STATEMENT OF PROBLEM:Intraoral scanning for complete arch implant-supported prostheses has been associated with directional deviations that may compromise prosthetic fit. However, the clinical relevance of these deviations and their relationship with scan body height, scanner system, and implant location remain unclear. PURPOSE:The purpose of this in vitro study was to evaluate the directional deviations (X-axis, Y-axis, and Z-axis) of multiple implants in intraoral scans of edentulous maxilla, depending on scan body height, scanner type, and implant location. MATERIAL AND METHODS:A 3-dimensionally (3D) printed model of an edentulous maxilla with 6 implants, multi-units, and cylindrical polyetheretherketone (PEEK) scan bodies of 3 heights (4.5 mm, 6 mm, and 8 mm) was scanned with 3 intraoral scanners (TRIOS 5 [TR], Primescan [PS], and Infinite [IF]). A total of 144 scans were obtained, and a high-resolution industrial scanner (Artec Micro II) was used to acquire the reference model. Trueness evaluation was conducted using the Geomagic X software program. Directional deviations along the X-, Y-, and Z-axes were calculated for each scan body location. The data were stratified according to scan body height, scanner type, and implant location (molar, premolar, and lateral incisor). Statistical analysis with nonparametric tests (Shapiro-Wilk, Kruskal-Wallis, and post hoc pairwise comparisons) were used to assess differences in absolute deviations among groups (α=.05). Outliers were identified using the z-score method (|z|>3) and removed prior to analysis. Deviations were dichotomized (<90 µm or ≥90 µm), and simple and multiple binary logistic regression models were applied to the X- and Y-axis to evaluate the effects of scanner type, scan body height, and implant location on the likelihood of deviations ≥90 µm. Logistic regression was not performed for the Z-axis because of the absence of sufficient events. RESULTS:Shorter scan bodies showed significantly lower deviations across all scanners (P<.001). Scan bodies of 4.5 mm produced the smallest deviations on the X- and Z-axes, whereas 6 mm yielded the lowest deviations on the Y-axis (P<.001). Scanner performance was axis-dependent, with IF showing the largest deviations on the X- and Y-axes and increased odds of deviations ≥90 µm. Deviations increased with scan body height for all scanners. Implant location showed greater deviations at posterior sites, but this effect was limited after multivariable adjustment. Z-axis deviations remained consistently low. CONCLUSIONS:Scan body height and scanner type were the main factors influencing directional deviations in complete arch implant scans. Shorter scan bodies improved trueness, whereas taller scan bodies and IF increased the likelihood of clinically relevant deviations. Implant location had a limited effect after adjustment, and Z-axis deviations were minimal. Selecting appropriate scanning strategies may improve accuracy in complete arch implant rehabilitations.

STATEMENT OF PROBLEM:The influence of postprocessing cleaning solutions on the trueness and fit of additively manufactured (AM) definitive crowns fabricated from different photopolymer resins remains unclear. PURPOSE:The purpose of this in vitro study was to evaluate how different postprocessing cleaning solutions affect the fabrication trueness, marginal quality, and intaglio fit of crowns fabricated from 2 photopolymer resins using additive manufacturing. MATERIAL AND METHODS:Ninety-six crowns were printed using either a urethane acrylate (UA)-based resin or a composite resin (CR) and then subdivided into 4 cleaning groups: ethanol (96%), isopropanol (98%), water-based solution, and methyl ether-based solvent. Each crown underwent digital surface scanning, and trueness was measured by using the root-mean-square (RMS) metric for occlusal, external, intaglio, marginal, and overall surfaces. Intaglio fit was assessed by using a triple-scan protocol (TSP) to measure average gap values (AGVs). Statistical analyses included the Shapiro-Wilk test, Generalized Linear Models (GLMs) for trueness and AGVs, Kruskal-Wallis and Mann-Whitney U tests for margin quality, and Spearman rank correlation for association analysis (α=.05). RESULTS:Significant differences were found for both resin type and cleaning solution (P<.001). CR crowns showed higher trueness than UA crowns across all outer surfaces (P<.023), with the UA-S group exhibiting the lowest trueness values. Alcohol-based cleaning was associated with higher marginal trueness (P<.001), with CR-E and CR-I showing the highest marginal trueness values (27.3 ±6.4 and 26.9 ±6.2 µm; P<.015). AGVs were also affected by the cleaning solution (P<.001). Water-based and methyl ether-based solvent-cleaned groups showed smaller AGVs, indicating better intaglio fit, whereas crowns cleaned with ethanol or isopropanol showed larger AGVs. AGVs were negatively correlated with intaglio trueness (ρ=-0.47) and marginal trueness (ρ=-0.65) (P<.001). CONCLUSIONS:Both the cleaning solution and the resin type significantly influenced the trueness and fit of crowns. While alcohol-based solutions were associated with higher marginal trueness, water-based and methyl ether-based solvent cleaning yielded better intaglio fit. Composite resin crowns demonstrated more favorable trueness and margin quality than urethane acrylate crowns.

