MCQs on Oral Histology Enamel - Part 2

# All are true regarding the enamel spindles except :
A. Produced by ameloblasts
B. Found in the region of cusps
C. Surrounded by inter prismatic enamel
D. Terminated as rounded process

# Ionic exchange between enamel surface and environment :
A. Does not take place once enamel matures
B. Stops after 2 years of eruption
C. Continues till adult life
D. Continues throughout life

# Approximately how many enamel rods will be present in maxillary molar?
A. 5 million
B. 7 million
C. 9 million
D. 12 million

# All are true about the striae of Retzius except:
A. Constitute the rest lines within the enamel rods
B. Have high inorganic content
C. They are areas of increased porosity
D. Allow the movement of water and small ions

# Neonatal lines are found in all of the following except :
A. Enamel of primary incisors
B. Enamel of premanent canines
C. Enamel and dentin of permanent first molars
D. Dentin of permanent mandibular incisors
# On microscopic examination, enamel rods have :
A. Keyhole appearance in cross section
B. Paddle appearance in cross section
C. Lanullate appearance in cross section
D. None of the above

# Which of the following structures is not of ectodermal origin ?
A. Hunter Schreger bands
B. Enamel spindles
C. Enamel Tufts
D. Enamel lamellae

# The formative cells of which of the following dental tissues disappear once tissue is formed ?
A. Enamel
B. Dentin
C. Periodontal ligament
D. Cementum

# Which of the following tissues have no reparative capacity ?
A. Enamel
B. Dentin
C. Cementum
D. Periodontal ligament

# The enamel has no capacity of self repair because :
A. It has only small percent of organic content
B. Its formative cells are lost once it is completely formed
C. It is essentially a keratin tissue and has no blood vessels
D. It has no direct connection with the active cells of the dental pulp

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MCQs on Odontogenic cysts and Tumors - Oral Pathology Part 2

# Ghost (Shadow) cells are seen in:
A. Ameloblastic fibroodontoma
B. Calcifying odontogenic cyst
C. Compound Odontoma
D. All of the above

# A 25 year old male patient reports with a bony expansile swelling of the right body of the mandible & mild paraesthesia of the IDN. OPG shows a multilocular  radiolucency without root resorption.
i) What would be your choice of next investigation?
A. Excision biopsy
B. Aspiration cytology
C. CT scan
D. PET bone scan

ii) A dirty white aspirate with a protein estimation of <4gm% is suggestive of:
A. Ossifying fibroma
B. Dentigerous cyst
C. Mucoepidermoid carcinoma
D. Odontogenic keratocyst

iii) Odontogenic keratocyst is noted for its:
A. Malignant transformation
B. Daughter cysts and high rate of recurrence
C. Impacted teeth
D. Nodal metastasis

iv) Management of odontogenic keratocyst involves :
A. Marsupialization
B. Enucleation
C. Enucleation with peripheral ostectomy
D. Resection and radiation

# Treatment for cementoma : (two answers)
A. No treatment
B. Pulpectomy
C. Resection of jaw
D. None of the above

# Lesions associated with vital tooth :
A. Condensing osteitis
B. Cementoma
C. Periapical abscess
D. None of the above

# Destructively invasive, locally malignant with rare metastasis, the lesion is:
A. Fibroma
B. Ameloblastoma
C. Papilloma
D. None of the above

# Compound odontoma shows :
A. Mixed tissue of dental origin with no rsemblance to tooth structure
B. Numerous tooth like structure with denticles commonly found in maxillary lateral incisors
C. Haphazardly arranged calcified mass
D. all of the above

# Dentigerous cyst is suspected if the follicular space is more than:
A. 2-3 mm
B. 3-4 mm
C. 1-2 mm
D. >5 mm

# After entering a radiolucent lesion in a 30 yr old man, hollow cavity without epithelial lining is seen, the most probable diagnosis is :
A. Aneurysmal bone cyst
B. Static bone cavity
C. Hemorrhagic bone cyst
D. Ameloblastoma

# A patient with ameloblastoma of the jaw can best be treated by:
A. Irradiation
B. Excision
C. Enucleation
D. Surgical removal followed by cauterization
# Dentigerous cyst is associated with the following :
A. Impacted third molar
B. Impacted supernumerary tooth
C. Odontome
D. All of the above

