Wedge Shaped Defect in Dentistry

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The term “wedge-shaped defect” figuratively describes a hard substance defect that often appears on the cheek, but also in the mouth at the neck of teeth.

It can primarily be found in prominently positioned teeth, i.e. in canines and premolars; in rare cases even in all teeth. First, the tiniest, groove-shaped usures appear at the transition from the enamel to the dentin, which grow larger and deeper over time. The surface of the defects looks smoothly polished and hard. Macroscopic symptoms of caries are missing, although a regular carious process may also appear in later stages due to increased plaque retention.

To date, the causes and the development of these defects have not been definitely explained. They are called a “multifactorially conditioned event” involving primarily mechanical abrasion due to improper dental care, i.e. the horizontal brushing of teeth with sharp-edged toothbrush bristles and abrasive toothpastes. This is suggested by characteristic injuries and dehiscences on the gingival margins, which can be frequently observed in these cases.

Wedge Shaped Defect

Wedge Shaped Defect

Besides those, other causal mechanisms are discussed. In case of elastic deformations of the tooth in the area of the tooth neck, for example, through eccentric contacts, chipping of the hard tooth substances seems possible; an acid-related progression of the erosions is perfectly conceivable. However, to date, these hypotheses could not be sufficiently substantiated. In any case, an onset at the neck of the tooth is characteristic as this region seems morphologically and structurally more vulnerable to mechanic abrasion than other sections of the enamel-covered dental crown.

When left untreated, the wedge-shaped defect continues to deepen to the point of absurd grooves that frequently provoke the formation of secondary dentin in the root canal. An overlay of caries accelerates the process. In most cases, the progress of the formation of the wedge-shaped defect cannot even be stopped with a correction of the tooth brushing method. The bristles of the tooth brush are pressed together in the already existing wedge-shaped indentation (like in a guiding groove) and the sawing and abrasive effects can hardly be avoided, even if techniques recommended for periodontal diseases are applied.

Besides endangering the pulp, a fracture of the tooth may also occur due to the wedge-shaped defect. Up to now, there is a widespread opinion that only larger wedge-shaped defects must be treated with a filling or a crown.

However, the unstoppable development from the first small usures seems to indicate that an early therapy is appropriate if there is a possibility – with the brushing technique modified at the same time – to prevent a further progression. If the crown of the tooth has been pre-damaged beyond the wedge-shaped defect by carious processes, then a crowning of the tooth may become necessary. This also requires a modification of the tooth brushing technique, since otherwise new wedge-shaped defects would develop within a short time below the crown margin.

Amalgam fillings or inlay fillings require a further loss of tooth substance due to the preparation of undercuts or box-like forms. Composite filling materials are only suitable to a limited extent. The pronounced polymerization shrinkage (the shrinking taking place during the hardening of the plastic composites) almost regularly leads to a marginal gap, particularly in the case of micro-filled materials, and thus, to new leaks – secondary caries being the consequence.

However, after trials lasting several years, the experience gained in treating wedge-shaped defects with glass ionomer cements give rise to hope. These materials adhere to dentin and enamel, when they are freed from organic deposits by having been processed with a cleaning compound and being dry on the surface. Whether an additional pretreatment with citric acid improves the bond cannot yet be said with the necessary certainty.

The quality of the glass ionomer cements to adhere to the dentin does not exclude the necessity of an effective protection of the pulp (the dental nerve): Fillings near the pulp must first be covered with zinc oxyphosphate cement. With regard to their sophisticated processing, glass ionomer cements can be compared with silicate cements. Here, too, a premature contact with moisture leads to an incomplete setting with a significantly increased solubility of the filling.

This post is also available in: German

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