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Aim: Tongue thrust is a parafunction caused by the persistence of an infantile swallowing pattern. If this pathological swallowing pattern persists, it can cause malocclusion and can have a negative effect on the growth of the stomatognathic system. Tongue interposition can be treated with passive (orthodontics) and active (myofunctional) therapy. The aim of this study is to evaluate the stability of occlusion after orthodontic treatment in patients with tongue thrust. Material and methods: 146 patients with tongue thrust were selected and divided into a group of patients with extractions (EXO) and a group without extractions (NON-EXO), consisting of 50 and 96 patients, respectively. Each patient had dental cast models taken at the start of treatment (BB), after treatment (BR) and during follow-up (AB). Plaster models were digitally scanned, on which various measurements were taken; overjet, overbite, intercanine and intermolar distance, arch length, ALD and Bolton indices. Statistical analysis was performed using a two-way ANOVA to evaluate the difference between the BB, BR and AB groups for stability. An unpaired student t-test was performed to detect the differences between the EXO and NON-EXO group. Results: At the end of the study, it may be concluded that a spontaneous readaptation or settling of the teeth could be observed for overjet, which was shown by a slight relapse (only significant in the NON-EXO group for OJ p<0.05). No relapse was seen in overbite for EXO as well as NON-EXO group. Furthermore, extraction is useful for stabilizing the overbite and controlling the verticality with orthodontic treatment. This is because the reduction of the overbite was less significant in the EXO group and here less relapse is seen between BR and AB. The intermolar distance in the maxilla shows more relapse in the EXO group. Conclusion: After orthodontic treatment, a stable resettling of the teeth occurs and thus slight relapse is seen for the overjet in the groups with and without extractions. The vertical dimension or overbite is more stable in the extraction group. Lastly, the extraction of premolars causes less transversal expansion of orthodontic treatment.

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Introduction and aim: The terms hypodontia or agenesis, refer to congenitally missing teeth. Hypodontia of one or two teeth is relatively prevalent, while the most severe forms are rather rare and often combined with a syndrome. The second lower premolar and the upper lateral incisors are the most common agenetic teeth. Agenesis can be caused by genetic, epigenetic and environmental factors that disrupt the initial stages of tooth development. Since mutations in a particular gene have multiple phenotypes, hypodontia often correlates with other dental abnormalities. The ideal treatment is still a matter of debate, and information on the long term stability is rather scarce, which is an important matter since agenesis can prolong treatment time and compromise its outcome. The aim of this retrospective study is to investigate the occlusal stability of orthodontically treated patients with at least 1 agenetic tooth. Material and methods: Patients with at least one agenetic tooth (excluding third molars), treated orthodontically at Department of Orthodontics of the Service of Dentistry of UZ Leuven and with orthodontic models available before (BB) and after treatment (BR) and at a follow up time point (AB) were retrospectively selected from the archive of said Department. Patients with syndromes affecting the craniofacial region were excluded. The following occlusal traits were measured on the digital models by two observers: intercanine and intermolar distance, irregularity index, overjet, overbite, mandibular midline shift and sagittal molar occlusion, by using the software Ortho Analyzer. The occlusal traits were statistically compared along the timepoints by using one- and two-way ANOVA, Tukey’s, Dunn’s and Šídák's multiple comparisons and Kruskal-Wallis test. ICC was calculated for both observers. Results: A final sample of 18 patients could be included (11 female, 7 male, mean age 11.75 years at BB, 14.50 years at BR and 15.91 years at AB, which was on average 3 years). 13 patients presented 1 or 2 agenetic teeth (G1, mean age 12.22 years at BB, 15 years at BR and 16.44 years at AB) and 5 patients presented 3 or more agenetic teeth (G2, mean age 10,33 years at BB, 13 years at BR, 15 years at AB). A significant decrease in irregularity index was found between BB and BR, which remained stable at follow up. Significant decrease of overbite was found at BR, which slightly increased again at follow – up, remaining within a normal range. Comparing groups, there was a significant difference at AB for the irregularity index (p=0,035), which increased less in G2 and overbite (p=0,035), which increased more in G2. Conclusion: This study shows that patients with hypodontia maintain occlusal stability on average 3 years after orthodontic treatment. However, crowding in the lower jaw and overbite tend to increase slightly at follow up. Patients with 3 or more agenetic teeth have less tendency for instability regarding irregularity index and present more tendency to deep bite at follow up compared to patients with 1 or 2 agenetic teeth. The results of this study need to be taken with caution due to the limited sample size and its retrospective nature.

