This article was updated for the latest in zirconia crown prep guidance, it was originally published in July of 2022.
For years, dentistry sought a robust material with customizability for crowns and partials. Enter zirconia oxide or simply zirconia.
Zirconia exploded in popularity in the 2000s with its improved esthetics, colors, and translucent material offerings. According to one study, “The clinical use of this [zirconia] ceramic has continuously increased because of its high aesthetic potential, superior biocompatibility, chemical and dimensional stability, fracture toughness, hardness and frictional resistance compared to conventional dental ceramics.”
It is now the patient’s choice for visual appeal, natural esthetics, and ability to match natural teeth. Zirconia is favored by prosthodontists for durability. It is less stressful on the crown and abutment teeth, leading to fewer cracks and damage. The caveat is the crown preparation and design which must reflect natural tooth dimensions and placement.
Dandy offers procedural criteria as a guide for dental professionals to aid in the proper prep of full zirconia crowns. The preparation is comparable to alternative crown materials. However, there is a necessary exactness due to the complexity of the entire procedure.
Familiarizing yourself with the correct steps for zirconia restoration and crown preparation creates greater longevity. Additionally, the right technology and tools aid in preparation and installation. That, too, bears a requirement of a well-trained and experienced technical team. Doing the procedure accurately will extend the life of the zirconia crown and foster the patient’s overall health.
Patient assessment and crown impressions
For optimal success of a zirconia crown restoration, there are needed assessments. Answer the following:
- What type of crown is necessary?
- What is the location of the crown?
- What kind of crown is required?
- What is the health of existing abutment teeth?
- What are the patient’s aesthetic goals?
The last assessment depends on whether it is for an anterior or posterior crown. We shall give more detail on this later.
Secondly, there are impressions of the patient’s teeth. The usual method of capturing impressions was trays and impression material, such as putty. While they did capture the patient’s teeth contours, PVS lacked exactness and speed of use. Consider all the necessary steps:
- Taking impressions with PVS molds
- Creating stone models
- Shipping the models to a lab
When models arrive at a traditional dental laboratory, additional time is needed for the following:
- Scanning the models
- Designing the crown
- Printing or milling new models for fit
- Sending the crown back to your practice
This process may take 12 to 15 days for most labs to complete. However, some labs may take more than three weeks. That does not include adjustment time or reorders.
Digital impressions for zirconia crowns
Improved technology, like digital scanners, makes dentistry easier, cost-effective, and more efficient. That includes the zirconia prep process.
There are advantages to digital dental crown prep. Digital intraoral scanners provide scans of both the original and prepped tooth quickly. Lab software can copy the preexisting anatomy of the original tooth.
The advantages to digital impressions, besides time and money, are providing patients with a dental crown prep process that is faster and more accurate. Additionally, there is an average five to eight-day turnaround time. But envision the patient experience. There is less time in the chair and no gooey gag-worthy impression material. That is an experience the patient will remember and talk about.
A typical process includes:
- Performing the intraoral scan on the patient
- The digital scan is immediately sent electronically to the lab
- The dental lab can design using the digital impression and produce a more exact crown
- The lab sends the crown to the practice, fitting the patient the first time
The other benefit of intraoral scanners is they are multi-use. They can cover the denture process, orthodontic appointments, and dental implants optimizing all workflows.
Zirconia crown preparation guidelines
The zirconia crown prep dimensions depend on the natural tooth’s location. Visibility and continuity are essential for zirconia crown prep, whether anterior or posterior crowns. The guidelines and specific incisal edge reduction and clearance measurements are altered according to the crown’s location.
Tooth prep can be a complex process. However, using intraoral scanners and digital modeling facilitate a comparative evaluation and the prep process. Prosthetic restoration margins are essential factors in clinical success. Industry literature indicates a preference for supragingival preparation.
Preparing a tooth for a zirconia crown needs impeccable marginal finishing lines. There are two types: a vertical finishing line without a defined margin, known as feather edge preparation, or a sharp horizontal line with a clear finishing line, also known as a chamfer.
Zirconia crown prep for anterior crowns
Anterior zirconia crown prep requires closer attention to the following elements:
- Clearance – Leave at least 0.3 mm of space to accommodate the crown’s wall thickness. Additionally, you’ll need to account for an incisal reduction of 1 to 1.5 mm or 1.8 to 2.0 mm.
- Circumferential chamfer – The continuous circumferential chamfer should be visible and continuous. The gingival margin needs a reduction of at least 0.5mm.
With more visibility, the anterior crown necessitates prepping the tooth structure with an angle of approximately 5°, with no beveling. The incisal edge should be rounded using a football diamond bur to reduce the incisal edges of the crown facing the tongue, making it slightly concave.
Zirconia crown prep for posterior crowns
In the posterior of the mouth, zirconia crown prep involves many of the same considerations that apply to anterior crowns, plus a few aspects that are specific to the back of the mouth. This is because the posterior section of the mouth is a startlingly different environment than the front of the mouth, as it shoulders more mastication responsibility and can be more vulnerable to cavities.
When prepping for posterior zirconia crowns, pay close attention to:
- Clearance – Posterior crowns are slightly thicker than anterior crowns and thus need more room to accommodate their size. Approximately 0.5mm of space is recommended. The proper occlusal reduction is between 1 and 1.5mm or 1.5 to 2mm.
