Showing papers by "Amirali Zandinejad published in 2020"

Intraoral digital scans-Part 1: Influence of ambient scanning light conditions on the accuracy (trueness and precision) of different intraoral scanners.

Abstract: Statement of problem Digital scans have increasingly become an alternative to conventional impressions. Although previous studies have analyzed the accuracy of the available intraoral scanners (IOSs), the effect of the light scanning conditions on the accuracy of those IOS systems remains unclear. Purpose The purpose of this in vitro study was to measure the impact of lighting conditions on the accuracy (trueness and precision) of different IOSs. Material and methods A typodont was digitized by using an extraoral scanner (L2i; Imetric) to obtain a reference standard tessellation language (STL) file. Three IOSs were evaluated—iTero Element, CEREC Omnicam, and TRIOS 3—with 4 lighting conditions—chair light 10 000 lux, room light 1003 lux, natural light 500 lux, and no light 0 lux. Ten digital scans per group were recorded. The STL file was used as a reference to measure the discrepancy between the digitized typodont and digital scans by using the MeshLab software program. The Kruskal-Wallis, 1-way ANOVA, and pairwise comparison were used to analyze the data. Results Significant differences for trueness and precision mean values were observed across different IOSs tested with the same lighting conditions and across different lighting conditions for a given IOS. In all groups, precision mean values were higher than their trueness values, indicating low relative precision. Conclusions Ambient lighting conditions influenced the accuracy (trueness and precision) of the IOSs tested. The recommended lighting conditions depend on the IOS selected. For iTero Element, chair and room light conditions resulted in better accuracy mean values. For CEREC Omnicam, zero light resulted in better accuracy, and for TRIOS 3, room light resulted in better accuracy.

The potential of additive manufacturing technologies and their processing parameters for the fabrication of all-ceramic crowns: A review.

Abstract: OBJECTIVE This article aims to provide a review of the additive manufacturing technologies and the processing parameters that have been investigated for the fabrication of all ceramic crowns. OVERVIEW Additive manufacturing has crept its way into the field of dentistry for the fabrication of resin and metal prosthesis. To evaluate the current status of additive manufacturing for the fabrication of all ceramic crowns, literature review was targeted to include publications pertaining to the fabrication of dental ceramics and all ceramic crowns. With respect to the additive manufacturing of dental ceramics, five technologies have been investigated to date: stereolithography, material extrusion, powder based fusion, direct inkjet printing, and binder jetting. The processing parameters and experimental outcomes were collated and described for each of the aforementioned technologies. CONCLUSION Additive manufacturing has demonstrated promising experimental outcomes and corroborated to the fabrication all ceramic crowns. However, the technology is yet to witness a commercial breakthrough within this domain. CLINICAL SIGNIFICANCE Additive manufacturing mitigates raw material wastage and tooling stresses that are associated with milling of ceramics. Continued research and development can lead to its approbation as an alternate technology for manufacturing all ceramic restorations.

Intraoral digital scans: Part 2-influence of ambient scanning light conditions on the mesh quality of different intraoral scanners.

