Edentulism is a dentition defect that is defined as the loss of all permanent teeth in the maxilla or (and) mandible.1 It has a serious impact on eating, talking, facial appearance and the quality of life (QoL). Therefore, completely edentulous patients are handicapped according to the World Health Organization's (WHO) criteria.2 Although the prevalence of edentulism will be decreased with the improvement of oral health care, in seniors (aged 65+), the prevalence has still been estimated to be 26% in the United States, 15%–78% in Europe, and 11% in China.3
The conventional treatment for edentulism was a complete denture.4 However, for conventional complete denture (CCD) wearers, lack of stability and retention of mandibular dentures, together with residual bone resorption, and decreased chewing ability have been common complaints.5 The treatment with endosseous implants has changed these situations. This treatment significantly improves stability, retention, and chewing ability.6–8 A panel of experts reached a consensus at a symposium held at McGill University in 2002.9 Their statement is as follows: “The evidence currently available suggests that the restoration of the edentulous mandible with a conventional denture is no longer the most appropriate first choice prosthodontic treatment. There is now overwhelming evidence that a two-implant overdenture should become the first choice of treatment for the edentulous mandible.” Therefore, an increasing number of researchers have investigated the impact of implant-supported overdentures (IODs), such as QoL and denture satisfaction.4,7,8,10
The definition of QoL, which can be applied to most important domains of life,11 has evolved in terms of health by the WHO.12 QoL has been used as an indicator to evaluate oral health, especially in the elderly.11,13 Oral health-related quality of life (OHRQoL), which was introduced by Gift and Redford,14 refers to the assessment of an individual's oral health and function and emotional well-being.15 The main method of investigating OHRQoL is a questionnaire. The validity of the Oral Health Impact Profile (OHIP-49), which was first used to evaluate OHRQoL by Slade and Spencer, has been assessed.16 The OHIP-49 consists of 49 items that cover 7 domains: functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability, and handicap. The OHIP-49 has been used to evaluate the effectiveness of treatment for edentulous patients in clinical trials.4,10,17 However, as the OHIP-49 is a long questionnaire that is complex for most patients, and especially for the elderly, a shorter version of it was suggested by some researchers. The developer of the OHIP-49 introduced the first short version, the OHIP-14, and found that the latter had good reliability, validity, and precision.18 Then another short version, named the OHIP-EDENT, which was considered to be more appropriate for edentulous than the OHIP-14, was introduced by Allen and Locker.19 The OHIP-14 and the OHIP-EDENT have been widely used to evaluate the OHRQoL of edentulous patients.4,20–22
The aim of this systematic review was to evaluate the OHRQoL of IOD, measured by the OHIP-49, the OHIP-14, and the OHIP-EDENT, compared with CCD.
Materials and Methods
This systematic review was undertaken based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Guidelines.23
A broad literature search was performed for articles published between 1990 and July 2016 in the MEDLINE (through Ovid), PubMed, and Cochrane Library databases. The articles were limited to those published in English, and the search used the Medical Subject Headings (MeSH). The MeSH terms were as follows: “dental implant,” “dental implantation,” “dental prosthesis, implant-supported,” “denture, complete,” “denture, overlay,” and “quality of life.”
Two reviewers (L.Z. and C.L.) independently selected the articles first through reading the titles and abstracts based on the inclusion and exclusion criteria (Table 1). If they had different ideas about an article, a third reviewer (X.L.) participated in a negotiation. Then full-text documents were obtained from the databases mentioned above. For those that potentially met the inclusion criteria, including both the search results and the references, full-texts were obtained for further assessment.
The literature characteristics, which contained subjects and study design and quantitative results, were extracted from the original articles. The assessment of the study design was based on the classification of clinical epidemiology.24 The assessment of the methodological quality of articles was undertaken by 2 reviewers (L.Z. and C.L.) independently, based on the Cochrane collaboration's tool. The items were as follows: random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessors, incomplete outcome data, and selective reporting. If any of these items was considered to be “high risk” or “unclear risk,” the study was assessed as “high risk of bias” or “unclear risk of bias” correspondingly. Only when all the items were estimated as “low risk” was the study evaluated as “low risk of bias.” In the case of differences, a third reviewer was consulted.
From the included articles, the reviewers extracted the following data: authors, country, year of publication, study design, sample size, follow-up period (months), study description, type of measurement instrument, baseline, and posttreatment total scores. Data were extracted by 2 reviewers independently. When there was disagreement, a third reviewer provided an opinion.
Of 108 articles identified from the search, 88 were excluded after preliminary assessment through titles and abstracts. After the reviewers read the remaining 20 full-text documents, 15 studies were excluded for the following reasons: 1 article was a systematic review, 1 article was a review article, 2 articles did not have the total scores, 4 articles had no baseline or posttreatment scores, 3 studies had a design that only converted CCD to ICD without grouping, 2 articles had an unclear number of implants, 1 article was a commentary article, and 1 article did not report both groups' scores. Figure 1 presents the flowchart of the progress of selection following the PRISMA Guidelines.
