Radiant White

Radiant White

What is Tooth Whitening

Tooth whitening is used to correct discoloration of a tooth by removing the brown and yellow staining. The term "tooth whitening" or "tooth bleaching" can refer to a number of techniques to improve the brightness of the patient's tooth. Among them are chemical whitening, mild acid whitening, abrasive tooth brightening and the newest technique, laser tooth whitening.

How white can your teeth become?

How white your teeth can become from bleaching and whitening is a common question with a very subjective answer. Some whitening procedures claim they can whiten your teeth by up to nine shades, but that is highly unlikely. Just a change of two or three shades will make a significant difference in just about anyone's smile. There is no one standard system in the dental field to measure and determine tooth color. The most often heard about, however, is the Vita shade guide. This guide divides tooth color into four basic shade ranges:

A (reddish brown)
B (reddish yellow)
C (gray)
D (reddish gray).

In the A range there are five levels of darkness. Ranges B, C and D, each have four levels.

Not all of your teeth are the same natural color. Usually your eye teeth tend to be darker than the others, your front teeth are typically the whitest, and molars tend to be a shade between the two. The goal for everyone is to achieve their individual optimum whiteness while still looking natural. During your first consultation for tooth whitening, your dentist will go over what you personally can expect for your specific smile. How white teeth will become from a given procedure will vary from person to person. The structure of your teeth and the type of procedure implemented will affect the outcome.

What causes discoloration of a tooth?

Tooth enamel discoloration can be caused by staining, aging, or chemical damage to teeth. Some of the more common causes of tooth discoloration are medications, coffee, tea or cigarettes. People who drink significant amounts of cola soft drinks can experience similar staining. Damage to the root may also contribute to discoloration.

Aside from staining, there are other factors that can affect the color of a tooth. Genetics can play a role. Some people have naturally brighter enamel than others. Disease can also be a factor and certain medications can cause a discoloration of a tooth. If you suspect that there is an underlying medical cause for your tooth discoloration, be sure to inform your cosmetic dentist.

How long does tooth whitening last?

Tooth whitening is not a permanent procedure. Results can last for one to or more years, depending upon your personal habits. In most cases, the tooth whitening procedure is very effective and the patient is pleased with the results.

What is the Tooth Whitening (Tooth Bleaching) Procedure

Tooth bleaching is chemical process used to lighten the color of a patient's tooth. The procedure can be performed entirely in the cosmetic dentist's office in only one or two visits. Your cosmetic dentist may first try a regular abrasive cleaning of the tooth. This may be followed by a bleaching process on the stained tooth or teeth. Severely stained teeth may require the use of a special whitening gel activated by a laser. Your cosmetic dentist will carefully lighten the tooth until a near-perfect color match with your other teeth is achieved.

Types of Tooth Whitening Procedures

There are a few tooth whitening procedures available that correct discoloration of the tooth by removing the brown and yellow staining. While each work effectively, there are advantages and disadvantages to each procedure dependent upon your objectives and commitment to the processes. The type of procedures available should be discussed with your cosmetic dentist, and they will recommend the most appropriate tooth whitening procedure for you.

BriteSmile Teeth Whitening (In-Office)

Using a special light with a whitening gel, this is an in-office bleaching system. It is often followed up with an at-home bleaching kit if needed.

The translucent bleaching gel is applied to the teeth and a special activating light source is used to activate the crystals to absorb the energy from the light and penetrate the teeth enamel to increase the lightening effect on the teeth. The length of time in the cosmetic dentist's chair depends on the degree of discoloration you have, but two hours is common.

Advantage: One visit is usually all it takes for a bright smile. The tooth whitening treatment typically costs $600.

Disadvantage: The sudden change of color is likely to be noticed by those around you immediately.

Laser Bleaching (In-Office)

Using a laser with a whitening gel, this is an in-office bleaching system. The translucent bleaching gel is applied to the tooth and a laser light is used to activate the crystals to absorb the energy from the light and penetrate the tooth enamel to increase the lightening effect on the tooth. The length of time in the cosmetic dentist's chair depends on the degree of discoloration you have.

