Photo Essay: Post-and-Core Technique with BioTemps® Provisionals
Chairside Magazine: Volume 8, Issue 2
This was an interesting case because it took me away from the normal flow of procedures and forced me to think about the best way to accomplish the posts and cores for this 4-unit bridge. Because I would be doing posts and cores in conjunction with BioTemps® Provisionals (Glidewell Laboratories; Newport Beach, Calif.), I wanted to avoid having to toss the BioTemps in the trash and do chairside temps if I made the cores too large or they wouldn’t draw. I decided tooth #7 would be a cantilever pontic off of teeth #8 and #9, which would be two PFMs splinted together, and tooth #10 would be a single-unit PFM.
Figure 1: Looking at the radiograph of teeth #9 & #10, I can see the endo is a little suspect, although it helps that fistula are present. Tooth #8 also has endo that needs redoing, so I decide to let the endodontist redo all three teeth. It is clear that the post in tooth #9 is too short to be effective, and the other two teeth are without posts.
Figure 2: When the patient comes back from the endodontist, all three teeth have been re-treated. The endodontist left a minimum of 5–6 mm of gutta-percha in the apical third of each tooth, giving me an abundance of post space. I always prefer to have the endodontist remove the excess gutta-percha.
Figure 3: After the three endodontic re-treatments and removal of the existing PFMs, this is what we are left with. It’s clear that posts and cores will be necessary to properly restore this case. The patient was also presented with the option of replacing tooth #7 with a single-tooth implant to remove stress from tooth #8, but he declined because it would require the placement of a graft prior to implant placement and increased treatment time.
Figure 4: Considering that we aren’t going to prep virgin tooth #6 in order to accommodate the pontic on tooth #7, I don’t see an issue with this bridge. I will put an anti-rotational wing on the lingual of tooth #6 to keep the pontic from moving to the facial when the patient goes into protrusive.
Figure 5: I’m a little concerned about the post space on tooth #10 weakening the lingual wall, but I will cross my fingers that the resin cement I place in the post space will hold everything together. Fortunately, resin cements have very low expansion compared to RMGI cements and will not cause root fractures; nor will passive, flexible resin-based posts. Here, you can see that I have prepped the lingual wing on tooth #6.
Figure 6: Going back to the X-ray from the endodontist, I use an endo ruler to take a rough measurement from the end of the gutta-percha to about 2 mm short of the anticipated incisal edge. Recent studies show that the closer the end of the post is to the gutta-percha, the higher the long-term success rate of the tooth. There are also studies showing that the quality of the crown margins plays a more significant role in long-term endodontic success than the quality of the endo itself.
Figure 7: The three fiber posts (RelyX™ Fiber Posts [3M™ ESPE™; St. Paul, Minn.]) have been tried into place and cut roughly to length. The only mistake you can make at this point is to cut the posts too short. My criterion for deciding to place a post in a tooth is singular and simple: to retain a buildup. In other words, if I have enough healthy tooth structure present on a tooth to be able to bond a core into place, I am not going to place a post in that tooth just because. Digital X-rays make it simple to snap an X-ray of the posts to confirm complete seating.
Figure 8: By using a self-adhesive resin cement like the RelyX™ Unicem (3M ESPE) I am using here, I avoid having to use a separate etch. Imagine how difficult it would be to get acid etch down into the post space. It would be even more challenging to rinse it out completely from this closed-end system. Because the RelyX Unicem system comes with either an endo tip for the syringe system or an elongation tip for the Aplicap™ system (3M ESPE) as seen here, you can feel confident the cement is reaching the apical portion of the post space.
Figure 9: Once the canal is filled with the resin cement, quickly push the post down into place with a twisting motion. Because the RelyX Unicem is dual-cured, it begins to set immediately, so I like to have the post ready to go. Once it is down in the canal, I will light cure the coronal portion for two to three seconds so that I can clean up the excess cement. One of the benefits of using a fiber post is that it acts like a fiber optic bundle and carries your curing light to the deepest aspect of the post space to facilitate the dual-cure properties. Also, the elasticity modulus of these posts is very close to that of dentin, so the post will bend with the tooth.
