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Biomedical subjects

M Frentzen

Publications and source records attributed to M Frentzen.

At least 19 recordsLinked to original sources
PubMed1992

[Laser-induced photoacoustic effects in the dentin].

To study photoacoustic effects in dentin caused by UV-laser ablation, laser-induced shockwaves were measured using piezoelectric PVDF films. Above the tissue-specific energy threshold for photoablation the amplitude of the acoustic shock waves is proportional to the applied laser energy density. Laser energy densities of 2 J/cm2 cause pressure amplitudes of 50 bar, densities of 20 J/cm2 cause pressure amplitudes of 1000 bar. To avoid microcracks in dentine the maximum laser energy density to prepare dentin should be limited to approximately 20 J/cm2.

Biophysical Phenomena↗
PubMed1992

Excimer lasers in dentistry: future possibilities with advanced technology.

The thermal side effects of carbon dioxide and neodymium:yttrium-aluminum-garnet lasers limit their clinical applications. These high-powered, infrared lasers result in zones of charring and carbonization even in soft tissues and the bone. In contrast, the pulsed, ultraviolet radiation emitted by excimer lasers causes limited thermal, denaturative damage to surrounding tissues. Therefore, treatment of dental tissues with the nonthermal process of photoablation with excimer lasers may present alternatives to traditional dental practice. Possible future applications of the excimer laser include selective caries removal, the conditioning of tooth surfaces, and cleaning of root surfaces; the zones of necrosis are small, so that there is no residual debris.

Dental Caries↗
PubMed1991

Purification and cDNA sequencing of an oleate-selective acyl-ACP:sn-glycerol-3-phosphate acyltransferase from pea chloroplasts.

The soluble acyl-ACP:sn-glycerol-3-phosphate acyltransferase from chloroplasts of chilling-sensitive and -resistant plants differ in their fatty acid selectivity. Enzymes from resistant plants discriminate against non-fluid palmitic acid and select oleic acid whereas the acyltransferase from sensitive plants accepts both fatty acids. To use this difference for improving plant chilling resistance by biotechnology the gene for an oleate-selective enzyme is required. Therefore, the oleate-selective enzyme from pea seedlings was purified to apparent homogeneity. Tryptic peptides of internal origin were sequenced. Polyclonal antibodies raised in rabbits were used for an immunological screening of a pea leaf cDNA expression library in lambda gt11. A positive clone of 1800 bp was selected showing an open reading frame which codes for 457 amino acids. The deduced amino acid sequence coincides perfectly with the tryptic sequences. A tentative assignment of the processing site was made which divides the preprotein into a mature protein of 41 kDa in accordance with experimental findings and a transit peptide of 88 amino acids. At present the comparison between a selective (pea) and an unselective (squash) acyltransferase sequence does not provide a clue for recognizing the structural differences resulting in different selectivities.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1991

[Root canal preparation using Excimer lasers].

As an alternative in endodontics to mechanical methods for root canal treatment, the use of a XeCl-excimer laser to prepare the canal wall was studied. In a light microscopic investigation undecalcified sections of laser-treated extracted human teeth showed that it was not possible to remove dentine in the root canal. Pulpal tissues remained in all wall areas. The available energy densities of this laser type seem to be not sufficient to ablate pulpal tissues or wall dentine.

Dental Cavity Preparation↗
PubMed1991

[Laser technology in dentistry].

Although dental laser treatment is receiving great attention in basic and clinical research, only very few clinical applications have emerged as accepted standard methods. The most promising range of possible applications includes diagnostics and surgery. Most laser systems developed for therapeutic use are heat-producing units, i.e. they convert electromagnetic energy into thermal energy. These systems are employed above all in oral surgery for vaporization, cutting or coagulation of soft tissues and in prosthodontics for welding. More recently, new types of lasers have been developed allowing non-thermal modes of tissue interaction. A great number of technical and biological problems will have to be solved, however, before these laser systems will be practically applicable in such clinical fields as, for instance, caries therapy. In the near future, laser systems are expected to complete and supplement conventional methods in diagnosis and treatment, but not to replace them.