- Circumferential chamfer – Visibility and continuity are key when it comes to zirconia crown prep. For posterior crowns, provide for a 0.5m reduction at the gingival margin. Additionally, posterior crowns should be slightly tapered between 4° and 8°.
Like their anterior counterparts, it’s recommended that you avoid beveling posterior crowns. The edges of the crown surfaces that come into contact with food should be slightly rounded.
Monolithic Restorations
Solid or monolithic zirconia is favored for posterior crowns. The difference will be the zirconia state. Non-sintered zirconia, or green state, is soft, fragile, and moist. Pre-sintered is the process most manufacturers use. The pressed zirconia blocks are “sintered” at about 65% of the final sintering temperature. At this stage, the zirconia is still soft for milling and dry for easy shrinkage factor calculation. The pre-sintered zirconia state is more robust and has a predictable uptake of the coloring solution.
Recently, layering techniques have advanced creating zirconia crowns that are stronger due to the substructure. A layered crown does not chip or crack on the incisal surface of the tooth or the occlusal biting edge or the top of molars. The increased structural durability from pre-sintered or layered zirconia helps patients with a heavy bite, grind their teeth, or present a limited occlusal clearance.
Crowns using solid zirconia need an occlusal anatomy depth of 1.0 to 1.5 mm with functional cusp tips reduced by 1 to 1.5 mm and a 6° to 8° along the axial wall.
Chairside adjustments for zirconia crowns
Zirconia crowns may need marginal finishing when they are fitted. Using non-cutting, safe-end burs to finish will safeguard any soft tissue. Additionally avoid using too much cement, as it can create a place for plaque leading to sensitive teeth and even periodontal disease. Any roughness of the surface can be polished to an exceptionally smooth surface with a fine diamond bur. Do not use a heavy hand in the reduction or excessive heat. This can lead to micro-factures.
Non-suggested crown preparations
The factors that make tooth prep suboptimal for zirconia restorations.
- Undercuts
- Gutter preparation
- A 90° shoulder
- Parallel wall preparations
- Occlusal edges
- Sharp incisal
Be attentive to these situations, know the rules of zirconia crown prep, and follow them closely to avoid errors.
Why is tooth preparation for crowns important?
Proper zirconia crown horizontal and vertical preparation is crucial to a comfortable and correct prosthodontic fit. Precision fitting restorations, e.g., a zirconia dental crown, can impact how your patient’s mouth feels and operates, influencing their experience. It also affects the patient’s oral health. If an improper fit and excess cement are used, it can lead to issues. The wrong fit risks can include:
- Cavities and tooth decay
- Gum disease
- Core teeth fracture
- Tooth sensitivity
- Jaw pain
A zirconia crown prep done well will create a resilient crown and prevent complications. With modern technology and tools, there is no guesswork and fewer errors. Digital scanners aid in workflows providing a streamlined, user-friendly process that reduces the number of translations from impression to design.
There are definite advantages to digital dentistry. Contact Dandy to discuss how we can help you create an excellent patient experience.
Inspire more smiles with Dandy
Once you have all the information you need for a successful zirconia crown prep, you’ll be ready to send patients home with more beautiful smiles than ever. But if you’re still on the hunt for ways to improve patient experience, bolster your business output, and streamline every aspect of how you practice oral healthcare, then you need to meet Dandy as your next crown and bridge lab.
Dandy is pioneering digital dentistry and dental restoration, making it easier than ever for practices to get started. Our platform is the first of its kind, a complete dental lab that’s fully digital to bring the ease, convenience, and speed of the Internet to dentistry.
Ready to find out how you can save time and money by going digital? Meet Dandy today and learn more.
Sources:
International Journal of Oral Science. Surface roughness of zirconia for full-contour crowns after clinically simulated grinding and polishing. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5153586/
AVF Dental Group. Zirconia Crowns: Advantages and Disadvantages of Zirconia Crown. https://www.avfdentalgroup.com/zirconia-crown-advantages-and-disadvantages-of-zirconia-crown/#
International Journal of Dentistry. Three-Dimensional Accuracy of Digital Impression versus Conventional Method: Effect of Implant Angulation and Connection Type. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6008832/
Journal of Materials Research and Technology. Zirconia in dental prosthetics: A literature review. https://www.sciencedirect.com/science/article/pii/S2238785419300419#sec0040
Acero Crowns. How Many Times Can Posterior Crowns Be Replaced? https://www.acerocrowns.com/posterior-crowns
Science Direct. Influence of Preparation Design On the Quality of Tooth Preparation in Preclinical Dental Education. https://www.sciencedirect.com/science/article/pii/S1991790216300526#
Dentistry 33. Chamfer vs. Feather Edge for a Single Zirconia Crown https://www.dentistry33.com/clinical-cases/prosthodontics/318/chamfer-vs-feather-edge-for-a-single-zirconia-crowns.html#:~:text=To%20prepare%20a%20tooth%20for,finishing%20line%20(knows%20aschamfer).
European Journal of Oral Sciences. Effect of margin design on fracture load of zirconia crowns https://onlinelibrary.wiley.com/doi/full/10.1111/eos.12593
City Smiles of St. Louis. Does Your Crown Fit Right? https://www.citysmilesstlouis.com/blog/does-your-crown-fit-right/#
