Evaluating the accuracy (trueness and precision) of interim crowns manufactured using digital light processing according to post-curing time: An in vitro study

PURPOSEThis study aimed to compare the accuracy (trueness and precision) of interim crowns fabricated using DLP (digital light processing) according to post-curing time.MATERIALS AND METHODSA virtual stone study die of the upper right first molar was created using a dental laboratory scanner. After designing interim crowns on the virtual study die and saving them as Standard Triangulated Language files, 30 interim crowns were fabricated using a DLP-type 3D printer. Additively manufactured interim crowns were post-cured using three different time conditions-10-minute post-curing interim crown (10-MPCI), 20-minute post-curing interim crown (20-MPCI), and 30-minute post-curing interim crown (30-MPCI) (n = 10 per group). The scan data of the external and intaglio surfaces were overlapped with reference crown data, and trueness was measured using the best-fit alignment method. In the external and intaglio surface groups (n = 45 per group), precision was measured using a combination formula exclusive to scan data (₁₀C₂). Significant differences in accuracy (trueness and precision) data were analyzed using the Kruskal-Wallis H test, and post hoc analysis was performed using the Mann-Whitney U test with Bonferroni correction (α=.05).RESULTSIn the 10-MPCI, 20-MPCI, and 30-MPCI groups, there was a statistically significant difference in the accuracy of the external and intaglio surfaces (P <.05). On the external and intaglio surfaces, the root mean square (RMS) values of trueness and precision were the lowest in the 10-MPCI group.CONCLUSIONInterim crowns with 10-minute post-curing showed high accuracy.     

Accuracy of additively manufactured zirconia four-unit fixed dental prostheses fabricated by stereolithography,digital light processing and material jetting compared with subtractive manufacturing

ObjectiveTo evaluate the manufacturing accuracy of zirconia four-unit fixed dental prostheses (FDPs) fabricated by three different additive manufacturing technologies compared with subtractive manufacturing.MethodsA total of 79 zirconia FDPs were produced by three different manufacturing technologies, representing additive (one stereolithography [aSLA] and one material jetting [aMJ] device, two digital light processing [aDLP1/aDLP2] devices) and subtractive manufacturing (two devices [s1/s2]), the latter serving as references. After printing, additively manufactured FDPs were debound and finally sintered. Subsequently, samples were circumferentially digitized and acquired surface areas were split in three Regions Of Interest (ROIs: inner/outer shell, margin). Design and acquired data were compared for accuracy using an inspection software. Statistical evaluation was performed using the root mean square error (RMSE) and nonparametric Kruskal-Wallis method with post hoc Wilcoxon-Mann-Whitney U tests. Bonferroni correction was applied in case of multiple testing.ResultsRegardless the ROI, significant differences were observed between manufacturing technologies (P < 0.001). Subtractive manufacturing was the most accurate with no significant difference regarding the material/device (s1/s2, P > 0.054). Likewise, no statistical difference regarding accurary was found when comparing s2 with aMJ and aSLA in most ROIs (P > 0.085). In general, mean surface deviation was< 50 µm for s1/s2 and aMJ and< 100 µm for aSLA and aDLP2. aDLP1 showed surface deviations> 100 µm and was the least accurate compared to the other additive/subtractive technologies.SignificanceAdditive manufacturing represents a promising set of technologies for the manufacturing of zirconia FDPs, but not yet as accurate as subtractive manufacturing. Methodological impact on accuracy within and in between different additive technologies needs to be further investigated.     

三维数字化模型测量牙齿和牙弓的精确性研究

目的 通过与手工测量法比较,评估三维数字化法模型测量牙齿和牙弓的可靠性和精确性。方法 选择喀什地区维吾尔族成年人石膏模型150副,采用结构光扫描仪对石膏模型扫描获得三维图像后,运用Geomagic Studio 13.0分析软件进行分析和测量,分别测量牙冠高度、宽度、牙弓长度和宽度,与手工测量方法进行比较和分析。结果 虽然三维数字化法与手工法测得的牙冠宽度、高度和牙弓长度的部分数值具有统计学差异,但不具有临床意义,组内相关系数均>0.75。结论 结构光数字化模型的准确性好,在临床的诊断和治疗过程中可替代石膏模型。     

口内扫描系统虚拟咬合记录准确性的体外研究

目的:研究缺牙区域的跨度对于口内扫描系统虚拟咬合记录(virtual interocclusal record,VIR)准确性的影响.方法:从标准模型中复制了超硬石膏模型,然后分成5个研究组,A组:单侧1个游离后牙缺失;B组:单侧2个游离后牙缺失;C组:单侧3个游离后牙缺失;D组:单侧4个游离后牙缺失;E组:完整牙列组...     

