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Biomedical subjects

F Lutz

Publications and source records attributed to F Lutz.

At least 145 records · Page 8Linked to original sources
PubMed1991

[The marginal adaptation of Cerec-Dicor-MGC restorations with dentin adhesives].

Dicor MGC Cerec inlays were placed in 53 teeth clinically and in 24 extracted teeth. Both main groups were subdivided into the following four test subgroups: 1. monofunctional dentin adhesive without linings. 2. bifunctional dentin adhesive without linings. 3. monofunctional dentin adhesive with linings. 4. bifunctional dentin adhesive with linings. The marginal adaptation of the occlusal surfaces of the restorations placed clinically was evaluated from replicas using the scanning electron microscope at x 200 magnification. In contrast, the marginal adaptation of all the restored enamel surfaces and the disto-cervical dentinal margins of the restorations placed in the extracted teeth were similarly evaluated. These margins were examined before and after thermomechanical stressing. The restorations were stressed 120,000 times at 300 cycles of 5-55-5 degrees C, chemically degraded by immersion in ethanol of 75% for 20 h and brushed for 30 min with a toothbrush at 1,96 N load. The in-vitro restorations were also subjected to dye penetration tests. The percent "excellent margin" recorded along the enamel-composite interface of the occlusal surfaces of the clinically placed restorations varied between 83.6 and 88.2%. The corresponding scores for the in-vitro specimens were at least 95% before and 90% after the thermomechanical and chemical stressing. The bifunctional dentin adhesive "Prisma Universal Bond 2" had a 93.6% "excellent margin" along the dentin-composite margin before stressing which decreased to 84.4% after stress. These scores were not significantly different.

Ceramics↗
PubMed1991

[The finishing of adhesive tooth-colored inlays made of composite and ceramic].

The destruction potential of 4 different finishing and polishing systems was evaluated using 104 occlusal direct inlays made from composite and ceramic, respectively. An inhomogeneous microfilled composite, a fine particle hybrid composite, a glass ceramic and a fine porcelain were utilized as filling materials. Finishing diamonds, white stones, flexible discs and silicon rubber polishing cups were examined as finishing and polishing instruments. Replicas were examined using a scanning electron microscope (SEM) to reveal enamel, composite and inlay margin fractures. Results were described as percentages of perfect margin. The surface roughness of composite and ceramic blocks was measured by means of a profile meter after surface finishing and polishing with the instruments mentioned above. Except for the fine porcelain, the flexible disc finishing and polishing system provides constantly the best results with greater than or equal to 95% of excellent margin. Similar results were achieved by fine finishing diamonds only. The surface roughness was reduced significantly by the flexible discs and by silicon rubber polishers only. Finishing diamonds and flexible discs are the most suitable instruments for finishing and polishing of tooth-colored adhesive inlays. They are nondestructive against enamel, the inlay and the cement surfaces.

Ceramics↗
PubMed1991

Quantitative in vivo evaluation of four restorative concepts for mixed Class V restorations.

This study was performed in vivo over a 6-month period to assess restorative margins in Class V restorations placed with different techniques. The margins were evaluated quantitatively under the scanning electron microscope using the replica technique. Results indicated that the sandwich technique using a glass-ionomer cement base and a composite resin restoration was not able to prevent marginal gaps in dentin. However, the experimental Gluma/Clearfil system resulted in a quality of dentinal margins not statistically significantly different from that of enamel margins. These in vivo findings substantiate in vitro results.

Adhesives↗
PubMed1991

Enamel remineralization: how to explain it to patients.

The term remineralization of initial enamel caries is frequently used, but mainly at research conferences and in lecture rooms. Clinicians avoid discussing remineralization and white-spot enamel lesion formation with patients because details of the processes are complex. Patients, therefore, incorrectly assume that cavitation occurs right at the onset of caries and that a restoration must be placed to halt further progression of the lesion. Although laboratory and clinical studies have shown that initial white-spot enamel lesions can remineralize, patients have little or no access to this information. The schematic diagrams in this paper explain the diffusion of organic acids from plaque between enamel crystals, the partial loss of mineral from enamel crystals, and subsequent demineralization and remineralization that produces the white-spot lesion. Further, these diagrams may help clinicians explain remineralization as simply as possible to patients who present with white-spot enamel lesions.

Dental Caries↗
PubMed1991

[The hydrodynamic behavior of dentinal tubule fluid under occlusal loading].

