Comparative Study of the Rock-breaking Mechanism of a Disc Cutter and Wedge Tooth Cutter by Discrete Element Modelling

The operation of a shield tunnel boring machine(TBM)in a high-strength hard rock stratum results in significant cutter damage,adversely affecting the thrust and torque of the cutter head.Therefore,it is very important to carry out the research on the stress characteristics and optimize the cutter parameters of cutters break high-strength hard rock.In this paper,the rock-breaking performance of cutters in an andesite stratum in the tunnel of Qingdao Metro Line No.8 was investigated using the discrete element method and theoretical analysis.The rock-breaking processes of a disc cutter and wedge tooth cutter were simulated by software particle flow code PFC^(3D),and the rock-breaking degree,stress of the cutter,and rock-breaking specific energy were analyzed.The rock damage caused by the cutter in a specific section was divided into three stages:the advanced influence,crushing,and stabilizing stages.The rock-breaking degree and the tangential and normal forces of the wedge tooth cutter are larger than that of the disc cutter under the same conditions.The disc cutter(wedge tooth cutter)has the highest rock-breaking efficiency at a cutter spacing of 100 mm(110 mm)and a penetration depth of 8 mm(10 mm),and the rock-breaking specific energy is 11.48 MJ/m^(3)(12.05 MJ/m^(3)).Therefore,two types of cutters with different penetration depths or cutter spacing should be considered.The number of teeth of wedge tooth cutters can be increased in hard strata to improve the rock-breaking efficiency of the shield.The research results provide a reference for shield cutterhead selection and cutter layout in similar projects.

TOOTH CROWN DEFORMABLE DESIGN BASED ON DIRECT MANIPULATION OF FFD

A flexible and adaptable design method for the tooth crown is presented based on the direct manipulation of free-form deformation （FFD）. The correct shape of the tooth crown can be obtained by adding, modifying, and deleting constraint points or load points based on stretching and compressing operation. Finally, an example is given to illustrate the method to be efficient.

Tooth wear against ceramic crowns in posterior region: a systematic literature review

The objective of this systematic review was to assess tooth wear against ceramic crowns in posterior region in vitro and in vivo. An electronic PubMed search was conducted to identify studies on tooth wear against ceramic crowns in posterior region. The selected studies were analyzed in regard to type of crowns, natural antagonist, measuring protocol and outcome. From a yield of 1 000 titles, 43 articles were selected for full-text analysis; finally, no in vitro and only five in vivo studies met the inclusion criteria. As there is heterogeneity in design, used measuring method, ceramics and analysis-form, a meta-analysis was not possible. Results of these studies are very controversial which makes a scientifically valid comparison impossible. This review indicated that some all-ceramic crowns are as wear friendly as metal-ceramic crowns. Up to now, it has been impossible to associate tooth wear with any specific causal agent. The role of ceramic surface treatment that might be responsible for the changing in rate of tooth wear seems undetermined as yet through clinical trials. The literature reveals that studies on this topic are subject to a substantial amount of bias. Therefore, additional clinical studies, properly designed to diminish bias, are warranted.

Large Chip Production Mechanism under the Extreme Load Cutting Conditions

There has existed a great deal of theory researches in term of chip production and chip breaking characteristics under conventional cutting and high speed cutting conditions,however,there isn＇t sufficient research on chip formation mechanism as well as its influence on cutting state regarding large workpieces under extreme load cutting.This paper presents a model of large saw-tooth chip through applying finite element simulation method,which gives a profound analysis about the characteristics of the extreme load cutting as well as morphology and removal of the large chip.In the meantime,a calculation formula that gives a quantitative description of the saw-tooth level regarding the large chip is established on the basis of cutting experiments on high temperature and high strength steel2.25Cr-lMo-0.25V.The cutting experiments are carried out by using the scanning electron microscope and super depth of field electron microscope to measure and calculate the large chip produced under different cutting parameters,which can verify the validity of the established model.The calculating results show that the large saw-toothed chip is produced under the squeezing action between workpiece and cutting tools.In the meanwhile,the chip develops a hardened layer where contacts the cutting tool and the saw-tooth of the chip tend to form in transverse direction.This research creates the theoretical model for large chip and performs the cutting experiments under the extreme load cutting condition,as well as analyzes the production mechanism of the large chip in the macro and micro conditions.Therefore,the proposed research could provide theoretical guidance and technical support in improving productivity and cutting technology research.

