Failure of Restorations PDF

# Failure of Restorations ## **FAILURE OF RESTORATIONS** The restorative dentistry is provided with a wide range of materials to choose from to restore any derangement of lesion in hard tooth substance. These lesions include caries, erosion, attrition, traumatic fracture, discoloration as well as...

# Failure of Restorations ## **FAILURE OF RESTORATIONS** The restorative dentistry is provided with a wide range of materials to choose from to restore any derangement of lesion in hard tooth substance. These lesions include caries, erosion, attrition, traumatic fracture, discoloration as well as minor abnormalities in form, size alignment or occlusion of teeth. In such cases, operative dentistry continues to be the sole means for logical treatment. ### Objectives of operative dentistry: Operative dentistry comprises procedures whereby a preparation of definite biomechanical and esthetic design features is provided in the remaining hard tooth tissues to accommodate a restoration which is relied upon to perform specific functions including: 1. Stop of the original insult of caries, erosion or attrition and prevention of its recurrence. To achieve this goal: - The preparation should have the correct outline form featuring complete elimination of caries and retentive pits and fissures establishing esthetic margins in sound smooth enamel which are minimally (1/4 m) extending past the contacts. - The restoration should be able to seal its interface with the preparation hermetically to prevent marginal leakage, which may cause recurrent caries, marginal discoloration and pulp irritation. To achieve this purpose: - The restoration should be condensed against perfectly smooth, dry, and clean enamel walls and margins. - The restorative material must ideally wet and adhere to walls of the preparation or properly condensed to effect maximum initial adaptation to all walls of the preparation. - The restoration should be free from dimensional changes on setting and should not exhibit any differential dimensional change from that of the tooth on thermal cycling. - Restorative material should have adequate rigidity so that it does not yield under force of mastication which will cause opening at the margins. - The remaining tooth substance must be strong enough so that the walls of the preparation do not open away from the restoration when stressed under mastication force: overcutting should be avoided. - Retention of bacterial plaque at the critical marginal areas of the restorations should be inhibited. This necessitates elimination of any retentive pits and fissures, marginal overhangs or crevices and proper polishing of the restoration. 2. Restoration of comfortable and efficient mastication: - Lesions of hard tooth tissues may be detected and treated early, or may be neglected until they inflict other influences such as dysfunction because of pain, food impaction loss of normal inter-arch articulation and lately disturbances in the temporomandibular joints. - Restoration of comfort and efficient mastication would mean sedation of the pulp and dentin by elimination of caries and application of necessary protective liners, bases or temporary restorations and finally insertion of the permanent restoration which should be strong enough to sustain the multiple forces of mastication without distortion, fractures, wear or loss of smooth surface textures. This restoration should have the normal harmonious occlusion without any prematurities. It must have tight interproximal contacts of correct size form and location, and present correct contours with deflective planes to avoid food impaction or retention of bacterial plaque and to help massaging of the gingiva. - Teeth drifted because of loss of contact may need to be moved slightly back by immediate or slow separation before restoration of contact or "plus contact". The opposing plunger cusp must be ground down to correct occlusion and smoothened. - The restorative material and procedures should be biocompatible with dentin, pulp, gingival and periodontal tissues and should exert no noxious effects either locally or systemically. 3. Restoration of esthetics: - The cosmetic appearance of the dentition depends on normal and harmony of color, translucency, form surface texture and size of individual teeth, their alignment in the dental arches and their occlusal relationship during all jaw movements. These parameters must be strictly observed and reproduced by the restoration. - Not only the restorative material but also the preparation itself should be esthetic. Thus, cavity outlines should be very conservative and run in even, smooth geometrical finishing lines parallel to corresponding tooth surface or known land marks. ### Criteria of successful restoration: In the light of the above-presented outline on objectives of operative dentistry, the clinically successful restoration should satisfy such objectives and should be durable, less costly and easy to do. ### The criteria of a clinically successful restoration include: 1. Be an exact replica of the missing part of the tooth in size, form, color, translucency and texture. 