Accuracy Of "All-on-4" Implant Placement Using Computer-assisted Surgery

Objective:For patients with bone resorption of the jaw,the computer-aided template was used to guide the "All-on-4" implant surgery accurately.Subsequently,the error between the actual position and the simulated position of the implant in the jaw was systematically evaluated,and the relevant factors affecting its accuracy were further explored.Methods:A retrospective collection of 5 patients with poor chewing function and severe periodontitis had been done the "All-on-4" surgery by the guidance of digital guides in the Implant Center of the Affiliated Stomatological Hospital of Zhejiang University School of Medicine from January 2017 to November 2018.Among them,3 patients underwent mandibular surgery,while others underwent maxillary surgery.The patients'CBCT imaging data were collected preoperatively.And according to the acquired data and the patients' functional and aesthetic restoration requirements,the computer-assisted simulation teclinique was used to digitally simulate the 3D position of implants in the jaw bone,then on this basis,design and produce a personalized digital half-guided template.Under the guidance of the template,the procedure was accurately performed and the CBCT was taken again after surgery to obtain the actual position of the implant in the jaw.Finally,the virtual position of the 20 implants was compared with the actual position in many aspects,including angle,depth,bucco-lingual and mesio-distal point,to obtain various offset errors for statistical analysis.At the same time,the offset distance in each dimension is converted into a percentile error score table,and an error analysis map is drawn to visually evaluate the deviation difference of the implants between the tilt group(anterior region)and the non-tilt group(posterior region).Results:20 implants were in good position,and their initial stability was 35N*cm and above.After the operation,none were loose,and all combined well.Both temporary dentures could be loaded immcdiately.And the postoperative images were reconstructed in three dimensions and matched with patients ' simulated model.By digital analysis and comparison,in the anterior region(non-tilted implants),the angle deviation(a)is(2.82±0.83)°?and the apical deviation(a)is(0.87±0.39)mm,the crown deviation(c)is(0.77±0.27)mm,the depth deviation(d)is(0.40±0.14)mm,the bucco-lingual deviation(b)is(0.49±0.14)mm,and the mesio-distal deviation(m)is(0.55 ± 0.15)mm.While,in the posterior reg,ion(inclined implant),angle deviation(a)is(2.23±1.05)°,the apical deviation(a)is(0.98±0.44)mm,the crown deviation(c)is(0.71 ±0.27)mm,and the depth deviation(d)is(0.53±0.25)mm,the bucco-lingual deviation(b)is(0.39 ± 0.19)mm,and the mesio-distal deviation(m)is(0.49 ± 0.23)mm.There was no significant difference in the error parameters between the tilt group(rear tooth area)and the non-tilt group(anterior tooth area)(P>0.05).Conclusions:(1)Using computer-assisted simulation of "All-on-4" implant surgery,a personalized treatment plan can be designed for patients with severe bone resorption of the jaw.(2)Compared with the existing digital templates,the half-guided templates designed and manufactured in this study has higher accuracy,and can guide the surgeon to perform the implant surgery more accurately,avoiding the damage of the important anatomical structure of the jaw bone;and the accuracy control did not show significant differences between the tilted and non-tilted implants.However,the specific level of accuracy is subject to further statistical results in the future.(3)Analysis of the error factors can help to further improve the accuracy of“All-on-4”surgery guided by the half-way templates,which is of great significance for the design of preoperative implant sites,reducing the bone mass requirements of the operation area,and appropriately relaxing the indications.