cavity prep / restoration Flashcards
What factors do you consider in deciding which material to use for restoration?
Aesthetics of material, hardness of material, thermal expansion of material, ease of handling material, compressive strength, polymerization shrinkage, water absorption, wear resistance, filler content, elastic modulus
You decide to place a composite restoration. What problems can arise during or after placing a posterior composite restoration in a proximal box cavity and how do you overcome them?
- Polymerisation contraction shrinkage (overcome by placing composite in increments)
- Microleakage (overcome by designing cavity appropriately – bevelling Cavo-surface Margin)
- Insufficient curing of composite (overcome by incremental placement of composite)
- Over-etching tooth surface, leading to a collapse of collagen network (overcome by following manufacturer’s instruction on how to apply etch)
- Overhangs of composite in proximal region (overcome by use of wedge & matrix band to get the same contour as a natural tooth’s shape)
- Premature setting of composite (move light source away from restoration)
- Overfilling the cavity causing pain on occlusion (trim the restoration appropriately)
- Overhangs in proximal region (removed with filing strip)
How do you ensure your matrix band placement does not cause a narrow contact point near the marginal ridge of the tooth?
The matrix band could be adapted against the adjacent tooth using a flat plastic or probe instrument to ensure that the contact area is not narrow. Once this position is achieved, it could be secured with a wedge to prevent it from moving during placement of composite
5 things which could go wrong during or after placement of a composite restoration and how to overcome these
Bonding failure: could be due to insufficient tooth preparation, contamination of the tooth surface, or inadequate curing of the composite material.
Solution: To overcome bonding failure, the tooth surface should be cleaned and etched properly before bonding, and the composite material should be cured thoroughly to ensure proper bonding. Also, the dentist should ensure adequate tooth preparation and isolation to minimize contamination.
Postoperative sensitivity: After the placement of a composite restoration, the patient may experience tooth sensitivity to hot or cold food and drinks.
Solution: To overcome postoperative sensitivity, the dentist should use desensitizing agents during the placement of the composite restoration and advise the patient to avoid hot and cold foods for a few days. If the sensitivity persists, the dentist may recommend a desensitizing toothpaste or other treatments.
Marginal leakage: Marginal leakage occurs when the composite material separates from the tooth surface, allowing bacteria to penetrate and cause recurrent decay.
Solution: To overcome marginal leakage, the dentist should ensure that the composite material is properly placed and contoured, with adequate margin adaptation. Proper isolation and drying of the tooth surface are also important to minimize the risk of leakage.
Cracking or fracture: Composite restorations can crack or fracture over time, especially if they are subjected to excessive biting or chewing forces.
Solution: To overcome cracking or fracture, the dentist should ensure that the composite material is properly placed and contoured, with adequate occlusal adjustment. Patients should be advised to avoid biting hard objects or eating sticky or chewy foods that could damage the restoration.
Discoloration: Composite restorations can become discolored over time due to exposure to food, drinks, and other staining agents.
Solution: To overcome discoloration, the dentist should advise the patient to avoid or minimize exposure to staining agents and maintain good oral hygiene. If the restoration becomes discolored, it may need to be replaced or polished to restore its appearance.
Features you would want in a cavity preparation for a composite restoration (4 marks)
- Retentive form: The cavity preparation should have a retentive form that provides mechanical retention for the composite restoration. This can be achieved by creating undercuts, grooves, or small boxes in the tooth structure.
- Minimal invasiveness: The cavity preparation should be as minimally invasive as possible, preserving as much healthy tooth structure as possible. This can be achieved by using conservative cavity design principles and removing only the minimum amount of tooth structure necessary to accommodate the restoration.
- Smooth internal surface: The internal surface of the cavity preparation should be smooth and free from any irregularities or undercuts that could interfere with the placement and adaptation of the composite restoration. This can be achieved by using high-speed diamond burs or carbide burs to prepare the cavity walls.
- Adequate isolation: Adequate isolation of the tooth is necessary to prevent contamination of the cavity preparation and ensure proper bonding of the composite restoration. This can be achieved by using a rubber dam, cotton rolls, or other isolation techniques.
principles of preparation are driven by
caries removal, necessary finishing, no attempt to remove healthy tooth tissue
principles of cavity design and preparation
- Identify and remove carious enamel
- Remove enamel to identify the maximal extent of the lesion at the amelodentinal junction & smooth the enamel margins
Need to know how far it spread ! - Progressively remove peripheral caries in dentine – from the ADJ first, then circumferentially deeper.