In an in-vitro study, the fluid movements were quantitatively recorded in natural teeth incorporated rigidly in a closed measuring system and exposed to an occlusal load of 122.6 N. Fluid movements under load are the result of elastic deformations of the tooth. Occlusal loads which were repeated within a short period of time caused a reversible plastic deformation. In comparison to the unfilled tooth the placement of an MOD restoration combined with a glass ionomer cement base caused the following alterations in fluid movements: composite inlay -24.7%, ceramic inlay +34.7%, MOD amalgam -3.1%; the placement of the base per se induced a reduction of -12.7%. In this in-vitro study, the physical properties of the restorative materials governed the magnitude of the fluid movements under load. The results are in contradiction to clinical findings and favor the pulpitis-related genesis of postoperative sensitivity. The intratubular and intrapulpal fluid movements under occlusal load simply seem to trigger the pain sensation.

Biomechanical Phenomena↗
PubMed1991

[The x-ray opacity of tooth-coloring inlay materials and composite cements].

For a proper radiographic diagnosis of secondary caries and interproximal overhangs or undercuts, tooth colored inlays and their appropriate luting agents have to be radiopaque. With the help of a spectrophotometer the radiopacity of 1 mm thick samples made of enamel, dentin, seven tooth colored inlay materials and seven composite cements was quantitated and related to 99.5% pure aluminum. The mean radiopacity values of three inlays (two of them significantly, p less than 0.05) and of three composite cements (one of them significantly, p less than 0.05) were lower than enamel. All other materials tested exhibited a higher radiopacity than enamel. A radiopacity value of 1 mm thick samples greater than 2.5 mm of 99.5% pure aluminum is advocated by the authors. Four of the materials tested fulfilled this requirement.

Color↗
PubMed1990

The cytotoxin of Pseudomonas aeruginosa: cytotoxicity requires proteolytic activation.

The primary structure of a cytotoxin from Pseudomonas aeruginosa was determined by sequencing of the structural gene. The cytotoxin (31,700 Mr) lacks an N-terminal signal sequence for bacterial secretion but contains a pentapeptide consensus sequence commonly found in prokaryotic proteins which function in a TonB-dependent manner. The cytotoxin gene has a [G + C]-content of 53.8% which is considerably lower than generally observed for genes from Pseudomonas aeruginosa. The cytotoxin gene was exclusively detected in strain 158 but not in three other clinical isolates, as determined by Southern and Northern hybridization. The latter technique revealed that the toxin is translated from monocistronic mRNA. The promoter of the cytotoxin is inactive in Escherichia coli. Upon site-directed modification of the 5'-noncoding region by the polymerase chain reaction the gene was expressed under control of the trc-promoter. The gene product obtained in Escherichia coli was nontoxic. Toxicity was induced by subsequent treatment with trypsin. [35S]methionine-labeled cytotoxin with high specific radioactivity was obtained by in vitro transcription/translation. Like [125I] labeled material from Pseudomonas aeruginosa this polypeptide bound to membrane preparations from Ehrlich ascites cells, as evidenced by sedimentation through a sucrose gradient at neutral pH.

Amino Acid Sequence↗
PubMed1990

Mixed Class V restorations: the potential of a dentine bonding agent.

The marginal micromorphology and seal of mixed Class V restorations (i.e. restorations with margins located 50 per cent in dentine and 50 per cent in enamel) using Scotchbond VLC or Scotchbond 2 bonded to dentine in conventional and saucer-shaped cavities were evaluated. The four operative systems tested included a two-step incremental filling technique using the light-curing composite Silux, two direct inlay techniques using Silar or Silux as a luting cement and an inlay technique utilizing a Ca(OH)2 liner. All restoration types showed poor marginal adaptation in dentine irrespective of cavity design and bonding agent used. The inlay technique, tested in seven different variations, did not optimize marginal adaptation. Cavity lining with the Ca(OH)2 base material adversely affected dentine bonding. In mixed Class V restorations, marginal adaptation at the dentinal cavosurface line angle continues to pose a problem.

Acrylic Resins↗
PubMed1990

Human root caries: histopathology of advanced lesions.

The histopathology of human root caries was examined in extracted teeth. The present study details several stages of advanced carious lesions in root dentin. Lesions of different severities were assessed by different optical methods. Four major root caries patterns were defined and significant differences between coronal and root caries elucidated. The patterns were distinguishable by (1) their location at the exposed root surface, (2) their mode of spreading towards the root canal and over the root surface, (3) their mode of bacterial spreading in dentin and (4) the role of dentinal defense mechanisms. In addition, a comparison of clinical and histological classification of lesions revealed that the carious process extended much deeper towards the root canal and had a higher degree of both bacterial infection and dentin demineralization than could be predicted by clinical examination.

