Influence of various fabrication techniques and porcelain firing on the accuracy of metal-ceramic crowns.

BACKGROUND: The fit of a metal-ceramic restoration is essential to its long-term durability. Regarding marginal and internal fit, there is not enough information about the technologies used in the production of metal-ceramic restorations. The aim of this in vitro study is to compare, both before and after porcelain firing, the marginal, axial, axio-occlusal, and occlusal fit of metal-ceramic restorations manufactured using casting, additive or subtractive computer-aided design, and computer-aided manufacturing techniques (CAD/CAM). METHODS: CAD/CAM were used to create 50 prepared maxillary first molar-shaped Co-Cr die models, which were randomly divided into 5 groups (n = 10). Cobalt-chrome copings were produced by casting (C), hard metal milling (HM), soft metal milling (SM), selective laser melting (SLM), and selective laser sintering (SLS) techniques. Before and after porcelain firing, discrepancies of the copings were measured using the silicone replica technique. The data obtained by measurements with a stereomicroscope at x80 magnification were analyzed statistically in the SPSS program. The ROBUST three-way analysis of variance (ANOVA) method was used to compare the discrepancy values. RESULTS: There were statistically significant differences among fabrication methods (P < .001). The HM method showed the highest discrepancy (90.1 µm), and the C (63 µm) method showed the lowest discrepancy in terms of the die model- crown fit. The C, SLS, and SM methods (63 µm; 61.6 µm; 67.7 µm) were statistically similar (P > .001). The highest discrepancy was observed on the occlusal area (87.1 µm), and the lowest discrepancy was observed on the axial area (47.7 µm) of the coping. Porcelain firing had a decrease in the discrepancy values (P = .001). CONCLUSION: All CAD/CAM techniques are appropriate for clinical use; selective laser sintering and soft milling can be the more recommended methods for the compatibility of metal-porcelain restorations, as they have lower discrepancy values than the SLM and HM methods.

Effect of 3D printing technology and print orientation on the trueness of additively manufactured definitive casts with different tooth preparations.

OBJECTIVES: To evaluate the fabrication trueness of additively manufactured maxillary definitive casts with various tooth preparations fabricated with different 3-dimensional (3D) printers and print orientations. METHODS: A maxillary typodont with tooth preparations for a posterior 3-unit fixed partial denture, lateral incisor crown, central incisor and canine veneers, first premolar and second molar inlays, and a first molar crown was digitized with an industrial scanner. This scan file was used to fabricate definitive casts with a digital light processing (DLP) or stereolithography (SLA) 3D printer in different orientations (0-degree, 30-degree, 45-degree, and 90-degree) (n = 7). All casts were digitized with the same scanner, and the deviations within each preparation site were evaluated. Generalized linear model analysis was used for statistical analysis (α = 0.05). RESULTS: The interaction between the 3D printer and the print orientation affected measured deviations within all preparations (P ≤ 0.001) except for the lateral incisor crown and canine veneer (P ≥ 0.094), which were affected only by the main factors (P < 0.001). DLP-90 mostly led to the highest and DLP-0 mostly resulted in the lowest deviations within posterior tooth preparations (P ≤ 0.014). DLP-30 led to the lowest deviations within the first premolar inlay and DLP-45 led to the lowest deviations within the central incisor veneer preparation (P ≤ 0.045). CONCLUSIONS: Posterior preparations of tested casts had the highest trueness with DLP-0 or DLP-30, while central incisor veneer preparations had the highest trueness with DLP-45. DLP-90 led to the lowest trueness for most of the tooth preparations. CLINICAL SIGNIFICANCE: Definitive casts with tooth preparations fabricated with the tested DLP 3D printer and the print orientation adjusted on tooth preparation may enable well-fitting restorations. However, 90-degree print orientation should be avoided with this 3D printer, as it led to the lowest fabrication trueness.

Effect of 3D printer, implant analog and angulation on the accuracy of analog position in implant casts.

