Complex sentence: Dental caries, left untreated, follows a predictable natural history to where it causes reversible pulpitis which transitions to irreversible pulpitis, then to necrosis, then to necrosis with periapical periodontitis and finally to necrosis with periapical abscess.
Split into simpler sentences: Dental caries, left untreated, follows a predictable natural history as it nears the pulp of the tooth. First causing reversible pulpitis which transitions to irreversible pulpitis, then to necrosis, then to necrosis with periapical periodontitis and finally to necrosis with periapical abscess.