Fracture resistance of class II preformed ceramic insert and direct composite resin restorations

Objectives. This study aimed to compare the fracture resistance of two different posterior restorations in class II cavities.Methods. In this study 24 extracted intact human mandibular molars (for testing) and 24 extracted intact human teeth (for achieving contact) were used. The test teeth were divided into two groups and then mounted in normal anatomic relationship with intact human teeth on the same holder. Thus 12 pairs of teeth were constituted in each group. Class II MO cavities were prepared on testing teeth in each holder. The other tooth was used for achieving contact. The cavities in group 1 were restored with direct composite resin with the manufacturer's flowable composite. The cavities in group 2 were restored with SONICSYS inlays (preformed ceramic insert) according to the manufacturer's instructions. The marginal ridges of the restorations were loaded at an angle of 13.5 degrees to the long axis of the tooth in an Instron testing machine until failure occurred.Results. Analysis of mean failure loads indicated that class II SONICSYS inlay restorations (group 2) had a significantly greater fracture resistance than did class II direct composite resin restorations with flowable composite (P=0.000).Conclusions. The SONICSYS inlay system provided greater fracture resistance than direct composite resin with flowable composite.     

Marginal adaptation of ceramic inserts after cementation

The advantage of using ceramic inserts is to prevent major drawbacks of composite resins such as polymerization shrinkage, wear and microleakage. This in vitro study evaluated the marginal adaptation of two approximal ceramic insert systems after cementation to the cavities opened with ultrasonic tips. Proximal cavities with margins in enamel were prepared in 20 intact molars using ultrasonic tips (SONICSYS approx tips [microtorpedo size #2 and #3]; Siplus Instrument approximal [U-shaped]). Inserts of similar sizes (n=10) from two systems corresponding to the ultrasonic tips were placed in the cavities (SONICSYS Inlay; SDS-Inlay system), one on the mesial side and the other on the distal side of the same molar. Following cementation and thermocycling (5000 cycles, between 5-55 degrees C), cement thickness was measured at the buccal, lingual walls and pulpal floors of the proximal boxes under light microscope (x150). The mean cement thickness values recorded for SONICSYS inserts #2 (25 microm) was not significantly different (p>0.05) from that of SDS inserts of similar size (26 microm). There was a significant difference (p<0.05) in cement thickness values between SONICSYS #3 inserts (34 microm) and SDS inserts of similar size (23 microm). Comparison of mean values between the ceramic insert systems examined revealed that marginal adaptation was better at the buccal and lingual proximal walls than those at the pulpal floor in the SDS system, however, there was no difference for SONICSYS at both sizes. Ceramic inserts placed in cavities prepared with ultrasonic tips provide clinically acceptable marginal quality.     

Polymerization contraction stress of resin composite restorations in a model Class I cavity configuration using photoelastic analysis

PURPOSE: An important factor that contributes to deterioration of resin composite restorations is contraction stress that occurs during polymerization. The purpose of this article is to familiarize the clinician with the characteristics of contraction stress by visualizing the stresses associated with this invisible and complex phenomenon. MATERIALS AND METHODS: Internal residual stresses generated during polymerization of resin composite restorations were determined using micro-photoelastic analysis. Butt-joint preparations simulating Class I restorations (2.0 mm x 5.0 mm, 2.0 mm in depth) were prepared in three types of substrates (bovine teeth, posterior composite resin, and transparent composite resin) and were used to examine contraction stress in and around the preparations. Three types of composite materials (a posterior composite, a self-cured transparent composite, and a light-cured transparent composite) were used as the restorative materials. The self-cured composite is an experimental material, and the others are commercial products. After treatment of the preparation walls with a bonding system, the preparations were bulk-filled with composite. Specimens for photoelastic analysis were prepared by cutting sections perpendicular to the long axis of the preparation. Fringe patterns for directions and magnitudes of stresses were obtained using transmitted and reflected polarized light with polarizing microscopes. Then, the photoelastic analysis was performed to examine stresses in and around the preparations. RESULTS: When cavity preparations in bovine teeth were filled with light-cured composite, a gap was formed between the dentinal wall and the composite restorative material, resulting in very low stress within the restoration. When cavity preparations in the posterior composite models were filled with either self-cured or light-cured composite, the stress distribution in the two composites was similar, but the magnitude of the stress was greater in the light-cured material. When preparations in the transparent composite models were filled with posterior composite and light-cured transparent composite material, significant stress was generated in the preparation models simulating tooth structure, owing to the contraction of both restorative materials. CLINICAL SIGNIFICANCE: Polymerization contraction stress is an undesirable and inevitable characteristic of adhesive restorations encountered in clinical dentistry that may compromise restoration success. Clinicians must understand the concept of polymerization contraction stress and realize that the quality of composite resin restorations depends on successful management of these stresses.     

