الفهرس 
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Abstract
Objectives: The clinical trial aimed to evaluate and compare the periodontal responses and clinical performance of Class II resin composite restorations with deep subgingival proximal margins that were elevated using four different restorative materials, namely resin-modified glass ionomer (RMGI), a glass hybrid (GH), flowable bulk-fill resin composite (Bulk Flow), or a bioactive restorative material (Activa) as lining materials. The laboratory investigations aimed to evaluate and compare: 1) the marginal and internal adaptation of four lining materials used for deep margin elevation, and to evaluate the interface of each lining material with the overlying resin composite, 2) the consistency of the marginal quality of GH material used to elevate dentin gingival margins obtained by three methods, 3) the elemental analysis and microhardness of Activa and the marginal tooth structure after storage in different media, and 4) the periodontal bacterial biofilm adhesion to four different restorative materials during two, 24, and 48-hour incubation periods. Materials and methods: Considering the clinical trial, eighty-five adult patients were enrolled with a total of 120 compound Class II cavities with gingival margins below CEJ. The dentin/cementum gingival margins of the cavities were elevated by lining using four different restorative materials, then completed with the same overlaying resin composite. Different periodontal and clinical evaluations were performed at varying time intervals after restoration, including baseline (2 weeks), six months, one year, and two years. For the laboratory investigations: 1) fifty-six molars received class II cavities with dentin/cementum gingival margins. They were divided into four groups and their gingival margins were elevated using either of the same lining materials used in the clinical trial. The rest of the cavities were completed with the same overlying composite. Half of the teeth in each group were either; kept in sterile water for one week, or subjected to 18 months of water storage and 15,000 thermal cycles. Lining materials/gingival dentin interfaces, both externally and internally, were examined under a scanning electron microscope (SEM) at different magnifications, the percentage of continuous margin (% CM) and maximum gap width (MGW) were analyzed. 2) Ten teeth received compound class II cavities with dentin/cementum gingival margins. The dentin gingival margins were elevated with GH, followed by resin composite. Glass hybrid/gingival dentin interfaces were examined under the digital microscope, SEM using resin replicas, and ranked according to the FDI criteria, immediately and after 10,000 thermal cycles, in addition to energy dispersive spectroscopy (EDS) analysis for the interfacial zone of two specimens. Marginal quality was expressed as % CM at 200× for microscopic techniques and as the frequency of each score for FDI ranking. 3) Fifteen teeth received cervical restorations using Activa, five of them on the four axial surfaces and the other ten on the two proximal surfaces only. The first five teeth were sectioned into four restorations each, then randomly divided and stored in four different media; deionized water, dulbecco’s phosphate buffered saline (DPBS), Tris buffer, and saliva. The storage period for deionized water was 24 hours while it was three months for the other media. Each section was analyzed by SEM-EDS for different substrates/distances and the relative weight percentages (wt. %) of calcium, phosphorus, silica, and fluoride were calculated. The other ten teeth were sectioned across the restoration, stored in either Tris buffer or saliva for 24 hours or three months, and were evaluated for microhardness of different substrates/areas. 4) Discs were produced from the same four lining materials used in the clinical trial. Proximal root dentin was used as a control group. Specimens were coated with saliva and used to culture a biofilm comprised of three strains of periodontopathic bacteria for two, 24, and 48 hours. Bacterial adherence was quantified by crystal violet staining [optical density (OD) 562 nm] and visualized using a confocal laser scanning microscope (CLSM). Statistical analysis was performed based on each study’s data and variables. Results: For the clinical trial: the values of all periodontal parameters increased with time. However, the type of lining material did not affect the periodontal evaluations. There were no statistically significant differences between different time intervals or material groups in any of the evaluated FDI parameters. Activa scored significantly worse in the radiographic evaluation than any of the other material groups. For the laboratory investigations: 1) both Bulk Flow and Activa exhibited better marginal integrity than RMGI and GH. All lining materials were adversely affected by aging. All lining materials/overlying composite interfaces were continuous and age-defying. 2) There were moderate and strong significant correlations between the testing techniques. Elemental analysis results revealed the presence of an ion exchange layer along the GH/gingival dentin interface of the aged specimens. 3) Enamel and dentin interfaces in the DPBS group exhibited a significant increase in calcium and phosphorus contents. Levels of silica and fluoride both increased significantly in tooth structure up to a distance of 75 μm in the groups that were stored for three months, relative to teeth in the immediate groups. Storage media did not affect the microhardness values. 4) Bulk Flow had significantly the least OD values among the other tested groups. The two-hour incubation period had significantly the lowest OD values among other periods regardless of the tested group. The 48 hours data was higher than the 24 hours data in all groups except the control and Bulk Flow. Microscopic imaging supported the findings of the OD measurements. Conclusion: Considering the clinical trial, from periodontal and clinical perspectives, both glass ionomer and resin-based materials could be successfully used for proximal margin elevation. Considering the laboratory investigations, 1) in terms of marginal integrity, Bulk Flow and Activa might be preferable for proximal dentin margin elevation under direct restorations compared to the other tested lining materials. 2) The replica SEM and FDI ranking results had a stronger correlation with each other than that between either SEM or FDI with the digital microscope results. 3) SEM-EDS analysis suggests that an ion exchange must have occurred between Activa and the tooth structure while stored in DPBS via a universal adhesive. 4) It could be concluded that in terms of periodontopathic bacterial adhesion, the tested formulation of Bulk Flow may be preferable for subgingival use compared to the other tested materials.