Cytotoxicity of resin-based restorative materials on human pulp cell cultures

OBJECTIVE: The objective of this study was to determine the cytocompatibility of 5 different extracts of resin-based restorative materials (2 resin-modified glass ionomer cements, 1 compomer, and 2 composite resins) on human pulp cells. STUDY DESIGN: Set specimens from 2 resin-modified glass-ionomer cements (Fuji II LC and Fuji IX), 1 compomer (Dyract), and 2 composite resins (Tetric and Superfil) were eluted with culture medium for 2 and 5 days. The effects of resin-based restorative materials on human pulp cells were evaluated with cytotoxicity and mitochondrial activity assays. RESULTS: The results showed that the eluates from resin-modified glass-ionomer, compomer, and composite resins were cytotoxic to primary human pulp cells. In addition, Superfil, Fuji IX, and Tetric demonstrated an inhibitory effect on mitochondrial activity of human pulp cells. It was found that composite resin Superfil was the most toxic restorative material among the chemicals tested. CONCLUSION: The influence of the cytotoxicity depended on the materials tested. Compomer or light-curing resin-modified glass ionomer may initially react more favorably to pulp cells.     

Cytotoxicity of components of resins and other dental restorative materials

Cytotoxicity testing of dental restorative materials must be viewed as an assessment of hazards, that is the potential of the material to cause pulpal problems. In this context, composites, glass ionomers, amalgams, zinc-based cements and peroxide bleaching agents are all possible hazards to the pulp. The risks that these materials will cause pulpal toxicity in vivo can be partly estimated by assessing the cytotoxicity of the substances which are released from these materials in vitro and comparing these cytotoxic concentrations with those concentrations that are present in vivo . The resin components of composites, metal ions and hydrogen peroxide, all of which are released from dental restorative materials, have been shown to be cytotoxic in vitro in sufficient concentrations. The potencies of these substances are quite diverse. However, the Cytotoxicity of these substances in usage tests, and therefore the risks of pulpal toxicity, depends on their ability to diffuse through the dentine and accumulate in the pulp.     

Resin-based composites and compomers in primary molars

Resin-based composite resins and polyacid-modified resin-based composites (compomers) have become popular for the restoration of primary anterior and posterior teeth. In some European countries, resin-based composites or glass-ionomers are the materials of choice for primary teeth because of the controversy over dental amalgam and its alleged adverse health effects resulting from the release of mercury, although a clear correlation between amalgam restorations and health has not been determined. Another reason for the worldwide increased use of resin-based composites and glass-ionomers in pediatric dentistry could be attributed to the growing demand from parents to provide esthetic restorations to their children. More conservative preparations can be performed maintaining more tooth structure because of the adhesive properties of the composites and compomers. The most conservative treatment planning and meticulous care in the placement of the resin-based composites and compomers would produce long-term satisfactory results. These restorations should be placed in patients with low-to-moderate caries risk, and after placement the restorations should be monitored carefully to avoid complications mainly produced by recurrent caries and wear.     

Restorative pulpal and repair responses

BACKGROUND: Each year, about 90 million new restorations are placed in the United States and 200 million are replaced. Controversy surrounds the pulpal reactions and frequency of bacterial microleakage associated with common restorative materials. The authors investigated and compared pulpal reactions to different types of restorative materials. METHODS: Two hundred seventy-two teeth with standardized rectangular Class V unexposed cavities were restored with resin-based composite bonded to dentin; resin-based composite bonded to enamel; resin-modified glass ionomers, or RMGI; amalgam lined with zinc polycarboxylate, or ZnPC; amalgam lined with calcium hydroxide, or Ca(OH)2; or zinc oxide-eugenol, or ZnOE. Teeth were extracted for orthodontic reasons between 20 and 381 days later. The authors categorized pulpal responses according to standards set by the Federation Dentaire Internationale and the International Organization for Standardization. Bacteria were detected using Brown-Brenn-stained sections. Pulpal responses were evaluated using histomorphometric analysis and analysis of variance statistics. RESULTS: The results showed that RMGI was the best material for preventing bacterial microleakage, and resin-based composite bonded to enamel was the worst. In regard to minimizing pulpal inflammatory activity, ZnOE was the best material and resin-based composite bonded to enamel was the worst. In terms of maximizing odontoblast survival beneath deep cavity preparations, Ca(OH)2, was the best material and RMGI was the worst. CONCLUSIONS: The results show that bacterial microleakage, pulpal injury and repair responses varied widely with different restorative materials. CLINICAL IMPLICATIONS: The authors recommend that RMGI be used to restore teeth with cavities that are shallow to moderate in depth, with the floor of deep cavities being lined with Ca(OH)2 before the teeth are restored with RMGI.     