Figure 10: I previously had a set of BioTemps Provisionals made for this case, so I don’t want to overbuild my buildups. The lab made me this thermoformed suck-down prep guide on the prep model they used to make the BioTemps, so I know if my buildups are the same size or smaller, they will drop right into place when I try them in. Getting a set of BioTemps to fit can sometimes require a lot of work, but this technique ensures they will fit and that my preps will be close to ideal. I now use this prep guide for all my BioTemps cases — not so much to ensure that I have reduced enough tooth structure (the Reverse Preparation Technique takes care of that), but rather to confirm parallelism between multiple preps on larger cases.
Figure 11: When I had the prep guide in place, I noticed that one of the posts was contacting the stent on the lingual portion of the post. This is an example of the type of thing I might not have caught on my own; however, the stent showed me the post was outside the ideal prep form. The post preparations were so large that there was almost 30 degrees of travel between the most facial position and the most lingual position the post could go. Here, I am using a football bur (379-023 [Axis Dental; Coppell, Texas]) to reduce the lingual aspect of the post.
Figure 12: Even though I already used the stent to verify that my posts are within the ideal prep design, I try-in the actual BioTemps over the posts to make sure they fit passively. There is very little chance they won’t fit passively at this point, but I want to see what they look and feel like when they sit passively in place. I also want to be able to compare this fit to the passive fit I am trying to achieve after I do the actual buildups. Doing this is not unlike checking to see how a patient’s contralateral teeth come together before you try-in a bridge, and then watching those same contralateral teeth as you have them bite together again with the bridge in place.
Figure 13: Another advantage of fiber posts is how easy they are to bond to; simply etch and apply bonding agent as you would for natural tooth structure. As you are essentially bonding composite to composite, there is no need for mechanical retention on the head of the post as with many metal posts. I have cleaned the excess cement from around the post-tooth interface in an earlier step, and now I apply 37 percent phosphoric acid to the post and all exposed tooth structure for 10–15 seconds.
Figure 14: Now I rinse off the etch before placing the bonding agent. Note that I try to leave the dentin moist. At this point, I decide if I am going to place individual matrices for the preps such as ACCOR® Matrices (Premier Products Co.; Plymouth Meeting, Penn.), which I prefer for individual preps because they are quick, easy and accurate. Otherwise, I will use what I call the “soft-serve ice cream” method. This is a technique in which I swirl material around the post once or twice and my assistant light cures. Then I go around two more times, she cures, I swirl and she cures — until we are about 10 percent overbuilt.
Figure 15: After rinsing off the etch, the goal is to not desiccate the dentin. I use the Warm Air Tooth Dryer (A-dec Inc.; Newberg, Ore.). Alternately, you can use your high volume suction next to the tooth, in conjunction with some cotton rolls or pellets, to remove most of the moisture and accumulated water in any shoulder margins. Remember: Bone dry is not the goal here, as you are much more likely to reduce bond strengths by over-drying the dentin than by leaving it too moist. Here, I am coating the posts and the preps with OptiBond® Solo Plus™ (Kerr Corporation; Orange, Calif.), and then we will air thin for three seconds and light cure.
Figure 16: I am now filling the prep stent with Ti-Core® Auto E core buildup material (Essential Dental Systems; South Hackensack, N.J.) in shade A2. Ti-Core is a dual-cured hybrid composite core material reinforced with titanium and lanthanide to help it match the strength of dentin. When prepping a tooth that has been built up, there is nothing worse than when the bur dives into the composite when going from dentin to composite. The hardness of a buildup material is the most important physical characteristic to help prevent the bur from ditching and grooving the prep at the dentin/buildup interface.