Custom Fit Tray Bleaching (In-Home)

A custom fitted tray is worn over your teeth. A small amount of the bleaching gel is placed in the tray and worn for a brief amount of time each day. This is a common technique because it's easy to use and costs less. Impressions are taken of your mouth and a thin custom made plastic tray is made which you take home and wear for about one to two hours per day. While some results may be seen in a couple days, it usually takes one to two weeks to see the full whitening of your teeth. This procedure is sometimes used in conjunction with the in-office laser bleaching if you have severe discoloration (dark grey or purple) or internal teeth staining.

Advantage: A gradual whitening of your teeth over time will be less noticeable to others that you're undergoing this procedure. The cost is relatively low.

Disadvantages: This procedure will require two to four visits to the cosmetic dentists office.

Tooth Bleaching (In-Office)

A small amount of the bleaching abrasive is applied to the tooth. This is the most common technique because it costs less, but is most effective for mildly stained teeth. This procedure is sometimes used in conjunction with the in-office laser bleaching if you have severe discoloration (dark gray or purple) or internal tooth staining.

Tooth Veneers (In-Office)

Often an alternative to crowns, veneers are very thin pieces of specially-shaped porcelain or plastic that are glued over the front of your teeth with little or no anesthesia needed. They are the cure for teeth that are severely discolored, chipped, have small holes or pits, misshapen or crooked, or for the correction of unwanted or uneven spaces. Unlike crowns, veneers won't require the dentist to remove much of the tooth itself. Veneers are created from an impression taken in your cosmetic dentist's office. Your custom veneer is then glued directly onto your tooth. Typically costing less than crowns, veneers won't stain, making veneers a very popular solution for many people seeking that perfect smile. Strong and very durable, veneers last from ten to fifteen years, and come in colors that will brighten dark teeth without the worry of them changing color.

Store-Bought Whitening Strips (In-Home)

A whitening strip is fitted over your upper and lower teeth. You'll wear them for a half hour to one hour once a day depending on the brand. This is the most common technique because it's easy to use and costs less. The strips are comfortable and have no trouble staying in place. Speaking is slightly awkward while wearing them. While some results may be seen in a couple days, it usually takes one week for the faster strips to one month for the slower systems for you to see the full whitening of your teeth. This procedure is sometimes used in conjunction with the in-office laser bleaching if you have severe discoloration (dark grey or purple) or internal teeth staining.

Advantage: You can whiten your teeth as fast or slow depending on which system you select. Some whiten in as little as seven days. Usually you only wear the strips for a half hour at a time. Some even dissolve. The cost is relatively low compared to other methods. Also a good solution for "touch-ups" when needed.

Disadvantages: This procedure may not be as powerful as other procedures which require visits to the cosmetic dentists office.

In-Mall Whitening Stores or Stands (In-Store)

This is a newer whitening option but is basically the same as the in-home kits. A custom fitted tray or strips are worn over your teeth. While some results may be seen right away, it is usually recommended that you return to the treatment center weekly to achieve the full whitening of your teeth.

Advantage:You will likely see immediate results after the first visit. If you are uncomfortable using the at-home whitening kits or strips, this may make you feel more assured.

Disadvantages:This teeth whitening option isn't much different than the at-home strips and tray systems and costs more. It also requires regular trips to the treatment center. The materials used are not necessarily up to dental professional standards.

How much does Tooth Whitening cost?

The standard fee for teeth whitening and teeth bleaching procedures is dependent on which procedure or procedures are required. Costs can vary depending upon the area of the country you live in and the type of whitening treatment you undergo. A simple cleaning of one tooth may only cost $80, whereas the laser procedure for your entire smile will cost $600 to $1000 In-home tray bleaching can cost between $50 and $100 dollars for a total teeth whitening system. Store-bought whitening strips can cost as little as $25 for a total treatment whitening system. Teeth whitening stores, stands and kiosks typically cost between $50 and $150 dollars per treatment.

Generally speaking, the price of tooth whitening increases with the number of in-office treatments required by the patient. Dental insurance does not typically cover the cost of the tooth whitening procedure.

Advantages & Disadvantages of Tooth Whitening

Pros and Cons of Tooth Whitening


People typically have a tooth whitened to improve their appearance. Teeth that are all of the same bright color are associated with beauty and a healthier lifestyle. When people have a brighter smile, they tend to smile more often and are less self-conscious.

In addition, a whiter smile tends to minimize the appearance of facial wrinkles, giving way to a more youthful and energetic appearance.

