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Hovedbudskap Simulering ved hjelp av virtuell virkelighet («Virtual Realty simulators» VRS) er godt egnet som læringsverktøy i flere odontologiske prosedyrer og kan gjøre overgangen fra preklinisk til klinisk undervisning lettere. Simulering i odontologisk undervisning kan gi økt pasientsikkerhet ved at studentene blir øvet i ulike behandlingssituasjoner på forhånd. Det er ingen VRS-systemer i dag som kan erstatte alle aspekter ved preklinisk ferdighetstrening, men den hurtige teknologisk utviklingen gjør VRS stadig mer anvendelig og klinisk relevant.

Objectives The aim of this retrieval study was to analyze the fracture features and identify the fracture origin of zirconia-based single crowns that failed during clinical use. Methods Thirty-five fractured single crowns were retrieved from dental practices (bi-layered, n = 15; monolithic, n = 20). These were analyzed according to fractographic procedures by optical and scanning electron microscopy to identify fracture patterns and fracture origins. The fracture origins were closely examined. The crown margin thickness and axial wall height were measured. Results Three types of failure modes were observed: total fractures, marginal semilunar fractures, and incisal chippings. Most of the crowns (23) had fracture origins at the crown margin and seven of them had defects in the fracture origin area. The exact fracture origin was not possible to identify due to missing parts in four crowns. The crown wall thickness was 20% thinner and wall height 30% shorter in the fracture origin area compared to the opposite side. Conclusions The findings in this study show that fractography can reveal fracture origins and fracture modes of both monolithic and bi-layered dental zirconia. The findings indicate that the crown margin on the shortest axial wall is the most common fracture origin site. Clinical significance Crown design factors such as material thickness at the margin, axial wall height and preparation type affects the risk of fracture. It is important to ensure that the crown margins are even and flawless. publishedVersion

Higher yttria content enhances the translucency and appearance of dental zirconia materials. Alterations in material composition also affect mechanical properties. The aim of this study was to compare the fracture load after artificial short-term aging of monolithic, full-contour zirconia crowns with different amounts of yttria-stabilization. Sixty crowns (thirty super high translucent crowns (5Y-Z) and thirty high translucent crowns (3Y-Z)) were produced to fit a model of a premolar with a shallow chamfer preparation. The crowns were cemented with self-adhesive resin cement on composite abutments. For each zirconia type, three groups of crowns (n = 10) were allocated to: (i) cyclic loading (200 N, 1 Hz, 30,000 cycles), (ii) hydrothermal aging (3 × 20 min, 134°C 3.2 bar), or (iii) no treatment (control). Surviving crowns from the aging process were quasistatically loaded until fracture. The 3Y-Z crowns had statistically significantly higher fracture values (3,449 N) than the 5Y-Z crowns (1,938 N). The aging procedures did not affect load at fracture. Fractographic analysis showed that fractures started either at the crown margin or at the occlusal intaglio area. Higher yttria content leads to a reduction in material strength and damage tolerance, and this should be reflected in recommendations for clinical use.

Purpose: High-translucent dental zirconia has been introduced as a suitable material for anterior monolithic restorations. The material composition differs from traditional 3Y-TZP both with regard to yttria content and grain size. Little is known regarding how these alterations affect other properties than translucency and flexural strength. The aim of this study was to evaluate the crack propagation resistance and hardness of dental zirconias with different yttria content and different manufacturing methods. Materials and methods: Measurement of hardness (HV2/5) and crack propagation from the indents (damage tolerance) was performed using a hardness tester(Vicker) on a flat polished surface of five crowns from six different commercial dental zirconias; one hard-machined 3Y-TZP, three soft-machined 3-5% yttria-stabilized zirconias and two soft-machined zirconias with 5% yttria content. Results: Damage control varied greatly among dental zirconias with different compositions and fabrication methods. The hard-machined 3Y-TZP had better crack propagation resistance than soft-machined, 3-5% yttria-stabilized zirconias Conlcusion: The ultra-translucent zirconias with 5% yttria content had the lowest crack propagation resistance. Hardness is not a suitable indicator for damage tolerance. publishedVersion

