Comparison between Conventional and Digital Impressions for Determining Axes and Distances of Three Implants in Straight and Curved Lines: An In Vitro Study.

Background: In this study, we aimed to compare the effects of conventional and digital impressions on several parameters (inter-implant distance, intra-implant distance, inter-implant axis, and intra-implant axis) of three implants in curved lines and straight lines by using a laboratory scanner (LBS) versus an intra-oral scanner (IOS). Methods: Two 3D models were fabricated using a printer, each model with three internal hex implants analogues at the positions of 15#,16#,17# (straight line) and 12#,13#,14# (curved line). Standard intra-oral scan bodies (ISBs) were used, and the two models were scanned using 7 Series dental wings (LBS, reference model), followed by ten scans with Primescan (digital method). Standard Tessellation Language (STL) files were created. Five polyether impressions were taken from each model (straight and curved), and gypsum type 4 models were poured; each model was scanned five times to create a total of 25 STL files for each group (conventional method). The comparison between all the STL files (conventional and digital) was made by superimposition of the STL files on the STL reference model laboratory file using a 3D analyzing software. A Kolmogorov-Smirnov test was performed, followed by Mann-Whitney tests and Wilcoxon signed-rank tests. (p < 0.05). Results: For the conventional method, the mean errors were significantly higher for the curved line model (12-14) compared to the straight line model (15-17) for most parameters (p < 0.05). For the digital method, the mean errors were significantly higher for the curved-line model (12-14) compared to the straight line model (15-17) in half of the parameters (p < 0.05). Within the curved line model (12-14) and the straight line model (15-17), the mean errors between the conventional method and the digital method were not significant for most variables. Conclusions: The difference between curved lines and straight lines has an impact on the mean error of the conventional method. Both methods are reliable for straight and curved lines in partially dentate situations.

SEM Evaluation of the Marginal Gap of Zirconia-Reinforced Lithium Silicate Full Crowns and the Effect of Post Crystallization: An In Vitro Study.

BACKGROUND: This study compared the influence of crystallization on marginal gap adaptation by using computer-aided design and manufacturing (CAD-CAM) for producing monolithic zirconia-reinforced lithium silicate (ZLS) ceramic crowns. METHODS: A total of 25 plastic teeth were scanned using a Primescan intra-oral scanner (IOS), and ZLS crowns were ground. For each unit (abutment and crown), the marginal gap was evaluated pre crystallization and post crystallization at four regions of interest through the use of a scanning electron microscope (SEM). To compare the marginal gap between the two groups, a Kolmogorov-Smirnov test performed on the study variables indicated a normal distribution (p > 0.05) followed by paired samples T-tests (α = 0.0005). RESULTS: After crystallization, there were significantly higher circumferential marginal gaps (CMGs) for all four surfaces (distal (p = 0.0005), mesial (p = 0.0005), palatal (p = 0.0005), and buccal (p = 0.0005)). The total mean marginal gap (MMG) revealed a significantly higher result for the post-crystallization group (79.82 ± 7.86 µm) compared to the pre-crystallization group (24.25 ± 5.49 µm). CONCLUSIONS: The post-crystallization group showed a significantly higher marginal gap compared to the pre-crystallization group in all parameters, but both groups were in the clinically accepted threshold (<120 microns). In terms of the marginal gap, it is arguable whether to carry out post-crystallization for CELTRA® DUO crowns and achieve better mechanical properties but significantly increase the marginal gap.

Analysis of Strain Distribution in Common Clinical Designs of Posterior Implant-Supported Fixed Partial Restorations: Comparison between Six Configurations.

The configuration of implant-supported prostheses is considered to influence the magnitude of stress concentrations, affecting their survival rate. The purpose of this study is to determine, through strain gauge measurements during load application, the dispersion and magnitude of strain concentrations in different implant-supported prosthesis designs. All designs matched those commonly used in posterior partially edentulous states. Three implants were inserted into an epoxy resin model (PLM-4B Vishay Measurements Group Inc., Raleigh, NC, USA), allowing for the delivery of three- and four-unit crowns in different cemented configurations. Loads were applied at vertical and oblique directions over the cast crowns in six different configurations representing various posterior partially edentulous restorations. The readings from the strain gauges adhered to the implant necks' presented data on implant strain. Prostheses including cantilevers showed the highest strain among the three-unit prostheses within the prosthetic complex, and three single units showed the least (8133 µs vs. 201 µs, respectively). Angulated load application also had a role in amplifying the strains recorded, resulting in total strains of between 3.5 and 20 times higher than during vertical loading in all configurations. It can be concluded that the configuration of implant-fixed partial prosthesis changes the loads engaging the restoration, the implant, and, probably, the supporting bone.

