NEET MDS Lessons
Conservative Dentistry
Nursing Bottle Caries
Nursing bottle caries, also known as early childhood caries (ECC), is a significant dental issue that affects infants and young children. Understanding the etiological agents involved in this condition is crucial for prevention and management. .
1. Pathogenic Microorganism
A. Streptococcus mutans
- Role: Streptococcus mutans is the primary microorganism responsible for the development of nursing bottle caries. It colonizes the teeth after they erupt into the oral cavity.
- Transmission: This bacterium is typically transmitted to the infant’s mouth from the mother, often through saliva.
- Virulence Factors:
- Colonization: It effectively adheres to tooth surfaces, establishing a foothold for caries development.
- Acid Production: S. mutans produces large amounts of acid as a byproduct of carbohydrate fermentation, leading to demineralization of tooth enamel.
- Extracellular Polysaccharides: It synthesizes significant quantities of extracellular polysaccharides, which promote plaque formation and enhance bacterial adherence to teeth.
2. Substrate (Fermentable Carbohydrates)
A. Sources of Fermentable Carbohydrates
- Fermentable carbohydrates are utilized by S. mutans to form
dextrans, which facilitate bacterial adhesion to tooth surfaces and
contribute to acid production. Common sources include:
- Bovine Milk or Milk Formulas: Often high in lactose, which can be fermented by bacteria.
- Human Milk: Breastfeeding on demand can expose teeth to sugars.
- Fruit Juices and Sweet Liquids: These are often high in sugars and can contribute to caries.
- Sweet Syrups: Such as those found in vitamin preparations.
- Pacifiers Dipped in Sugary Solutions: This practice can introduce sugars directly to the oral cavity.
- Chocolates and Other Sweets: These can provide a continuous source of fermentable carbohydrates.
3. Host Factors
A. Tooth Structure
- Host for Microorganisms: The tooth itself serves as the host for S. mutans and other cariogenic bacteria.
- Susceptibility Factors:
- Hypomineralization or Hypoplasia: Defects in enamel development can increase susceptibility to caries.
- Thin Enamel and Developmental Grooves: These anatomical features can create areas that are more prone to plaque accumulation and caries.
4. Time
A. Duration of Exposure
- Sleeping with a Bottle: The longer a child sleeps with
a bottle in their mouth, the higher the risk of developing caries. This is
due to:
- Decreased Salivary Flow: Saliva plays a crucial role in neutralizing acids and washing away food particles.
- Prolonged Carbohydrate Accumulation: The swallowing reflex is diminished during sleep, allowing carbohydrates to remain in the mouth longer.
5. Other Predisposing Factors
- Parental Overindulgence: Excessive use of sugary foods and drinks can increase caries risk.
- Sleep Patterns: Children who sleep less may have increased exposure to cariogenic factors.
- Malnutrition: Nutritional deficiencies can affect oral health and increase susceptibility to caries.
- Crowded Living Conditions: These may limit access to dental care and hygiene practices.
- Decreased Salivary Function: Conditions such as iron deficiency and exposure to lead can impair salivary function, increasing caries susceptibility.
Clinical Features of Nursing Bottle Caries
- Intraoral Decay Pattern: The decay pattern associated with nursing bottle caries is characteristic and pathognomonic, often involving the maxillary incisors and molars.
- Progression of Lesions: Lesions typically progress rapidly, leading to extensive decay if not addressed promptly.
Management of Nursing Bottle Caries
First Visit
- Lesion Management: Excavation and restoration of carious lesions.
- Abscess Drainage: If present, abscesses should be drained.
- Radiographs: Obtain necessary imaging to assess the extent of caries.
- Diet Chart: Provide a diet chart for parents to record the child's diet for one week.
- Parent Counseling: Educate parents on oral hygiene and dietary practices.
- Topical Fluoride: Administer topical fluoride to strengthen enamel.
Second Visit
- Diet Analysis: Review the diet chart with the parents.
- Sugar Control: Identify and isolate sugar sources in the diet and provide instructions to control sugar exposure.
- Caries Activity Tests: Conduct tests to assess the activity of carious lesions.
Third Visit
- Endodontic Treatment: If necessary, perform root canal treatment on affected teeth.
- Extractions: Remove any non-restorable teeth, followed by space maintenance if needed.
- Crowns: Place crowns on teeth that require restoration.
- Recall Schedule: Schedule follow-up visits every three months to monitor progress and maintain oral health.
Inlay Preparation
Inlay preparations are a common restorative procedure in dentistry, particularly for Class II restorations.
1. Definitions
A. Inlay
- An inlay is a restoration that is fabricated using an indirect procedure. It involves one or more tooth surfaces and may cap one or more cusps but does not cover all cusps.
2. Class II Inlay (Cast Metal) Preparation Procedure
A. Burs Used
- Recommended Burs:
- No. 271: For initial cavity preparation.
- No. 169 L: For refining the cavity shape and creating the proximal box.
B. Initial Cavity Preparation
- Similar to Class II Amalgam: The initial cavity
preparation is performed similarly to that for Class II amalgam
restorations, with the following differences:
- Occlusal Entry Cut Depth: The initial occlusal entry should be approximately 1.5 mm deep.
- Cavity Margins Divergence: All cavity margins must
diverge occlusally by 2-5 degrees:
- 2 degrees: When the vertical walls of the cavity are short.
- 5 degrees: When the vertical walls are long.
- Proximal Box Margins: The proximal box margins should clear the adjacent tooth by 0.2-0.5 mm, with 0.5 ± 0.2 mm being ideal.
C. Preparation of Bevels and Flares
- Primary and Secondary Flares:
- Flares are created on the facial and lingual proximal walls, forming the walls in two planes.
- The secondary flare widens the proximal box, which initially had a
clearance of 0.5 mm from the adjacent tooth. This results in:
- Marginal Metal in Embrasure Area: Placing the marginal metal in the embrasure area allows for better self-cleansing and easier access for cleaning and polishing without excessive dentin removal.
- Marginal Metal Angle: A 40-degree angle, which is easily burnishable and strong.
- Enamel Margin Angle: A 140-degree angle, which blunts the enamel margin and increases its strength.
- Note: Secondary flares are omitted on the mesiofacial proximal walls of maxillary premolars and first molars for esthetic reasons.
D. Gingival Bevels
- Width: Gingival bevels should be 0.5-1 mm wide and blend with the secondary flare, resulting in a marginal metal angle of 30 degrees.
- Purpose:
- Removal of weak enamel.
- Creation of a burnishable 30-degree marginal metal.
- Production of a lap sliding fit at the gingival margin.
E. Occlusal Bevels
- Location: Present on the cavosurface margins of the cavity on the occlusal surface.
- Width: Approximately 1/4th the depth of the respective wall, resulting in a marginal metal angle of 40 degrees.
3. Capping Cusps
A. Indications
- Cusp Involvement: Capping cusps is indicated when more than 1/2 of a cusp is involved and is mandatory when 2/3 or more is involved.
B. Advantages
- Weak Enamel Removal: Helps in removing weak enamel.
- Cavity Margin Location: Moves the cavity margin away from occlusal areas subjected to heavy forces.
- Visualization of Caries: Aids in visualizing the extent of caries, increasing convenience during preparation.
C. Cusp Reduction
- Uniform Metal Thickness: Cusp reduction must provide for a uniform 1.5 mm metal thickness over the reduced cusps.
- Facial Cusp Reduction: For maxillary premolars and first molars, the reduction of the facial cusp should be 0.75-1 mm for esthetic reasons.
D. Reverse Bevel (Counter Bevel)
- Definition: A bevel given on the margins of the reduced cusp.
- Width: Varies to extend beyond any occlusal contact with opposing teeth, resulting in a marginal metal angle of 30 degrees.
E. Retention Considerations
- Retention Form: Cusp reduction decreases the retention form due to reduced vertical wall height. Therefore, proximal retentive grooves are usually recommended.
- Collar and Skirt Features: These features can enhance retention and resistance form.
Onlay Preparation
Onlay preparations are a type of indirect restoration used to restore teeth that have significant loss of structure but still retain enough healthy tooth structure to support a restoration. Onlays are designed to cover one or more cusps of a tooth and are often used when a full crown is not necessary.
1. Definition of Onlay
A. Onlay
- An onlay is a restoration that is fabricated using an indirect procedure, covering one or more cusps of a tooth. It is designed to restore the tooth's function and aesthetics while preserving as much healthy tooth structure as possible.
2. Indications for Onlay Preparation
- Extensive Caries: When a tooth has significant decay that cannot be effectively treated with a filling but does not require a full crown.