N-acetyl cysteine protects pulp cells from resin toxins in vivo

Potential risks of the use of resin-based restorative materials include direct damage to the pulp cells and the induction of hypersensitivity reactions in patients. In this study, we tested the hypothesis that N-acetyl cysteine (NAC) inhibits resin toxicity and restores the function of pulp cells. Analysis of our data demonstrates toxicity of composite resins on pulp cells in both an in vivo rat and an ex vivo human model system. Moreover, cells that survive after the placement of composites are weaker, and they are induced to undergo cell death when exposed to 2-hydroxyethyl methacrylate (HEMA). The toxic effect of composites on pulp cells is neutralized by NAC. Therefore, NAC protects the cells from damage induced by clinically relevant levels of restorative materials, in both rat and human model systems. The addition of N-acetyl cysteine prior to or concomitant with the application of restorative materials may be beneficial for the health and safety of dental patients.     

Long-term cytotoxicity of resin-based dental restorative materials

Highly filled composites, Ormocers (organically modified ceramics) and 'smart' materials have been developed to overcome the polymerization shrinkage problems of conventional composite materials. The purpose of the current study was to investigate the effect of longer-term (up to 8 weeks) ageing of these resin-based dental restorative materials and determine the effect of post-curing on cytotoxicity. Twelve discs of each material (Colombus/IDR, Definite/Degussa, Ariston pHc/Vivadent) were either light-cured (Lc) or light-cured and post-cured (Pc). For cytotoxicity testing, the discs were placed in contact with cell culture medium (DMEM) and incubated at 37 degrees C. Extracts from composite materials were collected after 24 h and weekly over a time period of 8 weeks. Cytotoxicity of the eluates to cultured fibroblasts (Balb/c3T3) were measured by the succinic dehydrogenase (SDH) activity (MTT assay) and the results expressed in percentage of negative controls (Teflon discs). The results showed that ageing significantly influenced the cytotoxicity of the materials. Except for Ariston pHc, materials were less cytotoxic after 8 weeks of ageing than they were in early intervals and post-curing was not generally useful in reducing cytotoxicity. The Ariston pHc was initially moderately toxic, but then become highly cytotoxic for 5 weeks before returning to initial levels. The current study demonstrated the importance of assessing the cytotoxicity of resin composite materials at multiple times.     

CYTOTOXICITY AND BIOCOMPATIBILITY OF DIRECT AND INDIRECT PULP CAPPING MATERIALS

There are several studies about the cytotoxic effects of dental materials in contact with the pulp tissue, such as calcium hydroxide (CH), adhesive systems, resin composite and glass ionomer cements. The aim of this review article was to summarize and discuss the cytotoxicity and biocompatibility of materials used for protection of the dentin-pulp complex, some components of resin composites and adhesive systems when placed in direct or indirect contact with the pulp tissue. A large number of dental materials present cytotoxic effects when applied close or directly to the pulp, and the only material that seems to stimulate early pulp repair and dentin hard tissue barrier formation is CH.     

Dental regeneration and materials—a partnership

Considerable focus on the biocompatibility of dental materials over the last three decades has provided a platform for a wealth of studies on the cellular and molecular responses of the cells of the pulp to injury, both from the disease process and from subsequent restorative intervention. These studies have been fundamental to understanding not only how we can achieve a biocompatible response during restoration of dental disease but also how we can exploit the pulpal cellular responses to achieve wound healing and tissue regeneration in the dentine–pulp complex. This article examines the responses of the pulp to injury and the events leading to tissue regeneration. As new biologically based regenerative therapies emerge for the dental tissues, it is important that these develop in partnership with more traditional approaches using dental materials.     

