|Year : 2014 | Volume
| Issue : 1 | Page : 62-65
Implants not for all: Many can be sensitive!!!
Sheela Kumar Gujjari, Nada Musharraf Ali
Department of Periodontology, JSS Dental College, Mysore, Karnataka, India
|Date of Web Publication||19-Apr-2014|
Nada Musharraf Ali
Department of Periodontology, Room No. 9, JSS Dental College, S.S. Nagar, Mysore - 570 015, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Dental implants have revolutionized oral rehabilitation in partially and fully edentulous patients. High implant success rates in healthy as well as medically compromised individuals are reported by various studies. Nevertheless, a failure rate of 1.5-6.7% is also evident. Titanium (Ti) alloys are considered the material of choice in implantology due to their high strength, biocompatibility and corrosion resistance in a physiological environment. This metal has been somewhat surrounded by mysticism in the world of dentistry to the extent that there is a general belief, though biologically inexplicable, that it cannot cause allergic reactions. However, this phenomenon, which seems to be either overlooked by clinicians or weakly researched upon, exists and may have a worrying correlation to implant failure. This is an attempt to review the literature on allergy to Ti and its relevance in dental implantology.
Keywords: Allergy, dental implants, titanium
|How to cite this article:|
Gujjari SK, Ali NM. Implants not for all: Many can be sensitive!!!. J Dent Implant 2014;4:62-5
| Introduction|| |
Dental implant treatment has improved the quality of life for many of our patients. Although success rates are high (81-85% in maxilla and 98-99% in mandible), a failure rate of 1.5-6.7% is still existent and presents a significant clinical, psycho-social and financial challenge for clinicians and patients alike.  Implant failure during the initial healing period and after osseointegration has been extensively reviewed in the literature.  Factors including surgical trauma, impaired healing ability, bone characteristics, systemic reasons and implant-related factors have also been implicated and studied as leading causes of implant failures. Out of the various causes of implant failure, allergy or hypersensitivity to dental implant material seems to have been neglected and overlooked by dentists world-wide.
From when dental implants were first introduced 30-40 years ago, various materials such as gold, cobalt-chromium alloys, platinum palladium alloys, titanium (Ti) alloys and commercially pure Ti have been used for their manufacturing. Out of these Ti was considered to be the material of choice for dental implants owing to its high resistance to corrosion in a physiological environment and the excellent biocompatibility that gives it a passive, stable oxide film. 
Owing to these properties, Ti has been somewhat surrounded by mysticism in the world of dentistry to the extent that there is a general belief, biologically inexplicable, yet still shown in some literature, that it cannot cause allergic reactions.  It should be noted, however, that no material can be considered universally biocompatible and this does include Ti.  Thus, allergy due to Ti might be accountable for the failure of implants in some cases (known as "cluster patients"). 
| Pathogenesis of Ti Allergy|| |
Corrosion is the deterioration of a metal due to interaction (electrochemical attack) with its environment, which results in the release of ions into the surrounding microenvironment. 
All metals in contact with a biological environment undergo corrosion, which leads to the formation of metallic ions that may trigger the immune system by forming complexes with endogenous proteins. Therefore, in order for Ti to tempt an allergic reaction, it must have antigenic characteristics. Even though, Ti is renowned for its high corrosion resistance, the possibility of some degree of corrosion of the metal in a biological system cannot be disregarded. ,
Ti has been reported to stimulate bone resorption by inducing differentiation of murine osteoblasts and thus contributing to aseptic loosening of dental implants.  Furthermore, Ti has also been reported to cause deoxyribonucleic acid damage.  In a study, the prevalence of Ti allergy in 1500 consecutive patients with dental implants was investigated. The results confirmed the occurrence of allergic reactions in patients with dental implants; however, the definite incidence of allergic responses to Ti dental implants could not be estimated. 
When metal particles/ions are released from the implant surface, they can migrate systemically, remain in the intercellular spaces near the site where they were released, or be taken up by macrophages.  The presence of metallic particles in peri-implant tissues may not only be due to a process of electrochemical corrosion, but also due to frictional wear, or a synergistic combination of the two. The corrosion products formed as a result of metal-environment interactions have an effect on the biocompatibility and long-term stability of the prostheses/implants.
