[Research on friction and wear behaviors of silicon-lithium spray coating on zirconia ceramics].

OBJECTIVE: To study microstructure, friction and wear behaviors of silicon-lithium spray coating on the surface of zirconia ceramics and to preliminarily evaluate its esthetic so as to provide support and guidance for the clinical application. METHODS: Zirconia ceramic specimens were randomly divided into three groups: coating group (two subgroups), polishing group (two subgroups), and glazing group (four subgroups), with 10 samples in each subgroup. The two subgroups of coating group were the zirconia ceramics with the untreated and preliminary polishing surfaces sprayed with silicon-lithium coating, respectively. The two subgroups of polishing group were preliminary polishing and fine polishing of zirconia ceramics, respectively. The four subgroups of glazing group were preliminarily polished zirconia ceramics glazed with Biomic and Stain/Glaze products, respectively; and untreated zirconia ceramics glazed with Biomic and Stain/Glaze products, respectively. The above 8 subgroups of zirconia ceramic specimens were used as friction pairs with 80 steatite ceramics for 50 000 chewing cycles under 50 N vertical load and artificial saliva lubrication using chewing simulation. Scanning electron microscope was used to observe the microstructure of the surface and section of the coating group, and the thickness of the coating and glazing were measured. The linear roughness of the coating and polishing groups was mea-sured using a laser confocal scanning microscope. Vickers hardness was measured using a microhardness tester and the esthetic of zirconia ceramic full crown sprayed with silicon-lithium coating was preliminarily evaluated. White light interferometer was used to measure the width, the maximum depth and the volume of the wear scars of each group, and the wear depth of steatite ceramics and wear rate of zirconia ceramic specimens were calculated. Kruskal-Wallis nonparametric test and Dunn's multiple comparisons test were used to analyze the wear depth of each group (α=0.05). RESULTS: The microstructures of the silica-lithium spray coatings on the untreated and preliminarily polished zirconia ceramic surfaces showed the protruding defects, and the line roughness of coating group was larger than that of the polishing group. The median thickness of the silica-lithium spray coating on the preliminarily polished zirconia ceramic was 13.0 µm (interquartile range, IQR: 11.6, 17.9), while that of the silica-lithium spray coating on the untreated zirconia ceramic was 4.4 µm (IQR: 4.1, 4.7). The Vickers hardness and wear rate of the coating group were between the polishing group and the glazing group. The wear depths of the wear scars of steatite ceramics were the glazing group, coating group, and polishing group in descending order, and there was statistically significant difference between glazing and polishing groups (P < 0.05). With the increase of polishing procedure, the wear depth of steatite ceramics decreased in each subgroups. The orders of maximum depth and volume of wear scars of zirconia ceramic were the glazing group, coating group, and polishing group in descending order, and there was statistically significant difference in the maximum depth of wear scars between glazing and polishing groups (P < 0.05). CONCLUSION: The silica-lithium spray coating on the zirconia ceramic, can be used as a new method for zirconia ceramic surface treatment, because it can increase the esthetic of zirconia ceramics compared with polishing and reduce the wear of steatite ceramics compared with glazing.

[Independent innovation research, development and transformation of precise bionic repair technology for oral prosthesis].