Characteristics of Included Articles
The 5 included studies were all random control trials (RCTs). In total, 334 participants were involved, of which 34 participants were elders who were older than 75 years and who needed help for activities of life. One study reported the outcome measured by the OHIP-49. Three studies evaluated OHRQoL using the 20-item questionnaire (OHIP-EDENT). One study used the OHIP-14 to evaluate OHRQoL (Table 2).
Quality of Studies Included
Risk of bias assessment (Table 3) showed that no study had low risk of bias, 4 studies10,25–27 had a high risk of bias, and 1 study22 had an unclear risk of bias.
OHRQoL of Implanted-Supported Overdenture and Conventional Complete Denture
Table 4 shows the included study data, which consisted of baseline and posttreatment scores of CCD and IOD. Muller et al25 evaluated the outcomes through the interaction term (time × treatment) between the IOD and CCD groups. Cakir et al27 assessed the data through pre- and post-treatment score differences. The rest of the studies10,22,26 evaluated the group's differences through posttreatment scores directly. All the studies showed that IOD had a significant effect on improving the edentulous individuals' QoL.
For the studies that compared the impact on edentulous individuals' OHRQoL of IODs versus CCDs, it was necessary to explain the treatment progress to the patients and ask them whether they were willing to participate in the trials or not; moreover, the researchers would know the allocation of the group in the course of the trials, so a blind method was not possible, and the risk of bias would be high. However, because of the obvious differences between IOD and CCD, a nonblind method was inevitable.
When evaluating the rehabilitation of the elders' edentulism, several aspects should be considered, such as diet, esthetics, and degree of comfort. OHRQoL could provide some explanations for those problems.14 Therefore, it was applied in the studies that compared edentulous individuals' OHRQoL of IODs versus CCDs. The OHIP questionnaire was a valid tool for evaluating OHRQoL. The studies included in this systematic review showed that the OHRQoL of the IOD group was better than the CCD group (the OHIP scores of the IOD group was lower than that of CCD group) using different OHIP questionnaires. This could broadly explain that they (OHIP-49, OHIP-EDENT, OHIP-14) had similar reliability and validity.18,19
Although the IOD's OHIP total scores were lower than the CCD's, and there was a significant difference between the IOD group and CCD group, not all of the scores of each domain had a significant difference. In the study by Heydecke et al,22 there were 3 domains that did not show a significant difference between the IOD group and CCD group. In the study of Gjengedal et al,26 there were only 3 domains that had a significant difference between the IOD group and CCD group. Other control trials showed similar outcomes when comparing the scores of each domain.28,29 That might be due to an insufficient sample size. It also noted that further studies should focus on those domains in which improvement was not obvious in the IOD group compared with the CCD group.
These studies showed that the difference was significant between the CCD group and IOD group in the short-term. Meanwhile, 2 studies25,26 showed that the difference after 24 months was significant, and the difference in the interaction term after 12 months was significant in Muller's study,25 with the approximate posttreatment OHIP scores using the same questionnaire (OHIP-EDENT). However, there were different conclusions reported by 2 systematic reviews.30,31 Maybe these different conclusions were caused by improvement in the adaptability of the denture and (or) the change of the oral condition and (or) because of the cultural difference.30,32 Therefore, more longer-term RCTs with lower risk of bias need to be designed to solve the discrepancies.
It has been shown that IOD was better than CCD at improving the edentulous patients' OHRQoL in the studies included in this systematic review and in other control trials and crossover trials.29,33–35 Therefore, some researchers have proposed that IOD should be the first choice for rehabilitating the edentulism.9,36 Another topic is the number of implants. Some experts have stated that IOD with 2 implants was the standard option. Therefore, in this systematic review, we selected the studies using a 2-implant–supported mandibular overdenture. However, considering the quality and mass of alveolar bone, the number of implants varied in some studies.37,38 Some studies that evaluated an overdenture supported by 2 or 4 implants showed that there was no significant difference.39–42 In addition, cost must be taken into consideration. Hence, an overdenture supported by 2 implants should be offered first.
For an edentulous mandible, patients benefited more from an IOD with 2 implants, as assessed by the OHRQoL. Considering the difference in each domain of the Oral Health Impact Profile (OHIP) questionnaire and the lack of long-term performance, more RCTs with sufficient sample sizes need to be designed to investigate long-term performance after treatment.
The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
Not required-the study did not involve human subjects.
Roles/Contributions by Authors
L. Zhang and C. Lyu: Designed this study; Z. Shang and A. Niu: Searched the literature; L. Zhang and C. Lyu: Analyzed data; L. Zhang, C. Lyu, and Z. Shang: Drafted the manuscript; C. Lyu: Critically revised the manuscript. All authors have read and approved the final manuscript.
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