The Influence of Laboratory Scanner versus Intra-Oral Scanner on Determining Axes and Distances between Three Implants in a Straight Line by Using Two Different Intraoral Scan Bodies: A Pilot In Vitro Study.

BACKGROUND: The purpose of this in vitro study was to compare the inter-implant distance, inter-implant axis, and intra-implant axis of three implants in a straight line by using a laboratory scanner (LBS) versus an intra-oral scanner (IOS) with two different intra-oral scan bodies (ISBs). METHODS: A 3D model was printed with internal hex implant analogs of three implants in positions 15#, 16#, and 17#. Two standard intra-oral scan bodies (ISBs) were used: MIS ISB (two-piece titanium) and Zirkonzhan ISB (two-piece titanium). Both ISBs were scanned using 7 Series dental wings (LBS) and 30 times using Primescan (IOS). For each scan, a stereolithography (STL) file was created and a comparison between all the scans was performed through superimposition of the STL files by using 3D analysis software (PolyWorks® 2020; InnovMetric, Québec, QC, Canada). A Kolmogorov-Smirnov test was performed followed by a Mann-Whitney test (p < 0.05). RESULTS: The change in inter-implant distance for the MIS ISB was significantly lower compared to the ZZ (p < 0.05). The change in intra-implant angle was significantly lower for the ZZ ISB compared to MIS (p < 0.05). The changes in inter-implant angle between the mesial and middle and between the middle and distal were significantly lower for MIS compared to ZZ in contrast to mesial to distal, which was significantly higher (p < 0.05). CONCLUSIONS: Both ISBs showed differences in all the parameters between the LBS and the IOS. The geometry of the scan abutment had an impact on the inter-implant distance as the changes in the inter-implant distance were significantly lower for the MIS ISB. The changes in the intra-implant angle were significantly lower for the ZZ ISB. There is a need for further research examining the influence of geometry, material, and scan abutment parts on the trueness.

The Light Reflection Changes of Monolithic Zirconia and Lithium Disilicate after Using Two External Staining Kits following by Thermocycling.

BACKGROUND: The purpose of the study was to evaluate the changes of light reflection% on two materials (monolithic zirconia and lithium disilicate) after using two external staining kits following by thermocycling. METHODS: Specimens were sectioned from monolithic zirconia (n = 60) and lithium disilicate (n = 60) then divided into six groups (n = 20). Two different types of external staining kits were used and applied to the specimens. The light reflection% was measured before staining, after staining and after thermocycling using a spectrophotometer. RESULTS: The light reflection% of zirconia was significantly higher compared to lithium disilicate at the beginning of the study (p = 0.005), after staining with kit 1 (p = 0.005) and kit 2 (p = 0.005) and after thermocycling (p = 0.005). For both materials, the light reflection% was lower after staining with Kit 1 compared to kit 2 (p < 0.043). After thermocycling, the light reflection% of lithium disilicate increased (p = 0.027) and was unchanged with Zirconia (p = 0.527). CONCLUSIONS: There is a difference between the materials regarding light reflection% as the monolithic zirconia showed higher light reflection% comparing lithium disilicate throughout the entire experiment. For lithium disilicate, we recommend using kit 1 as we found that, after thermocycling, the light reflection% of kit 2 was increased.

Immediate versus Delayed Attachment Incorporation Impact on Prosthetic Aftercare among Mandibular Implant-Supported Overdenture Wearers.

