Comparison of 3D positional accuracy of implant analogs in printed resin models versus conventional stone casts: Effect of implant angulation.

PURPOSE: To study the effect of implant angulation on 3D linear and absolute angular distortions of implant analogs in printed resin models and conventional stone casts. MATERIALS AND METHODS: Three sectional master models with two implants with total inter-implant angulations of 0°, 10°, and 20° were fabricated. For each master model, five conventional stone casts (CS) and printed resin models (PM) were fabricated (n = 5). Test models were made with nonsplinted impression copings and open tray polyether impressions for the CS groups and scan bodies scanned using an intraoral scanner for the PM groups. The physical positions of the implants and implant analogs were measured with a coordinate measuring machine. 3D linear distortion (ΔR) and absolute angular distortion (Absdθ) defined the 3D positional accuracy of the analogs in the test models. Univariate ANOVA was used to analyze data followed by post hoc tests (Tukey HSD, α = 0.05). RESULTS: Mean ΔR was significantly greater for PM10 (73.5 ± 8.9 µm) and PM20 (65.5 ± 33.3 µm) compared to CS0 (16.8 ± 14.1 µm), CS10 (22.2 ± 13.0 µm), CS20 (15.6 ± 19.9 µm), and PM0 (23.9 ± 16.1 µm). For Absdθ, there were no significant differences between test groups. CONCLUSIONS: With conventional stone casts, implant angulation had no significant effect on 3D linear and absolute angular distortions. Amongst printed resin models test groups, angulated implants had significantly greater ΔR. Amongst angulated implants test groups, printed resin models had significantly greater ΔR than conventional stone casts. Compared to the master model, all test groups, regardless of inter-implant angulation, produced greater inter-analog distances.

Three-dimensional analysis of the interchangeability of a semiadjustable articulator system in service over time.

STATEMENT OF PROBLEM: Some contemporary articulator systems claim to be highly precise in their interchangeability, with tolerances below 10 µm in vertical error; however, the claims have not been independently verified. PURPOSE: The purpose of this study was to investigate the interchangeability of calibrated semiadjustable articulators in service over time. MATERIAL AND METHODS: A calibrated mounting articulator served as the master articulator, while the test groups were used articulators with a minimum of 1-year use by predoctoral dental students (n=10); used articulators with a minimum of 1-year use by prosthodontic residents (n=10); and new articulators (n=10). One set of mounted maxillary and mandibular master models was positioned in the master and test articulators. High-precision reference markers on the master models were used to determine interarch 3D distance distortions (dRR, dRC, and dRL), interocclusal 3D distance distortion (dRM), interocclusal 2D distance distortions (dxM, dyM, and dzM), and interocclusal angular distortion (dθM) relative to the master articulator. All measurements were conducted three times using a coordinate measuring machine and then averaged to derive the final data set. RESULTS: For interarch 3D distance distortion, the mean dRR ranged from 4.6 ±21.6 µm for new articulators to 56.3 ±47.6 µm for articulators used by prosthodontic residents; mean dRC ranged from 65 ±48.6 µm for new articulators to 119.0 ±58.8 µm for articulators used by prosthodontic residents; and mean dRL ranged from 12.7 ±39.7 µm for articulators used by prosthodontic residents to 62.8 ±75.2 µm for new articulators. For interocclusal 3D distance distortion, the mean dRM ranged from 21.5 ±49.8 µm for new articulators to 68.6 ±64.9 µm for articulators used by predoctoral dental students. For the 2D distance distortions, the mean dxM ranged from -17.9 ±43.4 µm for articulators used by predoctoral dental students to -61.9 ±48.3 µm for articulators used by prosthodontic residents; mean dyM ranged from 18.1 ±59.4 µm for new articulators to 69.3 ±115.1 µm for articulators used by prosthodontic residents; and mean dzM ranged from 29.5 ±20.2 µm for new articulators to 70.1 ±37.8 µm for articulators used by prosthodontic residents. Mean dθM ranged from -0.018 ±0.289 degree for new articulators to 0.141 ±0.267 degree for articulators used by prosthodontic residents. One-way ANOVA by articulator type revealed statistically significant differences among the test groups for dRR (P=.007) and dzM (P=.011) only, where articulators used by prosthodontic residents fared significantly poorer than the other test groups. CONCLUSIONS: The new and used articulators tested did not fulfill the manufacturer's claim of accuracy of up to 10 µm in the vertical dimension. Up to 1 year of time in service, none of the investigated test groups fulfilled the criterion for articulator interchangeability, even if the more lenient threshold of 166 µm were accepted.

