Journal of Dental Implant Research 2022; 41(3): 42-49
Single and two implant-supported overdentures: A comparison of objective prognostic parameters and QOL
Niharika Yadav, Deeksha Arya , Saumyendra Vikram Singh , Kamleshwar Singh, Mayank Singh, Divya Mehrotra
Department of Prosthodontics, Crown and Bridges Faculty of Dental Sciences, King George's Medical University, Lucknow, India
Correspondence to: Deeksha Arya,
Department of Prosthodontics, Crown and Bridges Faculty of Dental Sciences, King George's Medical University, C-503, Shalimar Gallant Mahanagar, Lucknow 226006, India. Tel: +9935025789, Fax: +91-522-4238653, E-mail:
Received: May 10, 2022; Revised: July 4, 2022; Accepted: July 27, 2022; Published online: September 30, 2022.
© The Korean Academy of Implant Dentistry. All rights reserved.

This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Purpose: This study compared a) crestal bone loss, b) implant stability quotient (ISQ), c) probing depth, d) denture fracture incidence, and e) posterior residual ridge resorption (RRR) of two implant and single implant-supported overdentures and assessed the quality of life (QOL) was evaluated before and after giving the prosthesis.
Materials and Methods: The study was a randomized longitudinal cohort study. Eighty subjects were selected for the study and divided randomly into two groups (n=40): Group 2IOD— two implant-supported overdentures; Group 1IOD— Single implant-supported overdentures. Except for the number of implants, the common surgical, implant, and the prosthetic protocol was followed for the two groups. An oral health impact profile EDENT questionnaire was completed by the patients before giving the implant-supported overdenture and after one year of prosthesis delivery to evaluate the effects of oral health on the quality of life. Probing pocket depth (mm), ISQ (resonance frequency analysis), denture fracture incidence, posterior RRR (mm), and crestal bone loss (mm) were assessed and compared at the baseline and one year after implant placement (early loading protocol) for the two groups. Standard statistical tests, including an unpaired t-test with SPSS software, were used for the analysis.
Results: The average crestal bone loss in group 2IOD was insignificantly lower than group 1IOD. The ISQ values were higher for group 2IOD than group 1IOD at one year. The ISQ values for both groups at 12 months were similar (P>0.05). The probing depth at both time intervals yielded insignificant intergroup differences. No denture fracture was reported in either group. At 12 months, posterior ridge resorption in group 2IOD was 0.33±0.08, which was significantly lower than in group 1IOD.
Conclusions: A one implant-supported overdenture is a comparable treatment option with two implant-supported overdentures for edentulous patients, having the advantages of lower cost and less surgical trauma. However, there may be more posterior RRR with this treatment modality.
Keywords: Implant supported overdenture, Implant stability, Crestal bone loss, Residual ridge resorption, Fracture incidence, RFA (resonance frequency analysis)

Complete dentures (CD) have been the treatment of choice for the edentulous patients. However, this treatment has several complications like lack of retention and stability which can be solved with implant supported overdenture (ISOD) or implant retained fixed prosthesis (IRFP)1-5).

Implant supported overdentures (ISOD) are considered as one of the best replacements of CD as for not being very expensive and are within the reach of many patients who are on limited financial support. Advantages are decreased bone resorption, reduced prosthesis movement, better esthetics and increased occlusal function6). It provides some advantages over an implant retained complete fixed prosthesis like fewer implants and less bone grafting required before treatment in ISOD as comparison to IRFP. Esthetics is better in IOD because papilla and tooth size are easier to reproduce or control and nocturnal parafunction are also reducing which increases stresses in the implant support system.

The use of the mandibular conventional complete denture is more problematic than that of the maxillary conventional denture due to several factors such as thin mucosal coverage of the edentulous ridge, a reduced support area and the mobility of the floor of the mouth, the movement of the mandible and the tongue which affects the speech. So, it is better to replace only mandibular conventional denture with ISOD7).

Mandibular implant overdenture with 2∼4 implants has confirmed success and productive outcome. Current consensus is that reducing the numbers of implants from four to two does not affect the implant or the prosthodontic success rates8).

In developing countries, financial constraints of socioeconomic groups could also make the provision of a proposed minimum standard of care (with mandibular two-implant overdentures). Hence, the option of less invasive implant surgery in the anterior mandible, with reduced implant components and prosthodontic component costs, the concept of the mandibular single-implant overdentures (to oppose the successful conventional complete maxillary dentures) is a reality for elderly edentulous populations. Traditionally, the anterior mandible has been considered a rather safe, preferred site for implant placement for overdentures9,10). It prevents bone loss, improved esthetics, prosthesis retention, speech and limits lateral movements and direct longitudinal forces11,12). Although use of anterior implants reduced the bone loss in anterior region but posterior ridge resorption continues (four times faster than anterior region). This PRR is reduced when patient wearing fixed implant supported prosthesis.

