Occlusal parafunction includes bruxism (clenching, grinding), lip biting, thumb sucking, and abnormal posturing of the jaw. In contrast to functional behaviors such as mastication, deglutition, or speaking, activities classified as “parafunctions” seem to have no functional purpose.1 Concerning the overloading related to parafunction, it can cause various complications, such as occlusal surface wear, fracture, loosened screws, or abutment and implant fracture.2 As the frequency of parafunction is very common,1 the usage of implants in patients with parafunctional habits is unavoidable. Moreover, a significantly high percentage of newly gained parafunction was reported in patients with implant-supported superstructures.3 Some authors have suggested that overloading of implants or abnormal occlusal stress, as seen in patients with bruxism habits, may contribute to failure.4 As the possible occurrence of parafunctional habits is evident in any stage of dental treatment, the risks for implant therapy must be considered.2 Therefore, bruxism is often considered a contraindication for implant treatment although the evidence for this is usually based on clinical experience only.5
The ability to anticipate outcomes is an essential part of risk management in an implant practice. Recognizing conditions that place the patient at a higher risk of failure will allow the surgeon to make informed decisions and refine the treatment plan to optimize the outcomes.6 The use of implant therapy in special populations requires consideration of potential benefits to be gained from the therapy. To better appreciate this potential, we conducted a systematic review and meta-analysis to compare the survival rate of dental implants, postoperative infection, and marginal bone loss of dental implants inserted in bruxers and non-bruxers patients.
Materials and Methods
This study followed the PRISMA Statement guidelines.7 A review protocol does not exist.
The purpose of this review was to test the null hypothesis of no difference in the implant failure rates, postoperative infection, and marginal bone loss after the insertion of dental implants in patients being diagnosed as presenting bruxing habits compared with the insertion in non-bruxers against the alternative hypothesis of a difference. The following focused question was raised: In patients being rehabilitated with dental implants, what is the effect of bruxism on the implant failure rates, postoperative infection, and marginal bone loss?
An electronic search without time or language restrictions was undertaken in June 2014 in the following databases: PubMed, Web of Science, and the Cochrane Oral Health Group Trials Register. The following terms were used in the search strategy on PubMed: (dental implant OR oral implant [topic]) AND (bruxism OR bruxers OR parafunctional OR clench [topic]) (dental implant OR oral implant [topic]) AND (excessive occlusal load OR overload [topic])
The following terms were used in the search strategy on Web of Science, in all databases: (dental implant OR oral implant [topic]) AND (bruxism OR bruxers OR parafunctional OR clench [topic]) (dental implant OR oral implant [topic]) AND (excessive occlusal load OR overload [topic])
The following terms were used in the search strategy on the Cochrane Oral Health Group Trials Register:(dental implant OR oral implant AND [bruxism OR bruxers OR parafunctional OR clench])
A manual search of dental implants-related journals, including British Journal of Oral and Maxillofacial Surgery, Clinical Implant Dentistry and Related Research, Clinical Oral Implants Research, European Journal of Oral Implantology, Implant Dentistry, International Journal of Oral and Maxillofacial Implants, International Journal of Oral and Maxillofacial Surgery, International Journal of Periodontics and Restorative Dentistry, International Journal of Prosthodontics, Journal of Clinical Periodontology, Journal of Dental Research, Journal of Dentistry, Journal of Oral Implantology, Journal of Craniofacial Surgery, Journal of Cranio-Maxillofacial Surgery, Journal of Maxillofacial and Oral Surgery, Journal of Oral and Maxillofacial Surgery, Journal of Oral Rehabilitation, Journal of Periodontology, and Oral Surgery Oral Medicine Oral Pathology Oral Radiology and Endodontology, was also performed.
The reference list of the identified studies and the relevant reviews on the subject were also scanned for possible additional studies. Moreover, online databases providing information about clinical trials in progress were checked (clinicaltrials.gov; www.centerwatch.com/clinicaltrials; www.clinicalconnection.com).
