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RESEARCH REPORT |
1 National University of Ireland, Cork, Ireland; and
2 University of Newcastle upon Tyne, UK
* corresponding author, University Dental School & Hospital, Wilton, Cork, Ireland; f.allen{at}ucc.ie
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: implants • overdentures • quality of life • randomized controlled trial
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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Osseointegrated dental implants offer the possibility of stabilizing oral prostheses and thus overcoming some limitations of conventional dentures. The outcomes of this procedure have been largely reported in terms of success of the clinical procedure, and the technique is accepted as safe and reliable (Adell et al., 1990; Collaert and De Bruyn, 1998). In chronic conditions, where reduction in morbidity rather than cure is the most realistic outcome, it is often found that objective measures of function do not necessarily reflect the way a patient feels or functions (Wilson and Cleary, 1995; Fiske et al., 1998). Subjective measures of outcome allow for patient-based assessment of both health status and evaluation of therapeutic interventions. Recently proposed frameworks for assessing outcomes of implant therapy have included patient-based assessment (Guckes et al., 1996; Anderson, 1998; Carr, 1998). Research conducted into patient-based assessment of implant therapy to date has been weakened by problems of trial design, specifically, a lack of randomized controlled trials (RCTs). Previously reported RCTs have indicated that patient satisfaction with implant-retained prostheses has been significantly better than with conventional complete dentures (de Grandmont et al., 1994; Boerrigter et al., 1995; Geertman et al., 1996). However, there are inherent difficulties in conducting RCTs of implant prostheses, including management of treatment preference bias (Feine et al., 1998). A particular difficulty arises when patients expecting to have dental implants are allocated to the control group, and respond in a manner which reflects their disappointment with their treatment allocation. Accordingly, the aim of this study was to compare implant-retained mandibular overdentures and conventional complete dentures in a randomized controlled trial (RCT) designed to reduce the possibility of treatment preference bias previously reported. Our a priori hypothesis was that implant-retained mandibular overdentures would be significantly better than conventional complete dentures.
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METHODS |
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The inclusion criteria for entry into the trial were: (a) that the individuals were medically fit enough to undergo minor oral surgery; (b) that dental implants could be placed into the lower jaw without the need for bone augmentation procedures; (c) that patients had been edentulous for more than five years; and (d) that patients were no more than 80 years of age.
Information about the study was provided in a standardized manner by means of an information leaflet and demonstration aids. The study protocol had received approval from the Joint Ethics Committee of Newcastle & North Tyneside Health Authority and the University of Newcastle upon Tyne, UK, and all participants gave informed, written consent to participate in the study.
Assignment
Suitable patients were randomly allocated by gender and operator assignment to two experimental groups, designated the Implant Group and the Conventional Denture Group, according to random number tables generated by Minitab version 11. Those allocated to the Implant Group would be offered an implant-retained prosthesis in the lower jaw and a conventional complete denture in the upper jaw in the first instance. If they refused implants, they would be offered conventional dentures in both jaws. Those allocated to the Conventional Denture Group would be offered conventional complete dentures in both jaws only, as planned.
Following randomization, individuals were invited to participate in the study, at their first visit, by a member of the research team not involved in their treatment. Only those in the Implant Group were informed about the two treatment options, and those who refused to have implant-retained prostheses were retained in the Implant Group according to the "intention to treat" principle. Information about these participants, particularly why they refused to have implants, was recorded.
Outcome Measures
In addition to providing data on denture-wearing experience (number of sets of complete dentures, yrs edentulous), all participants completed a validated oral health status questionnaire pre-treatment, and 3 mos following their final review visit post-treatment. The questionnaire consisted of the 49-item Oral Health Impact Profile (OHIP), an oral-specific health-related quality-of-life measure, and a validated denture satisfaction questionnaire. The OHIP has been used in previous studies of implant therapy outcomes (Awad et al., 2000; Allen and McMillan, 2003), and its measurement properties have been determined. We calculated summary scores by summing the response codes (range, 0–196), with higher scores indicating poorer oral-health-related quality of life. According to a global measure, all participants were also asked to rate their general satisfaction with their mandibular denture and maxillary denture on a 1 (extremely satisfied) to 5 (extremely dissatisfied) Likert scale. This measure had been used in previously reported trials of implant therapy outcomes (de Grandmont et al., 1994; Allen and McMillan, 2003).
Treatment Protocol
Participants in the implant group had surgery ad modem Brånemark for the placement of 2 implants in the interforaminal region of the lower jaw. Following a suitable healing period, they then received a denture attached to the implants by a ball attachment mechanism. Conventional dentures for both groups were constructed according to conventional replacement denture techniques. Surgical placement was undertaken by two of the authors (FN/DGS), and the prostheses were provided by three authors (NJ/JMT/FN) on a random allocation basis. These prosthodontists were experienced in providing conventional and implant-stabilized oral prostheses.
