Role of dendritic cells in MYD88-mediated immune recognition and osteoinduction initiated by the implantation of biomaterials / 国际口腔科学杂志·英文版

Bone substitute material implantation has become an important treatment strategy for the repair of oral and maxillofacial bone defects. Recent studies have shown that appropriate inflammatory and immune cells are essential factors in the process of osteoinduction of bone substitute materials. Previous studies have mainly focused on innate immune cells such as macrophages. In our previous work, we found that T lymphocytes, as adaptive immune cells, are also essential in the osteoinduction procedure. As the most important antigen-presenting cell, whether dendritic cells (DCs) can recognize non-antigen biomaterials and participate in osteoinduction was still unclear. In this study, we found that surgical trauma associated with materials implantation induces necrocytosis, and this causes the release of high mobility group protein-1 (HMGB1), which is adsorbed on the surface of bone substitute materials. Subsequently, HMGB1-adsorbed materials were recognized by the TLR4-MYD88-NFκB signal axis of dendritic cells, and the inflammatory response was activated. Finally, activated DCs release regeneration-related chemokines, recruit mesenchymal stem cells, and initiate the osteoinduction process. This study sheds light on the immune-regeneration process after bone substitute materials implantation, points out a potential direction for the development of bone substitute materials, and provides guidance for the development of clinical surgical methods.

Biometry of width between labial transitional line angles in anterior teeth:an observational study

PURPOSE@#The maximum width between the mesial and distal labial transitional line angles, described as “esthetic width” herein, could significantly influence the visual perception of the teeth and smile. This study aimed to conduct biometric research on esthetic width and to explore whether regular distribution exists in the esthetic width of human teeth. @*MATERIALS AND METHODS@#A total of 4,264 maxillary and mandibular anterior teeth were measured using the Geomagic studio software program. The proportions of maxillary to mandibular homonymous teeth and proportions between the adjacent teeth were calculated. Bilateral symmetry and the correlation between the esthetic and mesiodistal widths were both accounted for during the measurement procedures. @*RESULTS@#The mean esthetic widths were 6.773 ± 0.518 mm and 4.329 ± 0.331 mm for maxillary and mandibular central incisors, respectively, 5.451 ± 0.487 mm and 5.008 ± 0.351 mm for maxillary and mandibular lateral incisors, respectively, and 3.340 ± 0.353 mm and 5.958 ± 0.415 mm for maxillary and mandibular canines, respectively. Except for the mandibular canines, no significant difference in esthetic width was found among homonymous teeth from the same jaw. A high linear correlation was found between the esthetic and mesiodistal widths of the same tooth, except for the maxillary canines. Esthetic width proportions among different tooth categories showed some regular patterns, which were similar to those of the mesiodistal width. @*CONCLUSION@#Esthetic width is regularly distributed among the teeth in the Chinese population. This could provide an important reference for anterior dental restorations and dimension recovery in esthetic reconstruction of anterior teeth.

Evaluation of functional suitable digital complete denture system based on 3D printing technology

PURPOSE@#To improve the clinical effects of complete denture use and simplify its clinical application, a digital complete denture restoration workflow (Functional Suitable Digital Complete Denture System, FSD) was proposed and preliminary clinical evaluation was done. MATERIALS AND METHODS Forty edentulous patients were enrolled, of which half were treated by a prosthodontic chief physician, and the others were treated by a postgraduate student. Based on the primary impression and jaw relation obtained at the first visit, diagnostic denture was designed and printed to create a definitive impression, jaw relation, and esthetic confirmation at the second visit. A redesigned complete denture was printed as a mold to fabricate final denture that was delivered at the third visit.To evaluate accuracy of impression made by diagnostic denture, the final denture was used as a tray to make impression, and 3D comparison was used to analyze their difference. To evaluate the clinical effect of FSD, visual analogue scores (VAS) were determined by both dentists and patients. @*RESULTS@#Two visits were reduced before denture delivery. The RMS values of 3D comparison between the impression made via diagnostic dentures and the final dentures were 0.165 ± 0.033 mm in the upper jaw and 0.139 ± 0.031 mm in the lower jaw. VAS ratings were between 8.5 and 9.6 in the chief physician group, while 7.7 and 9.5 in the student group; there was no statistical difference between the two groups. @*CONCLUSION@#FSD can simplify the complete denture restoration process and reduce the number of visits. The accuracy of impressions made by diagnostic dentures was acceptable in clinic. The VASs of both dentists and patients were satisfied.