Objective The addition of nanographene to denture base material has been recently implemented, but its impact on surface properties and microbial resistance remains unclear. This study aimed to evaluate the effect of polishing on the surface roughness, hydrophobicity, and biofilm formation of three different polymethyl methacrylate (PMMA) denture base materials before and after thermocycling. Methods Thirty disk-shaped specimens (Ø10 × 1.5 mm) were fabricated from nanographene-reinforced PMMA (GDM), prepolymerized PMMA (MDM), and conventional heat-polymerized PMMA (CDM). Surface roughness was measured before and after polishing using a noncontact optical profilometer, whereas hydrophobicity was assessed after polishing via water contact angle analysis. Candida albicans biofilm formation was quantified after 48 h using colony-forming unit analysis. Specimens underwent 10,000 thermal cycles in artificial saliva, followed by repeated measurements. Data were analyzed using one-way analysis of variance, followed by Tukey’s post hoc test for multiple comparisons. Additionally, paired t-tests were conducted to evaluate changes before and after thermocycling (α=.05). Results Surface roughness differed significantly before polishing and after thermocycling (p<0.001) but not after polishing (p=0.129). CDM had the highest roughness, and GDM showed the lowest after thermocycling (p<0.001). Water contact angle did not differ significantly among materials (p≥0.136). GDM initially showed higher C. albicans biofilm than CDM (p=0.009), but levels decreased after thermocycling (p<0.001), with no differences thereafter. Biofilm formation after thermocycling correlated positively with contact angle (r=0.478) and negatively with roughness(r=-0.401). Conclusions Surface polishing decreased the roughness of all tested materials, with GDM exhibiting the lowest roughness values. The incorporation of nanographene in a prepolymerized PMMA denture base reduces roughness and C. albicans biofilm formation.

OBJECTIVES:To compare the fabrication accuracy and fit of three-unit fixed dental prostheses (FDPs) manufactured additively from a 3Y-TZP slurry with those manufactured subtractively from a translucent or a strength-gradient zirconia. METHODS:Forty-five three-unit posterior FDPs were fabricated either additively from a 3Y-TZP slurry (Cera-P, AM) or subtractively from a translucent (4Y-TZP, n!ce Zirconia HT, SM-HT) or a strength-gradient zirconia (3/5 Y-TZP, IPS e.max ZirCAD Prime, SM-SG) (n = 15). Surface deviations (external, intaglio, marginal, and overall) and average gaps (fit) of the FDPs were digitally analyzed. Data were analyzed with one-way analysis of variance and Tukey (surface deviations) or Tamhane tests (average gaps). Precision was defined as the average of measured values from the mean value, and analyzed similar to each outcome (α = 0.05). RESULTS:AM FDPs exhibited the highest deviations across all surfaces but the lowest gaps (P < 0.001) and no significant differences were detected between SM-HT and SM-SG (P ≥ 0.360). There was no difference in the precision of measured deviations (P ≥ 0.057). When the precision of average gap values was considered, AM FDPs had higher values than SM-SG FDPs (P = 0.024). CONCLUSIONS:AM FDPs demonstrated the lowest fabrication trueness, while SM-SG and SM-HT FDPs had similar fabrication accuracy. Although AM FDPs exhibited improved fit, their fit precision was inferior to SM-SG FDPs, whereas SM-SG and SM-HT FDPs had similar fit accuracy. The fit of all FDPs remained within clinically acceptable limits. CLINICAL SIGNIFICANCE:Tested additively manufactured three-unit posterior fixed dental prostheses may be alternatives to those subtractively manufactured from translucent and strength-gradient zirconia, as their fit was clinically acceptable. However, lower fabrication trueness and reduced fit precision may result in increased adjustment time for additively manufactured restorations.

PURPOSE:The purpose of this in vitro study was to investigate the effect of alcohol-free cleaning solutions on the mechanical properties and reliability of additively manufactured occlusal device resins, compared with isopropyl alcohol (IPA), while considering the influence of aging. MATERIALS AND METHODS:Bar-shaped (64×10×3.3 mm) specimens were additively manufactured from two occlusal device resins (Freeprint Splint 2.0; FS, KeySplint Hard; KS) and divided into three groups based on the cleaning solution used (IPA, methylether solvent (MES), and a water-based solution) (N = 30). After postprocessing, each set of specimens was further divided into two groups based on their aging condition as nonaged or aged (n = 15). Specimens in nonaged subgroups were tested for 3-point flexural strength and microhardness, while those in aged subgroups were subjected to 5000 thermal cycles between 5°C and 55°C before testing. Both data sets were analyzed with a generalized linear model either with a normal distribution and identity link function (microhardness) or a gamma distribution and logarithmic link function (flexural strength). The maximum likelihood estimation method was used for the Weibull analysis of the flexural strength data and further evaluated with the chi-squared test (α = 0.05). RESULTS:Aged KS had higher flexural strength than its FS counterpart when IPA and MES were used (P ≤ 0.014). MES led to the lowest flexural strength for aged FS, which had lower values than nonaged FS when MES and the water-based solution were used (p ≤ 0.002). Nonaged MES-cleaned KS had lower hardness than its FS counterpart (p<0.001). Water-based solution led to higher hardness than MES for aged KS, and aged KS had higher hardness than nonaged KS when the water-based solution and MES were used (p ≤ 0.028). KS mostly had higher reliability than FS; MES use tended to result in lower reliability among the aged specimens, and aging reduced the reliability of MES-cleaned FS and KS specimens as well as of FS specimens cleaned with a water-based solution (p ≤ 0.027). CONCLUSIONS:Flexural strength, microhardness, and reliability of the KS resin were mostly similar to or better than those of the FS resin. Cleaning with MES or aging may compromise mechanical properties and reliability, depending on the resin.

