To investigate the effect of titanium tetrafluoride (TiF₄) solution on bonding strength of acid-etched dentin.

Tooth crown dentin proximal to the pulp cavity was obtained from 24 freshly-extracted human third molars and randomly divided into 6 groups (n=4 each) . Among them, 4 groups were modeled for artificial acid-etched dentin by means of acid-etching and mechanical friction. The other 2 groups were used as sound dentin controls. One each of the artificial acid-etched dentin groups and sound dentin control groups were randomly selected and studied under scanning electron microscope and microhardness tester to measure the surface morphology and hardness, and to evaluate the effectivity of the modeling for artificial acid-etched dentin. The other 3 groups of artificial acid-etched dentin and remaining group of healthy dentin were used for bonding test, re-assigned into 4 groups according to different treatments: etched dentin treated with 4.0% TiF₄ (4.0% TiF₄-ED group) , etched dentin treated with 2.5% TiF₄ (2.5% TiF₄-ED group) , untreated etched dentin (ED group) and sound dentin control (SD group) . All dentin samples were then bonded with a self-etching system (SE bond) , layered by AP-X composite resin with light-curing. Microtensile bonding strength (μTBS) test was used to measure the immediate bonding strength and to determine the fracture pattern.

The microhardness values of artificial acid-eched dentin and sound dentin were (56.92±5.27) HV and (60.19±4.52) HV, respectively, with significant difference between groups (P<0.05) . Scanning electron microscopy confirmed that the artificial acid-etched dentin presented microscopic morphological characteristics consistent to natural acid etching. The μTBS of 4.0% TiF₄-ED group, 2.5% TiF₄-ED group, ED group and SD group were (28.94±8.04) MPa, (46.08±8.19) MPa, (20.39±7.46) MPa and (45.16±7.86) MPa, respectively. The μTBS did not differ significantly between the 2.5% TiF ₄-ED group and the SD group (P=0.529) , and both were higher than those in the 4.0% TiF₄-ED group and the ED group (all P<0.05) . The fracture patterns differed significantly among the 4 groups (χ²=54.91, P<0.001) . In the 2.5% TiF₄-ED group, cohesive dentin fracture was the main cause, suggesting that the bonding strength may be higher than the mean measurements from the micro-tensile test.

The bonding strength of acid-etched dentin is lower compared with sound dentin. 2.5% TiF₄ solution can significantly improve the bonding strength of acid-etched dentin.

Acid-etched tooth; Dentin; Dental bonding