There are 7 categories of additive manufacturing (AM) technologies, and a wide variety of materials can be used to build a CAD 3D object. The present article reviews the main AM processes for ...polymers for dental applications: stereolithography (SLA), digital light processing (DLP), material jetting (MJ), and material extrusion (ME). The manufacturing process, accuracy, and precision of these methods will be reviewed, as well as their prosthodontic applications.
Additive manufacturing (AM) processes are increasingly used in dentistry. The underlying process is the joining of material layer by layer based on 3D data models. Four additive processes (laser ...stereolithography, polymer jetting, digital light processing, fused deposition modeling) are mainly used for processing dental polymers. The number of polymer materials that can be used for AM in dentistry is small compared to other areas. Applications in dentistry using AM are limited (e.g. study models, maxillo-facial prostheses, orthodontic appliances etc.). New and further developments of materials are currently taking place due to the increasing demand for safer and other applications. Biocompatibility and the possibility of using materials not only as temporarily but as definitive reconstructions under oral conditions, mechanically more stable materials where less or no post-processing is needed are current targets in AM technologies. Printing parameters are also open for further development where optical aspects are also important.
Abstract Objective An ideal dental adhesive should provide retentive strength, marginal seal, be relatively simple to achieve and demonstrate clinical durability. Future improvements in adhesive ...bonding to tooth structure require in vitro test methods that provide reliable data for materials development and/or evaluation of experimental variables. The objective of this project was to identify a test method that is relatively easy to perform, repeatable and ultimately useful for predicting clinical outcomes. Methods The Academy of Dental Materials initiated a project to develop and distribute guidance documents on laboratory test methods that are useful for the evaluation of dental adhesives and cements, composite resins and ceramics. Results The dental adhesive sub-group has identified the micro-tensile bond strength test, especially after subjecting the specimens to a durability challenge, as currently the best practical surrogate measure of dental composite restoration retention. Conclusion The following μTBS guidance is meant to aid the researcher in conducting the μTBS test. The authors, while recognizing the limitations of a static, strength-based test method, welcome comments and suggestions for improvements of this guidance document in future revisions.
Abstract Polymer additive manufacturing (AM) technologies have been incorporated in digital workflows within implant dentistry. This article reviews the main polymer AM technologies in implant ...dentistry, as well as their applications in the field such as manufacturing surgical guides, custom trays, working implant casts, and provisional restorations.
Purpose
To evaluate the color stability of CAD/CAM complete denture resins.
Materials and Methods
A total of 176 resin specimens were manufactured from conventional heat‐polymerizing (pink: CONHCP: n ...= 16; tooth‐shade: CONHCT: n = 16), CAD/CAM subtractively manufactured (pink: WIMP: n = 16, AVMP: n = 16, MEMP: n = 16, POMP: n = 16; tooth‐shade: AVMT: n = 16, MEMT: n = 16, POMT: n = 16), and additively manufactured (pink: NDRPP: n = 16; tooth‐shade: NDRPT: n = 16) denture resins; four different aging processes (thermal cycling, distilled water, red‐wine, and coffee) were used. A spectrophotometer evaluated the color change (ΔE) using two modes of measurements (specular component included (ΔESCI) and specular component excluded (ΔESCE)) recorded at baseline (T0) and at day#30 (T30). ANOVA and post hoc tests were used for statistical analysis (alpha = 0.05).
Results
Additively manufactured resins (NDRPP and NDRPT) demonstrated significant ΔE in comparison to the other groups in all aging media (p < 0.001). WIMP demonstrated higher ΔESCI in comparison to the other subtractively manufactured groups in distilled water (p < 0.001). In red‐wine, AVMT revealed significantly more ΔESCE than POMT (p = 0.039). In coffee, the ΔESCE was higher for CONHCT than MEMT (p = 0.026) and POMT (p = 0.011). Similarly, in coffee the ΔESCE for AVMT was higher than POMT (p = 0.030).
Conclusion
Additively manufactured denture resins demonstrated the maximum color change compared to conventional heat‐polymerized and CAD/CAM subtractively manufactured denture resins. Furthermore, CAD/CAM subtractively manufactured denture resins were not inferior to conventional resins in terms of color stability.
This review compared Computer-aided designand Computer-aided manufactured (CAD-CAM) and conventionally constructed removable complete dentures (CDs).
Seventy-three studies reporting on CAD-CAM ...(milled/3D-printed) CDs were included in this review. The most recent literature search was performed on 15/03/2021.
Two investigators searched electronic databases PubMed (MEDLINE), Embase, CENTRAL, online search engines (Google) and research portals. Hand searches were performed to identify literature not available online.
Studies on CAD-CAM CDs were included if they reported on trueness of fit, biocompatibility, mechanical, surface, chemical, color , microbiological properties, time-cost analysis, and clinical outcomes. Inter-investigator reliability was assessed using kappa scores. Meta-analyses were performed on the extracted data .
