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.

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.

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.

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.

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.

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.

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.

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.

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.

Effect of scan-path length on the scanning accuracy of completely dentate and partially edentulous maxillae.

STATEMENT OF PROBLEM: The accuracy of fit of fixed partial dentures is directly dependent on the accuracy of a digital scan. However, the influence of scan-path length on scanning accuracy is unclear. PURPOSE: The purpose of this in vitro study was to evaluate how scan-path length influenced the scanning accuracy of a completely dentate or partially edentulous maxilla captured by 3 intraoral scanners: Omnicam AC (OC), TRIOS 4 (TR), and Primescan (PS). MATERIAL AND METHODS: Each intraoral scanner was used to make 30 scans each of the 2 clinical scenarios (completely dentate and partially edentulous) simulated with a reference model. The partially edentulous model simulated a maxilla with 6 prepared teeth to support a complete arch fixed partial denture. The missing teeth were then added to create a completely dentate model. The prepared teeth were later used to determine distance, angular, and tooth-axis deviations between the reference model (digitized with high precision before the tests) and the intraoral scans. Data were statistically analyzed by using a linear model or, if not applicable, a type II ANOVA (α=.05). RESULTS: Distance deviations increased linearly as the scan-path length increased. In contrast, angular and tooth-axis deviations did not increase linearly. All types of deviation differed depending on the scanning system used. Regarding the 90% quantile values, total distance deviations related to scan-path length amounted to 1.31 µm/mm (OC), 1.00 µm/mm (PS), and 1.45 µm/mm (TR) for the completely dentate maxilla and 1.10 µm/mm (OC), 1.46 µm/mm (PS), and 1.40 µm/mm (TR) for the partially edentulous maxilla. CONCLUSIONS: Distance deviations became larger as the scan-path length increased.

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.

Three-dimensional accuracy of partially guided implant surgery based on dental magnetic resonance imaging.

OBJECTIVES: To measure in vivo 3D accuracy of backward-planned partially guided implant surgery (PGIS) based on dental magnetic resonance imaging (dMRI). MATERIAL AND METHODS: Thirty-four patients underwent dMRI examinations. Tooth-supported templates were backward planned using standard dental software, 3D-printed, and placed intraorally during a cone beam computed tomography (CBCT) scan. Treatment plans were verified for surgical viability in CBCT, and implants were placed with guiding of the pilot drill. High-precision impressions were taken after healing. The 3D accuracy of 41 implants was evaluated by comparing the virtually planned and definitive implant positions with respect to implant entry point, apex, and axis. Deviations from the dMRI-based implant plans were compared with the maximum deviations calculated for a typical single implant. RESULTS: Twenty-eight implants were placed as planned in dMRI. Evaluation of 3D accuracy revealed mean deviations (99% confidence intervals) of 1.7 ± 0.9mm (1.2-2.1mm) / 2.3 ± 1.1mm (1.8-2.9 mm) / 7.1 ± 4.8° (4.6-9.6°) for entry point / apex / axis. The maximum deviations calculated for the typical single implant surpassed the upper bounds of the 99% CIs for the apex and axis, but not for the entry point. In the 13 other implants, dMRI-based implant plans were optimized after CBCT. Here, deviations between the initial dMRI plan and definitive implant position were only in part higher than in the unaltered group (1.9 ± 1.7 mm [0.5-3.4 mm] / 2.5 ± 1.5 mm [1.2-3.8 mm] / 6.8 ± 3.8° [3.6-10.1°] for entry point / apex / axis). CONCLUSIONS: The 3D accuracy of dMRI-based PGIS was lower than that previously reported for CBCT-based PGIS. Nonetheless, the values seem promising to facilitate backward planning without ionizing radiation.

Disposable plastic trays and their effect on polyether and vinyl polysiloxane impression accuracy-an in vitro study.

OBJECTIVES: To evaluate the dimensional accuracy of impressions taken by use of disposable stock plastic trays and to compare performance with that of metal trays. MATERIALS AND METHODS: From a metallic model incorporating three precision balls and three abutment teeth, one-step dual-phase polyether (PE) and vinyl polysiloxane (VPS) impressions were taken using either metal or disposable plastic trays (n = 10 for each of the resulting four test groups). Respective plaster cast scans were aligned with the reference dataset to evaluate global (distance and angle deviations) and local (trueness and precision) accuracy. Analyses of variance (ANOVA) were conducted to determine group differences. RESULTS: For all impression tray and material combinations, global accuracy was good (mean distance changes < 100 µm) with greatest deviations being observed for distances exceeding one quadrant of the dental arch. In general, distances measured in the plaster casts were too short. Only VPS impressions with plastic trays showed a different behavior with a large percentage of cross-arch distances exceeding the reference value. Mean local accuracy ranged between 6 and 14 µm (trueness), and 6 and 16 µm (precision). On abutment tooth level, metal trays were associated with a significantly better precision (p = 0.015). CONCLUSIONS: The observed distortions of the studied impression trays and materials are small and should enable satisfying clinical impression-taking. CLINICAL RELEVANCE: Cleaning and processing of metal trays before re-use are time-consuming. Especially for patients' management with single crowns and small fixed dental prostheses, disposable plastic trays can be a viable and cost-effective alternative.

