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.

NO

NE

SLI

GH

T

SIG

NIF

ICA

NT

SE

VE

RE

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