Objectives To evaluate the surface and positional trueness of removable dies fabricated using fused filament fabrication (FFF), compared to dies produced with digital light processing (DLP), addressing the limited evidence on the deviations of FFF-based removable dies. Methods A typodont with a prepared right mandibular first molar was digitized to design a removable die and corresponding hollow partial arch cast. Forty dies (n = 10) and four casts (n = 1) were fabricated using FFF (Filadent Aligner [FF-AL], Filadent Gypsum [FF-GP], Filadent Tray [FF-TR]) or DLP (DentaModel [DM]). Dies and their positions in the casts were digitized to assess surface (crown, root, root base, overall) and positional (crown region and point-based) deviations. Data were analyzed either with one-way analysis of variance (surface deviations) or Kruskal-Wallis tests (positional deviations, α = 0.05). Results DM exhibited the lowest crown region and overall deviations, followed by FF-TR (P < 0.001). Root deviations increased in the order of DM, FF-TR, FF-AL, and FF-GP, whereas FF-TR had the lowest base of the root deviations (P < 0.001). Seated FF-GP dies had lower crown region deviations than the other FFF-based dies, while DM led to lower deviations than FF-TR (P ≤ 0.041). FF-AL showed lower point-based deviations than FF-GP (P = 0.001). Conclusions FFF-fabricated dies showed lower surface trueness than DM dies, with FF-TR achieving the highest trueness among FFF dies. Positional deviations remained within clinically acceptable limits, though FF-TR dies tended to be positioned coronally and the others apically. FFF may be used to produce clinically acceptable dies, but DLP offers superior surface trueness. Clinical Significance Removable dies produced with the tested polylactic acid filaments and FFF printer may serve as alternatives to those fabricated with the tested resin and vat polymerization printer, given the small and potentially clinically irrelevant differences in surface deviations and clinically acceptable mean positional deviations.

Statement of problem Whether the manufacturing protocol (build orientation and sintering schedule) of additively manufactured (AM) zirconia impacts the bond strength compared with subtractively manufactured (SM) zirconia remains unclear. Purpose The purpose of this in vitro study was to evaluate the effect of build orientation (45 degrees and vertical), sintering schedule (1-step and 2-step), and resin cement on the shear bond strength (SBS) and failure mode of AM zirconia bonded to dentin compared with that of SM zirconia. Material and methods One hundred fifty 3Y-TZP zirconia cylinders (Ø2×4 mm) were produced by AM (INNI Cera BCM-W1000) or SM (IPS e.max ZirCAD MT). AM specimens were printed vertically at 90 degrees or at 45 degrees and subjected to 1-step or 2-step sintering; SM specimens were milled and sintered. The specimens were divided into 3 subgroups to be luted to human dentin (n=10) with 3 dual-polymerizing resin cements (SpeedCEM Plus; Ivoclar AG, RelyX Ultimate; 3M Dental, Panavia V5; Kuraray Noritake Dental). Dentin and zirconia surfaces were pretreated per cement and manufacturer protocols. After 24 hours, SBS was measured, and failure modes evaluated. The data were analyzed using 2-way ANOVA to assess the effects of manufacturing technique (AM or SM) and resin cement and using 3-way ANOVA exclusively within the AM group to evaluate the effects of build orientation, sintering schedule, and resin cement, followed by Tukey post hoc tests (α=.05). Results According to the 2-way ANOVA, zirconia manufacturing technique (AM or SM) did not significantly influence SBS, whereas resin cement had a significant effect (P<.001). Within the AM groups, the 3-way ANOVA revealed that resin cement was also the only factor significantly affecting SBS (P<.001), with no significant effects of build orientation or sintering schedule (P>.05). SpeedCEM Plus (8.9 ±3.7 MPa) showed the significantly lowest SBS and RelyX Ultimate (15.1 ±5.3 MPa), and Panavia V5 (15.7 ±4.9 MPa) yielded similar SBS. No significant difference was found in failure mode between AM and SM zirconia (P=.647), but differences existed between cements (P<.001). Almost all failures (98%) in SpeedCEM Plus groups were adhesive at the dentin-cement interface. The RelyX Ultimate and Panavia V5 groups had approximately 20% adhesive and approximately 50% cohesive failures within dentin. Conclusions No significant differences in SBS or failure mode were found between AM and SM zirconia. Build orientation and sintering schedule of AM zirconia had no influence on the bond strength of zirconia to dentin, whereas resin cement had a significant effect. In general, SpeedCEM Plus resulted in the significantly lower bond strength of AM and SM zirconia to dentin than did RelyX Ultimate or Panavia V5.

