Factors influencing fixed retention practices in German-speaking Switzerland : A survey.

AIM Several surveys evaluate different retention approaches among orthodontists, but none exist for general dentists. The primary aim of this survey was to record the preferred fixed retainer designs and retention protocols amongst general dentists and orthodontists in Switzerland. A secondary aim was to investigate whether retention patterns were associated with parameters such as gender, university of graduation, time in practice, and specialist status. METHODS An anonymized questionnaire was distributed to general dentists (n = 401) and orthodontists (n = 398) practicing in the German-speaking part of Switzerland. A total of 768 questionnaires could be delivered, 562 (73.2 %) were returned and evaluated. Descriptive statistics were performed and responses to questions of interest were converted to binary outcomes and analyzed using multiple logistic regression. Any associations between the answers and gender, university of graduation (Swiss or foreign), years in practice, and specialist status (orthodontist/general dentist) were assessed. RESULTS Almost all responding orthodontists (98.0 %) and nearly a third of general dentists (29.6 %) reported bonding fixed retainers regularly. The answers were not associated with the practitioner's gender. The university of graduation and number of years in practice had a moderate impact on the responses. The answers were mostly influenced by specialist status. CONCLUSION Graduation school, years in practice, and specialist status influence retention protocol, and evidence-based guidelines for fixed retention should be issued to minimize these effects. Based on the observation that bonding and maintenance of retainers are also performed by general dentists, these guidelines should be taught in dental school and not during post-graduate training.

Étude clinique randomisée prospective du taux de survie d'un fil lingual mandibulaire de rétention utilisant les méthodes de collage direct et indirect à court et moyen termes

Introduction : Après un traitement orthodontique, la rétention (ou contention) est essentielle pour éviter les récidives vers la malocclusion initiale. Le fil de rétention lingual est un appareil fixe, relativement facile à installer et bien accepté par les patients pour maintenir la position finale des dents antérieures inférieures. Étant de plus en plus utilisé, il devient important de s’assurer de sa fiabilité pour la stabilité de l’alignement dentaire. Objectif : Le but de cette étude clinique randomisée prospective est de déterminer le taux de survie d’un fil lingual mandibulaire de rétention en comparant les méthodes de collage direct et de collage indirect à court et moyen termes. Méthodologie : L’échantillon est constitué de 117 patients consécutifs aléatoirement distribués dans 2 groupes : collage direct (n=58) et collage indirect (n=59). Les fils torsadés de diamètre 0,0175’’ sont préformés par un technicien de laboratoire soit selon la méthode de collage direct, soit selon la méthode de collage indirect. Une matrice de transfert en silicone assure le positionnement précis du fil lingual en bouche. Assure® et Filtek™ Flow ont été utilisés pour le collage direct. Filtek™ Flow, Assure®, and Sondhi™ ont été utilisés pour le collage indirect. Les fils de rétention ont été évalués pour le décollement, l’infiltration, la distorsion et le bris à 2 mois (T1) et 6 mois (T2). Résultats : À T1, le taux de survie du fil de rétention est de 90,2% pour le groupe de collage direct, comparativement à 79,5% pour le groupe de collage indirect (p=0,232). À T2, le fil est resté intact pour 74,1% des participants dans le groupe de collage direct et pour 70,0% des participants dans le groupe de collage indirect (p=0,481). Les différences ne sont pas statistiquement significatives entre les 2 groupes. La fréquence du décollement est plus haute que les autres problèmes enregistrés à T1 (p<0,022), représentant 85,7% des échecs. À T2, le décollement est plus fréquent que la distorsion ou le bris (p<0,04), mais pas statistiquement plus fréquent que l’infiltration (p=0,109). Il représente alors 86,4% des échecs. Conclusion : Le décollement est la principale cause d’échec d’un fil de rétention lingual. Il n’y a pas de différence statistiquement significative du taux de survie d’un fil lingual mandibulaire de rétention entre les techniques de collage direct et de collage indirect à court et moyen termes.