Study on functional occlusal morphology by using three-dimensional printed diagnostic crown and functional generated path technology / 中华口腔医学杂志

Objective@#To establish the functional occlusal morphology of fixed prostheses by using functional generated path (FGP) technology on a three-dimensional-printed diagnostic crown in order to decrease the chance of occlusal adjustment during try-in procedure of the complete crown, and to avoid the risk of occlusal interference after cementation of prosthesis.@*Methods@#A double-blind clinical trial was performed. Ten subjects (4 males, 6 females) who needed a first molar complete crown restoration were enrolled in Department of Prosthodontics, Peking University School and Hospital of Stomatology from July 2018 to December 2018. The working models with the abutment teeth of the ten participants were scanned to obtain the digital models, then the occlusal surfaces of crown were formed by either FGP technology on a three-dimensional (3D) printed diagnostic crown and then were scanned directly for computer aided design and computer aided manufacture (CAD/CAM) crown fabrication as experiment group, or conventional technology based on database as control group. Then zirconia crowns were fabricated for two groups. During crown try-in of the two groups, preferred crowns of subjects were recorded, the occlusal contact criteria including the occlusal contact area (mm2), the heights of occlusal high spot (mm) before and after the adjustment of crowns were digitally analyzed, and the amount of adjustment (mm and mm3) were calculated on digital models by using a reverse engineering software (Giomagic Sudio & Quality). Differences of values were compared statistically with paired t-test (α=0.05).@*Results@#The amount for occlusal adjustment for crowns in the experiment group [(7.320±4.238) mm3] was statistically less than that in the control group [(20.178±9.650) mm3] (P<0.05), the occlusal contact area of experiment group [(11.430±4.102) mm2] was statistically bigger than that of the control group [(4.808±3.223) mm2] (P<0.05), the heights of occlusal high spots for crowns in the experiment group was (0.043±0.019) mm while it was (0.594±0.201) mm in the control group with statistically significant differences (P<0.05).@*Conclusions@#This method could lead to a crown with less adjustment of occlusion, less occlusal high spot and less risk of occlusal interferences.

Etiology and clinical technology of the food impaction with tight proximal contacts / 中华口腔医学杂志

Food impaction with tight proximal contacts, also known as kinetic food impaction and food impaction without anatomical structure destruction, is mainly caused by a transient separation in contacts area during mastication. It′s an intractable food impaction with high morbidity and low cure rate. There are two kinds of pathogenesis accepted: the shifting of anterior teeth incongruous with adjacent teeth or lack of anterior shifting; lack of food escape grooves. The preferred treatment is occlusal adjustment, but it′s difficult to determine the area and extent of selective grinding, to quantify the occlusal adjustment, or to predict the prognosis. This review summarized the pathogenesis and treatment modality for kinetic food impaction in order to provide evidence for future researches and clinical application.

Preliminary study on the automatic preparation of dental implant socket controlled by micro-robot / 中华口腔医学杂志

