下颌第一恒磨牙隧道洞型的应力分析

目的：观察下颌第一恒磨牙邻面龋损时，将牙体制备成隧道洞型，其邻面洞上部的边缘嵴在不同厚度时，对牙体应力及变形的影响。方法：在下颌第一恒磨牙设计咬合面一邻面隧道洞型，在邻面设计椭圆与圆形2种洞形，保留边缘嵴厚度分为1．5、2．0、2．5mm3种。再应用复合树脂充填洞型。利用牙CT机扫描牙体，应用ANSYS9．0软件，采用三维有限元法在计算机上重建制备了隧道洞型并充填完成的牙体模型，对牙体承受垂直力和侧向力后所产生的应力及变形分别进行模拟计算分析。结果：6种洞型中，边缘嵴为2mm及2．5mm厚的椭圆与圆形邻面的隧道洞型应力分布最均匀。边缘嵴受力方向一致。圆形与椭圆形邻面的隧道洞型，牙体的应力与变形相同。结论：临床上制备磨牙的隧道洞型时。边缘嵴应至少保留2mm以保证一定的抗力强度。     

Ⅱ类洞复合树脂充填的洞型设计

复合树脂的物理特性与汞合金不同,充填时需要改变传统的洞型设计。本文讨论了后牙Ⅱ类洞复合树脂充填的洞型设计原则。 (牙合)面洞形状和深度:(牙合)面洞型比汞合金修复洞型浅而窄。复合树脂有较高的抗张强度,挠曲强度,能密封边缘,但耐磨性低,聚合时发生收缩。其导热性能比汞合金低,需要减小洞底绝缘层厚度,不作预防性扩张。(牙合)面不断的磨损是复合树脂后牙充填的缺点,咬合接触点的磨损比非接触区大2.5倍,应该尽量减少(牙合)面尤其是边缘嵴部分的复合树脂修复。聚合时复合树脂体积收缩为1.5～2％,故洞型宜小,以减少边缘裂缝出现。     

上颌前磨牙非龋性颈部缺损修复的有限元研究

目的:探讨充填治疗非龋性颈部缺损时,洞型设计、窝洞深度及充填材料和咬合调整因素的影响。方法:构建成人上颌第一前磨牙三维有限元模型,其颊侧颈部有不同洞型(楔形、矩形和弧形)和窝洞深度(0.5mm、1.0mm和1.5mm),模拟用玻璃离子黏固剂(GIC)、复合树脂和银汞合金充填,计算模型在正常的侧向、垂直向加载及创伤的侧向、垂直向加载时,应力值和应力分布。结果:正常颊侧颈部主要为拉应力,近根尖向出现压应力,应力分布较均匀;创伤时主要也为拉应力但应力集中,且较正常产生更大的应力。2种咬合状态在侧向加载都比垂直向产生更大应力和加重应力集中。不同窝洞深度间应力差异小,但有深度加深、应力变大的正相关性。深度0.5mm、1.0mm的楔形、弧形和矩形洞型差异小。但在1.5mm时,矩形洞型产生的应力远大于楔形(约4倍),楔形洞型应力略大于弧形(0.8～4.1MPa)。相同条件下,银汞合金充填体界面应力值大于GIC和复合树脂(3～9倍),GIC小于复合树脂(0.2～2.4MPa)。结论:窝洞较浅时,洞型不是影响治疗的首要因素,窝洞较深则应避免矩形洞型。     

上颌第一前磨牙不同形态Ⅱ类洞形对应力影响的三维有限元分析

目的：分析上颌第一前磨牙不同形态的Ⅱ类洞形设计对不同材料充填体的应力影响。方法：在上颌第一前磨牙上制备3种不同的Ⅱ类洞形，假设分别由银汞合金和复合树脂充填，采用三维有限元法对承受垂直和侧向力所产生的应力计算分析。结果：在所设计的洞形中，以复合树脂充填，鸠尾设计与狭缝设计最大应力相差较小，为1％左右；以银汞合金充填，特别是垂直受力时，狭缝设计最大拉应力、切应力和压应力分别下降41％、29％和27％。结论：在前磨牙充填中，龋齿仅限于邻面，建议以狭缝设计并采用复合树脂充填修复。     

