[Effects of femtosecond laser treatment on surface characteristics and flexural strength of zirconia].

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.

Accuracy of detecting vertical root fractures in non-root filled teeth using cone beam computed tomography: effect of voxel size and fracture width.

AIM: To investigate simultaneously the effect of voxel size and fracture width on the accuracy of detecting vertical root fractures (VRFs) in non-root filled teeth when using cone beam computed tomography. METHODOLOGY: Fifty-one of 161 extracted human permanent teeth (16 anterior teeth, 132 premolars and 13 mandibular molars) were selected randomly for VRF induction with two fracture widths. All teeth were scanned with four CBCT units at different voxel sizes provided by the units. Three observers classified the presence or absence of VRF using a 5-point scale. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and area under the ROC curve (AUC) were calculated. AUCs amongst voxel sizes and between the fracture widths were compared using the Z test. Intra- and inter-observer agreement was assessed using weighted Cohen kappa. RESULTS: For the NewTom VGi and ProMax 3D Mid CBCT unit, no significant differences were found amongst voxel sizes for the AUCs, irrespective of the fracture width (P > 0.05). There were significant differences between images scanned with voxel size 250 and 160 µm (P = 0.02), and images scanned with voxel size 250 and 80 µm for AUCs in the narrow VRF group for the 3D Accuitomo 170 unit (P = 0.03). For i-CAT FLX, significant differences were found between the voxel protocols of 300 µm and of the other three voxel sizes for AUC, sensitivity and NPV (P < 0.05). Significant differences between the wide and the narrow VRF groups for AUCs were found for 3D Accuitomo 170 (P = 0.01) and ProMax 3D Mid (P < 0.01). CONCLUSIONS: Cone beam computed tomography was accurate for detecting VRF in non-root filled teeth. Fracture width had an effect on the detection of VRF. The effect of the voxel size on the detection of VRF depended on the CBCT unit used.

[Preliminary study on the automatic preparation of dental implant socket controlled by micro-robot].

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, R(2)=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.

[Three-dimensional analysis of the early correction of anterior crossbite using eruption guidance appliance].

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.

[Study on the appropriate parameters of automatic full crown tooth preparation for dental tooth preparation robot].

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.

[Effect of dibutyl phthalate on demodicidosis].

OBJECTIVE: To evaluate the curative effect and safety of dibutyl phthalate on demodicidosis. METHODS: A single blinded and controlled study of human demodicidosis treated with dibutyl phthalate was conducted. One hundred and forty three patients with demodicidosis, including 81 acne and 62 rosacea, randomly divided into trial and control groups. The trial group was treated with dibutyl phthalate and control group with "new fumanling" cream twice a day in the early morning and evening respectively for six weeks consecutively. RESULTS: The rates of excellent, good, and fair efficacy and total effective rate in the trial group with acne were 53.7%, 41.5%, 4.9% and 100% respectively, with a significant difference to the control group (P < 0.05). The rates in the trial group with rosacea were 40.6%, 40.6%, 18.8% and 100% respectively, with no statistical difference to the control group (P > 0.05). No complaint of side effects in the trial group was recorded. CONCLUSION: Dibutyl phthalate is highly effective to demodicidosis without prominent adverse reactions.