How Whitening Chemistry Works
Teeth whitening lightens tooth colour with a peroxide-based gel, either hydrogen peroxide or carbamide peroxide, which breaks down the pigmented compounds staining the enamel and the dentine underneath it. The peroxide releases oxygen molecules that react with the stain molecules, breaking them into smaller, less pigmented fragments, which is what produces a lighter shade over the course of treatment. This is the same underlying chemistry whether the gel is applied in a dental chair or at home in a custom tray; what changes between methods is the concentration of peroxide used and who controls the application.
Whitening only changes the colour of natural tooth structure. It has no effect on the colour of an existing crown, veneer or filling, since those materials are not affected by the same chemical process, so a tooth that has been restored will not lighten to match its neighbours during a whitening course.
Products use either hydrogen peroxide directly or carbamide peroxide, which breaks down into hydrogen peroxide once it is in contact with saliva and releases its active ingredient more slowly. Both work through the same underlying chemistry described above; the difference is release speed and typical concentration, which is why an in-clinic gel and a take-home tray gel are not simply the same product at different prices.
The chemistry also explains why whitening reaches a natural limit rather than continuing indefinitely: once the pigmented compounds within the visible layers of the tooth have been broken down, further peroxide exposure does not keep lightening the tooth further in the same way. This is one reason a dentist records a starting shade against a shade guide before treatment, since it gives an objective marker to compare against rather than relying on how the teeth look from memory once the course is finished.
In-Clinic vs Take-Home vs Over-the-Counter
The three common ways to whiten teeth in Tasmania are in-clinic bleaching, a dentist-supplied take-home kit, and an over-the-counter product bought without a dental visit, and they differ mainly in peroxide concentration and who supervises the process.
| Method | Where it happens | Who applies it | ADA item |
|---|---|---|---|
| In-clinic (in-chair) | Dental practice | Dentist, with the gums protected first | 118 |
| Take-home kit | At home, in a custom tray from the dentist | Patient, following the dentist's instructions | 119 |
| Over-the-counter strips or kits | At home | Patient, unsupervised | Not a dental item; not dentist-provided |
In-clinic bleaching keeps the gel isolated from the gums during application, since peroxide contact temporarily irritates gum tissue, which is one reason a dentist applies it rather than the patient. A take-home kit still starts with a dental visit, where the dentist checks the teeth and gums first and provides a custom tray designed to hold the gel against the teeth rather than the gums. An over-the-counter product skips that check entirely, which matters most for anyone with untreated decay, cracked teeth or gum disease, covered further under sensitivity, risks and eligibility below. For a closer look at how the two supervised methods compare, see home vs professional whitening.
A custom tray matters more than it might seem, because an ill-fitting tray, whether a generic over-the-counter tray or a poorly made one, lets gel spread onto the gums rather than staying against the tooth surface, which is exactly the contact that causes gum irritation. A tray made from an impression of the individual patient's teeth avoids that by fitting the tooth contours closely, which is part of what the take-home kit's dental visit is paying for beyond just the gel itself.
Cost Compared
There is no official fee for teeth whitening in Australia, so no single statewide price applies to any of the three methods; whitening is elective and cosmetic, and every practice sets its own fee. What can be stated is the item structure: in-clinic whitening is itemised under ADA item 118 (per tooth), and a take-home kit under item 119.
| Method | ADA item | What drives the fee |
|---|---|---|
| In-clinic | 118 (per tooth) | Number of teeth treated, chair time, the gel concentration used |
| Take-home kit | 119 | The custom tray fitting appointment, plus the gel supplied |
| Over-the-counter | Not applicable | Retail price of the product; no dental appointment involved |
Ask a practice for a written quote showing the ADA item number before starting, and treat any headline "whitening price" advertised without that detail as incomplete. There is no official private fee schedule in Australia to compare it against (only a clinic's own published, dated price counts as a real figure).