Finally, a whiter smile gives people to whom you are speaking a place to focus on and gives you a friendlier appearance.


Although tooth bleaching is very effective, there can be short term disadvantages, such as sore gums or tooth from the bleach. This disappears when bleach use is discontinued. Some individuals are more chemically sensitive. If you are one of them, inform your cosmetic dentist so that you can be tested for sensitivity to the solution.

Research indicates that tooth bleaching is completely effective in more than 78% of people. In cases of serious tooth discoloration, bleaching may not be the best choice. Veneers or crowns may be the superior choice. Bleaching is usually the first solution to try due to its lower cost.


Should teeth be white?

Teeth in adults contain a mixture of yellow, red and grey colours, and between individuals there is a wide range of tooth shades that are normal. There is no one correct colour that teeth are supposed to be. It is normal for healthy unfilled teeth to darken and yellow with advancing age. Moreover, because of natural aging process within teeth, the effects of tooth whitening can not last forever, and in several years there may be a need for a "touch up" whitening treatment.

The portrayal of tooth shade in the mass media is not realistic since tooth shades are often manipulated by digitally touching up images, to remove yellowness from teeth. In addition, some models, actors and television personalities have had porcelain veneers or porcelain crowns placed on their teeth, and the shades of these may be lighter than the range of normal shades. Trying to achieve these more extreme shades of white by bleaching may be impossible or may involve using products well in excess of the manufacturers recommendations.

Which dentist can bleach my teeth?

All dentists have the skills to assess your teeth for whitening and advise you on the chances of a good result. It largely depends on how badly your teeth are stained and what colour they are naturally as to whether the treatment will work. It is best to see your dentist and discuss your options.

There is a concern that when whitening treatments are not supervised by a dentist, people can become "bleaching junkies" and attempt to gain tooth shades which are unnaturally white. A consequence of excessive treatment and over-bleaching is that the teeth become opaque and lose their natural translucency.

What are the likely causes of tooth discolouration?

Surface stains (also known as extrinsic stains) are superficial stains located on the surface of the tooth. Common surface stains are dental plaque and calculus, tars (in tobacco), tannins (in tea or coffee), coloured foods such as soy sauce, cola drinks, and the ingredients in some dental mouth rinses when these rinses are used very often.

Internal stains (also known as intrinsic stains) are coloured molecules and pigments that have become incorporated into the internal structure of the tooth. This can occur as the tooth is developing, or after the tooth has been present in the mouth. Some fifty conditions have been associated with changes to tooth structure as it forms.

Examples of these developmental discolourations include:

  • Severe illnesses and fevers in childhood
  • Antibiotics such as tetracyclines taken in childhood
  • Uncommon genetic conditions where there is a pattern of inheritance
  • Medical conditions affecting the blood system or liver in childhood
  • Excessive levels of fluoride intake in early childhood because of swallowing toothpaste, which can result in areas of whiteness (opacity).

Conditions which can lead to internal colour changes in teeth that have already erupted in the mouth include:

  • Advancing age, which leads to greater yellow colouration of teeth
  • Corrosion products from amalgam restorations, which can give grey stains
  • Tooth decay
  • Problems with the dental pulp (nerve" ), after decay, root canal work, or damage to the tooth in an injury.

Why is it important to know the likely causes of tooth discolouration?

Reaching an accurate diagnosis of the cause of dental discolouration allows your dentist to select the most appropriate treatment options. Over-the-counter products may not be effective against some types of discolouration, and your dentist can advise you whether the problem can be managed by various professional lightening or whitening treatments, or whether more extensive cosmetic procedures (such as veneers or crowns) are needed. Some patterns of tooth shade change such as whiteness from fluoride intake can be treated using methods other than whitening to return tooth enamel to its normal colour. They can also provide advice on the type of improvement expected and the duration of treatment. Documenting the tooth shade using a dental shade guide (or taking photographs) is normally undertaken before starting a whitening treatment.

How are surface stains treated?

There are at least 3 options to consider.

  • Surface stains can be removed by a dentist or dental hygienist using a number of cleaning and polishing methods. This is the quickest method, and it can also achieve "tooth lightening"
  • The second option is to use a whitening toothpaste. These have special abrasives included in the paste which allow them to also remove some surface stain from easy-to-reach surfaces during normal toothbrushing.
  • The third option is a paint-on whitening treatment , since these have ingredients which can dissolve surface stains.

