Academic literature on the topic 'Retainers'

ABSTRACT EVALUATION OF FIT FOR 3D PRINTED RETAINERS AS COMPARED TO THERMOFORM RETAINERS By David Cole, D.M.D. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Dentistry at Virginia Commonwealth University Thesis Directors: Eser Tüfekçi, D.D.S., M.S., Ph.D., M.S.H.A. Professor, Department of Orthodontics Sompop Bencharit, D.D.S., M.S., Ph.D. Associate Professor and Director of Digital Dentistry, Department of General Practice Introduction: Despite recent advances in three-dimensional (3D) printing, little information is available on 3D printed retainers Methods: Three reference models were used to fabricate traditional vacuum formed, commercially-available vacuum formed, and 3D printed retainers. For each model, three retainers were made using the three methods (a total of 27 retainers). To determine the trueness, the distances between the intaglio surface of the retainers and the occlusal surface of the reference models were measured using an engineering software. A small difference was indicative of a good fit. Results: Average differences of the traditional vacuum formed retainers ranged from 0.10 to 0.20mm. The commercially-available and 3D printed retainers had a range of 0.10 to 0.30mm and 0.10 to 0.40mm, respectively. Conclusions: The traditional vacuum formed retainers showed the least amount of deviation from the original reference models while the 3D printed retainers showed the greatest deviation.

Orthodontic retainers may be considered as removable implants and confer the same problems as other implants with regard to colonisation by microorganisms. Thus, biofilms forming on their surface may compromise the oral health of patients and jeopardise the efficiency of the therapy. The first part of the project involved a clinical study, a cross-sectional observational cohort, to assess the effect of orthodontic treatment on the oral microbiota and the carriage state of opportunistic pathogens during the course of treatment. High proportions of health-associated species were detected in the retainer group. However, Staphylococcus and Candida species were frequently (69% and 36% respectively) isolated from the retainers and the oral cavity of retainer wearers, where Staphylococcus spp. comprised up to 5% of the microbiota. The increase in Staphylococcus spp. including Methicillin Resistant Staphylococcus aureus (MRSA) on retainers was associated with an increase in numbers of these species on the oral mucosa of the cheek and tongue. Orthodontic retainers could, therefore, be a reservoir for pathogens and act as a source of cross-infection. A series of in vitro investigations were subsequently carried out to evaluate the effect of the surface characteristics of retainer materials, including surface roughness, hydrophobicity and surface free energy, which may affect colonisation by opportunistic pathogens. After polishing the surface of the acrylic substrata the results revealed that Atomic Force Microscope was the most appropriate device to measure the surface roughness of the acrylic and thermoplastic materials in a consistent manner. Additionally, the acid-base interactions, especially the electron donor interaction, influenced the bacterial attachment onto the thermoplastic samples. Finally, assessment of novel antimicrobial-containing acrylic resins was carried out. Firstly, incorporation of chlorhexidine showed a prolonged antimicrobial effect against MRSA but was detrimental to the mechanical properties. Thymol was successfully incorporated in heat cured acrylic materials. It reduced the surface free energy of the modified resin with no effect on the mechanical properties and was strongly antimicrobial against C. albicans. However, it showed a lesser antimicrobial effect against MRSA. This PhD has shown the potential of orthodontic retainers as reservoirs for opportunistic pathogens and that surface characteristics are significant in the retention and potential removal of these pathogens. The use of antimicrobial acrylic materials may be of potential therapeutic benefit following further development.

