Dr. Shnall's Dental Blog
The Difference Between Tooth Erosion and Tooth Decay
Most everyone knows that if you eat too much sugar you risk getting a cavity. However, cavities or tooth decay are not the only way that our teeth can deteriorate. Tooth erosion is a very common yet underappreciated cause of tooth wear.
In this series of articles I will discuss what tooth erosion is, how it is different from tooth decay and how erosion can be prevented.
First let’s discuss what a cavity is and how it starts by way of some pictures.
Figure 1 shows a typical tooth, covered by a layer of enamel. Enamel is the hardest tissue in the human body, harder than bone.
Under the enamel layer is a softer layer of tissue called dentin.
Once you get below the gum line the tooth is covered by a layer of cementum, which is similar to dentin in strength, both being softer and more porous than enamel.
Figure 2a shows that the enamel layer of our tooth is made up of rods that run from the outer surface of the tooth to the inner dentin layer. These rods in turn are made up of minerals: mainly calcium and phosphate (I only illustrated rods on one half of the tooth).
Enamel rods can be visualized like the metal rods in fig 2b.
Enamel rods run alongside each other but there are gaps between each rod.
Figure 3 shows a layer of plaque is sitting on the surface of the enamel. Plaque is actually made up of clumps of bacteria that live on the surface of our teeth.
Fig 4 shows a white coating of plaque at the gum line of the teeth.
Figure 5 shows how when we eat or drink sugary food, the bacteria ( plaque) turns this sugar into acid. The acid and bacteria then travels down crevices between the enamel rods into the undersurface of the enamel. Interestingly, the acid being produced by the bacteria does not damage the outer surface of the enamel.
In Fig 6 acid and bacteria has penetrated the inner part of the enamel layer, causing the inner enamel to break down.
The enamel is decalcifying, that is, the calcium and phosphate in the enamel is breaking down.
Fig 7 The outer enamel is still left intact. The bacteria in the plaque produce acids that travel through small microchannels in the enamel, which starts the next step: the destruction or demineralization of the inner enamel.
When a Cavity Starts Can it be Reversed?
Under the right conditions, the process described above can be reversed.
Figure 8 shows that if a tooth is exposed to phosphate, calcium or fluoride these minerals can travel down the same microchannels that the acid and bacteria travelled, into the inner surface of the enamel and remineralize or reharden the broken down enamel.
The fact that these minerals travel down microchannels is important. They don’t rebuild the surface of the tooth. They rebuild the inner tooth.
In Fig 9 The inner enamel has remineralized and the tooth surface is left intact.
Special repairative toothpastes and creams containing calcium, phosphate and fluoride can deliver these minerals into the tooth and repair the demineralized enamel.
Another key point is that in the early decay process, the enamel rods are not completely destroyed. They can serve as a scaffold to rebuild the enamel.
As well, this reversal of decay can only occur if the bacteria has not reached the inner dentin layer. If that has occurred the tooth will not remineralize and the decay will go on to infect the entire tooth unless the decay is removed and a filling is placed.
Now that you are an expert in how cavities start, let's compare this to another type of damage we see in teeth, as mentioned early, tooth erosion and we will discuss how it is different from tooth decay.
Tooth erosion is the dissolving or breakdown of tooth structure (enamel and sometimes dentin) caused by exposure of the teeth to acid either from the diet (extrinsic erosion) or from our own stomach acids (intrinsic erosion).
The acid that causes tooth erosion is not produced by the bacterial plaque on our teeth. Instead it is caused by the acid found in soft drinks/pop, many kinds of fruit juices,some sports drinks and citrus fruits.
In fact, many people who people whose teeth wear down due to acid erosion often keep their teeth very clean so it is not a plaque related issue.
Figure 10 shows the appearance of a normal tooth. It has a hard enamel outer coating and softer dentin inner layer.
