Exam 2, Part 2: Fixed Prosthodontics, RPD & Digital Dentistry
cingulum rest preparation criteria
-"V" or "U" shape peaked toward the incisal -placed occluso-gingivally at the junction of the middle 1/3 and gingival 1/3 of the clinical crown (does not interfere with occlusion) -extends mesio-distally from 1 marginal ridge to the other -floor inclined toward the center of the tooth (establish a positive rest) -entire prep in enamel -smooth surface
gold inlay preparation guidelines
-1 single path of draw -pulpal wall depth 1.5mm -divergence of 2-5 degrees taper per wall (as the occluso-gingival height of the prep increases, the divergence should increase to allow proper seating of the restoration) -axial wall depth 0.8mm -gingival clearance from adjacent tooth 0.5mm -bevel of occlusal and gingival margin: 30-40 degree flaring of interproximal wall margins
premolar occlusal rest preparation criteria
-1.5mm marginal ridge reduction -1/3 B-L width of tooth -1/3 M-D dimension of tooth -rounded triangular outline form with base at the marginal ridge -spoon shaped -axial inclination establishes a positive seat -entire prep in enamel
molar occlusal rest preparation criteria
-1.5mm marginal ridge reduction -1/3 B-L width of tooth -1/4 M-D dimension of tooth -rounded triangular outline form with base at the marginal ridge -spoon shaped -axial inclination establishes a positive seat -entire prep in enamel
posterior tooth guide plane preparation criteria
-1/3 B-L width of the tooth (2/3 cusp tip to cusp tip) -2/3 length of the tooth from marginal ridge toward the cervical aspect of the clinical crown
goals for scanning opposing teeth
-100% of the occlusal and buccal surfaces -2-3mm gingival tissue on the buccal surface -lingual data not necessary
goals for scanning preparations
-100% of the prep and interproximal contacts -90% of adjacent teeth -good axial data for design -2-3mm of gingival tissue on the buccal surface -verify all required data is obtained (yellow areas highlighted with arrows = missing data)
altered cast impression
-a functional impression technique performed when previous impression taken using the single step impression technique doesn't work -puts forces onto distal extension areas (final base fitted to functional form) - helpful because it prevents torquing of the distal abutment tooth -metal framework on your master cast is returned from the lab -2 impressions are taken: anatomic/non-pressure impression for framework fabrication and functional/selective-pressure impression with trays attached on the framework -custom tray with non- or limited relief (viscous impression material allows for a functional impression in distal extension areas) -intimate contact of base to tissue under load only -this method involves more clinical and laboratory steps than single step technique (possibility of more procedural errors) -higher possibility of bone loss due to increased pressure (more frequent relines necessary) -less torque on distal abutment tooth
Akers clasp
-a suprabulge clasp of choice for tooth-supported RPDs -terminal tip engages 0.01" undercut below the HOC on B or L -reciprocal arm on the other side
embrasure clasp
-a suprabulge clasp used when a clasp is necessary in a quadrant where there is no edentulous space -when a small space exists between two natural teeth to retain RPD and fill the space to restore occlusion -basically 2 Akers clasps adjacent to each other -adequate preparation is necessary to prevent fracture of the framework (must prepare through the embrasure - marginal ridge reduction through and through without breaking interproximal contact) -positive rest seats are necessary to prevent wedging between teeth -may need to prepare opposing teeth if patient is a bruxer and has excess wear on the teeth you want to prepare an embrasure clasp for
primary retention for RPD
-accomplished mechanically by direct retainers on abutment teeth -retainer: any unit of a removable dental prosthesis that engages an abutment tooth or implant to resist displacement of the prosthesis away from the basal seat tissue (i.e. that component of an RPD used to retain and prevent dislodgement, which consists of a clasp assembly or precision attachment)
checking appropriate thickness
-activate the "minimal thickness surface tool" -areas thinner than the established minimum will be highlighted -use "minimum thickness tool" in automatic tools to adjust the thickness -wax knife and morph tools can also be used
metal-ceramic bond: ceramic wetting of the alloy surface
-alloy surface is mechanically prepared with Al2O3 stones or Al2O3 air-particle abrasion to enhance wettability -in this process, we are creating micro-roughness on the surface which will improve the ceramic wettability and also will contribute to mechanical interlocking -after Al2O3 treatment, we will have a more HOMOGENEOUS and ROUGHER surface (NOT smoother!)
working FPD cast
-also called definitive cast -cast made from final impression of prepared teeth -used by lab to fabricate the indirect restoration -teeth are connected to base with a pin system -pins allow precise removal and repositioning of teeth from the base
extent of ridge coverage by denture base
-also contributes to support and stability of RPD -the greater the surface area covered, the more distribution of stress (less load per unit area) -this is the reason why extension areas are fully covered to the extent of the vestibule (as in a complete denture) - must border mold!
adjusting metal FPD frameworks
-always work in one direction on metal surface to avoid overlaps and formation of cavities -diamond-coated instruments not recommended as diamond particles may become embedded in alloy and form bubbles in ceramic during firing process
biocompatibility of noble dental cast alloys
-any toxic, allergic, or other adverse biological response is primarily influenced by elements released from these alloys (corrosion) into the oral cavity -influenced by numbers and types of phases, and composition of the phases -identalloy certification program (must attach to patient chart)
bottom line: how much tooth structure do I need?
-at least 1.5-2mm of sound tooth structure coronal to the planned finish line of the restoration -at least 3mm of tooth structure from the planned finish line to the crest of the bone -total: 4.5-5mm of tooth structure coronal to the crest of the bone
RPD disclosing wax
-at the clinical appt, melt a thin layer of disclosing wax in all areas of the metal framework that would touch the teeth -gently place the framework in the patients mouth (don't force it in) -remove and adjust any areas of binding/pressure with high speed coarse diamond bur (leave broad, even contacts and remove small metal show through) -repeat until fully seated and check fit again
beryllium (Be)
-base metal -improves castability -potential carcinogen (use proper PPE and equipment when handling)
cobalt (Co)
-base metal -increases elastic modulus, strength, and hardness -used for rigidity in RPD frameworks
nickel (Ni)
-base metal -interchangeable element with cobalt (similarly increases mechanical properties) -5-8% of females have an allergy
chromium (Cr)
-base metal -tarnish and corrosion resistant -alloy should not contain more than 28-29% of chromium (more than 30% will be difficult to cast and will make the alloy more brittle)
decision-making process: why choose indirect restorations?
