PREPARATIONS FOR ANCHORING TO THE CAST CROWN

PREPARATIONS FOR ANCHORING TO THE CAST CROWN

1. Definition

The cast crown (or metal covering crown) is a prosthetic device which consists of completely covering the coronal part of a previously prepared tooth, in order to give it a morphology adapted to its different functions.

2. Advantages

Resistant
Well tolerated by the marginal gingiva.
Little damage to dental tissue.
Better Retention and Excellent Adjustment at the Cervical Level
Low cost.
Easy lab build.

3. Disadvantages: Unsightly

4. Indications

To protect reconstructed teeth that have fragile walls
Improve the occlusal function on a posterior tooth whose occlusal surface does not physiologically mesh with the antagonists (malposition)
Indicate as hook or attachment support in PPAC
To restore the occlusal plane
Indicate as a means of bridge anchoring

5. Contraindications

Anterior Tooth
Significant malposition

6. Materials

Precious alloys: Gold (Au) – platinum (Pt) – palladium (Pd) (type III and IV)
Semi-precious alloys: silver-palladium reinforced with nickel-chromium (risk of corrosion)
Non-precious alloys: cobalt-chromium / nickel-chromium

7. Preparations for Metal Crown

Preparation (or trimming) consists of reducing the coronal surfaces of a certain volume of tissue, in order to separate them from the adjacent and antagonist teeth, to interpose the prosthetic element. This reduction is economical (alloys are much more resistant under low thicknesses).
If the tooth is vital, local-regional anesthesia is administered.
Throughout the cut, it is necessary to work according to the chosen insertion axis and under cooling
Silicone key: to check the quantity and homogeneity of tissue removed

a. Occlusal Reduction

For this reduction, a round-ended cylindrical-conical diamond bur can be used. The latter will be directed towards the center of the FO.
The preparation must be sufficiently reduced so that the reconstruction material, in sufficient thickness, is neither perforated nor deformed.
The thickness of the reduction of the occlusal surface depends on the material chosen. For a gold crown, it is 1.5 mm on the support cusps and 1 mm on the guide cusps. A harder material requires a less significant reduction.
Occlusal reduction reflects the morphology of the prosthetic element for which the preparation is intended. It follows the inclination of the sides and slopes of the antagonistic, vestibular and lingual cusps.

Chamfer of the external slope of the support cusps

It is essential for the sustainability of reconstruction.

b. Reduction of the Vestibular and Lingual Face:

The principle is to remove the bulges using a truncated cone cutter with a rounded end parallel to the axis of the tooth while giving a clearance of 5° to 10° (convergence towards the FO)
The cervical limit will be started at a supragingival type limit
Dual-role stabilizing groove: to prevent rotational movement and to guide the installation. Made with the No. 170 cutter.

c. Reduction of Proximal Faces:

The quality of a stump lies mainly in the preparation of its proximal faces.
Trimming involves removing the contact points with neighboring teeth, as well as the anatomical bulges of these faces.
To do this, a fine truncated cone diamond bur or Fissure mounted on a turbine begins the reduction in a VL direction then in an LV direction until the Mesial then Distal contact point is removed.
In no case should the neighboring teeth be touched (protection by a metal matrix).
A larger conical bur will then give the general orientation of the M and D faces, increasing the separation with the adjacent teeth, and fixing the degree of convergence towards the occlusal face (undercut) from 3° to 10° depending on the coronal height.

d. Finishing the Preparation:

The surfaces cut using diamond burs are rough (pulling during impression taking). Their polishing is essential and will be done with multi-blade tungsten carbide finishing burs then using silicone cones and grinding wheels used under water spray.
Finishing the occlusal face: Sharp angles between the inclined planes should be avoided on the preparation (increase in stresses, and would hinder the complete placement of the reconstruction). They should be rounded, the grooves in the center of the occlusal face shallow and therefore the angulation of the inclined planes not very marked.
Rounding of connection angles with a conical round-end diamond cutter
Finishing the cervical limit using an enamel chisel

8. The Footprint (same session)

The impression is intended to provide the laboratory technician with good definition and reading (cervical limits)
Taking an impression of the arch concerned by the preparation With the wash Technic or other techniques, then an impression of the antagonist arch using a standard impression tray is made with alginate (This will allow the crown to be constructed in the laboratory, cast in the physiological occlusal position, both in OIM and in movement)

9. Temporary prosthesis (same session)

The stump, whether pulped or depulped, must be protected by a temporary crown.
This temporary protection is obtained using prefabricated metal crowns made of silver-tin alloy or polycarboxylate resin.

