
==== Front
Clin Oral Investig
Clin Oral Investig
Clinical Oral Investigations
1432-6981
1436-3771
Springer Berlin Heidelberg Berlin/Heidelberg

38772987
5723
10.1007/s00784-024-05723-1
Research
Mandibular overdenture with a single implant in the canine region (c-SIMO): a feasibility study
Maniewicz Sabrina sabrina.maniewicz@unige.ch

1
Curado Thalita Fernandes Fleury 2
Srinivasan Murali 13
Leles Cláudio Rodrigues 234
Müller Frauke 15
1 https://ror.org/01swzsf04 grid.8591.5 0000 0001 2175 2154 Division of Gerodontology and Removable Prosthodontics, University Clinics of Dental Medicine, University of Geneva, Geneva, Switzerland
2 https://ror.org/0039d5757 grid.411195.9 0000 0001 2192 5801 Department of Oral Rehabilitation, School of Dentistry, Federal University of Goias, Goiania, Brazil
3 https://ror.org/02crff812 grid.7400.3 0000 0004 1937 0650 Clinic of General-, Special Care and Geriatric Dentistry, Center for Dental Medicine, University of Zurich, Zurich, Switzerland
4 https://ror.org/02k7v4d05 grid.5734.5 0000 0001 0726 5157 Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland
5 https://ror.org/01m1pv723 grid.150338.c 0000 0001 0721 9812 Division of Geriatrics, Department of Rehabilitation and Geriatrics, University Hospitals of Geneva, Thônex, Switzerland
21 5 2024
21 5 2024
2024
28 6 33017 1 2024
13 5 2024
© The Author(s) 2024
https://creativecommons.org/licenses/by/4.0/ Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Objectives

The aim of this multi-center pilot study was to assess the viability and feasibility of a novel treatment concept – the canine-positioned single implant mandibular overdenture (c-SIMO), with the single implant placed on the patient's preferred chewing side instead of the midline.

Materials and methods

Participants received a single implant in the canine region of their preferred chewing side, based on an Asymmetry Index observed during mastication. The pre-existing mandibular denture was transformed into a c-SIMO on a spherical attachment. The primary outcome was oral health-related quality of life (OHRQoL), measured with GOHAI and OHIP-EDENT. Secondary outcomes included denture satisfaction index (DSI), chewing efficiency (CE), maximum bite force (MBF), implant survival and success, and prosthetic maintenance. Data analysis included descriptive statistics and bivariate comparison tests.

Results

Fifteen participants received the c-SIMO treatment (mean age: 69.9 ± 7.0). Implant success and survival rates were 100% at 1 year. Patient-reported outcome measures improved significantly compared to pre-treatment values (OHIP-EDENT: p = 0.001; DSI: p = 0.001; GOHAI: p = 0.002). Masticatory outcomes also improved significantly (CE: p = 0.001; overall MBF: p = 0.005). Post-implant, MBF was significantly higher in the ipsilateral side compared to the contralateral side at 2 weeks (p = 0.019) and 3 months (p = 0.015), but no longer at T3 (p = 0.730). Common prosthodontic events included denture base adjustments (n = 17) and matrix activation (n = 9).

Conclusions

This pilot study concludes that c-SIMO is a promising treatment option, and a potential alternative to the single midline implant overdenture.

Clinical relevance

The novel treatment concept of a canine-positioned single implant mandibular overdenture could be a viable treatment alternative to the midline positioning.

Keywords

Implant overdenture
Single-implant overdenture
Dental prosthesis
Pilot study
University of GenevaOpen access funding provided by University of Geneva

issue-copyright-statement© Springer-Verlag GmbH Germany, part of Springer Nature 2024
==== Body
pmcIntroduction

Although it is widely accepted by the scientific community that using two implants in the mandible is the preferred method for ensuring the stability and retention of a mandibular complete denture, other treatment alternatives may be considered [30, 67]. The choice of different treatment strategies may vary not only internationally and regionally, but will also vary individually, due to a multitude of both operator- and patient-related reasons [31]. Many individuals who have lost all their teeth are still rehabilitated with a conventional complete denture. Low economic resources, the invasiveness of the intervention as well as general health issues are frequent barriers for elderly and fragile patients concerning dental implants or implant-related treatment options [45, 51, 72]. If economic barriers restrict treatment options, then it is imperative to consider affordable treatment alternatives. Furthermore, minimally invasive treatment approaches are one of the cardinal objectives of optimal surgical treatment today, especially in frail and geriatric patients. Minimizing the number of implants required for dental treatment remain within the spectrum of minimally-invasive treatment concepts and will help invariably reduce surgical complications and morbidity, treatment burden, patient and operator stress, postoperative complications and/or morbidity, and finally, cost [61].

A single implant placed in the midline of the mandible to retain a mandibular denture (single implant mandibular overdenture; SIMO) is a proven treatment concept for edentulous patients [16, 39, 54, 59, 62, 66, 71]. The benefits of this treatment protocol are multiple [2, 5–8, 16, 17, 20, 22, 24, 25, 39, 41, 52, 54, 57, 59, 62, 66, 71]. Observational studies in the literature have evaluated the performance and success of the SIMO concept with regard to the biologic success of the implant supporting the reconstruction, the rate of prosthodontic complications and the need for maintenance. Most studies comparing SIMOs directly to 2-IODs have demonstrated no differences in implant survival rates between both modalities [2, 5, 6, 16, 59, 66, 71]. Studies have reported that the frequent prosthodontic complications and maintenance events encountered with SIMOs included denture fracture around the midline implant and matrix activation or replacement, respectively [5, 16, 20, 22, 24, 25, 41, 52, 59, 71]. Furthermore, SIMOs have been evidenced with increased patient satisfaction and improved Oral Health-Related Quality of Life (OHRQoL) [5, 7, 8, 16, 17, 20, 52, 57, 71]. Although only a limited number of studies have objectively examined and quantified masticatory function, reports show that both masticatory efficiency and bite force increase along with a positive influence on the muscular activity and chewing patterns in patients rehabilitated with SIMOs [7, 8, 18, 37, 43, 56].