Statement of problem Biobased dental cast resins and nonhazardous postprocessing cleaning solutions have been introduced in efforts to improve the sustainability of additive manufacturing. However, the combined effects of these components on the surface roughness (Ra) and microhardness of additively manufactured dental casts have not been investigated. Purpose The purpose of this in vitro study was to evaluate the Ra and microhardness of biobased dental cast resins cleaned with different postprocessing cleaning solutions and to compare them with those of a conventional dental cast resin cleaned with isopropyl alcohol (IPA). Material and methods Disk-shaped specimens (Ø10×2 mm) were fabricated from 3 biobased dental cast resins, plant-based resin gray (AC), soy-based resin (EX), and FotoDent biobased model resin (FD), and cleaned using methyl ether solvent (MES), IPA, or a water-based cleaning solution (n=12). Additional 12 specimens were fabricated from a conventional dental cast resin (KeyModel Ultra Ivory [KM]) and cleaned with IPA to serve as the control group. After fabrication, the Ra and Vickers microhardness values of all specimens were measured, and representative laser microscope images were made. Test groups were compared with generalized linear model and Bonferroni-corrected post hoc tests, whereas comparisons with the control group were made with 1-way analysis of variance and post hoc Dunnett tests (α=.05). Results For both outcomes, a statistically significant interaction was observed between biobased cast resin and cleaning solution, and significant differences were found between the test and control groups (P≤.009). The water-based solution led to the highest Ra for AC (P≤.001). When MES and IPA were used, FD had the highest Ra (P≤.001). FD also had higher Ra than EX when the water-based solution was used (P=.031). Except for FD and AC cleaned with the water-based solution (P≥.086), all test groups had lower Ra than the control group (P≤.003). MES cleaning led to the highest hardness for EX and FD (P<.001), whereas IPA cleaning led to the highest hardness for AC (P≤.042). EX resin had the highest hardness, regardless of the cleaning solution (P<.001). KM had lower hardness than all test groups (P<.001). AC showed pronounced irregularities with MES and water-based solutions, EX appeared similar across solutions, FD had heterogeneous debris after IPA cleaning, and KM exhibited superficial scratches. Conclusions FD resin generally exhibited higher roughness, while the water-based solution increased AC resin’s roughness. EX resin showed the highest microhardness across all cleaning solutions. Microhardness was the highest after IPA cleaning for AC and after MES cleaning for the other biobased resins. Most test groups had lower roughness than the control, while all showed higher microhardness.

OBJECTIVE:To compare the scan trueness and marginal gaps of monolithic zirconia implant-supported fixed complete prostheses (iFCPs) fabricated using direct and indirect digital workflows. In addition, to compare average marginal gap values of digital analysis and stereomicroscopic image analysis, performing 1-screw test, evaluating potential correlations between them. METHODS:A master model of an edentulous maxilla with four implants following the all-on-4 concept was fabricated and digitized to design a 12-unit zirconia iFCP for evaluating scan accuracy and marginal fit. Two digital workflows-direct (multi-unit abutment level intraoral scanning) and indirect (digitized stone casts from conventional impressions)-were used to design iFCPs (n=8). iFCPs were milled out of zirconia discs in a centralized milling center. Scan trueness and marginal fit were assessed using 3D analysis software through trueness evaluation and vertical gap measurements, including 1-screw test. Vertical gaps were measured also using stereomicroscope images. The scan trueness and vertical gap were analyzed with two-way ANOVA with Bonferroni post hoc, Mann-Whitney U and Dunn's tests, and Spearman's Rho was used for correlation. RESULTS:The IOS scans showed significantly higher scan body distance deviations than LBS scans overall (P ≤ 0.001) and at abutments 13 and 16, with significant effect of scanner-scan body location interactions at y- and z-axes (P ≤ 0.018). Marginal gap values at abutments 13, 16, and 23 were higher for IOS scans in both stereomicroscope and TSP analyses (P =0.038, P =0.001, and P =0.015, respectively), except at abutment 23, where similar marginal gap values were found with TSP. Positive correlations were found between scan body deviations and average gap values using both measurement methods, and between the two methods themselves. CONCLUSIONS:Indirect digital workflows resulted in superior trueness and marginal fit compared to direct digital workflows using IOS. TSP enabled marginal gap values mostly comparable and correlated to those from stereomicroscope, which revealed promising findings for the validity of the technique. CLINICAL SIGNIFICANCE:Investigated indirect digital workflow may provide superior impression trueness and marginal fit for monolithic zirconia implant-supported complete-arch fixed dental prostheses, compared with tested digital workflow, potentially reducing the risk of mechanical and biological complications related to misfit.

