Presentation of cracks

• When examining teeth, apart from from caries, restorations and the periodontal condition, cracks are a common finding, more so the older the patient is. Common places that cracks are seen are the mesial and distal marginal ridges of posterior teeth as well as the mid buccal and lingual grooves.
• Craze lines are often seen on the labial surface of anterior teeth. Cracks are most commonly seen on mandibular molars, then upper premolars. Teeth more posterior are closer to the muscles of mastication and to the fulcrum point of the TMJ therefore forces tend to be higher on these teeth.
• Upper molars tend to erupt tipping towards the buccal and the palatal cusps as a result protrude occlusally. These plunger cusps tend to interfere with the lower molars cusps on lateral excursion and predispose to cracks. When a crack is detected, carefully view the level of the posterior occlusal plane in a mouth mirror from the palatal aspect. You should be able to see if a plunger cusp sits above the level of the occlusal plane. 
• Cracks undermining the DP cusp of upper 7s as well as M-D cracks on lower molars anecdotally have the poorest prognosis due to their higher risk in having subgingival fracture points and cracks to the pulp floor.
• Stained cracks may point to a long term crack that has had time to pick up stain or one that is overlaid by an amalgam restoration. 
• Enamel only cracks won't block light from transillumination. It is important to question the cause of cracks. 
• There won't always be anterior wear or posterior wear facets in bruxers. Clenching only bruxism will result in crack lines without tooth wear.