The selection of a proper dental material for use in oral cavity is very important for the long-term success of the treatment. There are several factors that play an important role in selection of an ideal restorative dental material for the use in a particular patient. However, to understand the various factors, which guide us in the selection of proper dental material to be used for restoration of the teeth in oral cavity, we should be aware of the objective of the filling or the restoration.
OBJECTIVES OF RESTORATIVE PROCEDURES
The various objectives of the filling procedures can be broadly outlined as follows:
1. Prevention of recurrence of dental caries.
2. Arrest of loss of tooth structure from caries.
3. Establishment of proper occlusion.
4. Accomplishment of ideal aesthetics.
5. Resistance against masticatory forces.
6. Maintenance of normal inter proximal spaces and contact point.
To achieve the above-mentioned purposes, we need to select the proper dental material, taking into the consideration the various factors, expectations, environment and forces to which the selected material will be exposed.
FACTORS AFFECTING THE SELECTION OF dental material
Some of the important factors, which directly affect the selection of the dental material for use in the oral cavity, are as follows:
Digestion is the process of breaking down food both mechanically (physically) and chemically. This process begins in mouth, where food is mechanically broken down into small pieces through biting, chewing, and grinding actions. So, any restoration of the tooth is continuously exposed to these heavy masticatory loads in the oral cavity. The oral environment is particularly conducive to breaking down or dissolving materials.
The combination of saliva and the mechanical forces of biting/chewing that begin the digestive process require any restorative (repairing) dental material to be strong and insoluble. Those biting forces average 28,000 pounds per square inch (psi). Because of this, the amalgam and composites used extensively as restorative dental material in modem dentistry, feature strengths in excess of 85,000 psi.
The oral environment is exposed to different kinds of acids. Enzymes found in saliva, which help in digestion of food chemically, are acidic in nature. There are acids in many of the common foods. Ascorbic acid, for example, is found in citrus fruits. In addition of acidic nature of many food items, the normal bacteria present in the mouth also liberate acids. Because acids accelerate the breakdown of dental material, teeth and the restorative materials must be insoluble and resistant to the acidic substances. Many of the early generation of non-metallic restorative dental material used to show deterioration over time, dissolving away in this acidic environment.
However, on the contrary, because of the properties of the metals used in dental amalgam, the amalgam restoration corrodes in a “controlled fashion” that could improve the marginal seal of the restoration.
Everyday the oral cavity is exposed to different temperatures as we eat and drink foods that are so varied in temperature, from hot drinks to frozen ice cream. Teeth expand marginally when exposed to hot food and contract on exposure to cold food. Therefore, any restorative dental material placed in a tooth must not only be able to withstand extreme temperature changes, but also closely match the thermal expansion and contraction of the tooth. If the difference in thermal expansion between the tooth and restorative material is too great, the margin between the restorative dental material and tooth can open up, creating a microscopic space, which may lead to micro leakage.
Microleakage is the leakage of very small amounts of fluid, debris, and/or microorganisms (e.g., bacteria or viruses) into a microscopic space between a tooth and its restorative dental material. As just mentioned, differences in thermal expansion between a tooth and restorative dental material can create such a space. The inability of dental restorative material to seal the margins of a cavity preparation also can result in a microscopic space at the junction.
So, improper bonding of restorative dental material with the tooth surface may also cause micro leakage. Continued microleakage will lead to restoration failure, secondary caries and pulpal irritation causing sensitivity or permanent pulpal damage.
If microleakage is severe, sensitivity of the tooth (pain in the tooth that lasts a short period of time) and failure of the restoration may occur. Another type of sensitivity may occur when two different metals of dental material are present in the mouth. An ionic or galvanic reaction may occur in this moist environment, producing a small electric current This reaction can cause a galvanic shock and associated sensitivity.
This situation particularly happens, when two different types of metals are used for restoration of two opposing teeth. This sensitivity may also occur when a metal eating utensil touches a metallic restoration. Mother sensitivity is produced when proper sedative layer is not used below the metallic fillings causing the transmission of hot or cold sensation to the underlying living tissue of the tooth.
Retention of the restoration must be achieved by mechanical and/or adhesive methods. Traditional restorative techniques rely on mechanical retention. They must take into consideration the factors of biting stress and tooth structure removal. Adhesive retention (bonding) is complicated by the moist environment of the mouth, varying thermal expansions of materials involved, and the differences associated with the inorganic and organic dental material of the tooth structure and restorative.
The bio-compatibility of the restorative dental material is extremely important. The material must be harmless to the teeth and oral tissues to be suitable for use in oral cavity. The materials must not be irritating, allergenic, poisonous, or harmful to the body.
It is also one of the important factor or criteria for selection of proper restorative dental material as generally the main concern of the dental patients are about how they all look after their dentist repairs or replaces their teeth. They want to maintain a pleasing appearance or aesthetics. Permanent restorations in the posterior of the mouth are not generally visible in a normal smile, so the silver color of dental amalgam was traditionally accepted.
However, restorations in the anterior regions of the mouth demand a tooth shade matching the individuals existing dentition. The modem composite materials offer nearly unlimited color matching and have excellent color stability.
Age of the Patient
Age of the patient is also an important factor taken into consideration, before selecting some dental material to be used in the particular patient. The material, which may be good for short-term use in deciduous teeth of a small child, may not be the ideal material for use in a permanent tooth of a young patient. The structural difference, particularly of the pulpal tissues and the size of dentinal tubules in deciduous and permanent teeth, also affect the decision of selection of dental material. Similarly in a very old patient, who may be having more reparative dentin formation with the aging, giving more pulpal tissue protection, the material choice may be different.
The cost or economics of the dental material also play an important role in selection of restorative material, particularly in case of developing countries with large population under the poverty line. Sometimes, even the dental material may be an ideal choice on the basis of its physical and chemical properties, due to the cost factor and inability of the patient to afford the cost of the procedure, the material may not be used in that particular patient.
IDEAL REQUIREMENT OF THE FILLING dental material
After taking into consideration the objective of the dental filling (or restoration) and the various factors responsible for selection of the dental material, we can outline the following requirements of an ideal filing material:
1. Indestructibility in the oral fluids.
2. It should not damage or irritate the pulp or any other underlying tissues.
3. Good adaptability to cavity walls.
4. Harmonious in color.
5. Resistance to masticatory or occluding forces.
6. Resistance to attrition and good edge strength.
7. Non-conductivity to thermal or electric changes.
8. Free from postoperative dimensional changes.
9. It should be bio-compatible.
10. It should have same amount of thermal expansion or contraction as that of natural tooth structure.
11. It should not be very expensive.
12. It should be easy to use for the operator.