Techniques Of Fabrication Of Provisional Restoration

Techniques Of Fabrication Of Provisional Restoration

Describe different types of provisional restorations. Describe various techniques used for making provisional restoration for anterior and posterior tooth preparation.

Provisional Restorations Definition

A fixed or removable prosthesis designed to protect enhance esthetics, stabilization/or function for a limited period of time after which it is replaced by a definitive prosthesis.

Also known as interim, transitional, temporary, and treatment restorations

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Classification

• Custom made
• Prefabricated.

Custom made

• Cast metal (precious–gold scrap and nonprecious – Ni-Cr)
• Heat-polymerized resin treatment restorations (custom)
• Visible light-cure composite (Mortan et al. 1984).

Prefabricated

• Aluminum shell, (Brotman – 1952) copper band temporization (Amsterdam – 1950)
• Preformed metal crowns
• Cellulose acetate forms/Vinyl polymethyl methacrylate crowns (Snap and Trim – 1960)
• Prefabricated polycarbonate forms (Charles et al. 1973)
• External surface forms include polycarbonate cellulose acetate, aluminum tin-silver, and nickel-chromium.

Depending on the period of use as

• Short-term (up to 2 weeks, e.g. – polycarbonate or aluminum crowns )
• Medium-term ( >2 weeks, e.g. – resin-based provisionals)
• Long-term (for months, e.g.- cast-metal crowns).

Cas t- metal treatment restorations

• Indications
  • Patients with maladies difficult to diagnose
  • Patients with gross maxillomandibular discrepancies
  • As a healing matrix for medically compromised patients
  • For maintenance of vertical dimension
  • For duplication of the pretreatment canine function.

Variation

Preformed metal crowns can be modified at the gingival and then cast.

Heat-polymerized resins

• A wax pattern with the desired shape is made on the mounted casts
• Wax patterns are flasked, dewaxed, and packed with heat-cured acrylic resin and cured
• If the provisional restoration was fabricated on mock tooth preparations then the crown needs to be relined with resin before cementation.

Variation

Plastic denture teeth can be trimmed and lined with tooth-colored self-curing acrylic on the lingual aspect of the crown to fabricate aesthetically pleasing, functional treatment restorations.

Visible light-cured resin

• Based on urethane dimethacrylate (Provipont DC, Kristall)
• Good mechanical properties
• More shades available
• No residual monomer.

Visible Light – Light-Cured Resin Disadvantages

• Stains
• Expensive
• Lacks good marginal fit.

Aluminum shell crowns (aluminum and tin-silver)

Visible light Availability

• In anatomic tooth forms and cylindrical shells resembling a tin can.

Visible light Indication

• Only to be used in premolars and molars.

Visible light Technique

• A shell of suitable diameter is selected and festooned to adapt to the preparation and height of the gingival crest
• A resin mixture is placed within the shell for patients with a reduced interocclusal distance to enhance retention
• The shell is then removed, trimmed for adequate occlusal relationships, and seated with a sedative cementing media.

Visible light Technique Disadvantages

• Less marginal strength and proximal contacts
• Copper band temporisation is not biocompatible and has poor occlusion.
  • Preformed metal crowns
• Nickel–chromium shells are used primarily for children with extensively damaged primary teeth
• Nickel–chromium shells are not lined with resin but are trimmed and adapted with contouring pliers and luted with a high-strength cement
• Nickel–chromium alloy is very hard and thus can be used for longer-term provisional restorations.

Provisional Restorations Indications

• For the posterior teeth
• In pedodontics for fractured teeth.

Provisional Restorations Advantages

• Improved occlusal and axial surfaces
• Better biocompatibility than aluminum shells.

Cellulose acetate crown forms

• Cellulose acetate is a thin (0.2–0.3 mm), soft, and transparent material available in all tooth types and sizes
• Shades are dependent on the auto polymerizing resin
• Mold guides for different sizes and shapes are available.

