The main finding of this study indicates an immediate improvement of denture satisfaction and OHRQoL after treatment with mandibular overdentures retained by two implants, which was maintained throughout the follow-up period of 10 years. The striking effect of such treatment on OHRQoL and denture satisfaction is further demonstrated by the fact that the RCD group only showed a modest improvement after baseline, but a radical one after they received IODs.
One of the most important objectives of any kind of treatment is that the patients are satisfied with the outcome. Seeing that the data upon which these results are based are subjective assessments by the patients, and the positive effect is maintained over such a long period of time, this objective is undoubtedly achieved for the present patient sample. These findings thus tend to corroborate the McGill Consensus Status on Overdentures (11) and the York Consensus Status (12), that implant retained overdentures should be regarded as the first-choice standard of care for edentulous patients.
An important consideration is to what extent findings can be regarded as representative for the general edentulous population. On the one hand, there is no doubt that the present patient sample was highly selected: One of the original intake criteria was that they should all be dissatisfied with their existing mandibular denture (23). Also, some of them had dentures made by dental students under the supervision of qualified university teachers, and might for that reason be atypical. Furthermore, both the surgical and prosthodontic two-implant mandibular overdenture treatment were performed by specialists in their fields, and the number of participants was fairly small. The fact that many participants were lost, mainly due to mortality during the follow-up period, may theoretically also bias the results.
On the other hand, it seems likely that patients who were dissatisfied with their mandibular denture, would also be the most challenging to satisfy. Less than 1/3 of the patient sample was recruited from dental school patients. The rest were recruited, either by advertisements in seven newspapers in the city of Bergen and surrounding regions, or by referrals from several general dental practitioners (23). Thus, patients from both urban and rural areas participated.
True, the patient sample of this study was small. However, treatment with two-implant mandibular overdentures is presently shown to have a striking and long-lasting favourable effect on patient satisfaction with the dentures and OHRQoL. This makes bias due to a small patient sample less likely. The same is indicated by the fact that, excluding deceased patients, 76% of the patients responded at 10 years. Also, in Norway, public subsidy of such treatment is on condition that insertion of implants is performed by specialists in oral surgery and overdentures made by prosthodontists or specially trained and qualified general practitioners.
Moreover, the theoretical possibility of bias due to differences between remaining patients and drop-outs seems less likely, as no statistically significant differences were found between the two groups for any of the variables of denture satisfaction or OHRQoL at baseline. Even though, for the above reasons, it seems likely that the present findings might also be representative for other edentulous patients, this supposition must be tested with other patient samples and other settings.
Presently, to our knowledge, there is only one investigation in which the 5, 10 and 20 years findings on patient-reported outcomes with IODs have been reported (20–22). Different methods of recording patient satisfaction and OHRQoL were used in each of these. Consequently, the development over time could not be reported; only the end outcomes. In the 20-years report (20), OHRQoL was measured with the non-disease-specific EQ-5D and EQ VAS QoL (25). Neither OHRQoL, as measured by these instruments, nor the level of the outcomes can therefore be directly compared with the present OHIP-20 results. Nevertheless, the concurrent main findings of these two long-term studies unequivocally indicate that the level of satisfaction and OHRQoL remains high, even after such long periods of observation.
Other studies, with shorter follow-up periods of 3 (15, 26) and 5 years (14) respectively, appear to show similar significant improvement of OHRQoL after being treated with IODs. By contrast, no such difference was found in a retrospective study (27) conducted after four years between patients treated with IODs and conventional dentures. Unlike the follow-up studies, these patients were not seeking treatment, which might explain the difference. Also, the considerable human capacity to adopt to difficult situations may have played a part. The shorter-term reports all used OHIP-14, the results of which are not directly comparable with the presently used OHIP-20.
Two of these studies also report denture satisfaction (26, 27), but with instruments different from each other and the present study. Even if not directly comparable, apparent high levels of denture satisfaction were recorded.
As indicated above, not only changes over time, but also the level of OHRQoL and denture satisfaction are of clinical interest. In the present study, the OHIP-20 sum score was 38.61 at the end of the observation period. This level is 18.61 points from the theoretically most favourable score of 20 of this scale (range 20–120), which appears to be similar to short-term post-operative results reported by others (9). However, a major problem when comparing present OHIP sum scores with those of others, is that different numbers of items and categories are sometimes used measuring basically the same phenomenon.
A case in point is OHIP-EDENT, which, compared to OHIP-20, contains 19 items versus 20, categories ranging from 0–4 versus 1–6 and a theoretical range of 0–95 versus 20–120. A pre-intervention sum score norm of 28.6 has been reported, based on a meta-analysis of OHIP-EDENT (28). However, if the OHIP-EDENT range is regarded as a continuum ranging from 0–100 per cent, then this sum score is 30.1% (28.6/95) from the theoretical minimum. The corresponding present post-intervention OHIP-20 sum score was 18.61% (38.61- 20) from the minimum value, which may appear lower and perhaps more favourable. This supposition is strengthened by the fact that the wording of all but one of the items of the two OHIP versions are identical.
Denture dissatisfaction ranged between 0 and 3 patients (0–11%) for all variables in our study. Although these levels cannot be directly compared with others, the steep decline of OHIP-20 score depicted in Fig. 1, indicating radical improvement of OHRQoL, and the low number of denture dissatisfaction, testify to a subjectively successful treatment.
Of the present OHIP-20 domains, handicap, psychological disability and psychological discomfort show low scores, indicating that these areas are the least challenging for the patients. Similar short-term results have been reported by others (10).
Over the 10-year follow-up period a number of maintenance problems arose. Thus, about ¼ of the patients reported that their mandibular denture had to be relined or had fractured. Even more patients had their dentures remade. Some of the remakes may be related to the fact that new mandibular dentures were not made at baseline, but the existing dentures were converted to overdentures (23). Furthermore, almost half of the patients experienced problems with the stability of the overdentures, most likely because of wear caused by Locator matrixes that frequently had to be replaced.