Operative Dentistry 2: Class II Cavity Preparation for Amalgam Restoration

Flashcards covering the detailed features of Compound Class II Cavity Preparation for Amalgam Restoration as presented by Dr. Florence Mae Arquillo-Posecion.

What is Feature #1 of the compound Class II cavity for amalgam restoration?

The cavity preparation has an inverted truncated cone form.

According to Feature #1, how does the width of the occlusal orifice compare to the pulpal and gingival floor?

The occlusal orifice is narrower than the pulpal and gingival floor.

What is the rationale for the inverted truncated cone form in Feature #1?

For mechanical retention of the prepared cavity.

What specific retentive features are described in Feature #2?

There is an occlusal and proximal dovetail.

What is the rationale for having an occlusal and proximal dovetail?

For the retention of the amalgam in both occlusal and proximal surfaces.

Which specific tooth does NOT have a dovetail according to the transcript?

Mandibular first molar.

Why is a dovetail omitted on the mandibular first molar?

Because there is a distal cusp, and a dovetail would encroach upon both cusps.

What shape is created instead of a dovetail on the mandibular first molar?

A FISHTAIL only.

What is the primary mechanical purpose of a dovetail?

It prevents lateral dislodgement of the restoration.

According to Feature #3, what is the required width of the isthmus relative to the intercuspal distance?

The isthmus is $\frac{1}{4}$ of the intercuspal distance.

What is the specific measurement for the isthmus width in molars?

$$1.7-2.0\,mm$$

What is the specific measurement for the isthmus width in premolars?

$$1.6-1.7\,mm$$

What is the rationale for the specific isthmus width in Feature #3?

To conserve tooth structure and to prevent cusp inclusion or encroachment.

Where does the inverted truncated cone shape focus in the Class II preparation?

On the proximal box.

How is the proximal box shaped in terms of orifice width compared to the gingival floor?

The orifice at the occlusal is narrower than the gingival floor.

Why must a proximal box be present for amalgam restorations?

Since amalgam does not adhere to the tooth, the proximal box holds it in place.

What type of dislodgement does the proximal box prevent?

Occlusal dislodgement of amalgam.

How can the inverted truncated form be visually checked in the mesial or proximal area?

The lingual line and buccal line should slant towards the gingival.

What tool is used to check the retention of the cavity preparation?

The cowhorn end (straight end) of the explorer.

In the cowhorn test, what does it mean if the explorer end slants?

There is retention.

In the cowhorn test, what does it mean if the explorer end stands?

There is no retention.

Is the isthmus considered a retention or resistance feature?

A resistance feature.

How does the isthmus contribute to tooth resistance?

It makes the tooth resistant to fracture.

What is the guiding principle regarding the width of the isthmus?

Make the isthmus as narrow as possible; the smaller the better.

What is the definition of the 'isthmus' in cavity preparation?

The narrowest portion of the cavity preparation.

Which instrument is suggested to achieve the smallest isthmus?

The smallest round bur.

What does having a small isthmus indicate about the preparation technique?

Little tooth structure was removed, following grooves/pits/fissures without encroaching the cusp.

At what point in the preparation is the isthmus typically created?

As the clinician goes around the cusps.

Why is the isthmus in premolars smaller than in molars?

The intercuspal distance in premolars is lesser.

What is Feature #4 regarding line angles?

There is a bevel in the axio-pulpal line angle.

What are the two primary rationales for the axio-pulpal line angle bevel?

To remove an area of stress/fracture and to increase the bulk and strength of amalgam around the isthmus.

Which hand instruments can be used to remove sharp axio-pulpal line angles?

Chisels, margin trimmers, or hatchets.

What are sharp line angles inside a cavity preparation considered?

Areas of stress.

What is the colloquial Filipino term used to describe a restoration failure if a line angle is not beveled?

Mabuka ang pasta.

What is Feature #5 regarding cavosurface angles for amalgam?

No bevel of the cavosurface angles or margins.

What type of joint should be present in all areas for amalgam?

A $90$-degree butt-joint.

What is the rationale for Feature #5?

To prevent fracture of amalgam margins and the production of 'ditches filling'.

Is the butt-joint considered a retention or resistance feature?

A resistance feature.

What defines a butt-joint in cavity preparation?

The amalgam restoration and the external surface of the cavity preparation meet at $90$ degrees.

What is Feature #6 regarding the intact wall (mesial or distal)?

No undercuts on the existing intact wall.

How should the intact wall be oriented according to Feature #6?

The wall slightly diverges pulpo-occlusally.

What is the rationale for the slight divergence of the intact wall?

To not undermine the intact marginal ridge, which is subjected to stress during mastication.

What is the function of the intact wall following the direction of enamel rods?

To avoid undermining or removing more tooth structure than necessary.

What happens if retention is required in an area where the wall should be divergent?

It will cause undermined enamel.

What does the term 'diverge' mean in this context?

To flare outwards or widen.

What is the warning regarding the degree of wall divergence?

Do not exaggerate the divergence.

What is Feature #7 regarding the outline form?

The internal outline form meets the external outline form at a $90$-degree angle.

What is another name for the $90$-degree angle in Feature #7?

Blunt joint or butt joint margin.

What is the rationale for Feature #7?

To create a definite interface and prevent knife-edged margins that lead to 'ditched' fillings.

What is Feature #8 specifically for the buccal proximal areas?

An S-curve or reverse curve.

What is the rationale for the S-curve in Feature #8?

