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DentalXS

 

Access Portal for Dental Informatics, Computerized Dentistry and Dental CAD/CAM

 Research Reports

Making crowns with a CAD/CAM system. J.M. van der Zel, Elephant Holding B.V., Hoorn, The Netherlands.

Problem: CAD/CAM stands for Computer Aided Design/Computer Aided Manufacturing, thus computerized design and production. CAD/CAM has received much attention in the news because of a strong increase in IT-applications that work on a PC. Processes where mainframe computers were necessary, can now be now be executed on normal PC’s, because of increased memory capacity, high capacity hard disks and much higher calculation speed. The latest application for the PC is CAD/CAM. Conclusion: Many programming tools have been developed that can now be used in dentistry, specifically in the design and production of indirect dental restorations.

Published in SPIN Bulletin, Ministry of Economic Affairs, No. 4, December 1988, p. 11-12.

 

Maximum functional occlusion for a metal ceramic crown with the “CICERO” Scan/CAD/CAM-system. J.M. van der Zel, D. de Groot and C.L. Davidson. Department of Materials Science, Acedemic Centre for Dentistry, Amsterdam NL.

Statement of the problem: The Cicero-system is a CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) system for the production of “state-of-the-art” ceramic-fused-to-metal (CFM) restorations that makes use of near net-shape metal and ceramic sintering techniques. Existing CAD/CAM applications for the production of restorations are based on milling of massive materials, which has evident negative effects on esthetics. A novel sintering technique makes it possible to build-up and model the restoration in different layers such as metal, opaque, dentin and incisal porcelain for maximum esthetics. It is to be used for the production of restorations with maximal static and dynamic occlusion. Material and methods: A first mandibular premolar (46) was designed. The preparation and its immediate surroundings and antagonists were digitized with a laser-strip surface scanner. The theoretical 46 crown was deformed by a seven step algorithm to give maximum tooth-to tooth contact with the antagonist. The occlusal surface of the machined crowns were tested for efficacy in static and dynamic occlusion. Conclusion:  It could be concluded that occlusion in porcelain can be obtained by the automated way of production with the Cicero CAD/CAM-system.

Published as Abstract No. 75 in the Proceedings of the European Prosthodontics Association Congress 1991, Amsterdam, The Netherlands and in Imaging Techniques in Biomaterials, ed. M.A. Barbosa, 1994 Elsevier Science B.B., p. 361-383  

 

Influence of Cement gap Design on Fracture Resistance of CICERO Full-Porcelain CAD/CAM Restorations. J.M. van der Zel, C.L. Davidson, Department of Dental Materials Science, Academic Centre for Dentistry, Amsterdam, NL, Cicero Dental Systems bv, Hoorn, NL.   

Statement of the problem: The CICERO CAD/CAM system not only produces porcelain restorations supported with sintered metal or high-strength ceramic, but also full-porcelain restorations. The latter might be more susceptible to cracking by localized stresses depending on the way the restoration is supported. Aim: The aim of this study was to investigate the influence of cement gap design on the fracture resistance. A master steel die with a rounded chamfer preparation was duplicated in gypsum and scanned. Forty identical crowns were produced with four different cement gap geometries and cemented under constant load on the master steel die with zinc phosphate cement. Specimens were tested in a Zwick 1454 universal testing machine with a crosshead speed of 0.5 mm/min. The types of cement gap design (restoration inside) were: even cement gap (A), supporting ridge at the margin (B), supporting ridge 1 mm inside from the margin (C) and supporting ridge in the higher part of the restoration (D). Results: The mean fracture force of group A (1298.9±64.8 N) was not significantly different from group B (1272.2±53.7) and that of group C (1468.8±79.2) was not signifantly different from group D (1474.6±59.1) (p<0.05). However the restorations with a supporting ridge created inside the crown at more than 1 mm distance from the margin (C,D) had significantly higher (15%) fracture resistance (pŁ0.05) than restorations supported near the margin (A,B). Conclusion: Hence, we conclude that designing an inside ridge might significantly enhance the fracture resistance of CICERO full-porcelain CAD/CAM restorations in vitro.

Published: Van der Zel, J.M., and Davidson, C.L (1997): Influence of Cement gap Design on Fracture Resistance of Cicero Full-Porcelain CAD/CAM Restorations. , J Dent Res 76, Abstr 987:137.

 

Influence of Crown Layer Build-up on Fracture Resistance of CICERO All-ceramic CAD/CAM Restorations. J.M. van der Zel, C.L. Davidson, Department of Dental Materials Science, Academic Centre for Dentistry, Amsterdam, NL, Cicero Dental Systems bv, Hoorn, NL.

The CICERO CAD/CAM system produces ceramic restorations supported with high-strength high-alumina core ceramic (Synthoceram, Elephant), but also full-porcelain restorations. The novel supporting ceramic understructure material is based on a alumina-zirconia-mullite-system with a modulus of rupture of 350 MPa. The core is sintered on a pre-milled refractory die. This supporting material might provide the restorations with the necessary survival durability. The aim of this study was to investigate the influence of crown layer build-up on the fracture resistance. A master steel die with a rounded chamfer preparation was duplicated in gypsum and scanned. Twenty identical crowns were produced with two different layer make-ups and cemented under constant load on the master steel die with zinc phosphate cement. The cementgap design provided for a supporting ridge 1 mm inside from the margin. Specimens were tested in a Zwick 1454 universal testing machine with a crosshead speed of 0.5 mm/min. The two groups of layer build-up tested were: with (A) and without (B) supporting core. The mean fracture force of group A (3093.2±136.5) was significantly different from group B (1468.8±79.2) (p<0.05). The restorations strengthened with high-strength ceramic core (A) had significantly higher (110%) fracture resistance (pŁ0.05) than full-porcelain restorations (B). Conclusion: Hence, we conclude that strengthening CICERO all-ceramic CAD/CAM restorations with high-strength alumina core ceramic significantly enhances their fracture resistance.

Published: Van der Zel, J.M., and Davidson, C.L. (1998): Influence of Crown Layer Build-up on Fracture Resistance of CICERO All-ceramic CAD/CAM Restorations., J Dent res 77, Abstr 102: 65.

 

Dispersion Strengthening of CICERO All-ceramic Core Material. M. Bosman, J.M. van der Zel, C.L. Davidson, Department of Dental Materials Science, Academic Centre for Dentistry, Amsterdam, NL, Cicero Dental Systems bv, Hoorn, NL.

Statement of the problem: The CICERO CAD/CAM system automatically produces ceramic restorations supported by an high-strength high-alumina core ceramic (Synthoceram, Elephant)*. The novel supporting ceramic understructure material is based on aluminiumoxide ceramics with a glassy phase. The strength of the material might be increased if the glassy component is strengthened. Aim: The aim of this study was to investigate the influence of the addition of zirconia on the fracture resistance of the alumina-glass composite. The two groups of alumina-glass composites tested were: with 4 wt.-% zirconia (A) and without (B) the addition of zirconia to the glassy phase. Material and methods: For each group twenty specimens were prepared for three points bending tests, according to ISO 6872. Specimens were tested in a Zwick 1454 universal testing machine with a crosshead speed of 0.5 mm/min. The specimens were investigated with scanning electron microscopy. Results: The results showed that the mean flexural strength of group A (412.4±18.7 MPa) was significantly higher than group B (332.5±14.2 MPa) (p<0.01). SEM investigation in combination with Energy Dispersive X-ray Analysis showed evidence of the presence zirconia crystals in the glassy phase that can attribute to an higher strength of the material. Conclusion: Hence, we conclude that strengthening CICERO All-ceramic Core Ceramic with the addition of zirconia significantly enhances the flexural strength by the formation of zirconia crystals in the glassy phase of the alumina-glass composite.

