Discoloration and force degradation of orthodontic elastomeric ligatures.

OBJECTIVE:: The aim of the present study was to evaluate color changes and force degradation of orthodontic elastomeric ligatures in different stretching patterns during a 8-weeks period. METHODS:: Two elastomers with the minimum and two with the maximum color changing, and gray elastomers of two brands (American Orthodontics and Ortho Technology) were selected according to an opinion poll with clinicians and color changes after 4 weeks of intraoral use were evaluated. These elastomers were mounted on special jigs fabricated using a CAD-CAM technique, underwent different stretching patterns and the force was measured in 0, 24 hours, 2, 4 and 8 weeks. During in vivo part of the study, force levels of elastomers were measured after 4 weeks on a material testing machine. Data were analyzed with four-way ANOVA and Tukey post hoc tests. RESULTS:: All the elastomers showed color changing but the degree of color stability was significantly different. The mean force degradation was higher in 1-mm stretch groups. After 8 weeks, the average residual force of elastomers was 1.45 ± 0.18 N and the maximum force decay was seen in the elastomers that exhibited the maximum initial force. CONCLUSION:: There is significant relationship between the stretching pattern and the amount of residual force of elastomers. Elastomers with higher initial forces exhibited higher percentages of force loss after 8 weeks. It seems that there is a relationship between initial color and color changing of elastomers.

Measurement of the levels anxiety, self-perception of preparation and expectations for success using an objective structured clinical examination, a written examination, and a preclinical preparation test in Kerman dental students.

STATEMENT OF THE PROBLEM: Examinations have an important role in evaluating students' learning outcomes and their mastery of a subject. Passing or failing an examination can have far-reaching consequences for the students. Therefore, it is not surprising that international studies consistently show that dental students report examinations and grades among the highest ranking stressors in dental schools. PURPOSE: The aim of this research was to measure the levels of anxiety, self-perception of preparation and expectations for success using an objective structured clinical examination (OSCE), a written examination and a preclinical preparation test, and to examine the effects of the three predictive variables on the outcomes of assessments. MATERIALS AND METHODS: The present research is a cross-sectional study. The population under consideration was students of Kerman Dental School in 2013. Examination anxiety was measured with Spielberger's state anxiety inventory. Preparation for the assessment (I am fully prepared = 4, I am prepared = 3, I'm not prepared = 2, I'm not fully prepared = 1) and expectation to succeed (I am quite successful = 4, I am successful = 3, I'm not successful = 2, I'm not quite successful = 1) were quantified with Likert scale. The questionnaire was completed during an OSCE, a written examination, a preclinical crown and bridge preparation test and a nonexamination situation. RESULTS: The study population consisted of 138 4th, 5th, and 6th year Kerman dental students (65 males and 73 females). The results showed that all the assessment methods induced a significant increase in state anxiety compared to baseline levels with the highest anxiety levels reported during an OSCE (62.4 ± 8.1, P = 0.04) and a written examination (48.8 ± 9.2, P = 0.04). The preparation levels in females were significantly higher than those in males in OSCE (P = 0.03) and written (P = 0.04). CONCLUSION: State anxiety was high in all the three assessment methods. OSCE induced more anxiety than other assessment formats. However, anxiety was not predictive of performance outcomes in contrast to preparation and expectation to succeed, which were good predictors of the outcome scores. Also, this study showed that despite a better answer to the assessment of (I prepared myself well for the test), the students showed high levels of state anxiety.

Evaluation of the effect of different stretching patterns on force decay and tensile properties of elastomeric ligatures.

BACKGROUND: There have been numerous researches on elastomeric ligatures, but clinical conditions in different stages of treatment are not exactly similar to laboratory conditions. The aim of this in vitro study was to simulate clinical conditions and evaluate the effect of three stretching patterns on the amount of force, tensile strength (TS) and extension to TS of the elastomers during 8 weeks. MATERIALS AND METHODS: Forces, TS and extension to TS of two different brands of elastomers were measured at initial, 24 h and 2, 4, and 8-week intervals using a testing machine. During the study period, the elastomers were stored in three different types of jig (uniform stretching, 1 and 3 mm point stretching) designed by the computer-aided design and computer-aided manufacturing technique in order to simulate the different stages of orthodontic treatment. RESULTS: The elastomeric ligatures under study exhibited a similar force decay pattern. The maximum force decay occurred during the first 24 h (49.9% ± 15%) and the amount of force decay was 75.7% ± 8% after 8 weeks. In general, the TS decreased during the study period, and the amount of extension to TS increased. CONCLUSION: Although the elastic behavior of all ligatures under study was similar, the amount of residual force, TS and extension to TS increased in elastomers under point stretching pattern.