# The epithelium of a dentigerous cyst is :
A. 15-20 cell thick
B.  6-10 cell thick
C. 2-4 cell thick
D. 1-2 cell thick

# Clear cells are commonly seen in which of the following lesions ?
A. Pleomorphic
B. Warthin's tumor
C. Mucoepidermoid
D. Adenomatoid odontogenic tumor

# Multiple periapical radiolicencies are seen in:
A. Jaw cyst basal cell nevus syndrome
B. Odontogenic keratocyst
C. Cherubism
D. Thyroid disorders

# A 36 year old male with an asymptomatic swelling in the body of the mandible with radiographic features of radiolucency with radiopaque flecks is suffering from :
A. Odontogenic keratocyst
B. Calcifying epithelial odontogenic tumor (CEOT)
C. Ameloblastoma
D. None of the above

# Pindborg tumor arises from : (two answers correct)
A. Basal layer of cells
B. Stratum intermedium
C. Stratum corneum
D. Dental lamina

# A six year old child patient has blue dome shaped swelling in posterior mandibular region, what will be the treatment plan?
A. reassure the patient without any treatment
B. Excise the lesion
C. Marsupialization
D. Surgical excision

# The pathogenesis of periapical cyst is :
A. Increased pressure within the cyst
B. Immune mediated bone destruction
C. Proliferation of  epithelium
D. None

# Adenomatoid odontogenic tumor is characterized histologically by :
A. Polyhedral epithelial cells
B. Tubular/duct like cells
C. Stellate shaped cells
D. Stratified squamous epithelial cells

# Cyst arising from dental lamina :
A. Radicular cyst
B. Paradental cyst
C. Eruption cyst
D. Glandular odontogenic cyst
# The most common odontogenic cyst is:
A. Primordial cyst
B. Dentigerous cyst
C. Radicular cyst
D. Mucocele

# Standard treatment of ameloblastoma :
A. Segmental resection with 1 cm of normal bone
B. Enbloc resection
C. Enucleation
D. Enucleation with cauterization

# The most aggressive and destructive cyst is :
A. Periapical cyst
B. Dentigerous cyst
C. Globullomaxillary cyst
D. Nasopalatine cysst

# Facial nerve paralysis is common with:(D>B)
A. Pleomorphic adenoma
B. Epidermoid carcinoma
C. Warthin's tumor
D. Lymphoepithelial carcinoma

# COC is now called as:
A. Odontogenic ghost cell tumor
B. Dentinogenic ghost cell tumor
C. Keratocystic Odontogenic tumor
D. A and C

# Multiple bilateral dentigerous cysts are seen in:
A. Down's syndrome
B. Maroteaux Lamy syndrome
C. Treacher Collins Syndrome
D. Gorlin Goltz syndrome

# The cyst that remains behind in the jaws after removal of the tooth is :
A. Lateral periodontal cyst
B. Radicular cyst
C. Residual cyst
D. None of the above

# Corrugated collagenous rings surrounding lymphocytes and plasma cells in the walls of inflammatory cysts are called:
A. Rushton bodies
B. Hyaline bodies
C. Howell-Jolly Bodies
D. Papenheimer bodies

# Potential complications stemming from dentigerous cyst are:
A. Ameloblastoma
B. Epidermoid carcinoma
C. Mucoepidermoid carcinoma
D. All of the above

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MCQs on Odontogenic Cysts and Tumors - Oral Pathology

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# All of the following lesions may be classified as odontogenic tumors except :
A. Acanthomatous ameloblastoma
B. Branchial cleft cyst
C. Myxoma
D. Simple ameloblastoma

# Bifid ribs, Multiple radiolucent lesions of the jaws, multiple basal cell nevi and falx cerebri calcification are found in :
A. Basal cell nevus syndrome
B. Sturge weber syndrome
C. Horner syndrome
D. Hereditary internal polyposis

# Ameloblastoma most frequently occurs in:
A. Mandibular molar region
B. Maxillary molar region
C. Mandibular premolar region
D. Maxillary premolar region

# Compound odontoma shows on a radiograph as:
A. Supernumerary teeth
B. Radiolucent and radioopaque areas
C. Masses of calcified areas
D. Distinguishable tooth like structures

# Which of the following is true neoplasm of functional cementoblasts ?
A. Periapical cemental dysplasia
B. Familial cemental dysplasia
C. Benign cementoblastoma
D. Hypercementosis

