Assignment #2 – Paper Review

Effects of tooth whitening and orange juice on surface properties of dental enamel

By:  Yan-Fang Ren, Azadeh Amin, Hans Malmstrom

Link to paper

Introduction:

In this study they wanted to determine how 6% hydrogen peroxide (tooth whitening product) effected the surface of enamel in comparison to orange juice. Whitening products contain an oxidizing agents such as hydrogen peroxide which is thought to diffuse into the enamel and dentin, oxidizing organic and inorganic colored compounds resulting in change in tooth color (Ren et al., 2009).  The concern though is that it might causes chemical, structural and mechanical changes in the enamel surface. Orange juice is a highly acidic drink (pH less than 5.5) that initiates enamel demineralization. Microhardness testing and surface 3D topography evaluations are used to determine and compare the effects on the enamel.

Experimental procedure:

Enamel discs were prepared using a slow speed diamond saw from freshly extracted human third molars, which had been sterilized. Enamel surfaces were ground and polished to obtain a smooth flat surface. A total of 40 enamel discs were used (15 for whitening treatment, 15 for organic juice treatment and 10 for normal saline controls) and they were stored in clarified human whole saliva at room temperature until use. Prior to the experimental treatment of enamel discs surface microhardness testing (Knoop indenter) and surface 3D topography evaluations (3D focus variation scanning microscopy) were completed to obtain a baseline.

The eBright Tooth Whitening Accelerator Home Edition LED activated tooth whitening product was used which contained 6% hydrogen peroxide at a pH of 5.5. In well culture plates enamel discs were treated with whitening gel and submitted to LED light irradiation for 20minutes followed by washing with distilled water for 30 seconds. This was repeated 4 more times to stimulate 5 days of treatment. Between treatment cycles enamel discs were store in fresh human whole saliva. For the orange juice challenge the enamel discs were placed in the well culture plates containing 1.0 ml of orange juice at pH of 3.8 (Minute Maid). Samples were placed in a rocking incubator for 20 minutes to simulate sipping a drink followed by rinsing with distilled water for 30 seconds. Like the whitening products this was repeated 4 more times and stored in saliva between treatments. The control enamel discs underwent the same treatment as the orange juice except normal saline was used.

Microhardness and surface topography of the enamel discs were evaluated again like before (baseline evaluation). Changes in surface microhardness and surface topography were compared before and after treatment using statistical analyses (StatView 5.0.1).

Results:

Comparing the surface microhardness results only the treatment was orange juice showed a significant difference (p<0.0001) in microhardness following treatment. The hardness for enamel discs treated with orange juice decreased 84% from 287.3 to 45.3. For enamel discs treated with the whitening product hardness decreased 5.6% from 279.4 to 260.7 and the saline controls decreased 3.1% from 275.3 to 266.8.  (Table 1). Although there was no significant change in the hardness of the enamel for the whitening products and control groups they noted that there was a significant variation in the change in hardness for the individual specimens.  4 of the 15 whitening treatment and 2 of the 10 control group had a change in microhardness greater than 10%. 

For the 3D topography evaluations they looked at  surface area roughness (Sa),  surface maximum peak to valley distance (Sz) and developed surface area ratio (Sdr). They found that the enamel surfaces after the orange juice treatment were visibly rougher than those of the whitening gel and normal saline and had more well developed peaks and valleys on surface (Ren et al., 2009).  Changes in the three surface roughness and topographical measures  (Sa, Sz, and Sdr) were only significant for the treatment with orange juice. An interesting note is the Sz and Sdr measures slightly decreased for the whitening and control group in comparison with the orange juice, which increased (Table 3 and 4).

The results show that the effects of the 6% hydrogen peroxide whitening product on the enamel surfaces were not significant in comparison to orange juice. The softer and rougher enamel makes teeth more susceptible to the development of dental caries and non-carious lesions such as abrasion (mechanical forces from daily activities such as toothbrushing) and attrition (tooth grinding) (Ren et al., 2009). 

