人工牙解剖形态三维坐标系的建立

目的 探讨建立人工牙解剖形态三维直角坐标系及测量人工牙外部形态的方法。方法 在人工牙三维数字化数据的基础上，利用逆向工程软件平台，根据人工牙牙长轴、近远中向、颊舌向及[牙合]平面等专业术语，定义人工牙三维直角坐标系，并对人工牙的外部形态（如牙冠颊舌径、近远中径，牙尖高度、斜度等）进行测量。结果 定义了28个人工牙三维直角坐标系，并在相应坐标系下得到部分人工牙外部形态的数值。结论 可用数学语言定义人工牙解剖形态三维坐标系，其是全口义齿计算机辅助设计（CAD）必要的基础工作。     

应用CEREC3 CAD/CAM对上颌隐裂磨牙牙尖斜度的研究

目的：通过隐裂磨牙牙尖斜度的测量,从牙体解剖结构上探讨磨牙隐裂的病因。方法：选取隐裂组、对照组磨牙模型,应用CEREC3 CAD/CAM测量出各自的牙尖高度、牙尖斜嵴的长度及牙尖之间的距离,利用三角函数计算出牙尖斜度及近中颊舌斜面夹角、远中颊舌斜面夹角。结果：在近中颊尖斜度、近中舌尖斜度、远中颊尖斜度、远中舌尖斜度方面隐裂组比对照组大;在近中颊舌斜面夹角、远中颊舌斜面夹角大小方面隐裂组比对照组小,经成组t检验,有显著差异（P〈0.05）。结论：牙体解剖学因素与牙隐裂发病关系密切,牙尖斜度的大小是磨牙隐裂重要病因之一,牙尖斜度越大,牙尖斜面夹角越小,隐裂发生的可能性越大。     

口腔修复工艺学问答(六)

95、何谓牙尖斜度、牙尖工作斜面斜度和侧向牙尖斜度? (1)后牙牙尖顶至牙尖底的垂线距离为牙尖高度。后牙颊尖的近远中斜面与牙尖底相交的角度叫牙尖斜度(也叫绝对牙尖斜度),是人造牙所固有的。牙尖高度大则牙尖斜度也大,二者可以换用。 (2)牙尖斜面与水平面相交的角度,叫牙尖工作斜面斜度(也叫相对牙尖斜度),它是随排牙时牙     

下颌第一恒磨牙咬合应力分析

目的：分析在不同工况下下颌第一磨牙的应力分布变化,以期从学角度探讨咬合异常与牙裂综合征的关系。方法：选取一颗青年下颌第一恒磨牙数字化,应用ANSYS Workbench对其进行模拟加载,观察不同作用力大小、作用部位及作用方向下应力分布情况,分析比较不同工况下应力集中的差异。结果：加载部位的影响：当加载作用点处于近中颊尖顶及颊斜面时,牙本质内牙髓顶角部无应力集中;随着加载点逐渐由近中颊尖颊斜面移向中央窝方向,牙颈部应力集中区由近中颊颈部经由近中颈部转移至舌侧颈部,当加载点趋近于中央窝时,则在近、远中颊髓角和近、远中舌髓角以及近、远中颈部出现较为广泛的应力分布区;加载方向的影响：在颊尖顶不同方向加载时,应力集中主要出现在牙尖局部及牙颈部,而且加载方向与颈部应力集中变化方向一致。舌侧方向加载时髓室顶还出现小的应力集中点,总体表现为加载方向与牙体应力分布变化一致;加载强度的影响：加载强度增大时未见牙髓顶角有应力集中的现象。结论：下颌第一磨牙近颊尖局部加载方向和加载部位对其牙颈部和牙本质髓角处应力集中具有明显的影响,而加载大小影响不明显。     

前伸平衡的相关因素及各因素间的相互关系

目的：探讨前伸He平衡的相关因素间的相互关系，方法：从前伸He平衡的基本要求及前伸He运动过程中，下颌后牙颊尖的运动轨迹，提出牙尖运动斜度这一新的概念，并运用数学轨迹及坐标轴转换原理推导出牙尖运动斜度的计算公式。结果：牙尖运动斜度等于牙尖工作斜面斜度是获得前伸He平衡的首要条件。牙尖运动斜度与髁道斜度、切道斜度和牙坐标值成正比例关系，牙尖工作斜面斜度与牙尖斜度和牙长轴倾斜度成正比例关系。结论：牙尖运动斜度是前伸He平衡中最基本、最重要的因素。     

