Prosthodontics Flashcards
mechanical properties of resins are influenced by
- MW of the polymer
- degree of cross-linking
- composition of monomers
- EXPAND in water and distort when dried out
acrylic resin powder (polymer) is made of
polymethyl methacrylate (PMMA) polymer, benzoyl peroxide initiator -cross linking contributes to strength
acrylic resin liquid (monomer) is made of
PURE methyl methacrylate (MMA) monomer, hydroquinone inhibitor, cross-linking agents, checmical activator (dimethyl-p-toluidine)
-other monomers like ethyl methacrylate are less irritating to the pulp
heat is used as an accelerator to decompose ___ (initiator) into free radicals to initiate polymerization of MMA PMMA
benzoyl peroxide
the liquid monomer most frequenly used in polymer systems in dentistry
MMA
heat cured resins have more/less residual monomer and higher MW than self-cured resins
LESS, so they are stronger and have better color
in self-cured materials, a chemical activator like __ (tertiary armine) is added to the monomer MMA to decompose the benzoyl peroxide into free radicals -> polymerization
dimethyl-p-toluidine
what kind of resins are used for repairs
self-cured (instead of heat) because risk of distorting the denture is less
denture STABILITY involves
- relationship of denture base to bone that resists DISLODGEMENT in horizontal direction
- resistance to horizontal, lateral, torsional forces
denture SUPPORT involves
resistance to VERTICAL seating provided by rests and the denture base
MOST important design characteristic for oral health
denture RETENTION involves
resisting force to gravity, sticky foods, forces assoc. with mandibular movement
-direct and indirect retainers, clasps in undercuts provide retention
denture RECIPROCATION involves
part of restoration counters effects in another
ex. lingual clasp arm counteracts buccal arm
- achieved by opposing flexible retainers with guide planes, minor connectors, rigid clasp arms, plating
bracing is
horizontal force ransmission by placing rigid parts of clasps or other parts in non-undercut areas of abutment teeth
guidance is
during insertion and removal, obtained by contact of rigid parts of framework with areas on axial tooth surfaces parallel to path of insertion
impression taking for complete dentures recommend
- border molding
- best for pt with loose hyperplastic tissue is to register it in a PASSIVE position
primary indicator of accuracy of border molding is
stability and lack of displacement of custom tray in mouth
most critical area in border molding for max denture is the
mucogingival fold above the maxillary tuberosity
- important for retention
- other areas: labial frena in midline and bicuspid area
in border molding, the distofacial extension is determined by position and action of the __ muscle
distolingual is limited by action of the __ muscle
MASSETER (anterior fibers pass outside buccinator)
-the buccinator lies under the flange in this area but the fibers run anteroposterior in a horizontal plane and their action is weak
SUPERIOR CONSTRICTOR
most likely tissue rxn to gross overextension is
epulis fissuratum
- due to clefts found in hyperplastic tissue
- occurs in vestibular mucosa
- appears as PAINLESS FOLDS of fibrous tissue
localized or generalized chronic inflammation. trauma and secondary fungal infection are the most likely causes
denture stomatitis
tx: better OH, rest, anti-fungal (Nystatin)
condition frequently observed under ill-fitting denture, esp. with a relief chamber, masses are painless, firm, pink or red nodular proliferations, candida albicans may contribute
inflammatory papillary hyperplasia
masseter’s superficial layer originates from the maxilla’s __ and inserts in the mandible where?
maxilla’s zygomatic process and inserts at the angle and lower lateral side of the ramus of the mandible
a tendon that lies btw the buccinator and superior constrictor is the
pterygomandibular raphe
a thin, curved bony process extension of the medial pterygoid plate of sphenoid bone that serves as the superior attachment of the pterygomandibular raphe
hamulus
thin cleft btw maixllary tuberosity and hamulus, where a max denture must extend into is the __ __
hamular notch
group of mucous gland ducts, posterior to jxn of hard and soft palates near midline is
fovea palatini
palatoglossus, superior pharyngeal constrictor, mylohyoid and genioglossus are influential in border molding what area?
LINGUAL of mandibular impression
difference btw border molding with ZOE instead of modeling plastic is that
ZOE has to be border molded in one insertion and within setting time
what regulates the paths of the condyles in mandibular movements?