不同垫底材料对全瓷嵌体修复应力分布影响的三维有限元研究

目的应用三维有限元应力分析法对采用不同垫底材料的上颌前磨牙Ⅱ类洞全瓷嵌体进行应力计算分析,为临床全瓷嵌体修复垫底材料的选择提供理论参考。方法建立垫底厚度为1.0mm的上颌前磨牙Ⅱ类洞嵌体修复三维有限元模型。采用ANSYS10.0有限元分析软件,计算分析应用3种不同弹性模量的垫底材料时,全瓷嵌体修复各个部分的应力分布状况。结果随着垫底材料弹性模量的增高,且越接近牙本质弹性模量时,嵌体、牙釉质和粘结剂层的最大主应力逐渐减小;而牙本质的最大主应力逐渐增高。结论当牙体缺损较小,洞型较浅时,可采用弹性模量较高,并与牙本质弹性模量接近的垫底材料;而当牙体缺损洞型较深,洞底部牙本质较薄弱时,应采用弹性模量较低的垫底材料。     

不同垫底材料对髓腔固位冠抗折性能影响的三维有限元分析

目的:应用三维有限元应力分析法对根管治疗后使用不同垫底材料的上颌前磨牙全瓷髓腔固位冠进行计算分析,为临床髓腔固位冠修复时垫底材料的选择提供理论参考.方法:用Micro-CT扫描数据创建离体上颌第一前磨牙经根管治疗后,以髓腔固位冠修复的三维有限元模型,根据垫底材料分为玻璃离子组(A)、流体树脂组(B)及纳米复合树脂组(C...     

不同洞型设计时基底材料和充填体对牙应力影响的三维有限元分析

目的:分析不同洞型设计时基底材料和充填体对牙应力的影响.方法:建立上颌第一前磨牙(牙合)而洞、邻(牙合)而洞及邻(牙合)邻面洞的三维有限元模型,采用四因素不同水平析因实验设计,在牙尖顶点、牙尖与充填体边缘连线的中点、充填体表面分别垂直加载100N的力,用ANSYS9.0有限元分析软件分析不同工况下(牙合)面、颊侧颈部和远中边缘嵴牙体主应力的大小,采用SPSS13.0软件包对数据进行多变量方差分析.结果:受力部位、窝洞类型、充填体和基底材料种类对牙应力的影响有统计学意义,受力部位影响最大;基底材料仅对(牙合)面应力有影响,牙颈部为高应力区.结论:(牙合)面的受力部位是影响应力分布的最主要因素,充填体和窝洞类型也是影响应力的重要因素.     

后牙区正畸托槽定位高度的研究

目的测量正畸患者后牙段牙齿边缘嵴到牙尖的垂直高度,为后牙托槽的定位提供参考。方法选择采用非拔牙矫治且矫治后符合Andrews正常标准的60例患者为研究对象,男女各30例,平均年龄13.2岁。取矫治后的研究模型,利用激光三维测量仪测量每副模型后牙段牙齿边缘嵴到近中牙尖最高点的垂直距离。数据输入SPSS6.0软件进行统计分析。结果相同牙位不同性别的数据无统计学差异;上下颌左右侧相同牙位边缘嵴到牙尖的高度无统计学差异（P>0.05）。上颌第一前磨牙、第二前磨牙和第一磨牙边缘嵴到牙尖的高度分别为（1.70±0.50）、（1.24±0.45）、（0.83±0.40）mm,三者间比较均有统计学差异（P<0.01）;下颌第一前磨牙、第二前磨牙和第一磨牙边缘嵴到牙尖的高度分别为（2.25±0.45）、（1.55±0.45）、（1.18±0.40）mm,三者间比较均有统计学差异（P<0.01）。将本研究得出的数值按最接近0.5 mm倍数的数值进行舍入,得到推荐的托槽垂直定位高度。结论为了获得良好的矫治效果,使矫治后后牙边缘嵴处于同一平面,后牙托槽的垂直定位高度推荐为：若第一磨牙颊面管高度为X mm,则第二前磨牙托槽的垂直高度为（X+0.5）mm,第一前磨牙则为（X+1.0）mm。     

