When a tooth is prepared for a permanent crown, a provisional or temporary crown is placed to protect the prepared tooth structure while the definitive crown is being custom-fabricated in a dental laboratory. To hold this provisional crown in place, a specific dental adhesive is used. This cement must provide adequate retention for daily function but also allow for easy, non-destructive removal by the dentist later. The cement’s role is strictly temporary, ensuring the patient’s comfort and maintaining the correct tooth position until the final seating appointment.
Identifying the Most Common Temporary Cements
The most frequently utilized material for temporarily securing provisional crowns is Zinc Oxide Eugenol (ZOE) cement. This cement is widely favored due to its composition, which includes eugenol derived from clove oil. Eugenol has a palliative effect on the pulp tissue, helping to soothe sensitivity that often occurs after the tooth preparation procedure.
The standard ZOE formulation is an oil-based cement that provides a good marginal seal, preventing the ingress of bacteria and fluids. This seal is important for pulpal health during the temporary phase. Furthermore, ZOE exhibits natural antimicrobial properties, contributing to a healthier environment beneath the provisional restoration.
A significant alternative to the traditional ZOE is Zinc Oxide Non-Eugenol (ZONE) cement. The eugenol component in ZOE is known to interfere with the setting reaction and bonding strength of certain resin-based permanent cements that may be used for the final restoration. When a dentist plans to use a resin-based cement for the definitive crown, a non-eugenol temporary cement is chosen to ensure compatibility and optimal bonding for the final crown. Other options, such as resin-based temporary cements, are sometimes selected for their better aesthetics or higher retention.
The Functional Mandate: Why Low Strength is Necessary
The primary functional requirement of temporary cement is a carefully balanced strength. The cement must be strong enough to withstand the forces of chewing and speaking without dislodging the provisional crown. However, this retention must be relatively weak when compared to a permanent adhesive.
The low bond strength is by design, as it ensures the dentist can remove the provisional crown easily without causing trauma to the prepared tooth structure. If the cement were too strong, the force required for removal could fracture the temporary crown, damage the margins of the tooth preparation, or even cause pain to the patient. The goal is an atraumatic removal process that leaves the prepared tooth intact and ready for the final restoration.
This balance allows the temporary crown to perform its protective duties while minimizing the time and discomfort associated with its eventual removal. The cement should ideally fail cohesively, meaning the bulk of the cement remains inside the temporary crown upon removal, leaving minimal residue on the prepared tooth surface. Any remaining cement must be simple to clean off without extensive scraping or aggressive instrumentation.
Comparing Temporary and Final Cement Adhesion
Temporary cements, such as ZOE and ZONE, achieve retention primarily through mechanical interlock and very low compressive strength. They are formulated to be weak and minimally adhesive, relying on the physical fit of the provisional crown to the tooth for stability. Their deliberate weakness allows the bond to be broken easily, fulfilling their short-term mandate.
In stark contrast, final or permanent cements are engineered for high strength, insolubility, and longevity, designed to last for many years in the harsh oral environment. These definitive materials, which include resin cements, glass ionomer cements, and resin-modified glass ionomers, utilize powerful bonding mechanisms. Resin cements, for example, achieve a micro-mechanical bond by penetrating and interlocking with the microscopic porosities and collagen fibers of the prepared dentin and enamel.
Other permanent options, like glass ionomer cements, form a true chemical bond with the calcium ions in the tooth structure. This chemical adhesion, combined with their resistance to dissolution from oral fluids, creates a hermetic seal and a highly durable connection that resists the constant forces of mastication. The distinction is that temporary materials prioritize easy removal for a scheduled procedure, whereas permanent materials prioritize an irreversible, high-strength connection for the life of the restoration.
The composition of final cements is optimized for a permanent application, offering properties like high flexural strength and low film thickness for a precise fit, qualities that are not necessary or even desirable in a temporary cement. Understanding this difference in bonding mechanism—weak, mechanical retention for the temporary phase versus strong, micro-mechanical or chemical adhesion for the final restoration—is the key to appreciating the specific role of the cement used with provisional crowns.