Objective@#To analyze the quantitative relationship between the number of layers of laser pulses and the amount of step in ultra-short pulse laser cutting of cortical bone, optimize the robot's vertical single stepping parameters, and to explore the feasibility of automatic preparation of dental implant cavity using robot controlling ultra-short pulse laser, in order to lay the foundation for automated dental implant surgery.@*Methods@#Eight pig ribs were segmented into to make 16 specimens. Using the robotic surgical system and path planning software independently developed by our group, circular holes with a diameter of 4 mm were cut two-dimensionally in the rib segments to obtain the quantification relationship of the number of laser pulse layers (n) and the depth of two-dimensional (2D) cutting (d). When conducting the three-dimensional (3D) cutting procedure, the number of pulse layers were set to 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 layers, the vertical single step amount was an integer value corresponding to the results of 2D cutting depth, and the number of pulses (n') corresponding to the minimum difference between the theoretical depth of cut and the actual depth of cut was obtained. The n' was taken as the most suitable single step pulse layer, the rib segment was cut, and the depth of single cut was measured while the integer value was taken as the most appropriate vertical single step amount (d'). The vertical parameters of laser single stepping were set as n' layer pulse and d′ μm step size. The 3D cutting produces a cylindrical cavity with a diameter of 4 mm and a height of 2 mm to evaluate the 3D cutting accuracy (the difference between the measured value and the theoretical value of cutting diameter or depth). Ten 4 mm×3 mm implant holes were automatically prepared on the bilateral femurs of 5 Japanese big white rabbits, and ten 4 mm×3 mm implants made by 3D printer were artificially implanted, and the preparation effect of the implant cavities was evaluated.@*Results@#The quantitative relationship curve between the number of laser pulses (n) and 2D depth of cut (d) showed a linear upward trend. The linear fitting obtained the quantitative relation function formula d=9.278 4 n±26.763 0, R2=0.988 9. The optimum number of single step pulse layers was 5 layers, and the vertical single step amount was 50 μm, so as to set the vertical parameters of a single step of a 3D cutting, and the 3D cutting diameter accuracy was (3.98±2.87) μm, with a depth accuracy of (15.42±5.44) μm. Automated preparation of 10 implant cavities on the femur of the rabbit were completed. When the implants were placed into the implant cavities, there was resistance, but they were fully seated and primary stability has been achieved after seating implant placement.@*Conclusions@#The method of non-contact automatic preparation of dental implant cavities using robot controlling ultra-short pulse laser is feasible. By optimizing the single cutting process parameters, precise control of laser cutting cortical bone can be realized.

A preliminary study on the three-dimensional trajectory of condyle / 中华口腔医学杂志

Objective@#To calculate the three-dimensional trajectory and motion morphology of condyle by combining the trajectory of the mandible movement and the three-dimensional model of the mandible.@*Methods@#Cone beam CT (CBCT) scanning was performed on the volunteer. The mandible three-dimensional model was built with image data transferred to the graphical user interface of the computer workstation. The novel virtual articulator PN300 recorded the three-dimensional trajectory of mandible. All these data were transferred to software system of computer workstation calculating the three-dimensional trajectory of condyle. The motion morphology of condyle was simulated by merging function surface at each point.@*Results@#When the mandible moved in an opening process, the recorded data was calculated and it was shown that: the condylar functional surface moved moved forward and downward inward in advance, and in the process of continuously increasing the opening degree, the function faced the front upper inner side. The straight-line distance between the position and the final position was 8.34 mm. During the forward movement of the mandible, the coracoid process slided forward downward and inward with a sliding distance of 8.64 mm. During lateral movement, the range of the working side condyle function surface motion was small, only slight rotation, the maximum range of motion was 1.97 mm; in the process of row side movement, the non-working condyle function surface had a larger movement range than the working side, the movement direction was the front lower inner side, and the movement distance was 7.65 mm.@*Conclusions@#The novel virtual articulator PN300 and digital technology can achieve the accurate measurement of three-dimensional trajectory of the condyle, and furthermore simulate the motion morphology of the condyle.

Research status of tooth preparation quantitative guide technique / 中华口腔医学杂志

Tooth preparation is a basic operation in prosthodontics treatment and the quality of preparation influences the effect of treatment directly. How to achieve a precise and quantitative tooth preparation is always one of the main aims of dental prosthodontics. The known types of tooth preparation guide technique can be divided into visual guidance, passive constraint guidance and active constraint guidance (automated tooth preparation), respectively represented by silicon rubber index, tooth preparation guide plate and computerized numerical control cutting system (CNC cutting system). Studies in advanced manufacturing technologies such as robot systems and numerical control ultra-short pulse laser (USPL) have also been reported recently. This review comprehensively introduced tooth preparation quantitative guide techniques and partially summarized the application effects and limitations to provide reference for relative researches and clinical application.

Research and development of digital design and fabrication of complete denture / 中华口腔医学杂志

Removable complete denture are still the primary prosthetic solution for edentulous patients. Functional pressure impression obtaining, jaw relation recording, personalized balance occlusion and highly precise fabrication of denture are difficult. The digital restoration technique represented by intraoral three-dimensional scanning and three-dimensional (3D) printing compensates for the shortages of the manual techniques, but there are still many limitations in the application of complete dentures. At present, a few computer aided design and computer aided manufacture (CAD/CAM) complete denture systems have been developed both domestically and abroad, and these system are mainly focused on the digital design and manufacture of denture, and are seldom used for the recording of impression and jaw relation. This review is based on the main clinical procedures of the traditional complete denture restoration, elaborating the research and application status of digital technique in each steps, in order to provide reference for clinical application.

