Different surface preparation techniques of porcelain repaired with composite resin and fracture resistance.

BACKGROUND: Porcelain from prosthesis such as crown or bridge can be fractured if exposed to trauma; and, can be repaired at chairside using composite resin. AIM: To investigate the fracture resistance of few techniques of surface preparation in repairing fractured porcelain using composite resin.
MATERIALS AND METHODS: Eighty samples of porcelain blocks were divided into 4 groups for different surface preparations, such as, Cimara repairing kit; porcelain etch kit containing hydrofluoric acid; Panavia F resin cement; and, sandblasting using aluminium oxide, before composite resin (Filtek Z250, 3M ESPE) was bonded to the prepared porcelain blocks. Twenty others samples in the control group comprised of pure porcelain blocks. The fracture resistance of each sample was tested using Instron machine (UK).
RESULTS: With the exception of the group repaired using hydrofluoric acid (3.04±1.04 Mpa), all the other groups showed significant difference in the fracture resistance values when compared to the control group (3.05 ± 1.42 MPa) at P<0.05.
CONCLUSIONS: Etching of the porcelain blocks with hydrofluoric acid holds promise in the repair of fractured porcelain with composite resin at chairside.

INTRODUCTION

Dental porcelain is one of the most popular materials used in fixed prosthodontics. This is due to its excellent aesthetic value, biocompatibility and stability.[1] However, failure of porcelain is of multifactorial causes, and could occur externally under certain conditions such as trauma, motor vehicle accident (MVA), etc.[2] Fractured porcelains will affect aesthetics and function of the prostheses, which may warrant patients to seek immediate treatment. Removal and reconstruction of the prostheses is a costly affair;[3] and it is therefore worthy to attempt repair with composite resins intraorally, especially in less severe cases. The use of 8% hydrofluoric acid etching and silane coupling agent for the repair of the fractured porcelain with composite resin has been recommended.[45] Although a few other techniques are commercially available, some of the materials are difficult to be acquired in certain countries and their effectiveness is also controversial.

Hence, this study was carried out with the aim of finding an effective technique for repairing fractured porcelain at chairside by using the materials that are commercially available in Malaysia.

MATERIALS AND METHODS

This was an experimental laboratory study carried out using dental porcelain (IPS Design, Liechtenstein) and composite resin (CR) (Filtek Z250, 3M ESPE). Twenty porcelain samples (12 mm length × 5 mm width × 2 mm thickness) for control group, and 80 porcelain samples (6 mm length × 5 mm width × 2 mm thickness) for tested groups were molded in silicon and fired in the porcelain furnace (Progra mmat®P100, Ivoclar-Vivadent). Polishing was carried out by using ceramic polishing bur. Later, the 80 samples were randomly divided into following groups according to different surface treatment techniques used for the porcelain blocks, as below:-

Group 1

Using Cimara repairing kit (Voco, Germany) which involved roughening of the porcelain surface with Cimara grinder, application of silane coupling agent, drying for 2 minutes, applying Scotchbond bonding agent (3M ESPE) and Filtek Z250 incrementally with light-curing of 40 seconds.

Group 2

Using hydrofluoric acid porcelain etch kit (Ultradent, USA), which involved roughening of the surface with high speed diamond bur, etching with porcelain etch for 2.5 minutes, washing, silanating and bonding with CR.

Group 3

Using Panavia F resin cement (Kuraray Dental, USA) which involved etching of the porcelain surface with the K etchant gel for 10 seconds, and then washing, silanating, and application of enamel/dentine primer (ED Primer) and CR, which was bonded with Panavia F paste followed by light-curing for 20 seconds.

Group 4

Sandblasted using aluminium oxide particles type Cobra; grain size: 90 μm; grit percentage: 99.6% (Dental Technology, Germany) for 1 minute before similar bonding to the CR.

Group 5

The control group (pure porcelain).

For Groups 1-4, after their respective surface treatment, they were bonded with composite resin following each manufacturer's instructions, and kept in wet tissue paper in a dry-closed container at room temperature. The fracture resistance of each sample was tested using Instron Machine 8874 (Instron Corp., UK). The fracture resistance of samples was calculated using the formula:

where, r = flexural strength (MPa)

P = maximum load (N)

L = displacement at maximum load (mm)

b = width of samples (mm)

d = thickness of samples (mm)

The statistical analyses were done using numerical data analysis of Independent t-Test (Statistical Package for the Social Sciences, SPSS version 13.0.1) and One-way Analysis of Variance (Anova) to compare differences among mean score values of fracture resistance for each group. P value < 0.05 was considered statistically significant.