-better control of anatomy and contours -long term occlusal stability -less risk of contamination while delivering -long term color stability -esthetics -isthmus width 1/3-1/2 of intercuspal distance
muscular force potential
-can help determine/predict total occlusal load -determined by: 1) age (older patients record less force than young adults) 2) body mass (large adults can generate greater forces) 3) gender (women generate 20lbs less force than men) 4) Frankfort-Mandibular Plane Angle/FMA (lower FMA = more occlusal forces generated and transferred onto tissues)
under-trimming the die
-can lead to more difficulty with waxing -can also lead to a bulky (over-contoured) restoration
cross-sectional form of different retentive clasps and its impact on flexibility
-cast clasps are half-round in cross-section and flex in 1 plane only (less flexible) -wrought wire clasps are round in cross-section and flex in all spatial planes (more flexible)
cast vs wrought
-cast structure: appears crystalline and sometimes has dendritic structure -wrought structure: grains are elongated and have a more fibrous structure
metal-ceramic bond: residual stress
-ceramic is placed into a state of compression during cooling as a result of having a slightly lower thermal coefficient of expansion than the alloy (metal contracts more than porcelain) -this residual stress in the porcelain helps with the bond
metal-ceramic bond: chemical bonding
-certain metals in the alloy (Sn, In, Ga) migrate to the surface upon firing and form an oxide layer during the oxidation process -this oxide layer can chemically bond to the porcelain
alloys in dentistry
-choice of alloy depends on which properties are required for specific clinical situations -examples include: 1) inlays and onlays 2) partial or full crowns 3) bridges 4) endodontic posts 5) partial denture frameworks 6) implant abutments 7) orthodontic wires 8) endodontic files
results of violating biologic width
-chronic pain -chronic inflammation of soft tissues -unpredictable alveolar bone loss
post length
-clinical success of the post is directly related to its length -post length must be at least equal to the length of the clinical crown of the final restoration, OR at least 2/3 length of the root in bone (whichever is greater) -maintaining 4-5mm of apical gutta percha seal is critical -inadequate post length is less retentive and increases risk of root fracture
post
-commonly made of metal or polymer -2 types: pre-fabricated and custom -fitted into prepared root canal of a natural tooth -provides additional retention for core build-ups (a good option for compromised teeth that don't have enough remaining tooth structure to support a build up)
ordered vs disordered alloy microstructure
determined by how fast or slow the cooling process occurs: 1) slow cooling (heat hardening): -slow cooling of an alloy from an elevated temperature -allows time for the mass to form an ordered and organized solution -alloy product is harder, stronger, and less ductile 2) fast cooling (quenching): -rapid cooling of an alloy from an elevated temperature -prevents the ordered phase formation and results in a random, disordered arrangement -alloy product is softer, weaker, and more ductile
accuracy and fit of denture base
determined by: 1) intimate contact of tissue surface of the base to the tissues covering the residual ridge 2) accuracy of the impressions (must include all anatomic landmarks; proper extensions verified by border molding) 3) impression technique (anatomic/non-pressure, selective pressure, or functional/altered cast) 4) impression materials (PVS, alginate, polysulfide)
total occlusal load
determined by: 1) number of denture teeth (greater the number, greater the occlusal load) 2) width of occlusal surfaces (narrow width of occlusal surfaces to decrease amount of vertical and horizontal forces acting on the prosthesis) 3) occlusal efficiency (anatomic or non-anatomic)
lateral forces on teeth and implants
elliptical mastication cycle generates lateral forces
goal of treatment planning
enhance the probability of success by accounting for the risks associated with the treatment
casting
fabricating an object by pouring molten metal into a mold
requirements for clasp assembly: flexibility
flexibility of a retentive clasp is determined by: 1) length 2) diameter 3) cross-sectional form 4) degree of taper 5) type of alloy
crown preparation dimensions
for adequate resistance and retention form: 1) minimum occluso-cervical height: -premolar and anterior crown preps: 3mm -molar crown preps: 4mm 2) taper: 6-10 degrees total occlusal convergence
elongation
how easily the alloy can be burnished
evaluating mounting
how to know if casts are mounted correctly: -contacts should match what you see in the mouth -accuracy of mounting is checked with foil shimstock
HOC adjustments
ideally, the reciprocating arm should be at the junction of middle and gingival 1/3's of the tooth
framework misfit
if framework still doesn't fit after adjustments are made, you must determine where error has occurred during the fabrication process in order to make the correction
casting process
lost wax technique: a process in which a pattern, prepared in the shape of missing tooth structure, is embedded in a casting investment and burned out to produce a mold cavity into which molten metal is cast (will give a replica of the initial wax pattern)
restoring endodontically treated teeth
may be restored with: 1) direct restoration (composite) - only for anterior teeth with minimal loss of tooth structure 2) indirect restoration (onlay or crown) - most cases and virtually all posterior teeth (decreased risk of fracture and bacterial recontamination)
secondary retention for RPD
provided by the same factors which contribute to retention of a complete denture, including: 1) adhesion forces 2) cohesion forces 3) atmospheric pressure (full palate and beading - for upper RPDs) 4) physiologic molding around the polished surfaces of the denture base 5) gravity (for lower RPDs)
general treatment after an implant failure
replacement with another implant (however, significantly lower success rates compared to initial implant placement)
yield strength
the amount of stress that the alloy can resist before permanent deformation
transverse forces on implants
the distance from the point of occlusal contact to the abutment-fixture junction forms the lever arm for the bending movement induced by a transverse force
classification of dental alloys based on composition
the most important classification of dental alloys: 1) high noble alloys: -must have 60% noble metal content and 40% gold 2) noble alloys: -must have at least 25% or greater noble metal content 3) base materials: -less than 25% noble metal content
texture scan tool
used to evaluate definition of the prep and finish lines
using metal on occlusal surfaces
when using metal on occlusal surface, porcelain-metal junction must not be located in occlusal stress-bearing area due to high risk of fracture
RPD laboratory prescription forms
-communication tool with the dental lab tech -aim for clear and concise communication -draw design for RPD framework -don't assume; include all info: 1) major connector (beading, distance from gingival margins, etc) 2) guide planes 3) rest seats, including indirect retainers 4) retentive clasps (type, location, amount of undercut to engage) 5) reciprocal clasps 6) minor connector for acrylic resin base (open lattice or mesh) 7) shade if tube teeth or facings 8) tissue stops (if necessary)
purpose of FPD framework try-in
-confirm fit before application of porcelain -verify mounting is accurate
support for distal extension RPDs
-contour and quality of residual ridge -extent of coverage of residual ridge -accuracy and fit of denture base -design considerations -determine occlusal load
sectioning the working cast
-cuts made with saw to allow removal of individual segments and teeth from the base -important not to cut or damage margins -cuts must be parallel to the pin and the long axis of the preparation to ensure the die is readily removable
working cast fabrication
-impression trimmed and boxed -impression poured in die stone (type IV gypsum) for increased strength and decreased expansion -must be vacuum mixed -evaluate cast (no voids on margins, minimal voids on occlusal axial surfaces) -cast trimmed to horse-shoe shape (15mm width and 10-12mm height) -index system ("pindexed cast") created with pins (small holes drilled into the bottom of the cast- metal pins are glued into place) -pins must be rigid and have only 1 path of insertion (2-pronged double pins are naturally retentive; single pronged pins usually have some anti-rotation component built in) -stone base poured around pins -after stone sets, final trimming is done (first and second pours flush with each other)
solubility and microstructure configuration of dental metals and alloys
-in their molten state, metals dissolve to various degrees into one another, allowing them to form alloys in the solid state -therefore, we can have alloys where: 1) elements are completely soluble in one another (single phase alloys) 2) elements assume specific and regular configurations (ordered solutions) 3) elements are not soluble in one another (multiple phase alloys) - leads to higher corrosion
ideal ceramic preparations
-isthmus 1/3-1/2 intercuspal distance -pulpal floor depth 1.5-2mm -occlusal reduction 2mm (functional cusp) and 1.5mm (non-functional cusp) -butt joint margin -internal axial walls taper 6-10 degrees (divergent) -interproximal flare 100-120 degrees -supragingival margins -always check adjacent tooth condition of restorations over-contoured or rough on the surface (read image better and help build an ideal contact)
decision-making process: why choose an onlay?