Exploring the practice of common oral diseases among the patients visiting in the selected dental college and hospital in Bangladesh

Background:Having the ability to identify potential health risk factors such as lifestyle,ethnicity,health status,and social determinants associated with oral health status risk,health care providers can take an active role in health screening to discover any need for clinical preventive services,including dental preventive services,and can detect health problems.Methods:A descriptive type of cross-sectional study was conducted to explore the practice of common oral diseases among the patients visiting in the selected dental college and hospital in Bangladesh from October 2019 to December 2019.About 100 patients were interviewed through a semi-structured questionnaire,followed by an oral examination through a checklist and a face-to-face interview.A systematically random sampling technique was employed to select the study population.Results:Among them,the(21-30)year age group shows a maximum 20%,whereas the(71-80)year age group represents the minority with only 2%.Among them,56%were male and 44%were female.Students represent the majority of 26%,whereas others(day laborers)represent only 4%.Decayed teeth remained in 72%of cases,teeth were missing in 31%of cases,and filled teeth were present in 24%of cases.A majority of 71%clean teeth once daily,whereas only 29%clean teeth twice daily.Again,only 30%brush teeth at night and a maximum of 95%brush teeth in the morning.Moreover,a maximum of 68%use toothpaste and brushes,while only 4%use meswak for cleaning their teeth.About 4%of cases with no debris,51%of cases with less than 1/3rd of the tooth with debris,32%of cases with 1/3rd-2/3rd of the tooth with debris,and 13%of cases with more than 2/3rd of the tooth with debris were present.Again,about 30%had no calculus,52%less than 1/3rd of tooth,16%in between 1/3rd and 2/3rd of tooth,and 2%more than 2/3rd of the calculus was present.About 47%of mild,22%of moderate,6%of severe and 25%had no inflammation.Furthermore,for treatment purposes,20.69%was advised for scaling,19.66%for filling,16.90%for root canal treatment,17.59%for extraction,17.24%for prosthodontic treatment,1.03%for orthodontic treatment,2.07%for pulpotomy,2.41%for pulpectomy,and 2.41%for minor surgery.Overall,about 72%of the respondents,mostly the students,are suffering from decayed teeth,which may be due to a lack of frequency of brushing,indicating 95%that it is once daily.In addition,the most alarming situation among them is about 20.69%required scaling,which may be due to improper and inadequate brushing maintenance.Conclusion:to some extent,the above scenario may reflect the negative hallmark for our country’s younger generation in terms of oral health practice.Therefore,the establishment of a preventive oral health policy by our policymakers for the general population,mostly school-going students,on an emergency basis.

Tooth arrangement design of retractable DTH hammer bit used for drilling while casing

Down-the-hole(DTH)hammer with casing while drilling(CWD)is a technology that has been proven to be able to alleviate many of the problems faced by complex formations.However,the drill bit is suffered from rapid wear,low drilling efficiency,and high energy consumption due to the unreasonable tooth arrangement and impact energy selection in drilling process,which affect the application effect of this technology.ABAQUS software was used for numerical simulation of rock breaking behavior under impact load with the single,three,and five teeth arrangement drill bit respectively,to improve the application effect and solve the aforementioned technical problems.Based on the calculated parameters of tooth arrangement,we designed a novel drill bit for hard rocks and provided a theoretical basis for the tooth arrangement of largediameter drill bits.

Effect of iRoot BP Plus Pulpotomy for Immediate Repair in Children with Young Permanent Teeth Crown Fracture

Objective:To explore the clinical effect of iRoot BP Plus pulpotomy for immediate repair in children with young permanent teeth crown fracture.Methods:From September 2017 to October 2018,80 children(80 affected teeth)with young permanent teeth crown fracture who treated in the hospital were selected as the research objects.Random number table method was used to divide them into observation and control groups with each group of forty patients(40 affected teeth).The children in the control group were treated with calcium hydroxide resin,while the observation group were treated with iRoot BP Plus for immediate repair.The surgical success rate was compared between the two groups,and the pulp vitality before and after treatment were compared.Results:At 3 months and 6 months after surgery,the success rate of children in the observation group was higher than that in the control group,and the difference was statistically significant(P<0.05).The percentage of children with negative pulp activity in the observation group was higher than that in the control group,and the difference was statistically significant(P<0.05).Conclusion:Immediate repair with iRoot BP Plus pulpotomy in children with young permanent teeth crown fracture has significant clinical effect.