Polymerization Contraction Stress of Resin Composite Restorations in a Model Class I Cavity Configuration Using Photoelastic Analysis

Purpose: An important factor that contributes to deterioration of resin composite restorations is contraction stress that occurs during polymerization. The purpose of this article is to familiarize the clinician with the characteristics of contraction stress by visualizing the stresses associated with this invisible and complex phenomenon. Materials and Methods: Internal residual stresses generated during polymerization of resin composite restorations were determined using micro‐photoelastic analysis. Butt‐joint preparations simulating Class I restorations (2.0 mm ± 5.0 mm, 2.0 mm in depth) were prepared in three types of substrates (bovine teeth, posterior composite resin, and transparent composite resin) and were used to examine contraction stress in and around the preparations. Three types of composite materials (a posterior composite, a self‐cured transparent composite, and a light‐cured transparent composite) were used as the restorative materials. The self‐cured composite is an experimental material, and the others are commercial products. After treatment of the preparation walls with a bonding system, the preparations were bulk‐filled with composite. Specimens for photo‐elastic analysis, were prepared by cutting sections perpendicular to the long axis of the preparation. Fringe patterns for directions and magnitudes of stresses were obtained using transmitted and reflected polarized light with polarizing microscopes. Then, the photoelastic analysis was performed to examine stresses in and around the preparations. Results: When cavity preparations in bovine teeth were filled with light‐cured composite, a gap was formed between the dentinal wall and the composite restorative material, resulting in very low stress within the restoration. When cavity preparations in the posterior composite models were filled with either self‐cured or light‐cured composite, the stress distribution in the two composites was similar, but the magnitude of the stress was greater in the light‐cured material. When preparations in the transparent composite models were filled with posterior composite and light‐cured transparent composite material, significant stress was generated in the preparation models simulating tooth structure, owing to the contraction of both restorative materials. CLINICAL SIGNIFICANCE Polymerization contraction stress is an undesirable and inevitable characteristic of adhesive restorations encountered in clinical dentistry that may compromise restoration success. Clinicians must understand the concept of polymerization contraction stress and realize that the quality of composite resin restorations depends on successful management of these stresses.     

Hardness and in vitro wear of a novel ceramic restorative cement

The aim of the present work was to compare a new ceramic restorative cement for posterior restorations, DoxaDent, with other types of tooth-colored materials for direct use as regards hardness and in vitro wear. Four hybrid resin composites, one polyacid-modified resin composite, one resin-modified glass ionomer cement, one conventional glass ionomer cement, one zinc phosphate cement, an experimental version as well as the marketed version of the ceramic restorative cement, were investigated. Hardness of the materials was tested with the Wallace indentation tester and wear was tested with the ACTA wear machine. All tests were carried out on 2-wk-old specimens. DoxaDent was as hard as the zinc phosphate cement and the hardest resin composite. The ceramic restorative cement wore significantly more than the resin composites, the same as the zinc phosphate cement, and less than the glass ionomer cements. No correlation between hardness and wear was found. It can be concluded that the ceramic restorative cement is a rather hard material but with a relatively low wear resistance.     

Does layering minimize shrinkage stresses in composite restorations?

Polymerization shrinkage of resin composites may impair restoration longevity. It is hypothesized that layering, rather than bulk, techniques result in less stress in the tooth-restoration complex. The aim of this study was to compare shrinkage stresses for different restorative techniques used for cusp-replacing restorations with direct resin composite. In a 3-D FE model, the dynamic process of shrinkage during polymerization was simulated. Time-dependent parameters (shrinkage, apparent viscosity, Young's modulus, Poisson ratio, and resulting creep), which change during the polymerization process, were implemented. Six different restorative procedures were simulated: a chemically cured bulk technique, a light-cured bulk technique, and 4 light-cured layering techniques. When polymerization shrinkage is considered, a chemically cured composite shows the least resulting stress. The differences seen among various layering build-up techniques were smaller than expected. The results indicate that the stress-bearing locations are the interface and the cervical part of the remaining cusp.     

Polymerization eficiency of dual-polymerized resin cements light-irradiated through ceramics and laboratory-processed resin composite

The purpose of the study was to determine the influence of light-irradiation through two ceramic and one resin composite materials on the degree of remaining double carbon bonds in 3 dual-polymerized resin cements. After mixing, the cement was inserted into a 0.5 mm deep recess in a silicon mold, covered with one ceramic or resin composite rectangular block and exposed through the block with the light from a halogen polymerization unit for 40 s. Infrared spectroscopic analysis was used to record the degree of remaining double carbon bonds. Light irradiation through 2 mm-thick ceramic and resin composite materials increased the degree of remaining double carbon bonds relative to the direct photopolymerization analogues.     

