Photo Essay: Ensuring Adequate Reduction with the Reverse Preparation Technique
Chairside Magazine: Volume 10, Issue 3
As I mentioned in the Editor’s Letter, an inadequate amount of reduction on crown and bridge preparations continues to be the biggest challenge faced by all of the U.S. dental laboratories that I communicate with regularly. In this case, I get to utilize the Reverse Preparation Technique on one of the crowns, but not on the other because the tooth was previously prepared. While working on a previously prepared tooth seems easier because some of the reduction has already been done, I know I have more control using the Reverse Prep Technique, where I always know exactly how much tooth I have removed. I am doing BruxZir® Anterior crowns on teeth #8 and #9; it will be interesting to see how they blend with the surrounding natural dentition.
Figure 1: Following my own advice, I am taking the shade before I do anything else to ensure that the teeth have no chance of dehydrating. When teeth dehydrate, they appear to be higher in value than they actually are. I am using the VITA Easyshade® Compact (VITA Zahnfabrik; Bad Säckingen, Germany) to determine the shades on the adjacent teeth. Typically, I try to position the tip of the device in the middle third of the tooth, avoiding the increased chroma in the gingival third and the increased translucency in the incisal third.
Figure 2: This case does a good job of illustrating why I like the VITA 3D-Master® shade guide better than the VITA® Classical shade guide (VITA Zahnfabrik). Notice that on tooth #7, the VITA Easyshade Compact is telling me that the closest Classical shade is A2, while the closest 3D-Master shade is 2.5R2. It will soon be evident why it’s helpful that the VITA Easyshade Compact takes both shades simultaneously.
Figure 3: While the VITA Easyshade Compact has a relatively short learning curve, the first step in using it successfully is understanding how to maximize the surface area of the tip that is in contact with the tooth surface. As the facial surfaces of anterior teeth are rarely flat, the tip will not fit completely flush against the tooth structure. I always have a finger ready to stabilize the tip and allow me to make slight rotations so that most of the tip comes in contact with the tooth.
Figure 4: The shade reading from the middle third of tooth #10 also is an A2 on the Classical guide, but a 2R2 on the 3D-Master guide. Because of the considerable jumps between adjacent shades in the Classical system, many teeth that register as Classical A2s can be more accurately classified within the 3D-Master system. (View the “Modern Shade Taking Methods for Enhanced Lab Communication” video here for an in-depth explanation of this.)
Figure 5: This is the shade taken from tooth #8, the natural tooth that I will be prepping. Again, the measurement from the middle third of the tooth gives us an A2 reading on the Classical scale, while the 3D-Master shade registers as a 2M2.5. That’s three different 3D-Master shades that are being called an A2 by the Classical system. In an instance such as this, I can assure you that our technicians can make a closer shade match with a 3D-Master shade.
Figure 6: The VITA 3D-Master Linearguide is definitely my shade guide of choice today. Because my three shade choices are all in the “2” family, I remove the 2 shade guide and check to see how these shades compare to the natural adjacent teeth. Even if teeth #7, #8 and #10 are all different shades, we will have to make some compromises because #8 and #9 have to be identical to avoid asymmetry.
Figure 7: I decide on 2M2.5 as my final shade for the BruxZir Anterior crowns on #8 and #9. Shade 2M2.5 is made by mixing 2M2 and 2M3 in equal amounts, something not possible in the Classical system (there is no such thing as A2.5). Even if the lab uses an A2 shade in the material you request, they will have the 2M2.5 shade tab to help with characterization before it leaves the lab. This is why 3D-Master shades work better, even if you request a material that is only available in VITA Classical shades.
Figure 8: Correctly selecting the closest shade is half the battle. No shade matches a tooth perfectly, so it is incredibly helpful to the dental technician if you take and include a digital photograph of the selected shade tab next to the tooth you are matching. There is no easier way to immediately improve your esthetic results than to email some digital shade pictures with your case. Technicians simply try harder when you give them a road map to follow.
Figure 9: Now, I am placing the PFG gel (Steven’s Pharmacy; Costa Mesa, Calif.), an important first step in giving a pain-free injection. Placing the gel with an Ultradent syringe makes it easier to “sneak” some of the anesthetic into the sulcus, so that the patient does not feel the insertion of the needle through the attachment. After 60 seconds, we wash the PFG gel off #8 and #9 and begin the injection.
