Effect of a calibration aid and the intraoral scanner on the registration of a partially edentulous maxilla: An in vitro study.

STATEMENT OF PROBLEM: Precise data are a prerequisite for accurately fitting restorations. Therefore, intraoral scanners have to be reliable. Data on differences between the same model of intraoral scanning systems are lacking. PURPOSE: This in vitro study evaluated differences in the scanning accuracy of a partially edentulous maxilla between combinations of new intraoral scanners of a single model from the same manufacturer (Primescan; Dentsply Sirona) and several calibration aids. MATERIAL AND METHODS: The in vitro reference model simulated a maxilla with 6 prepared teeth for a complete arch fixed partial denture. Five precision ceramic balls were used to detect dimensional deviation between the reference model and the scan. Distances were divided into 4 categories, from short distances between 2 neighboring precision balls to the cross-arch distance with the scan path comprising all 5 balls. For each combination of 4 new intraoral scanners and their respective calibration aids, 12 model registrations were generated. The data were statistically analyzed using ANOVA (α=.05). RESULTS: Distance deviations increased with increasing scan path length and were significantly affected by the covariates "scanner" (P≤.023) and, for 3 of 4 distance categories, the "calibration aid" (short, medium, and long distances: P≤.013). For short and medium distances, acceptable scanning results were achieved for all test groups. The largest deviation was 539 µm for the cross-arch distance. CONCLUSIONS: Scanning accuracy depends on the scanner and the calibration aid used, in particular, for spans exceeding a single quadrant.

Biaxial flexural strength of 3D-printed 3Y-TZP zirconia using a novel ceramic printer.

OBJECTIVES: To compare the strength and reliability of 3D-printed 3Y-TZP zirconia manufactured with various printing orientations and staining. MATERIALS AND METHODS: A total of one-hundred cylindrical zirconia specimens were designed and fabricated using 3D printing and processed according to ISO 6872 standards. Of these specimens, 80 were 3D printed using the new ZIPRO-D (ZD) 3D ceramic printer. In this ZD group, 60 specimens were printed in a vertical orientation and were either stained after debinding (ZD1, x-orientation, n = 20) or not stained (ZD2, x-orientation, n = 20; ZD3, y-orientation, n = 20) and the remaining 20 specimens out of n = 80 were printed in a horizontal orientation (ZD4). Further 20 specimens out of the entire sample N = 100 were printed vertically with the CeraFab7500 3D ceramic printer (LC). All completed specimens were loaded until fracture using a universal testing machine. Biaxial flexural strengths and Weibull parameters were computed for the ZD groups and for the LC group. Group and sub-group effects were evaluated using Welch ANOVA (alpha = 0.05). RESULTS: The mean (standard deviation, SD) biaxial flexural strengths of vertically oriented ZD samples with (ZD1) and without (ZD2/ZD3) staining were 811 (197) and 850 (152) MPa, respectively (p > 0.05). The ZD4 (horizontally printed), 1107 (144) MPa, and LC (1238 (327)) MPa samples had higher mean (SD) flexural strengths than the ZD1-3 specimens. No difference was observed between the ZD4 and LC group (p > 0.05). Weibull moduli were between m = 4.6 (ZD1) and 9.1 (ZD4) in the ZD group and m = 3.5 in the LC group. CONCLUSIONS: All tested 3D-printed zirconia specimens exceeded the flexural strengths required for class 5 restorations according to ISO 6872 standards. While the flexural strengths of zirconia printed using the novel ZD device in the vertical orientation are lower than those of zirconia printed using the LC printer, the ZD printer shows at least comparable reliability. CLINICAL RELEVANCE: 3D-printing of zirconia is a new technology in dental application. Based on the presented strengths values, clinical application of 3D-printed zirconia for fixed dental protheses can be recommended.

Initial damage and failure load of zirconia-ceramic and metal-ceramic posterior cantilever fixed partial dentures.

