Tooth decay does not begin with a hole. It begins with a dull, chalky-white patch that does not hurt and that almost nobody treats as a disease. It is this moment that decides whether treatment ends with a fluoride application or with a filling.
The shortest answer is this:
- Only a white spot lesion can be reversed, and only for as long as the enamel surface remains intact.
- A shallow cavity confined to enamel can still be arrested, but the cavity itself will not disappear.
- Once the process reaches dentine, the tooth has to be prepared and restored.
The boundary lies in one place: where the enamel surface breaks down. Below we show how to recognise which side of that boundary a given tooth is on.
This article describes the course of the disease rather than ways of avoiding it. Day-to-day protection of the teeth is covered separately in tooth decay prevention. Here we start at the point where the process has already begun.
Tooth decay as a process, not as a hole in a tooth
Bacteria in dental plaque convert sugars into acids. Acid leaches calcium and phosphate out of enamel, which is what demineralisation means. After a meal, saliva gradually restores the pH and some of the minerals return to the tissue. This is enamel remineralisation. For most of our lives the two processes balance one another.
The disease begins when, over weeks and months, the losing side gains the upper hand. Three things make this more likely:
- frequent snacks and sweet drinks, because what counts is how often sugar is consumed rather than how much of it is eaten at once,
- plaque that accumulates where a toothbrush does not reach,
- reduced saliva flow, for example after certain medicines or in general illness.
Six small snacks spread across the day place a greater burden on enamel than one larger dessert eaten after lunch.
This is why contemporary dentistry treats tooth decay as a disease with its own dynamics, one that can be arrested or slowed down, rather than as a single defect to be drilled out. Current guidelines on the management of deep caries point in the same direction: less tissue removal, more tissue preservation [1].
The four stages of tooth decay
Stage 1: the white spot lesion, the only fully reversible stage
The enamel surface is still intact, but immediately beneath it the tissue has become porous and depleted of minerals. Light scatters on these micropores, which is why the lesion looks chalky and dull rather than glossy like healthy enamel. It is easiest to see once the tooth has been dried.
This is early tooth decay. There is no cavity yet, only weakened tissue beneath an intact surface, and that tissue can be partly rebuilt.
White spot lesions develop where plaque sits for months: around orthodontic brackets, along the gingival margin, in the fissures of newly erupted molars. In adolescents undergoing appliance treatment who drank at least two energy drinks a day, the proportion of affected surfaces rose during treatment from around 15% to over 50% [2]. This is an extreme scenario, but it shows clearly how quickly the disease progresses when an acidic diet and difficult cleaning come together.
Stage 2: a cavity confined to enamel
The weakened surface layer eventually collapses. The first true cavity appears, still shallow and often no larger than a pinhead. Patients sometimes feel it with the tongue as roughness, or notice that food starts to catch in one particular spot.
There is usually no pain, because enamel has no nerve supply. This is the main reason why patients present later than they should. On a bitewing radiograph the lesion appears as a radiolucency confined to enamel, and such early lesions account for more than half of all lesions detected on the proximal surfaces of adult teeth [3].
Stage 3: dentine caries, the point at which the drill comes into play
Dentine lies beneath enamel, is less mineralised and is in direct communication with the pulp. The process accelerates and the tooth begins to respond to sweet foods, to cold and to food packing in the cavity. Softened, brownish tissue appears, and the undermined enamel above the cavity can fracture off in a larger piece than the small opening on the surface would suggest.
This is where the practical threshold for placing a restoration lies. The deeper the lesion, the more often the dentist reaches for the drill: for a lesion at the enamel and dentine border a filling is placed in roughly one case in twelve, whereas for a lesion reaching the middle third of dentine it is three times out of four [3].
Stage 4: pulp involvement
When the process reaches the vicinity of the pulp chamber, the pulp becomes involved, that is, the tissue containing blood vessels and nerves that fills the inside of the tooth. The pain changes character. It is no longer a brief response to a stimulus but becomes spontaneous, prolonged, often worse at night and hard to pinpoint.
