Adhesion of tooth fragment after trauma: effect of adhesion strategy and storage in the rescue box.

This study aims to investigate the impact of storage conditions for crown fragments (specifically, whether they were stored within a tooth rescue box or in tap water) on their adhesion to fractured teeth when subjected to two different adhesive systems (namely, total etch and self etch). Sixty maxillary premolars were sectioned to obtain tooth fragments. These fragments were stored briefly (2 hours) and reattached in the following groups: Group 1 (fragments stored in tooth rescue box and reattached with etch and rinse (E&R) technique), Group 2 (fragments stored in tap water and reattached with E&R technique), Group 3 (fragments stored in tooth rescue box and reattached with self-etch (SE) technique), and Group 4 (fragments stored in tap water and reattached SE technique). After reattachment, the bonded tooth fragments underwent thermal cycling (500 cycles, 5-55 °C) and bond strength testing using a universal testing machine. Two-way Analysis of Variance (ANOVA) and Tukey's tests were used for bond strength comparison (p ≤ 0.05). A two-parameter Weibull distribution was conducted to evaluate the reliability of the storage medium and adhesion modality on bond strength. The results showed that measured shear bond values (MPa ± Standard deviation (SD); arranged in descending order) for each group were: Group 2 (Tap water/E&R = 6.5 ± 2.1), Group 1 (Rescue box/E&R = 6.0 ± 2.5), Group 4 (Tap water/E&R = 5.1 ± 2.8), and Group 3 (Rescue box/SE = 3.6 ± 3.2). Significant differences were found only between Groups 2 and 3 (p = 0.002). In conclusion, storing crown fragments in a tooth rescue box did not significantly affect the shear bond strength of the restored tooth. However, fragments reattached using the self-etch technique showed comparable shear bond strength but a higher rate of adhesive failures compared to the E&R technique.

Mechanical and chemical characterization of contemporary occlusal splint materials fabricated with different methods: a systematic review.

OBJECTIVE: To systematically review studies on various occlusal splint materials and describe their mechanical and chemical properties. METHODS: MEDLINE (PubMed), Scopus, and Web of Science searches were conducted for in vitro studies focusing on occlusal splint materials. Two reviewers performed an assessment of the identified studies and data abstraction independently, and this was complimented by an additional hand search. The articles were limited to those in the English language that were published between January 1st, 2012, and December 1st, 2022. RESULTS: The initial search yielded 405 search results of which 274 were selected for full-text review following abstract evaluation. 250 articles that did not meet the inclusion criteria were excluded, and the remaining 25 articles (with 1 article identified from the reference lists of included articles) providing mechanical and chemical values were used in this review. Poly methyl methacrylate (PMMA) -based occlusal splint materials showed the highest values in terms of hardness, wear resistance, flexural strength, flexural modulus, e-modulus, and fracture toughness. The material group with the highest water sorption and water solubility was 3D printed (PR) splint materials. In addition, the lowest degree of double bond conversion was also observed in this group of materials. CONCLUSIONS: The outcome of this review suggests that mechanically and chemically acceptable properties can be attained with PMMA-based occlusal splint materials using both conventional and digital production methods. PR splint materials should not be considered as the primary choice for long-term treatments due to their low mechanical and chemical properties. CLINICAL RELEVANCE: This review provides clinical recommendations for selecting the appropriate material and fabrication method for occlusal splints while taking the patients' needs and the materials´ mechanical and chemical properties into account.

Effect of additional reference objects on accuracy of five intraoral scanners in partially and completely edentulous jaws: An in vitro study.

