According to McGill consensus, two-implant overdentures has been accepted as the gold standard treatment care for the edentulous mandible¹⁾. Retention is considered as one of the most significant factors in determining patient satisfaction in removable prosthodontics and is defined as the force that resists withdrawal along the path of insertion and stabilizes the overdenture during its function²⁾.

The retention of the implant overdentures is provided by using attachments, and many attachment systems are available¹⁾. Regardless of the attachment system, hygiene and cleansing procedures should be recommended to the patient. The effective and regular cleaning of the dentures is important for maintaining oral health and the prostheses. Dentures can be cleaned using different methods such as mechanical cleaning, chemical cleaning, or a combination of both. Most patients clean their dentures by brushing (mechanical method), however brushing alone is not sufficient to control biofilm formation^1,3,4). Chemical solutions for denture cleansing should be used because they are more effective than mechanical methods⁵⁾. Therefore, many patients use commercial denture cleansers like Efferdent and Polident dissolved in water and dentures are immersed in it. These cleansers have been shown to be more effective than water in reducing Candida and Streptococcus mutans. Another commonly used denture cleanser is sodium hypochlorite (NaOCl), which has been found to be an effective immersion plaque removal agent⁴⁾. Despite their efficacy, these denture cleansing solutions may have deleterious effects on overdentures and they can lead to deterioration of the denture base material, bleaching and wear of the plastic material, corrosion of metal and destruction of soft lining materials^1,3,5). Previous study had comparatively evaluated the retention and capacity of ball, bar and Locator attachments in implant overdentures⁶⁾. Another study had compared the retentive capacity of different color codings of a single attachment system⁷⁾.

Many authors have studied the retention capacity of overdenture attachments soaked in sodium hypochlorite (NaOCl) denture cleansing solution simulating different periods of clinical usage^4,5,8). Nguyen et al.⁸⁾, You et al.⁴⁾ and Kürkcüoğlu et al.¹⁾ demonstrated that the Locator attachments soaked in NaOCl produced significant reduction in retention. Derafshi et al.⁵⁾ concluded that NaOCl caused more reduction in retention value of Dio orange O-rings when compared to effervescent cleansers.

Studies evaluating the effect of oral rinses on overdenture attachments are scarce. Few authors have used Listerine oral rinse as a cleansing agent for overdentures due to its antiseptic and antimicrobial property and they are easily accepted by the patients⁹⁾. You et al.⁴⁾ studied the retention capacity of Locator attachments when immersed in Listerine oral rinse and concluded that Listerine significantly increased the retention of the Locator attachments. Felipucci et al.⁹⁾ concluded that Listerine caused reduction in retention values of O-ring attachment.

One major concern with attachment systems for implant overdentures is that wear changes over time, reflected clinically by loss of retention. The factors which are associated with the clinical wear of attachments includes masticatory forces, parafunctions, temperature and composition of saliva, products used for the maintenance of denture and the presence of food residues. The wear of overdenture retentive mechanisms has been identified as the most common prosthodontic complications which is about 33%¹⁰⁾. Few studies have also evaluated the amount of wear and its effects in the attachment systems²⁾. Felipucci et al.⁹⁾ stated that NaOCl solution exhibited significant dimensional deformation in the O-ring attachment and Listerine did not cause any deleterious effects on the surface of O-ring, after simulation of 90 days of use.

Currently, studies evaluating the effect of chemical oral rinses on the retention and wear of overdenture attachments are limited and studies evaluating the effect of herbal oral rinses on the retention and wear of overdenture attachments are lacking. The aim of the present in vitro study was to compare and evaluate the effect of two different oral rinses on the retention and surface topography of ball attachment housing in implant supported overdentures.

The null hypothesis for the present study was that the oral rinses does not affect the retention and surface topography of ball attachment housing in implant supported overdentures.

One rectangular stainless steel metal die of dimension 20 mm×20 mm×30 mm with 2×2×2 mm depressions on right and left side of the die was custom made to serve as an index for the fabrication of master wax block of similar dimensions (Fig. 1, left side) and another rectangular stainless steel metal die of dimension 20 mm×20 mm×30 mm with 2×2×2 mm notches on right and left side of the die was custom made to serve as an index for the fabrication of prosthetic wax blocks to be used in this study (Fig. 1, right side). Condensation silicone impression material of putty (Zhermack, Zetaplus, Italy) and light body consistencies (Zhermack, oranwash L, Italy) were used for obtaining the index in a single step procedure. The putty was hand mixed with appropriate amount of Indurent gel (catalyst) to obtain a homogenous dough. Equal lengths of Light body impression material and Indurent gel (catalyst) were dispensed on a mixing pad and mixed using a stainless steel mixing spatula (Dentex store, India) to form a homogenous mixture and the material was applied gently over the two custom-made stainless steel metal dies. The mixed putty was also placed over the metal dies and left undisturbed until set. After setting, the metal dies were removed from the indexes and the mold space areas were inspected for defects and acceptability. The putty indexes thus obtained were used to fabricate the test samples of standardized dimensions for this study.

