ObjectiveThe aim of this study was to compare recycled and unused orthodontic miniscrews to determine the feasibility of reuse. The comparisons included both miniscrews with machined surfaces (MS), and those with etched surfaces (ES).MethodsRetrieved MS and ES were further divided into three subgroups according to the assigned recycling procedure: group A, air-water spray; group B, mechanical cleaning; and group C, mechanical and chemical cleaning. Unused screws were used as controls. Scanning electron microscopy, energy-dispersive X-ray spectrometry, insertion time and maximum insertion torque measurements in artificial bone, and biological responses in the form of periotest values (PTV), bone–implant contact ratio (BIC), and bone volume ratio (BV) were assessed.ResultsMorphological changes after recycling mainly occurred at the screw tip, and the cortical bone penetration success rate of recycled screws was lower than that of unused screws. Retrieved ES needed more thorough cleaning than retrieved MS to produce a surface composition similar to that of unused screws. There were no significant differences in PTV or BIC between recycled and unused screws, while the BV of the former was significantly lower than that of the latter (p < 0.05).ConclusionsThese results indicate that reuse of recycled orthodontic miniscrews may not be feasible from the biomechanical aspect.

(Table 1).일정한 회전속도와 수직력을 갖는 구동 모터식 토크 시험기(Biomaterials Korea Inc., Seoul, Korea)를 이용하여 삽입 및 제거 시의 토크를 연속적으로 측 정하였다 (Fig 2). 연속적으로 측정된 데이터는 시간 에 따른 토크의 변화량으로 도시하여 삽입 시간 및 토크를 쉽게 알아볼 수 있도록 하였다. (Fig 4). 이후 나머지 모든 미니 임플랜트들도 제거되었으며 제거된 미니 임플 랜트들은 토크에 영향을 줄 수 있는 미니 임플랜트 tip이나 thread의 변형이 없는지 확인하기 위해 공구 현미경(MF-A1010H, Mitutoyo, Japan)을 이용하여 5 배율로 관찰하였다 (Fig 5). (Table 3). 피질골 두께가 2 mm에서 4 mm로 증가함에 따른 총 삽입 시간의 변 화는 A군에서 가장 큰 증가를 보였으며, C군에서 가장 작은 증가를 보였다 (Fig 6). 최대 삽입 토크(Maximum insertion torque)미니 임플랜트의 식립 과정 중 나타나는 최대 토 크를 비교한 결과, 2 mm 두께의 피질골을 갖는 인 공골에서는 A군이 다른 두 군에 비해 높은 값을 보 였으나 (Table 2), 4 mm 두께의 피질골을 갖는 인공 골에서는 C군, A군, B군 순으로 높은 토크 값을 보 였으며 세 그룹 간의 차이는 모두 통계학적으로 유 의하였다 (Table 3). 윤순동, 임성훈 대치교정지 39권 2호, 2009년100 최대 제거 토크(Maximum removal torque)미니 임플랜트의 제거 과정 중 나타나는 최대 토 크를 비교한 결과, 2 mm 두께의 피질골을 갖는 인 공골에서는 세 군 간에 유의할 만한 차이를 보이지 않았다 (Table 2). 하지만 4 mm 두께의 피질골을 갖 는 인공골 시편에서는 C군이 다른 두 군에 비해 유 의하게 높은 토크 값을 보였다 (Table 3) Objective: The purpose of this study was to evaluate the effect of length and shape of cutting flute on mechanical properties of orthodontic mini-implants. Methods: Three types of mini-implants with different flute patterns (Type A with 2.6 mm long flute, Type B with 3.9 mm long and straight flute, Type C with 3.9 mm long and helical flute) were inserted into the biomechanical test blocks (Sawbones Inc., USA) with 2 mm and 4 mm cortical bone thicknesses to test insertion and removal torque. Results: In 4 mm cortical bone thickness, Type C mini-implants showed highest maximum insertion torque, then Type A and Type B in order. Type C also showed shortest total insertion time and highest maximum removal torque, but Type A and B didn't showed statistically significant difference in insertion time and removal torque. In 2 mm cortical bone thickness, there were no significant difference in total insertion time and maximum removal torque in three types of mini-implants, but maximum insertion torque of Type A was higher than two other Types of mini-implants. Conclusions: Consideration about length and shape of cutting flute of mini-implant is also required when the placement site has thick cortical bone.