We want to avoid exposing the pulp ! - Only then remove deep caries over pulp
- Outline form modification (cavo-surface margins)
- Enamel finishing
- Occlusion
- Requirements of the restorative material
- Internal design modification
- Internal line and point angles - stress concentrators
Requirements of the restorative material
- Internal line and point angles - stress concentrators
Picture of tooth – label dead tracts, primary, secondary and tertiary dentine, cellular cementum (5 marks)
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Cervical smooth surface cavity
Configuration factor
the configuration factor, also known as the C-factor, describes the ratio of bonded to unbonded surfaces in a cavity preparation.
It can affect the degree of polymerization shrinkage and stress within the restoration, which can lead to microleakage, marginal staining, and failure of the restoration over time.
In a cervical smooth surface cavity, the C-factor is typically low, as there is generally only one or two surfaces of the cavity that are bonded to the composite restoration. This means that the polymerization shrinkage and stress are generally lower in these types of cavities compared to more complex preparations, such as Class II or Class V cavities.
However, it is still important to consider the C-factor when placing composite restorations in cervical smooth surface cavities, as the degree of polymerization shrinkage and stress can still have an impact on the longevity and success of the restoration. Dentists may use techniques such as incremental layering, soft-start curing, or low-shrinkage composite materials to minimize the impact of polymerization shrinkage and stress on the restoration in cervical smooth surface cavities.
Why bond to dentine may fail in cervical smooth surface cavity
NEED selective etching to remove the SMEAR layer, desensitisers to penetrate SCLEROTIC dentin, and ISOLATION techniques to control moisture.
SMEAR LAYER
During cavity preparation, a smear layer is created on the surface of the dentin, which is a LAYER OF DEBRIS that can inhibit bonding. If the smear layer is not adequately removed or modified, it can interfere with the penetration of bonding agents and reduce bond strength.
DENTINAL SCLEROSIS
Cervical dentin can become sclerotic, or LESS PERMEABLE, due to aging or pathology, which can make it difficult for bonding agents to penetrate and bond to the dentin.
MOISTURE CONTROL
Adequate moisture control is critical for successful bonding, as excess moisture can interfere with the penetration of bonding agents and reduce bond strength. In cervical smooth surface cavities, moisture control can be difficult due to the location and shape of the cavity, as well as the presence of saliva and gingival fluids.
C-FACTOR IS LOW
As mentioned in the previous answer, the C-factor of a cavity can affect bond strength. In cervical smooth surface cavities, the C-factor is typically LOW, which can reduce the bond strength and make bonding more challenging.
how would you detect caries?
radiograph, by eye, staining, white/brown spot lesion
principles of removing dental caries
FIRST ADJ, LAST PULPAL FLOOR
- Residual carious dentine must be removed first from the amelo-dentinal junction (ADJ) and last from the pulpal floor
- Caries here should be removed using
- Hand-held excavator
- Round bur
- Chemo-mechanical caries removal
- Caries detector dyes may be helpful
- Caution: exposure
Remove Caries
* Caries on the pulpal floor should be removed last using the largest instrument which will conveniently work in the cavity:
- Large round bur
- Large hand-held excavator
- Chemo-mechanical caries removal
* Small burs and excavators will cut deeply more quickly – risk of pulp exposure
* Carious pulp exposure is a necessity – pulp therapy
- Direct and Indirect Pulp Cap (CaOH)
- Exposing a healthy pulp
- Importance of symptoms
* Traumatic exposure is to be avoided!
describe clinical and pathological sequence of leaving caries untreated
it will spread from enamel to adj
adj = wider dentinal tubules = bacterial invasion through the dentine to the pulp
inflamed pulp = pulpitis = toothache
eventually becomes necrotic
inflammation spreads around the tooth apex, an abscess, granuloma or cyst will eventually form
what is hybrid layer?
the zone of resin-dentin interaction that is created when bonding agents are applied to the prepared dentin surface. The hybrid layer is formed when the bonding agent INFILTRATES THE DENTINAL TUBULES AND FORMS A MICROMECHANICAL INTERLOCKING NETWORK with the collagen fibers of the dentin.
The hybrid layer is composed of a MIXTURE OF RESIN AND COLLAGEN, which creates a strong bond between the tooth structure and the restorative material. The thickness and quality of the hybrid layer can affect the strength and durability of the bond, as well as the marginal sealing and resistance to microleakage.
Why would it be difficult to bond to dentine with deep caries
BACTERIAL CONTAMINATION
Deep carious lesions are often associated with bacterial contamination, which can interfere with bonding agents and reduce bond strength. Bacteria can produce endotoxins, enzymes, and other factors that can degrade dentin and interfere with the formation of a strong hybrid layer.