Abstract: Statement of problem Digital scans should be able to accurately reproduce the different complex geometries of the patient's mouth. Mesh quality of the digitized mouth is an important factor that influences the capabilities of the geometry reproduction of an intraoral scanner (IOS). However, the mesh quality capabilities of IOSs and the relationship with different ambient light scanning conditions are unclear. Purpose The purpose of this in vitro study was to measure the impact of various light conditions on the mesh quality of different IOSs. Material and methods Three IOSs were evaluated—iTero Element, CEREC Omnicam, and TRIOS 3—with 4 lighting conditions—chair light, 10 000 lux; room light, 1003 lux; natural light, 500 lux; and no light, 0 lux. Ten digital scans per group were made of a mandibular typodont. The mesh quality of digital scans was analyzed by using the iso2mesh MATLAB package. Two-way ANOVA and Kruskal-Wallis 1-way ANOVA statistical tests were used to analyze the data (a=.05). Results Significant differences in mesh quality values were found among the different IOSs under the same lighting conditions and among the different lighting conditions using the same IOS. TRIOS 3 showed the highest consistency and mesh quality mean values across all scanning lighting conditions tested. CEREC Omnicam had the lowest mean mesh quality values across all scanning lighting conditions. iTero Element displayed some consistency in the mesh quality values depending on the scanning lighting conditions: chair light and room light conditions presented good consistency in mesh quality, indicating better mesh quality, and natural light and no light conditions displayed differing consistency in mesh quality values. Nevertheless, no light condition led to the minimal mean mesh quality across all IOS groups. Conclusions Differences in the mesh quality between different IOSs should be expected. The photographic scanning techniques evaluated presented higher mesh quality mean values than the video-based scanning technology tested. Moreover, changes in lighting condition significantly affect mesh quality. TRIOS 3 showed the highest consistency in terms of the mean mesh quality, indicating better photographic system in comparison with iTero Element.

Digital workflow for an esthetic rehabilitation using a facial and intraoral scanner and an additive manufactured silicone index: A dental technique.

Abstract: The present article describes a digital workflow for planning an esthetic treatment by using a facial and intraoral scanner, the dental and open-source software design of a facially generated diagnostic waxing, and additive manufactured (AM) clear silicone indices. A virtual design was created to fabricate a unique 3-piece AM index composed of flexible, clear silicone at the labial and lingual aspects and a rigid clear custom tray. The 3-piece AM clear indexes provided advantages compared with conventional procedures, including accurate reproduction of the digital diagnostic waxing, control of index thickness, various insertion paths of the silicone indices, flexibility of the indices, and online storage of the designs.

Internal and marginal discrepancies associated with stereolithography (SLA) additively manufactured zirconia crowns.

Abstract: Statement of problem Stereolithography (SLA) additive manufacturing (AM) technologies can be selected to fabricate zirconia crowns; however, the internal and marginal discrepancies associated with these new technologies remain unclear. Purpose The purpose of this in vitro study was to measure and compare the marginal and internal discrepancies of milled and AM zirconia crowns by using the silicone replica technique. Material and methods An implant custom abutment was manufactured and scanned by using a laboratory scanner (CARES Software; Institut Straumann AG). An anatomic contour crown was digitally designed, and the standard tessellation language (STLC) file was obtained. The STLC file was splinted into 2 pieces, simulating the parts of the crown that would replace the enamel (STLG1 file) and dentin (STLG2 file) structures. Three groups were determined: anatomic contour zirconia milled (CNC group), AM anatomic contour zirconia (AM group), and AM splinted zirconia (SAM group). For the CNC group, the STLC file was used to manufacture milled (CARES zirconium-dioxide crown; Institut Straumann AG) zirconia specimens. For the AM group, the STLC file was used to additively fabricate (CERAMAKER 900; 3DCeram Co) the zirconia (3DMix ZrO2 paste; 3DCeram Co) specimens. For the SAM group, the STLG2 file was selected to AM (CERAMAKER 900; 3DCeram Co) the zirconia (3DMix ZrO2 paste; 3DCeram Co) specimens. Ten specimens per group were manufactured. The silicone replica technique was used to measure the marginal and internal discrepancies. The cement gap was measured on images captured by using a digital microscope at ×100 magnification. For the internal gap, 50 measurements were made for each specimen, and for the marginal gap, 25 measurements were made for each specimen. The normality test, Shapiro-Wilk test, was conducted. The results indicated that the distributions were not normal; therefore, nonparametric Kruskal-Wallis H and pairwise Mann-Whitney U-tests were used to analyze the data. The Spearman correlation coefficient was used to determine the correlation between marginal and internal discrepancies in all 3 groups. Results Significant differences were found in marginal and internal discrepancies among the groups. The CNC group had the least marginal and internal discrepancies compared with the AM and SAM groups. The SAM group had significantly lower values for marginal and internal discrepancies than the AM group. The AM group showed the highest marginal and internal discrepancies. The CNC group had a weak correlation coefficient of 0.13 (P=.046), the AM group had a moderate correlation coefficient of 0.32 (P Conclusions CNC and SAM groups had clinically acceptable marginal and internal discrepancies, while the AM group had a clinically unacceptable marginal and internal crown discrepancies. Furthermore, a weak correlation was encountered between the marginal and internal discrepancies measured in all groups.