粘接剂和窝沟封闭剂对复合树脂修复体微漏现象的影响

本文目的是研究用牙本质粘接剂和窝沟封闭剂封闭复合树脂修复的Ⅴ类洞边缘对微漏现象的影响。材料和方法选择30只拔除的无龋前磨牙,在颊面的釉牙骨质界处制洞,洞深1.5mm,近远中径4mm,(牙合)龈壁距2mm。酸蚀(牙合)壁30秒钟,用ScotchbondDual Cure(3M Dental Products Div)处理,颈     

上颌前磨牙全瓷嵌体修复三维有限元模型的建立与应力分析

目的建立上颌前磨牙Ⅱ类洞全瓷嵌体修复的计算机三维实体模型和有限元模型,并进行应力分析,以期为临床全瓷嵌体修复提供理论参考。方法利用Micro-CT扫描获得牙体原始数据,建立上颌前磨牙Ⅱ类洞全瓷嵌体修复的三维有限元模型,采用有限元分析软件ANSYS10.0计算分析牙釉质、牙本质、嵌体及粘结剂层的最大主应力。结果建立了包含牙釉质、牙本质、牙髓腔、牙周膜、嵌体及粘结剂层的上颌前磨牙Ⅱ类洞嵌体修复的精细三维有限元模型。牙釉质的应力集中部位在洞型龈壁的位置,最大主应力值为10.52MPa;牙本质的应力集中部位在牙本质近牙髓腔的位置,最大主应力值为3.76 MPa;嵌体的应力集中部位在其与龈壁对应的位置及嵌体底面,最大主应力值为5.82 MPa。结论上颌前磨牙Ⅱ类洞全瓷嵌体修复后,牙釉质的薄弱部位在龈壁;牙本质的薄弱部位在窝洞底部近牙髓腔的位置;嵌体的薄弱部位在其与龈壁对应的位置。     

Fracture resistance of posterior teeth restored with glass ionomer-composite resin systems

This study compared the fracture resistance of posterior teeth restored with one of four composite resin systems or amalgam. Mesio-occlusodistal cavity preparations were placed in 50 maxillary premolars. Dimensions of the preparation were such that remaining tooth structure was weakened. Five groups of 10 specimens each were designated as follows: I, amalgam; II, Ketac-Bond glass-ionomer base; III, Ketac-Silver glass-ionomer base; IV, GC lining cement glass-ionomer base; and V, Tenure dentinal bonding agent. Specimens in groups II through V were restored with P-30 posterior composite resin. Testing was accomplished by applying an occlusal load to the point of failure for each specimen. Results indicated no significant difference among restorative systems in resistance to cuspal fracture. These findings suggest that neither Tenure nor glass-ionomer cement used in conjunction with posterior composite resin strengthen weakened cusps to any greater extent than does amalgam.     

Fracture strength of Class I versus Class II restored premolars tested at the marginal ridge. I. Standard preparations

Two groups of maxillary premolars with Class I cavities were prepared with one marginal ridge thickness to a width of 1.0 mm. One group was restored with amalgam and the other group with composite resin. Two groups of Class II cavities also were prepared and restored with amalgam and composite resin. The teeth in the four treatment groups were subjected to a centric load at the marginal ridge until fracture occurred. A two-factor analysis of variance revealed a statistically significant difference between the class of preparation (Class I preparations were weaker than were Class II preparations) but differences in strength between restorative materials (composite resin versus amalgam) and the interaction effect (class of preparation x restorative materials) were not found to be statistically significant (alpha = .05). A Newman-Keuls sequential range test found no statistically significant differences in strength between groups (alpha = .05). Fracture patterns were observed under scanning electron microscope. Fractures extended into the enamel and into the material in the Class I composite resin, Class I amalgam, and Class II composite resin restorations. Fractures extended only into the material in Class II amalgam restorations.     