Long-term effectiveness of canine-to-canine bonded flexible spiral wire lingual retainers

The flexible spiral wire (FSW) canine-to-canine lingual retainer bonded to all 6 anterior teeth is a frequently used type of mandibular fixed retainer. This study aimed to assess the long-term effectiveness of FSW canine-to-canine lingual retainers in maintaining the alignment of the mandibular anterior teeth after orthodontic treatment.

Development of labial gingival recessions in orthodontically treated patients

INTRODUCTION Our aim was to assess the prevalence of gingival recessions in patients before, immediately after, and 2 and 5 years after orthodontic treatment. METHODS Labial gingival recessions in all teeth were scored (yes or no) by 2 raters on initial, end-of-treatment, and posttreatment (2 and 5 years) plaster models of 302 orthodontic patients (38.7% male; 61.3% female) selected from a posttreatment archive. Their mean ages were 13.6 years (SD, 3.6; range, 9.5-32.7 years) at the initial assessment, 16.2 years (SD, 3.5; range, 11.7-35.1 years) at the end of treatment, 18.6 years (SD, 3.6; range, 13.7-37.2 years) at 2 years posttreatment, and 21.6 (SD, 3.5; range, 16.6-40.2 years) at 5 years posttreatment. A recession was noted (scored "yes") if the labial cementoenamel junction was exposed. All patients had a fixed retainer bonded to either the mandibular canines only (type I) or all 6 mandibular front teeth (type II). RESULTS There was a continuous increase in gingival recessions after treatment from 7% at end of treatment to 20% at 2 years posttreatment and to 38% at 5 years posttreatment. Patients less than 16 years of age at the end of treatment were less likely to develop recessions than patients more than 16 years at the end of treatment (P = 0.013). The prevalence of recessions was not associated with sex (P = 0.462) or extraction treatment (P = 0.32). The type of fixed retainer did not influence the development of recessions in the mandibular front region (P = 0.231). CONCLUSIONS The prevalence of gingival recessions steadily increases after orthodontic treatment. The recessions are more prevalent in older than in younger patients. No variable, except for age at the end of treatment, seems to be associated with the development of gingival recessions.

Stability and relapse after orthodontic treatment of deep bite cases-a long-term follow-up study.

The purpose of this long-term follow-up study was twofold-firstly, to assess prevalence of relapse after treatment of deep bite malocclusion and secondly, to identify risk factors that predispose patients with deep bite malocclusion to relapse. Sixty-one former patients with overbite more than 50% incisor overlap before treatment were successfully recalled. Clinical data, morphometrical measurements on plaster casts before treatment, after treatment and at long-term follow-up, as well as cephalometric measurements before and after treatment were collected. The median follow-up period was 11.9 years. Patients were treated by various treatment modalities, and the majority of patients received at least a lower fixed retainer and an upper removable bite plate during retention. Relapse was defined as increase in incisor overlap from below 50% after treatment to equal or more than 50% incisor overlap at long-term follow-up. Ten per cent of the patients showed relapse to equal or larger than 50% incisor overlap, and their amount of overbite increase was low. Among all cases with deep bite at follow-up, gingival contact and palatal impingement were more prevalent in partially corrected noncompliant cases than in relapse cases. In this sample, prevalence and amount of relapse were too low to identify risk factors of relapse.

