Comparative Study of Temporomandibular Articular Fossa Bone Surface and the Envelope Surface of the Condyle Movement.

OBJECTIVE: To investigate the differences between temporomandibular articular fossa bone surface and the envelope surface of the mandibular condyle movement. METHODS: Thirty-four healthy adults underwent skull base and mandible scans using CBCT and performed mandibular border movement using the mandibular movement recording system. Landmarks of the fossa and tubercle were indicated and distance and angle parameters were measured on the 3D models reconstructed from the CBCT. The condyle movement envelope surfaces were formed according to models reconstructed from CBCT and the mandibular movement trajectory using computer simulation. The highest and lowest points of the envelope surface were indicated to create parameters. The data were analysed using a paired t test in SPSS (version 24.0, IBM, Armonk, NY, USA). RESULTS: The mandibular fossa bone surface was statistically different to the envelope surface for the height of the first peak of the envelope surface (3.280 ± 1.319 mm) and depth of the mandibular fossa (6.338 ± 2.389 mm) (the ratio was 51.75%), the height of the second peak of the envelope surface (1.463 ± 0.745 mm) and the height of the tubercle (2.000 ± 0.968 mm) (the ratio was 73.15%), and the downwards angle of the envelope surface (25.933 ± 7.539 degrees) and the posterior slope angle of the articular tubercle (35.059 ± 5.224 degrees) (the ratio was 73.97%). CONCLUSION: The downwards angle of the envelope surface was statistically significantly smaller than the posterior slope angle of the articular tubercle, suggesting that the condyle movement is flatter than the mandibular fossa bone surface.

Scanning Accuracy of 10 Intraoral Scanners for Single-crown and Three-unit Fixed Denture Preparations: An In Vitro Study.

OBJECTIVE: To evaluate the accuracy of 10 intraoral scanners for single-crown and three-unit preparation models. METHODS: A maxillary partially edentulous model was fabricated. A dental cast scanner was used to obtain standard tessellation language (STL) data. Ten intraoral scanners, namely Trios 2 (TR2; 3Shape, Copenhagen, Denmark), True Definition (TD; 3M, Saint Paul, MN, USA), CEREC AC Omnicam (OM; Dentsply Sirona, Charlotte, NC, USA), Organical Scan Oral (OS; R+K, Berlin, Germany), PlanScan (PS; Planmeca, Helsinki, Finland), DWIOP (DW; Dental Wings, Montreal, Canada), Xianlin (XL; Hangzhou Xianlin, Hangzhou, China), DL-100 (DL; Guangzhou Longcheng, Guangzhou, China), Trios 3 (TR3; 3Shape) and i500 (MD; MEDIT, Seoul, South Korea) were used to obtain stereolithography data as test groups. Trueness, precision and surface accuracy were evaluated by deviation analysis using 3D image processing software. One tooth with a three-unit preparation for each test group was registered with the reference scan data, and the absolute distance from another tooth was calculated as the absolute accuracy. The data were analysed using a Mann-Whitney U test and Dunn-Bonferroni test (α = 0.05). RESULTS: The best trueness, precision and surface accuracy of scanning single crown preparation were recorded with TD (trueness 2.9 µm and precision 1.9 µm) and XL (surface accuracy 20.3 ± 2.9 µm). The best trueness, precision, surface accuracy and absolute accuracy of three-unit preparations were recorded with TD (2.6 µm), XL (1.9 µm), OM (27.1 ± 5.2 µm) and TR3 (79.2 ± 19.6 µm), respectively. There was no statistically significant difference in trueness between single- and multiple-unit preparations for any of the intraoral scanners (P > 0.05). A statistically significant difference in the surface accuracy between single and multiple preparations was found for TR2, TD, OM, DW, XL, DL and MD (P < 0.05). CONCLUSION: The trueness and precision of intraoral scanners for scanning three-unit preparations were nearly the same as those for single-crown preparations; however, with the exception of OS, PS and TR3, the surface accuracy of single-crown preparations was significantly better than that for three-unit preparations.

Clinical application and research progress of digital complete denture.

