Class v LesionsClass V lesions are those occurring at the cervical aspect of the buccal or lingual surfaces of teeth. Conventionally, based on the etiology, a class V lesion is broadly classified as Carious and Non-Carious lesions. The non-carious cervical lesions are further categorized into abrasion, erosion and abfraction. Shafer, Hine and Levy asserted that abrasion and erosion are separate and distinct processes, each of which results in loss of tooth substance. A study done by Bader et al provided a strong evidence of multifactorial etiology for the development of class V lesions. According to him, factors such as brushing, diet and occlusal mechanisms may act independently at different points on the same tooth and result in a class V lesion. Pintado et al in his longitudinal case study over a time span of 14 years showed a direct correlation between occlusal wear and growth of non-carious cervical lesions. Survey by Khan F and Young WG et al also concluded that cervical lesions may have a multifactorial etiology with either erosion as the primary factor in conjunction with stress or tooth brush abrasion as the primary etiologic factor. Due to the diverse dynamics that take place in the oral cavity in the form of both external and internal contributing factors, most of the cervical lesions may be the result of a combination of two or more processes. Hence a more appropriate classification for these lesions could be explained on the basis of four combined or synergistic events which can lead to loss of dental hard tissues.
- Erosion Corrosion
- Abrasion Corrosion
- Material of choice for a class V lesion.
- Reasons for using the particular material.
- Factors to consider during the selection of material for a class V situation.
The class V lesion occurs in a small area which is structurally diverse. This region contains enamel (96% inorganic and 4% organic matter), dentin (65% inorganic and 35% organic matter) and cementum (45% inorganic and 55% organic matter).The Cementoenamel junction that acts as the fulcrum of the tooth is subjected to stress concentration during occlusal loading. Any lesion (carious or non-carious) occurring in this region of the tooth has to be analyzed critically, for a better understanding of the multifactorial etiology and the restorative treatment to be carried out. Overlooking this important aspect could lead to failure of treatment.
Erosion CorrosionThe glossary of metallurgical terms endorsed by the American society of metals, defines the term 'erosion' as "the abrasive destruction of materials by the movement of liquids or gas, with or without solid particles". 'Corrosion' is defined as the physical deterioration of a material by chemical or electrochemical attack. Corrosion can be metallic or non-metallic. Teeth are nonmetallic and crystalline. The process of corrosion more precisely relates to the common misnomer "dental erosion". Pure erosion in the sense of wearing away by fluid flow such as water consumed by humans or flow of other noncorrosive materials may not cause significant loss of dental hard tissues. Repeated exposure of dental hard tissues to corrosive chemicals such as highly acidic beverages is considered to be the primary cause for these lesions. Studies have also reported that any substance with a critical pH of <5.5 can demineralise the hard tissues of the tooth.The wasting of teeth as seen in bulimia, termed as perimylolysis and Gastroesophagal reflux disease (GERD) are also examples of the combined activities of erosion and corrosion during the flow of regurgitated acidic stomach contents over the teeth. These lesions appear clinically as smooth and spoon shaped. Rarely, occupational hazards such as continued exposure to fumes of corrosive acid such as hydrochloric and sulphuric acid may also lead to erosion corrosion lesions.
In each of the above mentioned situations, it is the mechanical flow (erosion) by a corrosive material that causes the combined degradation of the teeth; the major factor being that of corrosion or chemical dissolution.
In deciding upon the restorative treatment of these lesions, Glass ionomer cements are not to be used as there is dissolution of the glass matrix in the acidic environment leading to failure of the restoration. Composite resins which are highly esthetic and have good retention and wear resistant properties are the materials of choice.
Abrasion CorrosionThe abnormal loss of tooth substance resulting from direct frictional forces between the tooth and the external objects or between components in the presence of an abrasive medium following demineralization by some endogenous or exogenous acidic agent could be termed as Abrasion Corrosion.
Two mechanisms can be attributed for the development of these lesions:
- Brushing the teeth immediately after drinking an acid beverage such as lime or citrus fruit juice.
- Faulty brushing techniques, wherein the gingival crevicular fluid (GCF) itself acts as a source of acid.