Dynamic covalent chemistry (DCC) in dental restorative materials: Implementation of a DCC-based adaptive interface (AI) at the resin–filler interface for improved performance

ObjectiveDental restorative composites have been extensively studied with a goal to improve material performance. However, stress induced microcracks from polymerization shrinkage, thermal and other stresses along with the low fracture toughness of methacrylate-based composites remain significant problems. Herein, the study focuses on applying a dynamic covalent chemistry (DCC)-based adaptive interface to conventional BisGMA/TEGDMA (70:30) dental resins by coupling moieties capable of thiol–thioester (TTE) DCC to the resin–filler interface as a means to induce interfacial stress relaxation and promote interfacial healing.MethodsSilica nanoparticles (SNP) are functionalized with TTE-functionalized silanes to covalently bond the interface to the network while simultaneously facilitating relaxation of the filler–matrix interface via DCC. The functionalized particles were incorporated into the otherwise static conventional BisGMA/TEGDMA (70:30) dental resins. The role of interfacial bond exchange to enhance dental composite performance in response to shrinkage and other stresses, flexural modulus and toughness was investigated. Shrinkage stress was monitored with a tensometer coupled with FTIR spectroscopy. Flexural modulus/strength and flexural toughness were characterized in three-point bending on a universal testing machine.ResultsA reduction of 30% in shrinkage stress was achieved when interfacial TTE bond exchange was activated while not only maintaining but also enhancing mechanical properties of the composite. These enhancements include a 60% increase in Young’s modulus, 33% increase in flexural strength and 35% increase in the toughness, relative to composites unable to undergo DCC but otherwise identical in composition. Furthermore, by combining interfacial DCC with resin-based DCC, an 80% reduction of shrinkage-induced stress is observed in a thiol–ene system “equipped” with both types of DCC mechanisms relative to the composite without DCC in either the resin or at the resin–filler interface.SignificanceThis behavior highlights the advantages of utilizing the DCC at the resin–filler interface as a stress-relieving mechanism that is compatible with current and future developments in the field of dental restorative materials, nearly independent of the type of resin improvements and types that will be used, as it can dramatically enhance their mechanical performance by reducing both polymerization and mechanically applied stresses throughout the composite lifetime.     

The surface status of polished restoration biomaterials after the use of a sodium bicarbonate spray: scanning electron microscopy

The effects of an air-abrasive system on polished surfaces of restorative materials have been studied using scanning electron microscopy, metrology and profilography. Polished surfaces of composite resin, of amalgam and gold alloy show different alteration types in microtopography, in profile tracings and significant increased surface roughness after air-abrasive spraying; but ceramic and non-precious alloy surfaces are not affected. The composite resin surfaces should be repolished and amalgam and gold alloy surfaces made glossy after use of an air-abrasive system.     

Using opaquers under direct composite resin veneers: an illustrated review of the technique

In restorative dentistry direct composite resin materials can be used to conservatively resolve many esthetic problems. Opaque resins are often necessary to mask discolorations and/or dark backgrounds when restoring anterior teeth. This article presents a direct composite resin veneer technique using opaquers. Potential problems with the tone of restorations after the use of opaquers are discussed. Advantages, limitations, and the clinical technique are presented. Training, as well as attention to the technique, contributes to an acceptable result.
CLINICAL SIGNIFICANCE
Resinous opaquers can be used as a valid adjunct to the direct composite resin veneer technique when conservatively restoring dark teeth.     

Visible light-curing: part II

Multiple studies on composite light-curing have focused on the effects of polymerization contraction stresses on restoration margins. Those stresses can potentially cause debonding of restorations and gap formation if they exceed resin bond strengths to enamel and dentin. Such gaps may permit microleakage, resulting in postoperative sensitivity or clinical failure of the restorative treatment. The effects of polymerization shrinkage are dependent on the configuration of the cavity, properties of the restorative material, and the kinetics of polymerization shrinkage. This review analyzes several studies that have been published on the subject     

Developments in Shrinkage Control of Adhesive Restoratives

Purpose: This article reviews material properties and application techniques important in minimizing effects of polymerization shrinkage during the curing reaction of resin composite restorative materials used in adhesive dentistry.
Materials and Methods: Relevant scientific publications were critically reviewed.
Results: Since it was recognized that shrinkage, which takes place during the curing reaction of resin composite restorative materials, may cause severe problems in adhesive dentistry, considerable effort has been put into reducing the negative effects. The most important problem is the debonding of the restoration-tooth interface, resulting in increased microleakage and, ultimately, in secondary caries. Despite all efforts, there is still no material or general application method that guarantees a leak-proof and durable restoration.
CLINICAL SIGNIFICANCE
It is of the utmost importance that dental practitioners know how to deal with the problems related to resin composite shrinkage, so that they can choose the material and procedure most likely to produce a leak-proof and durable restoration, maximizing the potential for clinical success.     

