Abstract Statement of problem The application of 3-dimensional printing technology is emerging in dentistry and is being increasingly used to fabricate dental restorations. To date, scientific ...evidence is lacking regarding the effect of different factors on the mechanical properties of the printed restorations with the additive manufacturing technique. Purpose The purpose of this in vitro study was to evaluate the effect of build direction (layer orientation) on the mechanical properties of a novel 3-dimensionally (3D)-printed dental restorative material. Material and methods Based on the printing direction, 2 groups were tested. In the first group (n=20), the specimens were vertically printed with the layers oriented perpendicular to the load direction. In the second group (n=20), the specimens were horizontally printed with the layers oriented parallel to the load direction. All specimens were fabricated using the DW028D 3D-printer. The specimens were loaded with a universal testing machine at a crosshead speed of 1 mm/min with a 10-kN load cell. The test was performed at room temperature (22°C) under dry testing conditions. The compressive strength was calculated for both groups, and the results were compared using the unpaired t test (α=.05). Results The mean ±SD compressive strength for the vertically printed specimens was 297 MPa (±34) compared with 257 MPa (±41) for the horizontally printed specimens ( P =.002). Conclusions Within the limitations of this study, the layer orientation was found to influence the compressive strength of the material. Vertically printed specimens with the layers oriented perpendicular to load direction have improved mechanical properties more than horizontally printed specimens with the layers oriented parallel to load direction.
Statement of problem In the past 5 years, the use of intraoral digitizers has increased. However, data are lacking on the accuracy of scanning implant restorative platforms for prosthodontics with ...intraoral digitizers. Purpose The purpose of this clinical pilot study was to assess the applicability and accuracy of intraoral scans by using abutments designed for scanning (scan abutments) in edentulous mandibles. Material and methods Twenty-five participants with complete mandibular overdentures retained by 2 implants and frameworks were included in this study. Scan abutments were placed on the implants intraorally and scanned with the iTero intraoral scanner. Also, scan abutments were placed on the implant analogs of the definitive casts and scanned with an extraoral laboratory scanner (Lava Scan ST scanner). Two 3-dimensional computer-aided design models of the scan abutments with predetermined center lines were subsequently imported and registered, together with each of the scanned equivalents. The distance between the centers of the top of the scan abutments and the angulations between the scan abutments was assessed. These values were compared with the measurements made on the 3-dimensional scans of the definitive casts, which were the participants' original definitive casts used for fabrication of soldered bars. The threshold for distance error was established to be 100 μm. Results Four of the 25 intraoral scans were not suitable for research because the intraoral scanner was not able to stitch the separate scans together. Five of the 21 suitable scans demonstrated an interimplant distance error >100 μm. Three of the 25 intraoral scans showed interimplant angulation errors >0.4 degrees. Only 1 scan showed both an acceptable interimplant distance (<100 μm) and an acceptable angulation error (<0.4 degrees). Conclusions Based on the intraoral scans obtained in this study, distance and angulation errors were too large to fabricate well-fitting frameworks on implants in edentulous mandibles. The main reason for the unreliable scans seemed to be the lack of anatomic landmarks for scanning.
To assess the literature on the accuracy and clinical performance of static computer-assisted implant surgery in implant dentistry.
Electronic and manual literature searches were applied to collect ...information about (1) the accuracy and (2) clinical performance of static computer-assisted implant systems. Meta-regression analysis was performed to summarize the accuracy studies. Failure/complication rates were investigated using a generalized linear mixed model for binary outcomes and a logit link to model implant failure rate.
From 2,359 articles, 14 survival and 24 accuracy studies were included in this systematic review. Nine different static image guidance systems were involved. The meta-analysis of the accuracy (24 clinical and preclinical studies) revealed a total mean error of 1.12 mm (maximum of 4.5 mm) at the entry point measured in 1,530 implants and 1.39 mm at the apex (maximum of 7.1 mm) measured in 1,465 implants. For the 14 included survival studies (total of 1,941 implants) using static computer-assisted implant dentistry, the mean failure rate was 2.7% (0% to 10%) after an observation period of at least 12 months. In 36.4% of the treated cases, intraoperative or prosthetic complications were reported, which included: template fractures during the surgery, change of plan because of factors such as limited primary implant stability, need for additional grafting procedures, prosthetic screw loosening, prosthetic misfit, and prosthesis fracture.