Additive manufacturing technologies for processing zirconia in dental applications.

Abstract: Objective The objective of this narrative review was to summarize the current status and future perspectives of additive manufacturing (AM) technologies with a particular emphasis on manufacturing zirconia-based materials. AM technologies include vat photopolymerization, material jetting, material extrusion, selective laser sintering (SLS), and selective laser melting (SLM) technologies based on either powder bed fusion (PBF) technologies or direct energy deposition, or sheet lamination based on binder jetting technologies. Materials and methods A comprehensive literature review was performed, specifically evaluating AM technologies assigned for processing zirconia. An electronic database search was performed using keywords and MeSH terms. The search was confined to full-text articles written in English and published in peer-reviewed journals between 1999 and 2018. Results A total of 62 articles were included in this review, of which 56 described the AM processes and 6 reported on AM applications in the field of dentistry. A broad diversity of literature exists regarding AM technologies for ceramic materials, which complicates the establishment of a classification system for the current AM technologies for zirconia. The variations in the composition of zirconia slurries or mixtures across different technologies often made it difficult to identify the proper nature of such information. Mechanical properties of printed zirconia materials utilizing different technologies were investigated through a wide range of tests. Overall, the review indicates that manufacturing zirconia using AM technologies could be achieved without issues, but mechanical properties appear to be poor compared with conventional manufacturing procedures. Conclusions The results of this review indicate the necessity for further potential improvement in AM technologies for manufacturing zirconia reconstructions along with advances in material composition before zirconia could be considered as a material for standard care.

Influence of scan body design and digital implant analogs on implant replica position in additively manufactured casts.

Abstract: Statement of problem Additive manufacturing (AM) technologies can be used to fabricate definitive casts for implant-supported restorations. However, information regarding the accuracy of the implant replica position on the polymeric AM cast generated with different scan bodies and digital implant replica systems is lacking. Purpose The purpose of this in vitro study was to compare with a conventional stone cast the linear and angular discrepancies of the implant analog positions in a polymeric AM cast obtained from 3 different scan body and digital implant replica systems. Material and methods A partially edentulous maxillary typodont with 3 implant replicas (Implant replica RP Branemark system; Nobel Biocare) was prepared. Two duplicating methods were evaluated: conventional (CNV group) and AM (AM group) procedures. For the CNV group, polyvinyl siloxane open-tray implant impressions (CNV) were made at room temperature (23 °C). The AM group was further divided into the subgroups Elos Medtech, Nt-Trading, and Dynamic Abutment. For the Elos Medtech subgroup, the corresponding scan bodies were placed on each implant, and the typodont was digitized by using a laboratory scanner (E3 scanner; 3Shape A/S). The same procedure was repeated with the remaining subgroups. All the AM polymer casts were fabricated at once by using the same 3D printer (Eden 500V; Stratasys). Ten specimens of each group were obtained (n=10). A coordinate-measuring machine (CMM) was used to measure the position of each implant replica, and distortion was calculated for each system at the x-, y-, and z-axes and 3D distortion measurement ( 3 D = x 2 + y 2 + z 2 ). The Shapiro-Wilk test revealed that the data were not normally distributed. The Kruskal-Wallis and pairwise Mann-Whitney U tests (α=.05) were used for the analysis. Results The CNV group presented significantly higher linear discrepancy than the Dynamic Abutment group on the x- and y-axes. On the z-axis, however, the CNV group showed significantly lower linear discrepancy than the Nt-Trading and Dynamic Abutment groups. The 3D linear discrepancy was 12 ±12 μm for the CNV group, 4 ±100 μm for the Elos Medtech group, 8 ±52 μm for the Nt-Trading group, and 5 ±19 μm for the Dynamic Abutment. The CNV group demonstrated a significantly higher angle than the Nt-Trading group but a significantly smaller angle than the Elos Medtech and Dynamic Abutment groups. Conclusions The AM groups had lower 3D discrepancies than the CNV group. The Dynamic Abutment group had significantly better accuracy for the mesiodistal and buccolingual implant replica positions than the CNV group, but the conventional procedures had significantly better results for the apicocoronal implant replica position. Scan body and digital implant replica design systems only influenced the accuracy of the angular implant replica position on the AM casts.

