How to Cement a Dental Crown: A Step-by-Step Guide for Dental Professionals

Cementing a dental crown is a fundamental procedure in restorative dentistry. A well-cemented crown ensures longevity, proper function, and patient satisfaction. This comprehensive guide provides a detailed, step-by-step approach for dental professionals to effectively cement a crown, covering everything from material selection to post-cementation care. This guide assumes you have already prepared the tooth and have a well-fitting crown ready for cementation.

## I. Pre-Cementation Assessment and Preparation

Before even thinking about cementing the crown, several critical steps must be taken to ensure a predictable and successful outcome.

**1. Crown Fit Verification:**

* **Marginal Fit:** This is the most critical aspect. Use an explorer to carefully examine the margins of the crown under magnification. The margins should seamlessly blend with the tooth structure. Any gaps, overhangs, or discrepancies must be addressed *before* cementation. These could lead to microleakage, recurrent decay, and periodontal issues. If the crown doesn’t fit perfectly, adjustments will be necessary by either the dentist or sending it back to the lab. Discrepancies of even a few microns can lead to failure.
* **Internal Fit:** Use disclosing wax, occlude spray, or fit checker material inside the crown to check for internal interferences. These materials will highlight areas where the crown is binding on the preparation. Remove any interference using a bur designed for ceramic, metal, or composite, depending on the crown material. Repeatedly apply and remove the crown, checking the fit until it seats passively and completely.
* **Proximal Contacts:** Check the proximal contacts with dental floss. The floss should have a slight resistance when passing through the contact, indicating a tight but not overly retentive contact. Adjustments can be made using interproximal strips or burs to achieve the ideal contact. Insufficient contacts will lead to food impaction, while overly tight contacts can make seating the crown difficult.
* **Occlusion:** Verify the occlusion using articulating paper. Ensure that the crown is in harmony with the surrounding dentition in centric occlusion, protrusive, and lateral excursions. Adjust any heavy contacts with a fine diamond bur and polish after adjustments. Premature contacts can lead to pain, TMJ issues, and crown fracture.

**2. Shade Verification:**

* Ensure the shade of the crown matches the adjacent teeth under various lighting conditions. Patient approval of the shade is crucial. If the shade is unacceptable, the crown should be sent back to the lab for adjustments.

**3. Patient Communication:**

* Explain the procedure to the patient, including the steps involved and the expected outcome. Address any questions or concerns the patient may have. Informed consent is essential.

**4. Preparation Cleaning:**

* **Thorough Cleaning:** The prepared tooth *must* be meticulously cleaned. Use a slurry of pumice and water with a rotating prophy cup to remove any debris, saliva, or temporary cement. Alternatively, chlorhexidine can be used.
* **Evaluate for Contamination:** Check for any remaining temporary cement. Even small remnants can interfere with the final cementation and lead to failure. Temporary cement is often radiopaque, so a radiograph can be helpful.
* **Isolation:** Isolation is paramount. Use a rubber dam whenever possible. This provides a clean, dry field, preventing contamination from saliva and blood. If a rubber dam is not feasible, use cotton rolls, dry angles, and saliva ejectors. Frequent suctioning is necessary.
* **Desensitization (Optional):** If the preparation is sensitive, consider applying a desensitizing agent containing potassium nitrate or fluoride. Follow the manufacturer’s instructions. Many dentists prefer glutaraldehyde-based desensitizers.

**5. Crown Internal Surface Preparation:**

* **Cleaning:** Clean the internal surface of the crown according to the manufacturer’s instructions for the chosen cement. Some cements require specific cleaning protocols.
* **Etching/Priming (If Applicable):** Certain crown materials, such as lithium disilicate (e.max), require etching with hydrofluoric acid followed by the application of a silane coupling agent. Follow the manufacturer’s instructions precisely for etching time and silane application. This creates a micromechanical bond between the ceramic and the resin cement.
* **Metal Crowns:** Metal crowns may benefit from micro-etching or tin plating to improve retention.

## II. Cement Selection

Choosing the appropriate cement is crucial for the long-term success of the crown. The selection depends on several factors:

* **Crown Material:** Ceramic, metal, porcelain-fused-to-metal (PFM), zirconia, and composite crowns each require different cement types for optimal bonding.
* **Retention and Resistance Form:** Preparations with limited retention and resistance form may necessitate the use of adhesive resin cements.
* **Esthetics:** For highly esthetic crowns, translucent resin cements are preferred to avoid compromising the shade.
* **Ease of Use:** Some cements are easier to handle and clean up than others.
* **Biocompatibility:** Consider the patient’s history of allergies and sensitivities when selecting a cement.