An important aspect to consider is that the choice of the implant positioning in the mandibular midline is not based on evidence demonstrating its superiority compared to an alternative position, which could present similar or improved results. Chewing support, whether provided by teeth or by implants, is most effective when the support is closest to the chewing center, located in the second premolar – first molar region [35]. The closer the support to this area, the more effective the support from the abutment. Hence, positioning the implant closer to the chewing center might significantly increase the chewing efficiency (CE) as well as the maximum voluntary bite force (MBF). Therefore, a valid hypothesis would be that if the single implant was placed in a more lateralized position in the mandible on the patients’ preferred chewing side rather than the midline, then it could potentially improve the masticatory outcomes even further with a SIMO.

The use of a single implant positioned in the canine region (c-SIMO) instead of in the midline could further enhance the performance of SIMOs, particularly concerning prosthodontic drawbacks. The relatively high denture fracture rates reported in previous studies may be attributed to a fulcrum effect that the midline implant might have when posterior occlusal forces act on the overdenture. Furthermore, the available prosthetic volume for incorporating the attachment housing into the denture is limited, and therefore at higher risk of developing cracks and fractures during posterior functional loading. By placing the implant in a more lateralized position, firstly the fulcrum effect is eliminated thus potentially reducing the fracture risk of the denture base, and secondly there is more prosthetic volume in the denture to accommodate the retentive element and the corresponding housing which further minimizes risk for fracture. Another important benefit in the canine positioning of the single mandibular implant is the future possibility of adding another implant in the contra-lateral canine region, to convert the existing c-SIMO to the gold-standard two-IOD, if requested.

The aim of this pilot study was therefore to determine whether the novel treatment concept of stabilizing a mandibular complete denture with a single implant placed in the canine region (c-SIMO) of the patient’s preferred chewing side is a viable and feasible treatment option, by assessing implant and prosthetic survival/success, masticatory function (CE), OHRQoL and patient satisfaction.

Materials and methods

This multi-center, single-arm pilot study is reported with adherence to the CONSORT extension to pilot and feasibility trials and the STROBE statement, as far as applicable, and according to the available guidelines for non-randomized studies [28, 44, 70]. The trial was approved by the relevant ethical committees of each research centers (Swiss centers: 2020–01780; Brazilian center: CAAE 39165920.1.0000.5083). Written and informed consent was obtained from all the included participants.

Participants

Participants were recruited from the patient pools of the University Clinics of Dental Medicine of the University of Geneva, Switzerland, the Center for Dental Medicine of the University of Zurich, Switzerland, and the School of Dentistry of the Federal University of Goias, Brazil. Participants were screened regarding the inclusion and exclusion criteria listed in Table 1, and the preferred chewing side was determined. Table 1 Inclusion and exclusion criteria for participant recruitment

Inclusion criteria	
  • 55 years or older

  • Willing to participate and sign an informed consent

  • Completely edentulous participants who live independently and are not dependent for care

  • Participants rehabilitated with maxillary and mandibular conventional complete dentures considered sufficient or ones that can be rendered sufficient via reline and/or renewal of the prosthetic teeth

  • Healed edentulous mandible (minimum 6–8 weeks since last extraction in the anterior zone (4–4) and one year in the posterior zone (5–8))

  • Physical status of ASA1 or ASA2*

	
Exclusion criteria	
  • Contraindications to the medical devices used, e.g. known hypersensitivity or allergy

  • Inability to perform adequate oral hygiene

  • Incapability to provide written informed consent and compliance to the protocol

  • History of repeated unjustifiably missed appointments

  • Surgical risk factors such as, but not limited to, uncontrolled diabetes, immunosuppression, radiation, chemotherapy, or antiresorptive medication (ex. bisphosphonates)

  • Heavy smoking habit of > 20 cigarettes per day

  • Moderate/severe dementia† or depression‡

  • Xerostomia with less than 0.7 ml/min of Stimulated Salivary Flow Rate (SSFR)§

  • Reported severe bruxism or clenching habits, clinically present oro-facial pain

  • Incorporated metal framework in any of the complete dentures

  • Excessive occlusal wear of the denture teeth with loss of more than 1/3 of cuspid height or worn denture resin

	
Post-hoc exclusion criteria	
  • Ridge dimensions less than 6 mm (width) by 10 mm (height) in the canine area

  • Ridge defects requiring bone augmentation procedures

	
*ASA Physical Status Classification System [1]

† Mini Mental State Examination [33]

‡ Geriatric Depression Scale [63]

§ Stimulated Salivary Flow Rate of whole saliva [27]

Intervention and protocol

Prosthetic and surgical diagnostics were completed in a preoperative visit with thorough examination of the patient’s medical and dental history, as well as a clinical examination including the determination of the preferred chewing side. A radiological assessment was performed with an Orthopantomogram (OPT). The existing mandibular denture was marked with gutta-percha dots in the canine regions prior to image-taking for the purpose of spatial reference. The dentures were stabilized during image-taking with cotton rolls placed in between the upper and lower posterior teeth, to preclude denture displacement during the biting on the anterior fork of the OPT machine (Fig. 1a).Fig. 1 a Baseline OPT with gutta-percha markings for spatial referencing; b OPT after 1 year with normal peri-implant bone levels; c and d Occlusal and frontal view of spherical patrix on implant 33, e Close-up of elliptical matrix; f Denture base with incorporated matrix

Implant surgery was performed under local anesthesia, with a mid-crestal incision and elevation of a minimal mucoperiosteal flap. The incision was further extended crestally or with releasing incisions where ridge flattening or ridge defects or proximity of sensitive anatomical structures (e. g. the mental foramen) required a more extended overview. The existing denture was used as a surgical template and the implant surgery was performed according to the manufacturer’s instructions. Participants received one 4.1 × 8 mm Straumann Standard Plus Regular Neck implant (Institut Straumann AG, Basel, Switzerland). The implant was placed either in the tooth position of 33 or 43, depending on the participant’s preferred chewing side. Primary implant stability was measured immediately after insertion. The appropriate healing abutment was placed on the implant and the flap was sutured allowing for transmucosal healing whenever applicable. The existing denture was adapted for unloaded wound healing. The implant placement was verified with a post-operative OPT or intraoral radiograph. Post-surgical recall visits were scheduled at 7 to 15 days after implant placement for suture removal and denture adaptation or upon request.