Application and outlook of three-dimensional printing in prosthetic dentistry / 中华口腔医学杂志

At present, three-dimensional (3D) printing has been applied in many aspects in the field of prosthodontics, such as dental models, wax patterns, guide plates, dental restoration and customized implants. The common forming principles include light curing, sintering and melting-condensation, the materials include pure wax, resin, metal and ceramics. However, the printing precision and the strength of multi-material integrated forming, remains to be improved. In addition, as a technology by which the internal structure of a material can be customized manufacturing, further advantage of 3D printing used in the manufacture of dental restoration lies in the customization functional bionic micro-structures, but the related research is still in its infancy. The review briefly summarizes the commonly used 3D printing crafts in prosthetic dentistry, and details clinical applications and evaluations, provides references for clinical decision and further research.

Quantitative evaluation of printing accuracy and tissue surface adaptation of mandibular complete denture polylactic acid pattern fabricated by fused deposition modeling technology / 中华口腔医学杂志

Objective@#To quantitatively evaluate the adaptation of polylactic acid (PLA) pattern of mandibular complete denture fabricated by fused deposition modeling (FDM) technology.@*Methods@#A mandibular complete denture digital model was designed through a complete denture design software based on a pair of standard maxillomandibular edentulous plaster model and their occlusion bases. Ten PLA mandibular complete dentures were printed with a FDM machine. The dentures were scanned with and without the plaster model using a three-dimensional (3D) scanner. In Geomagic software, the scanning data of printed dentures were registered to its computer aided design (CAD) data, and the printing error was analyzed using the multipoint registration command. For quantitatively evaluating the adaptation of the denture, the data of plaster model and PLA denture were registered to the whole data of denture located in the plaster model using the best-fit alignment command, the 3D deviation of the plaster model and tissue surface of the denture represent the space between them. The overall area was separated into three parts: primary stress-bearing area, secondary stress-bearing area and border seal area, and the average deviations of these three parts were measured. The values were analyzed using analysis of variance.@*Results@#Compared with the CAD data, the printing error was (0.013±0.004) mm. The overall 3D deviation between PLA denture and plaster model was (0.164±0.033) mm, in which the primary stress-bearing area was (0.165± 0.045) mm, the secondary stress-bearing area was (0.153 ± 0.027) mm, the border seal area was (0.186 ± 0.043) mm. These showed a good fit in the majority parts of the FDM denture to the plaster model. No statistically significant difference was observed between the three areas (F=1.857, P=0.175>0.05).@*Conclusions@#Combined with the 3D scanning, CAD and FDM technology, a FDM 3D printing process of complete denture for injection moulding can be established. As a result, high efficiency and low cost can be used to print out the complete denture, to lay the basis for further clinical applications.

Study on the appropriate parameters of automatic full crown tooth preparation for dental tooth preparation robot / 中华口腔医学杂志

Objective@#To further study the most suitable parameters for automatic full crown preparation using oral clinical micro robot. Its purpose is to improve the quality of automated tooth preparing for the system and to lay the foundation for clinical application.@*Methods@#Twenty selected artificial resin teeth were used as sample teeth. The micro robot automatic tooth preparation system was used in dental clinic to control the picosecond laser beam to complete two dimensional cutting on the resin tooth sample according to the motion planning path. Using the laser scanning measuring microscope, each layer of cutting depth values was obtained and the average value was calculated. The monolayer cutting depth was determined. The three-dimensional (3D) data of the target resin teeth was obtained using internal scanner, and the CAD data of full-crown tooth preparation was designed by CAD self-develged software. According to the depth of the single layer, 11 complete resin teeth in phantom head were automatically prepared by the robot controlling the laser focused spot in accordance with the layer-cutting way. And the accuracy of resin tooth preparation was evaluated with the software. Using the same method, monolayer cutting depth parameter for cutting dental hard tissue was obtained. Then 15 extracted mandibular and maxillary first molars went through automatic full crown tooth preparation. And the 3D data of tooth preparations were obtained with intra oral scanner. The software was used to evaluate the accuracy of tooth preparation.@*Results@#The results indicated that the single cutting depth of cutting resin teeth and in vitro teeth by picosecond laser were (60.0±2.6) and (45.0±3.6) μm, respectively. Using the tooth preparation robot, 11 artificial resin teeth and 15 complete natural teeth were automatically prepared, and the average time were (13.0±0.7), (17.0±1.8) min respectively. Through software evaluation, the average preparation depth of the occlusal surface of 11 resin teeth was approximately (2.089±0.026) mm, the error was about (0.089±0.026) mm; the average convergence angle was about 6.56°±0.30°, the error was about 0.56°±0.30°. Compared with the target preparation shape, the average shape error of the 11 resin tooth preparations was about 0.02-0.11 mm. And the average preparation depth of the occlusal surface of 15 natural teeth was approximately (2.097±0.022) mm, the error was about (0.097±0.022) mm; the average convergence angle was about 6.98°±0.35°, the error was about 0.98°±0.35°. Compared with the target preparation shape, the average shape error of the 15 natural tooth preparations was about 0.05-0.17 mm.@*Conclusions@#The experimental results indicate that the automatic tooth preparation for resin teeth and the teeth were completed according to the specific parameters of the single cutting depth by the micro robot controlling picosecond laser respectively, its preparation accuracy met the clinical needs. And the suitability of the parameter was confirmed.

