NEET MDS Lessons
Prosthodontics
Bevels are the angulation which is made by 2 surfaces of a
prepared tooth which is other than 90 degrees. Bevels are given at various
angles depending on the type of material used for restoration and the purpose
the material serves.
Any abrupt incline between the 2 surfaces of a prepared tooth or between the
cavity wall and the Cavo surface margins in the prepared cavity
Bevels are the variations which are created during tooth preparation or cavity
preparation to help in increased retention and to prevent marginal leakage.
It is seen that in Bevels Occlusal cavosurface margin needs to be 40 degrees
which seals and protects enamel margins from leakage and the Gingival Cavo
surface margin should be 30 degrees to remove the unsupported enamel rods and
produce a sliding fit or lap joint useful in burnishing gold.
Types or Classification of Bevels based on the Surface they are placed
on:
Classification of Bevels based on the two factors – Based on the shape and
tissue surface involved and Based on the surface they are placed on –
Based on the shape and tissue surface involved:
1. Partial or Ultra short bevel
2. Short Bevel
3. Long Bevel
4. Full Bevel
5. Counter Bevel
6. Reverse / Minnesota Bevel
Partial or Ultra Short Bevel:
Beveling which involves less than 2/3rd of the Enamel thickness. This is not
used in Cast restorations except to trim unsupported enamel rods from the cavity
borders.
Short Bevel:
Entire enamel wall is included in this type of Bevel without involving the
Dentin. This bevel is used mostly with Class I alloys specially for type 1 and
2. It is used in Cast Gold restoration
Long Bevel:
Entire Enamel and 1/2 Dentin is included in the Bevel preparation. Long Bevel is
most frequently used bevel for the first 3 classes of Cast metals. Internal
boxed- up resistance and retention features of the preparation are preserved
with Long Bevel.
Full Bevel:
Complete Enamel and Dentinal walls of the cavity wall or floor are included in
this Bevel. It is well reproduced by all four classes of cast alloys, internal
resistance and retention features are lost in full bevel. Its use is avoided
except in cases where it is impossible to use any other form of bevel .
Counter Bevel:
It is used only when capping cusps to protect and support them, opposite to an
axial cavity wall , on the facial or lingual surface of the tooth, which will
have a gingival inclination facially or lingually.
There is another type of Bevel called the Minnesota Bevel or the Reverse Bevel,
this bevel as the name suggest is opposite to what the normal bevel is and it is
mainly used to improve retention in any cavity preparation
If we do not use functional Cusp Bevel –
1. It Can cause a thin area or perforation of the restoration borders
2. May result in over contouring and poor occlusion
3. Over inclination of the buccal surface will destroy excessive tooth structure
reducing retention
Based on the surface they are placed on:
1. Gingival bevel
2. Hollow ground bevel
3. Occlusal bevel or Functional cusp bevel
Gingival bevel:
1. Removal of Unsupported Enamel Rods.
2. Bevel results in 30° angle at the gingival margin that is burnishable because
of its angular design.
3. A lap sliding fit is produced at the gingival margin which help in improving
the fit of casting in this region.
4. Inlay preparations include of two types of bevel Occlusal bevel Gingival
bevel
Hollow Ground (concave) Bevel: Hollow ground bevel allows more
space for bulk of cast metal, a design feature needed in special preparations to
improve material’s castability retention and better resistance to stresses.
These bevels are ideal for class IV and V cast materials. This is actually an
exaggerated chamfer or a concave beveled shoulder which involves teeth greater
than chamfer and less than a beveled shoulder. The buccal slopes of the lingual
cusps and the lingual slope of the buccal cusps should be hollow ground to a
depth of at least 1 mm.
Occlusal Bevel:
1. Bevels satisfy the requirements for ideal cavity walls.
2. They are the flexible extensions of a cavity preparation , allowing the
inclusion of surface defects , supplementary grooves , or other areas on the
tooth surface.
3. Bevels require minimum tooth involvement and do not sacrifice the resistance
and retention for the restoration
4. Bevels create obtuse-angled marginal tooth structure, which is bulkiest and
the strongest configuration of any marginal tooth anatomy, and produce an acute
angled marginal cast alloy substance which allows smooth burnishing for alloy.
