Matts Andersson

Five-year clinical evaluation of Procera AllCeram crowns ☆ ☆☆ ★ ★★ ♢ ♢♢

STATEMENT OF PROBLEMnEsthetic demands of patients and practitioners for an all-ceramic crown in both anterior and posterior regions of the dental arches has prompted the development of the Procera AllCeram crown. Long-term clinical trials that evaluate the strength and naturalness of the Procera AllCeram crown are lacking.nnnPURPOSEnThis prospective study was initiated to evaluate the clinical performance of 100 Procera AllCeram crowns after 5 years in service.nnnMATERIAL AND METHODSnOne hundred Procera AllCeram crowns were fabricated for 58 patients (20 men and 38 women). Patients were treated by 4 general dental practitioners. Crown placement involved both the anterior and posterior regions of the dental arches. Crowns were examined at baseline and once a year during the 5 years that followed and evaluated at each appointment with the California Dental Associations quality assessment system.nnnRESULTSnOf the 97 crowns remaining in the study after 5 years, only 3 crowns had experienced a fracture through the veneering porcelain and the aluminum oxide coping material. Two additional crowns were replaced as a result of fractures of only the veneering porcelain. One crown was replaced as a result of recurrent caries. All remaining crowns were ranked as either excellent or acceptable for surface/color, anatomic form, and marginal integrity.nnnCONCLUSIONnThe 5-year clinical observations and ranking with the California Dental Associations quality assessment criteria supported the conclusion that Procera AllCeram crowns may be used in all areas of the mouth.

Digitization of simulated clinical dental impressions: Virtual three-dimensional analysis of exactness

OBJECTIVESnTo compare the exactness of simulated clinical impressions and stone replicas of crown preparations, using digitization and virtual three-dimensional analysis.nnnMETHODSnThree master dies (mandibular incisor, canine and molar) were prepared for full crowns, mounted in full dental arches in a plane line articulator. Eight impressions were taken using an experimental monophase vinyl polysiloxane-based material. Stone replicas were poured in type IV stone (Vel-Mix Stone; Kerr). The master dies and the stone replicas were digitized in a touch-probe scanner (Procera) Forte; Nobel Biocare AB) and the impressions in a laser scanner (D250, 3Shape A/S), to create virtual models. The resulting point-clouds from the digitization of the master dies were used as CAD-Reference-Models (CRM). Discrepancies between the points in the pointclouds and the corresponding CRM were measured by a matching-software (CopyCAD 6.504 SP2; Delcam Plc). The distribution of the discrepancies was analyzed and depicted on color-difference maps.nnnRESULTSnThe discrepancies of the digitized impressions and the stone replicas compared to the CRM were of similar size with a mean+/-SD within 40microm, with the exception of two of the digitized molar impressions. The precision of the digitized impressions and stone replicas did not differ significantly (F=4.2; p=0.053). However, the shape affected the digitization (F=5.4; p=0.013) and the interaction effect of shape and digitization source (impression or stone replica) was pronounced (F=28; p<0.0001). The reliability was high for both digitization methods, evaluated by repeated digitizations.nnnSIGNIFICANCEnThe exactness of the digitized impressions varied with shape. Both impressions and stone replicas can be digitized repeatedly with a high reliability.

The accuracy of a high-precision digitizer for CAD/CAM of crowns

An alternative method for manufacturing fixed prostheses that uses machine digitalization and a combination of milling and spark erosion has been developed. The digitizer used has a contact probe with a ball-shaped tip. This study evaluated the accuracy of the device and the transfer of data from the individual die to the computer. The dimensions of a square gauge as read by the machine were compared with the known dimensions of the object with a computer, which allowed determination of the accuracy of the digitalization. Procera machining and the implications for reliable prosthodontic treatment are discussed.

