Pretend you are a teacher preparing a quiz for the text I will provide. 
            Each quiz question should follow the format below. 
            Ensure that you carefully recheck the questions and answers for accuracy. 
            The output should be a ready-to-use list of dictionaries for the Python eval function:

            [

                    "question": "WRITE THE QUESTION HERE",
                    "options": ["A) OPTION_1", "B) OPTION_2", "C) OPTION_3", "D) OPTION_4"],
                    "answer": INDEX_OF_CORRECT_ANSWER_IN_OPTIONS_LIST,
                    "explanation": "EXPLAIN WHY THE ANSWER IS CORRECT"

            ]

            Text:
            ital tissue without 
vascular supply or innervation, it is 
nevertheless able to respond to thermal, 
chemical or tactile external stimuli 
because of the presence of dentinal 
tubules that permit stimuli transmission 
to the pulp. 
www.drcube.org 
5 
www.drcube.org 
Dentin can be distinguished from enamel (during tooth preparation), by: 
Dentin is normally yellow-white and slightly 
darker than enamel. In older patients, dentin is 
darker and become brown or black in cases in 
which it has been exposed to oral fluids, old 
restorative materials or slowly advancing caries. 
Color 
1 
Dentin surfaces are more opaque and dull, being 
less reflective to light than enamel surfaces, 
which appear shiny. 
Reflectance 
2 
www.drcube.org 
Dentin can be distinguished from enamel (during tooth preparation), by: 
When moving an explorer tip over the tooth, enamel 
surfaces provide a sharper, higher pitched sound than 
dentin surfaces. 
Sound 
4 
Dentin is softer than enamel, sharp explorer tends to catch 
and hold in dentin. The hardness of dentin averages one 
fifth that of enamel, and its hardness near the DEJ is about 
three times greater than near the pulp. Although dentin is 
a hard, mineralized tissue, it is flexible. This flexibility helps 
support the more brittle, less resilient enamel. Dentin is 
not as prone to fracture as is the enamel rod structure. 
Hardness 
3 
www.drcube.org 
Dentin can be distinguished from enamel (during tooth preparation), by: 
Ename
l 
Dentin 
Whitish blue or white 
gray 
Yellowish white or slightly 
darker than enamel 
Sharp, high-pitched sound 
on moving fine explorer tip 
Dull or low-pitched sound on 
moving fine explorer tip 
Hardest structure of the 
tooth 
Softer than enamel 
More shiny surface and 
reflective to light than dentin 
Dull and reflects less light 
than enamel 
Reflectanc
e 
Hardnes
s 
Sound 
Colo
r 
www.drcube.org Permeability of Dentin 
Permeability of Dentin 
The permeability of dentin can compromise its 
protective function because of the presence of 
dentinal tubules, which are very important 
during formation of dentin, however, when the 
external layer of enamel and cementum is lost 
from the periphery of the dentinal tubules 
through caries, preparation with burs or 
abrasion and erosion, the exposed dentinal 
tubules become channels between the pulp and 
the external oral environment. 
www.drcube.org Permeability of Dentin 
Permeability of Dentin 
However, in case of dentin cutting with bur, 
these 
exposed 
dentinal 
tubules 
usually 
occluded by a layer of tenacious grinding debris 
called the smear layer, which adheres to the 
surface and partially plugs the tubular orifices. 
However, the removal of the smear layer with 
acid etching during dentin bonding procedures 
causes an increase in the local dentinal 
permeability along with an outward fluid 
movement from the tubules, which results in 
adverse conditions for adhesive bonding by 
creating wet environment which may reduce 
bond stren

            Quiz: