Dimensional change of elastomeric impressions after disinfectant immersion]

One method to prevent cross-contamination in dental clinic is to immerse the impressions in disinfectants before making master models. This study to evaluate the effect of disinfectants on dimensions of the elastomers namely polyether, condensation silicone, addition silicone and polysulfide, the disinfectant used in this study is 1% Sodium hypochlorite, 0.13% Sporicidin and 10% Gigasept. Being left under room temperature and immersed in distilled water are two types of controls. Dimensional changes can be measured on master model and compared with the brass standard model. The study reveals that the three disinfectants have no effect on vertical dimensions of all four elastomers but have statistically effect on horizontal dimensions of only polyether (p less than .05). It concludes that all the elastomeric impressions except polyether should be immersed in disinfectants before making master models.     

Dimensional change over time of extended-storage alginate impression materials

Objectives:To evaluate the dimensional change over time of two extended-storage alginate impression materials.Methods:Impressions were made of stainless steel dies in accordance with ADA Specification No. 18 using three alginates: two extended-storage alginates and one conventional alginate. The impressions were stored for 30 minutes, 48 hours, or 100 hours (n  =  10 impressions/material/storage time). Following the respective storage times, dimensional change was measured by comparing the length of the middle horizontal line in the impression with the same line on the die and computing percent difference.Results:Significant differences in dimensional change were noted between materials across time (P < .05). All materials exhibited shrinkage after 30 minutes, with the conventional alginate continuing to shrink over time and the extended-storage alginates expanding with increased storage time. The conventional alginate was most accurate after 30 minutes. In contrast, one extended-storage alginate demonstrated minimal dimensional change at all storage times, and another was most accurate after 100-hour storage.Conclusions:Evidence suggests that delayed pouring with dental gypsum should not adversely affect dimensional accuracy of the generated casts with both extended-storage alginates. However, only one of the extended-storage materials appears suitable for both short-term and extended-storage applications.     

Dual-arch impressions

All dual-arch impression techniques utilize special stock impression trays of various designs. These trays are made of flexible plastic with fabric or mesh material placed across the occlusal surfaces of the teeth connecting their buccal and lingual flanges. The presence of this material will result in errors by (1) not allowing complete intercuspation during impression-taking; (2) producing incorrect recording of centric occlusion; and (3) because of the elastic memory of the tray/fabric, creating distortion of the elastic impression material. An impression technique is presented which provides a simple and effective method of obtaining dual-arch impressions for single restorations, post and cores, and small bridges. This technique obivates the need for impression trays thus eliminating the errors outlined.     

Effect of wash bulk on the accuracy of polyvinyl siloxane putty-wash impressions

Variations in the bulk of wash in a putty-wash impression technique can result in dimensional changes proportional to the thickness of the wash material during setting. The purpose of the study was to determine the amount of wash necessary to achieve accurate stone models while using a two-step putty-wash impression technique with polyvinyl siloxane (PVS) impression material. A total of 45 impressions were made of a stainless steel master model, 15 impressions for each wash thickness (1, 2 and 3 mm). The model contained three full-crown abutment preparations, which were used as the positive control. Accuracy was assessed by measuring six dimensions (occlusogingival and interabutments) on stone dies poured from impressions of the master model. One-way analysis of variance (ANOVA) showed statistically significant differences amongst the three wash bulk groups, for all occlusogingival and interabutment measurements (P < 0.001). The overall discrepancies of the groups using wash thickness of 1 and 2 mm were smaller than the group with 3 mm wash thickness. Therefore, wash bulks of 1 and 2 mm were most accurate for fabricating stone dies, using PVS impression materials. This can be achieved by using the temporary crown to create the desired wash space in the preliminary putty impression. Wash thickness > 2 mm was inadequate to obtain accurate stone dies.     

不同灭菌法对齿科高速裂钻力学性能的影响

目的研究齿科常用的3种灭菌方法（干热法、湿热法、化学浸泡法）对牙科高速裂钻力学性能的影响。方法将200根全新的钨钢高速裂钻随机分为10组。分别通过弯曲实验和扭转实验观察高速裂钻在不同灭菌方法处理后弯曲强度、弹性模量和扭转强度等力学指标的改变。结果干热灭菌法、化学浸泡法和湿热灭菌法对裂钻的力学性能均有影响,随着灭菌次数的增加,裂钻的弯曲强度、弹性模量和扭转强度均相应减弱。3种灭菌方法比较发现,湿热处理引起裂钻的力学性能降低最明显,而化学浸泡和干热处理引起的变化相似,且较小。结论不同灭菌方法对高速裂钻产生一定的作用,影响大小排列依次为：湿热法、化学浸泡法、干热法。鉴于干热灭菌腐蚀作用最弱,建议齿科常用的小型器械可使用干热灭菌法进行灭菌。     

数字化口腔修复(2)——数字化印模

义齿采用数字化的加工方法,有助于提高修复体质量,改善护理质量,并为患者提供最佳就诊体验.数字化印模易于储存,不占空间,且无需消毒,极大地避免了气泡、裂痕和收缩变形的发生.随着新技术的迅猛发展,优化数字化印模的操作,降低数字化印模的成本,将有助于其发展.     