OBJECTIVE:To evaluate the effects of margin configuration and pulp chamber depth on the fabrication trueness and internal fit of resin-based endocrowns fabricated with additive (AM) and subtractive manufacturing (SM). METHODS:Four mandibular first molar typodonts prepared with butt joint or 1 mm-wide shoulder margins and 2 mm or 4 mm pulp chamber depths were digitized to design reference endocrowns. These designs were used to fabricate endocrowns with AM (Crowntec [AM-CT], FREEPRINT Crown [AM-FP], Tera Harz TC80DP [AM-GR]) or SM (Tetric CAD [SM-TC]) (n = 7). Surface deviations (external, intaglio, and marginal root mean square, RMS) and triple scan protocol (average gap) were used for digital analyses. Data were analyzed with generalized linear models (α = 0.05). RESULTS:Intaglio RMS was affected by the interaction of all main factors, while all surface deviations were affected by material type-margin configuration interaction. Material type-pulp chamber depth interaction affected intaglio RMS and average gaps, whereas margin configuration-pulp chamber depth interaction affected all outcomes, except intaglio RMS (P ≤ 0.001). AM-GR mostly led to lower intaglio and marginal RMS, while SM-TC mostly led to lower external RMS (P ≤ 0.022). SM-TC endocrowns with 4-mm depth had the highest and AM-GR endocrowns with 4-mm depth mostly had lower average gaps (P ≤ 0.024). CONCLUSIONS:The interactions among the main factors affected the trueness of the tested endocrowns. However, no clear trend emerged that would highlight any subgroup as having the highest trueness. Most endocrowns demonstrated clinically acceptable internal gaps. CLINICAL SIGNIFICANCE:Tested additively manufactured resin-based endocrowns had favorable internal adaptation. However, they may require more chairside adjustments on external surfaces compared to tested subtractively manufactured endocrowns.

STATEMENT OF PROBLEM:Grinding is often required for the clinical adjustments of zirconia restorations; nevertheless, the effects of following regeneration firing processes on additively manufactured zirconia are still unclear. PURPOSE:The purpose of this in vitro study was to evaluate the effects of grinding and regeneration firing (RF) on the phase transformation and biaxial flexural strength (BFS) of additively or subtractively manufactured 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP). MATERIAL AND METHODS:A total of 108 disk-shaped (Ø15×1.5 mm) 3Y-TZP specimens (n=54) were fabricated using either subtractive manufacturing (SM) or additive manufacturing (AM) techniques. Grinding was performed using a 150-μm-grit diamond rotary instrument with a high-speed handpiece, and RF was carried out at 1000 °C for 15 minutes in a sintering furnace. The crystalline phases were analyzed using X-ray powder diffraction (XRD). All specimens were loaded until fracture using a universal testing machine for a biaxial flexural strength test at a crosshead speed of 1 mm/minute. Microstructure and fracture surfaces were examined using scanning electron microscopy. BFS data were statistically analyzed using 1-way ANOVA, followed by the Tukey post hoc test for pairwise comparisons. (α=.05). The Weibull modulus and characteristic strength were calculated to assess the reliability of strength data. RESULTS:Tetragonal-to-monoclinic phase transformation was detected in ground specimens of both AM and SM groups, whereas only the tetragonal phase was observed in their corresponding RF groups. The highest BFS (1427.2 MPa) was observed in ground AM specimens (P<.001). Grinding and RF did not significantly affect the BFS of SM zirconia (P=.927 and P=.999, respectively) but significantly increased the BFS of AM zirconia (P<.001). RF increased the Weibull modulus in both AM (from m=6.98 to 12.25) and SM (from m=5.91 to 8.35) zirconia. CONCLUSIONS:The implementation of RF after grinding is crucial, particularly for AM zirconia, to improve mechanical strength and structural reliability.

OBJECTIVE:To assess how resin type (water-washable [WW] and non-water-washable [NWW] and cleaning solution (water, methyl ether solvent [MES], or isopropyl alcohol [IPA]) affect the dimensional stability of additively manufactured casts over a three-month period. METHODS:Maxillary casts were fabricated using two WW (WW1 and WW2) and one NWW (NWW) cast resins (N = 24). These casts were divided into groups depending on the cleaning solution (water, MES, and IPA) used (n = 8), and digitized one day (T0), one week (T1), two weeks (T2), three weeks (T3), and three months (T4) after fabrication. Deviations were analyzed across regions (anterior, posterior, entire arch, soft tissue, and overall). A generalized linear model was used for statistical analysis (α = 0.05). RESULTS:NWW casts had the lowest anterior, posterior, and entire arch deviations (P < 0.001). WW1 casts mostly showed higher deviations than WW2 casts in these regions when cleaned with water or MES (P ≤ 0.028). WW1 casts had the highest soft tissue deviations within each cleaning solution (P < 0.001). With water, WW1 casts had higher deviations than with MES, while WW2 casts showed lower deviations than NWW casts (P ≤ 0.032). NWW resin or MES led to the lowest entire cast deviations, with the lowest values observed at T0 (P ≤ 0.007). CONCLUSIONS:NWW casts mostly had the highest stability, while WW2 casts mostly had higher stability than WW1 casts. MES led to higher stability for WW resins and resulted in similar or higher stability for NWW resin compared to IPA. CLINICAL SIGNIFICANCE:Tested water-washable resins, particularly when cleaned with methyl ether solvent, may be sustainable alternatives to non-water-washable resin for dentate casts, as their deviations were acceptable for diagnostic and orthodontic purposes for three months. Methyl ether solvent can improve eco-friendliness of the fabrication of casts in tested non-water-washable resin.