前牙高透氧化锆全瓷冠修复单颗前牙缺损的美学效果分析

目的:探究高透氧化锆全瓷冠修复单颗前牙缺损的美学效果。方法:选取2018年1月-2020年10月笔者医院收治的单颗前牙缺损患者80例(共80颗患牙),按随机数表法分为观察组(高透氧化锆全瓷冠修复)和对照组(钴铬烤瓷冠修复),每组40例(40颗患牙),比较两组的修复效果,修复前、修复后1个月的牙周指标及龈沟液指标[碱性磷酸酶(Alkaline phosphatase,ALP)、白介素6(Interleukin-6,IL-6)、白介素8(Interleukin-8,IL-8)]水平,对比两组修复后1年的满意度及并发症发生情况。结果:修复后1年,两组颜色对比、边缘着色、解剖外形、边缘密合度、龋齿等修复效果评估观察组均高于对照组(P<0.05)。修复后1个月,两组牙周探诊深度、菌斑指数、出血指数均升高,但观察组低于对照组(均P<0.05);两组龈沟液ALP、IL-6、IL-8水平均降低,且观察组均低于对照组(均P<0.05)。修复后1年,观察组修复总满意度高于对照组(P<0.05);修复后1年期间,两组均未发生牙体腐蚀,疼痛、牙龈炎、根折发生率差异无统计学意义,观察组并发症总发生率低于对照组(P<0.05)。结论:采用高透氧化锆全瓷冠修复单颗前牙缺损的美学效果较好,可减轻牙周组织炎症,值得临床推广应用。

拔除下颌近中水平完全埋伏阻生牙保留颊侧骨板的效果探讨

目的:探讨微创手术拔除下颌近中水平完全埋伏阻生牙时保留颊侧骨板的效果。方法 :选取近中低位水平埋伏阻生牙86颗,随机分为2组,试验组以球钻开窗,暴露牙冠远中面,保留颊侧骨板,使用仰角手机配合加长车针行多次T形截冠,去除牙冠,微创拔除。对照组采用球钻去除远中及颊侧骨板,暴露远中及颊部牙冠,T形截冠,其余操作均一致。观察2组患者术后肿胀程度、开口受限程度以及疼痛视觉模拟量表(VAS)评分,检测C反应蛋白水平以及抗溶血链球水平;1个月后检查邻近第二磨牙牙周探诊深度(probing depth,PD)、出血指数(bleeding index,BI)及临床附着丧失(clinical attachment loss,CAL)水平。采用SPSS 25.0软件包对数据进行统计学分析。结果:试验组术后肿胀程度显著轻于对照组(P<0.05),开口受限与疼痛程度无显著差异(P>0.05)。试验组C反应蛋白水平显著高于对照组(P<0.05),抗溶血链球菌水平2组之间比较无显著差异(P>0.05)。术后1个月,对照组PD和CAL均显著高于试验组(P<0.05),2组BI比较无显著差异(P>0.05)。结论:保留颊侧骨板微创拔除下颌近中水平完全埋伏阻生牙患者术后反应更轻,创口愈合更好。

恒前牙外伤冠折露髓患儿术后预后不良的危险因素分析及模型构建

目的探究断冠再接术联合活髓切断术治疗儿童恒前牙外伤冠折露髓不良预后的危险因素,同时基于筛选出的危险因素构建风险列线图模型,并对构建的模型进行验证。方法选取98例儿童恒前牙外伤冠折露髓患儿为研究对象,均为2020年1月至2023年12月间在本院行断冠在接术联合活髓切断术治疗者。将受试者根据预后结果分为预后良好组和预后不良组,收集两组患儿临床资料,筛选患儿术后预后不良的危险因素。基于危险因素构建预后不良风险列线图模型,并对构建的模型进行验证。结果98例患儿中有18例发生预后不良,预后不良率为18.37%(18/98)。预后不良组牙髓暴露时间>24 h、牙龈炎、露髓孔直径>1 mm、口腔溃疡、牙周炎、牙根发育程度(根尖接近形成)占比高于预后良好组(P<0.05)。牙髓暴露时间>24 h、牙龈炎、牙周炎、牙根发育程度(根尖接近形成)均是影响恒前牙外伤冠折露髓患儿术后预后不良的危险因素(P<0.05)。列线图风险模型预测恒前牙外伤冠折露髓患儿术后预后不良受试者工作特征(ROC)曲线下面积(AUC)、95%CI、灵敏度、特异度分别为0.868、0.633~0.992、95.10%、79.30%(P<0.001)。列线图预测模型C指数为0.842(95%CI:0.789~0.994),预测值与实际预测值均在理想曲线附近,且Hosmer-Lemeshow拟合优度曲线检验χ^(2)=2.743,P=0.671。结论本研究综合牙髓暴露时间、牙龈炎、牙周炎、牙根发育程度等4个危险因素构建的风险列线图模型对患儿预后不良具有较高的预测价值。