To avoid undermining the mesio-buccal or disto-buccal cusp.

What is the second benefit of the S-curve mentioned in the rationale?

Creation of a blunt joint margin and bulk amalgam at the bucco-proximal margin.

In which specific location is the S-curve found?

Only on the buccal proximal area of the cavity prep.

What does the S-curve do to the margin of the buccal wall?

Brings it out of contact.

Why is thickness of amalgam important in the S-curve area?

To withstand masticatory forces.

Why is the S-curve only found in the buccal and not the lingual area?

The interproximal space is narrower and the contact area is broader on the buccal area.

Is the lingual wall typically in contact with the adjacent tooth?

No, the lingual wall is already out of contact.

What is Feature #9 regarding adjacent tooth contact?

The tooth must be out of contact with the adjacent tooth by about $0.5\,mm$ in the proximal area.

In what directions should contact be cleared according to Feature #9?

Buccally (facially), lingually, and gingivally.

What are the two rationales for clearing contacts in Feature #9?

To bring margins into self-cleansing areas and to allow insertion of the matrix.

How does clearing contacts prevent recurrent caries?

It ensures the patient can clean all boundaries of the restoration and tooth surface.

What is the best practical way to check if contact has been removed?

Visually (if they aren't touching, it's okay).

If visual inspection is uncertain, how do you check contact clearance using an explorer?

Run the explorer at the gingival floor, buccal wall, and distal wall.

What is Feature #10 regarding cavity depth on the occlusal surface?

$0.5-1.0\,mm$ beyond the DEJ.

What is the rationale for Feature #10?

To provide adequate bulk of amalgam for resistance to biting forces and retention.

What is the measurement for 'initial depth'?

$$0.2-0.8\,mm$$

What is the measurement for the 'deepest cavity prep' relative to the DEJ?

Less than $1.0\,mm$ from the DEJ.

How thick must amalgam be to withstand stresses?

$$1.5-2\,mm$$

What is the depth measurement from the enamel/occlusal surface?

$$1-1.5\,mm$$

What is Feature #11 regarding proximal secondary retention?

Proximal grooves starting at the bucco-axiogingival and linguo-axiogingival point angles.

Up to where should the proximal grooves extend?

Up to where the axial wall meets the pulpal floor (axiopulpal angle).

How does the depth of the proximal groove change as it goes upwards?

It decreases its depth gradually to the top.

What are the rationales for Feature #11?

Added retention, preventing flow during setting, and preventing amalgam creep.

In Feature #11, where should the retention holes be placed?

On the dentin structure, not on the enamel.

How do you use a round bur to create proximal grooves?

Embed the head at the 2 point angles and move it upwards to the axiopulpal angle.

How do you use a tapering fissure bur to create proximal grooves?

Orient the bur slanted so the ends create the slots without embedding the whole bur.

What is Feature #12 regarding the gingival floor?

It is placed above the crest of the healthy gingiva.

What is the rationale for Feature #12?

To free the wall of contact and bring margins into self-cleansing areas.

How is the gingiva managed in a live patient to establish a margin?

Using wedges or gingival cord soaked in epinephrine.

What is the ideal level of the gingival floor on a typodont?

Below the contact point and above the healthy gingiva.

What is Feature #14?

Inclusion of all deep, uncoalesced developmental grooves in the cavity preparation.

What is the rationale for including developmental grooves?

Cutting for immunity or extension for prevention of recurrence of decay.

Should developmental grooves be included even if they don't have caries?

Yes, they should be included.

Why include non-carious grooves in the proximal-focused prep?

They may be attacked by caries in the future; including them prevents recurrent caries.

What is Feature #15 regarding the lingual proximal area?

No S-curve or reverse curve on the linguoproximal areas.

What is the rationale behind Feature #15?

The lingual surface presents a wider lingual embrasure compared with the buccal area.

According to Feature #16, what is the width of the gingival floor in premolars?

About $0.8\,mm$

According to Feature #16, what is the width of the gingival floor in molars?

About $0.8-1.0\,mm$

What is the rationale for the gingival floor width in Feature #16?

To create a definite seat for the amalgam filling following the gingival profile.

What is Feature #17 regarding the axial wall?

The axial wall is $0.2-0.5\,mm$ within the DEJ.

What does the axial wall follow or stay parallel to?

The external contour of the tooth.

What is the rationale for Feature #17?

To provide sufficient separation and protection for the pulp.

Why does following the external contour ensure uniform reduction?

It maintains a uniform width of reduction in the proximal area (curving inwards).

In lower molars (Feature #18), what is the outline of the bucco-proximal wall?

More or less parallel to the contour of the buccal surface.

In lower molars (Feature #18), what is the outline of the linguoproximal wall?

Parallel to the long axis of the tooth (vertical or straight).

In upper molars and premolars (Feature #18), what is the outline of the linguo-proximal wall?

More or less parallel to the contour of the lingual cusp or surface.

In upper molars and premolars (Feature #18), what is the outline of the bucco-proximal wall?

Parallel to the long axis of the tooth (vertical or straight).

What is the rationale for Feature #18?

To preserve tooth structure and prevent a too wide base for the gingival floor of the proximal dovetail.

What is Feature #19 regarding upper molars with occluso-lingual grooves?

The lingual extension cut is made at the expense of the mesio-lingual cusp.

Which cusp is NOT involved in the lingual extension for upper molars in Feature #19?

The disto-lingual cusp.