Figure 10: Part of the advantage of using The Wand® Computer Assisted Anesthesia System, formerly the STA® (Single Tooth Anesthesia) System (Milestone Scientific; Livingston, N.J.), is not having to give painful infiltrations right under a patient’s nose. The handpiece allows me to predictably get pulpal anesthesia with a pain-free PDL injection. I slide the 30-gauge extra short needle into the sulcus without going through the attachment. I step on the unit’s foot pedal and give a few drops of Septocaine into the sulcus prior to going through the attachment. I honestly don’t know if this helps in any way, but I know it doesn’t hurt, and it makes me feel better. Once I give the few drops, I continue to express the Septocaine while the needle tip is advanced through the attachment until it reaches the crest of the bone.
Figure 11: Because of the pressure that is generated with any PDL injection, if you move the needle to reposition it, anesthetic that we don’t want the patient to taste will squirt out. Likewise, when we finish the injection and remove the needle, anesthetic will also squirt out. My assistant places a saliva ejector next to the insertion point to make sure that when the anesthetic spills out, she is able to control it. A cotton roll placed next to the needle tip can serve the same purpose.
Figure 12: Another benefit of The Wand Computer Assisted Anesthesia System is the nature of the syringe itself. In order to inject with a typical syringe, the thumb, index and middle fingers must be in predetermined positions to generate the force to express the anesthetic. With this system, you are able to grasp the syringe anywhere, so I typically hold it much closer to the tip. This gives me a greater degree of control and assists me in rolling the syringe if I need to reorient the bevel.
Figure 13: The fastest way I’ve found to remove an existing PFM is to use an aggressive carbide like the Razor® Carbide bur (Axis Dental; Coppell, Texas). This bur easily cuts through the ceramic material and the metal substructure. In the past, I would use an old diamond to cut though the porcelain material and would then switch to a carbide to cut through the metal substructure. The Razor Carbide does the job of both these burs and can be used with a light touch when cutting through the metal, so as not to inadvertently damage the tooth underneath.
Figure 14: Once the prep is exposed, I use a Christensen Crown Remover (Hu-Friedy; Chicago, Ill.) to loosen the crown. You will notice that I do not cut through the metal coping at the gingival margin. Too often when I try to cut through that last strap of metal, I inadvertently tear up the facial tissue in the one area where I would like to have really healthy tissue. Using the Christensen Crown Remover, I can usually rock the crown loose without having to cut through the last strip of metal.
Figure 15: Now that the crown on tooth #9 has been removed, we can start prepping tooth #8. Because this tooth has not yet been prepared, I am able to take advantage of the Reverse Preparation Technique. The mesial contact is already broken from when I removed the adjacent crown, so I now break the distal contact with a #55 bur as you can see here. The reason we break the contacts first is because this technique requires the first retraction cord to be placed immediately.
Figure 16: The first cord I use is an Ultrapak® cord #00 (Ultradent; South Jordan, Utah). This is a plain cord that has not been soaked in any medicaments, and I literally floss it into place on the mesial and distal as though it were dental floss. With the two interproximal portions of the cord locked into place, I now pack the facial segment into the sulcus.
Figure 17: On the lingual, I cut the two ends of the retraction cord so they will butt up against each other, as I do not want them to overlap. Because this #00 cord is hollow, it packs very easily into the sulcus; I have yet to find a sulcus that it will not fit into. It is important to make sure that none of this cord is visible supragingival because in addition to not providing vertical retraction, there would be a chance the bur could catch it while prepping.
Figure 18: The preexisting crown on tooth #9 has irritated the gingiva, so before I try to pack a #00 cord around this tooth, I do a preemptive strike with some ViscoStat® Clear (Ultradent). This is a 25 percent aluminum chloride gel, so it will not discolor either the gingival tissue or the prep itself. Even when there is no bleeding, I often use ViscoStat Clear in the anterior to “pre-seal” the capillaries before I pack the cord.
Figure 19: I take a look with the mirror and can see some of the #00 cord peeking out from under the tissue. Now that the rest of the retraction cord is in place, it is often easier to get any difficult-to-pack segments subgingival. Not having the #00 cord subgingival also presents problems later in the pre-preparation technique when we place the #2E cord on top of this cord. It is imperative that when the #2E cord is placed it does not get underneath the #00 cord; otherwise, when we pull out the top cord, the bottom cord will come out as well, which will lead to bleeding right before we take the impression.
Figure 20: The #00 bottom cord provides about 0.5 mm of vertical retraction of the tissue. This retraction allows us to prep the gingival margin right at the free margin of the gingiva, knowing that when the #00 cord is removed, we will end up with a margin that is slightly subgingival. Even though we have many esthetic choices for anterior crowns, I still prefer to hide my margin just slightly subgingival.
Figure 21: I use the 801-021 round diamond bur from the Reverse Preparation Kit (Axis Dental) to cut a half-circle into the gingival third of the tooth. This half-circle is the formation for the perfect margin. After we do the axial reduction, we will be left with a perfect quarter-circle, which will end up being our deep chamfer or shallow shoulder. Not only do we end up with a simple, nearly perfect margin, but we also ensure that we reduce enough in the gingival third, an area that is typically under-reduced.
Figure 22: I then take the 801-021 round diamond bur and trace it around the gingival margin on the lingual as well. BruxZir crowns work with feather-edge margins, so I don’t necessarily have to do this, but because most of our dentists would use IPS e.max® (Ivoclar Vivadent; Amherst, N.Y.) in a situation like this, this ends up being a great margin for either restoration. As this round bur is typically too large to fit interproximally, I take the bur from mesial contact to distal contact. I will connect the facial and lingual round bur cuts later with an 856-025 diamond (Axis Dental).
Figure 23: I make my first depth cut to ensure adequate incisal reduction. I use the MADC-020 bur (Axis Dental) to place 2 mm depth cuts into the incisal edge of tooth #8. This 2 mm of reduction will give the technician a good opportunity to build an esthetic, strong incisal edge. It also helps to keep the final restoration from being too far to the facial, aka too “bucky.” However, if you are planning on adding some length to the central — 0.5 mm, for example — you only need to reduce 1.5 mm to give your technician 2 mm of space.
Figure 24: I now switch to the MADC-015 bur (Axis Dental), which gives me a self-limiting depth cut of 1.5 mm. I turn the handpiece so that it is perpendicular to the facial surface of the tooth and place a 1.5 mm depth cut at the junction of the incisal and middle thirds. The placement of this depth cut ensures that there will be enough facial reduction to enable the technician to create a flat facial profile on the final crown. When crowns are too “fat” facially, they will never blend in naturally with the surrounding natural dentition.
Figure 25: At this point, all of the depth cuts are in place. We can see the half-circle in the gingival third that is approximately 1 mm deep. The 1.5 mm depth cut is at the junction of the incisal third and the middle third, and the 2 mm depth cuts in the incisal edge are there as well. The beauty of these depth cuts is that there is no guessing whether we have reduced enough — we simply prep until the depth cuts are no longer present. Once you break through the enamel surface with a diamond, it becomes very difficult to judge how much you have reduced. I haven’t found an easier way to prep teeth than with depth cuts.
Figure 26: It’s now time to connect all the depth cuts with the workhorse bur in the Reverse Preparation Kit: the 856-025 bur. I love prepping with this large bur because it cuts very smoothly and does not have a tendency to dip into the tooth, even if you have buildup material on the tooth. As shown here, the reduction is already finished in the gingival third, so we are working on reducing the incisal and middle thirds and blending these planes together.
Figure 27: This is also the time when we need to blend our facial reduction with the interproximal reduction that was started with the #55 bur. Because tooth #9 has already been prepped, we were able to use the round bur interproximally on the mesial, which we usually cannot do. A glance back at Figure 25 shows that round bur cut on the mesial of tooth #8. Because tooth #9 is already prepped, we are also able to take the 856-025 bur onto the mesial surface. Typically, we have to switch to the 856-016 bur (Axis Dental) to do this, which is the same shape, but has a smaller diameter.
Figure 28: The reduction on the lingual surface is accomplished with an Alpen® 379-023 football bur (Coltène/Whaledent Inc.; Cuyahoga Falls, Ohio). I typically do not place a depth cut on the lingual surface of anterior teeth because I find it easy to have the patient close and check the reduction against the lower anterior teeth. On posterior teeth, eyeballing occlusal reduction is very difficult (especially on lingual cusps), but I don’t have this same problem on maxillary anterior teeth. Of course, if you wanted to place a 1 mm depth cut on the lingual, there would be nothing wrong with that.
Figure 29: Toward the end of the preparation sequence, when most of the gross reduction has been done, I need to be able to visualize what I am doing at the margin. I turn off the water to my KaVo ELECTROtorque handpiece (KaVo Dental; Charlotte, N.C.), turn the speed down to around 3,000 rpm, and slowly take my 856-025 bur back and forth across the margin, smoothing it out. With the water off, I can see everything I am doing, and by turning the rpm down low, I can keep from overheating the tooth. Being able to run a handpiece at low speeds with no water and high torque is the No. 1 reason I insist on using electric handpieces.
Figure 30: Using Seek® Caries Indicator (Ultradent), I notice we still have some decay on the mesial of tooth #8, so I remove that now with a small round bur. I find it easier to remove any remaining caries at the end of the preparation sequence rather than at the beginning, mainly for better access to the lesion itself, but also because I find I can do a better job with the bonding steps with better access.
Figure 31: I have intact tooth structure on all sides of the carious lesion, so I have a high degree of confidence about the retention of this small composite filler I am doing to restore this. Vertise™ Flow (Kerr Corp.; Orange, Calif.) is a self-etching flowable composite that is perfect for small situations like this. Because it is a self-etching product, there is no etch step separate from the bond step. Vertise Flow also works very well for small Class I restorations, sealants, preventive resin restorations, and quick little buildups like this one.
Figure 32: Next, we syringe an initial layer of Vertise Flow into the preparation. As previously mentioned, this composite contains a self-etching bonding agent and is activated by using a disposable brush as shown here to burnish the material into the dentin for 20 seconds. In reality, you end up removing most of the first layer from the prep while doing this, but the point is to get a very thin layer in close contact with the dentin.
Figure 33: Here, we are light-curing the initial layer of Vertise Flow for 20 seconds. The light curing actually stops the self-etching of the dentin that was taking place. Now that we have that layer bonded to the dentin, we can add 2 mm layers of Vertise Flow, curing for 20 seconds between each increment. As we are just bonding composite to composite at this point, there is no need to use the brush or agitate the material any more. The process is simply to add some material, light-cure and repeat. Most flowables won’t support their own weight, so you are better off placing smaller increments.
Figure 34: I always slightly overbuild these types of small buildups, or fillers. I want to be able to prep it back flush against the natural tooth, so that I don’t leave an undercut in the tooth. We receive far too many maxillary anterior impressions at the lab with multiple undercuts in the teeth where direct composites used to be. Not only does this cause the impression to distort, but it also creates weakened dies. It is my hope that a simplified buildup technique like this one with Vertise Flow will help more dentists invest the time needed to place and charge for these buildups.
Figure 35: The next step of the Reverse Preparation Technique is to place the top cord, the #2E Ultrapak cord (Ultradent). The “2” in the cord’s name refers to its size, while “E” refers to it being an epi cord. I know there may be some controversy with the use of epinephrine, but my experience has always been that if a patient can tolerate epinephrine in a local anesthetic injection, then they can tolerate it in the retraction cord. If a patient requires a non-epi vasoconstrictor in their anesthetic, epi cord would not be an option.
Figure 36: Packing this second cord, or top cord, is more difficult for a number of reasons. You can’t floss it into place interproximally like you can with the first cord because doing so would disrupt the bottom cord, which we want to stay firmly planted at the base of the sulcus. Also, even though this cord is hollow, it can be hard to pack in certain clinical situations where there is minimal attached gingiva. Because of this, on some maxillary bicupids and lower anteriors, I will use a smaller #1E cord instead. In extreme cases, a cordless technique with Access® Edge gingival retraction paste (Centrix; Shelton, Conn.) can be used in place of the top cord.
Figure 37: Once the top cord is in place, you get one last look at your margin. In this case, I am not entirely happy with what I see. I can see that the shape of my margin does not match the contour of the gingiva. The margin is not as smooth as it could be, but keep in mind that it was prepped with a super-coarse 856-025 bur. This bur is fantastic for quick tooth reduction, but because of the size of the diamond particles, it leaves little chips in the margin. At this point, I switch to my fine-grit 856-025 bur with the red stripe to get rid of that choppiness in the marginal surface.
