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matrices and wedges l Preclinical Operative MCQ

 Dental matrices (Tofflemire, Omni, automatrix and sectional matrix) and wedges (piggy back, wedge wedging and double wedging technique) l Preclinical Operative MCQ for dental students


Dental matrices (Tofflemire, Omni, automatrix and sectional matrix) and wedges (piggy back, wedge wedging and double wedging technique) l Preclinical Operative MCQ for dental students


Dental Matrices and wedges

  • Is a piece of metal or non-metal which is used to support and give form to the restoration during its packing and hardening.
  • A matrix system provides and takes the place of the proximal tooth surface that removed during preparation.

Importance of Dental Matrices:

  • It serves as a temporary wall during condensation of plastic restorative material to apply force which is necessary for condensation or packing of these materials into compound cavities.
  • It maintains the form of the restoration until hardening.
  • It restores contours of the tooth to restore its function, shape and esthetics, and also prevent marginal overhangs of the restoration that maintain supporting structures “alveolar bone, periodontium, and the gingiva".

  1. The height of contour allows the flection of the food during mastication to protect the gingiva from injury by hard food. also it makes some gentle massaging ta gingiva.
  2. If over contour: food impaction and chronic inflammation
  3. If under contour: continuous trauma on the gingiva and chronic inflammation.
  4. Generally in the anterior teeth, the height cf contour located in:

    • Buccaly: is present at the junction between the cervical and incisal two thirds.
    • Lingually: in the gingival one third.
  • But in the posterior teeth:

  1. Buccally: is present between the occlusal two thirds and the cervical one third.
  2. Lingually: at the mid of the middie third.

It restores the accurate contact between two adjacent teeth:

  • The contact area is formed by the convexity of the proximal surfaces of two adjacent teeth.
  • The contact area displaces the body of the tooth from the body of the other adjacent tooth to allow the presence on interseptal bone.
  • The contact area is a future of a contact point (teeth touch each other's in a point not area) with natural physiologic attrition.

Functions of the contact area:

  1. Prevent food impaction with subsequent pocket formation recurrent caries and bone resorption
  2. Prevent the teeth drifting by the anterior component of force that happen naturally after extraction.

The position of the contact area:

  1. At the incisal one third, and by moving posteriorly the contact area increases in size and moves more apically
  2. In the anterior teeth: the contact area in the labial one third
  3. In the posterior teeth: the contact area is in the middle of the middle third

Surface texture of surface under the contact is very important as:

  • The inter-proximal surface below the contact area is considered caries prone area due to food impaction in it, so if this surface is rough then high food retention will occur and increase the caries incidence. So the contact area surface should be smooth
  • Duplicate the size of restored C.A to the same size of the natural tooth, because the presence of a contact area creates an embrasure (triangle all around the C.A)

Embrasure functions:

  • Buccally and lingually are spillways to the food. So when mastication occttrs, the food escapes buccal and lingual then the cheek and the tongue push the food up again to the occkrsal table.
  • Gingival embrasure contains the Gingival col and the healthy gingiva lead to healthy interseptal bone.

It restores the marginal ridge:

  • It's a triangular elevation connecting the buccal with the lingual walls and from the lingual towards the buccal to meet in mid mesial or mid distal fossa.

Function of the marginal ridge:

  1. Augmentation of the buccal and lingual lobes of the tooth
  2. This gives thickness to the restoration and increases its strength
  3. Increase the tightness of the contact during function; and this prevents food impaction (During cusp to fossa relation).

Requirements of dental matrix:

  1. Easy application and removal.
  2. Smooth, to create smooth proximal that won't need finishing.
  3. Thin thickness to avoid the need of addition after removal.
  4. Rigid enough.
  5. Contourable (can maintain the contour).
  6. Compatible with the restoration, doesn't stick to the restoration when removed, otherwise the whole restoration will be removed.

Classification of dental Matrix:

1. According to the mode of retention:

  • With retainer
  • Without retainer

2.According to the material

  • Celluloid (clear)
  • Metallic (not clear)

3.According to the contouring of the matrix band:

  • Straight
  • Contonred

4. According to the class:

  • Class 1 cavity with in the buccal, palatal extensions: by tofflemire with Double banding technique.(Baton matrix)
  • Class 2:  

  1. Ivory number 8 “The same as tofflemire” Used when missed 2,3, or 4 surfaces. The retainer clamps the ends of the band and tightens it around the tooth and narrowing the band lobe ,
  2. Ivory number 1Rarely used when missing one proximal surface.
  3. Tofflemire
  4. Auto-matrix
  5. Supermat
  6. Omni-matrix
  7. Sectional matrix
  8. Compound-supported matrix

  • Class 3:

  1. Clear celluloid matrix
  2. S-shaped matrix

  • Class 4:

  1. celluloid strip
  2. rubber base index matrix

  • class 5:

  1. cervical clear matrix

Occlusal stamp technique

  • To restore the anatomy of the occlusal surface in composite.
  • Before cavity preparation, application of Vaseline or any separating medium on the occlusal surface and flowable composite over it to duplicate the details, then leaving the brush of bond within the flowable composite and curing. 
  • This creates an impression of the ccclusal surface. 
  • After cavity preparation and restoration with composite, restore the stamp again on it so this stamp will give the contour so it's considered a matrix

 

Rules of band and matrix application:

  • the proximal should be contoured, otherwise no contact area will be formed + the marginal ridge will touch the neighboring so it will fracture or cause food impaction
  • When the matrix band is folded, the loop will have two circumferences:

  1. The larger circumference of the band is the occlusal edge and is always placed toward the occlusal surface.
  2. The smaller circumference of the band is the gingival edge and it is always placed toward the gingiva.

  • The matrix band should be placed in the retainer so that the slotted side of the retainer is placed gingivally.
  • The straight matrix retainer is normally placed on the buccal side.
  • The loop of the band could be placed centralized from right or Left depending on the location of the tooth so that the retainer is parallel to buccal surfaces of teeth and not disturbed by cheek movement.

Double matrix technique:

  • Indicated when using tofflemire matrix for compound class l(OP/OB).
  • A piece of stainless matrix material is cut and fitted between the tooth surface and the band, a compound coated wedge is inserted in between and adapted by a burnisher.
  • Indicated to provide a well-adapted matrix buccally and palataly.

 

Dental matrices used for Class 2 tooth cavity preparation

  • Examples are : Ivory number 8 “The same as tofflemire”,Ivory number 1, Tofflemire, Auto-matrix,  Supermat, Omni-matrix, Sectional matrix, Compound-supported matrix
  • All of them use circumferential bands that have the same disadvantage: problem of contact and contouring, and Push & pull effect, and the difference is in easing the use only.

Tofflemire dental matrix

  • The most universal type : used since 1946. It's TOO OLD!

Advantages of Tofflemire dental matrix :

  1. Easy in application and removal.
  2. Smooth proximal surface
  3. Contour-able

Disadvantages of tofflemire dental matrix:

  1. This band is Un-contoured, which must be contoured by the dentist, otherwise the proximal surface would be straight. So if contact area is present, it would be at the marginal ridge with subsequent food impaction and fracture of the marginal ridge will occur.
  2. In MOD cavity especially in wide cavity: every time when making pressure on the amalgam with the band distally by burnisher to touch neighboring, the band will open mesially and vice versa (Push & pull effect).
  3. In composite it will lead to open contact, as composite doesn't have the property of maintaining form after condensation like amalgam, but it-relapse after the removal of the condenser leading to open contact.

  • There is a contoured tofflemire band where the whole proximal surface is contoured (convex), but it is expensive and not available in markets.
  • The clinical solution is to make some loosening in the band, so the band will touch mesially and distally. But opened facially and lingually that leads to excess restoration on the facial and lingual surfaces. From this they found that what they need is to shift to another type of matrices and bands.

B. Omni dental matrix

  • It's a pre-assembled tofflemire (ready-made disposable)
  • It's simplifies the application
  • It still has the problem of contact and contouring, and Push & pull effect.

C. Automatrix

  • It has multiple diameter bands (pre-rolled, coil) and this coil has a loop for tightening and loosening adjusted with tightening device.
  • It has different sizes (premolar and molar) and it has different heights.
  • It was introduced to facilitate the application only, but still has the previous problems.

D. Supermat system

  • Mixed system between Omni matrix and automatrix.
  • Consists of tightening device +plastic head +traditional bands (pre-contoured or contour-able).
  • Advantage: cheaper than auto matrix.
  • Disadvantage: the same problems as it's circumferential too "Push pull effect, contour problem and C.A problem"
  • To solve all of these problems, sectional matrix was introduced that is just limited to the proximal wall instead of circumferential around the whole tooth.

E. Sectional matrix:

  1. Rigid material supported sectional matrix system
  2. sectional matrix system "Early and modern or modified"
  3. Adhesive sectional matrix

WEDGES:

  • These are the third component of matrix system.
  • Wedge must be triangular or trapezoidal in cross section.

Technique in placement of wedges

PIGGY BACK

  • It is useful in patients with gingival recession.
  • A second smaller wedge is placed on the first wedge to prevent gingival overhanging.

DOUBLE WEDGING

  • It is useful in case of wide proximal box.
  • Wedges are placed from both lingual and facial surfaces.

WEDGE WEDGING

  • Indicated in case of maxillary 1st molar due to the presence of mesial concavity, a second wedge is inserted between the first wedge and band.

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