This does not yet settle the question of root canal treatment. In deep cavities, current guidelines recommend removing carious tissue selectively, that is, leaving a thin layer of affected dentine over the pulp instead of excavating everything down to hard tissue. The aim is to avoid exposing the pulp [1]. After five years, teeth managed in this way retained vitality in more than nine cases out of ten, compared with roughly three out of four where excavation went deeper [5], although the quality of the evidence comparing the two strategies remains low [4]. In typical clinical cases this means a real chance of avoiding root canal treatment, but the final decision depends on the individual diagnosis and on whether the pulp is already irreversibly inflamed.
When drilling can be avoided
The four stages along a single axis: what the dentist sees, what the patient feels and what can be done.
| Stage | What the dentist sees | What the patient feels | Possible management |
| 1. White spot lesion (early tooth decay | dull, chalky patch, enamel surface intact | usually nothing | arrest without drilling: fluoride application, plaque and diet control, resin infiltration in selected cases |
| 2. Cavity confined to enamel | small break in the surface, radiolucency within enamel on a radiograph | usually nothing, occasionally roughness | most often still non-invasive management with monitoring; a filling where the cavity makes cleaning impossible |
| 3. Dentine caries | softened, brownish tissue, undermined enamel | response to sweet foods and cold, pain that subsides once the stimulus is removed | cavity preparation and a filling |
| 4. Pulp involvement | deep cavity extending towards the pulp chamber | spontaneous, prolonged pain, often at night | vital pulp therapy or root canal treatment |
Remineralisation: fluoride and fluoride-free products
An early lesion is arrested with professional fluoride products applied in the surgery, together with consistent oral hygiene at home. Fluoride is incorporated into the tissue as it rebuilds and makes it more resistant to further acid attacks.
In children with early lesions on first permanent molars, after six months the lesion was no longer detectable in close to nine teeth out of ten following silver diamine fluoride, and in roughly two out of three following fluoride varnish [6]. Silver products have one significant drawback: they permanently darken the arrested lesion, which usually rules them out for front teeth, and the evidence for their ability to rebuild tissue comes mainly from laboratory studies [7].
Fluoride is not the only route. Products based on peptides and calcium compounds also reduced the severity of white spot lesions over the course of a year, although those patients were also given oral hygiene instruction, so the effect cannot be attributed to the products alone [8]. This is emerging evidence rather than established standard practice. Each of these methods requires repeated applications and a change in whatever caused the disease in the first place.
Resin infiltration
Resin infiltration sits between monitoring and drilling. The surface of the lesion is etched with acid, dried and then soaked with a very fluid resin that fills the micropores and is light cured. Nothing is drilled and no tissue is removed.
There is one condition: the enamel surface must be intact. Effectiveness depends on how deeply the resin penetrates, and thorough cleaning of the surface before the procedure increases that penetration [9]. Besides arresting the process, infiltration has an optical effect: the lesion stops standing out as a white patch against the surrounding enamel. Honesty is needed here: the aesthetic result can be unstable and varies considerably between patients [10], although after two years it is clearly better than brushing alone [11].
In our dental practice at Modern Dental & Orthodontics (Klinika MDO) we observe that patients are most satisfied when they know before the procedure that the primary aim is to arrest the disease, and that the improvement in appearance, although usually marked, is not always complete.
What drill-free methods will not do
- They will not rebuild a cavity in which the enamel surface has already broken down.
- They will not arrest a lesion that cannot be kept clean.
- Resin infiltration will not work where the surface is broken.
- They do not work on their own: without less frequent snacking and better plaque removal, the process returns.
From the perspective of the clinical team at Modern Dental & Orthodontics (Klinika MDO), one more point matters: restorative treatment of tooth decay without a drill is not a one-off procedure but a plan spanning several months with review appointments. If the lesion progresses regardless, the cavity has to be prepared before the process reaches dentine.
How the dentist assesses the stage
Three tools that complement one another:
- Visual examination of a cleaned and dried tooth. Moist enamel masks early lesions. The dentist checks whether the surface is intact and classifies the lesion according to the international ICDAS scale (a system describing successive degrees of caries severity). It is this classification that lies behind the words “we will monitor it” or “we will fill it” at the end of the appointment.
- The bitewing radiograph. It shows the proximal surfaces that cannot be inspected directly and allows the depth of the lesion to be assessed. It is the depth, and not the mere fact that something is visible, that determines further management [3].