# Botryoid odontogenic cyst is a variant of:
A. Lateral periodontal cyst
B. Apiccal periodontal cyst
C. Gingival cysts of the newborn
D. Gingival cysts of adult

# Eruption cyst:
A. Transforms into dentigerous cyst
B. Regresses after eruption of the tooth
C. Is found in the place of the missing tooth
D. Is a type of dentigerous teeth

# Leisegang rings are found in:
A. Calcifying epithelial odontogenic cyst
B. Primordial cyst
C. Calcifying epithelial odontogenic tumor
D. Odontoma

# Which of the following is an odontogenic tumor ?
A. Arrhenoblastoma
B. Astrocytoma
C. Ameloblastoma
D. Granular cell tumor

# The most common odontogenic tumor which occurs in relation to an unerupted tooth in the anterior maxilla:
A. Odontogenic adenomatoid tumor
B. Odontoma
C. Myxoma
D. Cementifying fibroma

# Which of the following shows the presence of cholesterol crystals ?
A. Keratocyst
B. Periodontal cyst
C. Aneurysmal cyst
D. Hemorrhagic cyst

# Nodular growth of alveolus is seen in :
A. Paget's disease
B. Osteomas
C. Cementifying fibroma
D. All of the above

# Basal layer in primordial cyst is arranged in the form of:
A. Tennis racket
B. Picket fence
C. Linear
D. Irregular
# Which of the following is the most common lesion of the mandible ?
A. Adamantinoma
B. Osteogenic sarcoma
C. Squamous cell carcinoma
D. Osteoclastoma

# One of them is not a true cyst:
A. Hemorrhagic cyst
B. Medial palatal
C. Globulomaxillary
D. Nasolabial

# Dentigerous cyst is likely to cause which neoplasia ?
A. Ameloblastoma
B. Osteogenic sarcoma
C. Squamous cell carcinoma
D. Osteoclastoma

# Odontogenic Keratocyst has the following feature:
A. Occurs due to infection periapically
B. is developmental in origin
C. Can be treated by aspiration
D. Has low recurrence rate

# Primordial cyst develops :
A. in place of missing teeth
B. in teeth in which crown development is completed
C. In periapical region
D. In mandibular body

# Robinson's classification of ameloblastoma does not include :
A. Multicentric
B. Non functional
C. Anatomically benign
D. Clinically persistent

# Radiographic finding in Pindborg tumor is :
A. Sun-burst appearance
B. Onion-peel appearance
C. Driven - snow appearance
D. Cherry - blossom appearance

# Unicentric, non functional, anatomically benign, clinically persistent tumor is :
A. CEOT
B. Enameloma
C. Odontoma
D. Ameloblastoma
# The most ideal explanation for recurrence of odontogenic keratocyst is:
A. Increased mitotic activity of the epithelial lining
B. Friability of the epithelial lining
C. Presence of satellite cysts or daughter cysts
D. Continued proliferation of rests of dental lamina

# The cyst with highest recurrence rate is :
A. Keratocyst
B. Periapical cyst
C. Nasoalveolar cyst
D. Globulomaxillary cyst

# A multilocular cyst of the jaw is most likely:
A. Dental cyst
B. Dentigerous cyst
C. Keratocyst
D. Simple bone cyst

# Keratocyst has all of the following features except:
A. It is more common in mandible
B. May be filled with thin straw colored fluid
C. Low recurrence rate
D. Expansion of bone clinically seen

# Each of the following cyst is associated with an impacted tooth except :
A. Dentigerous cyst
B. Calcifying epithelial odontogenic cyst
C. Keratocyst
D. Primordial cyst

# Which of the following is wrong about keratocyst?
A. has low recurrence rate
B. has low protein content
C. high recurrence rate
D. B and C

# A 40 year old woman has ameloblastoma, the histomorphologic features will be:
A. Peripheral palisading cellular strand with central loose stellate reticulum
B. Peripheral palisading with central stromal retraction artefact
C. Peripheral palisading cellular strand with peripheral loose stellate reticulum
D. Central loose stellate reticulum shows marked nuclear atypia and numerous mitotic

# Which histopathological type of odontogenic keratocyst is commoner, more invasive and has a greater tendency for recurrence ?
A. Orthokeratinized
B. Parakeratinized
C. Non keratinized
D. Dyskeratinized

