口腔材料学教学实验课设计:光照条件对光固化复合树脂性能的影响

光固化复合树脂经光固化灯照射后固化,其临床性能在很大程度上受所用的光固化灯的影响,特别是光照强度和光照时间对其影响更为显着。为了帮助学生了解光照条件对光固化复合树脂性能的影响,北京大学口腔医学院在口腔材料学实验课教学中设计了两个实验:光固化复合树脂的固化深度实验和光固化复合树脂的挠曲强度实验。通过实验使学生掌握光照射时间和光照强度对光固化复合树脂固化深度和挠曲强度的影响规律。实验设计完成后,在2008级的八年制学生中进行了实际使用,并根据实验内容设计了调查问卷。问卷结果显示,实验课效果良好。     

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提要：光固化复合树脂应用于口腔医学已经有30年历史,光固化灯作为固化光源直接影响了复合树脂的性能及修复效果。目前临床常用的固化灯类型有传统卤光灯、速效卤光灯、发光二极管灯、等离子弧光灯、氩激光灯。本文主要介绍了每种光固化灯的特点、对复合树脂聚合固化的影响因素及使用注意事项。     

光固化灯与光固化复合树脂

随着光固化修复在临床上广泛地应用,光固化灯也有了很快地发展。本文介绍了可见光固化灯的性能、光强度与光固化复合树脂固化深度的关系以及影响固化灯输出强度的因素。     

影响光固化灯使用效率的相关因素

光固化复合树脂应用于口腔医学已有30多年的历史,而光固化灯作为复合树脂的照射光源对其性能及修复效果影响甚大。本文通过综述影响光固化灯使用效率的相关因素,为临床合理使用光固化灯提供理论依据和指导。     

光固化复合树脂分层固化及层间粘结

光固化复合树脂聚合反应程度是树脂修复体使用寿命的关键。固化光进入树脂的深度有限导致了复合树脂聚合固化程度受限,所以对较大的,复杂的修复体,树脂需多层多次成形固化——分层固化技术,各层之间粘结为一整体。 1 分层固化及层间粘结的机制 光固化复合树脂在每次光照聚合后,表面留有一薄层约100μm厚度发粘的未固化层即弥散层或厌氧层、复合树脂填加层之间就是靠这种弥散层起化学性粘结。填加层之间的化学粘结是光固化复合树脂分层固化技术的主要环节。Kilian等报告,体外实验可见光固化复合树脂固化层厚度为2～8mm     

复合树脂的不同固化方法对抗压强度影响

目的 探讨不同固化方法处理后对复合树脂抗压强度的影响。方法 采用光固化、光固化＋光固化、光固化＋热固化，3种不同固化方法处理3M和贺利氏复合树脂，在万能验试机上测试抗压强度。结果 2次处理的复合树脂抗压强度均比1次处理的复合树脂有较大提高，范围在51.8%-91.6%之间。不同的2次固化方法相比，统计学无显著差异。结论 复合树脂经2次固化方法处理，其抗压强度高于1次光固化方法的处理。     

光固化与化学固化复合树脂黏接正畸托槽的对比研究

目的对比光固化、化学固化复合树脂黏接正畸托槽的抗剪强度和牙釉质脱矿程度。方法20颗离体前磨牙随机分为光固化复合树脂组(1)和化学固化复合树脂组(2),检测抗剪黏接强度;将116例正畸患者左右侧上前牙随机分为2组,试验组用光固化复合树脂黏接托槽,对照组用化学固化复合树脂黏接托槽,对比正畸治疗结束后两组牙釉质脱矿的差异。结果2组黏接抗剪强度为:(1)组(17.45±7.06)MPa,(2)组(13.02±5.38)MPa,两组间有差异(P<0.05)。试验组与对照组正畸治疗结束后牙釉质脱矿程度有显著差异(P<0.01)。结论光固化型复合树脂的抗剪强度优于化学固化型。光固化复合树脂黏接正畸托槽能减少正畸治疗中牙釉质脱矿。     

