Definition

Minimum Intervention Dentistry (MID) is a modern medical approach that is aimed at the control and prevention of dental caries through early intervention of the causes of the dental caries.¹

Principles

The principles of MID include early recognition of dental caries, reduction of risk factors, optimal prevention to aid in regeneration, minimum intervention through restoration.²

Rationale

The rationale behind Minimum intervention dentistry is the prevention of extension and drilling without filling. This requires the involvement of two components: Dentist as a physician for early detection and assessment of dental caries and dentist as a surgeon for minimum surgical intervention of cavitated lesions.³

Treatment Modalities

The treatment modalities in MID can be categorised into different phases.

Phase 1: Diagnostic phase: Non-Invasive Interventions:

The first step is to detect the initial and early caries. If the caries are detected at an early stage, then their progression can be arrested by appropriate preventive measures. This early detection is highly subjective and thus should be carried out using proper diagnostic aids.

Conventional approach:

Assessment of risk factors:

Patient's age, Oral health status, Fluoride exposure, Dietary habits, Nutritional status, Medical illness and other caries risk activities should be assessed.

Visual examination:

The size, shape, structure and colour of the tooth is examined to detect any changes. Presence of plaque, debris and other local factors should be checked to assess the texture of the enamel. Gingival and periodontal status is also assessed by the presence or absence of bleeding.

Probing:

The extent and depth of the caries is determined by probing using an explorer. This is not highly reliable as it is a subjective method.

Radiographic examination:

Radiographic examination is a useful tool to decide the treatment plan. The radiograph of choice is bitewing radiograph as they reveal early caries, especially, the proximal caries.

Newer Diagnostic Aids:

Transillumination and fluorescence are the newer diagnostic aids for the early detection of caries. They are used in conjunction with the conventional ones for achieving a proper diagnosis and treatment planning.

Phase2: Preventive phase: Selective Invasive Intervention:⁷

The carious lesion begins due to an imbalance between the process of remineralization and demineralization. This preventive phase is aimed at the remineralisation of early lesions regaining the lost mineral structure of the tooth. The process of remineralization can be obtained by:

Alteration of pH which can be done by the following methods:

Reduction of cariogenic bacteria

Reduction of carbohydrate intake

Reduction of plaque and other local factors

Increasing salivary flow

Preventive Aids:

Fluoride exposure:⁸

Fluoride application stimulates the calcium and phosphate ions present in the saliva to form fluorapatite crystal which has an acidic pH of nearly 4.5 thereby preventing demineralization. Fluoride application can be systemic or topical. The systemic fluoride application is achieved through public water supply and topical fluoride application is through fluoride rinses, fluoridated dentifrices or professional application of fluoride gels.

Antimicrobial agents:⁹

Antimicrobial agents like chlorhexidine and povidone iodine can reduce the number of cariogenic bacteria. Chlorhexidine is available as mouth rinses, gels and dental varnishes in various concentrations ranging from 0.1 to 40%. Povidone iodine is usually available as 10% solution for topical application.

Mechanism of action:

The development of decay can be effectively prevented using antimicrobial agents in conjunction with other preventive aids. Chlorhexidine reduces the cariogenic micoorganisms in the oral cavity leading to a decrease in the production of acids, thereby preventing dental caries while povidone iodine is a water soluble compound and it liberates iodine which has antimicrobial action. The slow release of iodine from povidone iodine allows for long term antibacterial effect in the prevention of dental caries.

Xylitol gums:^10,11

Xylitol chewing gums prevent dental caries by inhibiting the binding of sucrose molecule. An increased antimicrobial effect is seen when xylitol is used in combination with chlorhexidine.

Mechanism of action:

Xylitol is a five carbon sugar alcohol that resembles sucrose and is therefore a good sugar substitute and it has antibacterial properties because it is not metabolized by the cariogenic bacteria.

Advantages:

Increased patient convenience as it can be easily chewed. Pleasant taste and thus effective compliance is seen among pediatric patients.

Disadvantages:

Dosage should be controlled. The recommended dosage is 8 grams a day. If it exceeds, then symptoms like diarrhoea can occur.

Pit and fissure sealants:¹²

Acid resistant resin sealants are filled in the deep pits and fissures which prevents the caries attack and also aids in effective tooth brushing.

Rationale:

Application of sealants will modify the patent pits and fissures into smooth surface which prevents bacterial growth in these surfaces.