Different levels of quantity and quality of evidence were available for static computer-assisted implant placement, with tight-fitting high implant survival rates after only 12 months of observation in different indications achieving a variable level of accuracy. Future long-term clinical data are necessary to identify clinical indications; detect accuracy; assess risk; and justify additional radiation doses, effort, and costs associated with computer-assisted implant surgery.
Objectives
To assess the literature on the accuracy of static computer‐assisted implant surgery in implant dentistry.
Materials and Methods
Electronic and manual literature searches were conducted to ...collect information about the accuracy of static computer‐assisted implant systems. Meta‐regression analysis was performed to summarise the accuracy studies.
Results
From a total of 372 articles. 20 studies, one randomised controlled trial (RCT), eight uncontrolled retrospective studies and 11 uncontrolled prospective studies were selected for inclusion for qualitative synthesis. A total of 2,238 implants in 471 patients that had been placed using static guides were available for review. The meta‐analysis of the accuracy (20 clinical) revealed a total mean error of 1.2 mm (1.04 mm to 1.44 mm) at the entry point, 1.4 mm (1.28 mm to 1.58 mm) at the apical point and deviation of 3.5°(3.0° to 3.96°). There was a significant difference in accuracy in favour of partial edentulous comparing to full edentulous cases.
Conclusion
Different levels of quantity and quality of evidence were available for static computer‐aided implant surgery (s‐CAIS). Based on the present systematic review and its limitations, it can be concluded that the accuracy of static computer‐aided implant surgery is within the clinically acceptable range in the majority of clinical situations. However, a safety marge of at least 2 mm should be respected. A lack of homogeneity was found in techniques adopted between the different authors and the general study designs.
The invention of computerized axial tomography (now known as computerized tomography) and developments of interactive software to allow virtual planning, with the aim to guide the surgery precisely ...toward a specific target, has dramatically improved general, as well as oral, surgery. Virtual dental implant planning allows for a prosthetically driven approach, resulting in the best possible design of the prosthesis, better esthetics, optimized occlusion and loading. This approach has also changed the surgical paradigm of using extensive flaps to obtain a proper view of the surgical area because flapless implant surgery, with or without immediate loading, has become more predictable. Two types of guided implant surgery protocols – static and dynamic – are described in the literature. The static approach, better known as computer‐guided surgery, refers to the use of a tissue‐supported surgical template. This reproduces the virtual implant position directly from computerized tomographic data and this information can be converted to guide templates to be used during surgery, with or without raising a mucoperiosteal flap. Dynamic guided surgery, also called navigation, reproduces the virtual implant position directly from computerized tomographic data and uses motion‐tracking technology to guide the implant osteotomy preparation. As the technology developed further, different levels of evidence were presented that showed various degrees of accuracy. Several protocols for guided surgery are available in the literature and are distinguished by different guide production techniques, methods of support and drilling/placement protocols. Currently, implant planning software using cone‐beam computerized tomography data has made it possible to plan the optical implant position virtually the optimal implant position, taking the surrounding vital anatomic structures and future prosthetic requirements into consideration. This paper summarizes the evolution and ongoing trends in digital and virtual planning and in implant surgery. The purpose of this overview was to clarify the different concepts in guided surgery and their respective advantages, disadvantages and limitations. The outcome of guided surgery is assessed in terms of implant survival, precision and complications. Clinical cases are given to demonstrate briefly the workflow and clinical guidelines for safe use of these approaches.
The aim of the present study was to evaluate the effect of the build angle and the support configuration (thick versus thin support) on the dimensional accuracy of 3D-printed full-coverage dental ...restorations.