下颌第三磨牙的解剖形态观察

目的：探讨下颌第三磨牙的解剖外形及其根管口的形态特点,为牙体牙髓病的临床治疗提供理论依据.方法：收集临床拔除的下颌第三磨牙159颗,观察牙尖和牙根数目,测量牙体长度、牙冠最大近远中径和最大颊舌径;拍摄颊舌向和近远中向X线初始片;开髓、拔髓、疏通根管,体视显微镜测量各根管口之间的距离.结果：外形上,下颌第三磨牙根长大于冠长,近远中径大于颊舌径.单根居多,占54.09%,其次是两根,占40.51%.下颌第三磨牙的根管数目1～4,以两根管（55.35%）居多.S型根管14例,C型根管36例（22.80%）,其中Ⅰ型50.0%,Ⅱ型36.1%,Ⅲ型13.9%.多根管牙的各根管口之间的距离最小0.35 mm,最大5.00mm;均值2.13～3.95.结论：下颌第三磨牙根管系统较为复杂,可以出现C型、S型及弯曲根管.     

银汞粘结对牙尖无基釉抗折的影响—体外实验

目的　确定Scotch -bondMP粘结剂对增加银汞充填后牙尖无基釉抗折力的作用。方法　取健康新鲜离体、牙体的近远中径及颊舌径一致、牙尖高度相等的双尖牙 2 0颗。磨除近远中邻面 ,使之近远中径为 4mm ,在颊牙尖釉质层下制备 4mm× 4mm× 3mm的洞型并随机分成两组。实验组在洞璧上涂一层粘结剂 ,自然固化 6 0秒后填入调拌好的银汞合金 ,对照组仅填入银汞合金。 37℃生理盐水中保存 1周 ,在Instron测试机上测定使牙尖折裂的力。结果　实验组和对照组的力值分别为 775 .7± 5 5 1.7和 5 89.7± 30 2 .0 (牛顿 ) ,但统计学检验无显著性差异。结论　Scotch bondMP粘结剂增加余留牙体抗折的力量是有限的     

下颌第一磨牙全瓷冠强度可靠性的三维有限元分析

目的 对随机载荷作用下全瓷冠强度的可靠性进行三维有限元分析,探讨不同加载模式对全瓷冠强度可靠性的影响.方法 建立用于下颌第一磨牙全瓷冠可靠性分析的三维有限元模型,通过概率统计方法 处理获得3～300 N区间内的随机载荷,确定3种加载模式:异常(牙合)接触加载:随机载荷分别单独加载于颊尖尖部、颊尖舌斜面和中央窝,加载面积均为0.4 mm~2;咀嚼骀接触加载:随机载荷加载位置同异常(牙合)接触加载,加载面积为1.5 mm~2;广泛(牙合)接触加载:随机载荷广泛加载于牙尖交错位时的(牙合)接触面,加载面积为12.6 mm~2.根据可靠度计算公式计算全瓷冠强度的可靠度.结果异常(牙合)接触加载时,全瓷冠颊尖尖部、颊尖舌斜面、中央窝强度的可靠度分别为97%、99%、100%;咀嚼(牙合)接触加载时,全瓷冠颊尖尖部、颊尖舌斜面、中央窝强度的可靠度分别为99%、100%、100%;广泛(牙合)接触加载时,全瓷冠骀面强度的可靠度为100%.结论 随机载荷作用下,早接触、过锐牙尖及咀嚼过硬食物造成的局部小面积集中载荷可显著降低全瓷冠强度的可靠度.     

