Optical properties of monolithic zirconia fabricated with nanoparticle jetting.

STATEMENT OF PROBLEM: Excellent optical properties are essential for esthetic dental materials. However, the translucency and color masking ability of zirconia fabricated with nanoparticle jetting (NPJ), a type of printed zirconia, are unknown. PURPOSE: The purpose of this in vitro study was to evaluate the translucency and color masking ability of zirconia fabricated using NPJ. MATERIAL AND METHODS: A total of 90 specimens with thicknesses of 1.5, 1.0, and 0.5 mm were fabricated using high translucent milled zirconia (HT), low translucent milled zirconia (LT), and NPJ. CIELab values (L*, a*, and b*) of the specimens over 7 backgrounds, black, white, VitaB1, VitaA2, VitaA4, gold alloy (Au), and titanium (Ti), were obtained using a spectral radiometer. The relative translucency parameter (RTP) and color difference (∆E) of specimens over VitaB1, VitaA4, Au, and Ti were determined using VitaA2 as the control with the CIEDE2000 color difference equation. The normality of the data distribution was determined using the Shapiro-Wilk test. Differences among groups were analyzed using 2-way analysis of variance and the Student-Newman-Keuls (SNK) post hoc test (α=.05). The ∆E of specimens was analyzed according to perceptibility (∆E=0.8) and acceptability (∆E=1.8) thresholds using the 1 sample t test. The correlation between RTP and ∆E and RTP/∆E and thickness was examined using the Pearson correlation analysis. RESULTS: Statistically significant differences were observed in translucency and color masking ability among HT, LT, and NPJ (P<.05). The RTP value was the lowest for zirconia fabricated with NPJ (P<.001) and highest for HT (P<.001). Monolithic zirconia fabricated with NPJ had lower ∆E values than those of HT and LT for the same thickness and background (P<.05). A positive correlation was found in RTP and ∆E (P<.001). A negative correlation was observed in RTP and thickness (P<.001) and ∆E and thickness across a constant background (P<.001). CONCLUSIONS: Zirconia fabricated with NPJ was less translucent and had a greater color masking ability for discolored backgrounds than HT and LT.

Development and accuracy assessment of a crown lengthening surgery robot for use in the esthetic zone: An in vitro study.

STATEMENT OF PROBLEM: Crown lengthening surgery has been widely used to enhance the health and esthetics of anterior teeth, and its accuracy significantly influences surgical outcomes. However, the feasibility and accuracy of a robot system for crown lengthening surgery remains unknown. PURPOSE: The purpose of this in vitro study was to develop a crown lengthening surgery robot and evaluate its accuracy. MATERIAL AND METHODS: A robotic crown lengthening surgery system consisting of a robotic arm, a robotic software system, and an optical tracking device was designed. Intraoral scanning and cone beam computed tomography (CBCT) were performed on 18 artificial dentition models. The data were imported into the planning software program to synthesize a surgical path for gingivectomy and alveolectomy. Subsequently, a robotic arm equipped with a high-speed handpiece was used to perform these surgical procedures. Postoperatively, the models were rescanned for evaluation, with the accuracy (trueness ±precision) of the surgical outcomes of gingivectomy and alveolectomy being assessed from the trajectories in the highest, lowest, and overall regions. Differences between groups were analyzed by using the independent sample t test and the Levene test (α=.05). RESULTS: Crown lengthening surgery was feasible in vitro using the robot developed in this study. The overall robot-assisted crown lengthening surgery accuracy (trueness ±precision) of gingivectomy (0.23 ±0.08 mm) was significantly higher than that of alveolectomy (0.33 ±0.11 mm) (P<.05). CONCLUSIONS: Robot-assisted crown lengthening surgery had acceptable accuracy generally and can be considered a feasible treatment option.

Effect of build angle on the dimensional accuracy of monolithic zirconia crowns fabricated with the nanoparticle jetting technique.

STATEMENT OF PROBLEM: The build angle is an essential parameter in additive manufacturing. Its effect on the dimensional accuracy of zirconia restorations fabricated using the nanoparticle jetting (NPJ) technique is unknown. PURPOSE: The purpose of this in vitro study was to evaluate the effect of the build angle on the dimensional accuracy of monolithic zirconia complete crowns fabricated by using NPJ. MATERIAL AND METHODS: Standardized artificial right maxillary incisors and mandibular first molars were prepared for ceramic complete crowns. In total, 100 monolithic zirconia crowns were fabricated using NPJ at build angles of 0, 45, 90, 135, and 180 degrees (n=10/angle for incisors and molars). The dimensional accuracies in the external, marginal, and intaglio regions were determined by superimposing the scanned data and computer-aided design data on the crowns. Root mean square (RMS) values were used to analyze the accuracy of the zirconia crowns overall and at the external, marginal, and intaglio surfaces. The Shapiro-Wilk test was used to examine the normality of data distribution. Differences among test groups were assessed using a 1-way analysis of variance and the post hoc least significant difference test (α=.05). RESULTS: Significant differences were found in the accuracy of monolithic zirconia incisor and molar complete crowns in the external, marginal, and intaglio regions among the 5 build angles (P<.05). For incisors, the external RMS value was lowest for a build angle of 45 degrees (18.2 ±3.0 µm), the marginal and intaglio RMS values were lowest for a build angle of 135 degrees (47.4 ±10.7 and 26.5 ±6.1 µm, respectively), and the overall RMS values did not differ significantly among the 5 build angles (P>.05). For molars, build angles of 0 degrees and 180 degrees yielded the lowest RMS values overall (22.3 ±1.5 and 21.8 ±3.2 µm, respectively) and in the external (23.2 ±2.9 and 22.3 ±2.5 µm, respectively) and intaglio (22.2 ±3.7 and 21.2 ±4.6 µm, respectively) regions. No significant difference was observed in the marginal area among the 5 build angles (P>.05). The overall RMS values reflecting dimensional accuracy for the 5 build angles were between 23.5 and 26.7 µm for incisors and 21.8 and 26.2 µm for molars. CONCLUSIONS: The dimensional accuracy of monolithic zirconia crowns fabricated by using NPJ was affected by the build angle and was within clinically acceptable limits.

