৪৮তম বিশেষ বিসিএস [স্বাস্থ্য] ⎯ ডেন্টাল অংশ [Archived]

Chlorhexidine – Summary Note

- Type: Cationic bisbiguanide antiseptic
- Formulations: Mouth rinse as CHX Gluconate (0.12%, 0.2%), gel, spray, chips
- Mechanism of Action:
- Disrupts bacterial cell membrane
- Causes leakage of cytoplasmic contents
- Bactericidal at high concentrations, bacteriostatic at low concentrations

- Spectrum:
- Broad-spectrum antimicrobial
- Effective against Gram-positive > Gram-negative bacteria
- Some antifungal & antiviral activity

- Substantivity:
- Binds to oral tissues and teeth
- Slow release maintains effect up to 12 hours

- Adverse Effects:
- Brown staining of teeth and tongue
- Altered taste sensation
- Mucosal irritation (rare)
- Increased calculus formation

- Contraindications:
- Known hypersensitivity to CHX
- Avoid immediate use after brushing (inactivated by anionic surfactants in toothpaste)

Fluoride 

1. Mechanism of Action
- Promotes remineralization of enamel by attracting calcium and phosphate ions.
- Converts hydroxyapatite into fluorapatite, which is more acid-resistant.
- Inhibits demineralization during acid attacks.
- Antimicrobial effect: inhibits bacterial enzymes, reducing acid production by cariogenic bacteria.

2. Sources of Fluoride
- Systemic: water fluoridation, dietary supplements, fluoride in food and beverages.
- Topical: fluoridated toothpaste, mouth rinses, gels, varnishes.

3. Water Fluoridation
- Optimal fluoride concentration: 0.7 to 1.2 ppm to prevent caries without causing fluorosis.

4. Topical Application
- Home use of fluoride toothpaste (1000-1500 ppm fluoride) is standard.
-usually as Sodium Fluoride. 

5. Fluoride Toxicity
- Acute toxicity: ingestion of large doses can cause nausea, vomiting, hypocalcemia, and in severe cases, death.
- Chronic toxicity: prolonged excess fluoride intake leads to dental fluorosis (enamel mottling) and skeletal fluorosis (bone changes).

Reference: The textbook of operative dentistry by Nisha Garg (Chapter: Caries)

Acute Apical Periodontitis (AAP)
Definition:
Acute inflammation of the periodontal ligament surrounding the apex of a tooth, typically resulting from pulp necrosis or trauma.

Clinical Features:
- Localized, sharp pain
- Pain on biting or percussion
- Tooth may feel elevated in socket
- Often non-vital on pulp testing
- No obvious swelling initially

Radiographic Features:
- Widened periodontal ligament space
- Possible loss of lamina dura
- May appear normal in very early stages

Sequelae of Pulpitis (if left untreated):

1. Reversible pulpitis
2. Irreversible pulpitis
3. Pulp necrosis
4. Periapical periodontitis 
5. Periapical abscess 
6. Chronic apical periodontitis
7. Radicular cyst or granuloma
8. Osteomyelitis or cellulitis
9. Systemic involvement (rare)

A pink tooth can be caused by both internal and external resorption, but the most common cause is: External cervical resorption.

- External cervical resorption: Granulation tissue invades the cervical region, and as it shows through the enamel, it gives a pink appearance (“pink spot”).
- Internal resorption: Can also cause a pink hue if it affects the crown, but it's less common.

Mummifying Agents 

Common Mummifying Agents:
- Formocresol
- Glutaraldehyde
- Cresatin
- Phenol derivatives

Formocresol:
- Buckley’s composition: 19% formaldehyde, 35% cresol, with glycerin and water
- Mechanism: Cross-links proteins, fixes tissue
- Used mainly in pediatric pulpotomy
- Concern: Systemic toxicity and mutagenicity

Mechanism of Action:
- Coagulation of pulp tissue proteins
- Bactericidal activity
- Preserves pulp as inert, devitalized tissue

Advantages:
- Easy to apply
- Temporary infection control
- Preserves tooth for delayed endodontic treatment

Disadvantages:
- Toxicity (especially formaldehyde-based)
- Potential systemic absorption
- Not preferred for permanent dentition
Clinical Application:
- Apply with cotton pellet on pulp stumps for 1–5 minutes
- Common in primary molars before restoration with SSC (stainless steel crown)

SLOB Rule (Same Lingual, Opposite Buccal):

Used to determine the position of an object (like a canal, root, foreign body) in radiographs.

