Health and disease are reciprocal concepts. Each is conventionally defined by the absence of the other. When micro organisms first associate with a host, the host is said to be contaminated.
If the micro organisms establish themselves and grow and multiply for a period of time, the host is said to be infected. If the infection causes damage, the host is said to have an infectious disease.
Micro organism should be identified to explain the etiology and pathogenesis of any infectious disease. It is necessary to introduce criteria for proving the claims that a micro organism isolated from a disease is indeed casually related to it. These criteria were first introduced by Henle and later on, defined by Koch and are known as “Koch’s postulates.”
According to Koch’s postulates, a micro organism should satisfy the following criteria if it is to be accepted as the causative agent of a particular disease. The criteria are,
a) The bacterium should be constantly associated with lesions of the disease
b) It should be possible to isolate the bacterium in pure culture from the lesion.
c) Inoculation of such pure culture into suitable laboratory animals should reproduce the same lesion of the disease
d) It should be possible to re-isolate the bacterium in pure culture from the lesions produced in the experimental animals.
Higher numbers of the suspected pathogens are found frequently in any infection rather than in individual without disease. As the root canal does not possess a normal microbiota all the microorganisms found are considered to be pathogenic. As long as the pulp is vital, it is a sterile tissue and infection occurs only after pulp necrosis. The micro organism present in the necrotic pulp is the source for the peri-radicular disease. Not all but only a few group of micro organisms in the root canal play a role in the pathogenesis of disease process .
Read More......
Endodontics is that branch of dentistry that deals with the diagnosis and treatment of diseases and injuries of the pulp and periapical tissues . The objective of the endodontic treatment is to render the teeth free of its disease and restore to its proper form and function in a healthy state.
Most changes in pulpal and periradicular tissues are of bacterial origin. Since they play a major role in the pathogenesis of pulp and periradicular lesions a fundamental knowledge of endodontic microbiology is needed to understand . The historical perspective of endodontic microbiology begins with the observation of oral flora by Antony Van Leeuwenhoek, which he referred to as ‘animalcules’.
In 1890, W.D. Miller, the father of oral microbiology authored a book called ‘Microorganisms of the Human Mouth’ which became the basis for dental microbiology. He demonstrated the presence of bacteria in necrotic human pulp tissue.
In 1939, Fish described the reaction of the periradicular tissues to bacterial products and antigenic agents from the root canal. He recognized four distinct zones of reaction namely zone of infection, zone of contamination, zone of irritation and zone of stimulation. Of these various zones, microorganisms are confined to the zone of infection by the polymorphonuclear leukocytes. He also theorized that removal of the nidus of infection would lead to resolution of the infection which became the basis for successful root canal treatment.
The true significance of bacteria in endodontic disease was proved by the study done by Kakehashi et al in 1965.When the pulp and periradicular tissues of germ free rats were exposed to the oral cavity flora they found no pathologic changes. Whereas in conventional animals pulp exposures led to necrosis of pulp and periradicular lesion.
Thus the association of the microorganisms with the pulpal lesions was documented through various studies.The disease and the process of tissue destruction is a combined end result of the interaction between the organism (offenders) and the host system (defenders). Therefore it becomes important for the clinician or the dental student to know the cause and effect of microorganisms on the host defense mechanism. Also the characteristics enabling the microorganisms to survive or perish within the endodontic environment must be understood to improve one’s clinical judgement in the treatment of pulp and periapical infections.
Thus the fundamental reason for accurate identification of bacteria from root canals is to disclose bacteria or its combination that may be resistant to conventional therapy or causative of treatment failure.
For many years scientific documentation of this intimate causal relationship and microorganisms was not possible because of the difficulty in isolation and identification of the bacteria related to the disease. In recent years with the advent of improved bacteriologic techniques and cultivation of the microbiota associated with the endodontic infections complex nature of the infection is revealed. Once the in-depth knowledge about the microorganisms is obtained the clinician develops proper understanding of the measures to control endodontic disease process and to manage the patients. Another consideration with the study of endodontic microbiology is the control over cross contamination with the help of aseptic techniques like sterilization and disinfection and also, the protection of the dentist and the patient.
Read More......
The principal effects of conditioning of dentin may be classified as
a) Physical changes
b) Chemical changes
Physical changes
Increases or decreases in the thickness and morphology of smear layer changes in the shape of dentinal tubules.