Digital technologies use high-precision three-dimensional scanning, intelligence-aided design software, and multi-axis numerical control milling or 3D printing, which can produce restorations with reliable precision and suitable function. However, the development of digital technologies in the field of complete denture restoration has been slow due to the complexity of prosthesis. This review article introduces the current research status and clinical applications of digital complete dentures in prosthodontic clinics and dental laboratories to provide beneficial references to prosthodontists and dental technicians.

Accuracy of root-end resection using a digital guide in endodontic surgery: An in vitro study.

BACKGROUND/PURPOSE: It is difficult to achieve accurate root-end resection clinically. This in vitro study was conducted to evaluate the operation accuracy of a digital endodontic surgical guide. MATERIALS AND METHODS: 56 extracted maxillary anterior teeth were prepared for endodontic surgical models. The models were randomly divided into 4 groups equally according to the guide (with guide/no guide) and the operator (experienced/inexperienced). Endodontic microsurgeries were performed on models in each group. The deviations in length and angle of the root-end resection were measured based on the optical scanning data of the pre- and postoperative teeth. The general linear model was performed to analyze the effect of a guide on root-end resection deviation. RESULTS: Using a guide, the mean length deviation for experienced/inexperienced operators reduced from 0.99 mm (95% CI [confidence interval, CI], 0.66-1.33 mm)/1.18 mm (95% CI, 0.50-1.86 mm) to 0.31 mm (95% CI, 0.20-0.42 mm)/0.31 mm (95% CI, 0.24-0.37 mm). The mean angle deviation for experienced/inexperienced operators reduced from 16.74° (95% CI, 10.61-22.86°)/15.06° (95% CI, 9.19-20.94°) to 5.04° (95% CI, 3.31-6.77°)/6.79° (95% CI, 4.91-8.67°). The difference was significant between procedures performed with and without a guide (P < 0.01). CONCLUSION: Application of the digital guide in vitro endodontic surgery could improve the accuracy of root-end resection.

Three-dimensional mandibular motion trajectory-tracking system based on BP neural network.

The aim of this study was to develop a prototype three-dimensional optical motion capture system based on binocular stereo vision, Back-propagation (BP) Neural Network and 3D compen-sation method for accurate and real-time recording of mandibular movement. A specialized 3D method of compensation to eliminate the involuntary vibration motions by human heart beating and respiration. A kind of binocular visual 3D measurement method based on projection line and a calibration method based on BP neural network is proposed to solve the problem of the high complexity of camera calibration process and the low accuracy of 3D measurement. The accuracy of the proposed system is systematically evaluated by means of electric platform and clinical trials, and the root-mean-square is 0.0773 mm. Finally, comparisons with state-of-the-art methods demonstrate that our system has higher reliability and accuracy. Meanwhile, the motion trajectory-tracking system is expected to be used in the diagnosis of clinical oral diseases and digital design of restoration.

3D Evaluation of Accuracy of Tooth Preparation for Laminate Veneers Assisted by Rigid Constraint Guides Printed by Selective Laser Melting.

OBJECTIVE: To design and fabricate 3D-printed rigid constraint guides for the tooth preparation for laminate veneers and to evaluate the accuracy of guide-assisted preparation. METHODS: Twenty maxillary right central incisor resin artificial teeth were randomly divided into two equal groups and prepared for laminate veneers. Tooth preparations were performed, assisted by guides in the test group and by depth gauge burs in the control group, and both were finished by freehand operation. The typodonts were 3D scanned before preparation, after initial preparation and after final preparation. The tooth preparation depths at each step, including initial preparation depth, final preparation depth and loss of tooth tissue during polishing, were measured by 3D deviation analysis. Statistical analyses were conducted to investigate differences. RESULTS: The initial preparation depth was 0.488 mm (median, quartile 0.013 mm) in the test group and 0.521 mm (median, quartile 0.013 mm) in the control group. A statistically significant difference was found between them (P < 0.05). The final preparation depth in the test group (0.547 ± 0.029 mm) was significantly less than that in the control group (0.599 ± 0.051 mm) (P < 0.05), and closer to the predesigned value (0.5 mm). There was no statistically significant difference in the loss of tooth tissue during polishing between the test group (0.072 ± 0.023 mm) and the control group (0.089 ± 0.038 mm) (P > 0.05). CONCLUSION: In maxillary central incisors, the tooth preparation for laminate veneers could be conducted using 3D-printed rigid constraint guides, the accuracy of which is better than that of depth gauge burs.

