Clinical performance of a hybrid resin composite with and without an intermediate layer of flowable resin composite: A 7-year evaluation

Abstract

Objective

The objective of this prospective clinical follow up was to evaluate the long term clinical performance of a hybrid resin composite in Class II restorations with and without intermediate layer of flowable resin composite.

Methods

Each participant received at least two, as similar as possible, Class II restorations of the hybrid resin composite. One resin composite restoration of each pair (59) was chosen at random to be restored with an intermediary layer with flowable resin composite. The other was restored without. The 118 restorations were evaluated using slightly modified USPHS criteria at baseline and then yearly during 7 years.

Results

Four drop outs were registered during the 7-year follow up (2 with and 2 without flowable) restorations. A prediction of the caries risk showed that 18 of the evaluated 46 patients were considered as high risk patients. Seventeen failures were observed, 8 in restorations with and 9 in restorations without an intermediate layer of flowable resin composite, resulting in a 14.9% failure rate after 7 years. The main reasons for failure were: fracture of resin composite (8), secondary caries (4) and cusp fracture (3). No statistical difference was seen between restorations restored with and without flowable layer.

Conclusion

The hybrid resin composite showed a good clinical performance during the 7-year evaluation. The use of flowable resin composite as an intermediate layer did not result in improved effectiveness of the Class II restorations.

Introduction

Today, resin composites are the first choice restorative material for Class II restorations . Bonding of resinuous materials to enamel is a well established technique in operative dentistry with good clinical evidence . Dentin bonding is more unpredictable despite large improvements since the introduction of amphyphilic adhesive systems. However, their clinical durability is still not of the same quality as that of the bond to enamel . Failure of the adhesive system to bond to the tooth tissues leads to interfacial gap formation which may contribute to post-operative sensitivity, marginal discoloration and secondary caries. The interface between tooth and restorative materials is subjected throughout its lifetime to different stresses which can potentially cause debonding and result in clinical failure. The first interfacial stresses occur initially during the volumetric shrinkage of the resin material. The magnitude of this contraction stress varies, depending on variables such as: volume of resin material cured, mechanical and physical properties of the material, monomer contents, filler type and amount, degree of polymerization, C-factor and application technique.

Resin composites are technique sensitive and there are difficulties in obtaining a tight bond in the proximal box of Class II restorations. The high viscosity and stickiness of some resin composites to insertion instruments, makes adaptation to the cavity walls difficult and improper placement results in an inadequate seal. Marginal leakage in the cervical proximal cavity margins has been reported . To improve the interfacial adaptation, sandwich methods have been suggested, using different types of glass ionomer cement or low-modulus resin-based materials . However, most of these techniques did not improve the clinical durability of the proximal resin composite restoration . Flowable resin composites have been recommended as intermediate layers placed in the cervical part of the proximal box of Class II resin composites. These composites contain the same, but 20–25% less, filler particles as the traditional resin composites, which makes them less rigid. The use of flowable composites as an intermediary layer is suggested to reduce interfacial debonding and cuspal deflection . Their easy handling properties, enhanced flow, reduced elastic modulus and better wettability may result in improved placing characteristics, reduce voids at the cervical interface and may counteract microleakage by improved interfacial bonding and by forming a stress-absorbing layer . Several in vitro studies showed that flowable resin composites reduced microleakage , while other studies could not confirm improved marginal adaptation . Despite the widespread use in general practice of this technique of placing flowable resin composite as an intermediate layer in Class II cavities, only two clinical studies evaluated its effectiveness in 2-year evaluations . No long term evaluation of the technique has been reported.

The aim of this prospective long term study was to evaluate, in an intra-individual comparison, the clinical performance of Class II resin composite restorations with and without a flowable resin composite as intermediate layer. The hypothesis tested was that restorations with flowable resin composite showed improved clinical effectiveness.

Material and methods

Patient selection and clinical procedure

During a period of 12 months, all patients in need of at least two comparable Class II resin composite restorations, visiting the authors’ clinic, were asked to participate in the study. The study design was approved by the Ethics Committee of the University of Umeå, Sweden. Informed consent was obtained from all the participants. No patient was excluded because of caries activity, periodontal condition or parafunctional habits. Forty-eight patients, 22 women and 26 men, with a mean age of 57.0 years (range 21–85) participated. In order to make an intra-individual comparison possible, each patient received at least two restorations. The first restoration was filled with Tetric Ceram (Vivadent-Ivoclar; Table 1 ). In the second cavity an intermediate layer of the Tetric flow (Vivadent;) was placed in the cervical part of the proximal box, followed by Tetric Ceram in the other parts of the cavity. In total, 118 Class II restorations were placed by two calibrated general dentists. Before the start of the study, the operative procedure was thorougly discussed and familiarized. Fifty-six (47.5%) were placed in molars and 62 (52.5%) in premolars. The majority, 108 restorations, were 2-surface resin composite restorations. Fifty-six were placed in the upper and 62 in the lower jaw. Eighty-six percent of the cervical margins of the approximal boxes were placed below the cemento-enamel junction. Reasons for placement were to replace existing failed restorations, in most cases amalgam, esthetic and non-amalgam reasons. All teeth were in occlusion and had at least one proximal contact with an adjacent tooth.