OBJECTIVES: The aim of this study was to compare failure load and initial damage in monolithic, partially veneered, and completely veneered (translucent) zirconia cantilevered fixed partial dentures (CFPDs), as well as completely veneered metal-ceramic CFPDs under different support and loading configurations. MATERIALS AND METHODS: Eight test groups with anatomically congruent CFPDs (n = 8/group) were fabricated, differing in CFPD material/support structure/loading direction (load applied via steel ball (Ø 6 mm) 3 mm from the distal end of the pontic for axial loading with a 2-point contact on the inner cusp ridges of the buccal and oral cusps and 1.3 mm below the oral cusp tip for 30° oblique loading): (1) monolithic zirconia/CoCr abutment teeth/axial, (2) monolithic zirconia/CoCr abutment teeth/oblique, (3) partially veneered zirconia/CoCr abutment teeth/axial, (4) partially veneered zirconia/CoCr abutment teeth/oblique, (5) completely veneered zirconia/CoCr abutment teeth/axial, (6) completely veneered CoCr/CoCr abutment teeth/axial (control group), (7) partially veneered zirconia/implants/axial, and (8) partially veneered zirconia/natural teeth/axial. Restorations were artificially aged before failure testing. Statistical analysis was conducted using one-way ANOVA and Tukey post hoc tests. RESULTS: Mean failure loads ranged from 392 N (group 8) to 1181 N (group 1). Axially loaded monolithic zirconia CFPDs (group 1) and controls (group 6) showed significantly higher failure loads. Oblique loading significantly reduced failure loads for monolithic zirconia CFPDs (group 2). Initial damage was observed in all groups except monolithic zirconia groups, and fractography revealed design flaws (sharp edges at the occlusal boundary of the veneering window) in partially veneered zirconia CFPDs. CONCLUSIONS: Monolithic zirconia CFPDs might be a viable alternative to completely veneered CoCr CFPDs in terms of fracture load. However, oblique loading of monolithic zirconia CFPDs should be avoided in clinical scenarios. Design improvements are required for partially veneered zirconia CFPDs to enhance their load-bearing capacity. CLINICAL RELEVANCE: Monolithic zirconia may represent a viable all-ceramic alternative to the established metal-ceramic option for CFPD fabrication. However, in daily clinical practice, careful occlusal adjustment and regular monitoring should ensure that oblique loading of the cantilever is avoided.

Fracture Resistance of Posterior Tooth-Supported Cantilever Fixed Dental Prostheses of Different Zirconia Generations and Framework Thicknesses: An In Vitro Study.

The rehabilitation of free-end situations is a frequent indication in prosthetic dentistry. Cantilever fixed dental prostheses (cFDPs) made of 1st and 2nd generation zirconia are one treatment option. Due to a unique gradient technology, combinations of different zirconium dioxide generations are thus feasible in one restoration. However, data about these materials are rare. The purpose of this study was therefore to investigate the fracture resistance and fracture modes of tooth-supported cFDPs fabricated from different zirconia materials (gradient technology) and different framework thicknesses. A total of 40 cFDPs were fabricated using the CAD/CAM approach and belonged to five test groups. The different groups differed in the yttria content, the proportion of the tetragonal/cubic phases, or in wall thickness (0.7 mm or 1 mm). After completion, the cFDPs were subjected to thermal cycling and chewing simulation (1.2 × 106 load cycles, 108 N load). Afterwards, cFDPs were statically loaded until fracture in a universal testing machine. A non-parametric ANOVA was compiled to determine the possible effects of group membership on fracture resistance. In addition, post-hoc Tukey tests were used for bivariate comparisons. The mean fracture loads under axial load application ranged from 288 to 577 N. ANOVA detected a significant impact of the used material on the fracture resistances (p < 0.001). Therefore, the use of cFDPs fabricated by gradient technology zirconia may not be unreservedly recommended for clinical use, whereas cFPDs made from 3Y-TZP exhibit fracture resistance above possible masticatory loads in the posterior region.

In vitro pilot study comparing a novel implantoplasty sonic instrumentation protocol with a conventional protocol using burs.

BACKGROUND AND OBJECTIVES: The aim of implantoplasty (IP) is to remove titanium implant layers that have been contaminated and to smoothen the implant surfaces so they retain less plaque. However, existing IP methods are very invasive and reduce implant wall thickness. AIM: To investigate the suitability of novel sonic tips in IP and to compare this novel protocol with conventional abrasive procedures. MATERIALS AND METHODS: Thirty dental implants (Ø 4.1 mm, 10 mm length) were distributed in three groups and investigated according to the protocol of Sivolella et al., with modifications to the instrument's feed rate, the applied contact force, and the speed of implant rotations per minute. The upper third of the implant was processed with a diamond-coated bur (BUR) or novel non-diamond-coated sonic tips (AIRSCALER). After standardized IP, the surfaces were analyzed by tactile profilometry and scanning electron microscopy (SEM). Changes in implant weight, implant material loss, and implant fracture strength were assessed. RESULTS: The mean roughness (Ra , Sa ), implant material loss, and change in implant weight were significantly lower in the AIRSCALER group than in the BUR group, whereas the mean compression resistance values were significantly higher in the AIRSCALER group than in the BUR group. CONCLUSIONS: IP with uncoated sonic tips smoothes the surfaces and reduces structural loss of the implant in the area of microthreads. This new IP method could be of great clinical importance, especially for implants with microthreads and reduced diameter or wall thickness.

