Clinical success and survival of indirect resin composite crowns: Results of a 3-year prospective study

Abstract

Objectives

The aim of this study was to test the new resin composite “NECO” as a material for indirect restorations clinically.

Methods

Forty-five patients were selected, of which 12 men and 33 women, with a mean age of 53. A total of 91 post-canine indirect resin composite NECO (Heraeus Kulzer, GmbH) restorations were placed, of which 86 full crowns and 5 onlays. Restorations were cemented with either resin cement (2bond2) or resin modified glass ionomer cement (Fuji Plus). The restorations were evaluated 1–2 weeks (baseline), 6 months, 1, 2, and 3 years after placement. At these recalls, success and survival data of the abutment teeth were documented. Survival was defined as the restoration being in situ, and success as the restoration in situ without complications.

Results

After 3 years in service, the restorations showed success and survival rates of 84.8 and 91.6%, respectively. Cementation with Fuji Plus showed a trend ( p = 0.054) toward higher success (93.1%) and survival (100%) rates compared to cementation with 2bond2 cement which showed success and survival rates of 81.4 and 87.9% respectively. Restorations on vital teeth resulted in success and survival rates of 86.8 and 95.3% respectively, while restorations on endodontically treated teeth showed success and survival rates of 82.6 and 87.5%. This difference was not statistically significant ( p = 0.296).

Significance

Three-year success and survival rates of NECO restorations were 84.8 and 91.6%, respectively. The design of the preparation and restoration should take the material properties into account in order to enhance the clinical performance.

Introduction

Ceramics with a framework of zirconium oxide have become the standard for esthetic indirect restorative materials. These full-ceramic systems have high fracture strength and high survival rates clinically. The short- and medium-term results are promising, although further clinical studies and preferably RCT’s are needed to obtain long-term clinical results .

There are, however, other possibilities for esthetic tooth-colored indirect restorations. Resin composites have been widely used for decades as tooth-colored direct restorative materials. These restorations are well accepted clinically, and clinical studies show satisfactory results , even for more extensive restorations . Numerous clinical studies concerning resin composites as indirect restorative materials for inlays and onlays have been carried out, and show promising results . Concerning full crowns, several clinical studies have been performed. Artglass crowns cemented with 2bond2 cement and solid bond showed a 3-year survival of 96% . The most common mode of failure was (partial) fracture of the crowns. The 5-year survival for the same type of crowns dropped to 88.5% .

Composites crowns have a number of advantages over zirconium oxide based ceramic crowns. With ceramics, a deep chamfer preparation with a depth of 1–1.5 mm is recommended , compared to a 0.5 mm chamfer for composite restorations . This less invasive tooth preparation leaves more natural tooth tissue intact, which will mostly result in a greater ferrule height and residual wall thickness. This is likely to be beneficial to the success of the restoration . Composites do not inflict the high levels of abrasion on antagonizing teeth that ceramics are known to do . Chipping is a major problem with ceramic restorations , and repairs are usually carried out with resin composite materials. Composite materials fit well into a “dynamic restoration concept”, in which repairs and alterations to the restoration are easily carried out. The restoration can be repaired with the same material as from which it is made, in case of for instance chipping, or repairing an endodontic access opening. Furthermore, adhesive resin cements are chemically compatible with composite crowns. In contrast, bonding of zirconium oxide frameworks to adhesive resin cements is still a problem , and damaging zirconium restorations with an endodontic opening leads to a significant loss of strength .

Indirect resin composite restorations may therefore be a viable alternative to ceramic restorations. A new resin composite, NECO (Heraeus Kulzer, GmbH, Hanau, Germany), was developed for the manufacturing of all types of indirect dental restorations as an alternative to other indirect restorative materials. The material is designed as an improved version of Artglass, a resin composite material previously introduced in the dental market for the same indication .