Critique:

I thought this was an interesting paper that was easy to follow and understand. I knew that acidic drinks such as orange juice were hard on the enamel of teeth but I had no idea that it could cause that much of a harmful effect. There have been many other papers published that look at the effect of tooth whitening products on the enamel surface, but without having something to compare your results to it is hard to get a clear picture on how harmful it really is. I thought it was a great idea to compare it to the effects to that of orange juice to give us a better perspective on the relative impact. The methods section was concise but also detailed enough that if I wanted to repeat their experiment I could. The figures in the results were easy to understand and clearly showed the different effects these products had on the enamel.

The discussion was informative but they didn’t directly suggest explanations for the findings. They referenced many papers to help explain the results but they never clearly stated why the orange juice was more harmful than the whitening product. I just had to assume it was due to differences in pH. They also didn't mention any ideas on why the mean maximum peak to valley distance (Sz) and developed surface area ratio (Sdr) decreased for the whitening and control groups but increased for the orange juice group. Since the microhardness decreased for all three I would figure both of those measures should have increased for all of the groups as well. The section on the effect of fluoride treatment was interesting but I thought it was out of place as they did not use any fluoride treatment within their experiment. It was odd that they were using their results from this paper to support  why fluoride treatment is more effective following whitening treatment than from soft drink/ acid erosion. Another complaint I have is that in the introduction they talk about how consumption of soft drinks has increased and that many studies has shown that these can cause surface enamel erosions, but the effect of whitening treatment relative to that of soft drinks on dental hard tissue is not known (Ren et al, 2009). I’m not sure why they would just switch to compare the whitening treatment to orange juice. Results were definitely interesting with the orange juice but I was a bit confused that they mentioned the soft drinks so extensively in the introduction. One last critical observation is that their references were not organized in alphabetical order. For a published paper I would not expect to see these types of errors. Overall I thought this was a good study with interesting results but the paper could have been written better. To end on a positive note, I liked that they mentioned the consequences of this decrease in surface microhardness and surface topography (roughness). It was a good way to clue up the paper.

Future research:

I noted from reading the discussion that saliva could contribute to the protection of the enamel surface through its remineralization effect so it would be interesting to see how it differs from distilled water. In a future study you could use distilled water instead of saliva as the storing medium and compare the change in microhardness and roughness to give an idea of how much of a protective effect saliva has. Based on what I have read I would predict that there would be a greater change in the surface microhardness and surface topography. Also since they noted that the mean surface microhardness change varied significantly within the whitening treated and control groups I would suggest using a larger sample size to ensure a more accurate result. Variation is to be expected since these were extracted teeth and they should not all be identical in strength and composition (variation exists between individuals). The larger sample would help control for these variations. One last suggestion I would have for a future experiment is to see the effects of fluoride treatment follow whitening and orange juice treatment. In the discussion the authors touched on the effects of fluoride treatment through referencing other papers. They mention that fluoride might be more effective following whitening treatment than following the orange juice erosion. It would be interesting to see results to go along with these statements.  

Ren, Y., Amin, A., Malmstrom, H. (2009) Effects of tooth whitening and orange juice on surface properties of dental enamel. Journal of Dentistry. 37:424-431.

Teeth

Assignment #1

My Favorite Tissue: Teeth

Figure 1: Teeth

Introduction

Figure 2: Diagram showing the dentition

 of the permanent teeth arches

During childhood humans have 20 deciduous teeth (also called primary of milk teeth). The first tooth erupts six to seven months after birth and are complete by 2 years of age. They are shed between 6 and 12 years of age as they are replaced by permanent teeth.

Adult humans normally have 32 permanent teeth arranged in two bilaterally symmetric arches in the maxillary and mandibular bones (Mescher, 2009).  The mouth is divided up into 4 quadrants with each containing 8 teeth (2 incisors, 1 canine, two premolars and 3 permanent molars)

Function of teeth

Teeth play a role in the digestive system within the body. Teeth are designed for chewing which breaks down foods into smaller pieces to help allow for better absorption of nutrients. The dentition of teeth vary depending on their specific function. The incisors have been modified for biting (thin and long) and the molars (thick and relatively flat with grooves) are for grinding food.

