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Year : 2014  |  Volume : 3  |  Issue : 2  |  Page : 75-79

Human gingival response to methacrylate and silorane-based composite restoratives

1 Department of Restorative Dental Sciences, King Khalid University, College of Dentistry, Abha, Saudi Arabia
2 Department of Preventive Dental Sciences, King Khalid University, College of Dentistry, Abha, Saudi Arabia; Department of Oral Medicine and Periodontology, Faculty of Dentistry, Suez Canal University, Ismailia, Egypt
3 Department of Restorative Dental Sciences, King Khalid University, College of Dentistry, Abha Saudi Arabia; Department of Conservative Dentistry, Mansoura University, Mansoura, Egypt
4 Department of Oral Pathology, Mansoura University, Mansoura, Egypt
5 Department of Diagnostic Sciences, Texas A and M University, Baylor College of Dentistry, Dallas, Texas, USA

Date of Web Publication20-Jun-2014

Correspondence Address:
Khalid M Abdelaziz
Department of Restorative Dental Sciences, College of Dentistry, King Khalid University, PO Box 3263, Abha 61471, Saudi Arabia

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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2278-0521.134853

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Objective: The clinical acceptance of restorative material normally depends on its biological safety. This in vivo study considered the clinical and histological gingival response to methacrylate and silorane-based composites. Materials and Methods: Sixty patients with sub-gingival tooth defects were treated in two groups (n = 30) with Tetric N-Ceram and Filtek P90 composite restoratives with minimal finishing procedures. An additional 10 patients with pre-existing gingival inflammation and no cervical tooth defects served as control. The gingiva in contact was assessed clinically and histologically at 2, 4 and 8 week intervals. Results: A significant time-dependent gingival response was noted in both test groups (t-test, P < 0.05). Inflammatory cell infiltrates, cellular degeneration, epithelial hyperplasia, keratinization, and erosion were found in selected gingival biopsies. Conclusion: The results confirmed that minimally finished subgingival composite restorations contribute to significant histopathological changes to the contacting gingival tissues. However, the silorane-based composite elicited less severe gingival inflammatory symptoms in comparison to the methacrylate-based resin system.

Keywords: Composite, gingiva, histopathology, response, silorane

How to cite this article:
Abdelaziz KM, Eid HA, Saleh AA, Gaballah ET, Murchison DF. Human gingival response to methacrylate and silorane-based composite restoratives. Saudi J Health Sci 2014;3:75-9

How to cite this URL:
Abdelaziz KM, Eid HA, Saleh AA, Gaballah ET, Murchison DF. Human gingival response to methacrylate and silorane-based composite restoratives. Saudi J Health Sci [serial online] 2014 [cited 2021 Sep 20];3:75-9. Available from: https://www.saudijhealthsci.org/text.asp?2014/3/2/75/134853

  Introduction Top

The success of materials for restorative dentistry is usually governed by their physical and mechanical properties, and their biological acceptance is essential. [1] Biologically acceptable materials elicit non-destructive responses in contact with tissues. [2] However, adverse systemic responses are not the body's only reaction against harmful dental materials as some local reactions have also been reported within periodontal, pulpal and hard tooth tissues. [3],[4],[5] The U.S. Medical Device Amendments of 1976 emphasized the need for biological standardization and testing of dental materials and the FDA, accordingly, classified dental materials relative to their levels of safety into materials of low risk (Class I), materials satisfying the ANSI/ADA requirements (Class II), and materials requiring full safety and efficacy assessment prior to marketing (Class III). [2],[6]

In spite of extensive laboratory testing, most of the materials may exhibit different biological behavior in vivo.[3],[4] Resin composites have been touted as safer, esthetically-pleasant and durable alternatives for dental amalgam. However, certain compositional ingredients have been reported to leach out of those materials causing adverse biological reactions. [7],[8],[9] Dental researchers recently introduced a novel minimal-shrinkage composite based on the silorane resin, which is the result of combining both siloxane and oxirane monomers. [10] This newly developed restorative demonstrated lower degrees of water sorption and solubility and showed excellent biocompatibility characteristics in vitro with low mutagenic potential. [11],[12]

Some researchers have reported minimal cytotoxicity of silorane-based composite in comparison to the methacrylate-based resins. [13] Other authors stated that induction of hypersensitivity reactions is possible when human leucocytes are exposed to the silorane-based composite. [14] In addition, the genotoxic behavior of the essential epoxy component within the silorane resin formulation was also demonstrated. [15] This in vivo study was designed to assess both the clinical and histological responses of the gingival tissues to both methacrylate and silorane-based cervical composite restorations.