-lack of supporting dentin under cusps (weakened/compromised) -horizontal cracks on tooth structure (cover cusps and protect them from fracture) -lack of occlusal clearance
indications for indirect ceramic restorations
-large carious lesions or large existing restorations which need repair -presence of horizontal cracks (protect cusps) -esthetics (ceramic) -allergies to metal (ceramic)
zoom tool
-lock surface -trim areas we want to re-scan -zoom in
RPI philosophy: Kratochvil vs Krol
-major difference is the length of the proximal plate: 1) Kratochvil advocates an extensive contact of the proximal plate with the tooth surface with physiologic relief (for secondary retention) 2) Krol advocates minimal contact of the proximal plate with the tooth surface and surrounding tissue (to avoid detrimental forces) -at UIC: we advocate somewhere in between (proximal plate should contact 1/2-2/3 of the occluso-gingival height of the distal proximal surface of the distal abutment tooth)
platinum (Pt)
-major metal -bluish-white (tends to lighten the color of yellow gold-based alloys) -tough, ductile, and malleable (increases hardness and elastic properties of gold) -very dense (easy to cast) -expensive
silver (Ag)
-major metal -hardener -effective in neutralizing the reddish color of copper-containing alloys -silver oxides can discolor ceramic ("greening" of porcelain)
copper (Cu)
-major metal -hardener -imparts a reddish color to gold-based alloys
palladium (Pd)
-major metal -hardener -pronounced whitening effect on gold-based alloys (white metal somewhat darker than platinum) -more than 10% palladium --> alloy will be white (even in the presence of gold) -low density (hard to cast)
gold (Au)
-major metal -yellow color -low tarnish and corrosion (biocompatible) -low strength and hardness (easy to finish and polish) -most ductile and malleable of all metals (able to burnish and adapt margins) -very dense (easy to cast) -readily alloyed with other metals
preliminary RPD design form (before the appointment)
-form is for you to make sure you do not forget any components -should include ALL information that you check off as you go during the appointment: 1) guide planes and their references 2) rest seats and reduction amount, including indirect retainers 3) undercuts that need to be created (location and depth) 4) height of contours that need to be adjusted (especially for suprabulge clasps and reciprocal clasps) 5) clasps 6) minor connectors 7) major connectors
risks associated with procedures for increasing clinical crown length
-furcation exposure -tooth mobility -poor C:R ratio -unacceptable esthetics
impressions for distal extensions
-goal: take impression of functional form of residual ridge for best support (prevent torquing of the abutment tooth when biting forces are applied to the distal extension) -techniques: 1) single step selective pressure impression with full-arch custom tray (used in all RPD classifications) 2) altered cast (2-stage) impression with partial arch custom tray attached to metal framework (mostly used for discrepancies)
bur selection for RPD tooth preparations
-guide planes: cylindrical diamond -cingulum rests: #35 inverted cone and/or cylindrical chamfer diamond -premolar occlusal rest: #4, #6 round burs -molar occlusal rests: #4, #6, #8 round burs
contraindications for indirect ceramic restorations
-high caries risk -heavy occlusal forces (parafunctional habits) -inability to maintain a dry operating field (ceramic bonded restorations) -subgingival preparations (same reason as above)
requirements for PFM alloys
-high strength (support porcelain and resist bending) -high castability (captures fine details and excellent marginal adaptation) -melting range above ceramic firing temperature (resist deformation) -CTE compatible to dental ceramic CTE -bonds to porcelain -stable color (greenish discoloration of stump teeth related to silver content in the metal alloy)
assessing remaining tooth structure
-how much tooth structure is remaining? -what is the apical extent of the caries? -how much tooth structure is anticipated to be remaining after caries excavation? **the single most important prognostic factor is the amount of remaining coronal tooth structure
crown to root ratio
-ideal = 1:2 -realistic optimum = 2:3 -minimum = 1:1
when is an interocclusal record indicated?
-if casts can be hand-articulated and casts are stable, an interocclusal record should NOT be used -occlusal registration should be used when casts cannot be hand-articulated due to lack of tripod contact (ex: FPD #19=21 with tooth #18 missing)
goals for scanning occlusion (bite registration)
-make sure patient is occluding properly -scan from most distal teeth captured on previous scans to most mesial ones -include at least 4 teeth (good axial data for design) -2-3mm of gingival tissue on buccal and lingual surfaces -support scanner on patient's cheeks (not their gums or teeth) -alignment of the bite depends on the quality of the data scanned from the buccal surfaces of the maxillary and mandibular teeth
elements to include on lab prescription for PFM FPD framework
-margin design -pontic design -occlusal design -type of alloy
RPI contraindications
-mesial rest not possible -soft tissue undercut is >1mm at 4-5mm below the buccal gingival margin of the abutment tooth -vestibular depth is 5mm or less -lack of attached gingiva -extremely tilted crowns -short clinical crowns
tin (Sn)
-minor metal -hardener -readily forms oxides (contributes to metal-ceramic bond)
zinc (Zn)
-minor metal -oxygen scavenger (minimizes gas porosities) -referred to as a deoxidizing agent
gallium (Ga)
-minor metal -readily forms oxides (contributes to metal-ceramic bond)
indium (In)
-minor metal -readily forms oxides (contributes to metal-ceramic bond) -replaces Zn as oxygen scavenger
iridium (Ir), ruthenium (Ru), and rhodium (Rh)
-minor metals -extremely high melting points -grain refiners (keep grain size small)
endodontic failures
-most common reason: inadequate cleansing/shaping and obturation of root canal system -success rate for specialists is higher than for general practitioners
restorative failures
-most common reason: marginal leakage around provisional or final restoration may re-contaminate canals -coronal sealing of root canal system must be accomplished ASAP after RCT completion
design casts and master casts
-must be sent with lab prescription -both casts should be surveyed but marked differently -master cast: tripods, exact points of undercut (red), HOC of abutment teeth -design cast: full design components -casted components in BLUE except tissue stop in RED -wrought wire and acrylic base extensions in RED
core build-ups
-necessary for teeth that require a crown and have significant amount of missing structure -help to provide ideal crown preparation retention and resistance form -completed with either amalgam or composite
noble alloys vs base alloys
-noble alloys: lower casting temperature, higher density, adequate strength for clinical application and lower elastic modulus (easier to cast compared to base alloys) -base alloys: higher casting temperature, lower density, increased hardness, lower elongation (rigid), higher strength (resists more stress) - harder to cast compared to noble alloys
ideal contour and quality of residual ridge (stress bearing areas)
-non-resorbing area (stress bearing area) -cortical bone covering dense cancellous bone -broad, flat crest -increase height of ridge (shallow vestibule/low ridge height = not as much horizontal stability against horizontal forces) -saddle shape to take occlusal loads -covered by firm, dense, fibrous CT (keratinized and attached)
occlusal design
-occlusal contacts may be in either metal or porcelain -porcelain is more esthetic and easier to adjust -metal indicated for limited interocclusal space
guide plane preparation criteria
-parallel to long axis of the tooth -flat occluso-gingivally -curved to follow original tooth contour bucco-lingually -no line angles -posterior teeth: 1/3 B-L width of tooth (2/3 cusp tip to cusp tip); 2/3 length of tooth from marginal ridge toward cervical aspect of clinical crown -anterior teeth: usually placed to the linguoproximal aspect for esthetics; may involve the proximal surface if increasing space for a replacement tooth
general guide plane preparation criteria
-parallel to the path of insertion (determined by surveying diagnostic cast) -flat occluso-gingivally -curved to follow original tooth contour bucco-lingually -no sharp line angles -entire preparation in enamel -smooth surface
