Can nonhazardous postprocessing cleaning solutions enable adequate surface properties for printed dental casts in different resins?

STATEMENT OF PROBLEM: Printed casts and dental devices and prostheses are increasingly being used, and the ecological impact of additive manufacturing should be considered in addition to the fabrication accuracy and surface properties of the printed object. To overcome the ecological drawbacks of alcohol postprocessing, water-washable, 3-dimensionally (3D) printable cast resins and postprocessing cleaning solutions that do not include alcohol have been introduced. However, whether using only water rather than chemical solvents would enable the surface smoothness and hardness required for accurate diagnostic and prosthetic procedures is unknown. PURPOSE: The purpose of this in vitro study was to evaluate the effect of resin type (water-washable or nonwater washable) and postprocessing cleaning solution on the surface roughness and microhardness of 3D printed dental cast resins. MATERIAL AND METHODS: One hundred eight disk-shaped specimens (Ø10×2 mm) were additively manufactured (AM) from 3 dental cast resins: 2 water-washable (Epax (WW1) and Phrozen (WW2)) and 1 nonwater-washable resin (KeyModel Ultra resin-beige (NWW)) with a printer (n=36). Specimens in each resin type were divided into 3 groups for the application of postprocessing cleaning solution (water, 98% isopropyl alcohol [IPA] or methyl ether solvent) and polymerized after cleaning. The surface roughness (Ra, µm) and Vickers microhardness (HV) were measured. Laser microscope images were made of 1 specimen from each group. RESULTS: NWW-IPA (control group) had a similar Ra to WW2-water (P=.81) and WW2-methyl ether solvent (P=.511). NWW-IPA had lower HV than WW2-water (P<.001) and WW1-methyl ether solvent (P=.001). Solutions had no significant effect on the Ra of WW1 (P≥.554) and WW2 (P≥.805). WW1 had higher surface irregularities with water, whereas no significant difference was visually observed with IPA or methyl ether solvent. Solutions had a similar effect on the surface of WW2 when evaluated visually with the laser microscope. CONCLUSIONS: Resin type and postprocessing cleaning solution affected the surface roughness and microhardness of 3D printed dental cast resins, except for the surface roughness of tested water-washable resins. Water or methyl ether solvent cleaned water-washable resin (WW2) had surface roughness and hardness similar to commonly used nonwater-washable cast resin.

Additive manufacturing trueness and internal fit of crowns in resin modified with a commercially available ceramic composite concentrate.

STATEMENT OF PROBLEM: Inorganic fillers can be incorporated into additively manufactured (AM) resins to improve their properties, and a ceramic composite concentrate has been recently marketed for this purpose. However, knowledge on the printability of AM resins modified with this concentrate is lacking. PURPOSE: The purpose of this in vitro study was to evaluate the manufacturing trueness and internal fit of AM crowns in a dental resin modified with a commercially available ceramic composite concentrate. MATERIAL AND METHODS: A maxillary right first molar typodont tooth was prepared and digitized to design a crown in standard tessellation language (STL) format. This STL file was used to fabricate a total of 30 AM crowns, 10 with a resin with no fillers for interim restorations (AM-I), 10 AM-I resin incorporated with ceramic composite concentrate (AM-IR), and 10 with a ceramic-filled resin intended for definitive restorations (AM-D). The modification of the AM-IR resin was performed by mechanically mixing 30 wt% of a commercially available ceramic composite concentrate into AM-I. An intraoral scanner was used to digitize all crowns, which were then seated on the prepared typodont abutment and rescanned. The manufacturing trueness of each crown was measured in 4 regions (overall, external, intaglio, and marginal) and reported with root mean square (RMS) estimates. The internal gaps were calculated by using a triple scan protocol. The intaglio surface deviations were assessed with the Kruskal-Wallis and Dunn tests, while the remaining data were analyzed with the 1-way analysis of variance and Tukey honestly significant difference tests (α=.05). RESULTS: AM-IR had the highest overall and external RMS and had higher intaglio RMS than AM-D (P≤.001). AM-I had the lowest marginal RMS (P≤.002). AM-IR had the highest average gap values (P≤.027). CONCLUSIONS: AM-IR crowns mostly had lower trueness and high internal gaps. However, the differences among the tested materials in fabrication trueness and average gap values were small, and internal gaps were within the previously reported thresholds.

Complete Digital Workflow for Fabricating an Occlusal Device Using Artificial Intelligence- Powered Design Software and Additive Manufacturing: A Dental Method.

Artificial intelligence (AI) has been expanding into areas that were thought to be reserved for human experts and has a tremendous potential to improve patient care and revolutionize the healthcare field. Recently launched AI-powered dental design solutions enable automated occlusal device design. This article describes a dental method for the complete digital workflow for occlusal device fabrication using two different AIpowered design software programs (Medit Splints and 3Shape Automate) and additive manufacturing. Additionally, the benefits and drawbacks of this workflow were reviewed and compared to conventional workflows.

Effect of Polymerization Unit, Polishing, and Coffee Thermocycling on the Color and Translucency of Additively Manufactured Resins Used for Definitive Prostheses.