Inclusion and Exclusion Criteria
Eligibility criteria included clinical human studies, either randomized or not, comparing implant failure rates in bruxers compared with non-bruxers. For this review, implant failure represents the complete loss of the implant. Exclusion criteria were case reports, technical reports, animal studies, in vitro studies, and reviews articles.
The titles and abstracts of all reports identified through the electronic searches were read independently by the 3 authors. For studies appearing to meet the inclusion criteria or for which there were insufficient data in the title and abstract to make a clear decision, the full report was obtained. Disagreements were resolved by discussion between the authors.
Quality assessment of the studies was executed according to the Newcastle-Ottawa scale (NOS).8 The NOS calculates the study quality on the basis of 3 major components: selection, comparability, and outcome for cohort studies. It assigns a maximum of 4 stars for selection, a maximum of 2 stars for comparability, and a maximum of 3 stars for outcome. According to that quality scale, a maximum of 9 stars/points can be given to a study, and this score represents the highest quality, where 6 or more points were considered high quality.
Data Extraction and Meta-Analysis
From the studies included in the final analysis, the following data were extracted (when available): year of publication, study design, unicenter or multicenter study, number of patients, patients' age, follow-up, days of antibiotic prophylaxis, mouth rinse, implant healing period, failed and placed implants, postoperative infection, marginal bone loss, bruxism definitions, implant surface modification, jaws receiving implants (maxilla and/or mandible), type of prosthetic rehabilitation, and opposing dentition. Contact with authors for providing missing data was performed.
Implant failure and postoperative infection were the dichotomous outcomes measures evaluated. Weighted mean differences were used to construct forest plots of marginal bone loss, a continuous outcome. The statistical unit for “implant failure” and “marginal bone loss” was the implant and for “postoperative infection” was the patient. Whenever outcomes of interest were not clearly stated, the data were not used for analysis. The I2 statistic was used to express the percentage of the total variation across studies due to heterogeneity with 25% corresponding to low heterogeneity, 50% to moderate, and 75% to high. The inverse variance method was used for random-effects or fixed-effects model. Where statistically significant (P < 0.10) heterogeneity is detected, a random-effects model was used to assess the significance of treatment effects. Where no statistically significant heterogeneity is found, analysis was performed using a fixed-effects model.9 The estimates of relative effect for dichotomous outcomes were expressed in risk ratio (RR) and in mean difference in millimeters for continuous outcomes both with a 95% confidence interval (CI). Only if there were studies with similar comparisons reporting the same outcome measures, meta-analysis was to be attempted. In the case where no events (or all events) are observed in both groups, the study provides no information about relative probability of the event and is automatically omitted from the meta-analysis. In this (these) case(s), the term “not estimable” is shown under the column of RR of the forest plot table. The software used here automatically checks for problematic zero counts, and adds a fixed value of 0.5 to all cells of study results tables where the problems occur.
A funnel plot (plot of effect size vs SE) was planned to be drawn. Asymmetry of the funnel plot may indicate publication bias and other biases related to sample size although the asymmetry may also represent a true relationship between trial size and effect size.
The data were analyzed using the statistical software Review Manager (version 5.3.3; The Nordic Cochrane Center, The Cochrane Collaboration, Copenhagen, Denmark, 2014).
The study selection process is summarized in Figure 1. The search strategy resulted in 840 articles. The combinations of terms used in the literature search of different databases resulted in a number of 292 duplicates. The 3 reviewers independently screened the abstracts for those articles related to the focus question. The initial screening of titles and abstracts resulted in 548 full-text articles; 491 were excluded for not being related to the topic. Additional hand-searching of the reference lists of studies not excluded so far yielded 7 additional articles. The full-text reports of the remaining 64 articles led to the exclusion of 54 because they did not meet the inclusion criteria (18 reviews, 16 did not inform of the number of implants inserted and/or lost per group, 7 case reports, 6 not evaluating implant failures, 5 animal studies, and 2 evaluating failed implants only). Thus, a total of 10 publications were included in the review.