size and shape of bony fossae and menisci and muscles
primary support for max denture are
- residual ridges
2. palatal rugae
if pt complains that when they smile, upper denture doesn’t hold, you need to adjust
buccal notch and buccal flange due to excessive thickness
if pt complains that max denture is loose when mouth is wide open, might be because
maxillary DB flange being too thick can interfere with movement of the coronoid process
if pt has sore gums and aching muscles at bottom of face after wearing dentures for hours it means
opposing teeth of denture have enough space -> reduce VDO
tingling or numbing at corner of mouth or lower lip after few days is caused by
excessive pressure from lower buccal flange in region of mental foramen
posterior palatal seal in max complete denture
- excessive depth usually causes unseating of the denture
- always done by the DENTIST
- width of seal AP is concave, 3 mm in midline and 6 mm in lateral areas
Functions
- completes border seal
- prevents food impaction
- improves retention
- ** compensates for polymerization and cooling shrinkage of denture resin during processing
posterior palatal seal landmarks
posterior outline - vibrating line, the hamular notch is ON the posterior border
anterior outline - formed by “blow” valsalva line at distal extent of hard palate, approximation of the jxn of hard and soft palate
changes on max arch in pt who wears complete max denture and LACKS posterior occlusion includes
- hyperplastic tissue on anterior max ridge
- poor bone structure
- fibrous tuberosities
- pt’s CC: loose denture, can’t see upper teeth
pt with upper complete and mand bilateral distal extension may show
decreased VDO, prognathic appearance
when a complete max denture opposes natural mand. anterior teeth, what happens to the max anterior ridge?
becomes FLABBY
when the posterior max buccal space is entirely filled with the denture flange, interference may occcur with movement of the
coronoid process -> dislodgement
max. sinus enlarges throughout life if it’s not restricted by teeth or dentures. as it enlarges, what happens to the tuberosity?
moves downward
-if there is no contact with the retromolar pad at VDO, the tuberosity must be reduced
submucosal vestibuloplasty
usually on upper arch to improve denture base area
palatal tori occur in __ % of population and are more common in males/females?
20-25%, women
- tissues covering it are thin with poor blood supply, post-op healing is slow
- NOT usually removed for denture fab but MANDIBULAR ones are!
indications for palatal tori removal include
impinging on soft tissue, fills vault and prevents formation of adequate denture base, undercut, extends so far posterior that it interferes with posterior palatal seal, psychologically disturbing to the pt
primary support area for mandibular complete denture is
BUCCAL SHELF (bone structure, right angle to occlusal plane) -if residual ridges are large and broad then it's also support
second peripheral seal for mand. coimplete denture is the __ border
anterior lingual
what will happen to the alveolar ridge is a mand. complete denture base terminates short of the retromolar pad?
RESORPTION of the alveolar ridge
underlying __ __ under the retromolar pad resists resorption
basal bone
mand. dentures don’t rely on suction, but rely on STABILITY from
covering as much basal bone as possible without impinging on muscle attachments
mandibular molars should NOT be placed over ascending area of the mandible because
the occlusal forces over the inclined ramus dislodge the denture
most common cause of POROSITIES in a denture is from
insufficient pressure on the flask during processing
- acrylic resin for repairs should be under 20-30 psi air pressure
- usually happens in THICKEST part of the denture
- also occur if packing and processing of powder and liquid is too plastic (stringy/sandy)
purpose of occlusal rims is to
determine and establish VDO
make jaw relation records
establish and locate future position of teeth
in a complete denture pt, when the teeth, rims and central bearing point are in contact and mandible in CR, then the length of the __ is the occlusal vertical dimension
length of the face
correct VDO is evaluated using 4 methods
- appearance of facial support
- observation of space btw rims at rest
- measurement btw dots on face
- observation when S sound is enunciated, check speaking space
excessive VDO can result in
trauma to underlying supporting tissues
__ is the most likely cause of cheilosis
closed vertical dimension
what has the greatest effect on setting of mandibular 2nd molars?
posterior determinants of occlusion (2/3 height of retromolar pads)
frankfort horizontal plane extends from
outer canthus of eye to ear tragus
what 3 factors affect correct positioning of the lips in complete dentures
- VDO
- thickness of anterior border
- teeth position
changes assoc. with the edentulous state
- deepening of nasolabial groove and narrowing of lips
- prognathic appearance, increase in columella-philtral angle
- loss of labiodental angle and decrease in horizontal labial angle
after first few days of new dentures, pt should expect some difficult in masticating most foods and excess saliva cause of
reflex parasympathetic stimulation of salivary glands
2-step schedule for tooth removal prior to delivery of immediate completes
step 1 - ext all posterior teeth except max 1st PM and opposing tooth (a stop to keep VDO)
step 2 - after ridges heal, anterior teeth are ext at time of insertion
1st day of wearing immediates instructions
not to remove denture
eat soft foods
return in 24 hrs for eval
primary role of anterior teeth is
esthetics
most common error is placing teeth directly over the edentulous ridge
labial surface of central incisor should be 8 mm anterior to the incisive papilla
BL width on denture teeth are more narrow to
reduce stress transferred to denture support area while eating, and increases tongue space
common errors when arranging denture teeth
-set mand teeth too far forward to meet max teeth
-fail to make canines turning point of arch
-set mand 1st PM buccal to canines
-establish occlusal plane arbitrarily
0not rotating anterior teeth enough to give narrower effect
why do you use plastic instead of porcelain teeth
plastic bonds well to acrylic resin
immediate dentures should be relined when?
