目的：通过测量分析下颌无牙颌患者的锥形束CT（conebeam computed tomography, CBCT）图像，测量可能植入种植体的A-P距离（anterior-posterior distance），分类前部颌弓形态，探究颌弓形态对“All-on-4”远中倾斜种植体临床设计的影响。方法：收集下颌无牙颌患者的CBCT图像共74例，其中男性35例，女性39例,拟行“All-on-4”种植固定义齿修复。在经颏孔并平行于牙合平面的平面上测量可能植入种植体的A-P距离，分类前部颌弓形态,测量由颏孔往近中方向7.5 mm的颌骨段所跨过的颌弓弧度，探究A-P距离与该弧度的相关性。结果：74例患者测得可植入的颏孔间区种植体的A-P距离为(8.5±1.5) mm（最小为4.5 mm，最大为11.8 mm），其中≤7 mm者占12.2%（男性3例，女性6例），颌弓为方圆形；>7 mm、≤9 mm者占54.0%（男性20例，女性20例）， 颌弓为卵圆形；>9 mm者占33.8%（男性12例，女性13例），颌弓为尖圆形。测量患者颏孔前方7.5 mm颌弓段转角弧度，左、右两侧共测得148个数据，平均为15.9°±5.5°（最小为5.6°，最大为35.2°）。统计分析发现，AP距离与转角弧度呈显著负相关。结论：本研究中下颌无牙颌患者的前部颌弓形态中，卵圆形所占百分比最多，尖圆形次之，方圆形最少。女性方圆形颌弓者多于男性，卵圆形和尖圆形颌弓与性别无明显相关。颌弓越方，A-P距离越小，颏孔前区颌弓弧度就越大，远中斜行种植体所需要的骨宽度就越大。下颌无牙颌患者的“All-on-4”种植固定修复采用远中斜行种植体，术前应评估颌弓形态，设计远中种植体的合理倾角，远中种植位点的骨宽度应在常规要求外留有余量。方圆形颌弓是“All-on-4”种植固定修复的不利因素。

Objective：To classify the interforaminal arch form of edentulous mandibles by measuring the anterior-posterior distance (A-P distance) of implants planned to be inserted in “All-on-4” protocol using conebeam computed tomography (CBCT) data, and to investigate the influence of the arch form on the “All-on-4” distally tilted implants. Methods: Seventy-four CBCT images of edentulous mandibles were collected, including 35 males and 39 females respectively. “All-on4”implant supported fixed prostheses were designed for these patients based on the CBCT data. The A-P distance was measured in the plane which crossed bilateral mental foramens and was parallel to the occlusal plane. The interforaminal arch form of edentulous mandibles were classified according to the A-P distance. The radian of the jaw arch 7.5 mm mesially to the mental foramen was measured bilaterally, and its correlation with the A-P distance was studied. Results: The average A-P distance of implant supported fixed prostheses planned in the interforaminal region was (8.5±1.5) mm (minimum 4.5 mm, maximum 11.8 mm). In the study, 12.2% of the subjects’ mandibles were classified as square arch form with A-P distances ≤7 mm, 54.0% were classified as ovoid with A-P distances >7 mm and ≤9 mm,  33.8% were classified as tapered with A-P distances >9 mm. Bilaterally, 148 results of the radian of the jaw arch 7.5 mm mesially to the mental foramen were obtained, and the average radian was 15.9°±5.5° (minimum 5.6°, maximum 35.2°). The radian and the AP distance showed a negative correlation with statistical significance. Conclusion: In this research, the ovoid arch form was the most common type in edentulous mandibles, followed by tapered arch form. The square arch form showed the lowest percentage. As the arch form went squarer, the A-P distance became shorter, the radian of the jaw arch mesially to the mental foramen went greater, and the bone width that distally tilted implants need became bigger. The interforaminal arch form of the edentulous mandible should be analyzed before an implant supported fixed restoration is designed in the interforaminal region. The angle of inclination of distal implants should be reasonable. The bone width of the distal implant site must be adequate. The square arch form contributes negatively to the structure of implant supported fixed prostheses with distal cantilever design.