The kappa score ranged between 0.897–1.000. Meta-analyses revealed that 3D-printed CDs were more true than conventional CDs (p = 0.039). Milled CDs had a higher flexural-strength than conventional and 3D-printed CDs (p < 0.0001). Milled CDs had a higher flexural-modulus than 3D-printed CDs (p < 0.0001). Milled CDs had a higher yield-strength than injection-molded (p = 0.004), and 3D-printed CDs (p = 0.001). Milled CDs had superior toughness (p < 0.0001) and surface roughness characteristics (p < 0.0001) than other CDs . Rapidly-prototyped CDs displayed poor color-stability compared to other CDs (p = 0.029). CAD-CAM CDs d displayed better retention than conventional CDs (p = 0.015). Conventional CDs had a higher strain at yield point than milled CDs (p < 0.0001), and had superior esthetics than 3D-printed (p < 0.0001). Fabrication of CAD-CAM CDs required less chairside time (p = 0.037) and lower overall costs (p < 0.0001) than conventional CDs.
This systematic review concludes that CAD-CAM CDs offer a number of improved mechanical/surface properties and are not inferior when compared to conventional CDs.
CAD-CAM CDs should be considered for completely edentulous patients whenever possible, since this technique offers numerous advantages including better retention, mechanical and surface properties but most importantly preserves a digital record. This can be a great advantage for older adults with limited access to dental care.
Purpose
To quantify the impact of ambient lighting conditions on the accuracy (trueness and precision) of an intraoral scanner (IOS) when maxillary complete‐arch and maxillary right quadrant digital ...scans were performed in a patient.
Material and Methods
One complete dentate patient was selected. A complete maxillary arch vinyl polysiloxane impression was obtained and poured using Type IV dental stone. The working cast was digitized using a laboratory scanner (E4 Dental Scanner; 3Shape) and the reference standard tessellation language (STL file) was obtained. Two groups were created based on the extension of the maxillary digital scans performed namely complete‐arch (CA group) and right quadrant (RQ) groups. The CA and RQ digital scans of the patient were performed using an IOS (TRIOS 3; 3Shape) with 4 lighting conditions chair light (CL), 10 000 lux, room light (RL), 1003 lux, natural light (NL), 500 lux, and no light (ZL), 0 lux. Ten digital scans per group at each ambient light settings (CL, RL, NL, and ZL) were consecutively obtained (n = 10). The STLR file was used to analyze the discrepancy between the digitized working cast and digital scans using MeshLab software. Kruskal‐Wallis, one‐way ANOVA, and pair‐wise comparison were used to analyze the data.
Results
Significant difference in the trueness and precision values were found across different lighting conditions where RL condition obtained the lowest absolute error compared with the other lighting conditions tested followed by CL, NL, and ZL. On the CA group, RL condition also obtained the best accuracy values, CL and NL conditions performed closely and under ZL condition the mean error presented the highest values. On the RQ group, CL condition presented the lowest absolute error when compared with the other lighting conditions evaluated. A pair‐wise multicomparison showed no significant difference between NL and ZL conditions. In all groups, the standard deviation was higher than the mean errors from the control mesh, indicating that the relative precision was low.
Conclusions
Light conditions significantly influenced on the scanning accuracy of the IOS evaluated. RL condition obtained the lowest absolute error value of the digital scans performed. The extension of the digital scan was a scanning accuracy influencing factor. The higher the extension of the digital scan performed, the lower the accuracy values obtained. Furthermore, ambient light scanning conditions influenced differently depending on the extension of the digital scans made.
Objective
To evaluate the short-term effects of hard and soft splints of different thicknesses on maximum bite force (MBF) and sleep quality (SQ) in participants with sleep bruxism (SB).
Methods
...One-hundred-fifteen patients were randomly allocated to five groups: Groups H2(Hard splint-2 mm), H3(Hard splint-3 mm), S2(Soft splint-2 mm), S3(Soft splint-3 mm), and C (control). Outcomes were MBF (assessed with a digital gnathodynamometer) and SQ (assessed with the Pittsburgh Sleep Quality Index). Measurements were performed at T0 (before the splints), T1 (1-month follow-up), and T2 (2-months follow-up). Data were analyzed using one-way analysis of variance(ANOVA), Tukey’s HSD, and chi-square tests (alpha = 0.05).
Results
At T1, the highest MBF values were observed in group H3 (658.01 ± 22.6 N), while the lowest in group S2 (585.45 ± 8.68 N). For T2, the highest values were obtained in H3 group (676.85 ± 21.9 N), and the lowest in group S2 (565.65 ± 10.9 N) (
p
< 0.05).For SQ, groups S2 and S3 revealed the lowest PSQI values at T1 (9.1; 9.6) and T2 (9; 9.5) (
p
< 0.001).