Rotational Load Fatigue Performance of Titanium vs Titanium-Zirconium Implant-Abutment Connections.

PURPOSE: Titanium-zirconium (Ti-Zr) alloy has been developed to strengthen the implant body, but clinically relevant information is still limited. The aim of this in vitro study was to compare the rotational load fatigue performance of implant-abutment connections in narrow-diameter (3.3-mm) and regular-diameter (4.1-mm) implants made with commercially pure grade 4 titanium alloy (CPTi-G4) and Ti-Zr. MATERIALS AND METHODS: Narrow-diameter (N) and regular-diameter (R) implants with CPTi-G4 (Ti) or Ti-Zr (Tz) materials were tested. This resulted in four test groups: NTi, NTz, RTi and RTz. Five specimens were made for each group (n = 5). Abutments used were milled from titanium-aluminum-niobium alloy abutment blanks. A rotational load fatigue machine applied a sinusoidally varying load at an angle of 45 degrees to produce an effective bending moment of 35 Ncm at a frequency of 14 Hz in air at 20°C. The number of cycles to failure was recorded. The upper limit was set as 5 million cycles. Results were evaluated using analysis of variance (ANOVA) and Tukey post hoc tests. Failure locations and patterns were evaluated with scanning electron microscope (SEM). RESULTS: All regular-diameter test groups reached the upper limit of 5 million cycles without failure. All narrow-diameter test groups failed within the range of 402,530 cycles to 3,374,353 cycles. It could be observed that NTz showed a higher mean cycle count as compared to NTi. NTi test group recorded two implants damaged, one implant fracture, five abutment fractures, and four screw fractures. NTz test group showed only abutment fractures at the level of implant platform, with no damage to the implant bodies. Significant difference was found between implants of different diameters. There was no significant difference between implants of different materials. CONCLUSION: Regular-diameter implants performed significantly better than narrow-diameter implants, regardless of material, while no significant difference in cyclic load to failure was found between groups of different alloys. All NTz failures were at the abutment only, without damage to the implant. This failure pattern can potentially be clinically advantageous in terms of retrieval and subsequent replacement of a failed prosthesis.

Three-dimensional positional accuracy of intraoral and laboratory implant scan bodies.

STATEMENT OF PROBLEM: In the implant digital workflow, scan bodies provide the 3D position of digital implants in the virtual dental arch. However, limited evidence is available on scan body accuracy, selection, and usage. PURPOSE: The purpose of this in vitro study was to evaluate the 3D positional accuracy of 4 intraoral and 6 laboratory scan body systems to the implants and laboratory replicas of an implant system under various torque magnitudes. MATERIAL AND METHODS: Ten test groups comprising 4 intraoral (I): Medentika L-Series (MS), Straumann CARES Mono (SM), Core 3D (CO), Straumann RC (SS); and 6 laboratory (L): Nobel Procera Pos Locator (NP), Sirona InPost (SR), Amann Girrbach (AG), Straumann CARES Mono (SM), Core 3D (CO), Straumann RC (SS) scan bodies were derived from 7 scan body systems. Of these, 3 systems (SM, CO, SS) are used for both intraoral and laboratory applications. The scan bodies were tested on Straumann Bone Level Regular CrossFit implants or laboratory replicas. Eight test groups allowed for the variation of torque application (5, 10, and 15 Ncm), while 2 test groups (NP, SR) were hand positioned only. Prefabricated metal abutments (ME) for both implants and laboratory replicas served as controls. A coordinate measuring machine measured four 3D positional accuracy variables: vertical linear distortion (dz), 2D tolerance displacement (dr), global linear distortion (dR), and scan body height discrepancy (ΔH) (n=10). The data were analyzed with 2-way analysis of variance tests and post hoc analysis with Tukey tests (α=.05). RESULTS: For both intraoral and laboratory test groups, 2-way ANOVA found that the system had a significant effect on all distortion variables (P<.001), while torque magnitude had a significant effect only on dz and ΔH (P<.001). Overall, mean dz ranged from 5 ±12 µm for L-AG at 15 Ncm to 23 ±14 µm for L-AG at 5 Ncm. Mean dr ranged from 5 ±4 µm for I-SM at 15 Ncm to 73 ±41 µm for L-SS at 10 Ncm, and mean dR ranged from 11 ±6 µm for I-SM at 10 Ncm to 74 ±41 µm for L-SS at 10 Ncm. Mean ΔH ranged from -5 ±10 µm for I-SM at 15 Ncm to 23 ±14 µm for L-AG at 5 Ncm. Among intraoral test groups, for dz and ΔH, all the test groups except for I-SM at 15 Ncm and I-MS at 10 and 15 Ncm were significantly more positive than the control (P<.001). For dr, I-SS at 5, 10, and 15 Ncm was significantly different from the control (P<.001). For dR, only I-SS at 5 Ncm was significantly different from the control (P<.001). Among laboratory test groups, for dz and ΔH, L-AG at 5 Ncm and L-CO at 15 Ncm were significantly more positive than the control (P<.001). For dr, L-SS at 10 and 15 Ncm were significantly different from the control (P<.001). For dR, only L-SS at 10 Ncm was significantly different from the control (P<.001). Intraoral and laboratory systems show comparable 3D positional accuracy. CONCLUSIONS: Overall, I-SS and L-SS were the least accurate. The system tested had a significant effect on 3D positional accuracy, while torque magnitude had no consistent effect across all systems.