- Fractured Teeth: For teeth that have fractured cusps or significant structural loss.
- Strengthening: To reinforce a tooth that has been weakened by previous restorations or caries.
3. Onlay Preparation Procedure
A. Initial Assessment
- Clinical Examination: Assess the extent of caries or damage to determine if an onlay is appropriate.
- Radiographic Evaluation: Use X-rays to evaluate the tooth structure and surrounding tissues.
B. Tooth Preparation
-
Burs Used:
- Commonly used burs include No. 169 L for initial cavity preparation and No. 271 for refining the preparation.
-
Cavity Preparation:
- Occlusal Entry: The initial occlusal entry should be approximately 1.5 mm deep.
- Divergence of Walls: All cavity walls should
diverge occlusally by 2-5 degrees:
- 2 degrees: For short vertical walls.
- 5 degrees: For long vertical walls.
-
Proximal Box Preparation:
- The proximal box margins should clear adjacent teeth by 0.2-0.5 mm, with 0.5 ± 0.2 mm being ideal.
C. Bevels and Flares
-
Facial and Lingual Flares:
- Primary and secondary flares should be created on the facial and lingual proximal walls to form the walls in two planes.
- The secondary flare widens the proximal box, allowing for better access and cleaning.
-
Gingival Bevels:
- Should be 0.5-1 mm wide and blend with the secondary flare, resulting in a marginal metal angle of 30 degrees.
-
Occlusal Bevels:
- Present on the cavosurface margins of the cavity on the occlusal surface, approximately 1/4th the depth of the respective wall, resulting in a marginal metal angle of 40 degrees.
4. Dimensions for Onlay Preparation
A. Depth of Preparation
- Occlusal Depth: Approximately 1.5 mm to ensure adequate thickness of the restorative material.
- Proximal Box Depth: Should be sufficient to accommodate the onlay while maintaining the integrity of the tooth structure.
B. Marginal Angles
- Facial and Lingual Margins: Should be prepared with a 30-degree angle for burnishability and strength.
- Enamel Margins: Ideally, the enamel margins should be blunted to a 140-degree angle to enhance strength.
C. Cusp Reduction
- Cusp Coverage: Cusp reduction is indicated when more than 1/2 of a cusp is involved, and mandatory when 2/3 or more is involved.
- Uniform Metal Thickness: The reduction must provide for a uniform metal thickness of approximately 1.5 mm over the reduced cusps.
- Facial Cusp Reduction: For maxillary premolars and first molars, the reduction of the facial cusp should be 0.75-1 mm for esthetic reasons.
D. Reverse Bevel
- Definition: A bevel on the margins of the reduced cusp, extending beyond any occlusal contact with opposing teeth, resulting in a marginal metal angle of 30 degrees.
5. Considerations for Onlay Preparation
- Retention and Resistance: The preparation should be designed to maximize retention and resistance form, which may include the use of proximal retentive grooves and collar features.
- Aesthetic Considerations: The preparation should account for the esthetic requirements, especially in anterior teeth or visible areas.
- Material Selection: The choice of material (e.g., gold, porcelain, composite) will influence the preparation design and dimensions.
Diagnostic Methods for Early Caries Detection
Early detection of caries is essential for effective management and treatment. Various diagnostic methods can be employed to identify caries activity at early stages:
1. Identification of Subsurface Demineralization
- Inspection: Visual examination of the tooth surface for signs of demineralization, such as white spots or discoloration.
- Radiographic Methods: X-rays can reveal subsurface carious lesions that are not visible to the naked eye, allowing for early intervention.
- Dye Uptake Methods: Application of specific dyes that can penetrate demineralized areas, highlighting the extent of carious lesions.
2. Bacterial Testing
- Microbial Analysis: Testing for the presence of specific cariogenic bacteria (e.g., Streptococcus mutans) can provide insight into the caries risk and activity level.
- Salivary Testing: Salivary samples can be analyzed for bacterial counts, which can help assess the risk of caries development.
3. Assessment of Environmental Conditions
- pH Measurement: Monitoring the pH of saliva can indicate the potential for demineralization. A lower pH (acidic environment) is conducive to caries development.
- Salivary Flow: Evaluating salivary flow rates can help determine the protective capacity of saliva against caries. Reduced salivary flow can increase caries risk.
- Salivary Buffering Capacity: The ability of saliva to neutralize acids is crucial for maintaining oral health. Assessing this capacity can provide valuable information about caries risk.
