Assessment of Marginal Integrity and Color Stability of Provisional Restoration Fabricated from Different Autopolymerizing Acrylic Resins - A Comparative Study.

AIM: The present study is aimed to assess the marginal integrity and color stability of provisional restorations fabricated from different autopolymerizing acrylic resins.
MATERIALS AND METHODS: Totally, 60 provisional crowns were fabricated. A mandibular first molar artificial typodont was mounted on a base of dental stone. The mandibular first molar which was mounted was prepared for full cast crown, using the tooth preparation standard principles with shoulder finish line of 1 mm and taper 6°. There were 20 samples in each acrylic resin group: Group I: Polyvinyl-ethyl methacrylate resin, Group II: Autopolymerizing bis-acrylic material, and Group III: Polymethyl methacrylate (PMMA) autopolymerizing resin. Crowns were verified for marginal adaptation using stereomicroscope at a ×40. The color stability was measured using spectrophotometer poststaining period.
RESULTS: Autopolymerizing bis-acrylic material group showed minimum mean vertical marginal discrepancy (128.68 ± 18.036 μm) followed by PMMA autopolymerizing resin group (147.49 ± 20.128 μm) and polyvinyl-ethyl methacrylate resin group (172.89 ± 22.118 μm). Analysis of variance demonstrated a statistically significant difference between different autopolymerizing acrylic resins. The color change values did not show any significant difference between the groups on numerous comparisons between different autopolymerizing acrylic resin groups. A statistically significant difference was seen between Groups I and II, Groups I and III, and Groups II and III (P < 0.05).
CONCLUSION: This study concluded that the autopolymerizing bis-acrylic material demonstrated significantly improved marginal integrity when compared to PMMA autopolymerizing resin and polyvinyl-ethyl methacrylate resin. Copyright:

INTRODUCTION

A provisional restoration performs an important function as a significant component for many dental procedures. Provisional is one for a transient period, awaiting a permanent procedure. Provisional restorations are models on which occlusal, visual, and functional modifications are made to augment the final prosthesis. Although a final prosthesis may be placed within 2 weeks of tooth preparation, the provisional restoration must fulfill important requirements of the dentist and patient.[1]

The rationale for the placement of a provisional restoration are maintenance of occlusion, protection of pulp, strength, esthetics, retention, positional stability, easy to clean, and nonimpinging margins. The biomaterials that are frequently used to make provisional restorations are composite resins and autopolymerizing acrylic resin. With the advent of acrylic resin in 1936, polymethyl methacrylate (PMMA) resins have been effectively used over many years in various dental applications such as complete dentures and all conventional removable partial dentures. Due to suitable physical properties and ease of processing, PMMA resins remain to be the chosen material for making the provisional partial fixed denture.[23]

The chief factors that govern the provisional restoration's success are acceptable vertical marginal fit.[4] Procurement of the greatest probable adaptation of provisional restoration along the margins averts plaque accumulation effectively and thus maintains the gingival health and shields pulp against chemical, bacterial, and thermal insults. Distinct marginal defects can lead to gingival recession, tissue inflammation, and pulpal sensitivity.[5] Therefore, this in vitro study was performed to measure the integrity along the margins and color stability of provisional restoration made from different autopolymerizing acrylic resins.

MATERIALS AND METHODS

Preparation of molds and provisional restoration

A mandibular first molar artificial typodont was mounted on a base of dental stone. The mandibular first molar, which was mounted was prepared for full cast crown, using the tooth preparation standard principles with the shoulder finish line of 1 mm and taper 6° using diamond burs and a standard handpiece. A die of metal was cast from the ready typodont tooth and mounted in autopolymerizing acrylic resin in the form of a cylinder, 15 mm high and 20 mm in diameter. The petroleum jelly was used to lubricate the base portion and then mounted in a block of dental stone that was fitted out with a metal box, and a metal top which fits closely was used to duplicate an impression tray.

At that point, a uniform coat of petroleum jelly was applied on the metal die, which was mounted and Type 2 inlay wax was used to prepare a wax pattern for full metal crown. The metal top was loaded with putty impression material and placed over the metal box-metal die assemblage along the indexing. The clamp was freed after the impression material was completely set, and the impression was removed. The wax pattern wedged in the putty impression was cautiously taken out. The impression was then examined for any flaws and fullness. It represented as a mold for provisional restoration preparation (60 provisional crowns were totally prepared, each group had 20).

