RESUMEN
Bonding orthodontic attachments to molars is difficult in the presence of extensive buccal amalgam restorations. The purposes of this study were (1) to examine different amalgam surface preparations, (2) to examine properties of adhesive cements to amalgam, (3) to determine the most shear-resistant bonding technique and (4) to discuss whether these shear bond strengths were of adequate magnitude to be of clinical acceptability. The sample consisted of 108 standardized amalgam cylinders divided into 9 groups of 12 based on surface treatment technique and resin type. SPEED brackets (Strite Industries, Cambridge, Ontario) were bonded to amalgam surfaces that were either polished, sandblasted with 50 microm aluminium oxide, or chemically corroded. Adhesives used were Phase II (Reliance Orthodontic Products Inc, Itasca, Ill), Panavia EX (J Morita USA Inc, Tustin, Calif), or C & B Metabond (Parkell, Farmingdale, NY). After thermocycling from 10 degrees C to 50 degrees C 10,000 times, all samples were tested for shear bond strength with the Universal Testing Machine (Instron Corporation, Canton, Mass). The results show significantly higher bond strengths for all of the resin systems when sandblasting of the amalgam surface is used (P <.0001). Only Panavia EX bonded strongly to polished samples, suggesting the presence of a chemical bond. Laboratory acceptable bond strengths to amalgam are possible. The surface characteristics of the amalgam appear to be more influential in the strength of the bond than does the nature of the resin.
Asunto(s)
Amalgama Dental , Recubrimiento Dental Adhesivo , Soportes Ortodóncicos , Cementos de Resina , Grabado Ácido Dental , Adhesividad , Análisis de Varianza , Compuestos de Boro , Corrosión , Amalgama Dental/química , Pulido Dental , Ensayo de Materiales , Metacrilatos , Metilmetacrilatos , Microscopía Electrónica de Rastreo , Fosfatos , Propiedades de Superficie , Resistencia a la TracciónRESUMEN
Three commonly used functional appliances; namely, the Herbst, Frankel, and a simulation of the Clark twin block appliances were used to test the lateral pterygoid muscle hypothesis. This hypothesis states that postural and functional activity of the superior and inferior heads of the lateral pterygoid muscle increases after the insertion of a functional appliance. This increased activity, especially in the superior head of the lateral pterygoid muscle then acts to stimulate increased condylar growth. The electromyographic (EMG) activity of the masseter, digastric, superior, and inferior heads of the lateral pterygoid muscles was monitored with chronically inserted EMG electrodes, in nonhuman primates, to determine whether functional appliances actually produce a change in functional activity of these muscles. The involuntary swallow was used to represent functional activity. Thus swallow-related EMG activity levels were monitored longitudinally and compared before and after the insertion of each appliance type. The insertion of these three appliances was associated with a decrease in functional EMG activity of the four muscles. This decrease was statistically significant in all muscles 3 and 6 weeks after appliance insertion. This is consistent with our previous findings that functional appliances are associated with a decrease in the postural activity of the above muscles in nonhuman primates. In view of the fact that the animals showed large skeletal changes in the temporomandibular facial area, this study could not support the lateral pterygoid muscle hypothesis.