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The aim of this master thesis was to get an overview of the current situation around surgically-accelerated tooth movement in orthodontics, for which the underlying biological principles were uncovered. Corticotomy, piezocision and micro-osteoperforations (MOP) were the main techniques to be found. Non-surgical techniques and medication and how they can possibly affect facilitated OTM were also investigated. Online databases were consulted and an online questionnaire was drafted to analyze how the Belgian orthodontists are aware of the newest developments and to know their application rate. The survey shows that MOP was the least known surgical technique, while everyone seemed to know corticotomy. Only a small group of orthodontists applied one of the surgical techniques in their daily practice. No consensus could be obtained around the effects of the techniques in relation to a target audience and their abilities to reduce treatment time. The non-surgical techniques seem to be less developed and the literature is not unanimous on the matter. Further research in the field is needed concerning the application of these techniques in humans

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Introduction and aim: Crowding after orthodontic treatment occurs frequently and can be frustrating for both patient and practitioner. Crowding is also common in patients who did not receive orthodontic treatment, often as a result of normal physiological processes that involve growth and aging. Lower anterior crowding is considered as one of the most common kinds of relapse. In this retrospective study, lower anterior crowding was followed up until five years after treatment. Materials and methods: Patients treated for crowding in the lower front without mandibular extractions were selected from the archives of the Orthodontic Department of the University Hospital in Leuven. Only patients with models available from before treatment, at the end of treatment and at least at one follow-up control (around 1, 2 and/or 5 years; AB1, AB2 and AB5 respectively) were included. For each of these models, Little's irregularity index (LII), Arch length discrepancy (ALD), Intercanine (IC) and Intermolar (IM) distance, Overjet (OJ) and Overbite (OB) were determined digitally. Data were statistically analyzed using scatterplots and one-way ANOVA, as well as descriptive statistics. Results: 148 patients were finally included from the initial sample, with a median age of 14,27 years after treatment. No significant correlation between the irregularity index and time after the end of treatment was found in the present study. Based on the median values at the different time points, an increase in LII of 0,30-0,55 mm was found. A significant, however weak increase in ALD was shown in the scatterplot, but not in ANOVA. Posttreatment changes in median ALD of respectively -0,19mm in the AB1 group, +0,15mm in the AB2 group and - 0,60 mm in the AB5 group were seen during follow-up. No significant changes were found after treatment for both IC and IM. OJ and OB increased slightly after treatment, although these values were small and of no clinical significance. Conclusion: This study shows that there is no significant correlation between crowding and time after the end of orthodontic treatment. All parameters examined showed a tendency to return toward initial values, however further investigation is needed taking into account the limitations of the present study.

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Aim: To investigate volumetric and circumferential pharyngeal airway space (PAS) changes as well as the stability of these changes over time as evaluated with cone beam computed tomography (CBCT) before and after orthognathic surgery in different dental and/or skeletal malocclusions up to two years post-operatively. Methods: Clinical records and CBCT data of 173 patients who underwent orthognathic surgery (maxillo-mandibular advancement (MMA) or maxillary advancement with mandibular setback (MMS)) were retrospectively reviewed at five time points: preoperative (T0), 1-6 weeks (T1), 6 months (T2), 1 year (T3), and 2 years postoperative (T4). Patients aged ≥16 years with a minimal follow-up of 6 months were included. Patients with a history of maxillofacial trauma or surgery, obstructive sleep apnoea syndrome or craniofacial anomalies were excluded. PAS volume and constriction surface area (mCSA) were measured at each time point. All measurements were performed using CBCT and were analysed in Mimics Medical 22.0 and Amira 6.7.0 software. Results: After exclusion, 129 patients were included in the present study. For MMA patients (n=69), enlarged oropharyngeal PAS volumes were observed post-surgery at each time point compared to the pre-surgical PAS volume, with a stable oropharyngeal PAS volume over the 2-year period post-operatively. In contrast, in MMS (n=60) patients, no significant oropharyngeal changes were observed. Even though mCSA was significantly enlarged until 2 years after surgery in MMA patients, in MMS patients mCSA only stayed significantly enlarged until 1 year postoperative and declined towards baseline values at 2 years post-surgery. Conclusion: Bimaxillary advancement osteotomy significantly increased oropharyngeal volume and mCSA over an extended period of up to 2 years. In contrast, no significant volumetric or mCSA changes were found 2 years post-operatively in the PAS of patients who underwent maxillary advancement with mandibular setback. Keywords: cone beam computed tomography, CBCT, pharyngeal airway, orthognathic surgery, bimaxillary advancement osteotomy, mandibular setback, constriction surface area.