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To compare the exactness of simulated clinical impressions and stone replicas of crown preparations, using digitization and virtual three-dimensional analysis.Three 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.The 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; p0.0001). The reliability was high for both digitization methods, evaluated by repeated digitizations.The exactness of the digitized impressions varied with shape. Both impressions and stone replicas can be digitized repeatedly with a high reliability.

Objectives. To determine the reproducibility of digitized dental stone replicas compared to the master model and the reliability of the computer aided analysis. Methods. Four 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 surfacemodels 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 colordifference-maps. Results. The precision of the measuring method, presented as the repeatability coefficient, ranged between 7 and 16m (entire surface), whereas the analysis of the stone replicas revealed a precision (repeatability coefficient) ranging from 19 to 26m. The accuracy of the replica to master (the mean discrepancy) ranged from 0.5 to 2.0m (95% confidence interval 1.5–2.9m). Significance. The 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 15m (2–25m) greater for the replica-to-master alignment than the repeated digitizations of the master.

Statement of problem The fit of a dental restoration depends on quality throughout the entire manufacturing process. There is difficulty in assessing the surface topography of an object with a complex form, such as teeth, since there is no exact reference form. Purpose The purpose of this study was to determine the repeatability and relative accuracy of 2 dental surface digitization devices. A computer-aided design (CAD) technique was used for evaluation to calculate and present the deviations 3-dimensionally. Material and methods Ten dies of teeth prepared for complete crowns were fabricated in presintered yttria-stabilized tetragonal zirconia (Y-TZP). The surfaces were digitized 3 times each with an optical or mechanical digitizer. The number of points in the point clouds from each reading were calculated and used as the CAD reference model (CRM). Alignments were performed by registration software that works by minimizing a distance criterion. In color-difference maps, the distribution of the discrepancies between the surfaces in the CRM and the 3-dimensional surface models was identified and located. Results The repeatability of both scanners was within 10 μm, based on SD and absolute mean values. The qualitative evaluation resulted in an even distribution of the deviations in the optical digitizer, whereas the dominating part of the surfaces in the mechanical digitizer showed no deviations. The relative accuracy of the 2 surface digitization devices was within ± 6 μm, based on median values. Conclusion The repeatability of the optical digitizer was comparable with the mechanical digitization device, and the relative accuracy was similar.

Procera Sandvik AB is now manufacturing a densely sintered high-purity alumina core for an all-ceramic crown designed for anterior and posterior restorations. Whereas the material holds promise on the basis of in vitro strength tests, the ability to alter the surface and use conventional bonded resin cements has not been reported previously in the literature. Samples of the core were treated by means of one of four methods routinely used for all ceramic restorations, and then a commercially available resin cement was bonded to the surface. A shear bond test of the adhesion showed that the highest shear bond strengths of 11.99 +/- 3.12 MPa were obtained with air abrasion at 80 psi and 50-microm alumina particles.

A method of manufacturing an all-ceramic crown composed of a coping of dense-sintered, high-purity alumina with dental porcelain is described. This method takes the sintering shrinkage of alumina into consideration and makes it possible to produce individual dental copings in dense-sintered, high-purity alumina, which is a biocompatible implant material. The alumina used has density, grain size, and flexural strength within the limits of the values required in ISO 6474-1981, 'Implants for surgery, ceramic materials based on alumina'.

As different implant abutments are introduced to obtain a sufficient soft tissue barrier, the aim of this study was to determine the effect of three different surface modifications of densely sintered high-purity aluminium oxide on morphology, attachment and proliferation of human gingival fibroblasts. Fibroblasts were cultured on pressed aluminium oxide, milled, and then sintered to full density (1), on pressed, densely sintered (2), and on pressed, densely sintered and then polished surfaces (3). The different surfaces were analyzed using a confocal laser scanner, an atomic force microscope and a scanning electron microscope. The cell profile areas were measured using a semiautomatic interactive image analyzer and the figures were expressed as percent of attachment. The polished specimens had the smoothest surfaces and the roughest were the milled surfaces in terms of height deviation. No difference was found in the spacing between the peaks on the polished surfaces compared to the milled surfaces. Fibroblasts on the milled ceramic appeared to follow the direction of the fine irregularities on the surface. The analyses showed the polished surfaces had significantly higher percentages of initial cell attachment than the other surfaces (P

Statement of problem. Esthetic 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. Purpose. This prospective study was initiated to evaluate the clinical performance of 100 Procera AllCeram crowns after 5 years in service. Material and methods. One 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 Association's quality assessment system. Results. Of 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. Conclusion. The 5-year clinical observations and ranking with the California Dental Association's quality assessment criteria supported the conclusion that Procera AllCeram crowns may be used in all areas of the mouth. (J Prosthet Dent 1998;80:450-6.)

