Second Shadow Day with Dr. Shelley

Yesterday I was able to observe a fitting for an oral sleep appliance and more CEREC crown fittings. The crowns that I had seen previously were for decayed molars, however one patient on Wednesday needed a crown for the lateral incisor. Incisors are in the front which makes appearance even more important and have a very different shape than molars. The restoration also needed to fit onto a dental implant and abutment, which I will go into more detail about in my post tomorrow. This means that in order to create a crown with the CEREC, Dr. Shelley had to go through a few more steps.

During the acquisition phase of the CEREC when the omnicam is mapping out the patients mouth for a crown over remaining natural tooth it would only need lower jaw, upper jaw and buccal views. Implants need a gingiva mask view as well in order for the computer to map it out correctly. 

CEREC acquiring gingiva mask view of implant

After the three-dimensional model of the mouth is made, the doctor places a screw and a plastic cap on the implant so the computer software will recognize the cap and design a crown to go over it. The doctor can then change the contact and anatomy of the abutment and crown before milling it out. I thought it would be interesting to post a short video of the crown being milled out of the lithium disilicate block in the chamber. In the video below the milling machine has just begun to mill out the crown from the block. 

Another interesting step Dr. Shelley had to take with this patient has to do with the color of the surrounding teeth. Since the incisor is in the front, appearance is very important. The patient had a very unique blue and gray coloring which was difficult to match with the standard palette that the lithium disilicate blocks that the office has. So, Dr. Shelley is sending the restorations to a lab that has an artist who will match the color of the crown much closer to that of the patient's surrounding teeth. 

CAD/CAM Technology

CAD/CAM stands for computer-aided design/ computer-aided manufacturing. This technology is revolutionizing dental restrains because the overall process is more efficient for the dentist and the patient. On the down side, this technology is expensive, costing upwards of $100,000. Not to mention the expense to purchase blocks of crown material in a variety of different shades. However, its chair-side convenience makes it worth the price for dentists and patients. 

The specific machine that Arrowhead Lakes Dentistry owns is called the CEREC (Chairside Economical Restoration of Esthetic Ceramics). When a patient comes in needing a crown the dentist will first clean up the tooth, which is basically cleaning up the decayed or broken parts of the tooth. Next the dentist will use the CEREC omnicam to scan the patient's mouth around the problem tooth. 

CEREC Omnicam

The scan takes continuous photos and strings them together based on the background so it can create an accurate three-dimensional image on the computer pictured below. The dentist will continue scanning the area until the computer has gathered enough pictures to complete the three-demential replica of the patient's mouth. The dentist needs to complete this process three times for each of the sides of the tooth; the lingual, occlusal and facial surfaces. 

Lingual is the inside surface
Occlusal is the top surface
Facial is the outside surface

Once the model of the patient's mouth is complete the computer software creates a crown and fits it onto the problem tooth. The dentist can then manually adjust how the crown will contact neighboring teeth on all three surfaces. As pictured below, the image will have highlighted areas of the crown with corresponding colors for how much contact there will be. 

CEREC computer unit

Once the dentist is satisfied, the computer sends the image of the crown to the milling unit where the crown will physically be made. In the picture below, the milling chamber is the center panel. 

CEREC milling unit

A block of zirconia or lithium disilicate is placed inside and then milled into the shape of the crown using diamond infused drills and a lubricant substance. 

Unmilled blocks of lithium disilicate

Zoomed in photo of a crown being milled

It takes about 12-15 minutes for the crown to be shaped, depending on the complexity of the tooth shape. After the crown is milled, the dentist will do a preliminary fitting with the patient to ensure that it is the correct size. Then the crown goes into an oven so it can achieve its maximum strength. During this process lithium disilicate looses its purple color and becomes a shade that mimics a natural tooth. The crown is in the oven for about 12 minutes at more 575 degrees celsius. 

CEREC oven

Once the crown has cooled the dentist can permanently cement the crown into the patient's mouth and the procedure is completed. 