Group I: Polyvinyl-ethyl methacrylate resin (Trim® II Harry J Bosworth Company, Illinois)

Group II: Autopolymerizing bis-acrylic material (Protemp-10:1 cartridge, 3M ESPE, Minnesota, USA)

Group III: PMMA autopolymerizing resin (DPI self-cure tooth molding powder and monomer liquid, Mumbai, Maharashtra).

The manufacturer's instructions were followed to manipulate the temporization materials and then loaded in the prepared mold. Attention was taken to ensure that the mold was entirely placed on the metal die setup with the indexing as reference. The metal die and temporary restoration were located in a water bath maintained at 37°C until the polymerization was complete. The restorations were later trimmed and finished. After this, the restorations were placed on the corresponding dies and the specimens were exposed to visually evaluate the marginal adaptation.

Evaluation of marginal integrity

For all the crowns, the provisional restorations were examined for marginal fit on the same day of fabrication. A stereomicroscope (Magnus MSZ-TR Olympus, India Pvt. Ltd.) was used at a ×40 to test crowns for marginal adaptation. The specimens were viewed with the microscope and a camera which was connected to the microscope was used to take photographs. The images were later moved to image analysis software program (Magnus Pro, Magnus Analytics, New Delhi) that measured the marginal gap vertically along the four points of reference at the shoulder finish line edge of the dies to the lower edge of the temporary fixed dental prostheses. The findings from each reference point were collected, and the mean of four surfaces was considered for every specimen. Subsequently, a total mean of the marginal gap were calculated for each test group.

Evaluation of color stability

The color change calculation ΔE* among the two-color positions (after storage and baseline) was calculated as per the following formula: ΔE = ([L2* − L1*]2 + [a2* − a1*]2 + [b2* − b1*]2)1/2.[6] Tea was the beverage used to dip each group samples. The tea beverage was prepared by immersing prefabricated tea bag of 2 g in boiling water (100 mL) for 5 min. The duration of immersion was standardized to 1 week. The samples were restocked on every 3rd day to avoid yeast or bacterial contamination. A spectrophotometer was used to measure the color of the samples after the staining period.

Statistical analysis

The data were analyzed using SPSS 17.0 for Windows (SPSS, Inc., Chicago, IL, USA). The marginal integrity and color stability were compared between different groups using analysis of variance (ANOVA) test and Tukey's post hoc statistical analysis methods. P < 0.05 is considered to limit the statistical level of significance.

RESULTS

The mean vertical marginal discrepancy of different autopolymerizing acrylic resins is shown in Table 1. The lowest mean vertical marginal discrepancy of 128.68 ± 18.036 was reported by autopolymerizing bis-acrylic material group followed by PMMA autopolymerizing resin group (147.49 ± 20.128) and polyvinyl-ethyl methacrylate resin group (172.89 ± 22.118).

Table 1

Mean vertical marginal discrepancy of different autopolymerizing acrylic resin

Groups	n	Mean (μm)±SD
Group I – Polyvinyl-ethyl methacrylate resin	20	172.89±22.118
Group II – Autopolymerizing bis-acrylic material	20	128.68±18.036
Group III – Polymethyl methacrylate autopolymerizing resin	20	147.49±20.128

SD: Standard deviation

The comparison of the mean vertical marginal discrepancy of different autopolymerizing acrylic resin is shown in Table 2. The ANOVA showed a statistically significant difference between different autopolymerizing acrylic resins.

Table 2

Comparison of mean vertical marginal discrepancy of different autopolymerizing acrylic resins

Groups	Mean (μm)±SD	F	P	Significance
Group I – Polyvinyl-ethyl methacrylate resin	172.89±22.118	28.162	0.001	HS
Group II – Autopolymerizing bis-acrylic material	128.68±18.036
Group III – Polymethyl methacrylate autopolymerizing resin	147.49±20.128

SD: Standard deviation, HS: High significant

There was no significant difference between the groups for change in color values. Among different groups, polyvinyl-ethyl methacrylate resin group had least color changes postimmersion in the liquid media (2.68 ± 1.22–1.42 ± 0.28) followed by autopolymerizing bis-acrylic material group (2.76 ± 1.53–1.18 ± 0.19) and PMMA autopolymerizing resin (2.90 ± 0.14–1.29 ± 0.42) [Table 3]. The multiple comparisons among different autopolymerizing acrylic resin groups are shown in Table 4. A statistically significant difference was found between Groups I and II, Groups I and III, and Groups II and III (P < 0.05).

