| 1. |
- Braian, Michael
(författare)
-
Digital dentistry : studies on the trueness and precision of additive manufacturing and intraoral scanning
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Artificial designs and features usually control production workflowsin the industry. The operator has the freedom to adapt designs toachieve the desired function; when the operator is satisfied, massproduction of the two objects is possible. The production workflowfor prosthetic restorations in dentistry is a fairly complicatedprocedure that requires several well-controlled processes, and eachunit is individually adapted to one unique situation. The aim of thefinal restoration is to replace damaged or missing soft and hard tissue,and to restore function, phonetics and aesthetics. The restoration hashigh material property requirements in order to withstand high forces,thermal changes, aging and humidity. If the fit of the reconstructionis insufficient there is a high probability for clinical failures rangingfrom inflammatory processes to reconstruction fractures. Thegrading of perfect, sufficient and insufficient fit is unknown althoughthe definition clinically acceptable fit has been used to describe andcontrol a reconstruction that is well seated and controllable by the clinician. Study I in this thesis focuses on the clearance (play) betweendifferent implant components in order to achieve a threshold value forhow accurate the production in dentistry needs to be. We found thatmetallic components on external hex connections have a clearanceof approximately 50 μm.Not only is every case individually designed and manufactured,but the receiving intraoral part also needs to be replicated into anextraoral part ahead of production, a procedure that has been possiblewith different impression materials. Subsequently, the production goes through a series of controlled compensations to fit the intraoralsituation. The conventional workflow starts by the selection of animpression tray, ranging from custom-made trays to plastic stocktrays. The ideal trays are rigid, thereby minimising flexure during theimpression taking. There are several types of impression materialswith different properties regarding setting time, volume changes andmechanical properties. The next step in the conventional workflowis the casting of the impression. There are various types of gypsumproducts utilised in dentistry, and they require different amounts ofwater. The differences depend on the shape and compactness of thecrystals. Type IV dental stone gypsum is often used in reconstructivedentistry with a typical setting expansion of 0.10%. For the partialdigital workflow the same volume changes can be seen for theconventional impression, the stone model production and the dieprocessing. In order to design the intended construction digitallyinstead of using wax, the model needs to be digitised in an extraoral scanner, also known as desktop scanner.The fully digital workflow consists of a direct digitisation of the oralcavity utilising intraoral scanning devices. All intraoral scanners havethe same goal, to digitise the size, shape and surface of a physicalobject into a geometrical virtual shape. This acquisition needs to berepeatable, reproducible and accurate. The IOS manufacturers tryto achieve these goals with different hardware and software setups.Study IV focuses on the acquisition accuracy of five different intraoralscanners for the digitisation of edentulous and dentated models. Theresults suggest that the devices had lower accuracy for the digitisationof the edentulous models when compared to the dentated model.Furthermore, Study IV presented observations suggesting that fullarchscans had lower accuracy when compared to shorter arch scanson both models. For the cross-arch measurements on the edentulousscans, the trueness values ranged from 6 μm to 193 μm, and, for the shorter arch measurements, the results ranged from 2 μm to 103 μm.For the dentated cast, the cross-arch trueness values ranged from6 μm to 150 μm, and, for the shorter arch measurements, the resultsranged from 4 μm to -56 μm.The digitised file is then utilised as a virtual model by a computeraideddesigner in order to virtually design the intended reconstruction.The designed file is then manufactured utilising computer-aidedmanufacturing, which can be performed either by a subtractivemachine (milling) or by additive systems (3D printing). Study II andStudy III explore the production tolerances for producing polymericand metallic objects from additive systems. Study III also containeda subtractive group. The results from these two studies suggest thatall tested additive systems for producing polymeric objects were, onaverage, 500 μm to
|
|
| 2. |
- Braian, Michael, et al.