An over-the-counter product, such as a whitening strip or a charcoal-based toothpaste, is usually the cheapest option on paper, but the comparison stops at price. The site's own evidence base does not support a claim that charcoal toothpaste whitens teeth as effectively as a peroxide-based product, so no such equivalence is stated here, and over-the-counter products are not supervised by a dentist in the way item 118 or 119 treatment is.
Sensitivity, Risks and Eligibility
Tooth sensitivity is the most commonly reported side effect of whitening, and it is common, not rare. A triple-blind randomised trial across two centres, using 35% hydrogen peroxide in-office, reported an approximately 96% overall absolute risk of tooth sensitivity among 105 participants (Coppla et al., 2018, Operative Dentistry). A separate trial using a lower peroxide concentration reported a lower rate of around 60% among 40 participants (de Paula et al., 2015, Journal of Dentistry), which suggests sensitivity risk scales with concentration, though the two studies used different products and are not directly interchangeable.
On enamel and dentine, the evidence does not support printing a specific percentage of damage or mineral loss. A review found that hydrogen or carbamide peroxide bleaching agents have no clinically significant influence on enamel or dentine mineral loss from erosion or abrasion (Demarco et al., 2011, Clinical, Cosmetic and Investigational Dentistry). That is a qualitative finding, not a number, and this page does not print one where none exists.
| Who should be assessed first | Why |
|---|---|
| Untreated tooth decay | Peroxide can reach the nerve through an unfilled cavity |
| Cracked or heavily restored teeth | The seal around a crack or restoration may not hold up to the gel |
| Active gum disease | Inflamed gum tissue is more sensitive to peroxide contact |
| Exposed tooth roots | Root surface lacks enamel and is more prone to sensitivity |
A dentist checks for each of these before recommending whitening, which is one reason professional whitening starts with an examination rather than a straight-to-tray appointment. If sensitivity does occur during a course, a desensitising toothpaste is commonly used, and the treating dentist decides whether to lower the gel concentration or pause the course; no product or dose is recommended generically here, since that is a clinical decision for the specific case. Whether whitening is appropriate during pregnancy, or for someone with already sensitive teeth, is also a question for the treating dentist rather than a general answer, since the published evidence available to this site does not support a blanket safety claim either way. For the full evidence on sensitivity and enamel safety, see is teeth whitening safe?
Results and Maintenance
How long a whitening result holds depends on diet, smoking and day-to-day oral hygiene, and professional whitening is typically followed by a maintenance routine the dentist sets for the individual patient. There is no sourced figure for how many shades whiter a course of whitening will make a specific patient's teeth, since that depends on the starting shade, the cause of the staining and the concentration used, which is why a dentist records the starting shade before treatment rather than promising a result in advance.
A dental check-up and scale and clean is worth having before whitening, since surface stain and calculus that whitening cannot change are removed by scaling (ADA item 114), and the dentist confirms there is no untreated decay, cracked restoration or gum inflammation before starting.
The type of staining also affects how well whitening works, which is a distinction worth raising with the dentist rather than assuming any discolouration will respond the same way. Staining sitting on the outer enamel surface, from coffee, tea, red wine or tobacco, generally responds well to peroxide-based whitening. Staining that originates inside the tooth, from a past injury, certain medications taken during tooth development, or ageing of the dentine underneath the enamel, can respond more slowly or incompletely to the same treatment, which is part of why the dentist examines the specific pattern of discolouration before setting expectations for the course.
Anyone part way through active orthodontic treatment, such as wearing clear aligners, should raise whitening with the treating dentist rather than starting on their own: aligner trays can trap gel against the teeth and gums for longer than a normal application, which turns timing into a clinical decision rather than a personal preference. Diet and smoking both affect how long a whitened result stays visible, since staining is an ongoing process that resumes as soon as new pigment is introduced, which is why a maintenance routine set by the dentist, rather than a one-off treatment, is what keeps the result looking the way it did straight after the course.