According to the fourth national oral health epidemiological survey report (2018), billions of teeth are lost or missing in China, inducing chewing dysfunction, which is necessary to build physiological function using restorations. Digital technology improves the efficiency and accuracy of oral restoration, with the application of three-dimensional scans, computer-aided design (CAD), computer-aided manufacturing (CAM), bionic material design and so on. However, the basic research and product development of digital technology in China lack international competitiveness, with related products basically relying on imports, including denture 3D design software, 3D oral printers, and digitally processed materials. To overcome these difficulties, from 2001, Yuchun Sun's team, from Peking University School and Hospital of Stomatology, developed a series of studies in artificial intelligence design and precision bionics manufacturing of complex oral prostheses. The research included artificial intelligence design technology for complex oral prostheses, 3D printing systems for oral medicine, biomimetic laminated zirconia materials and innovative application of digital prosthetics in clinical practice. The research from 2001 to 2007 was completed under the guidance of Prof. Peijun Lv and Prof. Yong Wang. Under the support of the National Natural Science Foundation of China, the National Science and Technology Support Program, National High-Tech R & D Program (863 Program) and Beijing Training Project for the Leading Talents in S & T, Yuchun Sun's team published over 200 papers in the relevant field, authorized 49 national invention patents and 1 U.S. invention patent and issued 2 national standards. It also developed 8 kinds of core technology products in digital oral prostheses and 3 kinds of clinical diagnosis and treatment programs, which significantly improved the design efficiency of complex oral prostheses, the fabrication accuracy of metal prostheses and the bionic performance of ceramic materials. Compared with similar international technologies, the program doubled the efficiency of bionic design and manufacturing accuracy and reduced the difficulty of diagnosis and cost of treatment and application by 50%, with the key indicators of those products reaching the international leading level. This program not only helped to realize precision, intelligence and efficiency during prostheses but also provided functional and aesthetic matches for patients after prostheses. The program was rewarded with the First Technical Innovation Prize of the Beijing Science and Technology Awards (2020), Gold Medal of Medical Research Group in the First Medical Science and Technology Innovation Competition of National Health Commission of the People's Republic of China (2020) and Best Creative Award in the First Translational Medical Innovation Competition of Capital (2017). This paper is a review of the current situation of artificial intelligence design and precision bionics manufacturing of complex oral prosthesis.

[Analysis of types and treatment methods of cervical massive hemorrhage].

Objective: To summarize the classification and clinical treatment experience of cervical massive hemorrhage in multiple centers. Methods: From April 2012 to October 2020, clinical data of 42 patients with cervical massive hemorrhage were retrospectively analyzed, including 27 cases from Shanghai Changzheng Hospital, 7 cases from Hunan Provincial People's Hospital, 4 cases from Longkou People's Hospital and 4 cases from Laizhou People's Hospital. According to bleeding position (P), bleeding vessel (V), cerebral blood supply (C), and the presence or absence of associated injury (A), 42 patients were classified as "PVCA", and summarize the methods of pre-hospital emergency and in-hospital treatment based on the "ABC" treatment principles: airway rebuild (A), effective arterial hemostasis and bleeding stop (B), and cerebral blood flow reconstruction within the time window (C). Results: Within the 42 cases of cervical massive hemorrhage, there were 3 cases of type P1 (below cricoid cartilage), 28 cases of type P2 (cricoid cartilage-mandibular angle), 11 cases of type P3 (mandibular angle-skull base); 22 cases of type V1 (arterial hemorrhage), 11 cases of type V2 (main venous hemorrhage), 7 cases of type V3 (simple superficial vein or small artery hemorrhage), 2 cases of type V4 (mixed arteriovenous hemorrhage); 5 cases of type C0 (no symptoms of cerebral ischemia and neurological dysfunction), 33 cases of type C1 (transient cerebral ischemia without sensory disturbance), 4 cases of type C2 (symptoms of cerebral ischemia and neurological dysfunction); 39 cases of type A0 (no other system damage was involved) and 3 cases of type A1 (combined with other system damage). All 42 patients received operations, 25 patients received open surgery of vascular reconstruction+hematoma/foreign body removal (7 cases of vascular ligation, 14 cases of direct suture repair, 4 cases of vascular interposition), 17 patients received hybrid surgery (carotid angiography+covered stent repair+hematoma/foreign body removal). The surgical technique success rate the was 100%. All the hemorrhagic shock was corrected, hematoma compression was relieved, and the symptoms of cephalic ischemia were improved. There were 4 cases of local cranial nerve injury, 1 case of incision hematoma and 6 cases of postoperative hyper perfusion. During the average 14.3 months follow-up, there was no operation related myocardial infarction, stroke or death, no re-rupture or re-dissection, and 50% asymptomatic restenosis was found in 1 case one year after received covered stent endovascular repair. Conclusion: Based on the "PVCA" classification and "ABC" treatment principle, it is safe and effective to rescue cervical massive hemorrhage.

