Effect of different tooth preparation designs on the marginal and internal fit discrepancies of cobalt-chromium crowns produced by computer-aided designing and selective laser melting processes

PURPOSE@#To evaluate the impact of five different tooth preparation designs on the marginal and internal fit discrepancies of cobalt-chromium (CoCr) crowns produced by computer-aided designing (CAD) and selective laser melting (SLM) processes. @*MATERIALS AND METHODS@#Five preparation data were constructed, after which design crowns were obtained. Actual crowns were fabricated using an SLM process. After the data of actual crowns were obtained with structural light scanning, intaglio surfaces of the design crown and actual crown were virtually superimposed on the preparation. The fit-discrepancies were displayed with colors, while the root means square was calculated and analyzed with one-way analysis of variance (ANOVA), Tukey’s test or Kruskal-Wallis test (α =.05). @*RESULTS@#The marginal or internal color-coded images in the five design groups were not identical. The shoulder-lip and sharp line angle groups in the CAD or SLM process had larger marginal or internal fit discrepancies compared to other groups (P < .05). In the CAD process, the mean marginal and internal fit discrepancies were 10.0 to 24.2 µm and 29.6 to 31.4 µm, respectively. After the CAD and SLM processes, the mean marginal and internal fit discrepancies were 18.4 to 40.9 µm and 39.1 to 47.1 µm, respectively. The SLM process itself resulted in a positive increase of the marginal (6.0 – 16.7 µm) and internal (9.0 – 15.7 µm) fit discrepancies. @*CONCLUSION@#The CAD and SLM processes affected the fit of CoCr crowns and varied based on the preparation designs. Typically, the shoulder-lip and sharp line angle designs had a more significant effect on crown fit. However, the differences between the design groups were relatively small, especially when compared to fit discrepancies observed clinically.

Accuracy and reproducibility of 3D digital tooth preparations made by gypsum materials of various colors

PURPOSE: The study aimed to identify the accuracy and reproducibility of preparations made by gypsum materials of various colors using quantitative and semi-quantitative three-dimensional (3D) approach. MATERIALS AND METHODS: A titanium maxillary first molar preparation was created as reference dataset (REF). Silicone impressions were duplicated from REF and randomized into 6 groups (n=8). Gypsum preparations were formed and grouped according to the color of gypsum materials, and light-scanned to obtain prepared datasets (PRE). Then, in terms of accuracy, PRE were superimposed on REF using the best-fit-algorithm and PRE underwent intragroup pairwise best-fit alignment for assessing reproducibility. Root mean square deviation (RMSD) and degrees of similarity (DS) were computed and analyzed with SPSS 20.0 statistical software (α=.05). RESULTS: In terms of accuracy, PREs in 3D directions were increased in the 6 color groups (from 19.38 to 20.88 µm), of which the marginal and internal variations ranged 51.36 – 58.26 µm and 18.33 – 20.04 µm, respectively. On the other hand, RMSD value and DS-scores did not show significant differences among groups. Regarding reproducibility, both RMSD and DS-scores showed statistically significant differences among groups, while RMSD values of the 6 color groups were less than 5 µm, of which blue color group was the smallest (3.27 ± 0.24 µm) and white color group was the largest (4.24 ± 0.36 µm). These results were consistent with the DS data. CONCLUSION: The 3D volume of the PREs was predisposed towards an increase during digitalization, which was unaffected by gypsum color. Furthermore, the reproducibility of digitalizing scanning differed negligibly among different gypsum colors, especially in comparison to clinically observed discrepancies.

