Identification of risk patients in oral implantology (I)

Introduction

During decades, our medical colleagues have been developing methods to identify individuals at high risk for various diseases or conditions. High-risk individuals are then targeted for special programs, such as early detection and treatment, and risk reduction efforts. Risk assessment efforts applied to implant dentistry have only recently received attention, primarily because the prevalence of peri-implant disease and implant failures since the recent era of osseointegration has been low and therefore the number of investigations which have studied the causes and factors associated with them is very limited. As our knowledge and concepts of implant health and disease evolve, we have realised that some people are more likely to be affected with the condition than others.

In this review the possible risk factors associated with implant disease and implant failures which relate to the patient status will be evaluated.

To understand the influence of risk factors on disease pathogenesis, it is helpful to have a conceptual framework of pathogenesis upon which the effects of modifiers can be easily appreciated. There are several reviews of pathogenesis of implant failures ^{(Tonetti and Schmid, 1994} ; ^{Meffert, 1996} ; ^{Cochran, 1996)} and in all of them, the definition of failure generates considerable confusion, since it encompasses a whole variety of clinical situations that, if untreated, ultimately lead to loss of the implanted device.

Implant failures have been defined as the loss or the failure to achieve osseointegration and depending on the time frame, have been categorised as early failures which occur weeks to few months after implantation, and late failures which occur much later. Early failures result from the interaction of an etiological agent with the wound healing process leading to osseointegration. Conversely, the action of an etiological agent on a previously osseointegrated implant results in a break of osseointegration and therefore a late failure.

The possible causes of early failures are to be found in : either tissue damage due to inadequate surgical technique or insufficient maintenance care procedures during the healing period, such as infection, premature loading or instability of the implant. Late failures arise from pathological processes involving a previously osseointegrated implant. These pathological processes have been classified into disturbances in biomechanical equilibrium, or overload, and alterations of the host-parasite equilibrium : infection (^{Sanz et al., 1991} ; ^{Rosenberg et al., 1991}).

Since 1977, several prospective and retrospective studies have reported success rates of both individual implants and implant-supported prostheses, initially in completely edentulous and more recently in partially edentulous patients ^{(for a review see Cochran, 1997)}. While these studies present large sample sizes and important data on longer-term implant survival, they have generally focused on the high levels of success rates, but have spent little time analysing factors involved in implant failures.

This review examines the available evidence on patient related factors which have been associated with implant failures. These factors have been categorised in : age, patient medial status or systemic condition, tobacco use, patients with psychosocial stress and patients with periodontitis patients with osteoporosis, patients with cancer ^{(see Etienne, Sanz et al., 1998)}.

Age

The use of dental implants is widespread among the adult population. However, there are no studies demonstrating higher failure rates with the use of dental implants in patients with advanced ages. In studies considering the characteristics associated with the loss of tissue around endosseous implants ^{(Weyant, 1994)}, data from 598 patients and 2 098 implants were examined from an implant registry at the Department of Veteran Affairs in US. Using logistic regression models for outcomes related to independent variables, indicated that implant survival was not associated with age, gender or number of implants placed. In two longitudinal multicenter studies ^{(Friberg et al., 1991} ; ^{Hutton et al., 1995)} considering implant failures in large implant series (4 641 and 510 respectively), age, gender and treatment center were not associated with treatment failure. In another study, ^{(Salonen et al., 1993)} studied prospectively 204 implants (four types) in 68 patients during 60 months with the purposes of estimating causes of implant failures. No differences were found between failures among the four implant systems. The authors speculated that advanced age related to the poor general health of the patient and complications during the surgical procedures were the possible causes of failures. ^Smith studied the risk factors associated with dental implants in healthy and medically compromised patients. They studied 104 consecutive patients treated with 313 Brånemark implants. They found that the patient's age was not statistically associated with increased surgical complications or implant failure. In this study, 24 patients (23.07 %) were age 65 or greater. Sixty-three implants (20.12 %) were placed in this group, with three implant failures (0.95 %). The three failures occurred in two patients who had maxillary implants.

From these studies we can conclude that geriatric patients are no longer seen as poor implant candidates because of their chronological age alone. Surgically treatable disabilities (severe jaw atrophy) should be assessed in the context of the debilitating nature of the disability, the patient's ability to tolerate a corrective procedure, and the patient's remaining life expectancy. Biologic rather than chronological age would be a more accurate determinant of risk assessment in the elderly.

