Evaluation 2 - Paper Summary and Critique

This evaluation is on the article "The Relationship Between Dentine Hypersensitivity, Dietary Acid Intake and Erosive Tooth Wear"

To read the full article click here: https://www-sciencedirect-com.qe2a-proxy.mun.ca/science/article/pii/S0300571217302439

I chose this article because I find oral hygiene very important and interesting. This paper focused on a few known risk factors for tooth erosion and sensitivity including intake of acidic food/drink and tooth brushing habits. As many of us have seen in the news/media, acidic foods can cause erosion to our teeth because they are able to actually break down our enamel and dentin. Even foods that are considered to be healthy, such as citrus fruits, can be damaging if consumed in relatively high amounts.

Basic Erosive Wear Examination (BEWE)
https://www.dentalcare.com
/en-us/professional-education/ce-courses/ce517/
the-basic-erosive-wear-examination

Summary: This study was a secondary analysis of a previous study that involved 600 participants. 300 of them were people without any tooth erosion and the other 300 had severe erosion. To assess whether or not the subject had erosion, a Basic Erosive Wear Examination (BEWE) scoring system was utilized. This scoring system usually involves dividing the mouth into six regions and giving each region a score out of three, zero indicating no erosion and three indicating severe erosion (usually over 50% of the area). They also used self report measures to assess diet and tooth brushing habits. Results found that people with erosion spent more time eating fruit and had drinking habits that involved sipping, swishing and/or holding the drinks in their mouth compared to those with no erosion. These drinking habits all involve the participant holding beverages, which often contain acids or carbonation, in their mouth for longer periods of time than usual and therefore exposing the teeth to these beverages for longer than necessary. Other findings of those with erosion included that they were more likely to use a soft tooth brush, more likely to consume acidic drinks between meals and were more often women and younger adults. There was no significant difference in terms of tooth brushing habits (amount of time spent, how frequently people brushed etc). This is likely due to the fact that most people brush their teeth around two times per day. However, if you are consuming acidic food/beverages in between these meals, twice per day may not be sufficient. Therefore those who with and without acid erosion need not differ in terms of how many times per day they brush, because those with erosion are doing their damage in between brushing. They also attempted to determine a relationship between this dental erosion and dental hypersensitivity. Dental hypersensitivity can be defined as a painful oral condition with intense, transient pain resulting from exposed dentine, typically in response to chemical, thermal, tactile or osmotic stimuli. Hypersensitivity is found in people both with and without tooth erosion however most people with tooth erosion do experience this hypersensitivity. Therefore it seems that while erosion may lead to hypersensitivity, many people who unfortunately take great care of their teeth and do not have erosion will still experience the painful condition of hypersensitivity.

Unfortunately, this paper did not contain a definition for tooth erosion so I had to find a formal definition on my own. Dental erosion can be defined as "the physical result of a pathologic, chronic, localized, painless loss of dental hard tissue...by acid and/or chelation, without bacterial involvement" (Thomas Infeld, 1996).

Critique: I did like this paper. As a student who hasn't been exposed to a large number of research articles, I like when researchers use more common, everyday language in their literature. This paper did a great job at explaining some complex tooth pathology information in a way that someone with no dental knowledge could completely understand. I also enjoyed it because it was about a topic that everyone can relate to and learn from. Dental hygiene is incredibly important and this paper taught me a few things about taking care of my teeth that I have never considered before. It will definitely make you more conscious of how long you hold a drink in your mouth before you swallow it from now on!!!

Do the results support the authors claims? Yes, the authors expected to see a relationship between tooth brushing habits, acid intake and both dental hypersensitivity and tooth erosion. Their hypothesis was that, based on information obtained from other studies, that tooth brushing habits themselves will have no effect on erosion but that acid intake will. They did not predict the effect that the type of toothbrush (soft, medium, hard, electric) would have. However, they did mention towards the end of the article that there are limitations to the finding that people with tooth erosion were more likely to use a soft toothbrush since they may have been told by their dentists to switch to a soft toothbrush AFTER the erosion appeared (so it would be less painful during brushing). Therefore they can not attribute a soft toothbrush to causing erosion.