Principle:
Take two radiographs with different angulations (e.g. mesial and distal shift).

- If the object moves in the same direction as the tube head, it is on the lingual side.
- If it moves in the opposite direction, it is on the buccal side.

*
Mnemonic: SLOB
- *S*ame = *L*ingual
- *O*pposite = *B*uccal

Example:
If you move the X-ray tube mesially and the object appears to move mesially too → it's lingual.
If it appears to move distally → it's buccal.

Horizontal Radiographic Errors 
Common Types:
1. Overlapping of Contacts
- Cause: X-ray beam not directed perpendicular to interproximal spaces
- Result: Inability to assess caries or restorations properly

2. Cone Cut (Partial Image Missing)
- Cause: Beam not centered on film or sensor
- Result: Unexposed area (clear zone) on the image

3. Distorted Crown or Root Angles
- Cause: Improper sensor placement or beam angulation
- Result: Misleading image shape

Prevention:
- Position X-ray beam perpendicular to tooth and receptor
- Use paralleling technique with proper holder
- Ensure proper alignment with aiming ring or indicator device

Here’s a list of 'radiation hazards' relevant to dentistry:

1. Somatic Effects (Affect the individual exposed)
- Skin erythema (reddening)
- Hair loss (epilation)
- Cataract formation
- Radiation burns
- Reduced salivary gland function
- Oral mucositis (in high-dose exposure)
- Delayed wound healing
- Immunosuppression

2. Stochastic Effects (Probability increases with dose; no threshold)
- Carcinogenesis (oral cancer, leukemia)
- Genetic mutations
- Chromosomal aberrations

3. Deterministic Effects (Have a threshold dose; severity increases with dose)
- Radiation dermatitis
- Cataracts
- Oral tissue necrosis (in radiation therapy context)

4. Reproductive Hazards
- Infertility (with high-dose exposure to gonads)
- Fetal malformations (if pregnant woman exposed)

5. Developmental Hazards
- Growth disturbances (in children)
- Dental anomalies (if exposure occurs during tooth development)

6. Occupational Hazards for Dental Professionals
- Cumulative low-dose exposure risks
- Increased cancer risk over long term
- Thyroid dysfunction
- Genetic impact on offspring

(The textbook of endodontics by Nisha Garg – Chapter: Procedural Accidents)

Common errors during endodontic treatment:

1. Access Cavity Errors
- Incomplete access
- Perforation of the pulp chamber floor or wall

2. Instrumentation Errors
- Ledge formation
- Zipping
- Canal transportation
- Apical perforation
- Instrument separation (file breakage)

3. Obturation Errors
- Underfilling
- Overfilling
- Voids in obturation
- Missed canals

4. Irrigation Errors
- Sodium hypochlorite accident (extrusion into periapical tissues)

5. Post-endodontic Errors
- Fracture of tooth due to delayed restoration
- Coronal leakage

In primary teeth, obturation materials need to resorb at a rate equal to or faster than the physiological root resorption because:

- Prevent obstruction of permanent tooth eruption: If the material remains after the root is resorbed, it may block or alter the path of the erupting permanent tooth.

- Avoid chronic inflammation: Non-resorbing material left in periapical tissues may act as a foreign body, causing irritation or delayed healing.

Therefore, resorbable materials like iodoform-based pastes are preferred for pulpectomy in primary teeth.

Why Cold Lateral Condensation is Preferred Over Warm Techniques in Some Cases

1. Simplicity: Cold lateral is easy to perform, requires minimal equipment.
2. Control: Better control over obturation length and spreader placement.
3. Cost-effective: No need for heat carriers or thermoplastic devices.
4. Less extrusion: Lower risk of overfilling beyond apex.
5. Suitable for beginners and general practice.

