Furthermore, the removal of exposed collagen does not only reduce the bonding technique sensitivity but also produce a more porous surface (i.e., an increase in size of dentinal tubules with the presence of an extensive labyrinth of lateral tubules that open on intertubular and/or peritubular dentin
)  and larger resin tags  that would produce interfaces with high bond strength.
Dentin surfaces irradiated by Er:YAG laser were irregular, scaly, or flaky and dentinal tubules were opened without smear layer, cracked or melted; whereas protrusion of peritubular dentin
was revealed due to its less amount of water compared with intertubular dentin.(Fig2) Irregularities promoted by laser irradiation vary according to the energy density applied.
Desensitizers containing metallic salts, predominantly oxalates, form insoluble chemical precipitates in the peritubular dentin
. No acid etch or light curing is needed for oxalate use.
The qualitative evaluation considered dentin surface characteristics, intertubular and peritubular dentin
, dentinal tubules and smear layer deposits.
Dentin tubule occlusion takes place as teeth age via continued deposition of peritubular dentin
(40) which may influence the physical properties of the dentin.
According to Kawamoto and Tsujimoto, (23) the OH radical resulting from hydrogen peroxide degradation is responsible for tooth whitening, and acts on intertubular and peritubular dentin
, destroying its organic portion, increasing permeability, (24,25) and decreasing its hardness and elasticity modulus, (2,3) which can be intensified with a greater exposure time of the tooth to the bleaching agent.
Qualitative aspects of the inter- and peritubular dentin
were also assessed, taking into consideration the presence or absence of the smear layer.
Older teeth experience gradual enlargement of peritubular dentin
and intratubular mineral deposits, which often result in narrowed or completely occluded tubules.