Using packable composites for direct posterior placement

BACKGROUND: Although dentists have been using resin-based composites successfully to restore posterior teeth in Class II situations for several years, creating a functional, anatomical proximal contact remains a clinical challenge for many clinicians. OVERVIEW: This article presents a step by-step technique for creating a predictable proximal contact using a packable resin-based composite as the restorative material. Using a technique that is similar to that for amalgam will enable the dentist to make a successful transition to using composite as an alternative to amalgam in some posterior teeth. PRACTICE IMPLICATIONS: More patients today are well-informed about dental care and are seeking tooth-colored restorative alternatives. Excellent materials and proven techniques are making the transition from traditional metallic restorations easier and more predictable. With this article, the authors aim to help dentists gain confidence in their technique and enable them to provide this service for their patients.     

Cytotoxic effects of restorative materials on early passage cultured cells derived from human gingiva (in vitro)

This study evaluated the cytotoxic effects of three common restorative materials on early passage cultured cells derived from human gingiva (HG cells). Other early passage cultured cells derived from human dental pulp tissues (HP cells) and L cells established obtained from mouse subcutaneous tissues, were also examined. Cytotoxicity was assessed according to the uptake of neutral red and dye exclusion with nigrosin. The cytotoxicity was in the order of glass ionomer cement (highest), light cured composite resin and dental amalgam. HG cells were the least sensitive to the materials tested. Both filtration of extracts and addition of serum into the extract affected the cytotoxicity. Glass ionomer cement increased the acidity of the extract, but the two other materials did not. Dissolution of metal ions, aluminium, tin, copper, mercury and zinc occurred from the materials. The extract of the composite resin had a different absorbance. This study disclosed differences in the cellular reaction to the restorative materials. Thus, utilization of early passage cultured cells is necessary for biological evaluation of the dental materials in vitro.     

Composite-induced toxicity in human gingival and pulp fibroblast cells

Objective. The most important requirement for a material to be used in medical applications is its biocompatibility. Dental composite materials come into direct contact with oral tissues, especially gingival and pulpal cells. This study was performed to evaluate possible DNA damage in cells of human origin exposed to dental composites in vitro using a cytogenetic assay. Materials and methods. Two composite resins (Vertise Flow, Kalore) were tested on human gingival and pulp fibroblasts using the acridine orange/ethidium bromide viability staining and alkaline comet assay. Cultures were treated with polymerized composites in two different concentrations (20 mg/ml, 40 mg/ml) for 14 days. Chi-square and Kruskall-Wallis non-parametric test were used for the statistical analysis (p < 0.05). Results. Significant cytotoxicity was observed for 40 mg/ml of Vertise Flow in both cultures, while Kalore (40 mg/ml) showed cytotoxic effect only on human pulp fibroblasts. A significant level of DNA damage was detected for both materials and concentrations, in both cell cultures. Conclusion. If the two cell cultures are compared, the pulp cells were more sensitive to the cyto/genotoxic effects of dental composites. Based on the results, one can conclude that the use of tested materials may cause cellular damage in gingival and pulp fibroblasts in vitro.     

Preservation-based approaches to restore posterior teeth with amalgam,resin or a combination of materials

This review is a systematic assessment, from the literature, of the status quo of dental amalgam, resin-based composite and glass-ionomer restorations for carious lesions as it applies to new concepts, coupled with clinical research. Scientifically based and practical new materials and techniques are recommended to include in contemporary practice throughout the world. Clinical and laboratory studies which have been carried out in light of modern conservative principles, and in light of the current emphasis of treating dental caries as a disease process were reviewed and discussed. An approach to managing carious lesions based upon selected advantages of dental amalgam, resin-based composite and glass-ionomer technology applied to what is termed "preservation-based" approaches to restoring teeth has been synthesized. Researched evidence contradicts the notion of "extension for prevention" in favor of maintaining sound tooth structure which would translate into more patients with healthy dentitions for entire lifetimes.     