(författare)
-
Geometrical accuracy of metallic objects produced with additive or subtractive manufacturing : A comparative in vitro study
- 2018
-
Ingår i: Dental Materials. - : Elsevier. - 0109-5641 .- 1879-0097. ; 34:7, s. 978-993
-
Tidskriftsartikel (refereegranskat)abstract
- Objective. To evaluate the accuracy and precision of objects produced by additive manufacturing systems (AM) for use in dentistry and to compare with subtractive manufacturing systems (SM). Methods. Ten specimens of two geometrical objects were produced by five different AM machines and one SM machine. Object A mimics an inlay-shaped object, while object B imitates a four-unit bridge model. All the objects were sorted into different measurement dimensions (x, y, z), linear distances, angles and corner radius. Results. None of the additive manufacturing or subtractive manufacturing groups presented a perfect match to the CAD file with regard to all parameters included in the present study. Considering linear measurements, the precision for subtractive manufacturing group was consistent in all axes for object A, presenting results of <0.050 mm. The additive manufacturing groups had consistent precision in the x-axis and y-axis but not in the z-axis. With regard to corner radius measurements, the SM group had the best overall accuracy and precision for both objects A and B when compared to the AM groups. Significance. Within the limitations of this in vitro study, the conclusion can be made that subtractive manufacturing presented overall precision on all measurements below 0.050 mm. The AM machines also presented fairly good precision, <0.150 mm, on all axes except for the z-axis. Knowledge regarding accuracy and precision for different production techniques utilized in dentistry is of great clinical importance. The dental community has moved from casting to milling and additive techniques are now being implemented. Thus all these production techniques need to be tested, compared and validated. (C) 2018 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.
|
|
| 3. |
- Braian, Michael, et al.
(författare)
-
Production tolerance of additive manufactured polymeric objects for clinical applications
- 2016
-
Ingår i: Dental Materials. - : Elsevier. - 0109-5641 .- 1879-0097. ; 32:7, s. 853-861
-
Tidskriftsartikel (refereegranskat)abstract
- Objectives. To determine the production tolerance of four commercially available additive manufacturing systems. Methods. By reverse engineering annex A and B from the ISO_12836;2012, two geometrical figures relevant to dentistry was obtained. Object A specifies the measurement of an inlay shaped object and B a multi-unit specimen to simulate a four-unit bridge model. The objects were divided into x, y and z measurements, object A was divided into a total of 16 parameters and object B was tested for 12 parameters. The objects were designed digitally and manufactured by professionals in four different additive manufacturing systems; each system produced 10 samples of each objects Results. For object A, three manufacturers presented an accuracy of <100 mu m and one system showed an accuracy of <20 mu m For object B, all systems presented an accuracy of <100 mu m, and most parameters were <40 mu m. The standard deviation for most parameters were <40 mu m Significance. The growing interest and use of intra-oral digitizing systems stresses the use of computer aided manufacturing of working models. The additive manufacturing techniques has the potential to help us in the digital workflow. Thus, it is important to have knowledge about production accuracy and tolerances. This study presents a method to test additive manufacturing units for accuracy and repeatability. (C) 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved
|
|
| 4. |
- Braian, Michael, et al.
(författare)
-
Tolerance Measurements on Internal- and External-Hexagon Implants
- 2014
-
Ingår i: International Journal of Oral & Maxillofacial Implants. - : Quintessence. - 0882-2786 .- 1942-4434. ; 29:4, s. 846-852
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: To measure the horizontal machining tolerances of the interface between internal-and external-hexagon implants and analogs with corresponding components after delivery from the manufacturer. These values may be a valuable tool for evaluating increasing misfit caused by fabrication, processing, and wear. Materials and Methods: Seven implants and seven analogs with external-and internal-hexagon connections (Biomet 3i) with corresponding prefabricated gold cylinders and gold screws, prefabricated cylindric plastic cylinders, and laboratory screws were studied. One set of components from the external and internal groups was measured manually and digitally. Measurements from the test subjects were compared with identical measurements from the virtual model to obtain threshold values. The virtual model was then used to obtain optimally oriented cuts. Results: The horizontal machining tolerances for castable plastic abutments on external implants were 12 +/- 89 mu m, and for internal implants they were 86 +/- 47 mu m. Tolerance measurements on prefabricated gold abutments for external implants were 44 +/- 9 mu m, and for internal implants they were 58 +/- 28 mu m. Conclusion: The groups with metallic components showed the smallest tolerance at < 50 mu m for the external group and < 90 mu m for the internal group. The prefabricated plastic cylinder groups ranged from < 100 mu m for external and < 130 mu m for internal connection.
|
|
| 5. |
- Braian, Michael, et al.