Table 3

Color change values for the provisional restoration at baseline and after immersion to liquid

Groups	Immersion of provisional restoration in tea media		F	P	Significance
	Baseline	After immersion
Group I - Polyvinyl-ethyl methacrylate resin	2.68±1.22	1.42±0.28	26.184	0.634	NS
Group II - Autopolymerizing bis-acrylic material	2.76±1.53	1.18±0.19
Group III - Polymethyl methacrylate autopolymerizing resin	2.90±0.14	1.29±0.42

NS: Not significant

Table 4

Multiple comparisons Tukey honestly significant difference

Group	Compared with	Mean difference (I-J)	Significance
Group I	Group II	44.21*	0.001
	Group III	25.4	0.001
Group II	Group I	−44.21*	0.001
	Group III	−18.81	0.02
Group III	Group I	−25.4	0.001
	Group II	18.81	0.02

*Significant, P<0.05

DISCUSSION

Provisional restorations that are positioned after tooth preparation defend the pulp against thermal changes; reestablishes occlusion; preserves appropriate contacts; maintains function and esthetics for a restricted period of time; and subsequently gets replaced by a final prosthesis.[7]

In this study, autopolymerizing bis-acrylic material group reported the lowest mean vertical marginal discrepancy followed by PMMA autopolymerizing resin group and polyvinyl-ethyl methacrylate resin group. As per Dureja et al.,[8] although bis-acrylic resins have several benefits such as improved esthetics when compared to methacrylates, because of the associated brittleness, they may not be apt for Fixed partial dentures (FPDs) which are long span. Recently, bis-GMA resins have been introduced as provisional material. Haselton et al.[9] have demonstrated the improved esthetics and higher resistance of these resins approving their use in the anterior region where esthetics is important and also in cases where long-span FPDs may be needed. Finally, the current material in this group is urethane dimethacrylates resins which have sustained the inclination of improving the advantages of their prototypes in terms of esthetics and strength.

The findings in the present study are in contradiction to those obtained by Elagra et al.[6] who presented a maximum mean marginal gap (430.15 μm) for dual-cured bis-acryl interim material in comparison with the other groups. This was in accordance with Givens et al.[10] who proposed that most of the gap formation arises during the auto-cure phase of polymerization of dual-cured materials.

The present study found no significant difference in the values of color change between the groups. After immersion in liquid media, polyvinyl-ethyl methacrylate resin group showed the least color changes when compared to other groups followed by autopolymerizing bis-acrylic material group and PMMA autopolymerizing resin. A different threshold of values for color difference ranging from 1 to 3.7 have been reported by several studies and the color change becomes noticeable by the human eye when the value crosses the upper range.[11] A study by Elagra et al.[6] found a color change of (ΔE*) >3.3 with bis-acryl methacrylate-based resins, which was considered visually noticeable along with being clinically undesirable. In addition, auto-cured bis-acryl crowns displayed significantly the maximum color change. The results in this study were different from results obtained by Sulieman et al.[12] and Sham et al.[13] which propose that the registered chemical variations such as the polarity of the monomers, size dispersion of the PMMA particles, effectiveness of the initiator system for interim resins, and pigment stability may result in divergent grades of polymerization and water sorption, and therefore, color stability.

This in vitro study did not consider the effect of oral solutions on the extent of polymerization of provisional materials. Furthermore, there was no thermocycling of the specimens or aging experimentally, which probably resulted in a larger discrepancy along the margins. These results are pertinent to single crowns and the reported data may vary for multiple units.

CONCLUSION

This study concluded that the autopolymerizing bis-acrylic material demonstrated significantly improved marginal integrity when compared to PMMA autopolymerizing resin and polyvinyl-ethyl methacrylate resin.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.