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Objectives: To evaluate an in situ reference acquisition method for implant positions in complete edentulous maxillae using an industrial scanner and allowing for in vivo trueness analysis of the restorative workflow. To assess in vivo trueness and precision of intraoral scanners (IOS) using different acquisition protocols. Furthermore, to compare IOS trueness with impression-based models and implant-supported fixed dentures (IFD) in a parallel study on the same cohort using the same in situ reference scan., Methods: Six scan-bodies mounted to maxillary implants in five subjects were reference scanned (REF) using an industrial scanner. Subjects were scanned with IOS three times using three different protocols: control (CT), dental floss assisted (DF), and acrylic splint (SP). CAD-files of scan-bodies with inter-aligned analogues were geometry-aligned to REF, and SP. Scan-bodies were aligned to CT and DF in proprietary dental laboratory software and exported with analogue positions. Resulting six CAD-analogues per scan were Globally Aligned using a consistent geometry-based alignment. Deviations were computed after a Reference Point System Alignment at the implant/prosthetic platform for Cartesian axes with a linear Resultant., Results: Resultant trueness was CT: 41±11 µm, DF: 49±22 µm, SP: 55±8 µm. Resultant precision was CT: 48±7 µm, DF: 50±7 µm, SP: 45±6 µm., Conclusions: This method is applicable for assessing trueness of maxillary full-arch implant scans in vivo. The CT protocol was most accurate. CT trueness showed no difference to digitised impression-based models in parallel study. CT was more accurate than IFD in a parallel study. CT displayed similar numerical trueness as existing in vitro studies., Clinical Significance: Using IOS to acquire full-arch implant scans is controversial. The modified protocol in this pilot shows promising results in the maxilla where great care was taken to manage non-attached tissues when a modified scanning pattern was used. However, other IOS may show varying results in vivo. A completed scan does not necessarily equate to an accurate scan., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier Ltd.)

Abstract: Objectives: The objective of the research was to assess patient preference for a selective pressure impression technique for complete dentures by means of a Randomised Controlled Clinical Trial (RCT). Methods: A literature review revealed no reported RCT''s of selective pressure impressions for complete dentures. A cross-over, randomised, controlled, clinical trial was performed comparing selective pressure impressions with a placebo and an alternative method of re-distributing pressure. A sample size calculation yielded 65 patients. Sixty-nine patients, who had a superficial mental foramen on the lower denture bearing area, were recruited for the study. The primary outcome was the patients’ preference of the dentures provided. The hypothesis under investigation was that one of the dentures would be preferred by the patients. Results: Sixty-six participants completed the trial, 33 (50%) preferred the denture from the selective pressure impression, 19 (29%) the denture with traditional pressure relief, and 14 (21%) the placebo control. 95% confidence intervals showed that the preference for the selective pressure impression was greater than that of the other two techniques. The null hypothesis was rejected. Conclusions: The participants in this trial showed a preference for the denture constructed from the selective pressure impression technique, providing dentists with useful evidence for a clinical impression technique. [Copyright &y& Elsevier]

Abstract: Objectives: The aim of the present study was to compare the fit of all-ceramic crowns fabricated from intraoral digital impressions with the fit of all-ceramic crowns fabricated from silicone impressions. Methods: Twenty patients agreed to take part in the study to receive two Lava™ crowns each for the same preparation. One crown was fabricated from intraoral scans using the Lava™ Chairside Oral Scanner (Lava C.O.S.), and the other crown from a two-step silicone impression. Prior to cementation the fit of both crowns was clinically evaluated by two calibrated and blinded examiners; the marginal fit was also scored from replicas. Data from the replica scores were analysed by Anderson–Darling test, Levene''s test and Mann–Whitney test. All tests were performed with α-level of 0.05. Results: Median marginal gap in the conventional impression group was 71μm (Q1:45μm; Q3:98μm), and in the digital impression group 49μm (Q1:32μm; Q3:65μm). Mann–Whitney test revealed a significant difference between the groups (p <0.05). No differences were found regarding the occlusion, and there was a trend for better interproximal fit for the digitally fabricated crowns. Conclusions: [1.] Crowns from intraoral scans revealed significantly better marginal fit than crowns from silicone impressions. [2.] Marginal discrepancies in both groups were within the limits of clinical acceptability. [3.] Crowns from intraoral scans tended to show better interproximal contact area quality. [4.] Crowns from both groups performed equally well with regard to occlusion. [Copyright &y& Elsevier]

