双列球面滚子轴承力学分析及滚子受载计算方法

以球面滚子轴承为研究对象,运用切片法,综合考虑了滚子 滚道凸度以及轴承内圈倾斜角的影响,建立了滚子并排和滚子错排的球面滚子轴承滚子载荷的计算模型。数值计算了内圈倾斜角、径向游隙、滚子错排角、以及外载荷等参数对球面滚子轴承滚子载荷和轴承内圈径向位移量的影响。计算结果表明,在一定的外载荷作用下,轴承内圈倾斜角度与滚子最大载荷呈线性变化规律;错排滚子的球面滚子轴承最大滚子载荷比并排略小,内圈径向位移量也略小。     

牙科自动去冠器的研制与应用

目的:针对传统牙科去冠器拆除牙冠时存在的不足,研制一种发力恒定且发力大小可调的牙科自动去冠器.方法:该去冠器由壳体、冠钩、传导机构、发力机构、击发机构5个部分组成.利用弹簧蓄力实现冠头在瞬间产生爆发力,破坏冠内黏固剂的黏结力,使全冠松动,继而脱落.结果:该去冠器可安全有效地拆除牙冠,并能解放出一只手来进行基牙和黏膜的保护.结论:该自动去冠器结构简单、操作使用方便,是一种可有效拆除固定修复体的器械,值得临床推广.     

Predicting transmitted irradiance through CAD/CAM resin composite crowns in a simulated clinical model

ObjectiveTo predict the clinically relevant transmitted irradiance that is available for luting when a CAD/CAM restoration is inserted. The influence of irradiance, exposure distance, light curing unit (LCU) angulation and direction of polymerization is analyzed when curing through crowns of different thicknesses.MethodsThree modern CAD/CAM resin-based composites (RBCs) were used to produce 45 crown-shaped specimens. The distance between fissure and crown base was set at 1.0, 1.5 and 2.0 mm (n = 5). Transmitted irradiance, while using a violet-blue LCU, was measured with a photo-spectrometer. 180 exposure conditions per specimen were investigated by variation in LCU curing mode, angulation, exposure distance and direction. Data was analyzed using univariate ANOVA followed by Tukey HSD (α = 0.05) and comparison of 95% confidence intervals.ResultsThe CAD/CAM-RBC’s decadic absorption coefficient ranges from 0.317 mm^?1 to 0.387 mm^?1 and the reflection correcting factor for crowns ranges from 0.305 to 0.337. Transmitted irradiance decreases significantly with increasing exposure distance and decreasing incident irradiance. For tilt angles greater than 10°, transmitted irradiances are significantly reduced (?11% for 20°, ?23% for 30°). Significantly lowest transmitted irradiances were measured for vestibular curing direction (up to ?15%).SignificanceA calculation model can predict the transmitted irradiance through a CAD/CAM restoration in dependence of restoration thickness and radiant emittance. The practitioner can be supported by this model to adapt material choice of dental restoration and adhesive system to the individual situation. Variation in exposure conditions shows negative effect on the transmission of light and should be limited.     

Intentional partial pulpotomy to talon cusp for tooth crown morphology correction in orthodontic treatment

This report describes a case of talon cusp treated by an intentional partial pulpotomy, which made it possible to recontour the tooth crown into the desired shape. The patient was an 11-year-old boy with a large talon cusp on the lingual surface of the right maxillary lateral incisor. He was referred to our clinic for treatment of abnormality cusp because it was expected to impede orthodontic treatment. The talon cusp was amputated using an intentional partial pulpotomy. The procedure resulted in successful recontouring of the tooth crown into the desired morphology and the dental pulp exhibited a vital reaction at three years after the operation.     

临时冠塑形对前牙种植美学的临床观察

目的 在前牙区通过利用临时冠对种植体周围软组织进行塑形,观察最终修复的美学效果及软组织的稳定性。方法 选取本院种植科21例上前牙需要种植病例,牙种植后即刻或延期行临时冠修复,对种植体周围软组织进行塑形,待软组织稳定后,行个性化转移杆取模,制作最终修复体,使用红色美学指数（PES）来评价种植体周围软组织的美学效果。结果 11例患者PES≥12,9例8≤PES≤11,获得较好的美学效果。1例患者前牙区种植体支持固定桥修复,由于牙槽骨水平吸收,牙龈退缩,后期通过牙龈瓷进行美学处理。21例患者最终修复后观察1年,通过PES再次评价,同样获得较好的美学效果。结论 前牙种植术后利用临时冠对软组织进行塑形,能够将软组织调整到较好的美观外形,并且形态较稳定。此方法在前牙区种植修复是必要的,值得在临床中广泛推广。     

