Buccal enamel region and surface morphology affect the shear bond strength of lithium-disilicate veneer-analog specimens

To digitally characterize regional buccal enamel morphology and evaluate its association with the shear bond strength (SBS) of lithium-disilicate veneer-analog specimens bonded to cervical, middle, and occlusal enamel regions under standardized in vitro conditions. Eighty extracted sound human premolars were included in this controlled comparative in vitro study. The buccal enamel surface of each tooth was digitally scanned and analyzed using CAD-based morphometric assessment. Standardized circular bonding sites were prepared within cervical, middle, and occlusal enamel regions. Lithium-disilicate veneer-analog specimens were fabricated, surface conditioned, bonded using a total-etch adhesive protocol, and subjected to 5,000 thermocycles before SBS testing using an adapted ISO 29,022 configuration. Failure modes were evaluated stereomicroscopically. Statistical analysis was performed using linear mixed-effects models. A total of 238 bonded specimens were analyzed. Mean SBS differed significantly among enamel regions ( p < 0.001), with cervical enamel demonstrating lower SBS (22.5 ± 6.6 MPa) than both middle enamel (28.2 ± 5.9 MPa) and occlusal enamel (29.5 ± 5.2 MPa). No significant difference was observed between middle and occlusal enamel ( p = 0.12). Dental arch and tooth type showed no significant influence on SBS. Cervical enamel demonstrated a greater proportion of adhesive failures. Effective bonding surface area was significantly associated with SBS. Within the limitations of this in vitro study, cervical buccal enamel demonstrated significantly lower SBS than middle and occlusal enamel when bonded to lithium-disilicate veneer-analog specimens. Regional differences in enamel morphology were identified, and effective bonding surface area was associated with SBS under the present experimental conditions. Further studies are needed to clarify the contribution of enamel morphology to bonding behavior.