Dental Anatomy

Figure 3: Internal components of the tooth(4).

The main components of the tooth are:

- Enamel

- Dentin

- Pulp cavity

- Cementum

- Periodontal membrane (ligaments)

- Gingiva

Figure 4: Decalcified section of enamel 

showing rods (1).

Enamel

-       The hardest component of the human body (98% hydroxyapatite, mainly calcium and phosphate in the form of apatite crystals)

-       Covers only the crown of the tooth

-       Composed of rods or prisms, rod sheaths

-       Produced by ameloblasts

Figure 5: Histological section showing production
of dentin and layers of growth (1).

Dentin

- 30% organic matter and water and 70% inorganic material

- Organic substances consist of collagenous fibrils (arranged in random network)  and ground substance of mucopolysaccharides

- Inorganic component consists of hydroxyapatite crystals that a plate shaped and much smaller than those in enamel

- Produced by odontoblasts

                                                                            

Pulp cavity

-        - Pulp of the tooth is derived from mesenchyme of embryonic dental papilla and it fills the pulp cavity (pulp chamber and root canals)

     - A layer of epithelial-like, columnar cells called odontoblasts (derived from mesenchyme) underlie dentin and are responsible for dentin formation

-       - Contains sensory nerves that respond to stimuli such as heat, cold and pressure

-       - Lymphocytes and macrophages and leukocytes are present to aid in repair of the pulp following irritation

Figure 6: Histological section showing 

periodontal ligament, cementum, 

dentin and alveolar bone (1).

Cementum

-      Covers dentin of the root of the tooth

-      Attaches the tooth to the periodontal membrane

-      Similar histologically to bone with coarse budles of collagen fibrils in a calcified matrix

Periodontal membrane

-     Modified periosteum of alveolar bone and is a dense fibrous connective tissue.

-     Supports the gingiva at the neck of the tooth

-     Bundles of collagenous fibers connect alveolar bone and cementum

-    Functions as the suspensory ligament of the tooth

Gingiva (Gums)

- Oral mucous membrane that surrounds the tooth and connects to periosteum of alveolar bone

- Connective tissue underlying the stratified squamous epithelium consists of bundles of collagenous fibers and a rich vascular network of capillaries which is responsible for the pink color of the gums

- Is initially attached to the enamel but gradually recedes as it exposes the crown of the tooth

Tooth Bud 

Figure 7. Histological slide of tooth bud. 

A is the enamel organ, 

B is the dental papilla 

and C is the dental sac. 

From the lining of the oral cavity tooth buds are formed and develop into a tooth.  Tooth bud consists of three components:

- Enamel organ – derived from oral ectoderm and produces tooth enamel

- Dental papilla – derived from mesenchyme and produces the tooth pulp and dentin

- Dental sac – derived from mesenchyme and produces cementum and periodontal ligament

Stages of tooth development 

(Shown for a lower central incisor)

Figure 8: Tooth development stages of a lower central incisor. (3)

Figure 8A: Tooth development: 

Dental Lamina formation (3)

Tooth development begins during the sixth week of embryonic life (Bhaskar, 1976). The oral ectoderm give rise to the oral epithelium followed by the formation of dental lamina by the proliferation of cells. This is a band of epithelium that outlines the future dental arches along the jaws.

Figure 8B: Tooth development:

Cap stage of deciduous tooth(3)

Round swellings arise from the dental lamina (at 10 different points) to form the enamel organ and tooth bud. Unequal growth and differentiation of the bud leads to the formation of an invagination on the deep surface of bud. (7-8 weeks intrauterine)

  

Figure 8C: Tooth development: 

Early bell stage of deciduous tooth (3)

This bell shaped epithelial bud is called the enamel organ, which sits ontop of the dental papilla which is embedded in the dental sac (a layer of connective tissue).  Extension of the dental lamina will lead to the formation of the permant tooth.  (10 weeks intrauterine)

Figure 9: Section showing enamel and dentin producing cells within the enamel organ and dental papilla (2).