Functional cusp Bevel:
An integral part of occlusal reduction is the functional cusp bevel. A wide
bevel placed on the functional cusp provides space for an adequate bulk of metal
in an area of heavy occlusal contact.
| Clasp Type | Key Features | Indications |
|---|---|---|
| Circumferential (Akers) | Cast, engages undercut from opposite side | Common in tooth-supported RPDs |
| Bar (Roach) | Approaches undercut from gingival direction | Used when esthetics are a concern |
| Ring Clasp | Encircles nearly the entire tooth | Useful for tipped molars |
| Combination Clasp | Wrought wire retentive arm + cast reciprocal arm | Offers flexibility and adaptability |
| Hairpin Clasp | U-shaped; engages deep undercuts | Rarely used; specific anatomical needs |
Critical Dimensions & Measurements
- Minimum bone requirements: 10 mm vertical × 6 mm horizontal
- Implant biological width: 3–3.5 mm
- External hex dimension: 3 mm
- Minimum interocclusal clearance: 8 mm (for hex implant)
Safety Distances
- Mental foramen: Maintain 5 mm distance
- Inferior alveolar canal: Maintain 2 mm distance
Temperature Control
- Maximum osteotomy temperature: 47°C (Eriksson & Alberktsson study)
- Critical for preventing bone necrosis
Mandibular Implant Specifics
- Must engage superior cortex and medullary bone
- Provides optimal primary stability
Complications & Diagnosis
- Primary complication: Peri-implantitis
- Characterized by: Inflammation + tissue loss
- Diagnostic sign: Bone saucerization around implant
Surgical Planning Tools
- Implant analogue: Replicates implant position in cast
- Surgical template guide:
- Ensures implant parallelism
- Primary diagnostic tool for angulation assessment
Arrangement of Teeth in Complete Dentures
The arrangement of teeth in complete dentures is a critical aspect of prosthodontics that affects both the function and aesthetics of the prosthesis. The following five principal factors must be considered when arranging teeth for complete dentures:
1. Position of the Arch
- Definition: The position of the arch refers to the spatial relationship of the maxillary and mandibular dental arches.
- Considerations:
- The relationship between the arches should be established based on the patient's occlusal plane and the anatomical landmarks of the residual ridges.
- Proper positioning ensures that the dentures fit well and function effectively during mastication and speech.
- The arch position also influences the overall balance and stability of the denture.
2. Contour of the Arch
- Definition: The contour of the arch refers to the shape and curvature of the dental arch.
- Considerations:
- The contour should mimic the natural curvature of the dental arch to provide a comfortable fit and proper occlusion.
- The arch contour affects the positioning of the teeth, ensuring that they align properly with the opposing arch.
- A well-contoured arch enhances the esthetics and function of the denture, allowing for effective chewing and speaking.
3. Orientation of the Plane
- Definition: The orientation of the plane refers to the angulation of the occlusal plane in relation to the horizontal and vertical planes.
- Considerations:
- The occlusal plane should be oriented to facilitate proper occlusion and function, taking into account the patient's facial features and anatomical landmarks.
- The orientation affects the alignment of the teeth and their relationship to the surrounding soft tissues.
- Proper orientation helps in achieving balanced occlusion and minimizes the risk of denture displacement during function.
4. Inclination of Occlusion
- Definition: The inclination of occlusion refers to the angulation of the occlusal surfaces of the teeth in relation to the vertical axis.
- Considerations:
- The inclination should be designed to allow for proper interdigitation of the teeth during occlusion.
- It influences the distribution of occlusal forces and the overall stability of the denture.
- The inclination of occlusion should be adjusted based on the patient's functional needs and the type of occlusion being utilized (e.g., balanced, monoplane, or lingualized).
5. Positioning for Esthetics
- Definition: Positioning for esthetics involves arranging the teeth in a way that enhances the patient's facial appearance and smile.
- Considerations:
- The arrangement should consider the patient's age, gender, and facial features to create a natural and pleasing appearance.
- The size, shape, and color of the teeth should be selected to match the patient's natural dentition and facial characteristics.
- Proper positioning for esthetics not only improves the appearance of the dentures but also boosts the patient's confidence and satisfaction with their prosthesis.