Published: Van der Zel, J.M. and Davidson C.L. (1999): Dispersion Strengthening of CICERO All-Ceramic Core Material, J Dent Res 78, Abstr. 176:127.

 

Effect of condylar jaw movements on the occlusal contacts of CICERO CAD/CAM crowns. L.W. Olthoff, J.M. van der Zel and F. Bosman , Department of Oral-Maxillofacial Surgery, Prosthodontics and Special Dental Care, Utrecht University, NL, Cicero Dental Systems bv, Hoorn, NL.

Statement of the problem: The CICERO CAD/CAM system makes it possible to automatically produce all-ceramic crowns with a precision-milled occlusal surface and allows the imput of 3D condylar jaw movements for occlusal adjustments during articulation. The aim of this study was to evaluate the effect of different articulation concepts on the number of contact points on a standard 46 molar in the same patient model. Two groups of articulation computer models were used as imput and compared with static occlusion as a control: group 1: articulation using the average default values of a fully adjustable articulator with 0.6 mm immediate side shift and group 2: articulation using electronic registration data of 3D jaw movements with the Condylocomp LR (KAVO, Germany). After intrusal corrections the average number of occlusal contacts within 0.1 mm occlusal distance decreased with 86.2 and 10.3 percent for group 1 and 2 respectively, when compared with the situation in static occlusion (29 contact points). The results showed that the occlusal morphology change mainly takes place in the disto-buccal part of molar 46. The average number of contact points of group 2 was significantly higher than group 1.  Conclusion: It is concluded that using electronic registration as imput for the CICERO CAD/CAM system results in a significantly higher average number of contact points than the default settings of a fully adjustable articulator. The model proved to be useful in occlusal surface design.

Published: Olthoff, L.W., Van der Zel, J.M., and Bosman, F. (1999): Effect of condylar jaw movements on occlusal contacts of CICERO CAD/CAM crowns, J Dent Res 78.

 

Computer Copings for Partial Coverage, H.W. Denissen,J.M. van der Zel, J. Reisig, S. Vlaar, W. de Ruiter, M.A.J. van Waas, Department of Oral Function, Academic Centre for Dentistry, Amsterdam, NL, Cicero Dental Systems bv, Hoorn, NL.

Statement of the problem: Partial coverage posterior tooth preparations are very complex surfaces for computer surface digitization, computer design, and manufacture of ceramic copings. Aim: The aim of this study was therefore to determine whether the Computer Integrated Crown Reconstruction (Cicero®) system was compatible with a proposed partial coverage preparation design and capable of producing ceramic copings. Material and methods: Posterior teeth were prepared for partial coverage copings with deep gingival chamfers in the proximal boxes and around the functional cusps (buccal of  of mandibular and lingual of maxillary posterior teeth) were prepared with broad bevels following the inclined occlusal plane pattern. Optical impressions were taken of stone dies by means of a fast laser-line scanning method that measured the three-dimensional geometry of the partial coverage preparation. Computers digitized the images, and designed and produced the ceramic copings. Results: The Cicero® system digitized the partial coverage preparation surfaces precisely with a minor coefficient of variance of 0.2%. The accuracy of the surface digitization, the design, and the computer aided milling showed that the system was capable of producing partial coverage copings with a mean marginal gap of 74µm. This value was obtained before optimizing the marginal fit by means of porcelain veneering. Conclusion: In summery, Cicero® computer technology, ie, surface digitization, coping design, and manufacture, was compatible with the described partial coverage preparations for posterior teeth.Key words:   Computer copings, partial  coverage, CAD-CAM, accuracy, Cicero® system.

Published: International Journal of Computerized Dentistry 1999; 2: 113-127.

 

Effect of condyli movements on the occlusal morphology of CICERO CAD/CAM crowns. L.W. Olthoff, J.M. van der Zel and F. Bosman (Dep. Oral-Maxillofacial Surgery, Prosthodontics and Special Dental Care, Utrecht University, The Netherlands).

Statement of the problem: The CICERO CAD/CAM system makes it possible to automatically produce all-ceramic crowns with a high strength ceramic core, life-like layered ceramic and a precision milled occlusal surface. The CICERO software allows the imput of condylar jaw movements for occlusal adjustments during articulation. Aim: The aim of this study was to evaluate the effect of different occlusal concepts on the contacts of a standard 46 molar. Three groups of imput methods were compared: static occlussion only (STA), average articulator default values (DEF) and electronic registration data with Condylocomp (KAVO, Germany) (CON). The occlusal distance at central occlusion between antagonist and the 46 molar were divided in intervals with 0.05 mm increments.

 

 Occlusal contact distance, mm

          STA         CON         DEF     

 0.00   -   0.05   (contact)

           14              11             0

 0.05   -   0.10 

           15              15             4

 0.10   -   0.15

           17              17             7

 0.15   -   0.20

           25              22            28

 

Results: Electronic registration creates more contact points than the default articulator setting. No static contact points were found after articulation in group DEF. The results showed clear differences in the occlusal morphology of the occlusal surface after intrusal corrections between the groups CON and DEF compared to group STA, especially in the disto-buccal part. The number of contact points of group CON and group STA was higher than group DEF.  However, these differences were not statistically significant. Conclusions: It is concluded that using electronic registration as imput for the CICERO CAD/CAM system creates a functional occlusion without disturbances with more contact points than an average default setting of an articulator.

Published IADR Vancouver 1999

 

Measurement of the Margins of Partial-Coverage Tooth Preparations for CAD/CAM, H. W. Denissen, J. M. van der Zel,  M. A.J. van Waas, Department of Oral Function, Academic Centre for Dentistry, Amsterdam, NL, Cicero Dental Systems bv, Hoorn, NL.

Purpose: This study tested the hypothesis that a scanning laser 3-dimensional digitizer is a precise and accurate instrument to measure chamfered and beveled margins of partial-coverage tooth preparations fffor computer-aided design/computer-aided manufacturing (CAD/CAM). Material and methods: The margins were measured by the digitizer on stone dies and calculated by triangulation into a 3-D representation. Instrument precision was defined as the ability to reproduce the same margin in repeated measurements and expressed as the coefficinet of variation as a percentage. Instrument accuracy for chamfered and beveled margins was estimated by correlating their measurements to the measurement of the margin of a spherical calibration “phantom” with known dimensions. Accuracy was expressed as the standard deviation. Results: The precision errors for the box- and cusp-chamfered margins and cusp-beveled margins were 3.9%, 3.4%, and 2.4%, respectively. With regard to accuracy the standard deviations of the measurements of the box- and cusp-chamfered margins and cusp-beveled margins were 19 µm, 21 µm, and 24 µm, respectively, compared to 15 µm for the phantom. Conclusion: Measurements of chamfered and beveled margins by a scanning laser 3-D digitizer for CAD/CAM are (1) precise (error < 4%) and (2) accurate, with a standard deviation of less than 9 µm compared to optimal measurements of the spherical margin of the phantom. 

Published: Int J Prosthodont 1999; 12:395-400. 

 

Marginal fit and short-term clinical performance of porcelain-veneered CICERO, CEREC, and Procera onlays. Denissen H, Dozic A, van der Zel J, van Waas M.  Department of Oral Function and Prosthetic Dentistry, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands.

