A study on the changes in attractive force of magnetic attachments for overdenture
PURPOSE Although magnetic attachment is used frequently for overdenture, it is reported that attractive force can be decreased by abrasion and corrosion. The purpose of this study was to establish the clinical basis about considerations and long term prognosis of overdenture using magnetic attachments by investigating the change in attractive force of magnetic attachment applied to the patients. MATERIALS AND METHODS Among the patients treated with overdenture using magnetic attachments in Dankook University Dental Hospital, attractive force records of 61 magnetic attachments of 20 subjects who re-visited from July 2013 to June 2014 were analyzed. Dental magnet tester (Aichi Micro Intelligent Co., Aichi, Japan) was used for measurement. The magnetic attachments used in this study were Magfit IP-B Flat, Magfit DX400, Magfit DX600 and Magfit DX800 (Aichi Steel Co., Aichi, Japan) filled with Neodymium (NdFeB), a rare-earth magnet. RESULTS Reduction ratio of attractive force had no significant correlation with conditional variables to which attachments were applied, and was higher when the maintenance period was longer (P<.05, r=.361). Reduction ratio of attractive force was significantly higher in the subject group in which attachments were used over 9 years than within 9 years (P<.05). Furthermore, 16.39% of total magnetic attachments showed detachment of keeper or assembly. CONCLUSION Attractive force of magnetic attachment is maintained regardless of conditional variables and reduction ratio increased as the maintenance period became longer. Further study on adhesive material, attachment method and design improvement to prevent detachment of magnetic attachment is needed.
Oral rehabilitation of a cleft palate patient with tooth-supported, telescopic magnetic overdenture
A 49-year-old male patient with residual cleft palate and missing pre-maxilla presented with an ill-fitting and unaesthetic maxillary denture. The posterior teeth were periodontally sound but crowded and had defective restorations and secondary caries. We restored the bilateral maxillary canines and first premolars with conical telescopic crowns having magnetic keepers. A metal-reinforced acrylic overdenture with magnetic attachments corresponding to the keepers of the telescopic crowns was fabricated. The telescopic crowns provided a single path of insertion, retention and stability to the prosthesis. The magnetic attachments provided additional retention and self-centring properties. The prosthesis effectively sealed the oronasal communication and enhanced the function, aesthetics and oral hygiene. The 6-month and 1-year follow-ups revealed that the patient was delighted, and the prosthesis provided excellent obturation and function. Periodic follow-up, maintenance, patient education and meticulous oral hygiene are vital for long-term success of such prostheses.
Shear strength of orthodontic direct-bonding adhesives.
A total of 210 double-width stainless steel edgewise brackets with retentive lip bases were bonded to bovine incisors with seven commercially available direct-bonding materials. Ten samples for each of the seven direct-bonding materials were tested for shear strength using the Instron Universal Testing Instrument. The samples were tested after 1 day, 1 month, and 3 months of immersion in 30 per cent physiologic saline solution. The mean shear strength of each direct-bonding material at each time interval was compared statistically to the mean shear strength of each of the materials at each time interval with a matched 1 test. The same test was used to determine whether there had been a significant change in mean shear strength from start to finish of testing for each material. One product showed a significantly better mean shear strength than any other material at each test interval. The remaining materials were grouped in middle or low ranges, depending upon their final mean shear strengths and degrees of nonsignificance when compared to each other.