Fluid Wax Method
- Proper technique indicator: Glossy appearance
- Significance: Indicates intimate tissue contact
- Defective flow sign: PPS butt joint formation
- Butt joint cause: Inadequate wax flow
Special Conditions
- Submucous fibrosis: Addition silicone (preferred material)
- Reason: Better flow properties and biocompatibility
Complete Denture Occlusion
Complete denture occlusion is a critical aspect of prosthodontics, as it affects the function, stability, and comfort of the dentures. There are three primary types of occlusion used in complete dentures: Balanced Occlusion, Monoplane Occlusion, and Lingualized Occlusion. Each type has its own characteristics and applications.
Types of Complete Denture Occlusion
1. Balanced Occlusion
- Definition: Balanced occlusion is characterized by simultaneous contact of all opposing teeth in centric occlusion, providing stability and even distribution of occlusal forces.
- Key Features:
- Three-Point Contact: While a three-point contact (one anterior and two posterior) is a starting point, it is not sufficient for true balanced occlusion. Instead, there should be simultaneous contact of all teeth.
- Minimal Occlusal Balance: For minimal occlusal balance, there should be at least three points of contact on the occlusal plane. The more points of contact, the better the balance.
- Absence in Natural Dentition: Balanced occlusion is not typically found in natural dentition; it is a concept specifically applied to complete dentures to enhance stability during function.
- Importance: This type of occlusion is particularly important for patients with complete dentures, as it helps to minimize tipping and movement of the dentures during chewing and speaking.
2. Monoplane Occlusion
- Definition: Monoplane occlusion involves a flat occlusal plane where the occlusal surfaces of the teeth are arranged in a single plane.
- Key Features:
- Flat Occlusal Plane: The occlusal surfaces are designed to be flat, which simplifies the occlusion and reduces the complexity of the denture design.
- Limited Interference: This type of occlusion minimizes interferences during lateral and protrusive movements, making it easier for patients to adapt to their dentures.
- Applications: Monoplane occlusion is often used in cases where the residual ridge is severely resorbed or in patients with limited jaw movements.
3. Lingualized Occlusion
- Definition: Lingualized occlusion is characterized by the positioning of the maxillary posterior teeth in a way that they occlude with the mandibular posterior teeth, with the buccal cusps of the mandibular teeth being positioned more towards the buccal side.
- Key Features:
- Maxillary Teeth Positioning: The maxillary posterior teeth are positioned more towards the center of the arch, while the mandibular posterior teeth are positioned buccally.
- Functional Balance: This arrangement allows for better functional balance and stability during chewing, as the maxillary teeth provide support to the mandibular teeth.
- Advantages: Lingualized occlusion can enhance the esthetics and function of complete dentures, particularly in patients with a well-defined ridge.
Bite Registration
- Thin medium, no tooth contact
- Use low-viscosity materials (e.g., waxes, elastomers) to record occlusal relationships without interference from tooth contact.
- Ensures accurate centric relation or maximum intercuspation records.
Gingival Management & Impression Protocols
- Impression after cord removal
- Take impressions only after bleeding has stopped to avoid voids and distortion.
- Gingival Sulcus Closure
- Sulcus begins to collapse 20–30 seconds post cord removal—timing is critical for accurate impressions.
- Electrosurgery
- Used to enlarge the sulcus and control bleeding during crown preparation or impression procedures.
- Offers precision and minimal trauma compared to mechanical retraction.
Pre-Operative Medication
- Methantheline Bromide
- Anticholinergic agent; 50 mg dose, administered 1 hour pre-op to reduce salivary flow.
- Enhances moisture control during procedures.
Moisture Control
- Rubber Dam
- Introduced by S.C. Barnum in 1864.
- Provides isolation, retraction, and accessibility—essential for adhesive procedures and endodontics.
Diagnostic Aids
- Explorer + Air
- Most effective for detecting small occlusal cavities—air drying reveals chalky enamel and explorer detects surface roughness.
- Lactobacillus
- Acidogenic and aciduric bacteria; thrive in low pH and contribute to caries progression.
- Saliva Buffering
- Saliva neutralizes acids produced by bacteria like Lactobacillus, protecting enamel from demineralization.
Surface Preparation
- McLaughlin Etching Technique
- Combination of Hydrochloric acid (HCl) and Sulfuric acid (H₂SO₄) with ultrasonic activation for 99 seconds.
- Used for enamel conditioning in orthodontics or bonding procedures.