用于全口义齿的人工牙三维坐标系的建立

目的建立用于全口义齿人工牙的三维坐标系并测量其相应参数值。方法根据人工牙特征点来定义一个长方体,从而建立其人工牙坐标系,并采用三坐标测量仪进行特征点参数的测量。结果定义了28颗人工牙的坐标系,并得到相应参数在其坐标系下的测量值。结论用数学语言来定义人工牙的坐标系,是全口义齿计算机辅助设计的必要基础工作。     

下颌磨牙多尖变异牙一例

临床资料 :患者 ,男 ,38岁。在四川大学华西口腔医院关节科检查时发现 ,6 6舌侧 3牙尖变异。检查 :下颌共 1 5颗恒牙 ,牙列较整齐 ,无龋齿 ,牙周组织健康 ,牙齿钙化良好 ,面磨耗较大。6 6面可见 6个牙尖 ,颊侧 3牙尖短而圆 :从近中颊尖到远中颊尖、远中尖依次变小 ;舌侧 3牙尖长而锐 :近中舌尖 ,中舌尖 ,远中舌尖。有 2条舌沟从 3个舌尖之间通过 ,中舌尖舌轴嵴明显 ,其余舌轴嵴不明显。远中舌尖最大 ,近中舌尖次之 ,中舌尖最小。面沟嵴明显。在患者的 77舌侧也有变异 ,明显可见 3个牙尖 ,　8面呈多尖型。Ｘ线片显示牙根及牙槽骨发育…     

Occlusal schemes of complete dentures--a review of the literature

Occlusal scheme is defined as the form and the arrangement of the occlusal contacts in natural and artificial dentition. The choice of an occlusal scheme will determine the pattern of occlusal contacts between opposing teeth during centric relation and functional movement of the mandible. With dentures, the quantity and the intensity of these contacts determine the amount and the direction of the forces that are transmitted through the bases of the denture to the residual ridges. That is why the occlusal scheme is an important factor in the design of complete dentures. Three occlusal schemes are viewed in this review: bilateral balanced occlusion, monplane occlusion, and linear occlusion scheme. Each scheme represents a different concept of occlusion. Comparisons between these schemes are also reviewed and analyzed. The reasoning underlying the bilateral balanced occlusion scheme is that stability of the dentures is attained when bilateral contacts exist throughout all dynamic and static states of the denture during function. Anatomic teeth are used: the upper anterior teeth are set to satisfy aesthetics, and the posterior teeth are arranged in a compensatory curve and a medial curve. This scheme is adequate for well developed residual ridges, with skeletal class I relation. With highly resorbed residual ridges, the vectors of force that are transmitted through anatomic cusps will dislodge the lower denture and thus impair the comfort and efficiency of mastication experienced by the patient. In order to accommodate to the special needs posed by highly resorbed residual ridges and skeletal relations that are not class I, the monoplane scheme of occlusion was designed. This scheme consists of non anatomic (cuspless) teeth, which are set so that the anterior teeth provide the aesthetics, the premolars and the first molars are used for chewing, and the second molars do not occlude (although sometimes they are specifically used to establish bilateral contacts in lateral movements). Linear occlusion scheme occludes cuspless teeth with anatomic teeth that have been modified (bladed teeth) in order to achieve linear occlusal contacts. Linear contacts are the pin-point contacts of the tips of the cusps of the bladed teeth against cuspless teeth that create a plane. The specific design of positioning upper modified teeth on the upper denture and non anatomic teeth on the lower one is called lingualized occlusion. It is characterized by contacts of only the lingual (palatinal, to be more accurate) cusps of the upper teeth with the lower teeth. The lingualized occlusal scheme provides better aesthetics than the monoplane occlusion scheme, and better stability (in the case of resorbed residual ridges) than bilateral occlusion scheme of anatomic teeth. The results of studies that compared different occlusal schemes may well be summarized as inconclusive. However, it does seem that patients preferred anatomic or semi-anatomic (modified) teeth, and that chewing efficiency with anatomic and modified teeth was better than with non anatomic teeth. Similar results were found in studies of occlusal schemes of implant-supported lower dentures opposed by complete upper dentures. Conclusion: There isn't one occlusal scheme that fits all patients in need of complete dentures, in fact, in many cases more than one occlusal scheme might be adequate. Selection of an occlusal scheme for a patient should include correlation of the characteristics of the patient with those of the various occlusal schemes. The characteristics of the patient include: height and width of the residual ridge, aesthetic demands of the patient, skeletal relations (class I/II/III), neuromuscular control, and tendency for para-functional activity. The multiple characteristics of the occlusal schemes were reviewed in this article. Considering all of those factors in relation to a specific patient, the dentist should be able to decide on the most suitable occlusal scheme for the case.     