氧化锆全冠的临床应用原则及新进展

氧化锆全冠在口腔修复领域得到了广泛的应用。传统氧化锆机械性能佳,但半透性较差,透明氧化锆的出现大大提高了氧化锆的美学性能。但在临床中,应对影响全锆冠美学修复效果的因素进行综合考量,选择最合适的全锆冠修复体,同时临床医师需要根据患者实际情况合理设计牙体预备量以及预备方式。在氧化锆的临床粘接过程中,要对基牙和修复体做好表面处理,选择合适的粘接剂以获得良好的粘接强度和美观性。

网格化磨料射流割缝辅助截齿破岩试验研究

针对煤矿岩巷掘进过程中截齿破岩能力不足、效率低、磨损快等问题,提出了网格化磨料射流割缝辅助截齿破岩方法,并进行了正交化物理模拟试验,研究了工况参数对破岩效果的影响。结果表明:(1)磨料射流对岩石预制割缝,能够显著提高截齿单位时间的破岩体积,且试验中网格尺寸和割缝深度取值越大,破岩效率越高。(2)当射流割缝辅助破岩时,截齿等效应力峰值和均值均显著降低,有效减少截齿磨损。(3)网格化磨料射流辅助截齿破岩参数的优选工况组合为:横向和纵向网格尺寸分别为44、30 mm,喷嘴进给速度为600 mm/min。研究成果为网格化磨料射流辅助机械截齿破岩技术推广应用提供了理论基础与数据支撑。

正畸固定牵引断根结合修复治疗前牙龈下冠折的美学效果观察

目的:分析正畸固定牵引断根结合修复治疗在前牙龈下冠折美学修复中的临床应用效果。方法:选取2020年5月-2023年5月笔者医院收治的76例前牙龈下冠折患者,随机分为对照组(n=38)和观察组(n=38)。两组患者均给予牙髓摘除根管治疗,根管治疗1个月后,对照组切除牙龈后行烤瓷冠修复,观察组给予正畸固定牵引断根结合烤瓷冠修复。随访1年,记录两组患者治疗优良率、前牙咬合功能、牙周健康情况、美学效果、总治疗时长、治疗花费、满意度及并发症发生情况,并进行统计学分析。结果:观察组治疗优良率为97.37%,明显高于对照组的84.21%(P<0.05);观察组前牙咬合功能恢复情况优于对照组,牙尖交错位肌电值及最大紧咬合状态肌电值明显高于对照组(P<0.05);观察组牙周健康情况优于对照组,红色美学指数及白色美学指数明显高于对照组(P<0.05);观察组总治疗时长与治疗花费均明显高于对照组(P<0.05);观察组患者满意度为97.37%,明显高于对照组的73.68%,且观察组各项并发症发生率均明显低于对照组(P<0.05)。结论:正畸固定牵引断根结合前牙美学修复治疗前牙龈下冠折疗效肯定,有助于前牙咬合功能恢复,维持牙周健康及美学效果,降低并发症发生率,提高患者满意度。

镐齿滚刀的齿形及布齿参数优化试验研究

为研究镶齿滚刀上镐齿的齿形参数以及齿间距、排间距对其破岩效率及齿下岩石损伤区的影响规律,选用不同齿形的镐齿对尺寸为300 mm×300 mm×300 mm北山花岗岩进行侵入破岩试验,对镐齿侵入试验过程、侵入力、破岩体积、破岩效率、齿下岩石损伤区特征进行分析。试验结果表明:1)所选试验齿形中直径为18 mm镐齿破岩效率最高;2)齿间距和排间距为35~40 mm时,镐齿侵入破岩效率最高;3)应用荧光裂纹显现法分析齿下岩石裂纹分布特征,获得了不同齿形参数下岩石损伤区范围及裂纹扩展模式、裂纹特征分析结果,与通过侵入力、破岩比能分析得出的破岩效率结论一致。