Effect of bone quality and quantity on the primary stability of dental implants in a simulated bicortical placement.

OBJECTIVES: Conventional dental implants inserted in the molar region of the maxilla will reach into the sinus maxillaris when alveolar ridge height is limited. When surgery is performed without prior augmentation of the sinus floor, primary stability of the implant is important for successful osseointegration. This study aimed at identifying the impact of bone quality and quantity at the implantation site on primary implant stability of a simulated bicortical placement. MATERIALS AND METHODS: In our in vitro measurements, bone mineral density, total bone thickness and overall cortical bone thickness were assessed by micro-computed tomography (µCT) of pig scapulae, which resembled well the bicortical situation found in human patients. Dental implants were inserted, and micromotion between bone and implant was measured while loading the implant with an axial torque. RESULTS: The main findings were that primary implant stability did not depend on total bone thickness but tended to increase with either increasing bone mineral density or overall cortical bone thickness. CLINICAL RELEVANCE: Limited bone height in the maxilla is a major problem when planning dental implants. To overcome this problem, several approaches, e.g. external or internal sinus floor elevation, have been established. When planning the insertion of a dental implant an important aspect is the primary stability which can be expected. With other factors, the dimensions of the cortical bone might be relevant in this context. It would, therefore, be helpful to define the minimum thickness of cortical bone required to achieve sufficient primary stability, thus avoiding additional surgical intervention.

Color stability of individually stained monolithic zirconia following occlusal adjustment.

OBJECTIVE: To meet esthetic requirements, monolithic zirconia can be stained by color-infiltration. However, adjustments of occlusal surfaces are often necessary, leading to demasking effects if too much of the color-infiltrated layer is removed. The effect of subsequent material removal on color stability of individually stained zirconia is analyzed here. MATERIALS AND METHODS: Thirty-six white zirconia disks were divided into three groups. Standardized staining strategies for tooth colors VITA A2, A3.5, and A4 were developed and applied to the disks. Samples were grinded in nine successive steps from 20 to 500 µm. A spectroradiometer was used to measure the color differences after each step. Regression analyses were performed for color differences from baseline as a function of depth of material removal. Depth of material removal resulting in color changes surpassing the acceptability threshold of ΔE00 = 1.8 was estimated using inverse prediction. RESULTS: Up to 500 µm material removal, color difference ΔE00 changes linearly with the depth of material removal (P < 0.05). Regression analyses showed coefficients of determination (R2 ) of 0.97 (VITA A2), 0.87 (VITA A3.5), and 0.96 (VITA A4). Acceptability threshold was surpassed at 62, 87, and 92 µm, respectively. CONCLUSIONS: Discolorations occur within clinically relevant occlusal adjustments of <100 µm. The effect is more severe with lighter, less saturated tooth colors. CLINICAL SIGNIFICANCE: Staining that is resistant to occlusal adjustments and abrasion is only possible if the staining solution infiltrates sufficiently deep into the ceramic structure. This study provides for the first time in the literature numerical values that describe the thresholds of acceptability of color differences in zirconia ceramics. These values are essential because they determine the extent of possible occlusal adjustments, and thus the color stability. Further research is necessary to improve the infiltration depth of staining solutions.

Accuracy of complete-arch intraoral scans based on confocal microscopy versus optical triangulation: A comparative in vitro study.

