Effect of Deep Margin Elevation on Interfacial Gap Development of CAD/CAM Inlays after Thermomechanical Cycling

Abstract

SUMMARY The aim of this study was to evaluate interfacial gap formation of CAD/CAM lithium disilicate inlay margins before and after thermomechanical loading. Methods and Materials: Mesio-occlusal-distal cavities were prepared on 12 extracted mandibular molars. The gingival margin of one proximal box was elevated with resin modified glass ionomer (RMGI) by a height of 2 mm (Group E [elevation]), and the margin of the other side served as a control (Group NE [no elevation]). Lithium disilicate computer-aided design and computer-aided manufacturing (CAD/CAM) inlays were fabricated and bonded with a self-adhesive resin cement. An aging process was simulated on the specimens under thermomechanical cycling by using a chewing simulator. Marginal integration was evaluated under scanning electron miscroscopy (SEM) using epoxy resin replicas before and after cycling. Marginal areas were stained with silver nitrate solution, and the volumetric gap was measured at the bonded interfaces using microcomputed tomography (CT) before and after cycling. Statistical analyses were performed using paired t-tests, the Wilcoxon signed rank test, and the Mann–Whitney test (a<0.05). Results: SEM showed marginal discontinuities in Group NE that increased after thermomechanical cycling. Micro-computed tomography exhibited three-dimensional dye-penetrating patterns at the interfaces before and after cycling. Interfacial disintegration was larger in Group NE before cycling (p<0.05). Thermomechanical cycling increased the gaps in both Groups NE and E (p<0.05). The gap increment from thermomechanical cycling was larger in Group NE (p<0.05). Conclusions: Thermomechanical cycling induced interfacial disintegration at the lithium disilicate CAD/CAM inlays, with deep proximal margins. Margin elevation with RMGI placement reduced the extent of the interfacial gap formation before and after the aging simulation.

Deep margin elevation—Present status and future directions

“…In most of the included studies, indirect restorations were made after DME without delay 7,25,27,29,31–33,39,40,43,45–47 . In six studies, the teeth with DME were stored in water before the indirect restoration was bonded, with reported water storage periods ranging from 24 h to a fortnight 30,35–37,41,42 …”

“…In most of the included studies, the restored teeth were subjected to thermomechanical load cycling or mechanical load cycling 26,27,30–34,39–47 . In four studies, the specimens were not exposed to any loading or artificial aging 29,35–37 …”

“…Operators in one clinical study performed DME without a matrix 24 . Two reports of clinical investigations and 12 reports of in vitro studies furnished no information on matrix use 7,19,21,25,27,29–31,33,39,40,43,46,47 . Circumferential metal matrices were used in nine laboratory studies 26,32,32,35–38,44,45 .…”

“…In most of the included studies, indirect restorations were made after DME without delay. 7,25,27,29,[31][32][33]39,40,43,[45][46][47] In six studies, the teeth with DME were stored in water before the indirect restoration was bonded, with reported water storage periods ranging from 24 h to a fortnight. 30,[35][36][37]41,42 In most of the included studies, the restored teeth were subjected to thermomechanical load cycling or mechanical load cycling.…”

“…30,[35][36][37]41,42 In most of the included studies, the restored teeth were subjected to thermomechanical load cycling or mechanical load cycling. 26,27,[30][31][32][33][34][39][40][41][42][43][44][45][46][47] In four studies, the specimens were not exposed to any loading or artificial aging. Though some in vitro studies found the marginal quality of DME restorations to be inferior to that of indirect restorations bonded directly to dentin, 30,33,36,37 studies reporting no such negative effect of DME currently prevail in number.…”