2. The margins of the restoration are flush with the tooth surface, hermetically seal the preparation and remain free from any recurrence of discoloration. 3. The restoration remains integral, securely retained in the preparation and dimensionally stable. 4. The surrounding tissues are healthy and suffer no irritation. 5. The patient enjoys efficient and comfortable mastication and occlusion. The restoration does not cause any discomfort on thermal cycling, eating or drinking any food or drinks. 6. The restoration is durable. ### The ideal restoration is not yet developed consequently, success and failure will be multifactorial. ### Success and failure of restorative work depends on many factors which include: #### Patient related factors 1. The degree of involvement: The greater the derangement and the longer the time it was neglected without treatment, the more difficult it will be to achieve and maintain a success. 2. The tooth nature - The need to replace missing enamel and dentin by restorative material is difficult because of the great difference in properties between them. 3. Oral environmental factors - **Difficult access** - Access to the operative field presents a difficult problem. The operative dentist has to introduce his hands suction mechanisms and instruments into a very limited area of the mouth which is very constrained by the tongue, cheeks and teeth of the opposite arch. Under these circumstances, he has to prepare designs of highly refined engineering features and definitely directed walls, use instruments of high cutting potentials and avoid any slight damage to hard or soft tooth tissues. - **The corrosive potentials:** - The saliva with its salt content a good electrolyte. The warm atmosphere activates any oxidation, reduction or sulfurization of metallic restorations specially those of non-homogenous structures as amalgam. The accumulation of bacterial plaque at the gingival area of teeth causes variations in concentration of electrolyte as compared with that at the occlusal surface of restorations thus favoring concentration cell corrosion. At the depth of a crevice e.g., at the restoration tooth interface, oxygen tension will be different from that at the surface of restoration, and this creates corrosion cells. - The presence of any dissimilarity in composition, surface condition, stressing, pH, or metallic structure, forms galvanic cells and favors corrosion. - **The aqueous nature:** - Saliva in the mouth creates problems for the restorative dentist who has to work hard to eliminate it from the operative field through application of rubber dam, use of suction and cotton rolls as well as to seed up the condensation procedures because it adversely affect all restorations. - Moisture contamination of amalgam causes an electrolytic corrosion reaction which results in great loss of strength, delayed expansion and excessive corrosion of the clinical restoration. - Moisture contamination of cements during their manipulation and setting results in great loss of strength, increased solubility and loss of translucency. - Resin restoratives will lose adaptation and retention to etched enamel walls if moisture intervenes at the interface. Moreover, the clinical restoration is subject to variable degrees of water sorption in the mouth, which may cause discoloration or distortion. - Cavity liners, varnishes or cement bases require thoroughly dry cavities in order to be satisfactorily applied and retained. - Saliva cause dissolution of some restorative materials, especially cements which dissolves more in acidic pHs, e.g., at gingival areas where bacterial plaque collects more and cause fermentation reactions and acid production. This favors caries recurrence. - The dissolution of luting cements under cast restorations is a basic reason for caries recurrence under such restorations. - Dissolution of cement restorations increases their surface roughness at adversely affects their esthetic appearance. - **Thermal changes:** - Fluctuations in temperature are a common occurrence in the mouth. Thermal cycling of restorations and tooth results in variable degrees of differential expansion and contraction which can cause corresponding degrees of marginal percolation and gross leakage depending on the relative difference in coefficient of thermal expansion of the restorative material from that for the enamel and dentin. It also induces residual stresses which destroy any bond obtained between the tooth and restoration. - Metallic restorations transmit thermal stimuli to the underlying dentin and pulp which may cause discomfort or elicit pain response particularly during the early period following insertion of restoration. Unless