Dental Caries↗
PubMed1991

[Ultrasonic root cleansing with 0.1% chlorhexidine gluconate as a coolant].

In 10 patients with marginal periodontitis a systemic periodontal treatment approach was employed in which the root surfaces were cleansed by exclusive use of ultrasound. The effect of 0.1% chlorhexidine gluconate as a cooling medium during the application of ultrasound was studied in a cross over design study. PI, GI, SBI and the probing depths at 6 sites per tooth as well as the clinical attachment levels were the parameters for evaluating the treatment effect. An improvement of the clinical findings was observed during initial treatment both in the test and the control group. Except for PI, which was better after chlorhexidine gluconate application, no obvious differences could be found.

Adult↗
PubMed1990

Intraorganelle localization and substrate specificities of the mitochondrial acyl-CoA: sn-glycerol-3-phosphate O-acyltransferase and acyl-CoA: 1-acyl-sn-glycerol-3-phosphate O-acyltransferase from potato tubers and pea leaves.

The mitochondrial sn-glycerol-3-phosphate and 1-acyl-sn-glycerol-3-phosphate O-acyltransferases from potato tubers and pea leaves were investigated with respect to their intraorganelle localization, their positional and substrate specificities, and their fatty acid selectivities. In mitochondria from potato tubers both enzymes were found to be located in the outer membrane. The 1-acyl-sn-glycerol-3-phosphate O-acyltransferase of pea mitochondria showed the same intraorganelle localization whereas the sn-glycerol-3-phosphate O-acyltransferase behaved like a soluble protein of the intermembrane space. The sn-glycerol-3-phosphate O-acyltransferase of both potato and pea mitochondria used sn-glycerol-3-phosphate but not dihydroxyacetone phosphate as acyl acceptor and exclusively catalyzed the formation of 1-acyl-sn-glycerol-3-phosphate which subsequently served as substrate for the second acylation reaction at its C-2 position. Both acyltransferases of potato as well as pea mitochondria showed higher activities with acyl-CoA than with the corresponding acyl-(acyl carrier protein) thioesters. When different acyl-CoA thioesters were offered separately, the sn-glycerol-3-phosphate O-acyltransferase of potato mitochondria displayed no fatty acid specificity whereas the enzyme of pea mitochondria revealed one for saturated acyl groups. On the other hand, the mitochondrial 1-acyl-sn-glycerol-3-phosphate O-acyltransferases from both potato tubers and pea leaves were more active on unsaturated than on saturated acyl-CoA thioesters. Furthermore, these enzymes preferentially used oleoyl- and linoleoyl-CoA when they were offered in a mixture with saturated ones, although the fatty acid selectivity of the pea enzyme was less pronounced than that of the potato enzyme. The sn-glycerol-3-phosphate O-acyltransferase of potato mitochondria displayed a slight preference for saturated acyl groups.

1-Acylglycerol-3-Phosphate O-Acyltransferase↗
PubMed1990

Correlation between caries prevalence (DMFS) and periodontal condition (CPITN) in more than 2000 patients.

The CPITN (Community Periodontal Index of Treatment Needs) and DMFS (Decayed-Missing-Filled Surfaces) index were evaluated simultaneously to provide information on the mutual influences of periodontal disease and caries. With the aid of an electronic database system the data of the caries index and periodontal index of more than 2000 patients aged between 18 and 80 years were stored and calculated. As expected, the CPITN and DMFS values increased with age. When the CPITN was selected as a reference the DMFS was found to change with increasing CPITN. With the examination method used in this study no correlation could be established between the prevalence of caries and periodontal condition, although both conditions have a common aetiological factor: microbial plaque.

Adolescent↗
PubMed1990

[Spectroscopically controlled preparation of hard tooth structures using a UV laser].