Evaluating the accuracy (trueness and precision) of interim crowns manufactured using digital light processing according to post-curing time: An in vitro study

PURPOSEThis study aimed to compare the accuracy (trueness and precision) of interim crowns fabricated using DLP (digital light processing) according to post-curing time.MATERIALS AND METHODSA virtual stone study die of the upper right first molar was created using a dental laboratory scanner. After designing interim crowns on the virtual study die and saving them as Standard Triangulated Language files, 30 interim crowns were fabricated using a DLP-type 3D printer. Additively manufactured interim crowns were post-cured using three different time conditions-10-minute post-curing interim crown (10-MPCI), 20-minute post-curing interim crown (20-MPCI), and 30-minute post-curing interim crown (30-MPCI) (n = 10 per group). The scan data of the external and intaglio surfaces were overlapped with reference crown data, and trueness was measured using the best-fit alignment method. In the external and intaglio surface groups (n = 45 per group), precision was measured using a combination formula exclusive to scan data (₁₀C₂). Significant differences in accuracy (trueness and precision) data were analyzed using the Kruskal-Wallis H test, and post hoc analysis was performed using the Mann-Whitney U test with Bonferroni correction (α=.05).RESULTSIn the 10-MPCI, 20-MPCI, and 30-MPCI groups, there was a statistically significant difference in the accuracy of the external and intaglio surfaces (P <.05). On the external and intaglio surfaces, the root mean square (RMS) values of trueness and precision were the lowest in the 10-MPCI group.CONCLUSIONInterim crowns with 10-minute post-curing showed high accuracy.     

不同全瓷材料和厚度的种植牙冠应力分布有限元分析

目的通过有限元方法比较不同全瓷材料和厚度在种植牙冠修复的应力分布情况,为临床冠部修复材料的选择和设计提供参考。方法建立下颌第一磨牙种植牙冠修复有限元模型,并进行6种冠厚度和4种不同冠修复材料,即树脂基陶瓷(Lava Ultimate和Vita Enamic)、二硅酸锂玻璃陶瓷(IPS e.max CAD)和氧化锆陶瓷(Cercon)进行组合。在下颌第一磨牙面加载600 N,使用有限元软件ANSYS 10.0分析应力分布。结果冠部应力分析显示,4 mm?Cercon组156.05 MPa最高,1 mm?Lava Ultimate组18.85 MPa最低。树脂水门汀应力分析显示,4 mm?Lava Ultimate组62.52 MPa最高,1 mm?IPS e.max CAD组16.74 MPa最低。使用成品基台时,Lava Ultimate组在冠修复体、树脂水门汀中的应力集中较相同冠厚度的个性化基台高。结论随着冠厚度增加,冠修复体和树脂水门汀中的最大主应力集中呈现上升趋势;树脂基陶瓷使用个性化基台更有利于减少应力集中。     

Biodentine Pulpotomies on Permanent Traumatized Teeth with Complicated Crown Fractures

IntroductionThe aim of this multicentric prospective study was to evaluate the clinical and radiographic outcomes of Biodentine (BD) pulpotomies on permanent teeth with complicated crown fractures.MethodsThis study was carried out in 2 hospital-based dental departments in Quebec, Canada. Children seeking emergency care after trauma to anterior permanent teeth were invited to participate in this study. The treatment outcome was assessed clinically and radiographically at 1 week and 1, 3, 6, 12, 18, and 24 months after treatment.ResultsForty-five patients between the ages of 8 and 16 years (mean, 10.8 ± 2.4) were included in this study. Fifty-one teeth were treated with a BD pulpotomy. The study showed a survival rate of 100% and a success rate of 91%. Four failures were noted at 1-, 6-, and 15-month follow-up, and the teeth were subsequently treated with either conventional root canal therapy or regenerative endodontic procedure. Dental sensitivity to cold reported by patients reduced over time, and more teeth responded normally to pulp vitality tests during the course of this study. Slight discoloration was noted on 8 teeth (17%). Radiographic outcomes showed dentinal bridge formation in 91% of cases, and all immature teeth showed continued root formation.ConclusionsBD is a suitable material for pulpotomies on anterior permanent teeth with complicated crown fractures. It may be a good alternative to mineral trioxide aggregate pulpotomies because it does not cause significant discoloration, and it allows root maturation.     

Digital Workflow for Retrofitting a Surveyed Crown Using a Removable Partial Denture as an Antagonist

Digital workflow expedites the procedure of retrofitting a surveyed crown against an existing removable partial denture (RPD). This article describes a simple and straightforward technique of digital workflow where an existing RPD is scanned as an antagonist to design the rest seat, guide plane, and height of contour of a surveyed crown.