Complete edentulism is an irreversible condition, in which the oral health-related quality of life is decreased leading to compromised chewing efficiency, poor nutrition, and general body health. Previously conventional complete dentures were the only treatment option for the edentulous arches. This treatment modality remained popular for many years. But due to the detrimental long-term sequelae of wearing complete dentures that include inevitable bone resorption and reduced chewing efficiency over a period of time¹⁾, a conventional complete denture is no longer a treatment of choice.

It has been reported that more than 50% with mandibular complete dentures have problems with stability and retention²⁾. However, implants can be used to improve the functionality as well as the quality of life in patients with poor retention and stability of conventional complete dentures^3,4). Full-mouth prosthesis can range from implant-supported fixed prosthesis to implant-supported overdentures. However, there are certain disadvantages of implant-supported full mouth fixed prosthesis over implant-supported overdentures like economical constraints, systemic conditions not allowing invasive surgical procedures, oral conditions like decreased bone width and height, poor bone quality to support a large number of implants, due to which the latter is preferred^5-8).

Hence, implant-supported overdentures have emerged as a promising treatment modality in these situations⁹⁾. The major advantages of implant-supported overdenture include minimal bone resorption with enhanced chewing efficiency^10,11). It has been found that patients with complete dentures need 1.5 to 3.6 times more chewing strokes than patients with implant-supported overdentures¹²⁾.

An implant used for overdenture can be a conventional implant or a mini-implant. The length of the conventional and mini-implants can be the same, the only difference is in their diameter. The narrow diameter of these implants allows their easy placement in narrow or resorbed ridges.

A conventional implant can provide good long-term success. However, conventional implants also have some limitations, like they can’t be placed in narrow ridges without performing ridge augmentation surgery, can’t be placed in patients with chronic systemic diseases¹³⁾. Moreover, the cost of conventional implants is also an important factor that deters the patient from having an implant-supported overdenture^13-17). It has been reported that implant overdentures with two implants were 7 times costlier than a conventional denture¹⁸⁾. However, it has been found that mandibular overdentures retained by two mini-implants are more cost-effective than two or four conventional implant-retained overdentures¹⁹⁾. In these situations, mini-implants may provide an alternative option for rehabilitation. Mini implants are less invasive and technically easier compared to conventional implants. They require minimal osteotomy procedures regarding stabilization and loading^20,21). Mini implants offer better results in patients dissatisfied with conventional dentures or in patients where standard implants cannot be placed due to local or systemic reasons^22-25).

The number of implants supporting the overdentures can also vary, like 2 implants or 4 implants can be used to support an overdenture. However, it has been found that bone loss, patient satisfaction, and complications related to implants are not related to the number of implants supporting the overdenture²⁶⁾. The survival rate of mini-implant-supported overdenture has been observed up to 94.2%²¹⁾. Also, when compared to conventional implant-supported overdentures mini-implants provide better patient satisfaction²⁷⁾. Overdentures rehabilitated with short and narrow implants have high clinical and radiographic success^28,29). Survival rates of implant-supported mandibular overdentures in frail elderly patients also is reported to be high even after two decades despite compromised oral hygiene³⁰⁾.

Despite numerous advantages of mini-implants over conventional implants, their predictable use for overdenture prosthesis has not been well established as studies have also reported the low survival rate of mini-implants as compared to conventional implants²⁵⁾.

Therefore, the purpose of this study was to compare and evaluate the clinical and radiographic outcomes as well as to measure the patient satisfaction level in patients of mini-implant versus conventional implant-supported overdenture.

1. Study design

It was a randomized control prospective study. Ethical clearance from the committee of King George Medical University, Lucknow (India) was obtained (Ref No.-72^nd ECM Thesis II-B-Thesis/P36). An informed consent form was signed by every patient who participated in this study, all were willing for follow-up.

