Classification According to Origin of Infection

There are two types of failure depending to the origin of infection either orthograde or retrograde.

i)Peri-Implantitis (Infective Process— Bacterial Origin): Bacterial invasion of the peri-implant soft tissue results in its inflammation followed by rapid bone loss. Peri-Implantitis as defined by Meffert is the progressive loss of peri implant bone as well as soft tissue inflammatory changes. However, perimucositis and peri-implantitis have been differentiated as has been discussed earlier.It has been shown that Gram Negative rods including Bacteroides and Fusobacterium sp. are consistent with failing implants. Spirochaetes and motile rods with a predominance of Peptosteptococcus micros, Actinobacillus actinomycetemcomitans, Prevotella intermedia and Porphyromonas gingivalis have been shown to be associated with failing implants.

The similarity in clinical signs and the bacterial microflora suggest a similarity between failing implants and periodontitis. The role of bacterial infection in the aetiology of dental implant failure has been clearly documented, therefore in a partially edentulous situation, complete periodontal therapy should be completed prior to implant placement as the similarity of the microflora indicates a probable bacterial migration into the implant site.

ii) Retrograde Peri-Implantitis: It has been described by Misch as implant failure probably due to bone microfractures caused by premature implant loading or overloading, other forms of trauma or occlusal factors.The suggested mechanism is that once the biomechanical demand has exceeded the load bearing ability of bone, microfractures of the bone at the implant interface may occur; they may also occur if microdamages accumulate faster than they can be repaired, a fatigue fracture at the bone implant interface may result.Other Reasons for causing Periapical lesions around bone — (Retrograde) - include: Bacterial involvement resulting from placement of implant in infected socket.

• Infection from the adjacent natural tooth — cross infection.
• Excessive heat generation during implant placement.
• Premature loading.
• The periapical lesion may also be due to incomplete placement of implant to the full depth of the osteotomy site.
• The Features include:
• Periapical Bone loss without gingival inflammation.
• Microflora consisting mainly of streptococci and nonmotile organisms which is consistent with periodontal health.