A criterion for the selection of artificial posterior teeth

Mandibular movement and masticatory performance were evaluated in the edentulous patients with an experimental denture using posterior artificial teeth of different occlusal schemes in order to determine the criterion for the selection of posterior artificial teeth. Lower masticatory performance was observed with non-anatomic posterior teeth than with semi-anatomic or anatomic ones regardless of the condition of residual ridge and inclination of the horizontal condylar guidance. The value of the lateral component of the masticatory cycle was closely related to the inclination of the cusp and the value of masticatory performance. This suggested strongly that the component could be a criteria for the selection of the type of the artificial posterior teeth.     

全口义齿人工牙的选择与排列

选牙与排牙是全口义齿制作的关键步骤之一。前牙选择的要素包括人工牙的形态、大小和颜色。后牙则主要考虑型,一般包括三种类型:解剖式牙、半解剖式牙、非解剖式牙(例如舌向集中型牙)。排列前牙对于恢复患者唇部正常外形以及改善发音都有重要影响,应尽量避免左右牙齿过于对称而引起的"假牙面容"。后牙排列则侧重恢复咬合功能。全口义齿完成选牙和排牙后应进行临床试戴,目的是检查前牙美观是否满意、基托边缘是否合适、咬合是否良好等。     

全口义齿咬合接触的三维测量分析

目的采用三维数字化方法对咬合接触参数进行测量分析。方法应用非接触式激光三维扫描和三维数字化技术,在三维扫描和重建10副全口义齿人工牙面以及正中时咬合状态的基础上,测定咬合接触的数目和部位,并与T-Scan咬合仪的测量结果进行配对t检验。结果⑴咬合接触参数的测量结果显示,咬合接触区域主要集中在磨牙和前磨牙区;⑵应用激光扫描系统测量和T-Scan系统测量的咬合接触部位和数目比较,P>0.05,在统计学上无显著性差异。结论本研究将激光扫描技术引入全口义齿咬合接触研究领域,通过测量全口义齿咬合接触部位和数目,并与T-Scan系统的测量结果进行比较,进一步验证了该方法进行咬合检测的可靠性,为今后咬合接触的研究提供了新的思路。     

Lineal occlusion concepts for complete dentures

A rationale for using lineal occlusal-contact teeth in complete dentures was discussed. The vectors of occlusal force for anatomic, nonanatomic, and lineal occlusal-contact teeth were compared. Four combinations of plastic and porcelain occlusal tooth forms, which can be used or modified for lineal occlusal contact, were described. Rules for positioning of the teeth and methods for occlusal adjustment of each combination were considered.     

Development of an RPD CAD system with finite element stress analysis

Summary  The structural design of removable partial dentures (RPDs) is critical for preventing distortion of the prosthesis, protecting abutment teeth and residual ridges as well as for high masticatory performance. The aim of this study was to clarify the feasibility and utility of a computer-aided designing (CAD) system with finite element analysis (FEA) for molar teeth arrangement in unilateral distal extension base RPDs. The shapes of artificial teeth and residual ridge were measured and converted into point group data. Solid models were created from surface-modelled point group data in a 3D surface CAD format. An occlusal rim was created on the residual ridge mucosa and the occlusal rim - residual ridge mucosa model with FEA function was created. Stress distribution on the residual ridge mucosa was compared by changing the loading point. The artificial teeth were then arranged in locations with the lowest amount of stress. After building an artificial teeth – saddle – residual ridge mucosa model, stress distribution in the residual ridge mucosa was re-evaluated by simulating occlusal force. On the occlusal rim - residual ridge mucosa model, stress was reduced when the loading point was located around the buccal shelf where functional cusps of artificial teeth were charted. It was confirmed that stress distribution in the residual ridge mucosa was equalized on the artificial teeth – saddle – residual ridge mucosa model. This system might be clinically useful tool for designing RPDs if FEA-guided designing of retainers and connectors can be added.     

