Cavity preparation is necessary when teeth develop carious diseases, shatter, or lose substance owing to abrasion or erosion.
This will allow a substance to the place that will restore the tooth’s original shape and function.
Depending on the extent of the damage and the type of restorative material to employ, use several cavity preparation schemes.
For cavity preparation, special drilling equipment utilizes at varied speeds in conjunction with hand instruments.
The difficulty with cavity preparations is that they must finish with extreme caution to incorporate all critical design characteristics while preventing encroachment on the underlying crucial pulpal tissues, which contain a core within the teeth.
Materials used for tooth restoration splits into two categories: directly placed into a prepared cavity, such as amalgam and resin composite,
and manufactured to a stone cast of the cavity and then glued with special cement, such as cast gold and porcelain.
Directly-placed restorations, on the other hand, account for the vast majority of restorations utilized by dentists worldwide due to cost considerations.
When specific types of bacteria found in the mouth (Streptococcus mutans) digest carbohydrates leftover from food detritus to create acids, carious sores form.
This assaults the teeth’ surfaces, causing demineralization and the production of carious lesions as a result of the loss of calcium and phosphorous.
Lesions can appear on any tooth surface and advance from the outer surface of the enamel to the dentin.
Once the lesion has passed through the dentin-enamel junction and into the dentin, it has fully created a cavity.
Black, who regard as the father of operative dentistry, divided carious lesions into five classes over a century ago, with a sixth class, class 6, added subsequently.
These classifications are based on the type of surface(s) involved. Black’s original categorization utilize in education around the world today.
A cavity is normally somewhat larger than the size of the carious lesion when prepare to remove it.
It has an outline form on the tooth surface that alludes to the cavity’s perimeter.
This is usually a little bigger than the carious lesion’s perimeter.
To ensure the restoration’s endurance, the cavity must have subtle elements included in its form.
Retention and resistance forms are the terms that describe these characteristics.
Retention forms are characteristics that allow a cavity to keep a repair in situ without shifting.
If one imagines a Class I cavity as a box, and the base of the box (pupal floor) somewhat bigger than the aperture (occlusal), there absolutely no way for a restoration placed in such a cavity to come out in one piece.
The cavity design that avoids fracturing of the restoration or the tooth itself refers to as resistance forms.
Amalgam, for example, is a fragile substance that may shatter under mastication loads if employed in thicknesses less than 2 mm.
As a result, a cavity prepared for amalgam restoration must have at least 2 mm of amalgam thickness on the occlusal.
Dentin, which is softer than enamel, functions as a cushion to support enamel and prevent it from breaking.
Mastication forces may cause an enamel margin to fracture if left unsupported during cavity preparation for amalgam.
Cavities construct for many years with a combination of slow-speed rotary and manual instruments.
In the late 1950s, high-speed rotary instruments announced
These power by air turbines and spin at rates of over 400,000 rpm.
These handpieces include an air-water spray to promote appropriate cooling and prevent overheating of dental tissues.
cavity preparation finished quickly due to the high effectiveness of tungsten carbide burs utilized in these handpieces.
Diamond burs can also used to prepare the intra-coronal cavity.
Steel burs used with slow-speed handpieces with rotating speeds ranging from 500 to 15,000 rpm to remove soft deteriorated dentin, refine and finish cavities.
Cavities rinsed with water and cleaned of any remaining material once cavity preparation completed in preparation for the restoration.
Other cavity preparation techniques, such as air abrasion and laser, developed by the industry over the years,
but their utilization has never gained traction due to their inherent limitations.
CAVITIES IN CLASS I
Pits and fissure caries (occlusal surfaces of posterior teeth, lingual pits of upper incisors, and buccal/lingual pits of molars) are classified as Class I caries.
Once the amount of the damage has been assessed and the outline form to made has chosen, cavity preparation can begin.
For this type of evaluation, a direct clinical examination along with the interpretation of bitewing radiography images usually required.