OBJECTIVES: To evaluate the accumulative effect of 3D printer, implant analog systems, and implant angulation on the accuracy of analog position in implant casts. METHODS: A reference cast, presenting a case of a three-unit implant-supported prosthesis, was scanned with a coordinate measurement machine, producing the first reference data set (CMM, n = 1). The second reference data set (n = 10) was prepared using an intraoral scanner (IOS) (Trios4). Test quadrant casts were produced using three DLP type 3D printers, Max (MAX UV385), Pro (PRO 4K65 UV), and Nex (NextDent 5100), and three implant analog systems, El (Elos), Nt (Nt-trading), and St (Straumann) (n = 90). Stone casts were also produced via analog impressions (Stone, n = 10). After digitization, the accuracy of 3D distance, local angulation (angle between implants) and global angulation (angle between the implant center axis and an axis perpendicular to the global plane) was evaluated by comparing the reference (CMM, IOS), test (3D print), and control (Stone) groups using metrology software. Data were statistically analyzed using three-way ANOVA and Tukey`s tests (α = 0.05). RESULTS: IOS was truer in 3D implant distance and more precise in capturing local angulation than Stone (p ≤ 0.05). Other measurements were similar between both groups (p > 0.05). The amount of error introduced in the workflow by IOS and 3D printing was mostly similar (p > 0.05). 3D printed casts had similar or even higher accuracy than Stone group (p > 0.05). In most cases, higher trueness was achieved when using PRO 4K65 UV 3D printer and Elos implant analog system (p ≤ 0.05). CONCLUSION: 3D printer, implant analog system, and implant angulation have a significant effect on the accuracy of analog position in implant casts. Limited-span implant-supported cases could be reproduced digitally with similar accuracy as conventional methods. CLINICAL SIGNIFICANCE: A fully digital workflow with a carefully selected 3D printer and implant analog system can increase the accuracy of digitally produced implant casts with comparable accuracy to conventional workflow.

Comparing the trueness of 3D printing and conventional casting for the fabrication of removable partial denture metal frameworks for patients with different palatal vault depths: An in vitro study.

STATEMENT OF PROBLEM: The success of a removable partial denture depends on its fit, and, with conventional casting, the framework is more distorted in patients with a deep palatal vault. Questions remain about whether the three-dimensional (3D) printing technique for fabricating a framework can improve the accuracy of fit for these patients. PURPOSE: The purpose of this in vitro study was to compare the trueness of metal frameworks fabricated by selective laser melting, 3D printing pattern casting, and conventional casting for different palatal vault depths. MATERIAL AND METHODS: A total of 30 partially edentulous maxillary casts were custom-made in 15 medium and 15 deep palatal vaults. All stone casts were scanned as reference models in digital files. For the medium palatal vault casts, Co-Cr frameworks of the conventional casting (CON) group (n=5) were fabricated with the lost wax technique. For the 3D printing pattern casting (PPC) group (n=5), wax patterns of the framework were printed, followed by metal casting. The frameworks created for the selective laser melting (SLM) group (n=5) were printed directly by using the SLM machine. The same procedures were followed for the deep palatal vault group. All the metal frameworks were scanned and superimposed with the reference casts by using the Geomagic Control X software program. Discrepancies were measured as mean ±standard deviation (trueness), and the data were statistically analyzed with a 2-way ANOVA test to evaluate the interaction of 2 independent factors (fabrication techniques and palatal vault depths) on a trueness outcome (α=.05). RESULTS: The lowest mean ±standard deviation value was 0.092 ±0.023 mm, found from the SLM framework with deep palatal vault group, while the highest value was 0.194 ±0.017 mm, found from the CON framework with deep palatal vault group. Different fabrication techniques interacted with different palatal vault depths in terms of trueness (P<.05); however, no significant differences were observed in the medium palatal vault groups (P>.05). Additionally, color mapping demonstrated the gaps of metal frameworks among the 6 groups. CONCLUSIONS: With the conventional casting technique, the accuracy of the metal framework was affected by the depth of the palate. For medium palatal vaults, all fabricated frameworks had clinically acceptable fit. For deep palatal vaults, the SLM frameworks showed the lowest discrepancy. As a result, the SLM technique is advised for fabricating a better-fitting metal framework for patients with a deep palatal vault.

Positional accuracy of a single implant analog in additively manufactured casts in biobased model resin.