纤维桩+复合树脂+氧化锆全瓷冠修复根管治疗后后牙楔状缺损的疗效分析

目的:探究纤维桩+复合树脂+氧化锆全瓷冠修复根管治疗后后牙楔状缺损患者的效果及美观满意度。方法:纳入2022年1月-2023年1月在笔者医院就诊的102例后牙楔状缺损患者,根据患者自主选择意愿分为研究组(n=50)和对照组(n=52),对照组行金属桩核+金属烤瓷冠修复,研究组行纤维桩+复合树脂+氧化锆全瓷冠修复。6个月后,对比两组临床疗效,观察两组牙周健康情况(牙龈指数、菌斑指数、龈沟出血指数),检测牙周炎症[肿瘤坏死因子-α(Tumor necrosis factor-α,TNF-α)、白细胞介素-4(Interleukin-4,IL-4)、白细胞介素-6(Interleukin-6,IL-6)],调查美观满意度[美国公共健康服务标准(United states public health service,USPHS)]和实用度(咀嚼功能、咬合情况、语言功能),比较两组并发症发生情况。结果:治疗后,研究组治疗有效率达92.00%,高于对照组的76.92%(P<0.05);两组牙周健康相关指数及TNF-α、IL-4、IL-6均较治疗前降低,且研究组降低幅度大于对照组(P<0.05);治疗后,研究组牙齿表面形态、色泽协调性、边缘着色满意度均高于对照组(P<0.05),两组咀嚼功能、咬合情况、语言功能均较治疗前提高,但差异无统计学意义(P>0.05);两组并发症发生率比较治疗组低于对照组(P<0.05)。结论:采用纤维桩+复合树脂+氧化锆全瓷冠修复根管治疗后后牙楔状缺损能够减轻炎症反应,提升患者牙周健康,增加美观满意度及实用度,疗效显著,安全性高。

硬岩地质下镶齿滚刀齿形对破岩性能影响研究

为了降低镶齿滚刀的破岩比能耗和刀齿接触面应力,提高镶齿滚刀在硬岩地质下的破岩效率和使用寿命,采用LS-DYNA建立显示动力学仿真模型,并通过实验验证模型的可靠性。仿真分析镶齿滚刀的破岩机理及不同齿形的破岩效率,确定较优的齿形。通过正交试验法,分析齿宽、齿高、齿顶半径和齿数对破岩效率以及接触面应力值的影响,确定齿形参数对破岩性能影响权重。研究结果表明:在118 MPa硬岩地质下,镐齿滚刀的破岩效率最高,齿顶半径为破岩效率的最主要影响因素,权重达到50%,齿数与齿顶高为接触面应力值的主要影响因素,权重分别占31%、36%。齿形最优参数组合是齿宽为11 mm、齿顶高为1 mm、齿顶半径为10 mm、齿数为36个。该研究对于镶齿滚刀的齿形选择及参数优化具有参考价值。

矿用硬岩巷道机械化掘进破岩形式研究现状及展望

硬岩巷道快速掘进是实现煤矿智能高效开采的重要环节,悬臂掘进机、TBM和底切割装备都在尝试解决这一难点,掘进技术和装备的发展直接影响采矿的安全生产和经济效益。首先,总结了悬臂掘进机在硬岩截割工况的适用范围和截齿消耗现状,分析截割破岩形式的现场试验,发现在较高的岩石强度条件下,截齿消耗量较正常磨损翻倍,掘进速度与开采速度的不匹配,严重制约了矿井生产。其次,分析了滚刀破岩形式和装备在矿山领域的应用和新产品现状,得出移动式矿用掘进设备采用滚刀挤压破岩,块状渣土少,粉末多,刀盘推力小,导致破岩能力不足。最后,分析了线性底切割破岩技术和非线性底切割技术的原理和装备研发现状。结果表明:随着振荡频率的提高,切削力显著降低,非线性底切割破岩单位体积消耗能量少,优势明显。但在硬岩条件下的掘进效率、设备稳定性等关键问题有待验证,非线性底切割技术有望突破未来矿山硬岩掘进的技术难题。