Conclusions
The short-term use of both 2 and 3-mm thick soft splints resulted in a decrease in MBF. Improvement in SQ in patients using soft splints was observed in the 1st month and was maintained in the 2nd month.
Clinical Relevance
This study provides insights on short-term clinical effects as regards to increased sleep quality and regulated maximum bite force as a function of splint material type and the thickness of the splint.
Conventional implant impressions by using elastomeric impression material have been reported as a more reliable technique for a complete-arch implant record compared with intraoral ...scanner procedures. Photogrammetry technology may provide a reliable alternative to digital scanning or a conventional impression; however, its accuracy remains unclear.
The purpose of this in vitro study was to measure and compare the implant abutment replica positions of the definitive cast with the implant abutment replica positions obtained by the conventional technique, photogrammetry, and 2 intraoral scanners.
An edentulous maxillary cast with 6 implant abutment replicas (RC analog for screw-retained abutment straight) was prepared. Three impression techniques were performed: the conventional impression technique (CNV group) by using a custom tray elastomeric impression procedure after splinting the impression copings at room temperature (23°C), photogrammetry (PG group) technology (Icam4D), digital scans by using 2 different IOSs following the manufacturer′s recommended scanning protocol, namely IOS-1 (iTero Element) and IOS-2 (TRIOS 3) groups (n=10). A coordinate measuring machine (CMM Contura G2 10/16/06 RDS) was used to measure the implant abutment replica positions of the definitive casts and to compare the linear discrepancies at the x-, y-, and z-axes and the angular distortion of each implant abutment replica position by using a computer aided-design software program (Geomagic) and the best fit technique. The 3D linear gap discrepancy was calculated. Measurements were repeated 3 times. The Shapiro-Wilk test revealed that the data were not normally distributed; therefore, the Kruskal-Wallis test was used to analyze the data, followed by pairwise Mann-Whitney U tests (α=.05).
Significant y-axis linear and XY and YZ angular discrepancies were found among the CNV, PG, IOS-1, and IOS-2 groups (P<.05). The PG group obtained a significantly higher distortion on the y-axis and 3D gap compared with all the remaining groups (P=.004). The 3D discrepancy of the CNV group was 11.7 μm, of the IOS-1 group was 18.4 μm, of the IOS-2 was 21.1 μm, and of the PG group was 77.6 μm. In all groups, the interquartile range was higher than the median errors from the discrepancies measured from the definitive cast, indicating that the relative precision was low.
The conventional technique reported the lowest 3D discrepancy for the implant abutment position translation capabilities of all the implant techniques evaluated. The intraoral scanners tested provided no significant differences in linear distortion compared with the conventional method. However, the photogrammetry system tested provided the least accurate values, with the highest 3D discrepancy for the implant abutment positions among all the groups.
Purpose
The objective of this systematic review was to elaborate the aging effect of cyclic fatigue tests on mechanical durability of all‐ceramic single crowns and fixed dental prostheses (FDP).
...Materials and Methods
Original scientific papers published in the MEDLINE (PubMed) database in English between 01/01/1950 and 12/31/2013 on cyclic loading on all‐ceramics were included in this systematic review. The following MeSH terms, search terms, and their combinations were used: “in vitro,” “stress mechanical,” “crowns,” “denture, partial, fixed,” “dentistry,” “fatigue,” “all‐ceramic,” “zirconia,” “fixed dental prosthesis,” “FDP,” “bridges,” and “cyclic loading.” Two reviewers performed screening and analyzed the data. Only the studies that reported on both static fracture strength and static fracture after fatigue of all‐ceramic single crowns and FDPs that allowed comparison of aging effect through cyclic loading were included.
Results
The selection process resulted in a final sample of 14 journal articles. In total, 9 articles were identified related to all‐ceramic single crowns, 3 of which were on anterior and 6 on posterior crowns, and 5 articles on 3‐unit FDPs, all of which were on posterior FDPs. Fatigue cycles varied between minimum of 1000 to maximum 1,200,000 cycles for crowns and 10,000 to 2,000,000 cycles for 3‐unit FDPs. The applied force during cyclic loading varied between 20 to 300 N for single crowns and 49 to 200 N for 3‐unit FDPs. For the 3‐unit FDPs, fracture strength results showed slightly decreased values after cyclic loading (659 ± 182 to 2333 ± 183 N) compared to static loading only (841 ± 244 to 2434 ± 154 N). For crowns similar trends were not observed, but cyclic loading decreased the fracture strength in only some materials after cyclic loading (659 ± 182 to 2333 ± 183 N) compared to static loading only (395 ± 96 to 2726 N).
Conclusions
An inclination for decreased static fracture strength could be observed after cyclic loading of all‐ceramic single crowns and FDPs, but this was material specific. Due to the heterogeneity of data such as aging, loading conditions, and fewer experimental groups, statistical analysis could not be performed. Cyclic loading tests require more standardized guidelines for testing and reporting.
PDF
