Variation in caries and treatment experience in 35-44-year-old Lithuanians

Data summarising caries levels differ between countries and often conceal large variations. These differences may reflect variations at individual, group, social and other levels. Caries and treatment experience differences are found to be significantly related to a variety of clinical and non-clinical factors. Variation in caries within Lithuanian children has been reported and related to background-, behavior-, dental care- and other factors. Variation in general or related to any factors in adult Lithuanian population has not been studied. The aim of the present study was to estimate variation in caries and treatment experience and relate them to biological-, psychosocial-, health-related, behavioral- and dental care related aspects. The existing knowledge from other oral health studies was used to select the factors found of importance in relation to variations in caries scores. The study consisted of clinical and self-reported data collected from a stratified random sample of 382 individuals (attendance rate 50%). Two statistical approaches, a bivariate and a multivariate, were applied. The two dependent variables DMFT and DS were tested with a set of independent variables. The bivariate analysis revealed significant associations for approximately one half of all variables studied. For multivariate testing, a backward linear multiple regression was used. Forty-one percent of the variation in DS was explained and 48% in DMFT scores. Differences in scores were related to various factors in the two analyses. The strength and significance of a few relationships differed in both of the analyses. The multivariate testing revealed some strong and significant associations with independent variables which were found to be weak and non-significant (P>0.05) when tested bivariately and vice versa. Less than half of the variation could be explained in dental caries scores in 35-44-year-olds and not only dental care related factors were important. In both of the analyses, the varying degrees of strength (significance levels) give rise to a hypothesis that this incomplete explanation of the variation can be due to interrelated effects of different estimates.     

二单位式与四单位式种植牙周骨界面应力分布规律差异的三维有限元分析

为了探讨人工种植牙的数目、上部结构对种植牙周骨界面应力分布的影响，本实验应用三维有限元分析方法，对二单位和四单位式杆式覆盖种植义齿种植牙周骨界面的应力分布规律进行了探讨。结果表明：最大压应力、最大拉应力二单位式与四单位式均位于颈周密质骨，二单位式大于四单位式，两者有显著差异性，（Ｐ＜０．００１）。四单位式最大拉、压应力，远中种植牙要大于近中种植牙。最大位移运动二单位式小于四单位式，四单位式近中种植牙大于远中种植牙。二单位式与四单位式位、压应力主要集中于颈部，其它部位与颈部相比有非常显著的差异性，（Ｐ＜０．０００１）。结论：种植牙数目的增加，可以减小种植牙周颈部密质骨内的最大应力值。四单位式种植义齿颈周骨内应力要小于二单位式种植牙，从这点上看，四单位式种植义齿要优于二单位式种植义齿。多个种植牙种植时，杆的连接，改变了种植牙周骨内的应力分布规律，其应力主要由种植牙颈周密质骨来承担     

氯化镧对人牙釉质人工龋的影响──扫描电镜、电子探针分析

借助体外人工龋方法从形态和内部结构变化上探讨了氯化镧（Ｌａ３＋）对人牙釉质龋的影响。磨片光镜下显示Ｌａ３＋预处理阻抑龋病发展的作用不如氟化钠（Ｆ－），但Ｌａ３＋与Ｆ－先后预处理能明显减轻龋损程度。扫描电镜观察发现Ｌａ３＋及Ｆ－预处理均能在牙面形成覆盖物，但以Ｌａ３＋与Ｆ－先后预处理产生的覆盖物较致密且与牙面结合较紧密。电子探针分析显示Ｌａ３＋处理后釉质表层内钙（Ｃａ２＋）含量明显减少，而Ｌａ３＋显著增加，表明Ｌａ３＋能与Ｃａ２＋发生离子交换反应而进入釉质。这种牙面覆盖物的形成及Ｌａ３＋－Ｃａ２＋交换反应可能是Ｌａ３＋预处理能防龋的关键之一。     

Clinical and quantitative marginal analysis of feldspathic ceramic inlays at 4 years