Strength of tunnel-restored teeth with different materials and marginal ridge height

ObjectiveThe aim of the study was to investigate the strength of the marginal ridge of tunnel preparations with different marginal ridge heights, using different restorative materials.Materials and methods120 sound premolars were randomly divided into three groups of standardized tunnel preparations with a remaining marginal ridge height of 1.5 mm, 2.5 mm and 3.5 mm, respectively. In each tunnel group, 10 teeth were filled with all four newly developed adhesive materials that had not previously been used in tunnel preparation: Ketac Aplicap, Fuji IX, Fuji II LC and Beautifil Flow F02. The control group comprised 10 sound teeth. All teeth were subjected to incremental dynamic force testing. Remaining marginal ridge height and restoration material were the independent variables. The mean maximum energy (MEI) score was the dependent variable. Data were analyzed, using one- and two-way analysis of variance. Scheffe's test and Student's t-test were used for comparison between groups.ResultsBoth restorative material (P < 0.0001) and remaining marginal ridge height (P < 0.0001) had a statistically significant effect on the mean MEI score of tunnel-prepared teeth. At the 2.5 mm of remaining marginal ridge height, no statistically significant difference in mean MEI score existed between Beautifil Flow F02-filled tunnel-prepared teeth and sound teeth.SignificancePremolars tunnel-restored with Beautifil Flow F02 at 2.5 mm distance from the marginal ridge were as strong as sound teeth.     

Effect of restoration method on fracture resistance of endodontically treated maxillary premolars

PURPOSE: The aim of the present study was to compare the fracture resistance of endodontically treated maxillary premolars with mesio-occlusodistal (MOD) cavities restored using various restorative materials and luting agents. MATERIALS AND METHODS: Eighty extracted human maxillary premolars satisfying certain predetermined criteria were subjected to seven different restoration methods (10 premolars per method). After endodontic treatment, an MOD cavity was prepared in each specimen, and restoration was carried out by one of the following methods: group 1 = control (intact premolars); groups 2 and 3 = restoration using a photo-cure resin composite with and without bonding, respectively; groups 4 and 5 = restoration using a cast-metal inlay with zinc phosphate and adhesive resin cements, respectively; groups 6 and 7 = restoration using a cast-metal onlay with zinc phosphate and adhesive resin cements, respectively; and group 8 = restoration using a hybrid resin onlay. A fracture test was conducted to determine the fracture resistance and fracture mode of each specimen. RESULTS: Fracture resistance was greatest for teeth restored using a cast-metal onlay cemented with adhesive resin cement, but those fractures that did occur were generally unrestorable. Fracture resistance of teeth restored using a cast-metal inlay was also high. Fracture resistance for teeth restored using a resin composite was significantly lower, but the majority of these fractures were restorable. CONCLUSION: Endodontically treated maxillary premolars with MOD cavities could be successfully restored by cast onlay and inlay restorations luted with adhesive resin cement, but their failure mode was often unfavorable.     

Influence of different transitional restorations on the fracture resistance of premolar teeth

Controversy exists over the most favorable material and type of restoration to be used to transitionally restore teeth destined to be crowned. This in vitro study uses fracture resistance testing to compare eight different transitional restorations in maxillary premolars. Ninety sound maxillary premolars were randomly selected and allocated to nine groups, each comprising 10 teeth. One group remained unrestored and was used as the control. Teeth in the remaining groups were prepared to a standard cavity form using: a copy milling process removing the palatal cusp. Restorations were placed using amalgam with dentin pins and cavity varnish; amalgam with an amalgam bonding agent; resin composite with dentin pins and a dentin bonding agent; resin composite with a dentin bonding agent only; resin-modified glass ionomer with dentin pins; resin-modified glass ionomer cement alone and cermet with dentin pins and cermet alone. Each restored tooth was then subjected to axial loading via a bar contacting the buccal and restored palatal cusps until failure of the restored tooth occurred. The mean load-to-fracture values were statistically compared and the modes of failure recorded. It was found that the choice of restorative material and type of restoration had little effect on the fracture resistance of the restored tooth with the exception of those teeth restored with reinforced glass ionomer cement alone, which exhibited a significantly lower resistance to fracture than the other restored teeth. However, the choice of restorative material/technique did influence the mode of failure. Failure in teeth restored with resin-modified glass ionomer cement alone produced the least damage to the remaining tooth tissue when failure occurred. Consequently, this material may offer the most favorable range of properties for the transitional restoration of extensively broken-down maxillary premolar teeth destined to be crowned. Furthermore, the findings of this study fail to support the use of dentin pins in the placement of bonded build-up restorations.     

