Joint prosthesis seals

Joint prosthesis seals

I. Introduction:

• Sealing represents a succession of acts constituting the last phase in the construction of a fixed prosthesis, if for many years this connection was made by sealing, over the last decades, the nature of the prosthetic rehabilitation materials that must be assembled has become significantly diversified, also favoring the development of new assembly methods by bonding.

II. Definition:

Sealing consists of bonding a prosthetic restoration to dental tissues with a bonding material which ensures the filling and sealing of the tooth-prosthesis interface. 

III. Objectives of sealing

• Create and maintain a seal by closing the dento-prosthetic gap
• Prevent marginal percolation phenomena.
• Participate in the retention of the prosthetic part.

The sealing cement must not under any circumstances repair:

• a misalignment of the anchor on the supporting tooth.
• a lack of concept of a restoration:

         _ failure to respect the parallelism of the walls resulting in a non-retentive stump.

          _ an insufficient number of pillars.

          _ a defective occlusion.

• an aesthetic error, that is to say, of shape, shade and height.

 V. Characteristics of the ideal material for the dento-prosthetic interface :

• Resistance to physical and chemical aggressions of the oral environment. 
• Resistance to mechanical stresses of mastication.
•  Resistance to water absorption and solubility. 
•  Have scientifically demonstrated biocompatibility. 
•  Have bioactivity by release of cariostatic antibacterial agents. 
• have simple and rapid clinical manipulation without risk of hazard.
•  Have working hours compatible with the installation of multiple prostheses. 
• Have a wide choice of shades for restorations with high aesthetic requirements. 
• Allow easy removal of excess. 
• Have versatility in compatibility with different prosthetic materials. 
• Be affordable.

VI. Classification of sealing cements

1. Temporary sealing cements

• Transitional sealing cements are intended for temporary sealing of the dento-prosthetic hiatus. 

Thanks to these transitional cements, we can:

• Managing the intermediate stages of prosthetic rehabilitation.
• Evaluate possible reactions of vital teeth after preparation.
• evaluate and validate the occlusal choice

1. Zinc Oxide Eugenol Cement: Eugenate

It is an organo-mineral cement that comes in the form of a powder and a liquid.

Properties of the dough:

• • low tensile strength.
•    • Low thermal conductivity;
•    • solubility of 2.5%.
•    • Antiseptic power.
•  Disadvantages:
•    • Proximity pulp cytotoxic;
•    • Slow setting;
•    • Irritating to the oral mucosa;
•    • Potential allergen;
•    • Short term degradation.

Indication:

• Temporary sealing of restorations (pulped/depulped tooth).
• Protective base.
• Temporary filling materials.

Presentation: 

**Powder – liquid: 

**Dough-dough

2. Zinc oxide cement without eugenol

The removal of eugenol was necessary because this product inhibits the polymerization of composites and interferes with the polymerization of glass ionomers.

An alternative for patients allergic to eugenol.

3. Improved zinc oxide cement: EBA (ethoxy benzoic acid)

consisting of a powder-liquid mixture:

• Powder: mixture of zinc oxide and aluminum oxide (20 to 30%).
• The liquid: mixture of orthoethoxybenzoic acid (2/3) and eugenol (1/3).

D. Calcium hydroxide:

These cements are mainly used as cavity liners because the presence of calcium ions promotes the formation of healing dentin.

• Thermal property:

     Very low thermal conductivity

•    • PH: strongly 
•    • Antiseptic action thanks to its alkaline PH;
•                      anti-inflammatory;
•                      sedative action;
•                      hemostatic action.
•                      dentinogenetic action.
• Protective E-Varnish
• These are organic materials intended for the protection of the dentino-pulp complex used in deep cavities under intermediate bases. 
• Varnishes are most often natural gums (calp-rosin) or synthetic resin dissolved in an organic solvent such as acetone.
• Used as protective bases against the acidity of cements and in deep cavities . 

2- the usual sealing cements

Indication

• Crowns cast in precious or non-precious alloy 
• Metal-ceramic restorations 
• Orthodontic bridges and braces 
• The spatula must be able to lift a thread of cement that does not break when starting from the glass plate. 

The cement is placed on the axial walls of the intrados of the crown, it is never necessary to fill or put cement in the bottom of the crown.

2. Polycarboxylate cements

powder: zinc oxide and magnesium oxide + polyacrylic acid 

Zinc polycarboxylate cement

Indications

• Sealing on vital teeth 
• long-term temporary seals 
• Temporary filling or cavity bottom
• Sealing of orthodontic bands and pedodontic crowns 
• 3. Glass ionomer cements:

Joint prosthesis seals

a. Conventional glass ionomer cement

Polyacrylic acid + Aluminosilicate glass = Polyalkenoate glass cement  

Indications:

• Crowns with a supragingival or juxta- gingival finishing line
• ¾ crowns, inlays, onlays, in non-precious alloys or in precious alloys  

b-Resin-modified glass ionomer cements

aluminofluorosilicate glass + polyacids = resin (HEMA or Bis-GMA)

c-compomers:

• The basic structure consists of a resin matrix to which monomers of hydrophilic carboxylic groups are added. They also contain fluoro-alumino-silicate type fillers.
• Presentation and packaging:
• Capsules
• Powder – liquid 
• Dough – dough 

Number of prosthetic pillars

When there are a large number of prosthetic abutments, the cement must have a sufficiently long working time to allow the total insertion of the prosthesis.

Pulp vitality

The acidic pH of zinc phosphate cement causes pulp irritation , which contraindicates its direct use on living teeth.

They are therefore only used on teeth 

perfectly mature provided that a pulp protection varnish, such as copalite, is applied before sealing

This varnish will however tend to reduce the surface roughness and therefore the quality of the microkeying.  

Sealing failure

• According to BACKER For tooth-supported prostheses. The most frequent technical complication is loss of retention.
• It is caused mainly by:

-Inadequate preparation of the stumps 

-Sealing failure

• Inappropriate choice of cement 
• Extended mixing time
•  Incorrect powder to liquid ratio either due to thinning of the mixture or thick mixing
•  The thick cement space
•  Inclusion of cotton fibers
•  Insufficient pressure during sealing
•  An old cement that has lost its mechanical properties.

The unsealing

corresponds to the removal of the prosthesis by disintegration of the cement joint. This allows the prosthetic element to be separated from the dental abutment(s). 

Disassembly

consists of removing the prosthetic element in order to gain access to the prosthetic pillar; when the priority is to preserve the integrity of the prosthetic pillar, it then becomes necessary to reversibly or irreversibly damage the prosthetic structure,

indications

• Local coronary-radicular complications (caries, pulpitis).
• Periodontal complications (retraction, mobility).
• overbite.
• Loss or discoloration of the cosmetic element.
• Repair, addition of one or more bridge elements.

Joint prosthesis seals

Conclusion :

1/4 of failures encountered in joint prostheses are due to a sealing failure.

 – This results in recurrences of caries, pulpitis, over-occlusion, and often loosening.

– To overcome this, we must know how to choose the sealing cement best suited to our clinical situation, know its properties and we must apply ourselves rigorously during the different stages. 

Good oral hygiene  Regular scaling at the dentist  Dental implant placement Dental x-rays  Teeth whitening  A visit to the dentist  The dentist uses local anesthesia to minimize pain  

Joint prosthesis seals