In this study, two different cements are used. The first one, 2bond2 (Heraeus Kulzer, GmbH, Hanau, Germany) is a dual-cured adhesive resin cement. This cement has been clinically tested for the cementation of resin-based restorations with satisfactory results . The other cement is a resin-modified glass-ionomer cement, Fuji Plus (GC Corporation, Tokyo, Japan), which has not been tested clinically for the cementation of resin-based crown restorations. Clinical results regarding ceramic inlays however, are promising , and in vitro results regarding fracture resistance of fiber-reinforced composite crowns show similar results compared to a resin cement . The use of a resin-modified glass-ionomer cement is less technique-sensitive compared to the use of a multiple-step adhesive cementation system, and might therefore be more appealing to the clinician.

The aim of this 3-year study was to determine clinical success and survival rates of NECO used as an indirect restorative material for the manufacturing of posterior full and partial single-unit indirect restorations, without any fiber reinforced or metal substructure or framework. Furthermore, the cementation with two different cements, 2bond2 and Fuji Plus, was evaluated.

Materials and methods

After obtaining approval of the Dutch medical ethical committee, 45 patients of the department clinic of the Department of Dental Materials Science of the Academic Center for Dentistry in Amsterdam (ACTA) were selected. Possible candidates, that met the inclusion and exclusion criteria as summarized in Table 1 , were asked to cooperate in this study. Restorations were made in the case of a large direct restoration which was an indication for an indirect restoration. After obtaining an informed consent from the patients, the abutment teeth were prepared by one dentist. Each patient received a maximum of three restorations. The restorations were to be placed with either a resin composite based cement (2bond2, Heraeus Kulzer GmbH) or a resin modified glass ionomer cement (Fuji Plus, GC Corporation, Tokyo, Japan).

Table 1
Inclusion and exclusion criteria for patients to participate in the NECO study.
Inclusion criteria
The patient is able and willing to maintain the patient–dentist relation during the whole study period
The patient is older than 18 years
The patient is willing to undergo the two X-ray evaluations at baseline and after 36 months
The patient has signed the informed consent form
The patient objectively needs a full or partial crown restoration
A minimum of 50% of core dentin should be remaining after preparation of the abutment tooth
Non-vital tooth can be incorporated in the study under the condition that a core build-up can be made to which an adhesive bond of the restoration is possible
Exclusion criteria
A known history of resin allergy
Pregnancy at the beginning of the study
Use of drugs that may interfere with the oral environment
Systemic diseases or malignancies at the beginning of the study
Sufficient drying or the specified application technique is not possible
Minimal layer thickness of restoration cannot be achieved
Abnormal stresses are foreseeable in the region of the occlusal surface of the molars, premolars and canines, as a result of – for example, bruxism or other parafunctional activities

The shade of the teeth was determined under daylight conditions using a Vita Lumin Vacuum shade guide. In the case that an abutment tooth contained old non-adhesively placed restorations, the restorations were replaced with a resin composite restoration (Filtek Z250, 3M ESPE, Seefeld, Germany), bonded with a three-step adhesive system (Scotchbond MP, 3M ESPE, Seefeld, Germany). Care was taken that the abutment teeth were completely caries-free and adequately restored according to the treatment protocols as were in force at ACTA to receive the indirect restoration. The teeth were prepared according to the preparation criteria as summarized in Table 2 . Full-arch impressions were taken using a polyvinylsiloxane impression material (Flexitime light-body, heavy body, and putty, Hereaus Kulzer GmbH, Hanau, Germany). The impressions of the opposing jaw were taken with an alginate impression material. Bite registrations were carried out using Memosil (Heraeus Kulzer GmbH, Hanau, Germany). Temporary crown restorations (PreVISION CB, Hereaus Kulzer GmbH, Hanau, Germany) made according to the crown duplication technique were placed with an non-eugenol temporary cement (PreVISION CEM, Hereaus Kulzer GmbH, Hanau, Germany). Anesthesia was applied when applicable.

