A dental crown is a custom-made, tooth-shaped cap used in restorative dentistry to cover a tooth that has been severely damaged or weakened. This restoration works by encasing the entire visible portion of the tooth, restoring its original shape, size, and function. The process of receiving a crown typically involves at least two appointments, which necessitates the use of both a temporary and a permanent restoration. The temporary crown serves a protective role during the interim period while the final, long-term crown is being fabricated in a dental laboratory.
The Role of Temporary Crowns
Temporary crowns are placed immediately after the natural tooth is prepared for the permanent restoration. Their primary function is to protect the underlying, newly shaped tooth structure from bacterial contamination and thermal changes, preventing hypersensitivity. These provisional restorations also maintain the correct spacing between teeth, stopping adjacent teeth from shifting before the final crown arrives.
Temporary crowns are generally crafted from materials like acrylic resin, composite resin, or prefabricated polycarbonate shells, chosen for their ease of manipulation and low cost. The materials used are designed for short-term wear, typically lasting only a few weeks until the permanent crown is ready for placement. Because they are often made quickly in the dental office, temporary crowns inherently lack the precise anatomical detail and strength of their permanent counterparts. They are cemented with a weaker, temporary adhesive, resulting in a fit that is not perfectly sealed around the gumline.
Precision and Purpose of Permanent Crowns
The permanent crown is the final, long-term solution, built to withstand years of chewing force. Unlike temporary crowns, the final restoration is fabricated in a specialized dental lab using highly accurate impressions or digital scans of the prepared tooth. These sophisticated methods allow for the creation of a crown with anatomical correctness and a precise fit that is measured in micrometers.
Permanent crowns are made from materials with higher strength and durability, such as full-contour zirconia, porcelain fused to metal, or all-ceramic options like lithium disilicate. The choice of material is based on the tooth’s location, the patient’s bite forces, and aesthetic requirements. The purpose of this restoration is to provide a restoration that is structurally sound, highly aesthetic, and capable of maintaining the tooth’s form for a decade or more.
Comparing Fit and Marginal Integrity
A permanent crown definitively fits better than a temporary one, primarily due to the concept of marginal integrity. Marginal integrity refers to the tight seal where the edge of the crown meets the tooth structure, ideally at or just below the gum line. A permanent crown is designed to minimize the marginal gap to prevent the ingress of oral fluids and bacteria, which causes secondary decay and pulp irritation.
The fit of a permanent crown is better because the laboratory process focuses on achieving a seal that minimizes this gap, often aiming for a clinical seal under 120 micrometers. This tight adaptation prevents microleakage, which occurs when bacteria seep under the restoration. Furthermore, the permanent crown is adjusted for precise occlusion, ensuring it meets the opposing tooth with correct force to prevent bite issues or jaw pain. The contour of the permanent crown is also meticulously shaped to allow for proper flossing and to support the surrounding gum tissue, which is rarely achieved with the bulkier, less refined shape of a temporary crown.
Indicators of a Poor Fit
After the permanent crown is cemented, it should feel secure and comfortable, integrating with the rest of the mouth. Persistent sensitivity to temperature, especially hot or cold stimuli, can be an indicator that the marginal seal is compromised, leaving the underlying tooth structure exposed. A noticeable change in the bite, where the crown feels “high” or causes other teeth to meet differently, suggests a problem with the crown’s occlusal surface.
Patients should also be aware of persistent pain when chewing or feeling a sharp edge or “ledge” along the gumline when running their tongue or floss over the area. This rough margin can irritate the gum tissue, leading to localized inflammation, redness, or bleeding. Additionally, if food repeatedly gets caught between the crowned tooth and its neighbor, it signals a flaw in the crown’s interproximal contour, indicating a poor fit that requires adjustment or replacement.