# Multiple odontogenic keratocyst are associated with:
A. Gardner's syndrome
B. Gorlin-Goltz Syndrome
C. Goldenhar's Syndrome
D. Grinspan syndrome

# Adenomatoid odontogenic tumor is most commonly found in :
A. Anterior mandible
B. Posterior maxilla
C. Anterior maxilla
D. Ramus of the mandible

# Adamantinoma is :
A. A tumour from embryonal cells of developing teeth
B. also known as ameloblastoma
C. is a complication of dentigerous cyst
D. All of these

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Dentigerous Cyst / Follicular Cyst

Dentigerous Cyst

• defined as an odontogenic cyst that surrounds the crown of an impacted tooth; caused by fluid accumulation between the reduced enamel epithelium and the enamel surface, resulting in a cyst in which the crown is located within the lumen.
• most common ; about 20% of all jaw cysts ; about 10% of impacted tooth form a dentigerous cyst
• almost always permanent tooth involved; rarely deciduous tooth involved

Clinical Features:

• always associated initially with the crown of an impacted, embedded or unerupted tooth
• most common sites of this cyst are the mandibular and maxillary third molar and maxillary cuspid areas, as these teeth are most commonly impacted
• mostly solitary; bilateral and multiple cysts are usually found in association with a number of syndromes including cleidocranial dysplasia and Maroteaux–Lamy syndrome.
• potentially agressive; due to continuous enlargement of the cyst, may result in expansion of bone with subsequent facial asymmetry, extreme displacement of teeth, severe root resorption of adjacent teeth and pain
• usually, no pain or discomfort associated with the cyst unless it becomes secondarily infected

Radiographic Features

• radiolucency associated in some fashion with an unerupted tooth crown is observed
• may be confused with the enlarged dental follicle; histologically identical
• normal follicular space is 3–4 mm, a dentigerous cyst can be suspected when the space is more than 5 mm

Three radiological variations may be observed:

Central - crown is enveloped symmetrically

Lateral - results from dilatation of the follicle on one aspect of the crown

Circumferential - results when the follicle expands in a manner in which the entire tooth appears to be enveloped by the cyst

Histologic Features

• no characteristic microscopic features which can be used reliably to distinguish the dentigerous cyst from the other types of odontogenic cysts
• usually composed of a thin connective tissue wall with a thin layer of stratified squamous epithelium lining the lumen
• unless secondarily infected, rete pegs are absent
• varying numbers of islands of odontogenic epithelium seen ( also seen in normal dental follicles )
• inflammatory cell infiltration of the connective tissue is common
• in cysts exhibiting inflammation, Rushton bodies, which are peculiar linear, often curved, hyaline bodies with variable stainability which are of uncertain origin, questionable nature and unknown significance, are seen within the lining epithelium
• content of the cyst lumen is usually a thin, watery yellow fluid, occasionally blood tinged

Treatment

• depends upon the size of the lesion - smaller lesions totally removed surgically, larger cysts are often treated by insertion of a surgical drain or marsupialization as larger cysts involve serious loss of bone and there is potential of fracturing the jaw if complete surgical removal is attempted
• recurrence relatively uncommon

Potential complications

Besides recurrence, following complications may occur:

• development of an ameloblastoma
• development of epidermoid carcinoma
• development of a mucoepidermoid

MCQs on Cardiovascular System - Physiology Part 2

# Absolute period when whole heart is in diastole is :
A. 0.7 sec
B. 0.3 sec
C. 0.2 sec
D. 0.4 sec

# The effects of adrenaline on heart are all except :
A. Increases heart rate
B. Decreases myocardial irritability
C. Increases force of contraction
D. Increases oxygen uptake by heart

# Cardiac output is maximum to :
A. Liver
B. Brain
C. Kidney
D. Heart

# Increase in carotid sinus pressure produces:
A. Reflex hyperpnea
B. Reflex bradycardia
C. Reflex tachycardia
D. Reflex hypercapnia

# Effect on force of contraction of heart is :
A. Chronotropic effect
B. Dromotropic efffect
C. Bathmotropic effect
D. Inotropic effect

# SA node acts as a pacemaker of the heart because of the fact that it:
A. is capable of generating impulses
B. has rich sympathetic innervations
C. has poor cholinergic innervations
D. generates impulses at the highest rate