  Materials and methods Top

0Patient Selection

A total of 70 male patients, 25-40 year old, were recruited for this study. All patients were in good health and not under any kind of drug therapy. Ten of the cases were selected as a control (Group 1) and required gingival surgery for esthetic and/or prosthetic purposes, but no restorations were required. The other 60 cases (Groups 2 and 3, n = 30 each) were selected due to cervical defects extending at least 3 mm beyond the free gingival margin, and gingivectomy with or without crown lengthening was indicated. These kinds of cases were selected in order to provide a significant area of gingival-restoration contact and to help reach a distinguishable histology results.

Patient Preparation

The whole experimental procedures were undertaken with the understanding and written consent of each patient and according to the ethical principles approved by the Committee of Scientific and research Affairs, College of Dentistry, King Khalid University, Abha, Saudi Arabia. All patients were subjected to thorough scaling and root planing. The existing cervical defects in Groups 2 and 3 were carefully polished using oil-free polishing paste (Prophy Paste, Henry Schein, Melville, NY) and the existing soft caries (if any) was thoroughly excavated. All defects were then restored with an Eugenol-free temporary filling (Cavit-G, 3M ESPE, St Paul, MN) for at least 2 weeks in order to control any existing gingival inflammation. During this lag period all patients were counseled to follow essential plaque control measures.

Evaluating the patients' plaque-control performance and gingival health status were carried out every third day using Trace disclosing tablets (Young Dental Manufacturing, Earth City, MO) and calculating the gingival bleeding index (GI). [16] Gingiva on the four surfaces of each tooth (M, D, B, L) was assessed for bleeding tendency by a blinded evaluator using a Williams' graduated periodontal probe (Nordent, Elkgrove Village, IL). A standardized lag period of 30 s was assigned before scoring the gingival bleeding for each location following the criteria listed in [Table 1]. The average score for each tooth was then calculated and the average GI for each individual was also obtained.
Table 1: Gingival bleeding scoring criteria

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Following the control of gingival inflammation, the temporary-restored cervical defects were then prepared to receive either methacrylate (Tetric N -Ceram, Ivoclar-Vivadent, Shaan, Lichtenstien) (group 2, n = 30) or silorane-based (Filtek P90, 3M ESPE, Saint Paul, MN) (group 3, n = 30) final composite restoration. Both materials were applied following their manufacturers' recommended instructions. Teeth in Group 2 were totally etched with 37% phosphoric acid gel (Total Etch, Ivoclar-Vivadent, Shaan, Lichtenstien) and the Heliobond single component adhesive (Ivoclar-Vivadent, Shaan, Lichtenstien) was then used to bond the methacrylate-based composite. In Group 3, the silorane system adhesive (3M ESPE, St. Paul, MN) was used to bond the silorane-based composite to the prepared teeth. An oblique incremental technique was used to apply the composite material into cavities 2 mm or more deep. Final contouring and smoothing of the applied composite were achieved only using clear cervical matrices (Cure-thru, Premier Dental Products, Plymouth Meeting, PA) at the time of composite curing with no subsequent polishing.

Clinical Assessment

The gingival tissues in contact with the composite restorations were clinically assessed at 2, 4 and 8 week intervals. Both the plaque control status and the signs of gingival inflammation were again evaluated using the previously described techniques. The gingival indices in each group were recorded and the resulted numbers were then tabulated for statistical analysis.