Effects of growth factors on dental pulp cell sensitivity to amalgam toxicity.

OBJECTIVES: The objective was to determine the effects of growth factor treatment on dental pulp cell sensitivity to toxicity. METHODS: The toxicity of zinc-containing and zinc-free dental amalgam was tested on four types of cells; glia, neurons, embryonic stem cells, and dental pulp cells. The effects of six different growth factors were tested on dental pulp cell sensitivity to amalgam toxicity. RESULTS: Zinc-containing amalgam was highly toxic to all cell types tested. Zinc-free amalgam was less toxic, but it was most toxic to dental pulp cells. Exposure of dental pulp cells to the growth factors IGF-I or BMP-7 had no effect on their morphology or rate of cell division, and did not alter their sensitivity to zinc-free amalgam toxicity. Exposure to EGF, bFGF, or TGF-beta altered the morphology and decreased the rate of cell division, and the cells were no longer sensitive to zinc-free amalgam toxicity. Exposure to BMP-2 also altered the morphology and decreased the rate of cell division, but the cells remained sensitive to zinc-free amalgam toxicity. SIGNIFICANCE: The results indicate that untreated dental pulp cells are highly sensitive to amalgam toxicity, but that sensitivity can be decreased by exposure to certain growth factors. Therefore, for treatment of conditions in which pulp cells may come in contact with substances released from dental materials, such as pulp capping, the use of amalgam should be avoided unless the pulp cells are first treated with the proper growth factors.     

Pulp capping with adhesive resin-based composite vs. calcium hydroxide: a review

Abstract – The results of some short-term experiments suggest that direct capping of a vital pulp with the modern resin-based composite systems may be as effective as capping with calcium hydroxide. Total cavity etching with 10% phosphoric acid seems to be safe for the exposed pulp, but unless annulled by calcium hydroxide 35% phosphoric acid may be disastrous. For hemostasis and cleaning of the pulp wound both sodium hypochlorite and saline seem suitable, whereas the effectiveness of a 2% chlorhexidine solution is questionable. Although hard-setting calcium hydroxide cements may induce the formation of dentin bridges, they appear not to provide an effective long-term seal against bacterial factors. Within a few years, the majority of mechanically exposed and capped pulps show infection and necrosis due to microleakage of such capping materials and tunnel defects in the dentin bridges. It is unknown whether newer types of resin containing calcium-hydroxide-products will act as a permanent barrier. The cytotoxicity of the resin-based composites and the temperature rise during polymerisation may not be of concern, but microleakage, sensitisation and allergic reactions may pose problems. Based on available data, pulp capping with resin-based composites may be said to be promising, but more and long-term research is mandatory before the method can be recommended.     

Pulp capping with adhesive resin-based composite vs. calcium hydroxide: a review

The results of some short-term experiments suggest that direct capping of a vital pulp with the modern resin-based composite systems may be as effective as capping with calcium hydroxide. Total cavity etching with 10% phosphoric acid seems to be safe for the exposed pulp, but unless annulled by calcium hydroxide 35% phosphoric acid may be disastrous. For hemostasis and cleaning of the pulp wound both sodium hypochlorite and saline seem suitable, whereas the effectiveness of a 2% chlorhexidine solution is questionable. Although hard-setting calcium hydroxide cements may induce the formation of dentin bridges, they appear not to provide an effective long-term seal against bacterial factors. Within a few years, the majority of mechanically exposed and capped pulps show infection and necrosis due to microleakage of such capping materials and tunnel defects in the dentin bridges. It is unknown whether newer types of resin containing calcium-hydroxide-products will act as a permanent barrier. The cytotoxicity of the resin-based composites and the temperature rise during polymerisation may not be of concern, but microleakage, sensitisation and allergic reactions may pose problems. Based on available data, pulp capping with resin-based composites may be said to be promising, but more and long-term research is mandatory before the method can be recommended.     

