计算机辅助设计与制造树脂暂时冠与自凝树脂、Luxatemp暂时冠的边缘密合度比较

目的 比较自凝树脂、Luxatemp与计算机辅助设计与制造（CAD/CAM）树脂暂时冠修复体的边缘密合度差异。方法 按全冠牙体制备标准预备牙体30个,取模并灌注石膏模型后,分别制作自凝树脂、Luxatemp与CAD/ CAM树脂暂时冠各30个,将其就位于石膏模型上。通过体式显微镜,对利用硅橡胶复制技术得到的暂时冠与石膏模型间的边缘间隙宽度代型进行测量,计算各组30个样本边缘间隙的平均值。采用SPSS 19.0软件包对实验数据进行单因素方差分析。结果 自凝树脂、Luxatemp与CAD/CAM树脂暂时冠边缘间隙平均值分别为（179.06±33.24）、（88.83±9.56）和（43.61±7.27） μm。CAD/CAM树脂暂时冠边缘间隙显著小于自凝树脂和Luxatemp暂时冠（P< 0.05）,自凝树脂暂时冠边缘间隙显著大于Luxatemp与CAD/CAM树脂暂时冠（P<0.05）。结论 CAD/CAM树脂暂时冠边缘密合度显著优于自凝树脂和Luxatemp暂时冠, CAD/CAM具有较高的临床应用价值。     

Dimensional accuracy and clinical adaptation of ceramic crowns fabricated with the stereolithography technique

Statement of problemThe stereolithography technique has been a promising method of fabricating fracture-resistant ceramic restorations efficiently. However, studies on the dimensional accuracy and clinical adaptation of ceramic crowns fabricated with the technique are lacking.PurposeThe purpose of this in vitro study was to evaluate the dimensional accuracy and clinical adaptation of ceramic crowns fabricated with the stereolithography technique.Material and methodsA typodont maxillary right first molar abutment tooth was scanned by using an extraoral scanner, and a crown was designed by using 3Shape Dental System CAD software. Ten ceramic crowns were fabricated with 2 different stereolithography systems, CeraFab7500 (CF) alumina and CSL150 (CL) zirconia, and a conventional computer-aided design and computer-aided manufacturing system, X-MILL500 (XM) zirconia. The crowns were scanned, and the digital casts were exported. Dimensional accuracy was measured by superimposing the digital casts with the reference model by using Geomagic Qualify software. The silicone replica method was applied to measure clinical adaptation. Results were statistically analyzed by using a 1-way analysis of variance (α=.05).ResultsCeraFab7500 reported better dimensional accuracy (41 ±11 μm) than CSL150 (65 ±6 μm) or X-MILL500 (72 ±13 μm) (P<.001). No significant difference was found between the CSL150 and X-MILL500 groups (P>.05). X-MILL500 reported significantly better adaptation in the marginal, corner, and occlusal areas but inferior adaptation in the axial area compared with CeraFab7500 and CSL150 (P<.05). Significant differences were only apparent in the axial and occlusal areas between CeraFab7500 and CSL150 (P<.05). No significant difference was found in the marginal or corner area between CeraFab7500 and CSL150 (P>.05).ConclusionsBoth CeraFab7500 and CSL150 can fabricate ceramic crowns with high dimensional accuracy and marginal adaptation within clinically acceptable limits. The results indicate that the fabrication of ceramic crowns by using the stereolithography technique seems to be promising.     

不同工艺制作钴铬合金基底冠适合性的实验研究

目的：：对比3种不同工艺制作的钴铬合金基底冠适合性。方法：制作18个树脂代型,随机分为A、B、C 3组,分别采用传统铸造技术、CAD/CAM技术、直接金属激光烧结技术制作钴铬合金基底冠各6个。将基底冠粘固于对应的树脂代型上并包埋片切。测量钴铬合金基底冠边缘及内部粘固剂的厚度。对实验数据进行统计学分析。结果：3组试件边缘间隙分别为A组(66.08±3.90)μm, B组(29.21±3.31)μm,C组(24.96±2.99)μm(P<0.01);3组试件内部间隙分别为A组(114.10±27.66)μm,B组(73.69±31.31)μm,C组(79.89±33.63)μm(A组与 B或 C组比较, P<0.01, B组与 C组比较, P>0.05)。结论：直接金属激光烧结技术制作的钴铬合金基底冠具有更好的边缘适合性;CAD/CAM技术及直接金属激光烧结技术制作的钴铬合金基底冠具有良好的内部适合性。3种技术制作的基底冠边缘及内部适合性均在临床允许范围内。     

Comparison of the dimensional and morphological accuracy of three-dimensional digital dental casts digitized using different methods

Odontology - The purpose of this study was to compare the accuracy of digital dental casts from plaster cast scanning (PCS), impression scanning (IPS), intraoral scanning (IOS), and cone-beam...     

