Lesson 8 & 9 Flashcards
metal-ceramic restoration, otherwise known as _____
PFM restoration (porcelain fused to metal)
one of the least conservative of tooth structures:
______ because incisal and occlusal surfaces are
always subjected to forces
thicker metal
one of the least conservative of tooth structures:
_______ maximum for incisal and _____ for molars
2 mm, 1.5 mm
porcelain fuse at temperatures of ____ and gold alloys melt
at this temperature
960 C
gold alloys melt
at this temperature
960 C
is a major consideration in the
fabrication of metal ceramic restoration
special alloy
FACTORS IN TOOTH PREPARATION
Biologic
Mechanical
Esthetic
Conservation of tooth structure
A. Biologic
B. Mechanical
C. Esthetic
A
Avoidance of overcontouring
A. Biologic
B. Mechanical
C. Esthetic
A
Supragingival margins
A. Biologic
B. Mechanical
C. Esthetic
A
Harmonious occlusion
A. Biologic
B. Mechanical
C. Esthetic
A
Protection againts tooth fracture
A. Biologic
B. Mechanical
C. Esthetic
A
Retention form, resistance form, deformation
A. Biologic
B. Mechanical
C. Esthetic
B
Minimum display of metal
A. Biologic
B. Mechanical
C. Esthetic
C
Maximum thickness of porcelain
A. Biologic
B. Mechanical
C. Esthetic
C
Porcelain occlusal surfaces, subgingival margins
A. Biologic
B. Mechanical
C. Esthetic
C
→ teeth that require complete coverage
→ gingival involvement
→ in conjunction with post & crown
METAL-CERAMIC CROWN PREPARATION
can be modified for cingulum & occlusal restorations
METAL-CERAMIC CROWN PREPARATION
→ if all-ceramic crown is contraindicated
o not efficacious for long spans
METAL-CERAMIC CROWN PREPARATION
CONTRAINDICATIONS
large pulp chamber
intact buccal wall
presence of active caries
→ untreated periodontal disease
→ when more conservative retainer is technically feasible
METAL-CERAMIC CROWN PREPARATION
ADVANTAGES
→ strength of cast metal with the esthetics of ceramics
→ retentive qualities are excellent
→ easy correction of axial form
→ preparation is much less demanding than for partial-coverage
retainers
METAL-CERAMIC CROWN PREPARATION
DISADVANTAGES
→ requires significant tooth reduction
→ difficulty obtaining accurate occlusion in glazed porcelain → shade selection can be difficult
→ inferior esthetics in comparison with all-ceramic crown
→ subject to brittle fracture
→ increases potential for periodontal disease
→ many procedural steps are required
METAL-CERAMIC CROWN PREPARATION
RECOMMENDED PREPARATION for
ANTERIOR:
Labially
1.5 mm
RECOMMENDED PREPARATION for
ANTERIOR:
Incisally
2 mm
STEP-BY-STEP PROCEDURE FOR METAL-CERAMIC TOOTH PREPARATION
(1) Depth Grooves
(2) Incisal (Occlusal) Reduction
(3) Labial (Buccal) Reduction
(4) Proximal Cut
(5) Lingual Reduction
(6) Finishing
(7) Smoothing and Finishing
DEPTH GROOVES
place (3) depth grooves:
o center of facial surface
o one each in mesiofacial and distofacial line angles
DEPTH GROOVES
placed in (2) planes:
Cervical Portion
Incisal (Occlusal) Portion
parallels the long axis of the tooth
Cervical Portion
(DEPTH GROOVES)
follows the normal facial contour (1.8 mm)
Incisal (Occlusal) Portion
(DEPTH GROOVES)
FACIAL REDUCTION
facial reduction in the _____ & ____
cervical and incisal planes
determines the path of placement of the completed restoration
Cervical Plane
(FACIAL REDUCTION)
provides the space needed for the porcelain veneer
Incisal (Occlusal) Plane
FACIAL REDUCTION
achieve the necessary. ____ mm clearance on the incisal depth grooves
2 mm
place three depth grooves (1.8 mm deep) in the incisal edge of an anterior tooth
A. Anterior Tooth
B. Posterior Tooth
A
clearance must be a minimum of 2 mm; cusp inclines 1.5 to 2 mm of clearance in intercuspal tapered
A. Anterior Tooth
B. Posterior Tooth
B
allow 2 mm of clearance for adequate material thickness to allow translucency in the completed restoration
INCISAL (OCCLUSAL) REDUCTION
in posterior teeth:
o may still be restorable with less reduction because esthetics
is not as critical
INCISAL (OCCLUSAL) REDUCTION
caution:
o excessive occlusal reduction will shorten the axial preparation walls and thus is a common cause of inadequacies in retention and resistance form in the completed preparation
o loss of retention form can be especially problematic on anterior teeth (on which, because of tooth form, most of the retention is derived from the proximal walls)
INCISAL (OCCLUSAL) REDUCTION
→ use a tapered, round-ended diamond bur
→ 1.2 - 1.5 mm of reduction for translucency in the restoration
→ greater thickness of alloy at incisal area than any other tooth
surface
→ bur position at 45 degrees linguo-incisally
→ reduce half of the incisla area at a time
→ reduce one cusp at a time
INCISAL (OCCLUSAL) REDUCTION
FACIAL REDUCTION
two plane reduction:
Cervical Plane-
Incisal Plane -
1.0 mm; 1⁄3, 1.3 mm; 2⁄3
→ 0.5 mm apical to crest of free gingiva
→ reduce with the bur in oblique position
→ tenon system
FACIAL REDUCTION
→ recommended:
o 6 degree taper between opposing axial walls
→ shoulder margin at 1 mm thick
→ parallel walls with another abutment
→ avoid hitting adjacent tooth
→ shoulder margin below the contact point
→ use flat-end diamond bur
PROXIMAL CUT OR REDUCTION
Size of Linguofacial Wall Reduction:
Chamfer Margin
Supragingival
0.5 mm
Size of Linguofacial Wall Reduction:
Axial Wall Height
1.5 mm
Size of Lingual Fossa Reduction:
Centric Contacts on Metal
1 mm thickness
Size of Linguo-axial Wall:
Height for path of placement and anti-rotation
1.5 mm
Size of Linguo-axial Wall:
Use round-ended tapered diamond bur and submerge halfway into the tooth structure to create chamfer margin
Size of the width?