Description of the Studies
Detailed data of the 10 included studies are listed in Tables 1 and 2. Two controlled clinical trials (CCT),13,16 3 prospective noncontrolled studies,11,12,14 and 5 retrospective analyses10,15,17–19 were included in the meta-analysis. The 2 CCTs here included were not controlled for the condition bruxism but for the implant surface treatment13 and for the occlusal loading.16
One study11 had a follow-up of only 12 months after loading. All studies had available data of the patients' age, and only one10 included non-adult patients. Some patients in 8 studies12–19 were smokers. In 4 studies,13,15–17 some implants were inserted in fresh extraction sockets. In 4 studies,12,14,17,18 the patients were rehabilitated with fixed full-arch prostheses only, and in another one,19 single crowns only. Patients were submitted to grafting procedures at the implant site in 3 studies.11,15,19 One study10 included only edentulous patients, and other 215,19 inserted implants only in the posterior segments. Some implants were submitted to immediate loading in 2 studies11,12 and exclusively in 3 studies.14,17,18 In the other 5 studies,10,13,15,16,19 the implant healing time before loading ranged from 2.3 to 12 months. Implants were inserted exclusively in maxillae in one study17 and in mandibles in another one.12 Five studies10,12,14,17,19 provided information about the dentition opposed to the implants being evaluated.
Eight studies10–13,15,16,18,19 did not report the adopted criteria to classify a patient as having bruxing habits. Only one study15 informed that the patients with bruxing habits were encouraged to wear night guards. None of the 10 studies provided information about postoperative infection. Six studies10,12,15,17–19 provided information about marginal bone loss, but in none of them, there was a distinction between bruxers and non-bruxers.
The 10 included studies reported a total of 760 dental implants inserted in bruxers (49 failures; 6.45%) and 2989 implants in non-bruxers (109 failures; 3.65%). Implants from the Nobel Biocare AB (Göteborg, Sweden) were the most commonly used in 6 studies10–12,17–19 but not exclusively in 2 studies.18,19 One study16 informed whether there was a statistically significant difference or not in the implant failure rates. There were no implant failures in one study.14 Four studies11,14,15,17 provided information about the use of prophylactic antibiotics. Two studies11,14 provided information about the use of chlorhexidine mouth rinse by the patients.
Two studies were of high quality, 6 of moderate quality, and 2 of low quality. The scores are summarized in Table 3.
In this study, a random-effects model was used to evaluate the outcome “implant failure” because statistically significant heterogeneity was found (P = 0.0007; I2 = 70%). The insertion of dental implants in patients being diagnosed as bruxers affected the implant failure rates (P = 0.002; Fig. 2) with a RR of 2.93 (95% CI, 1.48–5.81). Thus, the relative risk reduction (RRR) was −193%. Being RRR negative, the insertion of implants in bruxers increases the risk of implant failure by 193% in comparison with non-bruxers. Due to lack of information, meta-analyses for the outcomes “postoperative infection” and “marginal bone loss” were not possible.
The funnel plot (Fig. 3) showed asymmetry when the studies reporting the outcome “implant failure” were analyzed, indicating the possible presence of publication bias.