[Visual sensitivity threshold of lateral view of nasolabial Angle changes in edentulous jaw patients].

OBJECTIVE: To study the visual sensitivity threshold of physician's naked eye to the difference of nasolabial angle in edentulous jaw patients, and to provide a reference value for the study of aesthetic evaluation of soft tissue profile for the difference of nasolabial angle that can be recognized by human eyes. METHODS: Three-dimensional facial images of three edentulous patients with different diagnostic dentures introoral were obtained. Lateral screenshots of each patient's three-dimensional facial image with the same scale were obtained by using reverse engineering software (Geomagic studio 2014).The screenshot of the patient's three-dimensional facial image with suitable lip support (The suitable lip support was confirmed by both patients and prosthodontists who had clinical experience for more than 20 years) was taken as the reference picture, and the remaining pictures were grouped with it respectively. All the pictures were observed in random order by the subjects. Fifteen dentists were asked to judge the difference of nasolabial angle between the two pictures of each group on the computer screen. The difference of nasolabial angle between the two pictures in each group was measured and calculated. The ROC curve was drawn, and the best cut-off value was calculated as the visual sensitivity threshold. RESULTS: The data of the 15 subjects were used to draw ROC curves separately. The maximum and minimum best cut-off values were 5.55 degrees and 3.12 degrees respectively. The ROC curve of the whole 15 subjects was drawn after data aggregation, and the best cut-off value was 5.36 degrees (AUC=0.84>0.5, P=0.000<0.05). When the difference of nasolabial angle was above 5.36 degrees, the subjects could recognize it effectively. CONCLUSION: There is a visual limit in the observation of the nasolabial angle with the naked eye. In this study, a visual sensitivity threshold of 5.36 degrees for the difference of the nasolabial angle was obtained. The difference of nasolabial angle below this value can be regarded as no clinical significance. This result provides a reference value for human eyes to recognize the difference of nasolabial angle in soft tissue profile aesthetic evaluation. It can be applied to the aesthetic evaluation of soft tissue profile and can be used as the error level of related research with nasolabial angle as an index for accuracy evaluation.

[Independent innovation research of functionally suitable denture digital system].

Fabrication of conventional complete dentures involves a complex restoration method, requiring significant time and typically involving primary impressions, definitive impressions, jaw relation records, clinic try-in, and complete denture placement, which has been used for nearly a century without change. A novel digital system named Functionally Suitable Denture (FSD) was researched and developed so as to reduce clinical steps, operation difficulties and errors of complete denture restoration. It pioneered a unique diagnostic complete denture aided by computer aided design (CAD) & 3D printing, by which, the functional impression, jaw relation, and try-in (3 steps) were simplified to 1 step, thus the number of visits to the dentist was reduced by 2 times. Moreover, for the first time, it put forward a CAD software of template matching based on the expert design, which was an efficient and intelligent design scheme, and the excellent denture experts' experience and skills could be inherited and iterated. The system included the 3D scanner with appropriate accuracy and high efficiency, the CAD software, the special 3D printer and process software, and the innovative clinical operation process. The Patent Cooperation Treaty (PCT) patent international search report showed that all the 15 claims of the technology were of novelty, creativity and industrial utility. All the digital products were independently developed and made by Peking University School and Hospital of Stomatology, China. The design and manufacture process of denture prosthesis was fast, simple and accurate. At the same time, personalized functional and aesthetic matching of the patients after wearing prosthesis was realized. It effectively solved the global problems of "slow, difficult and inaccurate" of the traditional manual technology of complete denture, and brought good news to edentulous patients. Compared with the traditional complete denture treatment, FSD system has a wide range of applications for different types of edentulous patients, including those with severe resorption of the alveolar ridge or a high occlusal force. Furthermore, the low-cost of 3D printers, compared with expensive milling machines, may make the approach more accessible. This review describes that our research is related to the development of the FSD system, including multi-source data acquisition technology, three generations of complete denture design software, 3D printing systems of individual tray and complete denture pattern, the clinical and laboratory operation process of the FSD system.

