Effects of different tooth preparations on three-dimensional adaption of crowns based on the reverse engineering / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effects of different tooth preparations on three-dimensional adaption of computer aided design and computer aided manufacturing (CAD/CAM) crowns based on the reverse engineering.</p><p><b>METHODS</b>The tooth preparation model of the left maxillary first molar was scanned to build five different tooth preparations using the NX Imageware 13.2 software. The resin cores (n=8) were designed with the exocad software. The scanning data of the inner surface of each resin core were used to analyze the three-dimensional adaption with the Geomagic Qualify 12 software.</p><p><b>RESULTS</b>According to the color-coded deviation images, the deviation of the heavy chamfer shoulder was the smallest and the most uniform, whereas the other groups with sharp lines showed large deviation. After statistical analysis, the total deviation of the heavy chamfer shoulder, 135° shoulder, feather shoulder, 90° shoulder with lipped margins, and sharp marginal ridges preparation were (16.88±2.83), (26.88±3.61), (53.56±4.30), (51.38±4.46), and (47.19±4.62) μm. A statistical significance was observed between the heavy chamfer and 135° shoulders (P<0.05). The other groups fitted poorly, without statistical significance between each group (P>0.05).</p><p><b>CONCLUSION</b>Three-dimensional analysis using a computer is a preferable method to study the three-dimensional adaption of crowns. The heavy chamfer shoulder and round line preparation are clinically recommended. However, feather shoulder, 90° shoulder with lipped margins, and sharp marginal ridge preparation should be avoided.</p>

Contrast study on the clinical effects of electrosurgical retraction and secondary gingival retraction / 重庆医科大学学报

Objective:To observe and compare the clinical effects of electrosurgical retraction and secondary gingival retraction in fixed prosthodontics.Methods:68 teeth of 36 patients undergoing crown and bridge restoration were randomly distributed into 2 groups.Secondary gingival retraction and electrosurgical retraction were adopted to perform gingival retraction,take impression in sequence and make master cast respectively.Then,the time of gingival retraction and shoulder of preformed teeth,gingival condition and master cast were evaluated after gingival retraction.Results:25 of 33 teeth performed with secondary gingival retraction reached satisfactory level,while 8 teeth were unsatisfactory,with the satisfactory rate of 75.8%.28 of 35 teeth performed with electrosurgical retraction were satisfactory,but 7 teeth were not satisfactory,with the satisfactory rate of 80.0%.Time of gingival retraction by this two methods showed significant statistical difference,while the effects have no statistical difference.Conclusion:Electrosurgical retraction is a relatively good way of gingival retraction and worthy of clinical application because of easy and simple handling,easy exposure of clear dividing line between soft and hard tissue,satisfactory effects of gingival retraction,and quick recovery after surgery.