Primary and Secondary Chemical Bonds

• Primary and secondary bonds, including their charge and electrons are detailed.
• Primary bonds are strong bonds between atoms and involve the transfer of electrons between atoms:

Primary Bonds

• Metallic, Ionic, and Covalent are included.
• Ionic bonds transfer electrons.
• Covalent bonds share electrons between a pair.
• Metallic bonds share electrons by all the atoms that make up the object.

Secondary Bonds

• Secondary Bonds (Van der Waals forces) result from partial charges from an uneven distribution of electrons around an atom or molecule.
• Permanent Dipoles occur when shared electrons of a covalent bond are not shared equally, which means one of the bonded atoms is partially positive and the other is partially negative because of unevenly distributed electrons.
• Hydrogen Bonds: Stronger dipole bonding pulling positive or negative ions occurs.
• Fluctuating Dipole: Uneven distribution of atoms that are always changing leads to a weak attraction.
• Metallic bonds are similar to covalent bonds because valence electrons are shared between atoms.
• The difference is that the electrons in a metal object are shared by all atoms that make up the object, rather than just two atoms.
• The sliding of atoms past each other allows this material to bend, not fracture, and maintain its strength.
• Electrons are closer to the positive cores than the positive cores are to each other, so the attraction outweighs the repulsion, resulting in a weak primary bond in all directions.
• Covalent bonds involve partially positive and partially negative related atoms.
• Unequal distribution of electrons surrounding an atom results in a partial charge that creates a bond.
• Secondary bonds result from partial charges from the uneven distribution of electrons around an atom or a molecule.
• To produce the replica (or positive copy), an impression is made of the prepared tooth or remaining alveolar ridge.
• The dental impression (or negative copy) is then filled with a material that solidifies to form the replica:
• A cast is contructed if a restoration is constructed on the replica.
• A study model or diagnostic cast is used to study the size and position of the oral tissues
• A cast or study model results in a positive copy, while an impression results in negative copy.
• The impression is a negative reproduction
• The replica (the model or cast) is a positive reproduction once its poured and trimmed
• Study models are utilized for treatment planning in an orthodontic office.
• Casts or dies are utilized for crown or bridge work.
• A study model is used to plan observation of treatment progress for orthodontic purposes.
• A cast is a replica on which a restoration or appliance is fabricated, is more accurate than a study model, and is a replica of more than one tooth (such as a quad or full arch), and used for dentures.
• A die is a working replica of a single tooth, and is used for a crown or bridge.
• Dr. G.V. Black classified the most common sites for dental caries in the late 1800's.
• Ceramic materials' characteristics include strength, insoluble nature, similarity in color to teeth, and advantages.
• The disadvantage of dimensional stability and translucency is brittleness.
• Chains in dental polymer are linked by covalently boned atoms to form a three-dimensional structure, resulting in a stiff, strong material.
• Two liquids (oil and water) not blending is immiscible
• Emulsion/colloid is an example.
• Modulus of Elasticity = stress / strain
• Indication of stiffness of a material property
• The load (stress) and the change in length (strain) are proportional, and always occur together.
• The modulus of elasticity is characteristic of a material and its atomic bonds, and is the scientific term for the stiffness of a material.
• The higher the modulus of elasticity means the stiffer the material.
• Coefficient of thermal expansion measures the change in volume in relation to the change in temperature (a fractional change in volume or length).
• The balloon will shrink if a balloon filled with room temperature air is brought outside on a cold day
• Percolation is the process of heating and cooling, and the accompanying opening and closing of the gap, which leads to micro-leakage, tooth sensitivity, and recurrent decay.
• When the mismatch is significant, the restoration will shrink with cold beverages, which opens gaps between the restoration and the tooth.
• The gap is closed when the tooth heats up again and expands.
• The load (stress) and the change in length (strain) are proportional, and always occur together.
• Thermal conductivity: The rate of heat flow through a material
• Solubility: A material's ability to dissolve in liquid
• Mohs's hardness (enamel = 5-6): Measures relative resistance to scratching
• Gelation: The process by which gelatin, (Jell-O), changes from a liquid state to a semi-solid state when it cools
• Elasticity: The phenomenon of when a force is removed on an object, it returns back to its original position.
• Syneresis: The process when hydrocolloid materials contract slightly after setting and exude (discharge) water.
• Syneresis is occurs very slowly and is a second reason to pour hydrocolloid impressions as soon as possible.
• Alginate is irreversible, whereas agar is Jello that turns liquid when heated.
• Ceramic materials are colored to match the appearance of the patient's natural teeth and the materials are translucent, which means some light passes through, as in natural teeth.
• Ceramic material are strong when compressed because the atoms are forced together but ceramic material are weak and brittle when pulled or bent.
• For a Maxillary alginate impression the right-handed operator's position is on the side/in back of patient, at 11 o'clock position
• For Mandible alginate impression, the right-handed operator's position is on the side/ in front of the patient, at 7 o'clock position
• A suitable power to liquid ratio is necessary to achieve a good or desired outcome.

Alginate Set Up

• Patient tray
• Basic set up
• Impression tray (mand/max)
• rope wax
• wax bite registration, premeasured alginate:
• disposable cup
• mixing bowl
• spatula
• water measuring cup
• patient bib
• ziplock baggie
• disinfectant
• paper towels
• clinician PPE
• Mixing time: 1 min.
• Initial setting time is 3-4mins
• Working time is calculated by adding the mixing and setting times.
• Determining the initial gypsum set can be done by observing the “loss of gloss” on the surface of the mixed material.
• Gypsum usually takes 30-45 min to completely set (final gypsum set), but setting overnight is ideal.
• Dry strength is a product made of gypsum that does not include water is referred to as having a surplus of water.
• Dry strength is the strength measured when the excess water is not present in the sample.
• Dry strength may be two or more times the wet strength.
• The cast must sit in a dry environment OVERNIGHT to approach dry strength values.

Recommended Method of Mixing Gypsum

• Use powder to add the measured water into the mixing bowl first.
• The bowl is followed by gradual addition to the pre weighted powder.

Hand Mixing

• Done in flexible, plastic or rubber bowl with stiff-bladed spatula
• The mixture should be smooth/homogenous and free of air bubbles
• Mix by using a wiping motion against sides of bowl.
• Vibrators reduce bubbles in the mixture.
• Liquid silicone rubber is the best elastomeric substance that is liquid
• Polysulfides, Condensation silicones, polyethers, and additional silicones are all used for most dental procedures full dentures, partial dentures, inlay, crown, and bridge work.
• The setting process for all listed above is chemical and elastic.
• The strain is proportionate to the stress, and the material cannot shape when a material experiences stress that exceeds its yield strength.
• Alginate materials are irreversible, because they do not reverse to their original state
• Alginate materials are not as accurate as reversible hydrocolloid materials but are EASIER TO USE.
• Potassium sulfate acts as an accelerator, while borax acts as a retarder when both are added to gypsum to affect setting speed.
• Type IV, alpha-hemihydrate, pink stone is an improved stone that is strongest and most expensive.
• Most advantageous elastomeric material is PVS, polyvinyl siloxane
• Loss of gloss is an indicator of the initial set of gypsum products

This resource details primary bonds (Metallic, Ionic, and Covalent) involving electron transfer or sharing between atoms. It covers secondary Van der Waals forces like permanent dipoles, hydrogen bonds, and fluctuating dipoles, which arise from uneven electron distribution.