Figure 38: The margin has now been recontoured with the 856-025 fine bur. Again, the speed can be turned down to 2,000 rpm to avoid overheating the tooth. In my experience, I can clearly visualize the margin only if I turn the water off to see what I am doing. Now that I have dropped the prep margin down to the gingival margin with both cords in place, the resulting facial margin will be approximately 1 mm subgingival. I typically do this in cases with a dark prep shade to keep the dark shade from showing through.
Figure 39: Now we place two ROEKO Comprecap Anatomic compression caps (Coltène/Whaledent) onto the preps, and the patient bites down for 8–10 minutes. This time frame is really not negotiable, as these compression caps really work wonders if given enough time. Because they are “anatomic,” there is a cutout on the mesial and distal of each cap to prevent the interproximal papillae from getting blunted. We moisten the inside of the Comprecaps before placing them on the teeth so that when we remove them, we don’t have cotton fibers sticking to the prep. Comprecaps are a great way to prevent bleeding during the impression process.
Figure 40: After waiting 8–10 minutes, we remove both the Comprecaps and the top cord from the sulcus. We can expect no bleeding nearly all of the time thanks to the attention we have given the gingiva throughout the prep sequence. When you add in the epi strand in the top cord and the pressure hemostasis from the Comprecaps, it should not be surprising that there is no bleeding at this stage. Quality restorative dentistry is more dependent on a great impression than a great preparation, so this is the moment of truth!
Figure 41: The bottom cord provides the vertical retraction of the tissue, while the top cord provides the lateral retraction that creates the space for the impression material to flow into. It is imperative that we get a nice thickness to the marginal impression material, or it has a tendency to tear when the impression is removed. Keep in mind that the impression material is in contact with the #00 cord in the base of the sulcus, and the cord is preventing bleeding by remaining in place against the inflamed base of the sulcus.
Figure 42: When you remove the top cord after 8–10 minutes, you will find a wide-open sulcus in which to place the impression material. It is not the type of situation where you are racing against gingival blood flowing into the sulcus. Take your time and make sure to go around each tooth three or four times to prevent any pulls or voids in the material. These pulls and voids are especially difficult when you get back to the point where you started expressing the material. I have watched slow-motion footage of moisture being pushed around the sulcus in front of the material and creating a pull when the syringe tip gets back to the starting point, hence the recommendation to go around each tooth three or four times with the tip in the sulcus.
Figure 43: Here, I am using a custom impression tray. I never used a custom tray for two single anterior crowns in the past, so I admit this is overkill (perhaps I am a little spoiled by working within a lab), but I can confidently say that if you got them for free and they were always available, you would use them, too! In a case like this, it is perfectly acceptable to use an anterior double-arch tray for this impression. The biggest challenge when using anterior double-arch trays is being able to see whether the patient is in maximum intercuspation. Always hold the impression up to the light to verify that the un-prepped teeth are in contact.
Figure 44: When removing a vinyl polysiloxane impression from the mouth, do it gently with a slight rocking motion. This cord technique gives us a deep subgingival impression of the root structure, so we want to make sure we give the material the chance to stretch and pull the bottom cord off the sulcus if it is attached to it. This is the opposite of an alginate impression, which should be removed with a sudden snapping motion. One of the benefits of silicon impression materials is their ability to set in an undercut and be removed without tearing, so give it a chance to release.
Figure 45: Because I’m not using a double-arch tray, I have to take a bite registration so that the lab will be able to articulate the models. In reality, with full upper and lower models, it would be pretty easy for the lab to hand-articulate the models and verify with wear facets, but the use of a bite registration does a good job of verifying the mounting. A properly done bite registration should only contact the incisal third of the teeth that have been prepped, and the incisal third of the opposing teeth. It will be trimmed back in the lab, but try to keep the registration material off the soft tissue.
Figure 46: It has been five days, the temporaries have been removed, and the preps cleaned with Consepsis® (Ultradent). The more I shorten the time between prepping and seating, the fewer adjustments and the lower remakes I have. The best example of this is same-day restorations and their almost nonexistent remake rate. My hope is that as digital impressions continue to make inroads into more dental offices, three-day turnarounds will become the standard for model-less monolithic crowns. The temporary crown is the biggest source of error and movement in the crown fabrication timeline, and the less time it’s in the mouth, the better the chance the crown will drop into place with no adjustments.