0.5 - 0.6 mm width
Size of Linguo-axial Wall:
Use flame-shaped or football shaped diamond bur in preparing the lingual surface of anterior teeth
1 mm thickness
The margin must provide distinct resistance to vertical displacement of the tip of a periodontal probe or an explorer and it must be smooth and continuous circumferentially.
FINISHING LINE
FINISHING LINE
shoulder finish line should be_______ degrees
90-120
FINISHING LINE
use ___ in remaining unsupported enamel
chisel
FINISHING LINE
_____ finish line in lingual
chamfer
FINISHING LINE
avoid “ ____” of the chamfer margin
lipping
FINISHING LINE
→ controlled tissue displacement can be helpful when the margin is finished with a _____ or another rotary instrument
→ avoid undercuts
→ round-off internal line angles, incisal and occlusal margins
→ taper and parallelism
fine-grit diamond
(1) Platinum foil matrix adapted to a die
(2) Hot pressing/heat-pressed
(3) Sip-casting
(4) Milling
TECHNIQUES IN FABRICATION FOR ALL-CERAMIC RESTORATIONS
ZIRCONIA another name
SINTERING-MILLING
E-MAX another name
HEAT-PRESSED
→ three times stronger than porcelain
ZIRCONIA
(SINTERING-MILLING)
→ can withstand wear and tear without chipping
→ tolerate forces of mastication and bruxism
→ less stress and damage on opposing pieces
ZIRCONIA
(SINTERING-MILLING)
made from lithium disilicate ceramic
E-MAX
ideal for crowns
E-MAX (HEAT-PRESSED)
→ more translucent compared to zirconia
→ 10-15 years (fracture)
E-MAX (HEAT-PRESSED)
→ high esthetic requirement
→ considerable proximal or facial caries
→ incisal edge reasonably intact
o to support the restoration, particularly in the incisal area, where porcelain thickness must not exceed 2 mm
o otherwise, the brittle material will fail
→ endodontically treated teeth with posts and cores
→ favorable distribution of occlusal load because of the relative
weakness of the restoration
INDICATIONS for ALL-CERAMIC CROWN PREPARATION
→ when a more conservative restoration can be used
→ when superior strength is warranted and metal-ceramic crown is
more appropriate
→ extensive caries
→ insufficient coronal tooth structure for support
→ thin teeth facio-lingually
→ unfavorable distribution of occlusal load
→ bruxism
→ teeth with short clinical crowns
o they do not offer adequate support for all-ceramic crowns
CONTRAINDICATIONS for ALL-CERAMIC CROWN PREPARATION
→ esthetically unsurpassed; excellent translucency
→ good tissue response even for subgingival margins
→ slightly more conservative of facial wall than metal-ceramic
restorations
ADVANTAGES in ALL-CERAMIC CROWN PREPARATION
→ reduced strength in comparison with metal-ceramic crown
proper preparation extremely crucial
→ among least conservative preparations
→ brittle nature of material
→ can be used only as single restoration
DISADVANTAGES in ALL-CERAMIC CROWN PREPARATION
centric contacts are best confined to the middle third of the lingual surface
ALL-CERAMIC CROWN OCCLUSION
achieved by restricting the taper of proximal walls
Retention Form
wing-type preparation offers more resistance than wingless counterpart (crown length)
Resistance Form
should exhibit two plane reduction
Esthetic Zone
cervical plane is 1⁄3 of preparation height
Anteriors
Shoulder margin degree?
90-120 degree (hatchet/chisel)
Premolars and Molars
cervical and occlusal plane often ______ each other in height
approximate
____ should be avoided as it often leads to overreduction
Undercut
should be avoided because this may lead to pulpal exposure
Excessive Convergence
0.5 mm; should be smooth and continuous and provide distinct resistance to vertical displacement
Chamfer Margin
must be smooth and continuous circumferentially
Finishing Margin
Line Angles and Internal Line Angles should be _____
rounded
True or false
all-ceramic restoration are most esthetically pleasing because of the absence of underlying metals to block light transmission and it resembles natural tooth better in terms of color and
translucency
True
chief disadvantage is fracture susceptibility but lessened by use
of resin-bonded technique and higher strength ceramics
ALL-CERAMIC RESTORATIONS
one of the least conservative of tooth structures:
____ mm maximum for incisal and _____ mm for molars
2 mm, 1.5 mm
