Diagnostic Methods

A) Imaging Techniques

1. Plain Radiograph

2. Contrast Radiograph – Radiopaque substance introduced in body

Sialography:

– Iodine

Angiography

  • Fluorescent dye/fluoroscope
  • Catheter introduced into artery (external carotid)

TMJ arthroscopy

  • Patient discomfort
  • Contrast introduced in joint space

Radionuclide imaging

  • Technetium 99 – injected into blood stream – labelled with methylene diphosphonate (MDP) – affinity for bone
  • Indications:
    • Bone metastasis
    • Assess bone graft
    • Assess condylar growth
    • Assess thyroid function
    • Investigate salivary glands
  • Disadvantages:
    • High dose needed
    • Poor resolution
    • Non specificity

3. Digital Imaging – Receptor converts x-ray image into digital data and stores on computer

  • Receptor:
    • Charged couple device (CCD)
    • Photo stimulable sensor plate
  • Advantages:
    • Low radiation dose
    • No conventional processing
    • Manipulate image with software
    • Efficient record keeping
  • Disadvantages:
    • Expensive
    • Bulky sensor for intraoral space
    • Low resolution compared to x-ray film
    • Misuse of image manipulation
    • Occupy a lot of disc space

4. Conventional Tomography – Greater range of movement, image tissues in slices

5. Computed Tomography (CT Scan)

  • Radiographic tube passes in a circle around the body – detectors measure degree of attenuation (blocking) by tissues – value converted to numerical value (Hounsfield number) – digitally converted to graphic image
  • Indications:
    • Mid facial trauma
    • Bone dx

6. MRI

  • Patient in strong magnetic field – pulses of radiowaves – impart energy – hydrogen protons in body fluid – emit radiosignal – detected and processed by computer
  • Has no ionizing radiation (compared to CT or xray)
  • Types:
    • T1 – Highlights fat tissue eg. subcutaneous fate, bone marrow
    • T2 – Highlight water eg. CSF
  • Indications:
    • Soft tissue detail
    • Tumour staging
    • Intracranial dx
    • TMJ (except bone) lesions
  • C/I:
    • Pt with pacemaker
    • Ear implant
    • 1/3 of pregnancy
    • Ferromagnetic surgical clips
    • Bone lesions

7. Positron Emission Tomography (PET) – Radiation/nuclear medicine to produce 3D colour image

8. Ultrasonography

  • Indication – Superficial soft tissue eg. Salivary gland, thyroid

B) Specimens for Lab Investigations

1. Haematology

EDTA:

  • Cross matching
  • All red cell indices
  • White cell counts
  • Platelet counts
  • Serum vit B12
  • Blood films
  • RBC folate assays

Plain Tube:

  • Cross matching
  • Blood grouping
  • Serum iron
  • Serum ferritin
  • TIBC

Citrated Tube:

  • ESR
  • Prothrombin time

2. Biopsy – Histopathology

  • 10x volume of biopsy needed
  • Fixed in 10% solution of formal saline
  • Immediate freezing at -70 degrees Celsius for immunofluorescent exam

3. Microbiology – Culture and sensitivity

  • Collect before antimicrobe tx – if cannot process in 2 hours – place swab in transport media and store at 4 degree Celcius

NB: Don’t take samples for viral hepatitis and HIV, refer to VCT clinic


C) Biopsy Techniques

  1. Excisional – Entire lesion + margin of healthy tissues (benign lesions)
  2. Incisional – Portion of lesion + margin of healthy tissues
  3. Punch – Needle removes small portion (tumors with high risk of seeding)
  4. Smear/brush – Exfoliative cytology (superficial lesion on oral mucosa)
  5. Aspiration – Wide bore needle into lesion and aspirate (cysts)

D) Microscopic Techniques

1. Light Microscopy

  • Bright field/standard: Wet films – bacterial motility
  • Darkground microscopy: Dental ground sections – illuminate obliquely
  • Phase – contrast: Details of unstained microbes
  • Flourescent microscopy: Immunology

2. Electron Microscopy: Resolution of small microbes (virology)


E) Lab Isolation of Microbes

1. Bacteria

Stains:

a) Gram Stain – Lugol’s iodine, carbolfuchsin

b) Ziehl – Nielsen – Carbolfuchsin + methylene blue/ malachite green

  • Mycobacteria (thick waxy wall)
  • +ve: Red against blue background

Culture media:

a) MacConkey

  • Red fermenters – E.coli, Kleibsiella, Citrobacter, Enterobacter
  • Yellow/ non fermenters – Salmonella, Pseudomonas

b) Mitis Salivarius

  • > 2mm – Strep. Salivarius
  • < 1mm – Strep. Mitis

c) Mannitol Salt

  • Big, yellow – Staph. Aureus
  • Small, pink – Staph. Epidermidis

d) Lowenstein – Jensen

  • Rough – M. Tuberculosis
  • Smooth – Atypical Mycobacteria

e) TCBS (Thiosulphate, citrate, bile, saliva)

  • Yellow fermenters – V. Cholerae, Acromonas
  • Non Fermenters – V. Parahaemolyticus

f) Thayer Martin

  • Grey colonies – Neisseria

g) Charcoal Yeast

  • Cutglass colonies – Legionella

Universal transport media

Stuart transport media (semi – solid, non nutrient agar)

2. Fungi

Stains:

  • Periodic Acid Schiff
  • Gram stain
  • Methenamine silver

Culture media

  • Sabouraud’s agar
  • Blood agar
  • Cornmeal agar (cream colonies)

Identification test: Germ Tube Test

  • Unknown candida spp + Serum incubation for 3 hours at 37°C
  • +ve: Growth of new hyphae (germ tubes)
  • -ve: Persistance of candidal spores

Transport media

  • Nutrient agar/Broth

3. Viruses

Polymerase chain reaction

Smear biopsy

  • Examine cells for degenerative changes eg. rounding of epithelial cells, cell fusion, multinucleate cells

Serodiagnosis

  • ELISA
  • Immunoflourescence – Direct and indirect
  • Rising antibody titers
Direct and indirect flourescence

4. Parasites

Stains

  • Giemsa stain – Malaria, Leishmania
  • Periodic Acid Schiff stain – Amoebae
  • Silver stain – Pneumocystis