in 5 and 10 months post-ext
a flabby max anterior ridge under a complete denture is often assoc. with
retained natural mandibular anteriors
benefit of an overdenture (root-retained) is
PRESERVATION of the ALVEOLAR RIDGE
potential probs with new dentures
- cheek biting caused by
- posterior teeth set edge-edge, need proper horizontal overlap
- inadequate VDO
- bite corners of mouth -> reset canines and PMs - lip biting - caused by reduced muscle tone or overbite
- tongue biting - posterior teeth too far lingual
- speech - bad tooth position, palatal contours
pt edentulous for many yrs has more distorted speech than pt edentulous for a short time due to
loss of tonus of tongue muscles
what might you see in an uncontrolled diabetic
impaired healing
poor tissue tolerance
rapid bone resorption
Sounds
- S - bring mandible close to maxilla
- hissing - incisal edges almost touching
- Th - tongue protrudes 2-4 mm btw max and mand teeth
- F and V - incisals of max and lower lip
- P and B - lips
- T - if teeth are too lingual it will sound like a D and vice versa
- whistling - from high palatal vault or constricted palate, insufficient overjet, overbite, bad palatal contour
if pt complains of irritation of basal seat, can be cause of
premature occlusal contacts (most common cause!)
bad OH
nutrition imbalance
excessive VDO
pt with max denture complains of burning sensation means
pressure on INCISIVE FORAMEN
in mandibular anterior -> MENTAL FORAMEN
facebow records
pt’s maxilla/hinge axis relationship
- orients maxillary cast to hinge axis on articulator
- hinge axis facebow enables dentist to alter VDO on articulator
pantograph is used for
tracing paths of the condyle, uses 2 facebows
preferred method to preserve facebow transfer is a __ index
plastic index
2 methods
- plaster index of max denture before removing denture from articulator and cast
- place a piece of 10x wax on occlusal of mandibular and close the articulator in CR, chill, drop incisal guide pin to touch the table
ARCON articulator
condyle on LOWER member
condylar paths on UPPER
angle btw condylar inclination and occlusal plane is FIXED
-used for dx mounting of study casts
NON-ARCON articulator
condyle on UPPER member
condylar paths on LOWER
angle btw condylar inclination and occlusal plane is NOT fixed
-more proper to fabricate DENTURES
diabetes is assoc. with
delayed healing
rapidly progressing perio disease with bone loss
increased calculus
predilection for periapical abscesses
can surveying determine areas of support?
no
kennedy classifications are based on
the most posterior edentulous area to be restored
4 Kennedy Classes
I - bilateral distal extension
II - unilateral distal extension
III - unilateral edentulous spaces bound by teeth, tooth-borne
IV - anterior teeth missing and across midline
Craddock Classification is based on the denture type
Type I - mucosa borne
Type II - tooth borne
Type III - mucosa and tooth borne
major connector
connects parts of the prosthesis located on one side of the arch to the other
- must be RIGID
- should be free of movable tissues and shouldn’t impinge on gingiva
- relief should be provided
- bony and soft tissue prominences should be avoided
major connectors most frequently encounter interferences with what teeth
lingually inclined mandibular premolars
mandibular major connectors
- lingual bar
- lingual plate
- labial bar
- lingual bar - upper border at least 4 mm below gingiva
- lingual plate - upper border should be at middle 1/3 of lingual surface
- lingual bar - 3 mm below gingiva
maxillary (palatal) major connectors
- transpalatal bar
- horseshoe
- AP bar
- palatal plate connector
- palatal bar - lack rigidity, for toothborne, short span
- horseshoe - for torus
- AP bar - MOST RIGID
- palatal plate connector - for simple edentulous areas and full palatal coverage
distal extension RPD receives support from
residual ridge, tissue-bearing areas, selected abutment teeth, fibrous CT over alveolar process
most important factor in determining success of distal extension RPDs is
proper coverage over residual ridge
-should go over retromolar pad for stability and minimizing torque
if pt complains of sensitivity to percussion on abutment tooth of distal extension RPD, prob is most likely
OCCLUSION
-defective occlusal contacts can also cause a feeling of “looseness”
altered cast technique purpose
record form of edentulous segment without tissue displacement and to accurately relate edentulous segment of teeth via metal framework
impression materials can’t record anatomic form of teeth and physiologic form of soft tissue in a functional relationship simultaneously
stress breaker
device that relieves abutment teeth to which FPD or RPD is attached, of all or part of forces generated by occlusal function