(författare)
-
Trueness and precision of 5 intraoral scanners for scanning edentulous and dentate complete-arch mandibular casts: A comparative in vitro study
- 2019
-
Ingår i: Journal of Prosthetic Dentistry. - : Elsevier BV. - 0022-3913 .- 1097-6841. ; 122:2, s. 129-136
-
Tidskriftsartikel (refereegranskat)abstract
- Statement of problem. Limited information is available on the trueness and precision of intraoral scanners (IOSs) for scanning dentate and edentulous casts. Purpose. The purpose of this in vitro study was to evaluate the trueness and precision of 5 different IOS devices for scanning a dentate and an edentulous cast in a standardized way for short arches and complete arches. Material and methods. Five IOS devices were used to scan 2 computer metric measured casts using a coordinate measuring machine (CMM). Both were scanned 15 times. All scans were carried out by 1 experienced operator in a standardized way. One cast was edentulous, and 1 was dentate. Five cylindrical landmarks were added to each cast. These cylinders made the measurement of point-to-point distances possible, dividing the tests into cross-arch measurements and intercylindrical (short-arch) measurements. The Student t test, Mann-Whitney test, and Levene test for equality were used to calculate the difference between the edentulous and dentate scans for both cross-arch and intercylindrical measurements (alpha=.05). Results. For the cross-arch measurements on the edentulous scans, the trueness values ranged between 6 mu m (Emerald P1-P2) and 193 mu m (Omnicam P1-P5) and for the intercylindrical measurements, between 2 mu m (Itero P4-P5) and -103 mu m (CS 3600 P1-P2). For the dentate cast, the cross-arch trueness values ranged between 6 mu m (CS 3600 P1-P2) and 150 mu m (TRIOS 3 P1-P5) and for the intercylindrical measurements, between 4 mu m (Itero P4-P5) and -56 mu m (Emerald P4-P5). Conclusions. Significant differences were found in scanning edentulous and dentate scans for short arches and complete arches. Trueness for complete-arch scans were <193 mu m for edentulous scans and <150 mu m for dentate scans. Trueness for short-arch scans were <103 mu m for edentulous scans and <56 mu m for dentate scans.
|
|
| 6. |
- Mahmood, Deyar Jallal Hadi, et al.
(författare)
-
Fracture load of colored and non-colored high translucent zirconia three-unit fixed dental prosthesis frameworks
- 2018
-
Ingår i: Acta Biomaterialia Odontologica Scandinavica. - : Taylor & Francis. - 2333-7931. ; 4:1, s. 38-43
-
Tidskriftsartikel (refereegranskat)abstract
- The use of colored translucent zirconia may enable restorations of a more natural tooth-like appearance than previous opaque white zirconia. The shift from non-colored to colored zirconia may however entail a risk of reduced strength. The aim of the present study was to compare fracture load and fracture mode of fixed dental prostheses frameworks made of colored translucent zirconia to that of non-colored controls. A total of forty three-unit FDP frameworks were manufactured from two different high translucent zirconia materials (Zenostar, Wieland Dental, and DD cubeX2, Dental Direkt). Each group contained two subgroups, one colored and one non-colored. Coloring was performed before final sintering using two different infiltration techniques. All FDPs underwent an artificial aging process in the form of heat treatment, thermocycling and preloading whereafter the specimens were subjected to load until fracture. Fracture load and mode was registered. For one of the zirconia materials, Zenostar, the non-colored frameworks showed significantly higher fracture loads ( < .0001) compared to its colored counterpart. No significant difference ( > .05) was found between colored and non-colored frameworks in the other zirconia material, DD cubeX2. All FDPs fractured through the connector. Some fractures ran through the mesial and some through the distal side of the connector but there were no significant differences in fracture mode between groups. Coloring before sintering of high-translucent zirconia may decrease the fracture load of FDP frameworks for certain materials and techniques. Fracture mode however, does not appear to be affected.
|
|
| 7. |
- Mahmood, Deyar Jallal Hadi, et al.
