Assessment of undergraduate students’ tooth preparation for full veneer cast restorations

Purpose: To evaluate tooth preparation for full veneer cast restorations performed by final year dental students in Sudan. Materials and Methods: 117 stone dies from two different dental institutions were collected and evaluated. Polyvinylsilioxane impression material was used to produce two impressive replicas of which one was sectioned in faciolingual plane and the other in mesiodistal plane. Occlusal clearance was measured using a digital caliper. Amount of axial preparation was also measured. Impression silhouettes that were produced using an overhead projector were used to measure convergence angle. Working casts were examined for smoothness and evenness of the preparations, existence or absence of additional features of retention and the finishing line were evaluated for its position and continuity. All obtained data were statistically analyzed by using T-test, ANO-VA, and Pearson Chi square tests. P-values ≤ 0.05 were considered as statistically significant. Results: Average taper of the examined preparations was 39.98?, with 44.1? in the faciolingual, and 35.8? in the mesiodistal dimensions. Preparations for full coverage restorations were over prepared. 38.5% of the total number of preparations were found to have finishing lines in the sub and supra gingival positions. 19.66% were unable to maintain continuity of the finishing line all around the preparation. All preparations were generally smooth with no sharp angles, and 1.7% of the preparations had additional retentive features. Conclusion: Within the limitations of this study, it could be concluded that the convergence angle and finishing line preparations were less than adequate in a sizeable proportion of the preparations examined.

Assessment of the Quality of Composite Resin Restorations

Purpose: To evaluate the quality of the composite restorations. Material and Methods: A total of 246 composite restorations in 125 patients attending the Conservative Dentistry Clinics at the Faculty of Dentistry, University of Khartoum were examined. Both anterior and posterior composite restorations were included. California Dental Association Quality Evaluation System was used for the evaluation. Results: Fifty two percent of all restorations were found to be satisfactory, while the remaining 48% were not satisfactory. With regard to surface and colour criteria, colour mismatch within the range (34.8%) and slight surface roughness (26.6%) were the most common defects. The most frequent defects of the anatomical form were restoration overhang (26.8%). The majority of the restorations above 4 years old were of unacceptable anatomical form (66.7%), and their marginal integrity was less acceptable than more recent restorations (46.7%). Conclusions: Forty eight percent of the examined composite restorations needed to be replaced, and the unacceptable anatomic form was the main cause of failure of composite restorations.

Bond Strength of Orthodontic Bracket Cement Using a Bleaching Light for Curing

Aim: To investigate the bond strengths achieved by using a Bleaching Curing Light (BCL) to polymerize orthodontic bonding cement. Material and Methods: 160 anterior bovine teeth were used to form 20 average sized human dental arches, and distributed into 2 groups according to which light curing method used: Group 1: BCL for 40 seconds, or Group 2: LED for 10 seconds. After storage in a controlled environment, Shear Bond Strength (SBS) and Adhesive Remnant Index (ARI) were determined. Results: Group 1 showed significantly lower SBS in the most posterior (first molar) position of the dental arch, (Group 1: 0.7 ± 1.0 MPa, Group 2: 2.9 ± 1.7 MPa, p Conclusion: Simultaneous full-arch curing of orthodontic bracket cement using a BCL is clinically acceptable in all but the most posterior locations along the dental arch.

The Effect of the Light Intensity and Light Distances of LED and QTH Curing Devices on the Hardness of Two Light-Cured Nano-Resin Composites

Background: Effective polymerization of the composite resin is essential to obtain long term clinical success and has a great importance obtaining improved mechanical properties. The purpose of this study was to measure the effect of the light intensity of LED and QTH curing devices in relation to the light distances, on the hardness (KHN) of two light cure nano-resin composite. Material and Methods: The top and bottom surfaces of the two nanofill composite specimens were evaluated. Two LED and two QTH light curing devices were used at nine different distances. Light intensity was measured with two radiometers placed at these same distances from the curing tip. 360 pvc dies were prepared with circular cavity 3 mm in diameter and 2 mm thick. The tested materials were placed in each cavity. The different light curing distances were standardized by adding pvc spacers dies at different height matching the different distances. Top and bottom surface microhardness were evaluated with a Micro Hardness Tester in knoop hardness numbers (Kg/mm2). Data were statistically analyzed using: Three-way ANOVA, Tukey and Pearsons test. Results: It was revealed that there was a statistically significant difference in microhardness between the composites (p < 0.001), between the nine distances (p < 0.001) and between the four light curing devices (p < 0.001). Increasing the distance of the light source from composite resin, the light intensity and the microhardness values at the top and bottom surface decrease. LED light curing devices produced a greater microhardness results at the bottom surface of the specimens. The Filtek Ultimate nanocomposite (3 m) showed highest microhardness values on the top and bottom surfaces, polymerized with all four curing devices and all nine distances compared to Empress Direct nano composite (Ivoclar vivadent). Clinical significant: Even with high power LED curing light, the distance between the tip of the light source and the restoration surface should be as close as possible. In this study, Filtek Ultimate showed better results (highest microhardness values) than Empress Direct.