Radiographic pictures, on the other hand, are ineffective in the early stages of Class I caries.
A pear-shaped bur, tungsten carbide # 245, used in a high-speed handpiece with thorough water-cooling to first establish cavity depth on a lower molar,
for example, if the carious lesion found to involve all of the fissures on the occlusal surface.
The bur dropped into the central fossa until it reaches a depth of less than 2 mm.
The bur then pushed back and forth across the central developing groove, from mesial to distal, to remove carious dental tissues.
At the same time, the cavity outline will establish. To complete the caries clearance, the buccal and lingual developing grooves are similarly engaged.
THE PEAR SHAPED BUR?
The pear-shaped bur was chosen because it aids in generating a slight convergence of the cavity’s buccal and lingual walls towards the occlusal opening (undercut effect).
This will generate a cavity base that is slightly bigger than the occlusal aperture required to hold the restoration in place (retention form).
If the carious lesion has progressed beyond 2 mm in-depth, the decaying dentin is carefully removed with a spoon excavator.
The subfloor, which is often a rounded concavity that extends beyond the pulpal floor level, is formed as a result of this.
To finish the subfloor and remove any residual rotten dentin, a slow-speed handpiece is employed with a large-size round bur.
The cavity walls and floor are next finished and refined with slow-speed burs.
An occlusal carious lesion can occasionally be linked to one on the buccal or lingual surface.
The next step is to create a Class I cavity with a buccal or lingual extension.
Depending on the extent of the lesion, the extension may or may not entail the preparation of a step.
If the lesion on the buccal or lingual surface is below the pulpal floor, a step must be prepared.
CAVITIES IN CLASS II
Caries lesions of class II appear on the proximal surfaces of premolars and molars.
They can happen in conjunction with occlusal (Class I) caries or they can happen on their own.
A two-surface cavity is produced when caries are present on both the occlusal and proximal surfaces of the tooth.
However, the dentist frequently has to break through an otherwise healthy marginal ridge to obtain access to the proximal carious disease.
Because there are no other means to reach such lesions for comprehensive caries eradication
this is referred to as the “convenience form.”
The proximal box refers to the proximal section of the cavity that is produced during this procedure. It has a floor and walls (gingival) (buccal, lingual, and axial).
To offer retention against vertical displacement, the floor should be slightly larger than the occlusal opening (undercut effect).
Furthermore, because the proximal box has only three walls additional retentive methods
used to prevent the proximal component of the restoration from sliding out of the box horizontally.
For this aim, a small round bur (1/4 round) use to carve retention grooves in the box at strategic spots (axiobuccal and axiolingual lineagles).
When an oblique ridge not present, a dovetail outline followed on the occlusal region of the Class II cavity on some teeth,
such as maxillary molars, to offer retention against horizontal displacement of the proximal portion restoration.
HOW TO AVOID STRESS CONCENTRATION IN AMALGAM RESTORATION?
To avoid stress concentration in an amalgam restoration, the axiopulpal lineangle,
which generated by connecting the proximal box to the occlusal cavity, must round off.
In the long run, this could result in an isthmus fracture.
Beveling of the gingival Cavo-surface border another resistance element included in the proximal box.
This is to remove unsupported enamel rods that could otherwise break off under mastication forces leaving a gap at this vital margin.
A slot cavity, which is essentially the proximal component of the Class II preparation
prepared when a Class II carious lesion exists without occlusal involvement.
In such circumstances, retention grooves at the lineangles are critical because in the absence of the occlusal part,
they are the only method of preventing horizontal movement.
A large Class II cavity might potentially affect all five surfaces of molars.
This happens when occlusal caries extends buccally and lingually
through the grooves and there are carious lesions on both proximal surfaces.
Additional measures of retention, such as the implantation of pins
may be required in more severe cases where one or more cusps have been lost.
