A) Imaging Techniques

1. Plain Radiograph

2. Contrast Radiograph – Radiopaque substance introduced in body

Sialography:

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

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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

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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)

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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)

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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

4. Parasites

Stains

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