Evaluation of implant success: A review of past and present concepts.

Dental Implants have become the standard care of rehabilitation of missing teeth. This article intends to review the success criteria for implants from 1979 till date. Earlier days implant success was evaluated by immobility and peri-implant radiolucency. But currently, the width of the attached gingiva, co-existing medical conditions, smoking, and width of the implant also play a role in evaluating implant success. Genetic and immunological markers have also been identified.

A revolution in the research and technology of implants during the last two decades has made the replacement of missing teeth with endosseous implants the standard care and an implant supported prosthesis as the first line of treatment and long lasting rehabilitation.[1]

It all started when Professor Branemark used titanium chambers to investigate the anatomy and physiology of tissue injury. He observed that the titanium chambers were firmly attached to the bone and they could not be removed from the bone once it healed. After this chance observation, Branemark developed a new concept of osseointegration which led to dental implants. The use of titanium based implants in humans begun in 1965.

This article intends to review the past and the present concepts to evaluate the long-term success of a dental implant. Considerations are given to evaluating the following criteria durability, bone loss, gingival health, pocket depth, effect on adjacent teeth, function, esthetics, presence of infection, discomfort, parasthesia or anesthesia, intrusion on the mandibular canal, patient′s emotional and psychological attitude and satisfaction.[2]

Earlier Concepts

Schnitman and schulman,[3] 1979:

Mobility less than 1 mm in any direction.

Radilogically observed radilucency graded but no success criterion defined.

Bone loss no greater than one third of the vertical height of the bone.

Gingival inflammation amenable to treatment, absence of symptoms and infection, absence of damage to adjacent teeth, absence of parasthesia and anesthesia or violation of the mandibular canal, maxillary sinus or floor of the nasal passage.

Functional service for 5 years in 75% of patients.

Cranin et al.[4] 1982:

In place 60 months or more.

Lack of significant evidence of cervical saucerisation on radiographs.

Freedom from hemorrhage according to Muhleman′s index.

Lack of mobility.

Absence of pain or percussive tenderness.

No pericervical granulomatosis or gingival hyperplasia.

No evidence of a widening peri-implant space on radiograph.

McKinney et al.[5] 1984:

Subjective criteria

Adequate function

Absence of discomfort

Patient belief that esthetics and emotional and psychological attitudes are improved.

Objective criteria

Good occlusal balance and vertical dimension.

Bone loss no greater than one third of the vertical height of the implant, absence of symptoms, and functionally stable after 5 years.

Gingival inflammation vulnerable to treatment.

Mobility of less than 1 mm buccolingually, mesiodistally, and vertically.

Absence of symptoms and infection associated with the dental implant.

Absence of damage to adjacent tooth or teeth and their supporting structures.

Absence of parasthesia or violation of mandibular canal, maxillary sinus, or floor of nasal passage.

Healthy collagenous tissue without polymorphonuclear infiltration.

Success crieterion

Provides functional service for 5 years in 75% of implant patients.

Possible criteria for success

Mobility

A two point scale such as mobile or immobile implant can be used. An additional test is to tap the implant with an instrument. If the tap elicits a solid ring there is no mobility but if the sound is dull, the implant is not osseointegrated and surrounded by fribrous tissue.

Peri-implant radiolucency

An implant with radiolucency around it should not be judged as a success.

Marginal bone loss

Adell et al.[6] determined that the mean bone loss for Branemark Osseointegrated implants was 1.5 mm for the first year and followed by mean bone loss of 0.1 mm/year.

Mean bone loss of 0.2 mm per was accepted as a criterion for success.[2]

Albrektsson et al.[7] 1986

Individual unattached implant that is immobile when tested clinically

Radiography that does not demonstrate evidence of peri-implant radiolucency

Bone loss that is less than 0.2 mm annually after the implant′s first year of service

No persistent pain, discomfort or infection

By these criteria, a success rate of 85% at the end of a 5 year observation period and 80% at the end of a 10 year period are minimum levels for success.

Present Concepts

Though the earlier concepts form the basis of evaluation of implant success, recently lots of other factors have been found to play a vital role in long-term success of an implant.

Width of the attached gingiva

Implants failed if the width of the attached gingival is ≤ 2 mm. Other studies have shown that a thin or absent masticatory gingival was associated with bleeding on probing and a significantly greater mean loss of alveolar bone.[8]

Sutures

Silk sutures were less likely to support bacterial colonization than other suture materials which minimizes the chance of odontogenic infections.[9] Use of polyglactin 910 was associated with a higher incidence of early loss of implants.

Associated Medical Conditions

Studies have found that early loss of implants were common among patients with a co-existing medical conditions, but not significantly so. Despite the suggestion that type 2 diabetes has a possible adverse effect on survival of implants,[10] there is no conclusive evidence.[1]

Smoking

Smoking may have an adverse effect on the implant survival and success.[1011] There is evidence to suggest that smoking may have a dose related effect on osseointegration.[12]

Width of the Implant

A recent study described the largest early loss of implants with short and narrow implants.[13] One possible explanation is that narrow and short implants are usually placed in areas in which there is limited space or insufficient volume of bone.[1]

Genetic and immunological markers

A study evaluated diagnostic markers to predict titanium implant failure. TNF-α and IL-1β release on titanium stimulation were significantly higher among patients with implant loss.[14]

Implant success in radiated mandibles and fibula flap

The success of implants in fibula grafts was 89.2% and success in irradiated mandibles was 87.18% with the use of hyperbaric oxygen therapy.[1516]

Discussion

Earlier, the evaluation of implant success revolved around the mobility, peri-implant radiolucency, marginal bone loss and absence of infection or discomfort to the patient.

A study even proposed an Implant Quotient to assess the long-term success of the implant. Implant Quotient was derived by relating positive and negative factors of implant success.[17] Currently, implant success is evaluated by a lot of factors along with the earlier ones.

The width of the attached gingival, co-existing medical conditions, smoking, width of the implant, suture material used, all play an important role in implant success. Even genetic and immunological factors like TNF-α and IL-1β have been identified as markers for implant success.

Conclusion

The basic criteria for implant success are immobility, absence of peri-implant radiolucency, adequate width of the attached gingiva, absence of infection. A wider implant has long-term success than a narrow implant. Co-existing medical conditions and smoking also play an important role in evaluating the success of an implant.