The autotransplantation of teeth after cryopreservation has become an increasingly viable method for whole tooth replacement. While the immediate success rates are quite high, damage introduced by cryopreservation within the dentin or enamel could be detrimental to the durability of these teeth. Objective to determine whether cryopreservation alters the microstructure of dentin or causes a reduction of its resistance to mechanical failures. Methods Third molars were obtained from young donors (18≤ age ≤30 yrs) and subjected to a cryopreservation protocol involving storage for 10 days in cryoprotectant solution at −196 °C. After treatment, the mid-coronal dentin was characterized in terms of its elastic modulus, strength and fatigue behavior. Scanning electron microscopy and Raman spectroscopy were used to evaluate the microstructure and integrity of collagen after cryopreservation. Results There was no significant difference in the elastic modulus or flexural strength between dentin from the cryopreserved and non-cryopreserved (control) teeth. However, the cryopreservation treatment caused a significant decrease in the fatigue strength of dentin with respect to the controls, with average reduction of nearly 20%. While there were no differences apparent in the collagen matrix or fracture surfaces between the cryopreserved and control groups, the microstructure of dentin from the cryopreserved teeth exhibited unique features and damage that appear to have caused the decrease in durability. Significance Autotransplantation of cryopreserved teeth may be a viable option for whole tooth restorations, but hidden damage within the dentin could render these teeth more susceptible to mechanical failures by fatigue and fracture.

Zirconia‐based restorations are showing an increase as the clinicians’ preferred choice at posterior sites because of the strength and esthetic properties of such restorations. However, all‐ceramic restorations fracture at higher rates than do metal‐based restorations. Margin design is one of several factors that can affect the fracture strength of all‐ceramic restorations. The aim of this study was to assess the effect of preparation and crown margin design on fracture resistance. Four groups of bilayer zirconia crowns (with 10 crowns in each group) were produced by hard‐ or soft‐machining technique, with the following four different margin designs: chamfer preparation (control); slice preparation; slice preparation with an additional cervical collar of 0.7 mm thickness; and reduced occlusal thickness (to 0.4 mm) on slice preparation with an additional cervical collar of 0.7 mm thickness. Additionally, 10 hard‐machined crowns with slice preparation were veneered and glazed with feldspathic porcelain. In total, 90 crowns were loaded centrally in the occlusal fossa until fracture. The load at fracture was higher than clinically relevant mastication loads for all preparation and margin designs. The crowns on a chamfer preparation fractured at higher loads compared with crowns on a slice preparation. An additional cervical collar increased load at fracture for hard‐machined crowns. publishedVersion

Two zirconia-based 4-unit restorations intended for the same patient fractured during the veneering process even though the prolonged cooling protocol recommended by the manufacturers was used. Fractographic analyses revealed that both restorations fractured as a result of thermal shock, but at different times during production. Further investigation is necessary to optimize the firing protocols for large zirconia-based restorations and avoid fracture due to thermal shock.

Introduction The incidence of vertical root fracture in endodontically treated teeth increases with patient age. This study evaluated the microstructure, chemical composition, and mechanical properties of radicular dentin as a function of aging. Methods Single-rooted teeth were obtained from adult donors ranging from age 15 to older than 80 years. Beams were extracted from the middle third of the root and subjected to 4-point flexure to failure to evaluate strength of dentin in terms of donor age. Based on the strength distribution, the fatigue strength of root tissue from young (≤30 years) and old (≥55 years) donor teeth was evaluated via cyclic flexure loading. The microstructure and chemical composition of radicular dentin from the 2 groups were evaluated as a function of distance from the root apex using microscopy and Raman spectroscopy, respectively. Results The strength decreased with age by approximately 25 MPa per decade, which resulted in a significant difference (P ≤ .0001) between the young (199 ± 36 MPa) and old (122 ± 11 MPa) groups. There was also a significant difference (P ≤ .0001) in fatigue strength between the young and old age groups. Both the mineral-to-collagen ratio and degree of cross-linking increased with age, with the largest changes identified in the apical and middle thirds, respectively. Conclusions There is a reduction in the damage tolerance of radicular dentin with increasing age. This degradation appears to result from changes in the microstructure, corresponding chemical composition, and increase in collagen cross-linking with age, and is most severe near the root apex.

