Effects of femtosecond laser treatment on surface characteristics and flexural strength of zirconia / 北京大学学报(医学版)

OBJECTIVE@#To evaluate the effects of femtosecond laser treated microgrooved surface on microscopic topography, phase transformation, and three-points flexural strength of zirconia, and to provide reference for surface microstructure optimization of zirconia implant.@*METHODS@#According to different surface treatment methods, 57 computer aided design/computer aided manufacture (CAD/CAM) zirconia bars (20.0 mm×4.0 mm×1.4 mm) were evenly divided into three groups: sintered group, no treatment after sintering, taken as control; sandblasted group, sandblasted with 110 μm aluminium oxide (Al2O3) after sintering; microgrooved group, femtosecond laser fabricated microgrooves with 50 μm width, 30 μm depth, and 100 μm pitch. Surface microscopic topography was observed with scanning electron microscope (SEM) and 3D laser microscope. Further, surface roughness in each group and microgroove size were measured. Crystal phase was analyzed with X-ray diffraction. Specimens were subjected to three- points flexural strength test, and Weibull distribution was used to analyze their strength characteristics.@*RESULTS@#SEM showed that sintered surface was flat with clear grain structure; sandblasted surface exihibited bumps and holes with sharp margins and irregular shape; microgrooves were regularly aligned without evident defect, and nano-scale particles were observed on the surface inside of the microgrooves. Ra value of microgrooved group [(9.42±0.28)] μm was significantly higher than that of sandblasted group [(1.04±0.03) μm] and sintered group [(0.60±0.04) μm], and there was statistical difference between sandblasted group and sintered group (P < 0.001). The microgroove size was precise with (49.75±1.24) μm width, (30.85±1.02) μm depth, and (100.58±1.94) μm pitch. Crystal phase analysis showed that monoclinic volume fraction of sandblasted group (18.17%) was much higher than that of sintered group (1.55%), while microgrooved group (2.21%) was similar with sintered group. The flexural strength of sandblasted group (986.22±163.25) MPa had no statistical difference with that of sintered group (946.46±134.15) MPa (P=0.847), but the strength in microgrooved group (547.92±30.89) MPa dropped significantly compared with the other two groups (P < 0.001). Weibull modulus of sintered, sandblasted, microgrooved groups were 7.89, 6.98, and 23.46, respectively.@*CONCLUSION@#Femtosecond laser was able to form micro/nanostructured microgrooves on zirconia surface, which deleteriously affected the flexural strength of zirconia.

Three-dimensional analysis of the early correction of anterior crossbite using eruption guidance appliance / 北京大学学报(医学版)

OBJECTIVE@#To investigate the clinical effect of eruption guidance appliance in the treatment of anterior cross bite in mixed-dentition children.@*METHODS@#In the study,10 mixed-dentition children with anterior cross bite, totally 12 incisors, were selected. Alginate was used to take upper and lower dentition impression and make a hard plaster model,which served as the eruption guidance appliance for treatment. The pre- and post-operative dental casts were digitized with SmartOptics Activity 880 scanner,and the three-dimensional overlapping models were obtained by reverse engineering software,Geomagic Studio 2012,then the three-dimensional movements of the upper and lower incisors were analyzed using Imageware 13.2 software. The overbite and overjet were analyzed using the same methods. Measurement with copper wire was used to analyze the upper and lower arch length. Space analysis was the result by the sum of crown width minus the arch length. The crown width of unerupted permanent teeth was according to X-ray method to predict. The SPSS 17.0 software was used to analyze the pre- and post-operative measurements of the same child. The normality test of the measured data showed that it conformed to the normal distribution. Therefore,the t test and double side test were used,and the significance level was 0.05.@*RESULTS@#The course of treatment was (5.6±2.7) months. During orthodontic treatment, the upper incisors moved mainly labially (P<0.001) in three-dimensional displacement, and the lower incisors moved mainly the same direction (P=0.025). During the treatment of eruption guidance appliance,the average overbite decreased (1.01±0.9) mm (t=-3.531, P=0.006), and the difference was statistically significant. There was no statistically significant difference between the pre- and post-operative average overjet (t=0.771, P=0.460). The severity of crowding in upper arch decreased (1.9±0.99) mm (t=-6.042, P<0.001),and that in lower arch decreased (1.9±0.74) mm (t=-8.143, P<0.001), both of the differences were statistically significant.@*CONCLUSION@#The anterior cross bite in mixed dentition could be corrected by eruption guidance appliance, and at the same time, the normal overjet and overbite were established, and the teeth were aligned.

Accuracy evaluation of a new three-dimensional reproduction method of edentulous dental casts, and wax occlusion rims with jaw relation / 国际口腔科学杂志·英文版

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 / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the accuracy of four dominant methods of three-dimensional multisource data registration.</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSIONS</b>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.</p>