Is diet soda as bad for your teeth as regular soda or methamphetamine?

Question

I've heard of many claims about soda water itself containing carbonic acid (as claimed by a teacher I had in high school) and having a generally high pH that's enough to destroy one's teeth.

This article from Huffington Post cites a study that concludes that consumption of diet soda can have devastating effects on teeth similar to that of a meth user. However, this study seems to have only included a group of 3 subjects, only one of which drank diet soda. It also did nothing to prove that the condition of the subject's teeth were caused by the diet soda he drank.

That's the one study that I see referenced in any articles that make claims about diet soda and tooth decay. The full study is here. I am skeptical about the 3rd case report, because if diet soda was indeed causing this person's teeth to decay to such a degree, the person clearly wasn't competent enough to see the correlation and cease consumption. The person may not have been brushing & flossing, but the study says nothing about her dental hygiene.

Most of the sites and articles that make claims about the acidity of soda don't provide any information on the pH of soda or other beverages. This one does, however. It puts various beverages on a spectrum between water and battery acid. As for diet sodas, the lowest (Diet Pepsi) has a pH of 3.05 in contrast to that of battery acid (1.0) and water (7.0). Their source for this data is the Minnesota Dental Association.

I'm not sure I can accept this proposed spectrum since battery acid, which is sulfuric acid, is highly-caustic whereas carbonic acid is relatively weak. So unless my understanding of the science is flawed, a solution of carbonic acid with a pH of 3.05 =/= a solution of sulfuric acid with a pH of 3.05.

I am mostly skeptical because I often have diet sodas and have been drinking them for over a decade; my teeth are in great condition. Granted, I do brush and floss frequently, and the rest of my diet is very low on sugar and carbohydrates that would feed bacteria like streptococcus mutans, which are the biggest players in tooth decay.

Answer 1

In this answer, "diet soda" refers to any sugar-free version of the drinks known as soda. "In many parts of the U.S., soda is a sweet, fizzy drink (Vocabulary.com)."

Is diet soda as bad for your teeth as regular soda?

According to some experiemental studies, diet soda can be erosive to teeth, but seems to be less erosive than regular soda.

An in vitro study (on extracted teeth): Cariogenicity induced by commercial carbonated beverages in an experimental biofilm-caries model (European Journal of Dentistry, 2018):

Commercial sugary carbonated beverages seem to be as cariogenic as sucrose. The sugar-free versions may be less cariogenic than their sucrose-containing counterpart, albeit preserving a dangerous cariogenic and erosive potential.

Pop-Cola Acids and Tooth Erosion: An In Vitro, In Vivo, Electron-Microscopic, and Clinical Report (International Journal of Dentistry):

Pop-Cola drinks tested are acid and may decalcify tooth material. This study provides evidence that all these six common colas (Pepsi Cola, Diet Pepsi Cola, Coca Cola, Diet Coke, Selection Cola and Diet Selection Cola), leech calcium out of teeth, after rinsing with pop-colas.

Besides pH and buffering, calcium, phosphate, and to a lesser extent fluoride are important when considering erosive attack from beverages.

Is diet soda as bad for your teeth as methamphetamine?

The article mentioned in the question (General Dentistry, 2012) presents 3 individuals with generalized caries: 1) a 29-year-old meth user, 2) an 51-year-old cocaine user and 3) a 30+ year-old woman who was drinking 2 liters of diet soda/day for past 3-5 years.

The article shows how diet soda can cause caries of the same severity as meth or coke. BUT, we can't compare the doses of diet soda, meth and coke. Drinking a lot of diet soda could cause even worse caries than using little meth.

Also, they may not be just diet soda and meth themselves, but also other common contributing factors in soda and meth users that can be harmful. For example, the woman who was drinking diet soda had poor oral hygiene, no dental care for 20+ years, mouth breathing (which stimulates the growth of cariogenic bacteria S. mutans) and frequently snacked potato chips. Other eventual factors we do not know could include poor diet and family history of caries.

Long-term methamphetamine use can cause "meth mouth" with severe caries (American Dental Association) and destruction of the bone - osteonecrosis (Dentistry Journal), which is more severe than "simple" caries.

So, you can't say that diet soda is as harmful for teeth as meth because you don't know how to compare the doses. And meth can destruct the gingiva and bone, but diet soda not likely.

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Diet soda can be erosive to teeth because it is acidic.

According to American Dental Association, the pH of beverages <3 is "extremely" erosive, pH 3-4 is "erosive" and pH >4 is "minimally" erosive to teeth.

Diet sodas do not have a lower or higher pH than regular sodas; it depends on the brand.

pH of regular sodas:

• Coca Cola Classic: 2.37
• Pepsi: 2.39
• Schweppes Orange: 2.54
• Mountain Dew: 3.22
• 7Up: 3.24
• Sprite: 3.24

pH of diet sodas:

• Coca Cola Zero: 2.96
• Pepsi Diet: 3.02
• Coca Cola Diet: 3.10
• Mountain Dew Diet: 3.18
• Dr Pepper Diet: 3.20
• Hansen’s Cane Soda Black Cherry Diet 3.47

Tooth enamel can dissolve when the pH at the enamel surface falls below 5.5-6.5 (critical pH), depending on a person.

Answer 2

The only difference between diet and regular drinks is whether they contain sugar. The sugar itself doesn't cause tooth decay. That is caused by bacteria breeding in the sugary environment and producing acid that dissolves tooth enamel:

Tooth decay is the destruction of your tooth enamel, the hard, outer layer of your teeth. It can be a problem for children, teens and adults. Plaque, a sticky film of bacteria, constantly forms on your teeth. When you eat or drink foods containing sugars, the bacteria in plaque produce acids that attack tooth enamel. The stickiness of the plaque keeps these acids in contact with your teeth and over time the enamel can break down. This is when cavities can form. — Tooth Decay - American Dental Association

If you clean your teeth well, at least twice a day, the bacteria don't have a chance to build up to damaging levels.

But many soft drinks contain phosphoric, citric, or other acids, as added ingredients. The acid provides an extra tangy taste, but it also begins to dissolve the calcium from your teeth as soon as you drink it. An occasional drink won't hurt (it's not as strong as the vinegar most of us occasionally add to our food), but frequent use can add up.

Pop-Cola Acids and Tooth Erosion: An In Vitro, In Vivo, Electron-Microscopic, and Clinical Report concludes:

Pop-Cola acid activity is below the critical pH 5.5 for tooth dissolution, with high buffering capacities countering neutralization effects of saliva; (ii) calcium is leeched out of teeth after rinsing with pop colas; (iii) SEM evidence explains why chronic exposure to acid pop colas causes dental frangibles; (iv) a clinical case of pop-cola erosion confirms this.

Similarly, Influence of Various Acidic Beverages on Tooth Erosion. Evaluation by a New Method concludes:

… erosivity of common non-alcoholic drinks varies widely. For example, Sprite, apple juice, and orange juice are about five times more erosive than Coca-Cola light. The findings from the present study should be taken into account in choosing a diet that provides satisfactory nutrition while minimizing tooth erosion.

It is especially bad if one drinks an acidic beverage just before going to sleep at night, leaving the acid to work on the teeth for hours. But most people have enough sense not to do that without cleaning their mouths afterwards.

But what is really evil, is that many people will freely drink diet cola before going to bed because they think that its lack of sugar makes it safe to do so.