Chemical changes
a) Modification of the fraction of organic matter
b) Decalcification of the inorganic portion
Conditioning of dentin may be done by several means
1) Chemical
a) Acids
b) Calcium chelators
2) Thermal
a) Lasers
3) Mechanical
a) Abrasion
When dentin is cut for cavity preparation, the wrenched cutting debris of the dentin forms a thin smear layer on the surface. It is also driven into the dentinal tubule apertures displacing the odontoblast process and forming a smear plug at a depth of less than 10-micron meter. Etching dissolves the smear layer and part of the peritubular dentin, leaving tapered cylindrical holes of that depth.
In an experiment on monkey, dentin wall demineralized with a phosphoric acid jelly etchant for 60 sec was completely re-mineralized after 4 months. This results indicates that etching did not result in deleterious effect upon either the collagen fibers or the odontoblast processes, because the presence of collagen fibers maintaining their proper cross bonded structure as a base for apatite crystals to attach to and of the vital odontoblast processes to supply the calcium phosphate from the pulp is essential for remineralization of dentin.
A.J.Gwinnett and M.D.Jendresen (1978) have concluded from their experiments and observations that the surface of acid conditioned eroded dentin is significantly different from that of acid conditioned normal dentin. They further observed the depth of penetration of resin is also less in acid treated eroded dentin where many tubules remain partially occluded by intratubular insoluble deposits.
Ruse and Smith (1991) found when common conditioning agents were used, it has been found by X-ray photo electron microscopy that the outermost surface contains only 10% or less of the calcium and phosphorus initially present. They concluded that the treatment of dentin with acidic conditioners leaves the surface so depleted of calcium and enriched by organic residues that subsequently placed bonding systems should be based upon agents able to interact with organic components of dentin. Bonding agents that rely on chelation to calcium are unlikely to be successful when applied to acid etched dentin unless they penetrate into the demineralized matrix to reach normal, mineralized dentin.
Acid etching of dentin is not harmless but represents one more source of acute irritation to the pulpodentin complex in addition to the vibratory, thermal, mechanical and evaporative stimuli that accompany cavity a preparation. However, it is not as irritating as has been previously thought.
Nakabayashi (1982) introduced the concept of hybridization. The technique consists of applying an acid, ranging in concentration from 10% to 30% to the surface of dentin. Within 15 minutes the acid selectively dissolves away the inorganic component of the dentin to a depth of 5 to 10 microns. It then flows in the dentinal tubule for up to 100 microns at which point it diffuses laterally into the peri-tubular dentin for up to 10 microns.
As in the previous case the calcium component is selectively eliminated. Then these spaces are replaced by an insoluble resin component that completely encapsulates all exposed collagenous fiber.
He also reported that dentin conditioning by citric acid containing ferric chloride followed by a dentin bonding agent containing 4 META (methacryloxyethyl trimellitate anhydride) was effective method of dentinal bonding.
Concerning the bonding mechanism, he proposed that diffusion and impregnation of monomers into the subsurface of pretreated dentinal substrate and their polymerization, creating a hybrid layer of resin reinforced dentin. This newly formed hybrid layer may be thought of as an admixture of polymer and dentinal components, creating a resin dentin composite. This technique not only enhances the shear bond strength of the resin to the dentin but also increase the potential against micro leakage and postoperative sensitivity.
Nakabayashi (1985) suggested that the acidic treatment partially demineralized a zone of the dentin near the surface, facilitating an infiltration process of compatible monomers. The polymerized resin forms a reinforced zone of dentin on which a resin based restorative material can be bonded. The bond strength is not dependent upon interlocking at the dentinal tubules.
Kurosaki et al (1987) found that etching of dentin of the clinical cavity floor allows the chemically adhesive composite resin to produce resin tags of tapered, cylindrical or tubular form as well as impregnated dentinal layers. These changes will considerably improve the bond strength as well as the tubule aperture seal.
Read More......
Any discussion of the effects of acid conditioning of dentin must begin with the acid etching of enamel. This was first proposed by Buonocore (1955) as an attempt to clean enamel, increase the microscopic surface area for bonding, and infiltrate unfilled resins into enamel porosities. Many investigators were alarmed at what was then regarded as an unconventional and even reckless ap¬proach to the problem.
Buonocore, Wilernan and Brudevold (1956) not only intro¬duced the acid etching of enamel to dentistry, they also were among the first to attempt to bond resins to acid-etched (7% HCL, one minute) dentin.
