The effect of ultra-fast photopolymerisation of experimental composites on shrinkage stress,network formation and pulpal temperature rise

Objectives

to complement our previous work by testing the null hypotheses that with short curing times and high DC, TPO-based resin composites would exhibit (1) higher polymerization stresses and consequently display (2) higher temperature rise and (3) higher flexural modulus, flexural strength and hardness, compared to a conventional CQ-based experimental composite.

Methods

Two experimental resin composites using either Lucirin-TPO or camphorquinone/DMAEMA as photoinitiators were prepared. Light curing was carried out using spectral outputs adapted to the absorption properties of each initiator. Different irradiation protocols were selected (0.5, 1, 3, 9 s at 500, 1000 and 2000 mW/cm² for Lucirin-TPO based composites and 20 or 40 s at 1000 mW/cm2 for Lucirin-TPO and camphorquinone-based composites). Degree of conversion (DC) was measured in real time by means of FT-NIR spectroscopy. Pulpal temperature rise (ΔT) was studied in a tooth model. Polymerization stress was monitored using the Bioman instrument. For cured specimens, flexural modulus and flexural strength were determined using a three point bending platform and Vickers hardness was determined with a microhardness indentor on samples prior to and after 24 h incubation in 75/25 ethanol/H₂O. Premolars were restored with both materials and microleakage at the teeth/composite interfaces following restoration was assessed.

Results

Lucirin-TPO-based composites irradiated at radiant exposures of 3 J/cm² and more exhibited significantly higher DCs, associated with increased flexural moduli and hardness compared to CQ-based composites. For an ultra-short irradiation time of 1 s at 1000 mW/cm², TPO-composites displayed similar polymerization stresses compared to CQ-controls with yet a 25% increase for flexural modulus and 40% increase for hardness measured after EtOH/H₂O sorption. Higher stress rates were however observed in all curing protocols compared to CQ-composites. Microleakage was similar between TPO and CQ-composites irradiated at 1000 mW/cm² for 3 and 20 s respectively, while a significant increase was observed for TPO-composites irradiated for 1 s. ΔT measured through a 0.6 mm thick dentin layer were all below 5.5 °C; TPO-composites exhibited similar or lower values compared to controls.

Significance

The use of Lucirin-TPO in resin composites along with appropriate curing conditions may allow for a major reduction of irradiation time while improving mechanical properties. The amount of stress observed during polymerization in TPO-based composites can be similar to those using CQ and the cohesion at the restoration-tooth interface was not affected by short curing times. Contrary to other studies, we found that the temperatures increases measured during polymerization were all well below the 5.5 °C threshold for the pulp.     

3种树脂材料修复离体牙Ⅱ类洞的边缘裂隙和 微渗漏比较

目的 研究3种树脂材料修复离体牙Ⅱ类洞的边缘裂隙及微渗漏情况。方法 选取符合纳入标准的60颗离体磨牙,随机分为大块充填树脂组、传统树脂组和树脂嵌体组3组,每组20颗。制备Ⅱ类洞,并按照其充填或制作标准进行修复。扫描电镜下测量边缘裂隙宽度,经1%亚甲蓝染色,去除面2.0 mm釉质,抛光后在体式显微镜下观察边缘染色深度。结果 树脂嵌体组的边缘裂隙最小,大块充填树脂组次之,传统树脂组最大,差异具有统计学意义(P<0.05);树脂嵌体组的染色深度明显小于大块充填树脂组和传统树脂组,差异具有统计学意义(P<0.05);大块充填树脂组与传统树脂组间染色深度差异无统计学意义(P>0.05)。结论 从修复体的边缘裂隙和微渗漏两个方面来看,树脂嵌体效果良好,值得临床推广应用。     

金属预成冠边缘密合度及影响因素的研究进展

金属预成冠应用于乳牙及年轻恒磨牙大面积龋损的修复已取得了较好的治疗效果,在国内外儿童口腔疾病的治疗中广泛使用。金属预成冠边缘密合度不良引起的微渗漏是导致金属预成冠治疗失败的主要原因之一。本文就国内外关于金属预成冠边缘密合度及其影响因素做一综述,旨在为儿童口腔医生临床应用金属预成冠时获得更好的冠边缘密合度提供帮助。     

