Durability of a low shrinkage TEGDMA/HEMA-free resin composite system in Class II restorations. A 6-year follow up

Abstract

Objective

The objective of this randomized controlled prospective trial was to evaluate the durability of a low shrinkage and TEGDMA/HEMA-free resin composite system in posterior restorations in a 6-year follow up.

Methods

139 Class II restorations were placed in 67 patients with a mean age of 53 years (range 29–82). Each participant received at random two, as similar as possible, Class II restorations. In the first cavity of each pair the TEGDMA/HEMA-free resin composite system was placed with its 3-step etch-and-rinse adhesive (cmf-els). In the second cavity a 1-step HEMA-free self-etch adhesive was used (AdheSe One F). The restorations were evaluated using slightly modified USPHS criteria at baseline and then yearly during 6 years. Caries risk and parafunctional habits of the participants were estimated.

Results

Three molar teeth showed mild post-operative sensitivity during 3 weeks for temperature changes and occlusal forces. After 6 years, 134 Class II restorations were evaluated. Twenty-one restorations, 8 cmf-els (11.4%) and 13 ASE-els (20%) failed during the 6 years (p < 0.0001). The annual failure rates were 1.9% and 3.3%, respectively. The main reasons for failure were fracture followed by recurrent caries. Most fractures and all caries lesions were found in high risk participants.

Significance

The Class II resin composite restorations performed with the new TEGDMA/HEMA-free low shrinkage resin composite system showed good durability over six years.

Introduction

Despite the increasing use of resin composites, there are still several remaining problems to be solved. During curing of the monomers, a network of polymers is formed, which becomes rigid due to increasing cross-linking of the polymer chains. The free curing contraction for resin composites varies from 1.0% to 5.0% . In the pre-gel phase, the material is able to flow and stresses are relieved. Post-gel polymerization results in stresses in the material and tooth structures and their interfaces, which may affect the interfacial adaptation and durability of restorations . The magnitude of shrinkage stress depends on many factors like resin matrix formulation, amount of filler used in the resin composite and degree of conversion. Cuspal movement during polymerization may be perceived as post-operative pain . Increasing C-factor may result in greater stresses due to the larger number of bounded surfaces. Posterior Class I and II cavities will therefore show high stress formation. A few low shrinkage resin composites have been developed and marketed during the last years .

Biocompatibility of dental materials is an important consideration for the patient and clinician. Many in vitro studies have shown that the polymerization reaction, producing the cross-linked polymer matrix from the dimethacrylate resin monomers, is never complete. It has been reported that of the methacrylate groups, 25%–60% may remain unreacted and about 10% of the available groups are free to diffuse out in the oral cavity . Adverse reactions may be expected in sensitive operators or patients due to the release of non-polymerized monomers. Clinical studies have shown that dental resin composites may induce local and systematic adverse effects, which are caused by methacrylate (co)monomers . Two frequently used methacrylate monomers TEGDMA (Triethyleneglycol-dimethacrylate) and HEMA (2-hydroxyethyl-methacrylate) eluate from different resin composites, compomers, resin modified glass ionomers and adhesives and have been shown to be responsible for several cytotoxic reactions . The diluent monomer TEGDMA show biological significant properties, like low molecular weight, relatively high hydrophilicity and detergent activity in liposomes. It can penetrate all biological compartments, the extracellular and intracellular space, including cell nuclei and membranes. The monomer showed chemical–biological interactions with many cell structures or processes like inhibition of cell growth and decrease of the intracellular glutathione level . The quantity of TEGDMA leaching from restorative materials is predominantly dependent on the monomer–polymer conversion. But in addition, chemical processus like erosion, enzymatical hydrolytic disintegration and alcoholysis as well as physical processus like wear may also contribute to a release of degradation products from the polymerized resin in time . Geurtsen and Leyhausen concluded that it should be the aim of future studies to replace TEGDMA with more biocompatible diluent monomers. HEMA is frequently present in dental adhesives, resin-modified glass ionomers and poly-acid modified resin composites. In adhesives, in amounts from 30% to 55%, it reduces viscosity, promotes diffusion of co-monomers by expanding the demineralized collagen and enhances bond strength to dentin . Omission of HEMA in adhesives may lead to phase separation between water and the adhesive monomers . It has been shown that HEMA inhibited intracellular tyrosine phosphorylation , induced cell growth inhibition and cycle perturbation and is a potent inducer of apoptotic cell death . Cell mutation has been observed after exposure to both TEGDMA and HEMA as well as increased intracellular concentrations of reactive oxygen species (ROS) . Exposure to low concentrations of the monomers for a prolonged time reduced the rate of cell proliferation possibly as result of DNA damage .