STATEMENT OF PROBLEM: The effect of additional reference objects on the accuracy of different intraoral scanners for partially and completely edentulous patients has not been investigated sufficiently. PURPOSE: The purpose of this in vitro study was to evaluate the effect of an additional reference object in the form of additional artificial landmarks on the trueness and precision of different intraoral scanners in partially and completely edentulous areas. MATERIAL AND METHODS: Partially and completely edentulous models with 2 and 4 implants (BLT, RC, Institut Straumann AG), respectively, were used in the study. For the digital scan, scan bodies (CARES Mono Scanbody) were attached, and reference data obtained by using industrial scanners. Ten digital scans of the same model were made with each intraoral scanner: PRIMESCAN, TRIOS 3, TRIOS 4, Carestream 3600, and Medit. Then, additional artificial landmarks were attached, and 10 more intraoral scans were made with each device. Computer-aided design files of the scan bodies were aligned to obtain 3-dimensional surfaces with reference and test scanners. Trueness and precision of distance, angulations, and vertical shift between scan bodies were estimated. The Mann-Whitney Wilcoxon or Student 2-sample t test was applied to estimate statistically significant differences between groups (α=.05). RESULTS: In the partially edentulous model, distance trueness mean ±standard deviation values ranged from -46.7 ±15.4 µm (TRIOS 3) to 392.1 ±314.3 µm (Medit) in models without additional artificial landmarks. When additional artificial landmarks were applied, trueness of distance mean ±standard deviation values ranged between -35 ±13 µm (TRIOS 4) and 117.7 ±232.3 µm (CARESTREAM). Trueness mean ±standard deviation values of angulation varied from -0.0 ±0.5 degrees (CARESTREAM) to 0.2 ±0.0 degrees (PRIMESCAN) without additional artificial landmarks and from 0.0 ±0.2 degrees (TRIOS 3) to 0.4 ±0.5 degrees (CARESTREAM) with additional artificial landmarks. Vertical shift trueness measurements varied from -108 ±47.1 µm (TRIOS 4) to 107.2 ±103.5 µm (Medit) without additional artificial landmarks and from -15.0 ±45.0 µm (CARESTREAM) to -86.9 ±42.1 µm (TRIOS 4) with additional artificial landmarks. The additional artificial landmark technique improved the trueness of all measured parameters for the 5 tested intraoral scanners. No statistically significant differences were found among models with or without additional artificial landmarks, except for Medit in all parameters and PRIMESCAN in angle measurements (P<.05). The best precision for distance was found with TRIOS 3 and with PRIMESCAN for angulation and vertical shift. Larger deviations were observed in the completely edentulous situation. The effect of additional artificial landmarks was limited when the accuracy parameters of digital scans were considered. CONCLUSIONS: Scans with and without additional artificial landmarks of partially edentulous conditions scanned by any of the intraoral scanners tested did not influence precision and trueness, except for Medit i500 in the distance and vertical shift parameters and CARESTREAM3600 in vertical shift. Precision and trueness of digital scans of completely edentulous areas were affected, except for Medit i500 for distance, PRIMESCAN and TRIOS 4 for angle, and all systems except TRIOS 4 for vertical shift precision.

Influence of the layer thickness on the flexural strength of aged and nonaged additively manufactured interim dental material.

PURPOSE: To measure the flexural strength and Weibull characteristics of aged and nonaged printed interim dental material fabricated with different layer thickness. MATERIAL AND METHODS: Bars (25×2×2 mm) were additively fabricated by using a polymer printer (Asiga Max) and an interim resin (Nexdent C&B MFH). Specimens were fabricated with the same printing parameters and postprocessing procedures, but with 7 different layer thickness: 50 (control or 50-G group), 10 (10-G group), 25 (25-G group), 75 (75-G group), 100 (100-G group), 125 (125-G group), and 150 µm (150-G group). Two subgroups were created: nonaged and aged subgroups (n = 10). A universal testing machine was selected to measure flexural strength. Two-parameter Weibull distribution values were computed. Two-way ANOVA and Tukey tests were selected for statistical evaluation of the data (α = 0.05). RESULTS: Artificial aging methods (p < 0.001) were a significant predictor of the flexural strength computed. Aged specimens acquired less flexural strength than nonaged specimens. The Weibull distribution obtained the highest shape for nonaged 50-G and 75-G group specimens compared with those of other nonaged groups, while the Weibull distribution showed the highest shape for aged 125-G specimens. CONCLUSIONS: The flexural strength of the additively fabricated interim material examined was not influenced by the layer thickness at which the specimens were fabricated; however, artificial aging techniques reduced its flexural strength. Aged specimens presented lower Weibull distribution values compared with nonaged specimens, except for the 125-G specimens.

Assessing masticatory performance with a colour-mixing ability test using smartphone camera images.

BACKGROUND: Colour-mixing ability tests are frequently used to assess masticatory performance, but the image acquisition process may be cumbersome and technique sensitive. OBJECTIVES: To evaluate the reliability of smartphone camera images in assessing masticatory performance using a colour-mixing ability test. METHODS: Participants were recruited into three groups of dental state (n = 20 each): fully dentate, removable partial denture wearers and complete denture wearers. After performing a colour-mixing ability test, images of the gum specimens (Hue-Check Gum©) were captured with two smartphones and compared with the images obtained from a flatbed scanner by two examiners. The images were analysed with a subjective- (SA) and an opto-electronical assessment (VoH). Inter- and intra-rater reliability were tested. ANOVA models with repeated measures were used for statistical analysis (⍺ = .05). RESULTS: All three image acquisition techniques were able to distinguish masticatory performance between different dental states. For SA, inter-rater reliability was fair to substantial and intra-rater reliability was substantial to almost perfect. For VoH, inter-rater reliability with the smartphones was at times different between two examiners, but the intra-rater assessment was reliable. The opto-electronic analysis with smartphone images underestimated the masticatory performance significantly when compared to the flatbed scanner analysis. Seven-day ageing of the specimens did not significantly affect the results. CONCLUSIONS: The assessment of masticatory performance with the Hue-Check Gum© is a reliable method. The use of smartphones may occasionally underestimate masticatory performance; image acquisition with a flatbed scanner remains the gold standard. A centralised analysis of the photographed wafer may foster the reliability of the diagnosis.