STATEMENT OF PROBLEM:Studies on the effects of cleaning solutions and hydrothermal aging on the flexural strength and microhardness of additively manufactured (AM) resins are lacking. PURPOSE:The purpose of this in vitro study was to evaluate the effect of cleaning solution on the flexural strength and microhardness of resins marketed for AM definitive restorations. In addition, the effects of hydrothermal aging and material type on these properties were examined. MATERIAL AND METHODS:Rectangular or disk specimens (n=19) were additively manufactured for flexural strength and microhardness tests from 2 commercially available resins for definitive restorations: a glass-filled composite resin (AM-CR) and a urethane acrylate-based resin (AM-UA). The specimens were divided into 4 groups based on the cleaning solution: 96% ethanol, 98% isopropanol (IPA), water-based solvent, and methyl ether solvent. The specimens were divided into 2 subgroups, nonaged and hydrothermally aged (10 000 thermal cycles), and flexural strength and microhardness tests were performed before and after aging. RESULTS:AM-CR had higher flexural strength with ethanol, IPA, and water-based solvent than AM-UA (P<.004), whereas it had lower flexural strength than AM-UA with methyl ether solvent (P<.001), regardless of aging. AM-CR and AM-UA had higher microhardness with ethanol and IPA compared with the methyl ether solvent (P<.031). AM-CR had higher microhardness with all cleaning solutions than AM-UA, regardless of aging condition (P<.001). CONCLUSIONS:Resin type, cleaning solution, and aging condition affected the flexural strength and microhardness of AM resins intended for definitive restorations. Regardless of hydrothermal aging, AM-CR had the lowest flexural strength when the methyl ether solvent was used, while cleaning solution type did not affect the strength of AM-UA; AM-CR's strength was lower than AM-UA's with methyl ether. Regardless of hydrothermal aging, AM-CR and AM-UA had higher microhardness with ethanol and IPA than with methyl ether solvent. AM-CR had higher microhardness than AM-UA, regardless of cleaning solution. After hydrothermal aging, the microhardness of AM-CR decreased with the water-based solvent.

OBJECTIVE:To compare the fabrication and fit accuracy of additively (AM) and subtractively (SM) manufactured implant-supported fixed complete denture (ISFCD) frameworks in high-performance polymers with those in titanium. METHODS:An edentulous maxillary model with four implants (right first molar, right canine, left canine, and left right first molar) was digitized to design an ISFCD framework, which was used to fabricate a total of 50 frameworks in polyetheretherketone (AM-PEEK and SM-PEEK), polyetherketoneketone (AM-PEKK and SM-PEKK), and titanium (SM-Ti) (n = 10). A laboratory scanner was used to digitize each framework and when the frameworks were seated on the model at the left first molar site with the 1-screw test. The scan files of the frameworks were superimposed over the design file to evaluate the surface and interimplant deviations, while the fit at right first molar, right canine, and left canine sites was assessed with the average gap values. Data were statistically analyzed (α = 0.05). RESULTS:SM-PEEK and SM-Ti frameworks mostly had higher and AM frameworks mostly had lower surface accuracy (P ≤ 0.036). SM-Ti and SM-PEEK frameworks had the lowest molar-to-molar interimplant distance deviations, and AM frameworks had the lowest precision of interimplant distances (P ≤ 0.014) AM-PEKK frameworks mostly had lower average gap accuracy regardless of the abutment site, followed by AM-PEEK (P < 0.001). CONCLUSIONS:SM-PEEK and SM-Ti frameworks mostly had higher and AM frameworks mostly had lower accuracy. AM frameworks had larger marginal gaps. Tested frameworks tended to distort towards the midline.

PURPOSE:To evaluate how commercially available composite resins in varying filler content affect the fabrication and fit accuracy (trueness and precision) of additively manufactured (AM) definitive crowns with different margin thickness and cement gaps by comparing them to subtractively manufactured (SM) polymer-infiltrated ceramic crowns. MATERIALS AND METHODS:Two identical unprepared mandibular right first molars were prepared by an experienced prosthodontist for crowns with either 0.5 mm or 1.0 mm chamfer margins, verified using silicone indexes and a periodontal probe, and then digitized with an industrial-grade scanner. These scan files were used to design reference crowns with either 50-µm or 80-µm cement gaps in standard tessellation language (STL) format. These reference STLs were used to manufacture a total of 112 crowns, 28 crowns for each crown margin thickness-cement gap pair, using three additively manufactured resins with different filler ratios (AM-20-40%, AM-50%, AM-60%) and one SM polymer-infiltrated ceramic network (n = 7). After fabrication, an intraoral scanner was used to obtain STL files of each crown, the prepared typodont teeth, and each crown seated on its corresponding typodont. All STLs were imported into a metrology-grade 3-dimensional (3D) analysis software program to quantify the surface deviations (overall, external, intaglio, and marginal) of the crowns using the root mean square method and their fit with the average gap measurements. Precision was defined as the average of how much each measurement differed from the overall mean. All data were analyzed using generalized linear model analysis and Bonferroni-corrected post-hoc tests (Minitab Software, Version 17) with a significance level set at α = 0.05. RESULTS:The accuracy of external surface deviations and the precision of the average gaps were affected by the interaction among all main factors. The interaction between material type and margin thickness influenced the accuracy of intaglio surface deviations, while the interaction between material type and cement gap affected the accuracy of marginal surface deviations; both interactions impacted the average gaps. In addition, the accuracy of overall deviations was affected by the interaction between margin thickness and cement gap (p ≤ 0.040). AM-20-40% crowns mostly had higher overall accuracy and SM crowns mostly had higher external and intaglio surface accuracy (p ≤ 0.033). AM-20-40% crowns mostly had higher fit accuracy, while the crowns with 0.5 mm-thick margins or 50-µm cement gap had lower average gaps (p ≤ 0.044). CONCLUSIONS:AM crowns in resin with low filler ratio (AM-20-40%) and SM crowns mostly had higher fabrication accuracy, which may enable fewer clinical adjustments and more reliable fabrication than AM crowns in resins with higher filler ratios (AM-50% and AM-60%). Only AM-20-40% and SM crowns with 0.5 mm-thick margins or 50-µm cement gap had average gap values similar to previously reported clinical thresholds.

