Class V Cavity Preparation for Amalgam Restoration | PPT

December 17, 2012 | By | Reply More

Class V Cavity Preparation for Amalgam Restoration | PPT

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Smooth surface lesions located on the gingival third of labial, buccal and more rarely the lingual surfaces of all teeth.
Always simple lesions as it involves one surface of a tooth.

1.   Caries is not only the reason of cavitation, abrasion and erosion may also responsible for their causation.

2. The carious lesion usually starts as a white or chalky line or area near the center of the gingival 1/3 of the labial or buccal surfaces of teeth. If it occurs on the lingual surface, it is usually associated with denture clasps.

3. Marked sensitivity.

4. Tendency to spread mesially and distally near the axial angles of teeth, it may pass the axial angle of the tooth and unite with a Class II, III or IV cavity.

5. Bell-crowned teeth, and teeth with markedly convex surfaces, are more susceptible to this type of caries.

6. It occurs less frequently than the other types of caries.

7. It is usually affects multiple teeth. This indicates that the patient has a high caries susceptibility and requires careful extensions of cavity outline.

8-It is more frequent among old-aged patients and is called senile caries, yet it is not uncommon in childhood and adolescence and is often associated with improper oral hygiene and presence of bacterial plaque. In case of old aged individuals, caries may be found to extend gingivally and affect the cementum of the root. Sensitivity will increase and the caries may tend to recur around the margins in cementum.

Application of Principles:

1.The Outline Form:

  • A.  General shape: “Ferrier design, conventional or typical“

This is the most recent and accepted now. Generally the classical Class V cavity usually describe a trapezoidal outline with straight margins and round corners, with the short arm being the gingival.

Principles                                              Rationale

.  OUTLINE FORM –            rounded trapezoid in   gingival 1/3.

  • B. Location of margins

Occlusally:   It has to be at, but not including the height or just past the height of contour of the tooth or just include the defective area of the tooth.

Principles                                         Rationale

A. Occlusal /incisal          –>       More esthetic

outline is                                         and harmonious.


and parallel

to the occlusal plane.


Proximally: Far enough mesially and distally to include only the defective and/or the decalcified tooth tissues, yet not encroaching on the axial angles of the tooth, and placed just opposite the axial angles of the tooth.

Gingivally: At or ideally in the occlusal portion of the gingival sulcus space. In cases of gingival recession, the gingival margin should be located supragingivally.

2&3 :Resistance and Retention Forms:

a. Resistance Form:

No resistance form necessary for these preparation because they are not subjected to a direct functional loading.

A minimum dept of 0.5 mm in dentin is required for a uniform bulk of amalgam for strength of the material.

b. Retention Form

For retention, however, as the mandible moves in lateral excursion, the lingual slopes of the buccal and lingual cusps of maxillary teeth load the buccal slopes of the buccal and lingual cusps of mandibular teeth.

Assume that we have a facial Class V restoration in the lower molar tooth, as illustrated in the diagram, and so the tooth is firmly seated in bone, the tooth structure of the crown can move from position (1) to position (2), making a v-shape opening at the margin (usually the occlusal one), together with a facial component of force driving the restoration facially. So, retention will be placed in the occlusal (or incisal) and gingival walls in the form of grooves or retentive holes.

If the occlusal margins approximate the facial or lingual cusps or marginal ridges, it is advisable to make the occlusal walls devoid of any occlusal grooves as this may:

i. undermine the structure of these cusps or   marginal ridges.

ii. display the restorative through the enamel   and, therefore, causes objectionable   esthetics.

Although these locations are not mandatory in premolars and in prominent, easily cleansable molar tooth surfaces, locating the margins apical to the height of contour should be decided upon only after carefully considering the cleansing ability and plaque control technique of the patient as well as the natural pattern of cleansing these teeth.

Internal anatomy:

1.In a mesio – distal cross section:
i. The axial wall will be smooth and slightly curved mesiodistally, following the curvature of the facial or lingual surface. This is to provide resistance to the forces of condensation and to provide a maximal pulp protection.

ii. Mesial and distal walls, will appear divergent or flare mesially and distally respectively, going with the direction of enamel rods to form 90° cavo-surface angle. This is to provide strength for the tooth and the amalgam margins and to prevent undermined the enamel walls.