when a stress breaker is incorporated next to a free-end distal extension RPD, the functional stress is directed onto the
residual ridge, and only minimal transfer of functional stress to abutment teeth occurs
3 types of stress breakers
- wrought-wire clasp
- split-bar major connector
- stress-breakers with movable joint
- wrought wire - simplest form, higher yield strength, flexible, ductile, resilient, greater tensile strength
- split bar (Ticonium ‘hidden-lock’) - flexible btw direct retainer and denture base
- with movable joint - btw direct retainer and denture base (DE hinge, dalbo attachment, Crismani attachment, ASC-52 attachment)
cast metal is
any metal melted and cast into a mold
-when the casting is cold-worked ex. wire, it’s a “wrought metal” (tensile strength, hardness, strength > cast)
elongation is
the most important mechanical property involved when a base metal RPD clasp is adjusted
cast wire compared to wrought wire
less yield strength, less flexibility, less ductility and resilience
-cast wire has unavoidable POROSITIES
indirect retainers include
rests, minor connectors, proximal plates
- fxn to prevent/counteract vertical dislodgement of distal extension base of RPD
- ANTI-ROTATIONAL
- counteracts upward rotation of base and serves as a 3rd reference for seating the framework and making altered cast impressions
- protects soft tissues
minor connector
connects major connector or base of RPD with other units (clasps, indirect retainers, occlusal rests)
2 functions
- transfer functional stress to abutment teeth
- transfer effect of retainers, rests, stabilizing components
indirect retainer design
- should be at right angles to fulcrum line
- IR should be in rest seats
- IR located farthest from clasp tips closets to edentulous areas provides best leverage against lifting/dislodging
rests are to provide
- occlusal
- cingulum
- incisal
VERTICAL support for RPD
- occlusal - forms acute angles with minor connectors, thickness 1.5 mm
- cingulum - usually confined to maxillary canines, sometimes max centrals
- incisal - not esthetic
direct retainers
- intracoronal attachment
- clasps (extracoronal retainers)
- intracoronal - most esthetic!
2. clasps - most common, 2 types
2 types of clasps
- Suprabulge
- Infrabulge
- suprabulge - originate from ABOVE survey line
- circumferential
- ring clasp: encircles nearly all of tooth to engage an undercut on same side of tooth as the rest
- embrasure clasp: when no edentulous space
- reverse action clasp (hairpin): engage undercut on same side of abutment as the rest or any posterior tooth
- extended arm: circumferential that extends to increase splinting and get better undercut
- 1/2 and 1/2 clasp: one circumferential from rest and another from minor connector on opposite side - Infrabulge (Roach, I, J, U, L, T bar) - approaches crown from below height of contour, must not be placed in tissue undercuts
pros/cons of infrabulge retainers
pros - efficient retention, less distortion of coronal contours, cleaner, esthetic, adjustable
cons - irritating to vestibule, not good for bracing
infrabulge retainers provide retention by
resistance of metal to DEFORMATION (rather than frictional resistance by contact of clasp to tooth)
intracoronal retainers
produce mechanical and frictional retention, esthetic, not used for distal extension
short arm clasp < 7 mm should be made in a __ gauge wire
20 gauge, need finer gauge for flexibility
flexibility of a retentive clasp depends on
- clasp length
- thickness
- width
- cross-sectional form
- clasp taper
- clasp material
failure of RPDs due to clasp design is best avoided by
altering tooth contours
reciprocating element must be placed __ the direct retainer, and contact the abutment where?
OPPOSITE
-must contact abutment as the retentive tip passes over the tooth’s height of contour
clasp assembly consists of
retentive clasp arm, reciprocal (stabilizing clasp arm), minor connectors/rests
reciprocal clasp arm functions on RPD include
reciprocation, staiblization, indirect retention (bracing)
facial and proximal contours of __ and __ most often need to be altered
premolars and molars
guiding planes serve to assure
predictable clasp retention
precision attachment restoration
metal male and female parts that fit together
semi-precision attachment - cast into the crown and RPD
con - NEVER in distal extension RPD without stress breaker
base metal alloys
compared to gold: lower density, higher resistance to deflection, higher modulus of elasticity, higher melting point temp, lower yield strength
advantages of rpd cast chromium cobalt alloys
corrosion resistant, high strength, low specific gravity, low density, high modulus of elasticity (stiffness), cheap
BUT very inflexible (no ductility or malleability)
chromium responsible for
cobalt is for
nickel?