[New intraoral digital impression with pneumatic gingival retraction used in the restoration of crown for posterior teeth: a case report].

In fixed prosthodontics, clear exposure of the preparation margin is the prerequisite for obtaining accurate digital impressions and improving the marginal fit of restorations. To resolve the issues associated with the cord retraction technique, such as pain, acute injury, and prolonged procedural time, this study proposes a new technology for intraoral digital impression taking with pneumatic gingival retraction. The new scanning head blows a high-speed airflow that instantaneously separates the free gingiva, locally exposing the subgingival preparation margin. Combined with the farthest point preservation stitching algorithm based on the distance from the normal vector and high-speed laser scanning photography, it achieves global preparation edge data and gingival reconstruction, realizing painless, non-invasive, and efficient precise acquisition of the preparation margin. Using this new technique, a patient with a full porcelain crown restoration on a posterior tooth was treated. The digital impression revealed a clear margin of the preparation, and the crown made from this data has a good marginal fit.

[Effect of P311 microspheres-loaded thermosensitive chitosan hydrogel on the wound healing of full-thickness skin defects in rats].

Objective: To explore the effect of P311 microspheres-loaded thermosensitive chitosan hydrogel on the wound healing of full-thickness skin defects in rats. Methods: The method of experimental study was adopted. The polyvinyl alcohol/sodium alginate microspheres (simple microspheres), P311 microspheres, and bovine serum albumin labeled with fluorescein isothiocyanate (FITC-BSA) microspheres were prepared by water-in-oil emulsification, and then their morphology was observed under a light microscope/inverted fluorescence microscope. Chitosan solution was prepared, chitosan solution and ß-glycerol phosphate disodium hydrate were mixed to prepare simple thermosensitive hydrogels, and thermosensitive hydrogels loaded with simple microspheres or P311 microspheres were prepared by adding corresponding substances in simple thermosensitive hydrogels. The morphological changes of the prepared four liquids in the state of tilt was observed at 37 ℃. After being freeze-dried, the micromorphology of the prepared four liquids was observed under a scanning electron microscope. Eighteen 3-4-week-old male Sprague-Dawley rats were divided into normal group without any treatment, dressing group, chitosan group, hydrogel alone group, simple microspheres-loaded hydrogel group, and P311 microspheres-loaded hydrogel group, which were inflicted with one full-thickness skin defect wound on both sides of the back spine and were dealt correspondingly, with 3 rats in each group. Rats with full-thickness skin defects in the five groups were collected, the wound healing was observed on post injury day (PID) 0 (immediately), 5, 10, and 15, and the wound healing rates on PID 5, 10, and 15 were calculated. The wound and wound margin tissue of rats with full-thickness skin defects in the five groups on PID 15 and normal skin tissue in the same site of rats in normal group were collected, hematoxylin and eosin staining was conducted to observe the histological changes, immunohistochemical staining was performed to observe the expressions of CD31 and vascular endothelial growth factor (VEGF), and Western blotting was conducted to detect the protein expressions of CD31 and VEGF. The number of samples was all three. Data were statistically analyzed with one-way analysis of variance, analysis of variance for repeated measurement, and Bonferroni correction. Results: Simple microspheres were spherical, with loose and porous surface. The surfaces of P311 microspheres and FITC-BSA microspheres were smooth without pores, and the FITC-BSA microspheres emitted uniform green fluorescence. The diameters of the three microspheres were basically consistent, being 33.1 to 37.7 µm. Compared with chitosan solution and simple thermosensitive hydrogel, the structures of the two microspheres-loaded hydrogels were more stable in the state of tilt at 37 ℃. The two microspheres-loaded hydrogels had denser network structures than those of chitosan solution and simple thermosensitive hydrogel, and in the cross section of which microspheres with a diameter of about 30 µm could be seen. Within PID 15, the wounds of rats in the five groups were healed to different degrees, and the wound healing of rats in P311 microspheres-loaded hydrogel group was the best. On PID 5, 10, and 15, the wound healing rates of rats in dressing group and chitosan group were (26.6±2.4)%, (38.5±3.1)%, (50.9±1.5)%, (47.6±2.0)%, (58.5±3.6)%, and (66.7±4.1)%, respectively, which were significantly lower than (59.3±4.8)%, (87.6±3.2)%, (97.2±1.0)% in P311 microspheres-loaded hydrogel group (P<0.05 or P<0.01). The wound healing rates of rats in hydrogel alone group on PID 10 and 15, and in simple microspheres-loaded hydrogel group on PID 15 were (76.0±3.3)%, (84.5±3.6)%, and (88.0±2.6)%, respectively, which were significantly lower than those in P311 microspheres-loaded hydrogel group (P<0.05). The epidermis, hair follicles, and sebaceous glands could be seen in the normal skin of rats in normal group, without positive expressions of CD31 or VEGF. The wounds of rats in P311 microspheres-loaded hydrogel group on PID 15 were almost completely epithelialized, with more blood vessels, hair follicles, sebaceous glands, and positive expressions of CD31 and VEGF in the wounds than those of rats with full-thickness skin defects in the other four groups, and more protein expressions of CD31 and VEGF than those of rats in the other five groups. Conclusions: The P311 microspheres-loaded thermosensitive chitosan hydrogel can release the encapsulated drug slowly, prolong the drug action time, and promote wound healing in rats with full-thickness skin defects by promoting wound angiogenesis and re-epithelialization.

