Mechanical Properties of Hydrocolloid and Rubber Impression Materials
Hampson' has studied the elasticity of alginates under compression and has observed that materials with smaller amounts of permanent deformation were more suitable for use in the presence of undercut areas. Schoonover and Dickson2 report the breaking stress, percent strain, and percent set of alginates. Cresson3 suggested the revision of the testing procedure for compressive strengths of dental elastic impression materials that would apply the load at the rate of 18,000 Gm. per minute. Skinner et al.4 and Phillips5 point out the importance of the rate of deformation on the technic of handling alginate hydrocolloids. Warner" also shows that the breaking strength and percent deformation of alginates are functions of the loading rate where the higher the rate, the greater is the strength qualities. Anderson7 shows the recovery from deformation of alginate to be a direct function of time from the start of mixing. Donnison and Docking8 have measured the permanent deformation, stiffness, and toughness of alginates, the latter being determined as a combination of compressive strength and the strain at rupture. The ADA Specification 189 requires the compressive strength to be determined at a rate of 10,000 -+ 2 000 Gm. per minute. Based on an average strength of 7,000 Gm./cm.2 and a specimen '2 inch in diameter, the time required for rupture would be approximately half a minute. Recently, Braden'0 has determined the energy of tearing of one each of mercaptan, silicone, and alginate impression materials as a function of the rate of tearing and the temperature of testing. As the rate of tearing increased and the temperature decreased,
Antimicrobial activity and properties of irreversible hydrocolloid impression materials incorporated with silver nanoparticles.
STATEMENT OF PROBLEM
Conventional spray and the immersion disinfection of irreversible hydrocolloid impression materials may lead to dimensional changes.


PURPOSE
The purpose of this in vitro study was to investigate the antimicrobial activity and properties of irreversible hydrocolloid impression materials incorporated with silver nanoparticles.


MATERIALS AND METHODS
The antimicrobial activity and properties of 2 commercially available irreversible hydrocolloid impression materials were evaluated after incorporating varying concentrations of silver nanoparticles. Antimicrobial activity was determined using the disk diffusion method. The gel strength, permanent deformation, flow, and gelation time were measured according to American Dental Association specification #18. Analysis of variance was used to identify the significant differences within and across the groups (α=.05).


RESULTS
Adding silver nanoparticles to irreversible hydrocolloid impression materials resulted in superior antimicrobial activity without adversely affecting their properties. Adding silver nanoparticles to Zelgan significantly increased the gel strength compared with the control group, except at 5 wt%. However, the gel strength of Tropicalgin was unaffected except at 5 wt%. An increase in the permanent deformation was found with the incorporation of silver nanoparticles in both Zelgan and Tropicalgin. The flow of Zelgan increased with the incorporation of silver nanoparticles, whereas a decrease in the flow of Tropicalgin was observed at 1 wt% and 2 wt%. An increase in the gelation time of both Zelgan and Tropicalgin was observed with the incorporation of silver nanoparticles.


CONCLUSIONS
Based on this in vitro study, silver nanoparticles can be incorporated into irreversible hydrocolloid impression materials as antimicrobial agents without adversely affecting their properties.
A complete bridge technic utilizing the alginate hydrocolloids.
A s e a r c h of the dental literature shows A. wealth of material stressing the im­ portance of a complete roentgenographic examination prior to the con­ struction of a fixed partial denture or bridge. Much progress is also reported in esthetics, sanitation, abutment prepara­ tions, pontic design and in the technical procedures involved. The informed ob­ server, however, will readily note the absence of material on the application of the science of occlusion to bridgework. The standards by which a fixed par­ tial denture is judged have changed in recent years. Modem laboratory proce­ dures make the construction of a per­ fectly fitting crown or bridge common­ place; an artistically matched, shaded and stained facing or pontic is no longer a novelty. Harmony in function is the standard by which a restoration is judged today. No matter how perfect the mar­ gins are or how expertly matched the facings, if the occlusal surfaces of the new restoration are not shaped to function in harmony with the remainder of the teeth, the requirements of modern crown and bridgework have not been met. In the past, restorations have been made only to preserve a tooth or to fill a gap in the dental arch. Crowns and bridges were constructed to restore teeth individually or in small sections of the arch, but seldom did they transform it into a healthy functioning machine. All prospective bridge patients are den­ tal cripples in varying degrees, depending upon the number of missing teeth and other forms of dental pathosis present. A studied examination will usually reveal the presence of mobile and drifting teeth, elongated and malposed teeth, and vary­ ing degrees of cuspal interferences, all of which add up to a poorly functioning mouth. When treating these patients, it is fun­ damentally sound to assume that all the forces exerted by the muscles of masti­ cation should be as equally distributed throughout the remaining teeth as is mechanically possible. The correction of these forces or equilibration of occlusion must be accomplished before the abut­ ment preparations are begun and then must be maintained throughout the con­ struction of the prosthesis. If this pro­ cedure is not followed, some of the re­ maining teeth will be overloaded by poorly distributed stresses, resulting in a more rapid destruction of the supporting bony structures than otherwise would oc­ cur.