Histological Assessment

Three gingival biopsies, 3 mm from the free gingival margin, were obtained under local anesthesia from three patients from each group at 2, 4 and 8 week intervals following the insertion of the composite restorations. All biopsies were fixed in 10% buffered formalin solution for 24 h before embedding in paraffin blocks (Histowax, Histolab, Gotenborg, Sweden). Two specimens of 5-μm thickness were sliced from each paraffin block using a SLEE microtome (model 6062, SLEE, Mainz, Germany) and stained with Haematoxylin and Eosin. All stained specimens were then examined using a bifocal light microscope (Olympus B × 51, Olympus Corp, Tokyo, Japan) at X200 original magnification to assess tissue response.

Statistical analysis

The calculated gingival scores were statistically analyzed using the Student t-test (α=0.05) to identify differences detected between groups at each assessment interval.

  Results Top

The collected clinical gingival scores [Table 2] indicated no statistical difference (t-test, P > 0.05) between all groups at 2 weeks. A significant adverse effect (t-test, P < 0.05) was noticed after 4 and 8 weeks in patients treated with both methacrylate and silorane-based composite restoratives (Groups 2 and 3) when compared with the control group. No significant differences (t-test, P > 0.05) were found between patients in Groups 2 and 3 (treated with methacrylate and silorane-based composite, respectively) at any assigned assessment interval. The microscopic examination of the gingival biopsy samples revealed minor pathological changes (thin keratinization) within the control group patients [Figure 1]. However, longer term contact with the methacrylate-based composite restorations resulted in some evident cellular degeneration and epithelial hyperplasia, para-keratinization and erosion [Figure 2],[Figure 3] and [Figure 4]. Contact with silorane-based composites was characterized by the formation of ortho-keratin [Figure 5],[Figure 6] and [Figure 7].
Figure 1: Control gingival specimen 2 weeks after clinical intervention, showing central gingival mucosa with para-keratinized surface epithelium (blue arrow) and the absence of infl ammatory cell infiltrate in the underlying connective tissue

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Figure 2: Gingival specimen after 2 weeks in contact with methacrylate-based composite, showing hyperplastic epithelium (black arrow) covered with a thin keratin layer (blue arrow) and underlying connective tissue with focal infl ammatory cell infiltrate (red arrow)

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Figure 3: Gingival specimen after 4 weeks in contact with methacrylate-based composite, showing very thin para-keratin, hydropic degeneration of the superficial epithelial cells (blue arrow), hyperplastic epithelium (black arrow) and dense focal inflammatory cell infiltrate (red arrow)

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Figure 4: Gingival specimen after 8 weeks in contact with methacrylate-based composite, showing erosion of surface epithelium (blue arrow), hyperplastic epithelium (black arrow), and dense subepithelial inflammatory cell infiltrate (red arrow)

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Figure 5: Gingival specimen after 2 weeks in contact with siloranebased composite, showing moderate epithelium hyperplasia (blue arrow), foreign material in the sub-epithelial connective tissue (red arrow) and areas of hemorrhage in the same case (black arrow)

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Figure 6: Gingival specimen after 4 weeks in contact with siloranebased composite, showing ortho-keratinized surface epithelium (blue arrow) and subepithelial inflammatory cell infiltrate (red arrow) with dilated capillaries (black arrow)

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Figure 7: Gingival specimen after 8 weeks in contact with siloranebased composite, showing hyperplastic surface epithelium covered with a layer of ortho-keratin (blue arrow), and the absence of inflammatory cell infiltrate in the underlying connective tissue. The insert photomicrograph shows another case from the same group with ortho-keratinized hyperplastic epithelium (black arrow)

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Table 2: Percentage distribution of gingival scores for test groups

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  Discussion Top

Dental manufacturers follow established protocol testing for biocompatibility of their products. Variables affecting in vivo behavior of the functioning materials include mechanical, chemical and biological properties of the host. [3],[4] It has been established that a poor degree of conversion of polymeric materials could in some way irritate the dental pulp and the soft tissues in contact. However, the degree of irritation is often dependent on the nature of their monomer (s) and the amount that remains un-polymerized remains. [5] This study focused on the assessment of in vivo gingival tissue response to subgingivally placed methacrylate and silorane-based composite restorations. All participated cases were intentionally selected with the indication for gingivectomy either with or without crown lengthening. This protocol helped safe the participating individuals from the unnecessary harm and made the collection of samples for histology examination easier.

