Dr. Claudia C. Cotca

If we are speaking about an all ceramic crown, depending on the age of the crown, a black spot may be cement undergoing decomposition or breakdown, dye accumulation from foods, liquids, or smoke through a crack in the crown, the tooth, or through a margin channel, and/or it may be decay. A clinical investigation would be needed to depict the source and the nature of the finding.

In my professional opinion, as a general and esthetic dentist, and as a toxicologist, I should state that every substance has a dose at which it projects thrapeutic and toxic profile.  Sometimes those concentration dosages are far apart, sometimes they are very near to each other.  FDA cleared products ensure that the concentrations provided in therapeutic formulations are safe to be used and they elicit a therapeutic effect.  Hydrogen peroxide is a very strong oxidizer, a scavanger for free radical (anti-oxidant like) generating complexes, which scavanges, if you will, other unpaired free radical linked compounds which are sometimes harmful.  Hydrogen Perioxide bleaches through this mechanism.  Of course, once the dosage surpases that dose that elicits the therapeutic effect it can cause harmful effects, like tissue sloghing and other progressive tissue breakdown, which may or may not lead to extreme conditions like cancer.  These extreme cases again depend on concentration and time exposure.  Therefore, it is extremely important to follow manufacturer and FDA recommendations and instructions, and be under the care and supervision of an expert clinician.

In my professional opinion, venners like everything else in life will age and they may even fail with time. If venners move, the effect is often breakage.  If the gum line seems to move away from venners, and the margins of the veneers trap food, it does suggest retreatment.  Venners are kept in place by very thin cement which with time can breakdown if not maintained, cleaned or not protected from excessive load during biting or chewing, griding or clenching. However, venners can only be properly bonded to enamel not dentin, therefore, depending on how much enamel there is after the old veneers have been removed dictates if you would be a candidate for new venners or crowns.  Of course, clinical evaluation and radiographic diagnosis would finalize the treatment options available.