OBJECTIVES: To evaluate the positional accuracy of implant analogs in biobased model resin by comparing them to that of implant analogs in model resin casts and conventional analogs in dental stone casts. METHODS: Polyvinylsiloxane impressions of a partially edentulous mandibular model with a single implant were made and poured in type IV dental stone. The same model was also digitized with an intraoral scanner and additively manufactured implant casts were fabricated in biobased model resin (FotoDent biobased model) and model resin (FotoDent model 2 beige-opaque) (n = 8). All casts and the model were digitized with a laboratory scanner, and the scan files were imported into a 3-dimensional analysis software (Geomagic Control X). The linear deviations of 2 standardized points on the scan body used during digitization were automatically calculated on x-, y-, and z-axes. Average deviations were used to define precision, and 1-way analysis of variance and Tukey HSD tests were used for statistical analyses (α = 0.05). RESULTS: Biobased model resin led to higher deviations than dental stone (all axes, P ≤ 0.031) and model resin (y-axis, P = 0.015). Biobased model resin resulted in the lowest precision of implant analog position (P ≤ 0.049). The difference in the positional accuracy of implant analogs of model resin and stone casts was nonsignificant (P ≥ 0.196). CONCLUSIONS: Implant analogs in biobased model resin casts mostly had lower positional accuracy, whereas those in model resin and stone casts had similar positional accuracy. Regardless of the material, analogs deviated more towards mesial, while buccal deviations in additively manufactured casts and lingual deviations in stone casts were more prominent.

Influence of base designs on the manufacturing accuracy of vat-polymerized diagnostic casts using two different technologies.

STATEMENT OF PROBLEM: Diagnostic casts can incorporate different base designs and be manufactured using different vat-polymerization technologies. However, the influence of the interrelation between the base design and the 3D printing technology on the casts' final accuracy remains unclear. PURPOSE: The purpose of this in vitro study was to assess the influence of different base designs of 3D printed casts on the accuracy of 2 vat-polymerization technologies. MATERIAL AND METHODS: A digital maxillary cast was obtained and used to generate 3 different base designs: solid (S group), honeycombed (HC group), and hollow (H group). The HC and H groups were subdivided based on the wall thickness of the cast design, resulting in 2 subgroups with thicknesses of 1 mm (HC1 and H1) and 2 mm (HC2 and H2) (N=100, n=10). Eleven reference cubes were added to each specimen for subsequent measurements. Specimens were manufactured by using 2 vat-polymerization 3D printers: Nextdent 5100 (ND group) and Sonic Mini 4K (SM4K group) and a resin material suitable for both 3D printers (Nextdent Model 2.0). A coordinate measuring machine quantified the linear and 3-dimensional discrepancies between the digital cast and each reference specimen. Trueness was defined as the average absolute dimensional discrepancy between the virtual cast and the specimens produced through additive manufacturing (AM), while precision was delineated as the standard deviation in dimensional discrepancies between the digital cast and the AM specimens. The data were analyzed using the Kruskal-Wallis and Mann-Whitney U pairwise comparison tests (α=.05). RESULTS: For the NextDent group the trueness ranged from 21.83 µm to 28.35 µm, and the precision ranged from 17.82 µm to 37.70 µm. For the Phrozen group, the trueness ranged from 45.15 µm to 64.51 µm, and the precision ranged from 33.51 µm to 48.92 µm. The Kruskal-Wallis test showed significant differences on the x-, y-, and z-axes and in the 3D discrepancy (all P<.001). On the x-axis, the Mann-Whitney U test showed significant differences for the Phrozen group between the H-2 and H-1 groups (P=.001), H-2 and S groups (P<.001), and HC-2 and S groups (P=.012). On the y-axis, significant differences were found in the Phrozen group between the H-2 and H-1 groups (P=.001), the H-2 and S, H-1 and HC-1, and HC-1 and S groups (P<.001), the H-1 and HC-2 groups (P=.007), and the HC-2 and S groups (P=.009). The NextDent group exhibited significant differences, particularly among the HC-1 and H-2 groups (P=.004), H-1 (P=.020), and HC-2 (P=.001) groups; and on the z-axis significant differences were found in the Phrozen group between the H-2 and H-1 and S groups and the HC-2 group and H-1 and S groups (both P<.001). In the NextDent group, significant differences were found between the H-2 and HC-2 (P=.047) and HC-1 (P=.028) groups. For the 3D discrepancy analysis, significant differences were found in the Phrozen group between the H-2 and H-1 and S groups (P<.001), the H-1 and HC-2 groups (P=.001), the S and HC-1 and HC-2 groups (P<.001), and the H-1 and HC-1 groups (P=.002). In the NextDent group, significant differences were observed between the H-2 and HC-1 groups (P=.012). CONCLUSIONS: The accuracy of digital casts depends on the manufacturing trinomial and base design of the casts. The honeycomb and hollow based designs provided the highest accuracy in the NextDent and Phrozen groups respectively for the material polymer tested. All specimens fell in the clinically acceptable range.

Fit accuracy in the rest region of RPDs fabricated by digital technologies and conventional lost-wax casting: a systematic review and meta-analysis.