Causes of RCT (Root Canal Treatment) Failure 

1. Missed canals
2. Inadequate cleaning and shaping
3. Improper obturation (underfilling, overfilling, voids)
4. Coronal leakage due to poor restoration
5. Vertical root fracture
6. Persistent periapical pathology
7. Perforation during instrumentation or post placement
8. Instrument separation
9. Periodontal disease involvement
10. Complex root canal anatomy (curved, calcified, or ledged canals)

Removal of smear layer
-17%EDTA for inorganic part
-NaOCl for organic part

EDTA (Ethylenediaminetetraacetic acid) is a chelating agent that is used as a final rinse after NaOCl (sodium hypochlorite) during root canal irrigation. While NaOCl dissolves organic tissue, it cannot remove the inorganic portion of the smear layer. EDTA helps by chelating calcium ions, thus removing the inorganic smear layer from dentin walls and allowing better sealing of the root canal.

NaOCl → removes organic debris
EDTA → removes inorganic smear layer
 

RCT in Curved Canals 

Approach
1. Access cavity
- Ensure proper straight-line access to minimize stress on instruments

2. Canal negotiation
- Start with small pre-curved hand files (#6, #8, #10)
- Use watch-winding and balanced force technique
- Establish a smooth glide path

3. Instrumentation
- Prefer NiTi rotary files with high flexibility
- Crown-down or hybrid techniques help reduce stress
- Avoid forcing files into curvature
- Recapitulate with hand files frequently

4. Irrigation
- Use sodium hypochlorite and EDTA
- Passive ultrasonic irrigation improves cleaning in curved areas

5. Working length
- Use apex locator and confirm with angled radiographs
- Reassess frequently during instrumentation

6. Obturation
- Thermoplasticized gutta-percha or warm vertical condensation is preferred
- Flowable materials adapt better in curves

Access Cavity Outlines for Different Teeth
(The textbook of endodontics by Nisha Garg - Access Cavity Preparation)

- Maxillary Central Incisor: Triangular
- Maxillary Lateral Incisor: Triangular
- Maxillary Canine: Oval
- Maxillary First Premolar: Oval or Rounded Triangular
- Maxillary Second Premolar: Oval
- Maxillary First Molar: Rhomboid or Triangular
- Maxillary Second Molar: Rhomboid
- Mandibular Central Incisor: Triangular or Oval
- Mandibular Lateral Incisor: Triangular or Oval
- Mandibular Canine: Oval
- Mandibular First Premolar: Oval
- Mandibular Second Premolar: Oval
- Mandibular First Molar: Rectangular
- Mandibular Second Molar: Rectangular or Rhomboid

Beveling in Composite Restoration

Definition:
Beveling is the process of angling the enamel margins of the cavity preparation, typically at 45°, using a bur or hand instrument before placing composite.

Purpose
- Increases surface area for bonding
- Improves marginal seal
- Enhances esthetics by blending restoration with natural tooth
- Reduces marginal leakage and discoloration

C-Factor (Configuration Factor) in adhesive dentistry is the ratio of bonded to unbonded (free) surfaces in a cavity preparation.

Formula:
C-Factor = Bonded surfaces / Unbonded surfaces

Significance:
Higher C-factor increases the risk of polymerization shrinkage stress in composite restorations, leading to microleakage, postoperative sensitivity, and failure of bonding.

Examples:
Class I cavity has 5 bonded and 1 unbonded surface, so C-factor = 5
Class IV cavity has 1 bonded and 4 unbonded surfaces, so C-factor = 0.25

Clinical approach:
Use incremental layering techniques to reduce stress in high C-factor cavities.

Creep in Amalgam refers to the slow, time-dependent deformation of amalgam under constant stress, especially in the warm, moist oral environment.

In dental amalgam:
- Caused by occlusal forces (chewing)
- Occurs mainly at marginal areas of restoration
- Can lead to marginal breakdown and secondary caries

Factors affecting creep:
- Composition: High-copper amalgams have low creep
- Manipulation: Proper trituration and condensation reduce creep
- Time: More creep seen after long-term function

Clinical relevance:
- Low creep is desirable
- High-copper amalgams are preferred due to improved resistance to creep

Common sites:
- Proximal surfaces between teeth
- Near the gingival margin on buccal or lingual sides

Mechanism of formation:

- When files or rotary instruments cut dentin, they grind dentin into fine particles.
- These particles mix with:
- Saliva or irrigating solutions
- Necrotic pulp tissue
- Bacteria and their by-products (in infected canals)
- This mixture adheres to the dentinal walls, forming the smear layer.