Following an early loading protocol, participants were invited to return 6 to 8 weeks after implant placement, at which timepoint the implants were loaded by placing a spherical retentive anchor (Spherical retentive anchor; Institut Straumann AG, Basel, Switzerland) and a corresponding elliptical matrix with a rotational activation system (Swiss centers: Dalbo-PLUS, Cendres + Métaux SA, Biel, Switzerland; Brazilian center: Elliptical matrix; Institut Straumann AG, Basel, Switzerland) [34] (Fig. 1b-d). Depending on the clinical situation, the attachment housings were either directly incorporated using a pick-up technique with self-curing acrylic resin or indirectly processed in the pre-existing prosthesis following a reline wash-impression with polyether impression material (Impregum® Garant® L Duosoft®; 3 M Company, Saint Paul, MN, USA); the transformed prosthesis was delivered on the same day (Fig. 1e-f). Matrices were activated until adequate retention was obtained. Recall visits were scheduled as stipulated by the trial protocol. Additional adjustments and repairs were performed as required.

Outcome measures

The outcome measures were recorded at the following pre-determined timepoints: baseline (BL) before intervention, T1 (2 weeks after IOD insertion), T2 (3 months after IOD insertion) and T3 (1 year after IOD insertion).

Preferred chewing side

The preferred chewing side (PCS) was determined by using the method described by Mizumori and co-workers [48]. This method involves a calculation of the Asymmetry Index (AI), using the formula:AI=numberofrightchewingstrokes-numberofleftchewingstrokesnumberofrightchewingstrokes+numberofleftchewingstrokes×100% . AI was recorded via a video camera during mastication of a chewing-gum during 20 chewing cycles. In cases with a low masticatory laterality (AI < 30%), the preferred chewing side was determined according to the participants’ stated PCS using a Visual Analog Scale [32]. PCS was assessed at all time points.

Implant survival and success: clinical and radiographical outcomes

Implant success, survival and failure was determined using the Health Scale for Dental Implants [47], a scale which takes into account indices comprising pain, mobility, radiographic crestal bone loss, probing depths and peri-implant exudate. Peri-implant conditions were classified using the modified Plaque Index (modPI) and the modified Bleeding Index (modBI) [49]. The pocket probing depth (PPD) was measured in mm from the peri-implant mucosal margin to the bottom of the sulcus or pocket, while the width of the keratinized tissue, also measured in mm, was measured at the buccal and lingual side. Peri-implant clinical parameters were assessed at T1, T2 and T3.

Radiographical crestal bone levels were assessed on the digital OPTs [13, 15]. Reference markings in the form of parallel lines were made on all radiographs using reproducible reference points on the implants (implant shoulder and apex), as well as markings at the bone level on the mesial and distal side of the implant (Adobe Photoshop Elements 2.0; Adobe Systems Inc, San Jose, CA, USA). The distances between the reference markings and the crestal bone levels were calculated using an image analysis freeware to account for any distortion present (ImageJ, V1.54, National Institutes of Health). A single investigator (SM) performed these measurements, which were carried out at T3.

Chewing Efficiency (CE)

CE was evaluated with a two-color mixing ability test [60]. Participants were given a validated two-colored chewing gum and were requested to chew the specimen for 20 chewing cycles (Goiania and Zurich centers: Hue-Check Gum, Orophys GmbH, Muri b. Bern, Switzerland; Geneva center: Gum for 8020 Promotion Foundation, Lotte, Tokyo, Japan). The resulting bolus was evaluated visually (subjective assessment). The gum was then flattened to a wafer thickness of 1 mm, digitized, and opto-electronically analyzed [Variance of Hue (VOH)] using a purpose-built software (ViewGum, dHAL Software, Kifissia, Greece) [38]. Chewing efficiency was assessed at all time points.

Maximum Bite Force (MBF)

MBF was measured in Newtons using a digital force gauge (Swiss centers: Occlusal Force-Meter GM 10®, Nagano Keiki Co. Ltd., Tokyo, Japan; Brazilian center: DMD® Kratos, Kratos Equipamentos Industriais Ltda, Cotia, Brazil) placed in the first molar area with a stabilizing block of the same thickness (8.7 mm and 14.6 mm for the Occlusal Force-Meter GM 10® and the DMD®, respectively) on the contralateral side to avoid dislodgement of the prostheses. The participants were encouraged to use their maximum strength to bite on the instrument until a measurement was effectively recorded. Three recordings were carried out per side, and the mean of the highest value registered for each side was used for analysis. MBF was measured at each time point.

Denture Satisfaction Index (DSI)

Denture satisfaction was evaluated using a 100 mm visual analog scale (VAS)-based questionnaire [11]. It is used to evaluate “comfort, ability to chew, stability, esthetics, ability to speak and ease of cleaning” [11]. Participants were trained in filling out this type of VAS beforehand. Denture satisfaction was evaluated at all time points.

Oral Health-Related Quality of Life (OHRQoL)

The General Oral Health Assessment Index (GOHAI) was used to assess the impact of oral disorders on OHRQoL via a 12-statement Likert-format questionnaire [10, 26, 40, 68]. A shorter version of the 49-item Oral Health Impact Profile (OHIP) questionnaire that was specifically developed for edentulous persons, was also used to assess the OHRQoL [3, 4, 64, 65]. The OHRQoL is considered good when the GOHAI score is high, or when the OHIP-EDENT score is low. These instruments were filled independently by the participants at all time points.

Prosthetic survival and success: maintenance and complications

The prostheses were examined for any complications according to the criteria proposed by Brägger in the ITI Treatment Guide Volume 8 [14]. This includes complications concerning the attachment components, the overdenture itself, and the denture teeth. This assessment was carried out at all timepoints, as well as additional unscheduled timepoints when necessary.

Statistical analysis

A target sample of fifteen participants completing the study was considered adequate for obtaining sufficient preliminary data. Data analysis included descriptive statistics and bivariate comparison tests. Normal distribution of data was tested using the Shapiro-Wilks test (p < 0.05). The Wilcoxon signed-rank test was used for pairwise comparison of outcome measures between baseline (before intervention) and the follow-up assessments (2 weeks, 3 months, and 1 year) with the significance set to p < 0.05. The 1-year survival and success rates were recorded for the implants and the prostheses. The incidence rates of prosthodontic events were registered throughout the complete follow-up period. All statistical analyses were performed using Microsoft Excel and IBM-SPSS 24.0 softwares.