桩-桩道间隙的匹配对纤维桩修复牙根发育不完全牙的抗折性能的影响

目的:比较3种不同直径的纤维桩插入相同的根管桩道预备间隙对牙根发育不完全牙修复后抗折强度的影响,为临床使用桩核系统修复根尖诱导成形术后的牙提供依据。方法:收集符合纳入标准的因正畸需要拔除的第一、二前磨牙75颗,随机分为5组。其中,实验组3组(3种不同直径的纤维桩+材料充填)、阳性对照组1组(材料桩道充填)、阴性对照组1组(根管充填后不作处理),每组样本牙各15颗,常规进行相同的桩道预备后,用不同直径的桩核系统修复,将修复后的样本牙进行包埋,采用TY-8000型电子万能测试机分别测量牙根颈1/3和中1/3区域的抗折强度,比较桩—桩道间隙的匹配对牙根抗折强度的影响。采用SAS6.0软件包对数据进行统计学处理。结果:实验组1(在桩道预备间隙中插入1.3mm的玻璃纤维桩)的牙根颈部、中部的抗折强度分别为(811±33.85)N、(681±26.64)N;实验组2(在桩道预备间隙中插入1.6mm的玻璃纤维桩)为(901±39.85)N、(729±28.77)N;实验组3(在桩道预备间隙中插入1.9mm的玻璃纤维桩)为(999±75.40)N和(799±21.77)N,阴性对照组分别为(501±38.4)、(472±22.98)N,阳性对照组分别为(704±88.39)、(550±20.14)N,对实验组1、2、3,阳性对照组和阴性对照组进行两两比较,发现在牙根的不同部位,抗折强度均有显著差异(P<0.001),且与阴性对照组有显著差异。其中,插入直径最大的1.9mm玻璃纤维桩的牙根,各部位的抗折能力最强。结论:桩道预备间隙对牙根抗折性能有显著影响,植入直径最大的1.9mm玻璃纤维桩的牙,在牙根颈1/3和中1/3区域都显示出比植入其他2种直径玻璃纤维桩的牙具有更大的抗折强度。     

The effect of marginal ridge thickness on the fracture resistance of endodontically-treated, composite restored maxillary premolars

This study evaluated the effect of varying thicknesses of marginal ridge on the fracture resistance of endodontically-treated maxillary premolars restored with composite. Ninety non-carious maxillary premolars, extracted for orthodontic reasons, were selected for this experimental in vitro study. The teeth were randomly assigned to six groups (n=15). Group 1 received no preparation. In groups 2 through 6, the premolars were root filled and DO preparations were created, while MOD preparations were also created for group 2. The condition of the boxes was: the gingival seat was 1.5 mm above the CEJ and the buccolingual dimensions were 3.5 mm in gingival and 3 mm in occlusal. In groups 3 through 6, the dimensions of the mesial marginal ridge were measured using a digital caliper as follows: 2 mm, 1.5 mm, 1 mm and 0.5 mm, respectively. All samples in groups 2 through 6 were restored with a dentin bonding system (DBS: Single Bond, 3M) and resin composite (Z 250, 3M). Subsequently, premolars from all six groups were subjected to a thermocycling regimen of 500 cycles between 5 degrees C and 55oC water baths. Dwell time was 30 seconds, with a 10-second transfer time between baths. The premolars were submitted to axial compression up to failure at a 45 degrees angle to the palatal cusp in Universal Test Equipment (Tinius Olsen, Ltd, H5K-S model). The mean load necessary to fracture the samples was recorded in newtons (N), and data were subjected to analysis of variance (ANOVA) and LSD post-hoc test. According to these results, the mean loads necessary to fracture the samples in each group were (in N): group 1: 732 +/- 239, group 2:489 +/- 149, group 3: 723 +/- 147, group 4: 696 +/- 118, group 5: 654 +/- 183 and group 6: 506 +/- 192). Differences between group 1 and groups 2 and 6, and also differences between groups 3, 4 and 5 compared with group 2 and 6 were statistically significant (p < 0.05).     