# Distribution of blood flow is mainly regulated by the :
A. Arteries
B. Arterioles
C. Capillaries
D. Venules

# The following factors increase the cardiac output except:
A. Preload
B. Afterload
C. Heart rate
D. Myocardial contractility

# Ventricular muscle receives impulses directly from the:
A. Purkinje system
B. Bundle of His
C. Right and left bundle branches
D. AV node

# In determining blood pressure by auscultatory method,
A. The loudest sound is the diastolic pressure
B. Systolic pressure estimation tends to be lower than those made by palpatory method
C. The first sound heard is systolic pressure
D. The sounds that are heard are generated in heart

# Isovolumetric relaxation ends immediately after:
A. AV valve closes
B. When ventricular pressure falls below aortic pressure
C. When ventricular pressure falls below atrial pressure
D. None of the above

# Glomerular capillary pressure differ from other capillaries of body in:
A. Higher filtration pressure
B. Lower filtration pressure
C. Both of the above
D. None

# The hemoglobin oxygen saturation of blood entering the right ventricle is approximately:
A. 97 percent
B. 85 percent
C. 75 percent
D. 53 percent

# Which of the following increases turbulence in blood flow ?
A. Reynolds number <2000
B. Decrease in viscosity of blood
C. Decrease in density of blood
D. Increase in diameter of blood vessel
# In the case of heart muscle , all are true except:
A. Acts as syncytium
B. Has multiple nuclei
C. has gap junctions
D. has branching

# The velocity of conduction in the purkinje fibers of the heart is :
A. 1 to 4 m/s
B. 5 to 8 m/s
C. 9 to 12 m/s
D. more than 12 m/s

# Second heart sound is characterized by all except:
A. due to closure of semilunar valves
B. is occasionally split
C. has longer duration than first heart sound
D. marks the onset of diastole

# What is common between systemic and pulmonary circulation?
A. Volume of the circulation per minute
B. Peripheral vascular resistance
C. Pulse pressure
D. Total capacity

# Stimulation of the baroreceptors results in :
A. Increase in heart rate
B. Decreased vagal discharge
C. Increased sympathetic discharge
D. Decrease in blood pressure

# The function of carotid body is :
A. Measures the change in pO2 in arterial blood
B. Measures pO2 in venous blood
C. Measures the change in CO2 in arterial blood
D. Measures the change in CO2 in venous blood

# The dicrotic notch on the aortic pressure curve is caused by :
A. Closure of the pulmonary valve
B. Rapid filling of the left ventricle
C. Closure of the aortic valve
D. Contraction of the aorta

# Peripheral vascular resistance is best given by :
A. Mean arterial pressure responsible for blood flow to organ
B. Diastolic blood pressure as it decreases till mid-thoracic aorta
C. Pulse pressure as it relates to stroke volume and aortic compliance
D. Systolic pressure as it increase in descending aorta

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MCQs on Cardiovascular System - Physiology

# The first heart sound is produced by the :
A. Closure of the aortic and pulmonary valves
B. Opening of the aortic and pulmonary valves
C. Closure of the mitral and tricuspid valves
D. Opening of the mitral and tricuspid valves


# Parasympathetic stimulation of heart causes:
A. SA node decreases firing
B. Increased AV node excitability
C. Decreased ventricular contraction
D. Tachycardia

# Normally, the rate of the heart beat in a human is determined by:
A. Bundle of His
B. all cardiac muscles
C. the SA node
D. the cervical ganglion

# The ventricular repolarisation in ECG is best seen in:
A. "P" wave
B. "Q" wave
C. "R" wave
D. "T" wave

# Stroke output of each ventricle in normal adult is :
A. 30 ml
B. 130 ml
C. 70 ml
D. 5 liters

# Cardiac output is a measure of :
A. Peripheral resistance * tissue fluid
B. Peripheral resistance * cardiac rate
C. Blood pressure * Cardiac rate
D. Heart rate * Stroke volume

# Cardiac output is not affected by :
A. Heart rate
B. Peripheral resistance
C. Systolic blod pressure
D. Venous return

# The largest function of the total peripheral resistance is due to:
A. Venules
B. Arterioles
C. Capillaries
D. Precapillary sphincters

