| Popis: |
Orthodontic brackets were bonded to a total of 240 Biodent porcelain surfaces pretreated with a number of different porcelain primers. In a control group, 40 surfaces were pumiced, etched, rinsed and dried, and then bonded to similar brackets without the use of a primer. The test objects of group 1 (n = 140) and those of group 2 (n = 40) were tested for bond shearing strength in a material testing machine (Zwick 1441) after prior incubation in a corrosive fluid at a pH of 2.3 and a temperature of 37 degrees C for 24 hours and 21 days, respectively. The fracture sites were inspected and analysed. Incubation in corrosive fluid reduces the strength of the porcelain-composite bonding, the shearing strength and the number of fractures in the bonding decreasing. Damage to the porcelain was seen to occur after the use of Lee-Ortho-Prime and Bond-Por primers. All the primers tested can be used, although a bond shearing strength of less than 2 N/mm2 is at the lower limit of what can be accepted under the usual conditions of daily practice. |