2. Participants, settings and eligibility criteria

Participants were recruited from the subjects coming to the department of Prosthodontics and Dental Materials, King George’s Medical University, (U.P.), Lucknow. Inclusion criteria: 1) Edentulous patients above the age of 40 years, 2) Patients edentulous for minimum of six months and maximum 1 years, 3) Edentulous patients not wearing complete dentures, 4) Free from any medical conditions that might interfere with implant placement and/or osseointegration, 5) Non-smokers, 6) Had enough bone volume without the need to use any bone grafts. Minimum bone width for placement of mini-implant/implant should be 1 mm on each side of the implant at the crest and the height should be 2 mm more than the implant length, so only those patients who have minimum bone width of 5.5 mm and height of 13.5 mm at B and D locations on the mandibular ridge were included³¹⁾. Average span of edentulism was eight months.

1) Exclusion criteria

1) Insufficient interocclusal distance for implant placement and restoration, 2) Patient on any medication that influences bone metabolism, 3) Patients undergoing chemotherapy and/or radiotherapy.

3. Randomization

Computer-generated randomization was used as a method for randomization. It was an open label trial. Participants were divided into two intervention groups on a 1:1 basis. Two intervention groups were Group 1- mini-implant supported over-dentures (11 mm and 2.5 mm) and Group 2- conventional implant supported overdentures (11 mm and 3.3 mm) (Fig. 1).

Figure 1. Consort flow diagram. Time of assessment was 12 months and 36 months.

4. Intervention

200 patients were screened to be included in the study, out of which 15 patients did not meet the inclusion criteria and 11 declined to participate due to many reasons like long follow-up, fear of surgery, multiple visits, illness, transfer from sites etc. Hence, 174 subjects were included in the study. None of the patients drop-out over a 3-year period, and there was no implant failure by conventional standards. Single piece conventional and mini dental implants of suitable size (MYRAID Equinox Snap Implant, Equinox Medical Technologies, BV, Amersfoort, Netherland) were placed in patients of both the groups (n=87). Assuming 80% power and 5% significance level, the sample was calculated³²⁾.

5. Data collection

Data collection was done over a period of 3 years, first after 12 months of implant placement and then after 36 months of implant placement. At each visit following values were recorded- crestal bone loss, pocket depth, implant stability and pre-validated oral health impact profile EDENT questionnaire. EDENT questionnaire detects the impact of oral health on the quality of life of patients who wear total prostheses³³⁾. 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. It is specific to edentulous patients and presents questions addressing masticatory capacity, pleasure in eating, level of comfort and assuredness while wearing the prosthesis, and relationship problems, among others. For every question there is choice of three answers: (0)=Never; (1)=Sometimes; (2)=Almost always.

6. Study methodology

Detailed patient history along with the pre-operative clinical and radiographic assessment of all the patients (Orthopantomogram, Denta scan, and Intra oral periapical Radiographs) was carried out. Implants/ mini-implants were placed in mandibular anterior region at B and D location with D2 bone density (850 to 1,250 Hounsfield units) belonging to Division B category³⁴⁾. All selected patients were randomly allocated to either the mini-implant supported overdenture group or the conventional implant supported overdenture group. For the patients in mini-implant supported overdenture group, length and width of mini-implant patients were 11 mm and 2.5 mm respectively and for the conventional implant overdenture group the length and width of implant was 11 mm and 3.3 mm respectively.

Complete dentures were fabricated with a bilaterally balanced occlusal scheme following standard procedures. Then the mandibular complete dentures were duplicated in clear acrylic resin with metal sleeves placed at B and D location. Bone width and height have been measured by radiographic stent using a Denta scan. The same radiographic stent was used as a surgical template. Then the implant/ mini-implant was placed corresponding to B and D location depending upon the group to which the patient belongs. Torque achieved ranged from 30 to 32 Ncm.

Following implant placement, the complete denture was discontinued for 1 month. Following this, early loading of mini-implants was done, and housing was incorporated with acrylic.

Pocket depth was assessed around conventional and mini-implants supported overdenture by using a graduated pressure sensitive probe (Vivacare TPS, Vivadent, Schaan, Lichtenstein). Probing depth was measured at the mid-buccal, mid-lingual, mid-mesial and mid-distal surfaces of all the implants and the mean value for the scored surfaces for each implant was calculated.