Objectives This study investigated the effects of tungsten-carbide grinding on the surface characteristics and mechanical strength of dental 3 mol% yttria-stabilized zirconia (3Y-TZP). Methods Two types of tungsten-carbide burs (TC), 6-blade (TC1) and 8-blade (TC2) were used to grind 3Y-TZP, in a dental air-turbine handpiece with water-cooling and were also subjected to air-particle abrasion (APA): TC1 + APA and TC2 + APA; and rubber polishing (RP): TC1 + RP and TC2 + RP; one group received only rubber-polishing RP. The control group received no treatment. Surface characterization was examined by surface roughness (Ra) and atomic force microscopy. Specimens were also observed with scanning electron microscopy (SEM) and X-ray-diffraction (XRD) for microstructure and crystalline phases. A piston-on-three-balls biaxial-flexural strength (BFS) test was performed with 15 samples-per-group and the broken specimen were observed under SEM to investigate the fracture origin pattern. One-way ANOVA, Kruskal–Wallis test and Weibull analysis were performed at α = 0.05. Results Groups TC1 and TC2 had the lowest mean BFS (p Significance Tungsten-carbide burs (6- and 8-blade) are not recommended for zirconia grinding due to the significant reduction of biaxial-flexural strength and observed micro-structural surface and subsurface damage.

Additive manufacturing (AM) of ceramics, particularly of zirconia, is becoming of increasing interest due to the substantial freedom available in the design and fabrication process. However, due to the novelty of the field and the challenges associated with printing dense bulk ceramics suitable for structural applications, thorough investigations that explore the effects of printing on the mechanical performance are limited. Previous work has identified anisotropy in the mechanical properties and attributed it to the layer-by-layer deposition. However, substantiated fractographic evidence detailing the origins and effects of layer lines on the probability of failure are limited. This study investigates the mechanical properties of a dense (>99 %TD), partially stabilized zirconia fabricated by a digital light projection printing method following ASTM standards. Hardness and strength evaluations were conducted, followed by a Weibull analysis and fractography. The investigation entailed five unique build directions and a conventionally manufactured reference material that was used as a control. Although the strengths were comparable to the reference material for some orientations, fracture frequently initiated at layer lines and related defects in all orientations. The findings indicate that if the layer lines can be prevented or engineered, the strength of vat printed ceramics can be improved substantially.

Objectives The causes of in vivo fractures of all-ceramic dental crowns are not yet fully understood. The fracture origins often occur in the cervical margin in the approximal area, but the reason for this is unclear. The aim of this study was to evaluate the fracture origin of 22 of clinically-failed alumina crowns. Methods The fracture surfaces of alumina crowns fractured in vivo were inspected by optical microscopy to evaluate the fracture patterns and identify the cause of fracture. Fracture maps were constructed as needed to interpret the patterns of breakage and to back track to a fracture origin area. A scanning electron microscope (SEM) was used to characterize the fracture origins of the 22 cases where the origin site was available. Results The most common fracture origins were marginal defects either in the alumina core or in the veneer. The defects included thin, chipped, cracked or uneven crown margins and excess veneer on the inside of the crown. Multiple flaws were present along the margins in most specimens, but fracture origins were usually located in the region of the shortest axial wall. A few crowns had pores, contamination, or incomplete sintering that acted as fracture origins. Significance Production method, handling, design and material insufficiencies influence the fracture of dental ceramic crowns. Machining defects and other margin flaws seem to be the most detrimental factors for alumina crowns. Feather-edge or sharp margins should be avoided. Smooth and moderately thick crown margins would probably dramatically improve the durability.

Although the strength and toughness of dentin decrease with age, no study has explored if restorative treatments are a contributing factor.Multiple extracted teeth were obtained from randomly selected donors and categorized according to donor age and prior root canal treatment. The microstructure and chemical composition of radicular dentin were evaluated using scanning electron microscopy and Raman spectroscopy, respectively, and the strength was evaluated in 4-point flexure to failure. Data were compared using the Student t test.Dentin from the root canal-restored teeth exhibited significantly lower strength (P .05) than tissue from age- and donor-matched unrestored tooth pairs. Although there was no significant difference in the mineral-to-collagen ratio between the 2 groups, dentin obtained from the root canal-treated teeth exhibited more extensive collagen cross-linking and lower tubule occlusion ratios than the unrestored tooth pairs.There is a decrease in the strength of radicular dentin with aging, but prior root canal treatment increases the extent of degradation.

