CAVITY PREPARATIONS

Cl Ι :- Pits and fissure caries

- Upper anterior teeth palatal pits- Posterior teeth occlusal surface

Cl ΙΙ:Posterior teeth proximal surface

 Cl ΙΙΙ :

Anterior teeth proximal surface ( not involving the incisal angle )

Cl ΙV:Anterior teeth proximal surface involving the incisal angle

Cl V:All teeth cervical 1/3

 

Cavity preparation stages and steps:

Initial stage steps:

1. Out line form and initial depth2. Primary resistance form3. Primary retention form4. Convenience form

Final stage steps:

5. Removal of infected dentin and old restoration6. Pulp protection7. Secondary resistance and retention form8. Finishing extrenaal walls9. Final cleaning,inspecting,varnishing and conditioning.

Step 1:( Out line form)

- Mental image 1st → depth → rough out line → alter by seeing hidden problems.- Remove weakened enamel- Preserve cusp and marginal ridge strength - ↓ faciolingual extention- Connect two close cavities- ↓ dentin depth .2 - .8 mm- Care for D.C extension, esthetic, occlusion and cavosurface margin.

Step 2:( Primary resistance form)

- Flat floor- ↓ extension - Rounding internal line angels- Cap weak cusps- Provide enough thickness for restorative material- Box shape- Preserve cusps and marginal ridge- Care for occlusion, remaining tooth structure amount and restorative material type.

Step 3: (Primary retention form)

- Occlusal dove tail ( Cl ΙΙ) - Composite mechanical bond with tooth.- Amalgam:

* Cl ΙΙ walls converge occlusally*Cl ΙΙΙ and Cl V retention grooves*Adhesive systems

Step 4: (Convenience form)

- Observation- Accessibility- Ease prepare and restore

Step 7: ( Secondary resistance and retention form )

- Cavity wall conditioning by etch enamel and dentin bonding agents

- Mechanically:

* Retention grooves and locks* Pins, slots and steps* Bevel enamel margins

Step 8: (Finishing extrenal walls )

- Create:* Good marginal seal between tooth and the filling material*Smooth marginal junction* Maximum strength to tooth and the filling material

- Care for* Enamel rod direction and support ADJ and laterally.* Margin location* Filling material type → cavo surface angel:a. Amalgam: 90˚ → maximum strength of tooth and Amalgamb. Gold: bevel provide marginal metal ease burnishing and adaptation

Step 9: (Final cleaning,inspecting,varnishing and conditioning).

Cleaning by remove debris and smear by citric or polycarboxilic acid

New modified cavity preparation techniques:

Box only preparation

- Small D.C- Facial a lingual proximawalls occlusal convergence- Locks 0.5 mm depth in gingival point angels then decrease occlusally- ( ↓ retention )

Tunnel preparation

- Proximal D.C- Marginal ridge intact - ↓ access and visibility

Slot preparation:

- At root- Approach facial and lingual- High speed bur 2 , 4- Out line form : limited pulpal depth 0.75 – 1 mm gingivally and 1 – 1.25 mm occlusaly ( enamel )

- In facial approach :* Lingual wall face facially as much as possible* Provide access, visibility and convenience* Help in Amalgam condensation - Remove remaining D.C by bur 2 , 4- External walls 90 ˚ cavosurface angel- Retention grooves by bur 1/4 in occlusal and gingival walls at axial line angels, with 0.25 mm depth

Sandwich technique:

- G.I.C under composite- G.I.C bond to tooth and composite → ↑ retention and seal.- F → ↓ D.C

Bonded amalgam:

- Same preparation- Retain ↑ weakened remaining tooth structure- Need special adhesive materials

Adjoining restorations:

- Can repair or replace existing Amalgam filling defective part if the remaining Amalgam filling is good- Adjoining restoration on occlusal surface coz new restoration dove tail can be prepare without eliminating existing restoration dove tail- May prepare Amalgam filling in two or more phases ( eg. Cl ΙΙ lesion continued with Cl V , so 1st prepare and restore Cl ΙΙ before Cl V )

Composite cavity preparation

cavity preparation designs:

- Conventional- Beveled conventional - Modified- Combination of the above three

Conventional :

- Past design

- Out line form :* Extend external walls to initial limited uniform dentin depth* External walls follow enamel rod direction* External walls on root meet root surface at right angel

- Dentin retention grooves- For materials like ( Amalgam , silica , porcelain ) ( brittle and ↓ edge strength )- Not preferred for composite- For composite if lesion at root ( non enamel areas )

Beveled conventional :

- Similar to conventional but with beveled enamel margins- To replace existing filling with conventional ( in enamel area )- For resin filling with ↑ thermal expansion coefficient ( acrylic resin , microfilled composite )- Filling bled esthetically with surrounding tooth color ( not like in conventional that a white line appear between tooth and filling " coz marginal enamel racture during fininshing )

- Bevel :* By flame diamond bur ( 45˚to external tooth surface )* Rods are exposed → ↑ etched* ↑ etched surface area → ↑ enamel resin bond → ↑ retention and ↓ marginal leakage and discoloration* Width 0.25 – 0.5 mm