dental soldering
-performed to correct for minor misfit or dimensional change of FPD after casting -procedure: 1) framework is sectioned (to approximately the thickness of a business card) 2) individual segments are tried in and fit evaluated 3) if fit of each abutment is acceptable, pieces are re-joined in correct position intraorally with resin index 4) framework is returned to lab for soldering
post width
-post diameter should not exceed 1/3 of the total cross-sectional root diameter -increasing post diameter will reduce thickness and strength of radicular dentin and increase stress in the tooth (leading to root fracture)
requirements for clasp assembly: encirclement
-prevents horizontal tooth movement within the clasp assembly -clasp assembly must either: 1) encompass more than 180º of the circumference of the abutment tooth, OR 2) incorporate a minimum of 3 widely separated points (tripod) of contact on the abutment tooth
mandibular support for distal extension RPDs
-primary stress bearing areas of the mandible: 1) buccal shelf (dense cortical bone perpendicular to occlusal forces) 2) retromolar pad (does not resorb [can use as a reference point for setting denture teeth]; glandular and loose CT) -lingual slope of residual ridge provides secondary support -crest of residual ridge is NOT a supportive area in the mandible (continuous ridge resorption; cancellous bone in nature [needs relief])
maxillary support for distal extension RPDs
-primary stress bearing areas of the maxilla: 1) lateral hard palate (try to cover for more support) 2) posterior ridge (major support for distal extension RPDs) -B and L slopes will counteract horizontal rotational forces (secondary support) -relief is necessary on incisive papilla and median palatal raphe areas -tissues covering residual ridge must be less compressible than tissue covering palatal areas -pre-prosthetic surgery: tuberosity reduction, torus removal, CTG, etc
tooth and tissue supported RPD
-problem: movement around the fulcrum line (distal-most rest on one side to the distal-most rest on the other side) -anterior to this fulcrum line provides dental-alveolar support -posterior to this fulcrum line provides muco-osseous support (tissue is more depressible) -movement of the prosthesis during function should not introduce unfavorable forces to the teeth -goal is to minimize these unfavorable forces using stress-releasing clasp assemblies
requirements for clasp assembly: support
-provided by rests (vertical support for the RPD framework) -resist vertical forces applied towards the gingival tissue -ex: occlusal, cingulum, ball, incisal rests
requirements for clasp assembly: retention
-provided by retentive clasp -resist dislodging forces (retain prosthesis in proper position) -retentive arm engages undercuts 0.01" or 0.02" -ideal distance between the HOC and engaging undercut: shorter is better (more gingival convergence, more retention, patient feels like the prosthesis is more stable) - B in image
requirements for clasp assembly: reciprocation
-provided by the reciprocal arm -resists tipping forces as the retentive clasp arm flexes as it passes over the HOC and engages an undercut -contacts the tooth before the retentive arm is passed over the HOC -place in the middle or lower 1/3 of the tooth surface
requirements for clasp assembly: stabilization and bracing
-provided by the reciprocal arm (placed on the opposite surface of the retentive arm) -resist horizontal displacing forces in terms of the whole partial framework (stability) and also reciprocation of the movement around the vertical axis of rotation on the distal abutment tooth (bracing) -place in the middle or lower 1/3 of the tooth surface -must be rigid
denture base
-provides direct support and retention of denture teeth (make sure to embed enough denture tooth into acrylic denture base for sufficient retention) -transfers occlusal forces to supporting structures -provides esthetics (lip support, replacement of missing soft and hard tissues to establish VDO) -prevents migration of remaining teeth (vertical and horizontal) -stimulates underlying tissue (tissues placed under functional stress within their physiologic tolerance may maintain form and tone better; prevents atrophy)
components and characteristics of reciprocal clasps
-reciprocation: opposes tipping forces as the retentive clasp arm flexes as it passes over the HOC of the abutment tooth during seating of the RPD -stability: contributes to the horizontal stability of the RPD -tapers in thickness but NOT in width (to maintain rigidity) -stays above the HOC, which should be placed in the middle or lower 1/3 of the tooth
how to trim bite registration
-remove any material contacting soft tissue -shorten flanges to leave about 1.5mm depth of the cusps -remove marginal ridge detail and depths of fossae (only see cusp tips) using an acrylic bur -goal: no spring or bounce between the casts, no gap between recording material and casts
indirect retainers
-resist rotation around the fulcrum line when the distal extension area is moving away from tissue -ideally should be located perpendicular to half of the fulcrum line to be most effective -avoid using mandibular incisors and maxillary laterals (try to place on the healthiest/strongest teeth possible) -provide positive vertical stop by using a rest (occlusal, lingual ball, cingulum, etc)
milling
-restoration will be milled out of a block of ceramic -attachment between the restoration and the block of ceramic is called the sprue -sprue should be located as far away from the margin and contact areas as possible (place to the lingual) -milling modes: 1) posterior crowns: standard milling 2) anterior teeth: either standard or detailed milling 3) inlays and onlays: detailed milling
tooth supported RPD
-rests are adjacent to edentulous space -clasp options: Akers (clasp of choice for tooth-supported scenarios) or I-bar (for esthetics on anterior abutment teeth, if soft tissue and anatomy allows)
over-trimming the die
-results in poor emergence profile and over-contoured final restorations -bulky restorations promote plaque accumulation and gingival inflammation
degree of clasp taper and its impact on flexibility
-retentive clasps have uniform taper in both thickness and width (more flexible) -reciprocal clasps have uniform taper in thickness only (less flexible)
distal extension RPDs
-shared support and some retention from tissue of extension area and the abutment tooth (tissue is more compressible during function) -design must anticipate movements of RPD during function to prevent damaging forces (indirect retainers) -amount of movement is dependent upon: 1) surface area of mucosal contact (how many teeth are missing) 2) thickness and compressibility of supporting mucosa 3) adaptation of denture base to supporting tissues 4) refinement of occlusal factors
chemistry of alloys
-solid solution with 2 or more elements forming arrangements -many different properties (physical, mechanical, biological) -do not solidify at a fixed point (they instead have a solidification temperature range)
guidelines for core build-up
1) crown margin must be on solid, sound tooth structure (dentin or enamel), NOT on build-up material 2) crown/core build-up margin must not encroach on the biologic width 3) remaining tooth structure should provide adequate retention for core build-up material (need 2 remaining sound axial walls at least 1mm wide and 3-4mm high; all other walls must be at least 1.5-2mm high)
custom vs pre-fabricated posts
1) custom posts: -usually a single piece (cast post and core build-up together) -extremely strong 2) pre-fabricated posts: -post cemented/bonded into root canal -around the post, we build up with composite or amalgam
what is the minimum connector height for PFM FPDs?
2mm (may need to increase connector size in areas of high load or tension)
T/F: for mandibular partials, you must border mold only the anterior lingual area
F -- for mandibular partials, you must border mold the entire lingual area
T/F: use soft baseplate wax when setting denture teeth
F -- use hard baseplate wax (soft may move teeth)
what tool can you use to help verify margin lines if needed?
HD photo tool
T/F: overall, tooth loss rate for compromised teeth is not affected by aggressive disease when teeth are properly treated and maintained
T
T/F: second pours are NOT recommended for mounting dies
T
which metals readily form oxides and contribute to metal-ceramic bonding properties?
