A randomized controlled three year evaluation of “bulk-filled” posterior resin restorations based on stress decreasing resin technology

Abstract

Objective

The objective of this randomized controlled prospective clinical trial was to evaluate the efficacy of a flowable resin composite (SDR) bulk fill technique in posterior restorations and to compare it intraindividually with a conventional 2 mm resin composite curing technique in a 3-year follow up.

Materials and methods

Thirty-eight pairs Class II and 15 pairs Class I restorations were placed in 38 patients with a mean age of 55.3 years (range 32–87). Each patient received at random at least two, as similar as possible, Class II or Class I restorations of two restorative techniques. In all cavities a single step self-etch adhesive (Xeno V) was applied. In one of the cavities of each pair, a flowable resin composite (SDR) was placed, in bulk increments up to 4 mm as needed to fill the cavity 2 mm short of the occlusal cavosurface. The occlusal part was completed with a nano-hybrid resin composite (Ceram X mono) layer. In the second cavity, the hybrid resin composite was placed in 2 mm increments. The restorations were evaluated using slightly modified USPHS criteria at baseline and then yearly during 3 years. Caries risk and parafunctional habits of the participants were estimated.

Results

After three years, 76 Class II and 28 Class I restorations could be observed. One molar resin composite-only tooth showed post-operative sensitivity during 3 weeks for temperature changes and occlusal forces. Two failed Class II molar restorations in the resin composite-only group were observed during the first year, one cusp fracture and one resin composite fracture. An annual failure rate of 1.3% was found for the resin composite only restorations and of 0% in the bulk-filled restorations (n.s.). Ten participants were estimated as having high caries risk and eleven showed active bruxing habits.

Significance

The 4 mm bulk-fill technique with the flowable resin composite SDR showed highly clinical effectiveness, which was comparable during the 3-year follow-up with the 2 mm resin composite layering technique.

Introduction

In many countries resin composites do have almost totally replaced amalgam as restorative in posterior teeth . The majority of the resin composites are today methacrylate based and cure by means of a free radical polymerization. During curing of the monomers, a network of polymers is formed which becomes rigid due to increasing cross-linking of the polymer chains. In the post-gel contraction phase, the shrinkage manifests as a strain on the resin composite and cavity walls which may result in interfacial deficiencies, enamel fractures, cuspal movements and cracked cusps. Gap formation may increase the potential for post-operative sensitivity, microleakage and secondary caries. The resulting stress depends on factors like: resin monomers involved, filler technology, gel point, C-factor of the cavity, elastic modulus of the resin composite, curing technique and conversion rate. Several clinical techniques have been suggested to minimize interfacial stress formation like decreasing the C-factor by using selected layering technique, to use stress reducing curing techniques such as the soft start curing and placement of stress absorbing intermediary layers in sandwich techniques . Extensive efforts have been made during the last years to develop low shrinkage materials by changes in filler technology and monomer chemistry . The intensity of the curing light decreases when the light is transmitted through the resin composite. The conversion rate in the resin composite restoration will decrease at increasing distance from the curing light and by decreased energy . A lower conversion rate will influence the physical properties of the resin composite and increased elution of monomers have been reported . To prevent clinical failures because of a non-optimal cured resin composite and decrease the elution of non-reacted monomers, the resin composite restoration is cured in increments. The maximal incremental thickness which provides adequate light penetration and polymerization has been generally defined as 2 mm . The layering technique makes the restorative procedure time consuming, voids may be included and the failure risk increases . The main concern regarding applying thicker increments is whether the resin composite cures enough in the deeper parts to obtain acceptable mechanicical, physical and biocompatible properties. Recently, a new class of resin composite materials the bulk-fill resin composites have been introduced. During the early 2000th a first approach to apply posterior resin composite restorations with thicker layers was introduced as a rather high transluscent resin composite . More recently an on stress decreasing resin technology based flowable resin (SDR) was introduced to be used in 4 mm layers as open or closed dentin replacement beneath a conventional resin composite . The rheology of the material was suggested to be improved allowing improved adaptation to the cavity walls. A polymerization modulator, a patented urethane di-methacrylate, is chemically embedded in the resin backbone of the resin composite. This results in a slower modulus development, allowing for stress reduction without decreasing conversion rate . In vitro studies showed that the application of fewer and thicker increments could be equally successful as the conventional layering technique . Ilie and Hickel showed that SDR showed the lowest shrinkage stress and shrinkage rate in comparisons to regular methacrylate resin composites . The degree of cure and mechanical properties were shown to be constant within the 4 mm increment at a curing time of 20 s . The bulk-fill material exhibited an acceptable creep deformation and within the range exhibited by other resin composites . Cuspal deflections were significantly reduced when a single increment of the flowable resin composite was used as dentin replacement base to restore Class II cavities .