corrosion resistance
-RPD is resistant to tarnish and corrosion cause of its surface oxide layer
cobalt - incr. rigidity, strength
nickel - ductility
ADA Classes of Alloys (I-IV)
I: small inlays
II: larger inlays and onlays
III: onlays, crowns, short-span FPDs
IV: thin veneer crowns, long-span FPDs and RPDs
elongated grains in wrought wire indicates it has been
cold worked
Paget’s Disease (osteitis deformans) often discovered in dental office cause
pt’s dentures don’t fit due to widening of alveolar ridges
- a chronic bone disorder, bones enlarge and are deformed
- enlarged head, hearing loss, blindness
__ is the most common change assoc. with systemic disease
osteoporosis
veneers should be treated with
- silane, protected with light cured unfilled resin
- etch tooh and apply unfilled bond resin
- composite applied on veneer
- stick on veneer
a reverse 3/4 crown is most often made for what tooth
mandibular molar
7/8 crown is
3/4 crown with vertical distobuccal margin positioned slightly mesial to the middl of the buccal surface
-good esthetics, good abutment
bevel (feather-edge) margin
best for CAST FULL GOLD but in practice it’s hard to read on impression and die
least marginal strength
-> an ACUTE edge/angle is the optimum margin for casting
chamfer margin
PREFERRED FINISHING LINE for cast full gold
-adv of easily definable margin and minimal tooth prep
shoulder margin (BUTT)
for porcelain jacket and ALL CERAMIC
- edge strength of porcelain is low
- provides resistance to occlusal forces and minimizes stress
- disadvantage is inaccuracies in crown fit are reproduced at margin -> incr. thickness of cement
- POOREST for cast metal
shoulder with bevel
allows sliding fit
-for proximal box of inlays and occlusal shoulder of mand 3/4 crowns, labial margins of PFMs
most common cause of crown failure is
lack of attention to tooth shape, position, contacts
greatest potential for wear exists btw what 2 materials
porcelain and tooth
- gold is better for occlusal cause its wear is more like enamel
- porcelain wears opposing dentition faster
- gold preferred for bruxism
FULL GOLD CROWNS
circumferential and occlusal reduction 0.5-1.0 mm
ALL-CERAMIC CROWNS
tendency to fracture at minimum deformation
-LOW FLEXURAL STRENGTH
rank porcelain flexural strengths
- in-ceram zirconia = 800 Mpa
- procera
- in-ceram
- IPS empress
- aluminous = 100
- feldspathic = 60-90
preps for what restorations must be well rounded with no sharp angles
all-ceramic
porcelain is much stronger under __ forces than tensile forces from opposing teeth
compressive
CAD-CAM
ceramics processed via a computer controlled milling machine
porcelain layers - restoration is bulked out to compensate for 20% shrinkage
- opaque
- body
- incisal
- opaque - mask color of the metal
- body - makes up bulk and color shade
- incisal - translucent to incisal or cuspal 1/3
metamerism
phenomenon that causes teeth/porcelain to appear color matched under one light, but different under another
- staining porcelain decreases value and increases metamerism
- light source must contain wavelength of the color matched to see that color
fluorescence
optical property by which a material (teeth) reflects UV radiation
-contributes to brightness and vital appearance
human teeth fluoresce BLUE-WHITE (400-450 nm)
blue fatigue accelerates yellow sensitivity
color of a pigment is determined by
selective absorption and selective radiation
SHADE is matched on the color’s
- value
- chroma
- hue
- value - color’s brightness, almost impossible to increase value
- chroma - saturation, most important in shade matching
- hue - color families, orange is most often used
dental porcelain is a mixture of
feldspar*, quartz, metallic oxides
COMPRESSIVE strength > tensile or shear strengths
BRITTLE
3 classes of dental porcelains
- high fusing
- medium fusing
- low fusing
- high - DENTURE teeth
- medium - all ceramic and porcelain jacket
- low - PFM
- aluminum oxide to increase resistance to “slumping”
- calcium oxide
- other oxides to reduce cross linking to lower fusing temp
degassing (heat tx)
casting is heated in a porcelain furance to 980C to burn off impurities before adding porcelain
-too low of temp will form bubbles
causes of porcelain fracture at porcelain metal interface
main cause - bad metal framework design
also: degass at low temp ,contamination, fuse opaque coat too low temp
metal and ceramic must have closely matched
coefficients of thermal expansion (alloy usually harder) to avoid TENSILE stresses at PFM interface
alloys should have a high __ and high __ to reduce stress on porcelain
proportional limit
high modulus of elasticity
types of composition all ceramic crowns
feldspathic porcelain - conventional porcelain jacket
aluminous porcelain - to reinforce glass [Inceram]
mica glass - [Dicor, Cerapearl]
crystalline-reinforced glass - leucite added [Empress]
types of fabrication method all-ceramic crowns
refractory die technique - Inceram
casting - Dicor
press - Empress
3 stages in firing dental porcelain
- low bisque
- medium
- high
glazed porcelain is
non-porous, resists abrasion, esthetic, well tolerated by gingiva
PFMs requirements
porcelain 0.7 mm
metal coping 0.3-0.5 mm for high noble gold
(base metal alloys 0.2 mm)
need space for 1.5 mm, supporting cusps require 2.0 mm reduction -> ideal is 1.5-2.0 mm (labial is 1.5)
opposing walls converge < 10 deg
how do PFM and all ceramic compare in tooth reduction
SAME
1.5-2.0 mm
metal coping (substructure) must have all of its surfaces __ to prevent porcelain shrinkage
metal coping ensures __ and maximizes strength of the porcelain veneer
smooth and round
proper crown fit and maximizes strength of porcelain veneer
outer jxn of porcelain to metal should be at what angle
90 deg
to avoid burnishing the metal and prevent subsequent porcelain fracture
3 kinds of PFM alloys
- high gold noble alloys - 98% gold, platinum, palladium, don’t oxidize on casting, BEST
- palladium-silver: oxidizes on casting
- nickel-chromium: readily oxidizes
sprue diameter should be
equal or greater than the thickest portion of wax or plastic
gypsum bonded investments
for GOLD alloys
strength depends on amt of gypsum
CAN’T be used for titanium crowns/copings, Type IV gold alloys, susbstructure for PFMs
phosphate bonded investments
base metal alloys for PFMs
casting temp > 2100 F (1150 C)
silica bonded investments
base metal alloys for RPDs
mag phosphate + ammonium phosphate for room temp.