Statement of the problem: Onlay preparations are very complex surfaces for computer surface digitization, CAD, and CAM of all-ceramic onlay cores. Purpose: This study tested the hypothesis that onlays can be fabricated with CICERO, CEREC, and Procera core technologies. Material and methods: Fifteen mandibular and 10 maxillary molars were prepared for onlays in 17 patients (11 women and 6 men). The onlay design was experimental. Molars were prepared with deep gingival chamfers in the proximal boxes and around the functional cusps. The non-functional cusps were prepared with broad bevels. Eight stone dies of preparations were measured with a laser beam (CICERO), 10 dies with a light beam (CEREC), and 7 dies with a contact probe (Procera). Two onlay cores were produced for the same stone die. One core was used to analyze fit on the stone die, and the other core was porcelain veneered for optimizing anatomy, aesthetics, and fit of the onlay and cemented. The fit of the onlay core on the stone die and the cement width on a stone cast were measured by a microscopic digital imaging system. The onlays were evaluated for function every 6 months for 2 years. Results: Measurements of the margins by the CICERO system were (1) precise (error <4%) and (2) accurate with an SD of less than 9 micrometers. The proposed onlay preparation design met the requirement that all points of the surface be visible from a single point of view for optical 3-dimensional mapping by the CEREC system. For the surface measurements by the Procera contact probe, the orientation of the sapphire tip toward the preparation surface was critical, and it was necessary to apply wax to smooth internal edges. The marginal gaps of the CICERO, CEREC, and Procera cores on the stone dies were 74 microm (SD 15), 85 microm (SD 40), and 68 microm (SD 53), respectively. The cement width was 81 microm (SD 64). No fractures occurred. Conclusion: Marginal gaps for the onlay cores were no more than 85 microm. The cement width of the semicomputer-produced onlays of 81 microm was a favorable measurement value for a clinically acceptable, strong all-ceramic onlay. However, this value as well as anatomy and aesthetics of the onlay depended on the craftsmanship of the porcelain veneering by the dental technician.

 

Partial coverage copings by computer, H.W. Denissen, J.M. van der Zel, M.A.J. van Waas, Department of Oral Function, Academic Centre for Dentistry, Amsterdam, NL, Cicero Dental Systems bv, Hoorn, NL.

Aim: Aim of the study was to evaluate the Computer Integrated Ceramic Reconstruction (CICERO®)-system and the Ceramic Reconstruction (CEREC®)-system for the production of all ceramic copings for partial coverage. Material and methods: Posterior teeth were prepared and the stone dies were made. Accuracy analyses were performed on ceramic restorations made by means of the CICERO and by means of the CEREC technique. The marginal gaps were compared to that of a control cast metal restoration. Results: The results demonstrate that the marginal gaps of the CICERO and CEREC copings varied respectively for the premolar 58-80 µm (mean 69µm) and 71-91 µm (mean 81 µm). For the upper molar 63-92 µm (mean 78 µm) and 68-110 µm (mean 89 µm) and for the lower molar 54-98 µm (mean 76 µm) and 73-99 µm (mean 86 µm). Control cast metal partial coverage restorations showed marginal gaps of  33, 49 and 41 µm. Conclusion: It is concluded that computers can produce copings for partial coverage preparations on stone dies with a mean marginal gap for CICERO copings of  74 µm and  for CEREC copings of 85 µm. These values were obtained before optimizing the marginal fit by means of porcelain veneering.

Published: Ned. Tijdschrift Tandheelkunde 106 (1999)

 

Clinical Preparation Parameters for CICERO CAD/CAM crowns. C. Begazo, M. Bekius, H.W. Denisson, J. Reisig, J.M. van der Zel, M.A.W. van Waas, Department of Oral Function, Academic Centre for Dentistry, Amsterdam, NL, Cicero Dental Systems bv, Hoorn, NL.

Statement of the problem: With the advent of dental CAD/CAM as a new fabrication technology, is is likely that some paradigms on preparation technique will change, especially because CAD/CAM will likely increase the use of full ceramic restorations. Opposed to metal-ceramic crowns, full-ceramic crowns are prone to cracking by local stresses, as a ductile stress relief mechanism is absent. Full-ceramic restorations will therefore put more emphasis on "proper" preparation techniques. The CICEROR CAD/CAM system automatically produces shaded copings of an high-strength high-alumina core ceramic (Synthoceram, Elephant)  to be finished in the dental laboratory. Purpose: The purpose of this study was to collect data on clinical preparation parameters, such as axial reduction and shoulder angle in a clinical fieldtest of 100 CAD/CAM crowns. Material and methods: The gypsum dies received, were optically scanned and the axial reduction and shoulder angle were determined in four sections of the digitized surface. The results were compared against manufacturers' preparation instructions. For the field-test a group of 80 patients were selected randomly from group practices by general practitioners in the region north of Amsterdam. The recommended preparation parameters consisted of a minimum shoulder width of 0.7 mm with a maximum internal shoulder angle of 110° and a rounded inner edge. The copings were finished at one commercial dental laboratory. Results: Analysis of the digitized dies in four sections revealed that 10 percent could be considered under-prepared (mean shoulder width of 0.87 (0.41-1.16) mm and 97 percent over-angled (mean shoulder angle of 131.25  (103.15-152.25)°. A positive correlation could be found between both parameters (R=0.96). Clinical evaluation shows that 100 percent of the crowns could be seated easily with carboxylate cement (Poly F) and at half year control all crowns survived. Conclusion: Hence, we conclude from this study that a shoulder angle of 130 degrees and an axial reduction of 0.7 mm can be acceptable for use in a follow-up clinical study on CICERO CAD/CAM crowns.  

 

Strength Comparison of Alumina Copings of Procera and CICERO. H.F. Kappert and Krah, Department of dental materials, University of Freiburg, FRG-79106, Freiburg, BRD.

Objective: The objective of the study was to compare the mechanical strength of veneered aluminiumoxide copings produced by the Integrated Ceramic Reconstruction (CICERO®) -system and the Procera®-system, by applying an increasing static load until fracture occurs. A clinical canine type crown with a deep chamfer preparation and wall thickness in the range of 0.6 mm and thickness of the veneer ceramic of 0.2 mm (cervical) and up to 2 mm (incisal) were used. The aluminiumoxide copings of the crowns had wall thicknesses of 0.6 mm, the veneer thickness was up to 2 mm in the palatinal region (tension zone during testing), roughly 2 mm incisal and up to 1.8 mm labial. After checking the fit seven crowns were cemented with zinc phosphate cement (Harvard) onto a metallic abutment. At the earliest 1 h after cementing the specimens were loaded with axial inclination of 135o using a Zwick Z010/TN2S tensile testing machine at a cross head speed of 1.5 mm/min. until fracture. A 0.8 mm thick foil was placed over the incisal edge to achieve a homogeneous stress distribution. All fractures involved both the veneer material and the copings. The typical fracture pattern was chipping off the labial face of the veneered crowns and subsequent fracture of the coping.

System

  Static break strength, N

 Standard deviation, N

Procera (Nobel Biocare, Sweden)

                      929

                   291

CICERO (Elephant Dental BV, Holland)

                     1045

                    79

Results: Statistical analysis on two groups of ceramic restorations revealed that the veneered copings made by the CICERO system were significantly stronger than the Procera copings (p<0.01) and showed much less variation than Procera copings. Conclusion: Hence, we conclude that the strength of CICERO veneered copings are significantly stronger than Procera veneered aluminiumoxide copings.

