Introduction

An interim or provisional restoration functions as a temporary prosthesis for the prepared tooth before final one is delivered (1).  Success of provisional restoration depends upon good marginal adaptation as it promotes gingival health during the period between tooth preparation and placement of final restoration. It also prevents from any thermal, bacterial and chemical insults to the pulp. A poorly adapted provisional restoration induces plaque accumulation leading to periodontal disease ranging from gingival inflammation to periodontal support breakdown (2-11).Proper fit of provisional restoration and low solubility of cement are two factors that would reduce any discomfort for the patient during the interim period before permanent restoration delivery (8). The longer provisional restoration is on the tooth, the higher chance that its fit and contour will affect the health of gingival tissue. Various clinical situations may require a provisional restoration for an extended period such as surgical crown lengthening procedures, full mouth prosthetic rehabilitations and certain cases of immediate implant placement. Different interim restoration materials are used that can be divided into four groups according to their composition: polymethyl methacrylate (PMMA), polyethyl or butyl methacrylate, micro filled bisphenol A-glycidyl dimethacrylate (Bis-GMA) composite resin  and urethane dimethacrylate (light polymerizing resins). The primary monomer determines many of material characteristics such as polymerization shrinkage, strength and exothermic heat of reaction (10). Bis-acryl composite resin-based materials are commercially popular because of their handling properties, ease of use and superior mechanical properties, including hardness, flexural strength, and modulus of elasticity (2, 12-15).However, polymerization shrinkage, exothermic setting reaction and irritation associated with monomer are amongst the material’s disadvantagesand relatively lower levels of finish and fine marginal adaptation have been reported (4,16-18). Moreover, working and resultant biophysical properties can be influenced by monomer to powder ratio. Recently, visible light cured resins have been introduced based on urethane dimethacrylate. These relatively expensive resins have good mechanical properties and because of light cure polymerization, the operator has more control over material’s working time. Polymers made with low molecular weight urethane dimethacrylates have similar or slightly less water sorption than polymers prepared from bis-GMA (19, 20).Lately, a newer dual-cure material has been introduced as a provisional restoration material, i.e. rubberized urethane which provides a better marginal adaptation and ease of application compared to self-cure acrylic temporization materials. Further, it claims to have better strength and polishing characteristics that might serve as a promising evolution to the existing interim materials. Very limited literature exists on performance of dual cure rubberized urethane based temporary materials. Therefore, this study was undertaken to evaluate and compare the marginal accuracy of this material in comparison to already existing commercially popular interim restorative materials over two intervals: one hour after fabrication and after one week.

Materials and Methods

An Ivorine® mandibular right first molar typodont tooth (Columbia Dentoform Corp, New York) was prepared for a full coverage crown with a 1- mm chamfer (SO-21, Mani, Japan) finish line and a taper of approximately 5 degrees. An impression of prepared crown extending up to the apex of the typodont was made using polyvinylsiloxane (PVS) (Affinis, Coltene, Switzerland). Type II inlay wax was poured into impression of the prepared crown. In laboratory, a metal die using base metal was fabricated from the wax pattern using lost wax technique. The metal die was called as master die. Die was finished and polished and four vertical reference points were marked on the buccal, lingual, mesial and distal sides respectively.

The metal die was lubricated with petroleum jelly and a wax pattern was made on the metal die with Type II inlay wax. Wax pattern was made to simulate anatomy of mandibular first molar. It served two purposes; 1) To make matrix for fabrication of crowns using interim material 2) To mark the proper orientation of crown matrix with master die. A putty matrix was essential to hold the provisional restorative material over the prepared tooth. PVS putty impression of the die was made along with crown analogue. For this, an equal amount of base and catalyst material of the putty impression material was mixed as per the manufacturer’s directions with respect to proportioning and mixing and was placed over the die. The polymerized impression served as the matrix for making provisional restorations.

A total of sixty samples, twenty from each group were fabricated on prepared customized metal die following the manufacturer’s instructions. Three test groups were Group A - Protemp^TM 4 (3M ESPE AG Dental Products, Germany), a bis-acrylic based self-cure temporary material; Group B - Revotek LC^TM (GC Dental Products Corp., Japan), a urethane dimethacrylate based light cure temporary material and Group C - Tuff-Temp™ Plus (Pulpdent Corporation, U.S.A), a rubberized-urethane based dual cure temporary material. (Figure 1)

Figure 1 – Preparation of Samples

Group A; (Protemp^TM 4) was mixed with the help of dispensing gun (10:1) and was loaded onto the putty matrix and adapted on the lubricated metal die. The interim restorations were removed and reseated once during the elastic phase of polymerization. Before complete polymerization, excess flash was trimmed from the margins of interim restorations with scissors. After polymerization was completed, the crowns were trimmed and finished as per the manufacturer’s guidelines.

Group B; (Revotek LC^TM) interim restorations were made following the same protocol. Initial light curing (LED Woodpecker) was done for 10 seconds, to prevent possible deformation during removal. The interim restoration was removed and reseated once during the elastic phase of polymerization.  Each of the buccal, proximal, occlusal and lingual surfaces were light cured for 20 seconds. After final curing was done, finishing and polishing was done by similar operator using a micromotor hand piece.

Group C; (Tuff-Temp™ Plus) interim restorations were also made following the same protocol. After two minutes from its initial stage of polymerization, crown was removed from the matrix and excess flash was trimmed. Before the final light curing, removal of oxygen inhibited layer on the surface was done by using alcohol. Final light curing was done at each of the buccal, proximal, occlusal and lingual surfaces for 20 seconds.

The test samples that were stored in artificial saliva were taken for testing under a stereomicroscope. A total number of sixty samples prepared from three groups of interim materials were evaluated for marginal discrepancy, one hour after fabrication. The marginal gaps were measured at four vertical reference points on buccal, lingual, mesial and distal sides respectively. Measurements extended from edge of the chamfer finish line vertically above the mid-point of die’s score point to the inferior edge of the provisional crown using a stereomicroscope (Mode: XTL 3400E – Magnification:10X, Wuzhou New Found Instrument Co. Ltd., China) under 10x magnification. An image analyzing system (Chroma Systems PVT. Ltd, India; Model – MVIG 2005) was used to obtain numerical values in microns (µm). The readings thus obtained, were noted. The samples were stored in artificial saliva for a week and same tests were performed afterwards. (Figure2-7) Statistical results were drawn using one way ANOVA and Tukey’s Post-hoc test to understand the multiple individual comparison among different interim restorative materials to assess marginal discrepancies at one hour and one week intervals for the three test materials.

Results

One-way ANOVA test was used to determine which groups differ from each other, P-value < 0.05 was considered significant. It was found that there was statistical significant difference between the means of three interim restorative materials after one hour (f= 447.41, P<0.05). Among which, Tuff-Temp™ Plus  showed the least marginal discrepancy, while Revotek LC^TM  had the highest discrepancy. Also, there was a statistically significant difference between three means of marginal discrepancy of same materials after one week (f=580.612, P<0.05). Among which, Tuff-Temp™ Plus had the least marginal discrepancy, while Revotek LC^TM had the highest discrepancy.  Comparison of mean marginal discrepancy after one hour and one week interval by one-way ANOVA is depicted in Table I.  Also, theinter-group comparison is described in Table II and graphical summary of results is shown in Figure 8.  

Table I: Comparison of Mean Marginal Discrepancy after One Hour and One Week Interval by One-way ANOVA Test

Table II: Inter-Group Comparison using Tukey’s Post -Hoc Test

Figure 8 – Graphical Representation of Results