higher temps, SILICOPHOSPHATES give it strength
quartz or cristobalite
refractory materials to provide thermal expansion
4 mechanisms to compensate for solidification shrinkage of alloy during casting
- setting expansion - crystal growth, restricted by metal investment ring
- hygroscopic expansion - let investment set in water
- thermal expansion - when it’s heated in burnout oven
- wax pattern expansion - wax pattern warmed while investment is still fluid
porcelain adheres to metal primarily by
CHEMICAL BOND
silicon dioxide and metal alloy
cements do NOT increase crown retention, apply cement to both restoration and the tooth, 3 types
- composite resin - for CERAMIC crown, STRONGEST bond, after etching tooth
- zinc phosphate - can be used for ceramics, good compressive strength, high pH so must use varnish!
- zinc polycarboxylate or ZOE - bio compatible, better resistance to solubility than zinc phosphate, adhere to calcified dental tissue
occlusion of gold restorations is best checked with
silver plastic shim stock
radiographic signs of occlusal trauma
hypercementosis, root resorption, alteration of lamina dura, wide PDL space (NOT pockets)
non-rigid connector
key and keyway, SHORT-SPAN bridge replacing one tooth
indicated when retainers can’t be prepared to draw together without excessive tooth rdxn
T-shaped most common
path of insertion of key into keyway should be parallel to path of the RETAINER
solder joints
replacing how many teeth is the max?
3 teeth, under ideal conditions
most likely indication for tooth splinting is
tooth mobility with pt discomfort
can you splint natural teeth and implants in a FPD?
controversial, DON’T
types of pontics (3)
- modified ridge lap - esthetic zones, all convex surfaces for easy cleaning
- sanitary - space btw pontic and ridge, not esthetic, conical pontic for thin ridge
- saddle - looks most like tooth, covers ridge, hard to clean and NOT used! ovate pontic is a sanitary substitute
pontic should be convex/concave M-D? touch the ridge? be convex/concave F-L?
CONVEX M-D
touch residual ridge (passive pinpoint)
CONCAVE F-L
quenching
metal is rapidly cooled, to maintain mechanical properties assoc. with crystalline structure
to achieve a softened condition for Type III dental gold alloy, quench in 30-40 sec
advantages - noble metal alloy is left in an annealed condition, casting is more easily cleaned
burnishing
related to polishing, surface is drawn or moved
annealing (degassing)
soften metal by controlled heat and cooling
to make the metal TOUGHER and LESS BRITTLE
gold foil is annealed to remove volatiles prior to placement in cavity
fritting
manufacturing low and medium fusing porcelains
soldering
join 2 metals using a filler material or solder
gold - fixed bridges
silver - ortho
CLEANLINESS is most important prereq of soldering, cause it depends on WETTING surfaces to achieve bonding, flux displaces gases and removes corrosion products
fluxing
oxidative cleaning of area to be soldered
-potassium fluoride - agent most commonly added (steel or cobalt chromium alloys)
anti-flux: outline the area, soft graphite pencil
pickling
heat casting then place in acidic solution -> can warp! or you can place it in solution then heat it
50% HCl
removes surface oxide film on gold castings
cold work (strain hardening or work hardening)
HARDENING (deformation) of metal at room temp ex. bend a wire
- polycrystalline metal, defects build up at grain boundaries
- result of strain hardening with increase in cold work is FRACTURE
surface hardness, strength, proportional limit are INCREASED while ductility and resistance are DECREASED
SLIP
deformation process, simultaneous displacement of entire plane of atoms relative to plane and below plane
electrosurgery objectives
indications
contraindications
obj - coagulation, hemostasis, access to cavosurface margins, reduce inner wall of gingival sulcus
indications - remove hyperplastic tissue, in place of gingival retraction cord, for crown lengthening
contraindications - thin attached gingiva, dehiscence suspected, NOT pts with cardiac pacemakers
temperomandibular joint is?