Are the experiments well conducted/are the methods appropriate? Yes, I think they were well conducted. They used multiple methods to determine the subjects levels of dental pathologies and behaviours (both the BEWE test and self report measures). They used a large sample size (n=600) and looked at many different factors (even including age and gender). There are a few limitations to the methods that I did notice however.

• First, it is often very difficult to rely on self report measures when conducting a study. Often times people may give false answers if they think they will be judged for their answer (known in psychology as the social desirability effect). This could have occurred in this study if, for example, people did not want to comment on the fact that they don't brush their teeth enough or that they consume a lot of unhealthy, acidic food/drinks. If this is the case, then there may have in fact been a relationship between tooth brushing habits and tooth erosion. 
• They also did not look at the effect of genetics on the teeth. Characteristics such as strong vs weak teeth, small vs large teeth and even susceptibility to cavities can be passed down to us from our parents. Therefore regardless of tooth brushing or diet, some people may be more vulnerable to developing dental hypersensitivity and/or tooth erosion than others. Of course it is not possible to determine whether or not the state of someones oral health is a direct result of genetics or lifestyle, but I think this study would have been a little stronger if they took into consideration the subjects family history of dental pathologies. 

Are the figures adequate? This is another area of the paper that I think could have been revised. The only figures present in the article were large tables. The tables were difficult to interpret and had a large amount of information. Personally, I think relationships such as these are shown better with graphs. If they had shown the data in both tables and bar graphs I think they could've made it a lot easier for their readers to quickly interpret their results. Instead, if someone is trying to observe the findings of this paper, they have to spend a longer amount of time trying to find this information in the table. It is important for researchers to try to both 1) include all important information in their figures and 2) make them easy to understand. For these reasons I think a bar graph would've been a great addition to the figures.

Does the paper lack details? Yes, in addition to the fact that they did not include a few things in their methods and in their figures, there are a few things I think should have been added to this paper. First, they provided a definition for dental hypersensitivity but not tooth erosion. For someone without knowledge on dental pathologies, these definitions are essential for complete understanding of the article. Since these definitions were missing I had to go look for outside information on the topic first before I could completely understand. I also think it would've been nice if they discussed the reasons why increased acid consumption has this effect on tooth erosion. Maybe this information was provided in the primary analysis they performed, but it would also be important to know for people reading this article as well. Again, I had to look outside of this article for this information so I could really understand why this occurs.

Additional information: Since oral health is such an important part of our everyday lives I wanted to leave you with a few facts/tips about dental hygiene:

1. In addition to not sipping, swishing, or holding your drinks in your mouth, it is also best for our teeth to use a straw while drinking (and it's best for the environment if this straw is reusable!!!). This decreases the amount of exposure the beverage has to our teeth and therefore decreases the chance of erosion (Oral Health Foundation). 
2. We usually consume at least one item that is acidic with each of our meals (fruit, some vegetables, soft drinks, juice, coffee, alcohol etc). Instead of eliminating all of these items altogether to help prevent erosion, we can finish our meal with something like milk or cheese which helps to cancel out the acid left around our teeth (Oral Health Foundation). 
3. When you do consume these acidic foods, it is best to only eat them at meal times. This decreases the overall exposure your teeth have to these foods and the other foods in your meal will help cancel out the acid as well as wash the acids out of your mouth faster (Delta Dental of California). 

References:

Dentalhealthorg. “Dental Erosion.” Oral Health Foundation, 11 July 2018, www.dentalhealth.org/dental-erosion.

O'Toole, S., Bartlett, D. The Relationship Between Dentine Hypersensitivity, Dietary, Acid Intake and Erosive Tooth Wear. Journal of Dentistry Vol 57. December 2017. 

“Stop Acid Erosion.” Gum Chewing: Helpful or Harmful? - Delta Dental, www.deltadentalins.com/oral_health/acid_wear.html.

Thomas Imfeld. Dental Erosion. Definition, Classification and Links. European Journal of Oral Sciences. 1996. 