Results

Between May 2021 and July 2022, sixteen participants were recruited for this pilot study. One participant had an early implant failure before loading and was subsequently excluded from the study. Therefore, a total of 15 participants received the overdenture treatment and were analyzed in the study. The characteristics of the participant pool are detailed in Table 2, including the preferred chewing side and the edentulous ridge classification with the Prosthodontic Diagnostic Index [46]. Nine participants were treated at the University of Goias (Brazil), five at the University of Geneva (Switzerland) and one at the University of Zurich (Switzerland). Nine implants (60%) were inserted on the right side and 6 (40%) on the left, according to the predetermined preferred chewing side (PCS). All participants completed the 1-year follow-up, and none requested the placement of an additional implant during the observation period. Table 2 Participant demographics and characteristics

Mean age ± SD (years)	69.9 ± 7.0	
Sex N (%)	-	
  Total	15 (100)	
  Women	11 (73.3)	
  Men	4 (26.7)	
Preferred chewing side N (%)	-	
  Right	9 (60)	
  Left	6 (40)	
  None	0 (0)	
Prosthodontic diagnostic index N (%)	-	
  Maxilla	-	
    Type A	11 (73.3)	
    Type B	4 (26.7)	
    Type C	0 (0)	
    Type D	0 (0)	
  Mandible	-	
    Type A	6 (40.0)	
    Type B	2 (13.3)	
    Type C	3 (20.0)	
    Type D	4 (26.7)	
    Type E	0 (0)	
N Number; SD Standard deviation

Implant success and survival rates were 100% at T3. Table 3 summarizes the peri-implant findings, measured 2 weeks, 3 months, and 1 year after loading. Two weeks after loading, plaque accumulation was low (median = 0.84) and bleeding on probing was rarely observed (median = 0) and did not change significantly in all the subsequent follow-up periods. Similarly, probing depth and the width of keratinized mucosa remained unaltered throughout the study. Based on radiographic measurements of peri-implant bone loss, no or negligible changes were observed at T3 and, therefore, no data analysis were performed. Table 3 Measurements of the peri-implant outcome variables at the follow-up visits (n = 15)

	Plaque	Bleeding	Probing depth	KMW	
2 weeks (T1)	0.88 (1.6)	0.0 (0.56)	2.60 (0.81)	1.69 (2.50)	
3 months (T2)	0.50 (1.5)ns	0.0 (0.75)ns	2.25 (0.50)ns	1.13 (2.25)ns	
1 year (T3)	0.00 (2.0)ns	0.0 (0.50)ns	2.50 (0.75)ns	1.00 (2.25)ns	
Results are presented as median (and interquartile range)

ns Difference not significant – Wilcoxon signed-rank test (all tests compared to T1)

KMW Keratinized mucosa width [mm]

The 1-year results concerning patient-reported and functional masticatory outcomes are detailed in Table 4. There was a significant improvement in all patient-reported outcome measures after one year compared to pre-treatment values, including OHIP-EDENT scores (p = 0.001), Denture Satisfaction Index (p = 0.001), and GOHAI scores (p = 0.002). The improvements in outcomes were significant at the first post-insertion visit after implant loading (2 weeks) and persisted until the 1-year follow-up. There was also a significant improvement in masticatory outcomes assessed at one-year follow-up compared to baseline values (chewing efficiency: p = 0.001; overall maximum bite force: p = 0.005) with the improvements being significant from 3 months of use onwards. The magnitude of changes at 1-year were considered large (effect size ≥ 0.50) for all patient-reported outcome measures (PROMs). Overall, the average pooled MBF from both sides changed from 107.6N ± 71.9 to 151.2N ± 64.1 in the pre- and post-implant stages, respectively (p = 0.008). The overall mean MBF in the post-treatment period were 161.9N ± 67.5 and 140.6N ± 63.6 for the ipsilateral and the contralateral sides, respectively (p = 0.016). In addition, significant increase in the MBF after the implant placement was observed for both the ipsilateral (p = 0.013) and contralateral (p = 0.004) sides. MBF had been similar in the ipsi- and contralateral sides at baseline (p = 0.470). The measurements of the MBF in the ipsilateral and contralateral sides according to the study time points are shown in Fig. 2. In the post-implant stages, MBF was significantly higher in the ipsilateral side compared to the contralateral side at T1 (p = 0.019) and T2 (p = 0.015), but no longer at T3 (p = 0.730). Table 4 Measurements of the patient-reported and functional outcome measures at baseline and follow-up visits (n = 15)

	Patient-reported outcomes	Functional outcomes	
OHIP-EDENT	Satisfaction	GOHAI	VoH	Overall MBF [N]	
Baseline (BL)	28.0 (27.0)	67.9 (25.7)	36.0 (15.0)	0.65 (0.19)	80.4 (109.6)	
2 weeks (T1)	5.5 (8.5)**	94.7 (8.9)**	57.5 (7.0)**	0.49 (0.37)ns	125.0 (63.8)ns	
3 months (T2)	3.0 (5.0)**	98.4 (7.5)**	59.0 (7.0)**	0.36 (0.29)**	158.8 (121.1)**	
1 year (T3)	2.0 (6.0)**	98.0 (3.8)**	59.0 (5.0)**	0.35 (0.29)**	136.0 (96.4)**	
Mean difference (SD) at 1-year	−27.4 (19.2)	33.0 (25.3)	18.5 (13.4)	−0.26 (0.16)	54.2 (47.6)	
Effect size	0.88	0.88	0.80	0.88	0.72	
Results are displayed as median (and interquartile range)

* p < 0.05; ** p < 0.01; *** p < 0.001; ns difference not significant – Wilcoxon signed-rank test (all tests compared to baseline)

Fig. 2 Maximum Bite Force for each chewing side at baseline and follow-up visits. Results are presented as mean (and 95% Confidence Interval)

The number of post-insertion visits for maintenance ranged from 0 to 3 visits per participant, and the overall mean was 1.36 (SD = 1.2). The incidence of prosthodontic events is detailed in Table 5. Table 5 Incidence of prosthodontic events in the 1-year post-treatment period, and the overall prosthodontic outcome (n = 15)

	Switzerland (n = 6)	Brazil (n = 9)	Total (n = 15)	
# events	# patients	# events	# patients	# events	
Unscheduled visits	3	2	5	3	8	
Mandibular implant overdenture	
  Matrix activation	5	5	4	3	9	
  Matrix replacement	1	1	1	1	2	
  Matrix fixation	0	0	0	0	0	
  Teeth fracture	0	0	0	0	0	
  Denture fracture	1	1	0	0	1	
  Reline	0	0	4	4	4	
  Denture base adjustment	7	3	10	6	17	
Maxillary complete denture	
  Teeth fracture	2	2	0	0	2	
  Denture fracture	0	0	0	0	0	
  Denture reline	0	0	1	1	1	

Discussion

The novel treatment concept of stabilizing a mandibular complete denture with a single implant in the canine region of the preferred chewing side (c-SIMO) aims to enhance the performance of SIMOs, where, so far, the implant had been exclusively placed in the mandibular midline position. A controlled clinical setting was therefore necessary to determine the viability and feasibility of this treatment option. The findings of this pilot study, which can be considered as preliminary results, indicate that c-SIMOs provide a significant improvement of patient-related outcome measures, and have high implant survival and success rates with minor prosthodontic maintenance and complications, and may therefore be a viable treatment option.