Mechanical stability of dental CAD-CAM restoration materials made of monolithic zirconia, lithium disilicate, and lithium disilicate-strengthened aluminosilicate glass-ceramic with and without fatigue conditions.

STATEMENT OF PROBLEM: Studies investigating the mechanical stability of lithium disilicate-strengthened aluminosilicate glass-ceramic that do not require sintering after milling compared with other computer-aided design and computer-aided manufacturing (CAD-CAM) materials are lacking. PURPOSE: The purpose of this in vitro study was to investigate the flexural strength of CAD-CAM zirconia, lithium disilicate, and lithium disilicate-strengthened aluminosilicate glass-ceramics with and without fatigue conditions. MATERIAL AND METHODS: Specimens (N=90, n=15) (12×4×3 mm) from the following CAD-CAM materials were prepared and polished: lithium disilicate glass-ceramic (IPS e.max CAD); lithium disilicate-strengthened aluminosilicate glass-ceramic (N!ce); and zirconium dioxide ceramic (IPS e.max ZirCAD). All specimens were divided into 2 subgroups: immediate testing without aging and simulation of aging by using a mastication simulator for 1 200 000 cycles (5 °C-55 °C). Thereafter, flexural strength testing was performed by using a universal testing machine (1 mm/min) on nonaged and aged specimens. The data were evaluated by using nonparametric 2-way ANOVA and Wilcoxon rank post hoc tests (α=.05). RESULTS: Both the material type and aging significantly affected the results (P<.001). The interaction was not significant (P>.05). Under nonaged conditions, zirconium dioxide ceramic (1136 ±162 MPa) showed significantly higher mean ±standard deviation flexural strength (P<.001) than lithium disilicate (304 ±34 MPa) and lithium disilicate-strengthened aluminosilicate glass-ceramic (202 ±17 MPa). The glass-ceramic groups were also significantly different from each other (P<.001). After aging, zirconium dioxide (1087.9 ±185.3 MPa) also presented significantly higher mean ±standard deviation flexural strength (P<.001) than lithium disilicate (259 ±62 MPa) and lithium disilicate-strengthened aluminosilicate glass-ceramic (172 ±11 MPa) (P<.001). Aging significantly decreased the flexural strength of lithium disilicate (14.6%) (P=.03) and lithium disilicate-strengthened aluminosilicate glass-ceramic (14.5%) (P=.01) but had minimal effect on the zirconium dioxide ceramic (4.3%) (P=.29). CONCLUSIONS: Among the tested CAD-CAM materials, the mechanical performance of lithium disilicate-strengthened aluminosilicate glass-ceramic was comparable with that of lithium disilicate and considerably lower than that of zirconia. Aging decreased the flexural strength of both lithium disilicate and lithium disilicate-strengthened aluminosilicate glass-ceramic.

Effect of hydrothermal aging on the microhardness of high- and low-viscosity conventional and additively manufactured polymers.

STATEMENT OF PROBLEM: Studies on the microhardness of novel additively manufactured polymers compared with well-established low- and high-viscosity composite resins with regard to chemical composition are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the effect of hydrothermal aging on the microhardness of various conventional and additively manufactured polymers. MATERIAL AND METHODS: Cylindrically shaped specimens (N=240, n=10 per group) (Ø10×2 mm) were either additively manufactured (6 groups) or conventionally (6 groups) manufactured by using 3D (Optiprint Temp [OP; Dentona]; C&B MFH [ND; NextDent]; Saremco print CROWNTEC [SA; Saremco Dental AG]; Temp Print [TP; GC]; 3DELTA ETEMP [DM; Deltamed]; MED690 [ST; Stratasys, Ltd]) or conventional low (Gradia Direct [GR; GC]; Clearfil Majesty [CM; Kuraray Noritake]; Tetric EvoCeram [TE; Ivoclar AG]) and high (Gradia Direct Flo [GR-F; GC]; Clearfil Majesty Flow [CM-F; Kuraray Noritake]; Tetric EvoFlow [TE-F; Ivoclar AG]) viscous materials. All specimens were randomly allotted to 2 different aging methods (no-aging [dry] or aging by thermocycling [TC], ×6000, 5 °C-55 °C) and Vickers hardness (VH) tested (ZHV30; Zwick). Three indentations were made on each specimen (0.98-N load, duration 15 seconds). The calculated average microhardness value of each specimen was statistically analyzed by using 2-way ANOVA and Tukey post hoc tests (α=.05). Two-parameter Weibull distribution was calculated to predict the reliability of material type and aging method on VH. RESULTS: The mean ±standard deviation VH ranged between 17 ±0.5 VHN and 68 ±0.5 VHN in the following ascending order: group STa.05). The mean ±standard deviation of HV for aged (37 ±1 VHN) and nonaged (35 ±1 VHN) specimens were statistically similar (P>.05). The Weibull distribution values presented the highest shape for the aged group SA (37.81). CONCLUSIONS: The choice of the material had a significant effect and resulted in lower hardness for the 3-dimensionally printed materials than for the conventional composite resins. Under fatigue conditions, the choice of the material showed no significant difference when the Vickers microhardness was evaluated.