The crestal bone loss by digital Orthopantomogram using ‘J’ software around conventional implants supported overdentures and mini-implants supported overdentures. Assessment of crestal bone loss from baseline to 12 months and from 12 to 36 months was evaluated by registering a reference point on the implant surface on the x-ray image. The distance between the highest point of the bone at the implant bone interface to the point of the selected reference point was measured digitally on both sides (mesial and distal) using digital Orthopantomogram by Image J software. The mean value was then calculated for each patient.

Additionally, the implant stability by Periotest (MEDIZINTECHNIK GULDEN BENSHEIM, Germany) in conventional implants supported overdentures and mini-implants overdenture was also established. The Periotest unit is composed of measurement and control electronic devices with a flexible connection to a probe. The probe contains a rod weighing 8 grams that taps the implant 20 times in 5 seconds^35,36). A visual and acoustic signal is then given. An intergroup comparison has been done among mini-implant supported overdenture group and implant supported overdenture group.

Finally, the patient satisfaction based on oral health impact profile EDENT questionnaire in conventional implants supported overdentures and mini-implants supported overdentures was recorded^37,38).

7. Statistical analysis

Statistical analysis was done by using Statistical Package for Social Sciences (version 25.0) (SPSS Inc., Chicago, IL, USA). Chi-square test was used for the analysis of the data for satisfaction with complete dentures. P-value of less than 0.05 was considered statistically significant.

There was no significant difference (P>0.05) in the right and left crestal bone-mesial and distal level between the groups from baseline to 12 months and from 12 to 36 months. Similarly, there was no significant (P>0.05) difference in the right and left implant perio test-mesiodistal and labiolingual level between the groups at 12 months, and 36 months. Likewise, there was no significant (P>0.05) difference in the right and left pocket depth-mesial, distal, labial and lingual level between the groups at 12 months and 36 months . There was no significant (P>0.05) difference in the bone loss and implant perio test between the groups from 12 months to 36 months. The comparison of pocket depth between the groups had no significant (P>0.05) difference at 12 months and 36 months. The mean change in the pocket depth from 12 months to 36 months in Group 1 and Group 2 was statistically significant. No significant (P>0.05) difference in physical pain, psychological discomfort and disability.

The mean change in the crestal bone loss in Group 1 was 0.36±0.12 and in Group 2, this was 0.33±0.12. The mean change in the crestal bone loss was significant (P=0.0001) in both the groups being higher in Group 1 than Group 2 (Table 1). The mean change in implant perio test was 0.08±0.30 at 12 months and -0.26±0.37 at 36 months in Group 1 and in Group 2 this value was -0.02±0.27 and -0.02±0.27 respectively (Table 2). The mean change in the pocket depth value was 1.05±0.35 at 12 months and 1.26±0.27 at 36 months for Group 1 and 0.97±0.35 at 12 months and 1.23±0.25 at 36 months for Group 2 (Table 3). There was no significant (P>0.05) difference in physical pain, psychological discomfort, psychological disability, social disability and total score between the groups (Table 4).

Table 1 . Comparison of bone loss from baseline to 12 months and from 12 to 36 months in Groups

Groups	Mean change	P-value1
Group 1 (Mini)	0.36±0.12	0.0001*
Group 2 (Conv.)	0.33±0.12	0.0001*

¹Paired t-test, *Significant.

Table 2 . Comparison of implant perio test from 12 months to 36 months

Groups	12 months			36 months
	Mean change	P-value1		Mean change	P-value1
Group 1 (Mini)	−0.08±0.30	0.17		−0.26±0.37	0.001*
Group 2 (Conv.)	−0.02±0.27	0.61		−0.12±0.47	0.15

¹Paired t-test, *Significant.

Table 3 . Comparison of pocket depth from 12 months to 36 months

Groups	12 months			36 months
	Mean change	P-value1		Mean change	P-value1
Group 1 (Mini)	1.05±0.35	0.0001*		1.26±0.27	0.001*
Group 2 (Conv.)	0.97±0.35	0.0001*		1.23±0.25	0.001*

¹Paired t-test, *Significant.