Geometrical accuracy of metallic objects produced with additive or subtractive manufacturing: A comparative in vitro study

Objective

To evaluate the accuracy and precision of objects produced by additive manufacturing systems (AM) for use in dentistry and to compare with subtractive manufacturing systems (SM).

Production tolerance of conventional and digital workflow in the manufacturing of glass ceramic crowns

Objectives

To measure and compare the size of the cement gap of wax and polymer copings and final glass-ceramic crowns, produced from conventional and digital workflows, one additive and one subtractive.

Fit accuracy of metal partial removable dental prosthesis frameworks fabricated by traditional or light curing modeling material technique: An in vitro study

Objective

The aim of this study was to compare the fit accuracies of metal partial removable dental prosthesis (PRDP) frameworks fabricated by the traditional technique (TT) or the light-curing modeling material technique (LCMT).

Materials and methods

A metal model of a Kennedy class III modification 1 mandibular dental arch with two edentulous spaces of different spans, short and long, was used for the study. Thirty identical working casts were used to produce 15 PRDP frameworks each by TT and by LCMT. Every framework was transferred to a metal master cast to measure the gap between the metal base of the framework and the crest of the alveolar ridge of the cast. Gaps were measured at three points on each side by a USB digital intraoral camera at ×16.5 magnification. Images were transferred to a graphics editing program. A single examiner performed all measurements. The two-tailed t-test was performed at the 5% significance level.

Results

The mean gap value was significantly smaller in the LCMT group compared to the TT group. The mean value of the short edentulous span was significantly smaller than that of the long edentulous span in the LCMT group, whereas the opposite result was obtained in the TT group.

Conclusion

Within the limitations of this study, it can be concluded that the fit of the LCMT-fabricated frameworks was better than the fit of the TT-fabricated frameworks. The framework fit can differ according to the span of the edentate ridge and the fabrication technique for the metal framework.     

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。     

2种CAD/CAM口腔数字化导板精度的比较

目的： 比较2种CAD/CAM口腔数字化导板的精度。方法： 选择上海市静安区牙病防治所就诊的36例口腔种植患者,均行CBCT检查和口内激光扫描,所获数据导入3Shape软件,进行术前设计。每个病例生成2个导板,A导板数据来自CBCT,B导板数据为CBCT和口内激光扫描数据的拟合,随机选择导板类型并使用。术后拍摄CBCT并将数据导入设计软件,与种植前设计的位置进行比较。采用R语言4.1.0对数据进行统计学分析。结果： B导板组种植体顶部中心点距离偏差、种植体底部中心点距离偏差和两中心点连线的角度偏差显著小于A导板组（P<0.05）。结论： CBCT和口内激光扫描数据拟合生成的CAD/CAM口腔数字化导板精度更高,有利于提高种植体植入的三维位置精确度。     

数字光处理型3D打印参数对导板树脂机械性能的影响

目的 探寻多种数字光处理（DLP）型3D打印工艺参数对导板树脂成型件尺寸精度与性能的影响及规律。方法 分别以不同的单层固化时间、层厚、后固化处理时间及模型设置方向为因变量分组，每组使用Sisma everes uno DLP型3D打印机遵循标准分别制备精度、硬度、弯曲强度、拉伸强度的测试试样各15个，测试试样的长（X）、宽（Y）、高（Z），使用邵氏硬度计测试硬度，万能力学试验机测试弯曲强度与拉伸强度，并进行统计学分析。结果 打印件的尺寸精度随着单层固化时间的增加而先升高再降低，1.3 s时精度最高，随着层厚增加而先升高再降低，0.05 mm时精度最高，随着后固化时间的增加而降低，与模型设置方向无显著关系；打印件的硬度受到单层固化时间、层厚及后固化时间影响，与模型设置方向无显著关系；打印件拉伸强度及弯曲强度受到单层固化时间、层厚、模型设置方向及后固化时间的多因素共同影响。单层固化时间在1.3~1.4 s，层厚0.025 mm，模型根据实际形状向Y方向设置，后固化时间10~15 min时，DLP成型件在尺寸精度、硬度、拉伸强度、弯曲强度等综合方面表现相对较优。结论 DLP3D打印的参数与打印件的精度、物理性能之间存在一定的规律，并且不同因素间的影响强弱不同。通过对参数的筛选，可以实现对单层固化时间、层厚、模型设置方向、后固化处理时间的优化，从而提高打印件的精度和物理性能。     

Fracture resistance of porcelain veneered zirconia crowns with exposed lingual zirconia for anterior teeth after thermal cycling: An in vitro study

Statement of problem

In some clinical conditions minimally invasive complete crown tooth preparations are indicated. This is especially true when gross removal of tooth structure would weaken the remaining tooth or violate the vitality of the dental pulp.