Zn, Sn, In, and Ga -associated with the oxide layer on the surface of an alloy in contact with porcelain -very important in terms of the metal-ceramic bond
assessing tooth restorability
a complex decision taking into account: 1) restorative prognosis 2) periodontal prognosis 3) endodontic prognosis
inlay
a fixed intracoronal restoration made outside of a tooth (indirect) to correspond to the form of the prepared cavity, which is then luted into the tooth
prognosis
a prediction of the probable course and outcome of a disease, and the likelihood of recovery from a disease
onlay
a restoration that restores 1 or more cusps and adjoining occlusal surfaces (or the entire occlusal surface) and is retained by mechanical or adhesive means
implant success
an implant is considered successful when it provides functional service for at least 5 years in 75% of cases
metal representation on the periodic table of elements
as a group, metals represent about 2/3 of the periodic table
classification of dental alloys
based on: 1) type of restoration 2) composition 3) mechanical properties
tooth evaluation after RCT
before proceeding with the restoration, RCT-treated tooth must be assessed for the following: -apical seal -no sensitivity to pressure -no exudate -no fistula -no active inflammation
metallic elements in dental alloys
can be divided into 2 major groups: 1) noble metals: -resistant to oxidation, tarnish, and corrosion during heating, casting, soldering, and when used intraorally -ex: gold, platinum, palladium, grain refiners (Ru, Rh, Ir) 2) base metals: -any metallic element that does not resist oxidation, tarnish and corrosion -ex: copper, nickel, zinc, gallium, silver, tin, indium
metal RPD framework try-in
check the fit of the framework on your master cast: -is the design correct? -is there a rock? -rest seats are flush and fully seated? -clasps are engaging the correct undercut? -major connector is well-adapted to tissue surface? -note distance between lattice and tissue surface -check occlusion
base dental cast alloys
chromium, cobalt, nickel, beryllium, aluminum, etc
microstructure strengthening mechanisms
cold-working: squeezing, bending, shearing, and/or rolling cast metal to break down grains into smaller units which then become entangled in each other and develop an elongated fibrous structure which can be used for a specific dental use (from cast --> wrought)
what clasp assembly should we use for distal extension scenarios when RPI is contraindicated?
combination clasp
what happens when core build-up guidelines cannot be met?
consider: 1) placing finish line subgingivally 2) crown lengthening 3) orthodontic extrusion 4) post
what to do if there is less than 1.5-2mm tooth structure remaining for Ferrule effect?
consider: 1) placing finish line subgingivally 2) surgical crown lengthening 3) orthodontic extrusion
secondary retention of denture base
denture base requires B and L concavities on the tissue surfaces to replicate physiology and enhance retention
pros and cons of indirect gold restorations
1) pros: -high strength and ductility -ability to be cast accurately -malleability of the material (can seal margins) -less occlusal and axial reduction needed 2) cons: -not bonded -sensitivity to material (gold allergy) -esthetics
what components can provide reciprocation for RPD?
1) reciprocal clasp 2) plate 3) minor connector
indirect restoration materials
1) resin (CAD/CAM) 2) gold 3) ceramics (CAD/CAM or conventional)
requirements for clasp assembly
1) retention 2) flexibility 3) stabilization (bracing) 4) reciprocation 5) passivity 6) support 7) encirclement
components of clasp assembly
1) retentive clasp (for retention) 2) reciprocal clasp (for stabilization of RPD and reciprocation of abutment tooth) 3) rest (for support) 4) minor connectors/proximal plate (for encirclement)
clasp assembly options for tilted distal molar abutments
1) ring clasp 2) Akers clasp engaging 0.01" undercut created at DB 3) Akers clasp engaging 0.01" undercut at DL 4) elongated MO rest with or without bracing clasps **always survey HOC around the entire tooth and make adjustments to allow proper positioning of clasps**
types of extracoronal clasp assemblies
1) suprabulge clasps: -approach the undercut from the occlusal -ex: Akers clasp, embrasure clasp, ring clasp 2) infrabulge clasps: -approach the survey line from the gingival -ex: I-bar and variations (T, modified T, Y bar clasps)
classification of dental alloys based on mechanical properties
-defined based on gold-containing alloys (not very useful anymore; outdated) -classification uses type I-IV based on alloy hardness (each recommended for intraoral use based on hardness and amount of force the restoration is likely to receive) 1) type I alloy (soft): -used for restorations subjected to low stress (ex: some inlays) -good elongation values with lower strength 2) type II alloy (medium): -used for restorations subjected to moderate stress (ex: inlays and onlays) -good elongation values with slightly higher strength 3) type III alloy (hard): -used for restorations subjected to high stress (ex: crowns, thick-veneer crowns, short-span FPDs) -adequate strength but lower than extra-hard 4) type IV alloy (extra hard): -used for restorations subjected to very high stress (ex: thin-veneer crowns, long-span FPDs, RPDs) -hardest and strongest -cannot burnish (elongation values too low)
connector design
-design of connectors is extremely critical for strength -connector height is more important than width -bending varies inversely with the cube of the occluso-gingival thickness (height) of the pontic
RPD high speed bur block and tooth preparation
-diamond or carbide burs -polish with polishing burs after preparation is complete -do not anesthetize patient during preparation
FPD framework fabrication
-die spacer painted onto dies to provide space for cement -ISO standard for maximum film thickness: 25 microns (water based cements) or 50 microns (resin based cements) -full contour wax-up completed to ideal -wax cut-back to ensure adequate thickness of metal (0.2-0.3mm minimum), space for even thickness of porcelain (0.8mm minimum, 2.0mm maximum), and sufficient connector dimensions -after wax-up is completed, sprue is attached and will form a channel through which molten alloy will travel into a mold -pattern encased in a plaster-like material called investment to create a mold -wax is eliminated from investment using a high-heat furnace -molten metal is poured into the hollow mold in a process called casting -final adjustments are made (divestment, sprue removal, metal finished to make uniform surface and remove irregularities, porcelain-metal junctions refined)
components and characteristics of retentive clasps
-direct retainer which provides direct retention -3 parts: 1) proximal 1/3: rigid 2) middle 1/3: limited flexibility 3) terminal 1/3: flexible -tapers in width and thickness to increase flexibility -terminal tip of a flexible arm engages an external surface of an abutment tooth in an area cervical to the greatest convexity (HOC) or a prepared depression (dimple) -the arm of the rest is above the HOC
possible causes of mounting discrepancies
-distorted models -centric latch not locked -casts moved or shifted -casts not fully seated in bite record (if used) -bite record incorrect (if used)
clinical FPD framework try-in
-evaluate margins with explorer -margins should be closed on both preparations simultaneously -passive fit without rocking -if margins are not completely closed, check fit of intaglio surface using Fit Checker (silicone material used to identify areas that are binding and require relief) -radiograph should be taken to confirm complete seating and closed margins -check interocclusal clearance (minimum 0.5-0.8mm space needed) -adjust if needed with Al2O3 stone (preferred) or fine diamond -use calipers to check thickness while adjusting (minimum thickness of metal 0.2-0.3mm) - avoid perforating framework -verify mounting (may take "bite check" to verify accuracy of articulator mounting with PVS or resin)
MOD onlay #14
-evaluate occlusion -MOD prep using 856 diamond bur -proximal boxes rounded and clear at least 0.5-1mm -exit angle open beyond contact area -buccal and lingual walls 90 degrees to the cavosurface margin -gingival to occlusal divergence of 6 to 10 degrees -axial wall depth 1.25-1.5 M-D -no undercuts -occlusal reduction at least 1.5mm -buccal cusp butt joint (1.5-2mm reduction over functional cusps; at least 1.5mm over non-functional cusps) -line angles and point angles rounded
die trimming
-excessive stone is trimmed to better visualize finish line and facilitate ease of waxing by lab tech -large excess removed with carbide lab bur on slow speed ("ditching the die") -detailed trimming completed with sharp scalpel -use of magnification highly recommended -mark finish line with wax pencil (optional) -objectives: 1) ideal root form emergence profile (~3mm below the margin) 2) independently removable dies 3) smooth surfaces 4) access to margins
