dna and dna evidence 121bitemark for DNA. The forensic odontologist may also be approached with
questions regarding the buccal swab. As the name suggests, DNA from the
oral mucosa of the inner cheek is the target of the buccal swab technique.
It is a collection method that is rapidly supplanting the older phlebotomy
or finger stick techniques in which whole blood samples are collected for
DNA processing.7.6.1 Salivary DNA in Bitemark Evidence
Saliva derives from three major bilateral glands and hundreds of smaller ones
scattered throughout the oropharyngeal region. Over two-thirds of the 1.0 to
1.5 L of the saliva produced daily is from the submandibular gland, whereas
the parotid glands account for approximately 25% of the total volume and
the sublingual glands only 5%.^9 The biological composition of the fluid varies
between the glands, and the volume of salivary secretion at any given time of
day will change according to physiological stimulation or medical issues or a
pharmacological condition. But generally secretion is highest during eating.
Saliva is composed chiefly of water but also contains electrolytes, buffers,
glycoproteins, antibodies, and enzymes.9,10,45 The detection of one particular
group of enzymes, the human α-amylases, which are responsible for initial
polysaccharide digestion, is a traditional method for identifying evidentiary
stains for the presence of saliva.9,10,46 Although amylase is found in other
bodily fluids, its very high levels in saliva are unique in that they can be as
much as fifty times greater than those in other sources. Its stable biochemical
activity over time is distinctive as well.10,47
Amylase-dependent forensic screening tests are increasingly avail-
able in the commercial sector. Some are very specific and are based on
mono clonal antibody activity that focuses on human salivary α-amylase,
whereas others are more general in relying on the detection of amylase
act iv it y to release a colored dye suggest ing t he presence of sa liva.^9 However,
all such direct-contact assays risk consumption of portions of the sample
that are otherwise destined for DNA analysis. If used, consideration should
be given to selecting the most informative product that requires the least
volume of sample.48,49
Visual screening for evidentiary saliva stains should be augmented by
the use of alternative light sources. Although ultraviolet light is helpful in
uncovering the presence of biological fluids, short-wave ultraviolet light is
a potential health hazard and is also known to disrupt the DNA molecule
and compromise the ability to conduct forensic DNA testing. Alternative
light sources, such as lasers and high-intensity lights that can be filtered to
provide a single wavelength, are probably the best for screening evidence,
including skin, for the presence of saliva.10,50,51 The advantage of an alterna-
tive light source in screening for salivary stains on skin is that the potential