Objective

The purpose of this study was to investigate the influence of (1) exposed lingual zirconia with veneered zirconia crowns, and (2) reduced lingual thickness of monolithic lithium disilicate crowns on the fracture resistance of the crowns after cyclic loading. Metal-ceramic crowns with exposed lingual metal served as controls.

Materials and methods

Twenty-four maxillary central incisor crowns were fabricated in identical shape on metal testing dies in 3 groups: metal-ceramic crowns (MC, n = 8), veneered zirconia crowns (VZ, n = 8), and monolithic lithium disilicate crowns (MO, n = 8). A conservative preparation design with 0.75 mm lingual clearance was used for each crown system. All crowns were cemented to their corresponding crown preparations with self-adhesive resin cement (Multilink Automix). The crowns were subjected to 1000 cycles of thermal cycling, then cyclic loading of 111 N by means of a stainless steel ball, and 50,000 cycles of loading were applied for the fatigue test. Fatigue loading was followed by a continuously increasing compressive load, at a crosshead speed of 1 mm/min until failure. The compressive load (N) required to cause failure was recorded. Means were calculated and analyzed with one-way ANOVA and the Tukey HSD test (α = .05).

Results

There was a significant difference between MO vs. MC (P = .0001), MO vs. VZ (P = .0001), and VZ vs. MC (P = .012).

Conclusions

There was a significant difference in the mean fracture resistance of MC, VZ, and MO crowns in this in vitro study. The MC group recorded the highest mean fracture strength.     

Evaluating the influence of ambient light on scanning trueness,precision, and time of intra oral scanner

Purpose

This study evaluated the influence of illuminance and color temperature of ambient light on the trueness, precision, and scanning time of a digital impression.

Impact of digital impression techniques on the adaption of ceramic partial crowns in vitro

Objectives

To investigate the effects, digital impression procedures can have on the three-dimensional fit of ceramic partial crowns in vitro.

Methods

An acrylic model of a mandibular first molar was prepared to receive a partial coverage all-ceramic crown (mesio-occlusal-distal inlay preparation with reduction of all cusps and rounded shoulder finish line of buccal wall). Digital impressions were taken using iTero (ITE), cara TRIOS (TRI), CEREC AC with Bluecam (CBC), and Lava COS (COS) systems, before restorations were designed and machined from lithium disilicate blanks. Both the preparation and the restorations were digitised using an optical reference-scanner. Data were entered into quality inspection software, which superimposed the records (best-fit-algorithm), calculated fit-discrepancies for every pixel, and colour-coded the results to aid visualisation. Furthermore, mean quadratic deviations (RMS) were computed and analysed statistically with a one-way ANOVA. Scheffé’s procedure was applied for multiple comparisons (n = 5, α = 0.05).

Results

Mean marginal (internal) discrepancies were: ITE 90 (92) μm, TRI 128 (106) μm, CBC 146 (84) μm, and COS 109 (93) μm. Differences among impression systems were statistically significant at p < 0.001 (p = 0.039). Qualitatively, partial crowns were undersized especially around cusp tips or the occluso-approximal isthmus. By contrast, potential high-spots could be detected along the preparation finishline and at central occlusal boxes.

Conclusions

Marginal and internal fit of milled lithium disilicate partial crowns depended on the employed digital impression technique.

Clinical significance

The investigated digital impression procedures demonstrated significant fit discrepancies. However, all fabricated restorations showed acceptable marginal and internal gap sizes, when considering clinically relevant thresholds reported in the literature.     

