Class II Amalgam Preparation Design

class II

- caries affecting proximal surfaces of posterior teeth

- smooth surface lesion

where do class II lesions initiate?

just gingival to the contact area

spread of class II caries

1. conical entry thru enamel

2. lateral spread at DEJ

3. conical entry thru dentin (apex face pulp)

line angles vs point angles

line = junction of 2 walls

angles = junction of 3 walls

class II diagnosis

- bitewings (best)

- visual

for visual diagnosis of class II lesions, what will it look like?

marginal ridge = chalky, grey, opaque

which diagnosis method allows for early identification of incipient lesions?

bitewings radiographs

indications for class II restorations on previously unrestored tooth

DEJ has decay*

indications for class II restorations on previously restored tooth (5)

- fractured restoration

- gingival overhang

- bad contours

- light or no proximal contact

- bad margin integrity

modifying factors for class II restorations (4)

- poor OH

- high caries risk

- SES

- age

guidelines for class II restorations are

changing* based on new literature

don't need to do a restoration until at DEJ

vision for class II prep

indirect vision

general amalgam prep principles apply for class II preps such as (7)

- don't terminate on margins/ cusp tips

- remove unsupported enamel

- preserve cusps, marginal ridges, transverse ridges

- don't extend to unaffected fissures

- smooth curves

- 1.5mm pulpal depth

- 90º cavosurface margin

class II outline form is determined by

- tooth anatomy (pits/ fissures)

- adjacent structures (embrasures)

class II prep and adjacent teeth contact

contacts with adjacent hard tissues MUST be broken

how much should prep and adjacent tooth contact be broken? why is this important?

width of explorer

helps with restoration and finishing

class II amalgam resistance form requirement (8)

- internal walls 0.5mm into dentin

- flat pulpal floor

- flat gingival floor/seat

- rounded line angles

- divergent wall (when applicable)

- 90º cavosurface

- pulpal depth

- keep unaffected structure

class II resistance form summarized

- proper depth

- flat floor

- rounded line angles

- divergent walls, 90º cavosurface, don't remove too much

class II retention form occlusal and proximal portions should be

INDEPENDENTLY retentive*

class II retention form requirements (4)

- convergent occlusal walls

- occlusal dovetails

- convergent proximal walls

- proximal locks

what are proximal locks (part of retention form)? are they convergent or divergent?

proximal retention grooves

convergent

where are proximal locks most prominent?

gingivally because they fade out occlusally

where should proximal locks be placed?

0.5mm inside DEJ

class II prep convenience form

- cut thru occlusal surface + marginal ridge to access proximal lesion

- may need additional extension for access/ vision

class II removal of remaining decay for an amalgam prep

- remove tooth structure ONLY in area of lesion

- don't remove entire floor/ wall to depth of lesion

why is it important to not remove healthy tooth structure around a lesion?

- structural integrity

- pulpal considerations

finishing enamel walls: steps for class II prep

1. remove remaining debris (air/ water)

2. re-evaluate prep from multiple vantage points w/ mirror*

3. make needed modifications

process of cleansing prep

1. remove debris

2. re-eval isolation

3. eval soft tissue status (hemorrhage control may be needed)

what fissures should be included in class II preps?

cariously involved secondary fissures only

isthus width of class II prep relative to intercuspal distance

1/4 intercuspal distance

gingival floor dimension is

1-1.5mm axially

aka width of box

what is gingival floor length based on? depth?

adjacent tooth BL contacts

adjacent tooth G contacts

class II prep should have ___ curves, maintain ___ for strength, and an axial wall that follows ___

smooth

marginal ridges

external contour of tooth

steps for class II prep

1. occlusal outline form (same as class I)

2. create internal walls w/ correct depth, convergence, etc.

3. extend in direction of lesion to include affected marginal ridge

4. proximal trenching (create prox box)

it is necessary to include affected marginal ridge, but it is important to NOT extend

THROUGH the affected marginal ridge

what is proximal trenching? what walls does this create?

proximal box

axial, gingival, buccal proximal, lingual proximal walls

before preparing the proximal box, visualize

location of proximo-occlusal margins

bur needed to create proximal trenching?

245*

what direction do you move bur to create proximal box?

move BL at DEJ (maintain convexity)

considerations when trenching

- break B + L contact

- break gingival contact

- pay attention to axial depth (1-1.5mm)

why is it important to pay attention to axial depth when proximal trenching?

enamel is thinner in gingival 1/3

when creating proximal box with the bur, leave ___ b/c ___

thin enamel plate

it's protective

when do you remove the enamel plate?

after proper extension

how to remove enamel plate

use rotary instrument or hatchet to fracture weakened prox enamel

proximal trenching should create a proximal contact that is visually open

buccally and lingually

gingival clearance is defined as ___ and should be ___mm

horizontal measurement between adjacent teeth at gingival floor

0.5mm (tip of explorer)

buccal and lingual walls clearance to adjacent tooth

0.2-0.3mm ideally (0.5mm is fine tho)

after you finish occlusal walls

place retention locks/ grooves if indicated

are retention locks/ grooves present in standard preps?

no... they are a subtle prep feature added when needed

retention grooves must be opposed by ___ and only occur in ___

another groove or retention mechanism

dentin

retention grooves dimensions laterally + occlusally

0.5mm laterally

1.0mm occlusally

what is location of retention grooves based on?

anatomy (not prox box size)

what bur do you use to place retentive grooves?

1/4 round bur

once retention locks/ grooves are placed, what are the next 3 steps?

1. finish proximal enamel w/ hand piece or hatchet

2. round axio-pulpal line angle w/ hand piece or hatchet

3. double check prep w/ mirror

when double checking prep w/ mirror, look for

- proper extensions

- complete caries removal*

- sound enamel (non unsupported)

ideal amalgam angle and cavosurface angle and what it's called

90º

butt joint fit

when is a slot used?

when decay only involves proximal area (small lesion)

what burs are used to create a slot?

330 or 245

are slots used for amalgam restorations? why?

no

retention is a limitation

slots are based on visual convenience form only which means it is based on

access for infected caries removal and material placement

tool to help you avoid damaging the adjacent tooth

fender wedge

order of class 2 prep when caries are present

1. establish external outline form

2. establish internal outline form (remove decay from all internal aspects of prep)

3. modify + finish prep (proper retention/ resistance)

your external outline form is finished when

caries is only on axial and pulpal walls (internal walls)

where will caries NOT be once your external outline form is finished? where will caries still be?

M, D, L, B, G walls + DEJ

axial + pulpal walls