Contemporary English Pain Descriptors as Detected on Social Media Using Artificial Intelligence and Emotion Analytics Algorithms: Cross-sectional Study.

BACKGROUND: Pain description is fundamental to health care. The McGill Pain Questionnaire (MPQ) has been validated as a tool for the multidimensional measurement of pain; however, its use relies heavily on language proficiency. Although the MPQ has remained unchanged since its inception, the English language has evolved significantly since then. The advent of the internet and social media has allowed for the generation of a staggering amount of publicly available data, allowing linguistic analysis at a scale never seen before. OBJECTIVE: The aim of this study is to use social media data to examine the relevance of pain descriptors from the existing MPQ, identify novel contemporary English descriptors for pain among users of social media, and suggest a modification for a new MPQ for future validation and testing. METHODS: All posts from social media platforms from January 1, 2019, to December 31, 2019, were extracted. Artificial intelligence and emotion analytics algorithms (Crystalace and CrystalFeel) were used to measure the emotional properties of the text, including sarcasm, anger, fear, sadness, joy, and valence. Word2Vec was used to identify new pain descriptors associated with the original descriptors from the MPQ. Analysis of count and pain intensity formed the basis for proposing new pain descriptors and determining the order of pain descriptors within each subclass. RESULTS: A total of 118 new associated words were found via Word2Vec. Of these 118 words, 49 (41.5%) words had a count of at least 110, which corresponded to the count of the bottom 10% (8/78) of the original MPQ pain descriptors. The count and intensity of pain descriptors were used to formulate the inclusion criteria for a new pain questionnaire. For the suggested new pain questionnaire, 11 existing pain descriptors were removed, 13 new descriptors were added to existing subclasses, and a new Psychological subclass comprising 9 descriptors was added. CONCLUSIONS: This study presents a novel methodology using social media data to identify new pain descriptors and can be repeated at regular intervals to ensure the relevance of pain questionnaires. The original MPQ contains several potentially outdated pain descriptors and is inadequate for reporting the psychological aspects of pain. Further research is needed to examine the reliability and validity of the revised MPQ.

Accuracy of Implant Analogs in 3D Printed Resin Models.

