dental materials

: dental materials

p Essay title- what are the clinical benefits of adhesive restorative procedures ? Discuss and explain the main problems with current methacrylate-based adhesive resins

use references that are relatively up to date and make sure that they are varied and not all America sources

Buonocore began bonding resin restorative materials to the enamel in the mid-1950 's and that was when the field of adhesive restorative dentistry actually began (Tyas , 2004 . Zinc polycarboxylate cement was the first adhesive cement used . It was followed by the introduction of glass

ionomer cement (GIC ) and dentin bonding agents . Glass ionomer cements have several advantages over composite restorations including their ability to chemically adhere to enamel and dentin . The material that has undergone most changes is dentin bonding agents (Tyas , 2004

A dental restoration has to attach or bind itself to the tooth structure and derive some amount of retention . Adhesion is a process by which the restoration binds to another surface (tooth surface ) with the help of an adhesive joint . The substance that has to be bonded is known as the `adherent , whereas the adhesive is the substance that is present at the interface . The joint formed between the adhesive and the adherent is known as the `adhesive joint (Craig , 2002 . Adhesion may prevent two processes from occurring between the tooth and the restoration :-

It prevents the restoration from getting displaced

It prevents microleakage (entry of bacteria and oral fluids in the gap present between the tooth and the restoration

However , microleakage is a technique-sensitive property and mainly relies on proper handling and placement of the material (Mount , 1998

Every dental restorative procedure including crowns , dentures and cements use some amount of adhesion . A crown uses the luting cement and the irregularities present on the surface , whereas the dentures depend on clasps and undercuts . Dental adhesives were being developed as early as the 1950 's . They are frequently used in restorative dentistry nowadays . Usually , one or two interfaces are formed between the tooth surface , adhesive and the restoration (in a pit and fissure sealant a single interface is formed , whereas in a composite resin restoration a complex interface is formed . The elements of the restorative system that helps in bonding are known as `bonding agents . An adhesive joint formed has several clinical , mechanical and physical properties . It has some amount of resistance to failure . Several factors such as formation of cracks , extension of these cracks , etc , may interfere with the adhesion . The proprieties of the adhesive and the adherent and that existing in the environment of the mouth play a major role in developing resistance against failures of the bonded systems . The requirements of a surface that is able to bond properly include a clean surface flowable adhesives , the low contact angle formed , the adhesive should adapt to the surface of the adherent without entrapping air bubbles etc . Debonding should effectively be prevented through the development of physical , chemical and mechanical strength (Craig , 2002

Bonding agents were mainly developed as a solution to counteract high viscosity of composite resins . Enamel etching enabled greater wetability of the enamel surface . Basically , the enamel bonding agents contained a resinous matrix that was made less viscous by adding the monomer . These bonding agents encouraged the bond formed between the tooth and enamel through resin tags (Philips , 1992

The tooth surface has to be cleansed thoroughly before the adhesive is applied . Cleaning must ensure that the surface energy of the surface of the prepared tooth surface is high . If contaminants are present , a weak bond will be formed . Often during cavity preparations , a smear layer is formed which may act as an impediment during bonding . The smear layer should either be removed or sufficiently be penetrated with adhesives Chemicals may be utilized to remove a part or entire smear layer . Good wetting by the adhesive of the tooth surface is essential for bonding It suggests that the contact angle is low and the surface of the tooth is clean and has a high surface energy . The dentin and the bonding agent are usually hydrophilic and can flow into cracks and crevices of the prepared cavity . The adhesive should be retained into position after it flows to ensure that the physical , chemical and mechanical properties are achieved . During bonding , the distance between the adhesive particles and the adherent particles should be a few Angstroms Mechanical and micro-mechanical bonding can also be formed by ensuring interlocking and forming micro surface irregularities . These irregularities can be developed through cavity preparation sand-blasting and etching . During the procedure , the restoration should be bond with the adhesive . Curing usually occurs by light , self or dual activated means (Craig , 2002

Usually dental restorations may debond because of cracks formed and further propagations in the restoration-tooth interface . Several factors may bring about Debonding such as presence of contaminants excessive salvia , entrapped air voids , poor wetting of the adhesive presence of air bubbles in the adhesive , excessive curing shrinkage etc . The properties of the tooth and the restorative material are usually better than the adhesive joint formed and hence the weakest point in any restoration is the tooth restoration interface . Cracks formed during a poor manipulative technique may extend due to the conditions prevailing and finally debond the restoration . The shear strength of amalgam is 185 Mpa , that of dentin is 140 to 165 MPa and that of composite resins is about 140 MPa . On the other hand , dentin to amalgam adhesive has shear strength of 4 to 8 MPa , dentin adhesion to composite resin has shear strength of 20 MPa , and enamel adhesion to Composite resin has shear strength of 20 MPa . Cracks formed due to development of stress and release of these stresses . The entire restoration or a part of it may fail due to release or redistribution of stresses (Craig , 2002