Unpublished report Uni Freiburg, November 2000.

   

Thermal compatibility of CICERO in comparison with metal-ceramic systems. H.F. Kappert and Krah, Department of dental materials, University of Freiburg, FRG-79106, Freiburg, BRD.

Objective: The objective of the study was to compare the thermal shock resistance of veneered aluminiumoxide copings produced by the Computer Integrated Ceramic Reconstruction (CICERO®) -system and three metal-ceramic. A clinical canine type crown with a deep chamfer preparation and wall thickness in the range of 0.6 mm and thickness of the veneer ceramic of 0.2 mm (cervical) and up to 2 mm (incisal) were used. The aluminiumoxide copings of the crowns had wall thicknesses of 0.6 mm, the veneer thickness was up to 2 mm in the palatinal region, roughly 2 mm incisal and up to 1.8 mm labial.  To test the thermal compatibility of the crowns  a thermal shock test was used by warming the compound system in the temperature range of 105oC to 165oC and rapidly cooling down in ice water. 6 Veneered crowns were used for the thermal shock test. At first they were inspected with light microscope. No cracks could be observed. The oven for the test was calibrated with a thermo-couple and set to temperatures of 105, 120, 135, 150 and 165oC for each experiment. After 30 min the specimens were quenched in ice water.

Temperature in oC

Number of cracked crowns after the thermal shock test

Cicero-Sintagon

Galvano-Response

Degudent-Response

Golden gate

             105

             0

                0

0

          0

             120

             0

                0

0

          0

             135

             0

                1

0

          0

             150

             0

                0

2

          2

             165

             0

                1

0

          4

   Survived:

             6

                4

4

          0

Results: By inspection of the crowns after the thermal shock test using temperatures up to 165oC no changes of the veneer material of CICERO crowns in the form of cracks could be observed. All CICERO crowns remained intact. The comparative consideration shows that for conventional and very modern metal-ceramic systems only maximal 4 crowns out of 6 survived the thermal shock test. In contrast to this result, all crowns consisting of Cicero copings veneered with sintagon survived the test without any cracks. Conclusion: Hence, we conclude that the CICERO veneered copings have the best thermo shock resistance in comparison with metal-ceramic systems. This looks very promising for the clinical use.

Unpublished report Uni Freiburg,November 2000

   
Computer modeling of occlusal surfaces of posterior teeth with the CICERO CAD/CAM system.
OLTHOFF, L.W., VAN DER ZEL, J.M., DE RUITER, W.J. BOSMAN, F. University of Utrecht and Cicero Dental Systems, Hoorn, The Netherlands
Statement of the problem: Static and dynamic occlusal interference frequently needs to be corrected by selective grinding of the occlusal surface of conventional cast and ceramic-fused-to-metal restorations. CAD/CAM techniques allow control of the dimensional contours of these restorations. However, parameters responsible for the occlusal form need to be determined. In most articulators, these parameters are set as default values. Which technique is best for minimizing the introduction of occlusal interference in restorations has not been determined. Purpose: This study investigated differences in crown structure of a crown designed in static occlusion (STA) with designs adapted for dynamic occlusal interferences. Therefore, values from an optoelectronic registration system (String-Condylocomp, KAVO), an occlusal generated path (OGP) technique and default settings (DEF) were used in the CICERO CAD/CAM system. Material and Methods: Morphology of CON, DEF, and OGP crowns was compared with that of the STA crown with respect to differences in a buccolingual section and frequency of occlusal distances in an interocclusal range of 1 mm, measured from the occlusal surface of the crown. Results: All crown types fulfilled the aesthetic and morphologic criteria for restorations in clinical dentistry. Difference in the morphology of the OGP crown, compared with that of the STA crown, was greater than that for the CON and DEF crowns. These differences were seen especially in the distobuccal part of the occlusal surface; however, the number of occlusal contacts was considered sufficient to stabilize occlusion. Conclusion: Functional occlusion, adapted to dynamic occlusion in a CICERO crown for the first mandibular molar, can be obtained using data acquired with the String-Condylocomp registration system. The OGP technique was preferred to other techniques because of the simplicity of the technique for eliminating potential problems with opposing teeth during motion. However, this is achieved at the cost of fewer points of contact during occlusion than with the CON crown.

Published: J Prosthet Dent. 2000 Aug;84(2):154-62.

 

The influence of porcelain layer thickness on the final shade of ceramic restorations. Dozic A, Kleverlaan CJ,  Meegdes M, van der Zel J, Feilzer AJ. Department of Dental Materials Science, ACTA, Amsterdam, The Netherlands.

Statement of the problem: Ceramic restorations should be made of porcelain layers of different opacity, shade, and thickness in order to provide a natural appearance. By means of CAD/CAM layering technology such as CICERO, it is feasible to produce all-ceramic crowns with porcelain layers of predetermined thickness. However, it is not yet known whether changes in thickness of these porcelain layers within the clinically available space can perceivably influence the overall shade of the restoration. Purpose: The purpose of this study was to determine, quantitatively, the effect of different thickness ratios of opaque porcelain (OP) and translucent porcelain (TP) layers on the overall shade of all-ceramic specimens. Material and methods: The CIELAB values of 5 assembled specimens, each consisting of 2 or 3 discs (CORE 0.70 mm/OP--0, 0.25, 0.50, 0.75, or 1.00 mm/TP 1.00, 0.75, 0.50, 0.25, or 0 mm) were determined with a spectrophotometer for the Vita shades A1, A2, and A3. Distilled water was used to attain optical contact between the layers. Black or white backgrounds were used to assess the influence of the background on the final shade. Color differences (DeltaE) between layered specimens were determined. Correlation between the thickness ratio and the L*, a*, and b* values was calculated by 2-tailed Spearman correlation analysis. Results: The results indicated that small changes in OP/TP thickness ratio can perceivably influence the final shade of the layered specimens (DeltaE>1). Redness a* and yellowness b* increased with the thickness of OP for all shades. Redness a* (P<.01 for all shades) correlated more strongly with thickness than yellowness b* (P<.01 for A1 and A3; P<.05 for A2). The lightness (L*) was shade dependent. The correlation (r) between OP/TP thickness and L* was 0.975 (P<.01) for shade A1, 0.700 (not statistically significant) for shade A2, and 0.900 (P<.05) for shade A3. Conclusion: Small changes in thickness and shade of opaque and translucent porcelain layers can influence the final shade of the layered porcelain specimen.

Published: J Prosthet Dent. 2003 Dec;90(6):563-70.

 

A simple method to gain digital color information for use in CAD/CAM procedures. A. DOZIC, J.M. VAN der Zel, A.J. Feilzer. ACTA, dept. of Dental Materials Science, NL, Cicero Dental systems b.v. , Hoorn, NL.

Statement of the problem: In CAD/CAM restorative procedures, the determination of color is one of the last things that is still carried out manually. Therefore is there a need for digital color mapping algorithms that can be stored in computer memory for use in crown production. To improve the quality of whole-tooth-surface color representation, however, the accuracy of color determination must first increase and the results must be available as digital data. Purpose: Our aim was to investigate whether photographs made with a commercially available digital camera can provide us with color information (expressed in L* a* b* values) that corresponds to spectrophotometer color measurement data. Materials and methods: The ceramic specimen (Synthagon, Elephant Dental B.V.) in shade A3 was photographed with: Coolpix 990 (Nikon) and Camedia 2.1 (Olympus) camera equipped with a light directing attachment and a specially developed user set-up before a controlled background. Images received level adjustments with the aid of Adobe Photoshop and the Kodak Color Separation guide. Results: Initial results show that the digitally defined L* (lightness) and b* (yellow-blue) component of the specimen can be regularly adjusted to the spectrophotometer reference L* and b* value. The a* (red-green) component, however, appears to depend more on light temperature and shows twice higher values after the adjustment with all measurements. This initial clinical data suggests good possibilities for color mapping of the tooth surface using a simple to handle digital camera. Conclusion: The results imply that further development of digital imaging techniques in dentistry will be able to insure not only precise and reproducible data for the CAD/CAM industry, but will also simplify color management in general dental practice.  