In addition it has been observed that TEGDMA and HEMA are common sensitizers with a high sensitizing potential . The lower the molecular weight of the monomer, the higher the biophase penetration risk and allergic potential. The risk of allergic reactions increases due to unwary handling of the non-cured resin monomers . Fast penetration of uncured monomers through the skin and gloves cause contact dermatitis in dental staff . Patients with diagnosed allergies for HEMA and/or TEGDMA should not receive dental materials which can release these monomers.

Recently a TEGDMA/HEMA-free resin composite system was developed with low volumetric shrinkage and low contraction stress . In its 3-step etch-and-rinse adhesive, smaller hydrophilic monomers were omitted resulting in a more hydrophobic resin layer, which is less prone to water absorption and hydrolytic degeneration . The HEMA substitution for Bis EMA, which represents high molecular weight may result in reduced toxicity.

Clinical effectiveness of the resin composite system in Class V non carious cervical lesions was reported recently in a 5-year follow up , but no clinical study reported the durability in Class II restorations.

The aim of the present randomized controlled prospective study was to investigate the clinical longevity of Class II restorations performed with the TEGDMA/HEMA-free resin composite system. The 3-step etch-and-rinse TEGDMA/HEMA-free adhesive of the system was compared with a HEMA-free 1-step self-etch adhesive. The null hypothesis tested was that the adhesives showed similar clinical performance when used with the 1-step self-etch adhesive.

Materials and methods

Experimental design

The study was a randomized controlled prospective trial. In an intra-individual comparison each participant received one pair of similar sized Class II resin composite restorations. The two restorations in each pair were performed with the TEGDMA/HEMA-free low shrinkage resin composite (els; Saremco AG, Rebstein, Switzerland), and bonded either with the TEGDMA/HEMA-free 3-step etch-and-rinse adhesive of the system (cmf, Saremco) or a single-step HEMA-free self-etching adhesive in a pen delivery system (AdheSE One F, Vivadent Ivoclar, Schaan, Liechtenstein; ASE). The els resin composite does not contain co-monomers of low molecular weights and showed the lowest contraction stress of marketed resin composites .

During 2009, adult patients attending the Public Dental Health Service clinic at the Dental School Umeå, who at the yearly examination did need two Class II restorations were asked to participate in a clinical follow up. No patients were excluded because of caries risk, bruxing habits or not acceptable oral hygiene. All patients were informed on the background of the study and each participant provided informed consent to participate in the study. The study design followed the requirements outlined in the CONSORT 2010 statement. All participants were informed on the background of the study, which was approved by the ethics committee of the University of Umeå (Dnr 07-152M).

Reasons for placement of the resin composite restorations were carious lesions, fracture of old fillings or replacements due to esthetic or other reasons. No Class I cavities were included because of the relative good durability of these restorations. Operative procedures were performed under local anesthesia if necessary. Sixty-seven patients, 33 female and 34 male, with a mean age of 53 years (range 29–82) participated in the study. One hundred and thirthy-nine Class II restorations were placed in 46 premolars and 93 molars by one experienced operator (JvD) ( Table 1 ). All, except 5 patients, received at random two restorations with the two restorative techniques. The 5 participants received also one more Class II restoration with the cmf adhesive. All teeth were in occlusion. The majority of cavities had dentin bordered proximal cervical margins.

