Invented in 1955, acid-etching employs dental etchants and is used frequently when bonding dental restoration to teeth.[34] This is important for long-term use of some materials, such as composites and sealants.[12] By dissolving minerals in enamel, etchants remove the outer 10 micrometers on the enamel surface and makes a porous layer 5–50 micrometers deep.[35] This roughens the enamel microscopically and results in a greater surface area on which to bond.
The effects of acid-etching on enamel can vary. Important variables are the amount of time the etchant is applied, the type of etchant used, and the current condition of the enamel.[35]
There are three types of patterns formed by acid-etching.[35] Type 1 is a pattern where predominantly the enamel rods are dissolved; type 2 is a pattern where predominantly the area around the enamel rods are dissolved; and type 3 is a pattern where there is no evidence left of any enamel rods. Besides concluding that type 1 is the most favorable pattern and type 3 the least, the explanation for these different patterns is not known for certain but is most commonly attributed to different crystal orientation in the enamel
Tooth whitening
Tooth whitening or tooth bleaching are procedures that attempt to lighten a tooth's color in either of two ways: by chemical or mechanical action.[37]
Working chemically, a bleaching agent is used to carry out an oxidation reaction in the enamel and dentin.[38] The agents most commonly used to intrinsically change the color of teeth are hydrogen peroxide and carbamide peroxide.[39] A tooth whitening product with an overall low pH can put enamel at risk for decay or destruction by demineralization. Consequently, care should be taken and risk evaluated when choosing a product which is very acidic.[40]
Tooth whiteners in toothpastes work through a mechanical action. They have mild abrasives which aid in the removal of stains on enamel. Although this can be an effective method, it does not alter the intrinsic color of teeth.[37]
Microabrasion techniques employ both methods. An acid is used first to weaken the outer 22–27 micrometers of enamel in order to weaken it enough for the subsequent abrasive force.[41] This allows for removal of superficial stains in the enamel. If the discoloration is deeper or in the dentin, this method of tooth whitening will not be successful.
Systemic conditions affecting enamel
There are many different types of Amelogenesis imperfecta. The hypocalcification type, which is the most common, is an autosomal dominant condition that results in enamel that is not completely mineralized.[42] Consequently, enamel easily flakes off the teeth, which appear yellow because of the revealed dentin. The hypoplastic type is X-linked and results in normal enamel that appears in too little quantity, having the same effect as the most common type.[42]
Chronic bilirubin encephalopathy, which can result from erythroblastosis fetalis, is a disease which has numerous effects on an infant, but it can also cause enamel hypoplasia and green staining of enamel.[43]
Enamel hypoplasia is broadly defined to encompass all deviations from normal enamel in its various degrees of absence.[44] The missing enamel could be localized, forming a small pit, or it could be completely absent.
Erythropoietic porphyria is a genetic disease resulting in the deposition of porphyrins throughout the body. These deposits also occur in enamel and leave an appearance described as red in color and fluorescent.[45]
Fluorosis leads to mottled enamel and occurs from overexposure to fluoride.[23]
Tetracycline staining leads to brown bands on the areas of developing enamel. Children up to age 8 can develop mottled enamel from taking tetracylicne. As a result, tetracycline is contraindicated in pregnant women.
Celiac disease, an auto-immune disorder triggered by gluten allergies, also commonly results in demineralization of the enamel.
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