The Teeth

As humans, we are likely not able to imagine a life without our teeth. We would be unable to consume the foods we love, speak clearly to our friends and family, or show our emotions with a simple smile. However, teeth have not been around forever. They first emerged in the bony fishes over 200 million years ago. Throughout time they have evolved to take on different forms and different roles, allowing different species to get the nutrients they need. Depending on the shape and location of an animal's teeth, we are able to determine their lifestyle - are they a carnivorous predator? Or do they simply feed on grasses and other plants? This blog will briefly discuss the structure, evolution and function of teeth, focusing primarily on the teeth of modern humans.

Structure and Composition of the Mammalian Tooth

The component tissues of teeth include an outer enamel layer and an underlying
layer of dentin. These tissues surround and protect the inner pulp cavity, which

Structure of the Human Tooth
https://biologydictionary.net/teeth/

is filled with the nerves and blood vessels that enter our teeth.

To begin, the outer layer enamel is composed almost entirely of inorganic material. It is developed from the epithelium of the mouth (Lucas, 2006). The proteins belonging to the enamel fall in one of two classes - the amelogenins or enamelins. They are found in the extracellular matrix and their role is to control the mineralization of the enamel crystals; they compose the material that will make up the enamel. These proteins are secreted by cells called ameloblasts. Interestingly, enamel is the hardest substance found in the human body and is 85-92% mineral in a permanent human tooth (Lucas, 2006). A major component of the enamel is the mineral hydroxyapatite (HA) which gives our teeth the rigidity necessary to chew tough foods. The major function of the enamel is to protect the dentin (Ferguson et al., 2006). However, as we will see later, it is susceptible to degradation. Enamel is only found on areas of the dentin that are exposed to the outside, referred to as the crown of the tooth (see the diagram). The area surrounded by the gums, referred to as the root of the tooth, has an outer layer called the cementum - which is similar in composition to enamel but less mineralized and more closely resembles bone (Ferguson et al., 2006).

Relative Compositions of Enamel and Dentin Layers of the Teeth
https://www.muhadharaty.com/lecture/3374/dr-huda/enamel-pptx

Underneath the enamel is the dentin layer. It is the barrier between the sensory and vascular supply of the pulp and the functional surface of the tooth (Ferguson et al, 2006). It too is highly mineralized, composed of roughly 45% hydroxyapatite, but not nearly as strong as the enamel. Since the dentin is in close contact with nerves and blood vessels, it differs from enamel in the sense that it is sensitive. Contrarily to enamel, it can be formed throughout life and repaired when it is worn down (Lucas, 2006). The living tissue inside of the pulp cavity is responsible for this maintenance. The organic matrix of the dentin is based on collagen fibres with scattered regions of crystals, called calcospherites (Lucas, 2006). It has a critical role in the support and function of the teeth.

Finally is the dental pulp, the living component of our teeth. It serves to provide nutrition and functional requirements to the odontoblasts (tooth forming cells) so they can continue to form dentin throughout our lifetime (Lucas, 2006). As a result of the continuous dentin formation, our pulp cavity gradually becomes more narrow as our dentin layer thickens. Interestingly, the nerves that enter and exit our teeth are not necessary for the survival or functioning of our teeth (Ferguson et al., 2006). They have a sensory role - they provide sensation to hot or cold, which of course is helpful but definitely not essential. They are also involved in altering relative amounts of blood flow into the tooth (Abd-Elmeguid et al., 2009). It is because of these nerve fibres that we can sometimes feel pain in our teeth, referred to as toothache.

Histology of the Teeth

Tooth Development and Differentiation
into Various Types
https://www.ncbi.nlm.nih.gov/books
/NBK27071/

Mammalian teeth develop from oral ectoderm and neural crest derived mesenchyme, also known as embryonic tissue (Thesleff et al., 2009). From this embryonic tissue it continues to differentiate into the various different components of the teeth. First, the oral epithelium thickens and becomes the primary dental lamina which can be seen at the base where the future tooth will lie. Dental placodes will form along the dental lamina (Thesleff et al., 2009).

