INTERIM FIXED RESTORATIONS

INTERIM FIXED RESTORATIONSPRESENTED BY- MAHAK RALLIFINAL YEAR

DEFINITIONAn interim prosthesis is a fixed or removable dental prosthesis, or maxillofacial prosthesis, designed to enhance aesthetics, stabilization and/or function for a limited period of time, after which it is to be replaced by a definitive dental or maxillofacial prosthesis. Often such prosthesis are used in determination of the therapeutic effectiveness of a specific treatment plan or the form and function of the planned for definitive prostheis.

INTRODUCTIONThe word interim means established for the time being, pending a permanent arrangement. Even though a definitive restoration may be placed as quickly as 2 weeks after tooth preparation, the interim fixed restoration must satisfy important needs of the patient and dentist.Whatever the intended length of time of treatment, an interim restoration must be adequate to maintain patient health. It should not be casually fabricated on the basis of an expected short term of use.

REQUIREMENTS

BIOLOGIC REQUIREMENTSPulp protection : an interim fixed restoration must seal and insulate the prepared tooth surface from oral environment to prevent sensitivity and further irritation to the pulp.

Periodontal health : to facilitate plaque removal, an interim fixed restoration must have good marginal fit, proper contour and a smooth surface, specially when crown margin is placed apical to gingival margin.

BIOLOGIC REQUIREMENTSOcclusal compatibility and tooth position: the interim restoration should establish or maintain proper contacts with adjacent and opposing teeth. Inadequate contacts allow supra eruption and horizontal movement.

Prevention of enamel fracture : interim fixed restoration should protect teeth weakened by crown preparation.

MECHANICAL REQUIREMENTSFunction : Greatest stress in an interim fixed restoration occurs during chewing. Breakage occur more frequently in partial-coverage restorations and fixed partial denturesGreater strength is achieved by reducing the depth and sharpness of the embrasures.

MECHANICAL REQUIREMENTSDisplacement :Displacement is best prevented through proper tooth preparation and an interim restoration with a closely adapted internal surface.Excessive space between the restoration and tooth places greater demands on the luting agent, which has lower strength and cannot tolerate added force. Unlined preformed crowns should be avoided.

MECHANICAL REQUIREMENTSRemoval for reuse:Interim restorations often need to be reused and so should not be damaged when removed from the teeth.

If cement is sufficiently weak and restoration has been well fabricated, it does not break upon removal.

ESTHETIC REQUIREMENTSThe temporary must have adequate contours, color, translucency and texture.This is especially important in anterior teeth. Because acrylic tends to darken and discolor over an extended period of time, a different provisional restorative material may need to be selected if the temporary is to be worn for a long period. A smooth polished surface is important for esthetics as well as plaque removal.Crispin and Caputo studied the color stability of provisional materials.They found that methyl methacrylate materials exhibited least darkening, followed by ethyl methacrylate and vinyl-ethyl methacrylate materials. They also reported that increases in surface roughness induced increases in material darkening and pressure polymerizing did not influence discoloration relative to air polymerizing.

MATERIALS AND PROCEDURESAll the procedures that are followed to prepare an interim restoration include a common formation of mould cavity into which plastic material is poured or packed. Mold cavity is created by two correlated parts : the external contour of the crown known as External Surface Form (ESF) and the prepared tooth surface and the edentulous ridge (when present) known as the Tissue Surface Form (TSF).

External Surface Form (ESF)There are two categories : Custom and Preformed.CUSTOM A custom is a negative reproduction of either the patients teeth before preparation or a modified diagnostic cast.PREFORMEDVarious preformed crowns are available commercially.

CUSTOMMaybe directly obtained with any impression material (irreversible hydrocolloid and silicone are convenient)Easy accurate reseating done by trimming the thin areas of impression material (inter proximally or gingival margin)

Baseplate wax can be usedas it is more convenient and economical

PREFORMED These prefabricated crown rarely satisfy the requirements of a interim restoration, but they can be thought of as ESFs rather than as finished restorations and must be lined with autopolymerising resin. Most crown forms need modifications- internal relief, axial re-contouring, occlusal adjustment- in addition to lining procedure.

Preformed crowns are generally limited to use as a single restoration, because it is not feasible to use them as pontics for FPDs.

Materials from which preformed ESFs are made include: PolycarboxylateCellulose acetateAluminiumTin silverNickel chromium

PolycarboxylateHas the most natural appearanceAvailable in single shadeAvailable for incisor, canine and premolar teethPolycarbonate crown forms are more tolerable, selected to establish contact areas

Cellulose acetateCellulose acetate crown form consists of thin, soft, and transparent material. Sizes and shape can be selected from a mold guide. The crown form is trimmed and festooned to fit the preparation without impingement on the soft tissue.Available in all tooth types

Aluminium Suitable for posterior teethHave anatomical shaped occlusal and axial surface.Care must be taken during try in verification to avoid fracture of their delicate marginsAs it is highly ductile , it allows easy contouring

Tin-silverTin Silver preformed crowns are available for posterior teeth.This alloy is very soft and the margin of the crown can be flexed prior to seating with a swaging block. This produces a close marginal fit after the shell is trimmed with a bur. These should also be lined with acrylic resin to provide good internal adaptation and retention of the temporary

Nickel-chromium Used in children with extensively damaged primary teethThey cannot be altered with resin These crowns can be easily re-contoured using pliersIndicated for long term interim restorations.

