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In recent years, patients have benefited from the development of better and more esthetic materials, including all-ceramics dental restorative materials. Dental plaque formation on teeth and restorative materials plays an important role in the pathogenesis of oral diseases. This study investigates initial adhesion of stationary phase streptococcal species to different all-ceramics dental restorative materials. The saliva-coated materials were incubated with the bacteria for 1 h in an in vitro flow chamber which mimics environmental conditions in the oral cavity. Number and vitality of adhering bacteria were determined microscopically after staining. Surface roughness and the composition of the materials had no distinctive influence on bacterial adhesion. However, S. mutans and S. sobrinus adhered about tenfold less numerous to all materials than the other streptococcal species. Further, there was a correlation between bacterial vitality and materials’ glass content. The results showed that early plaque formation was influenced predominantly by the presence of the salivary pellicle rather than by material dependent parameters whereas the composition of the all-ceramics appeared to have influenced the percentage of viable cells during the adhesion process. This presented in vitro technique may provide a useful model to study the influence of different parameters on adherence of oral streptococcal species.

All-ceramic dental bridges for the molar region are not yet available at reasonable costs. The novel direct ceramic machining (DCM) process allows an easy, reliable and rapid fabrication for all-ceramic dental restorations with high mechanical strength and good biocompatibility. In DCM, an enlarged framework is easily milled out of a pre-fabricated porous ceramic blank made of zirconia. After sintering to full density, no further time-consuming hard machining with diamond tools is needed. For individual esthetical requirements, the framework is coated with a veneer porcelain. Compared to the commercially available In-Ceram Alumina and IPS Empress2 restorations, the mechanical strength of zirconia frameworks is twice as high, allowing the restorations to bear the high mastication forces in the molar region. In terms of reliability, zirconia bridges fabricated by the DCM process are also superior to In-Ceram Alumina and IPS Empress2. A clinical study of three-unit dental bridges in the molar region found no problems after the first year of observation.

Today's dental reconstructive therapeutic concepts require restoration of high esthetic quality and excellent biocompatibility. Full ceramic reconstructions accomplish these requirements but only for anterior teeth and premolars. For all-ceramic bridges the mechanical strength was insufficient to withstand the posterior chewing forces. Frequently the interdental connectors cracked, and the only way to prevent these fractures was to overconture the connectors to a size of approx. 16 mm2. The high-tech ceramic zirconia is a potential alternative for three-to five-unit full ceramic bridges in the functionally loaded posterior segments. Experimental zirconia bridges which were fabricated using the DCM system (Direct Ceramic Machining System at the ETH Zurich, were tested in vitro. The frameworks were digitally enlarged by 20% and were easily milled from a presintered yet porous zirconia blank. After the milling process, the framework was densely sintered and shrank to its original size. Due to these positive in-vitro results a clinical investigation was started. 22 veneered zirconia bridges were luted; 19 molars and 25 premolars were prepared. The connectors, max. 7 mm2, of all these bridges, have been functionally loaded by antagonists. After a mean observation time of 385 days (307 days to 488 days), all 22 bridges did not show any cracks in the framework or in the veneering porcelain. The patients commented particularly on the low heat conduction rate of zirconia. The only endodontic problem which occurred could not be directly connected to the type of bridge framework. The reliability of zirconia bridges in this investigation was connected to the DCM-Process. No statement about other zirconia-systems can be made on the results of this study.

This investigation was designed to determine whether heat pressing and/or simulated heat treatments affect the flexure strength and microstructure of the lithium disilicate glass-ceramic of the IPS Empress 2 system.Four groups of the lithium disilicate glass-ceramic were prepared as follows: group 1 = as-received material; group 2 = heat-pressed material; group 3 = heat-pressed and stimulated initial heat-treated material; and group 4 = heat-pressed and simulated heat-treated material with full firings for a final restoration. Three-point bending tests and scanning electron microscopy (SEM) analysis were conducted.The flexure strength of group 2 was significantly higher than that of group 1. However, there were no significant differences in strength among groups 2, 3, and 4, or between groups 1 and 4. The SEM micrographs of the lithium disilicate glass-ceramic showed a closely packed, multidirectionally interlocking microstructure of numerous lithium disilicate crystals protruding from the glass matrix. The crystals in the glass matrix of the heat-pressed materials (groups 2, 3, and 4) were a little more homogeneous and about 2 times bigger than those of the as-received material (group 1). These changes of the microstructure were greatest between groups 1 and 2. However, there were no marked differences among groups 2, 3, and 4.Although there were significant increases in the strength and some changes of the microstructure after the heat-pressing operation, the combination of heat pressing and simulated subsequent heat treatments did not produce an increase of strength of IPS Empress 2 glass-ceramic.

