Department of Restorative Dentistry, College of Dentistry, University of Illinois at Chicago, 801 South Paulina St, Chicago, IL 60612, USA.
Department of Restorative Dentistry, College of Dentistry, University of Illinois at Chicago, 801 South Paulina St, Chicago, IL 60612, USA; Department of Restorative Dentistry, School of Dentistry, Municipal University of São Caetano do Sul, Rua Santo Antônio 50, São Caetano do Sul, São Paulo 09521-160, Brazil.
J Biomech. 2020 Mar 5;101:109633. doi: 10.1016/j.jbiomech.2020.109633. Epub 2020 Jan 16.
This study investigated the contribution of small leucine rich proteoglycans (SLRPs) to the fracture toughness of the dentin extracellular matrix (ECM) by enzymatically-assisted selective removal of glycosaminoglycan chains (GAGs) and proteoglycans (PGs) core protein. We adapted the Mode III trouser tear test to evaluate the energy required to tear the dentin ECM. Trouser-shaped dentin specimens from crown and root were demineralized. Depletion of GAGs and PGs followed enzymatic digestion using chondroitinase ABC (c-ABC) and matrix metalloproteinase 3 (MMP-3), respectively. The legs from specimen were stretched under tensile force and the load at tear propagation was determined to calculate the tear energy (T, kJ/m). SLRPs decorin and biglycan were visualized by immunohistochemistry and ECM tear pattern was analyzed in SEM. Results showed T of crown ECM was not affected by PGs/GAGs depletion (p = 0.799), whereas the removal of PGs significantly reduced T in root dentin ECM (p = 0.001). Root dentin ECM exhibited higher T than crown (p < 0.03), however no regional difference are present after PG depletion (p = 0.480). Immunohistochemistry confirmed removal of GAGs and PGs. SEM images showed structural modifications after PGs/GAGs removal such as enlargement of dentinal tubules, increased interfibrillar spaces and presence of untwisted fibrils with increased diameter. Findings indicate that the capacity of the PGs to unfold and untwist contribute to the dentin ECM resistance to tear, possibly influencing crack growth propagation. The regional differences are likely an evolutionary design to increase tooth survival, that undergoes repetitive mechanical loading and load stress dissipation over a lifetime of an individual.
本研究通过酶辅助选择性去除糖胺聚糖 (GAGs) 和蛋白聚糖 (PGs) 核心蛋白，研究了小富含亮氨酸的蛋白聚糖 (SLRPs) 对牙本质细胞外基质 (ECM) 断裂韧性的贡献。我们采用 Mode III 裤型撕裂试验来评估撕裂牙本质 ECM 所需的能量。从冠部和根部切取裤型牙本质标本，进行脱矿处理。分别使用软骨素酶 ABC (c-ABC) 和基质金属蛋白酶 3 (MMP-3) 进行酶消化，以耗尽 GAGs 和 PGs。将标本的腿部拉伸至张力下，并测定撕裂传播时的载荷以计算撕裂能 (T，kJ/m)。通过免疫组织化学观察 SLRPs 核心蛋白 decorin 和 biglycan，并用 SEM 分析 ECM 的撕裂模式。结果表明，PGs/GAGs 耗竭对冠部 ECM 的 T 没有影响 (p = 0.799)，而 PGs 的去除显著降低了根部牙本质 ECM 的 T (p = 0.001)。根部牙本质 ECM 的 T 高于冠部 (p < 0.03)，但 PG 耗竭后没有区域差异 (p = 0.480)。免疫组织化学证实 GAGs 和 PGs 已被去除。SEM 图像显示 PGs/GAGs 去除后牙本质结构发生了改变，如牙本质小管扩大、纤维间间距增加以及出现直径增大的未扭曲纤维。研究结果表明，PGs 的展开和未扭曲能力有助于牙本质 ECM 抵抗撕裂，可能影响裂纹生长传播。区域差异可能是一种进化设计，旨在增加牙齿的存活率，因为牙齿在个体的一生中会经历反复的机械加载和载荷应力耗散。