# All the heart valves are open during which stage of cardiac cycle?
A. Systolic ejection
B. Isovolumetric relaxation
C. Isovolumetric contraction
D. None of the above

# Minimum blood Pressure is in:
A. Aorta
B. Arteries
C. Capillaries
D. Venules
# Starling's law of the heart
A. Does not operate in the failing heart
B. Does not operate during exercise
C. Explains the increase in cardiac output that occurs when venous return is increased
D. Explains the increase in cardiac output when the sympathetic nerves supplying the heart are stimulated

# Which of the followings is true ?
A. Starling's law of heart states that increase in force of contraction is directly related to cardiac output
B. Starling's law of heart states that the force of ventricular contraction is directly related to the end diastolic volume
C. Both A and B
D. None of the above

# Peripheral resistance is maximum in:
A. Aorta
B. Artery
C. Arteriole
D. Vein

# Stimulatuion of baroreceptor leads to :
A. Increased blood pressure, Increased heart rate
B. Decreased BP, decreased heart rate
C. Increased BP, decreased heart rate
D. Decreased BP, Increased heart rate

# Increased functional demand on the heart produces increased size of the myocardium by:
A. Hyperplasia
B. Hypertrophy
C. Fatty infiltration
D. Increased amounts of fibrous connective tissue

# Cardiac index is related to :
A. Cardiac output and body weight
B. Cardiac output and body surface area
C. Cardiac output and work of the heart
D. Stroke volume and pulse rate

# Absolute refractory period in heart :
A. Lasts till cardiac contraction
B. Longer than refractory period in skeletal muscle
C. A phase of cardiac cycle in which heart cannot be stimulated by any amount of stimulus
D. Corresponds with duration of action potential
E. All of the above

# Closure of the aortic valve occurs before the following event:
A. Isovolumetric contraction
B. Isovolumetric relaxation
C. Prediastole
D. Presystole

# Conduction velocity is least in:
A. AV node
B. SA Node
C. Purkinje fibers
D. Budele of His

# Fastest conducting tissue in human heart:
A. AV node
B. SA node
C. Bundle of His
D. Purkinje fibers

# Under resting condition, the cardiac output is ____ L/min:
A. 2.5
B. 4.25
C. 5.25
D. 9.5

# Coronary blood flow is usually predominantly controlled by :
A. Auto regulation
B. Hormones
C. Parasympathetic impulses
D. Sympathetic impulse

# Cardiac output in L/min divided by heart rate equals:
A. Cardiac efficiency
B. Cardiac index
C. Mean Stroke volume
D. Mean arterial pressure

# Cardiac cycle duration in man is:
A. 0.4 sec
B. 0.8 sec
C. 1.2 sec
D. 1.6 sec

# First heart sound occurs during the period of:
A. Isotonic relaxation
B. Isovolumetric relaxation
C. Isovolumetric contraction
D. Isotonic contraction

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Oral Cancer and Precancer of the Oral Mucosa : Histological Classification

Histological Classification of Cancer and Precancer of the Oral Mucosa
1. Carcinomas Squamous cell carcinoma Verrucous cell carcinoma Basaloid squamous cell carcinoma Adenoid squamous cell carcinoma Spindle cell carcinoma Adenosquamous carcinoma Undifferentiated carcinoma
2. Benign lesions capable of microscopically resembling oral squamous cell carcinoma and oral verrucous carcinoma Papillary hyperplasia Granular cell tumor Discoid lupus erythematosus Median rhomboid glossitis Keratoacanthoma Necrotizing sialometaplasia Juxtaoral organ of Chievitz Chronic hyperplastic candidiasis Verruciform xanthoma Verruca vulgaris Condyloma acuminatum
3. Precancerous lesions (Clinical classification) Leukoplakia Erythroplakia Palatal keratosis associated with reverse smoking
4. Precancerous lesions (Histological classification) Squamous epithelial dysplasia Squamous cell carcinoma in situ Solar keratosis
5. Benign lesions capable of resembling oral precancerous lesions White lesions resembling leukoplakia red lesions resembling erythroplakia Focal epithelial hyperplasia Reactive and regenerative atypia
6. Precancerous conditions Sideropenic dysphagia Lichen planus Oral submucous fibrosis Syphilis Discoid lupus erythematosus Xeroderma pigmentosum Epidermolysis bullosa