installed, the pulp may be irritated. - Although thermal expansion is doubted to cause better peripheral seal, yet contraction will surely bring about gross leakage. - **The oral microbes:** - Although the oral cavity contains many different types of bacteria, the oral flora, yet the restorative dentist is specifically concerned of those types, which are associated with the initiation or recurrence of caries. - In the presence of saliva, bacteria in dental plaque rapidly metabolize and cause decalcification of enamel and initiation or recurrence of caries. Consequently, factors, which favor retention of bacterial plaque, will make caries recurrence more likely. Such factors include remaining pits and fissures, the high surface energy of available restorative specially if left without proper polishing, the presence of marginal overhangs or crevices, open interproximal contacts, crowding and abnormal occlusal relationship of teeth, in addition, to the main factor of poor oral hygiene. Increased salivary viscosity and decreased salivary flow also favor accumulation and retention of bacterial plaque. - The presence of bacteria under restorations was once thought to be a potential cause for caries recurrence and recommendations were given of the necessity to eliminate it by cavity sterilization prior to insertion of restorations. This procedure, however, was discouraged because it was found that bacteria under properly adapted restorations would either die or remain dormant. Moreover, available sterilizing agents are either non effective and/or injurious to the pulp. - **Forces in the mouth:** - Restorations are subject to mastication forces of multiple types including the compressive, the tensile and shear, static and dynamic, which occur in repetitive cycles. These biting forces vary in magnitude from one individual to another and at different areas of the same mouth. It ranges between 9-25 kg. (20-55P) at the incisor, 14-34 kg. (30-75P) at cuspids, 23-46 kg (50-100P) at the bicuspid and 77 kg (170P) at the molar areas. - The maximum biting force generally increases with age, up to adolescence. The amount of force placed on the teeth during mastication varies greatly from individual to individual. - These forces induce in the restoration and the tooth, stresses of corresponding type and magnitude. As a result: - Both the tooth and the restoration may absorb the stresses elastically without any unfavorable response. - The restoration may creep or deform if the forces are just sufficient to induce that distortion, the warmth in the oral cavity enhances this deformation. - The cavity walls may yield elastically allowing gross marginal leakage if the stresses are within the elastic limits of the remaining little thickness of the dentin walls associated with over cutting of cavities. - The cavity walls may fracture if the stresses surpass the corresponding strength of the stressed cavity wall. - The whole restoration may get dislodged out of the preparation if the stresses surpass the retentive capacity of the preparation. - Portion, usually the auxiliary of the compound restoration may get fractured if the stresses surpass both the retentive capacity of the auxiliary preparation and the tensile or shear strength of the restorative material, usually a brittle one. - The development of unfavorable stress response in the tooth and/or the restoration constitutes a critical problem to the restorative dentist because: - The exact magnitude of mastication forces cannot be predetermined, and therefore, the resulting stresses can never be exactly predicted. - Most of the induced stresses are shear or tensile which are deleterious to the brittle substances. - Most of the materials the operative dentist deals with are brittle and have low tensile and still lower shear strength values. - To compensate, at least partly, for this inherent limitation, strict engineering principles of resistance and retention should be meticulously incorporated in the preparation. This may require additional sacrifice of healthy hard tooth structure, embedding in the restoration or dentin of certain metallic inserts to supplement retention and/or to reinforce the restoration. If other words, the increase in the strength of the restoration is done at the expense of the tooth. - Furthermore, the forces are repetitive in cycles, which may easily initiate fatigue failure. The presence of any surface or structural discontinuity will concentrate the stresses and initiate or propagate a crack causing gross fracture. - Moreover, impact forces and induced impact stresses may easily cause chip fracture of brittle materials especially at thin margins. Again impact strength can similarly be improved at the expense of tooth substance and/or the esthetic appearance of the restoration through provision for more bulk of materials. #### Material related factors - **Inherent material deficiencies:** - The need