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.
Window of Infectivity
The concept of the "window of infectivity" was introduced by Caufield in 1993 to describe critical periods in early childhood when the oral cavity is particularly susceptible to colonization by Streptococcus mutans, a key bacterium associated with dental caries. Understanding these windows is essential for implementing preventive measures against caries in children.
- Window of Infectivity: This term refers to specific time periods during which the acquisition of Streptococcus mutans occurs, leading to an increased risk of dental caries. These windows are characterized by the eruption of teeth, which creates opportunities for bacterial colonization.
First Window of Infectivity
A. Timing
- Age Range: The first window of infectivity is observed between 19 to 23 months of age, coinciding with the eruption of primary teeth.
B. Mechanism
- Eruption of Primary Teeth: As primary teeth erupt, they
provide a "virgin habitat" for S. mutans to colonize the oral
cavity. This is significant because:
- Reduced Competition: The newly erupted teeth have not yet been colonized by other indigenous bacteria, allowing S. mutans to establish itself without competition.
- Increased Risk of Caries: The presence of S. mutans in the oral cavity during this period can lead to an increased risk of developing dental caries, especially if dietary habits include frequent sugar consumption.
Second Window of Infectivity
A. Timing
- Age Range: The second window of infectivity occurs between 6 to 12 years of age, coinciding with the eruption of permanent teeth.
B. Mechanism
- Eruption of Permanent Dentition: As permanent teeth
emerge, they again provide opportunities for S. mutans to colonize
the oral cavity. This window is characterized by:
- Increased Susceptibility: The transition from primary to permanent dentition can lead to changes in oral flora and an increased risk of caries if preventive measures are not taken.
- Behavioral Factors: During this age range, children may have increased exposure to sugary foods and beverages, further enhancing the risk of S. mutans colonization and subsequent caries development.
4. Clinical Implications
A. Preventive Strategies
- Oral Hygiene Education: Parents and caregivers should be educated about the importance of maintaining good oral hygiene practices from an early age, especially during the windows of infectivity.
- Dietary Counseling: Limiting sugary snacks and beverages during these critical periods can help reduce the risk of S. mutans colonization and caries development.
- Regular Dental Visits: Early and regular dental check-ups can help monitor the oral health of children and provide timely interventions if necessary.
B. Targeted Interventions
- Fluoride Treatments: Application of fluoride varnishes or gels during these windows can help strengthen enamel and reduce the risk of caries.
- Sealants: Dental sealants can be applied to newly erupted permanent molars to provide a protective barrier against caries.
Dental Burs: Design, Function, and Performance
Dental burs are essential tools in operative dentistry, used for cutting, shaping, and finishing tooth structure and restorative materials. This guide will cover the key features of dental burs, including blade design, rake angle, clearance angle, run-out, and performance characteristics.
1. Blade Design and Flutes
A. Blade Configuration
- Blades and Flutes: Blades on a bur are uniformly spaced, with depressed areas between them known as flutes. The design of the blades and flutes affects the cutting efficiency and smoothness of the bur's action.
- Number of Blades:
- The number of blades on a bur is always even.
- Excavating Burs: Typically have 6-10 blades, designed for efficient material removal.
- Finishing Burs: Have 12-40 blades, providing a smoother finish.
B. Cutting Efficiency
- Smoother Cutting Action: A greater number of blades results in a smoother cutting action at low speeds.
- Reduced Efficiency: As the number of blades increases, the space between subsequent blades decreases, leading to less surface area being cut and reduced efficiency.
2. Vibration Characteristics
A. Vibration and Patient Comfort
- Vibration Frequency: Vibrations over 1,300 cycles per second are generally imperceptible to patients.
- Effect of Blade Number: Fewer blades on a bur tend to produce greater vibrations, which can affect patient comfort.
- RPM and Vibration: Higher RPMs produce less amplitude and greater frequency of vibration, contributing to a smoother experience for the patient.
3. Rake Angle
A. Definition
- Rake Angle: The angle that the face of the blade makes with a radial line from the center of the bur to the blade.
B. Cutting Efficiency
- Positive Rake Angle: Burs with a positive rake angle are generally desired for cutting efficiency.
- Rake Angle Hierarchy: The cutting efficiency is ranked
as follows:
- Positive rake > Radial rake > Negative rake
- Clogging: Burs with a positive rake angle may experience clogging due to debris accumulation.
4. Clearance Angle
A. Definition
- Clearance Angle: This angle provides clearance between the working edge and the cutting edge of the bur, allowing for effective cutting without binding.
5. Run-Out
A. Definition
- Run-Out: Refers to the eccentricity or maximum displacement of the bur head from its axis of rotation.
- Acceptable Value: The average value of clinically acceptable run-out is about 0.023 mm. Excessive run-out can lead to uneven cutting and discomfort for the patient.
6. Load Characteristics
A. Load Applied by Dentist
- Low Speed: The minimum and maximum load applied through the bur is typically between 100 – 1500 grams.
- High Speed: For high-speed burs, the load is generally between 60 – 120 grams.
7. Diamond Stones
A. Abrasive Efficiency
- Diamond Stones: These are the hardest and most efficient abrasive stones available for removing tooth enamel. They are particularly effective for cutting and finishing hard dental materials.
Rotational Speeds of Dental Instruments
1. Measurement of Rotational Speed
Revolutions Per Minute (RPM)
- Definition: The rotational speed of dental instruments is measured in revolutions per minute (rpm), indicating how many complete rotations the instrument makes in one minute.
- Importance: Understanding the rpm is essential for selecting the appropriate instrument for specific dental procedures, as different speeds are suited for different tasks.