Published IADR Abstract 2003

 

Effect of Shoulder Design on Failure Load of PTZ Crowns. J. VAN DER ZEL, T. GRINWIS, M. DE KLER, T. TSADOK, Elephant Dental, Hoorn, Netherlands 

Objectives: To evaluate the effect of shoulder design on the failure load of Press-to-Zirconia (PTZ). Methods: Two groups were studied: Overpressed crowns with a zirconia free PTZ shoulder (CS) and overpressed crowns with zirconia up to the margin (CC). The zirconia-free shoulder extended 0.8 mm over the finishing line of the coping. Eight zirconia copings per group of first maxillary anteriors were fabricated with Cercon CAM system (DeguDent, Germany). The thickness was 0.6 mm standard. After milling the copings were sintered at 1350oC to final density. After sintering the coping was waxed up to a standard contour, sprued and invested in Carrara Universal Dustless Investment (Elephant). The Sakura Volumia Press Ceramic (Elephant dental B.V., Hoorn, The Netherlands) was pressed at 940oC over the zirconia base. After devesting and separation from the sprues the crown was veneered with two layers Sakura Interaction (Elephant Dental B.V., Hoorn, The Netherlands). The crowns were cemented on a CoCr die with zinc phosphate cement and held under constant load of 5 kg during setting. The crowns were inspected using SEM for surface fracture analysis. Failure loads were measured using compression loading at 0.5 mm/min. Results: Failure loads [kN (SD) (m)]: Group CS:  4228.1 and group CC: 5407.5. Conclusion: A significant (p<0.05) decrease in breaking strength was observed with the overhanging shoulder as compared to fully supported crowns in Press-to-Zirconia Crowns. Surface fracture analysis revealed the crack initiation site was typically located on the inside of the coping at the glass-zirconia border. 

Published: CD IADR Hawai 2004.

  

Validation of CADCAM Systems, J.M. VAN DER ZEL, Academic Center for Dentistry Amsterdam, University of Amsterdam and Free University, Amsterdam, Netherlands

Statement of the problem: The need for proper validation and verification methodology for CADCAM systems is imminent. Objective: This study is part of the of the eDentalHealthTaskForce's Roadmap towards a guidance specification in particular on Optical Impression Systems. Two laser light section dental scan systems Denta Scope II (microSystems GmbH, Germany)[D] and Preciscan (DCS, Switzerland)[P] were evaluated. Methods: The method developed involved the measurement of two geometries: a precision ball (radius: 6.00 mm) and a calibrated cube (sides: 10.00 mm). The surface information of both geometries were received as unmatched, overlapping point clouds and the surface data information was reconstructed according to a new statistical software program (CYRTINA). For the ball radius a center was determined and the outside point cloud captured by using a small cone at an equidistance of 5° and the points captured in the cone averaged. The main vectors of cube's top and side planes were determined and the standard deviations of the points with the plane equation calculated. The angle between the top and side plane vectors were calculated, as a measure of the distortion of the measurement. Results: The radius S.D for D and P were 6.45 and 14.24 µm respectively. The S.D. of the top plane points for D and P were 1.34 and 1.65 µm respectively. The average S.D. of the side planes points were 2.63 and 3.49 µm respectively. The average angle deviation of the top plane vector with the side planes for D and P were 0.15 and 0.22° respectively. Conclusion: The DentaScope II (D) was significantly more accurate in the measurement of the ball geometry than the Preciscan (P)(p<0.05). Both Optical Impression Systems show adequate accuracy with respect to diameter and deformation for both geometries.

Published: CD IADR Baltimore 2005.

 

Computer Aided Diagnosis and Design of Implant Abutments. J.M. VAN DER ZEL, Departement of dental material science, Academic Centre for Dentistry Amsterdam, Universiteit van Amsterdam and Vrije Universiteit Amsterdam, The Netherlands.

Statement of the problem: Minimal invasive implant therapy has recently gained a growing interest as a standard prosthodontic treatment, providing complete restoration of the occlusal function. Computer aided pre-surgical implant planning based on computer tomography scan data and computer aided design of individualized abutments by using optical scan data are well established, although two distinctly separate techniques. A new treatment method (CADDIMA) is recently developed which combines both CT- and laser-scan data for planning and design of drill guides and implant abutments. Objectives: 1) To evaluate the possibility for implant diagnosis and drill hole planning using a combined CT and optical imaging method; 2) To evaluate the possibility for abutment design in the same stage. Methods: A NewTom Cone Beam CT-scanner (QR s.r.l., Verona, Italy) and a laser triangulation scanner DentaScope II (3DAlliance GmbH, Germany) were used for imaging. An impression with 3 markers was placed in the patient during CT-scanning and on the gypsum model during optical scanning, so that the surface of mucosal tissue with remaining dentition, antagonists and bone structure in the region of interest for implantation could be observed in a combined 3D-view by the operator. Results: The positioning of the implant in a virtual cross-sectional view resulted in an optimized drill guide supported by mucosa and dentition which eliminates the traditional flap surgery by limiting the intrusion size to the diameter of the implant. The new approach gives the operator full control over the design of the implant abutment for planning of proper occlusal relations.  This study was supported by SenterNovem grant TSIT2020.

Published: IADR CED-NOF Meeting 2005, 53:#159.

 

Influence of Crown Layer Build-up on Fracture Resistance of CICERO All-ceramic CAD/CAM Restorations. J.M. van der Zel, C.L. Davidson, Department of Dental Materials Science, Academic Centre for Dentistry, Amsterdam, NL, Cicero Dental Systems bv, Hoorn, NL.

The CICERO CAD/CAM system produces ceramic restorations supported with high-strength high-alumina core ceramic (Synthoceram, Elephant), but also full-porcelain restorations. The novel supporting ceramic understructure material is based on a alumina-zirconia-mullite-system with a modulus of rupture of 350 MPa. The core is sintered on a pre-milled refractory die. This supporting material might provide the restorations with the necessary survival durability. The aim of this study was to investigate the influence of crown layer build-up on the fracture resistance. A master steel die with a rounded chamfer preparation was duplicated in gypsum and scanned. Twenty identical crowns were produced with two different layer make-ups and cemented under constant load on the master steel die with zinc phosphate cement. The cementgap design provided for a supporting ridge 1 mm inside from the margin. Specimens were tested in a Zwick 1454 universal testing machine with a crosshead speed of 0.5 mm/min. The two groups of layer build-up tested were: with (A) and without (B) supporting core. The mean fracture force of group A (3093.2±136.5) was significantly different from group B (1468.8±79.2) (p>0.05). The restorations strengthened with high-strength ceramic core (A) had significantly higher (110%) fracture resistance (pŁ0.05) than full-porcelain restorations (B). Conclusions: Hence, we conclude that strengthening CICERO all-ceramic CAD/CAM restorations with high-strength alumina core ceramic significantly enhances their fracture resistance.