Immortalization of the SD rats' dental follicle cell with simian virus 40 large tumor antigen gene / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To construct SD rat immortalized dental follicle cells (rDFC) induced by simian virus 40 large tumor antigen (SV40Tag) gene to provide a reliable cell source for periodontal tissue engineering research.</p><p><b>METHODS</b>The rDFC was isolated by tissue mass method combined with enzyme digestion method and evaluated by immunohistochemistry. Cell293 were transfected with plasmid pSSR69/pAmpho containing SV40Tag gene by mediating liposome. Normal rDFC were infected with virus-contained supernate and the successfully transfected cell lines were screened with hygromycin, and positive clones were cultured. While non-transfected cells served as negative controls, the cell morphology was observed, the proliferation characteristics was evaluated by calculating cell population. The expression of SV40Tag gene and telomerase in cells was detected by reverse transcription polymerase chain reaction (RT-PCR) and Western blotting respectively. The biological property of immortalized rDFC was assessed with calculating formation rate of flat cloning, soft agar colony formation test and tumor-forming test.</p><p><b>RESULTS</b>Morphology of immortalized rDFC was not different from that of normal rDFC. The RT-PCR results of SV40Tag revealed amplification band at 357 bp, while no band was seen in the normal cells. The expression of telomerase in immortalized rDFC was higher than that in normal rDFC. The two groups had no significant difference in growth curves, but the immortalized rDFC exhibited stronger proliferative activity. No significant differences of formation rate in flat cloning were observed between the immortalized rDFC [34% (33/96)] and normal rDFC at passage four [22% (21/96)] (χ(2) = 3.71, P > 0.05). No cell cloning was seen in soft agar and the tumor formation was not observed in nude mice.</p><p><b>CONCLUSIONS</b>The rDFC induced by SV40Tag gene could be cultured and passaged in vitro, which retained the stable proliferation and differentiation characteristics and could be used for periodontal tissue engineering research.</p>

Low intensity pulsed ultrasound combined with guided tissue regeneration for promoting the repair of defect at canines periodontal fenestration in Beagle dogs / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the effects of low intensity pulsed ultrasound (LIPUS) combined with guided tissue regeneration (GTR) for the repair of the periodontal fenestration defect at the canines in Beagle dogs.</p><p><b>METHODS</b>Four Beagle dogs were used for establishing the periodontal fenestration defect. Sixteen canines of four Beagle dogs were simple randomly assigned into experimental group 1 [LIPUS (60 mW/cm(2), 20 min/d) irradiation + GTR + the periodontal fenestration defect], experimental group 2 [LIPUS (60 mW/cm(2), 20 min/d) irradiation + the periodontal fenestration defect], experimental group 3 (GTR + the periodontal fenestration defect) and control group (the periodontal fenestration defect). Experiments conducted 28 d. The temperature of the gingive's surface of each group was tested every 14 days (analyzed by Wilcoxon rank sum test with SPSS 13.0). The demineralized bone tissue slices of the periodontal fenestration were obtained for histologic staining after 4 weeks treatment.</p><p><b>RESULTS</b>Clinically all the treatment groups healed well. The change of gingive's surface temperature [M(Q)] before and after LIPUS irradiating were: 0.225 (0.463)°C (experimental group 1), 0.265 (0.133)°C (experimental group 2), 0.090 (0.115)°C (experimental group 3); -0.175 (0.370)°C (control group). The P value of experimental group 1 and 2 with pre-and post-treatment each time were both 0.027. Histology of the demineralized bone tissue revealed that in experimental group 1, the bone defect was filled with fresh bone-like tissues, proliferatively active osteoblasts and newly formed cementum-like tissues along the defect surface. In experimental group 3, there were more new cementum- and bone-like tissues than in experimental group 2 and control group. In experimental group 2, the new bone collagen was more mature than in experimental group 3 and control group. In control group, there was less growth of new cementum along the notch, and the new bone collagen was immature.</p><p><b>CONCLUSIONS</b>LIPUS combined with GTR may have the potential of promoting the repair of periodontal fenestration defect.</p>

Influence of the peri-implantitis to the microscrew-bone interface / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To study the histological change of microscrew-bone interface, detect the relative cytokine of gingival crevicular fluid, and explore the impossible mechanism of peri-implantitis.</p><p><b>METHODS</b>Four male Beagles were collected. Randomly select one side of animals jaw as the experimental group to induce the peri-implantitis, and another side as the control group. Four microscrews were implanted on each side. In the 1st, 2nd, 3rd, 4th weeks after implantation, collect peri-implant sulcular fluid (PISF) and detect tumor necrosis factor-alpha (TNF-alpha) levels before sacrificed, and the harvest tissue were observed in histological ways.</p><p><b>RESULTS</b>According to the extension of time after implantation, the experimental group showed visible progress of interface destruction: 1st week after implantation showed large numbers inflammatory cells collected at the neck but did not undermine the cortical bone; 2nd week after implantation, cortical bone were observed angular absorption; Bone resorption continued to develop and at the 4th week, bone resorption were enlarged to the second thread of microscrew and the interface was filled with a large number of collagen fibers.</p><p><b>CONCLUSION</b>The destruction of interface began at the neck of microscrew, and the further development was along the interface in depth. Both microscrews with peri-implantitis and the healthy controls showed the presence of TNF-alpha. Inflammation accumulation might trigger the up-regulation of TNF-alpha level, and the onset of inflammation would enhance the up-trend.</p>