Their success with acid etching of enamel led them to try to acid etch dentin. Unlike enamel, when dentin is etched, its surface becomes mineral -poor protein rich; and it tends to become wetter (Brannstrom and Nordenvall 1977). Unfortunately, Buonocore and his colleagues' suc¬cess with dentin was never realized, because the relatively crude resin materials that were available at that time would not wet dentin very well. Buonocore, however, was very much aware or the requirements for good bonding.
For clinical success, the conditioned dentin must be sealed to prevent sensitivity and to prevent the pathology (Brannstrom, 1981) associated with the increased permeability of the dentinal tubules. Conditioning of dentin will be defined as any alteration of dentin done after the creation of dentin cutting debris, termed the smear layer.
The objective of dentin conditioning is to create a surface capable of micro-mechanical and possible chemical bonding to a dentin-bonding agent.
Goals of acid conditioning of dentin
• Remove the intrinsic weakness of the smear layer to permit bonding to underlying dentin.
• Demineralize the superficial dentin matrix to permit resin infiltration into surface.
• Uncover both intertubular and peritubular dentin.
• Clean the dentin surface free of any biofilms.
It is important to define the purpose of the acid etching of dentin so that once identified, these goals can be tested in a systematic scientific manner.
As the smear layer is intrinsically weak, the first goal is to loosen it or remove it so that subsequently placed adhesive resins can interact with solid dentin adhesive resins can interact with solid dentin matrix. Most smear layers are 1-2 µm thick; they are composed of the cutting debris of the materialized tissue on which they lie. (Ruse and Smith 1991)
The reason for acid etching is to demineralize the solid dentin matrix (both intertubular and peritubular dentin) to increase the porosity of the dentin. While this is analogous to why enamel is etched, the porosities that are produced are of the order of 0.05 – 1-3 µm in peritubular dentin rather than the 5-7 µm diameter of enamel prisms. Further, acid-etched enamel can be thoroughly dried, while that foal is much more difficult in vital, normal dentin. Enamel contains little protein that is at risk of being denatured by acid treatment. Dissolving away hydroxyapatite mineral crystallites from the collagen component of dentin matrix creates dentin porosities. The crystals tend to stabilize collagen and prevent its denaturation.
There is a risk that the acid used to demineralize the dentin may denature or weaken the collagen. As denatured proteins generally change their dimensions, the pores may become smaller if the collagen is denatured. This may interfere with subsequent resin infiltration and prevent the formation of a hybrid layer (Nakabayashi, Nakamura and Yasuda 1991). Another danger in the etching step is that the demineralized zone may extend, for instance, 5 µm into the dentin, while the resin infiltration may only extend 4 µm, leaving a 1 µm demineralized zone at the base of the hybrid layer that is unpro-tected by mineral or resin and that may be structurally weak. If the pulpodentin complex can re-mineralize this unprotected basal 1 µm of demineralized dentin (Tatsumi, 1989; Tatsumi and others 1992), then the layer may become as strong as normal dentin, rather than be a zone of debonding that has been seen in vitro (Nakabayashi and others 1991).
Another purpose of acid etching dentin is to clean the dentin surface. Often dentin is inadvertently contaminated with blood during the cavity preparation. Acid etchant, by dissolving most of the smear layer, tend to float these biofilms on the dentin when it is rinsed. The low pH of the etchant may also denature the plasma proteins and hemoglobin. The purpose of acid etching may vary depending upon the material. If the intention is simply to remove the smear layer but leave the smear plugs in place, as when one uses glass-ionomer cements, then short etching times with dilute acids would seem to be indicated (Bowen 1978; Pashley and Others 1981; Hamlin and Others 1990a).
However, if one wants to create a resin hybrid layer (Nakabayashi and Others 1991) in the dentin rather than on the dentin, then one must demineralized more deeply and in the process, removes smear plugs. This can still be accomplished using dilute acids, but the etching time may have to be extended.
Read More......
Currently phosphoric acid is the acid of choice, but it is possible that other acidic etching agents such as pyruvic acid may be used in the future. A controversial issue, however, is the optimal concentration of phosphoric acid. The most widely used concentrations of phosphoric acid used in clinical practice exceed 30% phosphoric acid. This is partly based on the findings the phase diagram of the phosphoric acid +/- calcium hydroxide +/- water ternary system. They demonstrated that the application of phosphoric acid solutions greater than 27% phosphoric acid resulted in the formation of monocalcium phosphate monohydrate.
