CLASS I AMALGAM Design Principles
CLASS I AMALGAM
Design Principles
Dental Amalgam
macro mechanical(opposing walls,grooves, mortise-form)
right angle butt joints,adequate bulk, smooth& flat walls
right angle butt joints,remove all unsupportedenamel
break contact withadjacent teeth
micro mechanical(bonding)
bevel enamel, feather edgeacceptable
lesion dictates form, preserveunsupported enamel
contact with adjacent toothacceptable
Composite Resin
RetentiveForm
ResistanceForm,RestorativeMaterial
ResistanceForm, Tooth
ProximalClearance
CLASS I
CLASS I
Appearance ofClass I carieslesion on bitewing radiograph
Accepted Terminology
preparing a cavitycavity preparation
prepared cavity
Jargon
prepprepping
Lay Terms
drillinghole
Accepted Terminology
extendextension
incorporate
Jargon
widendeepenchase
Lay Terms
widendeependrill out
DISTALCUSP
DISTOBUCCAL CUSP
MESIOBUCCAL CUSP
MESIOLINGUAL CUSP
DISTOLINGUALCUSP
DISTALWALL
LINGUAL WALL
BUCCAL WALL
MESIAL WALL
PULPAL FLOOR
OUTLINE FORMFEATURE
• smooth flowing,gentle curves
RATIONALE
• angular contours can chipduring condensation
• angular contours canconcentrate stresses &lead to restoration fracture
• easier to find whencarving back freshamalgam
Angular IrregularitiesINVAGINATION
• susceptible to fractureduring condensation
EVAGINATION
• difficult to condense into
EXTENSION
a balance betweenconservation oftooth structure andthe need for accessand to removedefective toothstructure
EXTENSIONPRINCIPLE
• encompasses carioustissue
• eliminatesunsupported enamel
• encompassescontiguous fissures
• encompassescontiguousrestorations
RATIONALE
• eliminates infectedtissue
• eliminates weakenedtooth structure
• reduces risk ofsecondary caries
• maximizes restorationlifespan
BUCCO-LINGUAL EXTENSIONPRINCIPLE
• extends far enough up B& L grooves toterminate on gentlecontours
RATIONALE
• margin in sharpanatomy difficult tofinish & keep clean
MB
DB
L
BUCCO-LINGUAL EXTENSIONPRINCIPLE
• extend minimally in areaof triangular ridges(optimally: isthmuswidth is <1/3 intercuspaldistance)
RATIONALE
• provides convenienceform while preservingcusp strength
MESIO-DISTAL EXTENSIONPRINCIPLE
• stop short of marginalridge crests
RATIONALE
• preserve strength ofmarginal ridge(resistance form)
MESIO-DISTAL EXTENSIONPRINCIPLE
• groove extensions keptnarrow
RATIONALE
• preserve strength ofcusps (resistanceform)
OCCLUSAL DEPTHPRINCIPLE
• 0.5mm into dentin
• about 2 mm measured attriangular ridge
RATIONALE
• sufficient bulk ofamalgam to preventfracture
• maximum thickness ofdentin protecting pulp
PULPAL FLOORPRINCIPLE
• smooth & flat
• parallel to occlusal table
RATIONALE
• uniform bulk ofamalgam to preventfracture
• best resistance toocclusal stresses &forces of condensation
BUCCAL & LINGUAL WALLSPRINCIPLE
• smooth
• curved mesio-distally
• straight pulpo-occlusally
RATIONALE
• optimize adaptationof amalgam to walls
• elimination of weaktooth structure
BUCCAL & LINGUAL WALLSPRINCIPLE
• convergent 6° pulpo-occlusally undertriangular ridges
• divergent 6° pulpo-occlusally in grooveextensions
RATIONALE
• helps lock restoration intooth (retention)
• keep amalgam from beingtoo thin at margins(resistance form)
• preserves strength ofcuspal ridge (resistanceform)
A
A’
A-A’ B-B’B
B’
MESIAL & DISTAL WALLSPRINCIPLE
• smooth
• straight & divergent 6°pulpo-occlusally
RATIONALE
• optimize adaptationof amalgam to walls
• elimination of weaktooth structure
• preserves strength ofmarginal ridge(resistance form)
C-C’
C
C’
CAVITY REFINEMENTPRINCIPLE
• internal line angles well-defined but not sharp
RATIONALE
• maximizes amalgamresistance todislodgement
• reduces stressconcentration & riskof subsequent toothfracture
CAVITY REFINEMENTPRINCIPLE
• cavosurface marginsregular, well-defined,well-supported
RATIONALE
• easier to visualize &carve followingcondensation
• optimize adaptation ofamalgam to margins
• eliminates weak toothstructure
• maximizes marginalintegrity
enamel
cavosurface marginunsupported, rough poorly defined
CAVOSURFACE MARGINS
tooth surface
amalgam enamel
cavosurface marginunsupported, rough poorly defined
CAVOSURFACE MARGINS
tooth surface
amalgam enamel