Tissue Surface Form (TSF)Two categories : indirect direct

A third category: indirect-direct

Custom Indirect provisional restoration The technique involves fabrication of the interim restoration outside the mouth.

There is no contact of free monomer with the prepared teeth or gingival which might cause tissue damage and an allergic reaction or sensitization. The technique avoids subjecting prepared tooth to the heat evolved from the polymerizing resin. Indirect technique produces restoration with a superior marginal fit and as an auxiliary is involved in fabricating the restoration in the lab, it frees the patient and dentist for considerable amount of time

Custom Indirect Provisional RestorationPrincipal disadvantage of the technique includes increased chair side time and increased number of intermediate steps. It is a tedious task to perform if there is inadequacy of assistants or the laboratory facilities. In addition, the technique involves use and possible damage of diagnostic casts

Procedure (1) On the diagnostic cast, place a selected acrylic tooth on the area of the missing tooth, and seal it with the carding wax.

(2) Following this, a silicone putty index is made involving at least one tooth each beyond the abutment teeth.

(3) Prepare the patients teeth in the usual manner.

(4) Make a sectional impression of the prepared teeth and the adjacent structures and pour a check cast.

Procedure(5) Lubricate the check cast with a petroleum jelly or any suitable separating media, mix the provisional restorative material, and place it in the tissue surface of the index and seat it on the check cast.

(6) Try in the preformed restoration for its fit on the cast and intraorally.

(7) Reline the temporary restoration to perfect the internal fit.

(8)Finish, polish, and cement the restoration

Custom Indirect-direct interim restoration The technique produces a custom made preformed external surface form of the restoration but the internal tissue surface form if formed by the underprepared diagnostic casts

AdvantagesWith the combination indirect-direct technique, chair time can be reduced, since the provisional shell is fabricated before the patients appointment. Enhanced control over restoration contours minimizes the time required for chair side adjustments. Smaller amount of acrylic resin will polymerize in contact with the prepared abutment, resulting in decreased heat generation, chemical exposure, and polymerization shrinkage compared to the direct technique

DisadvantagesThe disadvantage of this procedure is the potential need of a laboratory phase before tooth preparation and the adjustments that are frequently needed to seat the shell completely on the prepared tooth.

Procedure (1) Pour an accurate pretreatment diagnostic cast from an impression of the unprepared teeth. For FPDs, wax a pontic into the edentulous area of the study cast, and modify with wax to obtain ideal contours, contacts, and occlusion.

(2) Lightly lubricate the modified diagnostic cast, and make an impression using a high-viscosity elastomeric impression material. To provide an adequate bulk of material at the margins of the provisional, trim the sharp edge on the elastomeric over impression that represents the gingival crevice with a round bur to allow for extra bulk of resin material in this area. The silicone putty index is made involving at least on tooth each beyond the abutment teeth.

Procedure(3)Remove the acrylic tooth and prepare the abutments on mounted diagnostic casts. (The diagnostic cast preparations should be more conservative than the eventual tooth preparation and should follow precisely the gingival margins

(4) Lubricate the prepared diagnostic cast with a petroleum jelly or any suitable separating media, mix the provisional restorative material, and place it in the tissue surface of the index and reseat it on the prepared diagnostic casts.

Procedure(5) After the acrylic resin has polymerized, finish the restoration. The provisional restoration should be paper thin and correctly contoured, and it should precisely follow the gingival margins on the cast

(6)Prepare the patients teeth in the usual manner (to the gingival margins).

(7)Try in the preformed restoration. (If the amount of tooth reduction is adequate, the provisional restoration will show optimal marginal fit with no need for adjustment.)

Procedure(8)Reline the temporary restoration to perfect the internal fit.

(9)Finish, polish, and cement the restoration

Direct interim restoration In the direct technique, patients prepared teeth and the gingival tissues directly provide the tissue surface form eliminating all the intermediate laboratory proceduresThis is convenient when assistant training and the office laboratory facilities are inadequate for efficiently producing an indirect restoration

Direct interim restorationHowever the direct technique has significant disadvantages like potential tissue trauma from the polymerizing resin and inherently poorer marginal fit.

Therefore, the routine use of directly formed interim restoration is not recommended when indirect techniques are feasible.

Procedure(1)Before the tooth preparation, place an acrylic tooth in place of the missing tooth and make an alginate impression or a putty index.

(2)Prepare the patients teeth in the usual manner.

(3)Lubricate the prepared teeth and the adjacent gingival margins with petroleum jelly, and reseat the index or the alginate impression with provisional restorative material in the dough stage on the tissue surface of the impression.

(4)Remove and reseat the restoration until it sets.

(5)Finish, polish, and cement the restoration

THANK YOU.