Tooth mobility restriction by multistranded and CAD/CAM retainers-an in vitro study.

OBJECTIVES: Orthodontic retainers should restrict physiological tooth mobility as little as possible. While this has been investigated for multistranded retainers, there is a lack of data for novel CAD/CAM retainers. To address this, the present study compared the restriction of physiological tooth mobility in multistranded retainers and different CAD/CAM retainers. MATERIAL/METHODS: One group of multistranded (n = 8) and five groups of CAD/CAM retainers (nickel-titanium (NiTi), titanium grade 5 (Ti5), polyetheretherketone (PEEK), zirconia (ZrO2), and cobalt-chromium (CoCr); each n = 8) bonded from canine to canine were investigated for their influence on vertical and horizontal tooth mobility using an in vitro model of a lower arch in a universal testing machine. Load-deflection curves were determined and statistically analysed. RESULTS: All retainers restricted tooth mobility to varying extents. The retainers had less of an influence on vertical tooth mobility, with less of a difference between retainers (14%-38% restriction). In contrast, significant (P ≤ 0.05) differences were observed between retainers in the restriction of horizontal tooth mobility. ZrO2 retainers had the greatest impact, restricting horizontal tooth mobility by 82% (68 ± 20 µm/100N), followed by CoCr (75%, 94 ± 26 µm/100N) and PEEK (73%, 103 ± 28 µm/100N) CAD/CAM retainers, which had comparable effects on horizontal tooth mobility. Ti5 (54%, 175 ± 66 µm/100N) and NiTi (34%, 248 ± 119 µm/100N) CAD/CAM retainers had less of an influence on horizontal tooth mobility, and were comparable to multistranded retainers (44%, 211 ± 77 µm/100N). LIMITATIONS: This is an in vitro study, so clinical studies are needed to draw clinical conclusions. CONCLUSIONS: Multistranded and CAD/CAM retainers have different effects on tooth mobility in vitro. These effects should be further explored in future in vivo studies.

Effect of firing time and wall thickness on the biaxial flexural strength of 3D-printed zirconia.

OBJECTIVES: To evaluate the effect of accelerated firing on 3D-printed zirconia. METHODS: To check if formulae provided by ISO 6872 can be extended to thin samples, finite element analyses were carried out in advance of fabricating 3-mol% yttria-stabilized tetragonal zirconia polycrystal discs by milling and by 3D-printing. Four groups (n = 38 each) of 3D-printed specimens were produced with two nominal thicknesses (0.6 mm and 1.2 mm) and two firing strategies (long: 51 h, accelerated: 14.5 h). In the milled group (thickness 1.2 mm, n = 30), a standard firing program (9.8 h) was selected. Biaxial flexural strength tests were applied and mean strength, characteristic strength, and Weibull modulus were calculated for each group. Differences were analyzed using Welch ANOVA and Dunnett-T3 post-hoc tests. RESULTS: Maximum tensile stresses occurring during biaxial strength testing can be calculated according to ISO 6872 for thin samples with b > 0.3 mm. Variability of measured strengths values was smaller for milled zirconia compared with 3D-printed zirconia. The 1.2-mm-thick 3D-printed samples had significantly decreased strength after accelerated firing than after long firing. However, for the 0.6-mm-thick samples, comparable mean biaxial strength values of about 1000 MPa were measured for both firing protocols. SIGNIFICANCE: At the moment, long fabrication time for zirconia restorations is a major drawback of 3D-printing when compared with milling technology. This investigation showed that the strength of 0.6-mm-thick zirconia discs fabricated by 3D-printing was not impaired by accelerated firing. Thus, overnight firing of thin-walled 3D-printed zirconia restorations could be possible.

The Effect of Titanium Anodization on the Bond Strength of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) Resin Cement.