Table 2
Preparation criteria for NECO restorations.
Preparation criteria
Occlusal reduction of 1.5 mm at minimum
Uniform removal of hard tooth tissue; at occlusal and incisal sites it should follow the original tooth shape
A supragingival position of the crown margin should be intended
The preparation shoulder should be rounded and approximately 0.5 mm wide (chamfer type). Avoid sharp edges, beveled margins or undercuts
The preparation angle is preferably 7–10°
For partial crowns the dentin-composite edge should not be in the antagonist contact area
The surface of the core should be smooth

The restorations were manufactured by the ACTA dental laboratory. For the fabrication of the master model a super hard stone gypsum (type 4) was used, in a neutral light-grey color. For easier removal of the crown from the master model, the die walls and occlusal surface were covered with a thin layer (0.05–0.10 mm) of neutral colored wax, ending approximately 1 mm from the preparation margin. The preparation margin was marked, and the stone areas not covered by wax were covered with insulating gel (Hereaus Kulzer GmbH, Hanau, Germany). The crown was built up with different layers with a maximum thickness of 2 mm, and, if applicable, different colors of NECO composite. NECO is a light curing nano hybrid composite. The monomer matrix includes a mixture of polyether and urethane based (meth-)acrylate monomers, and a new TCD (tricyclodecane) monomer. The composite material does not contain Bis-GMA monomer making it toxicologically advantageous, as no Bisphenol-A can be released . The filler particles are a mixture of various particle size fractions of a commonly used, radiopaque dental glass. The composite material contains non-agglomerated nano-particles cross-linking and reinforcing the polymer network. The composition and properties of the used materials are summarized in Table 3 . After applying each layer, the restoration was light-cured for 90 s (Heraflash, Hereaus Kulzer GmbH, Hanau, Germany). To simplify the adaptation of the composite, small amounts of C&B liquid (Hereaus Kulzer GmbH, Hanau, Germany) were applied to wet the dental instrument. This was also used to restore the inhibition layer in case it was damaged. Individual color characterization of the crowns was carried out using cre-active colors (Hereaus Kulzer GmbH, Hanau, Germany). These stains are not wear-resistant and had to be covered with a final layer of NECO. After applying the final layer, a final polymerization of 180 s was carried out. Finishing and polishing was done using metal carbide burs at low speed and low pressure, silicone polishers, Kevlar brushes and diamond paste (Amalgant HK-A). High gloss was achieved by polishing with a rotating wool instrument “wollschwabbel”. After cleaning, the inside of the restoration was roughened with 50 μm Al 2 O 3 at a pressure of 2000 hPa. For each crown the minimal wall thickness was measured by the dental technician on four locations: cervical, equatorial, fissures, and cusps, before insertion. These data, together with used composite material and color, were documented.

Table 3
Chemical composition and properties of used materials.
Product Manufacturer Composition E -Modulus Fracture strength Filler load
NECO Hereaus Kulzer GmbH, Hanau, Germany Filler particles: Silanized Ba–Al–B–F–silicate glass (particle size 400–8000 nm), silanized non-agglomerated SiO 2 -nanoparticles
Monomers: Tricyclodecane (TCD)-urethane diacrylate, urethane dimethacrylate, polyether dimethacrylate, >3% triethyleneglycoldimethacrylate (TEGDMA)
Others: Rheological modifiers (hyperbranched polyurethane), photoinitiators (camphorquinone-based), stabilizers, color pigments
14–16 GPa Flexural strength 160–170 MPa
Flexural strength 129.3 MPa
Fuji Plus cement GC Corporation, Tokyo, Japan Powder: alumino-silicate glass particles
Liquid: HEMA 37%, polyacrylic acid 22%, proprietary resins 10%, tartaric acid 6%, distilled water 25%
Flexural modulus 2.1 GPa Flexural strength 23.8 MPa 67 wt.%
Fuji Plus conditioner GC Corporation, Tokyo, Japan Citric acid 10%, ferric chloride 2%, distilled water 88%.
2bond2 cement Hereaus Kulzer GmbH, Hanau, Germany UDMA, 1,12-dodecandiodimethacrylate, multifunctional methacrylates, Ba–Al–B–Si glass (700 and 2000 nm), highly dispersed silicon dioxide (10–40 nm), strontium fluoride (<1000 nm) Base: 69.5 wt.% Catalyst: 63.2 wt.%
Gluma comfort bond and desensitizer Hereaus Kulzer GmbH, Hanau, Germany Methacrylate, 4-META, polyacrylic acid, ethanol, photoinitiators, glutaraldehyde
All data from manufacturer, unless otherwise stated.