Reducing the Risk of COVID-19 Transmission in Dental Offices: A Review.

Abstract: The COVID-19 epidemic has become a major public health challenge around the world. According to the World Health Organization (WHO), as of August 2020 there are more than 833,556 dead and over 24,587,513 people infected around the world. This pandemic has adversely affected many professions around the globe, including dentistry. COVID-19, caused by the Corona virus family, is transmitted mainly by direct contact with an infected person or through the spread of aerosol and droplets. Dentistry by nature is considered to be one of the most vulnerable professions with regards to the high risk of transmission between the dentist, dental team, and patients; therefore, a protocol for infection control and the prevention and spreading of the COVID-19 virus in dental settings is urgently needed. This article reviews essential knowledge about this virus and its transmission and recommends preventive methods based on existing scientific research and recommendations to prevent the spread of this virus in dental offices and clinics.

Digitally Created 3-Piece Additive Manufactured Index for Direct Esthetic Treatment.

Abstract: Facial and intraoral scanners as well as additive manufacturing (AM) technologies can be integrated to virtually plan restorative procedures. The present article describes a digital workflow protocol for treatment planning an esthetic rehabilitation using direct composite restorations. The combination of facial digitalization and intraoral scans allowed a facially driven diagnostic waxing, while additive manufacturing technologies facilitate the translation of the digital waxing into the patient´s mouth through an AM 3-piece silicone index which was designed into a buccal and a lingual clear flexible silicone indices that were fitted into a clear and rigid custom tray. This procedure facilitated the treatment planning procedures as well as assisted the direct composite restoration procedures, providing several advantages compared with conventional procedures such as precise translation of the digital diagnostic waxing into the patient´s mouth, horizontal path of insertion of the silicone index, and minimized time of the clinical intervention.

Esthetic dental perception comparisons between 2D- and 3D-simulated dental discrepancies.

Abstract: Statement of problem Intraoral scanners (IOSs), facial scanners (FSs), and computer-aided design (CAD) software programs have become powerful tools for treatment planning. However, discrepancies in perception regarding 2-dimensional (2D) or 3-dimensional (3D) simulations by dentists, dental students, and laypeople have not been analyzed. Purpose The purpose of this observational study was to analyze the perceptions of laypersons, dental students, and dentists regarding disparities of the maxillary dental midline and the occlusal plane when analyzing the dental discrepancies on 2D- and 3D-clinical simulations. Material and methods A female model was digitized by using an FS, IOS, and a full-face smile photograph. Dental discrepancies were simulated by using a 2D photograph (2D group) and 3D scan (3D group) of the model. In both simulation groups, 2 subgroups were produced. The occlusal plane of the first subgroup was modified in 1-degree increments without changing the dental midline or the position of the maxillary dental incisors. In the second subgroup, the occlusal plane was modified by using the same increments, but the maxillary central incisors and dental midline were altered to match the inclination of the occlusal plane. A total of 300 participants (N=300) were asked to rate the 2D images (N=12) and 3D videos (N=12) on a 1-to-6 scale and answer a questionnaire. Ordinal logistic regression was used to analyze the ratings. Results The ratings decreased with the increased tilt of the occlusal plane, and the layperson group gave consistently higher ratings than the other 2 groups. For dentists, the odds of giving a higher versus lower rating decreased by almost a half for each degree of tilt. However, for students, that effect was diminished by a positive interaction term, and for laypersons, the effect was even less. Students gave similar ratings to dentists, but laypersons gave higher ratings. As the age of the participants increased, however, the ratings also increased. The use of 3D versus 2D images had a positive effect on the ratings, but the effect decreased for the student observers and decreased even further for laypersons. Furthermore, midline alteration led to higher ratings but also resulted in worsening of the odds ratio for the tilt. Seventy percent of the dentists, 57% of the dental students, and 52% of the laypersons preferred 2D simulations to 3D simulations. Conclusions Dentists, dental students, and laypersons decreased their ratings with increased inclination of the occlusal plane; however, laypersons still graded all the 2D and 3D images as esthetically pleasant, giving consistently higher ratings than the dentists and dental students. Overall, 3D simulations obtained higher ratings than 2D images, but the positive effect decreased for the student observers and decreased even further for laypersons.