Clinical outcomes and costs of conventional and digital complete dentures in a university clinic: A retrospective study.

STATEMENT OF PROBLEM: Scientific data analyzing the clinical outcomes and costs of complete dentures fabricated by using conventional and computer-aided design and computer-aided manufacturing (CAD-CAM) processes are lacking. PURPOSE: The purpose of this retrospective study was to compare the treatment duration, financial costs, and postdelivery adjustments of CAD-CAM and conventional removable complete dentures. MATERIAL AND METHODS: Thirty-two edentulous participants (16 women, 16 men; age 35-85 years) who had received either CAD-CAM (n=16) or conventional (n=16) maxillary and mandibular removable complete dentures provided by prosthodontists with a minimum of 2 years of experience were evaluated. The CAD-CAM denture systems were either DDS-AV (AvaDent Digital Dental Solutions) (n=11) or DD-IV (Wieland Digital Denture) (n=5). The total treatment period (days) was recorded at 3 different time points (T0: preliminary alginate impression; T1: denture delivery; T2: last scheduled postdelivery adjustment). Adjustments during the follow-up (after T2) were noted and included the removal of areas of excessive pressure, relining, or repairs. The costs of the dental treatment and the laboratory fees were calculated. The Wilcoxon rank sum tests were used for statistical analysis (α=.05). RESULTS: No statistically significant difference regarding the treatment duration between digitally and conventionally fabricated removable complete dentures was found: T0-T1 (P=.889); T1-T2 (P=.675); T2- T3 (P=.978). No significant difference was found in the number adjustments for areas of excessive pressure, relines, or repairs (P=.757, P=1.000, P=1.000) during the period. Laboratory costs of CAD-CAM removable complete dentures were significantly lower than those of conventional removable complete dentures (P<.001), but clinical fees were similar between groups (P=.596), resulting in a reduction in the overall total costs for the CAD-CAM removable complete dentures (P=.011). Regarding the number of clinical visits, neither the group (conventional/CAD-CAM (P=.945)/DDS-AV/DD-IV [P=.848]) nor the interaction group (conventional/CAD-CAM and DDS-AV/DD-IV)/period (P=.084/P=.171) showed any significant differences. CONCLUSIONS: CAD-CAM removable complete dentures can be considered a viable alternative to conventional removable complete dentures regarding treatment duration, clinical and follow-up visits, adjustments, and maintenance requirements.

Influence of postprocessing rinsing solutions and duration on flexural strength of aged and nonaged additively manufactured interim dental material.

STATEMENT OF PROBLEM: Additive manufacturing procedures for fabricating interim restorations include rinsing postprocessing procedures. However, the impact of different rinsing solutions and times on flexural strength is unknown. PURPOSE: The purpose of this in vitro study was to assess the influence of the rinsing solutions and duration, as well as accelerated aging (thermocycling) procedures, on the flexural strength and Weibull characteristics of an additively manufactured interim dental material. MATERIAL AND METHODS: A bar design (25×2×2 mm) file was used to fabricate all the specimens with 3D printing and an interim material (Nextdent C&B MFH). Five groups were created based on the rinsing solution used during the postprocessing procedures: 91% isopropyl alcohol (IPA) (control or IPA-91), 99% IPA (IPA-99 group), bio-ethyl alcohol 100% (BE group), tripropylene glycol monomethyl ether (TPM) 100% (TPM group), and water miscible formula (Resinaway) (RA group). Each group was divided into 4 subgroups depending on the total rinsing time: 5, 6, 7, and 8 minutes (5, 6, 7, and 8 subgroups). Additionally, each subgroup was distributed between nonaged and aged thermocycling procedures (n=10). Flexural strength measurements were made by using a universal testing machine. Two-parameter Weibull distribution values, including the Weibull modulus, scale (m), and shape (0), were calculated. Three-way ANOVA and pairwise multiple comparison Tukey tests were used to analyze the data (α=.05). RESULTS: Three-way ANOVA showed that the rinsing solution (P<.001), rinsing time (P=.004), and thermocycling procedures (P<.001) were significant predictors of the flexural strength values obtained. The IPA-91 and IPA-99 groups obtained the highest flexural strength, while the RA, TPM, and BE groups obtained the lowest flexural strength. The 7- and 8-minute subgroups obtained the highest flexural strength, while the 5-minute subgroup obtained the lowest flexural strength. The nonaged specimens obtained significantly higher mean flexural strength values than the aged specimens. CONCLUSIONS: The vat-polymerized additively manufactured interim dental material tested with differing rinsing solutions and times demonstrated significant differences in the flexural strength values measured. Accelerated artificial aging procedures significantly decreased the flexural strength of the vat-polymerized interim dental material tested.

