Four is the sum and product of two with itself: 
  
    
      
        2
      
    
    {\displaystyle 2}
   + 
  
    
      
        2
      
    
    {\displaystyle 2}
   = 
  
    
      
        4
      
    
    {\displaystyle 4}
   = 
  
    
      
        2
      
    
    {\displaystyle 2}
   x 
  
    
      
        2
      
    
    {\displaystyle 2}
  , the only number 
  
    
      
        b
      
    
    {\displaystyle b}
   such that 
  
    
      
        a
      
    
    {\displaystyle a}
   + 
  
    
      
        a
      
    
    {\displaystyle a}
   = 
  
    
      
        b
      
    
    {\displaystyle b}
   = 
  
    
      
        a
      
    
    {\displaystyle a}
   x 
  
    
      
        a
      
    
    {\displaystyle a}
  , which also makes four the smallest squared prime number 
  
    
      
        
          p
          
            2
          
        
      
    
    {\displaystyle p^{2}}
  .
Definitive options include:
Bonded intra-coronal restoration
Onlay restoration, either direct or indirectly placed (currently the recommended technique)
Crown restoration (though this is associated with a high incidence of loss of vitality in teeth with CTS)Teeth originally presenting with CTS may subsequently require Root Canal therapy (if pain persists after above) or Extraction

History
The term "cuspal fracture odontalgia" was suggested in 1954 by Gibbs. Subsequently, the term "cracked tooth syndrome" was coined in 1964 by Cameron, who defined the condition as "an incomplete fracture of a vital posterior tooth that involves the dentin and occasionally extends into the pulp." References


== External links ==