[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.

Endodontic management of a fused left maxillary second molar and two paramolars using cone beam computed tomography: A case report

BACKGROUND

Fused teeth usually involve several complications, such as the development of caries in the groove between fused crowns, tooth impaction, diastemas, aesthetic and periodontal problems, and pulpal pathosis, due to the complex anatomical structure of fused teeth. A thorough diagnosis is paramount to forming an accurate treatment plan and obtaining a favourable prognosis. With the advent of cone-beam computed tomography (CBCT), accurate 3-dimensional images of teeth and their surrounding dentoalveolar structures can now be readily obtained, and the technology can accurately provide a minimally invasive approach to acquire detailed diagnostic information. Therefore, we utilize CBCT data herein to generate a digital model for the infected region in a patient, and this model enables us to better plan the management of his case.

CASE SUMMARY

This report details the diagnosis and endodontic treatment of a rare case involving a fused maxillary second molar and two paramolars with apical periodontitis. The patient experienced pain upon biting and cold sensitivity in the area of the maxillary left molar. No caries or other defects were identified in these teeth, and a normal response to a pulp electric viability test was observed. With the aid of CBCT and digital model technology, we initially suspected that the infection originated from the isthmus between the maxillary second molar and two paramolars. Therefore, we only treated the isthmus by an endodontic approach and did not destroy the original tooth structure; furthermore, the vital pulp was retained, and good treatment outcomes were observed at the 24-month follow-up.

CONCLUSION

This finding may provide new insights and perspectives on the diagnosis and treatment of fused teeth.

The effects of endodontic access cavity design on dentine removal and effectiveness of canal instrumentation in maxillary molars

AIM

To evaluate in a laboratory setting, the impact of three designs of endodontic access cavities on dentine removal and effectiveness of canal instrumentation in extracted maxillary first molars using micro-computed tomography (micro-CT).

METHODOLOGY

A total of 30 extracted intact maxillary first molars were selected and scanned by micro-CT with a voxel size of 24 µm and randomly distributed into three groups: the traditional endodontic cavity (TEC) group, the conservative endodontic cavity (CEC) group and the guided endodontic cavity (GEC) group. The pulp chambers of teeth in the groups were accessed accordingly. After root canal preparation, the teeth were rescanned. The volume of dentine removed after canal preparation, the noninstrumented canal areas, canal transportation and centring ratio were analysed. Data were analysed statistically using one-way analysis of variance. Tukey's post hoc test was used for multiple comparisons. The significance level was set at p < .05.

RESULTS

The total volume of dentine removed was significantly greater in the TEC group after root canal preparation (p < .05). No significant differences in the volume of dentine removed occurred between the CEC and GEC groups (p > .05). The volume of dentine removed in the crown, pericervical dentine and coronal third of the canal was significantly lower in CEC and GEC groups when compared to that in the TEC group (p < .05), no difference was observed in the middle third of the canal and apical third of the canal amongst the three groups (p > .05). There was no significant difference in noninstrumented canal area, canal transportation and centring ratio amongst the TEC, CEC and GEC groups (p > .05).

CONCLUSIONS

In extracted maxillary molars tested in a laboratory setting, CEC and GEC preserved more tooth tissue in the crown, pericervical dentine and coronal third of the canal compared with TEC after root canal preparation. The design of the endodontic access cavity did not impact on the effectiveness of canal instrumentation in terms of noninstrumented canal area, canal transportation and centring ratio.

[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.

Application of robotics in stomatology

The application of robots in oral treatment can not only reduce the work intensity of clinicians but also improve the accuracy of treatment. In this article, the application and research status of robots in stomatology are reviewed.

Development and application of a rapid rehabilitation system for reconstruction of maxillofacial soft-tissue defects related to war and traumatic injuries

BACKGROUND

The application of a maxillofacial prosthesis is an alternative to surgery in functional-aesthetic facial reconstruction. Computer aided design/computer aided manufacturing has opened up a new approach to the fabrication of maxillofacial prostheses. An intelligentized rapid simulative design and manufacturing system for prostheses was developed to facilitate the prosthesis fabrication procedure.

METHODS

The rapid simulation design and rapid fabrication system for maxillofacial prostheses consists of three components: digital impression, intelligentized prosthesis design, and rapid manufacturing. The patients' maxillofacial digital impressions were taken with a structured-light 3D scanner; then, the 3D model of the prostheses and their negative molds could be designed with specific software; lastly, with resin molds fabricated by the rapid prototyping machine, the prostheses could be produced directly and quickly.

RESULTS

Fifteen patients with maxillofacial defects received prosthesis rehabilitation provided by the established system. The total clinical time used for each patient was only 4 hours over 2 appointments on average. The contours of the prostheses coordinated properly with the appearance of the patients, and the uniform-thickness border sealed well to adjacent tissues. All of the patients were satisfied with their prostheses.

CONCLUSIONS

The rapid simulative rehabilitation system of maxillofacial defects is approaching completion. It could provide an advanced technological solution for the Army in cases of maxillofacial defect rehabilitation.