The crown cast.
Full metal crown.
Summary :
Introduction………………………………….1
I-Definition……………………………………1
II-Advantages and disadvantages……………1
III-Indications and contraindications……2
IV-Specifications for coronary preparation …………………………………….2
V-Methodology of preparations………4
VI-After preparation ………………….6
-The temporary crown…………………..6
-taking fingerprints……………………..6
-Casting of prints ………………….6
-Laboratory steps………………7
VI-Clinical trial and sealing…………7
VII-Conclusion ……………………………..7
Bibliographic references…………….7
4th year dental medicine course
Academic year 2023-2024
Introduction: [1]
The cast metal crown does not meet today’s aesthetic criteria, yet it is still one of the most frequently used prosthetic methods.
- Definition: [1]
The cast crown or metal crown is a prosthetic device which consists of completely covering the coronal part of a tooth previously cut using specific instrumentation, in order to give it a morphology adapted to its needs.
- Advantages and disadvantages: [2,3]
- Only one drawback: unsightly (metal).
- On the other hand, many advantages:
- Resistant, solid
- well tolerated by the marginal gingiva
- Little damage to dental tissues
- Low cost
- Easy construction in the laboratory.
The cast crown
- Indications when and why? [3,4]
In the absence of aesthetic requirements, it is indicated when the carious decay of the tooth concerns all axial faces.
It is also indicated when it provides a prosthetic pillar function.
The indications for cast crowns are:
– Pulped cuspid teeth, presenting losses of substances or large coronal reconstructions
Contraindications:
– Apical or periapical lesions that are difficult to treat and stabilize
-Intra-radicular lesions (furcations)
-Bone lysis reducing the clinical crown-root ratio.
-Unstabilized periodontal disease.
-A low coronal height within a tight occlusion.
IV- Specifications for coronary preparation: [3]
- Dental reduction:
Dental reduction has two major objectives:
- Allow sufficient space for the prosthetic crown to avoid any over-contouring or over-occlusion
– The preparation must be regular, homothetic and respect the orientation of the axial walls, the position of the grooves and the inclination of the cusp faces.
- Achieve morphology and contour shapes with a draft angle
- Cervical limit:
The cervical limit separates the prepared part from the unprepared part of the tooth. It must be perfectly readable by the practitioner.
Situation :
The cervical limit can be located at a distance from the marginal periodontium or, on the contrary, in contact with it. This supra-gingival, juxta-gingival or intra-sulcular situation is dictated by the need for retention and by the pulp volume.
- Outline shape:
The shape of the cervical limit outline for a cast crown of choice is the fillet . This finishing line is in fact perfectly readable for the practitioner and for the dental technician. In addition, it allows a thickness of metal at the neck which guarantees sufficient rigidity of the edges (3 to 5/10ths of a millimeter). Fig 1
The cast crown
Fig1: Cervical margin in the form of a fillet of a cast crown preparation.
- Nature of the alloy:
- Precious alloys: noble metals have excellent resistance to corrosion and are very well tolerated in the mouth.
- Non-precious nickel-chromium and chromium-cobalt alloys: Proposed mainly because of their lower cost. They have excellent mechanical properties and greater rigidity than gold alloys. However, they are sometimes implicated in hypersensitivity reactions.
- Instrumentation:
- Diamond burs for dental preparation. The end allows to obtain a perfectly readable “quarter round” type cervical limit:
-The strawberry marked with a green ring, of fine grain size.
-The cutter marked with a red ring, of lower grain size, is used for finishing the preparation.
- Methodology of preparations: [2]
The two essential notions to take into consideration during the clinical act are, on the one hand, the quantity of dental tissue to be removed and, on the other hand, the clearance to be respected .
The cast crown
The control method using a silicone key cut along a vestibulo-lingual axis, serving as a reduction guide (quantity of tissue to be subtracted).
Fig. 2: A silicone key, made before preparation, allows the depth and orientation of the reduction to be controlled.