Comparison of different designs of implant-retained overdentures and fixed full-arch implant-supported prosthesis on stress distribution in edentulous mandible - A computed tomography-based three-dimensional finite element analysis

A finite element analysis was used to compare the effect of different designs of implant-retained overdentures and fixed full-arch implant-supported prosthesis on stress distribution in edentulous mandible. Four models of an human mandible were constructed. In the OR (O'ring) group, the mandible was restored with an overdenture retained by four unsplinted implants with O'ring attachment; in the BC (bar-clip) -C and BC groups, the mandibles were restored with overdentures retained by four splinted implants with bar-clip anchor associated or not with two distally placed cantilevers, respectively; in the FD (fixed denture) group, the mandible was restored with a fixed full-arch four-implant-supported prosthesis. Models were supported by the masticatory muscles and temporomandibular joints. A 100-N oblique load was applied on the left first molar. Von Mises (σvM), maximum (σmax) and minimum (σmin) principal stresses (in MPa) analyses were obtained. BC-C group exhibited the highest stress values (σvM=398.8, σmax=580.5 and σmin=-455.2) while FD group showed the lowest one (σvM=128.9, σmax=185.9 and σmin=-172.1). Within overdenture groups, the use of unsplinted implants reduced the stress level in the implant/prosthetic components (59.4% for σvM, 66.2% for σmax and 57.7% for σmin versus BC-C group) and supporting tissues (maximum stress reduction of 72% and 79.5% for σmax, and 15.7% and 85.7% for σmin on the cortical and trabecular bones, respectively). Cortical bone exhibited greater stress concentration than the trabecular bone for all groups. The use of fixed implant dentures and removable dentures retained by unsplinted implants to rehabilitate edentulous mandible reduced the stresses in the periimplant bone tissue, mucosa and implant/prosthetic components. © 2013 Elsevier Ltd.

Long-term follow-up of maxillary fixed retention: survival rate and periodontal health.

AIM To assess the long-term success of maxillary fixed retainers, investigate their effect on gingival health, and analyse the survival rate after a mean period of 7 years (minimum 5 years) in retention. SUBJECTS AND METHODS Forty one subjects were included in the study A clinical examination of the upper canine to canine region including gingival index (GI), plaque index, probing depth, and bleeding on probing (BOP) was performed. Intraoral photographs and dental impressions were taken and irregularity index was determined and compared to the values of the immediate post-therapeutic values; failures of retainers were also recorded and analysed. RESULTS The mean observed retention time was 7 years and 5 months. Irregularity index: Changes occurring during retention were statistically different between the lateral incisors bonded to retainers and the canines not bonded to retainers. Only six patients showed changes in irregularity index of the lateral incisors in spite of a retainer in place. Periodontal health: The median value of the GI for all teeth bonded to upper retainers was 1.10 and the median value of the plaque index (PI) was 1.14. PI was not a significant predictor of GI. The overall BOP of the bonded teeth to the retainer for each participant was 22.3 per cent. Failure rate: Twenty-eight out of 41 patients experienced no failure of the upper bonded retainer (68.3 per cent). Detachments were the most frequent incidents. CONCLUSION Although plaque accumulation might be increased in patients with already poor oral hygiene, maxillary bonded retainers caused no significant negative effects on the periodontal health.

Characteristic analysis for multisampled digital implementation of fixed-switching-frequency closed-loop modulation of voltage-source inverter

In this paper, a fixed-switching-frequency closed-loop modulation of a voltage-source inverter (VSI), upon the digital implementation of the modulation process, is analyzed and characterized. The sampling frequency of the digital processor is considered as an integer multiple of the modulation switching frequency. An expression for the determination of the modulation design parameter is developed for smooth modulation at a fixed switching frequency. The variation of the sampling frequency, switching frequency, and modulation index has been analyzed for the determination of the switching condition under closed loop. It is shown that the switching condition determined based on the continuous-time analysis of the closed-loop modulation will ensure smooth modulation upon the digital implementation of the modulation process. However, the stability properties need to be tested prior to digital implementation as they get deteriorated at smaller sampling frequencies. The closed-loop modulation index needs to be considered maximum while determining the design parameters for smooth modulation. In particular, a detailed analysis has been carried out by varying the control gain in the sliding-mode control of a two-level VSI. The proposed analysis of the closed-loop modulation of the VSI has been verified for the operation of a distribution static compensator. The theoretical results are validated experimentally on both single- and three-phase systems.