Figure 17: Here is the prep stent completely filled with the Ti-Core. Because this is a stent of the preps and not the diagnostic wax-up or the final contours of the BioTemps, we want to make sure that we fill it completely, leaving no voids. We also want to make sure that the stent extends at least one tooth in each direction onto unprepared teeth. This allows us to verify that the stent is completely seated onto the preps we are building up. If the stent doesn’t rest on the unprepared teeth, it is too easy for it to rotate out of place to the facial or lingual, making esthetic restorations a challenge to achieve.
Figure 18: To ensure that the core material is seated completely onto both the posts and the remaining tooth structure, we need to make sure to place positive pressure apically on the stent on the portions over the preps and the unprepared teeth. As I hold the stent down, my assistant moves in and cures the dual-cure buildup material from the facial, before moving to the lingual to cure from that aspect.
Figure 19: After we are finished curing, the stent typically will slide off without too much effort. If needed, an explorer can be used to help pop off the stent. The stent material is inert and will not bond to the composite buildup material, so there is no need to place any kind of separator inside the stent before filling it with the composite. You may be wondering if we could have accomplished an even better result if we would have filled the BioTemps themselves with the Ti-Core and seated them on the preps. This is perhaps true, but there would be too great a chance that we would have locked the BioTemps onto the posts, which would have given us a below-average result.
Figure 20: All of the cores are connected at this point due to the limitations of a thermoformed stent; however, they can easily be separated and shaped into preps. I am using the thin bur (856-016) from my Reverse Preparation Set (Axis Dental) to break the contacts between the preps. The current size of the preps would allow the BioTemps to seat, but many permanent restorations require more reduction than BioTemps, so I will continue to reduce these preps after breaking the contacts.
Figure 21: I will be placing PFMs in this case because I am using an anti-rotational wing on the lingual of tooth #6. Metal is still the only material I trust at a thickness of .04 mm to stand up to that kind of force without breaking. If you had a patient who was adamant about having the best possible esthetics, who was also OK with paying to have their restoration repeatedly replaced when it broke, then I suppose you could go with an all-ceramic bridge. This patient didn’t have those kind of high esthetic demands, so we decided to stick with porcelain fused to metal.
Figure 22: Here, I am placing Ultrapak® #00 cord (Ultradent Products, Inc.; South Jordan, Utah) around the three preps. This is a plain cord that has not been soaked in any medicaments because it will be in place for some time at the base of the sulcus. I typically place this cord at the very beginning of the prep sequence, as soon as I break the contacts, but this has been an unconventional prep sequence. Even though this first cord is small, it is responsible for nearly all of the vertical retraction of the tissue we get in the Two-Cord Impression Technique, which allows us to prep subgingival margins without ever having to take a bur subgingivally.
Figure 23: With the #00 cord in place and the gingival tissue retracted about 0.5 mm, I am now using the 856-016 fine-grit bur to smooth out the prep, especially at the gingival margins. The red stripe on the shank of the bur identifies it as a 40-micron, fine-grit diamond. The days of having to leave the prep rough in order to retain a crown are essentially gone because our weakest RMGI cements now give us 6–10 MPa of bond strength to dentin without any etching. Now that we design nearly every crown at the lab using CAD software, we are looking at margins at 10-times magnification, so it sure is nice when they are smooth.
Figure 24: Here, I am using a Sof-Lex™ contouring and polishing disc (3M ESPE) to smooth the incisal edge and round off the mesial and distal line angles of the incisal edge. In the old days, we had to round off these corners because the weaker ceramic materials would crack if they sat on top of a sharp line angle and were subjected to stress. Today’s stronger all-ceramics aren’t affected by sharp angles in the same way and are more than strong enough to withstand stress; however, most crowns of this type are milled, and the burs in the milling units can’t mill these sharp angles, which leads to overmilling. This overmilling weakens today’s crowns, so the advice remains the same: smooth off sharp incisal-edge angles.