infrabulge clasps (bar clasps)
-extracoronal clasp assemblies of the bar-type (I-bar, T-bar, Y-bar and their modified versions) -come from below the HOC (near gingiva) and then extend outward towards the HOC to engage the undercut - clasp arm engages 0.01" undercut in the gingival 1/3 of the tooth and continues to the HOC -only 1 terminal of the clasp arm engages an undercut -more esthetic than suprabulge clasps (contacts less coronal tooth structure so you don't see it as much)
aspects to avoid for ceramic preparations
-feather edge margins (too thin and too weak for ceramic) -parallel walls and sharp internal line angles (stress areas for ceramic) -insufficient isthmus width -interproximal undercuts (won't be able to properly seat restorations)
RPI clasp assembly
-first choice clasp assembly for distal extension scenarios -in a properly designed RPI clasp assembly, the I-bar retentive clasp disengages when the distal extension is loaded -basically changes the class lever (moves fulcrum line anterior by putting a mesial rest instead of a distal one) -R: mesial rest -P: distal proximal plate -I: I-bar engaging 0.01" undercut located either at the greatest curvature of the buccal surface of the tooth (mid-B) or mesial (but still distal to the positive mesial seat)
prognosis classification rules
-five classes (A, B, C, D, and X) -requires 3 steps: 1) single most severe criterion determines the tooth's overall class 2) anatomic risk factors and/or iatrogenic compromising factors may result in a drop of a class for an individual tooth (more than 2 findings) 3) patient-level risk factors may result in a decreased prognosis for the dentition
clasp options for Kennedy class II modification cases
-for the tooth-supported edentulous area: Akers clasp (1st choice) -for the tooth and tissue-supported edentulous area: RPI (1st choice) -other options: 1) combination clasp engaging 0.02" MB undercut (flexible due to wrought wire) 2) cast clasp engaging 0.01" MB undercut (less flexible) -selection is case by case and is dependent on: 1) retention 2) span of the distal edentulous area 3) health of the abutment tooth 4) mastication forces
grain refinement and size
-specific metals with very high melting points (which do not melt during the casting process) are added in small amounts to develop centers for nucleating grains by acting as "seeds" around which grains will grow as the alloy cools (grain refinement process) -leads to more uniform and homogenous final alloy materials -tensile strength and elongation are improved significantly when these metals are added (up to 30%) -hardness yield strength is not affected as much from grain refinement -grain refining elements commonly used for this process include Iridium (Ir), Ruthenium (Ru), Rhodium (RH), or Rhenium (Re)
metal-ceramic bond: mechanical interlocking
-surface topography of the metal-ceramic interface plays a large part in adhesion -ceramic penetrating into a rough metal surface can mechanically interlock with the metal, improving adhesion
HD photo tool
-take an HD photo by tapping the button on the scanner -green box surrounds the image to be captured -gives an even clearer view of prep from different angles
metal framework fabrication
-technician designs and creates wax framework on working cast -this wax pattern is invested and cast in metal alloy -metal framework is contoured and refined before it is returned to dentist for try-in
corrosion
-the deterioration of metal through oxidative processes -all dental alloys will corrode to some extent intraorally -corrosion leads to poor esthetics, compromised physical properties, and increased biological irritation (poor biocompatibility) -higher percentage of base metals is associated with increased risk of corrosion -more phases (multiple phase alloys) associated with more corrosion
single step impression
-the final cast will be used to fabricate the entire RPD -the custom tray, amount of wax relief, and viscosity of impression material allows for a functional impression in distal extension areas -custom tray will have wax relief on all areas except the primary stress bearing areas -after this technique, you will receive a framework fabricated onto the master cast (if discrepancy exists in distal extension area, perform altered cast technique) -this method involves less clinical and laboratory steps than the altered cast technique (less procedural errors)
combination clasp assembly
-the second choice for stress-releasing clasp assembly needed for distal extension scenarios -can have either a mesial or distal rest -distal proximal plate -combination of wrought wire retentive clasp engaging 0.02" MB undercut and a cast reciprocal clasp -flexibility of the wrought wire makes it stress releasing
Ferrule effect
-there should be at least 1.5-2mm of sound tooth structure from core margin to finish line (this is critical for long-term prognosis) -crown should envelop remaining sound tooth structure to properly protect tooth from fracture after being prepared for a crown -when ferrule is absent, occlusal forces are concentrated at the junction of post and core (risk of post or tooth fracture increases)
requirements for clasp assembly: passivity
-there should be no active forces on the tooth after the RPD is fully seated -retention function is activated only when a dislodging force is applied (i.e. when you are removing the partial)
why don't we use pure metals?
-they don't have appropriate properties by themselves to serve useful in the oral environment -alloys are used to get adequate properties for dental applications because none of the metallic elements by themselves have properties that are suitable
pontic design
-tissue side of the pontic may contact in either metal or porcelain -both are very biocompatible if well-polished or glazed -porcelain is easier to adjust if contact is heavy or to add if contact is light -metal indicated when interocclusal space is limited and/or maximum strength is needed (parafunction)
checking occlusal clearance on Trios3Shape
-under analyze page, select "clearance" -evaluate if there is enough space for bulk of restorative material
checking for undercuts on Trios3Shape
-under analyze page, tilt the model -once you have the correct path of insertion, select "use view" tool to evaluate undercuts -red = undercut (bad)
refining anatomy
-use "morph tool" to adjust the shape of a surface of the tooth (shift + scroll on mouse to adjust tool diameter) -use "wax knife" to add/remove/smooth material on the tooth -use "cross-section tool" to slice the restoration and measure specific thickness and modify contours
hard and soft baseplate wax
-use hard baseplate wax for setting denture teeth -use soft baseplate wax for wax relief and block-outs
stress-releasing clasp assemblies
-used in distal extension scenarios (tooth and tissue supported RPD with unfavorable forces around fulcrum line) -examples: 1) RPI clasp 2) combination clasp
reverse Akers clasp
-used on bicuspids and cuspids when the undercut is located on the distal surface of the tooth -adequate space needs to be prepared on the ML surface for a minor connector -should not interfere with static and dynamic occlusion -could be used for distal extension cases but superior border of reverse Akers clasp should be in point contact with the HOC -need a mesial rest -don't use this type of clasp (unesthetic and technique sensitive)
ring clasp
-used specifically for tilted molars (very specific scenarios): 1) mandibular molars: mesially tilted with undercut on ML 2) maxillary molars: mesially and buccally tilted with undercut on MB -HOC's need to be low (near gingiva) all the way around, except at the point of undercut -ring clasp starts from the mesial rest seat all the way around and engages the terminal tip -has lots of components (need to prepare more tooth structure) -more flexible since it must adapt all the way around the tooth (distorts easily, difficult to adjust)
tube teeth
-used with metal base when there is very limited restorative space -minimally resorbed ridge (but not a recent extraction site) -cannot be relined -single tooth replacements -post hole is prepared in tissue side of denture tooth and the post is waxed and cast on the RPD metal framework (mechanical retention) -must provide denture tooth at time of framework fabrication, preferably set in its ideal location
facings
