Abstract
The successful restoration of teeth requires a good connection between the inlay and natural tissue. A strong bond may improve retention and reinforce tooth structure. The purpose of this study was to evaluate the influence of cement layer thickness on contraction stress generated during photopolymerization, and to determine the changes in stress state of the cement occurring during aging in water (over 84 days). Two cements were used: resin composite cement (NX3) and self-adhesive resin cement (Maxcem Elite Chroma). A cylindrical sample made of CuZn alloy was used to imitate the inlay. The stress state was measured by photoelastic analysis. The contraction stress of the inlay restoration was calculated for cement layer thicknesses of 25 µm, 100 µm, 200 µm, and 400 µm. For both tested materials, the lowest contraction stress was observed for the thinnest layer (25 µm), and this increased with thickness. Following water immersion, a significant reduction in contraction stress was observed due to hygroscopic expansion. Applying a thin layer (approximately 25 µm) of composite and self-adhesive resin cements resulted in high levels of expansion stresses (over −6 MPa) after water aging.
Highlights
Received: 4 December 2020Damaged teeth which are not able to support basic restorations are typically repaired using indirect restorations including inlays and onlays [1]
The lowest stresses were observed for the thinnest cement layer
Our research indicates that a very thin cement layer of resin composite or self-adhesive resin cements may create a significant degree of expansion stress state
Summary
Damaged teeth which are not able to support basic restorations are typically repaired using indirect restorations including inlays and onlays [1]. Inlays or onlays cover only the part of the tooth; metal-ceramic inlays are better at preserving natural tissue and tooth vitality, and reducing postoperative sensitivity than crowns, and they are less invasive. Metal-reinforced systems are very often chosen to manufacture posterior fixed partial dentures [4]. Such metal-ceramic inlay-retained fixed partial dentures (IRFPDs) offer a number of advantages such as greater tooth structure preservation, and a lower risk of gingival irritation and pulp vitality. The method of tooth preparation for inlays or IRFPDs is similar to that used for indirect preparation of class II cavities [5,6,7,8]
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