2. Speed Ranges of Dental Instruments
A. Low-Speed Instruments
- Speed Range: Below 12,000 rpm.
- Applications:
- Finishing and Polishing: Low-speed handpieces are commonly used for finishing and polishing restorations, as they provide greater control and reduce the risk of overheating the tooth structure.
- Cavity Preparation: They can also be used for initial cavity preparation, especially in areas where precision is required.
- Instruments: Low-speed handpieces, contra-angle attachments, and slow-speed burs.
B. Medium-Speed Instruments
- Speed Range: 12,000 to 200,000 rpm.
- Applications:
- Cavity Preparation: Medium-speed handpieces are often used for more aggressive cavity preparation and tooth reduction, providing a balance between speed and control.
- Crown Preparation: They are suitable for preparing teeth for crowns and other restorations.
- Instruments: Medium-speed handpieces and specific burs designed for this speed range.
C. High-Speed Instruments
- Speed Range: Above 200,000 rpm.
- Applications:
- Rapid Cutting: High-speed handpieces are primarily used for cutting hard dental tissues, such as enamel and dentin, due to their ability to remove material quickly and efficiently.
- Cavity Preparation: They are commonly used for cavity preparations, crown preparations, and other procedures requiring rapid tooth reduction.
- Instruments: High-speed handpieces and diamond burs, which are designed to withstand the high speeds and provide effective cutting.
3. Clinical Implications
A. Efficiency and Effectiveness
- Material Removal: Higher speeds allow for faster material removal, which can reduce chair time for patients and improve workflow in the dental office.
- Precision: Lower speeds provide greater control, which is essential for delicate procedures and finishing work.
B. Heat Generation
- Risk of Overheating: High-speed instruments can generate significant heat, which may lead to pulpal damage if not managed properly. Adequate cooling with water spray is essential during high-speed procedures to prevent overheating of the tooth.
C. Instrument Selection
- Choosing the Right Speed: Dentists must select the appropriate speed based on the procedure being performed, the type of material being cut, and the desired outcome. Understanding the characteristics of each speed range helps in making informed decisions.
Hybridization in Dental Bonding
Hybridization, as described by Nakabayashi in 1982, is a critical process in dental bonding that involves the formation of a hybrid layer. This hybrid layer plays a vital role in achieving micromechanical bonding between the tooth structure (dentin) and resin materials used in restorative dentistry.
1. Definition of Hybridization
Hybridization refers to the process of forming a hybrid layer at the interface between demineralized dentin and resin materials. This phenomenon is characterized by the interlocking of resin within the demineralized dentin surface, which enhances the bond strength between the tooth and the resin.
A. Formation of the Hybrid Layer
- Conditioning Dentin: When dentin is treated with a conditioner (usually an acid), it removes minerals from the dentin, exposing the collagen fibril network and creating inter-fibrillar microporosities.
- Application of Primer: A low-viscosity primer is then applied, which infiltrates these microporosities.
- Polymerization: After the primer is applied, the resin monomers polymerize, forming the hybrid layer.
2. Zones of the Hybrid Layer
The hybrid layer is composed of three distinct zones, each with unique characteristics:
A. Top Layer
- Composition: This layer consists of loosely arranged collagen fibrils and inter-fibrillar spaces that are filled with resin.
- Function: The presence of resin in this layer enhances the bonding strength and provides a flexible interface that can accommodate stress during functional loading.
B. Middle Layer
- Composition: In this zone, the hydroxyapatite crystals that were originally present in the dentin have been replaced by resin monomers due to the hybridization process.
- Function: This replacement contributes to the mechanical properties of the hybrid layer, providing a strong bond between the dentin and the resin.
C. Bottom Layer
- Composition: This layer consists of dentin that is almost unaffected, with a partly demineralized zone.
- Function: The presence of this layer helps maintain the integrity of the underlying dentin structure while still allowing for effective bonding.
3. Importance of the Hybrid Layer
The hybrid layer is crucial for the success of adhesive dentistry for several reasons:
- Micromechanical Bonding: The hybrid layer facilitates micromechanical bonding, which is essential for the retention of composite resins and other restorative materials.
- Stress Distribution: The hybrid layer helps distribute stress during functional loading, reducing the risk of debonding or failure of the restoration.
- Sealing Ability: A well-formed hybrid layer can help seal the dentin tubules, reducing sensitivity and protecting the pulp from potential irritants.
Various dyes have been tried to detect carious enamel, each having some Advantages and Disadvantages:
‘Procion’ dyes stain enamel lesions but the staining becomes irreversible because the dye reacts with nitrogen and hydroxyl groups of enamel and acts as a fixative.
‘Calcein’ dye makes a complex with calcium and remains bound to the lesion.
‘Fluorescent dye’ like Zyglo ZL-22 has been used in vitro which is not suitable in vivo. The dye is made visible by ultraviolet illumination.
‘Brilliant blue’ has also been used to enhance the diagnostic quality of fiberoptic transillumination.
Pouring the Final Impression
Technique
- Mixing Die Stone: A high-strength die stone is mixed using a vacuum mechanical mixer to ensure a homogenous mixture without air bubbles.
- Pouring Process:
- The die stone is poured into the impression using a vibrator and a No. 7 spatula.
- The first increments should be applied in small amounts, allowing the material to flow into the remote corners and angles of the preparation without trapping air.
- Surface Tension-Reducing Agents: These agents can be added to the die stone to enhance its flow properties, allowing it to penetrate deep into the internal corners of the impression.
Final Dimensions
- The impression should be filled sufficiently so that the dies will be approximately 15 to 20 mm tall occluso-gingivally after trimming. This height is important for the stability and accuracy of the final restoration.