A study on the machining accuracy of dental digital method focusing on dental inlay.

PURPOSE: The purpose of this study was to compare the cutting method and the lamination method to investigate whether the CAD data of the proposed inlay shape are machined correctly. MATERIALS AND METHODS: The Mesial-Occlusal shape of the inlay was modeled by changing the stereolithography (STL). Each group used SLS (metal powder) or SLA (photocurable resin) in the additive method, and wax or zirconia in the subtractive method (n=10 per group, total n=40). Three-dimensional (3D) analysis program (Geomagic Control X inspection software; 3D systems) was used for the alignment and analysis. The root mean square (RMS) in the 2D plane state was measured within 50 µm radius of eight comparison measuring points (CMP). Differences were analyzed using one-way analysis of variance and post-hoc Tukey's test were used (α=.05). RESULTS: There was a significant difference in RMS only in SLA and SLS of 2D section (P<.05). In CMP mean, CMP 4 (-5.3±46.7 µm) had a value closest to 0, while CMP 6 (20.1±42.4 µm) and CMP 1 (-89.2±61.4 µm) had the greatest positive value and the greatest negative value, respectively. CONCLUSION: Since the errors obtained from the study do not exceed the clinically acceptable values, the lamination method and the cutting method can be used clinically.

Accuracy (trueness and precision) of dental models fabricated using additive manufacturing methods.

OBJECTIVE: This study evaluated the accuracy (trueness and precision) of dental models fabricated using additive manufacturing (AM) methods such as PolyJet and fused deposition modeling (FDM). MATERIALS AND METHODS: 10 stone models were acquired for the control group by scanning a complete arch model. For the experimental groups, 10 PolyJet models and 10 FDM models were fabricated from digital impressions using an intraoral scanner. All 30 models were then scanned, and root mean square values were measured using three-dimensional (3D) analysis software. RESULTS: Trueness did not significantly differ between the stone and PolyJet models. The precision of the AM models was significantly higher than that of the stone models. The layer thicknesses of the FDM models were greater than those of the PolyJet models. CONCLUSION: The results of this study show that it might be possible for the dental models fabricated using additive manufacturing methods to be used in clinical settings.

Reproducibility of different coping arrangements fabricated by dental micro-stereolithography: Evaluation of marginal and internal gaps in metal copings.

BACKGROUND/PURPOSE: To evaluate the reproducibility of the marginal and internal gaps of metal copings fabricated using dental micro-stereolithography (µ-SLA), which is an additive manufacturing system. MATERIALS AND METHODS: A study cast of abutment tooth 46 was made from type-IV dental stone and was scanned to create a standard triangulation language file. Arrays of one (ORM), three (TRM), and six (SRM) resin copings were then fabricated on the µ-SLA build platform using investment, burnout, and casting (n = 12). The marginal and internal gaps of these metal copings were measured using a silicone-replica technique with a digital microscope (×160). The data obtained were analyzed using a non-parametric Kruskal-Wallis H test, a post-hoc Mann-Whitney U test, and a Bonferroni correction. RESULTS: The mean and standard deviation of the marginal gap for each group were measured and found to be 81.1 and 53.2 µm, 68.3 and 44.8 µm, and 90.3 and 57.7 µm for ORM, TRM, and SRM, respectively. There were no statistical differences in the marginal gaps of the three groups (p > 0.05). CONCLUSION: The marginal and internal gap of ORM, TRM and SRM groups were considered clinically acceptable.

Evaluation of accuracy and repeatability using CBCT and a dental scanner by means of 3D software.

OBJECTIVE: The objective of the present study was to compare and evaluate the accuracy of three-dimensional (3D) image data acquired from cone beam computed tomography (CBCT) and a dental scanner using 3D software. MATERIALS AND METHODS: After selecting the full-arch forms of the maxilla and mandible as the master cast, the master cast was scanned via a high-precision optical scanner for use as master model data. The model was scanned 12 times each using CBCT and a dental scanner. Scanned data were superimposed onto the master cast data for evaluation of accuracy and repeatability. RESULTS: Although significant differences in both accuracy and repeatability were seen between CBCT and dental scanner (P < 0.05), repeatability of the maxillary arch showed little difference, with CBCT and scanner having values of 17 ± 2 µm and 22 ± 5 µm, respectively. Meanwhile, repeatability of the mandibular arch with CBCT and scanner was 15 ± 0 µm and 19 ± 3 µm, respectively. Since good repeatability was shown, this demonstrated that data can be stably acquired. CONCLUSIONS: The present study demonstrated the feasibility of using a dental scanner to create a digital model as a substitute for a plaster model for use in orthodontic diagnosis and device fabrication.