to replace missing enamel and dentin in a restorative material and get exactly the same biomechanical and esthetic properties of both tissues combined, regardless of bulk limitations is too difficult to achieve because of the great differences in properties and variations in architectural design. - All restorations are brittle and suffer low tensile strength especially in limited thickness except cast restorations. - Some restorative materials employ sensitive techniques and others have a lack of stability under oral conditions and exhibit different types and degrees of time dependent biodegradation (wear resistance) #### Dentist related factors - **The skill of the operator** including his working knowledge of the demands for success with taking consideration of the nature of oral environment as well as the properties and limitations of existing restorative materials and techniques. The operator must have thorough knowledge of all factors which will affect or get affected by his choice of material (or combination of materials), plane of treatment and execution of the restorative procedures. - **Improper diagnosis and treatment planning.** - **Mis-selection of the restoration** - Selection of the appropriate restorative, which meets most of the demands of an individual case, is a pertinent factor for success of the clinical restorations. This selection should be based on logical and thorough analysis of all variables including properties of available restoratives, the demands and limitations of the oral environment and the past experience of the operator. - As an example, both amalgam and gold serve satisfactorily as individual restorations but if both are used in the same mouth failure by excessive tarnish and corrosion, possible patient discomfort due to galvanic activities and shocks of pain may be inevitable. Similarly, the use of permanent restorations for treatment of rampant caries is considered to be inappropriate because failure by recurrent caries is almost certain. Instead, caries should be thoroughly excavated and a temporary restoration, preferably fluoride-emitting cement is placed until after the period of active involvement is over when the suitable permanent restorative is made. - **Wrong cavity design** - The design of preparation furnishes the foundation in which the restoration is established. It has a decided influence on the mechanical integrity of both the tooth and restoration, the stability of the restoration, the post restorative biological influences of the restoration on the dentin and pulp and the health of the remaining tooth substance. It also has an important effect on esthetics. More than 60% of failure may be due to improper cavity preparation. - The stress response in both the tooth and restoration is largely a function of the cavity design, which can convert a compressive force into a destructive tensile or shear components; e.g., if inclined instead of vertical floors were provided. The cavity design should complement the physical properties of the restorative employed and, consequently should incorporate essential features, which are in accord with the properties of the particular restorative. **Faulty material manipulation** - Incorrect material manipulation is responsible for about 40% of failure of clinical restorations. Therefore, meticulous attention for details of material manipulation is mandatory for obtaining of consistently successful restorations. ## **FAILURE MANIFESTATIONS OF CONTEMPORARY RESTORATIONS** ### FAILURE OF AMALGAM RESTORATIONS #### Mechanical failure 1. **Marginal degradation** - **Definition:** - Marginal degradation, ditching, fracture or crevicing refers to breakage of a thin edge of a restoration creating an irregular V-shaped crevice. - **Causes:** - **Depletion of support at margins:** - Amalgam is a brittle material with low tensile and shear strength so, it must be supported by tooth structure. - Lack of support may be due to: Excessive expansion resulted from: - Under trituration - Excess mercury. - Moisture contamination. - Age dependent changes in the microstructure. - Creep: Time dependent change in the form of amalgam under constant loads and temperature. - N.B. High copper amalgam shows lower creep values than low copper amalgam. - Crevice corrosion of amalgam may be associated with marginal discrepancies and development especially in the high acidity. - **Insufficient bulk at margins:** - Strength of amalgam is essentially thickness dependent as it is a brittle material with low tensile and shear strength. - Lack of bulk may be due to: - Beveling of CSA. - Over carving. - Leaving thin marginal flashes. - **Voids:** - Voids in amalgam produces a decrease in density and strength of amalgam accelerating its fracture by stress concentration. - Voids may be resulted from: - Inadequate condensation force. - Too dry amalgam mix. - Moisture contamination of zinc containing