Dimensional change following setting of root canal sealer materials

OBJECTIVE: The study was designed to evaluate a method proposed for measuring dimensional changes of endodontic sealers, and to assess the dimensional changes of 11 commercial sealers after prolonged storage in water. METHODS: The method for linear dimensional change described in the draft standard for endodontic sealers was applied to 11 different types of endodontic sealers. One material (Sealapex) could not be tested by the method. The other 10 materials were followed for dimensional change over 48 weeks. RESULTS: The sealers showed markedly different dimensional properties. For most materials, the greatest dimensional changes took place within the first 4 weeks. Zinc-oxide-eugenol based sealers generally showed shrinkage ranging from 0.3 to 1%, while one product (Proco-Sol) exhibited expansion exceeding 6% after prolonged storage. The epoxy-based materials, AH 26 and AH 26 silverfree, exhibited a large, initial expansion of 4-5%. AH Plus expanded from 0.4% after 4 weeks up to 0.9%. Apexit, a Ca(OH)2-based material, showed only minor variation round baseline value, -0.14 to +0.19%. Roeko-Seal expanded to 0.2% within 4 weeks, but was stable thereafter. SIGNIFICANCE: The test methodology adequately assessed dimensional changes exceeding +/-0.2%, but some brands of material either could not be made into adequate test specimens or showed surface changes which interfered with dimensional change measurements. Theoretical approaches to the consequences of expansion by materials of low bulk strength question the necessity of a strict requirement against expansion, whereas bacterial penetration may be a real threat from sealers shrinking as little as 1%.     

消毒液浸泡消毒对藻酸盐印模尺寸稳定性影响的评价研究

目的评价用三种消毒液浸泡不同时间后,四种藻酸盐印模的尺寸稳定性。方法采用符合YY1027国家行业标准和ISO 1563国际标准的标准试验装置,制取四种藻酸盐印模材料的标准印模,每种材料制取6组,每组5个印模,共120个印模。分别用2%戊二醛和84消毒液浸泡30分钟和40分钟、邻苯二甲醛消毒液(Ortho-phthalaldehyde,OPA)浸泡20分钟和30分钟。使用工具显微镜测量浸泡消毒处理前后各组印模的标志线长度,比较浸泡前后印模线性尺寸变化率,并对所得结果应用SPSS10.0软件进行统计学分析。结果①使用2%戊二醛、84消毒液浸泡处理前后,全部印模均发生显著膨胀形变(P<0.05),且形变随浸泡时间的延长而增大。②使用邻苯二甲醛消毒液浸泡处理前后,全部印模均发生显著收缩形变(P<0.05),且形变随浸泡时间的延长而增大。③不同材料的印模之间尺寸变化率的差异有显著性(P<0.05)。登士柏翡翠Jeltrate的形变率最小。④不同消毒液不同浸泡时间处理对印模尺寸稳定性影响的差异有显著性(P<0.05)。在相同浸泡时间时,使用2%戊二醛浸泡处理的印模形变率比使用84消毒液浸泡处理的印模形变率要小。结论①消毒...     

Efficacy of chemical sterilization and storage conditions of gutta-percha cones

AIM: The objective of the present study was to assess the efficacy of 2.5% sodium hypochlorite and 2.2% glutaraldehyde ('Cidex') as sterilizing agents for gutta-percha cones. The efficacy of storage of gutta-percha cones in the presence or absence of paraformaldehyde was also evaluated. METHODOLOGY: Gutta-percha cones artificially contaminated with a suspension of Bacillus stearothermophilus (ATCC/7953) were treated with either 2.2% glutaraldehyde for 10, 15, 30 and 60 min and 10 and 12 h, or 2.5% sodium hypochlorite for 5, 10 and 15 min. The cones were then incubated in thioglycollate medium for the determination of microbial growth. In parallel, additional sterile gutta-percha cones were stored in sealed containers with or without paraformaldehyde tablets for 30 days. The containers were opened 30 min a day and exposed to the environment of a functioning dental clinic. Twelve cones were removed weekly from the containers to determine whether contamination had occurred. RESULTS: The results showed that 2.5% sodium hypochlorite was effective after 5, 10 and 15 min, whereas 10 and 12 h contact with 2.2% glutaraldehyde was necessary to obtain sterilization. There was no contamination of the gutta-percha cones when stored with or without paraformaldehyde. CONCLUSIONS: Sodium hypochlorite (2.5%) and 2.2% glutaraldehyde ('Cidex') proved to be effective as sterilizing agents for gutta-percha cones, with sodium hypochlorite requiring shorter periods of use. No difference was observed between the two methods of cone storage.     