PURPOSE: To evaluate the effect of polymerization unit, polishing, and coffee thermocycling on the color and translucency of additively manufactured polyurethane-based resins with different viscosities. In addition, their color behavior was compared with the color of the shade tab throughout the fabrication steps and aging. MATERIALS AND METHODS: Disk-shaped specimens (Ø10 × 2 mm) were fabricated from polyurethane-based resins with different viscosities (Tera Harz TC-80DP and C&B permanent; n = 30 per material). Baseline color coordinates were measured after cleaning. The specimens in each resin group were divided into three subgroups (n = 10 per subgroup) to be polymerized with different polymerization units (Otoflash G171 [FLN], Wash and Cure 2.0 [CLED1], and P Cure [CLED2]), polished, and subjected to coffee thermocycling. Color coordinates were remeasured after each process. Color differences (ΔE00) and relative translucency parameter (RTP) values were calculated. Data were statistically analyzed (α = .05). RESULTS: Time points and polymerization units affected the ΔE00 for each material (P ≤ .049). ΔE00 of each polymerization unit pair had significant differences within and among different time points within each material (P ≤ .024). ΔE00 (when compared with the shade tab) and RTP were mostly affected by polymerization units and time points within both materials (P ≤ .042). CONCLUSIONS: Tested polymerization units, polishing, and coffee thermocycling affected the color difference and translucency of tested resins. Color differences ranged from moderately unacceptable to extremely unacceptable, and the differences in translucency values mostly ranged from perceptible to unacceptable, according to previous thresholds. In addition, tested resin-polymerization unit pairs had unacceptable color differences when compared to the shade tab. CLED1 may enable higher color stability for tested resins.

Effect of Material Thickness and Coffee Thermocycling on the Color Stability and Translucency of Additively and Subtractively Manufactured Resin-Based Materials for Definitive Restorations.

PURPOSE: To evaluate the effect of material thickness and coffee thermocycling on the optical properties of definitive resin-based materials created via additive manufacturing (AM) and subtractive manufacturing (SM). MATERIALS AND METHODS: Specimens were prepared in three thicknesses (1, 1.5, and 2 mm) from three AM (3D-CB, 3D-TH, and 3D-CT) and two SM (G-CAM and VE) resin-based materials (n = 15 per material and thickness combination). Color coordinates of each specimen were measured after polishing and after 10,000 cycles of coffee thermocycling. Color differences (ΔE00s) and relative translucency parameter (RTP) values were calculated. After logarithmic transformation, ΔE00 values were analyzed with two-way ANOVA, while RTP values were analyzed with generalized linear model test (α = .05). RESULTS: 3D-TH had the highest pooled ΔE00 and G-CAM had the lowest (P ≤ .004). 3D-CB had higher pooled ΔE00 than VE and 3D-CT (P ≤ .002). For the SM group, the 1.5-mm and 2-mm 3DCT specimens and 1-mm 3D-TH specimens had lower ΔE00 than 1.5-mm and 2-mm 3D-TH specimens (P ≤ .036). Most of the AM specimens and 1-mm VE specimens had higher ΔE00 than 2-mm G-CAM specimens (P ≤ .029). Further, most AM specimens had higher ΔE00 than 1.5-mm G-CAM specimens (P ≤ .006). RTP values increased in order of 3D-CT, G-CAM, VE, 3D-CB, and 3D-TH specimens (P < .001). Increased thickness and coffee thermocycling mostly reduced RTP (P < .001). CONCLUSIONS: 3D-TH typically had higher color change values than SM specimens, while G-CAM typically had lower color change values than AM specimens. Only the 1.5-mm and 2-mm 3D-TH specimens had unacceptable color changes. Thickness and coffee thermocycling mostly reduced the translucency.

Effect of polymerization unit, polishing, and coffee thermocycling on the color and translucency of additively manufactured resins used for definitive prostheses.

PURPOSE: To evaluate the effect of polymerization unit, polishing, and coffee thermocycling on the color and translucency of additively manufactured polyurethane-based resins with different viscosities. In addition, their color behavior was compared with the color of the shade tab throughout the fabrication steps and aging. MATERIALS AND METHODS: Disk-shaped specimens (Ø10x2 mm) were fabricated from polyurethane-based resins with different viscosities (Tera Harz TC-80DP and C&B permanent) (N=30). Baseline color coordinates were measured after cleaning. The specimens were divided into 3 to be polymerized with different polymerization units (Otoflash G171, FLN; Wash and Cure 2.0, CLED1; CARES P Cure, CLED2) (n=10), polished, and subjected to coffee thermocycling. Color coordinates were remeasured after each process. Color differences (ΔE00) and relative translucency parameter (RTP) values were calculated. Data were statistically analyzed (α=.05). RESULTS: Time points and polymerization units affected the ΔE00 for each material (P≤.049). ΔE00 of each polymerization unit pair had significant differences within and among different time points within each material (P≤.024). ΔE00, when compared with the shade tab, and RTP were mostly affected by polymerization units and time points within both materials (P≤.042). CONCLUSION: Tested polymerization units, polishing, and coffee thermocycling affected the color difference and translucency of tested resins. Color differences ranged from moderately unacceptable to extremely unacceptable and the differences in translucency values mostly ranged from perceptible to unacceptable according to previous thresholds. In addition, tested resin-polymerization unit pairs had unacceptable color differences when compared to the shade tab. CLED1 may enable higher color stability for tested resins.