The hard tissues of the teeth - the enamel and dentin - are secreted by ameloblasts and odontoblasts that differentiate at the junction between the oral epithelium and the mesenchyme.

Following the development of the crown, root formation will occur and cementoblasts (differentiated from dental follicle mesenchyme) secrete cementum.

However, once teeth have matured most of the epithelial tissue has been lost (Thesleff et al., 2009). FUN FACT!!!: some rodents have continuously growing incisors due to epithelial stem cells that are maintained in the cervical loop. Since they are always gnawing on their food, this ensures that the incisors never wear down too far!

Dried, Non-Decalcified and Unstained Tooth
Atlas of Histology

This image shows the sections of a dried, non-decalcified and unstained tooth. The cementum contains lacunae with cementocytes and their connecting canaliculi. It also shows the pulp cavity which contains connective tissue, blood vessels, fibroblasts, histiocytes and odontoblasts (Eroschenko et al., 2013). The edge of this pulp cavity is composed of the secondary dentin secreted throughout life by the odontoblasts. The base of the tooth contains external and internal enamel epithelium, the latter will grow downwards and form the epithelial root sheath.

Developing Tooth 1
Atlas of Histology

These next two images show a tooth that is still developing. They show the rows of columnar ameloblasts and sections of enamel that contains calcified enamel rods. They also show the columnar odontoblasts that will secrete the
predentin, which can then calcify to form dentin
(Eroschenko et al., 2013).

Developing Tooth 2
Atlas of Histology

Evolution of the Mammalian Tooth

   

The primary origin of teeth was once believed to be derived from the dermal denticles. However, there has been much speculation about this hypothesis in the last 15 years (Witten et al., 2014). Now there are two main but opposing hypotheses regarding the origin of the teeth - the outside-in hypothesis and the inside-out. The outside-in hypothesis claims that, as previously stated, the teeth evolved from the denticles. Contrarily, the inside-out hypothesis states that they derived from an endodermal origin (from the neural crest mesenchyme) (Witten et al., 2014). The latter hypothesis believes that these endodermal teeth evolved independently among the different classes of vertebrates. This post will focus more on the evolution of mammalian teeth from our synapsid ancestors.

Early mammals evolved from synapsid reptiles - mammal-like reptiles evolved around 300 million years ago and the basal mammals about 210 million years ago (Lucas, 2006). The mouth of the early reptiles was extremely similar to extant reptiles and includes large numbers of simple, conical teeth. 

Differences Between Reptilian and Mammalian
Dentition
 https://jurassiccoast.org/fossilfinder/focus-on-fossils/mammals/

 Their teeth had no roots and were kept in position by simple fusion to bone (Lucas, 2006). They lost teeth periodically throughout their life, and these teeth could be continuously replaced.

As they began to evolve from their synapsid ancestors, the early mammals developed fewer teeth, housed in bony sockets along the jaw bone and that only replaced once (had two generations) (Lucas, 2006). There was also the development of a clear differentiation of tooth types including incisors, canines and post-canines.

Modern humans, and many other extant mammals, have these three classes of teeth. The incisors, found at the front of the jaws, have a simple shape. In most mammals they have come to a point at the bottom, but in higher primates (humans included) they are flattened to create a working surface (Lucas, 2006). These help us grip and tear our food.

Types of Teeth
http://biology-igcse.weebly.com/human
-teeth-and-dental-decay.html

The canines are used for ripping and tearing tough foods,
such as meats. Therefore they are not found in animals that are
strictly herbivorous - cows, sheep etc.

The postcanines - referred to as the molars and premolars - are the teeth at the back of the mouth that help us grind our food into smaller components to aid in swallowing and digestion.

Human Teeth - How Our Teeth Differ and How to Care for Them

Baby Teeth https://www.mamanatural.com
/when-do-babies-start-teething/

Humans are born without any teeth at all. It isn't until we are almost a year old before our twenty baby teeth push through our gums and into our oral cavity. However, these teeth won't be in our mouth forever. These teeth, commonly referred to as our baby or milk teeth, will be shed and replaced while we are children. They begin to loosen and fall out when the lower adult teeth push on them from below.

