Forensic Dentistry, Second Edition

dna and dna evidence 123

technique has a confirmed track record of success to include salivary DNA

collections from a block of cheddar cheese and a body submerged in water

for over five hours.54,55

7.6.2 Oral Mucosal DNA and Buccal Swabs

A successful conclusion based on DNA analysis is dependent on the oppor-
tunity to compare a questioned profile with a known profile. An investigator
has little control regarding the condition and sufficiency of questioned pro-
files found on the victim or at the crime scene, but a level of quality control
can be exercised in obtaining the known reference profile. Whole blood
samples drawn through a finger stick or veinapuncture procedure are the
traditional methods in obtaining a DNA reference. Well-meaning investiga-
tors occasionally have collected head hair believing that they were procuring
a simple noninvasive source of DNA. They did not realize that the laboratory
processing requirements for hair samples is resource-intensive, compared to
the more predictable blood sample. The taking of head hair as a DNA ref-
erence should be limited only to those cases where the questioned samples
consist of shed hairs and the use of mitochondrial DNA testing is likely.
For routine casework and long-term storage, whole blood applied to a
filter paper card provides the greatest amount of reference DNA by volume
with the least likelihood of contamination. However, the use of a buccal swab
as a rapid, noninvasive alternative to blood collection is increasingly com-
monplace.56,57 Because of the anatomical specificity of the forensic odontolo-
gist’s expertise, he or she may be consulted in the collection, storage, and
transportation of the buccal swab. Targets of this collection technique are the
stratified squamous epithelial cells that can be rubbed from the inner cheek,
although a certain amount of salivary DNA is naturally collected as well and
is beneficial.
When buccal swabs are being collected to help identify a missing or
unidentified family member, the laboratory will provide a list of the pre-
ferred donors according to their relationship with the victim. Exactly which
family members are targeted as donors depends on the anticipated DNA
typing system to be applied.30,58 Generally, when autosomal STRs are being
used, the preferred reference sources, ranked in order of desirability, include
a pristine sample from the:

1. Victim (collected before the event and properly preserved)


2. Victim’s biological parents


3. Victim’s biological child and this child’s other biological parent


4. Victim’s biological child


5. Victim’s full siblings


6. Victim’s half siblings