Materials used:

Resin composites and High viscosity glass ionomer cements

Procedure:

Oral prophylaxis:

All the local factors like plaque and calculus should be removed with the help of thorough scaling.

Isolation:

Optimum effect of the sealants is achieved only through proper isolation. Rubber dam placement is the ideal method for isolation. Cotton rolls can also be used.

Etching the tooth surface:

The tooth should be etched to create a dry surface with micro porosities for better penetration of the resin. Ortho Phosphoric acid is usually recommended.

Application of bonding agent:

Before placing the bonding agent, the surface should be completely washed and dried for the complete removal of the etchant. A hydrophilic bonding agent is applied to the tooth surface and then cured for better retention.

Placement of the sealant:

The sealant is placed into the pits and fissures as per the manufacturer's instructions. The surface is then cleaned with cotton pellets.

Advantages:

It is not only a preventive measure but can also arrest non-cavitated enamel caries.

Disadvantages:
This method is highly technique sensitive. Resealing is usually needed. Hence, timely recall and review is essential.

Phase 3: Recall phase: Minimally invasive intervention phase:

If there is cavitation, then caries excavation has to be done and the tooth has to be restored. Minimal intervention dentistry does not follow G.V. Black's classification as it requires definite cavity preparation regardless of the size, site and extent of the carious lesion. Hence, it follows Graham Mount and Hume's classification which emphasises gaining access to the caries and removal of infected dentin only, which is as follows:¹³

Site of Occurrence:

Site 1 - the pits and fissures on the occlusal surface of posterior teeth and other defects on otherwise smooth enamel surfaces.

Site 2 - the contact areas between any pair of teeth, anteriors or posteriors.

Site 3 - the cervical areas related to the gingival tissues including exposed root surfaces.

Size of the carious lesion:

Size 0 – the initial lesion at any Site that can be identified but has not yet resulted in surface cavitation – it may be possible to heal it.

Size 1 – the smallest minimal lesion requiring operative intervention. The cavity is just beyond healing through remineralisation.

Size 2 – a moderate sized cavity. There is still sufficient sound tooth structure to maintain the integrity of the remaining crown and accept the occlusal load.

Size 3 – the cavity needs to be modified and enlarged to provide some protection for the remaining crown from the occlusal load. There is already a split at the base of a cusp or, if not protected, a split is likely to develop.

Size 4 – the cavity is now extensive following loss of a cusp from a posterior tooth or an incisal edge from an anterior tooth.

Scoring is done on assessing both the site and size of the carious lesion. For instance, caries occurring in the pit and fissure with minimum cavitation is given a score of 1.1.

The caries removal can be done by one of the following methods: ^14,15

Mechanical method -Atraumatic Restoration (ART), Rotary instrumentation, Sonic oscillation

Chemomechanical method-Enzymes

Kinetic energy system-Air abrasion

Hydro kinetic method-Lasers

Ozone technology

Mechanical method:

ART:¹⁶
Atraumatic restoration is presently called as Interim Therapeutic Restoration which involves the removal of soft, completely demineralised carious tooth with hand instruments followed by restoring the cavity with an adhesive dental material that simultaneously seals any remaining pits and fissures which remain at risk.

Principles:

Only hand instruments should be used for caries excavation.¹⁷The restorative material should be adhesive.¹⁸

Case selection:

The success of the treatment depends mainly on case selection. ART is usually indicated in small cavities which can be excavated using hand instruments. In cases of deep caries or in cases where multiple surfaces are involved, ART is not preferred.

Materials used:

Glass ionomer cements and Resin based composites.

Glass ionomer cements are preferably used because it bonds chemically to both enamel and dentin. While, Resin based composites bond only to enamel.

Mechanism of action:

Adhesive dental materials do not require much of mechanical retentive features. Hence they are used in this technique after hand instrumentation. Glass ionomer cements chemically adhere to the tooth structure through the exchange of ions which prevents microleakage, secondary caries and pulp contamination.

Rationale for using Glass Ionomer Cements in ART:¹⁹

They are highly bio-compatible. They release of fluoride, calcium phosphate and strontium ions thereby promotes remineralization and prevents caries progression. They act as reservoir of fluoride by taking up fluoride ions from dentifrices and releasing it over time.

Procedure:

Step 1: Tray Set up:

Diagnostic instruments, Spoon excavator and Enamel hatchet for excavation, Cotton rolls, Applicator tip, Agate spatula for mixing the material, Plastic filling instrument for material placement, Dentin conditioner, Type II Glass ionomer cement, Surface protecting agents like vaseline, Cocoa butter or petroleum jelly. Before the treatment is started, all these required instruments and materials are arranged in sequence in which they are going to be used.