Table 1
Resin composites and bonding system used.
Tetric Ceram Highly filled hybrid small-particle resin composite Filler: mean size 1 μm Vivadent-Ivoclar, Schaan, Liechtenstein; Lot B37704
silanized barium glass (49.5 wt%),
mixed oxides (5 wt%),
silanized barium alumino-fluorosilicate glass (5 wt%)
silanized high-dispersed silica (1 wt%)
ytterbium trifluoride (17 wt%).
Monomer:
Bis-GMA (8.5 wt%),
urethane dimethacrylate (7.8 wt%)
TEGDMA (4.4 wt%).
Tetric flow Flowable resin composite Same fillers and momomers as Tetric Ceram Vivadent-Ivoclar,: Lot B30814
filler weight of 64.6%
mean filler size 0.7 μm (0.04–3.0 μm).
Excite One-step etch-and-rinse adhesive system conditioner: phosphoric acid 37% Vivadent-Ivoclar; Lot B41001
primer: ethanol (25%), phosphonate monomers, dimethacrylates, phosphonic acid acrylate (73.6%): HEMA. Highly dispersed silicon dioxid (nanofiller, 0.5%; cetylaminehydrofluoride); initiators, stabilizers (0.9%).

The restorative protocol was the same for both restorations, except for the placement of a flowable resin composite in the cervical part of the proximal box. The flowable resin was used at random in one cavity of each pair. Operative procedures were performed under local anesthesia if necessary. Existing restorations and/or caries were removed under constant water cooling. No calcium hydroxide base was placed and no bevels were prepared. The operative field was isolated with suction device and cotton rolls. The resin composite cavities were acid-etched with 35% phosphoric acid (Ultra-etch, Ultradent Products Inc., South Jordan, UT, USA). The gel was first placed on the enamel, while the dentin part of the cavity was conditioned during the last five seconds of the 15 s etching time. The cavity was then thoroughly rinsed with air–water spray for 10–15 s and carefully dried allowing a wet bonding technique. The primer (Excite; Table 1 ) was applied for 20 s, and then carefully air blowed to remove the primer’s ethanol. A second layer primer was applied, directly followed by air blowing and 10 s light curing. The thickness of flowable resin composite was 1.0–1.5 mm and the thickness of the first resin composite layer in the proximal box of the other restoration was 2 mm. Subsequent resin composite was applied in layers of maximally 3 mm. Each layer was light-cured for 60 s with a visible light curing unit (Astralis 7, Vivadent). The light curing unit was regularly controlled with an Optilux 100 radiometer (Kerr/Demetron, Danbury, CT, USA). The restorations were finished with fine diamond or carbide finishing burs to remove gross excess, followed by Shofu brownie finishing points.

Evaluation

Each restoration was evaluated according to slightly modified USPHS criteria for the following characteristics: anatomical form, marginal adaptation, color match, marginal discoloration, surface roughness, caries ( Table 2 ). The restorations were evaluated at baseline, and then blindly yearly for 7 years by the operators and at regular intervals by two calibrated evaluators. The caries risk for each patient at baseline was estimated by the treating clinician by means of clinical and socio-demographic information routinely available at the annual clinical examinations, e.g. incipient carious lesions and former caries history .

Table 2
Criteria for the direct clinical evaluations (van Dijken, 1986).
Category Score Criteria
acceptable unacceptable
Anatomical form 0 The restoration is continuous 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 or traumatic occlusion; restoration causes pain in tooth or adjacent tissue
Marginal adaptation 0 Restoration is continuous 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 evaluation

The evaluated characteristics of the restorations, including the number of non-acceptable restorations (failures) are described by descriptive statistics using frequency distributions of the scores. Durability of the two restorative techniques was compared intra-individually and tested using the Friedman’s two-way analysis of variance test. The null hypothesis was rejected at the 5% level.

