This chapter examines the evolution of dental implant treatment planning, particularly regarding optimal implant numbers for edentulous rehabilitation. Beginning with Carl Misch’s one-implant-per-tooth philosophy in the 1980s, the field has shifted toward more conservative approaches based on clinical evidence. The chapter critically analyzes six major hypotheses of marginal bone loss around dental implants, including periosteal reflection, implant osteotomy, bacterial colonization, biological width, foreign body reaction, and occlusal overload theories. Current evidence demonstrates that fewer strategically placed implants often achieve comparable or superior outcomes to configurations with more implants. Meta-analyses reveal similar survival rates and marginal bone loss between full-arch prostheses supported by four implants versus five or more implants. The All-on-Four concept shows promising results with over 95% success rates. For mandibular overdentures, two to three implants provide optimal patient satisfaction, while maxillary overdentures require at least four implants. Treatment decisions should prioritize tissue conditions, maintenance accessibility, and patient-specific factors rather than rigid implant number protocols.