Figure 1. Die for the preparation of master wax blocks (left). Die for the preparation of prosthetic wax blocks (right).

Modelling wax (Hindustan manufacturer, Hyderabad) was melted and poured into the mold spaces created by the putty indexes and was allowed to cool. After the wax had completely hardened, the wax blocks were retrieved carefully and placed at room temperature. Thirty-three such wax blocks were fabricated. Out of which three wax blocks were fabricated with the dimensions of 20 mm×20 mm×30 mm with 2×2×2 mm depressions on right and left side of the block and used as master wax blocks and thirty wax blocks were fabricated with the dimensions of 20 mm×20 mm×30 mm with 2×2×2 mm notches on right and left side of the block and used as prosthetic wax blocks. The prosthetic wax blocks were evaluated for complete seating on the master wax block. The three master blocks and the thirty prosthetic blocks were fabricated using heat polymerized acrylic resin.

The fabricated master and prosthetic wax blocks were invested in a denture flask (Star dental, India) using Type II dental plaster (Ramaraju Mills ltd, India). A two-pour technique was followed for flasking the wax specimens. Type II dental plaster was mixed with water using a stainless steel straight spatula in a rubber bowl (Classic, India) and poured into the lubricated base portion of the denture flask. The wax blocks were placed into the denture flask. The number of samples per denture flask was restricted to a maximum of three to ensure adequate space between the samples. After the plaster had set, the separating medium was painted over the plaster surfaces, and the lubricated body of the flask was placed over the base. It was filled with a fresh mix of Type II dental plaster and the lid was closed. The denture flask was tightened with a flask carrier and the excess plaster was removed.

The plaster was allowed to harden for one hour before the denture flask was placed in a boiling water bath. The clamps were loosened and the flasks were placed in boiling water for fifteen minutes. The flasks were removed from the water and the appropriate segments of the flasks were carefully separated in a vertical direction to avoid fracture of the invested plaster. The softened wax was flushed out from the surface of the mold with hot water. Wax solvent and warm detergent solution were used to remove wax residues and oily films respectively. Finally, the molds were flushed well with clean hot water. Both the halves of the flasks were placed slanting on the laboratory bench for few minutes to allow the water to drain completely. The flasks were allowed to cool completely prior to packing. After dewaxing, the rectangular mold spaces in the base of the denture flask were ready for packing of heat cure denture base acrylic resin.

A total of thirty-three heat polymerized acrylic resin blocks were obtained in a similar manner. The surveying platform was made parallel to the floor using spirit level indicator (Jinhua Hengda Tools, China). The master block was placed on the surveying platform of the surveyor (Marathon 103, Saeyang, Korea) and stabilized. A round hole of 4 mm in diameter and 16 mm in depth was made using a straight fissure bur (Dentex store, India) at the center of the master block with the aid of a dental surveyor in order to prepare space for ball attachment abutment replica (ADIN dental implants).

Then, the ball attachment abutment replica of diameter 4.0 mm and length 16.6 mm (Fig. 2) which represents implant analog and ball attachment as a single piece was positioned in the prepared hole perpendicular to the horizontal plane. The ball attachment abutment replica was placed 2 mm above the surface of the acrylic block. Clear auto polymerizing acrylic resin (RR cold cure, DPI, India) was mixed and poured into the prepared hole and left until polymerization was completed. Same procedure was carried out for all the master blocks used in this study. Modelling wax was used to block the undercuts around the ball attachment abutment replica in the master blocks. The metal housing of 4.7 mm diameter and 2.9 mm (Fig. 3) length along with nylon cap insert of standard retention (ADIN Dental Implants) was placed over the ball attachment abutment replica for picking it up onto the prosthetic block. The center of the prosthetic blocks were determined using a dental surveyor and the prosthetic blocks were now drilled with acrylic burs to create space for the metal housing with nylon cap insert.

Figure 2. Stainless steel ball attachment abutment replica – 4 mm diameter and length 16.6 mm.

Figure 3. Stainless steel metal housing – 4.7 mm diameter and length 2.9 mm.

In order to prevent the acrylic adhesion of two blocks, a thin layer of separating medium (Tejpal pharma and surgical) is applied on the master blocks. Clear auto polymerizing acrylic resin was poured into the space created in the prosthetic block and the metal housings with the nylon cap insert placed over the ball attachment abutment replica in the master blocks were picked up in the prosthetic blocks. Upon setting, the master block with ball abutment was retrieved from the prosthetic blocks with the metal housing and nylon cap insert. Excess flash was removed using the acrylic burs. Same procedures were carried out for all the prosthetic blocks used in this study.