CAVITIES IN CLASS III
Carious lesions on the proximal surfaces of incisors and canines are classified as Class III. Except for cavities on the distal surfaces of canines,
which may treated with amalgam, they usually restored with resin composite.
For access to the carious lesion, a Class III cavity usually involves the lingual or buccal surface.
Both the lingual and buccal surfaces implicated in more extensive lesions.
In a high-speed handpiece, a smaller pear-shaped tugsten carbide bur (#330) utilized to prepare them.
If the lesion is just on the proximal surface, access usually achieved through the lingual surface to preserve the labial surface’s continuity.
The cavity essentially box-shaped, with three walls and an axial floor (gingival, incisal, and labial or lingual depending on access direction).
A 12 mm bevel applied to the accessible cavo-surface margin to increase the surface area available for bonding and improve the seal.
CAVITIES IN CLASS IV
Class IV caries affect the incisal angles and occur on the proximal surfaces of incisors and canines.
They occur in two situations: when a Class III lesion left untreated it spread incisively until it reaches the incisal angle
or when teeth, most commonly maxillary central and laterals subjected to impact fracture in domestic incidents resulting in Class IV lesions.
Resin composite used to restore Class IV cavities.
Cavity preparation in the case of an incidental fracture usually limited to a wide 2 mm all-around bevel of enamel cavo-surface margin.
This ensures that the repair held in place by bonding.
All five tooth surfaces involved in extensive Class IV restorations.
When a Class III carious lesion developed to the incisal angle, the carious lesion excised first,
and then a retention groove inserted at the gingivo-axial lineangle.
After that, the cavo-surface margin beveled as shown above.
CAVITIES IN CLASS V
Class V lesions appear on the buccal and lingual surfaces of premolars and molars
as well as the cervical 1/3 of the labial surfaces of incisors and canines.
They occur in one of two ways: through the production of cavities or the loss of tooth material owing to abrasion/erosion.
The restoration of abrasion/erosion lesions that thought to be shallow is not possible.
Class V cavities commonly treated with resin composite on incisors, canines, and premolars
However, they are either resin composite or amalgam on molars.
Although a resin-modified glass ionomer used to restore them, resin composite offers superior aesthetics.
The floor (pulpal) and four walls of a Class V cavity essentially box-shaped (occlusal, cervical, mesial, and distal).
Retention grooves placed along the occluso-pulpal and cervico-pulpal lineangles when amalgam employed.
When resin composite utilized, the cavo-surface margin beveled all the way around to maximize the amount of surface area available for bonding and to improve the seal.
CAVITIES IN CLASS VI
Attrition causes Class VI lesions on the incisal surfaces of front teeth and the cusp tips of canines, premolars, and molars.
A worn-down center dentin island surrounded by a ragged enamel perimeter is the most common look of the lesion.
For posterior teeth, resin composite or amalgam can used to repair them.
Cavity preparation is essentially a box with four walls and a floor (pulpal).
When the cavity shallow resin composite advised because it does not have the same risk of fracture under occlusal loads
as amalgam when utilized in thin sections. Given that such lesions occur directly on top of pulp horns, this is a significant advantage.
IMPLICATIONS OF RESEARCH AND CLINICAL APPLICATIONS
Overheating of teeth never a problem as long as enough air/water cooling spray used during high-speed cavity preparation.
Overheating can avoid by using light intermittent pressure and sharp fresh burs while drilling.
Another key in minimizing heat buildup during cavity preparation especially when utilizing slow-speed burs
is frequent rinsing and removal of dental debris.
According to research, stress-concentration zones eliminated when internal lineangles of cavities produced circular rather than acute.
As a result, providing an even distribution of stresses created during mastication helps to prevent cuspal fracture or amalgam fracture.
If the occlusal was not engaged with caries research has revealed that it is best to prepare two independent slot cavities
while preparing premolars for MOD (mesio-occluso-distal) amalgam restorations.
This keeps the buccal and lingual cusps together and prevents them from breaking.