A quality porcelain fused to metal (PFM) crown means nothing if it isn’t prepared properly. PFM crowns have long been some of the most popular options for dental restorations. These crowns provide multiple benefits, as they are reliable, highly esthetic and one of the most affordable restoration options.
Preparing these crowns properly goes a long way toward providing patients with the best and most comfortable restoration possible. With this guide, you’ll learn all you need to know about placing PFM restorations, from proper PFM crown prep dimensions to accurate shaping of the tooth structure.
Why Is Preparation for Porcelain Fused to Metal Crowns Important?
Porcelain fused to metal crowns are crowns that have a metal foundation with a porcelain overlay. This construction means that they are almost as durable as fully metal crowns but also mimic the appearance of natural teeth, making PFM crowns a strong option compared to other materials.
Even with the advantages of porcelain fused to metal crowns, their durability, esthetics and comfort rely on a careful preparation process. Meticulous preparation ensures that the lab can create a natural-looking and fully functional crown while ensuring a proper fit. PFM crown prep requires reducing the tooth surfaces to the proper size and creating enough space for the restoration.
Meanwhile, improper preparation could lead to several issues. For example, a lack of clearance between the preparation and the surrounding teeth will prevent the lab from being able to use enough porcelain to create a naturally translucent restoration and hide the metal structure underneath. Altogether, a careful understanding of the preparation process makes a world of difference.
Steps for PFM Crown Prep
When preparing a porcelain fused to metal crown placement, the area of the tooth plays a key role in the procedure. Although the steps are similar, the approach and the PFM crown dimensions will be slightly different depending on whether you are placing a restoration on an anterior or posterior tooth.
Preparing Anterior Teeth for PFM Crowns
When preparing a restoration for anterior teeth, esthetics are often the priority, with functionality following closely behind. In order to create the proper esthetics, you will need to provide additional clearance for the restoration to have translucent ceramic.
To prepare anterior teeth for PFM crown placement:
- Reduce the lingual surface of the preparation by 1mm and the incisal surface by 2mm using a rotary instrument.
- Prepare the labial surface of the preparation by making a central cervical groove on the long axis of the tooth.
- Create two secondary grooves on both sides of the initial cervical groove.
- Place 1.8mm deep reduction grooves on the incisal edge of the tooth using a periodontal probe, ensuring they extend halfway along the labial surface.
- Reduce the incisal edge of the tooth by 2mm to create enough room for an esthetic tooth.
- Reduce the proximal contacts and create a 0.5mm lingual chamfer.
- Remove the tooth structure between the depth grooves.
- Create a cervical shoulder about 1mm wide that extends to the proximal embrasures.
- For best results, use a football-shaped diamond bur to shape the lingual surface.
Preparing Posterior Teeth for PFM Crowns
In contrast with anterior teeth, the posterior teeth are focused less on esthetics and more on strength and functionality. Although all PFM crowns should be prepared with longevity and stability in mind, durability is vital for posterior teeth. Since these teeth do most of the chewing, careful preparation is necessary. Durability is even more important for patients with bruxism.
To prepare posterior teeth for PFM crowns:
- Prepare depth holes in the occlusal surface to be used for occlusal depth cuts.
- Reduce the occlusion, and create a lingual chamfer and a buccal shoulder that extends lingually at a minimum of 1mm.
- Ensure that the mesial side of the preparation extends further than the distal side for esthetics.
- Create 1.5 to 2mm of occlusal clearance on the surface of the teeth. Crowns with a metal occlusal surface or bite stop may need less reduction.
- Ensure that all margins are distinct and continuous around the circumference of the preparation.
- Round each angle on the preparation without straight edges.
- Finally, finish the margins using diamonds or hand instruments.
Common Challenges for PFM Crown Prep
As with any process, PFM crown prep does offer some common challenges for even the most experienced dentists. Fortunately, the common challenges are easier to avoid with careful attention to detail and a proactive understanding of what to avoid.
Some of the common mistakes to be aware of before preparing a restoration include:
- Uneven preparation across the areas of the tooth.
- Inconsistent or uneven depth of the labial shoulder.
- Damage to the labial shoulder due to a poor choice of bur.
- Remaining bur marks left on the preparation.
- Overlooking finishing the incisal edges.
- Not leaving enough space between the preparation and adjacent teeth.
Final Considerations for PFM Crowns
Although the steps for PFM crown prep are fairly universal, always expect to make adjustments on a case-by-case basis. To ensure a comfortable and long-lasting restoration, you should consider a few final points depending on your patient:
- Patients who experience bruxism will benefit from a metal occlusion on the restoration.
- For porcelain margins, use a shoulder prep for the restoration and create a 90-degree angle.
- For crowns with conventional metal collars, consider adding a bevel or slope to the margin for better support of the porcelain.
Most importantly, remember that PFM crown dimensions and guidelines can differ depending on the patient. If you have a patient that has unique needs, then inform your lab so they can make the appropriate adjustments for you. At PRO-Craft Dental Laboratory, we put special care and attention into personalizing each restoration to fit each patient comfortably.
Start PFM Crown Prep with Quality Crowns
The PFM crown prep process makes a vital difference in patient comfort and restoration, but it all starts with choosing a high-quality crown. At PRO-Craft Dental Laboratory, we are committed to providing each patient with a quality, long-lasting restoration. Every crown is made with careful attention to detail in our state-of-the-art facility for a comfortable fit and reliable functionality.
When you work with PRO-Craft, we are proud to offer not just reliable restorations but also our expertise. If you come across any issues or questions during PFM crown prep, we are happy to help provide guidance. Explore our full selection of crowns and bridges, or contact us today to learn more about how our restoration crafting process takes the stress away from your practice.