Flexural strength of aged and nonaged interim materials fabricated by using milling, additive manufacturing, and a combination of subtractive and additive methods.

STATEMENT OF PROBLEM: Interim dental restorations can be fabricated from additively manufactured ingots. However, the flexural strength and surface roughness of restorations fabricated by using this technique are unknown. PURPOSE: The purpose of this in vitro study was to assess the influence of the manufacturing method (milling, additive manufacturing, or a combination of subtractive and additive methods) and accelerating aging on the flexural strength and surface roughness of interim dental materials. MATERIAL AND METHODS: A bar design (25×2×2 mm) was used to fabricate the specimens by using 3 methods: milling (M group), additive manufacturing (AM group), and a combination of subtractive and additive methods (AM+M group). In the M group, an interim material (CopraTemp PMMA) was used to fabricate the milled (350i imes-icore) specimens. In the AM group, specimens were fabricated by using a printer (Form3B+) and an interim resin (Temporary CB) according to the manufacturer's protocol. In the AM+M group, specimens were milled from AM ingots (Temporary CB) and with the same milling machine as in the M group. Two subgroups were created based on the artificial aging (thermocycling): nonaged and aged (n=10). Flexural strength was calculated by using a universal testing machine, followed by determination of the Weibull distribution. Surface roughness was measured by using a digital microscope. The Shapiro-Wilk test revealed that the flexural strength and surface roughness (Ra) data were normally distributed (P>.05). Two-way ANOVA followed by post hoc multiple comparison Tukey tests were used to examine the data (α=.05). The Shapiro-Wilk test revealed that the surface roughness area data were not normally distributed (P<.05). Therefore, the Kruskal-Wallis followed by pairwise multiple comparisons tests were selected (α=.05). RESULTS: Manufacturing methods (P<.001) and artificial aging (P=.043) were significant factors in the flexural strength measured. The M group had the highest flexural strength mean values (180 MPa), while the AM group showed the lowest flexural strength mean values (77 MPa). Additionally, nonaged specimens (128 MPa) had significantly higher flexural strength values than aged specimens (117 MPa). Manufacturing method (P<.001) was a significant factor in the surface roughness measured. The M group had the highest linear surface roughness mean values (0.86 µm), while the AM group showed the lowest linear surface roughness mean values (0.49 µm). CONCLUSIONS: Manufacturing method and thermocycling influenced the flexural strength and surface roughness of the groups tested.

Chemical Composition and Flexural Strength Discrepancies Between Milled and Lithography-Based Additively Manufactured Zirconia.

PURPOSE: To evaluate the chemical composition, flexural strength, and Weibull characteristics of milled and lithography-based additively manufactured (AM) zirconia. MATERIALS AND METHODS: A virtual design of a bar (25×4×2 mm) was completed using a software program. The standard tessellation language file was used to manufacture all the specimens: 3Y-TZP zirconia (Priti multidisc ZrO2 monochrome) milled (M group) and 3Y-TZP zirconia (LithaCon 3Y 210) lithography-based AM (CeraFab System S65 Medical) (AM group) bar specimens (n = 20). The chemical composition of the specimens was determined by using energy dispersive X-ray (EDAX) elemental analysis in a scanning electron microscope. Flexural strength was measured in all specimens using 3-point bend test according to ISO/CD 6872.2 with a universal testing machine (Instron Model 8501). Two-parameter Weibull distribution values were calculated. The Shapiro-Wilk test revealed that the data were normally distributed (p < 0.05). Flexural strength values were analyzed using independent Student's t-test (α = 0.05). RESULTS: There were no major chemical composition differences observed between M and AM groups. The AM specimens (1518.9 ± 253.9 MPa) exhibited a significantly higher flexural strength mean value compared to the milled (980.5 ± 130.3 MPa) specimens (DF = 13, T-value = -5.97, p < 0.001). The Weibull distribution presented the highest shape for M specimens (11.49) compared to those of AM specimens (6.95). CONCLUSIONS: There was no significant difference in the chemical composition of milled and AM zirconia material tested. AM zirconia tested exhibited significantly higher flexural strength compared with the milled zirconia evaluated.