窝沟封闭剂对托槽周围微渗漏影响的实验研究

目的 研究应用窝沟封闭剂封闭后金属托槽周围微渗漏的改变，为临床上应用窝沟封闭剂预防托槽周围釉质脱矿提供理论参考。方法 选择健康双尖牙72颗，随机分成3组，每组24颗，A组：37％磷酸酸蚀，京津釉质粘结剂粘结金属托槽。B组：37％磷酸酸蚀，3M Transbond光固化粘结剂粘结。C组：自酸蚀系统＋3M光固化粘结剂。再将每组的24颗牙随机分成实验组（A2、B2、C2）和对照组（A1、B1、C1），每组12颗，其中A2、B2、C2组用窝沟封闭剂涂布托槽周围，A1、B1、C1组不涂布窝沟封闭剂。所有样本进行冷热循环共500次，然后置于1％亚甲蓝溶液中浸泡染色24小时。将样本沿牙体长轴纵行切开，25倍立体显微镜下测量染料渗入最深点到托槽边缘的距离作为微渗漏的测量值，并对测量值进行方差分析和两两比较。结果 应用窝沟封闭剂与不用窝沟封闭剂组微渗漏的比较结果：A1组：A2组差别有高度统计学意义；B1组：B2组差别有统计学意义；C1组：C2组差别无统计学意义。结论 窝沟封闭剂能够明显减少磷酸酸蚀组的微渗漏而对自酸蚀组的作用不明显。     

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目的研究比较Er,Cr:YSGG激光预备与传统牙钻预备离体牙Ⅴ类洞对光固化复合树脂边缘微渗漏的影响。方法于2007年3月至7月,在中国医科大学实验设备处和中国医科大学口腔医学院中心实验室,将30颗离体前磨牙随机分为3组制备Ⅴ类洞:牙钻预备加37%磷酸处理组,单纯激光预备组,激光预备加37%磷酸处理组,每组10颗牙。经冷热循环染色后,采用染料渗入和扫描电镜方法观察充填体微渗漏情况。结果壁及龈壁处,染料渗入结果显示,牙钻预备加37%磷酸处理组的染料渗入评分最小,与其他两组比较差异有统计学意义(P<0.05),而单纯激光预备组与激光加37%磷酸处理组之间差异无统计学意义。充填体边缘微缝隙宽度的结果显示,单纯激光预备组的边缘微缝隙宽度最大,与其他两组比较差异有统计学意义(P<0.05),而牙钻预备加37%磷酸处理组与激光预备加37%磷酸处理组之间差异无统计学意义。结论Er,Cr:YSGG激光预备处理Ⅴ类洞不能增加光固化复合树脂与牙体组织的结合,减少微渗漏的发生;而应用激光加37%磷酸可以取代传统牙钻加37%磷酸进行窝洞预备。Er,Cr:YSGG激光预备离体牙Ⅴ类洞对光固化复合树脂边缘微渗漏的影响研究还有待于继续进行。     

4种黏接剂对全瓷颈缘和合金颈缘的金属烤瓷冠微渗漏影响的对比研究

目的对比4种黏接剂黏固全瓷颈缘和合金颈缘的金属烤瓷冠微渗漏。方法选择离体上颌第一前磨牙48颗,制作24颗全瓷颈缘金属烤瓷冠和24颗合金颈缘金属烤瓷冠,随机分4组,每组6颗牙,分别用4种黏接剂黏固,温度循环试验后,浸入2%亚甲基蓝溶液,恒温37℃保持24h后,沿牙体长轴纵行剖开,体视显微镜观察颈缘微渗漏情况。结果聚羧酸锌水门汀、玻璃离子水门汀、树脂加强型玻璃离子、树脂黏接剂黏固全瓷颈缘金属烤瓷冠的微渗漏依次减小,差异有统计学意义。同组黏接剂黏固金属颈缘与镍铬合金颈缘的微渗漏,差异无统计学意义。结论树脂黏接剂抗颈缘微渗漏性能优越,是黏接全瓷颈缘金属烤瓷冠的理想材料。     