Root-filled teeth with fractured or discolored coronal aspects invariably need to be restored by crowns. The prepared abutment tooth is usually reinforced by a metallic post and core system. The grayish discoloration of the root, and consequently of the gingiva, caused by the metal color may be an enormous esthetic disadvantage in the anterior teeth. In 1993 ceramic posts made of zirconia were introduced by the authors, allowing a new all-ceramic concept for nonvital abutment teeth. A new ceramic post and core system has now been developed with the idea of further improving esthetic appearance. In this system the core material is heat pressed directly onto the zirconia post. This article describes the material and the fabrication procedures (chairside and in the laboratory) of the system. Clinical results are presented. The retention of the core material is evaluated by in vitro tests.

Computer-aided design/computer-integrated machining (CAD/CIM) allows defect-oriented custom-shaping of the inside surfaces of all-ceramic crowns. The purpose of this study was to examine the effect of inside crown form on fracture strength of cemented and bonded crowns.Four preparation types were used: (1) "classic" with a butt shoulder of 1.2 mm, abutment height of 4 mm, and 6-degree convergence, (2) like type 1 with mesio-occlusodistal cavity, (3) like type 1 with height reduced by 50%, and (4) like type 1 with abutment reduced by 100% plus a pulp chamber cavity. Crowns were CAD designed on preparations 1 to 4 using identical outside morphology. Machined crowns were placed on abutments (a) without any media as controls (n = 15), (b) cemented (n = 15), and (c) bonded (n = 15), and were loaded until fracture.Zinc phosphate-cemented crowns (1b, 2b, 3b, and 4b) showed significant (P0.001) increase of fracture load values compared to uncemented control crowns (1a, 2a, 3a, 4a). Fracture load values of bonded crowns (1c, 2c, 3c) were significantly (P0.001) higher than those for cemented crowns. Bonded crowns with thick occlusal dimensions (3c and 4c) showed the highest fracture load values.Bonded all-ceramic CAD/CIM crowns with defect-oriented inside morphology and increased occlusal dimensions showed high fracture load values.

To evaluate the shear bond strength of one-bottle dentin bonding agents (DBA's) (PrimeBond 2.1, ART Experimental, Syntac Single Component) on pressurized human dentin.Freshly prepared dentin specimens of human teeth were perfused with horse serum which was diluted 1:5 in physiologic saline. Three different types of surface treatment were evaluated on the freshly prepared dentin. Group 1: One of the three one-bottle DBA's was applied onto freshly prepared dentin together with a cylinder of composite luting resin and cured. Group 2: A provisional cement (Freegenol, without eugenol, or Temp Bond, containing eugenol) was applied first on the dentin surface for 24 h. Only then was one of the three the one-bottle DBA's added onto the dentin together with a cylinder of composite luting resin after cleaning the dentin surface with pumice. Group 3: One of the three one-bottle DBA's was applied first on the dentin surface and light-cured. Then a provisional cement (Freegenol, without eugenol, or Temp Bond, containing eugenol) was added for 24 h. After cleaning with pumice, the respective one-bottle DBA was applied for a second time onto the dentin together with a cylinder of composite luting resin and light-cured. As control for Group 1 (freshly prepared dentin), the two- or three-step DBA's ART Bond and Syntac were used in a similar way. As control for Group 2 (single application of the DBA's after contamination of the dentin with a provisional cement) and Group 3 (dual application of the DBA's with intermediate contamination of the dentin with a provisional cement) the two-step DBA ART Bond was used. After 1500 thermal cycles with constant imitation of intrapulpal pressure, shear bond strengths were measured. Resulting shear bond strength values were displayed by means of a box plot and they were analyzed statistically by Student's t-Test or one-way ANOVA.Lowest and highest mean shear bond strength values were 0.26 +/- 0.47 MPa (single use of ART Bond with prior application of Temp Bond) and 16.34 +/- 5.02 MPa (dual use of ART Bond with intermediate application of Temp Bond). With respect to the surface treatment significant differences between the DBA's could be found in all groups.

