TOOTHPASTES are composed of active and inactive ingredients that must be compatible with each other to be effective and acceptable.
The active ingredients have therapeutic benefits and help to improve the oral hygiene status.
The inactive ingredients are necessary to make the formulation thick, bind the components together and have a specific colour or flavour for appeal.
Abrasives
Abrasive agents are meant to clean and polish teeth by enabling the removal of soft deposits and extrinsic stains adequately, thereby achieving a smooth and glistening surface.
The abrasive capacity of a toothpaste is required to be optimum.
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If the abrasive capacity is very low, the agent is not effective in removing the soft deposits or taints.
On the contrary, if it is very high, abrasion of the teeth results.
The abrasive component in dentifrices should be enough to remove any stains, but at the same time should not damage tooth structures.
Phosphates, carbonates and silicas are the most common abrasives incorporated in dentifrices.
Phosphates: They give the teeth a clean and white appearance.
Dicalcium phosphate dihydrate and calcium pyrophosphates are commonly used.
Calcium pyrophosphates are often used in toothpastes along with tin fluoride (SnF2)
Carbonates: They clean the teeth, remove mouth odour and have bactericidal properties.
Sodium carbonates and calcium carbonates are the two forms available.
The calcium present in abrasive agents tends to react with the ionic fluorides, thereby limiting their availability in toothpaste.
Hence, in toothpastes that utilise calcium carbonate as abrasive agents, the fluoride formulation is mostly sodium monoflurophosphate (MFP) since this form of fluorides gets hydrolysed only after contact with the saliva and its enzymes.
However, sodium carbonates are compatible with sodium fluoride (NaF) containing dentifrices.
Silicas: They mechanically clean the teeth as well as thicken the dentifrices.
Hydrated silica is inert and is compatible with NaF and MFP.
Silicas are the frequently used abrasives in toothpastes.
They are regarded as more expensive compared with other abrasive materials.
Mohs in 1812 proposed a 10-point scale of mineral hardness, with 1 being the softest and 10 being the hardest.
This scale is used to compare the hardness of tooth structure and the hardness of abrasive agents.
The hardness of dentin is 2-2,5 whereas that of enamel is 4-5.
Therefore, in patients with gingival recession where the roots are exposed, dentifrices with abrasive levels of <2 is recommended to prevent tooth sensitivity.
The hardness values of sodium bicarbonate, dicalcium phosphate dihydrate (2,5) is lesser than of alumina (9,25).
Harder abrasives like alumina are highly effective in the removal of extrinsic stains.
However, there is a risk of the tooth being abraded leading to dentinal hypersensitivity.
The abrasivesness of dentifrices can be modified by factors such as particle size, shape and hardness.
Even high abrasives can be made safe by altering their particle size and shape.
The larger the particles, the more they wear away the tooth structure.
A round particle is less detrimental to the tooth, whereas irregular shape is more likely to abrade the dental surfaces.
The harder the particles, the more the tooth is abraded.
Several other variables also affect the abrasive potential of the dentifrice they are: the brushing technique, the pressure on the brush, the hardness of the bristles, the direction and the number of strokes.