(författare)
-
Production tolerance of conventional and digital workflow in the manufacturing of glass ceramic crowns
- 2019
-
Ingår i: Dental Materials. - : Elsevier BV. - 0109-5641 .- 1879-0097. ; 35:3, s. 486-494
-
Tidskriftsartikel (refereegranskat)abstract
- Objectives. To measure and compare the size of the cement gap of wax and polymer copings and final glass-ceramic crowns, produced from conventional and digital workflows, one additive and one subtractive. Methods. Thirty wax copings were made by conventional manual layering technique and modeling wax on stone models with spacer varnish simulating a cement spacer. The wax copings were embedded and press-cast in lithium disilicate glass ceramic. Thirty wax copings were produced by milling from a wax blank, i.e. subtractive manufacturing, and thirty polymer burn-out copings were produced by stereolithography, i.e. additive manufacturing. These copings were embedded and press-cast in lithium disilicate glass ceramic in the same manner as the conventional group. The fit of the wax/polymer copings and subsequent crowns was checked using an impression replica method. Mean values for cement gap for marginal, axial, and occlusal areas were calculated and differences were analyzed using Student's t-test. Results. There were significant differences in mean values for accuracy/production tolerance among different manufacturing techniques for both production stages: wax and polymer copings and final pressed glass-ceramic crowns. In general, crowns produced from a digital additive workflow showed smaller mean cement gaps than crowns produced from a conventional workflow or a digital subtractive workflow. Additive polymer copings showed significantly smaller cement gaps than milled wax copings (p <=.001) and conventional wax copings (p <=.001) in the axial area. In the occlusal area, both additive polymer copings and conventional wax copings showed significantly smaller cement gaps than milled wax copings (p = .002 and p <=.001 respectively). Crowns produced from conventional manual build-up wax copings showed significantly larger mean cement gaps than crowns produced from milled wax and additively manufactured polymer copings in the marginal and axial areas (p <=.001). Among the crowns with smaller cement gaps, crowns produced from additively manufactured polymer copings showed significantly smaller mean cement gaps than crowns produced from milled wax in the marginal and axial areas (p <=.001). In the occlusal areas, the differences in mean cement gaps were only statistically significant between crowns produced from conventional manual build-up wax copings and crowns produced from milled wax where the latter ones showed smaller mean cement gaps (p = .025). Significance. The present study suggests that an additive manufacturing technique produces smaller mean cement gaps in glass-ceramic crowns than a conventional or subtractive manufacturing technique. (C) 2019 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.
|
|
| 8. |
- Mutwalli, Hussam, et al.
