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.

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.

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.

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.

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.

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.

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.

Marginal discrepancy of 3-unit Co-Cr metal copings fabricated with additive and subtractive manners: A comparative study.

BACKGROUND: Poor marginal adaptation may give rise to a series of biological complications. Despite its importance, comparative studies on marginal adaptation of metal-ceramic fixed restorations fabricated with newer methods are limited. AIM: Therefore, it was aimed to assess the marginal accuracy of copings fabricated with subtractive and additive manners used in contemporary dentistry. MATERIALS AND METHODS: For a typodont model, 60 three-unit cobalt-chrome metal copings were fabricated by selective laser sintering (SLS), hard alloy milling (HAM), and soft alloy milling (SAM) in comparison to casting (C). Marginal discrepancy assessment was performed by using replication technique. Mesiodistal and buccopalatal cross-sections of silicone replicas were investigated under a stereomicroscope at × 80 magnification. A total of 960 measurements were subsequently made by means of corresponding image-review software on captured images after calibration of the software to µm scale. Obtained data were subjected to nonparametric Kruskal Wallis and Tamhane post-hoc tests (α =0.05). RESULTS: Marginal adaptation of C group was significantly inferior to test groups in both canine- and premolar-teeth measurements (P < 0.05). Marginal fit was found to be tooth dependent (P < 0.001). HAM, SAM, and SLS groups exhibited analogous marginal discrepancy values on canine-tooth measurements. Differences among these groups were not statistically significant (P > 0.05). SAM and SLS groups demonstrated better marginal adaptation than others on premolar-tooth measurements. Also, no statistically significant difference was detected between SAM and SLS groups (P > 0.05). CONCLUSIONS: SAM group demonstrated superior marginal accuracy. All groups had clinically acceptable marginal discrepancy values (<120 µm), except cast group.

Profound approach to check legitimacy of an old technique used to gauge palatal rugae.

AIMS: The present study aimed at assessing two fixed points of reference from where the mesial and distal point of all rugae can be measured so that the exact movement of particular rugae in any direction can be evaluated and assessing the changes in the palatal rugae after orthodontic treatment. METHODS: A longitudinal study conducted among a sample of 20 (8 male and 12 female) adult patients. Pre- and post-orthodontic treatment casts of patients were obtained from the Department of Orthodontics College of Dentistry Jazan University. Antero-posterior linear distances (Technique I) between medial and lateral points of primary, secondary and tertiary rugae were measured. Also, the transverse linear distance (Technique II) between medial and lateral points of right and left rugae were measured. Technique III involved marking two fixed points and using these two points a third point is located on the medial or lateral end of rugae of right and left side in pre and post-treatment orthodontic casts. The independent sample t-test was employed to compare gender. Difference between the pre- and post-treatment mean values were checked by the paired t-test. RESULTS: Technique III successfully showed the statistically significant difference (P ≤ 0.05, 95% CI) in the overall pre and post-treatment values on the patients' cast (N = 20) which was not observed with a technique I and technique II. CONCLUSION: The triangle created by the three reference points in the technique III was able to identify the changes in the palatine rugae more precisely than the technique I and Technique II.

A surveillance study of the demand of titanium and titanium alloys in Japan.

The demand for titanium and titanium alloys in dentistry is high. A surveillance survey regarding the clinical and laboratory uses of titanium/titanium alloys in Japan was conducted in this study. The alloys used for casting demonstrated a decreasing tendency in quantity, whereas the use of non-casting titanium alloys increase in the market. This increasing trend is reflected the popularity of CAD/CAM devices. In Japan, the processing technologies of titanium alloys have been improved; therefore, the application of titanium and titanium alloys to dental procedures covered by the insurance is clearly worth considering.

Lingual orthodontics in an adult patient with upper premolar extraction: Case report.

OBJECTIVE: To show with this case report that lingual orthodontics can be a solution in complex adult situation and with interdisciplinary approach. MATERIALS AND METHODS: The patient presented a dental and skeletal high angle class II division 1 with a previous extraction of one mandibular incisor. The strategy of treatment was upper first premolar-extraction to obtain a correction of the incisal-class II relationship with a normal lip function, a class II molar relationship on the right side and a class I on the left side. A lingual appliance and miniscrews were used. RESULTS: The lingual orthodontic treatment with miniscrews responded to the occlusal objectives with a good upper incisors torque and retraction control. DISCUSSION: Limits and advantages of lingual orthodontics were discussed. CONCLUSION: Lingual mechanics can provide good results from both an aesthetic and function point of view in adult complex extractions case. It ensures aesthetics during treatment, incisor control during retraction. Miniscrews were also useful to overcome the periodontal limits and enhance the anchorage.