Retention forces between primary and secondary CAD/CAM manufactured telescopic crowns: an in vitro comparison of common material combinations.

OBJECTIVES: To analyze the retention forces between primary and secondary telescopic crowns milled from various materials and to compare them with the retention forces between cast telescopic crowns made of precious metal alloys. MATERIALS AND METHODS: Primary and secondary crowns (N = 60; n = 10 per group) were fabricated using various material combinations (1: zirconia [ZIR]/polyether ether ketone [PEEK]; 2: titanium grade IV [TI]/PEEK; 3: PEEK/PEEK; 4: non-precious alloy [NPA]/PEEK; 5:NPA/NPA), while precious alloy (PA) was used for the control group (6: PA/PA). The retention forces at 10, 1000, 5000, and 10,000 connection and disconnection cycles and the relative weights were analyzed, applying nonparametric repeated measures ANOVA and post hoc Mann-Whitney and Wilcoxon signed-rank tests (α < 0.05). RESULTS: Globally, significant differences in the retention forces among the materials (p < 0.0001), time points (p < 0.0001), and wear resistance for the various materials (p < 0.0001) were observed. No significant changes in retention forces compared to baseline were observed in groups 2, 4, 5, and 6. A significantly higher weight loss for both primary and secondary crowns was observed in groups 4 and 6. CONCLUSIONS: The material combination in telescopic attachments influences retention forces and wear. Interactions between materials and time were evident, indicating that the change in retention forces differs among the materials. The combinations of milled TI/PEEK and NPA/NPA qualify for further preclinical testing in a more clinically realistic setup, determining a material-specific double-crown design. CLINICAL RELEVANCE: The design of precious alloy telescopic crowns cannot be directly transferred to other milled material combinations due to different retention behaviors.

Flexural strength and Weibull characteristics of stereolithography additive manufactured versus milled zirconia.

STATEMENT OF PROBLEM: Zirconia restorations can be processed by using stereolithography additive manufacturing (AM) technologies. However, whether additive manufactured zirconia could achieve flexural strength values comparable with those of milled zirconia is unclear. PURPOSE: The purpose of this in vitro study was to compare the flexural strength and Weibull characteristics of milled and additive manufactured zirconia. MATERIAL AND METHODS: A total of 40 zirconia bars (25×4×1.2 mm) were obtained by using 2 manufacturing procedures, subtractive (CNC group) (IPS e.max ZirCAD; Ivoclar Vivadent AG) and additive manufacturing (AM group) (3DMix ZrO2; 3DCeram) technologies and assigned to 2 subgroups according to accelerating artificial aging procedures (mastication simulation): nonaged and aged (n=10). Flexural strength was measured in all specimens by using 3-point bend tests according to ISO/CD 6872.2 with a universal testing machine (Instron Model 8501; Instron Corp). Two-parameter Weibull distribution values, including the Weibull modulus, scale (m), and shape (0) were calculated. Flexural strength values were analyzed by using 2-way ANOVA and Student t statistical tests (α=.05). RESULTS: The manufacturing procedure (P<.001), the mastication simulating aging procedure (P<.001), and the interaction between them (P<.001) significantly affected flexural strength values. The CNC group exhibited statistically higher flexural strength values than those in the AM group when the specimens were tested before performing an aging procedure (P<.001) and after mastication simulation (P<.001). Moreover, mastication simulation produced a significant reduction in flexural strength for both the CNC group (P<.039) and the AM group (P<.001). CONCLUSIONS: The manufacturing process reported a significant effect on the flexural strength of the zirconia material tested. Mastication simulation as a means of accelerating artificial aging resulted in the significantly decreased flexural strength values of milled and additively manufactured zirconia material, with the Weibull moduli being significantly higher for the milled groups versus the milled specimens.

Chemical composition, surface roughness, and ceramic bond strength of additively manufactured cobalt-chromium dental alloys.