Goals of the Provisional Prosthesis:

Protect the stump against attacks (chemical, physical, etc.)
Maintain the Marginal Gingiva in a physiological position after preparation.
Facilitate healing of periodontal tissues
Improve and facilitate the conditions of the imprint.
Anticipate the morphology of the final prosthesis.
Avoid movements of the stump and opposing teeth.

10. Sealing of the Metal Crown (later session)

The cast crown, after a fitting in the mouth and any adjustments, must be sealed first provisionally, using a provisional cement (ZnO), for one week. The definitive sealing can take place thanks in particular to fluoride-enriched glass ionomer cements which are currently the materials of choice for definitive fixation on pulped and pulpless stumps.

B/ THE CROWN WITH VESTIBULAR INLAY

1. Definition

The CIV is a full-coverage crown made of cast metal, bearing on its vestibular face, a cosmetic element made of porcelain or resin, for aesthetic purposes.
The cosmetic element is a mask made by firing porcelain powder in the cavity provided on the vestibular face of the cast metal structure.

2. Advantages

The advantages of CC
Restoration of aesthetics
Inexpensive for cosmetic restoration
Low tissue mutilation

3. Disadvantages

Mutilation of the vestibular face
Usually due to resin:
Lack of adhesion of resin to underlying metal
Risk of loosening of the veneers
Aging, Discoloration, Odor…
Lack of hardness: Rapid wear under the influence of brushing or the hooks of a PPAC

4. Indications

They are a combination of the indications of the metal crown and the indications of the aesthetic crown.

For any single or multiple prosthetic reconstruction of anterior teeth
On the Premolars and even the Molars
Single medium or Can be used as an anchor for the bridge.
PPAC hook or attachment bracket
When the DVO does not allow a CCM
Economical “resin”

5. Contraindications

The lower teeth where the vestibular surface is used during chewing movements
On young teeth with large pulp (significant mutilation for the vest shoulder).

PREPARATIONS FOR ANCHORING TO THE CAST CROWN

6. Materials

Alloys: precious – semi-precious – non-precious (Nickel-chromium)
Cosmetic Product: Ceramic or Resin

7. Preparations for a CIV

It is essential to be able to reduce the tooth sufficiently, without damaging the pulp, while maintaining a secure support for the crown.
Otherwise, the thicknesses of resin and metal being too thin, it is the solidity and the aesthetics of the crown which are compromised.
Anesthesia (live and hypersensitive tooth)

7.1 On an anterior tooth

Making the silicone reduction guide

a. Reduction of the free edge and the vestibular face:

Preparation of the orientation grooves at the level of the Free Edge (2mm) and the vestibular face on the incisal and cervical part.

They are made using a flat-ended conical diamond cutter.
It is reduced in two planes: one cervical, one incisal to avoid any pulp lesion and to have an equal thickness of the prosthetic material on this face.
Reduction of the incisal part of the vestibular face
By removing the remaining enamel sections between the different orientation grooves
Reduction of the cervical part and development of the shoulder and proximal flats.

To do this, the flat-tipped conical diamond bur is held parallel to the cervico-vestibular plane and follows the gingival ring without damaging it.
The 1.2-1.5 mm shoulder is cut at right angles to the vestibular surface, and it extends on the proximal surfaces beyond the contact points to end in a fillet on the palatal surface.
This shoulder is first cut at a juxta-gingival level then lowered to its final sub-gingival level of 0.5 to 0.6 mm in depth for aesthetic reasons.

b. Reduction of the palatal face:

Reduction of the cervical axial wall:

It is done with a diamond bur with a rounded end; the 0.6 mm fillet is cut immediately at its final level (juxta gingivale).
The cutter is held parallel to the cervical portion of this face. The fillet extends over the proximal faces until it meets the shoulder.
The cervical 1/3 of the stump forms a cylindrical ring, which constitutes the main retention zone of the CIV at the level of the incisors and canines.
Reduction of palatal concavity:
It is done with a pear-shaped or olive-shaped diamond bur 0.6 to 0.8 mm thick in order to disengage it from the free edges of the opposing incisors.

Free edge reduction :

The free edge will be reduced by 1.5 to 2 mm (inclined in the palatal direction for the upper teeth, and in the vestibular direction for the lower teeth).
In the case of a canine, both sides of the cuspid tip must be respected.

c. Reduction of the Proximal Faces:

using a truncated cone bur with a rounded tip that is narrower than that used for the vestibular face, the proximal faces are cut, making them flush (5 to 6°), while marking a cervical limit in the form of a juxta-gingival fillet of 0.8 mm in the vestibular half and 0.4 to 0.6 mm in the palatal half.

d. Finishing, checking and polishing the preparation

All sharp connection angles must be rounded.
Eliminate all counter-spoilers
Check that the vestibular face of the stump is set back from the neighboring teeth,
Regularize the shoulder using an enamel chisel or a shoulder bur with smooth walls and an abrasive flat end without altering its internal angle and checking its vestibular subgingival level.
Polish the preparation as for the CC.