Overdenture (OD) attachment is considered as pillars for ISOD and permits movement during function and removal and controls the degree of retention. O-ring system, Hader Bar and clip, magnets and Telescopic attachments are different types of attachments. Retention of OD is determined by the number and type of attachment13,14). Numerous studies have reported differences between these type of attachments in terms of patient satisfaction, retention, prosthesis maintenance and peri-implant outcomes.

The present study was therefore conducted to compare single implant retained overdenture and two separate implant retained overdentures in completely edentulous patients.


Eighty-eight completely edentulous patients in age group of 45 to 65 years were included in the study after fulfilling informed consent process and obtaining approval from Institutional Ethical Committee (3257/Ethics/R. Cell- 19). The sample size was calculated after a comparison of two means using a power of 90%. Total number of subjects selected for the study was n=88. Criteria for inclusion was Class I maxillary arch15), minimum 6 month of edentulism16). and division B mandibular bone i.e., the height is more than 10 mm but the width at the crest atrophied to 2.5 to 5 mm in implant placement areas.

Patients with history of chemotherapy or radiation therapy, smoking, drug or alcohol abuse, psychiatric disorders, metabolic, skeletal or endocrine disorders, unrealistic patient demands, temporomandibular joint disorders, ankylosis, Sjogren syndrome and/ or other disease or medication causing xerostomia, bleeding disorders were excluded.

A randomized longitudinal observational in vivo study was designed to compare patient satisfaction in two implant and single implant retained overdentures after early loading of implants. Patients were randomly allocated to Group 2IOD: Two implant retained overdentures and Group 1IOD: Single implant retained overdentures.

All the implants placed in this study were Touareg-S spiral Adin implants (Adin implant system, Israel). After fabrication of complete denture in conventional manner, mandibular denture was duplicated and the duplicate was used as diagnostic and surgical stent.

1. Surgical phase

Patients in two implant groups had implants placed in A/B or D/E region, and C region in one implant group followed by early loading in both the study group. All patients received a prophylactic dose of antibiotics (2 gm amoxicillin) 1 hour prior to the surgery. After administration of 2% lignocaine with adrenaline (1:80,000) for local anesthesia, the selected implants of size 3.5 mm by 11.5 (Adin dental implant system, Israel) mm were placed at the prepared sites in all subjects to aid standardization. Surgical cover screws were placed with hex driver. The patient was told not to wear the lower denture for two weeks following surgery.

2. Prosthetic phase

After 14 days ball attachment was placed on implant with soft liner after relieving denture and metal housing were inserted in abutment. After 2 weeks, soft liner was replaced with self-cure acrylic resin. Follow up examinations were made at 1 year interval. Crestal bone loss was assessed with the help of intraoral periapical radiograph (IOPAR) at baseline and 1 year interval. Probing pocket depth was measured to nearest millimeter using a manual Hu Friedy PCP 15 periodontal probe (Hu Friedy Inc., Leimen, Germany) at mesial and distal surfaces of implant at baseline and 1 Year interval. For measuring implant stability resonance frequency analysis was performed at baseline and 1 year by RFA instrument Kit (Osstell TM; Osstell AB, Gothenburg, Sweden). Fracture incidence recorded when patient came with complaint of fractured denture or seen during recall appointment. A fracture was considered as either a visible crack in acrylic resin or a total separation of denture parts.

Panoramic radiographs were obtained from all patients after 1 year of treatment. Landmarks and outline of mandible were traced from the radiographs after placing on viewing screen. The method consisted of proportional area measurements of the posterior mandible. The areas were bounded by the line from the lowest point of the mental foramen to gonion and the crest of the residual ridge and were expressed as a proportion of areas that are not dependent on the crest of the residual ridge. Proportions were used to minimize errors related to magnification and distortion. To estimate the change in the height of the posterior mandibular residual ridge over 1 year, not taking into account the magnification or distortion of the radiographs, the mean of the change in bone area bounded by the residual ridge was divided by the length of the crest of the residual ridge. Radiographs were taken at baseline and 1 year interval17).