While dicalcium phosphate dihydrate was formed with phosphoric acid concentrations less than 27% phosphoric acid. The former product is readily soluble and would be completely washed away in the clinical situation, while the latter product is less soluble. The reaction products, if not completely removed after the etching procedure, may interfere with the bonding of composite resins to etched enamel surfaces.
The effect of phosphoric acid concentration on the tensile bond strength of a conventional composite resin to enamel surfaces etched with 10, 20, 30, 40, 50, 60, and 70% phosphoric acid was determined. The tensile bond strength to enamel surfaces etched with 70% phosphoric acid was significantly lower than the bond strengths recorded to enamel surfaces etched with other phosphoric acid concentrations.
The application of a phosphoric acid etching solution to freshly cut dentin may elicit a pulpal response. To prevent the flow of phosphoric acid applied to the enamel walls of preparations to the freshly exposed dentin at the floors of the preparations phosphoric acid gels were recently introduced. The objective was to confine the acid-etching agent to the intended site of application. It is recommended that the etching agent should be applied to the enamel surface using a dabbing action as opposed to rubbing. Another issue that has not been resolved is the optimal duration of etching with phosphoric acid.
It is surprising that some authors recommend that the etchant should remain on the tooth surface for at least 60seconds to develop an appropriate etched pattern. The etch duration is of particular importance in acid etching enamel prior to the direct bonding of orthodontic attachments, as it is practically impossible to confine the bonding site. Fluoride is not evenly distributed in enamel but allows a negative exponential distribution with fluoride concentration being in the surface enamel.
The loss of fluoride rich enamel surface during prolonged etching may make the adjacent enamel more susceptible to enamel decalcification during orthodontic treatment. The reaction products that are formed on the enamel surface after phosphoric acid etching should be removed completely, as incomplete removal may interfere with bond strength. Etched surface should be washed for at least 15 secs to remove the reaction products.
The tooth to be restored should be isolated with a rubber dam to prevent saliva contamination prior to acid etching and the placement of composite resin. It is generally recommended that saliva contaminated etched enamel should be washed and retched. O’Brien and others showed, however that it was not necessary to re-etch an enamel surface contaminated briefly with saliva, as a thorough washing of such a surface did not have a detrimental effect on bond strength.
Buonocore M (1955) introduced a simple conservative technique for bonding restorative resins to enamel. He placed a drop of self-curing acrylic resin on the labial enamel surface of upper central incisor of ten subjects. One surface was treated prior to resin placement with 85% phosphoric acid for 30 seconds. He noted that the acid conditioning of the enamel resulted in on uncontioned control surfaces lasted less than 12 hours. After three decades of laboratory and clinical research, Buonocore’s method is widely adopted and has added a new and exciting technical dimension to the practice of dentistry.
Gwinnett, Matsui and Buonocore (1969) suggested that formation of resin tags was the primary attachment mechanism of resin to phosphoric acid. Acid etching removes about 10 microns of the enamel surface and creates a porous layer ranging from 5-50 microns deep.
When a low viscosity resin is applied, it flows into the micro porosities and channels to this layer and polymerizes to form a micro mechanical bond with the enamel.
Fusayama et al (1979) introduced an etching technique for both the enamel and the dentin cavity wall using 37% phosphoric acid followed by a dentin-bonding agent containing methacryloxyethyl hydrogen phenyl phosphate (phenyl-P). This improved bond strength greater extent and dentinal etching has become fairly common practice in Japan. However, the concept of total etching only recently has gained acceptance in the United States.
Read More......
TIME
Increased Time Application
High fluoride content and primary teeth require longer etching time. The increased etching time is needed to enhance the etching pattern on enamel that is more a prismatic than that of permanent enamel. Currently 15 sec, a sufficient time to produce a bond equivalent to that produce by a 60 sec etching time is used routinely.
Shorter Etching Time
C.J. Guba et al (1994) highlighted that etching times and etchant consistency were not critical to enamel bond strengths. It yields acceptable bond strength. It conserves enamel and saves time.
They also found that on microscopic examination of a 10 secs etch versus a 60 sec etch showed that etching the enamel for 10 sec produced a very superficial etch compared to a very deep etch with a 60 sec etch. However this did not have significant impact on the tensile strength. Though some researchers suggested that the etching effect is reduced when the etching viscosity of the acid is high, this study showed no significant difference as related to their viscosities.