Step 2: Isolation of the tooth:

Like all other restorations, isolation is mandatory for good prognosis. Rubber dam is not necessary for isolation. Cotton rolls are sufficient.

Step 3: Caries Excavation:

After examining the carious lesion using probe, the soft carious dentin is removed using spoon excavator and for additional access, enamel hatchet can be used.

Step 4: Tooth conditioning:

Dentin conditioner is applied on the tooth and the adjacent pits and fissures. This is done to remove the smear layer.

Step 5: Restoring the cavity and surface protection:

The material is mixed in the recommended powder to liquid ratio and placed into the cavity before it sets. A small amount of petroleum jelly is applied over the restoration for finishing and then pressed with the finger which removes the excess material. This is then removed immediately using a probe or excavator and again petroleum jelly is placed to prevent moisture contamination. The patient is informed not to eat anything for the next one hour.

Advantages:
No drill is required. Hence, use of local anesthetics is not needed. There is minimal loss of tooth structure. This method is time saving and cost effective. Repair of the defective restoration is easy.

Disadvantages:
No actual disadvantages exist provided the case selection and the treatment procedure is carried out properly.

Rotary instrumentation:

High speed air turbine hand piece with slow speed bur is used for excavation. As discussed earlier, the cavity preparation is based on Graham Mount and Hume's classification. Only the infected dentin is removed leaving behind the affected dentin. The material of choice would be composites or amalgam. For caries occurring in the pits and fissures, minimal cavity preparation is sufficient. For proximal caries, a more conservative approach named 'Tunnel preparation' can be done. In this technique, the preparation starts from the occlusal surface and the marginal ridge is preserved. This method is technique sensitive and studies have proved that the longetivity is less when compared to the conventional Class II preparation. For cervical caries, the caries should be carefully removed using hand piece and slow speed bur and then can be restored. If the areas are self cleansible, then restoration is not needed. Proper oral hygiene maintenance by itself would prevent the caries progression.

Sonic oscillation:^20,21

High frequency sonic air scalers with modified abrasive tips are used for caries removal. The cutting tips are coupled to high-frequency, sonic, air-scaler hand pieces under water cooling. The hand piece oscillates in the sonic region < 6.5 kHz and the tips perform an elliptical motion.

Advantages:

This technique does not alter the surface topography of the dentin and the smear layer is completely removed.

Disadvantages:

An initial preparation of the enamel with burs is usually required. Hard carious structure is removed which may result in removal part of the dentin which can get remineralised. This system is not cost effective.

Chemomechanical method:

Chemomechanical method is the non-invasive hand excavation method with the aid of a chemical gel.²² They selectively remove the softened dentin and conserves the tooth structure and also aids in bonding adhesive restorations. Caridex system and Carisolv is the most commonly used method, while other enzymes like papacarie, papain, chloramine and toluidine blue can also be used.²³

Mechanism of action:

Within a carious lesion, there are normally two zones which can be identified. There will be an inner layer where there may be partially degradation but the collagen fibres would still be intact so this region would have the capability of being re-mineralised. There will also be an outer layer where the collagen fibres are partially degraded so this region cannot be re-mineralised. On application of these enzymes, this partially demineralised outer layer is completely degraded.

Procedure:²⁴

Caridex was the first found chemomechanical method. It has two solutions. Solution I has sodium hypochlorite and Solution II has glycine, amino-butyric acid, sodium chloride and sodium hydroxide. The two solutions are mixed immediately before use and a working reagent is formed which is stable for almost one hour. A special delivery system has to be used with the reagent where the solution would be warmed to body temperature using a heater and pumped through a tube into the hand piece which has an applicator tip. The applicator tip is available in various shapes and sizes and it loosens the carious dentine by a gentle scraping motion. The debris along with the applied solution is then removed by aspiration. Application will be continued until the sound dentin is formed.

Carisolv is similar to the Caridex system in its mechanism of action, but it is available in the form of a gel which can be applied directly to the carious lesion with hand instruments and no special delivery system is needed. More quantity of gel is then applied and the procedure repeated until no more carious dentine remains. When the gel removed from the lesion is clear, it indicates that the carious dentine has been removed. The time required for the procedure is about 9-12 minutes and the volume of gel required is vey less nearly 0.2-1.0ml. Rotary instruments may still be required for some cavities.