During preparation of hard tooth structures with a 193nm-(ArF)*-excimer laser, the laser beam produces a specific fluorescent light whose spectrum is governed by the structure of the specimen. These fluorescence spectra allow an analysis of the removed tissues. The data thus obtained may be used to control the laser system so that only specific structures, such as carious tissue, are removed: reproducible fluorescence spectra were established by means of standardized samples (pure synthetic hydroxyl apatite ceramics, enamel, dentine and carious dentine) and the characteristic absorption bands (peaks) for the different substances were measured. With the aid of electronic data processing these reference spectra could be compared with the fluorescence spectra obtained during preparation. When a spectrum differed from the predefined limits of relative intensities, preparation was stopped. Since ablation per pulse is only to a small depth (0.04-4 microns) with the 193nm-(ArF)*-eximer laser, this feedback system of ablation and fluorescence spectroscopy allows decisions as to continuing or stopping the preparation process to be taken within the range of a few microns.

Dental Cavity Preparation↗
PubMed1990

[Thermal effects in the dental pulp caused by laser radiation from various laser types].

In this in vitro study the temperature rises occurring in the dental pulp during laser irradiation were measured. Infrared laser radiation (CO2 and Nd: YAG) had great thermal effects on the pulp tissues. At an average power output level of 5 W temperature rises of approx. 40 degrees C within 100 s were observed. The effect of a cooling system was negligible. Radiation from an ArF excimer laser (193 nm) at an average output of 5 W caused only slight thermal changes, when an airstream was used to remove the fragments of photoablative decomposition of the dental tissues. The temperature in the pulp chamber increased by approx. 5 degrees C after 6 min. This result leads to the conclusion that only ArF excimer lasers may be effectively used in the mouth without producing inacceptable thermal effects in the dental pulp.

Dental Pulp↗
PubMed1990

Lasers in dentistry: new possibilities with advancing laser technology?

Although there are a considerable number of published papers on the role of laser treatment in dentistry, a critical review shows that laser technology is used only by specialists in a small therapeutic field. Most lasers are heat-producing devices converting electromagnetic energy into thermal energy. These lasers find uses in oral surgery for cutting or coagulating soft tissues or in the welding of dental prostheses. More recently, new types of lasers have offered non-thermal modes of tissue interaction, called photoablation, photodisruption and photochemical effects. Basic and clinical research is being carried out into the application of these devices in dentistry. However, much development will be required before lasers can replace conventional surgical methods for treating oral cancer or indeed replace the conventional bur for excavating carious lesions.

Dentistry↗
PubMed1989

[Surgical laser in dentistry in 1989].

After many years of microscopie, cellular and molecular studies, the use of Laser rays progressively developed in dentistry. This therapeutical "tool" is now well established in numerous dental fields: cariology, pathology of oral mucosa, periodontics... The Europeans have great advance in this research area and current progress is the clear proof of their work efficiency.

Dental Pulp Diseases↗
PubMed1989

[Preparation of hard tooth structure with Excimer lasers. In vitro study].

The present study will show, that caries removal and conditioning of tooth surfaces by an (ArF)*-Excimer-Laser is an alternative to conventional preparation methods without thermal and mechanical irritations. This promises caries removal without pain to the patient. The photoablative process leads to retentive surfaces of the treated cavities. These findings promise good results in adhesive techniques. In vitro studies show, that photoablation of dental tissue is effective enough to make clinical usage possible.

Dental Caries↗
PubMed1989

[Preparation of hard tooth structure with Excimer lasers].

In this study the possible application of photoablation with an Excimer UV laser for the creation of retentive surfaces was studied as an alternative to conventional enamel conditioning methods using acids. Surfaces of untreated enamel and of prepared cavities were irradiated with an argon fluoride Excimer laser at a wavelength of 193nm and evaluated in a scanning electron microscope. The bond strength of composites to these surfaces was measured in tear tests. "Laser conditioning" left the surfaces similarly roughened as chemical etching. The variable extension of the laser field allows a sharp delineation of the area to be conditioned. The tear tests with human tooth enamel showed bond strength values corresponding to approx. 75% of those obtained by acid etching techniques. The question if these bonds are durable is the subject of current studies.

Adhesiveness↗