Figure 25: Now the preps are finished. How do I know? My technician works one floor below me, and I call her to come up and tell me if I am done. She can picture in her mind’s eye if I have reduced enough for what she needs to do because she has seen the study models and has done the diagnostic wax-up. That’s when I know it’s time for the Ultrapak #2E cord (Ultradent Products Inc.), the top cord in the Two-Cord Impression Technique. This epinephrine knitted cord provides nearly all of the lateral retraction in the sulcus that creates space for the impression material.
Figure 26: ROEKO Anatomic Comprecaps (Coltène/Whaledent Inc.; Cuyahoga Falls, Ohio) can be real lifesavers at times, although this isn’t one of those times. For this case, they are very helpful in creating hemostasis, even though we already had decent hemostasis due to our atraumatic prep and use of the Two-Cord Impression Technique. They also help hold the loose end of the cord in place and give the patient something to relax against after being open for a while, all without blunting the interproximal papilla. We let the patient bite down on the Comprecaps for eight to 10 minutes. I am serious about this timeframe because it takes that long for the magic to happen — it’s not instantaneous. You are better off waiting 12 minutes than six minutes.
Figure 27: Here, we have removed the Comprecaps. NOTE: Had these been vital teeth, we would have moistened the Comprecaps before placing them because vital teeth do not like to be dry for 10 minutes at a time. We remove the top #2E cord, and I express medium body material into the sulcus while a second assistant fills the tray. It takes three people to make a multiple-unit impression predictably.
Figure 28: The BioTemps are now in place with temporary cement. As you can see, I like to keep the gingival embrasures open on my BioTemps cases. I learned this lesson the hard way because I used to try to make my BioTemps look too perfect and I would often blunt the papilla. I wouldn’t notice this until I tried in the permanent restorations and would see black triangles. Now I leave the gingival embrasures open so the patient can swish Tooth & Gums Tonic® (Dental Herb Company; Lancaster, N.H.) through the embrasures to promote gingival healing during temporization and eliminate black triangles at the seating appointment.
Figure 29: One week later, we are ready to remove the BioTemps and try-in the final restorations. Because we left the gingival embrasures open and had the patient swish with the tonic, we should see some healthy gingiva when we remove the provisional — and we do. I always tell patients that if I were to close the embrasures they would have to floss them twice a day, increasing the chance that those black triangles would be there with the permanent crowns. In my experience, leaving black triangles for the temporary ensures they won’t be visible when the permanent crowns are in place.
Figure 30: After trying in the restorations one at a time to verify marginal fit, we try them in as a group to check contacts and occlusion. Satisfied with the fit, I leave the room, and my assistant hands the patient a mirror so he can take a look at the final crowns, reminding him they are still loose. We want him to take a look to make sure he is happy with them, too. I want patients to be able to speak freely with my assistant and not fear offending me, which is why I leave the room.
Figure 31: Lingual view of the cemented crowns. Notice the anti-rotational feature on the lingual of the cuspid. Again, a single-tooth implant replacing that lateral would have been the ideal treatment had the patient accepted it. I had to prepare the rest of the tooth in order to gain occlusal clearance from the opposing tooth, but was careful to stay in enamel. Anytime I have tried to prep into enamel and bond something into that slot preparation, I have had premature de-bonding.
Figure 32: A postoperative radiograph showing the RelyX Fiber Posts luted in place with the RelyX Unicem after cementation of the crowns. On teeth #8 & #9, I got the posts exactly where I wanted them — right up against the gutta-percha. According to the latest research, this bodes well for the long-term prognosis of the teeth. The post in tooth #10 ended up just a little short (there appears to be about 2 mm of space between the end of the post and the gutta-percha). According to the research, this is slightly less successful than when the post is in contact with the gutta-percha. I am OK with this, however, because I can see that my resin cement filled all the way down to the gutta-percha, which is always preferable to empty space in a root canal.