(författare)
-
Trueness and Precision of Three-Dimensional Digitizing Intraoral Devices
- 2018
-
Ingår i: International Journal of Dentistry. - : Hindawi Publishing Corporation. - 1687-8728 .- 1687-8736. ; 2018
-
Tidskriftsartikel (refereegranskat)abstract
- Aim. To measure the trueness and precision under repeatable conditions for different intraoral scanners (IOSs) when scanning fully edentulous arch with multiple implants. Materials and Methods. Three IOSs and one industrial scanner were used to scan one edentulous master cast containing five implant scan bodies and three spheres. The cast was scanned thirty times with each scanner device. All scans were analyzed in the inspect software, and three-dimensional locations of the implants and the interarch distance between the spheres were measured. The values were compared to measurements made with one coordinate measuring machine (true value). One-way ANOVA was used to calculate the differences between IOSs and in comparison with the true value. Results. Significant differences were found between all IOSs. For the implant measurements, Trios 3 had the lowest trueness (<= 114 mu m), followed by Trios 3 mono (<= 63 mu m) and Itero element (<=-41 mu m). Trios had the lowest precision (<= 135 mu m), followed by Itero element (<= 101 mu m) and Trios 3 mono (<= 100 mu m). With regard to the interarch distance measurements, Trios 3 had the lowest trueness (<= 68 mu m), followed by Trios 3 mono (<= 45 mu m) and Itero element (<= 40 mu m). Trios 3 had the lowest precision (<= 206 mu m), followed by Itero element (<= 124 mu m) and Trios 3 mono (<= 111 mu m). Conclusion. The results from this in vitro study suggest that precision is low for the tested IOS devices when scanning fully edentulous arches with multiple implants.
|
|
| 9. |
- Segerström, Sofia, et al.
(författare)
-
A Validation Study of the Impression Replica Technique.
- 2019
-
Ingår i: Journal of Prosthodontics. - : John Wiley & Sons. - 1059-941X .- 1532-849X. ; 28:2, s. e609-e616
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To validate the well-known and often-used impression replica technique for measuring fit between a preparation and a crown in vitro. MATERIALS AND METHODS: The validation consisted of three steps. First, a measuring instrument was validated to elucidate its accuracy. Second, a specimen consisting of male and female counterparts was created and validated by the measuring instrument. Calculations were made for the exact values of three gaps between the male and female. Finally, impression replicas were produced of the specimen gaps and sectioned into four pieces. The replicas were then measured with the use of a light microscope. The values received from measuring the specimen were then compared with the values received from the impression replicas, and the technique was thereby validated. RESULTS: The impression replica technique overvalued all measured gaps. Depending on location of the three measuring sites, the difference between the specimen and the impression replicas varied from 47 to 130 mum. CONCLUSION: The impression replica technique overestimates gaps within the range of 2% to 11%. The validation of the replica technique enables the method to be used as a reference when testing other methods for evaluating fit in dentistry.
|
|
| 10. |
- Sumi, T, et al.
(författare)
-
Characteristics of implant-CAD/CAM abutment connections of two different internal connection systems
- 2012
-
Ingår i: Journal of Oral Rehabilitation. - : John Wiley & Sons. - 1365-2842 .- 0305-182X. ; 39:5, s. 391-398
-
Tidskriftsartikel (refereegranskat)abstract
- Titanium or zirconium computer-aided design/computer-aided manufacturing abutments are now widely used for aesthetic implant treatments; however, information regarding microscopic structural differences that may influence the biological and mechanical outcomes of different implant systems is limited. Therefore, the characteristics of different connection systems were investigated. Optical microscopic observation and scanning electron microscopy showed different characteristics of two internal systems, namely the Astra Tech and the Replace Select system, and for different materials. The scanning electron microscopic observation showed for the Astra Tech that the implant-abutment interface seemed to be completely sealed for both titanium and zirconium abutments, both horizontally and sagittally; however, the first implant-abutment contact was below the fixture top, creating a microgap, and fixtures connected with titanium abutments showed significantly larger values (23·56μm±5·44 in width, and 168·78μm±30·39 in depth, P<0·001). For Replace Select, scanning electron microscopy in the sagittal direction showed that the sealing of titanium and zirconium abutments differed. The seal between the implant-titanium and implant-zirconium abutments seemed to be complete at the butt-joint interface; however, the displacement of the abutment in relation to the fixture in the lateral direction was evident for both abutments with no statistical differences (P>0·70), creating an inverted microgap. Thus, microscopy evaluation of two commonly used internal systems connected to titanium or zirconium abutments showed that the implant-abutment interface was perfectly sealed under no-loading conditions. However, an inverted microgap was seen in both systems, which may result in bacterial accumulation as well as alteration of stress distribution at the implant-abutment interface.
|
|
