CEREC and Invisalign: How the Technologies Complement Each Other

In the ever-changing world of technology and dentistry, as one new wave of technology enters it alters existing clinical techniques. If necessity is the mother of invention, then new technology is the grandmother. Every time there is a change in technique there is a good chance that there is a change in other directions, some good and some not so good.
Invisalign (Align Technology) moves teeth with plastic trays or aligners, but if a tooth needs major treatment (crown, onlay, 3/4 crown) during active or retentive orthodontic treatment, it is now a new technique problem. For example, if Invisalign treatment has been prescribed using 30 aligners and a tooth needs a crown while in the fifth aligner, then the fifth aligner will no longer fit after the crown treatment is done; the next 25 aligners will not fit either. The challenge is to restore the tooth exactly so as not to interrupt treatment or cause treatment to be inaccurate.
I encountered this problem and decided I could deal with it in 3 conventional ways:

(1) Use composite inside the aligner, which may or may not work depending on how much tooth structure is broken.
(2) Send impressions and the aligner to the lab so the lab can fabricate a crown that will fit the aligner.
(3) Do a crown and take new impressions; send to Invisalign and have all new aligners made.

All of these options can be both expensive and time-consuming, and none seemed appealing to me. It then occurred to me to combine CEREC technology with the correlation mode; I thought in theory it should work. The following case report describes the technique I used.


Figure 1. Before photo of tooth Nos. 30 and 31.

Figure 2. Patient anesthetized with a Safe-Mate needle.

Figure 3. Optical impression taken with CEREC before prep of tooth No. 31.

Figure 4. Optical impression of tooth No. 31 preparation.

A 42-year-old female, whom I had just put in retention with an Invisalign retainer, needed major restorative treatment. She had decay on the lingual of tooth No. 31 and a large restoration. Tooth No. 30 had a large restoration, decay on the mesial, and decalcification on the lingual. I determined both teeth could be restored, and the treatment plan called for a full crown on tooth No. 31 and a 3/4 crown on tooth No. 30. The challenge was to restore the teeth so there would be no affect on her Invisalign treatment (Figure 1).
The area was anesthetized with a Safe-Mate needle (MedPro; Figure 2) with 2 carpules of lidocaine 2% 1:100,000 epinephrine. The CEREC machine was brought in before any restorative treatment was started. Vita CEREC Liquid was applied to teeth Nos. 31, 30, and 29, and the liquid was thinned with a quick burst of air. Next, the teeth were covered with ProCAD Contrast medium powder (Ivoclar Viva-dent) applied with a Powder Meister (David E. Lawler, DDS) and another quick burst of air was used to remove any clumps of powder.
The optical impression was taken with the CEREC 3 (Sirona; Figure 3) in correlation mode with 3 images.
Correlation optical impression captures the tooth or teeth and allows the clinician to duplicate the existing external dimension of the tooth. This includes but is not limited to mesial, distal, lingual, buccal, and occlusal. One can correlate a tooth for a crown, 3/4 crown, or onlay.
I then prepared tooth No. 31 for a crown with an inverted-cone diamond (Brasseler 807.310.018) and flat-end cylinder diamond (Neodiamond 0712C [Microcopy]). Tooth Nos. 31, 30, and 29 were covered with Vita CEREC Liquid, and powder was applied to the preparation (Figure 4). A quick burst of air was used to thin any clumps on teeth Nos. 30 and 31, and they were optically impressed with CEREC 3. I used the Isolite dryfield illuminator (Isolite Systems) to help control moisture.
I used a direct correlation technique on tooth No. 31 and an indirect correlation technique on tooth No. 30. I used correlation mode with the existing anatomy that the tooth currently had to design and fabricate the crown on tooth No. 31. This tooth was designed with correlation, and a 12-mm ceramic block shade A-2 (Vitabloc Mark II) was placed in the milling unit.

Figure 5. Composite without bonding placed in tooth No. 30.

Figure 6. Composite under Invisalign aligner.

Figure 7. Curing light to cure composite.

Figure 8. Crown in aligner to check external fit.