The use of Procera AllCeram laminates for patients with discolored teeth has been described. In our experience, these laminates are simple to use and provide possibilities for excellent esthetics.

The object of this prospective study was to compare the clinical behavior of composite and amalgam restorations with respect to anatomical form, marginal adaptation, caries adjacent to margin, and post-operative sensitivity. We selected children (n = 43) with an average age of 6.4 yr exhibiting proximal caries lesions in primary molars distributed on both left and right sides. In each child, one amalgam and one composite side were randomly chosen, resulting in 64 fillings for composite and 55 for amalgam. After a two-year period, significantly (p less than 0.05) more composite fillings (88%) were clinically classified as satisfactory compared with amalgam fillings (68%). No significant relationship was found between the success rate of proximal fillings and the caries activity of the individuals. The results indicate that composite can be used successfully as a class II filling material in primary molars in children.

Three types of amalgams, one conventional and two with a high copper content, were stored in phosphate-buffered 0.9% NaCl solution, at pH 6, for 35 weeks. Every 7 weeks the solutions were changed and analyzed with regard to Cu, Zn, Sn, Hg, and Ag. In one of the amalgam combinations, the conventional amalgam and one of the copper-rich amalgams in an area ratio of 2:1, contact between the amalgams clearly increased the amounts of Cu, Hg, and Ag released the first 14 weeks compared with when immersed in separate solutions. With the reversed area relation, Cu, Hg, and Ag decreased when they were in contact. The conventional amalgam in contact with the other copper-rich amalgam, in an area ratio of 2:1, reduced the amount of Cu but increased the Zn released. Polishing initially decreased the amounts of Cu and Zn released compared with the unpolished amalgams.

Recovery in aluminium has been studied by in situ technique with the aid of a high voltage electron microscope. It is shown how the dislocation density continuously decreased as the recovery proceeded. The recovery process changed the distribution of dislocation link lengths in such a way that the number of shorter links sharply decreased while there was a slight increase of the number of longer links. The observed recovery of the dislocation structure can satisfactorily be described by the dislocation network growth theory. In the formation of subgrain boundaries, high-angle grain boundaries and twin boundaries played an important role. They were often found to act as “nucleation sites” for the subboundaries. At high temperatures subgrains rapidly grew and coalesced. The growth can satisfactorily be described by analogy with the growth of dislocation network.

Twenty-seven gold crowns, removed from patients with problems such as diffuse pain and metallic taste, have been examined. The gold crowns were made of an ordinary casting gold alloy, type III. The crowns were built on amalgam cores or big amalgam fillings. Eight of these crowns had cracks beginning at the cervical margin and propagating occlusally. The crowns were examined in a scanning electron microscope equipped with an energy-dispersive detector. The study showed that the cracks propagated along the grain boundaries within the gold alloy. In the cracks corrosion products usually found on amalgam were identified. The cracks could be due to intercrystalline stress corrosion or overloading.

– The adhesion of Streptococcus rattus BHT and Streptococcus mutans IB to metal specimens of amalgam, silver, tin and copper was studied using (6-3H)thymidine labeled cells. In the standard assay the metal specimens were suspended by a nylon thread in an adhesion solution containing a chemically defined bacterial growth medium (FMC), sucrose, and radiolabeled bacteria, Maximum amounts of adhering bacteria were obtained after about 100 min of incubation. Saturation of the metal specimens with bacteria was not observed. Both strains also adhered in the absence of sucrose, indicating that glucan formation was not necessary for adhesion. However, in the presence of glucose, adhesion was only 26–45% of that observed in the presence of equimolar sucrose. Sucrose-dependent stimulation of adhesion seemed to be due to increased cell-to-cell adhesion capacity. Isolated radiolabeled water-insoluble and watersoluble polysaccharides produced from sucrose by S. rattus BHT were not adsorbed to the metal surfaces.

One conventional amalgam and two amalgams with a high copper content were stored in 0.9% NaCl solution buffered with phosphate to pH 6. In one experimental series the amalgams were placed in contact with a gold alloy. Every 7 weeks the solutions were changed and analyzed with regard to elements released from the amalgams. The microstructure of the specimens was studied in a scanning electron microscope before immersion and after 7 and 35 weeks in the solution. All the amalgams corroded along the grain boundaries in the gamma 1 phase. Corrosion was greatest in the gamma 2 phase of ANA 68, in the eta phase of ANA 2000 and in the reaction zone (eta + gamma 1) surrounding the Ag-Cu-eutectic particles of Dispersalloy. The microstructure of the corroded amalgams showed similarities to amalgams corroded in vivo. The change in microstructure observed in cross-sections of the corroded specimens was related to the amounts of corrosion products released into the saline solution.