Stress and displacement distribution of mandibular condyle advanced with Forsus under different occlusal reconstruction conditions / 医用生物力学

Objective To analyze changes of stress and displacement distribution of the mandibular condyle under different occlusal reconstruction conditions by using the Forsus, and to provide clinical reference for the application of the Forsus. Method The software Abaqus6.5 was employed to build the 3D finite element model of mandibular condyle for simulation. Under different occlusal reconstruction conditions, the distances of mandibular protraction were 3 mm, 4 mm, 5 mm, 6 mm and 7 mm and the mandibular's opening distances were got as 4 mm, 3.5 mm, 3 mm, 2.5 mm and 2 mm correspondingly. The stress, displacement and rotation trends of mandibula temporomandibular articulation were analyzed and the estimation of occlusal reconstruction contributing to the growth of the condyle was made. Results The 3D model showed that the maximum stress distributed on the mandibular condyloid process, sigmoid incisure of mandible and the posterior neck of condyle area under the five different conditions. With the increase of displacement in mandibular condyle, the stress increased slowly on the sigmoid incisure of mandible and the posterior neck of condyle area, but the stress still kept in the same order of magnitude (30 MPa). The stress distribution of mandibular condyloid process was in a steady state with no obvious stress concentration. The displacement of condyle in horizontal direction increased gradually and forward, and the displacement of condyle in vertical direction also increased gradually but downward. When the mandibular was stretched to the designed reconstructive location, the condyle moved downward. Conclusions The range of physiological occlusal reconstruction will not change the stress distribution trends of the condylar cartilage, even when the mandibular moves forwards in varying degrees. Considering the physiological nature of temporomandibular articulation and the growth of the condyle, when the mandibular retrusion is severe, it would be advisable by subsection protrusion.

Repairing effects of low-intensity pulsed ultrasound on alveolar bone defects in Beagle dogs / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the potential repairing effects of low-intensity pulsed ultrasound (LIPUS) irradiation on acute horizontal alveolar bone defects at the mandibular pre-molar areas in Beagle dogs.</p><p><b>METHODS</b>Horizontal alveolar bone defect models were established under enamelo-cemental junction 6 mm at the mandibular third and forth pre-molar buccal regions on both sides in 4 beagle dogs, and bilateral sides of each dog were randomly divided into two groups: Experimental groups with LIPUS irradiation (I(SATA) 30 mW X cm(-2), 20 min x d(-1)) and control groups without opening power source of LIPUS radiation. Dual energy X-ray bone densitometer was used to detect the bony density after an 8 weeks' irradiation. Meanwhile, decalcified bone tissue sections were used to assess the histological effects of new alveolar bone.</p><p><b>RESULTS</b>The results of new bony density detection in experimental group and control group were (0.6053 +/- 0.0566) g x cm(-2), (0.6047 +/- 0.0552) g x cm(-2), respectively, and there was no statistical significance between the differences of the two groups (P = 0.9839). Hematoxylin-eosin staining of decalcified bone tissue sections demonstrated that there were more osteoblasts lining at the edge of new alveolar bone in the experimental groups than that scattered in the control groups, and Masson staining revealed that collagens in new alveolar bone stained bright red indicating higher maturity in the experimental groups, while in the control groups mainly stained blue with some virescent areas indicating lower maturity.</p><p><b>CONCLUSION</b>LIPUS irradiation on acute horizontal alveolar bone defects has potential repairing effects.</p>

