Transillumination is defined in Veterinary Dentistry: Principles and Practice as “assessment of the reflectivity of the internal tooth structure to evaluate vitality of the pulp by placing a light behind a tooth and viewing it.”1 In this month’s column, I’ll shed light (pun completely intended) on the perceived role of transillumination in veterinary dentistry and how that role differs in human dentistry, based on studies in the human literature.
There are two basic types of tooth discoloration: intrinsic and extrinsic staining. Extrinsic staining is cosmetic and not an indication of tooth vitality. Intrinsic staining discolors from within. Generalized discoloration of a tooth in the form of intrinsic staining is one of the signs we look for when diagnosing a dead or inflamed tooth. Pulpitis is inflammation of the pulp, which may occur due to blunt trauma to a tooth. This trauma may be caused by the patient bumping the tooth or chewing on something that traumatizes the tooth without causing a fracture of the crown or root. The colors seen with pulpitis (pink, purple, gray, brown) are due to trauma to blood vessels within the center of the tooth, which results in leakage of red blood cells outside of pulp vasculature. The breakdown products of hemoglobin from lysed red blood cells travel from the pulp into dentinal tubules to just beneath the enamel, imparting discoloration of the crown. Over time the discoloration progresses to a gray, brown, or tan color.
Pulpitis can be a painful condition due to the fact that inflammation and swelling occurs within the confines of an unyielding hard tissue structure. Swelling within an enclosed structure results in damage to the remaining soft tissue in the root canal and pulp chamber of the tooth. Depending on the stage of the disease, the nerve fibers within the pulp may transmit sharp pain stimuli. Once the pulp within the tooth is dead, pain may subside until periapical disease develops.
Intrinsic staining may occur due to reasons other than loss of vitality of a tooth. Intrinsic staining can occur either before the teeth have emerged, while they are still developing, or after the teeth have erupted. Preeruptive staining, which occurs while the teeth are developing, is most often caused by medications or by fluoride. One of the most common causes of preeruptive intrinsic staining in humans is excess fluoride intake either by the mother during pregnancy or by the child while the permanent teeth are developing. Tetracyclines can also cause preeruptive discoloration. The most common cause of posteruptive intrinsic staining is trauma.
Is transillumination helpful for assessing tooth vitality?
Transillumination describes the use of a bright light that is placed behind the tooth to observe how light travels through the tooth. Normally a tooth should be translucent and light up like a jack-o’-lantern when transilluminated. If intrinsic discoloration is present, light will not transmit (see figure). The vital tooth lets light pass through the tooth very readily, whereas the dead tooth appears more opaque when comparing to contralateral vital teeth in the mouth. However, when trying to assess the vitality of a tooth, transillumination will not tell you anything more than what the naked eye has already seen. If you have any intrinsically discolored tooth, light will not pass through the tooth as readily, regardless of whether it is ambient light or focused light. One study from the Journal of Veterinary Dentistry showed that 92.2 percent of intrinsically discolored teeth were partially or completely necrotic inside.2 Therefore, if you see an intrinsically discolored tooth, odds are good that the tooth has vitality issues.
What does the human literature say about the use of transillumination to assess vitality of teeth? One study from 1986 suggested that transillumination is a useful adjuvant to conventional methods of pulp vitality testing, but warned that errors in diagnosis occurred most frequently in the most critical category of teeth, that is, nonvital teeth.3 One of the most commonly referenced textbooks of human endodontics, Pathways of the Pulp, states that fiberoptic transillumination, though it will reveal discoloration, should not be used to determine pulp vitality.4 Pathways suggests that the true benefit of transillumination is for determining if there are any vertical tooth fractures. Multiple studies have discussed use of near-infrared transillumination to detect caries lesions on proximal surfaces or beneath amalgam restorations.5
The take-home point is this: Though transillumination has its place, it is not “enlightening” when used as a test of tooth vitality. It’s greatest strength is likely in detecting hairline tooth fractures.
1 Wiggs RB, Lobprise HB. Oral examination and diagnosis. In: Wiggs RB, Lobprise HB. Veterinary Dentistry: Principles and Practice. Philadelphia: Lippincott-Raven; 1997.
2 Hale FA. Localized intrinsic staining of teeth due to pulpitis and pulp necrosis in dogs. J Vet Dent. 2001;18(1):14-20.
3 Hill CM. The efficacy of transillumination in vitality tests. International Endodontic Journal. 1986; 19: 198-201.
4 Cohen S, Liewehr F. Diagnostic procedures. In: Cohen S, Burns RC, eds. Pathways of the Pulp, 8th Ed. St. Louis, Mo: Mosby; 2002.
5 Angelino K, Edlund DA, Shah P. Near-Infrared Imaging for Detecting Caries and Structural Deformities in Teeth. IEEE J Transl Eng Health Med. 2017;5:2300107.
Dr. John Lewis practices veterinary dentistry and oral surgery at NorthStar Vets in Robbinsville, N.J.