amalgam. - Corrosion. - **Excess mercury:** - Excess mercury tends to lower the strength of amalgam. - Excess mercury may be due to: - Wrong proportioning of alloy / mercury ratio. - Under trituration and squeezing. - Inadequate condensation force. - Burnishing of amalgam at margins. - **Clinical picture:** - All cavity margins are prone to ditching especially buccal end of proximal marginal ridge because: - It is subjected to beveling. - Trapping of mercury. - Inadequate condensation. - Isthmus outline especially buccal wall of lower first molars are more common sites for marginal ditching so, this walls should be made in the form of reverse curve to provide CSA 90°. - **Complications:** - Food impaction resulting in recurrent caries - Isthmus fracture - Tooth fracture - **Treatment:** - Protection against marginal fracture by: - Following biomechanical principles of cavity design. - Proper selection of the alloy. - Proper manipulation of the material. - The actual treatment depends on the extent of ditching and presence of other sorts of ditching: - Very small ditching: Resurfacing with plug finishing bur. - Moderate ditching: Repair with cermet cement or amalgam, using adhesive amalgam bond. - Gross ditching: Total replacement of the restoration is indicated. 2. **Isthmus fracture** - **Definition:** - **Isthmus:** It is the narrowest junction between the principle portion (occlusal) and the auxiliary portion (buccal, lingual or proximal). - **Isthmus fracture:** A fracture of compound amalgam restoration at the junction between the principle portion and the auxiliary portion of the cavity. - **Causes:** - It is a must to have a state of balance between the flexural stresses at the isthmus area and the flexural strength of the amalgam at the same area. - So, the causes or factors attributed to isthmus fracture may be: - **Factors that increase flexural stresses:** - **Fracture due to faults in cavity preparation** - **Incorrect resistance and inadequate retention:** - Masticatory forces may easily break compound restorations, which are not adequately and independently retained. - So, the restoration should have adequate correct resistance in the form of: - Flat pulpal floor and gingival floor perpendicular to the direction of force. - Walls parallel to the direction of masticatory force. - CSA 90°. - The less effective the proximal retention the higher the tensile stresses developed at the isthmus and the greater the tendency for isthmus fracture. - The forms of proximal retention may be: - Proximal axial grooves. - Increased condensation to increase density, adaptation and strength of the restoration. - Using effective adhesive system. - If the remaining amount of tooth structure is not enough to provide sufficient retention for proximal portion, the following alternatives may be done: → - Change to cast restorations as they have high tensile strength. - Use of threaded pins or amalgapins to supplement proximal retention. - **Fracture due to faults in restoration** - **Presence of premature contact due to:** - Under carving of the marginal ridge. - Misplacement of marginal ridge. - **Surface and structural discontinuities:** - As a result of: - Poor polishing leaving the surface rough and full of pits and scratches. - Over carving into deep grooves not only creates stresses, but also weakens the restoration by decreasing its bulk. - Presence of internal voids due to corrosion, moisture contamination, too dry amalgam mix and lack of forceful condensation. - **Fracture due to patient factors:** - Sudden biting on a hard object. - Presence of protruded or over erupted opposing plunger cusp. - Biting on amalgam before sufficient setting. - **Factors that decrease flexural strength:** - Insufficient bulk of amalgam. - Excess mercury. - Structural discontinuities. - **Insufficient bulk of the amalgam:** - Amalgam is a brittle material with low tensile and shear strength, which needs bulk of at least 1.5-2 mm to have sufficient flexural strength. - Insufficient bulk may be due to: Over carving, and decreased cavity depth. - **Excess mercury:** - It lowers the strength of amalgam as it decreases the amount of (y) phase which provides the strength and increases (2) phase which is the weakest phase. - **Structural discontinuities:** - Due to: Corrosion, moisture contamination, dry mix, lack of condensation forces. - **Clinical picture:** - It starts as crack line propagates and widens with mastication force then fracture occurs. - Hypersensitivity with eating and drinking. - Food impaction and recurrent caries. - Periodontal irritation. - **Complications:** - Recurrent caries. - Tooth fracture. - Periodontal irritation. - **Treatment:** - Search for the cause of fracture. - Improve resistance and retention forms. - Removal of any surface discontinuity. - Selective grinding of opposing plunger cusp. - Increase bulk of amalgam at the isthmus area by: Rounding, beveling or saucering the axio-pulpal line angle and inclination of the axial wall. Proper handling and manipulation of amalgam restoration. Application of adhesive amalgam bond or metallic inserts. - N.B. : Remake of amalgam is preferable than repair due to: - Repair will not allow correcting the cavity preparation. - Lack of bond between the old and new amalgam. - Corrosion between old and new amalgam. 