Fig 11 shows this same tooth exposed to acid. If a tooth is exposed to a strong enough acid the outer enamel layer can breakdown or dissolve.
Although enamel is the hardest tissue in our body, food or drink that has a pH below 5.5 can dissolve enamel.
Almost every brand of pop/soft drink contains acid. Citrus juices are acidic as are most sports drinks. Lemons and other citrus fruits and even some brands of coffee and tea are acidic, below the critical ph of 5.5.
If our teeth are exposed to large volumes of acidic food/drink or exposed to small amounts but over long duration erosion or breakdown of the enamel and other tooth structure can occur.
Some people develop tooth erosion due to stomach acids entering the mouth in conditions such as acid reflux or in eating disorders such as bulimia. The mineral that composes our teeth will also erode and dissolve due to the strong acidity of stomach acids.
Key differences between tooth erosion and tooth decay
Above we discussed how in cavity formation, the outer enamel of the tooth is left intact while the inner enamel layer breaks down or demineralizes (see figures 6 and 7).
Fig. 12 In tooth erosion, the loss of tooth structure occurs at the surface of the tooth and works its way down into deeper areas of the tooth.
When a tooth is exposed to acid a certain amount of tooth material dissolves into the saliva.
Our saliva contains the buffering agent bicarbonate which can reduce the acidity at the tooth surface and limit erosion. The saliva also contains calcium and phosphate which if it is high enough amounts can limit the amount of calcium and phosphate that dissolves from the surface of the tooth. This is all happening on a microscopic level.
However if the amount of acid the tooth exposed to overwhelms the buffering and rebuilding ability of the saliva them loss of tooth material (erosion) will occur and once surface enamel or dentin is lost through erosion it cannot be regrown,, no matter how much you bathe the tooth in saliva, calcium, phosphate or fluoride.
This is why it is important to avoid the loss of enamel and other tooth material from erosion in the first place. This means managing diet and treating underlying conditions that lead to tooth erosion before erosion occurs.
Why can’t you rebuild loss enamel and dentin through tooth erosion while a tooth developing an early cavity can reharden or remineralize? Let me explain.
Fig 13 shows a tooth that has just been brushed. It has a clean surface. All of the plaque/bacteria has been removed.
ig 14 shows this same tooth a few seconds after it has been brushed.
After we brush our teeth, within seconds a thin film of called the dental pellicle forms on the tooth, shown as a blue thin coating in figure 15). The pellicle is thinner than the diameter of a human hair and is formed when proteins found in saliva coat the tooth.
The pellicle layer acts as a barrier to calcium, phosphate and fluoride and preevents these materials from binding or attaching to damaged enamel or dentin. So if your tooth loses enamel after drinking 2 cans of cola you cannot rebuild the lost enamel by applying a medicated calcium phosphate toothpaste. The pellicle coating prevents the tooth surface from rebuilding.
If it were not for the pellicle layer our teeth would continue to add layers of calcium phosphate from our saliva to our enamel and our teeth would become thickened.
This is also a reminder of how once our tooth surface is eroded the damaged tooth surface can not be regrown (although it can be filled or replaced with dental materials as needed).
It is the pellicle layer attracts bacteria/plaque to the surface of our teeth. In the situation where a tooth is developing a cavity, the pellicle layer does allow calcium, phosphate and fluoride to enter the dental plaque and these minerals can still heal or remineralize inner layers of demineralized enamel as we had discussed above. The pellicle does not play a disturbing factor in the repair of a tooth developing a cavity.
So it is important to know the causes of tooth erosion, namely the teeth being exposed to either dietary acids and/or stomach acids on an ongoing basis. Drinking one can of pop is not going to cause permanent loss of enamel, however if you sip on a can of cola each day for an hour or two while at work or while watching tv you almost assuredly will lose a noticeable amount of tooth enamel and or dentin, which will have consequences.
In my next article I will discuss other types of tooth wear related to erosion and also how to prevent and manage tooth erosion.