Accuracy of removable partial denture framework fabricated by casting with a 3D printed pattern and selective laser sintering.

PURPOSE: The present study aimed to compare the accuracy of removable partial denture (RPD) frameworks fabricated by 3D-printed pattern casting and those fabricated by selective laser sintering (SLS). METHODS: A partially edentulous mandibular model was used for the simulation model. Scanning of the model was performed using a dental scanner. The framework was designed by using CAD software. The 3D-printed resin pattern was formed using a 3D printer and casting was performed (AM-Cast framework), and a direct metal laser sintering machine was used for the framework of SLS (SLS framework). 3D scanning of fabricated two types of framework were performed, and these data were overlapped with design data. Fabrication accuracy was verified using the Mann-Whitney U test to compare the discrepancy between the AM-Cast and SLS frameworks. RESULTS: The range of differences for the AM-Cast and SLS framework were -0.185±0.138 to 0.352±0.143mm and -0.166±0.009 to 0.123±0.009mm, respectively. Statistically significant differences were observed at the rests, proximal plates, connectors, and clasp arms. Regarding the rests, both lateral and medial displacement in the two types framework was observed in relation to the design data. Large lateral discrepancies of the connectors were observed at the joining area on the tooth-supported side of the lingual bar for the AM-Cast framework. Localized discrepancies were observed at the center of the lingual bar for the SLS framework. CONCLUSION: The accuracies of RPD frameworks fabricated by AM-Cast and SLS differ depending on the specific structural component of the RPD.

Effects of build conditions and angle acuteness on edge reproducibility of casting patterns fabricated using digital light projection.

The aim of the present study was to evaluate the effects of build conditions and angle acuteness on edge reproducibility of the casting patterns fabricated using a digital light process. The prism-shaped patterns with various vertex angles were fabricated in three build orientations. The height from the base to the vertex angle point of the fabricated pattern was measured and the incomplete height was calculated as the discrepancy between the original and measured heights. Two-way ANOVA revealed that the vertex angle and build orientation and their interaction were significant (p<0.05). The incomplete height significantly decreased with an increase of the vertex angle. When the vertex angle was 20° and the build-up direction was parallel to the edge of vertex angle and perpendicular to the triangular base, the incomplete height was the smallest. Therefore, build orientation and angle acuteness influenced the edge reproducibility of the casting patterns fabricated using a digital light process.

Microstructure, topography, surface roughness, fractal dimension, internal and marginal adaptation of pressed and milled lithium-disilicate monolithic restorations.

PURPOSE: To characterize the effect of two processing techniques (pressing and CAD/CAM - Computer Aided Design/Computer Aided Machining) of lithium-disilicate (LD) based crowns on the microstructure, topography, roughness, fractal dimension, internal and marginal adaptation. METHODS: One-hundred identical preparations for monolithic crowns were made with dentin analogue material (G10 epoxy resin). One of the preparations was scanned and a monolithic crown in lithium-disilicate was planned in the CAD system. Fifty crowns were milled in a wax pattern and subjected to pressing (IPS e.max Press), while 50 crowns were machined at CAD/CAM (IPS e.max CAD) and posteriorly crystallized. Internal and marginal adaptation were assessed via replica technique at four manufacturing moments (Milled wax pattern; LDPRESS; Milled LDCAD; Crystallized LDCAD) and considering 5 regions (margin, cervico-axial angle, axial wall, axial-occlusal angle and occlusal wall). Complementary analysis considering microstructure and topography, roughness and fractal dimension were performed in Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). RESULTS: The processing technique resulted in different ceramic microstructure, topography, roughness and fractal dimension, whereas CAD/CAM lead to smoother, more homogeneous but more complex topography features (higher fractal dimension) in comparison to the pressing technique (P<0.05). Regarding marginal and internal fit, LDPRESS crowns showed to be more adapted at the margin, while LDCAD were more adapted at the occluso-axial angle; other regions were not statistically different (α=0.05). CONCLUSIONS: CAD/CAM and the pressing techniques for manufacturing LD crowns lead to completely different ceramic surface characteristics and affect crown adaptation at the margin and at occluso-axial angle.