PURPOSE: To examine the effects of anodization and different surface modifications of titanium on bond strength to 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) resin cement. MATERIALS AND METHODS: Grade 5 titanium alloy disks (n = 160) were assigned to one of five prebonding surface treatment study groups (polished; polished and anodized; polished, etched, and anodized; sandblasted; sandblasted and anodized). Disks were adhesively bonded with 10-MDP resin cement (Panavia 21; bonding area: 3.3 mm in diameter) to composite resin cylinders. In each study group, tensile bond strength tests were conducted after 24 ± 1 hours and after 6 months (180 ± 2 days) of water storage (n = 16 specimens per water storage subgroup). Debonded specimens were stereomicroscopically analyzed to determine their fracture mode. Statistics included one-way and multifactorial ANOVA and Tukey post hoc tests (α = .05). RESULTS: Anodization and water storage did not significantly (P ≥ .389) affect tensile bond strength. Although subgroups of polished samples had significantly (P ≤ .031) lower bond strengths (subgroup mean values: 20 to 26 MPa) than etched or sandblasted samples (subgroup mean values: 29 to 33 MPa), they nonetheless exceeded the empirical threshold of 10 MPa used as a criterion for clinical recommendation. The fracture mode of all test specimens was predominantly cohesive. CONCLUSIONS: Anodization of titanium surfaces can be performed without weakening the adhesion of 10-MDP-based resin cement to titanium.

Fit and Retention of Cobalt-Chromium Removable Partial Denture Frameworks Fabricated with Selective Laser Melting.

PURPOSE: To evaluate fit and retention of cobalt-chromium removable partial denture (RPD) frameworks fabricated with selective laser melting (SLM). METHODS: Three types of framework for clasp-retained RPDs were virtually designed and fabricated using SLM (n = 30). For comparison, 30 additional frameworks were produced using conventional lost-wax casting. A biomechanical model was created, incorporating extracted teeth mounted on flexible metal posts. Using this model, horizontal constraint forces resulting from a misfit were measured using strain gauges, while vertical forces were not recorded. The constraint force components and resultant forces were determined for all abutment teeth, and the maximum retention force during RPD removal from the model was also assessed. For statistical evaluation, the two fabrication methods were analyzed by calculating the means and standard deviations. RESULTS: The average horizontal constraint forces showed similar values for both fabrication methods (SLM: 3.5 ± 1.0 N, casting: 3.4 ± 1.6 N). The overall scatter of data for cast RPDs was greater compared to those fabricated using SLM, indicating a better reproducibility of the SLM process. With regard to retention, the intended retention force of 5-10 N per abutment tooth was not attained in one of the cast groups, while it was consistently achieved in all SLM groups. CONCLUSIONS: This in vitro study found that SLM is a promising option for the manufacture of cobalt-chromium RPD frameworks in terms of fit and retention.

A new CAD/CAM tooth mobility simulating model for dental in vitro investigations.

OBJECTIVES: To validate a new tooth mobility simulating in vitro model for biomechanical tests of dental appliances and restorations. MATERIAL AND METHODS: Load-deflection curves for teeth in CAD/CAM models (n = 10/group, 6 teeth/model) of the anterior segment of a lower jaw with either low tooth mobility (LM) or high tooth mobility (HM) were recorded with a universal testing device and a Periotest device. All teeth were tested before and after different ageing protocols. Finally, vertical load capacity (Fmax) was tested in all teeth. RESULTS: At F = 100 N load, vertical/horizontal tooth deflections before ageing were 80 ± 10 µm/400 ± 40 µm for LM models and 130 ± 20 µm/610 ± 100 µm for HM models. Periotest values were 1.6 ± 1.4 for LM models and 5.5 ± 1.5 for HM models. These values were within the range of physiological tooth mobility. No visible damage occurred during ageing and simulated ageing had no significant effect on tooth mobility. Fmax values were 494 ± 67 N (LM) and 388 ± 95 N (HM). CONCLUSION: The model is practical, easy to manufacture and can reliably simulate tooth mobility. The model was also validated for long-term testing, so is suitable for investigating various dental appliances and restorations such as retainers, brackets, dental bridges or trauma splints. CLINICAL RELEVANCE: Using this in-vitro model for high standardised investigations of various dental appliances and restorations can protect patients from unnecessary burdens in trials and practice.