Marginal accuracy of four-unit zirconia fixed dental prostheses fabricated using different computer-aided design/computer-aided manufacturing systems

Besides load-bearing capacity, marginal accuracy is a further crucial factor influencing the clinical long-term reliability of fixed dental prostheses (FDPs). The aim of this in vitro study was to evaluate the marginal fit of four-unit zirconia bridge frameworks fabricated using four different computer-aided design (CAD)/computer-aided manufacturing (CAM) systems. Ten frameworks were manufactured using each fabricating system. Three systems (inLab, Everest, Cercon) processed white-stage zirconia blanks, which had to be sintered to final density after milling, while with one system (Digident) restorations were directly milled from a fully sintered material. After manufacturing, horizontal and vertical marginal discrepancies, as well as the absolute marginal discrepancy, were determined by means of a replica technique. The absolute marginal discrepancy, which is considered to be the most suitable parameter reflecting restorations' misfit in the marginal area, had a mean value of 58  μ m for the Digident system. By contrast, mean absolute marginal discrepancies for the three other systems, processing presintered blanks, differed significantly and ranged between 183 and 206  μ m. Within the limitations of this study, it could be concluded that the marginal fit of zirconia FDPs is significantly dependent on the CAD/CAM system used, with restorations processed of fully sintered zirconia showing better fitting accuracy.     

Effect of rinsing time on the accuracy of interim crowns fabricated by digital light processing: An in vitro study

PURPOSEThis study was to evaluate the effect of rinsing time on the accuracy of interim crowns fabricated by digital light processing.MATERIALS AND METHODSThe maxillary right first molar master die was duplicated using a silicone material, while a study die was produced using epoxy resin. Scans of the epoxy resin die were used in combination with CAD software to design a maxillary right first molar interim crown. Based on this design, 24 interim crowns were fabricated with digital light processing. This study examined the trueness and precision of products that were processed with one of the three different postprocessing rinsing times (1 min, 5 min, and 10 min). Trueness was measured by superimposing reference data with scanned data from external, intaglio, and marginal surfaces. Precision was measured by superimposing the scan data within the group. The trueness and precision data were analyzed using Kruskal-Wallis, nonparametric, and post-hoc tests, and were compared using a Mann-Whitney U test with Bonferroni correction (α=.05).RESULTSThe trueness of the external and intaglio surfaces of crowns varied significantly among the different rinsing times (P =.004, P =.003), but there was no statistically significant difference in terms of trueness measurements of the marginal surfaces (P =.605). In terms of precision, statistically significant differences were found among the external, intaglio, and marginal surfaces (P =.001).CONCLUSIONInterim crowns rinsed for 10 minutes showed high accuracy.     

Three-dimensional comparative study on the accuracy and reproducibility of dental casts fabricated by 3D printers

Statement of problem

Studies investigating the precision of 3-dimensional (3D) printed casts for fixed prosthodontics are scarce.

Machining accuracy of CAD/CAM ceramic crowns fabricated with repeated machining using the same diamond bur

The purpose of this study was to investigate the effect of repeated machining up to 51 times using the same diamond bur on machining accuracy of inner and outer surfaces of CAD/CAM (computer-aided designing and computer-aided manufacturing) machined ceramic crowns. The surface topography of machined crowns was examined using photographs. It was found that machining accuracy was not affected by the number of machining times. In all measuring points, the inner surface was machined to a dimension larger than the die model (i.e., increased gap), whereas the outer surface was machined to a dimension smaller than the crown model (i.e., smaller crown). Photo observation showed that cervical contour was machined in a clear, rounded form from 1st to 11th crowns.     

Failures related to crowns and fixed partial dentures fabricated in a Nigerian dental school

The purpose of this investigation was to document the failure rate and length of service of crowns and fixed partial dentures (FPDs) fabricated in a Nigerian dental school. The reasons for failure of the initial restorations and their length of service were also ascertained. Also, the numbers of retainers, pontics, and the types of restoration were recorded. Poor esthetics was the most frequent cause of failure, 66 units (40.5%); followed by fracture, 58 units (35.6%); and dental caries, 25 units (15.4%). These outcomes were contrary to findings previously reported in studies from western countries where dental caries was principally responsible for failures (22.0% to 38.0% of cases). The resin-retained FPDs had the shortest mean years of service at 2.7 years, while the three-unit metal-ceramic FPDs had the greatest longevity at 8.6 years. The overall mean years of service for replaced restorations were 5.6 years. The study found a decrease in the mean years of service as the number of units in the fixed-fixed partial dentures increased. This is in sharp contrast to previous reports where no relationship existed between length of service and the number of units in a FPD.     