2. In an occluso – gingival longitudinal section:

i.  The axial wall:  Will be seen as flat to slightly convex occluso-gingivally depending on the extent of the preparation occluso-gingivally. This will provide maximal pulp protection, while maintaining a uniform minimum dept of 0.5m in dentine.

ii. Occlusal or incisal wall:

It can appear in one of two ways:

a. Smooth and straight forming a 90° cavo-surface angle following the direction of enamel rods. This is to facilitates condensation and the adaptation of the amalgam restoration and at the same time it prevents undermining of enamel rods.

b. If the occlusal margins is located at,the middle third of the facial or lingual surfaces, it will be formed of two planes; a grooved internal plane, and is made of dentin, and an outer amelo-dentinal plane going with the direction of enamel rods. This will provide a mechanical retention lock in occlusal wall without undermining the enamel rods.

iii. Gingival wall:

Also it can vary in appearance, depending on its location, if it is located on enamel, it requires a small cavo-surface bevel. This will protect the very short gingival enamel rods from fracture during condensation and, at the same time, it terminates the gingival wall with its enamel wall going with the direction of the enamel rods, thus, eliminates the unsupported rods.
In such a manner it appears with two planes; an internal grooved plane made of dentinand an outer flat plane made of enamel.
If the gingival wall is located on cementum of the root, it also appears with two planes, an internal grooved plane made of dentin and an outer flat plane made of dentin and cementum.
All internal line angles in dentine must be squared up except those on the corners, they must be rounded. Also, all point angles must be rounded. This is to facilitate condensation of amalgam.
4.Convenience form:
The trapesiodal shape with rounded corners and the isolation of the field of operation using the rubber dam will provide a better conveniency for cavity preparation and restoration.
5.Removal of carious dentine:

As described before.

6.Finishing of enamel walls and margins:

ØEnamel margins should be smoothened and should be provided with 90° cavo-surface angle . The gingival bevel is to be placed on the gingival walls that are terminated by enamel and not where the preparation terminates in cementum.
7. Cavity Debridement

As described before.


This Form of the Cavity :

. Meets the general principles of cavity   preparation.

2. Exhibits a pleasant appearance, and

3. Is easier to restore.


1.   Rubber dam , punch , clamp forceps and clamp no. 212.

2.   Burs nos. 330 , 256 , 1/2, 1 , 35 .

3.  Hand instruments : curved chisel, mon – angle hoe , hand excavator.

Instrumentation Resume for the Class V Preparation

1.    No. 256 or 335 bur for penetration and extension of the outline .

2.    Axial wall located with the same burs.

3.    If required , caries is removed with a slow – speed round bur , as dictated by convenience .

4.    Hand excavator may be advised.

5.    Gingival and incisal retention placed with no. ¼ or ½ bur.

6.    Enamel is finished and beveled with a no. 15 Wedelstaedt chisel and 7901 or 242 bur.



Principles                                  Rationale

B. Gingival        ——->> Will allow maximum retention

outline is                            to be placed in cavity walls if

straight                               occlusal and gingival outlines

and parallel to                  are parallel.

the occlusal outline.


C. Mesial and distal ——–>>> Conforms to

outline is straight                           the shape of the tooth.

and parallel to the

mesial and distal

tooth outline in

the gingival 1/3.


II. Extensions

Conservation of tooth structure is the basis for all cavity preparation; therefore, extend only far enough to remove defective tooth structure and create sufficient access (convenience form) for instrumentation and insertion of restorative material. In addition, access for finishing and maintenance of the restoration must be provided.

Principles                                                                Rationale


1. Decay, decalcification, and defects. —>> Eliminates weak or

2. Enamel unsupported by dentin.               defective tooth structure

3. Eroded, abraded areas.                               so that margins of the

4. Existing restorations                                  restoration will terminate

on sound tooth structure

(extension for prevention).