PURPOSE: To study the effect of implant analog system, print orientation, and analog holder radial offset on 3D linear and absolute angular distortions of implant analogs in 3D printed resin models. MATERIALS AND METHODS: A sectional master model simulating a 2-implant, 3-unit fixed prosthesis in a partially edentulous jaw was fabricated. Three implant analog systems for 3D printed resin models-Straumann (ST), Core3DCentres (CD) and Medentika (MD)-were tested. The corresponding scan bodies were secured onto the implants and scanned using an intraoral scanner. Models were obtained with a Digital Light Processing printer. Each implant analog system had 2 print orientations (transverse [X] and perpendicular [Y] to the printer door) and 2 analog holder radial offsets (0.04 mm and 0.06 mm), for a total of 60 models. The physical positions of the implants in the master model and the analogs in the printed resin models were directly measured with a Coordinate Measuring Machine (CMM). 3D linear distortion (ΔR) and absolute angular distortion (Absdθ) defined the 3D accuracy of the analogs in the printed models. Univariate ANOVA was used to analyse data followed by post hoc tests (Tukey HSD, α = 0.05). RESULTS: Mean ΔR for ST (-155.7 ± 60.6 µm), CD (124.9 ± 65.0 µm) and MD (-92.9 ± 48.0 µm) were significantly different (p < 0.01). Mean Absdθ was not significantly different between ST (0.57 ± 0.48°) and CD (0.41 ± 0.27°), but both were significantly different from MD (2.11 ± 1.14°) (p < 0.01). Print orientation had a significant effect on ΔR only but no discernible trend could be found. Analog holder radial offset had no significant effect on ΔR and Absdθ. CONCLUSIONS: Implant analog system had a significant effect on ΔR and Absdθ. Compared to the master model, CD produced greater mean interanalog distances, while ST and MD produced smaller mean interanalog distances. MD exhibited the greatest mean angular distortion which was significantly greater than ST and CD.

Crown preparations by undergraduate dental students: A comparison of conventional versus digital assessment via an intraoral scanner.

PURPOSE: This study aims to assess the effectiveness of the 3Shape TRIOS intraoral scanner (IOS) in student crown preparation evaluation. DESIGN: Students were tasked to perform a full metal crown preparation on the upper left first molar on a patient simulator within 45 minutes. Marginal Width, Occlusal Reduction, Presence of Undercuts, Taper, Planes of Reduction, Line Angles, Conformity to Gingival Contour, and Smoothness were evaluated via 3 assessment modes: (a) Conventional assessment by 2 supervisors; (b) Conventional assessment by students; (c) Digital assessment by students. Agreement between assessment modes was investigated using Kappa (κ), with a threshold set at κ > 0.4. Effectiveness of IOS for objective parameters was determined via physical verification, while that for subjective parameters was defined by agreement with the stricter supervisor grade. RESULTS: Substantial agreement (κ = 0.631) was found between IOS measurement of Marginal Width and physical verification. Two of 5 subjective parameters met κ > 0.4 for agreement between IOS and the stricter supervisor grade. Agreement between supervisors ranged from slight (κ = 0.103) for Occlusal Reduction to Fair (κ = 0.399) for Marginal Width. Agreement between conventional assessments of supervisors and students ranged from less than chance (κ = -0.142) for Occlusal Reduction to moderate (κ = 0.577) for Line Angles. Agreement between conventional assessments of supervisors and digital assessments of students ranged from slight (κ = 0.130) for Planes of Reduction to moderate (κ = 0.538) for Line Angles. CONCLUSIONS: IOS may be used to overcome limitations in conventional assessment of objective parameters and some subjective parameters. Digital assessment of crown preparations cannot completely replace conventional assessment.

Comparison of Three-Dimensional Accuracy of Digital and Conventional Implant Impressions: Effect of Interimplant Distance in an Edentulous Arch.