Fracture resistance of Class II approximal slot restorations

STATEMENT OF PROBLEM: Determination of the fracture resistance of various restorative materials in Class II approximal slot restorations has not been studied. PURPOSE: This study evaluated the effects of retention grooves and different restorative materials in Class II approximal slot restorations. To explore the possibilities for further research, the probable effects of preparation size and loading angle were investigated in a limited manner. MATERIAL AND METHODS: Ninety sound, caries-free human maxillary premolars were divided into 9 groups. The cavities were prepared either by hand or in a computer-controlled CNC machine with or without retention grooves. Four were restored with adhesive amalgam, another 4 with composite, and a single group with Compomer resin. The gingival floor depth was 1.5 mm. The specimens were loaded at an angle of 13. 5 degrees to their longitudinal axes by using a computer-controlled material testing machine until failure occurred. For one specific preparation of adhesive amalgam, loading was applied at 0 and 30 degrees to determine the probable effects of the loading angle. For a specific composite, resin application, the effects of the change in gingival floor depth were analyzed by assigning the depth to 2.0 mm. RESULTS: Composite and Compomer resin and composite exhibited better performance than amalgam. The existence of the retention grooves proved to be effective for adhesive amalgam restorations but did not have any advantageous effect in composite and Compomer restoration. CONCLUSION: For improved fracture resistance in small approximal restorations, the use of composite was the appropriate choice. Compomer also gave satisfactory results. Use of amalgam restoration should be accompanied with retention grooves and an adhesive system to improve its performance.     

Pulpal response to a newly developed MMA based resin cement for bonding tooth-colored indirect restorations

PURPOSE: To evaluate the pulpal responses to a newly-developed MMA-based self-etch resin cement, when used as a luting agent for indirect resin composite restoration, and to compare the results with those obtained from a total-etch luting agent, glass-ionomer cement, and amalgam restoration. METHODS: 120 cervical cavities were prepared in monkey teeth and divided into four equal groups according to the restorative materials used: (1) the cavities were restored with resin composite inlays using a self-etch resin cement as a luting agent (M-Bond); (2) the cavities were also restored with resin composite inlays but using a total-etch resin cement as a luting agent (Super-Bond C & B); (3) the cavities were directly restored with glass-ionomer cement (Fuji II); or (4) the cavities were directly restored with amalgam (Dispersalloy). The restored teeth were extracted at 3, 30, or 90 days after restoration, then fixed in 10% neutral buffered formalin. The specimens were prepared using routine histopathological procedures. Five microm-thick sections were stained with hematoxylin and eosin or Brown & Brenn gram stain for bacterial observations. Histological responses in the pulpal tissue and bacterial penetration were observed under a light microscope and evaluated using standard scores. The results were statistically analyzed using the Kruskal-Wallis test (P< 0.05). RESULTS: At all time intervals, no significant differences of pulpal inflammatory responses between M-Bond and Super-Bond C&B were observed (P> 0.05). Both resin cements showed no serious pulpal responses, such as necrosis or abscess formation. In general, both MMA-based resin cements showed similar pulpal responses to those of glass-ionomer cement except for congestion of pulpal blood vessels at 3 days after restoration in which glass-ionomer cement exhibited a lower level than that of the MMA-based resin cements. For the group restored with amalgam, at 3 days after restoration, severe odontoblastic disorders and blood vessel congestions with a large infiltration of inflammatory cells were detected. At 30 and 90 days after restoration, slightly inflammatory irritations were observed irrespective of the materials used. Reparative dentin formation and bacterial penetration were found mostly in the group restored with amalgam.