Placement of implants in children and adolescents occurs much less frequently, primarily because of lack of need. Anodontia, either primary or acquired, occasionally creates the opportunity for use of implants in younger patients. The use of implants in the growing patient presents additional considerations and creates special problems because their jaws are in a period of active, dynamic growth. The dental literature is replete with articles on the use of implants in adults, but there is a paucity of information concerning their use in the growing patient. Reports on the use of implants in younger patients has mainly been in patients with ectodermal dysplasia ^{(Bergendal et al., 1991} ; ^{Guckes et al., 1991} ; ^{Smith et al., 1993} ; ^{Perrot et al., 1994)}, and patients with congenitally missing teeth or traumatic tooth loss ^{(Lederman et al., 1993} ; ^{Oesterle et al., 1993} ; ^{Sanz et al., 1993} ; ^{Johansson et al., 1994)}. Since data concerning the clinical use of implants in this age are limited at the present time, a definite protocol for their use has not been developed.

^Oesterle compared dental implants to ankylosed primary teeth. They noted that ankylosed primary teeth are often associated with disturbances in alveolar bone growth. During growth, teeth normally continue to erupt, and they simultaneously form alveolar bone with vertical growth. They wrote that « Ankylosis arrests both dental eruption and alveolar bone formation in the affected area. An osseointegrated implant would behave much like an ankylosed primary tooth, with the same lack of alveolar growth and dental eruption, » and thus, it would appear to submerge into the alveolus. These authors proposed that implants placed in the posterior maxilla in children may become buried to the point that the apical portion may become exposed as the nasal and antral floor remodel. They also warned about the possibility of loss of implants placed in the anterior maxilla because of resorption in the infradental fossa and nasal floor.

In a similar study ^{(Cronin et al., 1994)} discussed rotational growth of the mandible as related to implants. In children with a strong rotational pattern, posterior teeth continue to erupt along with continued alveolar bone growth to maintain the occlusal plane, possibly causing implants to become deeply buried within the mandibular alveolar process. Children without this rotational growth would not be expected to exhibit this same submergence of implants. These concerns have been confirmed by ^Odman ; ^Thilander ; ^Sennerby who placed dental implants in young, growing animals. The four sites selected for implant placement included the maxillary primary lateral incisor, the mandibular primary canine, the mandibular primary first premolar, and the mandibular primary second premolar on the opposite side. Six of the 20 originally placed implants were lost. In the premolar regions with vertically erupting adjacent teeth, craterlike marginal defects were present in animals that retained their implants, essentially burying the implants. This was not observed in a pig that had lost the implant in this region. In addition, the retained implants were found to be located lingual to their original placement sites. No defects were observed in the canine and lateral incisor regions where vertically erupting teeth were lacking. The authors concluded that osseo-integrated implants behave like ankylosed teeth during development of the dentition in the growing pig, and that the implants fail to move together with the adjacent teeth. They recommended that implants should not be placed posterior to the canines during active growth. In light of the aforementioned data on growth of the facial skeleton, it seems that implants placed in the anterior regions of the jaws of the adolescent patient, especially in the mandible, are less likely to submerge than those placed in the posterior region. The increase in height of the alveolar bone during the pubertal growth phase of some patients places them at risk for implant submersion and lingual migration. Implants placed in the anterior region may have changes in angulation.

In the adolescent, the question of implant placement timing arises in an effort to preserve the bone, mostly in patients with congenitally missing teeth (^{fig. 1}, ²et ³). ^{Ostler and Kokich (1994)} studied changes in ridge width over time in patients who had congenitally missing mandibular second premolars. They found that ridge width decreases 25 % within 3 years after primary molar extraction. The rate of decrease diminishes to 4 % during the following 3 years. ^{Kokich (1996)} found that less than 1 % of the alveolar ridge width is lost after 5 years following orthodontic treatment when the canines are moved distally to create space for the lateral incisors. These data reduce the urgency for implant placement in these situations until growth cessation can be confirmed. Using various bone grafting or ridge widening techniques also allows the implant surgeon to compensate for any bone lost while waiting for growth completion.