It covers both the surface and occludes the openings of dentinal tubules.

Time of formation:
- Instantly during filing or shaping procedures

Clinical point:
If not removed, it can interfere with cleaning, disinfection, and sealing of the root canal.

G.V. Black’s Classification of cavity:
- Class I: Pits and fissures on occlusal surfaces of molars and premolars, buccal or lingual pits of molars, lingual pits of maxillary incisors.
- Class II: Proximal surfaces of premolars and molars.
- Class III: Proximal surfaces of incisors and canines without involving the incisal edge.
- Class IV: Proximal surfaces of incisors and canines involving the incisal edge.
- Class V: Cervical third of the facial or lingual surfaces.
- Class VI: Incisal edges of anterior teeth and cusp tips of posterior teeth.


Reference: The textbook of Operative Dentistry by Nisha Garg (Chapter: Cavity Preparation)

K-File, H-File, Reamer 

K-File (Kerr File)
- Made by twisting stainless steel wire
- Cross-section: square or triangular
- Used with push-pull filing or watch-winding motion
- Less aggressive, good for initial canal negotiation

H-File (Hedström File)
- Made by grinding a round wire
- Cross-section: teardrop or spiral
- Very sharp, cuts on pull stroke only
- More efficient at dentin removal, but prone to fracture

Reamer
- Made by twisting wire with fewer spirals per mm
- Cross-section: triangular
- Used with rotating motion (quarter turn and pull)
- Good for enlarging canals, not as aggressive as H-file

Prevalence rate is defined as “the total
number of all individuals who have
an attribute or disease at a particular
time divided by population at risk at
this point in time or midway through
the period”.
The relationship between prevalence
and incidence is
Prevalence = Incidence × Mean duration
Disease prevalence is important for several reasons:

1. It helps to estimate the burden of disease on a population and the health care system. 

2. It helps to identify the risk factors and determinants of disease. tion.

3. It helps to evaluate the effectiveness and impact of interventions.

There are three basic tools of epidemiology:
(a) Rate—the occurrence of some
particular event in a population
during a given time period
(b) Ratio—measures disease frequency and expressed as a relation in size between two random
quantities
(c) Proportion—is a ratio which indicates the relation in magnitude
of a part of the whole

Cohort is a group of individuals shar-
ing the same characteristics.
The steps of cohort study are:
(a) Selection of study subjects—the
cohort is assembled either from
the general population or select
groups.
(b) Obtaining data on exposure—in-
formation about exposure is ob-
tained by asking the cohort mem-
bers, reviewing records, medical
examination and environmental
surveys.
(c) Selection of comparison groups—
comparison groups can be either
internal comparisons, external
comparisons or comparison with
general population rates
(d) Follow up—can be done by pe-
riodic medical examination, re-
viewing records, routine surveil-
lance of death records and mailed
questionnaires
(e) Analysis—in terms of incidence
rates of outcome among exposed
and non exposed, and estimation

Isolation is the separation of infected
people or animals from others for
the period of communicability. This
prevents the direct or indirect trans-
mission of the infectious agent from
spreading to those susceptible.

 Quarantine is the limitation of free-
dom of movement of people who are
well for a period of time not longer
than the longest incubation period of
the disease.

The reasons for using hand instru-
ments are:
(a) Uses a biological approach,
which requires minimal cavity
preparation, hence conserves
tooth structure.
(b) Less trauma and limitation of
pain , so need for anaesthesia.
(c) Low cost of hand instruments.
(d) Simplified infection control.
(e) Makes restorative care accessible
to all groups.

A survey is an investigation, in which
information is systematically collected, but no experimental method is
used. So, it is a non experimental investigation.

Contraindications for a pit and fissure
sealants are:
(a) Carious pits and fissures.
(b) Broad, well coalesced pit and
fissures.
(c) Teeth caries free for four years or
longer.
(d) Carious proximal surface.

