牙冠与牙根交界处呈一弧形曲线，称为牙颈，又名颈缘或颈线。

Tooth coronal and tooth root boundary show one arc curve, call tooth neck, renown neck predestined relationship or neck line.

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结论：天然牙—种植体联合桥主要支撑力的部位是颈缘处，该处为种植体折断机率最大的区域；

Conclusion The main supporting force position is on abutments of the bridge supported by tooth-implant; The implant neck is the most possible area for fracture.

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用游标卡尺分别测量牙长、冠长、根长、颈宽、颈厚、冠宽和冠厚；

The Tooth Length, Crown Length, Root Length, Cervix Width, Cervix Thickness, Crown Width and Crown Thickness were measured with a vernier caliper.

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