- Transillumination, that is, shining near-infrared light through the tooth. It picks up more early enamel lesions than a radiograph and involves no radiation [12], but it misses a proportion of the lesions that are present [13]. It complements radiographic examination rather than replacing it.
None of these methods is perfect. In patients at increased risk, what matters is therefore not a single examination but a comparison of successive dental check-ups over time. In children and adolescents the assessment is supplemented by fissure sealing of teeth with deep anatomy that is difficult to clean.
Frequently asked questions
Is a white spot already tooth decay?
Yes, it is the earliest form of the disease. The enamel surface is still intact, but the tissue beneath it has lost some of its minerals. This is exactly why this stage matters so much: with the right management the lesion can be arrested and partly rebuilt, without removing any tooth tissue at all. Not every white spot has this origin, however; congenital disorders of enamel mineralisation look similar and call for different management.
Can tooth decay be reversed?
At the white spot stage, yes: weakened tissue can regain some of its minerals if the number of acid attacks falls and fluoride products are used regularly. Once the enamel surface has broken down, reversal is no longer possible, because the tissue does not grow back. A shallow cavity that can be kept properly clean can still be arrested; a deeper one requires preparation and restoration.
Does tooth decay hurt from the outset?
No. Enamel has no nerve supply, so the first two stages are usually painless. A response to sweet foods and cold appears only once the process reaches dentine. Spontaneous, prolonged pain at night suggests pulp involvement, the most advanced stage. An absence of pain is never proof that a tooth is healthy.
How quickly does tooth decay progress?
There is no single rate. The same lesion will remain unchanged for years in one person and turn into a cavity within a few months in another. What decides is how often sugars are consumed, how well the teeth are cleaned, how much saliva is produced and how much fluoride is available. This is why the intervals between check-ups are set individually rather than to one schedule for everyone.
Is tooth decay always visible on a radiograph?
Not always. Very early enamel lesions may not produce a clear radiolucency, and a radiograph shows depth only approximately, most often somewhat less than the true depth. This is why radiographic examination is combined with visual assessment and with a comparison of successive appointments, and, where there is any doubt, with transillumination.
Can tooth decay be arrested without drilling in adults as well?
Yes, the mechanism of remineralisation works at any age. In adults, however, lesions are more often found on the proximal surfaces and at the necks of the teeth, which are harder to clean at home. Non-invasive management then calls for greater consistency, the use of floss or interdental brushes and regular reviews, and its effectiveness is assessed after several months.
Can an arrested lesion come back in the same place?
It can, if the conditions that caused it persist. An arrested lesion remains a weakened site and is usually somewhat darker than the surrounding enamel, although its surface becomes hard and smooth. This is why, once non-invasive treatment is complete, such surfaces are assessed at every subsequent review appointment and compared with their baseline appearance.
Summary
Tooth decay runs through four recognisable stages and does not begin on the day the tooth starts to hurt. The boundary between treatment without a drill and drilling lies where the enamel surface breaks down. Before that boundary the realistic aim is to arrest the disease and rebuild tissue; beyond it, to remove the lesion and restore the cavity. Because the first two stages are painless, their detection depends on regular check-ups rather than on symptoms.
Read more:
- Aesthetic and restorative dentistry: scope of treatment
- How to protect your teeth from decay: the principles of prevention
- Comprehensive dental check-up: what it includes
- Fissure sealing in children
- Overlays and onlays: restoring large cavities
Content and liability disclaimer
This article is informational and educational in nature and does not constitute medical advice, a diagnosis or a therapeutic recommendation — it does not replace a consultation with a specialist. If you are experiencing symptoms, have doubts or are facing a decision about treatment, consult a dentist. The methods described and the data cited are general in nature. The results of scientific studies relate to populations, not to an individual patient. The course and outcome of therapy depend on the individual clinical situation and may vary between patients. No information contained in this article constitutes a guarantee of result. The content has been prepared with due care, based on publicly available medical knowledge and the scientific publications indicated in the Sources section. We do not advise taking or refraining from any health-related action solely on the basis of the content of this article, without prior consultation with a doctor.
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