Göran Sjögren

Laser welding of titanium in dentistry

Unalloyed titanium of the quality used for osseointegrated implants by the method of Brånemark is also sometimes used for the metallic part of the prosthetic superstructure placed on the fixtures and for crowns and bridges of conventional type. Forty bars of titanium, 8 of ASTM B 348 grade-1 quality and 32 of ASTM B 348 grade-2 quality, were laser-welded, using dissimilar laser joint variables. Tensile strength, 0.2% proof stress, and percentage elongation of the welded bars were measured and compared with the corresponding values for the titanium bars as delivered and with those of brazed type-3 gold alloy bars of similar dimensions. The type of fracture was evaluated from fractographs. The results showed that the use of certain defined laser joint variables during welding produced values for the mechanical properties studied which were more favorable than those obtained from the brazed gold bars. The fracture of the titanium specimens was ductile, with dimples occurring at the fracture surfaces.

Clinical evaluation of all-ceramic crowns (Dicor) in general practice.

STATEMENT OF PROBLEM There are few studies regarding all-ceramic full crowns placed by general practitioners; however, most dental restorations are carried out by general practitioners, and their clinical performance may be of particular interest. PURPOSE Ninety-eight all-ceramic Dicor crowns placed in 46 patients regularly visiting a general practice were evaluated with the California Dental Associations (CDA) criteria. Mean and median ages of the crowns were 6.1 and 5.8 years, respectively (range 1.4 to 10. 9 years). Crowns were luted with either a glass ionomer, zinc phosphate, or resin composite cement. RESULTS Of the 98 crowns, 82% were rated satisfactory. For marginal integrity, 51% were rated excellent. Fracture was registered in 14 all crowns, and 1 endodontically treated tooth with a Dicor crown was extracted because of root fracture; of the remaining 83 crowns, 55% were rated excellent for color. Corresponding figures for surface and anatomic form were 46% and 23%, respectively. The most common finding was slightly rough surfaces (64%). No statistically significant difference was observed for fracture rates obtained when the crowns luted with different luting agents were compared (P >.05). There was no more plaque or bleeding on probing (P >.05) in connection with the Dicor crowns than in the control surfaces.

A clinical examination of ceramic (Cerec®) inlays

Two hundred and five Cerec ceramic inlays placed by 8 dentists in 72 patients were examined independently by 3 calibrated evaluators 12-24 months after insertion, using the criteria of the California Dental Association (CDA) and also certain periodontal variables. Proximal dental plaque and bleeding on probing were not seen more often on Cerec surfaces than on control homologous surfaces. Ten patients reported postoperative sensitivity after treatment with Cerec inlays. Excellent CDA ratings for Color and Surface were obtained in 57% and 26%, respectively, and for Anatomic Form and Margin Integrity in 55% and 83%, respectively. Obvious differences were seen among the participating dentists with regard to the clinical quality of Cerec inlays. At present, the long-term performance of the Cerec technique cannot be predicted.

Retention of prefabricated and individually cast root canal posts in vitro

Objectives The aim of the study was to evaluate the retention of prefabricated root canal posts made of a variety of materials that have recently been introduced into dentistry.Materials and methods The posts studied were CosmoPost, Composipost carbon fibres, Composipost Æstheti-Plus, Composipost Light-Post and Para Post Fiber White. The posts were luted in extracted human premolars and the cores were built up with the resin composites recommended by the manufacturers. The retention of individually cast gold alloy posts luted with zinc-phosphate cement were used as reference. A universal testing machine was used to determine the retention of each cemented post. Data were compared using ANOVA supplemented with Fishers PLSD at a significance level of p < 0.05.Results Only the CosmoPost system exhibited retention values that were significantly lower than for the conventionally cast gold alloy posts luted with zinc-phosphate cement. The force necessary to loosen the CosmoPost specimens was significantly less than that needed to loosen the Composipost Æstheti-Plus (p < 0.05) and the Composipost Light-Post systems (p < 0.001). The force necessary to loosen the Para Post Fiber White specimens was significantly less than for the Composipost Light-Post system (p < 0.01). Other combinations did not differ significantly (p > 0.05).Conclusions When zirconium oxide ceramic posts are luted with resin composites the bonding between the ceramic and resin composite seems to be weak. Further studies are thus necessary to achieve improved retention of all-ceramic root canal posts.

Marginal and internal fit of four different types of ceramic inlays after luting. An in vitro study.

The marginal and internal fit of four different types of ceramic inlays--Cerec, Celay, Empress, and Vita In-Ceram Spinell--was determined after they had been luted on extracted premolars. For the Cerec inlays sharp and U-shaped proximal box shapings were also compared. There was no statistically significant difference either in the proximal fit or in the gingivoproximal fit between the four inlay systems studied, with the exception of the Cerec inlays made for preparations with sharp proximal boxes, which had wider marginal gaps. At the occlusal margins a significant-principle order of the gap width was established. The best internal fit was recorded for the Celay inlays, whereas there was no significant difference in the internal fit between the other systems. For the Cerec inlays the U-shaped proximal box shaping improved the marginal accuracy all around the restoration.

Interface gap size of manually and CAD/CAM-manufactured ceramic inlays/onlays in vitro.