RESULTS

The results showed that the fracture resistance between the five groups was statistically significant (P<0.05). The control group had the highest fracture resistance (3.05 ± 1.41), followed by Group 2 (3.04 ± 1.04), Group 3 (1.85 MPa ± 0.81), Group 1 (1.64 MPa ± 0.96) and Group 4 (0.66 MPa ± 0.49). The results are tabulated in Table 1. One-way Anova test used to compare significant differences between the groups showed that with the exception of group 2, all the other groups 1, 3 and 4 showed significant difference in the fracture resistance values when compared to the control group. The results are presented in Table 2.

Table 1

Comparing the fracture resistance mean values between each groups of the study

Table 2

Comparing the significant differences between the tested groups with the control group in the study using one way analysis of variance (ANOVA)

DISCUSSION

Fractured porcelain could be repaired clinically with composite resin using few techniques. Factors such as the effectiveness of bonding between porcelain surface and composite resin, which create maximum strength for porcelain-composite bonding, should be considered.[6] Rather than reconstructing the broken prosthesis which will involve longer time and higher cost, the repairing technique will benefit both the patient and the dentist.[3]

The porcelain and the Filtek Z250 were employed in the current study due to their routine use in School of Dental Sciences, Universiti Sains Malaysia. Cimara repairing kit was chosen as one of the materials in this experiment due to its ability to create permanent bond between porcelain and composite resin with adequate high bond strength value as claimed by the manufacturer. Panavia F is a resin cement used to bond several materials such as prostheses (crowns and bridges) or amalgam. The system is a self-etching, self-adhesive, dual-cure and contains 2 photoinitiators, providing a wider curing bandwidth to be used with any curing lights. It is also radiopaque and is claimed to be fluoride releasing.[7] Hydrofluoric acid etching and silanated techniques are among common repair techniques used worldwide nowadays.[58] The bond strength of hydrofluoric acid etching has been shown to have clinically good values and the use of 3-methacryloyl oxypropyl trimethoxy as a silane coupling agent works together with it to increase the bond strength of the composite-to-porcelain surface.[5] Sandblasting with aluminium particles is also among the famous techniques that have been suggested for surface treatment of porcelain before being silanated.[9] Aluminium oxide particles act as sharp, long lasting abrasive sandblasting cutting media, and can be re-used many times for grit blasting. The particles are harder than most other commonly used dry abrasive blast media, and come in a wide range of sizes. All these descriptions are detailed as claimed by the manufacturer.

The porcelain used in prosthesis should be of 1-2 mm thickness, as a thickness beyond this range can cause porcelain to break down.[13] Fracture resistance of porcelain and porcelain-composite samples could be evaluated with various techniques, for example, with the mechanical testing machine.[5] In this study, Instron Machine 8874 (Instron Corp, UK) was used for measuring the flexural strength. The comparison of fracture resistance was found to be statistically significant between the groups. Porcelain treated with hydrofluoric acid etching gel has the greatest fracture resistance value similar to the results observed by previous studies. It was reported that hydrofluoric acid etching action coupled with silane coupling agents strengthen the porcelain-composite bonding by producing great micromechanical retention.[510] This is due to the effective generation of microcracks in the porcelain molecules that can be filled with composite materials, which could create good micromechanical retention for the porcelain-composite bond.[11] Silane agents appear to be the essential components for a porcelain repair procedure and act by modifying its surface structure, thus rendering it more reactive to composite, and enabling chemical adhesion between the porcelain and composite surfaces.[12]

Silane coupling agents are organosilicone compounds having two functional groups with different reactivity. One of the two functional groups reacts with organic materials, and the other reacts with inorganic materials. Silane most commonly used in dentistry is the monofunctional gamma-methacryloxypropyltrimethoxysilane (or 3-trimethoxysilylpropyl methacrylate [MPS]), which is used to optimize and promote the adhesion through chemical and physical coupling between metal-composite, ceramic-composite, and composite-composite. Further, silane modifies the substrate surface oxide layer and forms a conversion layer.[13] This is all the more strengthened with bonding agents applied onto porcelain surface prior to composite restoration.[14] Groups 1, 3 and 4 depend on bonding by the chemical mechanisms of their respective reagents. As such they do not depend on micromechanical retention, which is why they have lower bond strengths compared to etching with hydrofluoric acid. However, studies have shown the potential dangers of hydrofluoric on biological tissues.[1516] Proper precautions, including application of rubber dam and use of gel etchant will help prevent tissue damage.

CONCLUSIONS

From this study, it can be concluded that the bond between porcelain and composites′ requires adequate micromechanical retention to achieve high strength, and to be stable over a prolonged period of time. Thus, hydrofluoric acid etching gel could be a material of choice in repairing fractured porcelain.