Comparison of six different CAD/CAM retainers vs. the stainless steel twistflex retainer: an in vitro investigation of survival rate and stability.

PURPOSE: To compare failure rates and maximum load capacity (Fmax) of six different computer-aided design/computer-aided manufacturing (CAD/CAM) retainers with those of the hand-bent five-stranded stainless steel twistflex retainer. MATERIALS AND METHODS: Six groups (n = 8 per group) of commercially available CAD/CAM retainers (cobalt-chromium [CoCr], titanium grade 5 [Ti5], nickel-titanium [NiTi], zirconia [ZrO2], polyetheretherketone [PEEK], and gold) and twistflex retainers were tested for long-term sufficiency and for Fmax using a self-developed in vitro model. All retainer models underwent a simulated ageing process of about 15 years (1,200,000 chewing cycles with a force magnitude of 65 N at 45° followed by storage in water at 37 °C for 30 days). If retainers did not debond or break during ageing, their Fmax was determined in a universal testing machine. Data were statistically analysed using Kruskal-Wallis and Mann-Whitney U­tests. RESULTS: Twistflex retainers did not fail (0/8) during ageing and had the highest Fmax (445 N ± 51 N). Ti5 retainers were the only CAD/CAM retainers that also did not fail (0/8) and had similar Fmax values (374 N ± 62 N). All other CAD/CAM retainers had higher failure rates during ageing and significantly lower Fmax values (p < 0.01; ZrO2: 1/8, 168 N ± 52 N; gold: 3/8, 130 N ± 52 N; NiTi: 5/8, 162 N ± 132 N; CoCr: 6/8, 122 N ± 100 N; PEEK: 8/8, 65 ± 0 N). Failure was due to breakage in the NiTi retainers and debonding in all other retainers. CONCLUSION: Twistflex retainers remain the gold standard regarding biomechanical properties and long-term sufficiency. Of the CAD/CAM retainers tested, Ti5 retainers seem to be the most suitable alternative. In contrast, all other CAD/CAM retainers investigated in this study showed high failure rates and had significantly lower Fmax values.

Thermo-flexible resin for the 3D printing of occlusal splints: A randomized pilot trial.

OBJECTIVES: To compare the clinical performance of occlusal splints printed from thermo-flexible resin with milled splints. METHODS: A parallel two-arm pilot trial was initiated. Forty-seven patients (n women=38) were recruited from a tertiary care center and randomized using an online tool (sealed envelope). Inclusion criterion was an indication for treatment with a centric relation occlusal splint due to bruxism or any form of painful temporomandibular disorder. Patients were excluded if they were younger than 18 years, unable to attend follow-up appointments, or required another type of splint therapy. Patients received either, a 3D-printed (intervention group, V-print splint comfort, VOCO) or a milled splint (control group, ProArt CAD splint, Ivoclar). Construction software Ceramill M-splint (AmannGirrbach), 3D-printer MAX UV 385 (Asiga) and milling unit PrograMill PM7 (Ivoclar) were used. Follow-up assessments were conducted after 2 weeks and 3 months. Outcome measures were survival, adherence, technical complications, patient satisfaction on a 10-point Likert scale, and maximum wear using superimposition of optical scans. RESULTS: After 3 months, 20/23 intervention group and 18/24 control group participants were assessed. All splints survived. Minor complications were small crack formations on 6 printed and 4 milled splints. Mean patient satisfaction was 8 (SD 1.7) for printed, and 8.1 (SD 2.3) for milled splints (r = 0.1, p = .52). Median maximum wear was highly dispersed with 153 (IQR 140) in posterior and 195 (IQR 537) in frontal segments of printed, and 96 (IQR 78) respectively, 123 (IQR 155) of milled splints, (both: r = 0.31, p = .084). CONCLUSIONS: Within the limitations of a pilot trial, 3D-printed and milled splints performed similarly in terms of patient satisfaction, complication rates and wear behavior. CLINICAL SIGNIFICANCE: Thermo-flexible material was proposed for 3D printing of occlusal splints to overcome mechanical weaknesses of previously available resins. This randomized pilot study provides evidence that this material is a viable alternative to milled splints for at least three months of clinical use. Further evidence on long-term use should be obtained.

Influence of geometric dimensions on early failures of adhesively retained composite resin core build-ups.