These lesions present clinically as sharp, flat and angular defects at the cervical third of the tooth.
When considering the restorative option in this case, conventional glass ionomer cement may not be ideal, although it has a modulus of elasticity similar to that of dentine and is referred to as dentin substitute, because of its low tensile strength, poor esthetics, moisture sensitivity and low wear resistance.
Materials of choice in these situations could be microfilled composite and resin modified glass ionomer cement.
Microfilled composites being highly esthetic, having good finish and good wear resistance also tend to flex with the tooth under occlusal load.
Resin modified Glass ionomer cement has the advantage of dual cure setting, higher compressive strength compared to conventional Glass ionomer cement, low solubility, fluoride release and better esthetics.
During mastication, every chewing stroke is associated with axial and horizontal forces caused by occlusal morphology and the cyclic movement of the mandible , but when abnormal forces act on the teeth, as in bruxism, fatigue and fracture of the most flexed zone i.e; the cervical area of the tooth takes place. This results in cracking or breakage of the tooth structure. Many investigators hypothesize that, these abnormal interocclusal forces create physical microfractures or abfractions at the cervical region which results in notch shaped or V shaped lesions in the CEJ. Studies conducted by McCoy in 1980 established a direct cause and effect relationship between abrasion and abfraction lesions. Citing engineering studies, he postulated that tooth flexure from tensile stresses lead to cervical tooth breakdown and class V restoration failure. Lee and Eakil later hypothetized that the primary etiological factor in a wedge shaped lesion is the tensile stress from mastication and malocclusion. According to them, when a tensile stress is generated as a result of lateral forces acting on the teeth, instead of dissipating, they concentrate at the cervical aspect of the teeth. Due to this, water or other small molecules could penetrate the broken hydroxyapatite molecules making the tooth highly susceptible to the action of the abrasive agents. Based on the the above studies, Grippo subsequently coined the term Abfraction from the Latin words 'ab' away and 'fractio'- breaking. He defined it as the pathological loss of tooth substance caused by biomechanical loading forces that result in flexure and failure of enamel and dentin at the location away from loading. Using FEM analysis, McCoy further demonstrated that eccentrically loaded teeth flex and that internal stress distribution occurred in such a way that the stress concentrated at the cement enamel junction, generating tensile stresses that pull apart enamel prisms, thereby increasing the susceptibility to loss of tooth substance.
Few other surveys also concluded that cervical lesions may be seen in conjunction with stress and abrasion as the primary etiologic factor. Clinically, these lesions are mostly wedge shaped and develop as hard tissue defects in the cervical region of the teeth commonly in the buccal aspect .
An associated terminology called as the "Dental Compression Syndrome"33 refers to tooth deformation related to malocclusion, para functional habits and TMJ disorders.
Disregard in understanding the etiological factor causing the lesion can lead to marginal leakage, debonding and restorative failure, Studies by have shown that following restoration of these abfraction lesions the rate of progress of tooth destruction reduces from an average of 7 microns to 2 microns a week. According to Grippo, the restoration would support the tooth, thereby minimizing flexure and abfraction and also prevent further loss of tooth structure.
One of the most effective methodologies advocated for the management of these lesions is the use of a bilayered restoration wherein the deeper layer is made up of a material with low modulus of elasticity. A study was conducted to show that, a restoration wherein, the deeper layer consists of a microfilled composite with low modulus of elasticity and high tensile strength and a superficial layer of hybrid composite performed the best.
Biocorrosion Abfraction:The combined effect of biocorrosion (caries) and abfraction is the pathologic loss of tooth substance associated with caries where plaque adheres preferentially to the tooth surface roughened by flexural microfracture (abfraction). A Study done by Grippo has suggested that root caries could be potentiated by the presence of plaque in areas of stress concentration resulting in stress corrosion . Measures to maintain good oral hygiene and bringing caries under control are as important as deciding on the final restoration which may be in the form of Composite resin.
Adequate history, case selection and treatment planning arc vital parameters in ensuring the successful management of class V lesions in the oral cavity. A thorough understanding of the factors causing the lesion and the methods of treating it will go a long way towards achieving this end.
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