Developments in shrinkage control of adhesive restoratives

PURPOSE: This article reviews material properties and application techniques important in minimizing effects of polymerization shrinkage during the curing reaction of resin composite restorative materials used in adhesive dentistry. MATERIALS AND METHODS: Relevant scientific publications were critically reviewed. RESULTS: Since it was recognized that shrinkage, which takes place during the curing reaction of resin composite restorative materials, may cause severe problems in adhesive dentistry, considerable effort has been put into reducing the negative effects. The most important problem is the debonding of the restoration-tooth interface, resulting in increased microleakage and, ultimately, in secondary caries. Despite all efforts, there is still no material or general application method that guarantees a leak-proof and durable restoration. CLINICAL SIGNIFICANCE: It is of the utmost importance that dental practitioners know how to deal with the problems related to resin composite shrinkage, so that they can choose the material and procedure most likely to produce a leak-proof and durable restoration, maximizing the potential for clinical success.     

Direct applications of a nanocomposite resin system: Part 1--The evolution of contemporary composite materials.

The delivery of functional, aesthetic restorations has been simplified by the introduction of contemporary composite materials. The most recent innovation in composite resin technology is the revolutionary application of nanocomposite theories in restorative materials. Contemporary nanocomposite materials deliver increased aesthetics, strength, and durability, combining scientific principles for increased longevity. This article discusses the application of nanocomposite resin systems and demonstrates the historical perspective of composite resin technologies in restorative treatment. The second installment to this series will address the clinical applications of such a system in the anterior region. LEARNING OBJECTIVES: This article addresses material selection considerations that must be addressed when selecting an appropriate direct restorative material. Upon reading this article, the reader should: Understand the historical background and application of nanocomposite materials. Be aware of the clinical implications of a nanocomposite resin system.     

Intra-oral adhesive systems for ceramic repairs: a comparison

The aim of this investigation was to compare the bond strength of restorative composite resin to dental ceramic conditioned with primers and adhesives of various commercial repair kits. Three intra-oral ceramic repair systems--Silistor (Heraeus Kulzer), Cimara (Voco), Ceramic Repair (Vivadent)--were used on all-ceramic (IPS Empress 2, Ivoclar-Vivadent) substrate. Shear bond strength of restorative composite resin to substrate was tested after thermocycling and without thermocycling (n = 10). Substrate surfaces of the specimen after loading were examined microscopically (SEM). The highest bond strengths in both water-stored (7.0 +/- 5.7 MPa) and thermocycled conditions (2.5 +/- 1.8 MPa) were obtained with the Vivadent repair system, while the lowest values were observed with the Cimara system (0.6 +/- 1.4 MPa and 0.0 +/- 0.0 MPa, respectively). Shear bond strengths appeared to be significantly affected by thermocycling (ANOVA, P < 0.05). It is concluded that there are significant differences in the bond strengths of resin composites and ceramic substrate. The roughened surface does not necessarily provide a better bond strength; the bond strength of composite decreases with storage in water and after thermocycling. Bond strength values were generally low for all of the tested materials.     

Effects of barriers on chemical and biological properties of two dual resin cements

The aim of this study was to investigate the degree of conversion, monomer release, and cytotoxicity of two dual‐cure resin cements (Cement‐One and SmartCem2), light‐cured across two indirect restorative materials in an attempt to simulate in vitro the clinical conditions. The results obtained show that the degree of conversion was influenced by both barriers, but the effect of the composite material was greater than that of the ceramic one. The amount of monomers released from the polymerized materials in the absence of barriers was significantly lower than that released in the presence of either the ceramic or the composite barrier. However, a higher amount of monomers was released in the presence of the ceramic barrier. All materials, in all the experimental conditions employed, induced slight cytotoxicity (5–10%) on human pulp cells. Our examinations showed that the two resin cements had similar chemical and biological properties. The decreased degree of conversion of the dual‐curing self‐adhesive composite showed that the light‐curing component of these materials has an important role in the polymerization process. In clinical practice, it is therefore important to pay attention to the thickness of the material used for the reconstruction.     

