Biomedical subjects

L A Lindén

Publications and source records attributed to L A Lindén.

At least 19 recordsLinked to original sources

PubMed1999

Highly cross-linked networks for dental applications obtained by photocuring of tris[2-(acryloyloxy)ethyl]isocyanurate, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate, and pentaerythritol triacrylate.

Highly cross-linked networks have been obtained by photoinitiated camphorquinone-amine polymerization of tris[2-(acryloyloxy)ethyl]isocyanurate alone and/or with 2-ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate or pentaerythritol triacrylate, which can be considered a new class of dental restorative resins. The most effective coinitiators in this system are amines such as ethyl-4-dimethylaminobenzoate, N,N-dimethyl-benzylamine, and 2,4,6-tris(dimethylaminomethyl)phenol. The volume shrinkages of polymerized samples were 8%-13%. The hardness of photocured resins in the presence of an inorganic filler (aluminum/fluoro/silicate glass, Ketac-Fil was slightly less than that of a restorative composite material (Z100 MP).

Acrylates↗

PubMed1997

Comparison of strength and failure mode of seven implant systems: an in vitro test.

STATEMENT OF PROBLEM: The mechanical weakness of implant systems is a problem in the clinical situation. PURPOSE: This study experimentally evaluated how joint design influences the strength and failure mode of dental implant systems. MATERIAL AND METHODS: The strength tests focused on the systems as a whole. Seven implant systems with different joint design were evaluated. RESULTS: Strength and failure mode varied significantly between the implant systems and deep joints, in contrast to shallow joints, favored resistance to bending moments. The mean failure force ranged between 138 to 693 Newtons for the various implant systems. CONCLUSION: In construction of implant systems, joint depth should be taken into consideration.

Analysis of Variance↗

PubMed1996

Irreversible hydrocolloids for crown and bridge impressions: effect of different treatments on compatibility of irreversible hydrocolloid impression material with type IV gypsums.

OBJECTIVES: The aims of this research were: 1) to determine if the compatibility between irreversible hydrocolloids (alginates) and type IV gypsums (die stones) is affected by different treatments of the impressions before pouring, and 2) to present a rating system based on Ryge's system for clinical evaluation in order to classify the quality of gypsum casts using detail reproduction and surface structure as criteria. METHODS: Impressions were taken on a Plexiglas staircase (heights of the steps 15-82 microns) with six irreversible hydrocolloids designed for crown and bridge and ten type I and II irreversible hydrocolloids. Impressions of each brand were divided into four groups. One group was treated with 2% potassium sulfate, the second with water, the third with an alginate stabilizer, Sorbanat (Guilini Chemie), and as a control, a fourth group which was not allowed to come into contact with any liquid, i.e., the impressions were poured dry. The differently treated impressions were poured with ten type IV gypsums. The quality of all gypsum casts was then judged according to the rating system. RESULTS: All the irreversible hydrocolloids, if correctly treated before pouring with a compatible gypsum, could reproduce details of 20 microns. Detail reproduction did not improve with the use of 2% potassium sulfate solution compared to water or if the impressions were poured "dry". In general, the alginate stabilizer produced casts with significantly better detail reproduction and surface structure. SIGNIFICANCE: The results show that dentists and dental technicians need to know how each specific irreversible hydrocolloid should be treated and also with which type IV gypsum it is compatible. This research also indicates that an irreversible hydrocolloid impression should not come into contact with any liquid within the first 15 min.

Alginates↗

PubMed1995

Human dentine as a hydrogel.

The pores (tubules) of human dentine in 0.02-cm planoparallel sections of newly extracted permanent teeth were investigated. By the conventional scanning electron microscopy these pores appear empty, but by the newly developed scanning-probe microscopy the presence of a complex matrix could be established. By measuring the transport of neutral myoglobin by diffusion alone and diffusion+bulk flow, the area of dentine occupied by the matrix was calculated to be 1.9 +/- 0.9% and 2.3 +/- 0.5%, respectively. The hydraulic conductivity was surprisingly small, 1.35 +/- 0.55 x 10(-7) ml/(s.cm2 dentine) at a pressure difference of 0.1 kPa across a 1-cm thick section. This suggests a hydrogel with a relatively dense network, the width of meshes estimated at 2 x 30 nm. In line with this concept, enzymatic degradation of the organic matter increased the hydraulic conductivity 3000 times. By studying the transport of negatively charged myoglobin, the matrix was calculated to carry 18 mEq/l of positive charges. Due to the consequent attraction of small, negative ions and thence of water, the pressure within the matrix would be about 1.33 kPa, a force which will act to immobilize the water in the channels. The concept of a hydrogel in the dentine tubules was also supported by the finding that shielding the charges with bathing media of high ionic strength reduced the hydraulic conductivity.