-used with metal base when there is very limited restorative space (a non-resorbed ridge but not a recent extraction site) -cannot be relined -single tooth replacements (usually in the anterior region) -metal framework has a post where the acrylic resin veneer will be cemented after fit, occlusion, and esthetics have been confirmed (metal framework extends all the way to the lingual surfaces of the tooth and a denture tooth which slides into a slot is attached on the facial aspect) -acrylic resin veneer will have metal show through (limited esthetics, shapes and sizes) -must provide denture tooth at time of framework fabrication (preferably set in its ideal location)
anterior tooth guide plane preparation criteria
-usually placed to the linguoproximal aspect to preserve esthetics -may involve the proximal surface if increasing space for a replacement tooth
verifying overall tooth position
-verify the position of the restoration in different angles and activate opposing teeth -use the "transform tool" to adjust the size and position of the restoration -use "connect margin tool" in automatic tools to connect restoration to your finish line
chemistry of metals
-very specific characteristics based on metallic bonding -metallic bonding units are composed of atoms with electrons in between (no giving or sharing of electrons occurs; they are simply floating and moving around to give each metal its properties) -very specific crystal arrangement (mixing of similar crystals is easy; other arrangements mixed together are less soluble) -have a fixed melting point
interocclusal record
-when bite registration is needed, it is preferable to place only in the area of prepared teeth (easier to verify that patient is occluding properly compared to full-arch record) -PVS is the most common bite registration material (very stable and easy to use; captures more detail in grooves and pits than alginate impression - needs to be trimmed to accurately seat between casts)
type of alloy used for different clasps and its impact on flexibility
-wrought wire clasps are more flexible than cast alloy clasps -cast gold alloy clasps are more flexible than Cr-Co clasps
physical and mechanical properties of noble dental cast alloys
1) (yield) strength: the stress at which permanent deformation of the alloy occurs 2) hardness: a good indicator of an alloy to resist local permanent deformation under occlusal load; related to yield strength and also gives some indication of the difficulty of polishing the alloy 3) elongation: a measure of the ductility of the alloy; will indicate whether the alloy can be burnished (alloys with high elongation can be burnished without fracture)
endodontic treatment plan
1) RCT not indicated: -tooth normal -reversible pulpitis 2) RCT indicated: -irreversible pulpitis -necrotic pulp -prophylactic -tooth requires post for restorative purposes
types of denture bases
1) acrylic resin base: -attached to a minor connector (open lattice or mesh) of the RPD metal framework -most commonly used denture base -replaces missing hard and soft tissues -can be relined -denture teeth 2) metal base: -largely used for short span tooth-supported RPD (limited restorative space) -thermal conductivity -used with facings and tube teeth -cannot be relined -contraindications: distal extensions (Kennedy class I and II), recent extraction sites (will resorb)
denture tooth selections
1) acrylic resin denture teeth: -chemical bonding of denture tooth to acrylic base -size and shape can be modified to fit in edentulous site (usually smaller than natural teeth to reduce transfer of occlusal forces) -most widely used tooth selection for prosthesis -wide array of shapes, sizes, and shades available 2) porcelain denture teeth: -no longer used (studies have shown that porcelain teeth may increase ridge resorption rate) -rely on mechanical retention (diatoric holes) rather than chemical bonding -susceptible to fracture -cause wear on natural dentition
using Fit Checker
1) apply a light layer of lubricant (vaseline) to typodont teeth 2) inject or apply Fit Checker material to the internal surface of the restoration and seat in the mouth 3) remove once material is set (approx. 1 min) 4) adjust metal in any areas where material appears extremely thin 5) repeat above steps until thin uniform layer of silicone with no perforations is present
single step impression: after the appointment
1) box the impression (obtain a good landing area all around ~3mm) 2) pour the impression with type III gypsum stone (Coe-Cal or Microstone) 3) after 24-48 hrs, soak cast in warm water to soften compound 4) gently separate impression from the cast 5) trim the cast while preserving the vestibule
carat and fineness
1) carat (k): refers only to the gold content of an alloy and represents as 1/24 part of the whole (ex: 24 carats indicates pure gold) 2) fineness: refers only to the gold content of an alloy and represents the numbers of part of gold in each 1,000 parts of alloy (ex: 18k gold would be designated at 750 fine or 0.750 fine)
factors affecting the metal-ceramic bond
1) ceramic wetting ability on the alloy surface 2) mechanical interlocking 3) chemical bonding 4) residual stresses that places ceramic into compression
single step impression: during the appointment
1) check that the custom tray (fabricated before the appointment) is not over-extended (want it to be under-extended to allow for border molding) 2) perform border molding in distal extension areas and all lingual vestibules (for mandibular cases) 3) reduce border molding to 0.5mm 4) remove baseplate wax 5) place relief holes 6) apply PVS adhesive (let dry for 10 minutes) 7) take PVS impression while border molding (light body on teeth and load tray with medium or heavy body)
indirect resin-based materials
1) composite resin (Paradigm MZ100) 2) resin-based ceramics (Cerasmart GC, Lava Ultimate 3M ESPE) 3) hybrids (Vita Enamic) - strongest of all resin-based materials
what can affect the castability of an alloy?
1) density of the alloy: -as density decreases, the alloy becomes harder to cast -density is important during the acceleration of the molten alloy into the mold during casting -alloys with high densities will generally accelerate faster and tend to form a complete casting more easily 2) melting range of the alloy: -as temperature increases, the alloy becomes harder to cast -desirable for dental casting alloys to have a relatively narrow melting range because it's easier to cast without problems -melting range determines the type of investment, burnout temperature, and type of heat source that must be used during casting -wider melting range = partially molten alloy for longer period of time (can lead to contamination in the alloy)
things to be submitted to the lab for RPD framework fabrication
1) design cast: -guide planes -rests -major connector -minor connectors (external finish line, lattice w/ or w/o tissue stop, etc) without any floating components -retentive clasp and reciprocal components -HOC and exact undercut to engage -tripod marks 2) master cast: -HOC and exact undercut to engage -tripod marks 3) lab prescription form: -clear and concise instructions -include all RPD components -draw design
indirect CAD/CAM ceramic materials
1) glass-based ceramics: -Feldspathic (Vitabloc Mark II, CEREC Blocs) -leucite-reinforced (IPS Empress CAD) -lithium disilicate (IPS eMax CAD) 2) high strength ceramics: -zirconia (IPS eMax ZirCAD)
gold vs traditional ceramic preparations
1) gold: -retention and resistance form critical -functional cusp: shoulder (collar) with bevel -non-functional cusp: external bevel (skirt) 2) ceramic: -retention and resistance form not as critical -NO bevels -rounded line angles
prognosis: evaluation of pathology and scale of severity
1) good prognosis (class A): -periodontal health and alveolar bone support: 80-100% -remaining sound tooth structure: 80-100% -endodontic condition: RCT for this tooth is straightforward or has a good existing RCT -occlusal plane and tooth position: tooth is in correct occlusal plane position and/or has slight deviation requiring minimal enameloplasty 2) fair prognosis (class B): -periodontal health and alveolar bone support: 50-80% -remaining sound tooth structure: 50-80% -endodontic condition: existing failing RCT that can be predictably re-treated or a tooth requiring more complex primary RCT -occlusal plane and tooth position: tooth disrupts the occlusal plane but can be adjusted to align it with the correct occlusal plane; tooth may require additional treatment to seal exposed dentin 3) questionable prognosis (class C): -periodontal health and alveolar bone support: 30-50% -remaining sound tooth structure: 30-50% -endodontic condition: tooth with acute or chronic failing RCT with a predictably difficult treatment -occlusal plane and tooth position: tooth disrupts the occlusal plane and requires multiple procedures to realign it with the occlusal plane 4) compromised prognosis (class D): -periodontal health and alveolar bone support: <30% -remaining sound tooth structure: <30% -endodontic condition: tooth has failing RCT that is not predictably treatable -occlusal plane and tooth position: tooth is severely out of occlusal plane or tilted such that treatment would reduce C:R ratio and affect the prognosis of the arch, or its position impacts adjacent teeth 5) non-restorable prognosis (class X): -periodontal health and alveolar bone support: tooth cannot be cleansed or maintained without acute outbreaks of periodontal infection -remaining sound tooth structure: no remaining supragingival sound tooth structure and/or internal resorption -endodontic condition: vertical root fracture or has repeated re-treatments including surgery without resolution -occlusal plane and tooth position: extreme super-eruption such that the tooth cannot be restored into function or would disrupt the arch as well as the opposing arch if attempted