Fixed retainer after orthodontic treatment is an increasing retention appliance. For the mandibular incisors there are two different fixed retainers that are commonly used, either a canine-to-canine retainer bonded only to the canines or a twistflex retainer bonded to each of the mandibular incisors and canines. Increased mandibular incisor irregularity seems to be a continuous process throughout life even in untreated patients. The natural physiological changes during aging causes changes like those that occur after orthodontic treatment and the removal of retainers. There are few long-term studies that have compared patients who have had a mandibular fixed retainer with patients without retention appliance after treatment, and then compared the treated patients with untreated subjects.The overall aim of this thesis was to compare and evaluate two different mandibular fixed retainers and also to compare orthodontically treated cases with untreated long-term. This thesis is based on two studies and a PAR Index evaluation was presented in the frame story:Paper I is a retrospective longitudinal study done on dental casts and lateral head radiographs from patients who had received either a canine-to-canine retainer or a twistflex retainer after treatment. Different variables were measured, were Little’s Irregularity Index was the main outcome measure. The measurements were done at four different occasions, were the last registration was 12 years after treatment, i.e. 9 years after removal of retainer. Paper II is also a retrospective longitudinal study with three different groups, one group received a fixed mandibular retainer, one group did not receive any retention appliance after treatment and the third group was untreated subjects. Measurements were done on dental casts and lateral head radiographs at four different occasions to analyze dental and skeletal changes 12 years after treatment. Also here Little’s Irregularity Index was the main outcome measure. PAR Index evaluation is done to evaluate the stability of orthodontic treatment outcome after treatment and long-term for two different retainer groups and one non-retention group. The following conclusions were drawn: Paper I•Both the canine-to-canine retainer and the twistflex retainer can be recommended since both are equally effective during retention period.•None of the retention types prevent long-term changes of mandibular incisor irregularity or available space for the mandibular incisors after removal of the retainers.•No differences in bonding failures between the two retainers were found. Paper II•There were no differences found 12 years after treatment in Little’s Irregularity Index for the mandibular incisors between the group that had a retainer and the group that had no retainer after treatment•In the untreated group, Little’s Irregularity Index was increased over time but not to the same extent as in the treated groups. •The crowding before treatment did not explain the crowding at the last registration.•The use of mandibular retainers for two to three years does not appear to prevent long-term relapse. •If the patient wants to constrain the changes that come with natural development, then lifelong retention is needed.•The overjet and overbite were stable long-term.PAR Index evaluation•Twelve years after treatment the mean reduction in PAR score was over 70 per cent only for the groups who had a mandibular retainer after treatment. However, the non-retention group had a PAR score of 66 per cent.•There were more cases in the retention groups that were ”greatly improved and/or improved” 12 years after treatment compared to the non-retention group. After treatment between 16 and 23.3 per cent of all the cases were ”worse or not improved”. Twelve years after treatment between 36 and 43.6 per cent of the total cases were ”worse or not improved”.

V-band retainers are widely used in the automotive, aircraft and aerospace industries to connect a pair of circular flanges to provide a joint with good axial strength and torsional rigidity. V-band retainers are manufactured using a cold roll forming process. Despite their wide application, once assembled to a pair of flanges little is known about the interaction between flange and band. Moreover the failure mode of V-band retainers when applying an axial load is not fully understood. In this thesis the ultimate axial load capacity of V-band retainers is predicted using finite element and theoretical models and validated using experimental testing. It was shown that the ultimate axial load capacity was strongly dependent on the joint diameter, increasing between 114mm and 235mm, and decreasing beyond that. Moreover, the peak in ultimate axial load capacity was dependent on parameters such as the axial clamping load and coefficient of friction, and its position lay between 235mm and 450mm, as predicted by the finite element models. Other geometrical parameters such as flange and band thickness showed large impacts on the ultimate axial load capacity as well. A theoretical model was developed that allowed the ultimate axial load capacity to be calculated from a single formula for larger bands and using a simple algorithm for smaller bands. This model supported the findings that, depending on the band diameter, the ultimate axial load capacity had a peak, but predicted its position at approximately 181mm. This position at 181mm was validated by the experimental data. However, when compared to the tests, the finite element and theoretical models both over-predicted the ultimate axial load capacity. Both the finite element models and practical tests showed that for small V-bands axial failure is due to a combination of section deformation and ring expansion, whereas large V-bands fail due to ring expansion only. These two distinct types of behaviour were incorporated into the theoretical model. The hardness development throughout the cold roll forming process was predicted using finite element models. This was validated by hardness measurements, for which a new technique was generated, that directly linked plastic strain and hardness values.

