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How Does Tooth Whitening Work?

How Does Tooth Whitening Work?

Tooth Whitening: Implications and How It Works

Tooth whitening, also referred to as ‘vital bleaching’, is a non-invasive way of lightening discoloured teeth. This procedure is often requested by patients and is considered cosmetic; therefore most insurance companies do not cover the cost. There are three primary reasons for having tooth whitening:

  1. Extrinsic stains: food, cigarettes, coffee, tea
  2. Aged teeth
  3. Intrinsic stains: mild tetracycline or fluorosis

Your teeth are made up of different layers, the first being enamel. Enamel is porous, so when you drink coffee, tea, smoke, or eat anything that has color dyes it creates a stain. When whitening is used, the chemicals get into the enamel which creates an ‘oxidation reaction’- a chemical reaction in which oxygen reacts with another atom, molecule, or compound to produce a new substance, thus making it able to break down the stain.

Treatment Options with Tooth Whitening Products

In-office whitening usually takes up to 1 ½ to 2 hours to complete. This results in immediate changes in your teeth. This type of whitening is only available in-office because of the high concentration in 38% hydrogen peroxide gels. When arriving at the office, your health care provider will place a barrier above your teeth just at the gingival to protect your gums from the product.

At-home treatment consists of custom-fitted bleaching trays. This is a very thin plastic that you place the whitening gel in and, depending on the percentage of hydrogen peroxide, these trays will stay in place from 4-10 hours a day. These are usually worn to bed unless you have time during the day to wear them.

Over-the-counter whitening strips are thin, clear strips that contain no more that 6% hydrogen peroxide. They are placed on the facial part of your teeth, and the remaining portion wraps around the inside of your teeth, making sure you adapt the strip to all facial surfaces (especially along the gum line). These usually stay on for no more than 30 minutes, twice a day. Because of the lower concentration, it will typically take a week to see results.


The main purpose of tooth whitening is to achieve a whiter smile. This could be easily achievable by doing either in office, take home, or strips. By doing an in-office procedure you will see results instantly, and will continue for the next 24 hours. Take-home is an easy application by putting the gel into your trays and going to sleep or leaving them in to do stuff around the house, though this approach could take anywhere from 30 min to 8 hours depending on the strength of hydrogen peroxide. White strips are simple and quick. Apply strips for 30 minutes 2 times a day, but because of the little percentage it could take a week to see results.


There are two major adverse effects of tooth whitening. The first is thermal hypersensitivity, 'temperature-sensitive teeth'. Breathing through your mouth, or drinking hot or cold beverages can cause sensitivity. When this happens, the best way to prevent sensitivity is to use a tooth-paste high in fluoride. The other side effect is tissue irritation. Excess gel can seep out of the trays or when in office the barrier can leak causing the hydrogen peroxide to have contact with your gums creating a stinging sensation. To prevent this from happening, when loading your custom trays you should apply very little into the wells. If some does leak out, you can wipe excess gel as soon as you notice it. Also, for those of you who have crowns, veneers, or fillings in the front teeth: these do not whiten. If you are thinking about whitening and have this issue, you can always whiten until you are happy with your shade and then get those fillings re-done so your dentist can match that shade.

Which Product Do We Use?

At Longworth Dental, our main whitening product is Opalescence. In-office and take-home products can be purchased. For take-home products, you will be required to come in for impressions of your teeth to make your custom bleaching trays. Once this is completed, you will receive a starter kit that contains 8 carpules. This should last 8 treatments. Instructions on how to take care and load your trays are included. For full-mouth whitening, it costs $300: $150 for your upper arch and $150 for the lower. ‘Touch up’ kits are also available containing 4 carpules for $25

For a more affordable approach we offer Crest White Strip Supreme. These different than over the counter strips by having 80% more hydrogen peroxide, they come with a strip for lower and upper arch in one pouch. You can purchace a box of 42 pouches (84 strips in total) for about $38.

How Does Local Anesthetic, or "Freezing" Work?

How Does Local Anesthetic, or "Freezing" Work?

What is Topical Anesthetic, or Superficial Freezing?

Anesthetic, commonly known as freezing  is “medication that produces the temporary loss of feeling or sensation”. It is used during many dental procedures for pain control. There are two main types used on a regular basis in any dental practice. The first is topical anesthetic. The purpose of topical anesthetic is to numb the oral mucosa in a specific area where the injection is going to take place. This creates a temporary numbing of the nerve endings, making the injection less painful. For this type of gel to have maximum effectiveness it should remain on the site for 3-5 minutes.

What is Local Anesthetic, or Full Freezing?

Local anesthetic is what actually numbs your teeth, cheek, lip or tongue. It is achieved by injecting a solution near a nerve, which temporarily blocks nerves from generating an impulse. A vasoconstrictor is used in anesthetic to slow down the intake of the agent and increase the duration, which is the “time from induction to complete reversal of anesthesia”. This agent prolongs the duration by decreasing blood flow and bleeding. The typical vasoconstrictor used with anesthetic is epinephrine. Since the solution is absorbed into the body, it can cause strain on your heart. Therefore, patients with heart conditions should receive freezing without a vasoconstrictor. This is why it is important to inform your dentist of any medical conditions and medications being taken.

Do Some Places Take Longer to Freeze Than Others?

When receiving local anesthetic on the mandible, it lasts longer and takes a little longer to start working because the bone is dense. Therefore, the dentist will perform a block injection. This freezes the entire area, which is approximately half of your mouth. Sometimes you will feel a shock to the lip or tongue. That just means the injection is in the appropriate spot. The second option is to utilize the maxillary arch, which uses infiltration. This area is more porous and reaches the apices and bone of your teeth more easily.

 How Long Does Freezing Last?

According to the Canadian Dental Association, the approximate duration of anesthetic is as shown:

Type of Anesthetic



Articaine 4% with epinephrine

3 hours 10 min

3 hours 50 minutes

Bupivacaine 0.5% with epinephrine

5 hours 40 min

7 hours 30 minutes

*Lidocaine 2% with epinephrine

2 hours

3 hours 10 minutes

Mepivacaine 2% with levonordefrin

2 hour 10 min

3 hours 5 minutes

Mepivacaine 3% plain

1 hour 30 min

2 hours 45 minutes

Prilocaine 4% with epinephrine

2 hours 20 min

3 hours 40 minutes

*Prilocaine 4% plain

1 hour 45 min

3 hours 10 minutes

* Used in our dental practice.

Are There Any Possible Complications?

As with everything in life, it is important to be aware of possible complications. While rare, complications such as the injection of air into a blood vessel are possible. To ensure this does not happen, your experienced dentist will alway aspirate the needle before injecting the solution. Another possible complication is paresthesia, which is freezing that lasts longer then it should. This can be temporary or permanent, but most cases are resolved within 8 weeks. Paresthesia can be caused by contaminated solution, bleeding in or around the nerve sheath or by trauma during injections.

However, the most common complications aren't nearly so severe, and are even more easily avoided. Since local anesthetic creates temporary numbing you have to make sure you do not bite your lip, cheek or tongue. If you do, you may feel swollen or have a ‘fat lip’, but this is completely normal and should pass in a few days.