lower and upper compartment contain
combined HINGE and GLIDING joint (ginglymoarthrodial joint)
lower (condyle-disc) compartment: HINGE (rotary), only in CR
upper (mandibular fossa-disc) compartment: SLIDING (translation), when lateral pterygoids contract simultaneously, discs and condyles slide forward down over articular eminence
muscle groups acting on TMJ include (3)
- elevator muscles (CLOSE) - masseter, medial pterygoid, temporalis (anterior fibers)
- depressor muscles (OPEN) - lateral pterygoid, anterior belly of digastric, omohyoid
- protrusion - lateral pterygoids
centric relation (retruded contact position)
-ligament guided, supero-anterior position of condyle along articular eminence of condyle with articular disc interposed btw condyle and eminence
most unstrained, retruded anatomic and functional position of mandibular condyle heads in the glenoid fossae
a BONE-to-BONE relationship independent of tooth contact
closing end point of the retruded border movement
centric occlusion (intercuspal position)
TOOTH-guided position, MI, during typical swallowing
- masseters contract and tongue tip touches roof of mouth
- tooth contacts are longer in swallowing than chewing
freeway space
2-6 mm, mandible at rest
- tonic stretch reflex of mandibular elevator muscles
- muscle guided position
vertical dimension of occlusion (VDO)
vertical length of face as measured btw 2 arbitrary points when teeth are in CR
- verify by phonetics
- excessive VDO causes CLICKING of denture teeth (also lack of retention can cause clicking)
- decreased VDO often results in cheek biting
vertical dimension of rest (VDR)
length of face measured btw 2 points when mandible is in rest
VDR = VDO + interocclusal difference
condylar guidance
- totally dictated by patient
- inclination depends on: shape and size of bony contour, action of muscles, limiting effects of ligaments
what record is the least reproducible maxillomandibular record?
protrusive record
retrusive movement requires condyles to move
backward, upward
in lateral movements, working condyle moves ___, non-working condyles move __
working - down, forward, laterally
non-working - down, forward, medially
what factor is the most important aspect of condylar guidance that affects the selection of posterior teeth with appropriate cusp height?
inclination of condylar path during protrusive movement
in complete dentures, the condyle path during free mandibular movements is governed mainly by the
shape of the fossa and meniscus (articular disc) and muscular influence
4 dentition features that directly effect PDL health & hard tissue anchorage to resist occlusal force
- anterior teeth have slight or no contact in MI
- occlusal table < 60% of F-L width
- occlusal table at right angles to long axis
- tooth position in arch
jaw relation most used in actual design of restorations is
ACQUIRED centric occlusion
compensating curve
anteroposterior and lateral curve
- under the DENTIST’S control
- helps balanced occlusion
5 factors that govern balanced articulation
- inclination of condylar guidance
- ” of incisal guidance (horizontal and vertical overlap)
- ” of occlusal plane (plane of orientation)
- convexities of compensating curve
- angle and height of cusps
bilateral eccentric occlusion
NOT for RPDs unless the it opposes a complete denture
group function occlusion (unilateral balanced)
NO non-working side contacts in natural dentition, only working side
purpose of protrusive record
register condylar path, adjust condylr guides of articulator
protrusive movement, mandible can protrude __ mm
how do the condyles move
10
condyles move DOWN and FORWARD
how do you correct centric interference (forward slide)
grind MESIAL inclines of maxillary teeth and DISTAL inclines of mandibular
mutually protected “canine guided” occlusion
anterior teeth protect posteriors in all mandibular excursions
-vertical overlap of max and mand canines cause disculsion of ALL posterior teeth when mandible moves to either side
anterior guidance (coupling)
result of horizontal and vertical overlap of anterior teeth, produce disclusion of posteriors
the greater the overlap, the longer the cusp height
incisal guidance
second end-controlling factor in articular movement, influenced by esthetics, phonetics, ridge relations, arch space, inter-ridge space
these are end-controlling factors
incisal guidance
right and left condylar mechanisms
supporting cusps (stam or centric cusps)
characteristics
more robust, suited to crush food
characteristics
- contact opposing tooth in intercuspal position
- support vertical dimension of face
- closer to F-L center of tooth
- outer incline has potential for contact
- broader, more round cusp ridges
non-supporting cusps (guiding or shearing)
maxillary buccal cusps
mandibular lingual cusps
have narrower and sharper cusp ridges
inner occlusal inclines leading to guiding cusps are guiding inclines
selective grinding in complete dentures in centric relation (CR)
what cusps can you grind and not grind?
primary centric holding cusps are - Max lingual cusps (NEVER GRIND)
secondary centric holding cusps are - Mand. buccal cusps ONLY grind if there is a balancing (non-working) side interference
only grind BULL cusps!
functionally generated pathway technique
allows cuspal movements of the dentition to be recorded in wax intra-orally then transferred to articulator in the form of a static plastic cast (functional index)
all mandibular motion must be directed from an ECCENTRIC centric position
in ideal intercuspation,
ML cusps of permanent mandibular molars occlude with __
buccal cusp tips of permanent maxillary premolars oppose __
- LINGUAL embrasure between their counterpart and the tooth MESIAL to it
- FACIAL embrasure between their counterpart and the tooth DISTAL to it
which maxillary cusps and mandibular cusps are GUIDING cusps?
maxillary buccal cusps
mandibular lingual cusps
guiding = guide away from midline
BENNETT movement
lateral transition (sideshift) of WORKING condyle during lateral excursions
- also called lateral shift or immediate side shift
- influences the MESIODISTAL position of the posterior teeth cusps
translation in mandibular opening occurs in lower/upper compartment of TMJ?