Two-body wear and fracture behaviour of an experimental paediatric composite crown in comparison to zirconia and stainless steel crowns dependent on the cementation mode

ObjectivesThe purpose of this in vitro study was to assess the two-body wear and fracture behaviour of an experimental additive manufactured composite crown in comparison to zirconia and stainless steel crowns and its cementation protocol for primary molars.Material and methodsThree different paediatric crowns – experimental composite crowns (CCs, 3M), zirconia crowns (ZCs, NuSmile), and stainless steel crowns (SSCs, 3M)–were cemented with an experimental resin-modified glass ionomer cement (RMGIC, 3M) and two self-adhesive cements (SACs; RelyX Unicem Automix 2, 3M; BioCem, NuSmile). Seven groups, each with eight specimens, were thermally cycled (55 °C/50 °C) and dynamically loaded (50N/ 1.2Hz) in a masticatory simulator with steatite antagonists. The areal and volumetric material loss of all specimens before and after 1,200,000 masticatory cycles was evaluated with a 3D profilometer. Light and scanning electron microscopy were used for qualitative analysis. Pairwise comparisons between all the groups were performed using the Mann–Whitney U test (p < 0.05).ResultsMicroscopic imaging revealed different wear patterns for each material. Lowest fracture rates were documented for the CCs. In contrast, all the SSCs showed perforations. The CCs cemented with RMGIC showed the highest significant volumetric wear (6.3 ± 0.72 mm³), followed by the SSCs cemented with RMGIC (3.6 ± 1.79 mm³) and CCs cemented with SAC (3.5 ± 1.92 mm³). No significant differences were found in terms of the wear among all the other groups, ranging between 0.4 ± 0.25 and 0.6 ± 0.32 mm³.ConclusionThe volume loss of the tested crowns differed for each material and was dependent on the type of cementation. With regard to in vitro wear and fracture patterns, cementation with SAC may increase the clinical performance of CC paediatric crowns.     

Effect of resin coating on adhesion and microleakage of computer-aided design/computer-aided manufacturing fabricated all-ceramic crowns after occlusal loading: a laboratory study

This study investigated the effect of resin coating and occlusal loading on adhesion and microleakage of all-ceramic crowns. Molars were prepared for an all-ceramic crown and were divided into two groups: non-coated (control) and resin-coated with Clearfil Tri-S Bond. Crowns were fabricated using CEREC 3 and cemented using Clearfil Esthetic Cement. After 24 h of storage in water, the restored teeth in each group were divided into two subgroups: unloaded, or loaded while stored in water. Mechanical loading was achieved with an axial force of 80 N at 2.5 cycles s⁻¹ for 250,000 cycles. After immersion in Rhodamine B, the specimens were sectioned and processed for microleakage evaluation by confocal microscopy, which was followed by further sectioning for microtensile bond testing. Loading had no significant effect on microleakage in either the resin-coated or non-resin-coated groups. Resin coating did not reduce the microleakage at the dentine interface but increased the microleakage at the enamel interface. All the beams fractured during slicing when non-coated and loaded. The bond strengths of non-coated and unloaded, resin-coated and unloaded, and resin-coated and loaded groups were 15.82 ± 4.22, 15.17 ± 5.24, and 12.97 ± 5.82 MPa, respectively. Resin coating with Clearfil Tri-S Bond improved the bonding of resin cement to dentine for loaded specimens. However, it was not effective in reducing the microleakage, regardless of whether it was loaded or unloaded.     

下颌切牙Empress 2瓷贴面与全瓷冠牙预备体及全瓷修复复合体的抗折裂研究

目的比较下颌切牙Empress 2瓷贴面和全瓷冠牙预备体及修复体粘接后复合体的抗折强度。方法选择人离体下颌切牙50颗,随机分为5组。A组为瓷贴面牙体预备组,B组为全瓷冠牙体预备组,C组为瓷贴面修复组,D组为全瓷冠修复组,E组为完整下颌切牙（对照组）。采用标准化牙体预备过程,Empress 2铸瓷系统及树脂粘接技术完成瓷贴面-牙体和全瓷冠-牙体复合体。使用Instron万能试验机测试5组牙齿的抗折裂载荷值,采用方差分析进行统计学分析。结果A、B、C、D、E组的抗折裂载荷值分别为：（576.11±91.53）、（204.13±85.88）、（451.50±116.81）、（386.16±117.75）、（566.05±121.37）N。经统计学分析,B组抗折裂载荷值低于其他组（P<0.01）;A、E组间的差异无统计学意义,其值最高,高于其他组（P<0.05）;C、D组间的差异也无统计学意义,其值低于A、E组,但高于B组（P<0.05）。结论下颌切牙瓷贴面预备后,牙体抗折能力无明显降低。下颌切牙Empress 2瓷贴面与全瓷冠粘接后,2种复合体的抗折裂能力无明显区别。