Marginal and internal fit and fracture resistance of lithium disilicate laminate veneers for teeth with proximal cavities: an in-vitro comparative study

BACKGROUND: The management of proximal cavities under porcelain laminate veneers remains a clinical challenge. Conventional strategies-such as placing an intermediate composite restoration or extending the preparation-require additional steps or sacrifice healthy tooth structure. While the literature reports conflicting findings on whether composite substrates affect veneer longevity, a comprehensive biomechanical evaluation of a monolithic veneer design that directly incorporates the proximal cavity has not been reported. This in-vitro study compared the marginal fit, internal adaptation, and fracture resistance of lithium disilicate laminate veneers fabricated for three substrate conditions: an intact tooth, a tooth with a proximal composite restoration, and a monolithic veneer with an integrated proximal cavity. METHODS: Thirty-six maxillary central incisor typodont teeth were divided into three groups (n = 12): control (intact tooth), composite restoration, and integrated cavity. Standardized proximal cavities were prepared in the latter two groups; the composite restoration group received a composite restoration prior to veneer fabrication, while the integrated cavity group had the cavity incorporated directly into the veneer design. Lithium disilicate laminate veneers were fabricated using a CAD/CAM system. Marginal and internal fit were evaluated at 19 points per specimen using a silicone replica technique examined under stereomicroscopy. Fracture resistance was assessed in a universal testing machine with a load applied at a 135° angle. Data were analyzed using one-way ANOVA or Kruskal-Wallis tests (α = 0.05). RESULTS: The integrated cavity group exhibited a statistically significantly larger marginal gap at the proximal margin compared to the control and composite restoration groups (p<0.001). A corresponding significant increase in cement gap thickness was observed in the mesial internal region of the integrated cavity group. No significant differences were detected at any other marginal or internal measurement points. Fracture resistance did not differ significantly among the three groups (p = 0.516), and the integrated cavity group recorded the highest mean fracture resistance value. CONCLUSIONS: Incorporating a proximal cavity directly into a monolithic laminate veneer design compromised marginal and internal fit in the cavity region but did not negatively affect overall fracture resistance. This preliminary proof-of-concept is promising; however, validation through thermomechanical aging and clinical trials is essential before routine application.