Tid og sted for prøveforelesning
Mandag 8. september 2014, kl. 14.15 og 15.15. Auditorium 1, Geitmyrsveien 69.
Bedømmelseskomité
- Professor, dr.odont. Urban Hägg (førsteopponent)
- Førsteamanuensis, dr.philos. Sigbjørn Løes (andreopponent)
- Førsteamanuensis, dr.odont. Bente Brokstad Herlofson (administrator)
Leder av disputas
Instituttleder Jan Eirik Ellingsen
Sammendrag
The thesis is based on six papers that have evaluated the effects of orthognathic surgery to correct Class III malocclusion on the hard and soft tissues of the face and the upper airways. The study samples were retrieved from 2 archives, one from the archives at the Department of Orthodontics at the Oslo University (papers I, III, IV,V) and one from Institute of Stomatology, Riga Stradins University (papers II, VI). The first sample consisted of 84 patients with follow up records up to 3 years, the second sample consisted of 51 patients who were followed up 1 year. The lateral cephalograms were used to measure the effects of surgery in five papers and in one paper the findings in the lateral cephalograms were compared with measurements on the computed tomography (CT) scans.
The first paper focused on quantifying relapse after bi-maxillary correction of Class III malocclusion. The changes in the jaw position were measured at 6 time points on a constructed coordinate mash. It was concluded that maxillary advancement and/or maxillary impaction in combination with mandibular setback provided good occlusal and skeletal stability in the sagittal plane. It appeared that the maxilla was more stable than the mandible. The amount of mandibular setback and inferior movement of the posterior maxilla were identified as potential factors causing mandibular relapse. In the vertical plane intrusion of the anterior maxilla was stable, while extrusion relapsed almost completely. Most of the sagittal mandibular relapse occurred during the first 6 months, while the vertical maxillary relapse took place during in the first 2 months.
The second paper compared 2 techniques of mandibular setback used in conjunction with maxillary repositioning: bilateral sagittal split osteotomy and vertical ramus osteotomy. No differences were found between the 2 methods and relapse in both groups was in line with the first paper, about 25% of the mandibular setback.
The third paper investigated the influence of the presurgical position of the upper incisors on the soft tissue response after surgery. In general the changes of the lower lip and chin were more predictable than those of the upper lip. On average the upper lip changed half as much as changed the upper incisors, while the response of the lower lip depended on the position of the incisors before surgery. When the upper lip was in contact with the lower incisors before surgery, the maxilla was moved forward into “an empty space” and no change in the profile of the upper lip was observed.
The aim of the forth paper was to compare skeletal relapse with the changes of the soft tissues after surgery. It could be concluded that the change in the anterior face height produced different skeletal relapse and response of the soft tissues. When the anterior facial height decreased as a result of surgery, relapse was small and the soft tissues closely followed relapse of the hard tissues. When the anterior face height increased, substantial relapse of hard and soft tissue was observed.
The fifth paper evaluated the changes in the upper airways in 4 groups based on the repositioning of the maxilla during surgery: only advancement, only intrusion, combination of intrusion and advancement and neither advancement nor intrusion of the maxilla. Mandibular setback, which was observed in all groups, produced the decrease in the upper airways at the oropharyngeal and hypo pharyngeal levels. It was to some extent compensated with the maxillary repositioning in the groups, where maxillary advancement was performed.
The sixth paper was a prospective study on CT scans. No decrease in the cross sectional area at any level of the upper airways after surgery was recorded. No correlation between the measurements of the upper airways on the lateral cephalograms and CT scans was recorded. It could be concluded that the lateral dimensions of the upper airways compensate for the apparent decrease in the upper airways in the sagittal plane measured on the lateral cephalograms.