Cells within the enamel organ separate by intercellular spaces which are filled with mucoid fluid rich albumin (this region is refered to as the stellate reticulum). (Bhaskar, 1976). Peripheral epithelial cells form a layer on either side of the stellate reticulum. The outer enamel epithelium has smaller cells and the inner enamel epithelium has taller columnar cells. These are ameloblasts which are responsible for enamel formation. The peripheral cells of the dental papilla (next to the inner enamel epithelium) differentiate into odontoblasts which are responsible for dentin formation.  Dentin formation precedes enamel formation.

Figure 8D: Tooth development: 

Advanced bell stage of deciduous tooth (3)

Cap of dentin has formed at the tip of the dental papilla and tooth bud as disconnected from the dental lamina by mesenchymal invasion.  (16 weeks intrauterine)

  Figure 8E: Tooth development: 

Deciduous tooth crown complete 

and permanent tooth development starting (3)

Crown of deciduous tooth is complete with enamel formation and the permanent tooth is in the bell stage. (Birth)

Root development occurs shortly before tooth eruption, progressing as the crown of the tooth emerges through the gingiva (Bhaskar, 1976).. The enamel organ forms the Hertwig’s epithelial root sheath, molding the shape of the roots and initiating dentin formation. Note that roots do not contain an enamel layer.

Figure 8F: Tooth development:
Deciduous tooht erupting and
permanent tooth developing

The deciduous tooth has started to erupt and the root is now formed. The crown of the permanent tooth is almost completely developed. (Six months postnatal). The collagen fibers and fibroblasts within the periodontal ligament are responsible for the eruption of the tooth (Bhaskar, 1976).

  Figure 8G: Tooth development: 

Resorption of deciduous tooth roots (3) 

As the permanent tooth starts eruption the resorption of the roots of the deciduous tooth occurs. When deciduous tooth is shed it consists only of crown (unless tooth is pulled before permanent tooth has fully erupted).  (6-7 years)

Odontoclasts are responsible for the resorption of the roots. (Bhaskar, 1976). They are most commonly found on the surface of the roots inrelation to the the assending permanent tooth. Demineralization of the dentin in the roots occurs. The pressure from the permanent teeth also aids in this process. 

                                      

Figure 8H: Tooth development: 

Permanent tooth erupting (3)

Permanent tooth is now erupting (7-8 years)

Figure 8I: Tooth development: 

Permanent tooth attrition (3)

Permanent tooth in attrition (reduction in size). Enamel and dentin layers are thinner. You can clearly see recession in the neck and roots of the tooth as well as secondary dentin forming. Lines around the root of the tooth are the periodontal ligament. (After 20 years).

Figure 9: Development of the Human Dentition
 (Shows the changes in dentition over time and the development stages for the different types of teeth ie molar, incisor)(5)

Dental Caries (Cavities)

Dental caries are one of the most prevalent chronic diseases of people worldwide and individuals are susceptible to it through out their lifetime (Selwitz et al., 2007). They are defined as localized destruction of hard tissue resulting from the demineralization of  tooth tissue due to acidic byproducts from the bacterial fermentation of dietary carbohydrates.  This process is initiated within the bacterial biofilms (dental plaque) that covers the surfaces of the teeth. Endogenous bacteria such as Streptococcus mutans and Lactobacillus spp present within biofilm metabolize fermentable sugars producing weak organic acids (Selwitz et al., 2007). This acid causes the pH to drop and when it reaches a critical level demineralization of the tooth tissues occurs. Cavitation occurs with the diffusion of calcium, phosphate and carbonate out of the tooth. This process however can be reversed in its early stage with the uptake of calcium, phosphate and fluoride. Fluoride acts as a catalyst for the diffusion of calcium and phosphate back into the tooth allowing for remineralization. First signs of demineralization are the presence of white spot lesions. 