cavosurface marginunsupported, rough poorly defined
CAVOSURFACE MARGINS
tooth surface
CLEANLINESSPRINCIPLE
• cavity is free of debris& moisture
RATIONALE
• facilitates adaptationof amalgam to thecavity
• improves physicalproperties of therestoration byelimination of voids& foreign material
CLASS I AMALGAM
Preparation Technique
Plaster tooth #302X normal size
#245rounded straight fissure bur3.5mm head length
1mm
3mm4mm
initial penetrationin central pit
perpendicular to occlusal table
penetrate 3mm(length of cutting head)
will translate into4mm at B & L walls
extend down centralgroove toward
M & D fossae
keep bur perpendicular toocclusal table & spatially at the same level to create
a flat pulpal floor
stop short of M & D pencil linesleave room for refinement
extend into B & L groovesstop short of pencil lines
tip bur slightly to create divergent M & D walls
0°
45°
0°
45°
22°
0°
45°
22°11°
0°
45°
22°11°6°
tip bur slightly to create divergent MB, DB, & L
groove terminuses
shape B & L walls into smooth flowing curvesperpendicular to the pulpal floor
extended to the pencil line
be careful not to widen the B & L groove extensions
round off sharp corner atD triangular ridge without
encroaching on cusp
measure occlusal depthwith perio probeat triangular ridge
create 6° convergenceat base of triangular
ridges
smooth pulpal floor withprimary cutting edge
smooth vertical walls andsharpen cavosurface margin with
secondary cutting edge
large straight hatchet
self-evaluate inpencil before
seeking instructorevaluation
CLASS I AMALGAM PREPARATION EVALUATION
DEVIATION
STUDENTS: Please evaluate your work prior to asking faculty to do so. Mark your assessment in pencil. This step is important in order for your instructor to help you develop appropriate self-assessment skills.
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PREPARATION FEATURES/PRINCI P L E S E R R O R S LOCATION 2 1 0 -1
I. OUTLINE FORM A. smooth, regular, flowing curves rough irregular
II. EXTENSION A. includes contiguous pits & fissures does not include B. bucco-lingual extensions 1 . ex tends into B & L grooves underextended overextended 2 . e x t e n ds minimally at triangular ridges overextended at triangular ridge C . m e sio-distal extensi o n
1. short of marginal / oblique ridge overextended 2 . min imal width of B and L grooves underextended overextended
III. OCCLUSAL DEPTH/PULPAL FLOOR A. depth = 1.5 - 2.5mm at triangular ridges <1.5 but 1.0 <1.0 >2.5 but 3.0 >3.0 but 3.5 >3.5 B. smooth and flat rough or uneven C. parallel to occlusal table slants
IV. OCCLUSAL WALLS A. smooth rough B. s t raight pulpo-occlusally not straight pulpo-occlusally C. converge at triangular ridges over-convergent not convergent divergent D. diverge at groove extensions over-divergent not divergent convergent C d iverge at mesial & distal walls over-divergent not divergent convergent
V. CAVITY REFINEMENT A. l ine angles well-defined line angles indistinct B. cavosurface smooth, crisp, supported rough nicked indistinct unsupported ename l
VI. TISSUE PRESERVATION, RUBBER DAM ISOLATION, CLEANLINESS A. preparation is clean preparation is contaminated B. rubber dam is intact rubber dam is torn C. uninvolved tooth structure intact d a m a ge is: slight moderate severe D. soft tissue is intact soft tissue dama g e
Name D a t e Tooth 30 Surfaces O Practical ID# (for practical exam only) PLASTER TOOTH INSTRUCTOR SIGNATURE
TOTAL (possible 1 2 )
Rubber Dam isolation full LR quadrant
Use W8A retainer ligated
planned: 30-O Class I cavity preparation for amalgam
imagine there is a Class I caries lesion
#245 has 3.5mm head length
occlusal depth 2.0mm (±0.5) measured at base of triangular ridge
30-O
#245 has 3.5mm head lengthextend into M & D fossae, stay shy of marginal ridges
extend into MB, DB & L grooves, stay shy of cusp ridges
#245 has 3.5mm head length1. round irregularities in perimeter walls, 2. add slight divergence at marginal ridges
and ends of groove extensions,3. add slight convergence at base of triangular ridges,4. smooth pulpal floor & refine internal line angles
#245 has 3.5mm head length
self-evaluate beforeseeking instructor evaluation