[Investigation of posterior teeth displacement under normal bite force by an intraoral scanner].

Objective: To quantitatively evaluate the change of the long axis angle and the relative displacement of the crown feature points of the posterior teeth under normal bite force utilizing an intraoral scanner, and to provide clinical reference. Methods: From May to December 2019, fifteen graduate volunteers (5 males and 10 females, aged from 22 to 30, with an average age of 25.7 years) from Peking University School and Hospital of Stomatology were recruited to participate in the study. The surface data (U1, L1) of the maxillary and mandibular posterior teeth were scanned by an intraoral scanner i500, and saved as original data. The volunteers were guided to bite in the intercuspal position with normal bite force. The buccal bite data of the posterior teeth were scanned as the basis for registration. The digital casts were imported into Geomagic studio 2013 software and the boundary lines along the gingival margin and mesial and distal contact area of posterior teeth of data (U1, L1) were determined. Long axis of the crown, crown centroid and mesial functional cusp vertex were establishd. The data (U1, L1) were segmented into single tooth. Single tooth was aligned to buccal bite data separately using best-fit alignment command based on the buccal common area of the crown and new casts data (U2, L2) were obtained as the data under bite force. The long axis angle and centroid distance between adjacent teeth (second premolar and first molar, second molar and first molar) were measured and the deviation between data obtained at mouth-open state and that at biting state was calculated. Negative value meant centroid distance became shorter under bite force. The first molar was set as the common area and registrate the U1, L1 to U2, L2. The angle of long axes, and displacement of centroid and of functional cusp vertex between second premolar of two casts were calculated, as well as between second molar of two casts. Wilcoxon signed rank test was used to analyze the differences of teeth displacement between second premolar and second molar, and between maxillary and mandibular jaws with SPSS 26.0 statistical software. Results: The result of second premolar and second molar in the same jaw had no statistical difference (P>0.05). The centroid distance deviation of mandibular second premolar-first molar [-0.022(0.046) mm] was larger than that of maxilla [-0.006 (0.040) mm] (P<0.05). The long axis angle of second premolar itself [0.913°(0.647°)] and centroid distance of second molar itself [0.102 (0.106) mm] on the mandibular jaw were different from that on the maxillary jaw, which were 0.590°(0.550°) and 0.074(0.060) mm respectively (P<0.05). Conclusions: Under bite force, displacement of the second premolar and second molar was present, including the displacement of centroids and deflection of long axes. The mandibular posterior teeth have larger displacement than the maxillary teeth.