Three-dimensional data fusion method for tooth crown and root based on curvature continuity algorithm / 北京大学学报(医学版)

Objective:To explore a three-dimensional (3D) data fusion and integration method of optical scanning tooth crowns and cone beam CT (CBCT) reconstructing tooth roots for their natural transition in the 3D profile.Methods: One mild dental crowding case was chosen from orthodontics clinics with full denture.The CBCT data were acquired to reconstruct the dental model with tooth roots by Mimics 17.0 medical imaging software, and the optical impression was taken to obtain the dentition mo-del with high precision physiological contour of crowns by Smart Optics dental scanner.The two models were doing 3D registration based on their common part of the crowns'' shape in Geomagic Studio 2012 reverse engineering software.The model coordinate system was established by defining the occlusal plane.crown-gingiva boundary was extracted from optical scanning model manually, then crown-root boundary was generated by offsetting and projecting crown-gingiva boundary to the root model.After trimming the crown and root models, the 3D fusion model with physiological contour crown and nature root was formed by curvature continuity filling algorithm finally.In the study, 10 patients with dentition mild crowded from the oral clinics were followed up with this method to obtain 3D crown and root fusion models, and 10 high qualification doctors were invited to do subjective evaluation of these fusion models.Results: This study based on commercial software platform, preliminarily realized the 3D data fusion and integration method of optical scanning tooth crowns and CBCT tooth roots with a curvature continuous shape transition.The 10 patients'' 3D crown and root fusion models were constructed successfully by the method, and the average score of the doctors'' subjective evaluation for these 10 models was 8.6 points (0-10 points).which meant that all the fusion models could basically meet the need of the oral clinics, and also showed the method in our study was feasible and efficient in orthodontics study and clinics.Conclusion: The method of this study for 3D crown and root data fusion could obtain an integrate tooth or dental model more close to the nature shape.CBCT model calibration may probably improve the precision of the fusion model.The adaptation of this method for severe dentition crowding and micromaxillary deformity needs further research.

Multi-source data acquisition technology in the restoration of the complete denture restoration / 中华口腔医学杂志

In complete-denture restoration of edentulous jaws, the following information is needed: functional impression of edentulous jaws, jaw relationship and facial fullness, parameters of individual mandibular movement, etc. Traditional clinical methods in obtaining these data, which depend greatly on practitioners' clinical experience and skills, are subjective, complicated and low efficient. With the development of the digital restoration of edentulous jaws, a variety of equipment for three-dimensional scan have been applied in acquiring three-dimensional source data concerning the needed information, which greatly simplifies the process of data obtaining, reduces the dependence on operational skills and subjective experience, improves efficiency and efficacy of diagnosis and treatment, and standardizes the restoration process.

Quantitative evaluation of the measurement accuracy of 2 three-dimensional facial scanners / 实用口腔医学杂志

Objective:To evaluate the actual measurement accuracy of 2 three-dimensional(3D)facial scanners for real person. Methods:3D digital face models of 1 0 volunteers with normal ficial form were obtained by 3dMD and FaceScan facial scanners respec-tively.The measurement values of 1 0 feature lengths and 5 feature angles were measured on each 3D model by the software respective-ly.The reference values of all characteristics were acquired by line laser scanner (Faro)with high accuracy.Statistical and surveying analysis were taken between the measurement values and reference values.Facial morphology measurement error and actual accuracy of facial scanners were obtained finally.Data were statistically analysed.Results:The length measurement accuracy of 3dMD and FaceS-can was(-0.37 ±0.68)mm and (-0.29 ±0.53)mm(P =0.223),the angle measurement accuracy was (-0.22 ±2.1 4)°and (0.1 2 ±2.69)°(P =0.428),respectively.Conclusion:The 3D data of ficial morphology obtained by the 2 scanners are not signifi-cantly different.