Dimensional accuracy of microcomputed tomography-scanned half-arch impressions

Statement of problem

Accuracy in impression making may be enhanced by digitizing the physical impression directly and thereby be unhampered by errors introduced by gypsum casts.

数字化印模在口腔种植修复中的研究进展

数字化印模是指使用口内扫描仪在患者口内无需直接接触即获取组织图像,并合成三维牙列影像的印模技术。数字化印模于口腔种植修复中的应用近年来开始受到关注,但其印模精度尚不明确,尤其是多颗种植体的数字化印模精度。本文详细介绍数字化印模的原理、在种植修复不同类型牙列缺损或缺失情况下的精度以及影响精度的相关因素,以期为数字化印模在种植修复中的临床应用提供参考依据。     

臭氧对口腔科诊室空气消毒效果的研究

目的 观察臭氧对口腔科诊室空气常见致病菌的杀菌效果。方法 用碘滴定法测定打开臭氧发生器不同机组及不同时间时的臭氧浓度,按平板自然沉降法采集细菌,根据细菌集落数,计算出空气中的细菌数量,并计算杀菌率,确定细菌的种类。所得数据采用SAS6.12软件包进行卡方检验。结果 ①随着打开臭氧发生器组数的增加和时间的延长,诊室内臭氧浓度逐步升高,最低为240mg/m3,最高可达2736mg/m3;②臭氧的灭菌率普遍高于紫外线;③浓度为2736mg/m3的臭氧作用45min对变链菌的杀菌率最高为100%。结论 臭氧灭菌效果高于紫外线,可作为口腔科诊室的常规消毒方法。     

Evaluation of Dimensional Stability and Accuracy of Autoclavable Polyvinyl Siloxane Impression Material

Dimensionally stable autoclavable impressions will be effective in controlling the cross-infection and contamination caused by patient’s saliva and other oral secretions. The accuracy of newly introduced autoclavable polyvinyl siloxane impression material was assessed for its dimensional stability and accuracy. A standard metal model (Dentoform, U-501, Columbia) was customised for impression making. The impressions were made using the newly introduced polyvinyl siloxane impression materials (AFFINIS, Coltene/Whaledent AG, 9450 Alstalten, Switzerland). Fifty impressions were made and were divided into two groups A and B of 25 each. Group A was the control sample (non-autoclaved impressions) and group B was the test sample (autoclaved impressions), which was subjected to the steam autoclave procedure at 134 °C for 18 min, casts were poured in type IV gypsum products. The customised metal model, casts obtained from control and test group were subjected to laboratory evaluation with help of a travelling microscope (×10 magnification), and digital vernier calliper (0.01 mm/10 μm accuracy). Data analysis was done using one-way ANOVA and One-Sample t test to evaluate the overall accuracy (P < 0.005). As a result, there was an average reduction of 0.016 μm in overall dimension between the test and the control group when compared with the master model, which is not statistically or clinically significant. The newly introduced polyvinyl siloxane impression material is accurate and dimensional stable for clinical use when steam autoclaved at 134 °C for 18 min.     

微波消毒根管的实验研究

目的：探讨微波消毒根管的确切疗效。方法：扫描电镜下观察根管各段细菌情况。结果：根管中、下段几乎未见细菌，内壁清洁度相对较高，玷污层少，根管下段牙本质小管呈熔融状。结论：微波消毒根管有满意效果。     

Dimensional stability of dental impressions after immersion disinfection

Disinfection of dental impressions via short-term immersion in 0.5% or 1% sodium hypochlorite does not significantly affect the dimensional accuracy of the resultant casts. In addition, immersion in glutaraldehydes, povidone-iodine diluted in water, or halogenated phenol has no apparent effect on the dimensional stability of rubber impression materials. The results of this study support the use of immersion disinfectants for treatment of impressions for study models or removable dental appliances or prostheses. Coupled with the findings of other authors, the data suggest that such disinfection also would be suitable for rubber base and vinyl polysiloxane impressions for cast restorations. Given the need for infection control in the treatment of all dental patients, the results of this study support the recommendations of the American Dental Association for disinfection of dental impressions via immersion in an appropriate disinfectant solution.