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复合树脂材料用于牙科已有20余年历史。这类材料既可用于前牙也可用于后牙。复合树脂发展到今天已经出现了许多专门应用于后牙的修复材料,并已取得满意的临床效果。银汞合金的许多缺点都可以为复合树脂所克服。因此,后牙复合树脂修复已为越来越多的患者和牙科医生所接受。然而,直接充填复合树脂材料仍旧被认为有许多局限性。比如边缘缺陷、面磨损、牙尖变形以及术后的牙髓敏感等。因此,近年来发展了复合树脂的一种新技术——间接性复合树脂嵌体与高嵌体修复技术。它的临床应用在某种程度上克服了上述直接充填树脂的局限性。复合树脂嵌体或高嵌体是作为固体黏固在预备洞型中的一种修复体。这种呈固态的修复体由复合树脂材料采用间接的方法制成,最后再黏固于口内。本文将最近的有关间接性复合树脂嵌体和高嵌体方面的资料进行综述,包括它的临床应用,优缺点以及面临的问题等。     

A review of polymerization shrinkage stress: current techniques for posterior direct resin restorations

In general excellent results cannot be guaranteed when using resin-based composites for posterior restorations. This is due to polymerization shrinkage which can still be regarded as the primary negative characteristic of composite resins. A review of available literature regarding the polymerization process, its flaws, and suggested strategies to avoid shrinkage stress was conducted. Several factors responsible for the polymerization process may negatively affect the integrity of the tooth-restoration complex. There is no straightforward way of handling adhesive restorative materials that can guarantee the reliability of a restoration. At present, the practitioner has to coexist with the problem of polymerization shrinkage and destructive shrinkage stress. However, evolving improvements associated with resin-based composite materials, dental adhesives, filling, and light curing techniques have improved the predictability of such restorations. This critical review paper is meant to be a useful contribution to the recognition and understanding of problems related to polymerization shrinkage and to provide clinicians with the opportunity to improve the quality of composite resin restorations.     

A comparison of fatigue resistance of three materials for cusp-replacing adhesive restorations

OBJECTIVES: To investigate the fatigue resistance and failure behaviour of cusp-replacing restorations in premolars using different types of adhesive restorative materials. METHODS: A class 2 cavity was prepared and the buccal cusp was removed in an extracted sound human upper premolar. By using a copy-milling machine this preparation was copied to 60 human upper premolars. In groups of 20 premolars each, direct resin composite restorations, indirect resin composite restorations and ceramic restorations were made. All restorations were cusp replacements made in standardized shape and with adhesive techniques. Cyclic load (5 Hz) was applied starting with a load of 200 N (10,000 cycles) followed by stages of 400, 600, 800 and 1000 N at a maximum of 50,000 cycles each. Samples were loaded until fracture or to 2,10,000 cycles maximum. In case of fracture, the failure mode was recorded. RESULTS: No differences were seen in fracture strength between the three groups (Wilcoxon P = 0.16). No differences were observed with regard to failure mode above or below the cemento enamel junctions (chi2 P = 0.63). The indirect resin composite and ceramic restorations showed significantly more combined cohesive and adhesive fractures than the direct resin composite restorations, which showed more adhesive fractures (chi2 P = 0.03 and 0.002). CONCLUSIONS: The results of this study suggest that ceramic, indirect resin composite and direct resin composite restorations provide comparable fatigue resistance and exhibit comparable failure modes in case of fracture, although the indirect restorations tend to fracture more cohesively than the direct restorations.     

The benefits of glass ionomer self-adhesive materials in restorative dentistry

Bonded, resin-based composite restorative materials have potential advantages. If the dentin bond achieved is not greater than the polymerization stress, loss of retention is likely, resulting in areas of microleakage and postoperative sensitivity. Class 5 lesions restored with no preparation have been used for testing the clinical performance of new adhesive restorative systems. Laboratory studies have demonstrated that bond strength varies according to the depth of dentin and the degree of calcification. Until the later generations of dentin bonding agents, retention rates for bonded, resin-based composites were typically more erratic and lower than glass ionomer (GI) and resin-modified glass ionomer (RMGI) restorative materials. Providing stress relief during setting is inherent in GI and RMGI materials, which helps to explain their good retention rates, despite their low bond strengths. GI and RMGI liners and lightly filled resin bonding agents provide similar stress relief. Current evidence supports the use of both RMGI and composite restorations placed with a liner of lightly filled resin in adhesive Class 5 restorations. Bonded, resin-based composite has the advantage of finishing to a high-gloss surface, making it more acceptable in areas of the mouth that are highly visible.