Published: Van der Zel, J.M., and Davidson, C.L. (1998): Influence of Crown Layer Build-up on Fracture Resistance of CICERO All-ceramic CAD/CAM Restorations., J Dent Res 77, Abstr. 102: 65.

 

Effectiveness of preparation guidelines for an all-ceramic restorative system. Begazo CC, van der Zel JM,  van Waas MA, Feilzer AJ.  Department of Oral Function, Academic Centre of Dentistry Amsterdam, University of Amsterdam, the Netherlands.

Purpose: To evaluate, in a clinical field-test, the implementation of manufacturer's preparation guidelines for the all-ceramic CICERO system. METHODS: General dental practitioners from the northwest region of The Netherlands were asked to make complete crown preparations in accordance with the specific guidelines of the CICERO system. 3,446 tooth preparations were evaluated with regard to shoulder angle, shoulder width and top angle. They were quantified using a special software program. The results were compared with criteria defined in the manufacturer's preparation guidelines. Results: On a multivariate level all (main and interaction) effects were significant (P < 0.05) excluding the interaction effect of the location of measurement on the tooth by the upper or lower jaw. The value of the shoulder angle showed a strong relation with the tooth position in the mouth as well as with the location of measurement on the tooth. The shoulder width in the lower jaw was significantly smaller when compared to the width in the upper jaw. The shoulder width of the lower incisors was the smallest and also showed the largest variance per tooth. On a group level (incisor, cuspid, premolar, molar), except for the shoulder width of the lower incisors, the average values of all preparation parameters were within the borders as defined in the preparation guidelines of the manufacturer. However, on an individual tooth level nearly all preparations showed to have one or more locations with imperfections.

Published: Am J Dent. 2004 Dec;17(6):437-42.

 

Validation of glass-ceramic veneered 3Y-TZP zirconia for dental restorations. J.M. van der Zel, Department of Dental Materials Science, Academic Center for Dentistry Amsterdam, Louwesweg 1, 1066 EA Amsterdam, Netherlands.

Statement of the problem: The research on the use of zirconia ceramics as biomaterials started about twenty years ago, and now zirconia (Y-YZP) is in clinical use in THR, but developments are in progress for application in dental devices. A newly developed esthetic glass-ceramic Sakura® (Elephant Dental B.V., Hoorn, The Netherlands) can be applied to CADCAM derived 3Y-TZP zirconia structures by automatic heat-pressing or with slib-casting by hand. The validation study involved the investigation of bonding properties and phase changes by thermal expansion mismatch stress between the glass-ceramic and zirconia core ceramic and by fatigue loading.

Material and methods: Biaxial flexion of bilayered disks was used to determine the flexural strength before and after fatigue loading in a simulated physiological environment. Low-angle XRD was used to study phase changes at the interface boundary. The reliability of strength was analyzed with the Weibull distribution. SEM was used to identify the initial crack and characterize the fracture mode.

Results: It became clear that the Weibull modulus for the fatigue failures was consistent with previously reported work on other ceramics. Tetragonal-to-monoclinic zirconia phase transformation was observed after some handling steps such as airborn alumina abrasion. However heat treatment above 850oC a complete reversal to secondary tetragonal phase was observed. A thermodynamic explanation for this phenomenon is given. Fatigue loading did not reduce the flexural strength. Failure of disk specimens was caused by typical inherent flaws commonly observed in ceramics.

Significance: The contribution of strong and tough zirconia core to the performance of all-ceramics restorations may be offset by the weaker veneering glass-ceramic if the actual distribution of the tensile stresses within the restoration is not taken into consideration.

Published: Transactions Euromat Prague 2005

 

Validation of CADCAM Systems, J.M. VAN DER ZEL, Academic Center for Dentistry Amsterdam, University of Amsterdam and Free University, Amsterdam, Netherlands

The need for proper validation and verification methodology for CADCAM systems is imminent. Objective: This study is part of the of the eDentalHealthTaskForce's Roadmap towards a guidance specification in particular on Optical Impression Systems. Two laser light section dental scan systems Denta Scope II (microSystems GmbH, Germany)[D] and Preciscan (DCS, Switzerland)[P] were evaluated. Methods: The method developed involved the measurement of two geometries: a precision ball (radius: 6.00 mm) and a calibrated cube (sides: 10.00 mm). The surface information of both geometries were received as unmatched, overlapping point clouds and the surface data information was reconstructed according to a new statistical software program (CYRTINA). For the ball radius a center was determined and the outside point cloud captured by using a small cone at an equidistance of 5° and the points captured in the cone averaged. The main vectors of cube's top and side planes were determined and the standard deviations of the points with the plane equation calculated. The angle between the top and side plane vectors were calculated, as a measure of the distortion of the measurement. Results: The radius S.D for D and P were 6.45 and 14.24 µm respectively. The S.D. of the top plane points for D and P were 1.34 and 1.65 µm respectively. The average S.D. of the side planes points were 2.63 and 3.49 µm respectively. The average angle deviation of the top plane vector with the side planes for D and P were 0.15 and 0.22° respectively. Conclusion: The DentaScope II (D) was significantly more accurate in the measurement of the ball geometry than the Preciscan (P)(p<0.05). Both Optical Impression Systems show adequate accuracy with respect to diameter and deformation for both geometries. E-mail: j.vd.zel@acta.nl
Published : CD IADR Baltimore 2005.

 

Computer Aided Diagnosis and Design of Implant Abutments. J.M. VAN DER ZEL, Department of dental material science, Academic Centre for Dentistry Amsterdam, Universiteit van Amsterdam and Vrije Universiteit Amsterdam, The Netherlands.

Statement of the problem: Minimal invasive implant therapy has recently gained a growing interest as a standard prosthodontic treatment, providing complete restoration of the occlusal function. Computer aided pre-surgical implant planning based on computer tomography scan data and computer aided design of individualized abutments by using optical scan data are well established, although two distinctly separate techniques. A new treatment method (CADDIMA) is recently developed which combines both CT- and laser-scan data for planning and design of drill guides and implant abutments. Objectives: 1) To evaluate the possibility for implant diagnosis and drill hole planning using a combined CT and optical imaging method; 2) To evaluate the possibility for abutment design in the same stage. Methods: A NewTom Cone Beam CT-scanner (QR s.r.l., Verona, Italy) and a lasertriangulation scanner DentaScope II (3DAlliance GmbH, Germany) were used for imaging. An impression with 3 markers was placed in the patient during CT-scanning and on the gypsum model during optical scanning, so that the surface of mucosal tissue with remaining dentition, antagonists and bone structure in the region of interest for implantation could be observed in a combined 3D-view by the operator. Results: The positioning of the implant in a virtual cross-sectional view resulted in an optimized drill guide supported by mucosa and dentition which eliminates the traditional flap surgery by limiting the intrusion size to the diameter of the implant. The new approach gives the operator full control over the design of the implant abutment for planning of proper occlusal relations. This study was supported by SenterNovem grant TSIT2020.

Published: IADR CED-NOF Meeting 2005, 53:#159.

 

Dental Glass Pressed-To-Zirconia Interface Study. Jef M. van der Zel, Academic Centre for Dentistry Amsterdam, Amsterdam NL.

