Primary stability of orthodontic miniscrews inserted into femurs of osteopenic rats

Aim: To test the hypothesis that bone quality may affect the stability of anchorage devices implanted in a rat model. Methods: Twenty male Wistar rats were divided into 2 groups: Group 1 (rats treated with FK506) and Group 2(rats treated with saline solution vehicle). The immunosuppressant tacrolimus was used with the intention of causing a condition of osteopenia in Group 1. A total of 20 orthodontic mini-implants were used. One mini-implant was inserted in the right femur of each rat. After sacrificing the animals, blocks of bone tissue containing the mini-implants were removed for mechanical pull-out tests to be performed in a universal test machine at a crosshead speed of 0.5 mm/s. The maximum insertion force values and pull-out test were recorded and submitted the nonparametric analyses including the Kruskal-Wallis test and Mann-Whitney tests (p<0.05). The test for Pearson’s correlation was used to verify the correlation between bone mineral density and the pull-out test. The dose of FK506 was 2 mg/kg/day. Densitometric analysis was performed to observe the effect of FK506 on the bone mineral density. Results: The mean insertion force values were similar in both groups, with no statistically significant difference between them (P > 0.05). The mean pull-out force values were higher in Group 2 than in Group 1, with statistically significant difference between the groups (P < 0.05). Conclusions: Bone quality may affect the stability of mini-implants. Orthodontic mini-implants did not present good primary stability in a rat model with osteopenia.

Long-term fluoride release from resin-reinforced orthodontic cements following recharge with fluoride solution

The aim of this study was to test the hypothesis that there is no difference in the fluoride release behavior of resin-reinforced glass ionomer cements before or after fluoride recharge. The materials were divided into 5 groups: 2 resin-reinforced glass ionomer cements used for attaching orthodontic bands, that is, group FOB (Fuji Ortho Band) and group MCB (Multi-Cure Glass Ionomer Orthodontic Band Cement); 2 resin-reinforced glass ionomer cements and a composite used for bonding orthodontic brackets, that is, group OGLC (Ortho Glass LC), group FOLC (Fuji Ortho LC), and group TXT (Transbond XT), respectively. Fluoride release was measured during a 60-day period by using selective ion electrodes connected to an ionic analyser. After 4 weeks, the samples were exposed to 0.221 percent sodium fluoride solution. The results showed that cements achieved a maximum fluoride release 24 h after initial setting. No statistically significant differences were observed between groups FOB and OGLC regarding the amount of released fluoride following fluoride recharge from day 31 to day 36 (p>0.05). In conclusion, FOB and OGLC cements showed a higher capacity of capturing and releasing fluoride compared to the other cements studied.

O objetivo deste estudo foi testar a hipótese que não há diferença no desempenho dos cimentos de ionômero de vidro reforçados com resina entre si quanto à liberação de flúor antes e após recarga com flúor. Os materiais foram divididos em 5 grupos: 2 cimentos de ionômero de vidro reforçados com resina utilizados para cimentação de bandas ortodônticas: Grupo FOB (Fuji Ortho Band) e Grupo MCB (Multi-Cure Glass Ionomer Orthodontic Band Cement); 2 cimentos de ionômero de vidro reforçados com resina e 1 compósito utilizados para colagem de bráquetes ortodônticos: Grupo OGLC (Ortho Glass LC), Grupo FOLC (Fuji Ortho LC); e Grupo TXT (Transbond XT), respectivamente. A liberação de flúor foi medida durante 60 dias, através de eletrodo íon seletivo conectado a um analisador de íons. Após 4 semanas, os corpos de prova foram expostos a solução de fluoreto de sódio à 0,221 por cento. Os resultados evidenciaram que os cimentos atingiram o pico máximo de liberação de flúor com 24 h após presa inicial. Não houve diferença estatisticamente significante entre a quantidade de flúor liberado após as recargas de fluoreto de sódio entre os grupos FOB e OGLC do 31° ao 36° dia (p>0.05). Concluindo os cimentos FOB e OGLC apresentaram maior capacidade de captação e liberação de flúor comparada aos outros CIVRRs.