Effect of 0.2% chlorhexidine on microbial and fungal contamination of dental unit waterlines.

BACKGROUND: It is known that dental unit waterline can be a source of infection. The aim of this study was to evaluate the efficacy of a mouthwash, chlorhexidine, in controlling microbial and fungal contamination of dental unit waterlines. MATERIALS AND METHODS: In the present experimental study, the water in high-speed handpieces and air/water syringes of 35 dental units in a dental school was investigated microbiologically. Five of the units and one tap water served as controls; 100-200-mL water samples were collected aseptically in sterile containers in the morning after a 2-min purge. Water reservoir bottles were emptied and 50 mL of 0.2% chlorhexidine mouthwash was introduced into the tank. Then the water syringe was used to flush the waterline until the pink-colored chlorhexidine was observed to flow from the water syringe. Before the next day's session and before the students used the unit, two water samples from the water syringe and water turbine was collected. The samples were transferred to the laboratory. After 48 h at 37°C, the microbial colonies were counted. The number of these colonies was evaluated using colony forming unit CFU. Data were analyzed with Mann - Whitney U test and SPSS 13.5 statistical program. The statistical significance was defined at P ≤ 0.05. RESULTS: All 35 units were contaminated before chlorhexidine use; no contamination was detected after adding chlorhexidine to the waterlines of the units. After week 1, 28 of the 30 treated dental unit waterlines (DUWLs) had values of CFU/mL less than 200. CONCLUSION: The present study showed that the use of chlorhexidine could reduce microbial counts in dental unit waterlines.

Discoloration and force degradation of orthodontic elastomeric ligatures

ABSTRACT OBJECTIVE: The aim of the present study was to evaluate color changes and force degradation of orthodontic elastomeric ligatures in different stretching patterns during a 8-weeks period. METHODS: Two elastomers with the minimum and two with the maximum color changing, and gray elastomers of two brands (American Orthodontics and Ortho Technology) were selected according to an opinion poll with clinicians and color changes after 4 weeks of intraoral use were evaluated. These elastomers were mounted on special jigs fabricated using a CAD-CAM technique, underwent different stretching patterns and the force was measured in 0, 24 hours, 2, 4 and 8 weeks. During in vivo part of the study, force levels of elastomers were measured after 4 weeks on a material testing machine. Data were analyzed with four-way ANOVA and Tukey post hoc tests. RESULTS: All the elastomers showed color changing but the degree of color stability was significantly different. The mean force degradation was higher in 1-mm stretch groups. After 8 weeks, the average residual force of elastomers was 1.45 ± 0.18 N and the maximum force decay was seen in the elastomers that exhibited the maximum initial force. CONCLUSION: There is significant relationship between the stretching pattern and the amount of residual force of elastomers. Elastomers with higher initial forces exhibited higher percentages of force loss after 8 weeks. It seems that there is a relationship between initial color and color changing of elastomers.

RESUMO OBJETIVO: o objetivo do presente estudo foi avaliar as alterações de cor e a degradação da força de ligaduras elásticas em diferentes padrões de estiramento, durante um período de 8 semanas. MÉTODOS: duas ligaduras elásticas com alteração mínima de cor, duas com alteração máxima de cor e ligaduras elásticas na cor cinza de duas marcas comerciais (American Orthodontics e Ortho Technology) foram selecionadas de acordo com uma pesquisa de opinião com clínicos, e mediante a avaliação das alterações de cor após quatro semanas em uso intrabucal. Essas ligaduras elásticas foram montadas em jigs fabricados por meio da técnica CAD-CAM e foram expostas a diferentes padrões de estiramento, e a força foi medida nos tempos de 0h, 24h; 2, 4 e 8 semanas. Durante a parte in vivo do estudo, os níveis de força das ligaduras elásticas foram medidos após 4 semanas, em uma máquina de teste de materiais. Os dados foram analisados com os testes ANOVA de quatro vias e post-hoc de Turkey. RESULTADOS: todas as ligaduras elásticas mostraram alterações de cor, mas houve diferenças significativas quanto ao grau de estabilidade da cor. A média de degradação da força foi mais alta nos grupos com estiramento a 1 mm. Após 8 semanas, a média da força residual nas ligaduras elásticas foi de 1,45 ± 0,18 N e a maior degradação na força foi observada nas ligaduras elásticas que apresentaram a maior força inicial. CONCLUSÃO: há uma relação significativa entre o padrão de estiramento e a quantidade de força residual nas ligaduras elásticas. As ligaduras elásticas com as maiores forças iniciais exibiram as mais altas porcentagens de degradação da força após 8 semanas. É, também, possível que haja uma relação entre a cor inicial da ligadura elástica e sua alteração de cor.