Fabrication of provisional restoration on freshly prepared tooth : indirect and direct technique

Background: Provisional restorations are fabricated to protect the prepared tooth structure during period between the preparation and the final restoration, and the techniques applied are direct, indirect and indirect direct. Various materials are used to fabricate provisional restoration, such as, preformed crown, acrylic, metal shell, composite, etc. Objectives: The study was designed to evaluate the advantages of fabrication of provisional restorations by indirect technique over direct technique. Methods: This prospective comparative study carried out in the Department of Prosthodontics, Faculty of Dentistry, Bangabandhu Sheikh Mujib Medical University, Dhaka, from January 2006 to December 2007, included 20 patients each for insertion of provisional restorations fabricated by indirect (group A) and direct (group B) technique. Outcome was evaluated on the basis of marginal adaptation, biocompatibility and aesthetic status. Results: On day 7 of provisional restoration, grade I marginal adaptation were observed in 75% and 40% of group A and group B patients, respectively, and on day 15 were 75% and 20%, respectively. Grade I biocompatibility on day 7 of group A patients were 100% and group B 30%, and on day 15 was 95% and 35%, respectively. Grade I aesthetic status on day 7 were in 100% of both group A and group B patients, and on day 15 was 95% and 85%, respectively. None of the patients was in grade III, either in marginal adaptation, biocompatibility or aesthetic status. Conclusion: Indirect provisional restoration is better and safer in relation to marginal adaptation, biocompatibility and aesthetic status. DOI: http://dx.doi.org/10.3329/bjms.v14i1.21560 Bangladesh Journal of Medical Science Vol.14(1) 2015 p.59-64

Mechanically the provisional restorations, during function, must resist functional loads that occur during chewing as well as resist removal forces without fracturing 6 .
There are several methods, such as, direct, indirect and indirect direct technique to fabricate provisional restorations.Various materials are used to fabricate provisional restoration, such as, preformed crown, acrylic, metal shell, composite, etc.In the direct technique, the prostheses are fabricated in the patient's mouth by inserting an impression which is previously taken before tooth preparation and loaded with acrylic resin material.In the indirect technique, it is fabricated outside the patient's mouth, on a mode which is prepared from an impression taken before tooth preparation.In practice, direct technique is commonly used; but it has some disadvantages, like it caused more polymerization shrinkage of the prostheses that results in poor marginal adaptation, adverse reaction to oral tissue because of its residual monomer, proper curing of the material is not possible in presence of oral fluid, and also exothermic heat produced during polymerization causes discomfort to the patient.On the other hand, as in the indirect technique, the prostheses is prepared outside the mouth in the laboratory, therefore, it is free from these disadvantages, though it takes more time and extra cost.Many dentists will not go for indirect provisional restoration because of high laboratory cost.However, indirect provisional restorations have certain advantages: (a) stronger and durable material like acrylic resin can be used; (b) any aesthetic or occlusal change can be made on an articulator, (c) there is also no contact of free monomer with the prepared tooth or gingival than cause tissue damage, and (d) it avoids subjecting a prepared tooth to the heat created from the polymerizing resin.).Separating medium is applied uniformly with a camel hairbrush, over the tissue surface form and allowed to dry.When the cast is thoroughly dry, the finished line of the preparation is marked with a sharp and soft lead pencil to serve later as a guide for trimming.Autopolymerizing resin (opaque variety) is mixed.The mixing is then poured into the tissue surface form (mould should not be overfilled and the resin should reach the level of the gingiva).The TSF is sealed into the external surface form, and lightly held together by rubber bands.The assembly is then placed in warm water.After five minutes it is removed and the external surface form is separated from the cured resin restoration, which usually remains in contact with the tissue surface form.
Resin flush is eliminated with an acrylic trimming bur and a fine grit garnet paper disk.Care is taken for any resin blebs or remnants of stone on the internal surface of the restoration.Finishing touch is given with carborundum bar and polishing is done with wet pumice powder.The final restoration is cemented with zinc oxide eugenol cement on the prepared tooth surface.