No clinical study has yet reported the clinical effectiveness of the SDR flowable base and its claimed 4 mm thick layer curing. The aim of this study was to investigate in a randomized controlled intraindividual comparison the clinical effectiveness of the flowable resin composite placed with maximally 4 mm increments (bulk fill) in large and deep Class I and Class II cavities. SDR is used to fill the cavity 2 mm short of the occlusal cavosurface and is then covered with a nano-hybrid resin composite. The SDR restoration is compared intraindividually with a nano-hybrid resin composite-only restoration placed and cured with a 2 mm layering technique. In both the experimental- and resin composite-only control cavity a one-step self-etching bonding system was used. The hypothesis tested was that bulk-fill restorations show similar durability as the resin composite-only restorations

Material and methods

During may-october 2010, all adult patients attending the Public Dental Health Service clinic at the Dental School Umeå who needed one or two pair similar Class II or Class I restorations, were asked to participate in the follow up. All patients invited, participated in the study. No participant was excluded because of high caries activity, periodontal condition or parafunctional habits in order to mirror the whole patient population. Pregnant female patients were excluded. All patients 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 primary and secondary carious lesions, fracture of old amalgam fillings or replacement because of esthetic or other reasons. In order to make an intra-individual comparison possible, each patient received two or four as similar sized and located restorations as possible. The cavity pairs in each individual were randomly distributed to be restored with either the experimental or the control restoration before the operative procedure started, according to a predetermined scheme of randomization. The participants were not aware in which cavity, the experimental and control restoration were placed. In the experimental cavity an intermediate layer of the SDR flowable RC (Dentsply/DeTrey, Konstanz, Germany; Table 1 ) was placed in the dentinal part followed by a covering layer of the nano-hybrid resin composite Ceram X mono (Dentsply/DeTrey; from now on called Ceram X). The control restoration was filled with Ceram X (resin composite-only restoration). Thirty-eight pairs Class II and 15 pairs Class I restorations were placed in 38 patients with a mean age of 55.3 years (range 32–87) by one experienced operator (JvD). The distribution of the involved experimental teeth is shown in Table 2 . The sample size was calculated on the basis of previous sample size calculations performed in similar designed studies of posterior restoration evaluations. The theoretical sample size was set to 40 restorations per group to determine significant differences in outcomes at the 95% confidence level, with an alpha value = 0.05 and 80% power. Significant differences between material groups in similar intraindividual comparison design evaluations have been possible to determine with this sample size in earlier evaluations . The number of participants was increased to safeguard against possible drop outs. All teeth were in occlusion and had at least one proximal contact with an adjacent tooth.

Table 1
Resin composites and adhesive system used.
Material Composition Type Application steps Manufacturer
SDR Filler: Barium-alumino-fluoro-borosilicate glass, strontium alumino-fluoro-silicate glass
Matrix: modified urethane dimethacrylate resin, ethoxylated bisphenol-A dimethacrylate (EBPADMA), triethyleneglycol dimethacrylate, camphorquinone, butylated hydroxyl toluene, uv stabilizer, titanium oxide, iron oxide pigments. The SDR flow base is covered with at least 2 mm RC.
4 mm layers, light cured 20 s Dentsply DeTrey, Konstanz, Germany
Ceram X
Mono
Filler: Barium–aluminum-borosilicate glass (1.1–1.5 μm), methacrylate functionalized silicone dioxide nano filler (10 nm)
Matrix: Methacrylate modified polysiloxane, dimethacrylate resin, fluorescent pigment, UV stabilizer, stabilizer, camphorquinone, ethyl-4 (dimethylamino) benzoate, titanium oxice pigments, aluminum silicate pigments
Nanohybrid
76%, w/w filler
57%, v/v filler average size nanofillers 10 nm and nano particles 2.3 nm
2 mm layers, light cured 20-30 s Dentsply DeTrey.
Xeno V 1-component one-step
Self-etching adhesive
Apply primer 20 s, careful air drying for >5 s, light cured 10 s. Dentsply DeTrey

Table 2
Distribution and size of the experimental restorations.
Surfaces Mandibula Maxilla Total
Premolars Molars Premolars Molars
1 surfaces 3 8 2 17 30
2 surfaces 16 8 26 20 70
≥3 surfaces 3 3 6
Total 19 19 28 40 106