Adult↗
PubMed1990

Histopathology of root surface caries.

The histopathology of active and arrested human root caries was examined in extracted teeth by different optical methods. Significant differences were observed between the mechanisms operating on the various dental structures. Three different patterns of initial cementum and dentin lesions could be distinguished, depending on the severity of the cariogenic attack, the degree of sclerosis of the peripheral dentin, and the presence of calculus. Advanced lesions were characterized by various patterns of demineralization. In particular, a massive lateral spread of bacteria into intertubular dentin was observed. Consequently, unaffected dentinal areas became continuously undermined. In arrested lesions, either a partial or complete mineralization of the intertubular dentin was apparent. Dentinal tubules were sclerosed passively by re- or precipitation of Ca and PO4 ions. In contrast, tubules filled with ghosts of bacteria appeared mineralized by fine-granular crystals. Our observations indicate that both the arrestment and the remineralization of active lesions depend on (1) the degree of active sclerosis of dentinal tubules in areas underlying the lesion, (2) the degree of the bacterial infection of the dentin, (3) the degree of progression of the lesions, and (4) the location of the lesions at the various root surfaces. It is suggested that remineralization of active lesions can occur. This supports the concept of non-invasive treatment of root caries lesions without cavitation.

Dental Caries↗
PubMed1990

CAD-CAM ceramic inlays and onlays: a case report after 3 years in place.

At least three different techniques are available for preparing computer-aided designed (CAD) and computer-aided manufactured (CAM) inlays and veneers. This paper details a clinical case in which 13 Cerec CAD-CAM inlays have been functioning for 3 years. Advantages and limitations of this system are discussed.

Adult↗
PubMed1990

[Dentin bonding with tooth-colored adhesive MOD immediate inlays made of composites].

Without the use of highly effective dentinal adhesives, the cervical margins of tooth-colored adhesive inlays localized in dentin are poorly adapted. It was the purpose of this study to optimize these margins with the help of the Gluma-Clearfil combination. This goal was achieved, but the results indicated, that the success depended on the choice of the luting composite. Perfectly adapted cervical dentinal margins of tooth-colored adhesive inlays are achievable. For routine use, the system has to be simplified.

Color↗
PubMed1990

[P-30: in vivo study of a posterior composite during 2.5 years].

P-30, a light-cured radioopaque hybrid composite was developed as a successor to the well known chemically cured P-10 for use as posterior composite. With the help of a computerized measuring method the occlusal wear of occlusally loaded conventional P-30 MOD restorations was analyzed after 6, 12, 18 and 30 months of clinical service. Simultaneously the wear patterns in occlusal contact areas and in contact-free areas were evaluated using the SEM. In addition, marginal adaptation immediately after the placement of the restorations and at all recall intervals was quantitated in the SEM. The long-term results indicated that P-30 was not suitable for use in unetched conventional posterior cavities.

Adult↗
PubMed1990

[Meaningful combinations of chemotherapeutic agents].

It is frequently assumed that, in general, combinations of antibiotics and similar chemotherapeutic agents are more efficient than the single chemotherapeutic, and that they can be combined without disadvantages for the activity of the single component. However, the specific properties of the combined substances, such as their antimicrobial spectrum and resistance, their pharmacokinetics and side effects, as well as their physical properties and formulation, have an enormous impact on the activity of combined chemotherapeutics. They may lead to an advantageous, but also to an indifferent or diminished activity of the combination in patients. Some of the important requirements for an advantageous combination of antibiotics and similarly functioning compounds will be reviewed and ways of avoiding mistakes are described.

Animals↗
PubMed1990

[An in-vitro test procedure for evaluating dental restoration systems. 2. Toothbrush/toothpaste abrasion and chemical degradation].

The development of an in-vitro test for evaluation of dental restorative systems comprised primarily the construction of a chewing simulator, which was able to produce occlusal mechanical load and thermal cycling. This machine was described in a previous publication. Additionally, chemical disintegration and toothbrush/toothpaste abrasion have to be included in the cycle. The aim of the present study was to develop appropriate test methods to simulate the two letter parameters and to integrate these methods in the in-vitro test cycle. The results indicated, that the toothbrush/toothpaste abrasion did not show any significant effect in the occlusal contact area. Chemical cycling induced a generalized swelling of the composite samples and a modified wear curve. The toothbrush/toothpaste abrasion led to a rough composite surface in the contact-free area.

Dental Restoration, Permanent↗