牙本质粘接界面微渗漏的观察方法比较

目的：比较光镜及扫描电镜观察牙本质粘接界面微渗漏的能力。方法：去除磨牙面釉质,暴露牙本质,分别用2种粘接剂（Prime＆Bond NT、Clearfil S3Bond）粘接牙本质,其上制作复合树脂冠。顺牙齿长轴,在相互垂直的两个方向片切牙齿,制备条状试样,将试样相继浸泡于氨化硝酸银溶液及显影液中,然后测定微拉伸粘接强度。最后在光镜及扫描电镜下观察混合破坏试样的断面。结果：光镜下可观察到断面残留粘接剂下面的银渗漏,而扫描电镜下却看不到这些银渗漏;扫描电镜二次电子图像可清晰显示断面的形貌,背散射电子图像清晰区别银渗漏与其它结构。结论：将光镜和扫描电镜观察相结合,可更全面地了解牙本质粘接断面的微渗漏。     

Pre-warming of dental composites

Objectives

Cavity lining with flowable composites have been proposed to improve initial marginal adaptation and minimize shrinkage stresses. The purpose of this study was to evaluate if prewarming of composites would influence the flow and enhance marginal adaptation thus the effect of pre-warming different types of composites on their properties are reported.

Methods

Six different composites were used in this study including a flowable and a polyacid modified composite. Uncured composites were pressed between two glass plates with a known load and the film thickness was measured to determine flow. Polymerization shrinkage was measured by means of a one-dimension contacting transducer. Flexural strength was determined using a three-point bend test. Microleakage was determined in human lower third molars on both enamel and dentin restoration interfaces. Cytocompatibility was analyzed with an Alamar Blue redox cell proliferation assay. The flow properties, linear shrinkage, flexural strength, microleakage and cytocompatibility were evaluated at 22 °C and 60 °C.

Results

The results indicated that the film thickness for each of the materials was significantly lower at 60 °C and the linear shrinkage was greater as a result of the higher degree of polymerization. The flexural strength of Spectrum TPH and Wave were found to be statistically significantly higher with pre-warming, however the other composites did not exhibit any differences. Microleakage studies showed that pre-warming had no significant bearing on the results and alamarBlue^® results showed that the pre-heating did not have an effect on the cytotoxicity however the levels of cytotoxicity varied between the composites that can be attributed to the composition.

Significance

Pre-warming of the composites studied enhanced flow as observed by measuring film thickness and did not significantly affect other properties.     

流动树脂衬垫对树脂充填Ⅱ类洞龈壁微渗漏的影响

目的：了解流动树脂衬垫对树脂充填Ⅱ类洞龈壁微渗漏的影响。方法：选择30颗离体前磨牙随机分成A、B、C组,每组10颗,在近远中面制备长方形Ⅱ类洞,分别用通用型树脂直接充填（A组）,龈壁全层流动树脂衬垫后通用型树脂充填（B组）,流动树脂部分衬垫轴壁、龈壁后通用型树脂充填（C组）。所有试件经过温度循环、染色、近远中向连续切片,在30倍体视显微镜下观察龈壁染料渗漏情况。结果：C组的微渗漏明显小于A组和B组（P〈0．05）,A组和B之间差异无统计学意义（P〉0．05）。结论：实验研究表明,使用流动树脂作为衬垫层能明显降低Ⅱ类洞龈壁的微渗漏。     

热牙胶连续波根充与冷侧压根充后根尖微渗漏的研究

目的：比较不同根管预备方法下,热胶牙连续波根充与冷侧压根充术后,根尖微渗漏的情况。方法：将100颗单根离体恒牙,随机分为2组,A组50颗牙采用ProTaper预备,B组50颗牙采用不锈钢K型锉预备。根管预备完成后,A组牙齿随机分为A1组25颗牙齿,A2组25颗牙齿,分别使用连续波热牙胶垂直根管充填以及冷侧压根管充填。B组做相同处理。染料渗透法染色后测量根尖微渗漏长度并进行统计学分析。结果：A1组的染色线长度为（1.28±0.39）mm,A2组的染色线长度为（1.36±0.42）mm,B1组的染色线长度为（1.68±0.44）mm,B2组的染色线长度为（1.96±0.41）mm。其中A、B组间在统计学上无显著性差异,即不同的根管预备方法下,根尖的微渗漏无明显不同。A1、B1,A2、B2组间在统计学上有差异（P〈0.05）,说明不同的根管充填方法下,根尖微渗漏不同。结论：在离体实验条件下,连续波热塑充填具有较好的根管壁适应性和密合度,充填效果优于冷牙胶侧压充填方法。而根管预备方法的选择对根尖微渗漏的影响尚未发现明显差异。