Prevalence of cusp fractures in teeth restored with amalgam and with resin-based composite

BACKGROUND: Complete cusp fracture in restored teeth is a common problem observed in general dental practice. Many dentists believe that teeth restored with amalgam are more likely to be associated with cusp fractures than are those restored with resin-based composite. METHODS. The authors noted the condition of 10,869 posterior teeth with amalgam or resin-based composite restorations with at least one cusp present, unrestored or missing in 1,902 consecutively seen adult patients in a private general dental practice. For each patient, the authors recorded age, type of restorations, number of surfaces of each restoration, and presence or absence of a complete cusp fracture and of caries. RESULTS: There was a lower percentage of cusp fractures in younger subjects than in older subjects and in teeth with a single restored surface than in those with more than one restored surface. There was no significant difference in the prevalence of cusp fracture rates in amalgam-restored teeth versus composite-restored teeth in subjects aged 18 through 54 years. In subjects aged 55 through 96 years, there was a marginally significantly greater cusp fracture rate in composite-restored teeth than in those restored with amalgam. Overall, there was no significant difference in the prevalence of cusp fracture in teeth restored with amalgam (1.88 percent) versus composite-restored teeth (2.29 percent). CONCLUSIONS: The prevalence of cusp fractures in amalgam-restored teeth and resin-based composite-restored teeth is not significantly different. Teeth with more than one surface restored with either resin-based composite or amalgam and teeth in older subjects were more likely to suffer a cusp fracture. CLINICAL IMPLICATIONS: Teeth restored with amalgam and with resin-based composite exhibited equally low cusp fracture prevalence. When choosing between amalgam and resin-based composite in consideration of the likelihood of a future cusp fracture, either restorative material is acceptable.     

Endodontic complications after plastic restorations in general practice

AIM: To test the hypothesis that dentine and pulp protection by conditioning-and-sealing is no less effective than using a conventional calcium hydroxide lining. METHODOLOGY: A cohort of healthy adults requiring a new or replacement restoration in a posterior tooth was recruited in six general practices. All procedures received local Ethics Committee approval. Exclusion criteria included signs and symptoms of pulp necrosis or inflammation, and patients unable to commit to a long-term trial. Cavity preparations were randomized to receive a calcium hydroxide lining or conditioning-and-sealing with a smear-removing bonding system. Choice of bulk restorative material (composite resin or amalgam) was at the discretion of the dentist. The key outcome measure was evidence of pulpal breakdown identified at unscheduled (emergency) or scheduled recall examinations. Postoperative sensitivity was recorded on 100 mm VAS at 24 h, 4 days and 7 days. Pulp status was assessed at 6, 12, 24 and 36 month recall, and at any emergency recall appointment. The relationship between pre-treatment and treatment variables and pulp breakdown was assessed by logistic regression (P = 0.05). RESULTS: A total of 602 teeth were recruited, with comparable numbers of cavities lined (288, 47.8%) or conditioned and sealed (314, 52.2%). The majority (492, 81.7%) were replacement restorations, and amalgam was the most common bulk restorative material (377, 62.6%). A total of 390 (64.8%) restored teeth were reviewed at 6 months, 307 (51%) at 12 months, 363 (60.3%) at 24 months, and 279 (46.3%) at 36 months post-restoration. Sixteen cases of pulp breakdown were identified within 36 months of restoration placement, 11 presenting as emergencies and five detected at routine recall examination. Logistic regression showed that preoperative pain, cavity treatment by lining or conditioning-and-sealing and the use of rubber dam isolation had no association with pulp breakdown. Pulp breakdown was associated with deep or pulpally exposed cavities (P < 0.001, odds ratio 7.8) and with composite rather than amalgam restorations (P = 0.001, odds ratio 2.13). Re-coding to identify teeth with pulp exposures revealed that pulpal exposure was the key determinant of adverse pulp outcomes (P < 0.0001, odds ratio 28.4) and that composite resin restorations were again more likely to be associated with pulp breakdown than amalgam (P = 0.017, odds ratio 3.92). CONCLUSIONS: Considered within the context of routine primary dental care: Dentists can be confident that pulps will be equally well protected from post-restorative breakdown up to 36 months by calcium hydroxide lining and conditioning-and-sealing with adhesive resins. Residual dentine thickness appears to be a key determinant of pulp responses after restorative dental treatment. In deep and pulpally exposed cavities in posterior teeth, composites were associated with more pulpal breakdown than amalgams.     

