Wikipedia has a good article on digital dentistry, or high tech dentistry – in which they go over the basics of many procedures that can take advantage of today’s digital capabilities.
Organization of this Chapter
You May Skip to Whatever Subject Interests You Now
Basics
Laser Dentistry
Bringing the Beam to the Tissue
Advantages and Disadvantages
Bottom Line for Lasers
CAD/CAM
The Milling Machine
In the Patient’s Mouth
Accuracy of CAD/CAM
Bottom Line for CAD/CAM
3D Printing
Bottom line for High Tech Dentistry
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High Tech Dentistry: Basics
If you recall from Chapter V.4 – the Rise of Adhesive Dentistry, the development of composite as a restorative material changed dentistry in a huge way.
Bonding with composite materials has allowed CAD/CAM technology to flourish, allows porcelain veneers, enables the entire field of cosmetic dentistry, AND lets a dentist fill the smallest lesions with sealants, and restore larger areas of missing tooth structure with composite instead of amalgam.
There ARE limits to the utility of composite, but this is mainly in terms of the size of the restorations that are reasonable to do with composite directly. There are few limits as to what composite materials and related technology will spin off into other areas.
We will review in more detail some of these spin-offs below.
High Tech Dentistry: Laser Dentistry
When I was a kid, lasers were a scientific novelty – and now you can get lasers in your key-fob!
One application of lasers has to do with the collimated beams that are produced – they are nothing like a flash-light. Everything from laser-sighting on guns, laser levelers for carpenters, laser printers to laser-based computer memory and many more things are based on this technology.
Another application of lasers has to do with the high amounts of energy that can be contained in a beam of light, when it is condensed in this way. We can weld with lasers, we an cut metal with lasers, and we can burn out decay and cut through tooth structure AND gingival tissue with lasers.
The effectiveness of lasers for putting energy into a substance depends on the amount of energy contained in the beam which has to do with the amplitude of the light wave, and the COLOR of the beam in relation to its target. The gum tissue, for instance, is pink because it absorbs bluish-green light and lets the complementary color bounce off so we can see it. If you use a bluish-green laser on gum tissue, it will be absorbed, transferring the energy of the light to the tissue, and this makes heat and will effectively CUT the gingival tissue, which is useful in several ways.
For dentin that has been invaded by decay-causing bacteria, there is a higher concentration of -OH groups in the substance. Low frequency laser beams beyond the visible spectrum past the red – infrared – can be absorbed by this material more than will enamel. These are effective in removing decayed structure with some selectivity.
Enamel can also be cut by lasers of the right frequency, but when the enamel has had many of its -OH groups replaced by fluoride, the cutting is not as efficient.
Bringing the Laser Beam to the Tissue
We can conduct some frequencies of laser light through flexible fiber-optic cords, with a tip that will allow the light to come out and impact whatever tissue is being treated. A simple handle allows the dentist to control well the position where the energy of the beam is deposited.
Longer infrared wavelengths may require a stiff hollow tube to conduct the light, so the device is a little more cumbersome.
It is important that the clinician manage the beam with great precision, so as to not damage any tissue unintentionally, and to make sure that the ENERGY of the beam is the lowest possible to get the job done. If a high energy is used in the beam it is possible that it will not just cut through tissue, but will carbonize it – damaging it to the point where healing cannot take place.
Also note, that this high-energy beam of light could do damage to your eyes, as the patient, and to the clinician’s eyes – so protective eyewear are always used by the dentist and the patient.
Advantages and Disadvantages
The major advantage is that tissues can be impacted selectively in the mouth. If the laser is selected correctly, decayed tissue can be cut out, gingiva can be cut back so impressions can be taken more accurately, excess gingival tissue can be removed, bacteria can be selectively killed in certain areas (even at a site of pulpal exposure, perhaps so that root canal therapy is not necessary – I’ve had this done in my mouth successfully), periodontal pockets can be cleaned and possibly even calculus removed, and sound tooth structure can be cut (within limits) to make a preparation for composite restoration.
Disadvantages include the fact that the beam ONLY cuts with its END! This is different from the use of cutting burs in a dental handpiece – where the SIDE of the bur is mostly used to create the appropriate shapes necessary in a tooth to permit restoration with various materials. There are only certain things that can be done with a laser because of the nature of the way energy is transferred to the hard or soft tissues.
Another disadvantage is that different lasers are required for different procedures, and if the dentist wants to do several different things, he’ll need several lasers, and they are expensive. He’ll have to recoup this cost, which is probably a lease fee to be paid every month, by charging for any procedure that utilizes the laser. It may be that the patient can have the work done for less cost with conventional methods.