OBJECTIVE: To determine the influence of the geometric dimensions of core build-ups on early core build-up failure, that is, loss before definitive prosthesis cementation. MATERIALS AND METHODS: Adhesive core build-ups of exclusively vital teeth in 114 participants were evaluated (n materials: 40 Rebilda DC, 38 Multicore Flow, 36 Clearfil DC Core; n teeth: 8 incisors, 54 premolars, 52 molars). Impressions of the abutment teeth were made (1) after removal of insufficient restorations/caries and (2) after core build-up and preparation for a fixed prosthesis. Digitized model surfaces of both situations were aligned (Geomagic Design X) and core build-up volume (VCBU ), remaining hard tissue volume (VAbut ), and size of the adhesive surface (Aadh ) were assessed. The derived measure dCBU  = VCBU /Aadh can be interpreted as mean arithmetic core build-up thickness. Associations between participant or core build-up design characteristics and the occurrence of early failures were statistically evaluated (SPSS v27, α = 0.05). RESULTS: A total of six (5.3%) core build-up failures were registered. Higher participant age, greater core build-up volume VCBU and greater arithmetic uniform thickness dCBU were associated with a greater incidence of failure in bivariate and univariate, however, not in multivariate statistics. CONCLUSIONS: Core build-up volume and thickness were associated with early success or failure. CLINICAL SIGNIFICANCE: In the case of voluminous/thick core build-ups in relation to the adhesive surface, additional measures, such as the preparation of retentive elements to increase the bonding area, might be considered to reduce the risk of early core build-up failure.

Fit of anterior restorations made of 3D-printed and milled zirconia: An in-vitro study.

OBJECTIVES: To evaluate the fit of zirconia veneers made by either 3D printing or milling. METHODS: A typodont maxillary central incisor was prepared for a 0.5-mm-thick veneer and was reproduced 36 times from resin. Restorations were designed with a 20-µm-wide marginal and a 60-µm-wide internal cement gap, and were made from 3D-printed zirconia (LithaCon 3Y 210, Lithoz, n = 24) and milled zirconia (Cercon ht, DentsplySirona, n = 12). For milled zirconia, a drill compensation was needed to give the milling bur access to the intaglio surface. The restorations were cemented, cross-sectioned, and the cement gap size was analyzed by two raters. Inter-rater reliability was studied at 12 3D-printed veneers (intraclass correlation coefficient, ICC, mixed model, absolute agreement). Twelve remaining 3D-printed restorations were compared with 12 milled restorations regarding fit at three locations: marginally, labially, and at the incisal edge (Mann-Whitney U-tests, α<0.05). RESULTS: Inter-rater reliability was excellent, with an ICC single-measure coefficient of 0.944 (95%-confidence interval: [0.907; 0.966]). Gap sizes (mean ± SD / maximum) were 55 ± 9 / 143 µm at the margins, 68 ± 14 / 130 µm labially, and 78 ± 19 / 176 µm at the incisor edge for 3D-printed veneers. For milled veneers, gap sizes were 44 ± 11 / 141 µm at the margins, 85 ± 19 / 171 µm labially, and 391 ± 26 / 477 µm at the incisor edge. At the margins, the milled veneers outperformed the 3D-printed restorations (p = 0.011). The cement gap at the incisor edge was significantly smaller after 3D printing (p < 0.001). CONCLUSIONS: 3D-printed zirconia restorations showed clinically acceptable mean marginal gaps below 100 µm. Because drill compensation could be omitted with 3D printing, the fit at the sharp incisal edge was significantly tighter than with milling. CLINICAL SIGNIFICANCE: The fit of 3D-printed ceramic anterior restorations meets clinical standards. In addition, 3D printing is associated with a greater geometrical freedom than milling. With regard to fit this feature allows tighter adaptation even after minimally invasive preparation.

Influence of artificial landmarks on the accuracy of complete arch scans in the partially edentulous maxilla: An in vitro study.

