Statement of problem

Automixing and dispensing cements is a straightforward approach with consistent dosing. Previous studies have demonstrated clinically significant differences in crown retention between power-liquid and paste-paste forms of the same cement, as the composition between the 2 differs. A self-adhesive modified-resin (SAMR) and a resin-modified glass ionomer (RMGI) cement, originally offered as a powder-liquid, are now in common use as paste-paste automixed cements. With the increased use of zirconia restorations, the long-term retention of zirconia crowns for these 2 automixed cements should be evaluated.

Purpose

The purpose of this in vitro study was to determine whether zirconia crowns cemented with 2 automixed cements provided clinically acceptable retention after 6 months of aging with monthly thermocycling.

Material and methods

Extracted molars were mounted in resin and prepared with a flat occlusal surface, 20-degree taper, approximately 4-mm axial length, and with the axio-occlusal line angle slightly rounded. Prepared teeth were equally distributed into 3 cementation groups (n=12) to achieve nearly equal mean preparation surface areas for each group. Zirconia crowns (IPS ZirCAD LT) were fabricated with an added occlusal bar to facilitate removal of the cemented crowns. Cement space was set at 45 μm axially and 55 μm occlusally. After sintering and before delivery, the intaglio surfaces were airborne-particle abraded with 50-μm alumina at 275-kPa pressure for 3 seconds and then steam cleaned. Cements were the original powder-liquid RelyX Luting (RMGI; RXL) as the control, paste-paste, automixed systems RelyX Luting Plus Automix (RMGI; RXLA), and RelyX Unicem 2 Automix (SAMR; RXUA). Crowns were cemented under 196 N force, placed in an oven at 37 °C and 100% humidity during setting and then thermocycled (5 °C-55 °C) for 5000 cycles monthly for 6 months. The crowns were removed axially with a universal testing machine at 0.5 mm/min. Removal forces were recorded and dislodgement stress calculated by using the surface area of each preparation. One-way ANOVA was used for dislodgement stress and force. Chi-square test was used for cement location after testing (α=.05).

Results

RXLA demonstrated considerably lower crown retention (1.3 MPa) and differed significantly (P<.001) from RXUA (3.1 MPa) and RXL (3.1 MPa). Modes of failure showed most of the cement remaining only in the crown intaglio for RXLA for all specimens, whereas half of the crowns for RXL and RXUA demonstrated cement adhesion to both dentin and the intaglio surface, indicating cohesive failure of the cement at separation. As the Levene test was significant, the Games-Howell test was used for mean differences. The χ² analysis was significant.

Conclusions

After long-term aging with monthly thermocycling, high-strength zirconia crowns were strongly retained by 2 (RXL, RXUA) of the 3 cements. Crown retention for RelyX Luting Plus Automix was less than half in comparison and with cement found only on the intaglio surface after separation.

中文翻译：

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用目前的自动混合水泥固结的氧化锆牙冠的长期保留

问题陈述

自动混合和分配水泥是一种具有一致剂量的直接方法。先前的研究表明，同一水泥的动力-液体和糊状-糊状形式之间的牙冠保持力在临床上存在显着差异，因为两者之间的成分不同。最初以粉末-液体形式提供的自粘改性树脂（SAMR）和树脂改性玻璃离聚物（RMGI）水泥现在普遍用作糊状-糊状自混合水泥。随着氧化锆修复体使用量的增加，应评估这两种自动混合水泥的氧化锆冠的长期保留性。

目的

这项体外研究的目的是确定用2种自动混合的胶结剂固结的氧化锆牙冠在每月热循环老化6个月后是否能提供临床上可接受的固位力。

材料与方法

将提取的臼齿安装在树脂中，并准备一个平坦的咬合面，20度锥度，大约4mm的轴向长度，以及轴向咬合线角略为圆角。将准备好的牙齿平均分为3个胶结组（n = 12），以使每组牙齿的平均准备表面积几乎相等。氧化锆牙冠（IPS ZirCAD LT）制作时增加了咬合杆，以利于去除牙冠。水泥空间轴向设置为45μm，咬合设置为55μm。烧结后和交货前，将凹版表面用50μm氧化铝在275kPa压力下研磨3秒钟，然后用蒸汽清洗浮雕表面。水泥为原始的粉末-液体RelyX Luting（RMGI; RXL）作为对照，粘贴，粘贴的自动混合系统RelyX Luting Plus Automix（RMGI; RXLA），和RelyX Unicem 2自动混音（SAMR; RXUA）。牙冠在196 N的力下固结，在凝固过程中置于37°C和100％湿度的烤箱中，然后每月进行热循环（5°C-55°C）5000个循环，共6个月。使用万能试验机以0.5 mm / min的速度轴向去除胎冠。记录脱模力，并通过使用每种制剂的表面积计算脱模应力。单向方差分析用于消除应力和力。测试后，卡方检验用于水泥定位（α= .05）。记录脱模力，并通过使用每种制剂的表面积计算脱模应力。单向方差分析用于消除应力和力。测试后，卡方检验用于水泥定位（α= .05）。记录脱模力，并通过使用每种制剂的表面积计算脱模应力。单向方差分析用于消除应力和力。测试后，卡方检验用于水泥定位（α= .05）。

结果

RXLA表现出较低的牙冠保持力（1.3 MPa），与RXUA（3.1 MPa）和RXL（3.1 MPa）显着不同（P <.001）。破坏模式表明，对于所有标本，大多数水泥仅残留在RXLA的冠凹内，而RXL和RXUA的一半冠显示出水泥对牙本质和凹面的粘附，表明分离时水泥的内聚破坏。由于Levene检验很显着，因此将Games-Howell检验用于均数差异。该χ ²分析是显著。

结论

经过每月热循环的长期老化后，三种水泥中的2种（RXL，RXUA）牢固地保留了高强度氧化锆冠。与之相比，RelyX Luting Plus Automix的牙冠保持力不到一半，并且仅在分离后的凹版表面上发现了水泥。