Dentin Bonding Performance of Universal Adhesives in Primary Teeth In Vitro

Abstract

(1) Background: The aim of this in vitro study was to evaluate the micro-tensile bond strength (µ-TBS) of universal adhesives to primary tooth dentin after different storage periods. (2) Methods: Dentin of 100 extracted primary molars was exposed. Dentin surfaces were bonded with six universal adhesives (Adhese^®Universal [AU], All-Bond Universal^® [ABU], G-Premio Bond [GPB], iBond^®Universal [IBU], Prime&Bond active™ [PBa], and Prime&Bond^®NT as control [PBN]) and restored with a resin composite build-up (Filtek™ Z250). After 24 h, 6 months, and 12 months of water storage, specimens were cut into sticks, and µ-TBS was measured and analyzed using one-way ANOVA (p < 0.05) for normal distributions and the Mann-Whitney U-test (p < 0.05) for non-normal distribution. Pretesting failures were recorded as 0 MPa. Fracture modes were analyzed under a fluorescence microscope; interfaces were visualized with SEM/TEM. (3) Results: Compared with the reference group (PBN: 32.5/31.2 MPa after 6/12 months), two adhesives showed a significantly higher bond strength after 6 months (AU: 44.1 MPa, ABU: 40.9 MPa; p < 0.05) and one adhesive after 12 months (AU: 42.9 MPa, p < 0.05). GPB revealed significantly lower bond strengths in all storage groups (16.9/15.5/10.9 MPa after 24 h/6 months/12 months; p < 0.05). AU and IBU did not suffer pre-test-failures [PTF]. (4) Conclusions: After 12 months, PBN, IBU, AU, and GPB showed significantly lower results compared ithw initial µ-TBS, whereas AU revealed the highest µ-TBS and no PTF.

Keywords: dentin; microtensile bond strength; pre-test failure; primary teeth; universal adhesives.

Figure 1

Step 1: Removal of 80% of roots; Step 2/3: grinding flat to expose dentin beneath the fissure; Step 4: adhesive pre-treatment; Step 5: resin composite build-up; Step 6: cutting the core into slabs; Step 7: cutting the resulting slabs into sticks; Step 8: microtensile testing after different storage periods.

Figure 2

Results for the µ-TBS to dentin compared with PBN. Asterisk indicates a significant difference within the different storage periods (* p < 0.05, ** p < 0.01, *** p < 0.00), sort by pH value (orange = medium, yellow 0 mild, green = ultra-mild).

Figure 3

Analysis of fracture failure modifications of the different adhesives investigated regarding the storage periods, sorted by pH value compared with PBN.

Figure 4

Fluorescence micrograph of a cohesive fracture. PBA after 6 months, fluorescence microscope with 40× magnification (bar: 500 µm).

Figure 5

Fluorescence micrograph of a mixed fracture. PBA after 6 months, fluorescence microscope with 40× magnification (bar: 500 µm).

Figure 6

Fluorescence micrograph of an adhesive fracture. PBA after 6 months, fluorescence microscope with 40× magnification (bar: 500 µm).

Figure 7

SEM interface (RC: resin composite; RT: resin tags; D: Dentin; hybrid layer: arrow). ABU after 24 h. 1500× magnification/bar: 20 µm.

Figure 8

SEM interface (RC: resin composite; RT: resin tags; D: Dentin; hybrid layer: arrow). IBU after 6 months, 2500× magnification/bar: 20 µm.

Figure 9

SEM interface (RC: resin composite; RT: resin tags; D: Dentin; hybrid layer: arrow). PBA after 12 months, 1500× magnification/bar: 20 µm.

Figure 10

TEM view of the homogenous adhesive layer, the hybrid layer (arrow; approx. 500 nm) and dentinal (D) tubules (filled with resin tags/RT). ABU after 6 months, 7000× magnification/bar: 1 µm.

Figure 11

TEM view of the adhesive layer with precipitations (asterisks), hybrid layer (arrow), and dentinal (D) tubules filled with resin tags (RD). AU after 24 h, 7000× magnification/bar: 1 µm.

Figure 12

TEM overview of the adhesive layer on dentin (D) with resin composite (RC) with the gradient and the hybrid layer (akterisk). IBU after 12 months. “Piano keys” appearance at the adhesive layer (arrow), 4000× magnification/bar: 1 µm.