Objectives The aim of this study was to assess the clinical outcomes and patient satisfaction with monolithic zirconia crowns in patients with severe tooth wear (≥1/3 of the tooth crown) in the aesthetic zone. Methods The historical prospective study sample consisted of 13 patients previously treated with a total of 84 monolithic zirconia crowns. The patients had been treated in a private clinic in Bergen, Norway, in the period 2012 to 2014. All patients were men, aged 35–67 years (mean age 56.3 years) and had been in need of prosthetic rehabilitation because of severe tooth wear in the aesthetic zone. Technical complications as well as biologic findings were registered when the crowns had been in function one to three years (mean 20 months). The patients completed a self-administered questionnaire regarding satisfaction with aesthetic and function. Results No biological complications were registered in 79 of the crowns (94%), and technical complications were registered in only two patients. All patients were satisfied with the aesthetic and function of the monolithic zirconia crowns and would choose the same treatment modality if they were to be treated again. Conclusions Within the limitations of this study, we conclude that the rate of clinical complications was low and that the patients were satisfied with the aesthetic as well as the function of the monolithic zirconia crowns. Clinical significance Monolithic zirconia crowns may provide a valid treatment modality in the aesthetic zone in patients with severe tooth wear.

Background Promising results of initial clinical trials with yttria-stabilized zirconia have led to more extensive use of zirconia in dental implant superstructures. The applications have extended to abutments and complex individually designed crown-abutment one-piece structures. Little is known about their clinical success and the primary cause of failures. Purpose The aim of this study was to identify the cause of fracture of retrieved implant-retained one-piece prostheses that failed during clinical use. Methods Nine fractured restorations were analyzed with fractographic methods and their fracture origins were identified. Results All but two of the fractures originated in an area of tight contact between the implant or titanium screw and the abutment base. Results of the evaluation showed that zirconia-based implant restorations with very thin walls in the region connecting the prosthesis to the implant are vulnerable to damage from the screw retaining process and fracture from non-axial loads. Two restorations failed due to veneer fractures. Significance The findings suggest that large crowns on narrow implants or implants with internal fixation should preferably not be made with zirconia abutments, or that a new design approach should be considered.

Purpose: Some patients experience adverse reactions to poly(methyl methacrylate)-based (PMMA) dentures. Polyamide (PA) as an alternative to PMMA has, however, not been well documented with regard to water sorption and water solubility. The aim of this in vitro study was to measure water sorption and water solubility of two PA materials compared with PMMA, and to evaluate the major components released from the PA materials and the effect on hardness of the materials. Methods: Ten discs (40.0 mm diameter, 2.0 mm thick) of each material (PA: Valplast and Breflex; PMMA: SR Ivocap HIP) were prepared according to manufacturers’ recommendations. The specimens were tested for water sorption and water solubility, according to a modification of ISO 20795-1:2008. Released substances were analysed by gas chromatography/mass spectrometry (GC/MS). Results: There were statistically significant differences among the materials regarding water sorption, water solubility and time to water saturation. Breflex had the highest water sorption (30.4 μg/mm3), followed by PMMA-material (25.8 μg/mm3) and Valplast (13.6 μg/mm3). Both PA materials had statistically significant lower water solubility than the PMMA. Both PA had a net increase in weight. Analysis by GC/MS identified release of the compound 12-aminododecanolactam from the material Valplast. No release was found from the Breflex material. Conclusions: The PA denture materials show differences in water sorption and solubility, but within the limits of the standard requirements. The PA showed a net increase in weight after long-term water sorption. The clinical implications of the findings are not elucidated. publishedVersion