Accuracy of Intraoral Scanning of Edentulous Jaws with and without Resin Markers.

Objective: To evaluate the accuracy of digital models obtained from intraoral scanning of edentulous maxilla and mandible models with and without resin markers. Methods: A pair of standard edentulous models were scanned using a laboratory scanner and saved as reference models. The edentulous models were fixed onto a phantom head and scanned with an intraoral scanner (IOS) five times each. Six resin markers were attached on the maxilla model and two on the mandible model, and another five intraoral scans were taken of each model. The scanning time and number of images were recorded. The digital models obtained using the IOS were superimposed on the reference models using image processing software. The trueness and precision of the models made using the IOS were evaluated, and the scanning time and number of images were also compared. Results: The average trueness and precision of the IOS in the maxilla model with resin markers were 135.50 ± 36.28 µm and 254.55 ± 40.62 µm, respectively, while those in the mandible were 161.40 ± 55.45 µm and 368.75 ± 91.03 µm, respectively. Placing resin markers on the edentulous maxilla and mandible did not improve the trueness of the IOS, but placing resin markers on the edentulous maxilla improved the precision and scanning efficiency. However, placing resin markers on the buccal shelf of the edentulous mandible decreased the precision and increased the scanning time. Conclusion: Resin markers placed on the hard palate of edentulous maxillae could improve the precision of the IOS and improve scanning efficiency. However, they did not affect the trueness of the IOS for edentulous maxillae or mandibles.

Osteogenic Differentiation of Three-Dimensional Bioprinted Constructs Consisting of Human Adipose-Derived Stem Cells In Vitro and In Vivo.

Here, we aimed to investigate osteogenic differentiation of human adipose-derived stem cells (hASCs) in three-dimensional (3D) bioprinted tissue constructs in vitro and in vivo. A 3D Bio-plotter dispensing system was used for building 3D constructs. Cell viability was determined using live/dead cell staining. After 7 and 14 days of culture, real-time quantitative polymerase chain reaction (PCR) was performed to analyze the expression of osteogenesis-related genes (RUNX2, OSX, and OCN). Western blotting for RUNX2 and immunofluorescent staining for OCN and RUNX2 were also performed. At 8 weeks after surgery, osteoids secreted by osteogenically differentiated cells were assessed by hematoxylin-eosin (H&E) staining, Masson trichrome staining, and OCN immunohistochemical staining. Results from live/dead cell staining showed that most of the cells remained alive, with a cell viability of 89%, on day 1 after printing. In vitro osteogenic induction of the 3D construct showed that the expression levels of RUNX2, OSX, and OCN were significantly increased on days 7 and 14 after printing in cells cultured in osteogenic medium (OM) compared with that in normal proliferation medium (PM). Fluorescence microscopy and western blotting showed that the expression of osteogenesis-related proteins was significantly higher in cells cultured in OM than in cells cultured in PM. In vivo studies demonstrated obvious bone matrix formation in the 3D bioprinted constructs. These results indicated that 3D bioprinted constructs consisting of hASCs had the ability to promote mineralized matrix formation and that hASCs could be used in 3D bioprinted constructs for the repair of large bone tissue defects.

[Osteogenesis of human adipose-derived mesenchymal stem cells-biomaterial mixture in vivo after 3D bio-printing].