PURPOSE: This study compared the three-dimensional (3D) accuracy of conventional impressions with digital impression systems (intraoral scanners and dental laboratory scanners) for two different interimplant distances in maxillary edentulous arches. MATERIALS AND METHODS: Six impression systems comprising one conventional impression material(Impregum), two intraoral scanners (TRIOS and True Definition), and three dental laboratory scanners (Ceramill Map400, inEos X5, and D900) were evaluated on two completely edentulous maxillary arch master models (A and B) with six and eight implants, respectively. Centroid positions at the implant platform level were derived using either physical or virtual probe hits with a coordinate measuring machine. Comparison of centroid positions between master and test models (n = 5) defined linear distortions (dx, dy, dz), global linear distortions (dR), and 3D reference distance distortions between implants (ΔR). The two-dimensional (2D) angles between the central axis of each implant to the x- or y-axes were compared to derive absolute angular distortions (Absdθx, Absdθy). RESULTS: Model A mean dR ranged from 8.7 ± 8.3 µm to 731.7 ± 62.3 µm. Model B mean dR ranged from 16.3 ± 9 µm to 620.2 ± 63.2 µm. Model A mean Absdθx ranged from 0.021 ± 0.205 degrees to -2.349 ± 0.166 degrees, and mean Absdθy ranged from -0.002 ± 0.160 degrees to -0.932 ± 0.290 degrees. Model B mean Absdθx ranged from -0.007 ± 0.076 degrees to -0.688 ± 0.574 degrees, and mean Absdθy ranged from -0.018 ± 0.048 degrees to -1.052 ± 0.297 degrees. One-way analysis of variance (ANOVA) by Impression system revealed significant differences among test groups for dR and ΔR in both models, with True Definition exhibiting the poorest accuracy. Independent samples t tests for dR, between homologous implant location pairs in Model A versus B, revealed the presence of two to four significant pairings (out of seven possible) for the intraoral scanner systems, in which instances dR was larger in Model A by 110 to 150 µm. CONCLUSION: Reducing interimplant distance may decrease global linear distortions (dR) for intraoral scanner systems, but had no effect on Impregum and the dental laboratory scanner systems. Impregum consistently exhibited the best or second-best accuracy at all implant locations, while True Definition exhibited the poorest accuracy for all linear distortions in both Models A and B. Impression systems could not be consistently ranked for absolute angular distortions.

Three-dimensional repositioning accuracy of semiadjustable articulator cast mounting systems.

STATEMENT OF PROBLEM: In spite of its importance in prosthesis precision and quality, the 3-dimensional repositioning accuracy of cast mounting systems has not been reported in detail. PURPOSE: The purpose of this study was to quantify the 3-dimensional repositioning accuracy of 6 selected cast mounting systems. Five magnetic mounting systems were compared with a conventional screw-on system. MATERIAL AND METHODS: Six systems on 3 semiadjustable articulators were evaluated: Denar Mark II with conventional screw-on mounting plates (DENSCR) and magnetic mounting system with converter plates (DENCON); Denar Mark 330 with in-built magnetic mounting system (DENMAG) and disposable mounting plates; and Artex CP with blue (ARTBLU), white (ARTWHI), and black (ARTBLA) magnetic mounting plates. Test casts with 3 high-precision ceramic ball bearings at the mandibular central incisor (Point I) and the right and left second molar (Point R; Point L) positions were mounted on 5 mounting plates (n=5) for all 6 systems. Each cast was repositioned 10 times by 4 operators in random order. Nine linear (Ix, Iy, Iz; Rx, Ry, Rz; Lx, Ly, Lz) and 3 angular (anteroposterior, mediolateral, twisting) displacements were measured with a coordinate measuring machine. The mean standard deviations of the linear and angular displacements defined repositioning accuracy. RESULTS: Anteroposterior linear repositioning accuracy ranged from 23.8 ±3.7 µm (DENCON) to 4.9 ±3.2 µm (DENSCR). Mediolateral linear repositioning accuracy ranged from 46.0 ±8.0 µm (DENCON) to 3.7 ±1.5 µm (ARTBLU), and vertical linear repositioning accuracy ranged from 7.2 ±9.6 µm (DENMAG) to 1.5 ±0.9 µm (ARTBLU). Anteroposterior angular repositioning accuracy ranged from 0.0084 ±0.0080 degrees (DENCON) to 0.0020 ±0.0006 degrees (ARTBLU), and mediolateral angular repositioning accuracy ranged from 0.0120 ±0.0111 degrees (ARTWHI) to 0.0027 ±0.0008 degrees (ARTBLU). Twisting angular repositioning accuracy ranged from 0.0419 ±0.0176 degrees (DENCON) to 0.0042 ±0.0038 degrees (ARTBLA). One-way ANOVA found significant differences (P<.05) among all systems for Iy, Ry, Lx, Ly, and twisting. CONCLUSIONS: Generally, vertical linear displacements were less likely to reach the threshold of clinical detectability compared with anteroposterior or mediolateral linear displacements. The overall repositioning accuracy of DENSCR was comparable with 4 magnetic mounting systems (DENMAG, ARTBLU, ARTWHI, ARTBLA). DENCON exhibited the worst repositioning accuracy for Iy, Ry, Lx, Ly, and twisting.