Table 2 . The Micro-Hardness Mean Values of the 5 Study Groups Before Bleaching.

Mean (µm)	Group
1.98	Group 1 (Bleaching with diode laser and Heydent gel)
2.18	Group 2 (Bleaching with Nd: YAG laser and Heydent gel)
1.61	Group 3 (Bleaching with diode laser and Biolase gel)
1.76	Group 4 (Bleaching with Nd: YAG laser and Biolase gel)
2.33	Group 5 or control (Bleaching with Kimia gel)