A comparative study of additive and subtractive manufacturing for dental restorations.

STATEMENT OF PROBLEM: Digital systems have recently found widespread application in the fabrication of dental restorations. For the clinical assessment of dental restorations fabricated digitally, it is necessary to evaluate their accuracy. However, studies of the accuracy of inlay restorations fabricated with additive manufacturing are lacking. PURPOSE: The purpose of this in vitro study was to evaluate and compare the accuracy of inlay restorations fabricated by using recently introduced additive manufacturing with the accuracy of subtractive methods. MATERIAL AND METHODS: The inlay (distal occlusal cavity) shape was fabricated using 3-dimensional image (reference data) software. Specimens were fabricated using 4 different methods (each n=10, total N=40), including 2 additive manufacturing methods, stereolithography apparatus and selective laser sintering; and 2 subtractive methods, wax and zirconia milling. Fabricated specimens were scanned using a dental scanner and then compared by overlapping reference data. The results were statistically analyzed using a 1-way analysis of variance (α=.05). Additionally, the surface morphology of 1 randomly (the first of each specimen) selected specimen from each group was evaluated using a digital microscope. RESULTS: The results of the overlap analysis of the dental restorations indicated that the root mean square (RMS) deviation observed in the restorations fabricated using the additive manufacturing methods were significantly different from those fabricated using the subtractive methods (P<.05). However, no significant differences were found between restorations fabricated using stereolithography apparatus and selective laser sintering, the additive manufacturing methods (P=.466). Similarly, no significant differences were found between wax and zirconia, the subtractive methods (P=.986). The observed RMS values were 106 µm for stereolithography apparatus, 113 µm for selective laser sintering, 116 µm for wax, and 119 µm for zirconia. Microscopic evaluation of the surface revealed a fine linear gap between the layers of restorations fabricated using stereolithography apparatus and a grooved hole with inconsistent weak scratches when fabricated using selective laser sintering. In the wax and zirconia restorations, possible traces of milling bur passes were observed. CONCLUSIONS: The results indicate that the accuracy of dental restorations fabricated using the additive manufacturing methods is higher than that of subtractive methods. Therefore, additive manufacturing methods are a viable alternative to subtractive methods.

Three-dimensional analysis of marginal and internal fit of copings fabricated with polyetherketoneketone (PEKK) and zirconia.

PURPOSE: The purpose of this in vitro study was to compare and analyze the three-dimensional marginal and internal fit of PEKK and zirconia copings. METHODS: Two acrylic models of the right maxillary canine, first molar were fabricated as master dies and duplicated by one-step dual viscosity impressions. Five stone replicas from each model were digitized with a blue-light scanner and copings were machined from Pekkton and Zirconia blanks. The inner surface of all the copings and two original acrylic models were digitized by a highly accurate optical scanner. By superimposing the digitized coping data with the CAD-reference die three-dimensionally, visual fit-discrepancies were drawn by calculating the root mean square (RMS) and visualized on a color-difference map. Each calculated RMS-value was statistically analyzed by 3-way ANOVA. In addition, Student's t-test was conducted in order to verify the significance (α=.05) of fit-discrepancies based on the type of abutment tooth and the materials. RESULTS: Mean RMS-values for marginal fit (internal fit) ranged from 51.64±1.5 (36.12±1.34) to 69.62±8.11 (41.6±1.63)µm. Differences in marginal fit (canine: P=.001; molar: P=.047) and internal fit (canine: P=.017; molar: P=.046) were statistically significant. The results of the 3-way ANOVA showed statistically significant differences in the RMS values of the two groups for the material (P<.001), the types of the abutment tooth (P<.001), and the measured region (P<.001). CONCLUSIONS: The marginal and internal fit of both PEKK and zirconia copings of both canine and molar were within the clinically acceptable range. However, the PEKK presented better fitness compared with the zirconia.

In vitro assessment of the marginal and internal fits of interim implant restorations fabricated with different methods.