Shadow Day with Dr. Shelley and Dr. Fellner

Today I shadowed at Arrowhead Lakes Dentistry, which is conveniently right down the road from Midwestern University. I began the day observing Dr. Shelley's patients. He had a variety of different appointments scheduled such as consultations, cavity fillings, crown work and routine checkups. The first patient need cavities filled on the left mandibular cuspid (for reference I included a diagram with corresponding names below). Dr. Shelley administered two shots to numb the left side of the patient's mouth before beginning removing the decay from the tooth. Then Dr. Shelley primed the surface, where the decay used to be, and added a bonding agent before filling the space with composite resin. The resin was then light cured in order to harden. Dr. Shelley smoothed the surface to the point where the patient felt no rough surfaces. The next patient had a failed crown on the left mandibular 3rd molar. Usually this means the integrity of the crown or the cement was compromised rather than the natural tooth itself allowing for an easy re-cementation procedure to permanently fix the problem. However, this patient only had a minimal amount of natural tooth left because the rest was still cemented inside the crown. Eventually the patient will need a root canal, but due to the patient's current dental condition Dr. Shelley decided it would be more beneficial for the patient to have the crown re-cemented even though the failure probability is high. He hopes it will provide some function between now and the scheduled appointment for the root canal, which is the permanent solution. The really interesting procedure I witnessed today was with Dr. Fellner because he used the CAD/CAM technology to fit a crown. In a later post I will go into a more in depth description on how the CAD/CAM works, but essentially it allows for the dentist to upload a three-dimensional diagram of the patient's mouth onto a computer equipped with software that can fit a crown for the problem tooth. The doctor can then make additional adjustment to the computer's suggestion. To get the actual crown the three-dimensional image is sent to the milling machine that takes a block of zirconia or lithium disilicate and shapes it to match the exact image created on the computer. After manually fitting the crown and making any additional adjustment it is baked in an oven to reach its maximum strength, then cemented into the patient's mouth. Typically, a crown fitting would take about a week and two different appointments because the initial mold would have to be taken and sent to a lab that has the capacities to make the crown, while the dentist fit the patient with a temporary crown in the mean time, then once the permanent crown comes in the dentist must remove the temporary crown and cement the permanent one. This is why the CAD/CAM technology is so fantastic! It can all be completed in one appointment with less moving parts. Overall, it was a really fun day and I learned so much about CAD/CAM technology in private practice.

Diagram of the Human Mouth

Week 5

This week I met with Dr. Kramer and set a meeting for next Tuesday to exchange the sources he had access to in Midwestern's library. I am really excited to continue working on my chart and filling in all the blank spaces. We also went over what each of the categories meant again and key words to look for to make it easier to pick out the information that I need specifically for my chart.  A few weeks ago I met another dentist who said he would love to have me shadow. His name is Dr. Folson and he specializes in periodontics and implants. I have already scheduled a time to shadow him next Thursday and I am so excited. I cannot wait to learn about dental implant surgery.

The Layers of a Restoration

Today when I met with Dr. Kramer we went over all of the general steps that have to be completed in order for a dental restoration to be successful. He a drew diagram for me so I could better understand how everything worked together as well as how those steps should be categorized into my chart for my research, so I thought I should share it.

The first layer is the crown, in this case it is zirconia, which would already be polished, shaped and fitted for the patients mouth before it is cemented. The next layer is the intaglio surface, the interior area of the zirconia crown. Part of my research is finding the most accepted and successful method to prepare the intaglio because at the moment there are a variety of approaches. Next, there is an optional step, the intaglio primer, which is typically a substance with a phosphate group base that enhances bonding with the surrounding layers. After is the cement which is the main bonding factor of the restoration. As I explained in a previous post "Cement Types", there are different types of cements which can change whether or not an the next layer, an etch layer, exists. For example, if a self-etching resin cement is used, then there is no need to etch the surface again. The final surface is the prepared tooth, or natural tooth. There are several ways to prepare the natural tooth for a restoration, which is why I am also researching the best protocol for preparing the natural tooth.

Top layer: Zirconia crown
Top blue layer: Intaglio surface
Green layer: Intaglio primer
Middle white layer: Cement
Pink layer: Etch
Bottom blue layer: Prepared tooth

Week 4

Last week I mentioned I would be making a chart that would organize my sources in order to make analyzing and comparing them easier. While it is still a work in progress, I have provided the link below to my Google sheet for anyone who is interested. For many of the sources, I have to wait for my next meeting with Dr. Kramer so I can get access to the full article for information like how the intaglio surface was prepared or what kind of etch was used. However, the abstracts of the articles do provide some of important information that I can use for my chart like what type of zirconia was used and what the results of the experiment were. I cannot wait to go over my chart with Dr. Kramer!

https://docs.google.com/spreadsheets/d/1UgR6Zo6ekmxPgEy_mbgAeCdgbhPnZg_dtK_bfNbEzko/edit?usp=sharing

New Vocabulary

As I have read through dental journals, I have often had to look up specific terms and phrases that I did not understand. I would like to share the definitions of some because they may show up in my blog and it would be helpful to have something to reference.

A systematic review is a literature review that compiles and studies various research papers. A meta-analysis is a statistical procedure for combining data from multiple studies. The difference between them is that systematic review answers a defined research question that summarizes all empirical evidence while meta-analysis is a statistical method to summarize results of studies.

In vitro means the study or experiment was done in a controlled environment outside of a living organism while in vivo, which means "within the living", is a study or experiment preformed using the whole organism.

A few abbreviations I had to get used to include: CAD/CAM, which is computer-aided design/computer-aided manufacturing and FPD, which means fixed partial denture.

More definitions to come!