I decided to utilize an indirect technique for tooth No. 30. The aligner was used to create the anatomy of this tooth. This was accomplished by using composite (Z250 [3M ESPE]) on the prepared tooth (Figure 5) with no bonding agent. I prepared tooth No. 30 for a 3/4 crown with an inverted-cone diamond (Brasseler 807.301.018). The Vita CEREC Liquid was applied inside the aligner in the area of tooth No. 30. The aligner was placed over the lower teeth to form the composite to the exact anatomy of the aligner or pre-existing clinical crown (Figure 6). The composite was cured for 5 seconds with a curing light (Virtuoso Phase 2 [Rembrandt]; Figure 7).
I then applied Vita CEREC Liquid on tooth Nos. 30, 29, and 28, thinned with air, and applied ProCAD Powder. The optical impression of tooth No. 30 was taken along with tooth Nos. 29 and 28. The correlation software was initialized, and a 3/4 crown was designed. A 10-mm ceramic block shade A-2 (Vitabloc Mark II) was selected and placed in the milling unit.
The crown for No. 31 was retrieved from the milling unit and steamed to remove any oils and contaminants, then placed in the aligner to confirm that the external dimensions fit the aligner (Figure 8). Next, the crown was placed in the mouth to see if it fit the preparation and the occlusion was correct (Figure 9). Next, I placed the aligner over the uncemented crown to verify the fit (Figure 10). Lastly, I polished the crown with the CeramiPro Dialite ceramic polishing system (Brasseler). Then, Diashine (VHT) was used with a straight nose slow-speed and a stiff Robinson bristle brush (Buffalo Dental).

Figure 9. Crown placed in mouth to check fit and occlusion.

Figure 10. Aligner over crown in place without cement to verify fit.

Figure 11. The 3/4 crown and crown next to each other in aligner to check fit.

Figure 12. Verify fit of 3/4 crown in prep.

Figure 13. Crown and 3/4 crown placed with aligner over them.

Figure 14. Isolite system helps maintain a dry field.

Figure 15. Tofflemire matrix band around prep.

Figure 16. Occlusion check before any adjusting is done.

Figure 17. Final restorations.

Figure 18. Aligner placed after both crowns were seated.

The 3/4 crown was removed from the milling unit and steamed to remove any oils and contaminants. I then tried in the 3/4 crown in the aligner beside the crown (Figure 11), in the preparation (Figure 12), and lastly in the preparation with the aligner over it without cement (Figure 13).
The 3/4 crown No. 30 and full crown No. 31 were both ready to cement. The full crown and 3/4 crown were both treated with Vita ceramic etchant for 60 seconds. The etch was rinsed off, and porcelain silane primer (Porcelain Primer [Bisco]) was applied for 60 seconds. The multilink cement was used. A and B primer were mixed together and applied to tooth No. 31. A and B must be applied to the tooth for 60 seconds and must not get wet after application or before the crown is seated. I believe this is the cause for sensitivity, if the patient has any. I use the Isolite system to help maintain a dry field and help with illumination (Figure 14).
The cement was placed in crown No. 31, and it was seated and cured for 30 seconds with the Virtuoso curing light. An explorer was used to remove most of the excess cement. A No. 1 Tofflemire matrix band (Ho band .0001 regular [Young Dental]; Figure 15) was placed around the prepared tooth No. 30. The cement was also placed inside the matrix band, and the 3/4 crown was seated. The 3/4 crown was held in place with a composite instrument firmly and cured for 30 seconds, then the ma-trix was removed with Wyman crown grippers (Miltex). The crowns were immediately flossed with Vaseline-covered floss to make sure no cement was in the contact area. The excess cement was removed with a long tapered medium diamond bur (Brasseler 859.31.018) with water. The occlusion was checked before any adjusting was done (Figure 16). The occlusion was adjusted with a fine diamond egg-shaped bur (Axis Dental) with water. The 3/4 crown was polished with Cera Glaze polishers (Axis Dental) in a latch head slow speed handpiece.
The final restorations were photographed (Figure 17), and the aligner was placed after both crowns were seated (Figure 18).

The technique described in this article provides clinicians a method for restoring teeth while a patient is undergoing Invisalign treatment, without interfering with that treatment. Technology in dentistry is now and will be forever changing. Learning how to be inventive with these technologies will allow us to be more efficient, predictable, and patient-friendly.

Dr. McFarland received his doctor of dental medicine degree from the University of Kentucky. He is a Fellow of the International Congress of Oral Implantologists and member of the Dental Organization for Conscious Sedation, ADA, Academy of Computerized Dentistry of North America, and the AACD. He maintains a private practice in Paris, Ky.  He has had the CEREC machine for 8 years, during which he has placed approximately 6,000 restorations, and he has been using the Water-lase combined with the CEREC machine to perform root canals. He also specializes in computerized dentistry. He can be reached at (859) 987-4775.

Disclosure: Dr. McFarland invented and patented the Safe-Mate needle that is used in this article.

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