkage as a function of the gel-point and vitrification transition point were also carried out in the study. RESULTS: Gel point of the five composite resins ranged from 0.77 s to 1.59 s, while vitrification transition point ranged from 1.99 s to 6.33 s. Post-gel shrinkage ranged from 33.35 µm to 53.18 µm and post-vitrification shrinkage ranged from 16.43 µm to 30.58 µm. Total shrinkage ranged from 39.25 µm to 64.84 µm. Significant differences in the gel point and vitrification transition point among the five composite resins were found (P < 0.01). Significant differences in the post-gel shrinkage, post-vitrification shrinkage and total shrinkage among the five composite resins were found (P < 0.01). The ranking of post-gel and post-vitrification shrinkage of these composite was different from that of their total shrinkage. CONCLUSIONS: Laser triangulation method is suitable for measuring clinically significant post-gel and post-vitrification shrinkage.

Evaluation of early macrophage activation and NF-kappaB activity in pulmonary injury caused by deep hypothermia circulatory arrest: an experimental study.

This study aimed to analyze changes in nuclear factor-kappa B (NF-kappaB), inflammation factors, and macrophages in pulmonary tissue under deep hypothermia circulatory arrest (DHCA) at different time points, which can be used to infer the role of early macrophage activation and NF-kappaB activity in pulmonary injury. The possible pathogenic mechanisms of DHCA-induced pulmonary injury were investigated in this study to provide an experimental basis for clinical lung protective strategies. Piglets (n = 12) were randomly divided into 2 groups, with 6 piglets in each group. The control group had ambient temperature cardiopulmonary bypass (CPB), and the experimental group had DHCA. Both groups had conventional CPB with 30 min of parallel circulation. Changes in NF-kappaB and inflammatory factors were examined in each group at 6 different time points. At 0.5 h after ischemia-reperfusion, NF-kappaB expression in the nucleus of pulmonary tissue reached its peak, and brown-stained nuclei were mainly polymorphonuclear antibodies. At 1 h after ischemia-reperfusion, plasma tumor-necrosis factor (TNF)-alpha in the experimental group was significantly increased compared with that before reperfusion (P < 0.05). The plasma levels of interleukin (IL)-8 and IL-6 in the experimental group were significantly increased at 1.5 h after ischemia-reperfusion compared with the levels before reperfusion (P < 0.05). Early activation of NF-kappaB under DHCA might play an important role in DHCA-induced pulmonary injury.