OBJECTIVE: To construct human adipose-derived mesenchymal stem cells (hASCs)-biomaterial mixture 3D bio-printing body and detect its osteogenesis in vivo, and to establish a guideline of osteogenesis in vivo by use of 3D bio-printing technology preliminarily. METHODS: P4 hASCs were used as seed cells, whose osteogenic potential in vitro was tested by alkaline phosphatase (ALP) staining and alizarin red staining after 14 d of osteogenic induction. The cells were added into 20 g/L sodium alginate and 80 g/L gelatin mixture (cell density was 1 × 10(6)/mL), and the cell-sodium alginate-gelatin mixture was printed by Bioplotter 3D bio-printer (Envision company, Germany), in which the cells'survival rate was detected by live- dead cell double fluorescence staining. Next, the printing body was osteogenically induced for 1 week to gain the experimental group; and the sodium alginate-gelatin mixture without cells was also printed to gain the control group. Both the experimental group and the control group were implanted into the back of the nude mice. After 6 weeks of implantation, the samples were collected, HE staining, Masson staining, immunohistochemical staining and Inveon Micro CT test were preformed to analyze their osteogenic capability. RESULTS: The cells'survival rate was 89%± 2% after printing. Six weeks after implantation, the samples of the control group were mostly degraded, whose shape was irregular and gel-like; the samples of the experimental group kept their original size and their texture was tough. HE staining and Masson staining showed that the bone-like tissue and vessel in-growth could be observed in the experimental group 6 weeks after implantation, immunohistochemical staining showed that the result of osteocalcin was positive, and Micro CT results showed that samples of the experimental group had a higher density and the new bone volume was 18% ± 1%. CONCLUSION: hASCs -biomaterial mixture 3D bio-printing body has capability of ectopic bone formation in nude mice, and it is feasible to apply cells-biomaterial mixture 3D bio-printing technology in the area of bone formation in vivo.

[Short-term effect of CaCl2on human adipose-derived mesenchymal stem cells proliferation and osteogenic differentiation].

OBJECTIVE: To examine the effect of CaCl2, a sodium alginate crosslinker, to stimulate cells for a short time period on human adipose-derived mesenchymal stem cells (hASCs) proliferation and osteogenic differentiation ability, and to determine the appropriate concentration of CaCl2for post three-dimensional biological experiments. METHODS: hASCs stimulated with or without CaCl2at various concentrations were seeded and cultured in control medium and osteogenic medium, respectively. The cell counting kit-8 (CCK8) was used to estimate the cell proliferation level of each group. After 7 days of osteogenic induction, alkaline phosphatase (ALP) staining and activity assays were performed using an ALP kit. After 14 days of osteogenic induction, alizarin red staining and quantitative detection were used to determine the calcium mineral density. The results were analyzed using analysis of variance (ANOVA) and Student-Newman-Keuls (SNK) tests for pairwise comparisons implemented in the SPSS 17.0 software. RESULTS: The CCK-8 assays showed that the differences between the control groups and experimental groups were not statistically significant, so different concentrations of CaCl2had no significant effect on hASCs proliferation. The ALP staining and activity assays showed that ALP activity first increased and then decreased as the CaCl2concentration increased. Furthermore, the differences between all the groups were statistically significant (P<0.05), except the difference between the 50 mmol/L CaCl2group and the 100 mmol/L CaCl2group, and between the osteogenetic medium(OM) group and the 200 mmol/L CaCl2group. Alizarin red staining and quantitative detection showed that the differences between all pairwise combinations of the groups were statistically significant (P<0.05). As the CaCl2 concentration increased, the calcium deposition increased, initially in the form of a scattered sheet and eventually a laminated sheet. CONCLUSION: Stimulation by a high concentration of CaCl2over a short time period can enhance hASCs osteogenic differentiation ability, but has no effect on hASCs proliferation.

[Application of patient-participated digital design in esthetic rehabilitation of anterior teeth].