UPPER
what are the muscles involved in closing (elevating) the mouth to centric
medial pterygoid
masseter
temporalis
what kind of load is the most destructive on the periodontium?
horizontal
bite registration material should
offer minimum resistance to pt’s jaw closure and have LOW FLOW at mixing
addition-reaction silicone materials
2 types of polymerization in impression materials
- addition - formation of polymer without forming any other chemical
- condensation - when chemicals or byproducts are produced that are not part of the polymer
hydrocolloids have the advantage of __
wetting intraoral surfaces BUT have limited dimensional stability
reversible hydrocolloid (agar-agar)
physical state can be changed from a GEL SOL by applying heat and is reversed back by removing heat
pros - easy to pour, no mixing req, no costum tray, good shelf life (1-2 yrs), cheap
cons - must be poured immediately, finish line difficult to read
irreversible hydrocolloid (alginate)
very limited dimensional stability
cons - unstable, fragile, must be poured immediately
sodium phosphate controls setting time (retarder)
FAST removal of impression from mouth increases the compressive and tear strength
alginate sets via a chemical rxn
double decomposition rxn
calcium sulfate + potassium alginate
gelation
setting process of alginate
- higher temp = shorter gelation time (sets faster)
- calcium sulfate “reactor”
- inaccuracies can be caused by fracture of fibrils
- SYNERESIS (shrinkage in alginate)
elastomers are?
4 types
NON-AQEOUS polymer based rubber impression materials with good elasticity
- polysulfides
- silicones
- polyvinyl siloxanes
- polyethers
Polysulfides (rubber base, mercaptan, thiokol)
base of liquid polysulfide polymer and accelerator of lead dioxide (brown, stinky).
- requires custom tray
- sets in 12-14 min (LONGEST set time)
- 18 mo. shelf life
- need occlusal stops
- good flow, high flexibility, good tear strength
Silicones (condensation or convention)
base is liquid silicone polymer (dimethyl siloxane) and reactor a cross-linking agent (ethyl ortho-silicate) and activator (tin octoate)
-evaporation of alcohol causes shrinkage of material and resultant poor dimensional stability
cons - custom tray req, low tear strength, pour shortly after removal, hydroPHOBIC, medium stiffness
- long setting time 6-10 min.
- “putty/reline” form allowing delayed pouring up to 6 hrs.
Polyvinyl Siloxanes (additional silicones or vinyl polysiloxanes)
upon mixing there’s an addition of silane hydrogen groups, PVS can be poured up to 1 week
- don’t wear latex! sulfur retards the setting
- moderate set time 6-8 min.
- very good dimensional stability and low permanent deformation
- poor tear strength, high stiffness, temp sensitive
most widely used, most accurate! less polymerization shrinkage, low distortion, can be poured up to 1 week
Polyethers (Impregnum/Premier & Polygel (Caulk))
rubber base has polyether, accelerator has cross linking agent (aromatic sulfonic acid ester)
pros - good dimensional stability, clean, fAST set, tolerates moisture the best
cons - most rigid (STIFFER!), difficult to remove from mouth, poor tear strength, adheres to teeth
shortest working and set time (6-7 min)
use custom tray, more accurate in uniform thin layers 2-4 mm thick
zinc oxide eugenol is an impression paste
pros
cons
accelerated by adding water. to retard the set add inert oils
pros - record soft tissue at rest, sets in 5 min, stable
cons - messy, sticky, tiissue irritant, not elastic, hard to manipulate
SET HARD in mouth
a chemical rxn to form a CHELATE
gypsum
weaker in tensile strength than compressive strength
-all products are reacted with water to form calcium sulfate dehydrate
Type I gypsum - Plaster
rarely used
Type II gypsum - Plaster, Model
model or lab plaster
- make casts when strength isn’t important (ortho)
- WEAKEST gypsum product
Type III gypsum - Dental stone
Class I Dental Stone
-high strength improved die stone
Type IV gypsum - Dental Stone, high strength
Class II Stone or improved stone
-for making stone “dies”
main constituent of dental plasters and stone is
calcium sulfate hemihydrate
dental stone (alpha) dental plaster (beta) (plaster of paris)
dental stone v. plaster
main diff is particle size and shape
-plaster requires 2x more water, has higher setting expansion
when packing cord for a pt with HTN< use a cord impregnanted with
ALUM - aluminum potassium sulfate
zinc chloride is caustic and causes delayed healing