The oral health impact profile EDENT questionnaire18) was filled by the patient 1 Year after prosthesis delivery. The OHIP-EDENT is a 19-question survey, grouped as seven subscales or domains: functional limitation, physical pain, psychological discomfort, physical disability; psychological disability, social disability, and handicap. This questionnaire assesses the effect of oral health on the quality of life of patients with total prostheses, before and after they have received them. It is particularly for edentulous patients and contains questions addressing masticatory capacity, pleasure in eating, level of comfort and assuredness while wearing the prosthesis, and relationship problems, among others18). For every question there is choice of three answers- (0)=never, (1)=sometimes, (2)=almost always.

Standard statistical tests including unpaired t-test with SPSS software (version 21.0) (SPSS Inc., Chicago, IL, USA). Were used for the analysis and comparison. The questionnaire was applied by one examiner/observer only.


Total 88 patients were selected for the study, out of which 3 patients were excluded as the implants placed in these patients failed to osseointegrate (1 in group 2IOD and 2 in 1IOD). Five patients were lost in follow-up (3 in 2IOD and 2 in 1IOD).

The basic characteristics of patients are summarized in Table 1. The overall proportion of males (81.3%) was higher than females (18.7%) in group 2IOD. In group 1IOD also overall proportion of males (52.9%) was higher than females (47.1%). Mean age of patient in group 2IOD was 56.75±5.75 years whereas in group 1IOD it was 57.38±6.35 years. Comparing the mean age and sex proportions of two groups, t-test and X2 test respectively, revealed similar age group and sex proportions between the two groups i.e., no statistical difference. It was concluded that subjects of two groups were matched and comparable.

Table 1 . Basic characteristics of patients

Basic characteristicsGroup 2IOD (n=40)Group 1IOD (n=40)t/X2 StatisticP-value
Age (yrs)56.75±5.7557.38±6.35−0.290.77
Male13 (81.3)9 (52.9)0.120.3
Female3 (18.7)7 (47.1)

1. OHIP 19

Table 2 shows that difference in patient satisfaction in Group 2IOD and group 1IOD in terms of functional limitation (Group 2IOD=0.5 and Group 1IOD=2.25), physical pain (Group 2IOD=0.63 and Group 1IOD=3.13), psychological discomfort (Group 2IOD=0.63 and Group 1IOD= 1.56), social disability (Group 2IOD=0.56 and Group 1IOD=2.5), physical disability (Group 2IOD=0.75 and Group 1IOD=2.63) was significant. The difference in patient satisfaction among both groups is statistically insignificant in relation to being handicap (Group 2IOD=0.75 and Group 1IOD=1.13).

Table 2 . Comparison of mean domain scores between the study groups

GroupGroup 2IOD (n=40)Group 1IOD (n=40)P-value

Mean (SD)MedianRangeMeanMedianRange
Functional limitation0.69 (0.79)0.5 (0∼1)0∼22.25 (1.29)2 (1.25, 3)0∼50.001*
Physical pain0.63 (0.62)0∼23.13 (1.03)3 (2.25, 4)1∼5<0.001*
Psychological discomfort0.63 (0.62)1 (0∼1)0∼21.56 (0.81)1.5 (1, 2)0∼30.002*
Physical disability0.75 (0.58)1 (0∼1)0∼22.63 (0.81)3 (2, 3)1- 4<0.001*
Psychological disability0.31 (0.60)0 (0∼0.75)0∼21.44 (0.63)1(1, 2)1∼3<0.001*
Socialdisability0.56 (0.96)0 (0∼1)0∼32.5 (0.73)3 (2, 3)1∼3<0.001*
Handicap0.75 (0.86)1 (0∼1)0∼31.13 (0.96)1 (0.25, 1.75)0∼30.22 (NS)
Overall4.31 (1.74)4.5 (2.25∼5.75)2∼714.62 (2.31)14.5 (13∼15.75)11∼13<0.001*

Mann Whitney U-test.

*P<0.05 Statistically significant, P>0.05 Non significant (NS).

2. Outcome measures

1) Crestal bone loss

Table 3 presents the comparison of crestal bone loss at 1 year between the groups. The bone loss on distal side of implants was lower in Group 2IOD (0.69±0.11) compared with Group 1IOD (0.79±0.19) at 1 year interval. Mesial side bone loss was also lower in Group 2IOD (0.71±0.11) compared with Group 1IOD (0.78±0.10) at 6 months. Average bone loss was lower in Group 2IOD (0.70±0.11) compared with Group 1IOD (0.79±0.23) at 1 year. The difference in crestal bone loss between the two groups was insignificant.