Introduction: The aim of this study was to evaluate the influence of different upper retainers in speech, through Perceptual Auditory Analysis by the laypersons and acoustic analysis. Methods: Eighteen volunteers were selected to use four types of upper retainers: conventional Wrap-Around (CWA), modified horseshoe Wrap-Around (HWA), modified anterior hole Wrap-Around (AHWA) and vacuum-formed (VF). They were used for 21 days each, with intervals of 7 days without use among them. Speech evaluation was performed in vocal excerpts recordings made before installation of the retainers (T0), immediately after the installation of each retainer (T1), and 21 days after the installation (T2). The Perceptual Auditory Analysis of laypersons was performed by means of the visual analogue scale of 100 mm, while the acoustic analysis consisted of the mean diadochokinesia (DDK) rate evaluation, as well as the formant frequencies F1 and F2 of the fricative consonants. One-way ANOVA and two-way ANOVA were used. Results: In the Perceptual Auditory Analysis of laypersons, there was a worsening in the values of T0 to T1 in all the retainers, but only for CWA and VF the values were statistically lower. In T2 the values increased, but for the VF the value still remained statistically lower than T0 while for the AHWA the difference of T0 for T2 was practically null. There were no changes in DDK values. For the formant frequencies, in general way there was a difference from T0 to T1 and a little difference from T0 to T2, whereas in the comparison among the devices the CWA presented greater changes in the F1 formants of some consonants, whereas AHWA presented lower values, with the others devices showing intermediate values. Conclusions: In both types of analysis (subjective and objective), there was a change in speech after the installation of each retainer, with an improvement after 21 days of use. The laypersons considered larger speech disorders involving VF, and smaller ones involving AHWA. For the acoustic analysis, the changes were greater for CWA, whereas for AHWA there were lower changes.<br>Introdução: O objetivo deste estudo foi avaliar a influência de diferentes contenções superiores na fala, através de análise perceptiva auditiva por leigos e análise acústica. Métodos: Dezoito voluntários foram selecionados para utilizar quatro tipos de contenções superiores, sendo elas: placa Wrap-Around convencional (WAC), Wrap- Around modificada em formato de ferradura (WAF) Wrap-Around modificada com orifício anterior (WAO) e contenção termoplástica transparente (CTT). Elas foram usadas por 21 dias cada, com intervalos de 7 dias sem utilização entre elas. A avaliação da fala foi realizada em gravações de trechos vocais realizadas antes da instalação das contenções (T0), imediatamente após a instalação de cada contenção (T1), assim como após 21 dias de uso destas (T2). A análise perceptiva auditiva dos leigos foi realizada através da escala visual analógica de 100 mm, enquanto a análise acústica consistiu na avaliação da média da taxa de diadococinesia (DDC), bem como a frequência dos formantes F1 e F2 das consoantes fricativas. Os testes ANOVA a um critério e ANOVA a dois critérios foram utilizados. Resultados: Na análise perceptiva auditiva dos leigos houve uma piora nos valores de T0 para T1 em todas as contenções, mas somente para WAC e CTT os valores foram estatisticamente menores. Em T2 os valores voltaram a aumentar, mas para CTT ainda houve um valor estatisticamente menor do que T0 enquanto para WAO a diferença de T0 para T2 foi praticamente nula. Não houve alterações nos valores da DDC. Para os formantes, de uma maneira geral houve uma diferença de T0 para T1 e pouca diferença de T0 para T2, enquanto na comparação entre os aparelhos a WAC apresentou alterações maiores nos formantes F1 de algumas consoantes, enquanto WAO apresentou valores menores, e os demais dispositivos valores intermediários. Conclusões: Nos dois tipos de análise (subjetiva e objetiva) houve alteração na fala após a instalação de cada contenção, havendo uma melhora após 21 dias de uso. Os leigos consideraram maiores as alterações da fala envolvendo a CTT, e menores envolvendo WAO. Para a análise acústica os valores foram piores para WAC, enquanto para WAO as alterações foram menores.

