The lower jaw does appear to be flexing but pretty close to normal limits as far as I can see. Here is a video of a Bearded Dragon eating a live mouse where you see the degree of flexibility of the mandible...
http://www.youtube.com/watch?v=vSass7hUGoc. A good indicator of bone strength is its ability to weight bear on its limbs. It appears to be able to stand on the front limbs with the body raised off the ground. If it can comfortably maintain this position then there is likely nothing to worry about.
All reptiles need two things to avoid developing MBD – adequate calcium in the diet and adequate vitamin D. Without vitamin D, reptiles are unable to absorb calcium from their gut or to make use of it in the body. So a diet rich in calcium is useless without vitamin D as the calcium will simply be all passed out with the normal wastes.
Adequate calcium can be achieved through dusting all insects offered every second feed.
Adequate vitamin D can be achieved through two means. Dusting of a meal no more than once a week with a reptile vitamin supplement containing vitamin D (but preferably no phosphorous). The other is to ensure adequate exposure to UVB light to allow reptiles to photosynthesis vitamin D in the skin, pretty much the same as humans do. Dragons are designed for extensive exposure to sunlight. This is the best source of vitamin D for them. So a sunbake for an hour of so three times a week around midday (depending on the time of year and prevailing temperatures and dryness etc) is ideal. Shade, cool water, protection from high temperatures and active supervision must always be provided to animals temporarily being exposed to sunlight.
Alternatively or in addition, a UVB light in the enclosure, above the basking spot, is a good substitute for natural sunlight. There are two main options - mercury vapour lamps and UV fluorescents. MV lamps are a heat source and UV all in one but are only suited to large enclosures due to their heat output. A straight fluorescent tube is the other best option, preferably with a UVB rating of 10% and usually recommended at about 30 cm from the basking reptile. These need to be replaced every 6 to 12 months (follow the manufacturer’s directions) as the UVB source degrades with use but being invisible this does not affect the visible brightness of the globe.
Blue