Table 3 . Comparison of crestal bone loss (mm) at 1 year

Group 2IODGroup 1IODt statisticP-value
Baseline- 1 year (mm)Mesial0.71±0.110.78±0.10−1.880.06

2) ISQ

Table 4 presents Implant Stability Quotient (ISQ) values in both groups at baseline and 1 year. Radiofrequency analysis shows almost equal ISQ values in both groups i.e., mesiodistal ISQ in group 2IOD (64.69±1.49) is almost equal to group 1IOD (64.44±1.71), labiolingual ISQ in Group 2IOD (64.69±1.40) is almost same as in group 1IOD (64.50±2.42) at the time of loading. Average ISQ values being 64.69±1.58 for Group 2IOD and 64.46±3.82 for Group 1IOD. The difference in implant stability quotient in both the groups is insignificant.

Table 4 . Comparison of radiofrequency analysis at baseline and 1 year

Group 2IODGroup 1IODt statisticP-value
At baselineMesiodistal64.69±1.4964.44±1.710.440.63
1 YearMesiodistal74.81±1.5674.75±1.570.110.91

It shows almost equal ISQ values in both groups i.e., mesiodistal ISQ in Group 2IOD (74.81±1.56) was almost equal to Group 1IOD (74.75±1.57), labiolingual ISQ in Group 2IOD (73.44±1.41) was almost same as in Group 1IOD (74±1.69) at 1year. Average ISQ values being 74.26±2.5 for Group 2IOD and 74.36±2.54 for Group 1IOD at 1 year. The difference in implant stability quotient in both the groups was insignificant.

3. Fracture incidence

In the present study no patient reported fracture of denture in any of the group.

4. Pocket depth

To assess the health of peri implant tissue, peri implant probing depth was assessed. Probing depth was measured for mesial, distal, labial and lingual surface of implant and an average is calculated. Average pocket depth in Group 2IOD was 1.59±0.48 which is less than for Group 1IOD is 1.89±0.79 at baseline. At 1-year average probing depth was 1.62±0.98 in Group 2IOD and 1.75±0.64 in Group 1IOD (Table 5). The difference in pocket depth between the groups is insignificant.

Table 5 . Comparison between pocket depth at baseline and 1 year

Group 2IODGroup 1IODt statisticP-value
At baselineMesial1.5±0.521.81±0.83−1.270.21
1 YearMesial1.64±0.531.74±0.67−0.470.64

5. Posterior ridge resorption

At 1 year, in Group 2IOD resorption was 0.33±0.08, which was significantly less than Group 1IOD 0.41±0.08 (P=0.006). Results were statistically significant (Table 6).

Table 6 . Comparison between posterior residual ridge resorption at baseline and 1 year

Group 2IODGroup 1IODt StatisticP-value
Baseline – 1 year0.33±0.080.41±0.08−2.980.006*

*Denotes a statistical significance; P<0.05.


Implant retained overdenture have statistical superiority over conventional denture19,20). Different types of attachments has been used to connect implant and denture which can be mechanical, magnetic and custom cast attaching bar design. The selection of the attaching mechanism for an implant retained over denture depend on: cost effectiveness, amount of retention needed, expected level of oral hygiene, amount of available bone, patient’s social status, patient’s expectation, maxilla mandibular relationship, inter-implant distance, and status of the antagonistic jaw21).

In our study we have used ball attachments because it is simplest of all attachments, low cost, ease of handling and minimal chair side time requirements. Other advantages are reduced mucosal hyperplasia, less technique sensitive and easier to clean22).

One of the studies compared load transfer and denture stability in mandibular implant retained over denture retained by ball, magnet, or bar attachments, suggested that the use of ball attachment was advantageous in regards to optimizing stress and minimizing denture movement23).

A study by Kenney and Richards evaluated the photo elastic stress patterns produced by implant-retained ODs and found that independent O-ring attachments transferred less stress to implants than the bar-clip attachments when their model was subjected to posterior vertical load24). Other advantages include controlled retentive forces due to different color coded nylon rings and better shock absorption due to multidirectional movement of both attachments. Most common complication in O-ring housing is abutment screw loosening25).

