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Biomedical subjects

P Lockowandt

Publications and source records attributed to P Lockowandt.

At least 19 recordsLinked to original sources
PubMed1998

Accuracy of irreversible hydrocolloids (alginates) for fixed prosthodontics. A comparison between irreversible hydrocolloid, reversible hydrocolloid, and addition silicone for use in the syringe-tray technique.

One reversible, seven irreversible hydrocolloids and two addition silicones were examined. The aim was to study their ability to reproduce six differently shaped abutments of a full arch stainless steel master model correctly, by measuring: 1) the accuracy of irreversible hydrocolloid impressions with different storage periods of 15 min, 2 h, 24 h and 95 h, reversible hydrocolloid stored 15 min and 2 h, and Type III addition silicones stored 24 h when the syringe-tray technique was used; and 2) whether mixing technique or tray design had any influence of the accuracy of irreversible hydrocolloid impressions. All the tested impression materials had difficulties in producing full arch casts, where the six abutments were correctly reproduced, because 58% of the heights and 45% of the diameters of the occlusal surfaces were shorter than the corresponding distances of the master model. Storage time, mixing technique and tray design were of significant importance for the irreversible hydrocolloids. Concerning the accuracy at the gingival margin, a shorter storage time resulted in improved accuracy, and mechanical mixing without a vacuum and a tray designed similar to a perforated stock tray gave most accurate impressions.

Alginates↗
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↗
PubMed1993

Crown retention and cyclic loading (in vitro).

Cast gold crowns were luted on extracted and prepared human teeth with zinc phosphate cement and subjected to a fatigue test by cyclic loading. The correlation between crown retention and three retention variables was determined by the fatigue test. The results show that the smallest convergence angle tested, 20 degrees, gave better retention than did angles of 40 degrees and 60 degrees, and that surface roughness, surface size, height, and base diameter of the preparations had no influence on crown retention within the parameter sizes tested.

Crowns↗
PubMed1993

Vertical forces developed by the jaw elevator muscles during unilateral maximal clenching and their distribution on teeth and condyles.

The activity of the jaw elevator muscles (EMG) was recorded during maximal clenching in ICP and unilaterally on 2nd and 1st molars, premolars, canines and central incisors in ten subjects with complete dentitions, normal occlusal relationships, and without signs and symptoms of craniomandibular disorders. The EMG activities were converted to relative muscle force. The distribution of this relative muscle force on teeth and condyles was then calculated by means of a three-dimensional mathematical model. The results suggest that the magnitude of the muscle force is strongly associated with the localization of the biting point. Thus the greatest muscle force is produced during clenching in the intercuspal position (100%). At unilateral clenching 75% of this ICP-force is reached during rubber pad clenching on 2nd molars, 85% during rubber pad clenching on 1st molars and 45% during clenching on incisors. The calculations of the mathematical model showed then that highest bite force should be produced on 2nd molars (55% of the muscle force produced in ICP-clenching) and lowest on incisors (20%). Highest condylar load should be found on non-biting side condyles (20% of the muscle force produced in ICP-clenching) and lowest on biting side condyles (0%).

Adult↗
PubMed1991

[Restorative materials and initial pellicle formation].

Information concerning initial pellicle forming (dental cuticle) are possible via contact-angle determination. Not only the type of the restorative material but also its surface processing (structure) influence the initial forming of the pellicle. The higher the surface energy of a material, the more complete and quicker the masking of the surface by the initial pellicle.

Dental Deposits↗
PubMed1989

[The porosity, microhardness, roughness and internal stresses of PMMA base materials in relation to their isolation. 1. Porosity and microhardness].

Selected material properties of hot and cold polymerized denture basic materials (polymethylmethacrylate) were investigated after different methods of isolation: alginate, tin foil and silicone. Both tin foil and silicone isolation the handling of which is much easier result in a decreased portion of porosities and an increased microhardness in the PMMA.

Dental Materials↗
PubMed1989

[Porosity, microhardness, roughness and internal stresses of PMMA base materials depending on the isolation method. 2. Roughness and internal stresses].

In the present paper hot and cold polymerized denture basic materials were investigated after isolation by means of alginate, tin foil and silicone. Measurements of roughness and internal stresses after polymerization show that the advantages of a silicone isolation correspond to those of a tin foil isolation, where the clinically important smoothing effect of a silicone isolation is convincing using simple laboratory handling.

Dental Materials↗
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↗
PubMed1976

An equipment for standardized casting of Co-Cr alloys in dentistry.

The temperature and the chemical character of an acetylene-oxygen flame change with change in the gasmixture. When heating a Co-Cr alloy with this flame both temperature and chemical character in the parts of the flame used may influence the temperature increase of the alloy. To study the influence of different acetylene-oxygen flames on the heating process of dental Co-Cr alloy, a gasmeasuring and casting equipment was constructed. This made it possible to cast in a standardized way.

Acetylene↗