Principles of bonding (Ch 5) Flashcards
what are the 2 ways of joining items together
- mechanical adhesion
2. chemical adhesion
what is mechanical adhesion
- physical interlocking
- weaker, called the secondary bond but is the first bond to take place in the bonding process
what is chemical adhesion
- stronger
- second bond to take place but is called the primary bond
what is bonding used for
- restorations (bonded amalgam, bonded composite resins)
- orthodontic brackets
- fixed retainers
- resin-bonded bridges
what is bonding
- the process of attaching restorative materials, such as a bonded amalgam or a bonded composite resin, to the tooth by adhesion
- definition: the attraction of atoms or molecules of two different contacting surfaces
how do we prepare for bonding (4 steps)
- removing biofilm and debris
- etching (conditioning) the cleaned surface (enamel or dentin) with an acid. this acid removes minerals from the surface to create roughness or microscopic porosity
- bonding agent is flowed over the etched surface and penetrates into microscopic pores. when it hardens it creates projections called resin tags. this resin tags lock into the pores and creates a mechanical bond = micro mechanical retention
- composite resins placed over the bonding agent will chemically bond to each other
what are the 2 types of bonds
- secondary bond = physical bond. is a weak physical attraction between two surfaces
- primary bond = chemical bond. is a true adhesion between atoms or molecules of the composite resin and the bonding resin
what is wetting
- increases the intimate contact of the bonding resin with the etched tooth structure
- improves the penetration of resin to form tags and therefore improves the bond
what is acid etching
- acid etching increases the ability of liquids to wet the surface of the tooth
why is bond strength important
- can enhance the longevity of the restoration and potentially allow for more conservative preparations, because cutting into healthy tooth structures to create mechanical locks can be minimized
what are some examples of acid etching agents and how long do they stay on the tooth
- maleic acid
- phosphoric acid (most common)
- 20-30 second rule for enamel
how should etched surfaces appear
- the etched surface should appear frosty
how long does acid need to stay on teeth for primary teeth and why
- primary teeth need 60 seconds as the enamel prism pattern is not as well structured making it more resistant to deep resin tag formation
how do we etch
- apply etchant with small brush, sponge or cotton pellet
- apply etchant for 20-30 seconds
- rinse for 10 seconds
what 2 situations does enamel etching create
- high-energy surface (attracts atoms)
2. low-tension surface (increases flow)
what can contaminate the working area when we’re trying to etch, how does this affect etching and what do we need to do to fix it
- saliva or blood
- will lower the bond strength
- must re-etch for 15 seconds
how can we avoid contaminating the working area during acid etching
- isolation of the working area
how long do we etch dentin
- maximum of 10 seconds
what happens if dentin is over etched
- expose too much collagen matrix
- results in a weaker bond, then post-operative sensitivity
how do we etch both enamel and dentin
- apply etch to enamel 1st for 10 seconds
- then etch dentin for 10 seconds
- so that enamel is etched for 20 seconds
what is the smear layer
- when a cavity preparation is cut with rotary or hand instruments, a layer of cutting debris forms on the surface of the cut dentin and enamel. this is the smear layer, composed mostly of cut tooth structure and may also contain plaque, bacteria, saliva and even blood
how does the smear layer affect the bond
- smear layer adheres tenaciously to dentin and occludes the tubules, greatly reducing the permeability of the dentin. we need a proper seal of dentin to prevent bacterial leakage and post op sensitivity
how do we remove the smear layer
- cannot be rinsed away
- bonding systems that use phosphoric acid to etch the enamel and dentin dissolve the smear layer and rinse it away with water for 10 secs
- bonding systems that use acidic primers to etch the enamel and dentin penetrate the smear layer and incorporate it into the bonding agent. does not get rinsed
what is the rinsing and drying procedure for acid etching
- rinse for 10 seconds to remove acid
- gentle drying with air, but leave dentin moist so that it glistens
- critical not to over dry the dentin as moisture keeps the collagen fibers fluffed uup
- if the collagen fibers are dry they will collapse and totally occlude the tubules and stop adequate penetration by the dentin bonding resins
what are bonding agents
- low-viscosity resins = good flow into microscopic porosities of etched surfaces
- dissolved in solvents that penetrate porosities in the tooth surfaces created by etching
what is resin primer
- penetrates etched enamel and dentin
- solvents contain hydrophilic properties to allow it to penetrate the wet etched dentin around the fluffed-up collagen fibers and thus into the dentinal tubules
- drying with air not removed the volatile solvents from the resin and any remaining water
- recap immediately to prevent evaporation of the solvent (will thicken)
what is adhesive resin
- applied over the primer
- the two resins chemically bond to each other
what is the hybrid layer
- a combination of dentin components and resin
- they bond to the dentin and the restorative material; is done through the hybrid layer
what are universal bonding agents
- can bond to all surfaces
- fluoride is added - the amount of fluorides too small for a therapeutic effect
what are self-etching bonding systems
- some two-component bonding agents incorporate acidic groups in the primer
- will etch enamel and dentin without the need for rinsing and drying, also primes them with resin
what are some advantages of self-etching bonding systems
- eliminates etching, rinsing and drying
- this decreases errors such as over etching, under etching, over drying, under drying – all contribute to postoperative sensitivity
what are some disadvantages of self-etching bonding systems
- do not etch uncut enamel such as:
- sealants, direct composite veneers, orthodontic brackets
what are total-etch bonding systems
- acid etch to both enamel and dentin with a separate step of rinsing off acid and lightly drying the tooth
- dentin is left slightly moist so solvents allow resins to penetrate through the water and around fluffed up collagen
how to resins bond to the tooth and restorations
- resins chemically bond to each other
- resins MECHANICALLY bond to the tooth and restoration
- metal or porcelain require roughening of their surface for the mechanical retention of a resin
what are the 3 modes of curing
- self-cure: a chemical reaction only
- light-cute: uses a light in the blue wave range
- dual-cure: a combination fo self-cure and light-cure
what is microleakage
- the leakage at the microscopic level at the junction of the restoration and the tooth surface
what contaminants can be present during microleakage
- blood
- saliva
- smear layer
- oils from handpieces
- prophylaxis paste
what steps do we take during the bonding process
- prepare the tooth and/or restoration
- rinse and dry
- acid etch 20 seconds enamel, 10 seconds dentin
- rinse 10 seconds
- dry to check for frosty white surface (to ensure it is acid-etched properly) - only when not dentin
- dry to a glistening wet surface
- apply resin, light cure, mechanical bond
- apply composite, light cure, chemical bond
how are porcelain restorations retained best
- when bonded instead of cemented
- bonding helps minimize microleakage
- porcelain veneers: remove a thin layer of enamel so they will not appear bulky
what does metal bonding do
- helps for better retention of metal to the tooth surface
- especially when cementing a crown
what was amalgam bonding originally thought to do
- increase the seal
- decrease the micro leakage and
- increase fracture resistance of the remaining tooth
- when bonding composite to amalgam – need to roughen the amalgam surface for added retention
how are orthodontic brackets bonded
- brackets have replaced bands especially anteriorly
- brackets are placed upon the labial surface and bonded into place
- self-cured and light-cured
how to use Endodontic posts
- a post is placed within the prepared root canal of the endodontically treated tooth
- the posts are bonded to the root with dentin bonding agents and resin cements
what 4 conditions contribute to tooth sensitivity
- over-drying and under-drying
- over-etched and under-etching
- not adequately sealed
- composite resin cured in overlarge increments