OBJECTIVE: To explore a new method of patient-involved digital design, esthetic outcome prediction and fabrication for the esthetic rehabilitation of anterior teeth, and to provide an alternative choice for the restoration of anterior teeth. METHODS: In this study, 32 patients with esthetic problems in their anterior teeth were included and divided into two groups randomly: the experimental group (16 patients) and control group (16 patients). In the experimental group, the dentition and facial images were obtained by intra-oral scanning and Three-dimensional (3D) facial scanning and then calibrated. The design of the rehabilitation and the esthetic outcome prediction were created by computer-aided design (CAD) software. After morphologic modification according to the patients' opinions, prostheses were fabricated according to the final design by computer-aided manufacturing (CAM) equipment. As for the control group, the regular design method was applied to restore their anterior teeth. The time consuming in the first insertion of each restoration in both groups was recorded. The quality of the prostheses was assessed by another prosthedontist. The satisfaction to prostheses and the facial appearance were evaluated by the patients. RESULTS: The process of the patient-involved digital design and outcome anticipation was successfully established. The patients were satisfied with the esthetic effects of the anterior restoration made by the digital technique. The acceptance rate of the patients on the digital rehabilitation in the experimental group was 100%. There was no significant difference of the quality of the prostheses between the two groups. The satisfaction rate of the patients on prostheses and facial appearance was significantly higher in the experimental group than in the control group (P < 0.05). In addition, the time consuming in the first insertion of the experimental group was much shorter than that in the control group (P < 0.01). CONCLUSION: The new method of the patient-involved digital design, esthetic outcome prediction and fabrication for the esthetic rehabilitation of anterior teeth is a practical technique. This method is useful in shortening the time consuming of the restoration of anterior teeth and improving the patient satisfaction with the esthetic outcome.

[Quantitative assessment on artifacts of dental restorative materials in cone beam computed tomography].

OBJECTIVE: To quantitatively evaluate the artifacts appearance of eight kinds of common dental restorative materials, such as zirconia. METHODS: For the full-crown tooth preparation of mandibular first molar, eight kinds of full-crowns, such as zirconia all-ceramic crown, glass ceramic crown, ceramage crown, Au-Pt based porcelain-fused-metal (PFM) crown, Pure Titanium PFM crown, Co-Cr PFM crown, Ni-Cr PFM crown, and Au-Pd metal crown were fabricated. And natural teeth in vitro were used as controls. These full-crown and natural teeth in vitro were mounted an ultraviolet-curable resin fixed plate. High resolution cone beam computed tomography (CBCT) was used to scan all of the crowns and natural teeth in vitro, and their DICOM data were imported into software MIMICS 10.0. Then, the number of stripes and the maximum diameters of artifacts around the full-crowns were evaluated quantitatively in two-dimensional tomography images. RESULTS: In the two-dimensional tomography images,the artifacts did not appear around the natural teeth in vitro, glass ceramic crown, and ceramage crown. But thr artifacts appeared around the zirconia all-ceramic and metal crown. The number of stripes of artifacts was five to nine per one crown. The maximum diameters of the artifacts were 2.4 to 2.6 cm and 2.2 to 2.7 cm. CONCLUSION: In the two-dimensional tomography images of CBCT, stripe-like and radical artifacts were caused around the zirconia all-ceramic crown and metal based porcelain-fused-metal crowns. These artifacts could lower the imaging quality of the full crown shape greatly. The artifact was not caused around the natural teeth in vitro, glass ceramic crown, and ceramage crown.

[Initial evolution research for design and process accuracy of one type of domestic computer aided design soft and computer aided manufacture].

OBJECTIVE: To evaluate the design and manufacture accuracy of a domestic computer aided design (CAD) and computer aided manufacture (CAM) system, and to compare it with similar foreign products. METHODS: Thirty models of posterior-teeth-single-crown preparations were collected, and STL data of these preparations was collected by Denmark 3Shape scanner. Three copings were made for each preparation, the one designed and manufactured using commercial CAD/CAM system (3Shape CAD software and Wieland T1 CAM equipment) was assigned into control group T0, the one designed and manufactured using domestic CAD software (developed by Peking University School and Hospital of Stomatology and Nanjing University of Aeronautics and Astronautics) and Wieland T1 CAM equipment was assigned into experimental group TCAD for design accuracy evaluation, and the one designed and manufactured using 3Shape CAD software and domestic CAM equipment (developed by Peking University School and Hospital of Stomatology, Tsinghua University and ShanDong XinHua Incorporated Company of medical apparatus and instruments) was assigned into experimental group TCAM for manufacture accuracy evaluation. Finally, the marginal fitness were compared and evaluated by using 3D & Profile measurement microscope laser. RESULTS: The marginal fitness of TCAD was 27.98 (19.10, 46.57) µm in buccal, 32.67 (20.65, 50.82) µm in lingual, 27.38 (22.53, 52.61) µm in mesial, 29.50 (22.68, 53.65) µm in distal; of TCAM was 21.69 (15.87, 30.21) µm in buccal, 18.51 (13.50, 22.51) µm in lingual, 19.15 (15.42, 26.89) µm in mesial, 22.77 (18.58, 32.15) µm in distal; and there were no statistical differences compared with T0 [20.16 (17.16, 48.00) µm in buccal, 21.51 (17.05, 28.31) µm in lingual, 23.54 (17.89, 30.04) µm in mesial and 23.94 (17.93, 28.19) µm in distal] except lingual data of TCAD. CONCLUSIONS: The design and machining precision of this domestic CAD/CAM system is at the same level of those comparable foreign products.