Assessment and Improvement of Masticatory Performance in Frail Older People: A Narrative Review.

According to the World Health Organization (WHO), the estimated number of older adults is around 962 million and is projected to increase to 2.1 billion by 2050. The oral frailty concept is associated with gradual oral function loss in relation to aging. There is a need to emphasize the improvement of oral function based on an evaluation of masticatory performance in patients with various oral conditions or systemic diseases and especially in the frail elderly. The present narrative review presents an overview of the current state of the assessment and improvement of masticatory performance in frail older people. To fully encompass oral frailty, oro-facial hypofunction, or oro-facial fitness, dental Patient Reported Outcomes (dPROs) should be included; nevertheless, there are limited evidence-based rehabilitation approaches. The concept of oral frailty, oro-facial hypofunction, or oro-facial fitness should involve dental Patient Reported Outcomes (dPROs), and in this sense, there are only a few evidence-based rehabilitation procedures to improve oro-facial hypofunction besides prosthodontics. It must be considered that reduced neuroplastic capacity in old individuals might preclude a positive outcome of these strategies that might need to be accompanied by functional training and nutritional counseling.

Digital and Analog Analysis of Occlusion in Conventional and Implant-Retained Complete Dentures: Preliminary Results of a Prospective Clinical Trial.

PURPOSE: To digitally evaluate the static and dynamic occlusion of patients treated with both removable conventional complete dentures (CCDs) and implant-retained removable overdentures (IODs) and to correlate two different methods of occlusal analysis. MATERIALS AND METHODS: Eleven totally edentulous patients were treated with bimaxillary CCDs. Later, mandibular CCDs were replaced by IODs retained by either two or four implants. The distribution of the occlusal contacts in static and dynamic occlusion was compared by means of the digital method (DM; T-Scan III) and the analog method (AM; articulating paper). Scores 0, 1, and 2 were assigned for inadequate, satisfactory, and adequate distribution of the occlusal contacts, respectively. The frequencies of scores were compared in relation to the types of denture by means of Fisher exact test (P < .05). The correlation between methods was assessed by means of the kappa agreement coefficient (κ) and the correlation coefficient phi (φ) (P < .05). RESULTS: Significant differences between CCDs and IODs were found in the right lateral mandibular movement (DM, P = .024; AM, P = .008), as well as in the left lateral mandibular movement (DM, P = .035). The methods of analysis of the occlusion showed a moderate agreement (κ = 0.604; P < .001) and a moderate correlation (φ = 0.605; P < .001). CONCLUSION: The digital and analog methods showed a significant agreement and moderate correlation, irrespective of the type of complete denture. The T-Scan III digital system seems to be a consistent and reproducible method to analyze occlusion.

Primary and Secondary Stability of Extrashort (4-mm) Implants in the Edentulous Mandible: Preliminary Results of a Prospective Clinical Trial.

PURPOSE: To compare the primary and secondary stability of conventional (≥ 8-mm) and extrashort (4-mm) implants in edentulous patients using different methods of assessment. MATERIALS AND METHODS: Patients underwent implant surgery and were randomly allocated into two groups: test, with two conventional implants in the anterior region and two extrashort (4-mm) implants in the posterior region; and control, with two conventional (≥ 8-mm) implants in the anterior region only. Primary stability (S1-implant placement) was assessed by insertion torque, implant stability quotient (ISQ, Osstell), and damping capacity (PTV, Periotest), while secondary stability (S221-21 days after S1; and S2clip-at prosthetic loading, ± 3 months after S1) was evaluated by ISQ and PTV. The statistical significance level was set at P < .05. RESULTS: Fifty conventional implants and 24 extrashort implants were placed in 25 patients. The overall survival rate was 97.3%. There was no statistically significant difference between the insertion torque of conventional and extrashort implants (P > .05). PTV values were significantly lower for conventional implants only at S2clip (P = .041). ISQ values were significantly greater for conventional implants at S1 (P = .004), whereas at S221 and S2clip, no differences were found (P = .413 and P = .490, respectively). Damping capacity showed no significant differences between S1-S2M21 and S1-S2clip. ISQ values showed a significant increase of stability between S1-S2clip, for conventional (P = .022) and extrashort (P = .005) implants, which was different from that observed between S1-S221. There was a moderate negative correlation between the PTV and ISQ variables (r = 0.5) of extrashort implants, and between the PTV and insertion torque (r = -0.3) of conventional implants. For extrashort implants, there was a null correlation between ISQ and torque (r = 0.0). There was a moderately positive correlation between ISQ and torque (r = 0.3) in the conventional implant group. CONCLUSION: The results suggest that extrashort and conventional implants present similar primary and secondary stability values and may similarly influence restorative protocols.