Provisional Restoration Procedure

• A selected crown form is trimmed and festooned to fit the preparation.
• The selected crown is filled with any of the resins (polymethyl methacrylate, vinyl polyethyl methacrylate or epimine).
• Commonly used resin is polymethyl methacrylate.
• The resin-filled crown is gently pressed upon the lubricated preparation while the excess is removed.
• The crown matrix is repeatedly removed and reseated to minimize distortion and to ensure removal after the resin is set.
• The cellulose shell is peeled off after the material has been set.
• The occlusion is adjusted and the treatment restoration is trimmed and polished.

Prefabricated polycarbonate crowns

Indications

Can be used for anterior teeth (incisor, canine, and premolar).

Requirements of provisional restoration

Biologic – Pulp protection, periodontal health, occlusal stability, and enamel fracture.

Mechanical – Resist functional load, resist removal, and maintain inter abutment alignment.

Esthetic – Restore tooth contour, color translucency, and texture.

Techniques in Fabrication of Provisional Restorations

• Shells – customs, such as beaded acrylic and milled crown, and proprietary, such as plastic shells – polycarbonate and metal shells, such as aluminum and stainless steel
• Matrices can be formed by impression, vacuum-formed thermoplastic, and proprietary celluloid by either direct or indirect technique
• Direct syringing.

Provisional restorations can be done in the following modes

• Indirect
• Direct
• Indirect–direct.

Indirect procedure

In this technique, the provisional restoration is fabricated outside the mouth. Impression is made of the prepared teeth and is poured in quick-setting gypsum.

Fabrication of Provisional Restorations Advantages

• No contact of free monomer with the prepared tooth or gingiva
• The risk of pulpal damage to the tooth is less
• The marginal fit is better for this technique than the direct technique
• More comfortable for the patient with less chair side time.

Direct technique

Autopolymerizing Resin–Alginate Impression Technique

• An alginate impression of the teeth is made before tooth reduction and the impression is stored in a damp environment
• After tooth preparations are completed, acrylic resin is mixed and placed in the corresponding section of the alginate impression
• A separating agent is applied to the tooth preparations and the alginate impression is filled with the resin and is then replaced in the mouth
• The impression is removed when the resin reaches a doughy stage, and once the rigid stage is almost reached the temporary crown is removed from the alginate impression
• After evaluating occlusion in the mouth crown is finished, polished, and luted with an appropriate luting agent.

Vacuum-Formed Plastic Template Technique

• Transparent sheets in cellulose acetate or polypropylene in various sizes and thicknesses are available. Polypropylene or Omnivac is adapted over the unprepared cast using a thermal vacuum machine
• A suitable shade of auto-polymerizing tooth-colored acrylic resin is selected filled in the template and seated onto the lubricated tooth preparations
• The matrix is removed and reseated
• The restoration is copiously irrigated with cold water
• After the resin has been completely set, the matrix is removed, the crown trimmed to the correct finish line with a convex tissue surface and luted with temporary cement.

Fabrication of Provisional Restorations Disadvantage

Can cause pulpal injury if the polymerization temperature is not controlled.

 Post Crown Technique

• For endodontically treated teeth
• A wire (paper clip) or a nonprecious metal post is adapted to the canal
• The selected polycarbonate crown form is then filled with an acrylic resin and placed over the post, including a portion of the radicular surface of the tooth
• The crown form must be removed and reseated repeatedly to prevent resin from locking into undercuts
• After the resin has set, the crown is removed with the temporary post set within the resin
• The entire assembly of post extension and crown form is cemented with a weak adhesive.

Indirect–direct procedure

• After selecting an appropriate preformed crown with the gingival margin adjusted to approximate the gingival termination, tooth-colored acrylic is mixed and placed inside the crown.
• The filled polycarbonate crown is seated onto the lubricated tooth preparation on the model; the seated crown is reseated repeatedly to prevent excess resin from setting into proximal undercuts.
• After the resin has been set, the excess resin is removed, and the emergence profile and fit of the gingival margin are evaluated.
• The crown is polished and is cemented with a temporary sedative luting agent.

Indirect – Direct Advantages

• Chairside time is reduced
• Less heat is generated in the mouth
• Contact between the resin monomer and soft tissues is minimized.