STATEMENT OF PROBLEM: Fully digital dentistry is contingent on an accurate digital scan of the complete arch; however, the dimensional accuracy of different scanners for digitizing a complete arch is unclear. PURPOSE: The purpose of this in vitro study was to compare the accuracy of 2 intraoral scanners, TRIOS 3 (TR) and CEREC Omnicam (OC). Accuracy was assessed from changes to reference distances defined along the complete arch of a reference cast including 3 precision balls and 3 prepared teeth. The local accuracy (trueness and precision) of the scanned surface of each prepared tooth was also assessed. MATERIAL AND METHODS: Each intraoral scanner was used to scan a metal mandibular reference cast 20 times in a randomized sequence. The complete dental arch of a mandible in which the second left premolar was missing contained 2 prepared teeth, the first left premolar (LP) and the first left molar (LM) to accommodate a fixed partial denture (FPD) with complete crowns. The arch also contained an inlay preparation on the right second premolar (RP). Stainless-steel precision balls (ball centers P1, P2, and P3), which were welded onto the left second molar (P1), the incisal contact point of the central incisors (P3), and the right first molar (P2), were used to determine dimensional changes over the complete arch. Powder (CEREC Optispray) was applied to the reference cast to reduce reflections. Deviations between the reference cast (digitized with high precision before the tests) and the intraoral scans were calculated using Matlab R2015a and Geomagic Design X. To evaluate dimensional changes, the centers of the balls were determined, and their absolute changes in distance (ΔP1P2, ΔP1P3, and ΔP2P3) were calculated. To calculate accuracy (trueness and precision) in relation to the prepared teeth, the mesh deviation between the intraoral scans and the superimposed reference teeth was determined. The data were statistically analyzed by using a nonparametric rank-based 2-way repeated-measures ANOVA, and differences in least square means for pairwise comparisons were calculated (α=.05). RESULTS: The following mean absolute changes in distance were determined: ΔP1P2, TR: 74.4 µm, OC: 119.6 µm; ΔP1P3, TR: 24.7 µm, OC: 17.2 µm; ΔP2P3, TR: 68.6 µm, OC: 41.2 µm. The scanner did not have a statistically significant effect (P=.118) for distance, and the different distances differed significantly from each other (P<.001). Both scanners provided results acceptable for the fabrication of inlays and short-span FPDs. A complete-crown scan was more accurate than an inlay scan (P<.001). Accuracy and precision were better for TR than for OC (P<.001). CONCLUSIONS: With maximum discrepancies of 192.5 to 294.6 µm across the dental arch, complete-arch scans cannot yet be recommended for the fabrication of long-span FPDs.

Color stability of polymer-infiltrated-ceramics compared with lithium disilicate ceramics and composite.

OBJECTIVE: To investigate the color stability of hybrid ceramics and to compare it to composite and lithium disilicate ceramics. MATERIALS AND METHODS: One hundred eighty samples were fabricated and processed with a semiautomatic grinding and polishing device (final step: 1200 grit). After thermocycling, samples were immersed in a staining solution (five subgroups: water, red wine, curry, black tea, cola) for 4 weeks. A spectroradiometer was used to determine the color of the samples in CIE L*a*b*. Color measurements were performed before staining (baseline, initial color), after thermocycling, after 2 and 4 week storage in staining solution and each after a two stage repolishing approach. Discoloration of specimens was calculated by means of ΔE00 compared to baseline values. RESULTS: All factors (material, staining solution, aging stage) were significantly associated with the extent of discolorations (P < .001). Maximum color changes occurred after 28 days staining (EN: ΔE00 = 4.5 ± 4.0; GB: ΔE00 = 5.0 ± 4.5; LS: ΔE00 = 3.0 ± 2.3) clearly exceeding the 50:50 threshold for acceptable color deviations. Due to repolishing, discoloration of LS samples was almost completely eliminated (ΔE00 = 0.4 ± 0.3) and significantly reduced for the other two materials (EN: ΔE00 = 1.0 ± 0.9; GB: ΔE00 = 0.9 ± 0.4; P = .428). CONCLUSION: Discoloration of hybrid ceramics ranged in-between lithium disilicate and composites, however more comparable to composites. Repolishing could reduce discolorations substantially. CLINICAL RELEVANCE: This study should help dental practitioners to estimate the color stability of common dental materials and the effect of polishing in removal of discolorations.

In vivo accuracy of tooth surface reconstruction based on CBCT and dental MRI-A clinical pilot study.

OBJECTIVES: Guided implant surgery (GIS) requires alignment of virtual models to reconstructions of three-dimensional imaging. Accurate visualization of the tooth surfaces in the imaging datasets is mandatory. In this prospective clinical study, in vivo tooth surface accuracy was determined for GIS using cone-beam computed tomography (CBCT) and dental magnetic resonance imaging (dMRI). MATERIALS AND METHODS: CBCT and 3-Tesla dMRI were performed in 22 consecutive patients (mean age: 54.4 ± 15.2 years; mean number of restorations per jaw: 6.7 ± 2.7). Altogether, 92 teeth were included (31 incisor, 29 canines, 20 premolars, and 12 molars). Surfaces were reconstructed semi-automatically and registered to a reference standard (3D scans of stone models made from full-arch polyether impressions). Reliability of both methods was assessed using intraclass correlation coefficients. Accuracy was evaluated using the two one-sided tests procedure with a predefined equivalence margin of ±0.2 mm root mean square (RMS). RESULTS: Inter- and intrarater reliability of tooth surface reconstruction were comparable for CBCT and dMRI. Geometric deviations were 0.102 ± 0.042 mm RMS for CBCT and 0.261 ± 0.08 mm RMS for dMRI. For a predefined equivalence margin, CBCT and dMRI were statistically equivalent. CBCT, however, was significantly more accurate (p ≤ .0001). For both imaging techniques, accuracy did not differ substantially between different tooth types. CONCLUSION: Cone-beam computed tomography is an accurate and reliable imaging technique for tooth surfaces in vivo, even in the presence of metal artifacts. In comparison, dMRI in vivo accuracy is lower. Still, it allows for tooth surface reconstruction in satisfactory detail and within acceptable acquisition times.