^{Westwood and Duncan (1996)} followed-up three young implant patients who received a total of five implants. Implant submersion was noted in the implant placed in the posterior alveolus of the boy who was still growing, requiring lengthening of the crown with additional porcelain. Implant submersion was questionable in the other boy who experienced no discernible growth. No problems were noted in the girl who received two implants in the anterior alveolus at the time when growth was ceasing. The experience with the small sample in this study appears to be consistent with results that can be expected by extrapolating data from animal studies and human growth studies. However, correlation of clinical experience from a large number of subjects with additional animal studies is necessary before valid guidelines for the placement of implants in the growing patient can be formulated. At the present time, it is recommended that implant placement be delayed until clinical signs of growth cessation are present. Serial cephalometric radiographs, 1 year apart, should be taken to confirm growth arrest. The urgency of placing implants in sites of congenitally missing teeth is reduced because the loss of alveolar bone in these situations has been shown to be predictable.

Patient medical status or systemic condition

Most implant textbooks and publications ^{(Laney, 1986} ; ^{Lekholm and Zarb, 1987} ; ^{Beumer and Lewis, 1989)} identify various local anatomic factors, as well as a few general systemic conditions, that may decrease the possibility of successful integration. Commonly, uncontrolled diabetes, blood dyscrasias, osteoporosis, alcoholism, psychiatric conditions, high levels of head and neck radiotherapy, and general surgical contraindications are among factors that may systemically decrease the potential for implant success. However, few, if any, studies exist that show a lower implant success rate when patients are treated in the presence of such systemic factors.

In the National Institute of Health Consensus Development Conference on Dental Implants ^{(Matukas, 1988)} when the health risks of dental implants were reviewed, little or no hard data could be found. In 1992 Smith et al., studied 104 consecutive patients treated with 313 implants with the purpose of determining the medical risks associated with dental implants. The univariate analyses to assess any associations between complications or implant failure and possible risk factors, i.e., age, sex, number of medical problems, ASA status, and number of implants placed failed to demonstrate any statistically significant association with surgical complications in general or implant failure, except for the number of implants. The number of implants placed was statistically associated with an increased risk of surgical complications (p = 0.016) and/or implant failure (p = 0.016). This study covered individuals with medical problems related to all organ systems, including disorders of the cardiovascular system, such as cardiomyopathy, pericarditis, coronary artery disease, hypertension, cardiac arrhythmias, rheumatic heart disease, and congestive heart failure. Although patients predisposed to infective endocarditis were treated with dental implants, to date no such condition has developed in them. There were three HIV-positive patients on zidovudine (AZT), one patient had thalassemia minor, and two patients had ectodermal dysplasia. These medical conditions and others did not appear to contribute to perioperative implant complications.

When studying if diabetes or patients taking corticosteroids had an increased risk of perioperative complications after implant surgery or implant failure, they could not find any difference between these group of patients and the rest of the population in this sample. Five of the 104 patients in this study were controlled diabetics, four with type I diabetes on insulin and one with type II diabetes on an oral hypoglycemic agent.

There was one postoperative infection after stage 1 surgery in one of the type I diabetic patients. Wound failure, particularly infection, is encountered in varying degrees in 5 % to 10 % of diabetic patients who undergo surgery ^{(Goodson and Hunt, 1979)}. As a group, diabetic patients experience more infection in clean wounds than nondiabetics ^{(McMurry, 1984)}. Therefore, current surgical opinion is that patients with well-controlled diabetes probably do not encounter inordinate operative risks, while patients with poorly controlled diabetes still frequently experience wound failure. Postponement of implant surgery until better glucose control and protein nutrition is achieved is then advisable when possible.

Chronic use of corticosteroids have also been associated with wound impairment and perioperative infections, although there are no studies which demonstrate a significant higher failure rate in these patients. On the contrary, the use of dental implants have been shown successful in patients with Sjögren's Syndrome. The associated xerostomia in these patients causes many problems in their traditional prosthetic management. The wearing of a removable prosthesis is often difficult, uncomfortable, or even impossible. Several case reports ^{(Atkinson and Fox, 1993} ; ^{Binon and Fowler, 1993} ; ^{Payne et al., 1997)} have shown the successful use of dental implants in these cases, even associated with regular use of corticosteroids.

Successful reconstruction of osseointegrated implants in the medically compromised patient have also being reported in several case reports. ^{Jensen and Sindet-Pedersen (1990)} reported on an implant placed in a patient with scleroderma, and ^{Sager and Theis (1990)} reported on implants placed in a patient with multiple myeloma.

