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Biomedical subjects

R Hickel

Publications and source records attributed to R Hickel.

115 records · Page 7Linked to original sources
PubMedDate not supplied

Physical properties and gap formation of light-cured composites with and without 'softstart-polymerization'.

OBJECTIVES: Recently it has been pointed out that light-initiated prepolymerization at low intensity followed by a post-light-cure at full intensity ('softstart-polymerization') may lead to light-cured composite fillings with improved marginal adaptation. The aim of this study was to examine the influence of this procedure with different initial cure conditions on physical material properties like flexural modulus, flexural strength and Vickers microhardness of different composites. Additionally, an in vitro study was carried out to investigate the influence of different initial cure conditions on the marginal quality of composite restorations in cases of Class V cavities with a cemento-enamel junction. METHODS: Physical properties of composite materials Tetric (Vivadent, Liechtenstein) and Charisma (Kulzer, Germany) were evaluated. Three hundred specimens were made for the flexural tests performed similar to EN 24049:1993. Microhardness was measured with a Vickers indenter. For the in vitro study of Class V composite fillings, cavities of 32 extracted teeth were filled with Tetric and analysed by quantitative marginal gap analysis and dye penetration test before and after thermocycling. RESULTS: The results indicate that initial cure with decreased light intensity followed by final cure with high light intensity has no influence on microhardness and increases flexural modulus and flexural strength. With the low-level initial cure/high-level final cure regime the marginal integrity was significantly better compared with the high light intensity curing system. CONCLUSION: Therefore, initial cure with low light intensity followed by final cure with high light intensity significantly improves the marginal integrity of light-cured composite fillings and also the material properties.

Chemical Phenomena↗
PubMedDate not supplied

Bond strength of composite to dentin treated by air abrasion.

This study compared the bond strength of composite to dentin produced by an air-abrasive dentin pretreatment and acid etch only. Two hundred sixty extracted human molars were randomly divided into 13 groups (n = 20). An occlusal dentin surface with a defined smear layer was exposed. Dentin was conditioned either with 37% H3PO4 for 20 seconds, or an air-abrasion unit (KCP 1000, ADT) was used with 120 and 160 psi pressure and two different particle sizes, 50 and 27 microns. A combination of both treatments beginning with air abrasion was tested as well as dentin specimens without pretreatment. The dentin adhesive Syntac Single-Component was applied under dry and moist conditions. Composite cylinders with a bond diameter of 2.5 mm were bonded in two increments to the teeth. Specimens were stored for 24 hours at 37 degrees C in distilled water and then thermo-cycled for 1000 cycles (5/55 degrees C). Shear bond strength was tested using a Universal Testing Machine at 0.5 mm/min cross-head speed. Means and standard deviations in MPa were calculated. Analysis of variance and Bonferroni pairwise comparison tests were performed. Lowest bond strengths were obtained in specimens without conditioning the dentin. Air-abraded specimens showed a significantly higher bond strength than the before-mentioned groups. The comparison for acid-etched groups and air-abraded specimens revealed higher values for the abraded groups. Air abrasion with 160 psi pressure produced a significantly higher bond strength than 120 psi. There was no significant difference between the 27 and 50 microns particles. Air abrasion in combination with a self-priming bonding agent produced bond strength on dentin at least comparable to conditioning with 37% H3PO4.

Acid Etching, Dental↗
PubMedDate not supplied

Impaired dentofacial development after radiotherapy of a non-Hodgkin lymphoma: report of case.

Since the advances in therapy of childhood malignancies have improved life expectancy attention is now increasingly focused on the long-term effects of antineoplastic therapy. Developmental abnormalities due to antineoplastic therapy have been claimed to preferentially occur in children treated before the age of six years. This report of a case demonstrates severe developmental disturbances following radiotherapy of a cervical non-Hodgkin lymphoma at the age of eight years. The morphological changes included microdontia, root shortening, blunting and thinning as well as mandibular hypoplasia.

Adult↗
PubMedDate not supplied

Marginal quality of tooth-colored restorations in class II cavities after artificial aging.

This in vitro study compared the proximal marginal adaptation of direct composite restorations with composite and ceramic inlays inserted with different resin cements. Standardized MOD Class II inlay cavities with one proximal box extending below and the other above the CEJ were cut in 48 extracted human molars and randomly assigned to six groups (n=8). Incrementally layered direct composite restorations (P60), composite inlays (P60) and ceramic inlays (Empress; Cerec Vitablocs Mark II) were placed in the cavities. Three different resin cements (RelyX ARC; Variolink II high viscosity; Panavia 21) were used for luting the composite inlays. All ceramic inlays were cemented with RelyX ARC. After finishing and polishing, the teeth were stored for 24 hours in Ringer solution at 37 degrees C before they were subjected to thermal and mechanical loading (5/55 degrees C, 2000x; 50 N vertical load, 50000x). Margins were evaluated on epoxy replicas using a scanning electron microscope at X200 magnification. Statistical analysis was performed with non-parametric test methods (alpha=0.05). The adhesive interfaces to enamel exhibited high percentages of perfect margins for all groups (91.8% to 96%) and a maximum of 5.2% marginal gap formation. Dentin-limited cavity segments demonstrated more marginal openings and less perfect margins than enamel-bound areas; however, this was only statistically significant for direct composite restorations and composite inlays inserted with Variolink II and Panavia 21. RelyXARC showed a significantly better adaptation to P60 inlays compared with the leucite-reinforced Empress ceramic but not the Vitablocs Mark II ceramic.

Aluminum Silicates↗
PubMedDate not supplied

A comparison of glass cermet cement and amalgam restorations in primary molars.

The aim of this clinical study was to compare the efficacy of GCC with amalgam as a filling material in primary molars. Two hundred fifteen restorations were placed in the first and second primary molars of seventy-four patients, ranging in age from four to ten years. The overall failure rate of amalgam is lower than that of GCC, but not significantly different. In older children, amalgam has greater advantages. An advantage of GCC is the short time required to fill the cavity. This might be an important factor in young and/or difficult children. In these cases amalgam cannot be placed under optimal conditions and, therefore, the results are less satisfactory. GCC is a viable alternative filling material.

Cermet Cements↗
PubMedDate not supplied

Experience with midazolam as sedative in the dental treatment of uncooperative children.

Shortage of capacity, and the limited range of therapies available for dental treatment of uncooperative children involve obvious problems which have given rise to new developments in treatment. Over the last two years, 83 children have been treated in 181 sessions after sedation with Midazolam. Rectal application is clearly superior to giving the drug orally. The results, and the good amnestic effect of Midazolam show that sedation employing this drug, while not a substitute for general anaesthesia in every case, does constitute an important alternative in the treatment of uncooperative children.

Administration, Oral↗