A mathematical analysis of the role of friction in occlusal trauma

STATEMENT OF PROBLEM: It is recognized that high or misdirected forces can cause occlusal trauma. It is also known that the coefficient of friction between contacting teeth depends on (salivary) lubrication and on the material surfaces in contact. Friction changes the directions and magnitudes of contact forces, but the exact influence of friction on occlusal trauma is unknown. PURPOSE: The purpose of this mathematical study was to ascertain the influence of changed friction (as a result of xerostomia or a restoration) on the forces experienced by contacting teeth and the temporomandibular joint (TMJ). MATERIAL AND METHODS: Equations were derived for the forces on teeth and the TMJ. To assess the effects of friction on these forces, a parametric analysis was performed in which the coefficient of friction between teeth was set to 0.0 (idealized frictionless contact), 0.2 (salivary lubrication), 0.4 (xerostomia), or 1.0 (some artificial saliva lubrication). RESULTS: The computations indicated that a change in friction influences the directions and magnitudes of the forces experienced by teeth and the TMJ. The effect can be subtle or profound depending on the cusp angle and the direction of impending motion. CONCLUSION: Within the limitations of this study, the results suggest that change in friction between teeth, for any reason, should be considered a possible cause of occlusal trauma.     

Selection of occlusal scheme on the basis of pressure distribution on supporting structures under complete dentures

In case of making complete dentures, we have to consider not only denture stability but also the restoration of aesthetics and function such as mastication and speech. However these are contradictory theoretically from the point of view of denture stability, and it is very difficult to satisfy both requirements in the case of a patient who has poor upper and lower alveolar ridges. We investigated the effect of artificial posterior teeth form and occlusal scheme on the distribution of pressure on supporting structures under complete dentures during mastication with upper and lower edentulous simulators. In this report, a guideline for the selection of occlusal scheme for complete dentures, based on our previous investigations, is described. The occlusal scheme remarkably affected the distribution of pressure under simulated complete dentures, as shown by comparing the distribution of pressure using two different occlusal schemes:fully balanced occlusion and lingualized occlusion. However other factors such as posterior teeth form and position affect the distribution of pressure as well, and are related to each other. Therefore, not only occlusal scheme but also posterior artificial teeth form has to be considered, and the form of posterior teeth should be carefully and comprehensively decided when making complete dentures.     

Two-centre evaluation of a resin composite/ self-etching restorative system: three-year findings

PURPOSE: This two-centre study evaluated the clinical performance of Class I and Class II restorations of the giomer material Beautifil, placed using Fluorobond, a self-etching adhesive system, to determine the suitability of the test system as an alternative for the restoration of posterior teeth. MATERIALS AND METHODS: A total of 108 restorations, comprising 72 Class II and 36 Class I restorations, was placed predominantly in molars (82%). Evaulations using modified USPHS/Ryge criteria were conducted at baseline and thereafter at 6 months and 1, 2, and 3 years. Die stone replicas of the restored teeth were examined retrospectively. RESULTS: A total of 5 restorations was found to fail during the study-- 3 in the first year and 2 during the third year of the study. Occlusal marginal adaptation was less than ideal at baseline in 11% of cases, primarily as a consequence of overcontouring, as observed in the die stone replicas. The combined percentage Alpha ratings at 3 years were: colour match, 98%; marginal adaptation (occlusal), 78%; marginal adaptation (proximal), 97%; anatomic form (occlusal), 99%; anatomic form (proximal), 95%; surface roughness (occlusal), 100%; surface roughness (proximal), 100%; marginal staining (occlusal), 90%; marginal staining (proximal) 81%; interfacial staining (occlusal), 99%; interfacial staining (proximal), 100%; contacts (occlusal), 95%; contacts (proximal), 93%; sensitivity, 100%; secondary caries, 100%; lustre of restoration, 100%. CONCLUSION: It is concluded that the 3-year performance of Fluorobond-bonded Beautifil for Class I and II restorations demonstrated some marginal changes, but most of the direct evaluation ratings were > 90% Alpha, with the performance observed being similar in the two centres.