The aim of this clinical study was to evaluate feldspathic ceramic inlays both by clinical criteria and quantitative margin analysis in continuation of an earlier, identically conducted 2-year study. Fifty feldspathic ceramic inlays were adhesively luted in Class II preparations with all margins located in enamel. The inlays were evaluated clinically according to modified USPHS criteria after 3 and 4 years. Quantitative margin analysis was performed with a scanning electron microscope (SEM). Clinically, the inlays showed no recurrent caries and no changes in colour, but superficial marginal discolouration (6%) was apparent after 4 years. Margins were perceptible clinically in 64% of the cases after 4 years. Quantitative margin analysis showed significantly more marginal gaps at the composite/ceramic interface than at the enamel/composite interface. There was neither a significant decrease in perfect margins nor a significant increase in marginal gaps and marginal imperfections at both interfaces between the third and fourth year. Clinically, the inlays performed very well up to 4 years. Clinical evaluation using an explorer only detected substance loss in the cementation gap. The SEM evaluation showed significantly higher changes in marginal qualities during the first 2-year interval of clinical service compared to the second 2-year interval following an exponential mathematical regularity. Quantitative margin analysis should be included in clinical long-term trials to detect early marginal deficiencies at the luting interfaces. Received: 1 September 1997 / Accepted: 31 October 1997     

牙尖覆盖厚度对全瓷高嵌体修复前磨牙应力分布影响的三维有限元分析

目的 应用三维有限元法探讨牙尖覆盖厚度对全瓷高嵌体修复前磨牙应力分布的影响,以期为临床全瓷高嵌体的设计提供参考。方法 采用显微CT扫描的数据建立全瓷高嵌体修复根管治疗后上颌第一前磨牙的三维模型,设计不同牙尖覆盖厚度为2、3、4 mm的3组模型,分别施加600 N垂直载荷和200 N侧向载荷,分析高嵌体、树脂粘接剂层及牙本质的应力分布。结果 随着牙尖覆盖厚度的增大,全瓷高嵌体内部的最大主应力峰值减小,粘接剂层边缘的最大主应力峰值增大,侧向载荷下冠部腭侧剩余牙本质的应力集中面积增大。结论 增大全瓷高嵌体的牙尖覆盖厚度可减小全瓷高嵌体破裂的风险,但可能会导致高嵌体脱落和腭侧牙本质折裂。     

弹性模量和初始应力对种植体骨界面应力分布影响的三维有限元分析

目的:分析种植体弹性模量与骨界面应力分布的关系。方法:用三维有限元的方法对不同弹性模量种植体在各种载荷下骨界面的应力大小和分布进行分析。结果:种植体周围界面骨组织应力强度随着材料弹性模量的增大而增大。结论:低弹性模量的钛合金材料作为种植材料时具有更好的生物力学相容性。初始应力在分析种植体骨界面应力分布时必须加以考虑。     

Evaluation of Stresses and Forces in Selected I-Bars Using the Finite Element Method

Purpose Three-dimensional models of half-round, tapered and full-round, untapered I-bar clasps of varying configurations and material properties were constructed. The purpose of this study was to examine the stresses and reaction forces produced within each model upon deflection to 0.01 in (0.254 mm), 0.02 in (0.508 mm), and 0.03 in (0.762 mm) at 1 mm from the tip using the finite element method. Materials and Methods Three-dimensional computer models of half-round and full-round clasps were constructed using solid eight-node brick elements. The half-round, tapered I-bar clasp model was 2.4 and 1.4 mm in diameter at the base and tip, respectively. The full-round, tapered I-bar clasp model was 1 mm in diameter. Three design groups were created for each clasp form. Group A had 25% of the total length in the straight anchor end of the I-bar clasp, B had 35%, and C had 50%. All models were 31 mm in length and had a radius of curvature of 5 mm. Different material properties were incorporated into the models. Each model was deflected at a point 1 mm from the tip to 0.01 in (0.254 mm), 0.02 in (0.508 mm), and 0.03 in (0.762 mm). Results The stresses and forces produced as a result of the deflection applied to each clasp were viewed and displayed graphically. The maximum von Mises stresses in megapascals and the reaction force in newtons (N) were recorded. Stresses varied in each clasp in the range of 0 to 154.3 MPa for the half-round, tapered I-bar clasp models, and 0 to 100.9 MPa for the full-round I-bar clasp models at 0.01-in deflection. Reaction force measured near the tip of the clasp models was between 1.60 N and 6.31 N for the half-round, and between 0.22 N to 2.13 N for the full-round I-bar clasp models. For all clasps studied, as the deflection increased, the location of stress within each group remained the same regardless of the material properties; however, the stress and force values increased linearly. Conclusions The location of maximum stress varied with the length of the anchor portion of the clasps studied. Maximum stresses were located on the flat side of the half-round, tapered I-bar clasp model.     