Nevertheless, this study presents with limitations which have to be considered when interpreting the results. The most important shortcoming of this study is the short follow-up time of one year, which is inherent to a pilot study. However, the total absence of peri-implant bone loss and of any implant-related complications during the first year after implant loading is a reassuring result. Various clinical trials on SIMOs have demonstrated very high 5-year implant survival rates in situations where (micro- and moderately) rough implant surfaces were used and a conventional loading protocol was followed [16, 19, 42, 55, 58, 59]. Evidently, no direct comparison to other studies can be made due to the difference in implant positioning, however, the protocols used in this study are in accordance with the parameters that seem to be associated with good long-term survival rates for SIMOs [58]. Therefore, even if a high implant survival is expected for c-SIMOs, the medium- and long-term survival rates are necessary to confirm the viability and success of this treatment modality.

The short observation period in this study may also influence the incidence and type of prosthodontic events reported with this novel treatment option, as it may be a time frame too short to detect complications that could arise during the long-term use of an IOD, such as material fatigue or wear [9]. Multiple studies have demonstrated that the SIMO concept was associated with high rates of denture fracture, as well as a frequent need for matrix replacement/reactivation, possibly due to an overload of the retentive system [16, 20, 22, 23, 36, 41, 59]. Four overdentures required an indirect reline, these were mainly in cases where a surgical osteotomy had been performed for implant placement. The most frequent maintenance events in this study were the adjustment of the denture base and the activation of the matrix. These events were considered normal maintenance events in the short-term follow-up after overdenture treatment. This is in accordance with a previous RCT comparing the prosthodontic maintenance and complications of 1- and 2-IODs over 4 years [24]. It was demonstrated that the majority of the aforementioned maintenance events occurred in the first year, irrespective of the treatment group, and that a longer follow-up did not increase the incidence of the events. Indeed, almost 80% of all denture base adjustments and approximately 50% of matrix activations occurred during the first year [24]. The expected additional maintenance during a longer follow-up may therefore be minimal for c-SIMOs as well.

As mentioned previously, denture fracture has also been reported as a frequent complication associated with SIMOs [16, 23, 36, 59]. Similar rates of this complication can be seen throughout various SIMO studies with no cast framework, with fractures occurring in 20 to over 30% of cases, and even increasing up to 55% in a long-term study [23, 24, 36, 59]. Different distribution patterns of the incidence of denture fractures can be seen, some studies having an increase in the yearly incidence during follow-up, while in another, almost half of the denture fractures occurred during the first year [16, 36]. The preliminary data from the present study shows a low denture fracture rate of less than 7% in one year. Although a very positive finding, it has to be considered that an increase in the incidence of fractures could be seen during a longer follow-up. Nevertheless, these results are in line with the hypothesis that the position of the implant and therefore the retentive element and corresponding housing in the canine region could reduce the risk of denture fracture due to the increased available prosthetic volume in the area compared to the midline.

The significant increase in chewing efficiency and maximum bite force detected in this study demonstrates the functional efficiency of c-SIMOs, despite the short follow-up. The almost two-fold increase in bite force already seen at one year can be attributed to an improved overall function with the c-SIMO, and agrees with previous studies reporting on bite force in patients treated with 2-IODs [12, 21, 50, 69]. The bite force measured in the present study with c-SIMOs seems to be similar to what is reported with midline SIMOs, although a direct comparison is difficult, as there are very limited studies available and evaluation methods differ [7]. The significantly higher bite force on the preferred chewing side (implant side) compared to the contra-lateral side supports the argument that placing the implant close the patient’s chewing center allows for increased bite forces. Nevertheless, after one year of observation, the bite force was similar for both chewing sides. An evaluation after a longer observation period and in a larger cohort is therefore necessary to better understand the influence of the implant position on bite force and overall chewing. This includes the evaluation of the evolution of the preferred chewing side and its potential effect on denture wear and occlusal stability. The significant increase in chewing efficiency detected in the present study in a short observation period is also a very promising finding, as it is not always detected even in studies on overdentures on multiple implants [29, 50]. A direct comparison with other SIMO studies also showing an increase in chewing efficiency cannot be made due to variations in methodology [18, 37, 56].

Last but not least, the patient-reported outcome measures analyzed in the present study also show a significant positive impact of c-SIMOs, with improvements in all tested domains, already present from the first post-insertion visit and persisting throughout the entire follow-up, with almost-perfect scores in all tests at 1 year. The majority of studies on midline SIMOs have also shown marked improvements both in OHRQoL and patient satisfaction [7, 8, 17, 18, 20, 52, 53]. However, there is limited information on PROMs with SIMOs even at medium-term follow-up [16, 20]. More medium- and long-term studies are therefore still necessary to confirm the success of SIMOs in achieving and maintaining high PROMs, and this is evidently the case for c-SIMOs as well.

An additional feature specific to the placement of the implant in the canine area instead of the midline region is the possibility to modify the treatment modality in the future if needed, by placing an additional implant in the contra-lateral canine area. The possibility of placing an additional implant could present a significant further medium- and long-term advantage compared to the midline position, as it maintains more treatment options open for patients according to their specific needs. In this study, none of the patients had requested an additional implant at the end of the observation period, which confirms c-SIMO as a viable minimal-invasive and low-cost treatment modality.

Conclusions

This pilot study concludes that the single canine-positioned implant for mandibular overdentures (c-SIMO) is a promising treatment option, and may be a viable alternative to the single midline implant overdenture. However, this clinical recommendation must be confirmed in clinical studies designed to evaluate both interventions within the same trial.

Acknowledgements

The authors would like to thank Dr Leuçon de Oliveira Moura-Neto, Dr Nicolas Fankhauser, Dr Benjamin Lazzarotto, and Dr Alkisti Zekeridou for their contribution to this study via their dedicated clinical work and expertise.