During the 1970 's , the bond formed in enamel adhesion was determined At first importance was given for the enamel bonding agent to offer protection against microleakage . The American Dental Association developed certain guidelines in 1994 to determine the bond strength of adhesives in class V restorations . The bonding success in non-carious small class V perorations is usually determined by post-operative sensitivity , secondary caries , staining , breakage or absence of restoration . The results obtained during clinical trials , however , do not suggest general practice conditions as they are performed in laboratory conditions . In clinical practice , a bonding agent may survive long-term only in about 40 of all cases , as compared to clinical trials or laboratory condition . Long-term studies to determine the performance of enamel bonding systems may need to be conducted (Craig , 2002

The body is usually weakened along the gingival crevice region , where dentin is present . Usually , in posterior teeth a class II would fail in the inter-proximal region due to the occurrence of secondary caries These areas are difficult to manipulate during composite restorative procedures . The Composite resin restoration is usually bonded to the cementum or dentin , rather than enamel (Craig , 2002

During adhesive restorative procedures , previously wrong beliefs exist It would often be advantageous to remove just the carious lesion and place an adhesive restorative material (composite resin . In this way an adhesive restorative material would help reducing the amount tooth material cut and also help in reducing the post-operative sensitivity An adhesive composite restoration placed on dentin that has been etched would be retained and would not harm the pulp . Frequently , the adhesive restorative materials function better compared to silver amalgam restorations . Effectively , adhesive restorative materials reduce the need to produce mechanical features in the tooth preparations . This is especially beneficial when it comes to sensitive dentin . Fusayama in 1980 identified a new method of restoring carried teeth using adhesive restorative material . In this technique , the caries infected tooth material (that was un-mineralized , softened and contained microorganisms ) was differentiated from the caries affected tooth (that was re-mineralized and was sensitive ) using a caries detector solution (contained basic fuchsin in propylene glycol . Once the caries infected teeth was identified , the material was removed using a rotary cutting instrument and could be immediately restored . There was no need of extending the cavity preparation into the caries affected tooth material in to increase mechanical retention , as it could be provided by the adhesive material . In this way , post-operative sensitivity could be effectively prevented . Both , the dentist and the patients were satisfied with this new technique . As reduced amount of tooth material was cut , the risk of further weakening the cusp was reduced . This resulted in greater fracture resistance and lower need to perform endodontic procedures , later . Thus the life of the tooth was significantly increased . Previous dental adhesive composites used inappropriate materials that did not seal the dental tubules properly and resulted in increased pulpal irritation and post-operative sensitivity . Using advanced etching and dentin bonding techniques , a good seal is formed in the dentinal tubules especially in the gingival regions resulting in reduced post-operative sensitivity and pulpal irritation . Frequently , dentists do not like to etch the dentinal surface , and this often results in failure of the restorative material Most of the time the restorative material is being criticized rather than the technique employed . If newer dentin bonding agents are employed , the chances of post-operative sensitivity and losing the restoration are reduced . Frequently , the dentists use liners below composite fillings , which tend to reduce the retention and loosen the marginal integrity . Sometimes , Glass Ionomer Cements are used beneath composite restorations . These cements bond better with the composite resin material than to the tooth resulting in creation of a micro-gap between the liner and the tooth surface . Hence , it would always be better to place the composite resin cement directly on the surface of the tooth , than placing a liner (as the seal would be much better (Fusyama , 1988

Adhesive composite resins can bond to both enamel and dentin . Good bonding with enamel would ensure that the marginal seal is proper and marginal fracture is prevented . On the other hand , bonding to dentin would ensure that the composite resin sufficiently penetrates the dentinal tubules , thus preventing the resin from separating out from the tooth . This would effectively help to reduce microleakage and prevent secondary caries beneath the fillings . In these terms , composite resins seem to be much superior to amalgam . It is not uncommon to see a secondary caries lesion beneath an amalgam filling . On the other hand a secondary caries lesion seldom occurs below a properly done composite resin restoration . Frequently , people would like to do a amalgam or composite filling for the time being and later get it converted into cast restoration . However , once an amalgam restoration is removed , it leaves it walls in a very poor state (stained , decayed and weak However , a composite restoration would leave its walls in a better state compared to an amalgam filling . This helps to extend the life of the next filling placed in the tooth . Compared to amalgam restoration , it seems to be very easy to repair a composite resin restoration . There is no need to remove the entire restoration . Only a part of it can be removed as sufficient retention can be obtained utilizing the adhesives (Fusyama , 1988