BACKGROUND: Digital technologies have recently been introduced into the fabrication of removable partial dentures (RPDs). However, it is still unclear whether the digitally fabricated RPDs fit better than conventionally cast ones in the rest region. The aim of this study was to evaluate the fit accuracy in the rest region of RPDs fabricated by digital technologies and compare it to those made by conventional lost-wax (CLW) technique. METHODS: A comprehensive search was conducted in Cochrane Library, PubMed, EMbase, Web of Science and SpringerLink. Studies published up to August 2022 were collected. Two authors analyzed the studies independently and assessed the risk of bias on the modified methodological index for non-randomized studies (MINORS) scale. The mean values of gap distance between rests and corresponding rest seats of each study were extracted as outcome. A random-effects model at a significance level of P < 0.05 was used in the global comparison and subgroup analysis was carried out. RESULTS: Overall, 11 articles out of 1214 complied with the inclusion criteria and were selected, including 2 randomized controlled trials (RCTs), 1 non-randomized clinical trial and 8 in vitro studies. Quantitative data from Meta-analysis revealed that fit accuracy in the rest region of RPDs fabricated with CLW showed no statistically significant difference with digital techniques (SMD = 0.33, 95%CI (-0.18, 0.83), P = 0.21). Subgroup analysis revealed a significantly better fit accuracy of CLW-fabricated RPDs in the rest region than either additive manufacturing (AM) groups or indirect groups (P = 0.03, P = 0.00), in which wax or resin patterns are milled or printed before conventional casting. While milled RPDs fit significantly better than cast ones in the rest region (P = 0.00). With digital relief and heat treatment, hybrid manufactured (HM) clasps obtained better fit accuracy in the rest region (P < 0.05). In addition, finishing and polishing procedure had no significant influence in the fit accuracy in all groups (P = 0.83). CONCLUSIONS: RPDs fabricated by digital technologies exhibit comparable fit accuracy in rest region with those made by CLW. Digital technologies may be a promising alternative to CLW for the fabrication of RPDs and additional studies are recommended to provide stronger evidence. TRIAL REGISTRATION: CRD42020201313.

Limitations of reuse for silver-palladium alloys -Evaluating post-recasting heat treatment impact on corrosion resistance.

The aim of this study was to investigate the effect of repeated casting and heat treatment on the corrosion resistance of a commercial Ag-Pd-Cu-Au alloy as evaluated by electrochemical techniques. After repeated casting, the fifth cast of the Ag-Pd-Cu-Au alloy exhibited dramatic degradation of properties, although upon heat treatment, this corrosion resistance did improve. Despite the improvement by heat treatment, after five castings, this alloy may not have satisfactory hardness for clinical use. These results of this study demonstrate that, up to the fourth cast and heat treatment, the Ag-Pd-Cu-Au alloy has acceptable corrosion resistance and hardness.

Three-dimensional evaluation of the dental arch in cleft lip and palate after prosthetic treatment.

PURPOSE: This study aimed to evaluate the stability of the surface of the maxillary teeth and mucosa in cleft lip and palate (CLP) patients with a maxilla defect or tissue deficiency according to the duration of observation and cleft type. METHODS: Pairs of maxillary casts taken from 18 patients at different time points after prosthodontic treatment were investigated in this study. All 36 casts were scanned with an intraoral scanner, and the acquired images were saved in standard tesselation language (STL) files. The two STL files for each patient were then superimposed using three-dimensional (3D) evaluation software, with 3D deviations shown as a color map. Areas with a 3D deviation within ±0.100 mm were defined as stable. The influence of cleft type and duration of observation on the ratio of stable areas to the entire maxillary surface comprising the teeth and mucosa was investigated using multiple regression analysis. Statistical significance was set at p <0.05. RESULTS: Multiple regression analysis showed that the duration of observation was significantly associated with the stable area ratio (B = -23.463, P<.001), whereas cleft type was not (ß = 0.13, P = 0.301). CONCLUSIONS: The maxillary teeth and mucosa of CLP patients changed over time, with stable areas showing a negative correlation with the observation period. However, the stability of the dental arch was not significantly affected by the cleft type. 3D analysis of the casts of CLP patients allowed for measurements and to accurately assess relapse of the maxillary arch after prosthetic treatment.

