Yoshitani Masazumi, Takayama Yoshiyuki, Yokoyama Atsuro
Division of Oral Functional Science, Department of Oral Functional Prosthodontics, Graduate School of Dental Medicine, Hokkaido University, Kita-13, Nishi-7, Kita-ku, Sapporo, 060-8648, Japan.
Removable Prosthodontics, Hokkaido University Hospital, Hokkaido University, Kita-14, Nishi-5, Kita-Ku, Sapporo, 060-8648, Japan.
Int J Implant Dent. 2018 Feb 27;4(1):4. doi: 10.1186/s40729-018-0117-7.
Dental implants are frequently applied to unilateral defects in the mandible. However, implant placement in the molar region of the mandible can be difficult due to anatomical structure. The aim of this study was to evaluate the distribution of occlusal force in a mandibular shortened dental arch (SDA) with implants.
Three-dimensional finite element (FE) models of the mandible with varying numbers of teeth and implants were constructed. Models Im6 and Im67 contained one and two implants in the defect of the left molar region, respectively. Models Im456 and Im4567 contained three and four implants in the defect of the left premolar and molar regions, respectively. Model MT67 contained a defect in the molar region with no implant placed. Model MT7 represented natural dentition without a left second molar, as a control. Modification of the condition of occlusal contacts assuming the intercuspal position was performed before analysis under load 400 N; therefore, the load condition as total force on the occlusal surface was 400 N. FE analyses were subsequently performed under load conditions of loads 100, 200, and 800 N. The distribution of reaction forces on the occlusal surface and the mandibular condyle was investigated.
Force distribution in models Im67 and Im4567 appeared to be symmetrical under all load conditions. Occlusal force distribution in models Im6 and Im456 was similar to that in model MT7. However, the occlusal force at the second premolars on the defect side in those models was larger under loads 100 and 200 N. Conversely, the occlusal force on the first molars was much larger than that in model MT7 under load 800 N.
Within the limitations of this theoretical study, we demonstrated that restoration with the same number of implants as missing teeth will show almost symmetric occlusal force distribution, and it will produce less biomechanically stress for a unilateral defect of the mandible. However, if restoration of a missing second molar with an implant is impossible or difficult, then an SDA with implants may also be acceptable except for individuals with severe bruxism.
牙种植体常用于下颌单侧缺损。然而，由于解剖结构的原因，在下颌磨牙区植入种植体可能具有挑战性。本研究旨在评估种植体在下颌短牙弓（SDA）中的咬合力分布情况。
构建了具有不同数量牙齿和种植体的下颌三维有限元（FE）模型。模型Im6和Im67分别在左侧磨牙区缺损处包含1枚和2枚种植体。模型Im456和Im4567分别在左侧前磨牙和磨牙区缺损处包含3枚和4枚种植体。模型MT67在磨牙区有缺损，未植入种植体。模型MT7代表无左侧第二磨牙的天然牙列，作为对照。在400 N载荷分析前，假设牙尖交错位进行咬合接触条件的修改；因此，咬合面上的总力载荷条件为400 N。随后在100、200和800 N的载荷条件下进行有限元分析。研究了咬合面和下颌髁突上的反作用力分布。
在所有载荷条件下，模型Im67和Im4567中的力分布似乎是对称的。模型Im6和Im456中的咬合力分布与模型MT7相似。然而，在100和200 N载荷下，这些模型中缺损侧第二前磨牙处的咬合力更大。相反，在800 N载荷下，第一磨牙上的咬合力比模型MT7中的大得多。
在本理论研究的局限性内，我们证明种植体数量与缺失牙齿数量相同的修复将显示几乎对称的咬合力分布，并且对于下颌单侧缺损将产生较小的生物力学应力。然而，如果用种植体修复缺失的第二磨牙不可能或困难，那么除了严重磨牙症患者外，种植体支持的SDA也可能是可以接受的。