BACKGROUND: Substantial effort is dedicated to finding the most favorable parameters that will ensure low aftercare demands among edentulous patients wearing mandibular implant supported overdentures (MISODs). The purpose of this retrospective cohort study was to compare prosthetic aftercare between MISOD patients with a simultaneous (group A) vs. a three-week settling in period (group B) prior to attachment incorporation. METHODS: Forty-five patients enrolled in this study. Two implants per patient were placed using a two-stage implant insertion protocol. Second-stage surgery was performed after three months. All patients received ball attachments using the direct (chairside) incorporation method. Twenty-two patients received their dentures with simultaneous attachment activation and the rest-twenty-three patients-after a three-week settling in period. Patients' files were scanned for aftercare visits. Outcome parameters included sore spot relief, attachment incorporation, and denture repair. Additionally, gingival index measurements were compared. Confounding factors included age, gender, and implant dimensions. RESULTS: The mean follow-up for the entire cohort was 84 ± 21 months, and the range 39-120 months. The mean number of visits for group A vs. B respectively: pressure sores relieve (3.63 ± 0.84 vs. 3.71 ± 0.61, p = 0.581), liner exchange due to loss of retention (2.09 ± 1.03 vs. 2.31 ± 1.04 p = 0.487), and gingival index (1.3 ± 0.3 vs. 1.03 ± 0.2, p = 0.653) exhibited no statistically significant differences between the tested groups. No statistically significant differences between the groups were also noted for the denture repair aftercare treatments (p = 0.318) and the independent variables including age, gender, and implant length. CONCLUSIONS: Prosthetic aftercare in MISOD wearers is similar whether a simultaneous or a three-week settling in period for attachment incorporation is applied.

Primary Teeth Supported Fixed Prosthesis-A Predictable Treatment Alternative.

BACKGROUND: Individuals with tooth agenesis often present a significant clinical challenge for dental practitioners. This retrospective study evaluated clinical and radiological long-term functional and esthetic outcomes following restoration using primary teeth to support fixed all-ceramic prosthesis in patients with teeth agenesis. METHODS: Patients with teeth agenesis and at least one year follow-up were included. Examinations included panoramic X-ray, clinical examination and family history records. Only primary teeth without permanent teeth underneath were chosen. All ceramic fixed restorations were used. All data were collected from patient files. Outcome parameters included: restoration parameters (restoration survival, restoration fractures, restoration detachment, restoration replacement, and secondary caries), plaque index, and gingival index. RESULTS: The study included 58 porcelain restorations inserted in 25 individuals; mean age 12 ± 2.1 years (range 10-19 years); mean number of missing teeth 12.3 ± 9 (range 6-12). Mean follow-up 48 ± 6 months (range 12-60 months). All restorations survived up to last follow-up, rendering a survival rate of 100%. Restorations outcome-porcelain chipping (9%), detachment (2%), no restoration replacement nor secondary caries, mean gingival index-0.7 ± 0.5 and mean plaque index-0.9 ± 0.3. CONCLUSIONS: In tooth agenesis, restoration using primary teeth to support fixed all-ceramic prosthesis is a viable treatment alternative.

The Precision of Electronic Apex Locators in Working Length Determination: A Systematic Review and Meta-analysis of the Literature.

INTRODUCTION: This study aimed to evaluate the precision of electronic apex locators (EALs) in locating the apical constriction (AC) during a root canal treatment compared with a histologic evaluation of the AC as well as the effects of possible influencing factors by means of a systematic review of the literature and meta-analysis. METHODS: A systematic search of the literature was performed to identify studies that histologically evaluated the precision of EALs in human teeth. The identified studies were subject to strict inclusion criteria followed by data extraction and meta-analysis. RESULTS: From 247 articles, 10 articles met the inclusion criteria, with a total of 1105 EAL measurements performed by 4 types of EALs: Root ZX (J Morita, Tokyo, Japan), Justy II (Hager & Werken GmbH & Co, Duisburg, Germany), Endy 5000 (Loser Co, Leverkusen, Germany), and Endox (Lysis Co, Milan, Italy). Root ZX, Justy II, and Endy 5000 were found to be significantly more accurate than Endox in determining the distance between the file tip and the apical constriction (P < .05). The longest mean distance was measured by Endox (1.35 ± 0.41 mm), and the shortest mean distance was measured by Justy II (0.25 ± 0.17 mm, P < .05). The mean distance measured by Root ZX and Justy II in the presence of hydrogen peroxide was shorter compared with the mean distance measured by them in the presence of sodium hypochlorite (P < .05). The pulp status (vital or necrotic) had no significant effect on the precision of the EALs. CONCLUSIONS: The precision of electronic working length measurement depends on the device used and the type of irrigation and is not influenced by the status of the pulp tissue.