STATEMENT OF PROBLEM: Selective laser melting (SLM) additive manufacturing (AM) technology is a current option to fabricate cobalt-chromium (Co-Cr) metal frameworks for dental prostheses. However, the Co-Cr alloy composition, surface roughness, and ceramic bond strength values that SLM metals can obtain are not well-defined. PURPOSE: The purpose of this in vitro study was to compare the chemical composition, surface roughness, and ceramic shear bond strength of the milled and SLM Co-Cr dental alloys. MATERIAL AND METHODS: A total of 50 disks of 5 mm in diameter and 1 mm in thickness were fabricated by using subtractive (control group) and AM with each of following SLM providers: SLM-1 (EOS), SLM-2 (3D systems), and SLM-3 (Concept Laser). The milled disks were airborne-particle abraded with 100-µm aluminum oxide particles. All the specimens were cleaned before surface roughness (Ra), weight (Wt%), and atomic (At%) percentages were analyzed. Three-dimensional profilometry was used to analyze the topographical properties of the surface parameters Ra (mean surface roughness). The chemical composition of Co-Cr alloy specimens was determined by using energy dispersive X-ray (EDAX) elemental analysis in a scanning electron microscope (SEM). Thereafter, the specimens were bonded to a ceramic (Dentine A3 and Enamel S-59; Creation CC) interface. Specimens were stored for 24 hours at 23 °C. The bond strength of the SLM-ceramic interface was measured by using the macroshear test (SBT) method (n=10). Adhesion tests were performed in a universal testing machine (1 mm/min). The Shapiro-Wilk test revealed that the chemical composition data were not normally distributed. Therefore, the atomic (At%) and weight percentages (Wt%) were analyzed by using the Kruskal-Wallis test, followed by pairwise Mann-Whitney U tests between the control and AM groups (AM-1 to AM-4). However, the Shapiro-Wilk test revealed that the surface roughness (Ra) and ceramic bond strength data were normally distributed. Therefore, data were analyzed by using 1-way ANOVA, followed by the post hoc Sidak test (α=.05). RESULTS: Significant differences were obtained in Wt%, At%, and Ra values among the Co-Cr alloys evaluated (P<.05). Furthermore, the control group revealed significantly lower mean ±standard deviation Ra values (0.79 ±0.11 µm), followed by AM-3 (1.57 ±0.15 µm), AM-2 (1.80 ±0.43 µm), AM-1 (2.43 ±0.34 µm), and AM-4 (2.84 ±0.27 µm). However, no significant differences were obtained in the metal-ceramic shear bond strength among the different groups evaluated, ranging from mean ±standard deviation 75.77 ±11.92 MPa to 83.65 ±12.21 MPa. CONCLUSIONS: Co-Cr dental alloys demonstrated a significant difference in their chemical compositions. Subtractive and additive manufacturing procedures demonstrated a significant influence on the surface roughness of the Co-Cr alloy specimens. However, the metal-ceramic shear bond strength of Co-Cr alloys was found to be independent of the manufacturing process.

Digital workflow for implant-supported fixed complete dentures based on backwards planning in an edentulous patient.

AIM: This case report describes a digital workflow for prosthetically driven surgical planning, implant placement, and the fabrication of two screw-retained, complete-arch, implant-supported dentures in an edentulous patient. The purpose of this case report is to present and discuss the digital steps in the workflow, especially the scanning technique to obtain the centric relation, through a clinical case. The limitations of the workflow are also discussed. MATERIALS AND METHODS: Static computer-aided implant surgery (s-CAIS) was planned three-dimensionally, based on cone beam computed tomography, intraoral optical scanning, and digital bite registration. Using s-CAIS, four and six implants were placed in the edentulous mandible and maxilla, respectively. The final screw-retained complete-arch monolithic zirconia restorations were manufactured based on a digital workflow, using the pre-existing modified radiologic guide for the digital maxillomandibular record. CONCLUSIONS: The evolution of digital processing methods allows for design, processing, and fabrication of implant-supported fixed complete dentures using a surgical, prosthetic, and technical workflow based on 3D restorative backward planning. A digital prosthetic setup and CAD/CAM can be used for the fabrication of intraoral try-ins that serve as a model for the final monolithic zirconia superstructure.

Salivary 8-hydroxyguanosine levels in smokers and non-smokers with chronic periodontitis.

This case-controlled clinical trial was performed on the salivary 8-hydroxyguanosine (8-OHdG) levels in smokers and non-smokers with chronic periodontitis after non-surgical periodontal therapy. Subjects (N = 40) with periodontitis (smokers and non-smokers) and with clinically healthy conditions (smokers and non-smokers) were assigned to this study. At baseline, clinical periodontal parameters (plaque index, gingival index, pocket probing depth and clinical attachment levels) were evaluated. Saliva samples were obtained pre- and post-treatment to quantify the 8-OHdG levels using Elisa technique. Subjects diagnosed with chronic periodontitis with smoking habit (CPs) and non-smokers (CPns) received scaling and root planing. In clinically healthy subjects with smoking habit (CHs) and non-smokers (CHns), only oral hygiene tutoring was performed. All clinical measurements and salivary collection were repeated in a 3-month recall interval. Data were analyzed using Anova, Tukey post hoc test and Mann-Whitney 'U' tests (P < 0.05). At baseline, CPs and CPns groups showed significantly higher PI, GI, PD and CAL values than those of CHns and CHs (P < 0.001). Baseline salivary levels of 8-OHdG were significantly higher in CPs group (14.775 pg/mL) (P < 0.001) compared to the other groups. All clinical parameters in chronic periodontitis group improved at the 3rd month recall interval, however, with regards to 8-OHdG values, the CP smoker category still had a higher level compared to CP non-smoker. This study reflects an on-going periodontal destructive status in smokers and salivary 8-OHdG levels could be recognized as an oxidative biomarker for determining periodontal tissue destruction.