[Preliminary evaluation of clinical effect of computer aided design and computer aided manufacture zirconia crown].

OBJECTIVE: To evaluate clinical effects of computer aided design and computer aided manufacturing (CAD/CAM) milled zirconia crown in three aspects: aesthetic, contact wear and fracture. METHODS: Sixty patients were divided into two groups.In one group, 35 full contour CAD/CAM zirconia crown were made on molars of 30 patients. The manufacturing process of zirconia crown was as follow. First, the three dimensional(3-D) data of working models, antagonist impression and check records were acquired by 3-D laser scanning Dental wings S50. Then full contour zirconia crowns, which had functional occlusal contacts with antagonistic teeth, and appropriate contact with adjacent teeth were designed with Zeno-CAD(V4.2.5.5.12919) software. ZENOSTAR Zr pure zirconia material was milled in digital controlled machine WIELAND 4030 M1.In the end, the zirconia crown were completed with the method of second sintering and polishing. After clinical try-in, the crown was cemented.In the control group, thirty gold alloy full crown were made and cemented on molars of 30 patients. According to the modified U S Public Health Service Criteria(USPHS) evaluation standard, all crowns were evaluated on the same day, at three months, half a year, one year and two years following delivery. There were three aspects we were focusing on in the evaluation: aesthetic, contact wear(restoration and antagonist), and fracture. RESULTS: In all the prosthesis we evaluated during the 24 months, no fracture was found. Contact wear of crowns varies according to different antagonist teeth. CONCLUSIONS: The zirconia crowns show privilege in aesthesis, toughness and anti-wearing.However, there is contact wear on antagonistic natural teeth. Thus it is a good choice when full zirconia crowns are indicated on two antagonistic teeth in both jaws.

[Effects of fluence and scanning velocity on the ablation efficiency of dentin and enamel by femtosecond laser].

OBJECTIVE: To measure the effect of laser fluence and scanning velocity on ablation efficiency of enamel and dentin. METHODS: Two extracted human incisors and two molars were cut transversely along the axial plane with a diamond saw to obtain dentin and enamel slices with thickness of about 1 mm. Samples were fixed on a motorized translation stage, the linear reciprocating movement in the plane perpendicular to the direction of laser incident was programmed by the controller, and the laser focused on the tooth surface, then 36 ablation lines on enamel and 48 ablation lines on dentin were produced. A femtosecond laser system with wavelength of 800 nm, pulse width 30 fs, repetition frequency 1000 Hz was used, and the diameter of the focused spot was approximately 25 µm. A group of different fluence (1.33, 1.77, 2.21, 4.42, 8.85, 17.69 J/cm(2) for enamel and 0.44, 0.66, 0.88, 1.33, 1.77, 2.21, 4.42, 6.63 J/cm(2) for dentin) and two scanning velocity (10 mm/s and 20 mm/s) were tested. Confocal laser scanning microscope was used to measure the ablation volume.Ablation efficiency for enamel and dentin was then calculated. RESULTS: Under the fluence of 8.85 J/cm(2) there was the highest ablation efficiency for enamel, 18.703×10(-3) mm(3)/J (20 mm/s), and the highest ablation efficiency for dentin was found under the fluence of 2.21 J/cm(2), ie.223.458×10(-3) mm(3)/J (20 mm/s). CONCLUSIONS: Fluence and scanning speed of this femtosecond laser can affect ablation efficiency for both enamel and dentin, and this suggests that with appropriate choice of fluence and scanning speed we can improve the ablation efficiency for enamel and dentin.