Preliminary study of cranio-maxillofacial hard tissue structure feature of young mandibular retrusion orthognathic patients with delaire cephalometric analysis / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To guide the orthodontic diagnosis, treatment planning and prognosis by analyzing the craniofacial morphology and reimbursement mechanism of young patients with mandibular retrusion in Chongqing territory by Delaire cephalometric analysis.</p><p><b>METHODS</b>Both conventional cephalometric analysis and Delaire cephalometric analysis were conducted on the basis of the lateral cephalograms from 56 young mandibular retrusion patients and 40 teenagers with normal occlusion.</p><p><b>RESULTS</b>Decreases in angle SNB, Co-Go, Co-Pog, U1-L1 and increases in angle ANB, angle SN-MP, L1-MP were seen in mandibular retrusion group by conventional cephalometric analysis. Decreases in angle 1, angle 5, (Cp-Oi)/C2 and increases in angle 2, (M-Cp)/C2, angle 3, angle 4 were seen in mandibular retrusion group by Delaire cephalometric analysis. Me-F1 and Me-Met were -8.70 mm +/- 2.48 mm and 5.74 mm +/- 2.58 mm respectively.</p><p><b>CONCLUSION</b>Delaire cephalometric analysis could evaluate cranio-maxillofacial architectural features of mandibular retrusion patients more visually and quantitatively, which suggests that mandibular retrusion is usually caused by the retrusion of mandibular position and the hypodevelopment of mandibule.</p>

Three dimensional finite element analysis of maxillary anterior teeth retraction with micro-implant anchorage and sliding mechanics / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the biomechanical effects of micro-implant anchorage technique with sliding mechanics on maxillary anterior teeth retraction under different implant insertion heights and different retraction hook heights.</p><p><b>METHODS</b>The three dimensional finite element model of maxillary anterior teeth retraction force system was constructed with CT scanning and MIMICS software and the relationships between brackets, teeth, wire and micro-implant were simulating the clinical factions. Then the initial tooth displacement was calculated when the insertion heights were 4 mm and 8 mm and the retraction hook heights were 1, 4, 7, 10 mm respectively.</p><p><b>RESULTS</b>With retraction hook height added, the anterior teeth movement changed from lingual crown tipping to labial crown tipping and the intrusion movement was more apparent when the micro-implant was inserted in a higher location.</p><p><b>CONCLUSION</b>The ideal teeth movement control could be achieved by different insertion heights of micro-implant and different retraction hook heights in straight wire retraction force system.</p>

Distraction osteogenesis in correcting facial asymmetry malformation caused by temporomandibular joint ankylosis: a case report / 华西口腔医学杂志

A facial asymmetry patient caused by temporomandibular joint ankylosis was operated by putting a distraction osteogenesis (DO)-appliance. One week after surgery, the right mandible was distracted. Twenty days after distraction, the height of right mandibular ramus and body increased obviously. Four months after retain of DO-appliance, the right maxilla down-grew automatically and the occluding relation recovered to normal. The DO-appliance was taken out. MEDPOR prosthesis was imbedded in new bone and genioplasty was operated. The facial asymmetry and abnormal occluding relation of the patient were improved obviously.

Three-dimensional finite element analysis of stress distribution in mandible advanced with Forsus / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To construct a three-dimensional finite element model of mandible and to analyze the stress distribution in mandible advanced with Forsus.</p><p><b>METHODS</b>One growing patient with mandibular retrusion was selected. After leveling and aligning with MBT (Mclaughlin Bennett Treriri) straight-wire appliance to achieve the request of forsus with the spiral CT, a three-dimensional finite element model was constructed and the stress distribution in mandible after advancing at 1 second, 15 seconds and 300 seconds was analyzed.</p><p><b>RESULTS</b>The three-dimensional finite element model included MBT straight-wire appliance. The stress concentration areas were located in the front side of the condylar process, the sigmoid notch and mandibular molar areas at 15 seconds and 300 seconds after mandibular advancement. The maximum stress values were 34.47 MPa and 34.45 MPa, respectively. With the extension of loading time, the largest displacement increased from 3.30 x 10(-2) mm to 1.15 mm and the region of the largest displacement extended backwards along the body of mandible. However, the displacement of condyle reduced from 1.65 x 10(-2) mm at 1 second to 3.27 x 10(-5) mm at 300 seconds after mandibular advancement.</p><p><b>CONCLUSIONS</b>The three-dimensional finite element model considered the viscoelasticity and viscoelasticity of mandibular. The result suggested that the stress distribution in the mandible gradually became stable after the application of Forsus and the appliance caused downward and forward mandibular modification.</p>