Author contributions

SM, MS, CRL and FM contributed to the design and conception of the study. SM and TFFC carried out the investigation and collected the data. CRL performed the formal analysis of the results. SM, MS, CRL and FM contributed to the interpretation of the results. SM, TFFC, MS, CRL and FM contributed to the writing, reviewing and editing of the manuscript.

Funding

Open access funding provided by University of Geneva. No external funding was received for this study.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

The trial was approved by the relevant ethical committees of each research center (Swiss centers: 2020–01780; Brazilian center: CAAE 39165920.1.0000.5083). All included participants provided a written informed consent.

Competing interests

The authors declare no competing interests.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
==== Refs
References

1. (2019) ASA physical status classification system. American society of anesthesiologists
2. Ahmed Elawady DM Kaddah AF TalaatKhalifa M Single vs 2 implants on peri-implant marginal bone level and implant failures in mandibular implant overdentures: a systematic review with meta-analysis J Evid Based Dent Pract 2017 17 216 225 10.1016/j.jebdp.2017.02.002 28865818
3. Allen F Locker D A modified short version of the oral health impact profile for assessing health-related quality of life in edentulous adults Int J Prosthodont 2002 15 446 450 12375458
4. Allison P Locker D Jokovic A Slade G A cross-cultural study of oral health values J Dent Res 1999 78 643 649 10.1177/00220345990780020301 10029462
5. Alqutaibi AY Esposito M Algabri R Alfahad A Kaddah A Farouk M Alsourori A Single vs two implant-retained overdentures for edentulous mandibles: a systematic review Eur J Oral Implantol 2017 10 243 261 28944354
6. Alqutaibi AY Kaddah AF Farouk M Randomized study on the effect of single-implant versus two-implant retained overdentures on implant loss and muscle activity: a 12-month follow-up report Int J Oral Maxillofac Surg 2017 46 789 797 10.1016/j.ijom.2017.02.001 28237542
7. Amaral CF Pinheiro MA Camara-SouzA MB Carletti TM Rodrigues Garcia RCM Bite force, masseter thickness, and oral health-related quality of life of elderly people with a single-implant mandibular overdenture Int J Prosthodont 2019 32 503 508 10.11607/ijp.6386 31664266
8. Amaral CF Pinheiro MA de Moraes M Rodrigues Garcia RCM Psychometric analysis and masticatory efficiency of elderly people with single-implant overdentures Int J Oral Maxillofac Implants 2018 33 1383 1389 10.11607/jomi.6557 30427971
9. Assaf A Daas M Boittin A Eid N Postaire M Prosthetic maintenance of different mandibular implant overdentures: a systematic review J Prosthet Dent 2017 118 144–152 e5
10. Atchison KA Dolan TA Development of the geriatric oral health assessment index J Dent Educ 1990 54 680 687 10.1002/j.0022-0337.1990.54.11.tb02481.x 2229624
11. Awad MA Feine JS Measuring patient satisfaction with mandibular prostheses Community Dent Oral Epidemiol 1998 26 400 405 10.1111/j.1600-0528.1998.tb01978.x 9870539
12. Bakke M Holm B Gotfredsen K Masticatory function and patient satisfaction with implant-supported mandibular overdentures: a prospective 5-year study Int J Prosthodont 2002 15 575 581 12475165
13 Bragger U Use of radiographs in evaluating success, stability and failure in implant dentistry Periodontol 1998 2000 17 77 88 10.1111/j.1600-0757.1998.tb00125.x
14. Brägger U Wismeijer D Buser D Chen S Hardware-related complications and failures Biologicial and hardware complications in implant dentistry 2015 Berlin Quintessenz
15. Bragger U Gerber C Joss A Haenni S Meier A Hashorva E Lang NP Patterns of tissue remodeling after placement of ITI dental implants using an osteotome technique: a longitudinal radiographic case cohort study Clin Oral Implants Res 2004 15 158 166 10.1111/j.1600-0501.2004.00988.x 15008927
16. Bryant SR Walton JN Macentee MI A 5-year randomized trial to compare 1 or 2 implants for implant overdentures J Dent Res 2015 94 36 43 10.1177/0022034514554224 25348544
17 Carletti TM Pinheiro MA Meira IA AmaraL CF Rodrigues Garcia RCM Prostheses satisfaction and diet of elderly wearing a single implant overdenture: a six-month assessment Spec Care Dentist 2019 39 471 477 10.1111/scd.12411 31368121
18. Cheng T Sun G Huo J He X Wang Y Ren YF Patient satisfaction and masticatory efficiency of single implant-retained mandibular overdentures using the stud and magnetic attachments J Dent 2012 40 1018 1023 10.1016/j.jdent.2012.08.011 22925922
19. Cordioli G Majzoub Z Castagna S Mandibular overdentures anchored to single implants: a five-year prospective study J Prosthet Dent 1997 78 159 165 10.1016/S0022-3913(97)70120-3 9260133
20. Coutinho PC Nogueira TE Leles CR Single-implant mandibular overdentures: clinical, radiographic, and patient-reported outcomes after a 5-year follow-up J Prosthet Dent 2022 128 949 955 10.1016/j.prosdent.2021.01.007 33640091
21. da Silva RJ Issa JP Semprini M da Silva CH de Vasconcelos PB Celino CA Siessere S Regalo SC Clinical feasibility of mandibular implant overdenture retainers submitted to immediate load Gerodontology 2011 28 227 232 10.1111/j.1741-2358.2010.00374.x 20609008
22. de Araujo SC Hartmann R Curado TFF Schimmel M Leles CR A 3-year prospective cohort on the incidence of prosthodontic complications associated with three implant treatment options for the edentulous mandible J Oral Rehabil 2022 49 1155 1162 10.1111/joor.13371 36103601
23. de Paula MS Cardoso JB de Menezes EEG Nogueira TE McKenna G Leles CR A prospective cohort on the incidence of fractures in single-implant mandibular overdentures J Dent 2020 103 103521 10.1016/j.jdent.2020.103521 33159977
