Cl.I cavity preparation

Cl.I cavity preparation may include certain cases of exception, in this lecture we will discuss the lower 4 and the upper 6. The lower first premolar; the occlusal surface of this tooth shows the presence of the transverse ridge joining the buccal and lingual cusps. This ridge separates between the mesial and distal fossae that are joining by the coalesced central fissure; therefore, caries index in this ridge is very low and and it must stay intact during cl.I cavity preparation of the lower 4 and two separate cavities should be prepared around the cusps . Only when the caries is extended and include this ridge (it s width is less than 0.5 mm), it should be prepared with the fossae to obtain only one cavity . This cavity has an anterioposteriorly tilted pulpal floor ; due to the fact that this tooth has high buccal cusp and lower lingual cusp ; consequently , the pulp horns are also of variable height , flat pulpal floor preparation may expose the pulp and cause pulp traumatic exposure , the tilt of the cavity is about (45°) and so the bur direction during making the entry to the cavity .
The anatomical picture of this tooth shows us that it has a stout ridge crossing the occlusal surface from the mesiolingual cusp to the distobuccal cusp, and therefore dividing the occlusal surface into mesial and distal fossae.
This oblique ridge shows less degree of susceptibility to the caries, it is a coalesced part of the tooth, and shouldn t included in our cavity preparation to preserve the tooth structure stronger and to maintain efficient tooth function.
In case of extensive caries that the oblique ridge was