Here’s an overview of common cement types:

* **Resin Cements:**
* **Advantages:** High bond strength, excellent esthetics (especially with translucent shades), low solubility.
* **Disadvantages:** Technique sensitive (requires strict isolation and adherence to bonding protocols), potential for post-operative sensitivity, can be difficult to remove excess cement.
* **Types:** Self-adhesive, total-etch, selective-etch.
* **Indications:** All-ceramic crowns (especially lithium disilicate and zirconia), composite crowns, preparations with limited retention.
* **Glass Ionomer Cements (GIC):**
* **Advantages:** Fluoride release (helps prevent recurrent decay), chemical adhesion to tooth structure, biocompatible.
* **Disadvantages:** Lower bond strength compared to resin cements, can be brittle, susceptible to moisture contamination during setting.
* **Types:** Conventional GIC, resin-modified GIC (RMGIC).
* **Indications:** Metal crowns, PFM crowns, situations where isolation is difficult, patients with high caries risk.
* **Resin-Modified Glass Ionomer Cements (RMGIC):**
* **Advantages:** Combines the benefits of resin and GIC cements, fluoride release, chemical adhesion, higher bond strength than conventional GIC.
* **Disadvantages:** Less esthetic than resin cements, potential for moisture sensitivity.
* **Indications:** Metal crowns, PFM crowns, zirconia crowns, situations where isolation is challenging.
* **Zinc Phosphate Cements:**
* **Advantages:** Long history of use, relatively inexpensive.
* **Disadvantages:** No chemical adhesion, potential for pulpal irritation due to acidity, soluble in oral fluids.
* **Indications:** Rarely used in modern dentistry due to the availability of superior cements.
* **Zinc Oxide Eugenol (ZOE) Cements:**
* **Advantages:** Sedative effect on the pulp.
* **Disadvantages:** Low strength, high solubility, can interfere with resin bonding.
* **Indications:** Temporary cementation only.

**Specific Cement Recommendations Based on Crown Material:**

* **Lithium Disilicate (e.max):** Resin cement (total-etch or self-adhesive).
* **Zirconia:** Resin cement (self-adhesive) or RMGIC. Surface treatment (air abrasion with alumina) is often recommended for increased bond strength when using resin cement.
* **Porcelain-Fused-to-Metal (PFM):** RMGIC or resin cement (consider the metal substructure when choosing the cement shade).
* **Metal Crowns (Gold, Base Metal Alloys):** RMGIC or glass ionomer cement.
* **Composite Crowns:** Resin cement.

## III. Cementation Procedure – Step-by-Step Guide

This section outlines the specific steps for cementation. The procedure will vary slightly depending on the cement type chosen. Always follow the manufacturer’s instructions for each specific product.

**A. Resin Cementation (Total-Etch Technique – Example for Lithium Disilicate Crown):**

This is a more complex but highly effective method for achieving strong bond strengths, particularly with lithium disilicate.

1. **Tooth Preparation Etching:**

* Apply 30-40% phosphoric acid etchant to the prepared tooth structure for 15-20 seconds. Avoid etching dentin for extended periods to prevent over-etching and post-operative sensitivity. Etching times may vary depending on the manufacturer’s recommendation.
* Rinse thoroughly with water for at least 15 seconds to remove all traces of the etchant.
* Gently air dry the tooth preparation. Do *not* desiccate the dentin. The surface should appear slightly moist (a “frosty” appearance of the enamel).

2. **Bonding Agent Application:**

* Apply a bonding agent (primer and adhesive) to the etched enamel and dentin according to the manufacturer’s instructions. Many bonding agents are available as single-bottle systems, simplifying the application process. Apply multiple thin coats and scrub actively into the tooth surface. This helps to ensure adequate penetration of the bonding agent into the etched enamel and dentin.
* Light cure the bonding agent for the recommended time (typically 10-20 seconds) using a high-quality curing light.

3. **Crown Preparation (if applicable – after hydrofluoric acid etching and silane application):
**
* Lightly air-abrade the internal surface of the crown with aluminum oxide.
* Apply silane coupling agent to the intaglio surface of the crown and allow it to react for the recommended time (usually 60 seconds).
* Apply a thin coat of bonding agent to the internal surface of the crown.
* Light-cure the bonding agent for the recommended time.

4. **Cement Application:**

* Dispense the resin cement onto a mixing pad or into an automix tip, as directed by the manufacturer.
* Apply a thin, even layer of cement to the internal surface of the crown. Avoid overfilling, as this can make cleanup more difficult. However, ensure that all internal surfaces are covered.

5. **Crown Seating:**

* Carefully seat the crown onto the prepared tooth. Apply gentle but firm pressure to ensure complete seating. Use a crown seating instrument or finger pressure.
* Remove any excess cement that extrudes from the margins *immediately* using a microbrush, explorer, or dental floss. Tack-curing the cement (short bursts of light curing for 1-2 seconds) can make cleanup easier.

6. **Final Light Curing:**

* Light cure the cement for the full recommended time (typically 20-40 seconds per surface – buccal, lingual, mesial, and distal) using a high-quality curing light. Ensure that the light is positioned as close as possible to the crown surface for optimal curing.
* Use a glycerin gel or air-blocking agent around the margins of the crown during light curing. This prevents the formation of an oxygen inhibition layer, resulting in a harder, more complete cure of the cement.

