A dental crown is a tooth-shaped cap placed over a damaged or weakened tooth to restore its size, shape, strength, and appearance. Molars, or back teeth, perform the function of grinding and crushing food, subjecting them to the highest forces in the mouth (occlusal load). This intense pressure requires a restorative material with superior durability and fracture resistance. Therefore, the material selection for a molar crown differs significantly from that for a front tooth.
Material Options for Molar Crowns
Gold alloy, or full metal, crowns are the traditional standard for back teeth due to their superior physical properties. Composed of gold mixed with metals like palladium, nickel, or chromium, they are extremely durable and resistant to fracture. Full metal crowns require the least amount of natural tooth structure removal for placement. They also cause minimal wear on opposing teeth, making them a reliable, long-term option for the posterior mouth.
Zirconia crowns are a modern ceramic option popular for combining strength and a natural appearance. Fabricated from zirconium dioxide, they offer a much higher level of fracture toughness compared to older porcelain materials, making them suitable for the high-stress environment of a molar. Monolithic zirconia, milled from a single block, is favored for molars due to its high flexural strength.
Porcelain-fused-to-metal (PFM) crowns combine the structural integrity of a metal base with a tooth-colored porcelain layer. The metal substructure provides the necessary strength to withstand occlusal forces, while the porcelain veneer allows the crown to blend with surrounding teeth. However, the porcelain layer can sometimes chip or wear down over time. A thin gray line may also become visible at the gum line where the metal is exposed.
Key Factors for Material Selection
The primary consideration for a molar crown is its ability to handle heavy grinding forces without failing, making durability and wear resistance paramount. Full metal crowns provide the highest resistance to breaking and chipping, and their wear rate is similar to natural tooth enamel, which is gentle on the opposing tooth. Zirconia is also exceptionally strong, often exceeding the strength of PFM, but its hardness can sometimes lead to increased wear on the opposing tooth’s enamel if the material is not highly polished.
Aesthetics plays a lesser role for molars, as they are generally hidden from view, allowing materials to prioritize strength over appearance. The metallic color of a gold alloy crown is its main drawback, but for molars deep in the mouth, this is rarely a concern. Zirconia offers a good compromise, providing a strong, tooth-colored option, while PFM is often selected when a reasonable aesthetic is desired without the highest cost.
The cost and longevity of the material are significant factors in the decision-making process. Full metal crowns, particularly those with high gold content, may have a high initial cost, but they boast the longest average lifespan, often exceeding 20 years. Zirconia crowns are typically priced in a mid-to-high range and offer a long expected life, often around 15 years. PFM crowns generally represent the most cost-effective solution, providing reliable performance for 10 to 15 years.
The Crown Placement Process
First Appointment: Preparation and Impression
The process of receiving a molar crown typically involves two separate appointments. The first appointment focuses on preparing the tooth by reshaping the molar and removing outer tooth structure to create space for the crown material. A highly accurate impression, either a physical mold or a digital scan, is then taken of the shaped tooth and surrounding area. This impression is sent to a dental laboratory, where technicians custom-fabricate the permanent crown.
Second Appointment: Placement
Before the patient leaves the first visit, a temporary crown, usually made of acrylic or resin, is cemented over the prepared tooth. This temporary restoration protects the tooth and maintains function while the permanent crown is being made, which usually takes about two weeks. The second appointment occurs when the permanent crown arrives from the lab. The dentist removes the temporary crown, cleans the underlying tooth, and checks the fit, color, and bite of the permanent restoration. Minor adjustments may be made to ensure comfort and proper occlusion before the crown is permanently bonded to the molar using a specialized dental cement.