Pre-treatment, end of treatment, and post-retention study models of 30 subjects with a Class II division 2 malocclusion were assessed, after a period of at least 3 years, in order to evaluate the long-term changes in occlusion, alignment, and arch dimensions. Molar relationship correction was found to be stable after retention. There were no variables which could be used to establish a prognosis of vertical stability. Over-correction of overbite was seen to relapse. Ten per cent of the cases showed unacceptable anterior maxillary irregularities after retention. Mandibular arch width and length usually showed a decrease after retention. An increase in lower intercanine width and arch length achieved by orthodontic treatment always relapsed. This relapse was associated with post-retention mandibular irregularity and crowding. Nine cases (30 per cent) showed an unacceptable degree of mandibular irregularity after retention. Pre-treatment crowding in the mandible showed a relationship with post-retention lower irregularity and crowding. There was a correlation between the number of years which had elapsed after retention, overbite relapse and post-retention mandibular irregularity.

A study was made of 31 patients with Angle Class II malocclusion. Fifteen patients did not undergo extraction of teeth (Group A), while 16 underwent extractions of four premolars (Group B). Data was obtained from the corresponding lateral radiographs of the head taken both before and after orthodontic treatment. The main aim of the study was to compare the response of the soft and hard tissues of the facial profile in Class II malocclusion treated with the extraction of four premolars and the response of borderline cases presenting with similar malocclusions, but not subjected to extraction. In this latter group reasonable doubt existed as to whether or not to remove teeth in order to solve the occlusal and aesthetic problems. It is concluded that significant hard tissue differences between the groups at the end of treatment were limited to a more retruded position of the incisors and a reduced overbite amongst those patients subjected to extraction. The main soft tissue differences between the groups at the end of treatment were a more retruded lower lip and a more pronounced lower labial sulcus in those patients subjected to extraction.

Tensile bond strength and bond failure location were evaluated in vitro for two types of aesthetic brackets (non-silanated ceramic, polycarbonate) and one stainless steel bracket, using bovine teeth as the substrate and diacrylate resin as the adhesive. The results show that metallic bracket had the highest bond strength (13.21 N) followed by the new plastic bracket (12.01 N), which does not require the use of a primer. The non-silanated ceramic bracket produced the lowest bond strength (8.88 N). Bond failures occurred mainly between bracket and cement, although a small percentage occurred between the enamel-cement interface with the metal and plastic brackets and within the cement for the plastic bracket. With the ceramic bracket all the failures occurred at the bracket-cement interface. This suggests that the problems of enamel lesions produced by this type of bracket may have been eliminated. The results also show that the enamel/adhesive bond is stronger than the adhesive/bracket bond in this in vitro study.

No abstract

In this work we studied some of the main effects of the maxillary protraction orthopedic device. The initial dento-craniofacial reactions induced by maxillary protraction similar to that commonly employed in clinical practice are reported. The fringe counting holographic interferometry technique is used to measure displacements. The experiments were performed on a dried human skull; traction application points were situated over the permanent lateral incisors or over the first permanent molars. The results fundamentally reveal an anterior rotation of the dentomaxillary complex, more intense when traction is applied to the lateral incisors, as shown by a more marked extrusion of the molars in this case. Moreover, major deformation patterns could be observed in inner hard structures of the skull base when applying orthopaedic forces.