A full-coverage dental crown was digitally designed and 3D-printed using stereolithography-additive manufacturing (SLA-AM) technology. Nine different angles were used during the build process: 90, 120, 135, 150, 180, 210, 225, 240, and 270 degrees. In each angle, the crown was printed using a thin and a thick support type, resulting in 18 specimens. The specimens were digitally scanned using a high resolution optical surface scanner (IScan D104i; Imetric 3D). The dimensional accuracy was evaluated by digital subtraction technique. The 3D digital files of the scanned printed crowns (test model), exported in standard tessellation language (STL) format, were superimposed with the STL file of the designed crown (reference model) using Geomagic Studio 2014 (3D Systems).
The root mean square estimate value and color map results suggest that the build angle and support structure configuration have an influence on the dimensional accuracy of 3D-printed crown restorations. Among the tested angles, the 120-degree build angle showed a minimal deviation of 0.029 mm for thin support and 0.031 mm for thick support, indicating an accurate fit between the test and reference models. Furthermore, the deviation pattern observed in the color map was homogenously distributed and located further away from the critical marginal area.
Within the limitations of this study, the selection of build angle should offer the crown the highest dimensional accuracy and self-supported geometry. This allows for the smallest necessary support surface area and decreases the time needed for finishing and polishing. These properties were mostly observed with a build angle of 120 degrees combined with a thin support type.
Aim
This systematic review and meta‐analysis were conducted to assess and compare the accuracy of conventional and digital implant impressions. The review was registered on the PROSPERO register ...(registration number: CRD42016050730).
Material and Methods
A systematic literature search was conducted adhering to PRISMA guidelines to identify studies on implant impressions published between 2012 and 2017. Experimental and clinical studies at all levels of evidence published in peer‐reviewed journals were included, excluding expert opinions. Data extraction was performed along defined parameters for studied specimens, digital and conventional impression specifications and outcome assessment.
Results
Seventy‐nine studies were included for the systematic review, thereof 77 experimental studies, one RCT and one retrospective study. The study setting was in vitro for most of the included studies (75 studies) and in vivo for four studies. Accuracy of conventional impressions was examined in 59 studies, whereas digital impressions were examined in 11 studies. Nine studies compared the accuracy of conventional and digital implant impressions. Reported measurements for the accuracy include the following: (a) linear and angular deviations between reference models and test models fabricated with each impression technique; (b) three‐dimensional deviations between impression posts and scan bodies respectively; and (c) fit of implant‐supported frameworks, assessed by measuring marginal discrepancy along implant abutments.) Meta‐analysis was performed of 62 studies. The results of conventional and digital implant impressions exhibited high values for heterogeneity.
Conclusions
The available data for accuracy of digital and conventional implant impressions have a low evidence level and do not include sufficient data on in vivo application to derive clinical recommendations.
Objectives
The first purpose of this study was to analyze the correlation between bone volume fraction (BV/TV) and calibrated radiographic bone density Hounsfield units (HU) in human jaws, derived ...from micro‐CT and multislice computed tomography (MSCT), respectively. The second aim was to assess the accuracy of cone beam computed tomography (CBCT) in evaluating trabecular bone density and microstructure using MSCT and micro‐CT, respectively, as reference gold standards.
Material and methods
Twenty partially edentulous human mandibular cadavers were scanned by three types of CT modalities: MSCT (Philips, Best, the Netherlands), CBCT (3D Accuitomo 170, J Morita, Kyoto, Japan), and micro‐CT (SkyScan 1173, Kontich, Belgium). Image analysis was performed using Amira (v4.1, Visage Imaging Inc., Carlsbad, CA, USA), 3Diagnosis (v5.3.1, 3diemme, Cantu, Italy), Geomagic (studio® 2012, Morrisville, NC, USA), and CTAn (v1.11, SkyScan). MSCT, CBCT, and micro‐CT scans of each mandible were matched to select the exact region of interest (ROI). MSCT HU, micro‐CT BV/TV, and CBCT gray value and bone volume fraction of each ROI were derived. Statistical analysis was performed to assess the correlations between corresponding measurement parameters.