To evaluate the effect of a dual application of dentin bonding agents (DBA) on their shear bond strength on dentin with intermediate application of a provisional cement.Freshly prepared flat dentin surfaces of human teeth were coated with a first layer of one of various dentin bonding agents (All-Bond 2, ART Bond, Syntac or an experimental DBA called P-Bond). After curing the DBA, a provisional cement (Temp Bond, Freegenol or Fermit, a soft provisional diacrylate) was applied to the bonded dentin surface. After 24 hours, the provisional cement was removed and the dentin surface scrubbed with pumice. A second application of the same DBA together with a composite cylinder followed. After curing and 1,500 thermal cycles with constant imitation of intrapulpal pressure, shear bond strengths were measured.Compared to a single application of dentin bonding agents following Temp Bond treatment (SBS in MPa: Syntac: 0.86 +/- 1.75, ART Bond: 0.26 +/- 0.47, P-Bond: 14.90 +/- 4.51) application of DBAs prior to use of Temp Bond as well as after its removal seems to be very beneficial to shear bond strength values (SBS in MPa: Syntac:13.36 +/- 4.70, ART Bond: 16.34 +/- 5.02, P-Bond: 19.04 +/- 2.01). Independent from the provisional cement, the values after serial application of P-Bond provided consistently high bond values which were not statistically different (Kruskal-Wallis, P0.05) from values of P-Bond on fresh dentin (18.19 +/- 2.29 MPa). The only exception from these findings in the present study was All-Bond 2. Regardless of the provisional materials used, the bond strength values of All-Bond 2 remained low (maximum SBS with Fermit as intermediate provisional cement: 4.63 +/- 2.91 MPa).

The aim of this investigation was to study the chemical solubility of 3 new low-fusing ceramics (Duceram-LFC, Duceragold and Vita Omega 800) in comparison with a conventional PFM-ceramic (Vita Omega) together with different surface treatments. Additionally, the three-point flexure strengths were measured. Although the test conditions were very stringent in comparison to the standard solubility test, all ceramics comply with ISO/DIS 6872 specifications, and are thus deemed to be well tolerated in the oral environment. Vita Omega demonstrated the lowest chemical solubility. Mechanical polishing of the surfaces of LFC and Duceragold ceramics produced lower solubility results as compared to glazing. Vita Omega and Omega 800 behaved contrarily. After repeated hydrolysis testings Ducera-LFC demonstrated the highest disintegration resistance. The three-point flexure strengths of low-fusing ceramics were generally higher than that of the conventional PFM-ceramic. As opposed to the other ceramic materials tested, the flexure strength of Duceram-LFC increased significantly after hydrolysis testing.

The flexural strength of bar samples (2 x 4 x 12 mm) of Vita Mark II, Dicor MGC DarkLight and CR-Polymer was examined after machining with the Cerec E-Drive unit using grinding wheels coated with coarse (126 microns) and fine (46 microns) diamonds. The flexural strengths of both Vita MK II (98.5-112.4 MPa) and Dicor MGC Dark (135.1-205.3 MPa) were significantly (p0.01) different after machining with the coarse and fine discs respectively. The flexural strengths of both Dicor-MGC Light (192.6-220.1 MPa) and of CR-Polymer (103.9-104.3 MPa) were not significantly changed by machining with coarse or fine diamonds, respectively. Bonded sandwich samples (2 x 4 x 12 mm) were made from parts (1.45 x 4 x 12 mm) of Vita MK II, MGC DL and CR-Polymer and of parts (0.45 x 4 x 12 mm) of bovine dentin using a dentin adhesive and a 100 microns layer of fine hybrid composite resin. The flexural strengths of the samples machined from porcelain and glass ceramic (2 x 4 x 12 mm) and the sandwich samples composed of ceramic (1.45 x 4 x 12 mm) and bovine dentin (0.45 x 4 x 12 mm), respectively, did not differ significantly (p0.001): Vita MK II 106.4 +/- 12.2/98.5 +/- 25.8 MPa. Dicor MGC Dark 195.6 +/- 34.6/145.6 +/- 31.2 MPa. Dicor MGC Light 204.1 +/- 29.1/171.5 +/- 18.2 MPa.(ABSTRACT TRUNCATED AT 250 WORDS)

A newly developed press-type all-ceramic crown system, the IPS-Empress system (Ivoclar), has recently been introduced. Two methods may be used to obtain the desired shade: surface staining and glazing; veneer technique. The purpose of this study was to determine whether these two methods affected flexure strength of Empress glass ceramic. Eight groups of test bars were pressed. In groups 1 and 2, one surface was stained and glazed. The bars were placed face down (1) or up (2) for testing. For comparison, group 3 was heat-treated only (simulating stain and glaze firing). In groups 4-7, one surface of the bars was either veneered with porcelain on the bottom (4) or top surface (5) and then subsequently glazed (6 and 7). Group 8 was just heat-treated (simulating veneer and glaze firings). The results showed that there were no significant differences in strength between groups 2, 5 and 7 compared to the reference groups 3 and 8 (159 +/- 28 and 175 +/- 32 MPa, respectively), indicating that, from the mechanical point of view, the two surface techniques can be equally used on Empress ceramic. If the porcelain veneer supported the ceramic (4), the strength was significantly decreased. The highest mean value was obtained in group 1 (220 +/- 34 MPa).