PURPOSE:This study aimed to compare the dimensional and positional deviations of additively manufactured removable dies fabricated using two bio-based resins and one conventional dental cast resin, while also evaluating these outcomes over a 4-week period. MATERIALS AND METHODS:A right mandibular first molar preparation on a typodont was scanned to digitally design removable dies and hollow partial arch casts. Based on a priori power analysis, a total of 30 dies (n = 10) and three hollow casts (n = 1) were fabricated using additive manufacturing (AM) from three different dental cast resins: DentaMODEL (DM), FotoDent bio-based model (CB), and soy-based resin (SB). The dies and their seated positions in casts were digitized 1 day (T0), 1 week (T1), 2 weeks (T2), 3 weeks (T3), and 4 weeks (T4) after fabrication. Dies' dimensional deviations (crown, root, base of the root, and overall) and positional deviations in casts (crown region surface and point-based) at T0 were defined as trueness, while deviations measured over 4 weeks (T0-T4) were defined as stability. The deviations measured at T0 were analyzed either using a generalized linear model (dimensional deviations) or one-way analysis of variance (crown region and point-based deviations). The deviations measured over the 4-week period were analyzed with generalized linear model analysis and Bonferroni-corrected post hoc tests (α = 0.05). RESULTS:CB dies mostly had the lowest and SB dies mostly had the highest dimensional deviations (p ≤ 0.001). The crown region had the lowest dimensional deviations, while the dimensional deviations measured at T3 were higher than those at T2 and T4 (p ≤ 0.003). SB dies had the highest and CB dies had the lowest positional deviations, while crown region deviations were lower at T0 and T1 than at T4, and point-based deviations were lower at T0 than at T4 (p ≤ 0.049). CONCLUSIONS:CB dies mostly had better dimensional and positional trueness and stability over 4 weeks. The changes in tested outcomes for all dies over time were small.

OBJECTIVE:To evaluate the effect of the manufacturing trinomial (manufacturing technology, three-dimensional printer, and material) and restoration thickness on the fabrication trueness, fit, and margin quality of additively manufactured resin-based ultrathin laminate veneers (LVs) by comparing to those produced subtractively. METHODS:Reference LVs were designed from the scan files of two identical maxillary central incisor typodonts prepared for 0.3 mm and 0.5 mm LVs. LVs were manufactured additively with resins of different compositions, either using a tilting stereolithography (Irix Max [AM-IX] and Irix Plus [AM-IP]) or a digital light processing printer (VarseoSmile Crown Plus [AM-VS] and Tera Harz TC- 80DP [AM-GR]), and subtractively (Tetric CAD [SM-TC]) (n = 10). All LVs were digitized to evaluate their fabrication trueness and fit. The margin quality was assessed through visual examination. The trueness and fit data were analyzed with two-way analysis of variance and Tukey tests, while the chi-squared test was used to evaluate the margin quality (α = 0.05). RESULTS:The interaction between the main factors and the manufacturing trinomial affected the fabrication trueness and fit, while restoration thickness affected the fit of tested LVs (P ≤ 0.001). AM-IP mostly had the lowest deviations, followed by AM-IX, and mostly had the lowest gaps (P ≤ 0.037). Thinner LVs had lower gaps (P < 0.001). Tested LVs mostly had slightly rough margins with small defects. CONCLUSIONS:LVs fabricated with the tilting stereolithography printer mostly had higher trueness. Using AM-IP or fabricating 0.3 mm LVs improved the fit. Nevertheless, all tested LVs had clinically accep fit. CLINICAL SIGNIFICANCE:Ultrathin laminate veneers fabricated with the manufacturing trinomial involving tested tilting stereolithography printer and resins may require less clinical adjustments. In addition, one of the resins (AM-IP) within this manufacturing trinomial or fabricating 0.3 mm laminate veneers may improve the fit.

