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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.
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“
. 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.
A. Occlusal /incisal –> More esthetic
outline is and harmonious.
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.
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.
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.
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:
As described before.
6.Finishing of enamel walls and margins:
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.
APPLICATION OF THE BASIC PRINCIPLES OF CAVITY PREPARATION CLASS V AMALGAM
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.
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
III. RESISTANCE/RETENTION FORM
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.
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
or incisal wall
1. Smoothly –>> Facilitates condensation, adaption.
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
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.
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
IV. CAVITY FINISH
A. Line Angles
1. Axial line angles—> Increase retention
are well defined and
conform to the
configuration of the
form (internal outline).
2. Mesio – occlusal, mesio- —-> Facilitates
gingival, disto-occlusal, condensation.
walls form rounded
B. Point angles are —> Facilitates condensation
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.
V. TISSUE/DAM PRESERVATION
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.
C. Soft tissue undamaged.
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