Bruxism has been suggested to cause excessive occlusal load of dental implants and their suprastructures, ultimately resulting in bone loss around the implants or even in implant failure,5 although some of the articles here included did not provide clear conclusions on the issue13,14,18 or did not support bruxism as a causative effect of dental implant failures.16 The present meta-analysis found a statistically significant difference when comparing dental implant failures in bruxers and non-bruxers. However, the included studies have some limitations, thus being not possible to suggest that the insertion of dental implants in bruxers affects the implant failure rates. Although this cause-effect relationship still needs to be confirmed with appropriately designed studies, it worth reminding that a high and unpredictable or uncontrolled loading of the implant could lead to micromotions above the critical limit, resulting in fibrous encapsulation of the implant instead of osseointegration.20 It is also important to stress that the periodontal ligament of natural teeth provides the central nerve system with feedback for sensory perception and motor control.21 Proprioception around dental implants is limited because of the absence of a periodontal ligament, causing lower tactile sensitivity. Consequently, the proprioceptive feedback mechanisms to the jaw-closing muscles are limited as well. In addition, the perception of forces is limited in implant patients.22 It is, therefore, not unlikely that forces that are applied to implants during bruxism are even larger than those exerted during mastication,5 making them more prone to occlusal overload and possible subsequent failure.21 Chewing is supposed to be a physiological load for dental implants; bruxism, an overload.5
Although there was no information regarding marginal bone loss comparing bruxers and non-bruxers to perform a meta-analysis, some comments on the subject will be made. Contrary to early failures, late biological failures are characterized by pathological bone loss after full osseointegration was obtained at an earlier stage. Late biological implant failures are, among other reasons, associated with overload.5 Occlusal overloading has been suggested to cause periimplant marginal bone loss and constitutes a high risk for early implant failure.23 Natural teeth have a lower detection threshold of minimal pressure compared with implants, but stresses are distributed evenly around them, whereas stresses around implants tend to concentrate at the crestal bone region instead of distributing themselves evenly.24 In case of overload, equilibrium between bone resorption and deposition is being disturbed, thereby causing fatigue-related microfractures at, and around, the bone-implant interface.25
In a clinical human study, Lindquist et al26 showed that parafunctional activity, such as bruxism reported as tooth clenching and occlusal wear on the prosthesis, led to increased bone loss around Brånemark implants. Animal studies also evaluated the relationship between implant occlusal overload and marginal bone loss. Miyata et al27 investigated the relationship between occlusal overload and periimplant tissue and suggested that there is a possibility of bone resorption around the implants caused by excess occlusal trauma, even when there is no inflammation in the periimplant tissue. Duyck et al28 showed that dynamic overload generated by the grinding of teeth resulted in severe angular bone loss. In a recent review,29 the authors pointed out that animal experimental studies indeed suggested the potential detrimental effect of excessive mechanical load on periimplant bone although randomized or CCTs of treatment interventions of oral implants designed to study overload are lacking. The authors also observed that the level of evidence of the studies on bone response to implant loading is weak and does not indicate that overload can lead to periimplant bone loss, except in case of inflammation. Thus, the subject is still controversial.
It is important to say that there is still a lack of agreement about the definition of bruxism, which makes it sometimes difficult to unequivocally interpret the available evidence.5 The clinical features for diagnosis of bruxism include complaint of jaw muscle discomfort, fatigue, stiffness, and/or occasional headaches, the presence of tooth wear, tooth sensitivity, muscle hypertrophy, temporomandibular joint clicking or jaw lock, and tongue indentation. The clinical diagnosis of bruxism is based on orofacial examination and is usually supported by patient history, self-reports, or parental/partner reports. Considering that many sleep bruxism patients are not aware of grinding if they slept alone or with a partner who sleeps deeply30 and that the overall prevalence of daytime clenching awareness has been reported by approximately 20% of the adult population,31 this may misguide the clinician to the correct clinical diagnosis.30 Polysomnographic analysis has been proposed for a more accurate diagnosis,2 although the process of diagnosing sleep bruxism by means of polysomnography is considered to be complicated by some authors.32 Thus, there seems to be a need to establish more accurate and objective methodology for detecting bruxism.2 Most of the studies10–13,15,16,18,19 here included did not even report the adopted criteria to classify a patient as having bruxing habits, that is, the mode of bruxism determination is not given at all. Without a definitive diagnosis of bruxism having been established, it is acknowledged that some of the outcomes illustrated in some of the clinical cases may be due to such load-increasing or material-related factors, rather than to bruxism per se.32 Therefore, the possible cause-effect relationship between bruxism and implant failure do not yield consistent and specific outcomes. This is partly because of the large variation in the literature in terms of both the technical aspects and the biological aspects of the study material.5
The use of grafting procedures in some studies11,15 is a confounding factor as well as the presence of smokers among the patients,12–19 the insertion of some implants in fresh extraction sockets,13,15–17 the insertion of implants in different locations, different healing periods, and different prosthetic configurations, including splinting of the implants, which allows a more even distribution of the occlusal forces, thereby reducing stresses at the bone-implant interface.33 In only 1 study,15 the patients with bruxing habits were encouraged to wear night guards. A hard stabilization splint for nightly use (night guard) contributes to optimally distributing, and vertically redirecting, the forces that go with nocturnal teeth grinding and clenching.2 Moreover, it is known that the surface properties of dental implants such as topography and chemistry are relevant for the osseointegration process influencing ionic interaction, protein adsorption, and cellular activity at the surface.34 The studies here included made use of implants with different brands and surface treatments. Titanium with different surface modifications shows a wide range of chemical, physical properties, and surface topographies or morphologies, depending on how they are prepared and handled,35–37 and it is not clear whether, in general, one surface modification is better than another.34 It is also important to comment that when overload occurs, the level of stress concentration at the implant-bone interface depends on several factors related to load transfer, such as the direction of the functional loads, the resiliency properties of the implant and alveolar bone, the implant macrogeometry and microgeometry, and the quality of the bone support,38 and it was impossible to control these variables in the included studies.