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

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 computed tomography (CBCT) scanning (CCS) methods. The maxillary and mandibular dental casts of 15 patients who needed CBCT scans for oral examination or treatment were digitized via four methods. 12 linear distance measurements of all digital dental casts were selected and acquired with software and compared to those of the reference plaster cast to evaluate the dimensional accuracy. Three-dimensional deviation analysis of the IPS, IOS and CCS groups with respect to the reference PCS group was performed to evaluate the morphological accuracy. The discrepancy in linear distances between the digital dental casts and reference plaster casts was statistically significant (p < 0.01). The dimensional accuracies of the PCS (0.06 ± 0.12 mm) and IPS (0.03 ± 0.05 mm) casts were better than those of the IOS (0.37 ± 0.30 mm) and CCS (0.54 ± 0.40 mm) casts. The one-sample t test showed that there were statistically significant differences between the discrepancies in 8 of the linear distances for the PCS group and 9 of the linear distances for the IPS group between the digital dental casts and reference plaster casts, with an ideal error of 0.00 (p < 0.05). The sequence of morphological accuracy from good to poor was maxillary and mandibular IPS, mandibular IOS; maxillary IOS; and maxillary and mandibular CCS. The accuracy of the digital dental casts from the PCS and IPS methods was greater than that of IOS and CCS methods. Although accuracy of the digital dental cast from IOS was low, it satisfied the clinical requirements for fixed restorations in small units. The accuracy of the digital dental cast from CCS was poorest and could only be used for procedures with lower accuracy requirements.

Analysis of microstructure and fatigue of cast versus selective laser-melted dental Co-Cr alloy.

STATEMENT OF PROBLEM: The forces exerted on teeth and prostheses during mastication are repeated and dynamic, resulting in fatigue damage to dental prostheses. Most fractures of dental restorations are fatigue failure. The 4-point bend fatigue behavior of Co-Cr-Mo-W alloys manufactured by investment casting (CAST) and selective laser melting (SLM) has received little attention. PURPOSE: The purpose of this in vitro study was to evaluate the 4-point bend fatigue property of dental Co-Cr alloys and determine the relationship between microstructure and the 4-point bend fatigue property of Co-Cr alloys created by traditional casting and SLM. These can guide the use of Co-Cr alloy in dentistry. MATERIAL AND METHODS: Co-Cr-Mo-W alloys were fabricated with a dimension of 45×2×2 mm by investment casting and SLM. The 3-point bend test measured the ultimate bend strength with 3 specimens in each group. The 4-point bend fatigue test evaluated the fatigue life under various stresses, with 6 specimens in each group. The specimens were mechanically ground, polished, and electrochemically etched. Scanning electron microscopy was used to identify the microstructures of both etched specimens and fracture surfaces. X-ray diffraction investigations were used to determine the phases. Significant differences in the bend strength were analyzed by using the independent samples t test (α=.05), and the fatigue test was analyzed with ANCOVA (α=.05). RESULTS: The mean ±standard deviation bend strength of SLM specimens was 1837 ±3 MPa, higher than the 1200 ±6 MPa for CAST specimens (P<.05). The maximum bend stress of the SLM specimens without fatigue failure was 735 MPa, which was statistically higher than the 394 MPa for CAST specimens (P<.05). The microstructure characteristics of the SLM alloy contributed to its excellent fatigue performance. In SLM alloy, the γ phase constituted the majority with some ε and Laves phases, while the cast alloy possessed higher ε and Laves phases. The grains of SLM alloy were equiaxed and fine, and the second phases were fine and dispersive. In contrast, the cast alloy possessed clear dendrites, and the second phases were sizable. CONCLUSIONS: The SLM dental Co-Cr-Mo-W alloy had statistically better 4-point bend fatigue properties than cast alloy, which was associated with an improved microstructure.

Electrochemical characterization of three types of Co-Cr based alloys manufactured by casting and selective laser melting according to ISO 10271.

OBJECTIVE: To characterize the effect of elemental composition and manufacturing process on the electrochemical properties of Co-Cr-Mo, Co-Cr-W and Co-Cr-Mo-W alloys. METHODS: Six Co-Cr based alloys were included in this study. All alloys are Co-Cr based alloys, classified in three different types according to their elemental composition. The first group has Mo as the third alloying element while the second one has W instead of Mo. The third one has both alloying elements. The groups are further divided by the manufacturing process (casting or Selective Laser Melting(SLM)). All groups were subjected to static immersion, open circuit potential, anodic scan, SEM/EDX analysis, static and cyclic tarnish testing according to ISO 10271 requirements. The ionic release was evaluated by inductively coupled plasma mass spectrometry and the results were statistically analyzed by two way ANOVA and Tukey test (a=0.05). RESULTS: No statistical differences were identified for Co-Cr-Mo alloy for all elements and their total ionic release between casting and SLM manufacturing processes, in contrast to significantly lower values for SLM groups for the other two groups. All groups tested demonstrated similar performance in OCP and AS testing while no gross elemental changes before and after AS were identified following EDX analysis. All alloys fulfilled the requirements of tarnish resistance CONCLUSIONS: The ionic release is dependent on alloy type and manufacturing process while all groups were found to fulfill the requirements of international standards for ionic release, corrosion and tarnish resistance and thus an acceptable clinical performance is anticipated.