Study of computer-assisted Delaire cephalometric analysis system / 华西口腔医学杂志

<p><b>OBJECTIVE</b>The purpose of this study was to establish the computer -assisted Delaire cephalometric analysis system with WinCeph8.0 in order to simplify the procedure of manual Delaire cephalometric analysis.</p><p><b>METHODS</b>On the basis of the theory of Delaire cephalometric analysis and the program module of WinCeph8.0, the landmark points and the auxiliary line were defined, the measurement and analysis program were written, then the computer-assisted Delaire cephalometric analysis system was established. Paired t-test and dispersion analysis of the computer-assisted and manual measurements were taken.</p><p><b>RESULTS</b>Computer-assisted Delaire cephalometric analysis system was convenient and accurate to trace the landmark points and the auxiliary line. It was able to proceed the measurement and calculation automatically and display the analysis results. Statistical analysis showed that computer-assisted analysis was more accurate than manual analysis.</p><p><b>CONCLUSION</b>This study provided a convenient, simplified, accurate computer-assisted analysis platform for Delaire cephalometric analysis which facilitated its clinical application.</p>

Time varied stress effects on the proliferation of myoblast in rats / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effects of time varied stress on the proliferation of myoblast in rats and provide the basic experimental data for the remodeling of tissue in functional orthopaedics.</p><p><b>METHODS</b>Based on the pulsatile mechanical system founded, this study loaded different strain (2.5, 5.0, 10.0 kPa) to the myoblast of lateral pterygoid muscle. The proliferation of myoblast was detected by 3H-TDR.</p><p><b>RESULTS</b>After 6 hours under time varied strain, the significant proliferation of myoblast (P < 0.05) was observed, and the 5.0 kPa group expressed the best proliferation. After 12 hours under time varied strain, all groups expressed a better proliferation. Meanwhile, the lower frequency (0.40 Hz) had the bigger effect on the proliferation more than in the higher frequency (1.25 Hz) under the same time varied strain.</p><p><b>CONCLUSION</b>The frequency of time varied strain had also the important influence on the proliferation, the lower frequency (0.40 Hz) had the bigger effect on the proliferation more than in the higher frequency (1.25 Hz) under the same time varied strain. In the certain period of time and certain magnitude of time varied strain, the proliferation of myoblasts rised.</p>

Construction of the three-dimensional finite element model of micro -implant -maxilla / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To explore a new method to construct the three-dimensional finite element model of micro-implant-maxilla using Materialise's interactive medical image control system (Mimics).</p><p><b>METHODS</b>The maxilla with all teeth was scanned with Spiral CT and the images were transferred into the Mimics 9.0 software to obtain the three-dimensional images. The Abaqus 6.5 software was used to mesh the three-dimensional model and to establish the finite element model.</p><p><b>RESULTS</b>A detachable three-dimensional finite element model of micro-implant-maxilla based on Mimics was constructed rapidly, which can be flexibly re-assembled.</p><p><b>CONCLUSION</b>The method of constructing the three-dimensional finite element model of micro-implant-maxilla is available and effective. The geometrical analogy of the model was greatly improved by using the Mimics system.</p>

Time varied stress effects on the shape-alteration of myoblast in rats / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effects of time varied stress on the shape-alteration of myoblast in rats and to provide a theoretic base to determine the mechanics of myoblast in orthodontic therapy.</p><p><b>METHODS</b>Based on the pulsatile mechanical system our group founded, this study loaded different strain (2.5 kPa, 5.0 kPa and 10.0 kPa) to the myoblast of lateral pterygoid muscle. The alterations in shape under time varied stress of 6 h and 12 h were assessed by phase-contrast microscopy, scanning electron microscope.</p><p><b>RESULTS</b>The orientation of myoblast seemed no obvious orderliness before loading. But after loading the lower time varied strain (2.5 kPa, 5.0 kPa), they were changed their orientation to paralel with the direction of strain along with the membrane. Meanwhile, there had one trend to set the shape of myoblast more upright along with the membrane after loading the higher time varied stress (10.0 kPa).</p><p><b>CONCLUSION</b>It was proved that the different time varied stress in vitro expressed the different influence on the remolding of myoblast.</p>