Accuracy evaluation of a new three-dimensional reproduction method of edentulous dental casts, and wax occlusion rims with jaw relation.

The article introduces a new method for three-dimensional reproduction of edentulous dental casts, and wax occlusion rims with jaw relation by using a commercial high-speed line laser scanner and reverse engineering software and evaluates the method's accuracy in vitro. The method comprises three main steps: (i) acquisition of the three-dimensional stereolithography data of maxillary and mandibular edentulous dental casts and wax occlusion rims; (ii) acquisition of the three-dimensional stereolithography data of jaw relations; and (iii) registration of these data with the reverse engineering software and completing reconstruction. To evaluate the accuracy of this method, dental casts and wax occlusion rims of 10 edentulous patients were used. The lengths of eight lines between common anatomic landmarks were measured directly on the casts and occlusion rims by using a vernier caliper and on the three-dimensional computerized images by using the software measurement tool. The direct data were considered as the true values. The paired-samples t-test was used for statistical analysis. The mean differences between the direct and the computerized measurements were mostly less than 0.04 mm and were not significant (P>0.05). Statistical significance among 10 patients was assessed using one-way analysis of variance (P<0.05). The result showed that the 10 patients were considered statistically no significant. Therefore, accurate three-dimensional reproduction of the edentulous dental casts, wax occlusion rims, and jaw relations was achieved. The proposed method enables the visualization of occlusion from different views and would help to meet the demand for the computer-aided design of removable complete dentures.

[Accuracy of different registration methods for laser-scanned dental cast data and maxillofacial cone-bean CT data].

OBJECTIVE: To evaluate the accuracy of four dominant methods of three-dimensional multisource data registration. METHODS: Laser-scanned dental model and maxillofacial cone-bean CT rebuilt model were collected for one orthodontic patient before treatment. Registration process was done based on locating spheres' center, anatomic landmarks, partial characteristic region and global data separately. The registration errors were detected by the function of Geomagic Studio 12.0 software. A comparison of the registration accuracy among these four methods was done by analyzing mean error and standard deviation. RESULTS: The mean errors and standard deviations of methods of locating spheres' center, anatomic landmarks, partial characteristic region and global data were -(0.082 ± 0.221), -(0.104 ± 0.218), -(0.047 ± 0.138) and -(0.025 ± 0.129) mm respectively. CONCLUSIONS: ICP registration methods had better reliability than landmark methods. The global registration was more accurate than partial characteristic region registration and the locating spheres' center method was better than anatomic landmarks method.

[Influence of intra-pulpal temperature when using femtosecond laser in specific parameters to prepare cavities in tooth enamel: an in vitro study].

OBJECTIVE: To take the Real-time measurement of the intra-pulpal temperature (IPT) when using femtosecond laser in specific parameters to prepare cavities in tooth enamel in vitro, and to preliminarily evaluate the effect of air cooling. METHODS: All pulp champers of extracted human teeth (premolars and molars) were exposed by roots amputated and pulp scraped out. All chambers were tightly filled with copper powder, and thermocouple was inserted into the center of the powder stack. The bottom of the chamber was sealed with insulating tape. Thermocouple wire was fixed at the same time. The 2.25 mm×2.25 mm square cavities were prepared using femtosecond laser in the enamel with the average scan speed of 0.4 mm/s. The real-time IPT change was measured with thermocouple digital thermometer. Air cooling was added to the procedure once the temperature increased to reach a balance. RESULTS: The IPT rising was defined as ΔT . Before the usage of air cooling, the maximum of the ΔT value of the sample premolar was 12.3 °C. After using air cooling, the IPT decreased and ΔT value became 3.0 °C . The maximum of ΔT of the sample molar before using air cooling was 1.8 °C , and decreased to -0.1 °C after it. CONCLUSION: When preparing a cavity whose average depth is about 250 µm by femtosecond laser system in specific parameters, the IPT rises while the depth increass, but it could be controlled effectively by air cooling.