B. Occluso-gingival extensions  —>>   Provides sufficient access for

1. Occlusally to the height of                instrumentation and condensation

contour (or to the occlusal extent        and for prevention.

of the lesion)

2. Gingivally to the gingival

extent of the lesion (frequently

subgingivally near the C.E.J.)


C. Mesio-distal extention is to —->>  Extention for prevention,

the line angles of the tooth (or             more esthetic and harmonious.

to the extent of the lesion mesially

and distally).



Principles                                                  Rationale

A. Depth ————–>>>>>>>   A minimum depth is

1. 0.5 mm in dentin                      required to provide retention

2. 1-1.25 mm (may vary              and uniform bulk of amalgam

slightly depending on size             for strength of material –

of tooth, thickness of enamel       further tooth reduction

and extensions); occlusally           is unnecessary and may result

1.5 – 1.75 mm depth may be         in pulpal encroachment or

required to achieve 0.5 mm          sensitivity.

in dentin.


B. Axial Wall ————–>> Easier to adapt amalgam to

1. Smooth                               smooth walls provides

2. Slightly curved                 resistance to forces of

mesiodistally.                           condensation and provides

3. Straight or slightly          maximumal pulpal protection

while maintaining uniform

curved occlusogingivally       minimum depth (0.5 mm

depending on the extent       in dentin).

of the preparation



C. Mesial and distal walls  —> Facilitates

1. Smooth and straight        condensation, adaption.



2. Flare mesially —>>>     provides strength for the

and distally respectively     tooth and amalgam margins (

to form 900 metal                prevents undermined enamel

margins).                               and provides a 700  – 900

amalgam margin) – Resistance



D. Occlusal

or incisal wall

1. Smoothly –>>            Facilitates condensation, adaption.

and straight



2. Forms a 900 —>>>  Prevents undermining of enamel

cavosurface angle           rods, assists in providing retention

(occlusal wall is               by opposing the gingival wall

parallel to the                 which forms an acute

enamel rods – 900        gingivocavosurface angle.

to a tangent to the

external surface).


3. Occlusal retention—>> Provides retention – a

– two undercuts .5               mechanical lock in

mm deep in the dentin       occlusal wall without

of the occlusal wall at         undermining enamel

the occluso-axial line          rods.

angle (one mesially

and one distally)


E. Gingival wall —–>>   Facilitates

1. Smooth and               condensation, adaption.

straight mesiodistally.

2. Gingival retention – —> Provides mechanical

an acute axio-gingival          lock to retain the amalgam

angle (700).                           (primary retention).

3. If terminated on—->> A small enamel bevel protects

enamel requires a             the very short gingival enamel

small cavosurface              rods from fracture during

bevel.                                   condensation, and eliminates

unsupported rods.



Principles                                   Rationale

A. Line Angles

1. Axial line angles—>    Increase retention

are well defined and

conform to the

configuration of the

cavosurface outline

form (internal outline).


2. Mesio – occlusal, mesio-  —-> Facilitates

gingival, disto-occlusal,                  condensation.

and disto-gingival

walls form rounded

line angles.

B. Point angles are —>  Facilitates condensation


C. Cavosurface


1. Well defined —>> Well defined, sound cavosurfaces

2. Strong (sound)        are required to resist condensation

forces and produce a well adapted,

durable tooth restoration margin

which will resist plaqueaccumulation

and prevent recurrent caries.


D. Cleanliness – —>>a clean, dry cavity preparation will allow

the cavity must            more intimate adaptation of amalgam to

be free of moisture      the cavity walls. An amalgam which is

and debris.                    placed in a dry environment will have

superior physical properties to one placed

in a moist environment.


Principles                                       Rationale

A. The rubber dam –>    damage of the dam will cause leakage and

is intact.                          loss of isolation (moisture contamination).

B. Surrounding   —-> conserves natural tooth structure eliminates

enamel, dentin, and       post-operative pain inflammation.

cementum are

preserved undamaged.

C. Soft  tissue  undamaged.


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