Refractory materials include:
- Plaster of Paris: The most commonly used refractory material in dentistry, plaster is composed of calcium sulfate hemihydrate. It is mixed with water to form a paste that is used to make study models and casts. It has a relatively low expansion coefficient and is easy to manipulate, making it suitable for various applications.
- Dental stone: A more precise alternative to plaster, dental
stone is a type of gypsum product that offers higher strength and less
dimensional change. It is commonly used for master models and die fabrication
due to its excellent surface detail reproduction.
- Investment materials: Used in the casting process of fabricating indirect
restorations, investment materials are refractory and encapsulate the wax
pattern to create a mold. They can withstand the high temperatures required for
metal casting without distortion.
- Zirconia: A newer refractory material gaining popularity,
zirconia is a ceramic that is used for the fabrication of all-ceramic crowns and
bridges. It is extremely durable and has a high resistance to wear and fracture.
- Refractory die materials: These are used in the production of
metal-ceramic restorations. They are capable of withstanding the high
temperatures involved in the ceramic firing process and provide a reliable
foundation for the ceramic layers.
The selection of a refractory material is based on factors such as the intended
use, the required accuracy, and the specific properties needed for the final
restoration. The material must have a low thermal expansion coefficient to
minimize the thermal stress during the casting process and maintain the
integrity of the final product. Additionally, the material should be able to
reproduce the fine details of the oral anatomy and have good physical and
mechanical properties to ensure stability and longevity.
Refractory materials are typically used in the following procedures:
- Impression taking: Refractory materials are used to make models from the
patient's impressions.
- Casting of metal restorations: A refractory mold is created from the model to
cast the metal framework.
- Ceramic firing: Refractory die materials hold the ceramic in place while it is
fired at high temperatures.
- Temporary restorations: Some refractory materials can be used to produce
temporary restorations that are highly accurate and durable.
Refractory materials are critical for achieving the correct fit and function of
dental restorations, as well as ensuring patient satisfaction with the
aesthetics and comfort of the final product.
Spray Particles in the Dental Operatory
1. Aerosols
Aerosols are composed of invisible particles that range in size from approximately 5 micrometers (µm) to 50 micrometers (µm).
Characteristics
- Suspension: Aerosols can remain suspended in the air for extended periods, often for hours, depending on environmental conditions.
- Transmission of Infection: Because aerosols can carry infectious agents, they pose a risk for the transmission of respiratory infections, including those caused by bacteria and viruses.
Clinical Implications
- Infection Control: Dental professionals must implement appropriate infection control measures, such as the use of personal protective equipment (PPE) and effective ventilation systems, to minimize exposure to aerosols.
2. Mists
Mists are visible droplets that are larger than aerosols, typically estimated to
be around 50 micrometers (µm) in diameter.
Characteristics
- Visibility: Mists can be seen in a beam of light, making them distinguishable from aerosols.
- Settling Time: Heavy mists tend to settle gradually from the air within 5 to 15 minutes after being generated.
Clinical Implications
- Infection Risk: Mists produced by patients with respiratory infections, such as tuberculosis, can transmit pathogens. Dental personnel should be cautious and use appropriate protective measures when treating patients with known respiratory conditions.
3. Spatter
Spatter consists of larger particles, generally greater than 50 micrometers
(µm), and includes visible splashes.
Characteristics
- Trajectory: Spatter has a distinct trajectory and typically falls within 3 feet of the patient’s mouth.
- Potential for Coating: Spatter can coat the face and outer garments of dental personnel, increasing the risk of exposure to infectious agents.
Clinical Implications
- Infection Pathways: Spatter or splashing onto mucosal surfaces is considered a potential route of infection for dental personnel, particularly concerning blood-borne pathogens.
- Protective Measures: The use of face shields, masks, and protective clothing is essential to minimize the risk of exposure to spatter during dental procedures.
4. Droplets
Droplets are larger than aerosols and mists, typically ranging from 5 to 100
micrometers in diameter. They are formed during procedures that involve the use
of water or saliva, such as ultrasonic scaling or high-speed handpieces.
Characteristics
- Size and Behavior: Droplets can be visible and may settle quickly due to their larger size. They can travel short distances but are less likely to remain suspended in the air compared to aerosols.
- Transmission of Pathogens: Droplets can carry pathogens, particularly during procedures that generate saliva or blood.