After try-in and occlusal adjustment if necessary, the restorations were repolished at the adjusted areas. Prior to cementation, the inner surfaces of the restorations were pretreated with C&B liquid. The abutment tooth was prepared for cementation, preferably with rubber dam, otherwise with cotton rolls. In the case of cementation with 2bond2 cement, the preparation was pretreated with 37% phosphoric acid for 15 s and the restoration was cemented in place under finger pressure with 2bond2 cement in combination with Gluma Comfort bond and desensitizer (Hereaus Kulzer GmbH, Hanau, Germany) according to manufacturers’ instructions. Excess cement was removed with explorers or scalers. Where necessary, finishing carbide burs were used to finish the margins of the restorations. In the case of cementation with Fuji Plus cement, the preparations were pretreated with Fuji Plus conditioner (GC Corporation, Tokyo, Japan) and the restorations were cemented with Fuji Plus, all according to manufacturers’ instructions. All restorations were prepared and placed by one dentist.

One to two weeks after placement of the restoration, the first recall (baseline) visit was made. Recalls were carried out by three dentists. Further recalls were carried out after 6 months, 1, 2 and 3 years after placement of the restorations. Documentation at recalls included recording occlusal contacts and possible complications. Most complications occurred in between recall data, and patients were seen to document the complications. Complications were analyzed, photographed if possible, and specified concerning failure reason, i.e. material breakdown, material weakness, indication limits, and failure behavior (i.e. chipping, total or partial breakage or hints on the breakage initiation point and risk) or other reasons like for instance total discoloration or loss of marginal integrity. The clinical success and survival of the crowns was recorded. Clinical success was defined as the restorations being present without any complications. A surviving restoration was defined as a restoration present in the mouth, with or without any kind of complication.

Statistical analysis was carried out using PASW statistics 18 (SPSS Inc.). Kaplan Meier curves were calculated for success and survival. The differences between the Kaplan Meier curves were statistically analyzed using the Log Rank test. The influence of the variables cement (2bond2 or Fuji Plus) and endodontic status (endodontically treated or vital teeth) on success and survival were statistically analyzed using the Cox Regression model. The significance level α was set at 0.05.

Materials and methods

After obtaining approval of the Dutch medical ethical committee, 45 patients of the department clinic of the Department of Dental Materials Science of the Academic Center for Dentistry in Amsterdam (ACTA) were selected. Possible candidates, that met the inclusion and exclusion criteria as summarized in Table 1 , were asked to cooperate in this study. Restorations were made in the case of a large direct restoration which was an indication for an indirect restoration. After obtaining an informed consent from the patients, the abutment teeth were prepared by one dentist. Each patient received a maximum of three restorations. The restorations were to be placed with either a resin composite based cement (2bond2, Heraeus Kulzer GmbH) or a resin modified glass ionomer cement (Fuji Plus, GC Corporation, Tokyo, Japan).

Table 1
Inclusion and exclusion criteria for patients to participate in the NECO study.
Inclusion criteria
The patient is able and willing to maintain the patient–dentist relation during the whole study period
The patient is older than 18 years
The patient is willing to undergo the two X-ray evaluations at baseline and after 36 months
The patient has signed the informed consent form
The patient objectively needs a full or partial crown restoration
A minimum of 50% of core dentin should be remaining after preparation of the abutment tooth
Non-vital tooth can be incorporated in the study under the condition that a core build-up can be made to which an adhesive bond of the restoration is possible
Exclusion criteria
A known history of resin allergy
Pregnancy at the beginning of the study
Use of drugs that may interfere with the oral environment
Systemic diseases or malignancies at the beginning of the study
Sufficient drying or the specified application technique is not possible
Minimal layer thickness of restoration cannot be achieved
Abnormal stresses are foreseeable in the region of the occlusal surface of the molars, premolars and canines, as a result of – for example, bruxism or other parafunctional activities