3. **Tooth fracture** - **Definition:** - Fractured cusp or ridge under functional forces due to lack of support and reinforcement. - **Causes:** - Amalgam lacks sufficient tensile strength to support remaining tooth substance and much less able to reinforce weak cusps and ridges. - **Treatment:** - Eliminate all undermined enamel as well as weak cusps and ridges. - N.B: The mean enamel thickness on the mesial and distal surfaces ranged from 1.35 mm (± 0.22) to 1.40 mm (± 0.17), - Preserve the integrity and continuity of the remaining tooth substance. - Roundation of line angles. - Ensure wide distribution of stresses. - Reinforce weak cusps and ridges using inlays, onlays or full coverage. 4. **Dislodgment of restorations** - **Causes:** - Inadequacy of the retention mechanism. - Fracture of the restoration. - Fracture of the tooth. - Recurrent caries. - **Clinical picture:** - Totally dislodged restoration. - It may show rocking. - Evaluation of the retention followed by replacing the restoration. ### Biological failure #### Post-restoration hypersensitivity - **Causes:** - Hypersensitivity in a recently amalgam restored tooth may be generated by stimulation of freshly exposed permeable virgin dentin surface by: → - Galvanic: Stimuli generated on immediate contact with opposing dissimilar metals. - Thermal: Thermal stresses conducted through large non- isolated metallic restorations. - Chemical and osmotic: Stimuli by osmotic fluids that penetrate through leakage, hairy crack or fracture in the tooth or restoration. - Tactile: Pressure of premature contact. - **Clinical picture:** - Pain occurring days or weeks after insertion of a restoration mostly indicates microbial pulp involvement following frank or microscopic exposure. - If it occurs on thermal stimulation and continues long after removal of stimulus, it suggests pulp pathology after exposure. - Pain on cold application indicates reversible pulpitis. - If it results from biting, it suggests periodontal involvement. - Dull aching pain several days after insertion of restoration may be due to delayed expansion of amalgam after moisture contamination of zinc-containing amalgam. - **Treatment:** - Prevention by dentin desensitization with cavity varnishes liners/basses. - Inhibition of leakage. - Elimination of occlusal interference and pre-mature contacts. ### Gingival and periodontal affections - **Causes:** - **During cavity preparation:** - Severing the epithelial attachment by overzealous preparation of gingival or subgingival walls. - Ragged cavity margins. - **During restoration procedures:** - Gingival overhangs. - Thick subgingival margin of the restoration. - Rough restoration margins. - Improper selection of the matrix band and wedges. - Food impaction due to open contacts, wrong contouring, disharmonies in height, size or contour of proximal marginal ridges, or incorrect embrasures. - **Clinical picture:** - Gingival and periodontal inflammation with increased bleeding tendency. - Discomfort. - Tooth mobility. - **Treatment:** Defining and removal of the cause. ### Recurrent caries - **Definition:** Caries developed in a previously restored tooth. - **Causes:** - **Incomplete elimination of the original lesion:** - Improper excavation of caries. - Improper evaluation of the case for indirect pulp capping. - **Improper outline form:** - **Under extended:** - Leaving defective and retentive pits and fissure. - Incomplete freeing of the contact. - Margins of the cavity will not be placed in self-cleansable areas. - Leaving undermined enamel. - **Over extended:** The cavity margins will be placed in areas of stresses - **Improper restoration of anatomy:** - Lack of adaptation due to: Marginal leakage, lack of condensation, moisture contamination and the use of dry amalgam mix. - Failure to restore anatomy, contact and contour leading to food collection and recurrent caries. - Improper finishing of restoration: due to over hanged margins, and rough amalgam surface. - Retention and colonization of bacterial plaque: - Remaining retentive pits and fissures. - Unpolished rough restoration surface. - Marginal over hangs. - Open interproximal contact. - Presence of cracks or fracture, e.g. marginal ditching or isthmus fracture. - Bad oral hygiene. - **Clinical picture:** - It is manifested as: - Caries extension : Under the restoration at the cavity floor. - Secondary Caries is detected at margins which are defective. - **Complications:** - Pulpal irritation. - Periodontal irritation. - Displacement of restoration. - Tooth