Clinical Implications
- Infection Control: Droplets can pose a risk for respiratory infections, especially in procedures involving patients with known infections. Proper PPE, including masks and face shields, is essential to minimize exposure.
5. Dust Particles
Dust particles are tiny solid particles that can be generated from various sources, including the wear of dental materials, the use of rotary instruments, and the handling of dental products.
Characteristics
- Size: Dust particles can vary in size but are generally smaller than 10 micrometers in diameter.
- Sources: They can originate from dental materials, such as composite resins, ceramics, and metals, as well as from the environment.
Clinical Implications
- Respiratory Risks: Inhalation of dust particles can pose respiratory risks to dental personnel. Effective ventilation and the use of masks can help reduce exposure.
- Allergic Reactions: Some individuals may have allergic reactions to specific dust particles, particularly those derived from dental materials.
6. Bioaerosols
Bioaerosols are airborne particles that contain living organisms or biological materials, including bacteria, viruses, fungi, and allergens.
Characteristics
- Composition: Bioaerosols can include a mixture of aerosols, droplets, and dust particles that carry viable microorganisms.
- Sources: They can be generated during dental procedures, particularly those that involve the manipulation of saliva, blood, or infected tissues.
Clinical Implications
- Infection Control: Bioaerosols pose a significant risk for the transmission of infectious diseases. Implementing strict infection control protocols, including the use of high-efficiency particulate air (HEPA) filters and proper PPE, is crucial.
- Monitoring Air Quality: Regular monitoring of air quality in the dental operatory can help assess the presence of bioaerosols and inform infection control practices.
7. Particulate Matter (PM)
Particulate matter (PM) refers to a mixture of solid particles and liquid droplets suspended in the air. In the dental context, it can include a variety of particles generated during procedures.
Characteristics
- Size Categories: PM is often categorized by size, including PM10 (particles with a diameter of 10 micrometers or less) and PM2.5 (particles with a diameter of 2.5 micrometers or less).
- Sources: In a dental setting, PM can originate from dental materials, equipment wear, and environmental sources.
Clinical Implications
- Health Risks: Exposure to particulate matter can have adverse health effects, particularly for individuals with respiratory conditions. Proper ventilation and air filtration systems can help mitigate these risks.
- Regulatory Standards: Dental practices may need to adhere to local regulations regarding air quality and particulate matter levels.
Bases in Restorative Dentistry
Bases are an essential component in restorative dentistry, serving as a thicker layer of material placed beneath restorations to provide additional protection and support to the dental pulp and surrounding structures. Below is an overview of the characteristics, objectives, and types of bases used in dental practice.
1. Characteristics of Bases
A. Thickness
- Typical Thickness: Bases are generally thicker than liners, typically ranging from 1 to 2 mm. Some bases may be around 0.5 to 0.75 mm thick.
B. Functions
- Thermal Protection: Bases provide thermal insulation to protect the pulp from temperature changes that can occur during and after the placement of restorations.
- Mechanical Support: They offer supplemental mechanical support for the restoration by distributing stress on the underlying dentin surface. This is particularly important during procedures such as amalgam condensation, where forces can be applied to the restoration.
2. Objectives of Using Bases
The choice of base material and its application depend on the Remaining Dentin Thickness (RDT), which is a critical factor in determining the need for a base:
- RDT > 2 mm: No base is required, as there is sufficient dentin to protect the pulp.
- RDT 0.5 - 2 mm: A base is indicated, and the choice of material depends on the restorative material being used.
- RDT < 0.5 mm: Calcium hydroxide (Ca(OH)₂) or Mineral Trioxide Aggregate (MTA) should be used to promote the formation of reparative dentin, as the remaining dentin is insufficient to provide adequate protection.
3. Types of Bases
A. Common Base Materials
- Zinc Phosphate (ZnPO₄): Known for its good mechanical properties and thermal insulation.
- Glass Ionomer Cement (GIC): Provides thermal protection and releases fluoride, which can help in preventing caries.
- Zinc Polycarboxylate: Offers good adhesion to tooth structure and provides thermal insulation.
B. Properties
- Mechanical Protection: Bases distribute stress effectively, reducing the risk of fracture in the restoration and protecting the underlying dentin.
- Thermal Insulation: Bases are poor conductors of heat and cold, helping to maintain a stable temperature at the pulp level.