ABSTRACT
Thermal analysis was used to measure the characteristics of dental resins cured with the use of a new light-activation unit equipped with high illuminant blue light-emitting diodes (LEDs). The characteristics were compared with those of resins cured with the use of two conventional halogen lamp units. The prepared base monomer consisted of a mixture of Bis-GMA and TEGDMA (60:40 by weight), with 0.5 wt% CQ/DMPT or CQ/DMAEMA. The two experimental visible-light-cured resins were polymerized for 40 s. Differential scanning calorimetry (DSC) was used to examine the thermal characteristics of the cured resins. The activation energy for the decomposition of the dental resin was calculated from the peaks of the endothermic curves obtained when the specimens were heated at three different rates (5, 10, and 15 C/min) during DSC. The activation energies calculated for the LED-cured specimens were more than 220 kJ/mol; specimens cured with the use of the halogen units had activation energies of less than 192 kJ/mol. The Knoop hardness number (KHN) of the same specimens was measured, and was higher with the blue LED units than with halogen lamp units. Therefore, dental resins cured using blue LEDs have a higher degree of polymerization and more stable three-dimensional structures than those cured with halogen lamps.
Subject(s)
Composite Resins/chemistry , Calorimetry, Differential Scanning , Composite Resins/radiation effects , Composite Resins/standards , Light , Methods , Photochemistry , ThermodynamicsABSTRACT
Castable apatite ceramic crowns are subjected to heat treatment during crystallizing and during coloring after casting. The dimensional accuracy of the heat-treated crowns was investigated with respect to its influence on dimensional changes in castable apatite ceramic crowns and on distortion of the interior of the crowns, using two investment techniques and a three-coordinate measuring machine. Dimensional changes were not influenced by the number of coloring firings. Distortion of the interior of crowns was slightly outward at the gingival plane. Shrinkage because of crystallizing was approximately 20 microns and the shrinkage of the gingival plane was equal to that of the occlusal plane.
Subject(s)
Apatites/chemistry , Ceramics/chemistry , Crowns , Dental Casting Investment/chemistry , Dental Casting Technique , Color , Crystallization , Dental Casting Technique/instrumentation , Denture Design/instrumentation , Hot Temperature , Materials Testing , Surface PropertiesABSTRACT
Thirty-three castable apatite ceramic crowns were constructed for 26 patients. The crowns were clinically evaluated for anatomic form, marginal adaptation, cavosurface marginal discoloration, surface roughness, and color match for a period of 2 years at regular intervals. Results showed that all restoration had satisfactory anatomic form; all but one exhibited good marginal adaptation. Slight abrasion was noticed at the functioning cusps and all but three of the restorations demonstrated excellent color matching.
Subject(s)
Apatites/chemistry , Ceramics/chemistry , Crowns , Adult , Aged , Cementation , Color , Crystallization , Dental Casting Technique , Dental Cavity Preparation , Denture Design , Evaluation Studies as Topic , Female , Humans , Male , Middle Aged , Surface PropertiesABSTRACT
The effects of ultraviolet (UV) light on fungi and impression materials were tested. UV light (250 microW/cm2) killed most Candida organisms (10(3) cells/ml) within 5 minutes. UV light (8000 microW/cm2) killed most C. albicans (10(7) cells/ml) within 2 minutes of exposure. The effect of UV light on dimensional change and surface roughness of impression materials (irreversible hydrocolloid, agar, and silicone rubber) was tested. The results showed that neither dimensional change nor surface roughness of the impression materials were affected. The results of this study indicate that UV light disinfects impression materials that are contaminated with Candida organisms.
Subject(s)
Candida/radiation effects , Dental Impression Materials , Disinfection/methods , Ultraviolet Rays , Agar/chemistry , Agar/radiation effects , Alginates/chemistry , Alginates/radiation effects , Calcium Sulfate , Dental Impression Materials/chemistry , Dental Impression Materials/radiation effects , Models, Dental , Silicone Elastomers/chemistry , Silicone Elastomers/radiation effects , Surface Properties , Time FactorsSubject(s)
Crowns , Dental Plaque/pathology , Adult , Dental Plaque/etiology , Female , Humans , MaleABSTRACT
This study demonstrated that plaque accumulation was reduced and plaque removal facilitated by the TFE coating. These findings suggest that the TFE coating has a practical application for pontics and the proximal and cervical surfaces of crowns. These inaccessible surfaces are not easily cleaned by brushing.
