Recently, several companies have marketed devices [following obtainment of FDA Class I (501c) device approval] intended to aid the dentist in the early detection and diagnosis of premalignant oral lesions. Among those intended to be used as oral cancer screening devices are Vizilite Plus® (Zila Pharmaceuticals, Inc., Phoenix, AZ), MicroLux-DL® (AdDent, Inc., Danbury, CT), Orascoptic® DK (Orascoptic by the Kerr Company, Middleton, WI), and VELscope® (L.E.D. Dental, Inc., White Rock, BC, Canada). Procedures intended for adjunctive diagnosis of oral premalignancies include The BrushTest® (formerly called the brush biopsy; OralCDx, Suffern, NY) and liquid-based cytology technology, ThinPrep® and SurePath® (TriPath, Burlington, NC, and Cytyc Corp., Boxborough, MA, respectively). It should be noted that the techniques described below have limitations, including false-positive and false-negative results, depending on the character and site of the lesion in question. Most prosthodontists do not have ready access to these tools, but should know that they are available for the care of their patients as well as to be able to interpret the results of these adjunctive techniques. A specialist such as an oral and maxillofacial surgeon is well trained in these technologies and can use them in appropriate situations when deemed necessary; however, the scalpel biopsy is still the gold standard for definitive histopathologic diagnosis, so if the prosthodontist is especially concerned with the clinical presentation of a lesion, a routine excisional or incisional biopsy should be specifically requested.
Tissue reflectance with chemiluminescence and vital dye marking
Following the conventional incandescent light soft tissue head and neck examination described above, the Vizilite Plus system (single use, disposable kit) uses a 30- to 60-second prerinse, nontoxic 1% acetic acid swish and spit mouth rinse (raspberry flavored) followed by the bending of a plastic lightstick that when shaken results in an endothermic blue-white light-producing reaction (with peak wavelength outputs near 430, 540, and 580 nm). During the ensuing 10 minutes, with the operatory ambient lights significantly dimmed, the illuminated lightstick is shined throughout the oral cavity following its placement into a two-piece plastic retractor. The mild acetic acid rinse is reported to prepare the oral mucosa by dehydration for the detection of epithelial cells with the increased nuclear/cytoplasmic ratio, including those that may be dysplastic, following the use of the diffuse blue-white light.45,46 If the suspicious oral lesion (i.e., leukoplakia, erythroplakia, erythroleukoplakia) noted during the routine operatory white light examination becomes visibly enhanced in coloration (e.g., leukoplakic) or darkened (erythroplakic), then it is considered a positive finding. Reports in the literature indicate that premalignant lesions (verified by subsequent surgical biopsy) that were not seen by dental experts in a high-risk patient population have been discovered following use of the Vizilite Plus system.47–51 The second step of this system includes a visual marking of the identified lesion by use of a metachromatic vital dye, toluidine blue (toloniun chloride), which has a reported affinity for DNA and, thus, binds to epithelial cells with the increased nuclear cytoplasmic ratio. Zila Pharmaceuticals, Inc., has produced a pharmaceutical grade of this vital dye and includes it in this system with the trade name TBlue630 (Zila tolonium chloride). Therefore, the clinician has the option of a three-step marking of the suspicious lesion with TBlue630 for documentation and as an aid in biopsy/cytology sampling or by referral to a dental colleague. It should be emphasized that TBlue630 is only FDA-approved for use in the Vizilite Plus system after the use of the chemiluminescent lightstick step.
Tissue reflectance with luminescence
There are two FDA-approved Class I light-emitting devices similar to the first step of the Vizilite Plus system—MicroLux-DL® and Orascoptic DK®. These oral cancer screening aids are manufactured by the same company (AdDent, Inc., Danbury, CT) but marketed by two different companies, hence their different trade names. Both devices are reusable, battery-operated light emitting diode dental transilluminators that have been adopted to emit a diffuse blue-white light (assumed to be the same wavelength as the Vizilite) by removing the transilluminator light tip and replacing it with a sterilizable, translucent glass tip. As with the Vizilite Plus system, patients prepare their oral mucosa by rinsing and spitting with the same 1% acetic acid rinse, but, unlike Vizilite, the battery-containing handle creates the diffuse blue light in a manner similar to the common flashlight. These adjunctive devices, as with the Vizilite Plus system, are to only be used following the conventional incandescent light intraoral examination with a positive finding defined as visual enhancement of a suspicious lesion.