Osteogenesis of human adipose-derived mesenchymal stem cells-biomaterial mixture in vivo after 3 D bio-printing / 北京大学学报(医学版)

Objective:To construct human adipose-derived mesenchymal stem cells (hASCs)-biomate-rial 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 1 4 d of osteogenic induction.The cells were added into 20 g/L sodium alginate and 80 g/L gelatin mixture (cell density was 1 ×1 06/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 osteogeni-cally 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 irregu-lar 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 1 8%±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.

roughness study of ytterbium-doped potassium yttrium tungstate [YB: KYW] thin-disk femtosecond ablated dentin

The aim of this study was to evaluate the morphological changes and quantitatively assess the roughness of dentin after the ablation with a Ytterbium-Doped Potassium Yttrium Tungstate [YB: KYW] thin-disk femtosecond pulsed laser of different fluences, scanning speeds and scanning distances. Twelve extracted human premolars were sectioned into crowns and roots along the cementum-enamel junction, and then the crowns were cut longitudinally into sheets about 1.5 mm thick with a cutting machine. The dentin samples were fixed on a stage at focus plane. The laser beam was irradiated onto the samples through a galvanometric scanning system, so rectangular movement could be achieved. After ablation, the samples were examined with a scanning electron microscope and laser three-dimensional profile measurement microscope for morphology and roughness study.With increasing laser fluence, dentin samples exhibited more melting and resolidification of dentin as well as debris-like structure and occluded parts of dentinal tubules. When at the scanning speed of 2400mm/s and scanning distance of 24microm, the surface roughness of dentin ablated with femtosecond pulsed laser decreased significantly and varied between values of dentin surface roughness grinded with two kinds of diamond burs with different grits. When at the scanning speed of 1200mm/s and scanning distance of 12microm, the surface roughness decreased slightly, and the surface roughness of dentin ablated with femtosecond pulsed laser was almost equal to that grinded with a low grit diamond bur. This study showed that increased laser influence may lead to more collateral damage and lower dentin surface roughness, while scanning speed and scanning distance were also negatively correlated with surface roughness. Adequate parameters should be chosen to achieve therapeutic benefits, and different parameters can result in diverse ablation results

Quantitative evaluation of three-dimensional reconstruction accuracy of edentulous models in centric relation / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To reconstruct the centric relation of upper and lower edentulous dental models with two methods, to compare the reconstruction accuracy of the vertical and horizontal distance, and to provide some references to computer aided design and computer aided manufacture for complete denture.</p><p><b>METHODS</b>Dental models and rims made from five edentulous patients in clinical were obtained.Each model was stocked with 10 identical size positioning cylinders (20 cylinders on each pair models) on 5 side-surfaces of basement. Twelve center point pairs were paired between upper and lower models from 20 cylinder bottoms. The vertical and horizontal distances of 12 center point pairs were regarded as the evaluation items. Firstly, upper and lower models and rims were scanned separately. Then, models and rims (fixed in centric relation respectively with positioning articulator and rubber banding) were scanned.In software, all the data were registered to reconstruct centric relation based on common region. Digital models were measured with software tools, and real models were measured with a contact measurement arm. The differences of the homologous items between two methods were analyzed with paired-t test.</p><p><b>RESULTS</b>The vertical distance errors for dental articulator positioning method was (0.356 ± 0.200) mm and that of the rubber band method was (0.382 ± 0.299) mm, and paired-t test between the two methods showed no significant differences (P > 0.05). The horizontal errors were (0.010 ± 0.411) mm and (0.104 ± 0.476) mm, and paired-t test showed significant differences (P < 0.05).</p><p><b>CONCLUSIONS</b>Comparing with rubber band method, dental articulator positioning can significantly increases three-dimensional reconstruction accuracy of edentulous jaw gypsum models' horizontal relation.</p>