The shade of the teeth was determined under daylight conditions using a Vita Lumin Vacuum shade guide. In the case that an abutment tooth contained old non-adhesively placed restorations, the restorations were replaced with a resin composite restoration (Filtek Z250, 3M ESPE, Seefeld, Germany), bonded with a three-step adhesive system (Scotchbond MP, 3M ESPE, Seefeld, Germany). Care was taken that the abutment teeth were completely caries-free and adequately restored according to the treatment protocols as were in force at ACTA to receive the indirect restoration. The teeth were prepared according to the preparation criteria as summarized in Table 2 . Full-arch impressions were taken using a polyvinylsiloxane impression material (Flexitime light-body, heavy body, and putty, Hereaus Kulzer GmbH, Hanau, Germany). The impressions of the opposing jaw were taken with an alginate impression material. Bite registrations were carried out using Memosil (Heraeus Kulzer GmbH, Hanau, Germany). Temporary crown restorations (PreVISION CB, Hereaus Kulzer GmbH, Hanau, Germany) made according to the crown duplication technique were placed with an non-eugenol temporary cement (PreVISION CEM, Hereaus Kulzer GmbH, Hanau, Germany). Anesthesia was applied when applicable.

Table 2
Preparation criteria for NECO restorations.
Preparation criteria
Occlusal reduction of 1.5 mm at minimum
Uniform removal of hard tooth tissue; at occlusal and incisal sites it should follow the original tooth shape
A supragingival position of the crown margin should be intended
The preparation shoulder should be rounded and approximately 0.5 mm wide (chamfer type). Avoid sharp edges, beveled margins or undercuts
The preparation angle is preferably 7–10°
For partial crowns the dentin-composite edge should not be in the antagonist contact area
The surface of the core should be smooth

The restorations were manufactured by the ACTA dental laboratory. For the fabrication of the master model a super hard stone gypsum (type 4) was used, in a neutral light-grey color. For easier removal of the crown from the master model, the die walls and occlusal surface were covered with a thin layer (0.05–0.10 mm) of neutral colored wax, ending approximately 1 mm from the preparation margin. The preparation margin was marked, and the stone areas not covered by wax were covered with insulating gel (Hereaus Kulzer GmbH, Hanau, Germany). The crown was built up with different layers with a maximum thickness of 2 mm, and, if applicable, different colors of NECO composite. NECO is a light curing nano hybrid composite. The monomer matrix includes a mixture of polyether and urethane based (meth-)acrylate monomers, and a new TCD (tricyclodecane) monomer. The composite material does not contain Bis-GMA monomer making it toxicologically advantageous, as no Bisphenol-A can be released . The filler particles are a mixture of various particle size fractions of a commonly used, radiopaque dental glass. The composite material contains non-agglomerated nano-particles cross-linking and reinforcing the polymer network. The composition and properties of the used materials are summarized in Table 3 . After applying each layer, the restoration was light-cured for 90 s (Heraflash, Hereaus Kulzer GmbH, Hanau, Germany). To simplify the adaptation of the composite, small amounts of C&B liquid (Hereaus Kulzer GmbH, Hanau, Germany) were applied to wet the dental instrument. This was also used to restore the inhibition layer in case it was damaged. Individual color characterization of the crowns was carried out using cre-active colors (Hereaus Kulzer GmbH, Hanau, Germany). These stains are not wear-resistant and had to be covered with a final layer of NECO. After applying the final layer, a final polymerization of 180 s was carried out. Finishing and polishing was done using metal carbide burs at low speed and low pressure, silicone polishers, Kevlar brushes and diamond paste (Amalgant HK-A). High gloss was achieved by polishing with a rotating wool instrument “wollschwabbel”. After cleaning, the inside of the restoration was roughened with 50 μm Al 2 O 3 at a pressure of 2000 hPa. For each crown the minimal wall thickness was measured by the dental technician on four locations: cervical, equatorial, fissures, and cusps, before insertion. These data, together with used composite material and color, were documented.

Nov 28, 2017 | Posted by in Dental Materials | Comments Off on Clinical success and survival of indirect resin composite crowns: Results of a 3-year prospective study
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