steps to RPD mouth preparation
1) guide plane preparation, HOC adjustments, undercut creation 2) take alginate impression and pour in snap stone 3) verify all preparations are correct on surveyor (if not, repeat steps 1-2) 4) prepare rest seats (verify again with another alginate impression) 5) final impression with custom tray, border molding, and PVS
types of alloys
1) high noble alloy: -≥40% gold content -≥60% noble metal 2) noble alloy: -no stipulation for gold content -≥25% noble metal 3) base metal alloy: -no stipulation for gold content -<25% noble metal
alloy properties
1) high noble and noble alloys: -good mechanical properties -lower corrosion -easier finishing/polishing -reduced allergy risk -easier casting and more predictable marginal fit -higher cost 2) base metal alloys: -superior mechanical properties (strength and stiffness) -higher corrosion in acidic environments -more difficult finishing/polishing -risk of patient allergy -more difficult casting and marginal fit -lower cost
special design considerations to minimize forces on remaining teeth and tissues
1) horizontal rotational axis: -rotation around an axis generated from distal-most rest on one side to the distal-most rest on the other side is inevitable -tissue is more compressible than tooth -the more teeth missing, more support from the residual ridge is necessary 2) direct retainers on posterior abutment: -RPI -combination clasp 3) placement of indirect retainers: -cingulum rest, etc
direct retainers
1) intracoronal retainer: -a retainer which is cast or attached within the restored abutment tooth (inside the crown of the tooth) -pre-fabricated machined key and keyway -opposing vertical parallel walls in the keyway limit movement and resist removal of RPD through frictional resistance -used for a tooth-supported RPD only (NOT used for distal extension RPDs - no stress-breaker, may torque the abutment tooth, leading to mobility or possible tooth fracture) 2) extracoronal retainer: -utilizes mechanical resistance to displacement by components placed on or attached to the external surfaces of an abutment tooth -2 types: 1) manufactured attachments (non-rigid attachment system allows for vertical movement) 2) clasp-type retainers
marginal design
1) metal collar: -excellent adaptation -unesthetic 2) disappearing margin: -metal less visible -gray hue at gingival margin 3) porcelain butt margin: -good esthetics -risk for porcelain chipping -more demanding for lab
metal vs alloy
1) metal: pure substance which exists in elemental form (ex: gold, silver, zinc, etc) 2) alloy: mixture of 2 or more metals (or a metal with a non-metal)
Frankfort-Mandibular Plane Angle (FMA)
1) normal FMA: 25° +/- 5 2) high FMA: >30° 3) low FMA: <20° **low FMA's are associated with higher occlusal forces (very developed masseter and other mastication muscles)
options for increasing clinical crown length
1) osseous crown lengthening: requires recontouring of supporting bone from tooth of interest and adjacent teeth 2) orthodontic extrusion: increase clinical crown length on tooth of interest without affecting osseous levels on adjacent teeth (more "conservative")
post considerations
1) post length 2) post width 3) Ferrule effect
pros and cons of indirect ceramic restorations
1) pros: -adhesion -esthetics -enhanced durability, wear, and fit 2) cons: -repair is difficult -wear of opposing dentition (must be properly treated/polished/glazed after adjustments are made) -expensive technology
pros and cons of indirect resin restorations
1) pros: -easy to repair (composite) -easy intraoral adjustments -improved wear with opposing dentition 2) cons: -cannot be used for onlays -weaker than ceramics
single step impression: before the appointment
1) take preliminary impression to produce a diagnostic cast to fabricate a custom tray 2) place 2 thickness of soft baseplate wax over the teeth and tooth-supported edentulous areas and place 1 thickness of soft baseplate wax over the distal extension area (cut out tripod stops to prevent excessive seating) 3) place triad or acrylic resin over 4) trim vestibular extension to be 2mm short of the full depth with a scalpel (add finger rest on 1st molar region and place handle not to impinge on the impression taking procedure) 5) cure for 2 minutes and then flip over to cure intaglio for 1 minute 6) remove 2mm of wax from the inside of the custom tray to allow space for border molding compound
general loss rate of teeth vs implants over 15 years
1) tooth loss: 3.5-13.5% 2) implant loss: 0-33%
custom tray fabrication
1) vaseline diagnostic cast 2) add soft baseplate wax (2 layers on teeth and tooth-supported edentulous areas; 1 layer on distal extension areas [avoid primary stress-bearing areas]) 3) expose tripod stops 4) add triad custom tray material 5) cut borders to be 2mm from vestibular depth and make finger stops/handle 6) cure for 1 min; remove then cure for 1 min again and another 1 min for the intaglio (wax should not melt) 7) smooth borders 8) cut out excess wax to expose space for border molding compound
altered cast impression: during the appointment
1) verify complete seating and fit of the framework intraorally with disclosing wax 2) observe a discrepancy of framework relation to edentulous area on cast versus intraorally or patient has flabby compressible tissue in distal extension area 3) vaseline edentulous area on master cast and add a layer of soft baseplate wax as spacer for impression material 4) heat up edentulous side of framework and fully seat on cast 5) remove wax on top of the lattice 6) add a layer of triad on top of lattice area 2mm short of vestibule to allow space for border molding compound 7) after curing the triad, remove baseplate wax (if triad is not secure, add a thin layer of pattern resin to secure the custom tray to the framework) 8) border mold distal extension ares with compound 9) reduce border molding compound to 0.5mm 10) apply PVS adhesive and wait 10 mins to dry 11) take impression of distal extension area with medium or heavy body PVS while border molding (make sure rest seats are fully seated and press on rest seats ONLY; do NOT press on distal extension areas) 12) send impression with framework to dental lab -the dental lab will section your master cast, make retentive undercuts, bead, box, and pour a new master cast which will be used to process your denture teeth on acrylic base
welding vs soldering vs brazing
1) welding: 2 pieces of metal are joined without adding another metal 2) soldering: 2 pieces of metal are joined below 450°C by adding another metal 3) brazing: 2 pieces of metal are joined above 450°C by adding another metal
solidification process of dental alloys (microstructure)
1) when molten alloy is cooled, the first solid alloy particles that form are called nuclei (in the process of nucleation) 2) as cooling continues, the nuclei grow into crystals called grains 3) the grains enlarge until all the liquid is gone and then they meet and form boundaries between each other (coalescence of individual grains to form a grain structure)
classification of dental alloys based on type of restoration
3 subcategories: 1) full cast alloys: -alloy itself will be used as the clinical restoration (no porcelain overlying the surface; not esthetic) -polish easily -acceptable strength and hardness (durable but minimal wear to opposing teeth) -able to burnish (adapts to margins well) 2) porcelain bonding alloys: -higher strength alloy (must support brittle porcelain and resist bending) -high castability (captures fine detail and excellent marginal adaptation) -melting range compatible with porcelain (must be higher) -bonds to porcelain -stable color 3) RPD framework alloys: -must be able to make thin (reduce bulkiness) -light (maximize patient comfort) -low cost (large amount of metal needed) -rigid and strong (withstand occlusal function) -high elastic modulus and yield strength
