Seydler Bodo, Rues Stefan, Müller Denise, Schmitter Marc
Department of Prosthodontics, Section for Biomaterial Research, University Hospital Heidelberg, Im Neuenheimer Feld 400, 69120, Heidelberg, Germany.
Private Dental Office, Bad Schoenborn, Germany.
Clin Oral Investig. 2014 May;18(4):1165-1171. doi: 10.1007/s00784-013-1062-8. Epub 2013 Aug 1.
The objective of this in vitro study was to assess the effect of wall thickness on the fracture loads of monolithic lithium disilicate molar crowns.
Forty-eight extracted molars were prepared by use of a standardized preparation design. Lithium disilicate crowns (e.max CAD, Ivoclar/Vivadent, Schaan, Liechtenstein) of different wall thicknesses (d = 0.5, 1.0, and 1.5 mm; n = 16 for each series) were then constructed and milled (Cerec MC-XL, Sirona, Bensheim, Germany). After placement of the teeth in acrylic blocks (Technovit, Heraeus Kulzer, Hanau, Germany), the crowns were adhesively luted (Multilink, Ivoclar Vivadent). In each series, eight crowns were loaded without artificial aging whereas another eight crowns underwent thermocycling (10,000 cycles, THE-1100, SD Mechatronik) and chewing simulation (1.2 million cycles, Willytec CS3, SD Mechatronik, F max = 108 N). All specimens were loaded until fracture on one cusp with a tilt of 30° to the tooth axis in a universal testing machine (Z005, Zwick/Roell). Statistical assessment was performed by use of SPSS 19.0.
Crowns with d = 1.0 and 1.5 mm wall thickness did not crack during artificial aging whereas two of the crowns with d = 0.5 mm wall thickness did. The loads to failure (F u) of the crowns without aging (with aging) were 470.2 ± 80.3 N (369.2 ± 117.8 N) for d = 0.5 mm, 801.4 ± 123.1 N (889.1 ± 154.6 N) for d = 1.0 mm, and 1107.6 ± 131.3 N (980.8 ± 115.3 N) for d = 1.5 mm. For aged crowns with d = 0.5 mm wall thickness, load to failure was significantly lower than for the others. However, differences between crowns with d = 1.0 mm and d = 1.5 mm wall thickness were not significant.
Fracture loads for posterior lithium disilicate crowns with 0.5 mm wall thickness were too low (F u < 500 N) to guarantee a low complication rate in vivo, whereas all crowns with 1.0 and 1.5 mm wall thicknesses showed appropriate fracture resistances F u > 600 N.
The wall thickness of posterior lithium disilicate crowns might be reduced to 1 mm, thus reducing the invasiveness of the preparation, which is essential for young patients.
本体外研究的目的是评估壁厚对整体式二硅酸锂磨牙冠折裂载荷的影响。
采用标准化预备设计对48颗拔除的磨牙进行预备。然后制作并研磨不同壁厚（d = 0.5、1.0和1.5 mm；每个系列n = 16）的二硅酸锂冠（e.max CAD，义获嘉伟瓦登特公司，列支敦士登沙恩）。将牙齿置于丙烯酸树脂块（Technovit，贺利氏古莎公司，德国哈瑙）中后，用粘结剂粘结冠（Multilink，义获嘉伟瓦登特）。在每个系列中，8个冠未进行人工老化处理就加载，而另外8个冠进行热循环（10000次循环，THE - 1100，SD Mechatronik公司）和咀嚼模拟（120万次循环，Willytec CS3，SD Mechatronik公司，Fmax = 108 N）。所有标本在万能试验机（Z005，德国Zwick/Roell公司）上以与牙长轴呈30°倾斜加载到一个牙尖折断。使用SPSS 19.0进行统计评估。
壁厚d = 1.0和1.5 mm的冠在人工老化过程中未出现裂纹，而壁厚d = 0.5 mm的冠中有两个出现了裂纹。未老化（老化后）的冠的破坏载荷（Fu）对于d = 0.5 mm为470.2±80.3 N（369.2±117.8 N），对于d = 1.0 mm为801.4±123.1 N（889.1±154.6 N），对于d = 1.5 mm为1107.6±131.3 N（980.8±115.3 N）。对于壁厚d = 0.5 mm的老化冠，破坏载荷显著低于其他冠。然而，壁厚d = 1.0 mm和d = 1.5 mm的冠之间的差异不显著。
壁厚为0.5 mm的后牙二硅酸锂冠的折裂载荷过低（Fu < 500 N），无法保证体内低并发症发生率，而所有壁厚为1.0和1.5 mm的冠均显示出适当的抗折强度（Fu > 600 N）。
后牙二硅酸锂冠的壁厚可减至1 mm，从而降低预备的侵入性，这对年轻患者至关重要。