STATEMENT OF PROBLEM: Scan path length and the presence of edentulous alveolar ridge sections have a negative influence on scanning accuracy. How different artificial landmarks combined with an adapted scanning method affect accuracy is unclear. PURPOSE: The purpose of this in vitro study was to determine the influence of 2 different artificial landmarks combined with an adapted scanning method on the scanning accuracy of a partially edentulous maxillary model. MATERIAL AND METHODS: The model simulated a maxilla with 6 prepared teeth to accommodate a complete arch fixed partial denture. Five ceramic precision balls (ball center P1-P5), distributed buccally to the dental arch, were used to detect the dimensional and angular changes between the reference model and the intraoral scans. One intraoral scanner (Primescan) was used to make 30 scans each with either the scanning strategy recommended by the manufacturer (M) or with an adapted scanning strategy and the use of a bar (B) or 4 plates (P) as artificial landmarks in the dorsal palate. Data were statistically analyzed using a generalized least squares regression model (α=.05). RESULTS: Scanning with artificial landmarks reduced the maximum absolute distance deviations (M: 249 µm, B: 190 µm, P: 238 µm) and the maximum angle deviations (M: 0.31 degrees, B: 0.28 degrees, P: 0.26 degrees). Vertical distance deviations were improved by 10 to 50% with the use of artificial landmarks. Absolute mean distance deviations were significantly lower for group M (P<.001). In contrast, with artificial landmarks, mean angle (P<.001) and mean vertical distance deviations (P<.014) improved significantly. CONCLUSIONS: Scanning with artificial landmarks in the dorsal palate combined with an adapted scanning method improved the scanning accuracy and reliability of vertical distance deviations.

Predictability and outcome of titanium color after different surface modifications and anodic oxidation.

To investigate the predictability and the outcome of surface modification techniques, including anodization. Four surface modification techniques were evaluated in this in-vitro study: sandblasting (S), polishing+anodizing (PA), sandblasting+anodizing (SA), polishing+etching+ anodizing (PEA). Color coordinates L*, a* and b* were collected using a spectroradiometer. Color differences between all groups were quantified by use of ΔE00. A possible influence of group membership was evaluated using 1-way ANOVA. Pair-wise inter-group comparisons were performed using post-hoc Tukey tests. PA specimens were the brightest and showed a pronounced yellowish and reddish hue. S and SA groups were significantly darker and predictability of outcome was higher compared to another groups. The most predictable surface treatment method is sandblasting. Anodizing techniques come along with the brightest and most chromatic color impression of the titanium.

The effect of titanium anodization on the bond strength of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) resin cement.

PURPOSE: To examine the effects of anodization and different surface modifications of titanium on bond strength to 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) resin cement. MATERIALS AND METHODS: Grade 5 titanium alloy disks (n = 160) were assigned to one of five prebonding surface treatment study groups (polished; polished and anodized; polished, etched, and anodized; sandblasted; sandblasted and anodized). Disks were adhesively bonded with 10-MDP cement (Panavia 21; bonding area: 3.3 mm in diameter) to resin cylinders. In each study group, tensile bond strength tests were conducted after 24 ± 1 hours and after 6 months (180 ± 2 days) of water storage (n = 16 specimens per water storage subgroup). Debonded specimens were stereomicroscopically analyzed to determine their fracture mode. Statistics included one-way and multifactorial analysis of variance and Tukey post hoc tests (α = .05). RESULTS: Anodization and water storage did not significantly (P ≥ .389) affect tensile bond strength. Although subgroups of polished samples had significantly (P ≤ .031) lower bond strengths (subgroup mean values: 20 to 26 MPa) than etched or sandblasted samples (subgroup mean values: 29 to 33 MPa), they nonetheless exceeded the empirical threshold of 10 MPa used as a criterion for clinical recommendation. The fracture mode of all test specimens was predominantly cohesive. CONCLUSION: Anodization of titanium surfaces can be performed without weakening the adhesion of 10-MDP-based resin cement to titanium.

Strength and reliability of zirconia fabricated by additive manufacturing technology.

OBJECTIVES: To test strength and reliability of 3D printed compared to milled zirconia. METHODS: Cylindrical specimens were fabricated from milled (group G1; e.max ZirCAD LT) and from 3D printed (group G2; LithaCon 3Y 230) 3-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP). While G1 and G2 were sintered in one step, a further series (G3) of 3D printed 3Y-TZP was sintered in two steps including intermediate color infiltration. In each group, two different conditioning strategies were applied (n ≥ 20 samples/subgroup): (1) final polishing with #1200 diamond discs according to ISO 6872, and (2) final polishing with #220 diamond discs resulting in imperfectly polished surfaces. All samples were tested to fracture with a universal testing device (cross-head speed: 1 mm/min). Characteristic strengths and Weibull moduli were calculated. Effects were analyzed by means of either ANOVA (homocedastic data) or Welch ANOVA (heterocedastic data). RESULTS: For samples conditioned according to ISO 6872, mean flexural strengths were 1462 ± 105 MPa (G1), 1369 ± 280 MPa (G2), and 1197 ± 317 MPa (G3). For the imperfectly polished subgroups, strength values were 1461 ± 121 MPa (G1), 1349 ± 332 MPa (G2), and 1271 ± 272 MPa (G3). Although all groups showed high mean strength values, the reliability of milled zirconia (Weibull moduli 14 < m <16) outperformed that of the 3D-printed material (3 < m <6). SIGNIFICANCE: Even after color infiltration in a partially sintered state, the tested 3D printed zirconia exceeded the ISO flexural strength criteria for all types of fixed ceramic restorations by far (800 MPa for class 6, ISO 6872), indicating its high potential for clinical use. Further optimization of the internal material structure after sintering might improve the reliability of 3D printed zirconia which is currently inferior to that of milled zirconia.