Summary: Objectives: To evaluate the effects of gingival retraction fluids (GRF) on prepared dentine surfaces, and to test the null-hypothesis that prior exposure of dentine surfaces for prolonged period to any of the fluids evaluated does not influence acid-etching of the exposed surfaces. Methods: The investigation was carried out using SEM and energy-dispersive X-ray analysis (EDX). The GRF studied were Hemodent™ (HMDT), Astringedent® (AST) and Ultradent® buffered 25% Aluminium Chloride (ULTB). Longitudinal sections of 220-grit ground dentine surfaces were exposed to GRF for 0.5-, 1-, 2- and 5-min (n=4 each). Another group of samples was produced by 20s application of 35% phosphoric acid (PA) on GRF-pretreated dentine. Control samples were not exposed to GRF. Differences in etching effect—a function of the Ca-contents detected by EDX, were analysed using Friedman''s and Wilcoxon''s rank test (P<0.05). Results: The SEM demonstrated the presence of a relatively non-porous amorphous dentine matrix, but many of the dentine tubule orifices remained occluded. Granular precipitates, which remained even after acid-etching, were noted on surfaces exposed to Hemodent™ for 5min. Characteristic crystal growth was observed on surfaces exposed to Astringedent® for 1- or 2-min prior to acid-etching. The EDX data demonstrated that there were differences in resulting Ca-content; ULTB >AST>HMDT>ULTB+PA>HMDT+PA>AST+PA>PA, but AST and HMDT were not significantly different. Conclusions: The exposure of dentine prepared surfaces to these three GRF altered its morphology and reduced the dentine''s susceptibility to acid-etching, thus the null-hypothesis is rejected. [Copyright &y& Elsevier]

Objective. Several studies have made comparisons in the dimensional accuracy of different elastomeric impression materials. Most have used two-dimensional measuring devices, which neglect to account for the dimensional changes that exist along a three-dimensional surface.Purpose. The aim of this study was to compare the dimensional accuracy of an impression technique using a polyether material (Impregum) and a vinyl poly siloxane material (President) using a laser scanner with three-dimensional superimpositional software.Materials and methods. Twenty impressions, 10 with a polyether and 10 with addition silicone, of a stone master model that resembled a dental arch containing three acrylic posterior teeth were cast in orthodontic stone. One plastic tooth was prepared for a metal crown. The master model and the casts were digitised with the non-contacting laser scanner to produce a 3D image. 3D surface viewer software superimposed the master model to the stone replica and the difference between the images analysed.Results. The mean difference between the model and the stone replica made from Impregum was 0.072mm (SD 0.006) and that for the silicone 0.097mm (SD 0.005) and this difference was statistically significantly, p=0.001.Conclusions. Both impression materials provided an accurate replica of the prepared teeth supporting the view that these materials are highly accurate. [Copyright &y& Elsevier]

Objectives: To assess the effect of clinical factors on the quality of intra-oral scans of crown margins. These factors are; presence of adjacent teeth, proximity to gingivae, encumbrance of wand positioning within oral cavity., Methods: A typodont lower molar (Frasaco, Germany) was prepared for an all-ceramic crown with 1.5mm supragingival (lingual) and equigingival (buccal) margins. The tooth was scanned in a model scanner, creating a master scan. An intra-oral scanner (IOS) (Omnicam, Sirona Dental) was used to acquire sets of 5 scans each, under varying conditions; (1) the presence/absence of adjacent teeth, (2) model mounted in manikin head/hand-held, (3) with/without a 1mm shim to elevate the margin. Every combination was investigated, yielding 40 scans (8 groups of 5). The master scan margin was identified by selecting the highest curvature region (>1.8). The master was aligned to each IOS scan, and 4 regions of each IOS scan margin were extracted, lying within 100μm of predefined mesial, distal, buccal and lingual sections of the master margin. The mean curvature of each margin section was calculated using Meshlab. The effect of each confounding factor on margin curvature was analysed using ANOVA., Results: Lingual margin curvature remained consistent regardless of scanning conditions. Buccal margin curvature was significantly affected when located equigingivally. Mesial margin curvature was significantly affected in the presence of adjacent teeth and proximity to the gingivae. Distal margin curvature was significantly affected by all three confounding factors., Conclusions: The curvature (sharpness) of the margin recorded by a commercial IOS is significantly affected by clinical factors obscuring visibility., (Copyright © 2017 Elsevier Ltd. All rights reserved.)