Table 1
Distribution and size of the experimental restorations.
Surfaces Maxilla Mandibula Total
Premolars Molars Premolars Molars
2 surfaces 20 32 15 22 89
3 surfaces 3 7 5 11 26
>3 surfaces 2 12 1 9 24
Total 25 51 21 42 139

Clinical procedure

After removal of the old restorations and/or caries excavation according to the principles of adhesive dentistry, the operative field was carefully isolated with cotton rolls and suction device. No bevel was placed. For all cavities a thin metallic matrix was used and carefully wedging was performed with wooden wedges (Kerr/Hawe Neos, Switzerland). No Ca(OH) 2 base or other base material was used. The cavities in each individual pair were randomly distributed to the two test adhesives, before the operative procedure started, by throwing dice. In this way, an intraindividual comparison was possible of the adhesive systems.

After rinsing of the cavities with water, application of the respective adhesive was performed according to the manufacturer’s instructions ( Table 2 ). Curing was performed with a well controlled light curing unit for at least 10 s (Astralis 7, Vivadent; Demetron light meter, Kerr, Orange, CA, USA). The low shrinkage resin composite (els, Saremco) was applied in all cavities in layers of maximally 2–3 mm with if possible, an oblique layering technique using selected resin composite instruments (Hu Friedy). Every increment was light cured for 20–40 s. After checking the occlusion/articulation and contouring with finishing diamond burrs, the final polishing was performed with the Shofu polishing system (brownie).

Table 2
Resin composites and adhesive system used.
Material Composition Type Application steps Manufacturer
cfm cmf etch : buffered phosphoric acid (pH = 1.5) 3-step etch-and-rinse light curing adhesive system
  • Etch for 15 s enamel and dentin

  • Rinse for maximally 10 s

  • Air dried carefully for ca 5 s.

  • The cmf primer was applied using a rubbing motion for 30 s, followed by a careful 5 s air blowing to remove solvent. Light cure 20 s

  • The cmf bonding was applied using a rubbing motion for 20 s

  • Light cure for 20 s

Saremco AG, Rebstein, Switzerland
cmf primer : metacrylated phosphoric salt, alcohol, aceton, CQ, co-initiator
cmf bonding : hydrophilic ethoxylated Bis-GMA, silanized barium glass, CQ, co-initiator.
AdheSE One F Bis-acrylamide derivative, bis-methacrylamide
dihydrogenphosphate, amino acid acrylamide, hydroxyalkyl methacrylamide 20–40%, water alcohol solvent 20–30%, stabilizers, initiators. highly dispersed silicon dioxide, pH 1.4
fillers <5%, potassium fluoride
single-step self-etching, light-cured, nano-filled, with fluoride release in a pen delivery system
  • Dry surface

  • An adequate amount of AdheSE One F was directly applied to the cavity with the VivaPen.

  • The adhesive was brushed into the entire surface for 30 s.

  • Air blow for more than 5 s until a glossy, immobile liquid film appeared.

  • Light-cure for 10 s.

Vivadent Ivoclar, Schaan, Liechtenstein
els (extra low shrinkage) Bis-GMA, Bis-EMA, IBMA, catalysts, inhibitors, pigment filler: Ba glass, Ba-Al-B-Si glass, silanized, ø 0,7 μm, max. 2,6 μm, 74 wt%, 50 vol.%. low shrinkage resin composite volume shrinkage 2.3%, shrinkage stress after 30 min: 2.6 MPa Applied in 2–3 mm layers, oblique when possible. Saremco, Switzerland
Light cured 20–40 s per layer
Abbreviations : HEMA 2-hydroxyethyl-methacrylate, 4-MET 4-methacryloxyethyl trimetellitic acid, IBMA, isobornylmethacrylate, PENTA Phosphoric acid modified acrylate resin, TCB resin carboxylic acid modified dimethacrylate, TEGDMA triethyleneglycol dimethacrylate, Bis GMA bisphenol A-glycidyl methacrylate, Bis EMA Bisphenol A ethoxylate dimethacrylate, UDMA urethane dimethacrylate; CQ camphoroquinon.