[Evaluating the accuracy of three-dimensional reconstruction of the intercuspal position for dentition casts aided by a mechanical appliance].

OBJECTIVE: To develop a aided mechanical appliance for rapid reconstruction of three-dimensional(3D)relationship of dentition model after scanning and evaluation of its accuracy. METHODS: The appliance was designed by forward engineering software and fabricated by a high precision computer numerical control(CNC)system. It contained upper and lower body, magnetic pedestal and three pillars. Nine 3 mm diameter hemispheres were distributed equally on the axial surface of each pedestal. Faro Edge 1.8m was used to directly obtain center of each hemisphere(contact method), defined as known center. A pair of die-stone standard dentition model were fixed in intercuspal position and then fixed on the magnetic pedestals with low expansion ratio plaster. Activity 880 dental scanner was used to scan casts after the plaster was completely set. In Geomagic 2012, the centers of each hemisphere were fitted and defined as scanning centers. Scanning centers were aligned to known centers by reference point system to finish the 3D reconstruction of the intercuspal occlusion for the dentition casts. An observation coordinate system was interactively established. The straight-line distances in the X(coronal), Y(saggital), and Z(vertical)between the remaining 6 pairs of center points derived from contact method and fitting method were measured respectively and analyzed using a paired t-test. RESULTS: The differences of the straight-line distances of the remaining 6 pairs of center points between the two methods were X:(-0.05±0.10)mm, Y:(0.02±0.06)mm, and Z:(0.01 ± 0.05)mm. The results of paired t-test showed no significant differences(P>0.05). CONCLUSIONS: The mechanical appliance can help to reconstruct 3D jaw relation by scanning single upper and lower dentition model with usual commercial available dental cast scanning system.

Sustained-release endotoxin. A model for inducing corneal neovascularization.

The rabbit corneal pocket assay is one of the most frequently used systems for the study of angiogenesis. This model particularly is useful to identify stimulators of new blood vessel formation. More recently, however, interest in inhibitors of angiogenesis has grown, and several antiangiogenic agents have been identified. Investigations of angiogenesis inhibitors require a reliable model for the stimulation of neovascularization. One method was modified to produce corneal neovascularization by implanting into the rabbit cornea a sustained-release polymer containing endotoxin (Escherichia coli lipopolysaccharide). The implant was prepared by mixing weighed quantities of endotoxin with ethylene vinyl acetate copolymer (Elvax) and forming 1-mm3 pellets containing 1%, 7.5%, 15%, 20%, 30%, and 40% (w/w) of endotoxin. Pure Elvax pellets were implanted as controls. Intrastromal corneal pockets were created in 92 eyes of male, albino New Zealand rabbits (n = 80), and sterilized endotoxin-copolymer implants were introduced. The growth rate of new vessels was measured by slit-lamp biomicroscopy. Endotoxin loads of 15% (n = 40) produced a strong neovascularization response with minimal stromal edema, with a mean growth rate of 0.21 +/- 0.12 mm/day. Loads of 1%, 7.5%, and 20% yielded 0.1 +/- 0.03 mm/day, 0.27 +/- 0.05 mm/day, 0.30 +/- 0.06 mm/day, respectively (n = 8, each group). Higher loads (30% and 40%; n = 8, each group) produced intense neovascularization, accompanied by severe corneal edema that obscured accurate measurement of the vessels. Corneal pockets that did not contain polymer implants were avascular. When endotoxin-Elvax pellets were removed, the new vessels regressed within 2 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)