What Are Craze Lines?
Craze lines are small, shallow cracks that are confined to the enamel — the hard outer layer of the tooth. They appear as fine, hairline marks on the tooth surface and are most commonly noticed on the front teeth, where the enamel is thinner and light can pass through more easily.
These lines are a normal part of tooth ageing and are extremely common in adults. They develop gradually over years of everyday use — chewing, biting, and exposure to temperature changes — and are generally painless. Craze lines do not typically affect the structural strength of the tooth or require treatment, though some patients seek cosmetic improvement if the lines are particularly visible.
In most cases, craze lines remain stable and do not progress into deeper fractures. Your dentist can confirm whether a visible line is a craze line during a routine examination.
What Are Tooth Fracture Lines?
Tooth fracture lines are cracks that extend beyond the enamel surface and may involve the dentine — the softer layer beneath the enamel. Unlike superficial craze lines, structural fracture lines can potentially affect the tooth's integrity and, in some cases, cause symptoms such as sensitivity or pain when biting.
It is important to distinguish fracture lines from cracked tooth syndrome, which involves a more defined crack that may extend from the biting surface toward the root of the tooth. Cracked tooth syndrome typically produces more consistent symptoms, including sharp pain on biting and temperature sensitivity, and generally requires more definitive treatment.
Fracture lines that involve the dentine or approach the nerve of the tooth may benefit from protective restorations to prevent further propagation. The appropriate management depends on the depth, location, and symptoms associated with the fracture, which your dentist can assess during a clinical examination.
Common Causes of Fracture or Craze Lines
Both craze lines and fracture lines can develop from a range of causes. The presence of visible lines does not always indicate damage — many are simply a reflection of normal enamel wear over time.
Natural Ageing and Enamel Wear
Over decades of use, enamel is subject to repeated stress from chewing, biting, and temperature changes. Fine craze lines develop as a natural consequence of this long-term wear and are particularly common in adults over 40.
Teeth Grinding or Clenching (Bruxism)
Habitual grinding or clenching places excessive lateral and compressive forces on the teeth, which can accelerate the development of both superficial craze lines and deeper structural fractures over time.
Temperature Changes
Repeated exposure to extremes of hot and cold — such as drinking very hot tea followed by cold water — can cause the enamel to expand and contract, gradually contributing to the formation of fine surface lines.
Minor Trauma or Impact
A knock to the mouth, biting unexpectedly on a hard object, or minor sports injuries can create fracture lines that may be superficial or, in some cases, extend into the deeper tooth structure.
Bite Imbalance
When the teeth do not meet evenly during biting, certain teeth bear a disproportionate share of the load. Over time, this concentrated force can contribute to crack formation in the affected teeth.
Symptoms to Be Aware Of
The symptoms associated with tooth fracture lines vary considerably depending on their depth and location. Many lines produce no symptoms at all, while deeper fractures may cause noticeable discomfort:
Visible Lines in Tooth Enamel
Fine, hairline lines visible on the tooth surface — often most noticeable on the front teeth under certain lighting. These are frequently craze lines and are typically cosmetic in nature.
Sensitivity in Some Cases
If a fracture line extends beyond the enamel into the dentine, the tooth may become sensitive to hot, cold, sweet, or acidic stimuli. Superficial craze lines rarely cause sensitivity.
Pain When Biting
Sharp or intermittent pain on biting can suggest that a crack has extended deeper into the tooth structure, potentially affecting the dentine or approaching the nerve. This warrants professional assessment.
No Symptoms in Superficial Cases
Many craze lines and superficial fracture lines cause no symptoms at all. They are often discovered incidentally during a routine dental examination or noticed by the patient for purely cosmetic reasons.
The absence of symptoms does not always mean a fracture line is insignificant. Equally, many visible lines are entirely harmless. Professional assessment provides clarity.
Why Professional Assessment Is Important
The depth and significance of a fracture line cannot always be determined by visual inspection alone. A line that appears superficial on the surface may extend deeper into the tooth structure, while a line that looks concerning may prove to be a harmless craze line confined to the enamel.
During assessment, your dentist may use techniques such as transillumination — shining a focused light through the tooth — and bite testing to evaluate the depth and clinical significance of any lines. Dental imaging may also be used where clinically indicated to check for root involvement or associated structural changes.
Regular monitoring of known fracture lines allows your dentist to track any changes over time. Early identification of progression can help preserve tooth structure and may reduce the need for more extensive treatment in the future.