DEMINERALISATION
In deep carious lesions, the dentin may be extensively demineralized, which can reduce the structural integrity and strength of the tooth. Demineralization can also CREATES A THICK layer of dentin that can be difficult for bonding agents to penetrate and bond to.
MOISTURE CONTROL
Adequate moisture control is critical for successful bonding, as excess moisture can interfere with the penetration of bonding agents and reduce bond strength. In deep carious lesions, moisture control can be difficult due to the location and shape of the cavity, as well as the presence of saliva and gingival fluids.
C-FACTOR IS HIGH
The C-factor, or the ratio of bonded to unbonded surfaces, of a cavity can affect bond strength. In deep carious lesions, the C-factor is typically high, which can reduce the bond strength and make bonding more challenging.
outline creation of a hybrid layer
- Tooth preparation: The tooth must be properly prepared for bonding by removing any decay or damaged tooth structure and cleaning the surface with an etchant, typically phosphoric acid. The etchant creates microscopic porosities in the enamel and dentin surfaces, which increase the surface area and improve bonding
- Application of bonding agent: After the tooth is prepared, a bonding agent is applied to the enamel and dentin surfaces. The bonding agent is designed to infiltrate the porosities created by the etchant and form a micromechanical interlocking network with the tooth structure.
Penetration of bonding agent: The bonding agent must be applied in a thin, uniform layer to ensure adequate penetration and coverage of the enamel and dentin surfaces. The agent should be agitated or scrubbed into the tooth structure to ensure penetration into the dentinal tubules. - Polymerization: After the bonding agent has been applied and penetrated into the tooth structure, it must be polymerized, typically with a curing light. Polymerization causes the bonding agent to harden and create a strong, durable bond between the restorative material and the tooth structure.
- Formation of hybrid layer: As the bonding agent polymerizes, it forms a hybrid layer that consists of a mixture of resin and collagen from the dentin. The hybrid layer creates a strong bond between the tooth structure and the restorative material and helps to seal the margins of the restoration to prevent microleakage and recurrent decay.
3 reasons why a bond to dentine may fail
- Inadequate moisture control: Bonding to dentin requires a dry surface to ensure optimal bonding. If moisture is present, it can interfere with the penetration and bonding of the adhesive. Inadequate moisture control can lead to bond failure, as well as post-operative sensitivity and discoloration.
- Incomplete removal of the smear layer: The smear layer is a thin layer of debris and mineralized tissue that covers the surface of dentin after tooth preparation. If the smear layer is not adequately removed, it can interfere with the penetration and bonding of the adhesive, leading to a weak bond.
- Insufficient penetration of the adhesive: The adhesive used for bonding to dentin must penetrate the surface of the tooth structure to create a strong bond. If the adhesive does not fully penetrate into the dentin or if there are voids or gaps in the bonding, the bond strength may be compromised, leading to bond failure.
Ditching has occurred in an amalgam restoration why?
No undercuts so amalgam not well retained as requires mechanical retention. Forces caused weak enamel to fracture off.
what can we do to prevent ditching in amalgam
tooth prep - proper undercuts
adequate condensation
proper carving - smooth margins
finishing and polishing
Secondary caries have formed under restoration: 4 factors contributing to this
- Amalgam not packed well so ingress of bacteria and toxins via microgap between restoration and cavity walls = MICROLEAKAGE
- Incomplete removal of bacteria from cavity prior to restoration placement
- POOR OH
- FRACTURE of amalgam = crack for BACTERIA INGRESSION
5 risk factors for high caries
- Low socioeconomic status
- High sugar diet
- Poor oral hygiene
- Lack of education about caries
- Smoking
contraindications/disadvantages of amalgam
aesthetics
allergy to Mercury
pregnant women
removal of uncesssary healthy tissue for tooth prep
poor thermal conductivity and expansion.
no bonding
easier to place as do not need moisture control
advantages - strength, durable, corrosion resistant
cavity prep - undercuts for retention/resistance, ensure to unsupported enamel which could fracture.
ensure internal line angles smooth so AM can be packed sufficiently and leave no gaps.
cavosurface margins no at contact points may cause creep
principles of cavity preparation
Remove carious enamel and find extent of caries along ADJ and smooth enamel margins with a high speed
Advance peripherally deeper in dentine using slow speed
Remove caries over pulp last using last bur possible or excavator.
Outline form modification - smooth cavosurface margins, requirement of material
Internal line modification - smooth internal line angles and point angles
2 causes of dry mouth
radiotherapy and sjondrens syndrome
drugs - anticholinergic, opiates, benzodiazepines