Evaluation of mechanical and adhesion properties of glass ionomer cement incorporating nano-sized hydroxyapatite particles.

Glass ionomer cement is a widely used luting agent for indirect restorations but presents inferior mechanical properties compared to resin cement due to its low elastic modulus. This study evaluated the mechanical and adhesion properties of glass ionomer luting cements reinforced with nano-sized hydroxyapatite particles (HA). The nano-sized HA particles were synthesized using the co-precipitation technique and the resulting precipitate was characterized using X-ray diffraction analysis (XRD), field emission scanning electron (FESEM) and transmission electron microscopy (TEM). HA particles were incorporated into the glass powder (FUJI I, GC) and the luting agent was manipulated in a liquid to powder ratio of 3:1 into 6% by weight after determining the best ratio. The flexural strength of the luting agent and shear bond strength of dentin were analyzed and compared to other luting agents namely, (a) glass ionomer (FUJI I), (b) resin-modified glass ionomer (RelyX Luting Plus) and (c) adhesive resin cement (RelyX U200). Failure types after debonding from dentin were evaluated under SEM. Flexural strength and bond strength data were analyzed using one-way ANOVA and Tukey's tests (alpha = 0.001). Addition of 6 w % HA particles in the range of 80-150 nm enhanced the flexural strength (30.97 ± 5.9 versus 11.65 ± 5.63) and shear bond strength (0.97 ± 0.41 versus 0.39 ± 0.16) of a conventional glass ionomer luting agent significantly compared to the non-reinforced ones when manipulated at a liquid to powder ratio of 3:1 (P < 0.001). While conventional glass ionomer, HA-reinforced glass ionomer and resin-modified glass ionomer specimens showed exclusively mixed type of failures, adhesive resin cement showed cohesive failures within the resin cement. Increased mechanical and adhesion potential of the experimental glass ionomer luting agent after incorporation of HA particles could expand the scope of application of this cement.

Correction To: Evaluation of mechanical and adhesion properties of glass ionomer cement incorporating nano-sized hydroxyapatite particles.

In the original publication of the article, the family name of the author.

A digital cast-free clinical workflow for oral rehabilitation with removable partial dentures: A dental technique.

The present report describes a technique for a digital cast-free clinical workflow for the fabrication of a combined tooth-implant-supported removable partial denture. This technique comprises digital intraoral scanning, computer-aided design, and subtractive computer-aided manufacturing for the denture base, denture teeth, and crowns and additive computer-aided manufacturing for the denture framework (CAD-CAM).

Effect of length of LOCATOR abutment and cement type on retention to intraradicular dentin in overdentures.

STATEMENT OF PROBLEM: Limited information is available on the effect of LOCATOR abutment length and luting cement type on retention to intraradicular dentin in overdentures. PURPOSE: The purpose of this in vitro study was to evaluate the effect of the length of a commercially available LOCATOR abutment and cement type on retention in the root canal. MATERIAL AND METHODS: Eighty LOCATOR abutments with a standard length of 6 mm were obtained. Half of them were shortened to 3 mm. Eighty recently extracted single-rooted teeth were divided into 2 groups. The post space was prepared to 6 mm in the first group and 3 mm in the second. After preparation, the LOCATOR abutments were luted with one of the following cements: dual-polymerized glass-reinforced resin cement (Parapost Paracore), dual-polymerized resin cement (Variolink II), self-adhesive resin cement (RelyX Unicem), and conventional cement (zinc phosphate). The tensile force required for the removal of the LOCATOR abutments from their corresponding roots was recorded. Data were statistically analyzed with 2-way ANOVA and the Tukey multiple comparison test. RESULTS: Both the cement type (P<.001) and the length of the LOCATOR abutment (P<.001) significantly affected the mean tensile forces. Dual-polymerized glass-reinforced resin cement (Parapost Paracore) presented significantly higher mean tensile forces for the LOCATOR abutment retention among all cements (P<.05). CONCLUSIONS: Regardless of the length, LOCATOR abutments luted with Parapost Paracore resin cement presented higher mean resistance to tensile forces compared with those luted with the other cements. LOCATOR abutments of 6 mm in length were more resistant to tensile forces than those of 3 mm in length in combination with all cements.