An evaluation of about 300 abutment teeth of resin-bonded bridges (Rochette, electrochemically etched) and resin-bonded extracoronal attachments was performed to determine the surface area and the length of the circumference of the retainers. By using a combined indirect (preparation of the specimen) and direct (automatic image analysis) method for the determination of both parameters a mean value of 50 mm2 for the surface area and 30 mm for the circumference, respectively, was evaluated. In addition, two indices (loading-index (BI): sigma surface area/width of pontic tooth; moisture penetration-index (FPI): sigma surface area/sigma circumferences) as predictors for the longevity of resin-bonded reconstructions were calculated. The loading-index was a good predictor for successful reconstructions: the clinical success was the better, the bigger the retention area, and the smaller the circumference of the retainer and the smaller the pontic tooth.

In rats a chronic uremic syndrome was induced by 5/6 resection and subsequent irradiation of the kidneys. After 5 weeks 45Ca and 89Sr were injected simultaneously, and the different metabolic handling of the two elements was determined applying an open two-compartment model of Calcium kinetics. The uremic animals were compared with two groups of rats which were pairfed, and fed ad libitum, respectively. Besides an elevenfold faster urinary excretion when calculated with Sr, and which was reduced to about one half in the uremic rats, a significant discrimination by bone in favour of Ca was found, with a rather stable factor of 1.2 in the three groups. This is considered to evidence that urinary excretion and bon uptake of Sr are independent processes.

Die Gleichstromleitfahigkeit von dunnen DNS-Filmen wurde mit Hilfe von Oberflachen- undSandwichzellen sowie an freitragenden Filmen untersucht. Es wurde eine neue Methode zur Herstellung freitragender Filme entwickelt. Als Kontakte dienten aufgedampfte Elektroden aus Cr, Ag, Au und Al sowie Gold- und Silberpaste. Der am freitragenden Film und mit Hilfe von Oberflachenzellen bestimmte Dunkelstrom zeigte ohmsches Verhalten, wahrend beiSandwichzellen (103 V/cm

The determination of mass in small parts of single nerve fibers using the X-ray absorption technique described by Engstrom and Lindstrom gave the following results. The myelin sheath has the weight 0.3–0.4 × 10 −12 g/μ 3 and the axon 0.08–0.09 × 10 −12 g/μ 3 . Lipids make up about 50 per cent of the central part of the myelin sheath. No lipids could be observed in the axoplasm. The axon of non myelinated fibers seems to have a greater mass per unit volume than the axon of myelinated fibers. The ultrastructure of the axon is briefly discussed.

By differential thermal analysis of some Au-Cu alloys the order-disorder transformation AuCu IAuCu II of the compound AuCu is shown to be a first order transformation accompanied by a variation of enthalpy. This method has also allowed to detect a certain order in alloys with more than 75 at-% Au.

Die kombinierte Einwirkung von ionisierender Strahlung und N-Isopropyl-p-(2-methyl-hydrazinomethyl)benzamid hydrochlorid (Natulan®) fuhrt zu einem wesentlich starkeren Abbau von Desoxyribonucleinsaure (DNS) als auf Grund der linearen Superposition zu erwarten ware. Der Synergismus ist am ausgepragtesten, wenn der Zusatz von Natulan unmittelbar nach der Bestrahlung erfolgt. Dieser Effekt kann als Folge der Bildung instabiler Peroxide wahrend der Bestrahlung erklart werden. Bekanntlich zerfallen die bei der Bestrahlung entstandenen organischen Peroxide zum grossten Teil innerhalb der ersten zwei bis drei Stunden nach der Bestrahlung unter Bildung freier Radikale. Diese konnen als Startradikale bei der Autoxydation von Natulan wirken und daher den Abbau von DNS beschleunigen.