Dimensional accuracy and clinical adaptation of monolithic zirconia crowns fabricated with the nanoparticle jetting technique.

STATEMENT OF PROBLEM: The nanoparticle jetting (NPJ) technique is a recently developed additive manufacturing method that may have useful dental applications. The manufacturing accuracy and clinical adaptation of zirconia monolithic crowns fabricated with NPJ are unknown. PURPOSE: The purpose of this in vitro study was to compare the dimensional accuracy and clinical adaptation of zirconia crowns fabricated with NPJ and those fabricated with subtractive manufacturing (SM) and digital light processing (DLP). MATERIAL AND METHODS: Five standardized typodont right mandibular first molars were prepared for ceramic complete crowns, and 30 zirconia monolithic crowns were fabricated using SM, DLP, and NPJ (n=10) with a completely digital workflow. The dimensional accuracy at the external, intaglio, and marginal areas was determined by superimposing the scanned data and computer-aided design data of the crowns (n=10). Occlusal, axial, and marginal adaptations were evaluated by using a nondestructive silicone replica and dual scanning method. The 3-dimensional discrepancy was evaluated to determine clinical adaptation. Differences among test groups were analyzed by using a MANOVA and the post hoc least significant difference test for normally distributed data or the Kruskal-Wallis test with Bonferroni correction for nonnormally distributed data (α=.05). RESULTS: Significant differences were found in the dimensional accuracy and clinical adaptation among the groups (P<.001). The NPJ group had a lower overall root mean square (RMS) value for dimensional accuracy (22.9 ±1.4 µm) than the SM (27.3 ±5.0 µm) and DLP (36.4 ±5.9 µm) groups (P<.001). The NPJ group had a lower external RMS value (23.0 ±3.0 µm) than the SM group (28.9 ±5.4 µm) (P<.001) and equivalent marginal and intaglio RMS values than the SM group. The DLP group had larger external (33.3 ±4.3 µm), intaglio (36.1 ±10.7 µm), and marginal (79.4 ±12.9 µm) deviations than the NPJ and SM groups (P<.001). With regard to clinical adaptation, the marginal discrepancy was smaller in the NPJ group (63.9 ±27.3 µm) than in the SM group (70.8 ±27.5 µm) (P<.001). No significant differences were found between the SM and NPJ groups in terms of the occlusal (87.2 ±25.5 and 80.5 ±24.2 µm, respectively) and axial (39.1 ±19.7 and 38.4 ±13.7 µm, respectively) discrepancies. The DLP group had larger occlusal (239.0 ±60.1 µm), axial (84.9 ±29.1 µm), and marginal (140.4 ±84.3 µm) discrepancies than the NPJ and SM groups (P<.001). CONCLUSIONS: Monolithic zirconia crowns fabricated using NPJ have higher dimensional accuracy and clinical adaptation than those fabricated using SM or DLP.

Accuracy of three types of digital guides for crown lengthening surgery: An in vitro study.

Background/purpose: The guided protocols always yield a higher accuracy than freehand surgery. However, the accuracy of digital guides for crown lengthening surgery (CLS) is unknown. The purpose of this study was to evaluate the trueness of 3 types of digital guides for CLS. Materials and methods: Twenty individually designed maxillary models were divided into 4 groups according to surgical guides: type I (T1), type II (T2), type III (T3), and free-hand. T1 comprised a planed gingival margin at the tissue level. T2 included both the planed gingival margin and alveolar crest at the tissue level. T3 consisted of a planed gingival margin at the tissue level and an alveolar crest at the bone level. CLS was performed under the indication of the guides. Trueness of the guides was evaluated through the deviation of the gingival zenith and alveolar crest height. Results: The control group had higher vertical and horizontal distance deviations of gingival zenith compared to the 3 digital guide groups (P < 0.001). There were no significant differences among the 3 test groups in terms of gingival zenith deviations (P > 0.05). With regard to height deviation of alveolar crest, the control and T1 groups were higher than T2 group (P < 0.001), while T3 group had the lowest deviations among the 4 groups (P < 0.001). Conclusion: The digital guides assisted CLS procedures are more accurate than free-hand method. The trueness of type III guide was better than type I and type II.