By Sarfraz Ahmed
It is impossible to achieve well-fitting restorations without clearly defined margins. Making sure the margins are prepared and designed correctly is essential.
outstanding ending bursts
For shoulder preparations, fine finishing burs should be used; for axial and occlusal reductions, coarse diamond burs should be used. In general, rougher surfaces improve cement retention and adherence.
Dental BurImage, from left to right, bevels, chamfer margination, and coarse for axial and occlusal reduction.
To help physicians purchase diamond burs for all clinical needs, manufacturers offer bur kits.
The kind of crown restoration, the material, and the location will all influence your choice of margin preparation (aesthetics, periodontal). The following lists the many sorts of margins and when to utilise them.
varieties of margins
1. Margin styles with a knife edge or a feather edge work well for:
· Full-cast crowns
Knife-edge or feather-edge margins require less tooth reduction than other types. For multilayer zirconia restorations, this preparatory design is inappropriate and may result in fitting or fracture problems.
2. Margin bevel-chamfer is appropriate for:
· Full-cast crowns
· Full Zirconia crowns
A 360-degree chamfer margin is appropriate for PFM, all-ceramic, and full-cast crowns.
When compared to knife-edged margins, bevel-chamfer margins give better marginal fit. When making crowns out of layered zirconia or IPS e.max®, this margin preparation is not ideal.
3. Chamfer margins work well for:
· Full-cast crowns
· Full Zirconia crowns
Options for High-Strength Dental Crowns
The marginal fit between the restoration and the tooth surface is improved by chamfer margins. For multilayer zirconia and IPS e.max restorations, they are less appropriate.
4. It’s acceptable to use shoulder or butt-joint margins for:
· Full zirconia crowns
· Layered zirconia
· IPS e.max
margin at the shoulder or butt-joint
The shape of the bur at the apical end determines the margins.
Shoulder-beveled margins minimise potential dark lines at the margin and offer a passive fit. LiS2 and layered zirconia are excellent materials for this preparation. Gingival retraction prior to preparation and the use of end-cutting burs can help ensure proper isolation of the margin during preparation.
5. Shoulder-bevel margins work well with:
· Full-cast crowns
· PFM crowns with porcelain shoulders
Generally speaking, shoulder-bevel margins produce precise marginal adaptation and clinically acceptable marginal fit. Metal collars may be seen, hence they shouldn’t be utilised in situations where aesthetics are an issue. They are not the best option for zirconia crowns that are stacked.
For well-fitting crowns, it’s essential to isolate the preparation margins. Additionally required are gingival healthy tissues, which reduces the risk of blood contaminating the scan or impression. There is a considerable likelihood that the Quality Control person will reject the case if your dental laboratory technician cannot perceive the margins of a traditional impression or if a digital scanner fails to record the margins adequately.
It is unacceptable to move forward with scans or impressions that are subpar. In the event that the case proceeds, there will probably be open or short margins, necessitating a new impression or scan in order to finish the case.
Data can be recorded and shown using digital technology, giving researchers the chance to examine minute characteristics that are difficult to see on traditional fixed prosthodontic impressions. However, conventional rules still hold true because the margins must be distinct and obvious.
How to Get a Great Margin Scan on Your iOS
Digital impressions can produce precise images, but there are a number of critical things to take into account.
Tissues are ready for retraction after preparations with 0.5mm subgingival margins were finished.
Accurate sub-marginal line of sight acquisition
The image that will be captured by the scanner is the one that is seen in the mirror. The tooth structure should be visible 0.5 mm apical to the edges. Digital imprints that have been poorly managed for tissue and moisture are regularly sent to dental labs. The margins must be readable and distinct.
Digital scanners only record the structures that are visible on the teeth, just like traditional imprints. You must be able to see the tooth structure from the apex to the edges when using your digital impression procedures.
Bringing Soft Tissue Back
Ø Packing cords into the sulcus before producing impressions is the greatest way to retract soft tissue.
Ø The size, shape, and depth of sulci vary.
Ø Retraction cables are offered in a variety of materials and sizes.
Ø In most cases, packaging doesn’t cause braided cords to unravel.
Ø Sulci typically start off narrower at the apex and gradually get wider as they approach the gingival crest. The majority of sulci have a V-shaped cross section.
Ø Therefore, if necessary, the thinner cords should be positioned first (000), then a thicker cord (00), and ultimately the thickest cord (0).
Ø The interproximal areas, where the sulcus depths are normally deeper, are where clinicians usually begin. During these processes, the least amount of pressure should be created.
The preparation is frequently at least somewhat apical to the free gingival edge. To get accurate scans or impressions, the tissue around any subgingival borders on the tooth preparation must be cut away. With exceptional quality retraction that displays clear margins, high-clarity scans can be produced.
It can be difficult to isolate the boundaries of inflamed gingival tissues due to continuous bleeding. It is crucial that there is no active bleeding present during scans or impressions, as well as no saliva.
Although teeth that are being prepared for crowns frequently had teeth that were previously treated with sub-gingival margins, supragingival margins allow a clear visibility of margins. The gingival tissues’ health has frequently been harmed in these situations.
Retraction cord usage
Cords for dental retraction
Gingival tissue is moved laterally away from the margin preparations by the retraction cord. Utilizing a thin packing device, it is delicately inserted into the sulcus. Retraction cord is an efficient way to remove gingival sulcular tissues.
However, haemorrhage could also result from it. There are hemostatic treatments that can be applied to the cords or the bleeding areas prior to the impressions or scans. Prior to continuing, bleeding must be stopped.
Retraction cords come in a variety of diameters, materials, and producers.
Using numerous cords can improve tissue displacement and make it easier to capture margins. Using two cables prevents tissue from folding over the edges during scanning or imprints if the patient has a particularly deep sulcus.
Pack a cord with a smaller diameter first while bundling the cords. In most cases, the first chord will cover the edges. Next, stuff a cord with a bigger diameter; this usually reveals the margins.
To fully expose all edges, it could occasionally be necessary to use a third cord with a bigger diameter. Before being removed, the larger cables must remain in place for at least five minutes. Occasionally, the original, thinner chord is still present during the scan or impression.
exposing edges using a soft tissue laser and retraction paste
By removing unhealthy and inflamed gingival tissue that may be obscuring the subgingival margins or causing excessive bleeding, a soft tissue laser can help reveal the subgingival margins. Lasers have the potential to permanently alter gingival tissues, so extreme caution must be taken.
Ø The rebuilding of healthier tissues is aided by the removal of inflammatory tissue.
Ø Hydrogen peroxide solution eliminates tissue debris after areas have been treated with a dental laser.
Ø After being injected into the sulcus, the paste is covered with a sturdy cotton roll.
Ø The paste is rinsed away, allowing a clear view of the margins as the patient chews down on the cotton for two to five minutes.
Whether using a traditional or digital impression, the proper margin preparation and tissue management techniques are essential for producing and fitting high-quality restorations. A great chart from MS Dental Arts Lab can help you increase your margins. You can download this chart, which is a useful resource.
Our trained and knowledgeable technicians can help you with case preparation and are always accessible for case consultations.
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