Since they were first introduced, dental crowns made from zirconia have become an increasingly popular option among the patients who need them and the prosthodontists who install them. Prized for their translucency, durability, and customizability, they represent not only the present of dental crowns but also the future.
If you’re a dental professional looking for a complete step-by-step guide to zirconia crown prep, look no further! You might also be interested in understanding the advantages and disadvantages of zirconia crowns compared to other materials, which we dive into here.
The prep process for zirconia crowns is similar to the process for a wide range of crown materials. While it can be a complicated procedure and requires careful precision, knowing the steps involved in a crown restoration—and the innovative tools that could help—can allow you to install a crown that lasts longer and promotes your patient’s overall health.
Patient Assessment and Impressions
Before prepping a patient’s teeth for zirconia crowns or other types of crowns, you’ll need to complete a number of assessments. This may include the type of crown needed, the location of the crown, the patient’s overall aesthetic goals (which is largely dependent if the crown is for an anterior or posterior tooth), and the health of their existing teeth.
In addition, you’ll need to take impressions of the patient’s teeth. Traditionally, the method for capturing impressions has involved the usage of trays and putty to map the contours of a patient’s teeth. However, this method can be an imprecise and time-consuming process with several steps:
- Taking impressions with PVS molds
- Creating stone models
- Shipping the models to a lab
Once the models are at a dental laboratory, you’ll also need to wait for them to complete the following:
- Scanning the models
- Designing the crown
- Printing or milling new models for fit
- Sending the crown to your office
On average, this might take somewhere between 12 to 15 days to complete.
The Digital Solution for Patient Assessment
Fortunately, innovative technology can make the prep process much smoother from the start. Today, intraoral scanners enable dentists to create highly accurate digital impressions within minutes. If you offer digital impressions in lieu of the analog method, your patients can benefit from more accurate crown prep and a faster process overall, often reducing the turnaround time to an average of 5 to 8 days.
With digital tools at your disposal, the process typically goes as follows:
- Perform the intraoral scan on the patient
- The digital scan is immediately and electronically sent to the lab
- With a digital impression, the dental lab can design and produce the crown more accurately
- The lab sends the crown to your office that will fit on the first fitting appointment
Best of all, intraoral scanners are multi-use. They can cover the denture process, orthodontic appointments, implants, and more.
Prepping the Tooth Structure for a Zirconia Crown
The process of zirconia crown prep will vary depending on the location of the natural tooth receiving the crown. Although there is some overlap, the guidelines and specific measurements for things like incisal reduction and clearance are altered according to whether the crown is located:
- In the anterior region of the mouth, or
- In the posterior region
While this process can be complex, those using intraoral scanners may benefit from the advantages of digital modeling—enabling them to closely evaluate and easily plan out the prep process before it takes place.
Zirconia Crown Prep for Anterior Crowns
Anterior crowns require extra attention to aesthetic considerations. That’s because they are located at the front of the mouth, and are therefore likely to be visible when the patient smiles, eats, or speaks.
For that reason, zirconia crown prep at the anterior of the mouth means paying close attention to the following elements:
- Clearance – When performing anterior zirconia crown prep, clearance is very important. You’ll need to 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 either 1 to 1.5 mm or 1.8 to 2.0 mm.
- Circumferential chamfer – The circumferential chamfer should be visible and continuous. At the gingival margin, you’ll need a reduction of at least 0.5mm.
Additionally, proper zirconia crown prep for anterior crowns includes prepping the tooth structure with an angle of approximately 5°, with no beveling. Be sure to round each incisal edge. You can use a football diamond to reduce the side of the crown that faces the tongue so that it is 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
In some situations, you may need to perform a monolithic crown restoration using solid zirconia dental crowns.
Solid or monolithic zirconia is well-suited to posterior crowns due to its increased durability and strength and may be an especially wise choice for patients who:
- Grind or gnash their teeth
- Have a heavy bite
- Present limited occlusal clearance
Crowns that use solid zirconia need an occlusal depth of 1.0 to 1.5 mm. Additionally, the cusp tips should be reduced by 1 to 1.5 mm with a taper of 6° to 8° along the axial wall.
Unacceptable Crown Preparations
Certain factors can make a crown prep ineligible for a zirconia crown. Knowing the rules of zirconia crown prep and following them closely can help you avoid errors that disqualify a prep, like:
- Undercuts
- Gutter preparation
- A 90° shoulder
- Parallel wall preparations
- Occlusal edges
- Sharp incisal
By being attentive to these situations, you’ll be better able to provide better-suited options for your patient’s specific circumstances.
The Advantages of Digital Crown Prep
Whether you’re prepping an anterior or posterior crown, digital intraoral scanners make it possible to quickly scan both the original and prepped tooth. From there, lab software copies the preexisting anatomy to produce a picture-perfect copy of the original tooth. Having a 1-to-1 copy eliminates much of the headache associated with tooth prep.
In addition to improving preoperative workflows, digital scanners can also optimize dental implant workflows. With digital scans, you can use a scan body or implant-positioning transfer device to determine the exact location of the implant. This can reduce errors and the frequency of retakes, helping to both streamline your process and reduce total patient chair time.
Why Is Tooth Preparation Important?
Proper zirconia crown prep is crucial to a prosthodontic that fits comfortably and correctly. For obvious reasons, comfort is paramount when it comes to improving patient experience. If they leave your office with minimal pain and discomfort, patients are more likely to view their experience in a positive light.
But the fit of a zirconia dental crown can have ramifications beyond how it feels in your patient’s mouth. Your patient’s oral health is also affected. When you’re diligent about zirconia crown prep, you’re better able to install a finished crown that fits well and dodge the oral health risks of an ill-fitting crown. Those risks can include:
- Cavities and tooth decay
- Gum disease
- Teeth fracture
- Jaw pain
There’s also evidence to suggest that adequate zirconia crown prep may help improve crown longevity by staving off complications that arise from biological health factors. According to some studies, improper preparation may contribute to crown failures in the face of tooth decay and other periodontal diseases.
While analog methods may have been adequate in the past, modern technology has rendered them obsolete. They simply relied too much on guesswork and trial and error. Not to mention the various translations within the impression process that can expose even the best dentists to potential errors.
Digital workflows have changed that, providing a streamlined, user-friendly process that can reduce the number of translations from impression to design—thus leaving fewer opportunities for an issue to occur.
Put simply, these tools can improve every aspect of the crown prep process.
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:
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#City Smiles of St. Louis. Does Your Crown Fit Right? https://www.citysmilesstlouis.com/blog/does-your-crown-fit-right/#