Statement of the problem: The demand for bio-inert, metalfree dental restorations has put pressure on industry to develop zirconia-base materials because of its promise for durability and longevity. Zirconia structures are produced by slib casting or by milling. Because of the opaqueness of zirconia a tooth-coloured dental glass is used to bring the proper natural aesthetics to the zirconia-base. Although the traditional layering technique could be used, thermal pressing of dental glass into a lost wax form is a more effective and economic way. It was hypothesised that partially stabilised zirconia under the coating stresses at the interface some conversion from tetragonal to monoclinic would take place with an accompanying volume increase. This volume increase could be the cause for defects in the zirconia surface and explains the frequently observed failure at the interface of dental glass and zirconia. Material and methods: A dental glass (PTZ) with a pressing temperature of 930 °C was pressed to a zirconia-structure embedded in silica-based refractory form. The dental glass had a thermal expansion coefficient of 10.0 µm/m.K (25-500°C) similar to the zirconia-base (ZrO2 – 3% Y2O3, Tosoh): 10.5 µm/m.K (25-500°C) and belonged to the system SiO2-Al2O3-K2O-Na2O-F. Thus, crack- free dental glass coatings on zirconia were obtained. The glass coating was well adhered to the zirconia and without residual porosity. The interface was studied by optical and scanning electron microscopy (SEM) in cross section and at the interface after removal of the glass by selective dissolution in hydrofluoric acid. Dental crowns consisting of a zirconia-base coping with an average thickness of 0.6 mm were pressed-on with a dental glass to obtain an occlusal surface. The interface was studied after thermal-cycling and mechanical oral stress simulation of five years (TCML: 6000 x 5°/55°C, water, 2 minutes, 1.2 x 106 x 50 N). These crowns were compared with crowns that were not subjected to a fatique cycling.

Conclusion: The study revealed that the interface had an extreme integrity with some diffusion of zirconia into the glass. Fatique cycling did not cause the formation of a monocline zirconia layer at the interface between dental glass and zirconia.

Published as abstract in NKV proceedings 2005.

 

Survey on Cyrtina® copings and bridges. I. Vervoort, S.J.J. van der Zel, J.M. van der Zel. Elephant Dental B.V., Hoorn, Oratio B.V. Zwaag, ACTA Amsterdam NL.

Objective: To validate the bridge quality of a new CAD/CAM system (CyrtinaCAD, Oratio B.V., Zwaag, The Netherlands) together with the veneering ceramic Sakura Interaction (Elephant Dental B.V., Hoorn, The Netherlands. Methods: Gypsum models were send in by fourteen dental laboratories in Germany and were scanned with a Cyrtina® scanner and a 3 unit bridge designed with CyrtinaCAD. The scan/design data were send to Cyrtina Center for centralized production. 16 3-unit bridges of differently shaded zirconia were evaluated externally evaluated by the customer and internally evaluated by 3 experienced dental technicians. Results: Fit was regarded good in 15 cases, 1 bridge showed a loose fit. The form of the pontic was regarded good for 15 cases, one pontic form was regarded as wrong. The place, form and size of the connectors were regarded as good. Regarding friction and movement all bridges but one were satisfactory. Conclusion: Generally the quality of the bridges was good considering the system has been introduced recently. 

Internal report available on request.

 

Effect of core material on stresses in veneered crowns. N. De Jager, M. de Kler, J. M. van der Zel. Academic Centre for Dentistry, Amsterdam NL.

Objective: All ceramic restorations without metal have great advantages in their biocompatibility and aesthetic aspects. With the introduction of new core materials, the cores are sufficiently strong to produce long lasting all-ceramic restorations, however the stresses in the veneering porcelain could still determine the longevity. The objective of this study was to evaluate, by finite element analysis (FEA), the influence of different core materials on the stress distribution in dental crowns. Material and methods: The model of  a multi-layer all-ceramic crown for posterior tooth 46 produced with CAD-CAM-technology was translated into a three-dimensional FEA program. This crown model was made with gold, zirconia, and alumina-based porcelain core and their matching veneering porcelains.  The stress distribution due to the combined influences of bite forces, residual stresses caused by the difference in expansion coefficient of the core material and the veneering porcelain, and the influence of shrinkage of the cement was investigated. Results: Stiffer core material does not always for various reasons result in lower stresses in the veneering porcelain. Significance: This study indicates that the actual distribution of the tensile stresses and the design of restorations must be taken into account; otherwise, the significant contribution of stronger and tougher core materials to the performance of all-ceramic restorations may be offset by the weaker veneering porcelain.

Published in Dental Materials 2005.

 

The influence of different abutment material on the FEA-determined stress distribution in dental implant systems. Niek de Jager, Siebe van der Zel, Jef M. van der Zel. , Oratio B.V. Zwaag, ACTA Amsterdam NL.

Objective: The objective of this study was to evaluate by finite element analysis (FEA) the influence of different abutment materials on the stress distribution in two dental implant abutments for the “Dyna Helix” implant system (Dyna Dental Engineering B.V., Bergen op Zoom, The Netherlands): with an internal and an experimental external octagon respectively. Methods: Two implant abutment designs were built in a three-dimensional FEA program. The abutment materials used were Titanium grade 5 and Y-TZP zirconia.  The stress distribution due to the combined influences of bite forces and the torque on the fixation screw was investigated. Results: For the implant system with an internal octagon the higher tensile stresses in the zirconia abutment offset the advantage of the higher strength of this material. The implant system with an external octagon is a better design for zirconia abutments. Significance: This study indicates that to exploit the high strength of zirconia as abutment material the actual distribution of the tensile stresses and the design of the dental implant system must be taken into account.

Dental Materials

 

Accuracy of dental digitizers. Simon T. Vlaar, Jef M. van der Zel.

Introduction: The need for proper validation and verification methodology for CAD/CAM systems is becoming an interest to dental professionals and custom dental device manufacturers. CAD/CAM systems existing of an optical impression system, design software and a fabrication machine have to perform to a certain level, whereby manufacturers needs to prove the effectiveness of the system as a whole. However, especially when dental surface digitization devices are used as open, stand-alone applications in dental outsourcing, a reliable standard test for comparison is necessary. Purpose: This study evaluates a proposed test method to be used to quantify “digitizing quality” with respect to accuracy and reproducibility of two dental surface digitization devices. Comparability of the characteristics should become ensured. Method: Two laser light section scanners: “DentaScopeII” (microSystems GmbH, Germany) [M] and “D200” (3Shape A/S, Copenhagen, Denmark) [D] were evaluated by means of the “Sphere Test”, that involved repeated measurements (N = 5) of a precision ball (radius: 6.00 mm) according to pre-defined protocol. The surface information was received as unmatched, overlapping point clouds and statistically processed with a newly developed software package “Cyrtina®CAD” (Oratio B.V., Hoorn, The Netherlands). The standard deviation of all points as well as a measure for undercutting the equator were determined. Results: The standard deviation for the radius for M and D were 7.7 (± 0.11) and 13.7 (± 0.23) µm respectively. The equator undercut elevations were –2.8o and –0.25o for scannerM and D respectively. Conclusion: Scanner M had a significantly higher accuracy than D (p<0.05), but also had a smaller field of view. Both devices show adequate accuracy and reproducibility and have an adequate ability to detect the equator. The test is also suitable for calibration purposes.

Published in Int Dent J 2006.

 

Influence of thermal expansion mismatch and fatigue loading on phase changes in porcelain veneered Y-TZP zirconia. Marcel de Kler a, Niek de Jager b, Marcel Meegdes, c Jef  M. van der Zel d

a and c PhD researcher, Department of Dental Material Science, Academisch Centrum Tandheelkunde Amsterdam, Universiteit van Amsterdam and Vrije Universiteit, The Netherlands.b Department of Dental Material Science, Academisch Centrum Tandheelkunde Amsterdam, Universiteit van Amsterdam and Vrije Universiteit, The Netherlands.d Professor of Computerized Dentistry, Department of Dental Material Science, Academisch Centrum Tandheelkunde Amsterdam, Universiteit van Amsterdam and Vrije Universiteit, The Netherlands.