The radiophysical properties of the material "Masonit" are examined by experimental methods. Indications are given as to atomic composition, density, effective atomic number, concentration of electrons, and linear attenuation coefficient. A comparison with water shows that "Masonit" is a suitable phantom material especially for the purposes of radiotherapy.

A combination of two different modifications indicated in the literature about the ferrosulfate dosimetry has been given. This permits a dose measurement which shows compared to the usual dosimetry of Fricke above all following advantages: dose specification related to water; displacement of the absorption maximum in the perceptible spectral sphere; increase of the sensibility and lower influence of pollutions. The molar coefficient of extinction of the modified solution has been determined from Co-60-gamma irradiation and is epsilonm = 1,46 - 10(4) L - Mol(-1) - cm(-1). The increase of extinction which has been measured with this method after the irradiation with 18 MeV electrons occurs linearly within the studied region to 1200 rd at least, the G-value is 15,5. The indicated method renders possible a relative simple calibration of the ionisation chambers which have been used in the practice.

The reproducibility and accuracy of an optical source-surface distance measuring device was systematically examined. The standard deviation of twenty equal distance settings was +/-0,5%. The error in dose-rate caused by one single adjustment did not exceed +/-2%. The position of the effective source-center is defined by a special inverse square plot. A periodical check is recommended.

In earlier experiments presented at the 8th Symposium (MEYER et al., 1971), we have investigated the different handling of 45Ca and 89Sr as tracers in a kinetic model of Calcium metabolism in the rat. We have shown highly significant higher excretion rates for Sr than for Ca in the urine (vu) and the endogenous fecal secretion (vf), which is in agreement with the literature (BAUER et al., 1955; COHN and GUSMANO, 1967; GREENBERG and TROESBER, 1942; PANY, 1967). Yet in contradiction to the findings of other workers, we have found a highly significant discrimination in favor of Ca for the bone accretion rate (vo+). These results have raised the question whether the lower accretion of Sr was only the consequence of the faster urinary excretion, or if it was really an independent process.

Correct setting of the patient dose within a range of about +/- 3% is only achieved if a second exposure monitoring system controls the output variations of a betatron beam. A sealed thimble chamber attached in the centre of the field on the patient, which switches off the betatron when a given exposure has exceeded proved as a safe device.

The purpose of this research was to analyze simultaneously the effect of 4 factors (metal conditioning, bonding agent, metal silicoating and water storage) on the tensile behavior of a Bis-GMA resin (microfilled) bonded Ni-Cr-Be alloy by analysis of variance with a multifactorial design. The results showed that metal surface conditioning and the presence of bonding agent had no effect. In contrast, water storage of 33 days or silicoating influenced significantly and positively the tensile bond strength. In addition, 2 significant factor-interactions were detected: a) between silicoating and water storage and b) between metal surface conditioning (sandblasting/etching) and silicoating. Metal sandblasting followed by silicoating reacted more favorably than the combination etching/silicoating. In all cases the mechanochemical adhesion (silicoating technique) resulted in a composite bond strength that was far superior to that of conventional, pure mechanical bonding.

The X-ray induced conductivity in DNA films of 50 mu m thickness was investigated. The current increases linearly with the exposure-rate and, below the saturation value, also with voltage. The product of the mobility and the charge carrier life-time was found to be approximately 10-7cm2/v.

The cytotoxic methylhydrazine derivative N-isopropyl-p-(2-methylhydrazino-methyl) benzamide hydrochloride (Natulan(R)) degrades DNA in solution by a similar mechanism to ionizing radiation. The combined treatment of DNA with ionizing radiation and with Natulan(R) causes more double breaks of DNA molecules than would be expected from a simple summation of the effects of radiation and of the cytotoxic agent. The synergism between ionizing radiation and Natulan(R) is demonstrated by means of dose-effect curves. To obtain the greatest synergistic effect Natulan(R) has to be added immediately after termination of irradiation. No synergism can be observed between irradiation and a cytotoxic compound of the alkylating type (“Nitrogen Mustard”.) It is suggested that the unstable peroxide products formed during irradiation of DNA are responsible for the synergism between irradiation and Natulan(R).

The rate of loss of charge, measured with a string electrometer, is dependent in addition to physical factors on the variance of the observer's reaction time. It has been shown on one skilled observer that this parameter is significantly reduced with chlordiazepoxide (Librium) compared with placebo.

It can be shown that the so-called “cross membrane” in the node ofRanvier, which occurs only in the specialized circumstances of low condensor aperture, does not really exist. It is interpreted as a kind ofBecke line.