Regardless of which option you choose lifestyle factors need to be considered since surface stains can reform quickly depending on your dietary and other habits.

What are conventional whitening toothpastes and how do they work?

Conventional toothpastes marketed for whitening contain ingredients that help remove external stains by a gentle abrasive or polishing action, however they will not be able to change the natural tooth colour. Conventional whitening toothpastes use abrasive particles such as modified silica, titanium dioxide, alumina, dicalcium phosphate, sodium bicarbonate, calcium carbonate, or similar particulate substances.

Many of these products also contain phosphate compounds (such as pyrophosphates and polyphosphates) to reduce the formation of calculus (tartar) and thus keep the tooth surface clean, to give an additional cosmetic benefit, even though this is not a direct whitening action in itself. Detergents in these toothpastes also help to remove loosely attached surface stains.

There is no physical or chemical mechanism by which products based solely on abrasives can influence chromogenic (coloured) organic and inorganic materials (stains) within the enamel or dentine of teeth, since their actions are entirely of a surface nature.

What is tooth lightening?

Removal of surface stains and professional polishing of the tooth surfaces by a dentist or hygienist is a physical treatment makes them reflect more light and thus appear lighter. It does not use peroxide or other bleaching chemicals. Special polishing pastes can be used in sequence to give a high surface polish to the natural teeth and to any fillings which may also be present.

How are internal stains treated?

Internal stains are normally treated using oxygen-releasing chemicals such as peroxides (typically hydrogen peroxide, carbamide peroxide, or sodium percarbonate peroxide) or chlorites which can penetrate into the tooth and give a bleaching effect. A level of 10% carbamide peroxide in the presence of water releases 3.5%, so this numerical relationship must be taken into account if comparing products with carbamide peroxide with similar products containing hydrogen peroxide. These chemicals can be applied in a variety of ways:

  • In an advanced whitening formula toothpaste where special activators are included to enhance the action of peroxides within the toothpaste
  • As a paint-on treatment where liquid is applied to the teeth as an at-home treatment
  • As adhesive films which are applied to one tooth at a time and left in place overnight
  • In a gel applied to the teeth for several hours using a stock tray or a custom-made tray. This is often called "nightguard vital bleaching."
  • As a professional treatment in the dental surgery in which a gel is applied to the teeth and then activated using high intensity lights, lasers or ozone. This is called "power bleaching" .
  • For teeth which have already had root canal treatment, whitening materials can be applied internally within the tooth and sealed in place for a longer period of time. This is known as a "walking bleach."

When staining is inside the tooth, well below the surface, there are a number of other ways to improve the appearance of the teeth. Sometimes simply replacing old, worn out fillings that are failing at the edges can produce better looking front teeth. Alternatively, when the teeth are heavily stained, veneers or crowns may be a useful and better option. ADA dentists have access to continuing education in the latest dental techniques and they can give advice as to the best choices for you.

Are there issues with oxygen-based bleaching methods?

They do not change the colour of dental fillings. After a whitening treatment, it may be necessary to have fillings resurfaced or replaced to match the new shade of the natural tooth structure.

  • The one (partial) exception to this principle is for teeth that have porcelain veneers bonded to their front surface, the use of whitening gel applied in custom-made trays may cause a lightening of the natural tooth enamel from the inside. The colour of the veneer itself does not change, but because of its translucent nature, some improvement in the overall shade may result.
  • They elevate the level of oxygen in the outer (enamel) surface of the tooth, and because this can affect dental adhesives used for bonding, any procedures on the same teeth which require bonding must be delayed for at least 2 weeks after the end of the bleaching treatment.

Are peroxides safe to use?

Hydrogen peroxide (the active agent of whitening systems) is actually produced in the body in small amounts, and its effects have been studied for many years. When bleaching is supervised and is carried out according to the dentist's instructions, it appears to be a safe, simple procedure.

The only minor complications are rare cases of slight gum irritation and of heightened sensitivity of the teeth particularly to cold stimuli. It would also be wise to check first with your dentist to see if all your teeth will be likely to bleach evenly.

What are advanced formula whitening toothpastes and how do they work?