Provisional restoration by direct technique
First, an impression is made with silicone rubber and sectional impression tray, and then tooth preparation is carried out by maintaining standard technique.
After tooth preparation and bleeding control, the prepared tooth and the surrounding tissue is coated with petroleum jelly.The autopolymerizing resin is mixed and loaded into the impression taken earlier.The resin is allowed start polymerization, When the rubbery stage of polymerization (about 2 min in the mouth), it is removed from the mouth and excess material is removed with a scissors and again inserted into the same place.During this procedure, sufficient aircooling is provided with a air syringe over the area.After the polymerization is complete, the tray along the restoration is removed from the mouth and the restoration is departed from the impression and soaked in warm water for 3

Table 1: Marginal adaptation of provisional restoration
the distribution was highly significant (P<0.001).On day 15, biocompatibility of grade I was seen in 19 (95%) and 7 (35%) patients, and biocompatibility of grade II was seen in 1 (5%) and 13 (65%) patients of group A and B, respectively.Variation was highly significant (P<0.001).Biocompatibility of grade I and grade II of group A patients on day 7 was 20 (100%) and 0 (0%), and on day 15 was 19 (95%) and 1 (5%), respectively.No significant variation was observed.Biocompatibility of grade I and grade II of group B patients on 7 was 6 (30%) and 14 (70%), and on day 15 was 7 (35%) and 13 (65%), respectively.The variation was statistically not significant.Choudhury M, Nahar N, Yazdi S, Choudhury F, Sultana A Most patients, however, require a more conventional approach.Fabricating provisional restorations directly on teeth using the 'direct method' is suitable for single units and up to 4 unit partial denture provisional restorations 23 .

Conclusion:
Provisional restorations fabricated by direct technique though cheaper and easier to fabricate but have certain disadvantages, like it shows poort marginal adaptation because of polymerization shrinkage, its residual monomer causes tissue inflammation and exothermic heat of polymerization causes pulpal damage and discomfort to the patient.On the other hand, indirect provisionals have certain advanges, such as, stronger and durable material like acrylic resin can be used, any aesthetic or occlusal change can be made on an articulator, no contact of free monomer with the prepared tooth or gingival that can cause tissue damage, and marginal fit is better.Although longer time is required to fabricate an indirect provisional restoration, it reduces the clinical time.We may conclude that marginal adaptation, aesthetic and biocompatibility, fabrication of provisional restorations by indirect technique on a freshly prepared tooth is better than restorations fabricated by direct technique.

Fabrication
Indirect technique (n=20) Group B : Direct technique (n=20) Fisher's exact test, ns = Not significant 5 min.Margins are marked with a pencil.Voids in the restoration is checked and corrected by additional material.Excess material is trimmed up to the finish line.The restoration is completed by carborundum bur and polished with polishing material (stone bur, sandpaper No. 0, pumice powder).The final restoration is cemented with zinc oxide eugenol cement on the prepared tooth surface.
Evaluation: The prepared provisional restoration was evaluated in patient's mouth for marginal adaptation of the prostheses to the prepared tooth, biocompatibility of the restoration and aesthetic status on day 7 and day 157-8.Any defect was corrected by adding resin.Marginal adaptation:The index was based on the adaptation of the restoration to the margin of the prepared tooth.Grade I: No visible evidence of crevice along the margin into which explorer will penetrated.Grade II: Visible evidence of slight marginal discrepancy with no evidence of decay; repair can be made or is unnecessary.Grade III: Discoloration on the margin between the restoration and the tooth surface.Biocompatibility: The index was based on the criteria of gingival redness and bleeding on probing.Grade I: No bleeding on probing and no plaque accumulation.Grade II: Mild to moderate bleeding.Grade III: Severe bleeding.Results: Table1shows marginal adaptation of provisional restoration of grade I and grade II (none in grade III) of group A and group B patients on day 7 and day 15.On day 7, marginal adaptation of grade I was seen in 15 (75%) and 8 (40%) patients, and marginal adapta-

Table 3
On day 7, marginal adaptation of grade I was seen in all 20 (100%) patients of both group A and group B. On day 15, aesthetic status of grade I was seen in 19 (95%) and 17 (85%) patients, and aesthetic status of grade II was seen in 1 (5%) and 3 (15%) patients of group A and B, respectively.Statistically, no signifi-

Table 3 : Aesthetic status of provisional restoration
be secured to the cast on which the provisional shell is polymerized 19-21 .Moreover, fabricating a provisional restoration wholly or in part using an indirect method reduces exposure of oral tissues to monomer, heat, shrinkage and reduces the volume of volatile hydrocarbons inhaled by a patient18,22 .