Data Analysis
Pre-treatment and post-treatment data were compared both within and between treatment groups, by Wilcoxon Ranks Sum and Mann-Whitney U tests, respectively. To determine the likely clinical significance of post-treatment change, we calculated effect size statistics. An effect size is a distribution-based measure of change calculated as follows:
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The magnitude of change likely to be clinically meaningful ranges from < 0.2 (small change) through 0.2–0.8 (moderate change) to > 0.8 (large change) (Cohen, 1977).
Based on preliminary data, and with the OHIP summary score as the outcome variable, 33 participants were required in each group to have 90% power to detect a difference of 10% between groups at the 5% level.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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). There were no significant pre-treatment differences between the groups in terms of oral-health-related quality of life (as measured by the OHIP summary score, Fig. 2) or denture satisfaction (Fig. 3). As expected, mandibular dentures were the principal source of dissatisfaction. Following completion of treatment, substantial improvements in oral-health-related quality of life (Fig. 2) and denture satisfaction (Fig. 3) were reported by both groups. However, there were no significant post-treatment differences between the groups. Within-group change was significant (p < 0.001) for both oral-health-related quality of life and denture satisfaction for each group. The pattern of between-group pre- and post-treatment differences in OHIP summary scores was the same when sub-scale scores were compared. In terms of the magnitude of change, effect sizes for change in OHIP score were 1.1 for the Implant Group (of which > 25% had conventional dentures) and 1.0 for the Conventional Denture Group, indicating large changes for both groups which were likely to be clinically meaningful.
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. Those who refused implants were older (mean age of "refusers" = 67.6 yrs, of "accepters" = 61.1 yrs), and had significantly lower pre-treatment OHIP scores. Pre-/post-treatment change scores were significantly greater for those who had implants compared with scores of those who refused.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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Clinical circumstances in the UK allowed us the opportunity to conduct a study designed to reduce the impact of treatment preference. The Dental Hospital Services in the UK follow guidelines which stipulate that implants are not the first line of treatment for patients where substantial improvement is possible with conventional dentures, or, for those who do not exhibit maladaptive tendencies. Under these guidelines, patients in our study would not satisfy the clinical criteria for the provision of dental implants financed by public money. Accordingly, the recruitment strategy reduced the likelihood of recruitment of patients with a bias against conventional treatment, and therefore the treatment aspirations for both groups are likely to have been similar. The results of this study indicate that both groups had significant improvement following completion of treatment. However, the expected difference between the implant group and denture group did not occur, and, unlike studies reported elsewhere, improvement of similar magnitude was reported by both implant and control groups. At face value, this suggests that the simple implant-retained mandibular overdenture offers little advantage compared with properly constructed conventional dentures. Unlike previous studies, our participants had no expectation of receiving implants, and we believe that this may contribute to the different outcome from our study.
However, this may be an over-simplistic interpretation, since the high implant refusal rate and the use of the "intention to treat" principle meant that one of four patients in the implant group received conventional dentures. The pre-/post-treatment change scores were significantly greater for those receiving implants than for those from the implant group who refused them. Secondary analysis of the data indicated that those who refused had significantly lower pre-treatment OHIP scores than did the 33 individuals provided with implants. This means that there was less scope for improvement. If the group had been comprised entirely of individuals provided with implant-retained prostheses, a greater difference attributable to a treatment effect may have been evident. Nevertheless, when these patients were excluded from the analysis, statistically significant differences between the groups were not apparent. This may be attributed to a lack of statistical power of this small subgroup, and a larger sample may be required for this difference to be detected. Furthermore, under NHS regulations, all treatment was provided free of financial cost to the study participants, and this may have influenced the Implant Group patients’ appreciation of the implant option. Given the similar treatment aspirations of both groups, it is possible that implant-retained overdentures are not perceived to be a big improvement over conventional dentures for patients who were not especially dissatisfied with wearing conventional dentures.
The findings of this study have implications from a public health perspective. Increasingly, patient-based assessment is used to help establish priorities for public health funding. This study may suggest that simply offering a more expensive treatment option, such as implant-retained overdentures, to patients with little prior knowledge of the treatment strategies may not yield a significant psycho-social benefit for patients willing to accept conventional dentures. Public funding for edentulous patients may, therefore, be better directed at patients likely to accept the treatment, as well as at developing educational strategies to reduce the rates of refusal of implant treatment. Further work is required to see if the impact of treatment is maintained equally for both groups over a greater length of time, and this could be influential in the allocation of public funding.
In conclusion, significant improvement in oral-health-related quality of life and denture satisfaction was reported by both groups. There were no significant post-treatment differences between the groups, but a treatment effect may be masked by the application of "intention to treat" analysis. The pre-/post-treatment OHIP change scores were significantly greater for those receiving implants than for those who refused them.
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ACKNOWLEDGMENTS |
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Received May 31, 2005; Last revision March 1, 2006; Accepted March 20, 2006
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REFERENCES |
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