Histomorphometric analysis of dentinal bridge formation and pulpal inflammation.

OBJECTIVE: The purpose of this study was to evaluate pulpal responses to the use of four resin composite materials as direct pulp capping agents. The importance and effects of individual pulp capping variables are not well understood; consequently histomorphometric analysis was used to analyze these variables. METHOD AND MATERIALS: Two hundred fifty standardized pulp-exposed cavities were prepared in nonhuman primate teeth. Exposed pulps were capped with calcium hydroxide and multistep and self-etching primer resin composites. Teeth were collected from 3 to 60 days to observe pulpal reactions. Following perfusion fixation, tissues were demineralized, sectioned, stained, and histomorphometrically measured. Bridge area, diameter of pulpal exposure, and cavity floor width were measured. Tunnel defects, operative debris, and pulpal inflammation were graded according to defined criteria. RESULTS: The variables correlated to dentinal bridge area were, in decreasing order of significance, time elapsed since exposure, diameter of pulpal exposure, pulp capping material, and tunnel defects. The variables correlated to pulpal inflammation were the type and curing of pulp capping material. Other variables were not statistically significant. CONCLUSION: Pulp capping with resin composite materials provided acceptable pulpal inflammatory and dentinal bridge repair responses, comparable with those of calcium hydroxide. Although resin composites are promising as direct pulp capping agents, further investigations are required to optimize their application protocols to reduce the penetration of potentially cytotoxic monomers into pulpal tissue.     

Cytotoxic effect of silorane and methacrylate based composites on the human dental pulp stem cells and fibroblasts

Objectives: The aim of this study was to compare the cytotoxic effect of a methacrylate-based and a silorane-based composite on the human dental pulp stem cells (DPSCs) versus human dental pulp fibroblasts (DPFs). Study Design: Samples of the Filtek Z250 and P90 were polymerized and immersed in the culture medium to obtain extracts after incubation for one, seven and 14 days. Magnetic cell sorting based on the CD146 expression was performed to purify DPSCs and DPFs. After incubation of both cells with the extracts, cytotoxicity was determined using the MTT test. Results: For the extracts of first and seventh day, both composites showed significantly lower cytotoxicity on DPSCs than DPFs (p=0.003). In addition, there was a significant difference in the time-group interaction of both materials indicating different cytotoxic behaviours (p=0.014). In contrast to Z250, exposure to the 14th day extract of P90 resulted in higher cell viability compared to that of day seven. Conclusions: DPSCs are less susceptible to the cytotoxic effect of the composites than DPFs. Compared to Z250, the cytotoxic effect of silorane-based composite decreases as the time passes on. This difference should be considered, particularly in deep cavities, in order to preserve the regenerative capacity of the pulp. Key words:Composite resins, Dental pulp, Mesenchymal Stromal Cells, Silorane, Toxicology.     

Biologic properties of eugenol and zinc oxide-eugenol. A clinically oriented review.

Eugenol-containing dental materials are frequently used in clinical dentistry. When zinc oxide-eugenol (ZOE) is applied to a dentinal cavity, small quantities of eugenol diffuse through the dentin to the pulp. Low concentrations of eugenol exert anti-inflammatory and local anesthetic effects on the dental pulp. Thus use of ZOE temporary filling may facilitate pulpal healing; on the other hand, high eugenol concentrations are cytotoxic. Direct application of eugenol to pulp tissue may result in extensive tissue damage. The ability of ZOE-based endodontic sealers to influence periapical tissue healing is considered in view of eugenol's anti-inflammatory and toxic properties.