Dental all-ceramic restorations of zirconia, with and without an aesthetic veneering layer, have become a viable alternative to conventional metal-ceramic restorations. The aim of this study was to evaluate whether factors of the production methods or the material compositions affect load at fracture, fracture modes, internal fit or crown margins of monolithic zirconia crowns.Sixty crowns made from six different commercially available dental zirconias were produced to a model tooth with a shallow circumferential chamfer preparation. Internal fit was assessed by the replica method. The crown margin quality was assessed by light microscopy on an ordinal scale. The cemented crowns were loaded centrally in the occlusal fossa with a horizontal steel cylinder with a diameter of 13mm at 0.5mm/min until fracture. Fractographic analysis was performed on the fractured crowns.There were statistically significant differences among the groups regarding crown margins, internal fit and load at fracture (p0.05, Kruskall Wallis). Fracture analyses revealed that all fractures started cervically and propagated to the occlusal surface similar to clinically observed fractures. There was statistically significant correlation between margin quality and load at fracture (Spearman's rank correlation, p0,05).Production method and material composition of monolithic zirconia crowns affect internal fit, crown margin quality and the load at fracture. The hard-machined Y-TZP zirconia crowns had the best margin quality and the highest load at fracture. Reduction of margin flaws will improve fracture strength of monolithic zirconia crowns and thereby increase clinical success.

Comparison of fracture strength and fracture modes of different all-ceramic crown systems is not straightforward. Established methods for reliable testing of all-ceramic crowns are not currently available. Published in-vitro tests rarely simulate clinical failure modes and are therefore unsuited to distinguish between the materials. The in-vivo trials usually lack assessment of failure modes. Fractographic analyses show that clinical crowns usually fail from cracks initiating in the cervical margins, whereas in-vitro specimens fail from contact damage at the occlusal loading point. The aim of this study was to compare three all-ceramic systems using a clinically relevant test method that is able to simulate clinical failure modes. Ten incisor crowns of three types of all-ceramic systems were exposed to soft loading until fracture. The initiation and propagation of cracks in these crowns were compared with those of a reference group of crowns that failed during clinical use. All crowns fractured in a manner similar to fracture of the clinical reference crowns. The zirconia crowns fractured at statistically significantly higher loads than alumina and glass-ceramic crowns. Fracture initiation was in the core material, cervically in the approximal areas. publishedVersion

Purpose: Despite the high fracture strength of modern dental core ceramics, fractures are a common cause of clinical failures. The aim of this study was to use a clinically relevant test method to evaluate the effect of the curvature of the cervical crown margins on load at fracture. Materials and Methods: Thirty zirconia crowns and 30 glass-ceramic crowns were produced for three premolar preparations with variation in the approximal crown margin curvature: low curvature (r = 12 mm), moderate curvature (r = 2.5 mm), and high curvature (r = 1.5). The crowns were loaded until fracture with a method that mimics clinical fracture modes. Results: Statistically significant differences were found among both crown margin curvature and material groups (P < .001). Most fractures originated from pre-existing flaws. Conclusion: A moderate to low curvature of the crown margins increases crown strength compared with a high curvature.

Objectives The use of all-ceramic restorations has been steadily increasing in the decades since the introduction of high-strength core ceramics as an alternative to metal cores. Even with high-strength ceramic cores, the crowns are susceptible to fractures during clinical function, probably the major concern associated with all-ceramic restorations. The aim of this study was to analyze fracture features of clinically fractured crowns in order to determine crack initiation sites and crack propagation paths. Methods Fractographic methods were used to analyze 27 all-ceramic full coverage crowns with alumina cores and feldspatic veneering ceramic. The fractured crowns were supplied by dentists in private and public practices with information of type of cement and time in function if available. Results The fractured crowns comprised 13 incisors, 3 premolars and 11 molars. The results revealed that all fractures initiated in the cervical margin of the crowns and usually from the approximal area close to the most coronally placed curvature of the margin. There was no statistically significant association between the cement used and time in function. Significance Fractography of clinically failed all-ceramic crowns can provide information on the fracture modes and design considerations. The findings are in contrast to fracture modes from in vitro tests. The results suggest that more clinically relevant in vitro test methods to study the durability of ceramic crowns should be developed.