Evaluation

The restorations were blindly evaluated and scored by using slightly modified US Public Health Service criteria at baseline (after performance of the restorations) and then yearly during the 6 year follow up ( Table 3 ) . During the evaluations, the evaluators had neither knowledge of which study the evaluated RC restorations belonged to nor of the earlier recall evaluation scores. Cohen-kappa values performed during the follow up were >86%. Bite-wing radiographs were taken at the yearly recalls. The participants were asked at their next visit and at all recalls if they had experienced symptoms in the region of the experimental teeth The caries risk of each participant and their parafunctional habits activity at baseline and during the follow ups was estimated by treating clinician by means of clinical and socio-demographic information routinely available at the annual clinical examinations, e.g. incipient caries lesions, former caries history, frequency, dietary habits, oral hygiene, medications, salivary properties and symptoms related to bruxing activity . All patients were informed about the follow up evaluations according to the rules at the PDHS clinic at the Dental School Umeå. Concomitant treatment was given to the patients in conformity with normal clinical routines at the clinic. Patients were instructed to contact the clinic immediately if any discomfort occur.

Table 3
Modified USPHS criteria for direct clinical evaluation (van Dijken ).
Category Score Criteria
Acceptable Unacceptable
Anatomical form 0 The restoration is contiguous with tooth anatomy
1 Slightly under- or over-contoured restoration; marginal ridges slightly undercontoured; contact slightly open (may be self-correcting); occlusal height reduced locally
2 Restoration is undercontoured, dentin or base exposed; contact is faulty, not self-correcting; occlusal height reduced; occlusion affected
3 Restoration is missing partially or totally; fracture of tooth structure; shows traumatic occlusion; restoration causes pain in tooth or adjacent tissue
Marginal adaptation 0 Restoration is contiguous with existing anatomic form, explorer does not catch
1 Explorer catches, no crevice is visible into which explorer will penetrate
2 Crevice at margin, enamel exposed
3 Obvious crevice at margin, dentin or base exposed
4 restoration mobile, fractured or missing
Color match 0 Very good color match
1 Good color match
2 Slight mismatch in color, shade or translucency
3 Obvious mismatch, outside the normal range
4 Gross mismatch
Marginal discoloration 0 No discoloration evident
1 Slight staining, can be polished away
2 Obvious staining can not be polished away
3 Gross staining
Surface roughness 0 Smooth surface
1 Slightly rough or pitted
2 Rough, cannot be refinished
3 Surface deeply pitted, irregular grooves
Caries 0 No evidence of caries contiguous with the margin of the restoration
1 Caries is evident contiguous with the margin of the restoration

Statistical analysis

The characteristics of the restorations are described by descriptive statistics using cumulative relative frequency distributions of the scores. The experimental and control restorative techniques were compared intra-individually with the non parametric Friedman two-way analysis of variance test

Materials and methods

Experimental design

The study was a randomized controlled prospective trial. In an intra-individual comparison each participant received one pair of similar sized Class II resin composite restorations. The two restorations in each pair were performed with the TEGDMA/HEMA-free low shrinkage resin composite (els; Saremco AG, Rebstein, Switzerland), and bonded either with the TEGDMA/HEMA-free 3-step etch-and-rinse adhesive of the system (cmf, Saremco) or a single-step HEMA-free self-etching adhesive in a pen delivery system (AdheSE One F, Vivadent Ivoclar, Schaan, Liechtenstein; ASE). The els resin composite does not contain co-monomers of low molecular weights and showed the lowest contraction stress of marketed resin composites .

During 2009, adult patients attending the Public Dental Health Service clinic at the Dental School Umeå, who at the yearly examination did need two Class II restorations were asked to participate in a clinical follow up. No patients were excluded because of caries risk, bruxing habits or not acceptable oral hygiene. All patients were informed on the background of the study and each participant provided informed consent to participate in the study. The study design followed the requirements outlined in the CONSORT 2010 statement. All participants were informed on the background of the study, which was approved by the ethics committee of the University of Umeå (Dnr 07-152M).

