[Exploration of making removable partial denture by digital technology].

To explore the digital manufacturing process of distal extension removable partial denture. From November 2021 to December 2022, 12 patients (7 males and 5 females) with free-ending situation were selected from the Department of Prosthodontics, School of Stomatology, The Fourth Military Medical University. Three-dimensional model of the relationship between alveolar ridge and jaw position was obtained by intraoral scanning technique. After routine design, manufacturing and try-in of metal framework for removable partial denture, the metal framework was located in the mouth and scanned again to obtain the composite model of dentition, alveolar ridge and metal framework. The free-end modified model is obtained by merging the digital model of free-end alveolar ridge with the virtual model with the metal framework. The three-dimensional model of artificial dentition, and base plate was designed on the free-end modified model, and the resin model were made by digital milling technology. The removable partial denture was made by accurately positioning the artificial dentition and base plate, bonding metal framework with injection resin, grinding and polishing the artificial dentition and resin base. Compared with the design data after clinical trial, the results showed that there was an error of 0.4-1.0 mm and an error of 0.03-0.10 mm in the connection between the resin base of artificial dentition and the connecting rod of the in-place bolt and the connection between artificial dentition and resin base. After denturen delivery, only 2 patients needed grinding adjustment in follow-up visit due to tenderness, and the rest patients did not find any discomfort. The digital fabrication process of removable partial denture used in this study can basically solve the problems of digital fabrication of free-end modified model and assembly of artificial dentition with resin base and metal framework.

[Trueness of 4 three-dimensional facial scanners: an in vitro study].

Objective: To investigate the trueness of 4 three-dimensional (3D) facial scanners and to evaluate the applicability of their clinical use. Methods: An art head model was used as the scanning object, and it was scanned by Handyscan 3D scanner in an enclosed environment with a fixed light source to obtain the reference digital model. Three fixed 3D facial scanners (A: 3dMDface; B: Facego Pro; C: RDS Facescan) and a portable hand-held 3D facial scanner (D: Revopoint POP 2) were used to scan the art head model 10 times, and 10 models of each scan group were obtained. The face of the reference model was divided into 16 regions according to anatomy and muscle distributions in the Geomagic Wrap software with saved boundary curves of whole face and each region. The test models were also divided into 16 regions through the curves above after registered with the reference model through "Best fit" function. The root-mean-square error (RMS) of the complete test models and their segmented regions compared with the reference model and its corresponding regions were calculated by 3D comparison function. The smaller the RMS, the higher the accuracy. One-way ANOVA and SNK post-test were used for statistical analysis. Results: RMS of complete test models scanned by A, B, C, D scanners were (0.295±0.005), (0.216±0.053), (0.059±0.012) and (0.103±0.026) mm (F=123.81, P<0.001), respectively. There was significant difference between any two groups (P<0.05). For each facial region, the group D had the best trueness in nasal region, lip region, left orbital region and right orbital region [RMS were (0.079±0.032), (0.061±0.019), (0.058±0.021), (0.081±0.032) mm, respectively], while the group C had the best trueness in frontal region, left buccal region, right buccal region, left zygomatic region, right zygomatic region, left parotideomasseteric region, right parotideomasseteric region, left temporofacial region, right temporofacial region, mental region, left infraorbital region and right infraorbital region [RMS were (0.039±0.011), (0.034±0.007), (0.033±0.007), (0.066±0.023), (0.038±0.022), (0.070±0.030), (0.067±0.024), (0.063±0.029), (0.045±0.023), (0.063±0.006), (0.039±0.010), (0.046±0.008) mm, respectively]. Conclusions: On the basis of art head model scanning, although the overall average deviation between the scanning model and the reference models obtained by the four kinds of 3D facial scanners were small, the portable handheld 3D facial scanner (D) has better accuracy than the fixed 3D facial scanners (A, B, C) in the orbital area, nasal area, lip area and areas with rich features.

[Animal experiment on the accuracy of the Autonomous Dental Implant Robotic System].

Objective: To evaluate the accuracy of the Autonomous Dental Implant Robotic System (ADIR) in vivo through animal experiments. Methods: Nine canine models with bilateral mandibular premolars loss were prepared. Two implants were placed in each side of canine's mandibular edentulous area. On each side, the two implants were completed by ADIR (robot group) and one experienced doctor using digital full-guided plate (guide template group) respectively. After the operation, the deviation between the actual implant position and the planned position was evaluated. The primary stability of the implant was measured, and the results of the robot group and the guide template group were statistically analyzed. Results: ADIR could successfully place implant for missing teeth in animals, and the coronal deviation, apical deviation and angular deviation [M(Q)] were 0.269 (0.152) mm, 0.254 (0.218) mm and 0.989° (0.517°) respectively, which were significantly lower than those of guide template group [the coronal deviation, apical deviation and angular deviation were 0.910 (0.872) mm, 1.179 (1.176) mm and 4.209°(5.208°) respectively] (P<0.05). Besides, there was no significant difference in the primary stability of the implant between the two groups (P>0.05). Conclusions: This study confirmed the accuracy of the ADIR in vivo, and laid a foundation for further clinical trials.

[Construction and application of the digital system for determining maxillo-mandibular relationship in jaw defects reconstruction].

Digital techniques are widely applied into jaw defects reconstruction. Influence of surgeon's personal factors on surgical results could be greatly reduced. The combined pattern of grafting bone segments and their fixed position in defect area have direct effects on the final results, and should be considered as a form of maxillo-mandibular relationship determination. Digital technology is an important basis for its realization. In the design process, the determination of the space position of the graft in the recipient area must follow some basic principles and methods. Only when the esthetic and masticatory function requirements are considered, can the ideal maxillo-mandibular relationship be obtained. In this paper, the principals and methods of maxillo-mandibular relationship determination and its application in digital jaw defects reconstruction were summarized, in order to provide clinical references and to improve the quality of jaw defects reconstruction.