A three-dimensional finite element analysis of permanent maxillary central incisors in different stages of root development and trauma settings.

BACKGROUND AND OBJECTIVES: Differences in dental maturation may affect the prognosis and clinical management of traumatized teeth. However, evaluation of the outcomes of dental trauma to the tooth and support structures in an in vivo model involves major methodological and ethical implications. Thus, the aim of the present study was to perform a three-dimensional finite element analysis of permanent maxillary central incisors in different stages of root development under different trauma settings. METHODS: The study factors included two trauma conditions (B, buccal; I, incisal) on upper permanent central incisors showing three different stages of root development (CR, complete rhizogenesis; IRA; incomplete rhizogenesis in the apical third of the root; and IRM, incomplete rhizogenesis in the middle third of the root) to yield six models. The complete rhizogenesis model was obtained with a cone-beam computed tomography examination of an extracted tooth. The two incomplete rhizogenesis models were modeled on the basis of similar examinations of patients. Trauma was simulated by applying a 300 N static surface to surface load on the incisal edge or perpendicular to the buccal surface of the tooth. The displacement and equivalent von Mises (σvM) stress values were obtained for alveolar bone, periodontal ligament, apical papilla, and dentin for the quantitative analysis. A σvM color-coded scale was used for qualitative analysis. RESULTS: The force direction had a greater influence on the stress than the root-formation stage. Buccal forces resulted in higher stress concentration in the bone and periodontal ligament, especially in B-CR. Lower stress was found on the periodontal ligament as the root formation progressed (decrease of 8% from B-IRA to B-CR and 11% from B-IRM to B-CR). The incomplete rhizogenesis models showed higher σvM stress peak values in dentin in comparison with complete rhizogenesis (increase of 52% from B-CR to B-IRA and 56% from B-CR to B-IRM). CONCLUSIONS: Buccal forces yielded greater stress values regardless of the stage of rhizogenesis. Teeth with fully formed roots showed a higher stress concentration in the alveolar bone and periodontal ligament in comparison with immature teeth, with the latter presenting high stresses in the tooth crown.

Effect of double flasking and investing methods on artificial teeth movement in complete dentures processing.

PURPOSE: The aim of this study was to evaluate linear dimensional alterations of artificial teeth for complete dentures when using different investment and flasking techniques. BACKGROUND: Dimensional changes in the vertical dimension may occur owing to changes in artificial teeth positioning caused by different investing and flasking techniques. MATERIALS AND METHODS: Thirty pairs of the complete dentures were manufactured and randomly divided into three groups (n = 10): (1) invested with type III stone in monomaxillary PVC flask; (2) invested with type III stone in bimaxillary PVC flask; and (3) invested with laboratory silicone in bimaxillary PVC flask. Dentures were polymerised by microwave, and 12 linear distances were measured before and after denture processing. Data were analysed by one-way anova, considering manufacturing technique as the study factor. Tukey's HSD was used as post hoc ANOVA (p = 0.05). RESULTS: Most of the linear distances were comparable for all groups. All transversal maxillary and mandibular distances were higher for group 1 compared with groups 2 and 3 (p < 0.05), except the distance 3-6 for mandibular arch, in which no difference was found between groups (p < 0.05). Both maxillary diagonal distances were higher in group 1 (p < 0.05), and no differences were found among all groups for mandibular measurements. CONCLUSIONS: Double flasking technique independent on the investment material is shown to be the most effective method to reduce changes in artificial teeth positioning.

Effect of a calcium glycerophosphate fluoride dentifrice formulation on enamel demineralization in situ.

PURPOSE: To evaluate in situ the effect and mechanisms involved in the anticariogenic effect of a calcium glycerophosphate fluoride dentifrice. METHODS: In a double-blind, crossover design, a non-F dentifrice (negative control), a F dentifrice and a F dentifrice containing 0.13% CaGP were compared regarding the inhibition of enamel demineralization. Both F dentifrices contained 1500 microg F/g (w/w) as sodium monofluorophosphate (MFP). Bovine enamel blocks were mounted in contact with a S. mutans test plaque, in palatal appliances worn by 10 volunteers. 30 minutes after treatment with the dentifrices, a sucrose rinse was performed and enamel demineralization was assessed after an additional 45 minutes. RESULTS: No significant difference was observed among groups in the calcium and inorganic phosphate concentrations in the fluid phase of the test plaque 30 minutes after the dentifrice use (P > 0.05), but F concentration was significantly higher for both F dentifrices (P < 0.05). Also, the dentifrices did not differ regarding the pH before or 5 minutes after the sugar challenge (P > 0.05). A higher mineral loss was observed for the non-F dentifrice group (P < 0.05), but no significant difference was observed between the F dentifrices containing CaGP or not (P > 0.05). Using this in situ model, the findings suggested that CaGP at the concentration tested did not enhance the inhibition of enamel demineralization promoted by F dentifrice.

Effect of interocclusal appliance on masticatory performance of patients with bruxism.

This study was designed to evaluate masticatory performance in bruxist patients. The experimental group was composed of 16 dentate volunteers presenting with bruxism and treated by interocclusal appliances and a control group, consisting of 16 dentate volunteers with no symptoms of bruxism. To evaluate masticatory performance, the volunteers chewed .03 grams of peanuts contained in polyvinyl wrapper for four and twelve masticatory cycles. The number of chewed particles was counted using an optical scanning method by Image-Pro Plus 1.4 software (Media Cybernetics, Inc., Silverspring, MD). The score was expressed as the mean of the number of chewed particles for each wrapper. Masticatory performance evaluations were carried out in a single period for the control group and for the experimental group, before interocclusal appliance insertion, and after seven, 15, 30, and 60 days. Comparison between groups, as well as between before and after interocclusal appliance insertion, showed no significant differences (P>.05), irrespective of the number of masticatory cycles.