Table 4 . Comparison of quality of life between the groups

	Group 1 (Mini) (n=29)	Group 2 (Conv.) (n=29)	P-value1
Functional	0.00±0.00	0.00±0.00	-
Physical pain	0.44±0.63	0.23±0.25	0.11
Psychological discomfort	1.85±0.52	1.46±0.79	0.10
Physical disability	0.00±0.00	0.00±0.00	-
Psychological disability	0.10±0.30	0.07±0.25	0.09
Social disability	0.31±0.47	0.26±0.15	0.10
Handicap	0.00±0.00	0.00±0.00	-
Total	2.67±0.86	1.98±0.95	0.07

¹Mann-Whitney U test.

Edentulous patients suffer from social, physical, functional and psychological limitations^39-41). Bone resorption after tooth loss leads to decrease in the size of the denture-bearing area, thereby reducing denture stability, which causes insufficient retention of the lower denture¹³⁾ causes challenges in providing a satisfactory solution for patient’s oral health problems²⁾.

According to the McGill Consensus statement on overdentures, implant-supported overdentures have proved to be superior to conventional dentures⁴²⁾. Increase in bite force, chewing efficiency, and patient satisfaction has been noted in patients implants supported overdenture wearer during the follow-up of 5 years^10,27).

In the present study, ball attachments were used as a part of single piece mini dental implants. Godfredsen and Holm⁴³⁾, compared implant retained overdentures and reported twice as many complications developed with the bar attachment than the ball and socket. MacEntee⁴⁴⁾, investigated outcome with a bar or ball attachment and reported that most complications developed in the first year with 90% of repairs occuring with the ball and socket⁴⁵⁾.

Mini-implants were used in this study to retain the Complete Dentures in edentulous mandibular arches. Their reduced diameter (<3.0 mm) enabled insertion in narrow ridges. Moreover, the insertion procedure was simpler and faster, as reduced series of drills were required. Survival rates of mini-implants were favourable when used for mandibular overdentures²⁷⁾.

The primary requisite that leads to the success of implant surgery is obtaining implant primary stability. If an implant is not sufficiently stable at the time of placement, micromotion may occur. The normal healing process may then be disrupted, and a capsule of fibrous tissue may form, resulting in mobility of the implant and its subsequent clinical failure⁴⁶⁾.

Insertion torque can provide assessment of bone quality as a function of density and hardness, either subjectively in experienced hands or quantitatively by electronic drill devices which measure the torque required to insert implant in the bone⁴⁷⁾. Ottoni et al.⁴⁸⁾ in their study, suggested that a minimum of 32 Ncm insertion torque was necessary for implants to achieve osseointegration.

Following implant placement, an increase in stability results from the regeneration and remodelling of bone at the implant-tissue interface. Once bone has formed at the interface, the requirements for success change: an implant now needs to be able to effectively distribute loads transmitted by the intraoral prosthesis to which it is attached^46,49). Hence early loading treatment protocol was used instead of immediate loading.

From the outcomes of the present study, using mini dental implants seems to be a treatment option as predictable as using standard diameter implants. Alveolar bone is critical to the establishment of the biological width⁵⁰⁾. The development and the location of the biological width relative to the implant and the alveolar crest become all the more important when a minimal alveolar bone is available to house the implant due to anatomical restrictions arising from structures such as the sinus floor, inferior alveolar canal, and the mental foramen or when the implant is placed in areas of aesthetic concern. Subsequent crestal bone loss around implants after placement may produce unfavourable crown: implant ratios or expose metal collars.

In the present study, the results of crestal bone loss showed statistically insignificant difference (Table 1). The changes in the bone height observed in the study may be because the implants were placed in the inter-foraminal region where bone quality is favourable. The above results were in confinement to the results obtained in the studies of Zarone et al.⁵¹⁾ and Astrand et al.⁵²⁾ that deal with the use of mini-implants or narrow diameter implants as an implant treatment.

Because of the severely resorbed alveolar arch in the mandibles with high floor of the mouth in all of the patients investigated, the panoramic radiograph was the only X-ray technique which could be applied in these patient situations, as intraoral films could not be positioned parallel to the implant axis without causing considerable discomfort to the subject⁵³⁾. Gomez-Roman et al.⁵⁴⁾ found no significant difference in the accuracy of measurement between intraoral periapical and Orthopantomogram whereas other studies focused on the suitability of panoramic radiographs. Moreover, Gomez-Roman et al.⁵⁴⁾ demonstrated that measurements aided by digital image processing methods are reliable and achieve a higher degree of precision than the visual metric method^53,55).