These use activators to maximize the effect of the peroxide which they contain. A typical product will contain hydrogen peroxide, a catalyst (such as manganese gluconate) to facilitate its breakdown, together with silica and pyrophosphates, to gain an effect on both internal and external stains. Used under normal conditions (brushed twice daily for 2 minutes each) these toothpastes can physically remove external stains, bleach external stains, and reduce internal stains.

What are Paint-on whitening treatments?

This consumer-level treatment can be applied selectively to just a single darkened tooth, or to many teeth to achieve an overall whitening action. They are not suitable for handling intense internal stains, but can give a useful effect where the discolouration is age-related and mild. They typically contain either hydrogen peroxide (6%) or carbamide peroxide, and are applied once daily for up to 14 days.

The treatment is inexpensive, easy to apply, and does not require a tray. The materials are clear and so it is not obvious to others that a bleaching treatment is being used. Most users can achieve coverage of about 85% of the area of their front teeth under normal domestic (bathroom) lighting conditions. The material contains binding agents which adhere to the tooth surface. It is important to remove the film of saliva from the teeth before applying the liquid as saliva will break down peroxides rapidly. For this reason, it is also recommended to avoid rinsing, eating, and drinking after applying the gel since these will affect the material. Any residues of the bleaching material can easily be removed by toothbrushing.

While paint-on teeth treatments should be regarded as an introduction to whitening techniques, they may also be useful to help maintain the results of professional whitening treatments since they can break down surface stains. When used as directed, paint-on treatments rarely cause irritation to the soft tissues of the mouth, and they do not damage the natural tooth surface or the surface of fillings.

What are Adhesive strips?

These use a thin flexible strip made from polyethylene or a similar plastic material to deliver a hydrogen peroxide bleaching gel to the front teeth. Once in position, the strips are pressed into place to gain the greatest contact with the tooth surface. This "trayless" delivery system provides for extended contact of peroxide (released from the undersurface of the strip) with the outer surface of the tooth. There are different shapes of strips to fit the upper and lower front teeth.

The strips typically carry 150-200 milligrams of whitening gel distributed uniformly across the strip surface, resulting in a hydrogen peroxide concentration of 6%. They are typically worn for 30 minutes twice daily for 14 days or longer. Adhesive strips are able to influence internal stains, and like paint-on products, can be applied to individual teeth.

When used as directed, adhesive strips can cause mild chemical irritation to the soft tissues of the mouth (particularly the gums), however they do not damage the natural tooth surface or the surface of fillings. Some patients will experience tooth sensitivity from the action of the peroxide within the teeth.

The potential for experiencing this side effect is related to the concentration of the peroxide in the product being used (6% versus 10%), however it will just take longer to gain the same whitening effect with a lower concentration product. Usually any sensitivity experienced will be mild, and will resolve within a few days after the treatment has ended.

What is Home tray vital bleaching?

With this treatment, a gel containing typically 5% hydrogen peroxide or 10% carbamide peroxide is applied to the teeth for several hours, or overnight, using a tray. When the applicator tray is of the stock design (one size fits all), more gel is needed and there is greater contact of gel with the gums, which can result in irritation. Stock trays are also bulky and uncomfortable. A custom-made tray is vacuum-formed onto a model of the individual mouth, and allows the dentist to determine the amount of gel which contacts the teeth. The design of the tray insures that there is close contact between the bleaching gel and the surface of the teeth, without the tray impinging on the gums and causing discomfort. The tray also prevents contact between the gel and the saliva. Custom-made trays are more comfortable to wear, and less visible to others as they can be made of a clear material. Irritation of the gums can occur because of chemical irritation from the peroxide, or from physical contact of the tray.

Both of these are more likely to occur with stock trays because of their poor fit. With custom-made trays, all of the excess gel can be removed easily by wiping it away from the edges of the tray as soon as the tray has been inserted into the mouth and pushed home into position over the teeth.

Gels supplied by dentists for home use in Home tray vital bleaching have higher levels of peroxide compounds than over-the-counter products and thus are more effective at treating internal stains. As with the adhesive strips, it is reasonably common to experience mild tooth sensitivity (particularly to cold and hit foods) from the action of the peroxide within the teeth, which resolves within several days after the treatment has stopped. Several professional products may have desensitizing agents such as potassium nitrate or fluoride included, which means that problems of tooth sensitivity will be less.