The results of this study have to be interpreted with caution because of its limitations. First of all, all confounding factors may have affected the long-term outcomes and not just the fact that implants were placed in patients who were diagnosed with bruxism or not, and the impact of these variables on the implant survival rate, postoperative infection, and marginal bone loss is difficult to estimate if these factors are not identified separately between the 2 different procedures to perform a meta-regression analysis. The lack of control of the confounding factors limited the potential to draw robust conclusions. Second, most of the included studies had a retrospective design, and the nature of a retrospective study inherently results in flaws. These problems were manifested by the gaps in information and incomplete records. Furthermore, all data rely on the accuracy of the original examination and documentation. Items may have been excluded in the initial examination or not recorded in the medical chart.39–41 Moreover, in a criterion for a valid cause-effect relationship to be established, the suggested cause, which would be bruxism, should precede the effect, that is, implant failure. In that case, a prospective approach with multiple evaluations of the study sample is required, because it is not possible to establish the order of events retrospectively.5 Third, much of the research in the field is limited by small cohort size. Fourth, the criteria for the diagnosis of bruxism were seldom reported by the included studies, which probably resulted in a poor homogeneity of the study group. Fifth, all included studies are characterized by a low level of specificity, where the assessment of bruxism as a complicating factor for dental implants was seldom the main focus of the investigation.
Unfortunately, most of the available data regarding bruxism as a risk factor in implant dentistry are extracted from case series. Because of conflicting data from studies with small sample sizes or case series, groups that were not completely comparable at baseline in some studies or studies involving multiple surgeons, clinicians are unable to provide concrete answers to questions posed by patients seeking dental implant treatment. The presented results do not reflect a high level of scientific evidence and may need modification when new research results appear. For a more definite conclusion, the authors of this study believe that future controlled studies with a larger number of patients in the bruxism group (most studies included far fewer bruxers than non-bruxers patients) are required to determine the real effect of the condition on the dental implant outcome.
The results of this study cannot suggest that the insertion of dental implants in bruxers affects the implant failure rates, due to a limited number of published studies, all characterized by a low level of specificity, and most of them dealing with a limited number of cases without a control group. Therefore, the real effect of bruxing habits on the osseointegration and survival of endosteal dental implants is still not well established.
This work was supported by CNPq, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil. The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
The authors would like to thank Dr. Miguel de Araújo Nobre for having sent us his article, Dr. Derk Siebers, Dr. Devorah Schwartz-Arad, Dr. Miguel de Araújo Nobre, and Dr. David Schneider, who provided us some missing information about their studies, and Dr. Monica Wahlström, Dr. Karin Wannfors, Dr. Giuseppe Luongo, Dr. Francesco Guido Mangano, and Dr. Anders Ekfeldt, who replied our e-mail, although it was not possible for them to provide the missing information requested.
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