Narrow-emission tissue fluorescence
The VELscope is an oral premalignant screening device that emits a concentrated blue light (peak wavelength outputs of 405 and 436 nm) that creates a natural fluorescence. In North America, it is powered by a 120-V AC electric current and emits a blue light by use of a replaceable metal halide bulb, a series of dichromatic mirrors, and a flexible fiber optic cable. In addition, the blue light emitter handpiece has an optical inline ocular eyepiece through which the clinician observes the oral mucosa tissue. A series of optical filters are located between the clinician's eye and the emitted light. The emitted blue light emission excites natural substances, fluorophores, within the oral epithelium and underlying lamina propria (connective tissue). When exited, fluorophores autofluoresce and emit an apple green color that can be appreciated by the clinician due to the filters contained within the eyepiece. As with other oral cancer light screening devices, the VELscope is only to be used following a conventional incandescent light intraoral examination. The clinician repeats the intraoral examination, after dimming the ambient operatory light, with the activated VELscope; normal oral mucosa will appear green. If an area of black (i.e., loss of fluorescence) is seen, it can correlate to a suspicious premalignant lesion previously appreciated during the incandescent light examination or, in some reported cases, an area of lost fluorescence is seen despite being unable to appreciate a suspicious lesion with the naked eye.52–53 The VELscope is reported to exhibit loss of fluorescence in the presence of dysplasia due to the destruction of the naturally occurring fluorophores in the affected epithelium and/or connective tissue. Oral lesions have also been documented in which the loss of fluorescence extends beyond the clinically visible lesion, and subsequent biopsy of the extended dark areas revealed the presence of microscopic dysplasia or squamous cell carcinoma.54
Adjunctive diagnostic procedures
During the late 1950s and 1960s many dental investigators attempted to adopt the Pap smear, the early 1950s' highly successful adjunctive diagnostic technique for uterine cervical cancer, for use within the oral cavity. This was an exfoliative cytology procedure in which surface epithelial cells were scraped in a minimally invasive manner and immediately transferred (“smeared”) to a glass microscope slide that was subsequently sprayed with an alcohol-based fixative to preserve the collected cells. The cells were then coverslipped following the use of Papanicolaou stain and examined with the light microscope. A pathology report was issued indicating that if any of the cells exhibited atypical morphological characteristics that could indicate the clinical presence of epithelial dysplasia or squamous cell carcinoma. Unfortunately, the Pap smear proved to be unreliable when used within the oral cavity, since there were numerous reports of unacceptably high incidence of false-positive and false-negative results.55 Thus, this noninvasive potential adjunctive oral diagnostic technique was not actively pursued for nearly 30 years. In 1999, the brush biopsy technique (recently renamed the BrushTest) was introduced to dentistry. It was reported to be an efficacious, sensitive, and specific diagnostic adjunct in which a transepithelial collection (from surface to basal cell layer) of disaggregated oral mucosa epithelial cells was removed by a helical-shaped, stiff nylon bristle brush and immediately transferred (“smeared”) to a clear glass microscope slide.56 The collected cells were fixed with an alcohol solution and, following drying, were placed in a plastic protective case and sent to a central laboratory for computer-assisted analysis followed by examination of computer-selected areas by a trained cytopathologist. The cells were to be collected in a painless or mildly uncomfortable manner verifying obtainment of all epithelial levels by the clinical sight of pinpoint bleeding and redness of the upper vascular plexus with the superficial underlying connective tissue. Subsequent to the seminal report of this technique, there has been a series of case reports and investigations that either tout or dispute the technique's accuracy.57–62 There have also been reports that all techniques that attempt to transfer collected cells from a brush device to the planar surface of a microscope slide can fail to transfer up to 80% of the cells distributed on the brush's bristles.63,64 There has also been controversy about the cost/benefit ratio of the brush biopsy, since a positive or atypical finding of possible epithelial dysplasia would mandate a second procedure, the gold standard surgically invasive biopsy.
During the 1990s a revolutionary new Pap smear technique garnered FDA approval following several large phase-3 clinical trials.64–67 The adjunctive diagnostic technique, known as liquid-based cytology, is reported to increase the accuracy of Pap smears.67 The major technical improvement is that the brush-collected cells are directly transferred into a container with methanol- or ethanol-based liquid preservative/fixative; the brush's bristle head is also placed in the liquid container. Upon arrival of the solution at the pathology laboratory, a patented machine then filters, disperses, collects, and transfers the epithelial cells of the solution to a glass slide. The cells are placed in a monolayer greatly reducing overlapping epithelial cells; in addition, obscuring elements such as inflammation, debris, mucous, and blood are also removed. Lastly, the cells are stained (Papanicolaou) and coverslipped prior to microscopic examination by a boarded medical pathologist.
More recently, the liquid-based technology has been adopted for use in nongynelogical clinical settings including within the oral cavity.64 As with cervical mucosa, this technique utilized to obtain a transepithelial sampling of oral mucosa has the same potential to result in an improved evaluation of the disaggregated cells obtained from a clinically suspicious premalignant lesion whether detected during the incandescent light examination or during one of the above-mentioned adjunctive oral cancer screening techniques.