Encaixes intracoronários de semi-precisão: relato de caso clínico / Intracoronal semi-precision attachments: a clinical case report

Os encaixes são elementos constituintes de uma prótese parcial remivível (PPR), alternativos aos grampos convencionais. Estes retentores podem ser classificados, quanto à localização, com intrarradiculares, intra ou extracoronários; quanto ao modo de confecção, como de precisão ou semi-precisão; e quanto às características de rigidez e resiliência. Os retentores de semi-precisão são conhecidos como encaixes fresados e são obtidos laboratorialmente. As próteses a encaixes são mais estéticas, confortáveis e, do ponto de vista biomecânico, mais favoráveis do que as próteses parciais removíveis convencionais, e requerem maior conhecimento, experiência e tempo, tanto por parte do Cirurgião-dentista quanto do Técnico laboratorial. O presente trabalho tem como objetivo a apresentação de um caso clínico de PPR retida por emcaixes intracoronários rígidos de semi-precisão e discutir os princípios de sua formação

Effect of a denture cleanser on weight, surface roughness, and tensile bond strength of two resilient denture liners / Efeito do detergente na dentadura pelo peso, superfície rugosa, e força adesiva de tensão de dois revestimentos resilientes na dentadura

Purpose: This study evaluated the effects of a denture cleanser on weight change, roughness, and tensile bond strength on 2 denture resilient lining materials. Material and methods: Forty specimens of microwave acrylic resin (Onda-Cryl), 30 mm in diameter and 4 mm thick, were prepared to verify weight change and surface roughness. The specimens were divided into 4 groups consisting of 10 specimens each, relined with a resilient liner (Coe Soft or Dentusoft), and treated (Polident or tap water). To evaluate tensile bond strength, 12 specimens were used for each group. All specimens were stored in artificial saliva for 15 days, immersed once a day in Polident or tap water, and evaluated at 0 hours and after 24 hours and 7 and 15 days. Roughness was evaluated by use of a profilometer. Weight changes were recorded in milligrams and expressed as the percentage of weight difference between the periods of evaluation. Tensile bond strength was determined with a universal testing machine. The specimens were placed under tension until failure by a cross-speed of 5 mm/min with a 500 Kg load cell. The type of failure was determined by use of stereoscopic microscopy at original magnification ž8. The data were submitted to analysis of variance and compared by Tukey's test (alfa=.05). Results: Specimens immersed in Polident showed higher and significant (P<.05) weight changes (percent) than those immersed in water between 24 hours and 7 days (Coe Soft-Polident: 0.48 ± 0.09; Coe Soft-water: 0.28 ± 0.09; Dentusoft-Polident: 0.44 ± 0.16; Dentusoft-water: 0.22 ± 0.15) and between 7 and 15 days (Coe Soft-Polident: 0.08 ± 0.04; Coe Soft-water: - 0.17 ± 0.05; Dentusoft-Polident: 0.01 ± 0.04; Dentusoft-water: - 0.24 ± 0.03). There was significant difference (P<.05) in roughness (in micrometers), between treatments after 7 days (Coe Soft-water: 4.07 ± 0.22; Coe Soft-Polident: 3.36 ± 0.52; Dentusoft-water: 3.68 ± 0.72; Dentusoft-Polident: 3.26 ± 0.41) and 15 days (Coe Soft-water: 4.88 ± 0.29; Coe Soft-Polident: 3.53 ± 0.61; Dentusoft-water: 4.42 ± 1.12; Dentusoft-Polident: 3.68 ± 0.37). Tensile bond strength was highest (P<.05) after 15 days (Coe Soft-water: 5.19 ± 0.93; Coe Soft-Polident: 4.40 ± 0.38; Dentusoft-water: 4.42 ± 1.15; Dentusoft-Polident; 4.84 ± 1.14). Most failures were cohesive (Coe Soft: 76.04 percent and Dentusoft: 82.29 percent)...

Mais ética nas pesquisas / More thics in research

O respeito e o cuidado com a vida de quem participa de experimentos científicos são o foco central da bioética

In situ study of sucrose exposure, mutans streptococci in dental plaque and dental caries

O objetivo deste estudo foi investigar a relação entre exposição à sacarose, níveis de estreptococos do grupo mutans e cárie dental. Voluntßrios adultos participaram neste estudo cruzado realizado em 4 fases de 28 dias cada. Os voluntários utilizaram dispositivos intra-orais palatinos contendo blocos de esmalte dental humano e gotejaram solução de sacarose 20 por cento sobre os blocos dentais de 0 a 8 vezes/dia. Após cada fase, as unidades formadoras de colônias (UFC) foram determinadas na placa dental e cárie foi avaliada atravéz de microdureza da lesão do esmalte. Freqüência do uso de sacarose não teve efeito estatisticamente significante nos níveis de estreptococos do grupo mutans. Nos testes de microdureza, diferenças significativas (p<0,05) em relação à área de perda mineral somente foram observadas quando a exposição à sacarose foi de 8 vezes/dia. Resultados similares foram obtidos quando a microdureza da lesão de cárie foi avaliada a cada distância da superfície do esmalte.