^{Weyant (1993)}, ^{Weyant (1994)} carried out a longitudinal study of dental implants at the VA's dental implant registry. Three variables associated with systemic medical conditions were associated with implant failure : ASA (surgical risk), MEDHX (medical history), and MEDS (medication history). Each one represented a non-specific assessment of general health status. Taken together, these variables suggest that systemic health factors contribute to implant survival. This finding also suggests that the reports of high correlation of implant failures found within patients can be attributed, at least in part, to patients'medical status. Unfortunately, a more detailed assessment of specific health factors was not possible using this data.

SMOKING

One question that is often discussed in considering the success or failure of implant therapy is the effect of smoking. In a large retrospective study, where 540 patients with 2 194 Brånemark implants were evaluated for a 6-year period. ^{Bain and Moy (1993)} showed a significant higher failure rate in smokers, when compared with non-smokers. In this study both partially and fully edentulous patients were assessed (^{fig. 4}, ⁵, ⁶, ⁷, ⁸, ⁹ and ¹⁰) and the presence or absence of smoking was taken from the patients histories and depended on self-reporting. No attempt was made to quantify the amounts of cigarettes smoked and the number of years that the patients had been smoking. Besides more implants were placed in non-smokers than in smokers (1 800 or 82 % versus 394 or 18 %, respectively) The smokers failure rate was 11.28 %, while the non-smokers was significantly less, 4.76 %. When considering the area of implant placement, there was no difference between smokers and non-smokers, when implants were placed in the posterior mandible, however, there were significant differences when implants were placed in the anterior mandible or in the maxilla. No differences were reported between smokers and non-smokers based of age, gender, number of implants per patient, or average implant length. However, failure rates for shorter implants were very high in smokers (30.7 % of 7 mm implants failed). The authors concluded that implant success is poorest in the posterior maxilla and in all areas, except the anterior mandible, the failure rate was significantly greater in smokers than in non-smokers.

In a more recent article that examined the effect of smoking on implant failure, a retrospective analysis was conducted before prosthetic loading ^{(De Bruyn and Collaert, 1994)}. This study showed no effect of smoking for 208 implants placed in the mandible, since only one implant failed. In the maxilla, 10 out of 244 (4 %) failed, 7/78 (9 %) in smokers and 3/166 (1 %) in non-smokers, which was statistically significant. The authors noted that 31 % of smokers had implant failures in spite of excellent bone quality, the use of long implants and good initial stability. They concluded that smoking had an adverse effect on initial implant survival before prosthetic loading.

^{Bain (1997)} has studied the impact of a smoking cessation protocol on implant success or failure. He has followed 223 consecutive implants for 3 years. Patients were divided into 3 groups : non-smokers, smokers who followed a cessation protocol and smokers who continued to smoke. Their results showed a statistically significant difference between the failure rates of non-smokers and smokers and between those who stopped smoking and those who continued smoking. There was no significant difference between the non-smokers and those who stopped smoking. These results show a clear benefit favouring patients who followed the cessation protocol.

These studies do not provide any insight into the mechanisms associated with failures in smokers however, it seems likely that these relate to any or all of factors such as systemic vasoconstriction, reduced blood flow, increased platelet aggregation, and polymorphonuclear leukocyte dysfunction, which have all been identified in smoking. Because all of these phenomena are reversible over time once the use of nicotine and associated tobacco by-products is discontinued, it seems logical that this form of reversal assisted the patients in the group who discontinued smoking from the Bain's study.

Commonly, poor bone quality and quantity have also been cited as risk factors in implant failures. ^{Jaffin and Bernman (1991)} identified a much higher failure rate in type IV bone. The presence of poor quality bone, has also been associated with smoking. ^{Hopper and Seeman (1994)} compared bone density in female twins, and the only identified discordant factor between the twins was a difference of 10 packs per year. The authors concluded that women who smoke a pack of cigarettes per day throughout their adult life will, by menopause, have an average bone deficit of 5 % to 10 %.

To date, although no clear evidence exist as to the mechanism whereby smoking contributes to the failure of dental implants, it has been clearly demonstrated that smoking is a risk factor for implant failure, mainly when implants are placed in the maxilla or in low quality bone.

Patients with psychosocial stress

Not all edentulous or partially edentulous patients are good candidates for dental implants irrespective of their medical status and local anatomic conditions. Criteria for the evaluation and selection of patients for restorative treatment utilising tissue-integrated prostheses have been presented by several authors ^{(Laney, 1986} ; ^{Lekholm and Zarb, 1987} ; ^{Belser et al., 1996)} and they all conclude that there are some psychologic or psychiatric conditions where dental implants should be avoided. However, there is not a single study where these recommendations have been validated.

