Luiza Guerra, DDS, MS, graduate student, Department of Dentistry, Federal University of Santa Catarina (UFSC), Florianópolis, SC, Brazil.
Renato Quirino Ramos, DDS, MS, graduate student, Department of Dentistry, Federal University of Santa Catarina (UFSC), Florianópolis, SC, Brazil; KU Leuven (University of Leuven), Department of Oral Health Sciences, BIOMAT & University Hospitals Leuven (UZ Leuven), Dentistry, Leuven, Belgium.
Oper Dent. 2023 May 1;48(3):294-303. doi: 10.2341/21-203-L.
This study aimed to compare the fracture toughness of molars with wide mesio-occlusal-distal (MOD) cavities restored with regular and flowable bulk-fill resin composite and a conventional resin composite after 250,000 mechanical cycles of chewing simulation. Thirty-two extracted mandibular third molars were selected and class II MOD cavities involving 2/3 of the intercuspal width and 4 mm depth were prepared. Teeth were divided into four groups based on resin composite type and insertion technique (n=8): (1) CT, unprepared teeth (control); (2) CV, conventional resin composite (Tetric N-Ceram, Ivoclar Vivadent) with incremental technique; (3) R-BF, regular bulk-fill resin composite (Tetric N-Ceram Bulk Fill, Ivoclar Vivadent) with a single increment; and (4) F-BF, flowable bulk-fill resin composite (Tetric N-Flow Bulk Fill, Ivoclar Vivadent) with a single increment, except for a 1-mm-thick layer at the occlusal surface, restored with conventional resin composite (Tetric N-Ceram). All specimens were evaluated to detect the presence and propagation of enamel cracks using a LED transilluminator before and after 250,000 mechanical cycles (SD Mechatronic GmbH). After a chewing simulation, they were subjected to a compressive force in a universal testing machine (DL-2000, EMIC) until fracture. The maximum fracture load of the specimens was measured (N) and the fracture patterns were classified based on the fracture site (above or below the cementoenamel junction [CEJ]). Data were statistically analyzed with one-way ANOVA. All specimens survived after 250,000 mechanical cycles, and no statistically significant differences among groups were observed regarding the fracture toughness (p<0.05). The fracture analysis demonstrated that failures below the CEJ were more common in CV (75%), while CT, R-BF, and F-BF showed this type of failure in 38%, 63%, and 63% of the specimens, respectively. The results of the crack analysis showed that the occurrence of new cracks and crack propagation was also higher in CV (33.3%), followed by R-BF, F-BF, and CT (14%, 14%, and 11% of the specimens, respectively). Teeth restored with regular and flowable bulk-fill composites showed similar fracture toughness after the chewing simulation compared to those restored with the conventional resin composite and unprepared teeth. Furthermore, teeth restored with both regular and flowable bulk-fill composites showed a lower incidence of enamel cracks and fractures below the CEJ compared to those restored with the conventional resin composite.
本研究旨在比较磨牙宽近中-远中（MOD）腔用常规和流动型大体积充填树脂复合材料以及传统树脂复合材料修复后，经 25 万次咀嚼模拟循环的断裂韧性。选择 32 颗下颌第三磨牙，制备涉及 2/3 牙尖间距和 4mm 深度的 II 类 MOD 腔。根据树脂复合材料类型和插入技术将牙齿分为四组（n=8）：（1）CT，未处理的牙齿（对照）；（2）CV，用增量技术的传统树脂复合材料（Tetric N-Ceram，Ivoclar Vivadent）；（3）R-BF，用单增量的常规大体积充填树脂复合材料（Tetric N-Ceram Bulk Fill，Ivoclar Vivadent）；（4）F-BF，用单增量的流动型大体积充填树脂复合材料（Tetric N-Flow Bulk Fill，Ivoclar Vivadent），但在咬合面保留 1mm 厚的层，用传统树脂复合材料（Tetric N-Ceram）修复。在 25 万次机械循环（SD Mechatronic GmbH）前后，使用 LED 透照仪评估所有标本以检测釉质裂纹的存在和扩展。经过咀嚼模拟后，在万能试验机（DL-2000，EMIC）上施加压缩力直至断裂。测量标本的最大断裂载荷（N），并根据断裂部位（CEJ 上方或下方）对断裂模式进行分类。采用单向方差分析对数据进行统计学分析。所有标本在 25 万次机械循环后均存活，组间断裂韧性无统计学差异（p<0.05）。断裂分析表明，CV 中更常见的是 CEJ 下方的失败（75%），而 CT、R-BF 和 F-BF 中分别有 38%、63%和 63%的标本发生这种失败。裂纹分析结果表明，CV（33.3%）中新裂纹的发生和裂纹扩展也更高，其次是 R-BF、F-BF 和 CT（分别为 14%、14%和 11%的标本）。与用传统树脂复合材料和未处理的牙齿修复的牙齿相比，用常规和流动型大体积充填复合材料修复的牙齿在咀嚼模拟后具有相似的断裂韧性。此外，与用传统树脂复合材料修复的牙齿相比，用常规和流动型大体积充填复合材料修复的牙齿发生釉质裂纹和 CEJ 下方骨折的发生率较低。