How Dentists Assess Fracture Lines
A structured clinical assessment helps determine the nature and significance of visible lines, guiding the most appropriate management approach:
Visual Examination
A careful inspection of all tooth surfaces under magnification and appropriate lighting to identify the location, extent, and pattern of any visible lines or cracks.
Transillumination
A bright light directed through the tooth can help reveal the depth and extent of a crack. Superficial craze lines typically allow light to pass through evenly, while deeper fractures may interrupt the light path.
Bite Testing
Selective pressure applied to individual cusps or areas of the tooth can help reproduce symptoms and identify the location of a deeper fracture line that may not be fully visible.
Dental Imaging
X-rays or other imaging where clinically indicated to assess root involvement, check for any associated bone changes, and evaluate the overall structural condition of the tooth.
Monitoring Over Time
Where the significance of a line is uncertain, your dentist may recommend periodic review to track any changes in depth, symptoms, or appearance before deciding on intervention.
Professional Management Options
The approach to managing fracture lines depends on their depth, symptoms, and the overall condition of the tooth. Your dentist will discuss the most suitable options based on the clinical findings. Management may include:
Monitoring Superficial Craze Lines
Where lines are confined to the enamel surface, cause no symptoms, and appear stable, your dentist may recommend periodic monitoring during routine check-ups to ensure no progression occurs.
Bite Assessment and Grinding Management
If grinding or bite imbalance is contributing to fracture lines, a custom night guard may be recommended to reduce mechanical stress on the teeth and help protect against further crack development.
Composite Bonding
For craze lines that are a cosmetic concern, or superficial fractures where a protective layer is beneficial, composite bonding can improve appearance and provide an additional barrier over the affected area.
Protective Restorations
Where a fracture line has extended into the dentine and weakened the tooth structure, an onlay or partial restoration may be recommended to stabilise the tooth and reduce the risk of further propagation.
Dental Crowns
In cases where a significant fracture compromises the structural integrity of the tooth, a crown may be recommended to encase the tooth, restore its shape and strength, and prevent the crack from progressing further.
Root Canal Treatment
If a fracture extends to the nerve of the tooth and causes persistent pain or infection, root canal treatment may be necessary to remove the affected nerve tissue before the tooth is restored with a crown or other restoration.
Not all fracture lines require active treatment. Many can be safely monitored over time. Your dentist will recommend intervention only where it is clinically appropriate.
Professional Evaluation of Fracture Lines
A professional dental assessment helps determine whether visible lines in your teeth are harmless enamel changes or structural fractures that may benefit from monitoring or treatment. Your dentist can evaluate the depth and significance of any lines and recommend an appropriate management plan.
Depending on the findings, your dentist may recommend general dentistry and monitoring, composite bonding for cosmetic improvement, dental crowns for structural protection, or root canal treatment if nerve involvement has occurred.
Assessment for tooth fracture lines and craze lines is available at our London clinics. You can attend our South Kensington dental clinic or our City of London clinic near St Paul's for a professional dental review.
Can Craze Lines Get Worse?
Many craze lines remain stable throughout a person's lifetime and never progress into deeper fractures. They are a normal feature of mature enamel and, in most cases, do not change significantly over time.
However, certain factors may increase the risk of a craze line developing into a more significant fracture. Teeth grinding or clenching places repeated mechanical stress on the enamel, which can cause existing lines to deepen. Similarly, bite imbalance that concentrates forces on specific teeth may contribute to progression in those areas.
Regular monitoring during dental check-ups allows your dentist to identify any changes early. If a craze line shows signs of deepening or begins to cause symptoms, appropriate intervention can be considered at that stage. Predictive statements about whether a specific line will worsen are not clinically reliable, which is why ongoing observation is the most prudent approach.
Reducing the Risk of Tooth Fractures
While craze lines from normal ageing cannot be entirely prevented, the following strategies may help reduce the risk of deeper fractures developing:
- Discuss any grinding or clenching habits with your dentist so a protective night guard can be considered
- Wear a custom-made night guard as advised to distribute biting forces and reduce stress on the teeth
- Avoid biting or chewing on very hard objects such as ice, hard sweets, pen caps, or fingernails
- Attend regular dental check-ups so any changes in existing lines can be identified and monitored early
- Use a mouthguard during contact sports to protect the teeth from impact-related fractures
- If you notice a new crack or experience sudden sensitivity, mention it at your next dental appointment