Patient selection is the critical factor for implant survival. The patients having certain systemic diseases have been excluded from study because these may affect oral tissues by increasing their susceptibility to other diseases or by interfering with healing26). Absolute medical contraindications exist and must be adhered to, lest the clinician contend with infection, implant failure, or even patient death. There are some relative contraindications which does not directly affect the implant success or failure. Smoking, drug abuse and excessive use of alcohol increases the risk of peri-implantitis. Osteoporosis can cause bone fragility, fracture and oral bone loss. Xerostomia frequently results in mucositis, candidiasis, and reduced denture retention and hence is a significant concern for conventional denture wearers. Although little is known about endosseous dental implants in patients with Sjögren syndrome, implant supported prostheses may be preferable to soft tissue–supported prostheses in patients with xerostomia. Bleeding disorders can cause problems during the implant surgery procedure. These patients were excluded from the study27).

Most important site for implant placement in anterior region is symphysis region as bone quantity and quality is very good.

Easy accessibility, minimal surgical trauma and time conservation are the other few benefits of symphysis region along with the potential risk of mandibular fracture because of the anatomical structure28).

In this study, the oral health–related quality of life of subjects who received mandibular 1IODs and 2IODs was compared using the OHIP Edent -19 which has been previously validated in the literature. This subjective indication allows the perception of oral health and evaluate the impact of oral rehabilitation. Based on the findings of this study, it is assumed that improved patient satisfaction and quality of life in both the groups29).

Kuoppala et al.30) evaluated the QOL of patient treated with implant supported mandibular overdenture and compared the attachment system and found that attachment type or the number of supporting implants did not have a significant influence on the oral health related QOL. Sadowsky reported mandibular two implant overdentures show higher patient satisfaction scores than complete dentures, even with patients who have undergone preprosthetic surgery13).

Implant health can be determined by the change in crestal bone region and can be measure at different time interval. The reason of bone loss can be multifactorial and each time period has a different cause for bone loss. After first year of function, the crestal bone loss range from 0∼0.2 mm.

Naert et al.31) found that the bone resorption for two implant retained overdenture was 0.55 mm at 1 year. When applying early/immediate loading, the implant-bone system is biomechanically challenged during healing. The type and magnitude of loading will probably influence the ongoing healing process and it is possible that in some cases, this may lead to demineralization of the bone-implant interface, loss of stability and eventually implant failure.

The probing depth is the distance between the gingival margin and the depth of the probe tip penetration into the pocket. Increased probing depth and loss of clinical attachment are pathognomonic of periodontal disease. Peri-implant probing provides an assessment of different parameters such as bleeding on probing, suppuration, and exudation from the sulcus and peri-implant tissues32). Studies have shown that, when used, probe pressure of 0.5 N penetrates an average of 0.7 mm deeper at implant sites. Clinical probing depth is higher around implants versus teeth, as the probe tip ends apically to the junctional epithelium into the connective tissue close to the bone crest33).

Success of osseointegration can be determined by implant stability which can be of two types: Primary and Secondary. Various methods used to measures are Microscopic or histologic analysis which is invasive methods. Non-invasive methods include reverse torque analysis, Radiographic analysis, Perio test, Percussion test and Resonance frequency analysis (RFA).

Out of these methods RFA is most reliable, non-invasive method to monitor osseointegration at different time interval by using vibration and principle of structure analysis. Higher RFA indicates better bone implant interface. This study showed increase in Implant stability quotient (ISQ) values in both the groups however the difference in implant stability quotient in both the groups was insignificant. Liddelow and Henry34) showed a generally high mean initial value (ISQ=74.1±5.3), and maintenance of this high value up to the 1-year review (ISQ=73.1±4.9) in single implant retained overdenture. Many implants showed a small increase in ISQ value after 3 months, although this was not statistically significant (P=0.630, F=0.580, df=2). There was no statistical difference between baseline, 3-month, and 12-month values (P=0.630).

Most common complication of Implant overdenture is posterior bone resorption as it resorbs faster than the anterior bone. In our study 2 implant supported overdenture show less resorption as comparison to single implant supported overdenture (Table 3). OPG was selected for evaluation of PRR as these are commonly use radiographs in dental set up and we can measure whole mandible from single radiograph. The techniques used for measurement of PRR evaluated only average bone resorption17).

Saunders et al.35) suggested that the resilient connection between overdenture and attachments, allowed free rotation during posterior loading, thereby contributing to increased resorption of the posterior ridge.

The limitation of this study includes small sample size, shorter duration of follow-up in single implant retained overdenture. Posterior ridge resorption, food lodgment and movement of prosthesis are as major problem with implant overdenture.


Single implant retained overdenture is a viable treatment option in completely edentulous patients who have financial constraints. Patient satisfaction level is high in two implant retained overdenture. Prosthetic complications were relatively rare for both the treatment modalities. Single implant overdenture can be work as transient dentures till the patient is ready for fixed implant supported prosthesis.

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