Dental Crowns and Bridges: Materials, Procedures, and Clinical Outcomes

Jul 20

Introduction

Dental crowns and bridges are among the most frequently performed fixed prosthodontic procedures worldwide. A crown (or cap) covers an individual tooth to restore its shape, size, strength, and appearance. A bridge replaces one or more missing teeth by anchoring artificial teeth (pontics) to adjacent natural teeth or implants. With advances in material science and digital dentistry, clinicians today have an unprecedented range of options for delivering durable, aesthetic restorations.

Dental Crowns: Indications and Material Selection

Clinical Indications

• Extensive caries or fracture: When tooth structure loss exceeds 50%, direct restorations (fillings) become inadequate. A crown provides circumferential protection against further fracture.
• Root canal treated teeth: Endodontically treated posterior teeth have increased fracture risk. Full-coverage crowns are recommended, particularly for molars and premolars.
• Severe attrition or erosion: Crowns restore vertical dimension and protect against further wear.
• Aesthetic improvement: Discolored, malformed, or severely misaligned teeth can be restored with all-ceramic crowns for optimal aesthetics.
• Implant restoration: Crowns are the final prosthetic component for single-tooth implants.

Crown Material Options

Dental Bridges: Classification and Design Principles

Traditional Fixed Bridges

• Conventional bridge: Pontic suspended between two or more abutment crowns. Requires preparation of adjacent healthy teeth. The most common design.
• Cantilever bridge: Pontic supported by a single abutment crown on one side only. Suitable when only one adjacent tooth is available. Higher leverage forces limit its use to areas of low occlusal load.
• Maryland bridge (resin-bonded): Pontic with metal or ceramic wings bonded to the lingual surfaces of adjacent teeth. Minimally invasive, preserves enamel. Single-wing designs show better survival than two-wing. 5-year survival approximately 87% in anterior applications.

Implant-Supported Bridges

When multiple teeth are missing, implant-supported bridges provide a fixed solution without involving natural teeth. Two or more implants support a connected prosthesis. This approach preserves adjacent tooth structure and provides superior long-term survival (10-year survival >95%). Compared to traditional bridges, implant-supported restorations show lower annual failure rates and better patient satisfaction.

Pontic Design Considerations

• Sanitary (hygienic) pontic: Easy to clean but poor aesthetics. Used in non-aesthetic posterior regions.
• Modified ridge-lap pontic: Slight tissue contact on the buccal aspect only, T-shaped cross-section. Good compromise between aesthetics and hygiene.
• Ovate pontic: Concave tissue surface extending into a prepared socket. Best aesthetics for anterior regions. Requires excellent oral hygiene.

Clinical Procedure: From Preparation to Cementation

Step 1: Tooth Preparation

Tooth reduction follows material-specific guidelines. All-ceramic crowns require 1.5–2.0 mm occlusal reduction and 1.0–1.5 mm axial reduction. PFM requires 1.5–2.0 mm occlusal and facial reduction, 1.0–1.5 mm lingual. Full metal requires least reduction (0.5–1.0 mm). Chamfer or rounded shoulder finish lines are preferred. Sharp line angles and undercuts must be eliminated.

Step 2: Impression and Temporization

• Conventional impression: Polyvinyl siloxane (PVS) or polyether materials for accuracy.
• Digital impression: Intraoral scanners (IOS) capture preparation geometry with high accuracy. Benefits include patient comfort, faster workflow, and reduced remakes. Systems such as CEREC, 3Shape TRIOS, and iTero are widely used.
• Temporary restoration: Provisional crowns fabricated from bis-acryl composite or PMMA, cemented with temporary (eugenol-free) cement to prevent sensitivity and maintain occlusion.

Step 3: Laboratory or CAD/CAM Fabrication

Conventional fabrication involves wax pattern, investing, casting, and porcelain layering. Digital workflows use CAD software to design the restoration, followed by CAM milling from pre-sintered blocks (lithium disilicate, zirconia) or 3D printing of patterns for casting.

Step 4: Try-In and Cementation

• Try-in: Assess marginal fit (<50 μm ideal), proximal contacts, occlusion, and aesthetics.
• Cement selection: Resin-modified glass ionomer (RMGI) for conventional cementation. Adhesive resin cement for all-ceramic restorations (especially lithium disilicate). Zirconia can be conventionally cemented with RMGI when retention form is adequate, or adhesively bonded with MDP-containing primers.
• Occlusal adjustment: Verify centric and excursive contacts. Polished zirconia causes minimal antagonist wear; unpolished or adjusted surfaces should be repolished.

Longevity and Complications

Systematic reviews report 5-year survival rates: all-ceramic crowns 93–96%, PFM 94–97%, full metal 97%, conventional bridges 88–94%. Common complications include secondary caries, ceramic fracture, loss of retention, endodontic complications, and periodontal issues around abutments. Factors reducing longevity: poor oral hygiene, bruxism, inadequate tooth preparation, and suboptimal cementation technique.

Cost Considerations and Treatment Planning

Crown costs vary by material: composite resin ($300–600), PFM ($600–1000), lithium disilicate ($800–1200), zirconia ($900–1500). Bridge costs multiply per unit. Implant-supported restorations have higher initial costs but lower long-term maintenance. Treatment planning should consider biological cost (tooth structure sacrificed), financial cost, aesthetic demands, and patient preferences.

Conclusion

Dental crowns and bridges remain essential tools in restorative dentistry, offering predictable solutions for tooth restoration and replacement. Material selection should be individualized based on clinical requirements, aesthetic demands, and functional considerations. Digital workflows continue to improve efficiency and precision, while evidence-based cementation protocols enhance longevity.

References

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