We have 32 adult teeth and unlike most of the reptilians, once our adult teeth have formed, thats all we are going to get. Therefore proper dental hygiene is extremely important in order to keep our teeth cavity free. Proper dental care includes brushing the teeth, at least twice a day, and flossing. We can also try to avoid food and drink that can damage our enamel including citrus fruits, carbonated drinks, sour candies and more. Although our enamel is responsible for protecting the internal structures of the tooth, it is susceptible to degradation by these foods and once it's gone, it's gone forever.

The teeth are held in and surrounded by our gum tissue. Proper cleaning of the gums is also very important. If we do not keep our teeth free from plaque and bacteria our gums may become inflamed, leading to gingivitis. This can be avoided by both brushing and flossing of the teeth.

Pathology

There are many things that can go wrong when it comes to our teeth. This post describes just a few dental pathologies:

Supernumerary Teeth https://link-springer-com
.qe2a-proxy.mun.ca/content/pdf/10.1007%2F
978-3-642-36714-4.pdf

1. Hyperdontia/Supernumerary Teeth: as the name shows, this is a condition where the person grows more teeth than they are supposed to (Slootweg, 2016). These teeth may look like all the others or completely different. This condition often results in irregular eruption of the other teeth, but usually isn't a major issue unless there is a large number of extra teeth.

Concrescence https://link-springer-com.
qe2a-proxy.mun.ca/content/pdf/10.1007%
2F978-3-642-36714-4.pdf

2. Concrescence: fusion of the cementum of two or more teeth (Slootweg, 2016). The teeth appear normal in size but contain two regions of dental pulp and an excess of cementum material.  

3. Dental Caries/Cavities: a pathology that many people have likely experienced. Begins with the destruction of the enamel by microorganisms attached to the teeth. This destruction of the enamel allows enzymes to access and destroy the dentin below (Slootweg, 2016). These can be prevented with regular brushing and flossing.

Oligodontia https://link-springer-com.
qe2a-proxy.mun.ca/content/pdf/10.1007%
2F978-3-642-36714-4.pdf

4. Tooth Agenesis: congenital absence of all or many teeth, can involve the milk teeth and/or the adult. There are multiple forms including: A) anodontia - absence of all teeth, B) hypodontia - absence of 2-10 teeth or C) oligodontia where more than half the teeth are missing (Slootweg, 2016). The missing teeth are most often the molars. Tooth agenesis can be caused by a variety of factors - environmental chemicals/radiation, genetics, and can sometimes be involved with a syndrome such as Down syndrome (Slootweg, 2016).  

References

Abd-Elmeguid, A., & Yu, D. (2009). Dental Pulp Neurophysiology: Part 1. Clinical and Diagnostic Implications. Journal of the Canadian Dental Association. Retrieved October 16, 2018, from http://www.cda-adc.ca/jcda/vol-75/issue-1/55.html

Eroschenko, Victor P., and Di Fiore Mariano S. H. Di Fiores Atlas of Histology with Functional Correlations. Wolters Kluwer Health/Lippincott Williams & Wilkins, 2013.

Ferguson, M. W., Smith, M. M., & Teaford, M. F. (2006). Development, function and evolution of teeth. Cambridge: Cambridge University Press.
Witten, P., Sire, J., & Huysseune, A. (2014). Old, new and new-old concepts about the evolution of teeth. Journal of Applied Ichthyology. Retrieved October 17, 2018, from https://onlinelibrary-wiley-com.qe2a-proxy.mun.ca/doi/epdf/10.1111/jai.12532.


Lucas, P. (2006). Dental functional morphology: How teeth work. Cambridge: Cambridge University Press.

Slootweg, P. J. (2016). Dental Pathology A Practical Introduction. Berlin: Springer Berlin.

Thesleff, Irma, and Mark Tummers. “Tooth Organogenesis and Regeneration.” StemBook, 31 Jan. 2009, doi:10.3824/stembook.1.37.1.