24. de Resende GP, de Menezes EEG, Maniewicz S, Srinivasan M, Leles CR (2023) Prosthodontic outcomes of mandibular overdenture treatment with one or two implants: 4-year results of a randomized clinical trial. Clin Oral Implants Res 34(3):233–242
25 de Souza Batista VE Vechiato-Filho AJ Santiago JF Jr Sonego MV Verri FR dos Santos DM Goiato MC Pellizzer EP Clinical viability of single implant-retained mandibular overdentures: a systematic review and meta-analysis Int J Oral Maxillofac Surg 2018 47 1166 1177 10.1016/j.ijom.2018.01.021 29459128
26. de Souza RF Terada AS Vecchia MP Regis RR Zanini AP Compagnoni MA Validation of the Brazilian versions of two inventories for measuring oral health-related quality of life of edentulous subjects Gerodontology 2012 29 e88 95 10.1111/j.1741-2358.2010.00417.x 20735490
27. Dormenval V Mojon P Budtz-Jorgensen E Associations between self-assessed masticatory ability, nutritional status, prosthetic status and salivary flow rate in hospitalized elders Oral Dis 1999 5 32 38 10.1111/j.1601-0825.1999.tb00061.x 10218039
28. Eldridge SM Chan CL Campbell MJ Bond CM Hopewell S Thabane L Lancaster GA GROUP, P. C. CONSORT 2010 statement: extension to randomised pilot and feasibility trials BMJ 2016 355 i5239 10.1136/bmj.i5239 27777223
29. Enkling N Saftig M Worni A Mericske-Stern R Schimmel M Chewing efficiency, bite force and oral health-related quality of life with narrow diameter implants - a prospective clinical study: results after one year Clin Oral Implants Res 2017 28 476 482 10.1111/clr.12822 27009835
30. Feine JS Carlsson GE Awad MA Chehade A Duncan WJ Gizani S Head T Heydecke G Lund JP Macentee M Mericske-Stern R Mojon P Morais JA Naert I Payne AG Penrod J Stoker GT Tawse-Smith A Taylor TD Thomason JM Thomson WM Wismeijer D The McGill consensus statement on overdentures. Mandibular two-implant overdentures as first choice standard of care for edentulous patients Gerodontology 2002 19 3 4 10.1111/j.1741-2358.2002.00003.x 12164236
31 Fitzpatrick B Standard of care for the edentulous mandible: a systematic review J Prosthet Dent 2006 95 71 8 10.1016/j.prosdent.2005.11.007 16399278
32. Flores-Orozco EI Rovira-Lastra B Peraire M Salsench J Martinez-Gomis J Reliability of a visual analog scale for determining the preferred mastication side J Prosthet Dent 2016 115 203 208 10.1016/j.prosdent.2015.07.006 26455536
33. Folstein MF Folstein SE McHugh PR "Mini-mental state". A practical method for grading the cognitive state of patients for the clinician J Psychiatr Res 1975 12 189 198 10.1016/0022-3956(75)90026-6 1202204
34. Gallucci GO Benic GI Eckert SE Papaspyridakos P Schimmel M Schrott A Weber HP Consensus statements and clinical recommendations for implant loading protocols Int J Oral Maxillofac Implants 2014 29 Suppl 287 290 10.11607/jomi.2013.g4 24660204
35. Gerber A Artikulation und Gestaltung des Kauflächenkomplexes Schweiz Mschr Zahnmed 1955 65 148
36. Gonda T Maeda Y Walton JN Macentee MI Fracture incidence in mandibular overdentures retained by one or two implants J Prosthet Dent 2010 103 178 181 10.1016/S0022-3913(10)60026-1 20188240
37. Grover M Vaidyanathan AK Veeravalli PT OHRQoL, masticatory performance and crestal bone loss with single-implant, magnet-retained mandibular overdentures with conventional and shortened dental arch Clin Oral Implants Res 2014 25 580 586 10.1111/clr.12111 23331716
38. Halazonetis DJ Schimmel M Antonarakis GS Christou P Novel software for quantitative evaluation and graphical representation of masticatory efficiency J Oral Rehabil 2013 40 329 335 10.1111/joor.12043 23452188
39 Hartmann R de Menezes Bandeira ACF de Araujo SC Mckenna G Bragger U Schimmel M Leles CR Cost-effectiveness of three different concepts for the rehabilitation of edentulous mandibles: Overdentures with 1 or 2 implant attachments and hybrid prosthesis on four implants J Oral Rehabil 2020 47 1394 1402 10.1111/joor.13071 32885482
40. Hassel AJ Rolko C Koke U Leisen J Rammelsberg P A German version of the GOHAI Community Dent Oral Epidemiol 2008 36 34 42 10.1111/j.1600-0528.2007.00351.x 18205638
41. Kern M Att W Fritzer E Kappel S Luthardt RG Mundt T Reissmann DR Radel M Stiesch M Wolfart S Passia N Survival and complications of single dental implants in the edentulous mandible following immediate or delayed loading: a randomized controlled clinical trial J Dent Res 2018 97 163 170 10.1177/0022034517736063 29045800
42. Kern M Behrendt C Fritzer E Kohal RJ Luthardt RG Maltzahn NFV Radel M Reissmann DR Schwindling FS Wolfart S Passia N 5-year randomized multicenter clinical trial on single dental implants placed in the midline of the edentulous mandible Clin Oral Implants Res 2021 32 212 221 10.1111/clr.13692 33258136
43. Lam Vo T Kanazawa M Myat Thu K Asami M Sato D Minakuchi S Masticatory function and bite force of mandibular single-implant overdentures and complete dentures: a randomized crossover control study J Prosthodont Res 2019 63 428 433 10.1016/j.jpor.2019.03.002 30956160
44. Lancaster GA Thabane L Guidelines for reporting non-randomised pilot and feasibility studies Pilot Feasibility Stud 2019 5 114 10.1186/s40814-019-0499-1 31608150
45. Leles CR Dias DR Nogueira TE McKenna G Schimmel M Jordao LMR Impact of patient characteristics on edentulous subjects' preferences for prosthodontic rehabilitation with implants Clin Oral Implants Res 2019 30 285 292 10.1111/clr.13414 30740777
46. McGarry TJ Nimmo A Skiba JF Ahlstrom RH Smith CR Koumjian JH Classification system for complete edentulism. The American College of Prosthodontics J Prosthodont 1999 8 27 39 10.1111/j.1532-849X.1999.tb00005.x 10356552