Four levels of prevention are:
(a) Primordial prevention—preven-
tion taken even when risk factors
are not present.
(b) Primary prevention—action tak-
en prior to the onset of disease,
which removes the possibility
that a disease will ever occur.
(c) Secondary prevention—action
which halts the progress of a dis-
ease at its incipient stage and pre-
vents complications.
(d) Tertiary prevention—measures
undertaken to reduce or limit im-
pairments and disabilities, and to
promote patient’s adjustment to
irremediable conditions.

The iceberg phenomenon of disease—
is a concept where the iceberg is com-
pared with the disease in a community. The floating tip represents what the
physician sees in the community, i.e.
clinical cases. The submerged portion
of the iceberg represents the hidden
mass of the disease which is either la-
tent, inapparent, undiagnosed or car-
riers in the community. The waterline
represents the demarcation between
apparent and inapparent disease.

Pathfinder surveys can be either pilot
or national, depending on the sam-
pling sites and age groups included:
• Pilot study—includes only
one or two index ages and the
most important subgroups in
a population.
• National pathfinder survey—
includes all the important
subgroups of the population
and at least three of the age
groups or index ages.

Probability sampling technique—also
called as random sampling technique.
Each and every unit of the population
has an equal chance of being selected
for the study. Types of sampling tech-
niques are:
• Simple random sampling—
each unit is selected by chance 
alone
• Systematic random sampling—
the first unit is picked in
random, then the sample is
chosen systematically. Say the
10th name in the list, 7th house
in the area.
• Stratified random sampling—
strata is a group of people.
All the sample units are
selected from each strata and
is employed if the population
is not a homogenous group.
• Cluster random sampling—
cluster is again a group of
people. In case of cluster
sampling, sampling units are
selected from the group
• Area sampling—areas are
geographical clusters. It is a
type of random sampling in
which maps rather than lists
are used
• Multiphasic sampling—in
this method, part of the infor-
mation is collected from the
whole complex and part from
the sub sample
• Multistage sampling—when
the study involves a large geo-
graphical area, like a nation
wide study, sampling is done
in stages, like states, then dis-
tricts, towns, blocks and fami-
lies
• Sequential sampling—a small
sample is tested in order to an-
swer certain questions about
the population. If the questions
are not answered, the number
of subjects or units in the sam-
ple is increased gradually until
conclusions are drawn
16. Non probability sampling technique—the sample is selected with the
aim of representing the population as
a whole. Types of non—probability
sampling techniques are:
• Convenience Sampling—sample is selected with the ease of
access
• Judgemental sampling—the
investigator assumes what he
considers representative sam-
ple
• Quota sampling—combines
both the convenience sam-
pling and judgemental sam-
pling
• Snow ball or network sampling—a few units are identi-
fied and later additional units
are incorporated with the help
of them

Index ages are:
• 5 years—children begin
primary school. The level of
caries in primary dentition can
be recorded
• 12 years—children leave
primary school and the last
age at which sample may
be obtained easily through
school system. It is chosen
as the global monitoring age
for caries for international
comparisons and monitoring
of disease trends
• 15 years—permanent teeth is
exposed to oral environment
for 3 – 9 years. An important
age for the assessment of
periodontal diseases.
• 35 – 44 years—is the standard
monitoring group for health
conditions of adults. The full
effect of dental caries, the
level of severe periodontal
involvement, and the general
effects of care provided is
monitored using data for this
group
• 65 – 74 years—with the
increasing life span, the
changes in the age distribution
brings in a necessity to plan
appropriate care for the elderly

Normal distribution—an important
concept in statistical theory.
• It is a smooth, symmetrical
curve formed when the values
in a data set are presented in
a frequency distribution with
narrow class intervals
• The shape of the curve depends
on the mean and standard
deviation, and on the number
and nature of observations
• The area under the normal
curve is one
• The mean, median and mode
coincide in the midline of the
curve
• The area between one
standard deviation on either
side of the mean will include,
approximately 68 percent of
the values in the distribution
• The area between two
standard deviations on either
side of the mean will include,
approximately 95 percent of
the values in the distribution
• The area between three
standard deviations on either
side of the mean will include,
approximately 99 percent of
the values in the distribution
• These limits on either side of
the mean are called confidence
limits
• Skewness—the horizontal
stretching of a frequency dis-
tribution to one side or the
other
• Kurtosis—characterized by
the vertical stretching of the