Clinical procedure

Existing restorations and/or caries were removed under constant water cooling. No bevels were prepared. The operative field was carefully isolated with cotton rolls and suction device. For all Class II cavities a thin metallic matrix was used and carefully wedging was performed with wooden wedges (Kerr/Hawe Neos, Switzerland). The cavities were cleaned by thoroughfull rinsing with water. In none of the cavities Ca(OH) 2 or other base materials was applied. Application of the 1-step self etching adhesive XenoV (DeTrey Dentsply) in both cavities was performed according to the manufacturers instructions ( Table 2 ). After 20 s gently agitating, the solvent was evaporated thoroughly during at least 5 s. Curing was then performed with a well controlled high power curing unit (Smartlite PS, Dentsply/DeTrey) for at least 10 s. In the by randomization chosen experimental SDR restoration, the flow material was dispensed directly into the cavity from the compula tip using slow steady pressure, starting dispensing at the deepest portion of the cavity, keeping the tip close to the cavity floor. The tip was gradually withdrawn as the cavity was filled. The material was available in one semi-transluscent universal shade. It was placed in bulk increments up to 4 mm as needed to fill the cavity 2 mm short of the occlusal cavosurface. After curing of the flow increment(s)(20 s), the occlusal part of the restoration was completed using the Ceram X resin composite material. In the control cavity the resin composite Ceram X was applied in 2 mm layers with, if possible, an oblique layering technique. Selected resin composite instruments (Hu Friedy) were used. The pairs of restorations were placed by the same with adhesive dentistry experienced operator (the first author). After checking the occlusion/articulation and contouring with finishing diamond burrs, the final polishing was performed with the Shofu polishing system (Brownie) or the Enhance polishing system (DeTrey Dentsply).

Evaluation

At baseline (after placement of the restorations) and after one, two and three years the restorations were assessed by the following parameters: anatomic form, marginal adaptation, marginal discoloration, surface roughness, color match and secondary caries by slightly modified USPHS criteria according to van Dijken 1986 ( Table 3 ) . The follow up registrations were performed blindly by the operator and at regular intervals by two calibrated evaluators. During the evaluation sessions, evaluators did not know which study or which restorative material group the scoring concerned. The caries risk for each participant and their parafunctional habits activity at baseline and during the follow ups was estimated by the treating clinician by means of clinical and socio-demographic information routinely available at the annual clinical examinations, e.g. incipient caries lesions and former caries history .

Table 3
Modified USPHS criteria for direct clinical evaluation .
Category Score (acceptable/unacceptable) Criteria
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 frequency distributions of the scores. The experimental and control restorative techniques were compared intra-individually with the non parametric Friedman’s two-way analysis of variance test .

Material and methods

During may-october 2010, all adult patients attending the Public Dental Health Service clinic at the Dental School Umeå who needed one or two pair similar Class II or Class I restorations, were asked to participate in the follow up. All patients invited, participated in the study. No participant was excluded because of high caries activity, periodontal condition or parafunctional habits in order to mirror the whole patient population. Pregnant female patients were excluded. All patients 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 primary and secondary carious lesions, fracture of old amalgam fillings or replacement because of esthetic or other reasons. In order to make an intra-individual comparison possible, each patient received two or four as similar sized and located restorations as possible. The cavity pairs in each individual were randomly distributed to be restored with either the experimental or the control restoration before the operative procedure started, according to a predetermined scheme of randomization. The participants were not aware in which cavity, the experimental and control restoration were placed. In the experimental cavity an intermediate layer of the SDR flowable RC (Dentsply/DeTrey, Konstanz, Germany; Table 1 ) was placed in the dentinal part followed by a covering layer of the nano-hybrid resin composite Ceram X mono (Dentsply/DeTrey; from now on called Ceram X). The control restoration was filled with Ceram X (resin composite-only restoration). Thirty-eight pairs Class II and 15 pairs Class I restorations were placed in 38 patients with a mean age of 55.3 years (range 32–87) by one experienced operator (JvD). The distribution of the involved experimental teeth is shown in Table 2 . The sample size was calculated on the basis of previous sample size calculations performed in similar designed studies of posterior restoration evaluations. The theoretical sample size was set to 40 restorations per group to determine significant differences in outcomes at the 95% confidence level, with an alpha value = 0.05 and 80% power. Significant differences between material groups in similar intraindividual comparison design evaluations have been possible to determine with this sample size in earlier evaluations . The number of participants was increased to safeguard against possible drop outs. All teeth were in occlusion and had at least one proximal contact with an adjacent tooth.

Nov 25, 2017 | Posted by in Dental Materials | Comments Off on A randomized controlled three year evaluation of “bulk-filled” posterior resin restorations based on stress decreasing resin technology
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