Objetivo: avaliar, por meio de modelos digitalizados, o comportamento transversal do arco dentário superior de pacientes submetidos ao tratamento da má oclusão de Classe II, corrigida com o aparelho Pendulum, seguido de aparelhagem ortodôntica fixa nos períodos inicial, pós-distalização, pós-tratamento e longo tempo póstratamento. Material e Métodos: Oitenta modelos de 20 pacientes (14 do gênero feminino e 6 do masculino), foram digitalizados no aparelho REXCAN DS2. A média da idade, ao início do tratamento (T1), foi de 14,02 ± 1,62 anos, pós-distalização (T2), foi de 14,54 ± 1,61, ao final do tratamento (T3), 18,38 ± 1,84 anos, e no póstratamento (T4), 22,94 ± 1,34 anos. As distâncias intercaninos, interpré-molares e intermolares foram realizadas no programa Geomagic Studio 5®. A análise de variância dependente para medidas repetidas (ANOVA) foi utilizada para avaliar as alterações entre os períodos. Resultados: não ocorreram alterações transversais na distância intercaninos nas fases estudadas. Os pré-molares demostram um aumento na fase de aparelhagem fixa (T2-T3), para os segundos pré-molares a diferença foi observada entre o período inicial (T1) e os período pós-tratamento (T3). A distância dos primeiros molares alterou durante a fase de distalização (T1-T2), retornando aos valores iniciais durante a fase pós-tratamento (T3). Para os segundos molares, as alterações ocorreram durante o período de distalização (T2) e pós-tratamento (T3). Não ocorreram alterações na fase de longo tempo pós-tratamento. Conclusão: Os resultados permitem concluir que, durante o tratamento com o aparelho Pendulum seguido pelo fixo, ocorrem alterações transversais no arco superior, no entanto, estas alterações permanecem estáveis cinco anos pós-tratamento.<br>Objective: The aim of this longitudinal study was to asses transversal changes in maxillary dental arch in twenty patients between 14 and 18 years old, treated first by Pendulum and followed by fixed appliances. Material and Methods: Dental measurements in eighty digital 3D models were obtained in pretreatment, postdistalization, post-treatment and long-term post-treatment phases. The statistical analysis was performed by ANOVA test. Results: Premolars and molars distances increased during the fixed appliance treatment (post-distalization and post-treatment phase) and in the long post-treatment phase there were no significant changes. No significant difference was observed in canines transversal distance. Conclusion: It was concluded that Pendulum followed by the fixed appliances, changes dental arch width during the full treatment and it was stable in the long-term post-treatment.

The aim was to explore the possibility to diagnose retained placental tissue and other placental complications with 3D ultrasound and to investigate the impact of previous caesarean section on placentation in forthcoming pregnancies. 3D ultrasound was used to measure the volumes of the uterine body and cavity in 50 women with uncomplicated deliveries throughout the postpartum period. These volumes were then used as reference, to diagnose retained placental tissue in 25 women with secondary postpartum haemorrhage. All but three of the 25 women had retained placental tissue confirmed at histopathology. The volume of the uterine cavity in women with retained placental tissue was larger than the reference in most cases, but even cavities with no retained placental tissue were enlarged (Studies I and II). Women with their first and second birth, recorded in the Swedish medical birth register, were studied in order to find an association between previous caesarean section and retained placenta. The risk of retained placenta with heavy bleeding (&gt;1,000 mL) and normal bleeding (≤1,000 mL) was estimated for 19,459 women with first caesarean section delivery, using 239,150 women with first vaginal delivery as controls. There was an increased risk of retained placenta with heavy bleeding in women with previous caesarean section (adjusted OR 1.61; 95% CI 1.44-1.79). There was no increased risk of retained placenta with normal bleeding (Study III). Placental location, myometrial thickness and Vascularisation Index were recorded on 400 women previously delivered by caesarean section. The outcome was retained placenta and postpartum haemorrhage (≥1,000 mL). There was a trend towards increased risk of postpartum haemorrhage for women with anterior placentae. Women with placenta praevia had an increased risk of retained placenta and postpartum haemorrhage. Vascularisation Index and myometrial thickness did not associate (Study IV). In conclusion: 3D ultrasound can be used to measure the volume of the uterine body and cavity postpartum, but does not increase the diagnostic accuracy of retained placental tissue. Previous caesarean section increases the risk of retained placenta in subsequent pregnancy, and placenta praevia in women with previous caesarean section increases the risk for retained placenta and postpartum haemorrhage.