Advantages:

By this method, Painful removal of sound dentin is avoided. There is a reduced need for local anaesthesia and also reduced risk of pulp exposure. This is helpful for the treatment of medically compromised patients as well as pediatric patients.

Disadvantages:

Chemomechanical method is time consuming. Rotary and hand instruments are still needed for removal of tissue or material other than degraded collagen.

Kinetic energy system:²⁵

Air abrasion in cavity preparation removes tooth structure using a fine stream of particles generated from compressed air or bottled Carbon dioxide or nitrogen gas. Minimal surface preparation can be achieved using kinetic air abrasion system.

Mechanism of action:

During air abrasion, an instrument like a mini sandblaster is used to spray away decay. A fine stream of particles made of silica, aluminum oxide, or a baking soda mixture are propelled towards the tooth surface by compressed air or a gas that runs through the handpiece. Small particles of decay on the tooth surface are removed as the stream of particles strikes them. The particles of decay are then suctioned away through a thin tube.

Advantages:

Cavity preparations obtained by air abrasion system has more rounded internal contours than those prepared with handpiece. This increases the longevity of the restoration by preventing fracture of the restoration. They create reduced noise, vibration and sensitivity.

Disadvantages:

The major drawback of air-abrasion excavation of carious dentin is that sound dentin is more efficiently removed than carious dentin. The air and abrasive particles can cause sensitivity. Only composite filling material can be used following air abrasion because it adheres well to the smooth surface created by the air abrasion. This cannot be used in patients with dust allergy, asthma, chronic obstructive lung disease, etc as it may result in air embolism.

Laser for caries removal:²⁶

LASER is an acronym for Light Amplification by Stimulated Emission of Radiation which emits coherent beams of very high intensity light .They can be used for carious dentin removal, fissure sealing, cavity cutting and for caries prophylaxis as well. They are used for a number of purposes in dentistry like caries diagnosis, cavity preparation, disinfection of root canals, disinfection of periodontal pockets and for the treatment of tumours as well.

Lasers used in MID:

Erbium lasers are the commonly used ones in the field of operative dentistry. Two types of Erbium lasers are available namely, the erbium-yttrium-aluminum-garnet (Er: YAG) and the erbium, chromium: yttrium-scandium-gallium-garnet (Er, Cr: YSGG). The lasers used in dentistry have a wavelength ranging from 0.5 microns to 10.6 microns (500 nanometers-10,600 nanometers) irradiated at 100-140 mJ pulse energy.

Advantages:

One of the main benefits of using dental lasers is that they are highly selective and precisely interact with diseased tissues. It Preserves tooth structure. It produces less pain when compared to conventional method.

Disadvantages:

Lasers are more expensive. They cannot be used on teeth with old fillings. They do not eliminate the need for anaesthesia. Drilling is still required for shaping the cavity.

Ozone technology:^27,28

Ozone, a triatomic molecule of oxygen is used in various forms such as oil, water and gas.

Ozone production and Mechanism of action:

Ozone is produced with the help of corona discharge units. Ozone exerts its action by oxidative killing of bacteria, virus and fungi with the release of hydrogen peroxide and carbon-di-oxide.

Method:

Patient uses ozonated water as a pre treatment rinse. Ozonated water is used in the unit water supply bottles. Ozone gas is applied to cavity preparation and crown preparation to sterlize the prepared tooth by oxidizing the remaining pathogens and organic matrix in the enamel, remaining caries and dentinal tubules. This produces a pathogen free oxidized surface that enhances bonding strength and decreases/eliminates post operative sensitivity.

Advantages:

Treatment is simple and inexpensive.

Lessens the treatment time.

No use of drill is required.

Requires no injection of anaesthetics.

No post operative sensitivity.

Prevention of further infection

Disadvantages:

Inhalation of Ozone is toxic to the pulmonary system.

Effective for treating only the early carious lesions.

CONCLUSION:

Minimum intervention dentistry has been more beneficial when compared to conventional therapeutic modalities. It is economical, minimally invasive and an atraumatic approach to dental practice. It eliminates the micro organisms more precisely and it is a painless treatment. Despite all these advances, it is still a challenging approach and needs more improvements for early recognition and prevention of dental caries.

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Received on 30.07.2014 Modified on 16.08.2014

Research J. Pharm. and Tech. 710: Oct. 2014 Page 1169-1174