Comparison of fracture strength.

Polylactic acid (PLA) has garnered attention for use in interim dental restorations due to its biocompatibility, biodegradability, low cost, ease of fabrication, and moderate strength. However, its performance under intraoral conditions, particularly under heat and moisture, remains underexplored. This study evaluated the mechanical properties of PLA interim crowns compared with those of polymethylmethacrylate (PMMA) and bisphenol crowns under simulated intraoral conditions with thermocycling. Three CAD/CAM polymers—PMMA (milling), PLA (fused deposition), and bisphenol (stereolithography)—were tested for fracture resistance, hardness, and surface roughness. For fracture strength, 25 crowns from each group were cemented onto dies. The Shore D hardness and surface roughness were measured on round discs before and after 10,000 thermocycles (5°C/55°C). The surface topography was assessed via scanning electron microscopy. PMMA exhibited the highest fracture strength (2787.93 N), followed by bisphenol (2165.47 N) and PLA (2088.78 N), with no significant difference between the latter two. PMMA and bisphenol showed vertical fractures and cracks, whereas PLA showed crown tearing or die deformation. Bisphenol had the highest Shore D hardness, followed by PMMA and PLA, with no significant changes after thermocycling. The surface roughness (Ra) was lowest for bisphenol and similar between PMMA and PLA. The roughness (Rz) increased from bisphenol to PMMA to PLA. The roughness of the PMMA remained unchanged after thermocycling, whereas the Ra but not the Rz of the PLA increased. Bisphenol showed a significant increase in both Ra and Rz (p聚乳酸（PLA）凭借其生物相容性、生物降解性、低成本、易于加工成型以及中等力学强度的特性，在临时牙科修复领域受到广泛关注。然而，其在口腔内环境下的性能，尤其是在热与湿环境中的表现，仍尚未得到充分探究。 本研究针对热循环模拟口腔内环境下的聚乳酸临时冠的力学性能展开评估，并与聚甲基丙烯酸甲酯（PMMA）冠及双酚类冠进行对比。本次实验共测试三种计算机辅助设计/计算机辅助制造（CAD/CAM）聚合物：铣削成型PMMA、熔融沉积成型PLA以及立体光刻成型双酚类材料，检测指标包括抗断裂性能、硬度及表面粗糙度。 针对抗断裂强度测试，每组制备25个冠修复体，粘接于代型上进行测试。在10000次热循环（5℃/55℃）前后，分别于圆形试样盘上测量肖氏D硬度（Shore D hardness）与表面粗糙度（Ra）。通过扫描电子显微镜（scanning electron microscopy）对表面形貌进行表征。 实验结果显示，PMMA的抗断裂强度最高，达2787.93 N，其次为双酚类材料（2165.47 N）与PLA（2088.78 N），后两者之间无显著性差异。PMMA与双酚类材料的冠修复体表现为垂直断裂与裂纹，而PLA冠修复体则出现冠部撕裂或代型变形的情况。 双酚类材料的肖氏D硬度最高，其次为PMMA与PLA，热循环后三者硬度均无显著变化。 双酚类材料的Ra值最低，PMMA与PLA的Ra值相近。微观不平度十点高度（Rz）则依次为双酚类< PMMA < PLA。热循环后，PMMA的表面粗糙度无显著变化；PLA的Ra值升高，但Rz值无明显变化。双酚类材料的Ra与Rz值均出现显著升高（p