Effects of build orientation on adaptation of casting patterns for three-unit partial fixed dental prostheses fabricated by using digital light projection.

STATEMENT OF PROBLEM: The lost-wax technique is commonly used for fabricating partial fixed dental prostheses. The casting patterns can be fabricated by using vat photopolymerization (a type of additive manufacturing), but the adaptation of these casting patterns has not been elucidated. PURPOSE: The purpose of this in vitro study was to evaluate the effect of build orientation on the adaptation of casting patterns fabricated by digital light projection (DLP). MATERIAL AND METHODS: A 3-unit partial fixed dental prosthesis with mandibular left second premolar and second molar abutment teeth was scanned and virtually designed with a computer-aided design software program. The cement space was designed to be 30 µm. Specimens were fabricated with 3 build orientations: 0 degrees (with the occlusal surface parallel to the platform), 30 degrees, and 45 degrees (by rotating the file along the long axis). The casting patterns were fabricated by using DLP (Cara Print 4.0) with a photopolymerizable monomer (dima Print Cast Q). Photopolymerization, cleaning, and postpolymerization processes were performed according to the manufacturer's instructions. The adaptation of the specimens was examined by using a silicone replica method. The vertical marginal discrepancy and axial wall, occlusal, and marginal gaps were measured by using a digital measuring microscope. The effect of build orientation at each cross-sectional area was statistically analyzed by using the Kruskal-Wallis test followed by the pairwise Wilcoxon rank sum test with Bonferroni correction (α=.05). RESULTS: Excess polymerized resin was observed along the intaglio buccal wall at build orientations of 30 degrees and 45 degrees. Vertical marginal discrepancies in the buccolingual section ranged from -50 to 248 µm, while those in the mesiodistal section ranged from -25 to 182 µm. The gaps in the buccolingual section ranged from 0 to 236 µm, while those in the mesiodistal section ranged from 0 to 177 µm. According to the observation of vertical marginal discrepancies and gaps, the 30-degree specimens inclined during insertion, and the 45-degree specimens were not completely seated. However, the marginal gaps of the 0- and 30-degree specimens were within the clinically acceptable limit of 120 µm. CONCLUSIONS: The limited data indicated that the build orientation influenced the adaptation of casting patterns for 3-unit partial fixed dental prostheses fabricated by using DLP. A build orientation of 0 degrees is recommended for fabricating casting patterns for 3-unit partial fixed dental prostheses because no excess polymerization of the intaglio buccal wall was observed.

Selective laser sintering versus conventional lost-wax casting for single metal copings: A systematic review and meta-analysis.

STATEMENT OF PROBLEM: Evidence comparing the marginal and internal fit of single metal copings fabricated via selective laser sintering and conventional lost-wax casting is inadequate. PURPOSE: The purpose of this systematic review was to compare the fit of single metal copings fabricated via selective laser sintering and lost-wax casting. Moreover, the effects of different variables on fit accuracy were determined. MATERIAL AND METHODS: Google Scholar, ScienceDirect, SpringerLink, and Wiley databases were searched electronically as well as manually. The mean absolute marginal gap, marginal gap, internal gap, axial gap, and occlusal gap values of single metal copings fabricated via selective laser sintering and lost-wax casting were statistically analyzed to determine and evaluate the factors affecting the fit accuracy (α=.05). RESULTS: Single metal copings fabricated via selective laser sintering had mean absolute marginal gaps and occlusal gaps similar to those of copings fabricated via lost-wax casting, based on a subgroup meta-analysis of gaps evaluated using stereomicroscopy (P>.05). The fit of single metal copings was not affected by the type of tooth (P>.05). The conventional impression, the indirect digital scan, and the direct digital scan led to similar values of mean axial gap, internal gap, and marginal gap for the copings fabricated via lost-wax casting (P>.05). The indirect and direct digital scans led to similar values of mean axial gap, internal gap, and marginal gap for the copings fabricated via selective laser sintering (P>.05). Printed wax patterns provided significantly smaller mean axial gap values than milled plastic or milled wax patterns for the copings fabricated via lost-wax casting (P<.05). Printed, milled, and conventional wax patterns had similar mean marginal gaps and internal gaps for the copings fabricated via lost-wax casting (P>.05). For single copings fabricated via lost-wax casting, Ni-Cr and Co-Cr had similar mean internal gaps (P>.05). CONCLUSIONS: No statistically significant differences were found between single metal copings fabricated via selective laser sintering and lost-wax casting. Selective laser sintering can satisfy the clinical requirement for single metal copings.