Objectives: This study was conducted to test the hypothesis that mismatch in coefficient of thermal expansion between porcelain and Y-TZP zirconia as used for all-ceramic dental crowns cause transformation of the tetragonal structure to the monoclinic structure in Y-TZP at the interface boundary, when exposed to fatigue loading. Methods: Three groups of porcelain veneered Y-TZP (Cercon® base 38, DeguDent GmbH, Hanau, Germany) zirconia discs (Ř 19.6 mm, hzirconia = 0.5 mm and hveneer = 1.5 mm) were used in this study. Group A was veneered with Sakura® Interaction veneering porcelain (Elephant Dental B.V., Hoorn, Netherlands), while group B and C were veneered with experimental versions of this porcelain having a coefficient of thermal expansion of 0.6 and 1.2 μm/m.K (20-500°C) lower than the control group. Group C with the highest expansion mismatch showed cracks in the veneering porcelain and were discarded for fatigue testing. The bi-layered discs were tested in the ACTA fatigue tester; the maximum applied force was 70% of the biaxial flexural strength. All tests were performed with the veneering ceramic in tension. The stress distribution was analyzed with finite element analysis. All fractured discs were examined with fractography and low angle X-ray diffraction was used to measure the ratio of monoclinic/tetragonal in the Y-TZP zirconia core at the zirconia porcelain interface after respectively sintering, sandblasting, veneering, and fracture. Results: Sandblasting resulted in a transformation at the surface to a monoclinic and pseudo-cubic structure unto 30µm depth. After the firing cycle the surface reverted back to tetragonal zirconia. There was no effect on phase changes due to thermal mismatch stress.

Published in J Oral rehab 2006.

 

Augmented Reality Model for Dentistry, Jef M. van der Zel, Academic Centre for Dentistry Amsterdam, Universiteit van Amsterdam and Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.  

Introduction: Minimal-invasive computer-aided implant planning and placement with surgical guides, computer aided regulation with orthodontic guides and occlusion rehabilitation with dental CADCAM are becoming well established applications, although mainly used separately as stand-alone applications in isolated dental practices. Because of their present character of these applications they have never reached the integration necessary to realize the virtual dental surgery with augmented reality. Mehods: To make computerized dentistry available to every dental clinic at the Point of Care an internet accessible product line of computerized dental treatments is proposed driven by a decision-support module. Results: ARMADA was developed as a model architecture that takes the applications into a common collaborative framework in which the different aspects of dental treatment are integrated and share the same main stakeholders’ concerns: Imaging, Diagnosis and Treatment. By clientless internet access to the ARMADA application server the virtual dental surgery can now outsource regional scan and local or off-shore diagnostic services and remote high-quality custom dental device production in a cost-effective way, bringing computerized dental treatment inside the reach of each dental clinic.

Published PEF Dublin 2006

 

Effect of virtual articulator settings on occlusal morphology of CADCAM restorations. Lambert Olthoff, DDS, PhDa  / Ivar Meijerb / William de Ruiterc, Frederik Bosman, PhDd  and Jef van der Zel, PhDe

a Assistant professor, Department of Oral-Maxillofacial Surgery, Prosthodontics and Special Dental Care, University Medical Center Utrecht, Utrecht, The Netherlands

b IT Engineer, CyberTech Telecom B.V., Heerhugowaard, The Netherlands.

c IT Engineer, Oratio B.V., Zwaag, The Netherlands.

dEmeritus professor, Department of Oral-Maxillofacial Surgery, Prosthodontics and Special Dental Care, University Medical Center Utrecht, Utrecht, The Netherlands.

eProfessor Computerized Dentistry,  Academic Centre for Dentistry Amsterdam, The Netherlands.

Purpose. Determinants of mandibular movements, like condylar inclination and incisal guidance should be considered in the fabrication of occlusal restorations to prevent posterior excursive occlusal interferences. This study investigated differences in the occlusal morphology of the right mandibular molar resulting from high, average and low values of settings for determinants of anteroposterior and transverse mandibular movement using a virtual articulation model. Material and methods. The articulation functionalities of a computer integrated restorative technology by imaging and new acquisition (CYRTINA) were used as a tool to examine the potential effect of determinants of mandibular movement on occlusal molar design. High, average and low values for condylar guide inclination, incisal guide angle and intercuspal contact area (antero-posterior determinants) and laterotrusion, mandibular lateral translation and intercuspal contact area (transverse determinants) were introduced and differences in molar morphology studied. The latter was done by comparing mesiodistal and buccolingual sections of the occlusal designs. These interocclusal differences were quantified as differences in frequency of occlusal distances in an interocclusal range of 1 mm, measured from the occlusal surface of the molar model. A correction value, reflecting the extent to which a standard crown had to be corrected to function without interferences, was calculated as well. Results. Among all parameters, the ipsilateral and contralateral mandibular lateral translation, sagittal condylar guide inclination, the ipsilateral laterotrusion and the incisal guide angle give substantial occlusal surface corrections. The high setting for the ipsilateral mandibular lateral translation required most correction. Conclusion. High and low setting values of mandibular movement determinants require considerable adaptation of the occlusal surface of a crown to facilitate functional occlusion without occlusal disturbances.

Published: Journal Computerized Dentistry

 

Comparison of Manual and Guided Implant Placement. S.T. VLAAR and  J.M. VAN DER ZEL*, Academic Center for Dentistry Amsterdam, University of Amsterdam and Free University Amsterdam, Netherlands.

Statement of the problem: Precision of manual placement of implants remains highly dependent on the skill of the operator. A higher accuracy of positioning of the implant is claimed when using drill guides. This study is an in-vitro validation of two methods of implant placement: manually and with the use of planning and drilling with drill guides using a new implant planning system to compare the accuracy of angulation and position. Material and methods: A partial dentate patient case was used for the study. Between the 44 and 46 a diastema was present. Twenty gypsum casts were produced and divided at random into two equal groups: group G and group M. Drilling of the implant hole in group M was done manual and group G was done with a stereolithographic drill guide (Cyrtina®Guide, Oratio B.V., Zwaag, The Netherlands). Individual drill guides were produced for the pilot drill (diameter 2.0 mm), the intermediate drill (diameter 3.6mm) and the final drill (diameter 4.0 mm).  A scannographic guide with three opaque glass spheres of 4.0 mm diameter was used as reference in CT- and optical scanning. Twenty Helix® implants (Dyna Dental Engineering B.V., Bergen op Zoom, The Netherlands) with a length of 10 mm and a diameter of 4.2 mm were screwed in the twenty drilled holes of group G and M and a cylindrical zirconia abutment was placed in the implant as scan marker. Two variables were calculated: ‘XY’ and ‘Angle’. Results: The mean XY SD 0.198 mm (± 0.0950) and 1.20 mm (± 0.681) for group G and M respectively. The mean Angle SD was 2.45° (± 1.55) and 7.05° (± 3.92) for group G and M respectively. The difference was statistically significant (p < 0.05) for both. Conclusion: This in-vitro study shows a statically significant improvement in implant positioning with drill guides as compared to manual drilling. This study was supported by SenterNovem grant TSIT2020.

Published as Abstract IADR New Orleans