Under hostile circumstances, lower pH phenomenon in a peri-implant region of implant facing extreme mechanical forces, or in the proximity of implant with other metals such as amalgam, gold alloy, or chromium-cobalt alloys, corrosion of Ti may occur. Ti ions or microparticles of Ti released in the area of periodontal tissue adjacent to the implant can cause inflammatory reactions in the surrounding tissues. Macrophages, activated by Ti, secrete cytokines which are responsible for the initiation of different diseases. Ti ions (haptens) released by surface degradation may combine with endogenous proteins to form antigenic molecules due to their high affinity with protein. These antigenic molecules (the allergen) are captured by Langerhans cells, related to T-lymphocytes. It produces Type IV allergy, known as delayed-type hypersensitivity reaction to the patient after repeated contact of an allergen with skin or mucosa.
| Clinical Manifestations of Allergy To Ti|| |
Patients with Ti allergy demonstrate various clinical features such as burning or tingling sensations, generally associated with swelling, oral dryness, or loss of taste. Occasionally more common signs and symptoms (e.g., headache, dyspepsia, asthenia, arthralgia, myalgia etc). Allergy in the oral cavity manifests as erythema of the oral mucosa, labial edema, or purpuric patches on the palate, mouth ulcers, hyperplastic gingivitis, depapillation on the tongue, angular cheilitis, perioral eczematous eruption, or lichenoid reactions. 
| Diagnosis of Ti Allergy|| |
An allergy evaluation for Ti is suggested in those Ti implant indicated patients who have a history of allergy to other metals. The most commonly used test is the lymphocyte transformation test (LTT) which is applied by an in vitro method in mucosal sensitizing allergens. The optimized version of LTT is known as memory lymphocyte immuno stimulation assay (MELISA). Local and systemic effects of hypersensitivity resulting from allergies can be analyzed by this method. 
It should be noted, however, that the MELISAs test is not without controversy. An in vitro comparative study found no significant difference regarding sensitivity and specificity between MELISAs and conventional LLT and because of the high number of false-positive results it was concluded that these tests (MELISAs and LLT) may not useful in the diagnosis of metal-related contact allergy MELISAs and LTT tests are still under scientific evaluation and are not yet approved as routine tests. 
An allergic reaction can be rationally guessed subsequent to metallic implant placement, based on the clinical features linked with allergy, such as rash, urticarial and pruritus, oral erythema, swelling in the region, eczematous lesions, or hyperplastic lesions of periodontal tissue (the peri-implant mucosa). In such cases, allergy testing must be carried out.
| Discussion|| |
It is uncertain whether a true Ti allergy exists. Ti has developed into a well-accepted metallic biomaterial due to its unique properties. It is now documented that environmental factors are contributing factors in the increasing occurrence of allergic disorders affecting the world population. 
In various studies, it was observed that patients with Ti dental implants presented with allergies such as skin rash, flush and eczema; however, should these allergic reactions be entirely attributed to Ti is a debatable issue. Ti-alloys (chiefly comprising of Ti, aluminum [Al] and vanadium [V]) are usually used in implant dentistry in comparison to pure Ti because of their higher strength.  However; small yet consistent amounts of other elements have been detected in Ti alloys which may act as "impurities." It may therefore be hypothesized that such impurities in the implant material may play a role in triggering allergic reactions in patients with Ti implants. 
Performing a metal allergy assessment in a high number of patients, expecting a low prevalence of subjects showing positive results does not justify carrying out allergy tests on all individuals, whereas a two stage assessment would be more reasonable. The first phase should be aimed at identifying potentially allergic patients based on the medical records (predisposing factors), on the examination of signs and symptoms associated with Ti allergy and on clinical events such as unexplained and de-keratinized hyperplasic reactions of the peri-implant mucosa, associated with Ti allergy in the literature (Ti allergy compatible reactions). The second phase should be aimed at performing more specific Ti allergy tests. 
Under unfavorable conditions (acidic pH, mechanical friction, close contact to amalgam or gold restorations, etc.), Ti implants may corrode and release ions or micro-particles which can induce inflammation in affected tissues which is clearly demonstrated in various case reports. , This mechanism has been suggested to play a role in the loosening of implants.
Although reports of allergic reactions to metallic implants and devices are common, but the literature on Ti hypersensitivity leading to oral implant failure is scarce, with only few case reports and studies of suspected Ti hypersensitivity. ,,, It may be that oral-implant-related Ti-hypersensitivity may be under-reported due to poor understanding or failure to investigate this as a potential etiological factor.  Furthermore, more studies are needed to establish the role of pure Ti dental implants in the development of hypersensitivity reactions. 
| Conclusion|| |
No metal or alloy is completely inert in vivo. All metals will undergo a slow removal of ions from the surface, largely because of local and temporal variations in microstructure and environment. The presence of ions/particles and their effects around metallic devices might affect implant outcome. A sensitive and precise test which will help to determine Ti hypersensitivity should be developed. Furthermore, it seems possible it seems possible that the incidence of allergic reaction to Ti implants may be under-reported due to a lack of recognition as a possible etiological factor in implant failure. Thus, Ti hypersensitivity should not be excluded as a reason for implant failure and further long-term studies are needed to establish the same.
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