Reasons for placement of the resin composite restorations were carious lesions, fracture of old fillings or replacements due to esthetic or other reasons. No Class I cavities were included because of the relative good durability of these restorations. Operative procedures were performed under local anesthesia if necessary. Sixty-seven patients, 33 female and 34 male, with a mean age of 53 years (range 29–82) participated in the study. One hundred and thirthy-nine Class II restorations were placed in 46 premolars and 93 molars by one experienced operator (JvD) ( Table 1 ). All, except 5 patients, received at random two restorations with the two restorative techniques. The 5 participants received also one more Class II restoration with the cmf adhesive. All teeth were in occlusion. The majority of cavities had dentin bordered proximal cervical margins.

Table 1
Distribution and size of the experimental restorations.
Surfaces Maxilla Mandibula Total
Premolars Molars Premolars Molars
2 surfaces 20 32 15 22 89
3 surfaces 3 7 5 11 26
>3 surfaces 2 12 1 9 24
Total 25 51 21 42 139

Clinical procedure

After removal of the old restorations and/or caries excavation according to the principles of adhesive dentistry, the operative field was carefully isolated with cotton rolls and suction device. No bevel was placed. For all cavities a thin metallic matrix was used and carefully wedging was performed with wooden wedges (Kerr/Hawe Neos, Switzerland). No Ca(OH) 2 base or other base material was used. The cavities in each individual pair were randomly distributed to the two test adhesives, before the operative procedure started, by throwing dice. In this way, an intraindividual comparison was possible of the adhesive systems.

After rinsing of the cavities with water, application of the respective adhesive was performed according to the manufacturer’s instructions ( Table 2 ). Curing was performed with a well controlled light curing unit for at least 10 s (Astralis 7, Vivadent; Demetron light meter, Kerr, Orange, CA, USA). The low shrinkage resin composite (els, Saremco) was applied in all cavities in layers of maximally 2–3 mm with if possible, an oblique layering technique using selected resin composite instruments (Hu Friedy). Every increment was light cured for 20–40 s. After checking the occlusion/articulation and contouring with finishing diamond burrs, the final polishing was performed with the Shofu polishing system (brownie).

Table 2
Resin composites and adhesive system used.
Material Composition Type Application steps Manufacturer
cfm cmf etch : buffered phosphoric acid (pH = 1.5) 3-step etch-and-rinse light curing adhesive system
  • Etch for 15 s enamel and dentin

  • Rinse for maximally 10 s

  • Air dried carefully for ca 5 s.

  • The cmf primer was applied using a rubbing motion for 30 s, followed by a careful 5 s air blowing to remove solvent. Light cure 20 s

  • The cmf bonding was applied using a rubbing motion for 20 s

  • Light cure for 20 s

Saremco AG, Rebstein, Switzerland
cmf primer : metacrylated phosphoric salt, alcohol, aceton, CQ, co-initiator
cmf bonding : hydrophilic ethoxylated Bis-GMA, silanized barium glass, CQ, co-initiator.
AdheSE One F Bis-acrylamide derivative, bis-methacrylamide
dihydrogenphosphate, amino acid acrylamide, hydroxyalkyl methacrylamide 20–40%, water alcohol solvent 20–30%, stabilizers, initiators. highly dispersed silicon dioxide, pH 1.4
fillers <5%, potassium fluoride
single-step self-etching, light-cured, nano-filled, with fluoride release in a pen delivery system
  • Dry surface

  • An adequate amount of AdheSE One F was directly applied to the cavity with the VivaPen.

  • The adhesive was brushed into the entire surface for 30 s.

  • Air blow for more than 5 s until a glossy, immobile liquid film appeared.

  • Light-cure for 10 s.

Vivadent Ivoclar, Schaan, Liechtenstein
els (extra low shrinkage) Bis-GMA, Bis-EMA, IBMA, catalysts, inhibitors, pigment filler: Ba glass, Ba-Al-B-Si glass, silanized, ø 0,7 μm, max. 2,6 μm, 74 wt%, 50 vol.%. low shrinkage resin composite volume shrinkage 2.3%, shrinkage stress after 30 min: 2.6 MPa Applied in 2–3 mm layers, oblique when possible. Saremco, Switzerland
Light cured 20–40 s per layer
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Nov 22, 2017 | Posted by in Dental Materials | Comments Off on Durability of a low shrinkage TEGDMA/HEMA-free resin composite system in Class II restorations. A 6-year follow up
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