While some dentists use lasers for decay removal and claim that less anesthesia is required, it is painless, or more conservative – that is debatable. If that is all they use for preparing the tooth, the form of the preparation cannot be made adequate for restoration with amalgam, and it is questionable, in my opinion, for restoration with composite. I prefer a dental bur for making ANY final preparation for ANY dental restorative material.
Bottom Line for Lasers
Probably the most advantageous use of lasers in dentistry is in soft-tissue removal. There are times when the dentist will have to cut down the side of the tooth deeply below the gingival level, either for a direct or indirect restoration. The tissue will be easily damaged when working in that area, and, while it will heal back, it will be bleeding during the procedure which has a chance to contaminate the restoration procedure. This is especially crucial for composite restorations.
When the dentist is doing indirect restorations with subgingival margins, taking an impression may be rather difficult due to excessive bleeding.
The laser, in each of these instances will allow the dentist to cut back the tissue in the area, giving better access, AND it will stop the bleeding as well. This makes for less possibility of a poor restoration to be done due to contamination, and makes impressions much easier.
One, relatively inexpensive, soft tissue laser is a good addition to any general dentistry office.
High Technology Dentistry: CAD/CAM
This technology has been somewhat described before as we covered various methods for making crowns. Let’s take a little more careful look at the subject.
The CAD and CAM terms refer to Computer Aided Design, and Computer Aided Machining. This technology is done in many areas, even for the making of signs using computer driven routers in a woodworking shop.
The Milling Machine
In dentistry it is only used for restoration of a tooth with porcelain or zirconia, solid ceramics. The “machining” part of the name refers to a milling machine that will cut the crown out of a block of porcelain inserted into the machine. This little machine is in the laboratory part of the dentist’s office. It uses very coarse diamond burs to cut out the crown, and the alignment of the bur with the block of porcelain is crucial to the accuracy of the result.
This is one of the problem areas with this method – the alignment. If we are to produce a restoration that fits the margins of the tooth preparation with no more than a 100 micrometer gap (.1 mm), we’d better have the alignment perfect. In fact, the dentist needs to LOVE his machine, and basically make a hobby of knowing everything there is to know to keep it in perfect condition. The technology is amazing, but only as effective as the operator, as usual.
On the other hand, there is the DESIGN part of the equation as well. In the computer there needs to be a precise digital description of what the crown should look like, so the milling machine can MAKE IT.
Now we need to look at what is happening in the patient’s mouth.
Since these restorations are made from ceramic, and ceramic is rather brittle, certainly compared with gold, the tooth needs to be reduced significantly both on the occlusal or biting surface and the side walls. AND, the preparation must not have any sharp angles, for three reasons. First, when ceramic is made to a sharp angle, it is far more likely to fracture – so the preparations are kept rounded internally. Second, with CAD/CAM technology, the impression is taken with an OPTICAL SCANNER, and this scanner needs to “SEE” every part of the preparation. Third, when the milling machine is making the crown, the bur that is used for cutting only has a rounded end.
This OPTICAL SCANNER is another amazing part of the technology. It is a camera with two lenses – so that the camera looks at the preparation from two directions and can create a 3 dimensional digital model of the preparation.
In order for the optical scanner to get a good DIGITAL IMPRESSION, it needs to see the margins well, and all of the walls around the tooth. So the preparation should have lots of taper, and the margins need to be readily seen and not obscured by the gingiva. Also, in order for the cameras to see the surface of the tooth preparation well, for some systems, the tooth is covered with a thin layer of a powder that reflects light well, so the cameras will get a very clear image. To get this powder to stay DRY all the way to the margins around the preparation is necessary – and can be clinically challenging. Cutting the gingival tissues back using a laser, coagulating any bleeding with a laser, and other specialized tissue retraction methods need to be used to get the best digital impression.
Once the digital impression is registered in the chair-side computer, the dentist can adjust the contact between a computer-generated crown and the adjacent tooth surfaces, which are also recorded, and with the opposing teeth, which are registered separately.
Then the final, “manually” adjusted digital crown file is sent to the milling machine in the other room.
As you can see, there are several areas where inaccuracies can arise – a poor impression due to contamination, a poorly cut preparation where the optical scanner cannot get every detail, and a poorly aligned milling machine that won’t cut a crown to match the digital model. But that, of course, is true for any methods used to make crowns – the skill and judgment of the provider determines the success of any method.
And – after the crown is made, it must be fired in an oven and glazed with porcelain and/or colorant to make it look more lifelike – because it is generally cut out from a perfectly uniform blank of ceramic (although expensive variable shade blanks are available). But – these days – there are labs that can make CAD/CAM crowns from zirconia blanks that are custom made for each patient. Only the largest labs can do this but it is a great service to their patients. The dentist simply emails the digital impression to the lab!
