Teeth that are completely knocked out of the mouth can be saved if the root isnt fractured or damaged, the socket isnt completely damaged, not too dirty, and replaced quickly. It will definately require a root canal, and there is still a good possiblity it will fail somewhere down the line. Has to be splinted in place for a few weeks with bonding and a wire ( almost looks like braces). Knocked out tooth shouldnt be scrubbed clean. Ideal thing to do is either place it in your mouth ( dont swallow it
) but the most common thing is to put it in milk. Dont try to clean it with anything else as it could damage the surface that is needed to reattach.
A loose tooth first has to be repositioned to its original position, then splinted in place similar to the above . Still likely to need root canal. And more likely to succeed than a completely avulsed tooth.
Any trauma, even if the teeth are not displaced could cause them to die, turn black, abscess, or become mobile. And usually, more than one tooth is involved. One may be loose, but the one next to it, that is solid, turns black in time.
Lemons as well as any acid will erode the enamel. Perfect example is a bulimic person. Not that you will have the opportunity, but check behind their upper incisors, and u will see it is thin, and yellow. The yellow is the 2nd layer of tooth ( just underneath the enamel) This is visible because the enamel has been worn away . Also people with acid reflux can cause the same, both due to the stomach acids.
over the counter whiteners are fine. Usually not as strong as the stuff in a dental office, but also usually 1/10 the price. May take longer to see a result, and most likely, but not always, will not have the same results. But still a good option.
Getting teeth cleaned makes them feel good, but unless you have a lot of external surface staining ( like smoking, coffee, tea) dont expect the teeth to look much whiter after a cleaning. The will feel nice and smooth, but the yellowness and staining you see is a result of internal staining, or stains that have really absorbed into the tooth. Only bleaching will lighten these up ( and not always, and not the same amount for each person) just as Bleaching will NOT remove the superfical smoking stains . So, ideal treatment to whiten teeth would be to get a cleaning first, then bleach immediately or soon after .
The one hour bleaching , usually 3X more expensive then the tray bleaching, wont necessarily make it any whiter. Just is a lot faster . so, u are paying for the in office chair time. If you have the time, patience and know u will follow the directions , save your money and just do the tray bleaching. Cold sensitivity is normal for all kinds of bleaching, usually goes away in time. Fluoride rinses could be used to minimize this side affect.
Finally, everything said is a generalization. DIfferent people, teeth, situations have differnt results. So I hope no one gets all wacky on me saying that they had a different experience, because I would be shocked if they didnt
Oh and about the soft vs hard food thing. Hard foods like pretzels, nuts , pop corn kernels are more likely to cause physical fractures in the teeth, where as softer foods are more likely to ' stick ' to your teeth, therefore, causing more cavities as the starchy sugars are adhering to your teeth. Dried fruit is just as bad as candy because of its high sugar content and ability to stick to your teeth. Not saying it shouldnt be eaten, just brush after you do .