The hybrid layer plays a very important role in the bonding of the resin restoration to dentin . Basically , the hybrid layer is considered to be a resin-penetrated layer of dentin , formed at the interface . The strength of the bond formed is not proportional to the thickness of the hybrid layer (which ranges from one micron to 5 micron . Self-etching priming material which produces only a thin hybrid layer , has good bond strengths (Fusyama , 1988

Application of an adhesive to the tooth surface would result in decreased release of fluorides . A study was conducted on conventional and resin modified GIC . A bond was formed between the resin component present in the glass ionomer and the adhesive used on the tooth surface A hybrid layer was formed which also obstructed release of fluoride on the tooth surface . However , some amount of fluorides was able to leach away from the GIC cement into the tooth material (Algarves , 2001

The adhesives help to improve bonding strengths between the restoration and the enamel and dentin and in reducing microleakage . As there is diffusion of the composite material into the dentin tubules and bonding with the collagen fibrils , the potential space between the restoration and the tooth interface is decreased . Microorganisms and oral fluids hence do not seep in and cause sensitivity . The shear bond strength was also improved when adhesives were utilized . The incidence of secondary caries is also low after utilizing adhesive procedures (Algarves , 2001

Bonding of dentin and enamel is a very technique-sensitive procedure and the final outcome including the strength of the bond and the longetivity of the restoration depends directly on the conditions prevailing whilst the material is introduced into the mouth . Several procedures performed during dentin bonding such as etching , washing and drying resulting in deterioration of the dentin and subsequent loss of the hydroxyapetite material . The resin was unable to enter and diffusion into the altered dentin which resulted in decreased bond strengths . Hence , it would be advisable to leave some amount of moisture on the prepared dentinal surface during bonding which permitted the primer to enter and diffusion into the collagen fibrils present in dentin . Frequently , clinicians find it very difficult to maintain a field in which excessive moisture is removed , and excess drying of dentin is prevented . Many dentin bonding agents systems permit nano-leakage (evident through entry of silver nitrate dye into the dentin (Tyas , 2004

GIC is known to bond to the tooth material and does not requires much of retentive form in the cavity . When used as luting cement , it is used in the powder to liquid ratio of 1 .5 to 1 . It does not posses much of tensile strength (2 to 3 MPa ) compared to when used in a high powder to liquid ratio . Hence poorly fitting restoration may not be well-boded with GIC cement . The compressive strength of the set luting cement is usually higher . In any cavity preparation , in which luting is done with GIC , it would be better to depend on the retentive design of the cavity than on the adhesive properties of the GIC cement . The bonding of GIC can be improved by using certain dentin conditioning agents that would remove a part of the smear layer and would permit the GIC to penetrate the dentin tubules and develop a better bond strength . However , a rather larger surface area of the tooth is involved in crown preparations , and the patient is at the risk of developing post-operative sensitivity (Mount , 1998 . GIC has a low fracture resistance and hence cannot be used in stress-bearing areas such as posterior teeth (especially in the cuspal regions (Tyas , 2004 . A composite resin usually retains to the tooth by micromechanical means whereas GIC cement bonds through chemical means . This forms the classification of the types of adhesive restorative materials Chemically ion exchange permits bonding (Mount , 1998

Resin cements are being frequently used in front teeth as they posses a high strength and offer translucency . They contain methacryalates along with HEMA , and also small amounts of fillers . However , they should not be used in eugenol-filled teeth as the cement can get softened . The resin cements usually offer higher retentive strengths . It is often very difficult to remove a restoration luted with resin cement . The cement usually bonds to the tooth through mechanical interlocking rather than chemical means . The bonding strengths with enamel is usually higher as compared to dentin . The bond strength of dentin can be improved by using acid-etching . Besides , bonding to the tooth , resins also bond with the restorations such as ceramic inlays or FPD 's . They are usually indicated to cement veneers , ceramic FPD 's , inlays , etc They have matching color and can provide some amount of translucency The cement can adapt to the margins up to a 100 micron in thickness They usually do not dissolve in oral fluids . However , these cements tend to deteriorate with time , and hence produce a space between the tooth and the restoration (Mount , 1998