种植支持式全瓷和金瓷修复龈色改变的分光光度计比较

目的:应用一种新的小型分光光度计,对上前牙种植支持式全瓷修复与金瓷修复的边缘牙龈的龈色改变进行比较,为临床选择修复材料提供依据。方法:选择口腔种植修复后复查患者18例(男7例,女11例),共计上前牙区种植支持式单冠29例(全瓷修复11例,钛合金基台金瓷修复9例,金合金基台金瓷修复9例)。通过仪器采集图片并输入计算机,应用相关软件测量种植冠颈部边缘牙龈与对照天然牙牙龈的CIELab颜色差异。另由医师对冠缘龈色改变进行临床牙龈变色指数(GDS)评价。采用SPSS 17.0软件包对数据进行统计学分析。结果:分光光度计测量结果显示,上前牙种植支持式全瓷修复组(3.4±1.8)与金瓷修复组(4.9±3.4)引起的龈色改变无统计学差异。其中,全瓷修复与钛基台金瓷修复方式(3.5±2.5)之间的差异和钛基台金瓷修复与金基台金瓷修复方式(6.3±3.8)之间的差异均无显著性,但全瓷与金基台金瓷修复方式之间的差异具有统计学意义(P=0.037)。此外,全瓷组与金瓷组间的主观牙龈变色指数(GDS)无统计学差异,临床牙龈变色指数与分光光度计测得的牙龈变色值之间具有相关性(rs=0.426,P=0.021)。天然中切牙、侧切牙和尖牙在牙龈色彩的明度上无显著差异,但在红绿色轴饱和度和黄蓝色轴饱和度方面,尖牙高于中切牙和侧切牙。结论:全瓷组与金瓷组的龈色改变在分光光度计评价和临床评价上均无显著差异,但高金合金基台联合金瓷冠修复方式引起的种植冠边缘牙龈色差显著大于全瓷修复方式。

上中切牙种植修复中种植体位置对临床冠长和龈乳头丰满度的影响

目的评价上中切牙种植单冠修复中种植体位置对临床冠长和龈乳头丰满度的影响。方法纳入158例因外伤导致上颌中切牙(11或21)缺失后进行种植支持式单冠修复的患者,以对侧天然牙为对照。拍摄患者种植冠技工模型的标准图片和种植冠戴牙后首次复诊的口内片及根尖周片,测得种植体各三维位置参数及龈乳头长度。配对t检验用于比较种植冠与对照天然牙的临床冠长及近中、远中龈乳头丰满度,种植冠近中、远中牙槽嵴高度和植体肩台参考平面上植体与天然牙间的近中、远中水平距离。Pearson相关检验用于分析种植体各位置参数与冠长差异和龈乳头丰满度的相关性。结果种植单冠的临床冠长长于对照天然牙[(10.9±1.1)mm vs.(10.4±0.8)mm,P<0.05],冠长差异为(0.3±0.7)mm。种植冠近中龈乳头和对照天然牙远中龈乳头均较种植冠远中位点更丰满(P<0.000 1)。种植冠近中牙槽嵴高度较远中牙槽嵴高[(2.2±1.4)mm vs.(1.2±1.5)mm,P<0.05]。种植体的唇腭向植入位置与冠长差异呈正相关(r=0.602,P=0.001)。种植体与缺牙区邻牙唇面凸点所在平面的矢状夹角、植体肩台和邻牙颈缘连线间垂直距离与冠长差异均无相关性。种植冠牙槽嵴高度与龈乳头丰满度间呈正相关(r=0.400,P=0.001)。结论种植体植入位点偏唇侧可导致种植冠临床冠长长于对照天然牙。种植体植入唇倾角度较小时可在修复时用常规角度基台加以修正,不会影响临床冠长。通过调整植入位点和深度或可避免牙槽嵴吸收并改善龈乳头丰满度。