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How Whitening Works

Course Number: 657

Chromogens On and In Teeth – Definitions and Origins

Molecules that can alter reflected light are defined as chromogens. They can be of natural origin or from external sources. Definitions follow below for sources of tooth color.

Intrinsic discoloration: Intrinsic discoloration of teeth arises from a variety of factors including chromogens in the enamel, in the dentin, and structural characteristics of the enamel. Sources of intrinsic natural coloration primarily originate during tooth development or through aging and the continual yellowing of dentin over time. This is thought to be related to the on-going production of secondary dentin. In some unique cases, intrinsic discoloration can arise from the use of antibiotics by either the mother or at a time when permanent dentition is developing. This is most commonly associated with the use of tetracycline and minocycline in the 1960s and 1970s. Structural defects in enamel impact the appearance of teeth, including dental fluorosis, enamel hyperplasia, and amelogenesis imperfecta. An image of a tetracycline-stained tooth and teeth with fluorosis are shown below (Figure 7).

Tetracycline-stained tooth

Fluorosis-stained tooth

Figure 7.

Image Source: Dr. Gerald Kugel, DMD, MS, PhD

Although the source of intrinsic discoloration is not from external origins, discoloration can be quite pronounced, this can be challenging to treat even with tooth bleaching techniques. Tetracycline, for example, requires chronic bleaching to obtain satisfactory levels of tooth whitening for patients.6-8

Extrinsic Stains: Here the source of tooth discoloration resides on the tooth surface and the source of the stain is from external origin. Sources of extrinsic stain are variable and related to the diet, habits and practices of patients. The most common sources of stain include tobacco, tea and coffee. Extrinsic stains accumulation can be promoted by using cationic antimicrobials such as chlorhexidine and cetylpyridinium chloride.9-11

Extrinsic stains vary in their tenacity, with some bonding strongly to the dental pellicle while others are incorporated into other deposits found on the teeth such as plaque and tartar. Some examples of common extrinsic stains are shown in the images below (Figure 8).

Figure 8.

Chlorhexidine Stains

Stains in a Cigarette Smoker

Stains on and around dental calculus

Figure 8.

Extrinsic stains are often quite noticeable due to their contrast with adjacent areas of a non-stained tooth. This often occurs due to actions of mastication or areas with lack of proper oral hygiene (toothbrushing).