Material and methods

Patient selection and clinical procedure

During a period of 12 months, all patients in need of at least two comparable Class II resin composite restorations, visiting the authors’ clinic, were asked to participate in the study. The study design was approved by the Ethics Committee of the University of Umeå, Sweden. Informed consent was obtained from all the participants. No patient was excluded because of caries activity, periodontal condition or parafunctional habits. Forty-eight patients, 22 women and 26 men, with a mean age of 57.0 years (range 21–85) participated. In order to make an intra-individual comparison possible, each patient received at least two restorations. The first restoration was filled with Tetric Ceram (Vivadent-Ivoclar; Table 1 ). In the second cavity an intermediate layer of the Tetric flow (Vivadent;) was placed in the cervical part of the proximal box, followed by Tetric Ceram in the other parts of the cavity. In total, 118 Class II restorations were placed by two calibrated general dentists. Before the start of the study, the operative procedure was thorougly discussed and familiarized. Fifty-six (47.5%) were placed in molars and 62 (52.5%) in premolars. The majority, 108 restorations, were 2-surface resin composite restorations. Fifty-six were placed in the upper and 62 in the lower jaw. Eighty-six percent of the cervical margins of the approximal boxes were placed below the cemento-enamel junction. Reasons for placement were to replace existing failed restorations, in most cases amalgam, esthetic and non-amalgam reasons. All teeth were in occlusion and had at least one proximal contact with an adjacent tooth.

Table 1
Resin composites and bonding system used.
Tetric Ceram Highly filled hybrid small-particle resin composite Filler: mean size 1 μm Vivadent-Ivoclar, Schaan, Liechtenstein; Lot B37704
silanized barium glass (49.5 wt%),
mixed oxides (5 wt%),
silanized barium alumino-fluorosilicate glass (5 wt%)
silanized high-dispersed silica (1 wt%)
ytterbium trifluoride (17 wt%).
Monomer:
Bis-GMA (8.5 wt%),
urethane dimethacrylate (7.8 wt%)
TEGDMA (4.4 wt%).
Tetric flow Flowable resin composite Same fillers and momomers as Tetric Ceram Vivadent-Ivoclar,: Lot B30814
filler weight of 64.6%
mean filler size 0.7 μm (0.04–3.0 μm).
Excite One-step etch-and-rinse adhesive system conditioner: phosphoric acid 37% Vivadent-Ivoclar; Lot B41001
primer: ethanol (25%), phosphonate monomers, dimethacrylates, phosphonic acid acrylate (73.6%): HEMA. Highly dispersed silicon dioxid (nanofiller, 0.5%; cetylaminehydrofluoride); initiators, stabilizers (0.9%).

The restorative protocol was the same for both restorations, except for the placement of a flowable resin composite in the cervical part of the proximal box. The flowable resin was used at random in one cavity of each pair. Operative procedures were performed under local anesthesia if necessary. Existing restorations and/or caries were removed under constant water cooling. No calcium hydroxide base was placed and no bevels were prepared. The operative field was isolated with suction device and cotton rolls. The resin composite cavities were acid-etched with 35% phosphoric acid (Ultra-etch, Ultradent Products Inc., South Jordan, UT, USA). The gel was first placed on the enamel, while the dentin part of the cavity was conditioned during the last five seconds of the 15 s etching time. The cavity was then thoroughly rinsed with air–water spray for 10–15 s and carefully dried allowing a wet bonding technique. The primer (Excite; Table 1 ) was applied for 20 s, and then carefully air blowed to remove the primer’s ethanol. A second layer primer was applied, directly followed by air blowing and 10 s light curing. The thickness of flowable resin composite was 1.0–1.5 mm and the thickness of the first resin composite layer in the proximal box of the other restoration was 2 mm. Subsequent resin composite was applied in layers of maximally 3 mm. Each layer was light-cured for 60 s with a visible light curing unit (Astralis 7, Vivadent). The light curing unit was regularly controlled with an Optilux 100 radiometer (Kerr/Demetron, Danbury, CT, USA). The restorations were finished with fine diamond or carbide finishing burs to remove gross excess, followed by Shofu brownie finishing points.

Evaluation

Each restoration was evaluated according to slightly modified USPHS criteria for the following characteristics: anatomical form, marginal adaptation, color match, marginal discoloration, surface roughness, caries ( Table 2 ). The restorations were evaluated at baseline, and then blindly yearly for 7 years by the operators and at regular intervals by two calibrated evaluators. The caries risk for each patient at baseline was estimated by the treating clinician by means of clinical and socio-demographic information routinely available at the annual clinical examinations, e.g. incipient carious lesions and former caries history .

Nov 28, 2017 | Posted by in Dental Materials | Comments Off on Clinical performance of a hybrid resin composite with and without an intermediate layer of flowable resin composite: A 7-year evaluation
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