Tooth substance removal for ceramic single crown materials-an in vitro comparison.

OBJECTIVES: The aim of this in vitro study was to compare the tooth structure removal required for currently available ceramic crown materials. MATERIAL AND METHODS: Ninety typodont teeth (60 incisors, 30 molars) were assigned to nine study groups. The teeth were digitized, weighed with a high-precision balance, and fixed in carriers in identical alignment. Full-crown restorations were prepared according to material-specific guidelines for monolithic zirconia (MZ), polymer-infiltrated ceramics (PIC), buccally veneered zirconia (BVZ), feldspathic ceramics (FC), fully veneered zirconia (FVZ), and lithium disilicate (LD). Tooth structure removal was assessed by weighing the teeth before and after preparation. Coronal volume loss was analyzed statistically by use of one-way ANOVA and post-hoc Tukey HSD tests with α = 0.05. RESULTS: Mean tooth structure removal for incisors was 42% (SD 2%) for MZ, 46% (SD 1%) for PIC, 50% (SD 2%) for BVZ, 57% (SD 1%) for FC, 57% (SD 2%) for FVZ, and 59% (SD 2%) for LD. Mean tooth structure removal for molars was 21% (SD 2%) for MZ, 31% (SD 1%) for PIC, and 35% (SD 1%) for LD. Inter-group differences were statistically significant, except for between FC and FVZ. CONCLUSIONS: Preparation of full ceramic crowns for restoration-free teeth is an invasive procedure. Selecting the ceramic material can, however, reduce loss of tooth structure substantially. CLINICAL RELEVANCE: Monolithic zirconia is the least invasive material for the preparation of incisor and molar ceramic single crowns. Prescribing buccally veneered instead of fully veneered zirconia reduces preparation invasiveness significantly.

Fracture behavior of all-ceramic, implant-supported, and tooth-implant-supported fixed dental prostheses.

OBJECTIVES: In vitro investigation of the effects of fixed dental prosthesis (FDP) support and loading conditions on the fracture behavior of all-ceramic, zirconia-based FDP veneered with computer-aided design/computer-aided manufacturing (CAD/CAM)-manufactured lithium disilicate ceramic. MATERIALS AND METHODS: Based on a model for a 3-unit FDP in the molar region (tooth in region 15, implant in region 17), 16 identical zirconia frameworks were fabricated and veneered with milled lithium disilicate ceramic. Another 16 FDPs were manufactured similarly, using a model in which the tooth was replaced by an implant. The specimens underwent 10,000 thermal cycles between 6.5 and 60 °C and 1,200,000 chewing cycles with a force magnitude of 100 N. All were then subsequently loaded until fracture in a universal testing device. Half of the FDPs were subjected to centric and axial loading on the pontic, the others to eccentric and oblique loading on one cusp of the pontic. RESULTS: No failures were observed after artificial aging. Fracture loads of tooth-implant-supported restorations were 1636 ± 158 and 1086 ± 156 N for axial and oblique loading, respectively; implant-supported FDPs fractured at 1789 ± 202 and 1200 ± 68 N, respectively. Differences were significant for load application (P < 0.001) and support type (P = 0.020). For the two types of load application, fracture mode differed substantially: complete fracture was observed for centric and axial loading whereas mixed cohesive/adhesive failure was observed for many FDPs loaded eccentrically and obliquely. CONCLUSIONS: The high incidence of chipping of manually veneered implant-supported all-ceramics restorations might be reduced by use of CAD/CAM-manufactured lithium disilicate veneers. CLINICAL RELEVANCE: FDPs veneered with lithium disilicate resist occlusal forces of 500 N, irrespective of load application and support type. The fracture resistance of implant-supported FDPs was, however, higher than that of combined tooth-implant-supported FDPs. Their clinical use seems to be justified.