Adolescent↗

PubMed1989

Variation in human salivary pellicle formation on biomaterials during the day.

Contact angle measurements were used to study the effects of pellicle formation on polymethyl-methacrylate, dental amalgam and gold. Samples were exposed to saliva in vivo for periods of 5-20 min at three separate occasions during the day. Pellicle drastically increased the wettability of all the materials and effectively sealed off the effect of the original surface activity. Variation in pellicle formation during the day was demonstrated. Pellicles formed at midday showed the least reduction in contact angles compared to those formed during the morning and afternoon. This difference coincided with an increased concentration of inorganic phosphate in saliva at midday. The method enables comparative studies of pellicle formation on hard biosurfaces. The findings indicate differences in the physical behaviour of saliva during the day, and illustrate the importance of making adhesion studies with this variation in mind.

Adhesiveness↗

PubMed1988

Permeability of amalgam restorative materials.

The beneficial effect of fluoride-containing amalgam in preventing recurrent dental caries depends on the ability of the material to deliver fluoride (F). A two-chamber diffusion cell has been employed to monitor the diffusion of F in freshly prepared amalgam sections (membranes) as well as in amalgam sections stored in F solution for 15 d. The diffusion of 125I was also monitored, as a reference. Five and ten successive measurements at 72 h intervals were made on the fresh and stored amalgam specimens, respectively. The average diffusion coefficient, D, of F and 125I in fresh amalgam was 2.39 x 10(-10) and 1.85 x 10(-10) cm2/s, respectively. For stored amalgam, the average D of F during a 30 d experiment was 1.35 x 10(-10) cm2/s. The average D of F in stored amalgam, during the first 15 d of the experiment, was 31% less than in fresh amalgam (p less than 0.01). A decline in the diffusion process was observed during the course of the experiments. During 15 d diffusion in fresh amalgam and 30 d diffusion in stored amalgam the cumulative diffused F were 0.79 and 0.88% of the F in the source. SEM findings revealed the deposition of corrosion products on amalgam stored for 3 months in 0.19% F solution.

Dental Amalgam↗

PubMed1986

The diffusion in vitro of fluoride and chlorhexidine in the enamel of human deciduous and permanent teeth.

The permeability of human dental enamel was studied by following the diffusion of [51Cr]-ethylenediaminetetraacetate (EDTA), F and [14C]-chlorhexidine using two-chamber diffusion cells. The [51Cr]-EDTA served as a marker to control the change in enamel permeability during the diffusion process. An average increase in enamel permeability of about 1.6-fold was recorded following the initial diffusion of the test compounds in the deciduous and permanent enamel. The permeability of deciduous enamel was much higher than that of permanent enamel. For [51Cr]-EDTA and [14C]-chlorhexidine, the average diffusion coefficient was about 30-fold more than in permanent enamel; for F it was 150-fold more. The difference was statistically significant (p less than 0.001). Co-administration of F and [14C]-chlorhexidine showed a higher diffusion rate for each compound than when separately diffused. Whether this is due to a synergetic effect or to increased enamel permeability following the initial diffusion of the compound, or both, is still uncertain.

Adolescent↗

PubMed1984

Micro-determination of phosphate in enamel biopsy samples using the malachite green method.

A simple and sensitive malachite green method was adapted for the determination of phosphate in enamel demineralizing solutions. Comparison with other methods indicates that malachite green was about 60 times more sensitive than Fiske and Subbarow's method and 10 times more than that of Chen et al. The high sensitivity of this method allows very small biopsy samples to be used. The linearity is good between the tested range of 0.025-3.0 mM P. The relative standard deviation was low and amounted to 1.4% in duplicate determinations. No statistical differences in phosphate concentration of enamel biopsy samples determined by the three methods were found. Fluoride concentration up to 80 micrograms/ml did not interfere with phosphate determined by the malachite green. For sampling enamel, the acid-etch technique was used, and the fluoride concentration at successive demineralization runs was monitored using fluoride-ion electrode.

Calcium↗

PubMed1984