When a tooth has sustained significant damage or decay, the dentist may recommend placing a large filling to restore structure and function. As fillings get larger, they become more prone to fracture. Therefore, one common question patients ask is whether a large filling also requires a crown to protect it.
What defines a large filling?
There is no universal definition for what constitutes a “large” filling, but it typically refers to those that take up 2 or more tooth surfaces. The size of a filling is determined by the extent of the decay and subsequent cavity preparation. Some examples of large fillings include:
- Mesial-occlusal-distal (MOD) – decay on the biting surface and both sides of a back molar
- Mesial-occlusal (MO) – decay on the front and biting surface of a premolar or molar
- Distal-occlusal (DO) – decay on the back and biting surface of a premolar or molar
In comparison, small or moderate fillings only require restoring one or two surfaces, such as just the occlusal (biting) surface.
Why do large fillings fracture more easily?
There are a few reasons why large fillings are more prone to fracture over time compared to smaller ones:
- More surfaces involved – The more surfaces of a tooth that require restoration, the weaker the remaining tooth structure.
- Increased chewing forces – Larger fillings have a greater surface area that must withstand repeated chewing forces.
- Polymerization shrinkage – Dental composites shrink slightly during curing, introducing internal stresses within the restoration.
In large fillings, these factors can contribute to breakdown of the remaining tooth structure and compromise the integrity of the restoration over the long term.
When are crowns recommended?
While there are no definitive rules, some general guidelines on when crowns are recommended for large fillings include:
- The filling involves 3 or more surfaces of the tooth.
- More than 50% of the tooth structure is missing due to decay or damage.
- The remaining tooth structure is very thin or fragile.
- A bonded restoration (such as a veneer) is also being placed.
- There is a need to improve the shape, size or color of the tooth.
- A tooth requires a post and core foundation due to excessive loss of tooth structure.
- The patient has a history of repeatedly fracturing fillings.
Crowns are also suggested for teeth that undergo root canal treatment or have very heavy biting forces, like back molars.
The advantages of crowning large fillings
Some key benefits of placing a crown over a large filling include:
- Protects the remaining tooth structure – Crowns cover the entire tooth and help prevent future fractures.
- Supports the filling– The crown splints together the weaker remaining tooth structure.
- Strengthens the tooth – Crowns are custom-designed for full coverage and even distribution of chewing forces.
- Restores proper tooth form – They can rebuild severely damaged teeth back to proper shape and function.
- Prevents future decay – Crowns seal off any underlying tooth decay and protect tooth roots.
- Improves tooth appearance – Crowns can mask unsightly damage or stains.
For patients with a history of fractured fillings or significant bites forces, crowns are often the only reliable long-term solution.
The potential disadvantages
While crowns have many benefits for protecting large fillings, there are some disadvantages to consider:
- Higher cost compared to a filling alone
- The process requires two dental appointments
- More tooth structure removed to accommodate the crown
- Potential for crown fracture or loss of retention
- Risk of damage to adjacent teeth during crown preparation
- Need for occasional crown replacement over time
Proper patient selection and quality treatment by an experienced dentist can help minimize these risks and maximize the longevity of the restoration.
What are the alternatives to crowns?
Some alternatives to crowning large fillings include:
- No additional treatment – If the tooth has adequate structure left, it may be reasonable to just observe the filling.
- Orthodontic treatment – Moving teeth to minimize heavy biting forces.
- Tooth-colored onlay – Less aggressive than a crown but still provides cuspal coverage.
- Ceramic veneer – Less tooth reduction than a crown if only facially restored.
However, these options may not provide the same longevity or definitive protection from fracture.
The decision-making process
Deciding between placing a crown or just restoring a tooth with a large filling alone involves:
- Considering the amount and condition of remaining tooth structure.
- Evaluating the costs and benefits of each option.
- Reviewing the patient’s bite forces and occlusal risk factors.
- Discussing both short and long-term prognoses.
With large fillings that encompass multiple surfaces, the best and most predictable restoration is often a full-coverage crown. An experienced dentist can advise whether an individual tooth would benefit from crown placement based on a thorough assessment.
Conclusion
While not all large fillings require full coverage crowns, many teeth with extensive decay or damage are at high risk of future fracture without a crown. Crown placement is especially indicated when over 50% of the tooth structure is missing, the remaining walls are thin, or the patient has a history of cracked fillings. A crown covers the vulnerable tooth surfaces, protects the filling, and strengthens the remaining structure. With proper patient selection and quality dentistry, crowns can greatly improve the long-term prognosis of extensively restored teeth.