Statement of problem New additive manufacturing techniques for nonprecious alloys have made the fabrication of metal-ceramic fixed partial dentures (FPDs) less expensive and less time-consuming. However, whether the mechanical properties produced by these techniques are comparable is unclear. Purpose The purpose of this in vitro study was to evaluate the mechanical properties of cobalt-chromium frameworks for FPDs fabricated by 3 different techniques. Material and methods Thirty frameworks for 3-unit FPDs were fabricated by traditional casting, computer-aided design and computer-aided manufacturing (CAD-CAM) milling, and selective laser melting (SLM), with n=10 in each group. The frameworks were weighed, and distal and mesial connector areas measured. The frameworks were cemented and loaded centrally (0.5 mm/s) until deformation above 1 mm occurred. Stiffness was measured as the slope of the axis between 500 and 2000 N. Microhardness was measured on sectioned specimens by Vickers indentation. The microstructure was also analyzed by scanning electron microscopy. One-way ANOVA with Tukey post hoc analysis was used to compare the groups (α=.05). Results The framework design differed among the groups, making a comparison of strength impossible. The milled frameworks appeared bulky, while the cast and SLM frameworks were more slender. Statistically significant differences were found in microhardness, stiffness, wall thickness, weight, and connector size ( P P Conclusions Fabrication method affects the design, stiffness, microhardness, and microstructure of cobalt-chromium FPD frameworks. The SLM frameworks were stiffer and harder than the cast and milled specimens.

The aims of this study were to assess the applicability and repeatability of qualitative and quantitative analyses of the fracture patterns of four different high-strength ceramics. Ten bar-shaped specimens of four high-strength ceramics with different material composition and fabrication methods had been fractured by three-point bending in water (n = 40). Commonly used fractographic patterns for brittle materials, such as mirror and mist, were used to characterize and quantify the fractured surfaces of these specimens. The analyses were performed twice, on separate occasions, by the same operator. Assessment of the association between fractographic patterns and fracture stress was carried out, and repeatability assessments of the measurements were performed. The fracture initiator site and the common fractographic markers surrounding this site were found in all specimens. Statistically significant correlations were found between certain fracture patterns and stress at fracture. The repeatability of the measurements of the different fractographic patterns varied among the materials. Fracture analyses seem applicable as a tool to determine the fracture initiation site and to estimate the force vectors involved in the fracture of dental high-strength ceramics.

Objectives. High-strength ceramics for dental restoration are used as an understructure (core) that subsequently is covered by veneering ceramic. The veneering process involves a firing procedure at high temperatures at least once, usually two to five times. The aim of this study was to investigate whether these firing procedures affect the mechanical properties of a zirconia ceramic. Methods. Thirty-three specimens of an industrially sintered yttria-stabilized zirconia ceramic (DC Zircon, DCS Dental AG, Allschwil, Switzerland) were cut into bars (1.2 mm × 4m m× 20 mm). One set of specimens (n = 13) remained untreated (controls). Another set of specimens (n = 10) was heat-treated once, corresponding to the first step of the veneering process. The third set of specimens (n = 10) was heat-treated five times to mimic the full veneering process. Flexural strength, microhardness, dimensions and surface roughness were measured. The fracture patterns were assessed by light microscopy. Results. The untreated specimens showed a statistically significant higher flexural strength (20%) and microhardness (9%) than both of the test groups (p ≤ 0.001). No significant differences were found for fracture patterns, dimensions or surface roughness. Significance. The heat treatment associated with the veneering procedure on a zirconia core material reduced the flexural strength of the core after the first firing. Subsequent firings were not detrimental to the properties measured.

The effect of anatomic contour design in all or parts of zirconia crowns is uncertain regarding clinical reliability and survival rates.The purpose of this in vitro study was to compare the load at fracture of monolithic, anatomic contour zirconia crowns with bilayered crowns with and without a cervical zirconia collar.Thirty zirconia crowns were fabricated for a shallow chamfer molar preparation, 10 with a normal core-veneer design, 10 with a core-veneer design with an additional cervical collar of zirconia, and 10 with a monolithic, anatomic contour design. Veneering ceramic was applied to the first 20 specimens to create an anatomic form. All crowns were cemented to epoxy abutments and loaded until complete fracture with a clinically relevant test method. The fracture modes and load at fracture were recorded.Statistically significant differences were found in the load at fracture and fracture modes among the test groups (P.001). All fractures except one initiated in the crown margin, mostly in the proximal region. The mean load at fracture was 4091 N for the normal core-veneer design, 4712 N for the collar design, and 6517 N for the monolithic, anatomic contour design.Monolithic, anatomical contour design gave higher loads at fracture than traditional core-veneer design. Crowns with a cervical zirconia collar had higher load at fracture than the core-veneer design, but lower than the monolithic crowns.