This is “conventional” CAD/CAM crown technology as it is carried out in many dental offices.
Accuracy of CAD/CAM
Studies that are done in the laboratory indicate that the method is CAPABLE of producing crowns with marginal gaps of as little as 50 microns, better than the maximum of 100 microns. On the other hand, these studies only work with the laboratory part, and don’t include errors that show up starting from the preparation stage.
Research studies suggest that this method CAN be done with acceptable results – at least the margins are good enough to minimize the gap and possibility of leakage and recurrent decay. Whether each dentist performs at that level is another matter.
My personal experience with CAD/CAM crowns has shown that even experienced clinicians can make errors in the method – as I had an open margin on one of mine so much that the gap could be seen on the X-ray. With a couple of years there was recurrent decay and the crown had to be replaced, with a conventional gold crown.
Another issue with CAD/CAM is the same issue that arises with any ceramic crown, the CEMENTATION. We need to use adhesive cementation methods, and sometimes this is the weak link. If the full technology that is available were to be used routinely, the results would be better – but often more abbreviated methods are used and the retention of these crowns is more questionable. I’ve had two CAD/CAM crowns fall out in my mouth due to poor cementation technique.
Bottom Line for CAD/CAM
Considering the potential for building an esthetic crown with variations in shade and apparent depth using this method, traditional hand methods for porcelain crown CAN be far superior. For the average situation the esthetics will probably be satisfactory, especially for the back teeth. For more complex cases with CAD/CAM the dentist will need to involve a large commercial laboratory.
The fact that the crown can be made immediately, not necessitating the wearing of a temporary crown for a few weeks, and not requiring a second visit, is a powerful appeal to many people.
When the clinician is skilled and takes every precaution there is no reason to expect that the crown cannot be made by this method with similar accuracy and success as a laboratory-made ceramic crown.
The amount of tooth reduction and the marginal discrepancies are distinctly less for gold crowns, especially partial coverage gold crowns with burnished margins. So, if longevity is the primary concern, and an esthetic gold crown can be made which is conversationally unobservable, there is a choice to make which may favor the gold crown.
High Technology Dentistry: 3D Printing in Dentistry
To the extent that the clinician can get a good digital impression of the tooth preparation, this is another way in which we can take advantage of that to make a crown – in this case even a gold crown.
Of course, we will not cut a gold crown with a milling machine! Can you imagine the amount of gold that would be wasted? But we can make the MODEL of the preparation from the optical digital impression. Some large laboratories even create a digital model by CAT scanning the rubber impression received from the dentist, and making a porcelain crown by CAD/CAM or a gold crown from a 3D printed die!
3D printing has become widely used in many fields, and has become more and more accurate over the last decade. The use of this technology to make a model of the tooth preparation, instead of using a conventional impression and pouring hard plaster into it has become commonplace.
What IS 3D printing? It is an ADDITIVE technology, as opposed to the milling machine above which is a subtractive technology.
The printer sections the digital file of the desired product into many thousands of layers, and builds these layers physically using an extremely fine tip which lays down some kind of plastic polymer, microscopic drop by drop. Can you believe even certain METALS can be laid down digitally, and used for dental crown components!
In the case of a crown, the printer knows the exact shape of the tooth as prepared in the patient’s mouth, and will duplicate the preparation in plastic. This plastic die can then be used by the technician to fabricate a traditional gold crown by making a wax pattern on the printed die. For ceramic crowns that will be fired in an oven, a polymer die will not be acceptable, but a CAM porcelain crown may be made that can be tested for fit onto the die.
AND – it is possible as well to make a “wax pattern”, from which a gold crown is cast, by 3D printing.
There is every indication now that the accuracy of a 3D printed die or pattern is adequate for dental applications.
Also, it is even possible to 3D print the temporary crowns, possibly in the dental office, and a laboratory may be able to 3D print a full denture!
Bottom Line for High Technology in Dentistry
We have yet to see the end of the rainbow as far as the application of modern digital techniques and lasers to dentistry.
It is clear that these methods offer significant advantages. But, as with many things, utilizing modern technology for something that can be done other ways may not always be the wise choice. And the benefits will ALWAYS depend on how much the dentist CARES to do good work.
We need to keep our feet on the ground as far as these methods, because, after all, it is the welfare of the patient that is the primary goal. Having a new toy to play with is fun for the dentist, but if it doesn’t make sense financially, in the practice, and it doesn’t offer the patient something tangible as an advantage – why do it?