The Periotest method is based on the empirical finding that the greater the implant solidity, the higher the deceleration of the tapping rod that touches the implant^36,56). Advantages of Periotest device are: it can offer reproducible findings by measuring the levels of subclinical mobility using an ultrasonically vibrating tool, it can successfully assess implant stability status⁵⁶⁾. However, the Periotest device has certain disadvantages also like, it cannot reliably detect the amount of crestal bone loss, and bony osseointegration⁵⁶⁾.

In the present study, no statistically significant difference was observed in the periotest values of two mini dental implants with the conventional implant group at both 12 and 36 months in edentulous mandibular arches (Table 2). The results obtained were in line with the results obtained by Romeo et al.⁵⁷⁾ In sequence of the Split Mouth Model Design, statistically insignificant difference was found between the implants placed in the left canine region and the right canine region from baseline to 6 months.

The probing depth (PD) is generally measured by using a William’s Periodontal Probe. It is the first probe to be used to assess probing depth of a pocket. It has the following markings- 1, 2, 3, 5, 7, 8, 9, 10 mm⁵⁸⁾. Pressure sensitive probes produce most accurate results when compared to other periodontal probes⁵⁹⁾. Although the values showed higher values in mini-implant group than in conventional implants, but there was a statistically insignificant difference between mini- implant and conventional implant group.

The results of the present study were in collaboration to the results obtained in the study of the Mostafa Omran et al⁶⁰⁾. In this study, he concluded that the mean value of the pocket depth of the first group was higher than the second group with no statistically significant difference.

Measuring PD is an appropriate method to detect deleterious changes in the peri-implant environment and should be performed every 3 to 4 months for 1 year after prosthesis delivery. Probing depth is not only important in measuring increase in sulcus depth but also allows evaluation of several peri-implant parameters like tissue consistency, bleeding, and presence of exudate at the same time and at the same site^61-65).

The oral health impact profile EDENT questionnaire³³⁾ was filled by the patient 36 months after prosthesis delivery. It has been used previously to compare the satisfaction of edentulous individuals treated with implant supported overdentures and fixed prostheses, and to assess the technical condition of these treatments in terms of patient satisfaction.

Result was statistically insignificant between Group 1 (mini) and Group 2 (conv.) patients. Although, scoring depicts satisfaction inclination more towards Group 2 (conv.). The results of this study suggest that conventional or implant-stabilized prostheses can have a positive impact on the health-related quality of life of edentulous patients. Improvement was possible with patients who preferred implant-stabilized prostheses but instead were treated with conventional techniques, but not to the same extent as with patients who received their desired treatment. Although expectations of implant therapy were high, they do not appear to have significantly affected the level of patient satisfaction with the outcome of treatment; thus, patient expectations appear not to be a good predictor of treatment outcome. Oral-specific health status measures helped identify the degree of impairment, disability, and handicap experienced by edentulous patients⁶⁶⁾. The literature indicates that implant-supported overdentures in the mandible provide predictable results with improved stability, retention, function and patient satisfaction compared with conventional dentures⁶⁷⁾.

However, this study has evaluated the implant stability, crestal bone, soft tissue changes (pocket depth) along with questionnaire in mini dental implants placed in edentulous mandibular arches through the 36 months follow up period, further studies are needed in controlled clinical trials before this approach can be used routinely.

Within limitations of the study and based on the results obtained, following conclusions have been drawn:

1.There was insignificant difference in the crestal bone loss between mini-implant supported overdenture group and conventional implant supported overdenture group both from baseline to 12 months and from 12 to 36 months interval.

2.There was insignificant difference in Periotest implant stability results between mini-implant supported overdenture group and conventional implant supported overdenture group both at 12 months and 36 months interval.

3.There was insignificant difference in pocket depth between mini-implant supported overdenture group and conventional implant supported overdenture group both at 12 months and 36 months interval.

4.Difference in patient satisfaction level was statistically insignificant between mini-implant supported overdenture group and conventional implant supported overdenture group at 36 months.