7. **Final Cement Removal:**

* After light curing, use a sharp scaler or explorer to carefully remove any remaining excess cement from the margins. Dental floss can be used to remove cement from the interproximal areas. Be extremely careful not to damage the crown or the adjacent tooth structure.
* Check the margins for any voids or overhangs. If any are present, they should be corrected.

8. **Occlusion Check:**

* Recheck the occlusion after cementation with articulating paper. Adjust as needed with fine diamond burs.

**B. Resin-Modified Glass Ionomer Cementation (Example for PFM Crown):**

1. **Cement Preparation:**

* Dispense the RMGIC cement capsules or powder/liquid according to the manufacturer’s instructions.
* Mix the cement thoroughly until a homogenous consistency is achieved.

2. **Cement Application:**

* Apply a thin, even layer of RMGIC cement to the internal surface of the crown. Again, avoid overfilling.

3. **Crown Seating:**

* Carefully seat the crown onto the prepared tooth with gentle but firm pressure.
* Remove any excess cement that extrudes from the margins using a microbrush, explorer, or dental floss.

4. **Setting Time:**

* Allow the cement to set for the recommended time, according to the manufacturer’s instructions. Some RMGIC cements require light curing, while others are self-curing.

5. **Final Cement Removal:**

* Once the cement has set, carefully remove any remaining excess cement from the margins with a scaler or explorer. Be careful not to damage the crown or adjacent teeth.

6. **Occlusion Check:**

* Recheck the occlusion after cementation with articulating paper. Adjust as needed with fine diamond burs.

**C. Self-Adhesive Resin Cementation (Example for Zirconia Crown):
**

1. **Surface Preparation of the Crown:**
* For zirconia, air-abrasion with aluminum oxide is recommended to increase micromechanical retention.
* Clean the intaglio surface of the crown.
2. **Cement Application:**
* Dispense and mix the self-adhesive resin cement according to the manufacturer’s instructions.
* Apply a thin, even layer to the intaglio surface of the crown.
3. **Crown Seating:**
* Seat the crown onto the prepared tooth with firm pressure.
* Allow excess cement to express and remove it with a microbrush or scaler after tack-curing for a few seconds (if recommended by the manufacturer).
4. **Light Curing:**
* Light-cure the cement according to the manufacturer’s guidelines.
5. **Final Cleanup:**
* Remove any remaining cement carefully with appropriate instruments, ensuring not to damage the margins.
6. **Occlusion Check:**
* Verify and adjust the occlusion as needed.

## IV. Post-Cementation Care

* **Check Occlusion:** Verify the occlusion with articulating paper and adjust any premature contacts to ensure proper function and prevent stress on the crown.
* **Radiographic Evaluation:** Take a radiograph to confirm complete seating of the crown and to check for any cement voids.
* **Patient Instructions:** Provide the patient with post-operative instructions, including:
* Avoid chewing hard or sticky foods for at least 24 hours.
* Maintain excellent oral hygiene, including brushing and flossing around the crown.
* Report any sensitivity, discomfort, or changes in occlusion to the dental office.
* **Follow-Up Appointment:** Schedule a follow-up appointment in 1-2 weeks to evaluate the crown and assess the patient’s oral hygiene.

## V. Troubleshooting Common Cementation Problems

* **Post-Operative Sensitivity:**
* **Cause:** Over-etching of dentin, inadequate bonding, microleakage, high occlusion.
* **Solution:** Use desensitizing agents, ensure proper bonding technique, adjust occlusion.
* **Cement Voids:**
* **Cause:** Inadequate cement application, incomplete seating of the crown, air entrapment.
* **Solution:** Apply sufficient cement, use a crown seating instrument, vent the crown during seating.
* **Marginal Discrepancies:**
* **Cause:** Poor crown fit, cement washout, recurrent decay.
* **Solution:** Ensure accurate crown fit before cementation, use appropriate cement, maintain excellent oral hygiene.
* **Difficulty Removing Excess Cement:**
* **Cause:** Cement setting too quickly, inadequate tack curing, using inappropriate instruments.
* **Solution:** Choose a cement with a longer working time, tack cure the cement for a shorter duration, use sharp scalers and floss.

## VI. Conclusion

Cementing a dental crown is a critical step in restorative dentistry. By following a meticulous, step-by-step approach, paying close attention to detail, and selecting the appropriate materials, dental professionals can ensure the long-term success and patient satisfaction. Careful pre-cementation preparation, proper cement selection, adherence to manufacturer’s instructions, and thorough post-cementation care are all essential components of a successful crown cementation procedure. Understanding the nuances of different cement types and their indications allows for tailored treatment planning that optimizes the outcome for each individual patient. Remember that continuous learning and staying updated on the latest advancements in dental materials and techniques are vital for providing the best possible care to your patients.