Long-term follow-up of conical crown-retained dentures fabricated using different technologies

This study presents the results of a long-term clinical evaluation of conical crown-retained dentures fabricated using different technologies. Four different material connections between the outer and inner crowns were used: cast gold/cast gold, cast gold/electroforming, nonprecious alloy/electroforming, and titanium abutment/electroforming. Technical failures and retention values were assessed. The best clinical outcome was found with dentures in which both crowns were cast from gold alloy. The most frequent technical failures were observed in restorations with electroformed outer crowns. Better clinical outcomes were noted when the electroformed outer crowns were used in dentures retained by implants as compared to dentures on natural dentition.     

A clinical study comparing marginal and occlusal accuracy of crowns fabricated from double-arch and complete-arch impressions

BACKGROUND: The double-arch impression technique is widely used in the provision of laboratory fabricated restorations. However, there is little clinical evidence to support or refute its use. The aim of this prospective clinical study was to evaluate the occlusion and marginal fit of posterior full crowns made from double-arch impressions, and to compare these to control crowns fabricated from conventional complete-arch impressions. METHODS: Ten patients requiring single posterior ceramo-metal full crowns had both double-arch and complete-arch impressions taken of the prepared tooth. Two crowns were fabricated for each tooth, using the casts made from both impression methods. Both crowns were tried in and the occlusion and margins evaluated. The results were composed using nonparametric statistical analysis with the probability level for significance at alpha=0.05. RESULTS: The crowns fabricated from the double-arch impression were found to be more accurate in closure to the intercuspal position and had fewer interferences in lateral excursions. There were no significant differences between the two crown groups regarding protrusive interferences and margin quality. CONCLUSIONS: Crowns fabricated from the double-arch impressions were equivalent in marginal accuracy and superior occlusally to crowns fabricated from the complete-arch impressions.     

选择性激光熔覆（SLM）制作钴铬合金冠的适合性研究

目的:评价选择性激光熔覆(SLM)技术与失蜡铸造法制作的钴铬合金单冠与三联冠的适合性。方法:采用2种SLM系统EOS M270与EOS M280及铸造法分别制作钴铬合金单冠与三联冠各5个,通过采用硅橡胶法在体式显微镜下测量边缘及内部垂直间隙。采用SPSS 17.0软件对实验数据进行单因素方差分析。结果:钴铬合金单冠的边缘间隙和内部间隙(μm)分别为:EOS M270组42.28±11.58、125.75±47.67,EOS M280组46.54±8.4、128.22±54.18,铸造组为48.66±12.08、135.37±46.89。三联冠的边缘间隙(μm)和内部间隙(μm)分别为:EOS M270组40.55±10.04、133.09±39.80,EOS M280组45.36±10、138.94±50.61,铸造组为54.24±12.04、151.87±61.94(P<0.05)。结论:SLM组边缘平均垂直间隙明显小于临床普遍接受的120μm的标准,精度可以满足临床要求。SLM钴铬合金单冠的边缘适合性优于铸造法,内部适合性无统计学差异。SLM钴铬合金三联冠的边缘适合性及内部适合性均优于铸造法。     

An evaluation of crowns and bridges in a general dental practice

In this article the results are presented of an evaluation of crowns and bridges in a general practice. The study includes 601 solitary crowns, 213 crowns on bridge abutments and 103 crowns on RPD abutments. In total eighty-four bridges were examined. All these restorations were constructed during a period of 11.5 years. By means of the Kaplan-Meier method a prognosis is given of the life span of the different solitary crown-types over periods between 1 and 11 years. The total amount of failures and follow-up treatments on bridge and RPD abutments was very small. The authors also examined whether the bridges were constructed according Ante's law. A follow-up of this study in other Dutch general practices in combination with experimental clinical trials is under way.     

Correlation between accuracy of crowns fabricated using CAD/CAM and elastic deformation of CAD/CAM materials

Full crowns were fabricated from three different materials (titanium, ceramic, and resin composite) at different rest diameters using a dental CAD/CAM system, and then their marginal discrepancy measured. The deflection of cylindrical specimens at 500 gf was measured using the same materials and diameters as for the accuracy measurement. Marginal discrepancy decreased as rest diameter increased, and at the same rest diameter the titanium crown had lower marginal discrepancy than ceramic and composite crowns. A significant correlation was found between marginal discrepancy of the crowns and deflection of the materials. This correlation was aptly expressed in the regression equation, MG = 4.54DF+53.9, where MG represented marginal discrepancy and DF represented deflection. This equation can be used as a good measure for new materials which have different modulus of elasticity.