Figure 10: White spots following orthodontic treatment 

In this figure this individual failed to thoroughly clean their teeth while undergoing orthodontic treatment.  When braces were removed permanent white rings are visible on each tooth surrounding where the brackets would have been. This is due to decalcification.

As bacteria penetrate further into the tooth tissue becomes softer and cavities (holes) start to form.

Figure 11: Individual with extensive tooth decay

In this figure this individual has extensive tooth decay. The holes are darker then the rest of the tooth since the enamel layer as been eaten away by the acids and the dentin layer is now visible (which is characteristically darker in color).

In both the crown and root surfaces of the tooth of primary and permanent teeth decay can be found. Along the root surface cavities form faster as the hard enamel surface is not present. Dentin is much softer so erosion occurs much quicker.

Some factors that affect the development of dental caries:

- The shape and positioning of the teeth can make cleaning more difficult leading to more plaque build up. Pits and cracks in the teeth make it easier for bacteria to infiltrate.

- Saliva provides a rinsing action for the teeth and neutralizes the acids produced by the bacteria helping slow down this process. Individuals with reduced saliva production results from head and neck irradiation or medications are more prone to rapid progressive caries.

- Foods containing fermentable carbohydrates such as sweets, pasta, rice, potato chips, fruits which increases acid formation in plaque.

- Baby bottle caries or nursing caries are caused by prolonged exposure to drinks containing sugars. When infants are put to sleep with a bottle of formula or juice that can be a particular problem as saliva flow is greatly reduced during sleep allowing for sugars to sit on teeth for extended periods of time allowing for tooth decay to develop.

Treatment:

 Dental caries significantly weaken the tooth, to prolong the life of the tooth restoration is usually completed. This involves removing all of the soft decalcified tissue to prevent further decay and filling in with either a composite of amalgam material. This however is not a permanent fix as overtime these materials break down and chip due to forces from mastication. A more permanent procedure would be cover the crown of the tooth with a cap. This protects and strengthens the tooth. Crowns can be made from a variety of different materials such as gold, porcelain or other metals. Porcelain fused metal crowns are popular as the porcelain gives the tooth a natural appearance while the metal provides extra support (important for molars).

-        

Some ways to prevent dental caries:

 - Many dentists recommend sealing the occlusal (top) surface with a resin based sealant (called pit and fissure sealants). The pits and groves in the top of the teeth are highly susceptible to the formation of cavities as food easily packs into these areas. The resin fills in these grooves preventing caries from occurring.

- Regularly brushing and flossing teeth

Brush and Floss

- Regular dental cleanings and checkups helps keep tartar (next stage after plaque) build up under control as well as catching dental caries in their early stages before there is extensive damage to the teeth.  

- Fluoride will strengthen the enamel making it more resistant to decay. Fluoride can be found in some city water systems (although many are choosing to remove fluoride), many tooth pastes and mouth rinses. Topical fluoride treatments are often given to children in office (more concentrated than toothpastes and mouth rinses). Although it is a bit of a controversial topic fluoride drops can be given to children between the ages of 6 months and 3 years to strengthen the enamel during the development of the permanent teeth!

Fluoride trays

Fluoride drops

Fun Fact:

Eating cheese can prevent tooth decay by increasing saliva flow and neutralizing acidity!

Now for a fun comic to finish it off!

References:

 1) Bhaskar, S.N. (1976) Orban’s Oral Histology and embryology: Saint Louis: The C.V Mosby Company.

2) Di Fiore, M.S. (1974) Atlas of Human Histology.Philadelphia: Lea & Febiger.

3) Leeson, C.R., Leeson, T.S. (1976) Histology. Philadelphia: W.B. Saunders Company.

4 )Mescher, A. (2009) Junqueira’s Basic Histology Text & Atlas, 12ed. Unites States of America. McGraw-Hill Companies.

5) Schour I., Massler M. 1944. Development of the Human Dentition. Chicago: American Dental Assoc. 350 p.

6) Selwitz, R.H., Ismail, A,I., Pitts, N.B. (2007) Dental caries. Lancet. 369:51-59