The clinical assessment of the gingival tissues in this study was conducted following a well-established protocol of Loe [16] at 2, 4 and 8 week intervals following the placement of composite restorations. The findings were compared with the response of gingival tissues in contact with natural tooth structure following non-invasive periodontal therapy. Gingival bleeding revealed the level of clinical inflammatory symptoms in the control group (G1) when tested 2 weeks after periodontal intervention. On the other hand, a time-dependent regression of the same clinical signs was noticed in subjects of both test groups (G2-G3). The experimental findings indicate a gingival response in the presence and absence of mechanical, chemical and microbial irritants. [17],[18] Normally, inflamed gingival tissues improve their GI status within days following non-invasive, routine periodontal therapy. However, in the presence of local irritants such as minimally finished subgingival composite restorations, the inflammatory gingival reaction persists longer. [19]

The FDA standards require biocompatibility testing of experimental prototypes as well as the final dental products before their approval and marketing [6] although the laboratory-approved material(s) may face a different environment depending on the host's behavior and physiology (i.e. differing dietary intake, oral pH, masticatory stresses, mouth breathing, etc.) and may exhibit chemical and mechanical degradation. [3],[4],[20] The leaching of either polymerized or un-polymerized compositional ingredients from the material may stimulate or irritate the gingival tissues in contact to respond in a defensive manner. [20],[21]

The histology images of the gingival specimens revealed an incidence of keratinized hyperplastic epithelium on the crevicular surface of the gingival biopsies of the control subjects [Figure 1]. This is a normal finding when calculus and plaque deposits are present for significant periods of time. [18] The gingival tissues in contact with the composite restorations exhibited the same features along with differing degrees of inflammatory cells infiltrates, cellular degeneration [Figure 3] and, in some instances, epithelial erosion [Figure 4]. However, the density of the detected infiltrates, the degree of epithelial hyperplasia and the type and thickness of keratinization may differ among gingival specimens depending on the type of composite and the time they were in contact [Figure 2],[Figure 3],[Figure 4],[Figure 5],[Figure 6] and [Figure 7]. In spite of its higher degree of polymerization, the methacrylate-based composite elicited a greater gingival response when compared with the silorane-based material. [22] This finding may be attributed to its higher solubility rate in oral fluids [23],[24] that may help some compositional ingredients to leach along with the un-polymerized monomer and irritate the gingival tissue in contact.

Most importantly, the presence of bacterial plaque on the restoration surfaces may stimulate the defensive gingival response and the further histopathological changes. [17],[18] Many studies [25],[26] confirm higher plaque and bacterial adhesion on the surfaces of methacrylate-based composites in comparison to the surfaces of the silorane-based restoratives. This finding together with the previously mentioned solubility could explain both the clinical and the histological findings of this study. However, additional studies to evaluate the temperature-dependent solubility of the chemically different composites as well as their solubility in solutions with different acidities could assist in determining more exact monomer-specific leaching rates, whenever other factors such as surface finishing and inhibition of bacterial plaque adherence are controlled.

  Conclusion Top

In spite of the encountered limitations, the results of this in vivo study confirm that minimally finished subgingival composite restorations contribute to significant histopathological changes to the contacting gingival tissues. However, the silorane-based composite elicited less severe gingival inflammatory symptoms in comparison to the methacrylate-based resin system.

  References Top

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2.Bayne SC, Thompson GY. Biomaterials. In: Roberson TM, Heyman HO, Swift EJ, editors. Sturdevant′s art and science of operative dentistry. 5 th ed. St. Louis: Mosby; 2006. p. 135-242.  Back to cited text no. 2
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17.Tung OH, Lee SY, Lai YL, Chen HF. Characteristics of subgingival calculus detection by multiphoton fluorescence microscopy. J Biomed Opt 2011;16:066017.  Back to cited text no. 17
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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]

  [Table 1], [Table 2]

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