47. Misch CE Perel ML Wang HL Sammartino G Galindo-Moreno P Trisi P Steigmann M Rebaudi A Palti A Pikos MA Schwartz-Arad D Choukroun J Gutierrez-Perez JL Marenzi G Valavanis DK Implant success, survival, and failure: the International Congress of Oral Implantologists (ICOI) Pisa Consensus Conference Implant Dent 2008 17 5 15 10.1097/ID.0b013e3181676059 18332753
48. Mizumori T Tsubakimoto T Iwasaki M Nakamura T Masticatory laterality–evaluation and influence of food texture J Oral Rehabil 2003 30 995 999 10.1046/j.1365-2842.2003.01086.x 12974859
49. Mombelli A van Oosten MA Schurch E Jr Land NP The microbiota associated with successful or failing osseointegrated titanium implants Oral Microbiol Immunol 1987 2 145 51 10.1111/j.1399-302X.1987.tb00298.x 3507627
50. Müller F Duvernay E Loup A Vazquez L Herrmann FR Schimmel M Implant-supported mandibular overdentures in very old adults: a randomized controlled trial J Dent Res 2013 92 154s s160 10.1177/0022034513509630 24158342
51. Müller F Salem K Barbezat C Herrmann FR Schimmel M Knowledge and attitude of elderly persons towards dental implants Gerodontology 2012 29 e914 e923 10.1111/j.1741-2358.2011.00586.x 22073988
52. Nogueira TE Aguiar FMO de Barcelos BA Leles CR A 2-year prospective study of single-implant mandibular overdentures: patient-reported outcomes and prosthodontic events Clin Oral Implants Res 2018 29 541 550 10.1111/clr.13151 29663516
53. Nogueira TE Dias DR Leles CR Mandibular complete denture versus single-implant overdenture: a systematic review of patient-reported outcomes J Oral Rehabil 2017 44 1004 1016 10.1111/joor.12550 28805255
54. Nogueira TE Dias DR Rios LF Silva ALM Jordao LMR Leles CR Perceptions and experiences of patients following treatment with single-implant mandibular overdentures: a qualitative study Clin Oral Implants Res 2019 30 79 89 10.1111/clr.13394 30520155
55. Padmanabhan H, Kumar SM, Kumar VA (2020) Single implant retained overdenture treatment protocol: a systematic review and meta-analysis. J Prosthodont 29(4):287–297
56. Passia N Abou-Ayash S Reissmann DR Fritzer E Kappel S Konstantinidis I Konigsmarck VV Mundt T Stiesch M Wolfart S Ali S Kern M Single mandibular implant study (SMIS) - masticatory performance - results from a randomized clinical trial using two different loading protocols J Dent 2017 65 64 69 10.1016/j.jdent.2017.07.005 28705728
57. Passia N Att W Freitag-Wolf S Heydecke G von Konigsmark V Freifrau von Maltzahn N Mundt T RadeL M Schwindling FS Wolfart S Kern M Single mandibular implant study - denture satisfaction in the elderly J Oral Rehabil 2017 44 213 219 10.1111/joor.12473 27973690
58. Passia N, Kern M (2023) The single midline implant in the edentulous mandible-current status of clinical trials. J Clin Med 12(11):3773
59. Passia N Wolfart S Kern M Ten-year clinical outcome of single implant-retained mandibular overdentures-A prospective pilot study J Dent 2019 82 63 65 10.1016/j.jdent.2019.01.006 30690111
60. Schimmel M Christou P Herrmann F Müller F A two-colour chewing gum test for masticatory efficiency: development of different assessment methods J Oral Rehabil 2007 34 671 678 10.1111/j.1365-2842.2007.01773.x 17716266
61. Schimmel M Müller F Suter V Buser D Implants for elderly patients Periodontol 2017 2000 73 228 240 10.1111/prd.12166
62. Schwindling FS Raedel M Passia N Freitag-Wolf S Wolfart S Att W Mundt T Reissmann D Ismail F von Konigsmark V Kern M The single mandibular implant study - short-term effects of the loading protocol on Oral Health-related Quality of Life J Prosthodont Res 2018 62 313 316 10.1016/j.jpor.2017.12.003 29402561
63. Sheikh J Yesavange J Geriatric Depression Scale (GDS): recent evidence and development of a shorter version Clin Gerodontol 1986 5 165 173 10.1300/J018v05n01_09
64. Slade GD Spencer AJ Development and evaluation of the Oral Health Impact Profile Community Dent Health 1994 11 3 11 8193981
65. Souza RF Patrocinio L Pero AC Marra J Compagnoni MA Reliability and validation of a Brazilian version of the Oral Health Impact Profile for assessing edentulous subjects J Oral Rehabil 2007 34 821 826 10.1111/j.1365-2842.2007.01749.x 17919248
66. Srinivasan M Makarov NA Herrmann FR Müller F Implant survival in 1- versus 2-implant mandibular overdentures: a systematic review and meta-analysis Clin Oral Implants Res 2016 27 63 72 10.1111/clr.12513 25350235
67. Thomason JM Feine J Exley C Moynihan P Müller F Naert I Ellis JS Barclay C Butterworth C Scott B Lynch C Stewardson D Smith P Welfare R Hyde P McAndrew R Fenlon M Barclay S Barker D Mandibular two implant-supported overdentures as the first choice standard of care for edentulous patients–the York Consensus Statement Br Dent J 2009 207 185 186 10.1038/sj.bdj.2009.728 19696851
68. Tubert-Jeannin S Riordan PJ Morel-Papernot A Porcheray S Saby-Collet S Validation of an oral health quality of life index (GOHAI) in France Community Dent Oral Epidemiol 2003 31 275 284 10.1034/j.1600-0528.2003.t01-1-00006.x 12846850
69. van der Bilt A Burgers M van Kampen FM Cune MS Mandibular implant-supported overdentures and oral function Clin Oral Implants Res 2010 21 1209 1213 10.1111/j.1600-0501.2010.01915.x 20572834
70. von Elm E Altman DG Egger M Pocock SJ Gotzsche PC Vandenbroucke JP Initiative S The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies PLoS Med 2007 4 e296 10.1371/journal.pmed.0040296 17941714
71. Walton JN Glick N Macentee MI A randomized clinical trial comparing patient satisfaction and prosthetic outcomes with mandibular overdentures retained by one or two implants Int J Prosthodont 2009 22 331 339 19639067
72. Walton JN Macentee MI Choosing or refusing oral implants: a prospective study of edentulous volunteers for a clinical trial Int J Prosthodont 2005 18 483 488 16335167