光固化复合树脂固化深度的逐步回归分析

目的:分析不同处理因素对光固化复合树脂固化深度的影响,探讨各因素对固化深度的影响程度.方法:采用多因素不同水平析因实验设计,共制备192例试件.所得试件经Planmeca曲面断层机扫描,并测量其固化深度.所有实验数据采用SPSS 11.5软件包进行t检验、多元逐步回归.结果:不同光源、不同投照距离、不同光照时间之间的差异具有统计学意义(P＜0.01);多元逐步回归分析表明,3个因素与固化深度存在显著的线性相关关系(P＜0.01).结论:3个因素均可影响光固化复合树脂的固化深度,以光照时间对固化深度的影响最大,且三者之间存在交互作用.     

电压与光固化时间对复合树脂固化深度的影响

本文测量了在不同电压下,不同的光固化时间时,光固化复合树脂的固化深度。发现：２２０Ｖ电压下,光固化时间从２０Ｓ延长到４０Ｓ时,光固化复合树脂的固化深度增加０．１５ｍｍ,延长到６０Ｓ时,增加０．２６ｍｍ。光固化时间延长,树脂的固化深度增加不多。２００Ｖ电压下,光固化时间从２０Ｓ延长到４０Ｓ时,固化深度增力００．４８ｍｍ,延长至６０Ｓ时,固化深度可增加０．８１ｍｍ。光固化时间延长,光固化复合树脂的固化深度明显增加。     

光固化复合树脂热膨胀系数影响因素及检测方法

光固化复合树脂的热膨胀系数是决定其能否与牙体组织形成稳定结合的重要因素之一。目前临床所用的光固化复合树脂的热膨胀系数均高于牙釉质及牙本质的,因而会影响到修复效果。影响光固化复合树脂热膨胀系数的因素有很多,内在因素包括复合树脂组成成分、转化率及交联密度等;外在因素包括树脂厚度、光固化灯光密度等。本文就光固化复合树脂热膨胀系数影响因素及检测方法做一综述。     

Dental curing lights--maintenance of visible light curing units.

Successful curing depends directly on many factors of which the most important is the correct functioning of the curing unit to emit light of sufficient intensity and quality. If the contribution of any of these factors is at a less than adequate level, the light-sensitive materials will not polymerise completely, which in the long term may be responsible for secondary caries and decreased longevity of the restoration. Factors which may reduce the light output include ageing of the bulb and filter, damage of the light guide or fibre optics, deposits on the light tip due to composite build-up or autoclave scale, erosion of light tip surface due to immersion sterilisation, and line voltage fluctuations. Recent studies carried out to investigate the effectiveness of curing lights in clinical use show that most practitioners are unaware of the importance of routine monitoring, care and maintenance of curing lights. This paper reviews some of the available literature on the monitoring, care and maintenance of curing lights, including information on the influence that some of these may have on the intensity emitted by the curing light.     

Effect of curing time and light curing systems on the surface hardness of compomers

This study compared the Vickers hardness of the top and bottom surfaces of two compomers (Compoglass F and Dyract AP) polymerized for 20 and 40 seconds with two different light curing systems. Five samples for each group were prepared using Teflon molds (9x2 mm) and were light-cured either with a conventional halogen lamp (Optilux 501) or LED light (LEDemetron I) for 20 or 40 seconds. After curing, all the samples were stored in distilled water for 24 hours at 37 degrees C. The Vickers hardness measurements were obtained from the top and bottom surfaces of each sample. ANOVA, Scheffé and t-test were used to evaluate the statistical significance of the results. For the top and bottom surfaces, the light curing systems and curing times tested showed no statistical difference, except for Optilux 501, which used 20 seconds for both compomers (p<0.05). There was no significant difference in the microhardness of both surfaces of Compoglass F and Dyract AP cured for either 20 or 40 seconds using LEDemetron I. With Optilux 501, the microhardness of samples cured for 40 seconds was significantly higher than 20 seconds (p<0.05).     

