Two damage regimes—“brittle” and “ductile”—have been identified in the literature on ceramic grinding, machining, grit blasting, and wear. In the brittle regime, the damage mechanism is essentially crack formation, while in the ductile region, it is quasiplasticity. Onset of the brittle mode poses the greater threat to strength, so it becomes important to understand the mechanics of ductile–brittle thresholds in these materials. Controlled microcontact tests with a sharp indenter are employed to establish such thresholds for a suite of contemporary computer-aided design/computer-aided manufacturing dental ceramics. Plots of flexural strength S versus indentation load P show a steep decline beyond the threshold, consistent with well-established contact mechanics relations. Threshold dimensions occur on a scale of order 1 µm and contact load of order 1 N, values pertinent to practical grit finishing protocols. The ductile side of ceramic shaping is accessed by reducing grit sizes, applied loads, and depths of cut below critical levels. It is advocated that critical conditions for ductile shaping may be most readily quantified on analogous S(P) plots, but with appropriate machining variable (grit size, depths of cut, infeed rate) replacing load P. Working in the ductile region offers the promise of compelling time and cost economies in prosthesis fabrication and preparation.

在有关陶瓷研磨、机械加工、喷砂和磨损的文献中已经确定了两种损伤状态——“脆性”和“延性”。在脆性区，损伤机制本质上是裂纹的形成，而在韧性区，则是准塑性。脆性模式的开始对强度构成更大的威胁，因此了解这些材料中的韧性-脆性阈值的力学变得很重要。使用带有锋利压头的受控微接触测试来为一套当代计算机辅助设计/计算机辅助制造牙科陶瓷建立此类阈值。抗弯强度S与压痕载荷P的关系图显示出超过阈值的急剧下降，这与已建立的接触力学关系一致。阈值尺寸出现在 1 µm 量级和 1 N 量级的接触载荷上，这些值与实际的磨砂处理协议相关。通过将磨粒尺寸、施加载荷和切削深度降低到临界水平以下，可以达到陶瓷成型的延展性。提倡在类似的S ( P ) 图上最容易量化延性成形的关键条件，但使用适当的加工变量（磨粒尺寸、切削深度、进给率）代替载荷P。在延展性区域工作为假体制造和准备提供了令人信服的时间和成本经济承诺。