Using an excessive number of pins in a dental restoration can lead to stress concentration within the tooth structure, which predisposes it to cracks and fractures. Each pin requires drilling into dentin, and multiple pins can cause loss of tooth integrity rather than reinforcing it. This weakening effect compromises the overall durability of the restoration, making it more prone to failure under functional loads. Therefore, while pins improve retention, their overuse is detrimental as it undermines the mechanical strength of the restored tooth.

Reference: Sturdevant's Art and Science of Operative Dentistry, 7th Edition.