fracture. - **Treatment:** - Prevention: - Adequate cavity extension. - Conservative treatment of non-carious pits and fissures by enameloplasty, cavity walls slanting or sealing with GIC or adhesive bond. - Management: - Replacement of restoration, removal of caries, correction of cavity design and proper manipulation of new restoration. - Marginal defects can be repaired with amalgam, bonded amalgam or glass ionomer cermet cement. ### Esthetic failure #### Excessive discoloration - **Definitions:** - **Tarnish:** Surface discoloration of amalgam with loss of its luster. - **Corrosion:** Actual disintegration of the bulk of amalgam. - **Amalgam blues:** The amalgam shown through enamel. - **Causes:** - **Tarnish:** Formation of a surface film of discoloring oxides and sulfides. This is enhanced by: Excess Hg, under trituration, improper condensation, Lack of finishing, moisture contamination, and bad oral hygiene. - **Corrosion:** - due to Lack of polishing and food stagnation which may lead to halogenation and sulferization. - Setting of electromotive force between two different electrodes of different electric potential through an electrolyte. This occurs between: - Two dissimilar metallic restorations, - Old and new similar metallic restoration. - Polished and unpolished areas of the same restoration. - The same restoration but heterogeneous in structure. - **Concentration cell corrosion:** It is a type of electric corrosion resulting from accumulation of certain types of food on a site of restoration making it different in its electric potential from other sites of amalgam. It is increased with rough surfaced amalgam and bad oral hygiene. - **Amalgam blues:** - It is mainly due to: - Thin or undermined enamel that shows dark blue discoloration of amalgam. - Penetration of metallic ions and corrosive products of amalgam through the dentinal tubules. - **Clinical Picture:** - **Tarnish:** Loss of surface luster. - **Corrosion:** Rough pitted amalgam surface. - **Amalgam blues:** Dark bluish discoloration. - **Treatment:** - Tarnish requires re-polishing. - Corrosion may require removal of old restoration followed by bleaching and correct replacement. ### FAILURE OF CAST RESTORATIONS - Clinical manifestations of cast restoration failures may be in the form of: - Recurrent caries. - Dislodgment of restoration. #### 1. Recurrent caries - **Causes:** - **Fitting discrepancies:** - Distortion of impression, dies or wax pattern. - Incorrect compensation of casting shrinkage leading to under or oversized restoration. - Roughness of the fitting surface. - Modifications by grinding. - **Poor cement or cementation:** - High solubility. - Low strength. - Thick consistency. - Moisture contamination. - Using old mix starting setting. - **Under extension of cavity outline:** - This may leave defective carious enamel or retentive pits and fissures. - Improper placement of the cavity margins in area self-cleansable. - **Stagnation of bacterial plaque:** - Due to lack of polish. - Presence of marginal overhangs. - Poor oral hygiene. - **Treatment:** - Evaluation of the cause followed by remake of the restoration. #### 2. Dislodgment of restoration - **Causes:** - This may be due to: - Inadequate mechanical retention due to over divergence of the cavity walls. - Recurrent caries. - Poor cementation. - Excessive torque by occlusal interference. - Breaking of the cement interlocks by injudicious finishing or premature loading of the restoration. - **Evaluation of the cause and remake of the restoration if needed.** ### FAILURE OF GLASS IONOMER CEMENTS - Failure of glass ionomer cements may be clinically manifested as: - Increased opacity or discoloration. - Loss or dislodgment of restorations. #### 1) Increased opacity or discoloration: - (Esthetic failure) - It may be attributed to: Development of cracks and porosity as a result of setting contraction stresses: - Dehydration with biodegradation by oral fluids. - Incorporation of air voids during mixing. - Inadequate amount of powder. - Injudicious finishing. - Poor oral hygiene. #### 2) Loss or dislodgment of restoration: - (Mechanical failure) - Moisture contamination during packing of restoration. - The use of incorrect consistency that results from wrong powder/liquid ratio. - Premature setting that results in weak bonding and retention of the restoration. - Excessive occlusal forces: Excessive functional or para-functional forces. ### FAILURE OF COMPOSITE RESIN RESTORATIONS #### Biological failure #### 1. Post-restorative tooth hypersensitivity - **Causes:** - Dentin hypersensitivity is more frequently experienced with composite particularly those in class 11 cavities and V cavities as a result of: - Leakage - These dentin walls are usually not covered by cavity liners, difficult for bonding and application of composite, bathed in fluids of low pH, and is closer to the pulp. - Cusp deflection by polymerization