Computer aided analysis of digitized dental stone replicas by dental CAD/CAM technology

OBJECTIVESnTo determine the reproducibility of digitized dental stone replicas compared to the master model and the reliability of the computer aided analysis.nnnMETHODSnFour master dies, prepared for complete crowns were fabricated in presintered yttria-stabilized tetragonal zirconia (Y-TZP). Eight vinyl polysiloxane impressions (PROVIL novo; Heraeus Kulzer) were taken of each die and stone replicas were poured in type IV stone (Vel-Mix Stone; Kerr). The master dies and the stone replicas were digitized in a touch-probe scanner (Procera Forte; Nobel Biocare AB), to create triangulated surface-models. The point-cloud from the first of the repeated digitizations of each master die was used as CAD-reference-models (CRM). Discrepancies between the points in the triangulated surface-models and the corresponding CRM were measured by a matching-software (CopyCAD 6.504 SP2; Delcam Plc). The distribution of the discrepancies was analyzed and presented in color-difference-maps.nnnRESULTSnThe precision of the measuring method, presented as the repeatability coefficient, ranged between 7 and 16 microm (entire surface), whereas the analysis of the stone replicas revealed a precision (repeatability coefficient) ranging from 19 to 26 microm. The accuracy of the replica to master (the mean discrepancy) ranged from 0.5 to 2.0 microm (95% confidence interval 1.5-2.9 microm).nnnSIGNIFICANCEnThe greatest precision of the measurement was seen in the jacket surface of the die. The size of the stone replicas varied and the repeatability coefficient was on average 15 microm (2-25 microm) greater for the replica-to-master alignment than the repeated digitizations of the master.

Virtual variation simulation of CAD/CAM template-guided surgeries performed on human cadavers: Part II.

STATEMENT OF PROBLEMnCAD/CAM template-guided surgery has gained attention as a method of improving the predictability of dental implant placement. However, due to possible variations during the manufacturing process and in the robustness of the template design, a virtual prediction of the potential positioning of the implants is needed.nnnPURPOSEnThe purpose of this study was to perform virtual variation simulations on virtually planned implant placements and to compare them with corresponding results from actual surgeries performed on human cadavers in a previous study.nnnMATERIAL AND METHODSnSeventeen computer-aided plans were used for virtual variation simulation of surgeries conducted on 17 human cadavers and 145 implants placed in the cadavers. For each surgery, 10,000 virtual surgeries were performed, resulting in 1,450,000 implant placements. The results from the virtual variation simulations were statistically compared with the results from the actual surgeries. The Mann-Whitney U test was used to compare the implant distributions (alpha=.05).nnnRESULTSnIn the maxillae, the difference between the simulated average mean of the mean and the compared surgical average of the median was 0.22 mm (apex) and -0.35 mm (hex), and for the mandible, the corresponding values were -0.19 mm (apex) and -0.69 mm (hex). The simulated average mean of the range compared to the mean range of the maximum deviation results from the surgeries of the maxillae was 2.96 mm (apex) and 0.44 mm (hex), and 2.3 mm (apex) and 0.26 mm (hex) for the mandible. The implant distributions between the simulations and the surgeries were significantly different at both the hex (P<.001) and apex (P<.001).nnnCONCLUSIONSnThe implant distributions were neither static nor normally distributed. Thus, within the limitations of this study, the definitive geometrical variations of the implants were not static, as they depend on the individual anatomy of the jaws and the ability to place the CAD/CAM-guided surgical template in the proper position.

The kilometer tax and Swedish industry–effects on sectors and regions

An introduction of a kilometer tax for heavy goods vehicles can be constrained by the risk of that higher production costs than competitors in other countries will negatively affect regions and industries of policy concern. We estimate factor demand elasticities in the Swedish manufacturing industry using firm level data for the 1990 to 2001 period on input prices and quantities. The results show that the introduction of a kilometer tax for heavy goods vehicles decreases transport demand and increases labour demand. The effects are less pronounced in terms of changes in output, though some industries (e.g. wood, pulp and paper) can be expected to be affected more than others due to their dependence on road freight transport. The regional dimension regarding the consequences of a kilometer tax seems to be small or even nonexisting.

Industrial Scale Production of Customized Ceramic Prostheses

Today, there are many solutions for dental rehabilitation. A damaged tooth can be replaced with a dental crown, and a toothless patient can be rehabilitated with implants and a corresponding bridge set-up. Traditionally, a dental crown is manufactured by veneering porcelain to a metal surface that is obtained through the use of casting principles. Implant rehabilitations used to rely on a high degree of handcraft by the dentist, where freehand drilling into the jaw- bone was supported by X-ray pictures and was done before implant insertion. Crown and implant rehabilitations can be provided at a much higher degree of industrialization by means of mass customization. The most common dental rehabilitations are crown restorations for single teeth, while full arch implant rehabilitations are the most comprehensive treatments. Trends in industry lean toward a higher degree of automation in production and manufacturing where key characteristics of a well-functioning ceramic prosthesis are cost reduction, patient satisfaction, and quality in both function and perception.