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Digital Impression under Rubber Dam Isolation


Digital impression of onlay preparation

Today we have access to extremely performing machines that allow us to go far beyond simply scanning dental arches. But technology and progress don’t always mean improvement, both when speaking about work, and life. This, in fact, is the leitmotiv that many lecturers strive to reiterate, especially when it comes to intraoral optical scanning. Let me share with you what I think the deal is.

By continuously opposing the concept of “progress” to that of “the past”, we wind up debasing both. Although machines today can be accurate up to 9-micron details, their potential is not the topic I want to discuss in this article. Intraoral scanners actually feature dozens of “alternative” utilities, which add to the simple possibility of “taking an impression” of the dental arches. Among these, I’d like to address one in particular, which might be described as a “hack” for a typically “annoying” clinical situation, even in case you’re taking a traditional impression. Deep preparation margins for adhesive indirect restorations.
As I’ll show in this case, preparation margins are often an issue when a precision impression is to be taken to fabricate an indirect restoration. These margins are often juxta- or slightly sub gingival, even though they can be isolated. Luckily.



old broken restoration on upper molar

Fig.1

Initial situation. The patient came to our clinic complaining about the fracture of the palatal cusps of her 26.
The patient reported no symptoms, so we decided to remove the whole restoration and to replace the missing part of the tooth with an indirect onlay restoration.



initial digital impression of upper molar

Fig.2

As a first step, we scanned the initial situation with Omnicam by Sirona Dentsply.



rubber dam isolation before old filling removal

Fig.3

Then we isolated the sextant with the rubber dam.



upper molar cavity and fender wedge

Fig.4

We removed the old composite restoration and the decayed tissue underneath, while protecting the adjacent teeth by a fender wedge.



cusp measurement for enamel preservation

Fig.5

We decided to maintain the mesio-buccal cusp with a thickness of 2.5 mm



cusp measurement before only preparation

Fig.6

On the other hand, we decided to remove the disto-buccal one, as it was cracked at the base and it was 2 mm thick.



onlay preparation before cavity build-up

Fig.7

After we prepared the tooth, the distal margin, although it was deep, was visible and isolated. As you can see in the picture, the rubber dam pulls the the interdental papillae away, displacing them apically, and exposing the preparation margins better. In fact, I often fend up facing juxta-, or slightly sub-gingival prosthetic margins after having removed the dam and rinsed the patient.



rubber dam isolated onlay cavity

Fig.8

So we built the cavity up using one single bulk composite mass (One Bulk fill, 3M). The LM Arte Condensa instrument was used to shape the composite in order to minimise the need for after-curing touch-ups, especially on the margins. These margins can be recovered through the use of retraction cords soaked in aluminum chloride, so as to limit bleeding as much as possible. This procedure requires the use of a thin cord to displace soft tissues apically and partially, also horizontally, so as to perfectly expose the margins and offer the technician a precise and detailed impression. The risk of contaminating the impression with blood or saliva, whether performed in analog or digital technique, is high and the focus of the operator, in this phase, must be maximum.



deleting part of intraoral scan

Fig.9

Intraoral scanning allow us to completely eliminate this risk, as we can take the impression while the rubber dam is still on! There is actually no better retraction device than the rubber dam itself!

So we deleted part of the initial digital impression with the dedicated feature of the software, to be replaced with a new scan of the prepared tooth.



digital impression molar scan

Fig.10

Then we took the impression of the prepared tooth, still isolated, as the software can match the position by superimposing the new scan of the adjacent teeth.



lithium disilicate before and after firing

Fig.11

In the meantime, Daniele Rondoni DT worked on the digital model designing the onlay, and started the milling of the eMax block.



automatrix to isolate before onlay cementation

Fig.12

A few days later, the onlay was ready for cementation. The artefact showed no problem in fitting, occlusion, and proximal contact. After positioning an automatrix in order to protect the adjacent teeth, we sandblasted with Aquacare, using aluminum oxide 53 micron particles, the entire surface, to clean and reactivate the composite, now ready for the cementation.



hydrofluoric acid etching of onlay

Fig.13

The onlay was etched with 9% hydrofluoric acid for 20 seconds.



veneer me for onlay restoration treatment

Fig.14

We used the Veneer Me (SmileLine) to rinse and then dry the onlay, and then to put it in an ultrasonic bath of 90% pure alcool for 5 minutes. After silanizing the onlay, we bonded by thoroughly brushing (20 seconds) the internal surface with Scotchbond Universal (3M), without light curing it.



selective enamel etching with automatrix

Fig.15

We always selectively etch the enamel for 30 seconds using 37% orthophosphoric acid (Scotchbond Universal Etch, 3M).



onlay cementation with composite flowing out

Fig.16

After brushing for 20 seconds the receiving surface of the preparation with Scotchbond Universal (3M), without light-curing, we cemented the onlay using pre-heated 3M Universal composite.



glycerine air-blocking for onlay cementation

Fig.17

After removing composite excess, under glycerine air-block, we cure, 2 minutes per side.



lithium disilicate onlay on upper molar



Fig.18

Final result after occlusal check, finishing and polishing.



Conclusions



Sometimes obsessing over new technologies may drive our focus away from the everyday issues we could actually solve, for good. Instead of trying to find new techniques we might just try to get the best out of what is already available to us and save ourselves all the struggle we have been getting used to for ages.

Open your eyes and think digital!



Bibliography



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8) Dietschi D, Olsburgh S, Krejci I, Davidson C. In vitro evaluation of marginal and internal adaptation after occlusal stressing of indirect class II composite restorations with different resinous bases. Eur J Oral Sci. 2003 Feb;111(1):73-80.

9) Renne W, Ludlow M, Fryml J, Schurch Z, Mennito A, Kessler R, Lauer A. Evaluation of the accuracy of 7 digital scanners: An in vitro analysis based on 3 dimensional comparisons. J Prosthet Dent. 2017 Jul;118(1):36-42.

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