shrinkage stresses. - **Clinical picture:** - Hypersensitivity is characteristically manifested as: Sharp, transient, and localizable sensation of exaggerated discomfort on drinking or food chewing. The response is evoked by non-noxious tactile, osmotic, thermal, or evaporative low-intensity stimuli. - **Treatment:** - Remake with proper bonding and adhesion to enamel and dentin. #### 2. Recurrent caries - **Causes:** - Recurrent caries results from penetration and colonization of bacterialplaque between the tooth and restorations as a result of: - Marginal leakage. - Polymerization shrinkage. - Rough restoration surface due to low wear resistance of the material. - **Clinical picture and treatment:** - If catching discrepancies are identified in a composite restoration caries recurrence must be expected, and the restoration must be considered for replacement. - Treatment involves replacement of the restoration after thorough tracing and elimination of the carious lesion. #### 3. Cyto-toxic pulp reactions - **Causes:** - Irreversible pulp reactions occur more frequently under composite resin restorations that may be due to: Acid etching and material compositional constituents, i.e. a chemical etiology. - Bacterial invasion associated with leakage, i.e. a bacterial etiology. - **Clinical picture:** - This is accompanied by signs and symptoms of irreversible inflammation. They do not occur immediately after placement of the fresh restoration but they are rather clinically manifested later with aging, parallel to the time-dependent increase in leakage. - No such influences have been clinically reported with adequately sealed composite restorations. - **Treatment:** - The restoration must be removed and the tooth examined carefully for caries recurrence and pulp involvement. ### Esthetic failure #### 4. Discoloration - **Causes:** - **Incorrect color determination:** - Due to poor illumination, use of a wrong light source, as well as operator's eye problems. - Good illumination by a neutral light source must be utilized. - Use of mocks of composite that are cured to unetched tooth surface help determination of correct color. - **Marginal discoloration:** - Gross marginal leakage of environmental fluids and smoke stains. - Poor application of bonding systems. - Moisture contamination. - Excessive thinning out of margins, premature polishing or overheating, may cause crevicing or pull of margins away from the preparation with subsequent marginal discoloration. - Softening of composite due to hydrolytic instability, and degradation increases their tendency to marginal discoloration especially at the gingival margins where local acidity tends to increase. - **Surface discoloration:** - It is largely a function of the surface roughness of the restoration. The rougher the surface the more dull it appears, and the greater is its tendency to retain food and smoke stains and get discolored. - Low wear resistance. - Surface and subsurface porosity due to inadvertent polishing. - Voids trapped by injudicious mixing or application of composite. - Moisture contamination. - Soft spots due to air-inhibited polymerization may roughen and soften the surface and thus accelerate discoloration. - Bio-degradation or gradual material breakdown by complex biologic activities in the mouth including oral fluids, food constituents, bacteria metabolic activities, and food chewing. - **Bulk discoloration:** - Chemical shift in peroxide-amine-cured resins on long exposure to UV light. - Excessive porosity is a most common attribute for bulk discoloration → thus, trapped air voids with resulting "spongy spots" cause unfavorable changes of optical characteristics. - Sorption of stain precursors in association with water sorption. - **Prevention:** - Elimination of all caries and undermined enamel. - Correct color determination with active decision-share of the patient. - Contaminants must be completely avoided. - Improving of oral hygiene and emphasis on routine check-up. - Standardization of the application technique. - **Treatment:** - It essentially depends on the extent of discoloration and generally ranges between resurfacing and total replacement. - If careful examination reveals presence of caries, this should first be eliminated and the restoration remade. - Surface discoloration may be limited, and preferably eliminated by proper polishing. - Nothing to do in color match that does not affect esthetics>>> - There is a (localized) discoloration or opaqueness in the restoration making it affecting esthetics >>>> Partial removal and repair (veneering) is possible. - If it is deep or involves the bulk of restoration total replacement or veneering would be indicated. - Veneers of adequate thickness may be required to mask the defect. - Again, the discolored portion is uniformly cut with a suitable size carbide round bur, the cut surface cleaned, washed, etched for additional cleaning, bonded,