Mechanical Properties of Various Glide Path Preparation Nickel-titanium Rotary Instruments

Introduction

The aim of this study was to compare the cyclic fatigue, torsional resistance, and bending stiffness of single-file glide path preparation nickel-titanium instruments.

Technical complications of implant-supported fixed partial dentures in partially edentulous cases after an average observation period of 5 years

OBJECTIVES: The purpose of this prospective long-term study was to evaluate the incidence of the most common technical problems, namely screw loosening, screw fracture, fracturing of veneering porcelain and framework fracture in implant-supported fixed partial dentures (FPDs), and assess the survival and success rate (event-free survival) after 5 years of function. MATERIALS AND METHODS: In 76 partially edentulous patients, a total of 205 3i-implants (machined surface) were placed and restored with 112 implant-supported FPDs (46 single crowns, 81 splinted crowns, seven FPD bridges and 23 FPDs with cantilevers). The survival rate of FPDs supported by implants was 94.5% (CI-95: 90.1-98.8) after an average observation period of 5 years. The success rate (event-free survival) of the FPDs was 80% (CI-95: 87.3-72.7). After an observation period of 5 years the cumulative incidence of screw loosening was 6.7% (CI-95: 1.8-11.5), the cumulative incidence for screw fracture was 3.9% (CI-95: 0.1-7.7). Fracture of the veneering porcelain occurred in 5.7% (CI-95: 1.2-10.2) of all FPDs. Fracturing of the suprastructure framework was rare (1%; CI-95: 0-2.9). The overall complication incidence after 5 years was highest in the group of FPDs with cantilever, which showed the lowest success rate 68.6% (CI-95: 50-87.3), followed by single crowns (77.6%; CI-95: 53.3-100) and splinted crowns (86.1%; CI-95: 59.5-100). No complication occurred in FPD bridges. CONCLUSION: Fixed partial dentures supported by 3i-implants showed low technical complications rates, the most common being loosening of the abutment screw. Managing these complications can cause extra amount of chair-side time and patient dissatisfaction.     

Scanning electron microscopic evaluation of the material interface of adjacent layers of dental materials

Objective

Many dental materials are used in contact with each other in sandwich techniques. Liners, bases and permanent restorative materials are placed adjacent to each other and allowed to set under the same conditions. The same applies for endodontic materials where irrigating solutions and root canal dressings come in contact with root canal obturating materials and root-end fillers. The aim of this research was to investigate the material interface of mineral trioxide aggregate (MTA) in contact with non-setting calcium hydroxide paste (CH), glass ionomer cement (GIC) and intermediate restorative material (IRM).

Methods

All materials were mixed according to manufacturer's instructions. Freshly mixed MTA (Dentsply) was placed in a plastic container and another dental material was compacted on it while still unset. These materials included GIC (Fuji IX), non-setting calcium hydroxide (Calasept) and IRM (Dentsply). The materials were allowed to set for 28 days at 37 °C and 100% humidity. The layered materials were sectioned longitudinally embedded in resin and polished to expose the interface between the two materials. Scanning electron microscopy (SEM) was performed of the interface and X-ray energy dispersive analysis (EDX) was conducted at 50 μm intervals to establish elements present at specific distances from the material interface.

Results

The calcium hydroxide paste did not affect the hydration of MTA. Migration of silicon, aluminum and bismuth from the MTA to the CH occurred. The GIC exhibited a high degree of micro-cracking and some porosity in the interfacial region. Strontium from the GIC was detected at 200 μm within the MTA. The zinc from the IRM cement was detected at 100 μm within the MTA. The zinc affected the hydration of the MTA leading to retardation of setting and increased porosity.

Conclusions

MTA interacts with other dental materials with resultant elemental migration in adjacent materials. Zinc oxide eugenol based cements should be avoided in the presence of MTA as zinc causes retardation of cement hydration with increased porosity. Glass ionomer cements absorb the water of hydration from the MTA also resulting in increased porosity and incomplete hydration of MTA.