REDM 101

Standardization of Dental Materials

• American Dental Association criteria for a new material
  • Must not be poisonous or harmful to the body
  • Must not be harmful or irritating to the tissues of the oral cavity
  • Must help protect the tooth and oral tissues of the oral cavity 
  • Must resemble the natural dentition 
  • Must be easily formed and placed in the mouth
  • Must conform to function   

The Council on Dental Materials, Instruments and Equipment, a subcommittee of the American Dental Association, works with federal agencies to ensure that strict specifications are followed by manufacturers in the development of new dental materials.

 What is an example of a dental material that has been the subject of a lot of public discussion about its safety? 

 Many materials may be harmful to the oral cavity when in their unset or unmixed component form yet, if handled properly, provide a safe and desirable restoration once completed.

Mechanical Properties

• Materials must be able to withstand the biting and chewing force in the posterior area of the mouth.
• Force is any push or pull on matter.
• Stress is the reaction within the material that can cause distortion.
• Strain is the change produced within the material that occurs as the result of stress. 

Mechanical properties of a material placed in the anterior area should also withstand various forces caused by factors, including occlusion and a patient’s habits. 

 A restoration will eventually reach a breaking point, causing permanent deformation (change) after a certain amount of both stress and strain is applied over a certain amount of time.

 Stress is the amount of load per unit of a cross-sectional area. What is an example of stress? 

 Remember that different materials have different properties under different types of force.

Types of Stress and Strain

• Tensile stress 
  • Pulls and stretches the material
• Compressive stress 
  • Pushes the material together
• Shear stress 
  • Breakdown of the material   

What type of stress may a material undergo if subjected to the following scenarios?

 A patient enjoys eating sticky candy. (Tensile stress.)

 A patient reports clenching his teeth when he is concentrating hard at work. (Compressive stress.) A patient has a habit of grinding her teeth at night, or nocturnal bruxism, (Shear stress.)

What type of stress does diagram A represent? (Tensile: eating sticky foods.)

 What type of stress does diagram B represent? (Compressive: clenching teeth.)

 What type of stress does diagram C represent? (Shear: nocturnal bruxism.)

 These types of stresses may also be demonstrated to students using the palms of your hands.

Thermal Changes

• A change in temperature in the oral cavity results from a hot or cold product.
• Contraction and expansion 
  • Dental materials contract or expand at their own rates. 
  • Changes in temperature can cause a dental material to pull away from the tooth, causing:
    • Microleakage
    • Faulty restoration 

 Has anyone experienced sensitivity caused by a hot or cold food or drink in his or her mouth?

 When the restorative material and surrounding tooth structure have different rates of contraction and expansion, microleakage may occur. Space between the tooth and the restoration allows saliva or bacteria to enter, causing sensitivity and or breakdown of that interface and ultimately destroying the restoration and permitting decay in the tooth. 

 The ideal restorative material is one that contracts and expands at a rate similar to that of the tooth within which it was placed.

Electrical Properties

• An electrical current, or galvanic action, is created when two different or dissimilar metals are present in the oral cavity.
• Factors leading to galvanic action:
• Saliva 
• Two metallic components of different composition 
• Electrical current 
• Galvanic action, or shock, is the coming together of all conditions

 What does galvanic shock feel like? (An undesirable tingling sensation.) 

One patient who may report such a feeling is someone who has teeth on opposing arches that contact each other in function. The teeth contain restorations composed of different metals (e.g., a full gold crown opposing a large amalgam).

 In the above scenario, the oral cavity acts like a battery, with saliva helping relay the electrical current.

Corrosive Properties

• Reaction of a metal that comes into contact with corrosive products
• Solubility 
  • The degree to which a substance will dissolve in a given amount of another substance

 What common drinks or foods have corrosive properties? (Soft drinks, concentrated lemonade, and other products that create a highly acidic oral environment.)

 Plaque that remains for an extended period on the margin between an amalgam and the tooth may also produce a more acidic environment locally.

 An acidic environment (lactic acid under dental plaque) drastically changes the solubility of tooth structure, such as enamel. Because enamel is the hardest substance in the body, the plaque must have been present for a considerable amount of time for a cavity to occur.

Application Properties

• Flow
  • The dental material must be pliable enough to be placed in the preparation. 
• Adhesion 
  • Differing materials must adhere to each other.
• Wetting 
  • A material must be able to flow over a surface.
•  Viscosity 
  • This property causes a material to not be able to flow easily.
• Surface characteristics
  • A liquid flows more easily on a rough surface than on a very smooth surface.
• Film thickness
  • In general, the thinner the film the stronger the adhesive junction.
• Retention
  • This is the ability to hold two things together firmly when they will not adhere to each other.
• Curing
  • Auto-cured material hardens as a result of a chemical reaction of the materials.
  • Light-cured material does not harden until it has been exposed to a curing light.  

When sealants that help prevent decay are placed on newly erupted permanent molars that are deeply fissured, the sealant material must flow well to plug up and protect areas that are not easily cleaned.

 Adhesion may be thought of as placing a piece of tape on a piece of paper.

 A consideration in wetting is whether two materials are hydrophilic (water-loving) or hydrophobic (water-hating). A hydrophilic surface would not be wet well by a hydrophobic liquid.

Restorative and Esthetic Materials

• Restorative 
  • To replace or bring something back to its natural appearance and function
• Esthetic
  • To replace or bring something back to a pleasing appearance. 

Numerous materials fulfill most of the aforementioned criteria, yet there is an ongoing search for new materials and improvements to existing materials so that they may fulfill all criteria.

Today much emphasis is placed on the esthetic aspect of restorative dentistry as patients seek to obtain, and dental professionals seek to create, a beautiful, natural-looking smile.

Direct Restorations

• Restorative materials are applied to the tooth while the material is pliable and can be carved and finish.
  • Amalgam
  • Composite resins
  • Glass ionomers
  • Intermediate restorative materials
  • Tooth-whitening products 

The first four materials are placed in the mouth and adjusted to a desirable finish. They replace tooth structures that are missing as a result of cavity removal, fracture, or a deficiency at the time of the appointment.

Tooth-whitening systems are examples of esthetic restorative dentistry.

There are very distinct methods of dispensing, preparing, placing, and finishing these materials. All are very technique-sensitive and offer a wide range of treatment options.