Modified :

- No specific pulpal depth- No specific wall configuration- Only remove lesion conservatively- Rely on enamel etching for retention- For lesion ( initial , small , new , surrounded by enamel ) - Bevel enamel margin- Retention by grooves if large lesion

AMALGAM Cl Ι:

out line form:

Include all pits and fissures

Resistance form:

- Go around cusps- Don’t go deep pulpally- Depth 1.5 - 2 mm ( 1/2 – 2/3 bur cutting portion) ( 0.1 – 0.2 mm into dentin )- Don’t extend facial and lingual margins more than half way between cusp tip and central groove (1/4 distance between cusp tips )- Eliminate weak enamel wall by joining two cavities near each other less than 0.5 mm- Enameloblasty:* Conserve tooth*Remaining fissure not deeper than 1/4 – 1/3 enamel thickness*Eliminate developmental fault by open it by flame diamond side →smooth surface*Surface left meet cavity preparation with cavosurface angle not greater than 100˚ ( Amalgam margin not less than 80 ˚)* Remove Amalgam from enameloplasty area.- Bur no. 245* 3 mm length * 0.8 diameter *Pear shaped* Produce walls occlusal clearance* Produce rounded internal line angels*Long axis rarallel to tooth long axis* Bur no. 330 smaller size- If marginal ridge remaining thickness more than 1.6 mm → occlusal convergence to mesial and distal walls (if 1.6 mm occlusal divergence )- Isthmus width not more than bur diameter ( not more than 1.5 mm )

Retention form:

Parallel or slight occlusal convergence of two or more opposing walls.

Removing remaining D.C:

- Bur no. 245 →deepen floor ( maximum 2 mm )- Round bur ( slow speed )- Spoon scavator- Large instruments safe ( ↓ penetration )- Stop if feel hard firm ( as sound dentin ) before all stained discolored dentin removed

Pulp protection:

- If ideal depth no need for liner or base- Two layers cavity varnish ( cotton pallet ) → D.T complete seal + ↓ microleakage ( ↓ tooth sensitivity and pulp inflammation )- Moderately deep lesion ( remaining dentin thickness 1 mm or more → place quick setting ZOE thin layer 0.5 mm ) ( don’t cover all pulp floor with ZOE because it is not strong senough to support Amalgam under ↑ occlusal forces )- Boded Amalgam to tooth * After acid etch by new dentin bonding agents contain 4-META*↓microleakage* ↑ Amalgam fracture resistance.- Extensive D.C* Distance between infected dentin and pulp less than 1 mm* ↓ D.C removal if pulp exposure expected ( by x-ray or by dentin pinkish hue )* If exposure occur decide direct pulp capping ( Ca(OH)2 )or R.C.T* Ca (OH)2 ( Dycal ) 0.5 mm base * Spherical Amalgam need ↓ condensational force

Cl Ι Composite: Conventional :

- After old Amalgam filling removal- Flat floor- Dentin under cuts- 90˚ cavo surface angel

Beveled conventional:- After old Amalgam filling removal- If large lesion- Use bur 245

Modified:- For small pits and fissures

Cl ΙΙ Amalgam:

Occlusal out line form:

- Similar to Cl Ι- Dove tail - Stop 0.8 mm before cutting proximal marginal ridge

- Proximal box:

* Bur 245 move faciolingually*Diverge gingivally* Cavo surface angle 90˚* Reverse curve * Lingual minimal reverse curve

Primary reseistance:

- Pulpal and gingival walls flat and perpendicular to tooth long axis- ↓ wall extension- Roundening internal line angels ( ↓ stresses )- Filling enough thickness

Primary retention:

- Facial and lingual walls occlusal convergence and occlusal step dove tail for the cavity occlusal portion- Mesiofacial and mesiolingual walls occlusal convergence for the proximal box

Remove remaining infected dentin D.C by slow speed round bur or use spoon scavator

secondary resistance:

Bevel ( roundening ) of the axio pulpal line angel → ↓ stresses concentration and ↑ material bulk there

secondary retention:

A. Locks:- Against proximal displacement - In axio lingual and axio facial line angels- 0.5 mm depth at axio lingio gingival point angel and then depth decrease gradually- By slow speed bur 1/4 , 33 1/2 , 169 ( ↑ control and tactile sensation )

B. Slots:

- In gingival floor- Bur 1/2 , 1/4- 0.5 - 1 mm deep- 2 – 3 mm length facio lingually

C. Pot holes:

- In gingival floor- Bur 1 , 1/2- 0.5 – 1 mm deep gingivally

Cl ΙΙ Composite : Conventional:- After old Amalgam filling removal- At root area- Flat floor- Dentin under cuts- 90˚ cavo surface angel- Box occlusal convergence- Proximal walls parallel or convergence occlusally

Beveled conventional:- Preferred over modified - Don’t extend into all occlusal surface fissues- Little faciolingual extension- Little isthmus width extension

Modified :- Bevel on all axio proximal walls