Thermal emission and curing efficiency of LED and halogen curing lights

The purpose of this study was to compare the thermal emission and curing efficiency of LED (LEDemetron 1, SDS/Kerr) and QTH (VIP, BISCO) curing lights at maximum output and similar power, power density and energy density using the same light guide. Also, another LED curing light (Allegro, Den-Mat) and the QTH light at reduced power density were tested for comparison. Increase in temperature from the tips of the light guides was measured at 0 and 5 mm in air (23 degrees C) using a temperature probe (Fluke Corp). Pulpal temperature increase was measured using a digital thermometer (Omega Co) and a K-type thermocouple placed on the central pulpal roof of human molars with a Class I occlusal preparation. Measurements were made over 90 seconds with an initial light activation of 40 seconds. To test curing efficiency, resin composites (Z100, A110, 3M/ESPE) were placed in a 2-mm deep and 8-mm wide plastic mold and cured with the LED and QTH curing lights at 1- and 5-mm curing distances. Knoop Hardness Numbers (KHN) were determiped on the top and bottom surfaces (Leco). Bottom hardness values were expressed as a percentage of maximum top hardness. No significant differences were found in maximum thermal emission or KHN ratios between the LED (LEDemetron 1) and the QTH (VIP) at maximum output and similar energy densities (ANOVA/Tukey's; alpha=0.05).     

Evaluating the efficacy of curing lights.

The use of light curing units has increased tremendously over the past few years with the introduction of photoactivated composite restorative resins. The advantages of light-cured composites are well documented especially the ease of placement of restorations as a result of extended working time and control of setting. Many of the advantages of these composites are dependent on the adequate polymerisation and therefore the source of the visible light, especially the wavelength and the intensity of the light source. The aims of this study were (i) to determine the intensity output of curing lights in state clinics, private dental practices and dental clinics run by trade unions using a radiometer and (ii) to relate their output to various factors that may affect the intensity of the light produced by each unit. The light intensity of each light curing unit was measured using the Efos Cure Rite radiometer (Cure Rite, Efos model #8000; Efos Inc, Mississauga, Canada). Mean readings ranged from a high of 448 to a low of 22 mW/cm2 for curing lights at the time of evaluation. Nineteen (54.3%) of the light curing units were functioning at optimal intensities, followed by 10 (28.6%) functioning at levels between 150 and 300 mW/cm2 and 6 (17.1%) functioning at levels far below that required to achieve adequate photocuring. No statistically significant differences were found when comparing intensity readings with age, last maintenance service and bulb replacement (P > 0.05). All of the clinicians interviewed (100%) expressed subjective satisfaction with the performance of the light curing units, even though 45.7% functioned below optimal intensities (P > 0.05). Not one of the clinicians expressed dissatisfaction with the performance of any of the light curing units. The results of this study showed that the light intensities f light curing units used within private dental practices, state and trade union dental clinics were inadequate for optimum curing.     

Effect of light curing modes and light curing time on the microhardness of a hybrid composite resin

AIMS: The aim of this in vitro study was to evaluate the influence of light curing modes and curing time on the microhardness of a hybrid composite resin. METHODS AND MATERIALS: Forty-five Z250 composite resin specimens (3M-ESPE Dental Products, St. Paul, MN, USA) were randomly divided into nine groups (n=5): three polymerization modes (conventional-550 mW/cm2; light-emitting diodes (LED)-360 mW/cm2, and high intensity-1160 mW/cm2) and three light curing times (once, twice, and three times the manufacturer's recommendations). All samples were polymerized with the light tip 8 mm from the specimen. Knoop microhardness measurements were obtained on the top and bottom surfaces of the sample. RESULTS: Conventional and LED polymerization modes resulted in higher hardness means and were statistically different from the high intensity mode in almost all experimental conditions. Tripling manufacturers' recommended light curing times resulted in higher hardness means; this was statistically different from the other times for all polymerization modes in the bottom surface of specimens. This was also true of the top surface of specimens cured using the high intensity mode but not of conventional and LED modes using any of the chosen curing times. Top surfaces showed higher hardness than bottom surfaces. CONCLUSIONS: It is important to increase the light curing time and use appropriate light curing devices to polymerize resin composite in deep cavities to maximize the hardness of hybrid composite resins.