Biomedical subjects
Publications and source records attributed to K J Reinhardt.
The marginal situation of class I restorations is determined by the intensity of the light used for curing. In all composites the use of an intensive light-source (Osram HBO 100) leads to marginal gaps. This effect was demonstrated in three composites cured with light sources that are commonly used in practice.
Using differential scanning calorimetry (DSC) a post-curing effect of 3.8% could be observed. In accordance with these data a heat-induced polymerization of photocured composites of up to about 3% was found by FMIR infrared spectroscopy. In a single case the additional degree of cure was 15%. After heat treatment the degree of conversion in areas deeper than 50 microns was 75% to 79%. In the outer layer the content of unconverted double bonds could not be reduced by heat treatment. The degree of conversion here was 54% to 72%. Thus, the effect of this post-curing procedure is limited to the bulk material.
Extraoral post-curing of composite inlays with the exclusion of oxygen is possible, by completely covering them with glycerin during the post curing process. This combined light and heat application improves the polymerization of inhibited surfaces as well as insufficiently cured parts of the inlay. Thus, an adequate homogenization of the composite material can be achieved. Surfaces treated without access of oxygen contain about 21 to 26% of double bonds, while surfaces treated in the conventional way contain about 28 to 48% of double bonds. The efficiency of this new post-curing technique is hardly influenced by conventional post-curing measures carried out prior to this procedure.
The marginal adaptation of six composites and one resin based inlay system was investigated. For all fillings maximum stress increased with time. Three days after insertion maximum stress increased up to more than 450 N for almost all fillings.
SEM studies of six visible light-cured composites showed no difference between the morphology of the layered area and of the compact zones, unless the inhibited layers are removed from the polymerized portions. Only in plugable materials did the removal of these layers result in an increased formation of air bubbles and in an interface of 10-20 microns thickness interspersed with cavities. The transverse strength of these specimens was in part approx. 35% less than in the control material. In all materials studied removal of the inhibited layers at their points of attachment resulted in an average decrease of transverse strength by 26%. When the inhibited layers were left in place this reduction was rarely more than 17%, on an average less than 13%. This slight reduction in the transverse strength of attached specimens with the inhibited layer retained may be attributed to the ability of this layer to polymerize when reirradiated after the exclusion of oxygen.
Analysis of the interfaces and contact surfaces of polymerized composites by infrared spectroscopy showed the amount of unconverted double bonds to be 29% to 48%. This conversion is limited to a surface layer of about 20 microns thickness and usually does not reveal any information on the quality of the bulk material. In depths of more than 60 microns, the amount of unconverted double bonds was 18% to 32%. An influence of polishing could not be proved. Samples containing more than 35% of unconverted double bonds tend to be highly susceptible to discoloration. Removing those layers improves color stability.
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Class I inlays were produced according to the direct method using six white light-cured composite, one inlay material and one veneer acrylic. They were subjected to extraoral heat treatment at 125 degrees C for 150 s. In addition, heat-cured inlays were produced according to the indirect method. In all cases heat treatment resulted in a considerable increase in transverse strength and modulus of elasticity as well as a material specific decrease in the specimen volume between 0.15% and 1.05%, and it facilitated finishing. With one exception heat-treated and heat-cured inlays could be inserted without open margins; even 5000 threshold load cycles of 500 N failed to cause marginal defects. However, these inlays also had no open margins when inserted without previous heat treatment. While in the case of four materials this resulted in no measurable reduction in fatigue strength, it reduced this value to a maximum of 100 N in three materials. Swelling of the polymeric inlays due to high water absorption resulted in extensive enamel cracks with one of the materials tested.
Threshold load tests have shown that the fatigue strength of Class I composite fillings may be increased up to 150 N by the application of a base material. This effect varied only with the consistency of the composite, not with the type of base material used. However, differences were found in the depths at which losses of marginal adaptation occurred: where glass ionomer cement base (polyalkenoate) was used, marginal leakage demonstrated by pigment penetration tests stopped at the interface between filling and base, while in those cases where phosphate cement was used as base material, pigment penetration was shown to extend down to the floor of the cavity. Mesiodistal sections through Class II MOD restorations with the same combinations of materials after 24 hours of storage in pigment solutions and without loading revealed that a close marginal fit in the area of the cervical step can be obtained with the use of glass ionomer cement as base material. In contrast to this observation the use of phosphate cement as base material is associated with marginal leakage down to the area of the floor of the cavity in about one half of the restorations.
Comparative in vitro trials concerning the problem of cavity liners detaching from the floor of the cavity when combined with photopolimerizable filling material demonstrated that gap formation occurred only if slowly setting glass ionomer cement was used. No such effect was seen with fast setting glass ionomer cement or phosphate cement. Gap formation is due to the curing process of slowly setting glass ionomer cement.
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Explore the source record for details and available documents.
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Cauterized dental enamel was fluoridized with a solution of sodium monofluorophosphate. Using ESCA methods of measurement, it was demonstrated that almost the entire amount of absorbed fluoride was present in the form of fluorphosphate.