Orthodontic shear bond strength and ultimate load tests of CAD/CAM produced artificial teeth.

OBJECTIVES: To investigate whether artificial CAD/CAM processed (computer-aided design/manufacturing) teeth could be a feasible option for the production of dental in vitro models for biomechanical testing. MATERIAL AND METHODS: Disks (n = 10 per group) made from two different CAD/CAM-materials, one fiber-reinforced composite (FRC; Trinia, Bicon) and one polymethylmethacrylate-based resin (PMMA; Telio CAD, Ivoclar Vivadent), as well as bovine teeth (n = 10), were tested for their shear bond strength (SBS) and scored according to the adhesive remnant index (ARI). In addition, CAD/CAM-manufactured lower incisor teeth were tested for their ultimate load (Fu). RESULTS: With regard to SBS, both PMMA (17.4 ± 2.2 MPa) and FRC (18.0 ± 2.4 MPa) disks showed no significant difference (p = 0.968) compared to bovine disks (18.0 ± 5.4 MPa). However, the samples differed with regard to their failure mode (PMMA: ARI 4, delamination failure; FRC: ARI 0 and bovine: ARI 1.6, both adhesive failure). With regard to Fu, FRC-based teeth could withstand significantly higher loads (708 ± 126 N) than PMMA-based teeth (345 ± 109 N) (p < 0.01). CONCLUSION: Unlike PMMA-based teeth, teeth made from FRC showed sufficiently high fracture resistance and comparable SBS. Thus, FRC teeth could be a promising alternative for the production of dental in vitro models for orthodontic testing. CLINICAL RELEVANCE: CAD/CAM-processed teeth made from FRC enable the use of standardized geometry and constant material properties. Using FRC teeth in dental in vitro studies has therefore the potential to identify differences between various treatment options with rather small sample sizes, while remaining close to the clinical situation.

In vitro accuracy of digital and conventional impressions in the partially edentulous maxilla.

OBJECTIVES: This in vitro study compared the dimensional accuracy of conventional impressions (CI) with that of digital impressions (DI) in a partially edentulous maxilla. DIs were made by two intraoral scanners, Omnicam (OC) and Primescan (PS). MATERIALS AND METHODS: CI and both intraoral scanners were used to take 30 impressions of two identical reference models. CIs were poured with type 4 gypsum and the saw-cut models were digitized. The reference models simulated a maxilla with six prepared teeth that accommodated a cross-arch fixed partial denture. Center points of five precision balls and center points at the margin level of each prepared tooth were used to detect changes in dimensions and tooth axis between the reference model and the scans. RESULTS: For DI, the largest deviations (176 µm for OC and 122 µm for PS) occurred over the cross-arch. For CI, the largest deviation (118 µm) occurred over the anterior segment. For shorter distances up to a quadrant, DI was superior to CI. For longer scan distances, DI was comparable (2 sextant and anterior segment) or inferior (cross-arch) to CI. Vertical and tooth axis deviations were significantly smaller for CI than for DI (p < 0.001). CONCLUSIONS: The impression method affected the impression accuracy of a partially edentulous maxilla with prepared teeth. DI is recommended for scans up to a quadrant. Larger scan volumes are not yet suitable for fabricating a fixed partial denture because of the high scatter of accuracy values. CLINICAL RELEVANCE: In contrast to conventional impressions, digital impressions lead to comparable or better results concerning scans up to a quadrant. Consequently, for larger scan volumes, several smaller scans should be performed or, if restoration-related not possible, it is recommended to take conventional impressions.