Figure 47: The BruxZir Anterior crowns fit well and the patient has approved them, so it’s time to start the cementation procedure. The more I work with BruxZir restorations, the more familiar I become with some of their unique properties, which hold true for all zirconia-based restorations. Zirconia crowns are susceptible to salivary contamination when they are tried in the mouth, which is something that doesn’t affect any other crowns to any great degree. The only materials that bond reliably to zirconia oxide are phosphate groups. The phospholipids in saliva bond to the internal surfaces of zirconia-based restorations, so if you simply rinse them out with water as I am doing here, you remove the visible saliva, but the phosphate groups remain bonded to the zirconia surface.
Figure 48: Fortunately, Ivoclean™ (Ivoclar Vivadent) was released specifically for the purpose of cleaning out restorations prior to bonding or cementation. I place a couple drops in both of the crowns that will stay in place for 20 seconds. Ivoclean is a concentrated zirconia-oxide solution. When placed in crowns, it sets up a concentration gradient so that the salivary phosphate groups bonded to the inside of the crowns are drawn across the gradient to the zirconia particles in the Ivoclean, which can then be rinsed away.
Figure 49: I use a microbrush to ensure that the Ivoclean is evenly distributed and has come in contact with all of the internal surfaces of the crowns, although it is not necessary to agitate it against the surface as we might do with a self-etching resin material. We just want to ensure that the purple Ivoclean material is coating the entire internal surface of the crown; then, after 20 seconds, it can be rinsed out.
Figure 50: Ironically, perhaps the worst thing you can do to clean out zirconia-based crowns after try-in is to use phosphoric acid. As you might imagine, phosphoric acid is full of phosphate groups, and in your attempt to clean the salivary phosphate groups still bonded to the zirconia, you will flood the area with phosphates from the phosphoric acid and occupy every receptor site on the zirconia. It is only by flooding the crowns with zirconia oxide that we can decontaminate the internal surfaces in preparation for cementation.
Figure 51: Now that we have freed up the bonding sites on the zirconia with the Ivoclean, there is no better way to cement a BruxZir crown than with a cement that contains the same phosphate groups that bond to zirconia. That cement is Ceramir® (Doxa Dental Inc.; Newport Beach, Calif.). Here, I am activating the Ceramir capsule in the activator by holding the handle down for three seconds.
Figure 52: It’s a good thing I didn’t get rid of my triturator! Next, I place the Ceramir capsule in the 3M™ ESPE™ RotoMix™ capsule mixer (St. Paul, Minn.) for 10 seconds to ensure a complete mix. I know this method of dispensing this cement seems a little 1980s compared to modern paste-paste cements, but I find it to be well worth the little bit of extra effort. Just the ease of cleanup alone makes Ceramir a no-brainer for me. Unlike most resin-modified glass ionomer cements, Ceramir has a “putty” stage that allows you to peel it all off in one piece. My dental assistant never has to call me in anymore to dig out chunks interproximally that have set rock hard.
Figure 53: I fill the crowns with the Ceramir and seat them simultaneously on the preps. Because the Ceramir is so moisture-tolerant, I no longer have to vigorously air-dry the preps prior to cementation. Instead, I often just place a few cotton roll pellets around the preps to remove any pools of moisture. Not having to blast the preps with air anymore, I find that I have to anesthetize far fewer patients for crown seatings than before. We use pinewood sticks to ensure that the crowns stay in place while the cement sets, in case there is any soft-tissue rebound.
Figure 54: As the Ceramir is moisture-tolerant, it is also OK if the patient’s tongue or saliva hits the cement while it sets. Many BruxZir crown preps tend to be slightly shorter clinical crowns than the ones shown in this case, so having the Ceramir cement bond to the BruxZir crown is a good insurance policy without having to use a silane. As promised, you can see I am able to remove the entire facial surface of excess cement in one piece, followed by the lingual. I then run some Oral-B® Super Floss® (Procter & Gamble; Cincinnati, Ohio) interproximally to remove those pieces.
Figure 55: Here are the cemented final crowns on teeth #8 and #9. Having an in-house technician makes it easier for me to match the shade on these BruxZir Anterior crowns. The esthetics of BruxZir Anterior are great. In fact, it’s my go-to restoration in the esthetic zone; it has a higher flexural strength than lithium disilicate, and has translucency and color similar to natural dentition. We are getting ever closer to using high-strength monolithic materials for every indication.