Results
Strong correlations were observed between CBCT and MSCT density (r = 0.89) and between CBCT and micro‐CT BV/TV measurements (r = 0.82). Excellent correlation was observed between MSCT HU and micro‐CT BV/TV (r = 0.91). However, significant differences were found between all comparisons pairs (P < 0.001) except for mean measurement between CBCT BV/TV and micro‐CT BV/TV (P = 0.147).
Conclusions
An excellent correlation exists between bone volume fraction and bone density as assessed on micro‐CT and MSCT, respectively. This suggests that bone density measurements could be used to estimate bone microstructural parameters. A strong correlation also was found between CBCT gray values and BV/TV and their gold standards, suggesting the potential of this modality in bone quality assessment at implant site.
Virtual implant planning systems integrate (cone beam-) computed tomography data to assess bone quantity and virtual models for the design of the implant-retained prosthesis and drill guides. Five ...commercially available systems for virtual implant planning were examined regarding the modalities of integration of radiographic data, virtual dental models and the design of drill guides for guided implant surgery. The purpose of this review was to describe the limitations of these available systems regarding the import of imaging data and the design and fabrication of a drill guide.
The following software systems were examined regarding the import of imaging data and the export of the virtual implant planning for the design and fabrication of a drill guide with the help of two clinical situations requiring dental implant therapy: coDiagnostiX™, DentalWings, Canada (CDX); Simplant Pro™, Dentsply, Sweden (SIM); Smop™, Swissmeda, Switzerland (SMP); NobelClinician™, Nobel Biocare, Switzerland (NC); Implant Studio, 3Shape, Denmark (IST). Assessment criteria included data formats and management as well as the workflow for the design and production of drill guides.
All systems have a DICOM-interface ("Digital Imaging and Communication in Medicine") for the import of radiographic data. Imaging artefacts could be reduced but not eliminated by manual data processing. The import of virtual dental models in a universal format (STL: Standard Tesselation Language) was possible with three systems; one system could only be used with a proprietary data format. All systems display three-dimensional surface models or two-dimensional cross-sections with varying orientation for virtual implant planning. Computer aided design and manufacturing (CAD/CAM) of drill guides may be performed by the user with the help of default parameters or solely by the provider of the software and thus without the influence of the clinician.
Data bases of commonly used implant systems are available in all tested software, however not all systems allow to plan and execute fully guided implant placement. An individual design and in-house manufacturing of the drill guide is only available in some software systems. However, at the time of publication most recent software versions showed flexibility in individual design and in-house manufacturing of drill guides.
PurposeTo evaluate the influence of fabrication method and finish line design on marginal and internal fit of full-coverage interim restorations.
MethodsFour typodont models of maxillary ...central-incisor were prepared for full-coverage restorations. Four groups were defined; knife-edge (KE), chamfer (C), rounded-shoulder (RS), rounded-shoulder with bevel (RSB). All preparations were digitally scanned. A total of 80 restorations were fabricated; 20 per group (SLA/3D-printed n=10, milled n=10). All restorations were positioned on the master die and scanned using micro-computed tomography. The mean gaps were measured digitally (ImageJ). The results were compared using MANOVA (α=.05).
ResultsInternal and marginal gaps were significantly influenced by fabrication method (P=.000) and finish-line design (P=.000). 3D-Printed restorations showed statistically significant lower mean gap compared to milled restorations at all points (P=.000). The mean internal gap for 3D-printed restorations were 66, 149, 130, 95μm and for milled restorations were 89, 177, 185, 154μm for KE, C, RS, RSB respectively. The mean absolute marginal discrepancy in 3D-printed restorations were (30, 41, 30, 28μm) and in milled restorations were (56, 54, 52, 38μm) for KE, C, RS, RSB respectively.
ConclusionsThe fabrication methods showed more of an influence on the fit compared to the effect of the finish-line design in both milled and printed restorations. SLA-printed interim restorations exhibit lower marginal and internal gap than milled restorations. Nonetheless, for both techniques, all values were within the reported values for CAD/CAM restorations.
Significance3D-printing can offer an alternative fabrication method comparable to those of milled restorations.
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