OBJECTIVE:To evaluate the effects of multi-stacking and resin type on the dimensional stability of additively manufactured (AM) dentate casts. METHODS:A master maxillary dentate model file was used to AM casts in a multi-stacked manner, consisting of four layers (L1-L4), using two different resins (DentaMODEL [DM] and KeyModel Ultra Ivory [KM], n = 10). Each cast was digitized one day, one week, two weeks, three weeks, four weeks, and three months after fabrication (T0-T5). The scan files were superimposed over the master file to evaluate the dimensional stability of the casts (anterior, posterior, and entire arch) using the root mean square method. Data were analyzed with a generalized linear model (α = 0.05). RESULTS:KM casts had their highest anterior and entire arch deviations when printed at L4 (P < 0.001). DM casts mostly had lower deviations than KM casts across tested layers and storage durations (P < 0.001). DM casts showed the highest anterior deviations at T1 and T2, while KM casts showed the highest at T0, T3, and T4 (P ≤ 0.009). Casts printed at L4 showed the highest anterior deviations at T0 and greater deviations than L1 at T3 and T5, regardless of resin (P ≤ 0.044). KM casts had lower entire arch deviations at T5 than at T3 (P = 0.027). CONCLUSIONS:While the differences due to stacking were minimal and clinically negligible, the DM casts mostly had higher stability. All casts remained within clinically acceptable limits over three months. CLINICAL SIGNIFICANCE:Multi-stacking during printing may be an efficient method for large-scale of plateless dentate casts with clinically acceptable dimensional stability for diagnostic and orthodontic use over three months, when tested resins and three-dimensional printer are used.

Statement of problem Additive manufacturing enables the fabrication of definitive resin 1-piece endodontic crowns, but information on how resin type and preparation design affect their fracture strength is limited. Purpose This in vitro study aimed to evaluate the effects of material type, margin configuration, and pulp chamber depth on the fracture strength of additively manufactured (AM) 1-piece endodontic crowns compared with those subtractively manufactured (SM). Material and methods One-piece endodontic crowns were designed by using the scans of 4 mandibular first molar typodonts prepared with either butt joint or 1-mm shoulder margins and pulp chamber depths of 2 mm or 4 mm. These designs were used to fabricate specimens either additively (Tera Harz TC80DP [GR], FREEPRINT Crown [FP], Crowntec [CT]) or subtractively (Tetric CAD [TC]) (n=7). Scans of the prepared typodonts were used to additively manufacture resin dies, and each specimen was cemented to its corresponding die using a dual-polymerizing resin cement. After cementation, all specimens were subjected to cyclic loading (1.2 million cycles, 49 N) before the load-to-fracture test. Fracture load data were analyzed with a generalized linear model and Bonferroni-corrected post hoc tests (ɑ=.05). Results All specimens survived cyclic loading and were subjected to the load-to-fracture test. The interaction among all main factors affected measured values (P=.028). CT led to the highest fracture load among the specimens with butt joint margins and 4-mm depth, while TC led to the highest values among those with shoulder margins, regardless of the pulp chamber depth (P≤.002). Butt joint margins resulted in higher values for GR and CT specimens with 4-mm depth, while shoulder margins led to higher values for FP and CT specimens with 2-mm depth, as well as for TC specimens (P≤.020). A depth of 4 mm resulted in higher values for all specimens with butt joint margins and for TC specimens with shoulder margins, whereas 2-mm depth led to higher values for FP specimens with shoulder margins (P≤.016). Conclusions The fracture strength of the tested 1-piece endodontic crowns was affected by the material type, margin configuration, and pulp chamber depth. However, all specimens had acceptable mean fracture load values according to the previously reported masticatory forces of the molar region.

STATEMENT OF PROBLEM:Research on the mechanical performance, particularly the fracture resistance, of recently introduced glass-composite and hybrid ceramic resin materials used with additive manufacturing (AM) and subtractive manufacturing (SM) techniques, and indicated for definitive restorations, remains limited. PURPOSE:The purpose of this in vitro study was to evaluate and compare the fracture resistance of AM or SM crowns in different resin-based materials through fatigue cyclic loading and load-to-fracture testing. MATERIAL AND METHODS:A standardized maxillary molar preparation was used to fabricate a zirconia master die, which was then scanned and reproduced in resin using a digital light processing (DLP) 3-dimensional (3D) printer. Two resins for AM (Pro Resins Crown X and Flexcera Smile Ultra+) and 2 resins for SM (Shofu HC and Brilliant Crios), all containing inorganic fillers (glass or ceramic), were used to fabricate identical computer-aided design (CAD) crowns (n=15). These crowns were then cemented using a standard protocol. Specimens underwent fatigue cyclic loading via 1.2 million cycles at 49 N, followed by the load-to-fracture test using a universal testing machine. Statistical analysis included 1-way ANOVA and the Tukey post hoc test (α=.05). RESULTS:All crowns withstood cyclic loading. A statistically significant difference in fracture load was observed across different crowns manufactured by using different resin-manufacturing technology pairs (P<.001). SM-S group exhibited the lowest fracture resistance (2184 ±660.2 N), whereas the other 3 groups exceeded 2500 N, with no significant differences among them (P>.05). CONCLUSIONS:AM crowns demonstrated fracture resistance comparable to SM crowns during and after fatigue cyclic loading and load-to-fracture tests. All crowns showed fracture resistance loads higher than previously reported clinically acceptable load values, supporting their potential for clinical use.