ACID CONCENTRATION
An interesting and important phenomenon is the existence of an inverse relationship between the etching effect of phosphoric acid and it’s concentration. The phenomenon was first observed and reported in 1965 and subsequently confirmed by others. The same etch time lower concentrations of acid tend to be more destructive of the enamel than higher concentrations
Concentrations of phosphoric acid over 65% tend to show minimal changes. The concentrations of acid, producing consistent, more or less evenly distributed relatively deep etch pattern, appear to be in the range of 30 to 50%. Bond strengths are greater with 30 to 50% acid concentration, the difference between their values and those obtained on surfaces etched with 10 to 70% acid were not as great. The higher concentration of acid may not produce a sufficient in depth etch to provide adequate resin penetration (tag formation) and / or sufficient bonding area to resist repeated long-term masticatory and other dislodging stresses encountered in the oral environment.
In an in vitro study carried out on bovine substrate by M.J.Shingi et al (2000) it was concluded that milder concentrations of phosphoric acid or less aggressive acids could be used to pretreated enamel for orthodontics adhesive systems and sealants if the diffusion potential of applied monomers is high enough.
According to Unos (1996) depths of demineralization increased by both acid concentration and conditioning times following a logarithmic relationship.
Chow and Brown (1973) demonstrated that the application of phosphoric acid solutions greater than 27% Phosphoric acid resulted in the formation of monocalcium phosphate monohydrate while dicalcium phosphate dehydrate was formed with phosphoric acid concentrations less than 27%. The former product is readily soluble and would be completely washed away in the clinical situations.
Read More......
The advantages of ART include the following:
- The use of easily available and relatively inexpensive hand instruments rather than expensive electrically driven dental equipment.
- A biologically friendly approach involving the removal of only decalcified tooth tissues, which results in relatively small cavities and conserves sound tooth tissue.
- The limitation of pain, thereby minimizing the need for local anesthesia.
- A straightforward and simple infection control practice without the need to use sequentially autoclaved handpieces.
- The chemical adhesion of glass ionomers that reduces the need to cut sound tooth tissue for retention of the restorative material.
- The leaching of fluoride from glass ionomers, which prevents secondary caries development and probably remineralize carious dentin.
- The combination of a preventive and curative treatment in one procedure.
- The ease of repairing defects in the restoration.
- The low cost.
From experience gained thus far, the ART technique is a non threatening oral procedure. This characteristic has the great advantage of making oral care more popular among the population – in particular, the young. Fear inducing situations caused by threatening dental equipment are not involved, and there is no noise from a drill or from suction equipment. The maximum number of instruments in the mouth at anyone time is similar to that used during an oral examination, the mirror in one hand and a work instrument in the other. AFT is therefore, patient –friendly.
Obviously, one of the greatest advantages of ART is that it makes it possible to reach people who otherwise never would have received any oral care. The technique allows oral care workers to leave the clinic and to visit people in their own living environments, e.g. in senior citizen homes, institution for the handicapped, villages in rural and suburban areas in economically less developed countries, and in their own homes. From a health point of view, these possibilities must be considered a huge advantage.
Furthermore, ART supports health education and promotion programs, particularly in areas where oral care relies heavily on pain relief through extraction and oral health education. Using ART, a comprehensive package of education / promotion, prevention, curative treatment, and pain relief can be established and delivered to the population through a low cost, out reach oral health program.
The limitations of ART include the following:
- Long – term survival rates for glass ionomer ART restorations and sealants are not yet available; the longest study reported so far is of three year’s duration. The techniques acceptance by oral health care personnel is not yet assured.
- At the moment tissue is limited to small and medium sized, one-surface lesions because of the low wear resistance and strength of existing glass ionomer materials.
- The possibility exists for hand fatigue from the use of hand instruments over long periods.
- Hand mixing might produce a relatively unstandardized mix of glass ionomer, varying among operators and different geographical/climatic situations.
- The misapprehension that ART can be performed easily – this is not the case and each step must be carried out to perfection.
- The apparent lack of sophistication of the technique, which might make it difficult for ART to be easily accepted by the dental profession.
- A misconception by the public that the new glass ionomer “white fillings” are only temporary dressings.
Some of these disadvantages of glass ionomers, such as low wear resistance and reduced strength, are being addressed. When improved materials become available, larger one surface and small to medium sized multisurface lesions might also be managed with the ART technique. Also, the variation in mixtures of hand mixed glass ionomer can be reduced by making the materials more user friendly, a particularly important factor in the economically less developed countries where less than optimal operating conditions exist. The development of appropriate hand instruments will facilitate the execution of the ART technique and, one hopes, reduce the possibility of hand fatigue.
Read More......