Comparison of the internal fit of metal crowns fabricated by traditional casting, computer numerical control milling, and three-dimensional printing.

This experimental study aimed to compare the internal fit (marginal fit and internal discrepancy) of metal crowns fabricated by traditional casting and digital methods (computer numerically controlled (CNC) milling and three-dimensional [3D] printing). Thirty standard master abutment models were fabricated using a 3D printing technique with digital software. Metal crowns were fabricated by traditional casting, CNC milling, and 3D printing. The silicon replica method was used to measure the marginal and internal fit. A thin layer of low-viscosity polyvinyl siloxane material was placed inside each crown and on the die (like a seat) until the material was set. Replicas were examined at four reference points under a microscope: the central pit (M1), cusp tip (M2), axial wall (M3), and margin (M4). The measured data were analyzed using a one-way analysis of variance (ANOVA) to verify statistical significance, which was set at p < 0.05. In the traditional casting group, the minimum distance measured was at M3 (90.68 ± 14.4 µm) and the maximum distance measured was at M1 (145.12 ± 22 µm). In the milling group, the minimum distance measured was at M3 (71.85 ± 23.69 µm) and the maximum distance measured was at M1 (108.68 ± 10.52 µm). In the 3D printing group, the minimum distance measured was at M3 (100.59 ± 9.26 µm) and the maximum distance measured was at M1 (122.33 ± 7.66 µm). The mean discrepancy for the traditional casting, CNC milling, and 3D printing groups was 120.20, 92.15, and 111.85 µm, respectively, showing significant differences (P < 0.05). All three methods of metal crown fabrication, that is, traditional casting, CNC milling, and 3D printing, had values within the clinically acceptable range. The marginal and internal fit of the crown was far superior in the CNC milling method.

The apoptotic and autophagic effects of cast Au-Pt, and differently manufactured Co-Cr and cp-Ti on three-dimensional oral mucosal model.

The application of digitally manufactured dental metals has aroused the attention on their biocompatibilities. Three-dimensional oral mucosal model (3D OMM) would provide excellent assessments to the biocompatibility. In the current study, we set to measure metal ion release levels in the extracts of cast gold-platinum alloy (Au-Pt), differently manufactured cobalt-chromium alloy (Co-Cr) and commercially pure titanium (cp-Ti). We further tested two scaffold materials of 3D OMM to determine the better one for the succedent work. Lastly, we evaluated the apoptotic and autophagic effects of cast Au-Pt, and differently manufactured Co-Cr and cp-Ti on mucosal cells based on 3D OMM. We found that, in the construction of 3D OMM, Matrigel showed better performance than bovine acellular dermal matrix. Thus, Matrigel was chosen to construct the 3D OMM in the succedent studies. The results of ion release and biological assessments showed that, firstly, cast Au-Pt and cp-Ti triggered less early apoptotic cells and ion release than cast Co-Cr, implying better chemical stability and biocompatibility of them; secondly, digitally manufactured (including CAD/CAM milling and SLM) Co-Cr showed significantly lower ion release levels and lesser early apoptotic effects on 3D OMM as compared to the cast one. Although cast cp-Ti released much more ions than CAD/CAM milling one, manufacturing methods had no impact on apoptotic effect of cp-Ti. Therefore, we believe that digital methods possess same or even better chemical stability and biocompatibility than conventional casting one. Thirdly, although increased autophagic levels are observed in all test groups, so far there is no evidence that the test metals trigger different levels of autophagy as compared to each other. In addition, correlation analysis indicates that Co, W, and Mn appear to be the potential inducements for the apoptotic and autophagic effects of Co-Cr.

Multidisciplinary analysis of bite marks in a fatal human dog attack: A case report.