Sensitivity can be reduced by using a desensitizing product supplied by your dentist, and by reducing the number of hours that the trays are worn each day, or by using the trays every alternate day. Patients whose teeth are sensitive to thermal changes before whitening commences are likely to notice an increase in this sensitivity during the whitening treatment.

You should keep the trays and obtain new stocks of bleaching gel from your dentist to repeat the whitening periodically (usually once a year). The trays will continue to fit your mouth for many years in most cases.

Bleaching using home trays will be unlikely to alter the staining effects of certain types of antibiotic drugs (e.g. tetracycline) that may have been used during childhood. Home bleaching seems to be slightly more effective for younger rather than

What is Power bleaching?

During this treatment, which is undertaken in the dental surgery, eye protection is first put on, and then a retractor is placed to hold the cheeks and lips away from the teeth. A material such as a flowable white resin is placed to protect the gums and any exposed root surfaces from chemical irritation from the gel, and from accidental heating if a high intensity light source is to be used. This material is simply peeled away from the teeth at the end of the appointment. The whitening gel is then mixed from powder and refrigerated hydrogen peroxide solution, typically resulting in a final hydrogen peroxide concentration of 35%. The gel is then activated, and left in place for some time to allow the oxygen products to penetrate into the teeth. The gel is then washed off and the fresh gel applied. Any leakage of the whitening gel onto the gums can cause irritation, and vitamin E may be applied to neutralize the peroxide and prevent any long term damage to the gums.

The treatment sequence can be repeated several times in the one appointment. Activation of the gel can use a chemical agent (such as ozone), or high intensity light sources that give controlled heating of the gel and break down the peroxide compounds within it. This response is termed photo-thermal bleaching. One system has been developed which uses visible light energy to directly energize oxygen molecules, a process termed photo-chemical bleaching.

While the effects of power bleaching are immediate, depending on the effect achieved it might be necessary or desirable to repeat the treatment over several appointments to achieve the desired level of whitening. A home product may also be supplied as a follow-up to the treatment, or for maintenance of the result over the ensuing months. As a generalization, for simple age-related shade changes, a one hour session of power bleaching using a state-of-the-art system may produce the same tooth whitening effect as using a professional level at-home gel in custom trays over several weeks.

Because of rapid penetration and greater levels of oxygen products within the teeth, some patients will experience sensitivity in the teeth during power bleaching, particularly when the energy source (light or laser) is applied. The dentist may reduce the exposure level of the tooth to the light source to reduce any discomfort. Sensitivity after the visit may be due to dehydration of the teeth or the bodys natural defense system which neutralizes the peroxide. Sensitivity is self-limiting and will resolve within several days. The dentist may recommend a desensitizing agent or an analgesic medication depending on the nature and severity of the symptoms experienced.

Is home bleaching safe?

Yes. Hydrogen peroxide (the whitening agent) is actually produced in the body in small amounts and the effects have been studied for many years. Dentists know that the whitening process should not be abused, because teeth being bleached repeatedly past the recommended level can damage the enamel. When bleaching is carried out according to an ADA dentist's instructions, it appears to be a safe, simple procedure.

The only minor complications are rare cases of slight gum irritation and heightened cold sensitivity in the enamel. It would also be wise to check first with your regular dentist to see if all your teeth will be likely to bleach evenly. Bleaching will not alter the effects of certain types of antibiotic drug use which may occur during childhood.

What is home bleaching?

Home bleaching involves wearing a very thin, transparent plastic tray molded to your teeth, which is used to hold a bleaching agent in contact with the tooth surface. It is normally worn for approximately ten days.

The active agent in the bleach is usually carbamide peroxide. This is a chemical which quickly breaks down to urea and 7% hydrogen peroxide. It is the hydrogen peroxide which lightens the teeth.

Are bleaching toothpastes very effective?

No. The active ingredients of bleaching toothpastes are present in much lower concentrations than those in home bleaching kits, and they tend to be immediately washed off the tooth surface by saliva.

How long does the bleaching last?

The bleaching is permanent, however teeth can still become dirty and they will continue to age in a normal way with the passage of time

How effective is home bleaching in whitening the teeth?

Home bleaching does not make the teeth as white as chalk. If it did the teeth would not look natural. Usually the whitening is subtle, but a real difference can usually be noticed between, for instance, upper teeth that have been bleached and lowers that have not. Home bleaching seems to be slightly more effective for younger rather than older people.