Patients with psychogenic problems with a history of difficult conventional denture experience must be carefully considered. The proven psychologic inability to adapt to well-constructed and well-fitting dentures may present a legitimate indication for tissue-integrated prostheses. Likewise, the patient who demonstrates patterns of avoidance behaviour precipitated by rejection or embarrassment related to removable prostheses could be a good candidate for fixture-based prostheses. However, these psychologic problems can also affect the patient's acceptance towards tissue-integrated prostheses. ^{Blomberg (1985)} has identified specific psychiatric contraindications to treatment involving osseointegrated fixtures. These include psychotic syndromes such as schizophrenia or paranoia ; severe character disorders and neurotic syndromes, i.e., hysteroid and borderline personality ; dysmorphophobia and patients with extreme and unrealistic expectations regarding cosmetic results as opposed to the effects of retention problems ; and syndromes of cerebral lesions and presenile dementia.

Patients with periodontitis

The quality of the bone as well as the height and orofacial dimension of the alveolar ridge are considered important criteria for selection of an adequate recipient site for an implant. The height and width of bone in an edentulous area are influenced by the history of tooth loss in the area. Tooth loss due to destructive periodontal disease is usually preceded by a considerable loss of alveolar bony support, which frequently results in a lower and narrower alveolar ridge. Besides, implant failures may be attributed to bacterial infection, mechanical stress or fracture of the implant ^{(Sanz et al., 1991} ; ^{Rosenberg et al., 1991)}. Recent studies have demonstrated that the microbiota associated with failing implants corresponds to similar sites with advanced periodontitis ^{(Mombelli et al., 1987} ; ^{Rams et al., 1984} ; ^{Sanz et al., 1990)}. Therefore, it has been suggested that pathogens present in the natural dentition may colonise newly inserted implants and give rise to tissue breakdown ^{(Mombelli et al., 1988} ; ^{Mombelli and Lang, 1992} ; ^{Gouvoussis and Yeung, 1997)}. In light of this facts it is logical the assumption that the risk of periimplant infections is higher in periodontal patients, particularly if the periodontal conditions have not been properly treated and therefore, implant therapy should not be carried out unless adequate periodontal conditions are met.

However there is no scientific evidence that can validate these presumptions and up to date we do not know if periodontitis patients are at a higher risk of implant failure or at a higher risk of developing peri-implant disease. ^Malmström presented a case report with a history of rapidly progressing periodontitis in which the subsequent placement of implants and the 12 year follow-up resulted in failure of most of the implants. However, ^{Nevins and Langer (1995)} did not validate this report. They placed implants in recalcitrant periodontitis patients and obtained survival rates similar to non-periodontitis patients. Similarly ^Ellegard placed Astra and ITI dental implants in severely periodontitis compromised patients. After 3 years follow-up they reported a survival rate of 95-100 % and 76-86 % of all implants remained free from radiographic bone loss > 1.5 mm. These studies clearly show that the implant treatment of patients with a previous history of periodontitis is not a relative contraindication. Both studies, however, used patients whose periodontal condition had been treated and who were actively participating in a regular program of periodontal maintenance. There is no data on the outcome of dental implants placed in non-treated periodontitis patients.

Although there is significant data demonstrating that the presence of periodontopathic bacteria could be a risk factor for peri-implant disease, we do not have enough evidence to apply the same presumption to the patient level. There is a real paucity of studies in this area and therefore, no valid conclusions can be drawn.

Conclusions

In this article potential risk factors of implant failures associated to the patient have been reviewed. Although in some specific situations, such as heavy smokers or high dose radiotherapy in cancer patientsÊ ^{(Etienne et al., 1998)} there is enough evidence that demonstrate the risk situation of these patients towards implant therapy, in the rest of the likely patient risk situations there is no evidence to support it. In spite of implant supported prosthesis being a predictable and highly successful mode of therapy for the rehabilitation of edentulism, when selecting the appropriate patient for implant therapy we currently do not have enough information to identify who is at risk for implant failure and therefore we can not provide appropriate modes of prevention or intervention.

There is a need of longitudinal studies in large series of patients bearing dental implants where the measurable outcomes are not success or survival rates, but rather failure rates and variables associated with them. Moreover, beyond the importance of the local anatomy and quality of bone of a specific site for implantation, the patient status and patient outcome variables should be considered and studied, and in this way we could be able to identify in the future more conditions or situations that place individuals at a higher risk when undergoing implant therapy.

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