Layperson and Dental Professional Perception When Evaluating Their Own Virtually 2D or 3D Simulated Esthetic Discrepancies.

Abstract: Purpose To analyze the perceptions of laypersons, dental students, and dentists regarding disparities of the maxillary dental midline and the occlusal plane (OP) when analyzing their own 2D or 3D clinical simulation. Material and methods 20 participants per group volunteered (N = 60). Intraoral and facial scans, and a photograph were obtained from each participant. Two simulation groups were created: 2D and 3D groups, which were subdivided into two subgroups. In the first subgroup, the OP was modified by 1-degree increments without changing the maxillary midline. In the second subgroup, the OP was modified by the same increments, but the maxillary midline was altered to match the OP inclination. Participants were asked to rate the simulations on a 1-to-6 scale and a question survey. Ordinal logistic regression (OR) was used to analyze the ratings. Results Tilt of the OP had the strongest negative effect on the ratings which was further amplified by the dental midline inclination (OR = 0.122). Midline modification alone did not affect the ratings (OR = 0.744). 3D simulations had a stronger positive effect on the ratings compared to 2D simulations. For dental students, the positive rating effect of 3D simulations was similar to dentists. For laypersons, the positive rating effect of 3D simulations compared to the 2D simulations decreased relative to dentists. The survey revealed that 45% of the dentists, 80% of the students, and 50% of the laypersons preferred the 3D simulation. Conclusions The type of dimensional representation affected the esthetic perception of all participants. 3D simulations obtained higher esthetic ratings for the same esthetic discrepancy than 2D simulations. However, all participants' ratings decreased with increased tilt of the OP and were further decreased with the inclination of the dental midline.

Fiber-reinforced composite fixed dental prosthesis using an additive manufactured silicone index.

Abstract: Objective Digital tools such as facial and intraoral digitizers and additive manufacturing (AM) technologies assist restorative treatments. The objective of the present manuscript was to describe a workflow procedure for treatment planning and fabricating a fiber-reinforced composite fixed dental prosthesis (FDP) replacing an absent maxillary lateral incisor, using additively manufactured silicone indices to facilitate the clinical intervention. Clinical considerations The elaboration of a direct fiber-reinforced composite restoration is a technique sensitive procedure which might be time-consuming for the clinician. The digital waxing helped to determine the exact position and size of the lingual wings and connectors of the fiber-reinforced FDP and to design a three-piece index. And the AM of the index helped to transfer the information to the patient's dentition accurately. Conclusions The protocol minimizes the time of clinical intervention by facilitating the transference of the virtual diagnostic waxing teeth into the patient's mouth. The three-piece silicone index provides an individualized path of insertion of each index part while also providing a customized space and location of the lingual wings of the restoration. Clinical significance The usage of AM silicone indices facilitates the clinical intervention by translating the size and position of the diagnostic wax-up teeth into the patient´s mouth, minimizing clinical procedure's time.