Na18F accumulates on the compressive side of peri-implant bone under immediate loading.

This study aimed to examine the dynamic change in bone metabolism by immediate loading in several sites around implants using high-resolution Na18F-PET scan. Two titanium implants (Ø 1.2 mm) were inserted parallel to each other in the right tibiae of Wistar rats (n = 4). The left tibia was set as control side. One day after insertion, closed coil springs of 4.0 N were attached to the expose superior portions of the implants to apply a continuous mechanical stress. The rats with fluorine-18 (18F) ion (5 mCi/rat) intravenously injected were scanned by PET scanner at 4, 7, 14, 28 days after load application. Round region of interests (ROIs) were set around the distal implant of the right tibia (loaded side) and same site (control) of the left tibia. Furthermore, four rectangular ROIs were set at the superior and inferior parts of traction side (mesial) and opposite side (distal) of the distal implant. Longitudinal dynamic changes in bone metabolism were evaluated by examination of the accumulation count of 18F ion at each ROI. The uptake values of ROIs (loaded side) initially increased until 7 days, and they gradually decreased from the peak level to the pre-loading level despite a static force being applied to the implants. In cancellous bone, the uptake values at the superior part of traction side and inferior part of opposite side showed significantly high value compared with those at other parts. In conclusion, immediate loading to the implant initially enhanced bone metabolism around it, especially at the part with compressive stress. Peri-implant bone metabolism varies according to different loading conditions.

Evaluation of peri-implant bone metabolism under immediate loading using high-resolution Na18F-PET.

OBJECTIVE: This study aimed to examine the influence of immediate loading on the dynamic changes of bone metabolism around dental implants using a high-resolution semiconductor sodium 18F-fluoride (Na18F)-PET. METHODS: Tibiae of 12 adult male rats were divided into 4 groups: immediate loading (IL), no loading (NL), bone defect (BD), and control (CTR). For the IL group, a 4.0-N load was applied continuously by two closed-coil springs attached between two implants in tibia. Each rat received an intravenous injection of Na18F and was scanned by high-resolution Na18F-PET at day 1 and then at weeks 1, 2, 3, 4, 5, 6, and 8 after surgery. Bone metabolism around the implant was evaluated by standardized uptake value (SUV), which indicates the outcome of Na18F accumulation. CT scanning was also performed, and PET and CT images were superposed to determine the anatomical orientation in PET images. RESULTS: Bone metabolism peaked at 7 days after surgery and then gradually decreased in all three test groups (IL, NL, and BD). SUVs of all three test groups were significantly higher than the baseline at 1, 2, 3, and 4 weeks after surgery, with SUVs in the IL group returning to baseline levels earlier than those in the NL and BD groups. CONCLUSIONS: Fluorine integrates preferentially with the initial low-calcified bone; thus, our results suggest that immediate loading promotes the calcification of the bone tissue in the early stage on peri-implant bone formation. CLINICAL RELEVANCE: Na18F-PET allows for an estimate of bone metabolism change around the implant.

Bone response to immediate loading through titanium implants with different surface roughness in rats.

Because of its high predictability of success, implant therapy is a reliable treatment for replacement of missing teeth. The concept of immediate implant loading has been widely accepted in terms of early esthetic and functional recovery. However, there is little biological evidence to support this concept. The objective of this study was to examine the interactive effects of mechanical loading and surface roughness of immediately loaded titanium implants on bone formation in rats. Screw-shaped anodized titanium implants were either untreated (smooth) or acid-etched. Two implants were inserted parallel to each other in the tibiae of rats, and a closed coil spring (2.0 N) was immediately applied. Trabecular and cortical bone around both implants was analyzed using microtomographic images, and a removal torque test was performed at weeks 1, 2, and 4. Immediate loading of acid-etched implants resulted in significant decreases in bone mineral density, contact surface area, and cortical bone thickness. These effects were not observed after immediate loading of smooth implants. Conversely, loading did not influence acid-etched implant fixation; however, smooth implant fixation at week 1 was significantly reduced. These results imply that surface roughness regulates bone response to mechanical stress and that immediate loading might not inhibit osseointegration for smooth and rough implants in the late healing stages.

Influence of immediate and early loading on bone metabolic activity around dental implants in rat tibiae.

OBJECTIVES: The aim of this study was to examine the influence of immediate and early loading on dynamic changes in bone metabolism around dental implants using bone scintigraphy. MATERIAL AND METHODS: Two titanium implants were inserted in the right tibiae of 21 rats. Closed coil springs with 4.0-N loads were applied parallel to the upper portion of the implants for 35 days. According to the load application timing, rats were divided into three groups: immediate loading (IL) group, early loading 1 day after implant insertion (1-D early loading [EL]) group, and loading 3 days after implant insertion (3-D EL) group. Rats were intravenously injected with technetium-99 m-methylene diphosphonate (Tc99 m-MDP) (74 MBq/rat) and scanned by bone scintigraphy at 1, 4, 7, 11, 14, 21, 28, and 35 days after load application. The ratio of accumulation of Tc99 m-MDP around the implants to that of a reference site (uptake ratio) was calculated to evaluate bone metabolism. RESULTS: In every group, the uptake ratio increased until 7 days after load application and then gradually decreased. It was significantly higher than baseline at 4, 7, 11, and 14 days (P < 0.001). The uptake ratio in the 1-D EL and 3-D EL groups were significantly higher than that in the control group and also that in the IL group (P < 0.001). CONCLUSIONS: Bone metabolism initially increased and then gradually decreased to baseline despite differences in load timing. Increases in bone metabolic activity differed according to load application timing; the later the load application, the more enhanced the bone metabolism.

Inhibition of necrotic actions of nitrogen-containing bisphosphonates (NBPs) and their elimination from bone by etidronate (a non-NBP): a proposal for possible utilization of etidronate as a substitution drug for NBPs.

PURPOSE: Nitrogen-containing bisphosphonates (NBPs) have powerful anti-bone-resorptive effects (ABREs). However, recent clinical applications have disclosed an unexpected side effect, osteonecrosis of the jaw. We previously found in mice that etidronate (a non-NBP), when coadministered with alendronate (an NBP), inhibited the latter's inflammatory effects. However, etidronate also reduced the ABRE of alendronate. The present study examined in mice the modulating effects of etidronate on the inflammatory and necrotic actions of zoledronate (the NBP with the strongest anti-bone-resorptive activity and the highest incidence of osteonecrosis of the jaw) and on ABREs of various NBPs including zoledronate. MATERIALS AND METHODS: NBPs were subcutaneously injected into ear pinnas of mice and ensuing inflammation and necrosis at the site of the injection were evaluated. ABREs of NBPs were evaluated by analyzing sclerotic bands induced in mouse tibias. RESULTS: Coinjection of etidronate reduced inflammatory and necrotic reactions induced by zoledronate, and also reduced the amount of zoledronate retained within the ear tissue. When both agents were intraperitoneally injected, etidronate reduced the ABRE of zoledronate and those of other NBPs. Notably, etidronate reduced the ABRE of zoledronate even when this non-NBP was injected 16 hours after the injection of zoledronate. Bone scintigram indicated that etidronate reduced the amount of zoledronate that had already bound to bone. CONCLUSIONS: These results suggest that etidronate may 1) inhibit the entry of NBPs into cells related to inflammation and/or necrosis, 2) inhibit the binding of NBPs to bone hydroxyapatite, 3) at least partly eliminate (or substitute for) NBPs that have already accumulated within bones, and thus 4) if used as a substitution drug for NBPs, be effective at treating or preventing NBP-associated osteonecrosis of the jaw.