amalgam 1 l Preclinical Operative MCQs

 

Dental Amalgam restorations ; describing definition , advantage , disadvantage ,   indications and contraindication of amalgam l Preclinical Operative MCQ for dental student

Amalgam Dental Restoration

• "Amalgam" : Alloy of mercury with another metal or metals.
• "Dental Amalgam" : Specific amalgam alloy that contains silver, tin and copper plus mercury.
• Amalgam is the most common and widely spread restorative material used in dentistry.
• The term "Amalgam" indicates that this amalgam is used in many fields as industry and dentistry while the term "Dental Amalgam" indicates that this amalgam is used in dentistry.
• Mercury is a liquid at room temperature, its freezing point is -39 0C.

Survey about using of amalgam in dental practice shows that :

• Amalgam users equal 68 %.
• Another material users as resin composite, glass ionomer and ceramic (Amalgam ) equal 32 %.

Advantages of amalgam restorations :

• Have superior adaptation to the cavity walls, and the adaptation is improved with time (aging)-
• Have high compressive strength which enables the restorations to withstand high forces of mastication without fracture.
• Their coefficient of thermal expansion is relatively close to (simulates) that of the tooth, this prevents overhang margin or gap.
• They are indestructible (insoluble) in saliva or any fluids taken by the oral cavity, this indestructibility helps in maintenance (stability) of :

1. From of the restoration.
2. Marginal sealing ability of the restoration.
3. Surface texture of the restoration.

• They have the ability to take and maintain a good polish, the good polishing gives the restoration a smooth and lustrous surface.
• They are inexpensive (cheap) and need no laborious procedures or expensive equipment.
• Its convenience of manipulation makes the materials a most Wide spread restorative, i.e. amalgam is easy in manipulation and the technique of amalgam is not sensitive.
• "Not sensitive" means that : If there is a defect in the amalgam restoration as improper insertion or improper manipulation, this defect Will not appear immediately after put the amalgam inside the cavity, it take long time to appear.

 

Some important question in dental amalgam

Q / Why the adaptation of amalgam restorations to the cavity walls is improved with time ? = Why the amalgam is termed "Self-sealing restoration" ?

• Answer : Due to their corrosion products which precipitate and seal the gaps between the amalgam restoration and cavity walls, this prevent (cut off ) saliva, food debris and bacteria form microleakage .

1. Corrosion products are materials result from the reaction between the amalgam and saliva.
2. Corrosion products are high in the low-copper amalgam (conventional type) while they are low in the high-copper amalgam (new type).
3. Microleakage leads to = Problems that may result from using a restorative material that isn't chemically boned with the tooth structure :

• Recurrent caries, Margins discoloration, Pulp affection, Hypersensitivity, Failure of the restoration.

Q / What will happen if the amalgam restorations are destructible or highly soluble in saliva or any fluids taken by the oral cavity ?

• Answer :

1. Form of the restoration Will change.
2. Marginal sealing ability of the restoration Will reduce.
3. Surface texture of the restoration Will be rough.
4. They have the ability to take and maintain a good polish, the good polishing gives the restoration a smooth and lustrous surface.

Q / Why any restoration should have highly smooth, shiny and lustrous surface ?

• Answer :

1. To prevent collection of food or calculus.
2. To prevent irritation of the gingiva if there is a direct contact With the gingiva.
3. To prevent stress concentration in a particular area, and thus prevent splitting of the tooth.
4. To prevent corrosion products and discoloration.

• Note : The technique of resin composite is sensitive, i.e. If there is a defect in the resin composite restoration as improper insertion or improper manipulation, this defect Will appear immediately.

 

Disadvantages of amalgam restorations :

1- Have low tensile strength = Have low edge strength = Amalgam is a brittle material.

• "Brittle" means that the amalgam can withstand the force of mastication in case of compressive stress, While the amalgam is weak in case of tensile or shear stress.

• The disadvantage number 1 may lead to the occurrence of fracture at the isthmus or the margins especially if :

1. There is no sufficient amount (bulk) of amalgam material at these areas.
2. They are subjected to relatively great tensile forces.

• Note : Because amalgam restoration is brittle, it should be put in a sufficient bulk or it should be put in non stress bearing area. If the amalgam restoration is put in thin section, it may fracture.

• To put the amalgam restoration in a sufficient bulk, the cavosurface angle for amalgam restoration should be butt joint, i.e. right angle (900) during cavity design. If the cavosurface angle is beveled angle, this Will result in thin edge and the restoration Will fracture.

2- Have the ability to conduct (transmit) thermal changes.

• The disadvantage number 2 may cause pulp affections that begins With pulp hyperemia, then may lead to pulpitis, then may lead to acute periapical abscess.

3- Amalgam has objectionable esthetics which prevents its use in the anterior teeth. Why ?

• Answer : Due to its :

1. Metallic color.
2. Inherent tendency to tarnish in the mouth.

• Note : Amalgam restorations are used in some cases in the anterior teeth as in cases of distal surface of canine class III cavities .

4- Their tendency to creep and flow under functional forces as indicated by (Clinical manifestations of creep) :

1. Flattened contact points.
2. Gingival overhangs (Overhang margin).
3. Saucering of occlusal anatomy.
4. Changes in the contour.
5. Changes of temperature : ↑ Wide range of temperatures → ↑ Creep.

Note in Creep :

• Creep has a relation With "Marginal integrity", low creep causes break down of the margins leading to gap.
• Example about alloys that may affected by creep : Low-copper amalgam, it is With inferior quality.
• Creep to occur in an alloy and affect marginal integrity, the creep percentage inside this alloy should be equal or more than 1 %.
• Creep percentage inside high-copper amalgam equals 0.1 %, so high-copper amalgam will not cause marginal break down.
• Creep percentage inside low-copper amalgam (Silver amalgam) equals 0.8 — 8 %, so all the low-copper amalgam that has a creep percentage more than 0.8 % Will cause marginal break down.
• Creep is inherent weakness.
• Creep is With inferior quality.

Indications of amalgam restorations :

1. Small and medium size cavities of class I, II and class V cavities except those of anterior teeth, Note : Class V caries occurs in the cervical third of the buccal (labial) and lingual (palatal) surfaces of all teeth.
2. Distal surface of canine class III cavities.
3. For building up cores and posts under full crown restorations : During root canal treatment, if there is no sufficient amount of tooth structure to put the crown above it, post and core of amalgam are indicated.

• Note : In case of large cavity, and the patient has no money enough to pay for cast or ceramic restoration, in this case a pin-retained amalgam restoration is used in the large cavity. (Pin-retained amalgam restoration is a type of amalgam restorations that requires placement of one or more pins in the dentin to provide adequate resistance and retention forms, i.e. for reinforcement of amalgam restoration.)

 

Contraindications 0f amalgam restorations :

• In conspicuous cavities in the anterior part of mouth. Why ?

1. Lack of aesthetic color, i.e. due to its metallic color.
2. Inherent tendency to tarnish in the mouth.

• In mouths containing another dissimilar metal
• Extensive lesions especially those including undermined cusps. (In this case, cast gold restoration serves better).
• Rampant caries ( occurs at young adult age.)