聚合瓷高嵌体与全瓷冠在下颌第一磨牙缺损修复中的应用及对咀嚼功能和美学效果的影响

目的:探讨聚合瓷高嵌体与全瓷冠在下颌第一磨牙缺损修复中的应用及对咀嚼功能和美学效果的影响。方法:选取笔者医院2020年1月-2021年12月收治的120例第一磨牙缺损患者作为研究对象,按照随机数字表法分为对照组(60例,采用全瓷冠修复)和观察组(60例,采用聚合瓷高嵌体修复)。观察两组患者的修复效果、牙周健康指标、咀嚼功能、美学效果及不良事件发生情况。结果:治疗后12个月,观察组修复总有效率高于对照组(P<0.05);观察组牙周健康指标评分均低于对照组(P<0.05);观察组咀嚼功能显著高于对照组(P<0.05);观察组患者的表面光滑、边缘密合性、固定良好及颜色匹配评分高于对照组(P<0.05);观察组继发龋、牙冠折裂、牙龈红肿、咬合痛不良事件发生率低于对照组(P<0.05);观察组患者修复成功率及存活率高于对照组(P<0.05)。结论:与全瓷冠治疗比较,应用聚合瓷高嵌体修复下颌第一磨牙缺损能够提高患者远期修复效果,改善牙周健康状况,提升咀嚼功能及美学效果。

358例年轻恒切牙冠折的临床特点及预后分析

目的分析年轻恒切牙外伤冠折的临床特点及其预后,探究不同因素对其预后的影响,为年轻恒切牙外伤冠折的临床诊治提供参考。方法本研究通过四川大学华西口腔医院医学伦理委员会审查批准,研究对象为2011年12月至2021年12月就诊于儿童口腔科的患者,对外伤致前牙冠折且至少随访1年的年轻恒牙进行回顾性分析,其诊断为釉质折断、釉质-牙本质折断及冠折露髓的年轻恒牙,首诊治疗方案为观察、恢复牙体外形、牙髓切断术等;采集患儿的年龄、性别、外伤后就诊时间、外伤牙位及松动度、牙根发育分期、诊断及治疗方式。患牙发生牙髓感染、牙髓坏死等事件定义为临床失败,记录其是否发生临床失败及其发生时间,分析不同类型年轻恒切牙冠折预后的相关因素并对外伤牙进行生存分析。结果358例年轻恒切牙中,诊断为釉质折断50例,釉质-牙本质折断176例,冠折露髓132例。其中冠折临床治疗后总体成功率为73.7%(264/358),釉质折断、釉质-牙本质折断和冠折露髓后发生牙髓感染、牙髓坏死的发生率分别为4%(2/50)、33.3%(58/176)和25.8%(34/132)。釉质-牙本质折断患牙行间接盖髓术+覆盖断面的临床失败率显著高于釉质-牙本质折断患牙行覆盖断面和釉质-牙本质折断患牙行牙髓切断术(χ^(2)=10.077,P=0.004);冠折露髓患牙行直接盖髓术临床失败率显著高于冠折露髓患牙行牙髓切断术(χ^(2)=5.501,P=0.038);釉质折断患牙在观察、调磨锐缘、恢复外形下的临床失败率差异无统计学意义(χ^(2)=0.588,P=0.999)。患者年龄>9岁(HR=2.11,95%CI:1.1~3.9,P=0.017)、外伤后就诊时间>3 d(HR=2.3,95%CI:1~4.8,P=0.028)、外伤冠折患牙伴有松动(HR=1.95,95%CI:1.2~3,P=0.004)、行覆盖断面的釉质-牙本质折断(HR=6.89,95%CI:1.6~29.6,P=0.010)、行间接盖髓+覆盖断面的釉质-牙本质折断(HR=13.8,95%CI:3.2~58.3,P<0.001)、进行直接盖髓术的冠折露髓(HR=46.07,95%CI:8~263.8,P<0.001)是本研究人群中临床失败的危险因素。结论年轻恒切牙釉质折断采用观察、调磨锐缘或恢复外形治疗、冠折露髓患牙采用牙髓切断术后预后较好。对于存在影响其预后危险因素的冠折年轻恒切牙应密切随访。

基于KISSsoft的齿轮崩齿故障仿真分析

针对某变速箱主变速3档从动齿轮在试验过程中产生的崩齿现象,在排除材料及热处理的因素后,采用KISSsoft软件对故障齿轮进行了仿真分析。结果显示,考虑轴具体结构及支承的影响,齿轮接触强度不足,受载不均匀,存在偏接触的现象,这与齿轮的试验故障现象一致。基于以上情况,对轴进行加粗处理,并对齿轮进行齿向鼓形修形,从而提高了齿轮接触强度,使齿向载荷分布较均匀,改善了偏载现象,有利于提高齿轮啮合质量,减小啮合冲击,从而减小振动和噪声。