7.2 On a posterior tooth

Same as CC except on the Vestibular Face in order to accommodate two materials: cut more with a LC in the form of a shoulder with a rounded internal angle of 1-1.2 mm

8. The Footprint (same session)

Taking an impression of the arch concerned by the preparation With the wash Technic or other techniques, then an impression of the opposing arch using a standard impression tray is taken with alginate.

9. Choice of color and Temporary Prosthesis (same session)

It is more appropriate to speak of color than of tint, because the tint is one of the components of the color. Taking the tint For the aesthetic product with the Tint Guide or other methods (daylight)
The stump, whether anterior or posterior, must be protected by a temporary crown.
This temporary protection is obtained using metal crowns (posteriorly) and with polycarboxylate resin caps (anteriorly), or with other Temporary Prosthesis techniques.
It will restore the aesthetics, function, and protection of the stump against any physicochemical aggression. Its role is also to prevent any movement of the stump.

10. Biscuit Testing (later session): to make adjustments before icing.

11. Final sealing (later session): the VSD must be sealed first provisionally, using a temporary cement (ZnO), for one week. Final sealing can take place afterwards.

PREPARATIONS FOR ANCHORING TO THE CAST CROWN

Conclusion

C/THE CERAMO-METAL CROWN

1. Definition

The CCM is a full coverage cap consisting of a metal cap made of precious or non-precious alloy covered entirely or partially with a ceramic cosmetic layer. The metal cap constitutes the infrastructure (cup) and the ceramic layer the superstructure.
It is one of the so-called aesthetic crowns.
Properly executed, it combines the hardness and precision of cast metal with the aesthetics of ceramic.

2. Clinical Forms of CCM: depending on the coverage of the aesthetic product

3. Advantages

Aesthetics (natural appearance)
Strength and precision of cast metal
Biocompatibility of ceramics: good biological integration
It has a relatively long lifespan.
It adapts to the most varied clinical forms

4. Disadvantages

Brittle fracture and very low tensile and shear strength are often the major drawback of CCM, which is fracture of the superstructure. This drawback is due to the glassy nature of the ceramic, and is amplified by possible failure in the design or manufacture of the crown in the laboratory.
Tissue mutilation, particularly at the cervical margins, in order to create sufficient space for the two restoration materials (metal and ceramic).
To achieve a good aesthetic result, the cervical limit is placed at an infragingival level, this can increase the potential for periodontal diseases of the crowned tooth.
Wear of opposing teeth can be accelerated due to the hardness of the ceramic especially if the occlusion is not balanced.
Choosing the exact colour of the ceramic and communicating it to the laboratory is a common, often underestimated problem.

5. Indications

Indicated on teeth that require total coverage (dilapidated pulped or depulped teeth)
Single medium or as a bridge anchor.
To correct the occlusal plane.
Support for a hook or attachment in PPAC
When the occlusion is tight and the volume is reduced “CIV”
Very dyschromic tooth

6. Contraindications

The same as for all fixed restorations, especially patients with active caries or untreated periodontal disease:

Teeth with increased mobility and reduced periodontium.
Teeth with periapical reaction difficult to stabilize.

Teeth that are too short or too thin in the vestibulo-palatal direction.
In young patients with large pulps (risk of pulp exposure)
Bruxism

7. Preparation On an anterior and posterior tooth

Same as CIV except thickness is more.
Control with the silicone guide

8. Impression, Choice of Color, Temporary Prosthesis, Biscuit Try-in, Final Sealing: Same as CIV

D/THE CROWN JACKET

Introduction

The crown jacket was born in the USA towards the end of the nineteenth century by LAND, thanks to other authors, it became common practice

1. Definition

The jacket crown is a full coverage crown, made only with the cosmetic product (ceramic or resin) without metal infrastructure and giving the defective tooth a natural appearance. It is a single restoration that often concerns the anterior teeth and is practiced on both pulped and depulped teeth.