STATEMENT OF PROBLEM: The fit of an interim implant restoration (IIR) is important for the effective treatment of patients with partial edentulism. However, no clinical trials have evaluated the marginal and internal fittings achieved with various fabrication methods. PURPOSE: The purpose of this in vitro study was to evaluate and compare the marginal and internal discrepancies in IIRs produced with 3 different methods. MATERIAL AND METHODS: Partially edentulous maxillary and mandibular casts from a transfer abutment were used. Prostheses were prepared by applying wax to the implant abutment. Shapes were copied using putty. IIRs were fabricated from poly(methyl methacrylate) for a conventional system with thermoplastic resin (CTR, n=40), a 4-axial milling machine with a crown-designed standard template library for a subtractive manufacturing system with Pekkton milling (SPM, n=40), and a 3-dimensional printer for an additive manufacturing system with digital light processing (ADL, n=40). The marginal and internal discrepancies were evaluated in each group using the silicone replica technique. The space between the abutment and the intaglio surface of the prosthesis was evaluated with a digital microscope (×160 magnification). Results were analyzed with nonparametric 2-way analysis of variance using rank-transformed values and Tukey post hoc test (α=.05). RESULTS: The fabricated IIRs were significantly different at all points (P<.001). Moreover, ADL was superior to CTR and SPM. IIRs were significantly different only at the intermarginal discrepancy (the vertical discrepancy between the crown and the point where the margin becomes round and changes to the axial wall), the axiogingival discrepancy (the vertical discrepancy between the internal surface and the axial wall adjacent to the gingival wall of the abutment), and the occlusal discrepancy (the vertical discrepancy between the occlusal wall of the abutment and the internal surface; this discrepancy comprises the internal discrepancy; P<.001). No significant differences were found among the IIRs at the marginal discrepancy (the vertical discrepancy between the abutment margin and the crown; P>.111) and the axio-occlusal discrepancy (the vertical discrepancy between the axial wall adjacent to the occlusal wall of the abutment and the internal surface; this discrepancy comprises the internal discrepancy; P>.257). CONCLUSIONS: ADL was superior to the other 2 fabrication methods. However, all 3 methods were suitable because they produced a marginal fit which was within the clinically acceptable range.

Translucency of zirconia-based pressable ceramics with different core and veneer thicknesses.

STATEMENT OF PROBLEM: Little information is available on the translucency of zirconia-based pressable ceramic restorations with a pressed ceramic veneer and zirconia core in various thickness combinations. PURPOSE: The purpose of this in vitro study was to assess the translucency of 3 types of zirconia-based pressable ceramics for different core-veneer thickness combinations. MATERIAL AND METHODS: A bilayered ceramic specimen was prepared with a pressable ceramic (IPS e.max Zirpress, Initial IQ, Rosetta UltraPress) veneer over a zirconia core (Zenostar Zr). Three groups of specimens (n=7) were formed with the following core+veneer thicknesses: 1 +0.5 mm, 0.7 +0.8 mm, and 0.5 +1 mm. To obtain consistent thickness and high translucency, all specimens were subjected to surface grinding with a grinding machine. To eliminate the effect of differences in roughness on the translucency, the surface roughness of the ground specimens was measured with a scanning profiler, and the consistency of these measured values was verified through statistical analysis. The luminous transmittance of the specimens was measured with a spectrophotometer. The effects of the pressable ceramic type and core-veneer thickness combination on transmittance were assessed using a 2-way ANOVA (α=.05). RESULTS: The consistency of the surface roughness among the tested specimens was confirmed using a 1-way ANOVA and the Tukey HSD post hoc test (P<.05). The luminous transmittance exhibited a statistically significant dependence on both the type of pressable ceramic and the core-veneer thickness combination (P<.05). CONCLUSIONS: The type of pressable ceramic and core-veneer thickness combination affected the translucency of the restoration.

Accuracy of complete-arch model using an intraoral video scanner: An in vitro study.

STATEMENT OF PROBLEM: Information on the accuracy of intraoral video scanners for long-span areas is limited. PURPOSE: The purpose of this in vitro study was to evaluate and compare the trueness and precision of an intraoral video scanner, an intraoral still image scanner, and a blue-light scanner for the production of digital impressions. MATERIAL AND METHODS: Reference scan data were obtained by scanning a complete-arch model. An identical model was scanned 8 times using an intraoral video scanner (CEREC Omnicam; Sirona) and an intraoral still image scanner (CEREC Bluecam; Sirona), and stone casts made from conventional impressions of the same model were scanned 8 times with a blue-light scanner as a control (Identica Blue; Medit). Accuracy consists of trueness (the extent to which the scan data differ from the reference scan) and precision (the similarity of the data from multiple scans). To evaluate precision, 8 scans were superimposed using 3-dimensional analysis software; the reference scan data were then superimposed to determine the trueness. Differences were analyzed using 1-way ANOVA and post hoc Tukey HSD tests (α=.05). RESULTS: Trueness in the video scanner group was not significantly different from that in the control group. However, the video scanner group showed significantly lower values than those of the still image scanner group for all variables (P<.05), except in tolerance range. The root mean square, standard deviations, and mean negative precision values for the video scanner group were significantly higher than those for the other groups (P<.05). CONCLUSIONS: Digital impressions obtained by the intraoral video scanner showed better accuracy for long-span areas than those captured by the still image scanner. However, the video scanner was less accurate than the laboratory scanner.