OBJECTIVES To determine the fit of ceramic inlays manufactured using a recently introduced CAD/CAM-system (Decim) and of two types of laboratory-made heat-pressed ceramics (IPS Empress and Opc). MATERIALS AND METHODS Extracted human premolars were prepared to receive mesio-occlusodistal (MOD) ceramic inlays, for which 10 Denzir, 10 IPS Empress, and 10 Opc were fabricated. The Denzir restorations were produced by the manufacturer of the CAD/CAM-system, and the IPS Empress and Opc by student dental technicians. Before luting the internal fit on the diestone models and on the premolars was determined using replicas. After luting on the premolars with a resin composite the marginal and internal fit were measured. The values were analyzed statistically using ANOVA and Scheffes test at a significance level of p<0.05. RESULTS Before luting there were no significant differences (p>0.05) in the internal gap width between the three systems studied when placed on their matching diestone models. When placed on the premolars a significant difference (p<0.01) in the internal fit was seen between Empress and Opc before luting, whereas there were no significant differences (p>0.05) between Empress and Denzir and between Opc and Denzir. Between the diestone models and the premolars there were significant differences (p<0.01) in the internal fit, except for IPS Empress. After luting there were no significant differences (p>0.05) between IPS Empress and Denzir, whereas the marginal gap width was significantly wider (p<0.001) for Opc than for IPS Empress and Denzir. The internal fit was significantly (p<0.001) wider for Opc than for IPS Empress, whereas there were no significant differences (p>0.05) between IPS Empress and Denzir or between Opc and Denzir. CONCLUSION After luting there were only slight differences in the fit between the restorations fabricated using the three different manufacturing techniques and ceramics. Therefore, long-term follow-up studies are needed to assess the clinical significance of the slight differences between the three systems.

Ceramic inlays (Cerec) cemented with either a dual-cured or a chemically cured composite resin luting agent A 2-year clinical study

On the basis of the criteria of the California Dental Association (CDA), 66 CAD/CAM-manufactured ceramic class-II inlays (Cerec) were compared intraindividually after they had been cemented with either a chemically cured or a dual-cured composite resin luting agent in 27 patients. Plaque and gingival conditions, the overall time consumption for producing each inlay, and the frequency of postoperative sensitivity were also evaluated. There was no statistically significant difference between the two luting agents with regard to the properties evaluated. One inlay was replaced owing to fracture of the restored tooth just before the 24-month re-examination. After 2 years excellent CDA ratings were obtained for color in 92% of the remaining 65 inlays. The corresponding figures for surface and for anatomic form were 100% and 85%, respectively. For margin integrity 85% of the 33 inlays cemented with the dual-cured luting agent and 88% of the 33 inlays cemented with the chemically cured luting agent were rated excellent after 2 years.

Fracture resistance of all-ceramic crowns placed on a preparation with a slice-formed finishing line

The purpose of this study was to determine the fracture resistance of all-ceramic crowns with a core of a zirconia ceramic, using various stabilizing oxides and luted on a preparation with a slice-formed finishing line. Ten cores made of HIPed yttrium-oxide partially stabilized zirconia (HIPed Y-TZP) and five cores of densely-sintered magnesia partially stabilized zirconia (Mg-PSZ) were made. The Mg-PSZ cores and five of the HIPed Y-TZP cores were made with a thickness of 0.2 mm. A further five cores 0.1-mm thick were made of HIPed Y-TZP. All 15 cores were then veneered with a feldspar ceramic and luted onto a stylized steel master die model with a slice-formed finishing line. The specimens were then loaded until fracture occurred. The HIPed Y-TZP specimens with the 0.2 mm core exhibited significantly higher fracture resistance than the Mg-PSZ specimens (P = 0.004) and the HIPed Y-TZP specimens with the 0.1 mm core (P = 0.001). The fracture resistance of the Mg-PSZ specimens was significantly (P = 0.015) higher than that of the HIPed Y-TZP specimens with the 0.1 mm core. The fracture resistance determined was equal or superior to reported values for bite forces and all-ceramic crowns. Thus, it seems likely that the type of restorations evaluated have the potential for successful use on a slice-formed preparation. However, long-term studies are essential in order to assess the performance of this ceramic system in a clinical context.

Piezoelectricity in. dental materials, a conceivable cause of postrestorative sensitivity

With the increased use of tooth-colored posterior inlays reports of postrestorative sensitivity have also increased. One of the symptoms the patients complain of is a sharp pain when the inlays are loaded through chewing and biting. Many explanations for the causes of dissimilar types of postrestorative sensitivity have been offered, but one conceivable explanation that has not hitherto been studied is the direct piezoelectric effect in dental materials. Direct piezoelectric effect means that when certain anisotropic crystals are mechanically loaded, a charge is generated on the surface. The aim of the present study was to examine whether this physical phenomenon occurs in certain materials intended for dental use. Specimens of four different dental ceramics and one indirect composite resin for inlays were mechanically loaded with various forces, and the current was directly recorded. Currents of up to 0.9 microA with a pulse duraton of 0.4 msec were extracted, and it cannot be excluded that the piezoelectric phenomenon and related properties may cause postrestorative sensitivity. This has to be taken into consideration when posterior inlays of the types concerned are used.

A 3D numerical simulation of stress distribution and fracture process in a zirconia-based FPD framework

In this study, a numerical approach to the fracture behavior in a three-unit zirconia-based fixed partial denture (FPD) framework was made under mechanical loading using a newly developed three-dimensional (3D) numerical modeling code. All the materials studied were treated heterogeneously and Weibull distribution law was applied to describe the heterogeneity. The Mohr-Coulomb failure criterion with tensile strength cut-off was utilized to judge whether the material was in an elastic or failed state. For validation, the fracture pattern obtained from the numerical modeling was compared with a laboratory test; they largely correlated with each other. Similar fracture initiation sites were detected both in the numerical simulation and in an earlier fractographic analysis. The numerical simulation applied in this study clearly described the stress distribution and fracture process of zirconia-based FPD frameworks, information that could not be gained from the laboratory tests alone. Thus, the newly developed 3D numerical modeling code seems to be an efficient tool for prediction of the fracture process in ceramic FPD frameworks.