GIC cement adheres to the tooth through an ion exchange process Calcium and Aluminum ions are released from the GI powder when mixed with polyalkenoic acid . A matrix is formed and the silica will also be transformed into a gel . Once the cement is placed on the tooth surface the polyalkenoic acid enters the dentin and enamel , and removes calcium and phosphate ions . The cement matrix will bond with the calcium and phosphate ions to produce a hybrid material . The matrix combines with the tooth surface on one side and the glass particles on the other . The matrix is the weakest material and has the potential to fail . GIC cement is not affected much by the presence of excessive moisture during manipulation . It usually fails due to a loss of cohesion . These results in a layer of cement being left behind on the tooth surface GIC cement usually seals the dentinal tubules and prevents secondary caries as well as microleakage from developing (Mount , 1998

Adhesive dental restorative materials have their own set of advantages and disadvantages . As adhesive procedures prevent leaching of fluorides , the risk of caries occurring below the filling is slightly higher . Hence , they are not indicated in individuals with poor oral hygiene (Manhart , 2002 . Composite resins are also known to fracture and frequently debond from the tooth surface . Composites may be time consuming and very technique-sensitive (patient and operator factors play an important role . Bonding often decreases when contaminants such as blood and other fluids are present on the prepared tooth surface (Pashley , 1991 . GIC restorations cannot be used in posterior teeth with high stresses as the risk of fracture is high . However , composites and bonding systems are improving slowly with time . They are usually suited for small filling even in high stress bearing areas . The individual should have good oral hygiene in to accept a composite restoration , as the risk of secondary caries is high (Manhart , 2002 It is also essential that during manipulation of the composite , each layer be placed which measures no more than 2 mm in thickness . Curing in greater thickness would result in the bulk of the restoration shrinking towards the light source and hence debonding (Pashley , 1991 .References

Algarves , L . Et al (2002 . Fluoride Release from Restorative Materials Coated with an Adhesive ' Braz Dent J , 13 (1 , 39-43 . HYPERLINK "http /www .forp .usp .br /bdj /bdj13 (1 /trab07131 /trab07131 .html http /www .forp .usp .br /bdj /bdj13 (1 /trab07131 /trab07131 .html

Craig , R . G (2002 . Restorative Dental Materials . St . Louis : Mosby

Dietschi , D Dietschi , J . M (1996 . Current developments in composite materials and techniques ' Pract Periodontics Aesthet Dent 8 (7 , 603-13 . HYPERLINK "http /www .ncbi .nlm .nih .gov /entrez /query .fcgi ?db pubmed cmd Retrieve do pt AbstractPlus list_uids 9242136 query_hl 1 itool pubmed_DocSum http /www .ncbi .nlm .nih .gov /entrez /query .fcgi ?db pubmed cmd Retrieve dop t AbstractPlus list_uids 9242136 query_hl 1 itool pubmed_DocSum

Fusayama , T (1988 . The Problems Preventing Progress in Adhesive Dentistry ' Adv Dent Re , 2 (1 , 158-161

Manhart , J (2002 . Direct posterior restorations : clinical results and new developments ' Dent Clin North Am , 46 (2 , 303-39 . HYPERLINK "http /www .ncbi .nlm .nih .gov /entrez /query .fcgi ?db pubmed cmd Retrieve do pt AbstractPlus list_uids query_hl 1 itool pubmed_DocSum http /www .ncbi .nlm .nih .gov /entrez /query .fcgi ?db pubmed cmd Retrieve dop t AbstractPlus list_uids query_hl 1 itool pubmed_DocSum

Mount , G . J , and Humes , W . R (1998 . Further Clinical Procedures Related to the Fabrication of Rigid Restorations . In : Mount , G . J Hume , W . R (Ed , Preservation and Restoration of Tooth Structure London : Mosby

Mount , G . J (1998 . Basic Principles of Restorative Dentistry . In Mount , G . J Hume , W . R (Ed , Preservation and Restoration of Tooth Structure , London : Mosby

Pashley , D . H (1991 . Dentin bonding : overview of the substrate with respect to adhesive material ' J Esthet Dent , 3 (2 , 46-50 . HYPERLINK "http /www .ncbi .nlm .nih .gov /entrez /query .fcgi ?db pubmed cmd Retrieve do pt AbstractPlus list_uids 1888543 query_hl 1 itool pubmed_DocSum http /www .ncbi .nlm .nih .gov /entrez /query .fcgi ?db pubmed cmd Retrieve dop t AbstractPlus list_uids 1888543 query_hl 1 itool pubmed_DocSum

Phillips , R . W (1992 . Science of Dental Materials . Philadelphia : W . B Saunders Company

Subbarao , V . K (2001 . Dental Materials , Hyderabad : Paras

Tyas , M . J (2004 . Adhesive Restorative Materials : A Review 'Aus Dent J , 49 (3 , 112-121

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