The step-by-step preparation of a maxillary molar intended to receive a cast crown is illustrated in Figures 2 to 9:
3- The occlusal reduction of this maxillary molar is performed starting with the internal cusp faces of the vestibular cusps. The orientation of the edges and grooves is respected. The unprepared part allows the depth of the reduction to be assessed.
4- The occlusal preparation is complete. The orientation of the reduction of the external cusp sides respects the functional anatomy of the tooth.
5- Preparation of the vestibular surface. The location of the cervical limit, of the fillet type, is established immediately.
6- Homothetic reduction of the lingual face. The preparation stops well below the proximal contact points.
7-The passage of the contact points requires a more tapered instrument, so as to “cut” the proximal wall. Thus, the adjacent tooth is not at risk of being damaged. It is then easier to perfect the continuity between the vestibular and lingual faces.
8-Occlusal view. The convergence of the walls is checked in monocular vision.
9-The finishing of the preparation is carried out using fine-grained diamond instruments. The protruding edges are softened.
- After preparation :[3,4]
- Temporary crown:
The stump, whether pulped or not, must be protected by a temporary crown that will protect the damaged (attacked) dental tissues from the salivary environment, and that will prevent the movements of the stump and neighboring teeth, and will also maintain the gingival limits at their level. This temporary protection is obtained:
• Using a prefabricated metal alloy crown.
• Using a preformed polycarboxylate resin crown.
- Taking a fingerprint:
Current impression materials from the elastomer family (polyethers, Thiocols; silicones) make it possible to obtain excellent impressions.
- Rebased imprint (wash technique)
The principle of the relined impression is simple; A first impression using a high viscosity elastomer, loaded into a standard impression holder, is carried out after
having placed a deflector cord in the gingival sulcus.
After complete setting, the impression is removed, rinsed, checked and its edges are shortened. The marginal gingival tab of the stump is removed with a scalpel and lateral evacuation vents (openings) are created starting from the vestibular and lingual surfaces of the preparation.
The stump and impression are dried, then the low viscosity elastomer is first injected using a special syringe into the impression and then onto the stump in the mouth and around the cervical margins.
Again, the impression is placed in the mouth and precisely centered on the arch, it will be maintained by fairly strong digital pressure for a few seconds.
- The antagonistic imprint with alginate
→Casting of prints:
- Casting the relined imprint:
Including the stump, its goal must lead to obtaining a precise model from which it is possible to detach a positive unit model (MPU) also called DIE corresponding to the preparation.
- Casting of the antagonistic imprint.
– Sculpture of the wax model:
The added wax technique allows to obtain a perfect anatomical and functional reproduction of the occlusal face of the crown. Fig 1,2,3
-Coating:
Cylinder Preparation: See Fig 4.5
Casting the coating
Metal casting
Finishing and polishing: Fig 6
- Clinical Trial and Sealing:
The cast crown, after fitting in the mouth and any necessary adjustments, must first be sealed provisionally using temporary cement (ZnO) for a week, then it will be sealed permanently using glass ionomer cement.
The cast crown
The cast crown
The cast crown
VII-Conclusion:
For over 100 years, the cast crown has stood the test of time with the assurance of a solid and resistant anchoring, its low cost combined with mechanical and functional qualities makes it a cap of choice to this day.
Bibliographic references:
1-Marcel Begin. The cast metal crown. Dental information No. 39, 2003
2-R Escalassan. Educational interests of the cast crown Prosthetic strategy April 2008 Vol 8 N°2
3-Shillingburg. Fixed prosthesis preparations: Principles and clinical application. CDP Edition
4-J Schittly. Manual of fixed single prosthesis. Masson Edition 1991
The cast crown
Wisdom teeth can be painful if they are misplaced.
Composite fillings are aesthetic and durable.
Bleeding gums can be a sign of gingivitis.
Orthodontic treatments correct misaligned teeth.
Dental implants provide a permanent solution for missing teeth.
Scaling removes tartar and prevents gum disease.
Good dental hygiene starts with brushing twice a day.