INTRODUCTION: Lethal injuries by animal attacks are a matter of concern for the forensic pathologist; the presented case illustrates a two dogs attack on a 61-year-old man. The authors have focused on a multidisciplinary approach involving forensic pathologists and veterinarians. MATERIALS AND METHODS: The victim was cycling in the countryside when he was attacked by two dogs that came out of a large house. He was found lying in the street by the homeowners who called for help. The victim was transported to the hospital where he died five days later. According to recovery data and medico-legal autopsy findings the cause of death was septic shock. RESULTS: Forensic pathologists and veterinarians multidisciplinary evaluation revealed lacerations, abrasions, and multiple small punctures constituting bite marks over the entire body. Six skin dowels with bite marks were taken and compared with the dental cast of the dogs. CONCLUSION: A comparison of the dog dental casts and the bite marks on the victim's body allowed the identification of the animals involved in the attack.

Influence of reinforcement bar on accuracy of removable partial denture framework fabricated by casting with a 3D-printed pattern and selective laser sintering.

PURPOSE: The purpose of this study was to investigate the accuracy of removable partial denture frameworks fabricated by 3D-printed pattern casting (AM-Cast) and selective laser sintering (SLS) under different co nditions with a reinforcement bar. METHODS: A partially edentulous model was scanned with a dental laboratory scanner, and CAD software was used to design the framework. Reinforcement bars (n=0-2) were set on the lingual side of the framework. 3D scanning of the fabricated frameworks by AM-Cast and SLS was performed, and the obtained data were overlapped with the design data. The differences in shape among setting conditions of the bar were statistically compared using the Bonferroni method after the Kruskal-Wallis test. RESULTS: The ranges in differences of the AM-Cast-0, AM-Cast-1, and AM-Cast-2 were -0.167 to 0.128 mm, -0.101 to 0.105 mm, and -0.185 to 0.015 mm, respectively. The ranges of SLS-0, SLS-1, and SLS-2 were -0.166 to 0.035 mm, -0.182 to 0.049 mm, and -0.138 to 0.038 mm, respectively. Large discrepancies were observed at the joining area of the lingual bar on the right side of the AM-Cast. A significant difference was found between the AM-Cast-0 and AM-Cast-1, and between the AM-Cast-0 and AM-Cast-2. CONCLUSIONS: The setting conditions of the reinforcement bar affected the accuracy of the lingual bar in the AM-Cast; however, no effect was observed on the displacement of the central area of the lingual bar in SLS. Setting a single reinforcing bar on the retentive latticework contributed to improving the accuracy of the lingual bar in the AM-Cast but not the displacement of the central area of the lingual bar in SLS.

Fabrication of titanium restoration by means of calcium aluminate-bonded magnesia investment material and one-chamber arc casting apparatus.

Cast titanium restoration for molars has high biocompatibility and is covered by the Japanese national health insurance. Titanium casting requires specific investment material and casting apparatus. A cast restoration for the mandibular left second molar was fabricated using titanium in this study. A wax pattern fabricated on a definitive cast was invested in calcium aluminate-bonded magnesia investment material. Titanium was cast using an argon gas pressure one-chamber casting apparatus. No defects were observed on the surface and the hole was clearly reproduced. A smooth surface on the restoration was obtained by polishing at low speed. Reproductivity and polishing properties of the titanium restoration fabricated in this study were comparable to those of conventional dental metal restorations.

Palatal rugae morphology is associated with variation in tooth number.

This observational study compared palatal rugae morphology in adolescent subjects with normal tooth number and tooth agenesis. Maxillary dental study casts were used to compare rugae number, length and shape. Each study group contained 60 subjects (30 females and 30 males) mean age 13.4 (SD, 1.55) in control and 13.56 (SD, 1.54) years in tooth agenesis groups (p = 0.576). Mean number of missing tooth units in the tooth agenesis group was 2.1. Mean number of primary rugae in the whole sample was 4.35 (SD, 0.98) on the right and 4.33 (SD, 0.92) on the left with no significant differences (p = 0.236 and p = 0.404, respectively). However, the number of secondary rugae on the left (p = 0.006) and fragmentary rugae on the right (p = 0.004) was significantly increased in the tooth agenesis group. The shape of left primary rugae 2 and 3 also differed between groups, tending towards a wavy pattern in the control group and curved in the tooth agenesis group (p = 0.012 and p = 0.004, respectively). In addition, primary rugae 3 was more convergent (p = 0.008) whilst left primary rugae 3 and 5 were orientated in an antero-posterior direction (p = 0.04 for both rugae) in the tooth agenesis group. Subgroup analysis also identified significant associations between patterns of tooth agenesis and rugae number, in addition to shape of primary rugae. The identification of significant differences in rugae pattern between subjects with normal tooth number and agenesis suggests potential commonality in signal pathway disruption during establishment of these structures.