2. Advantages

2.1 Ceramic jacket crown

Aesthetics: Optical qualities – Retention of color and shape over time
Thermal insulation
Biocompatibility: no allergy, no discomfort linked to metal, better gingival tolerance

2.2 Resin jacket crown

Speed of execution
High elasticity: adaptation to all pathological situations (Neuro-Musculo-Articular), and when the antagonist teeth are worn
The size is less mutilating
Cost is less than ceramic

3. Disadvantages

3.1 Ceramic jacket crown

Fragility: ceramic is fragile and not very elastic, does not support permanent traction
Low strength: ceramic is prone to fracture easily under low thickness.
Difficulty of execution.
Very significant mutilations
High cost.

3.2 Resin jacket crown

Porosity: if the resin is mishandled.
Low wear resistance.
Risk of deformation.
Infiltration and change of color over time.

4. Indications

Unsightly anterior teeth, pulpy or depulpated, particularly the upper incisors when affected by cervical caries or apparent proximal caries.
Enamel and dentin abnormality
Teeth in slight misalignment.
Change in color after pulp mortification.
Teeth affected by abnormal shape or volume.

5. Contraindications

Short clinical crown.
Teeth too thin in the vestibulo-lingual direction.
Significant overbite, Crossbite, End-to-end occlusion.
Tight occlusion.
Dysfunction & parafunction.
The jacket crown cannot be used as a bridge anchor under any circumstances.

6. Preparation for crown jacket

a. Reduction of the vestibular face

A slightly truncated cylindrical diamond burr mounted on a turbine is used. As with the CCM, orientation grooves are dug on the vestibular face in two directions:
Three 1mm deep grooves will be parallel to the cervical 1/3.
Two 2mm deep grooves will be parallel to the incisal two-thirds.
The vestibular face of the preparation must present these two orientations in order to allow a thickness of the material compatible with a good aesthetic result and without running the risk of pulp lesion.
The surface of the incisal half is regularized by removing the remaining dental substance between the grooves, the reduction will be about 2mm. The 1mm reduction of the cervical part will be done in the same way with a flat-ended diamond bur.
The end of the diamond bur traces the cervical limit in the form of a shoulder. The width of the shoulder is 1mm, it will be subgingival and perpendicular to the axis of the tooth.
At the end of the cut, if we look tangentially at the preparation, the vestibular face of the reduced tooth must be set back in the profile of the adjacent teeth taken as references.

b. Reduction of the palatal face

Creation of the palatal shoulder

Made using the diamond bur already used for the reduction of the vestibular face, it is cut immediately to its final level by holding the bur parallel to the cervical 1/3 of the tooth.
This shoulder, 0.8 to 1 mm wide, is extended around the linguo-proximal angles, uniting it with the other shoulders, thus the cervical 1/3 of the preparation forms a cylindrical ring and constitutes the main retention zone of the future jacket crown.
Reduction of palatal concavity

It is done using a diamond burr using mesio-distal back and forth movements.
The reduced thickness depends on the existing occlusal relationships between the prepared tooth and the antagonist teeth.
This must be sufficient, this area will have a concave shape in the horizontal and vertical direction.

c. Reduction of the incisal edge

Always carried out after the size of the vestibular and palatine faces, will be 1.5 to 2mm.
At the end of the preparation, the incisal edge should be beveled obliquely, from bottom to top in the palatal direction for the upper teeth and from the vestibular side for the lower teeth.

d. Reduction of proximal faces

A long, thin diamond bur is used to remove contact points and proximal bulges , placing the bur at the level of the enamel-dentine boundary and parallel to the axis of the tooth.
The proximal shoulders are created in the extension of the vestibular shoulder, the mesial and distal faces are made flush and convergent towards the free edge.

e. Preparation control

Ensure that the reduction of the stump is sufficient to meet the aesthetic and mechanical requirements of the jacket crown (check with the silicone key).
The stump must be exposed and parallel to the long axis of the tooth.
Well located and continuous shoulder.
Check the occlusal relationships: sufficient space between the preparation and the incisal edge of the opposing teeth in all occlusal positions.

f. Finishing the preparation

It is done with fine-grained cutters and at low speeds.
All sharp corners will be softened and rounded
The connecting angles between the different faces are rounded
The shoulder must have continuity between the different shoulders and must not present any irregularities.
The stump can be lightly polished to obtain a finer impression of the preparation.

7. Taking impressions, choosing the shade and temporary prosthesis

This step is the same as for other crowns. An impression will be taken using proper technique and suitable material.
The stump will be protected with varnish, then a temporary cap will be put on which will have both an aesthetic and prophylactic role.

8. After trying the jacket in the mouth (biscuit): we make the icing in the laboratory, the aim of this step is to obtain a shiny surface

9. Final Sealing : sealed temporarily with temporary cement then permanently

Preparation on a posterior tooth