Stress distribution in the mini-screw and alveolar bone during orthodontic treatment: a finite element study analysis.

OBJECTIVE: This study aimed to investigate the reason for high failure rates of mini-screws during orthodontic treatment. We hypothesized that decreasing the length of the mini-screw outside the bone relative to the length inside the bone (outside/inside length ratio) and equalising it to the tooth crown/root ratio would lead to increased stability of the mini-screw against lateral loading when assessed using finite element analysis. METHODS: We analysed stress distribution of mini-screws in the cortical and trabecular bone and von Mises stress levels when a 2-N force was applied to the head of four mini-screws of 6, 8, 10 and 12 mm in length. The direction of the force was perpendicular to the major axis of the screws. RESULTS: Stress levels of screws in cortical bone increased in proportion to the length of mini-screws outside the bone. The length of mini-screws inside the bone did not affect stress levels in the cortical bone. CONCLUSIONS: The results of this finite element analysis indicate that to stabilize the mini-screw, controlling the screw length outside the bone is more important than controlling the outside/inside length ratio.

Topographic and radiographic profile assessment of dental erosion. Part III: Effect of green and black tea on human dentition.

This study compared green and black tea to soda and orange juice in terms of their erosive effect on the human dentition. Vinegar and water were used as active and passive control fluids. An accelerated in vitro test was used to monitor how short- and long-term exposure to these fluids affected the topography and morphology of the coronal segments of the human dentition. This 20-week test was conducted under controlled conditions, independent of the influencing factors of the oral environment. The erosive effects of these fluids were categorized generally into three groups: highly erosive (vinegar), moderately erosive (soda and orange juice), and minimally erosive (black and green tea). The erosive effect of tea was similar to that of water, which has no erosion potential. Given the systemic and dental benefits of tea and the low potential for erosion, green and black tea should be highly encouraged for daily beverage consumption.

Topographic and radiographic profile assessment of dental erosion. Part II: effect of citrus fruit juices on human dentition.

This study sought to monitor changes in the topography, morphology, and radiographic profiles of human permanent teeth that had been exposed to citrus fruit juices. The effect of long-term exposure was monitored for a prolonged duration of 20 weeks according to set criteria. Topographic and morphologic changes were observed at weekly intervals following challenge by test fluids (orange, lemon, and grapefruit juices) and compared with control fluids (acetic acid and water). The qualitative changes in the specimens' topography and the morphology of citrus fruit juices and control fluids are described as a function of time, in specific details. The digitized radiographic images obtained at four-week intervals were analyzed and the changes were assessed. The results indicated that orange juice specimens demonstrated the mildest changes, while lemon juice specimens displayed the most severe damage to the coronal segments of the teeth. This damage manifested as loss of cusp height, cervical enamel, and coronal radius, as well as reduction of enamel cap height. Of the tested and control fluids, lemon juice displayed the most eros ion, followed by acetic acid, grapefruit juice, orange juice, and water, which had no effect. Continued immersion in the four acidic fluids led to varying degrees of enamel loss progression.

Topographic and radiographic profile assessment of dental erosion--Part I: Effect of acidulated carbonated beverages on human dentition.

Evidence-based case reports and epidemiologic surveys have indicated an association between dental erosion and high consumption of acidulated carbonated beverages (ACBs). This study sought to monitor the effect of exposure to ACBs on the topography and geometrical profile of disassociated human dentition. Two representatives of ACBs, caramelized (ACCB) and non-caramelized (AN-CCB), were evaluated along with control liquids. Following exposure to the fluids, qualitative assessment of topographic changes and quantitative analysis of digitized serial radiographic tracings were performed at four-week intervals for 20 weeks. Within the controlled perimeters of this in vitro test, the erosive effects of ACBs were closely similar but were lower than those caused by acetic acid (control fluid). These effects were indicated by changes in enamel topography (such as color, translucency, texture, and integrity) as well as reduction in specimen profile parameters. This amounted to an average weekly reduction in cusp tip height, a loss of cervical enamel, a reduction of enamel cap height, and reduction of crown radius for the ACBs and acetic acid.