Statement of problem Conventionally, the fabrication method for Co-Cr restorations has been casting by the lost-wax method. Milling and selective laser melting (SLM) are more cost effective and thereby increasingly used. The precision of the different methods regarding internal and marginal fit, however, is not fully known. Purpose The purpose of this in vitro study was to examine and evaluate whether the 3 fabrication methods of conventional casting, milling, and SLM differ in internal and marginal fit for Co-Cr fixed dental prostheses (FDPs). Material and methods Thirty Co-Cr metal frameworks for 3-unit FDPs were made with 3 fabrication methods for a model with 2 abutment preparations. Internal fit was measured with the replica method. A white silicone indicator material simulated the cement space. This was measured by light microscopy at ×20 magnification and a digital measurement program. Marginal fit was evaluated with the direct-sight technique at ×4.6 magnification and given a score from 1 to 5. One-way ANOVA and Tukey honest significance tests were used to evaluate differences among groups with regard to internal fit. The Kruskal-Wallis and Mann-Whitney U tests were used to calculate differences among groups with regard to marginal gap. The Pearson r test was used for correlations calculations (α=.05). Results Statistically significant differences were found in both internal and marginal fit among the test groups ( P Conclusions SLM restorations had the poorest internal and marginal fit, whereas the milling method had the best results. The SLM technique did not achieve clinically acceptable values for internal fit.

a b s t r a c t Objectives. Fracture strength measured in vitro indicates that most all-ceramic crowns should be able to withstand mastication forces. Nevertheless, fractures are one of the major clinical problems with all-ceramic restorations. Furthermore, the fracture mode of all-ceramic crowns observed in clinical use differs from that found in conventional fracture strength tests. The aim of the present study was to develop and investigate a method that simulates clinical fracture behavior in vitro. Methods. 30 crowns with alumina cores were made to fit a cylindrical model with a molarlike preparation design. These crowns were randomly allocated to 3 tests groups (n = 10). The crowns in group 1 were cemented to abutment models of epoxy and subsequently fractured by occlusal loading without contact damage. The crowns in group 2 were fractured by cementation with expanding cement. The crowns in group 3 were cemented on an abutment model of epoxy split almost in two and fractured by increasing the diameter of the model in the bucco-lingual direction. The fractured crowns were analyzed by fractographic methods and compared to a reference group of 10 crowns fractured in clinical use. Results. The fracture modes of all the in vitro crowns were similar to clinical fracture modes. The fracture modes in group 1 were most closely matched to the clinical fractures. These crowns also fractured at clinically relevant loads. Conclusion. Laboratory tests that induce a distortion of the abutment model during occlusal loading without occlusal contact damage can simulate clinical fractures of all-ceramic crowns.

The aim of the study was to assess the repeatability of shade determination of teeth by a spectrophotometer. Additionally, the influence of different sitting positions on the shade determination was evaluated. Two operators measured the shade of an incisor and a premolar of 24 subjects sitting in three different positions. 18 participants were measured twice. The shade was determined in three areas on each tooth; cervical, central and incisal. Intra- and inter-operator repeatability was calculated and the variance between sitting positions analysed. The results had low to moderate intra- and inter-operator repeatability. The patient's sitting position affected the shade determination.

The aim of this study was to identify the dental technicians' experiences with extra-coronal all-ceramic restorations. A questionnaire was mailed to all laboratories registered in The Norwegian Association of Dental Laboratory Owners (n=186). The response was 149 (80%). All-ceramic restorations were produced by 93 (62%) of the responding laboratories. A few of these (1 7%) produced the majority (67%) of the restorations. The dental technicians reported low rates of remakes (median 2%) for all-ceramic restorations. The low production and the limited number of laboratories that perform this work show that there is room for extended training and more expertise in this field.