Thirty prosthetic blocks with metal housing and nylon cap insert thus obtained were divided into three groups of ten blocks each according to the type of oral rinse used for immersion.

1.Group I (Control) (n=10) Prosthetic blocks with the test samples immersed in Water for 45 hours.

2.Group II (n=10) Prosthetic blocks with the test samples immersed in Listerine Cool Mint chemical oral rinse for 45 hours.

3.Group III (n=10) Prosthetic blocks with the test samples immersed in Colgate Vedshakthi oil based herbal oral rinse for 45 hours.

Total of thirty test samples were tested individually in the Universal testing machine (SHIMADZU AG-X plus 50 KN, Europe) to measure the force required to separate the prosthetic block from the master block. Both the master block with ball attachment abutment replica and the prosthetic test samples were positioned on the machine table and secured tightly into the upper and lower clamps of the universal testing machine. Engagement and disengagement of the attachments were carried out at right angles to the horizontal level of the blocks. Initial retention force of all the test samples were evaluated before immersion in their respective oral rinses. The tests were conducted in an open room at room temperature. The maximum vertical dislodging force required to separate the two blocks were recorded in Newtons at a crosshead speed of 50 mm/min and the retention force values were obtained in a computer-controlled software which is being attached to the testing machine.

The oral rinses used in this study were Listerine Cool Mint chemical oral rinse (Johnson & Johnson Pvt LTD, Bangalore, India) and Colgate Vedshakti oil based herbal oral rinse (Colgate-Palmolive Ltd., Uttarakhand, India). Water was used as the control. Ten prosthetic blocks with the test samples were immersed in water for 45 hours (Fig. 4, left container). Ten prosthetic blocks with the test samples were immersed in Listerine Cool Mint chemical oral rinse for 45 hours (Fig. 4, center container) and ten prosthetic blocks with the test samples were immersed in Colgate Vedshakti oil based herbal oral rinse for 45 hours (Fig. 4, right container). Assuming an immersion period of 15 minutes per day, 45 hours immersion period was chosen simulating a period of 6 months of clinical use.

Figure 4. Immersion of the prosthetic blocks with the test samples in Water (Group I, left). Immersion of the prosthetic blocks with the test samples in Listerine Cool Mint chemical oral rinse (Group II, center). Immersion of the prosthetic blocks with the test samples in Colgate Vedshakti oil-based herbal oral rinse (Group III, right).

In the same way as described for testing the initial retention force the master and prosthetic blocks were assembled in the Universal testing machine. The testing machine was programmed to apply 720 cycles of insertion-removals. Assuming that a patient removes and inserts his prosthesis four times a day, the retention force values of all the test samples after immersion in their respective oral rinses were evaluated at 360 cycles (simulating 3 months of clinical use) and 720 cycles (simulating 6 months of clinical use). The testing procedure followed was similar to that employed for obtaining initial retention force values. Each prosthetic block with the test sample was placed in the imaging platform of the stereo microscope after the completion of 720 (6 months) insertion-removal cycles at 40× magnification to assess the wear on the surface of the test samples.

The image was captured in the computer-controlled software attached to the system. The basic data obtained were tabulated using Microsoft Excel 10 (Microsoft, USA) and the mean and standard deviation were calculated. The data were subjected to statistical analysis for test of significance using SPSS Software version 23 (SPSS Software corp., Munich, Germany). Retention force within the test groups were analysed using Repeated Measures ANOVA test followed by Post hoc Tukey HSD test. Retention force among and between the test groups were analysed using One-Way ANOVA test and Post hoc Tukey HSD test and a P-value of <0.05 was considered statistically significant.

The retention force was tested at baseline and after immersion in their respective oral rinses at 360 cycles (simulating 3 months) and after 720 cycles (simulating 6 months) of clinical use using universal testing machine. These were considered as the basic data and the respective means derived and are represented in Tables 1∼3. Comparative evaluation of the mean retention force within the test groups were statistically analysed using Repeated measure ANOVA test and represented in Table 4 and multiple comparisons within the test groups were statistically analysed using Post hoc Tukey HSD test and represented in Table 5. Comparative evaluation of the mean retention force among the test groups were statistically analysed using One-Way ANOVA test and represented in Tables 6 and multiple comparisons between the test groups were statistically analysed using Post hoc Tukey HSD test and represented in Table 7. The percentage loss of retention forces were represented in Tables 8∼10.

Table 1 . Retention force of ball attachment housing at baseline and after immersion in Water at 360 (3 months) and 720 (6 months) insertion-removal cycles in Group I

Sample No.	Retention force values (N)
	At base line	360 cycles (3 months)	720 cycles (6 months)
1	27.37	26.20	26.67
2	24.42	22.98	22.48
3	26.69	25.10	24.48
4	27.56	25.54	24.36
5	26.98	24.15	24.74
6	24.93	22.57	22.91
7	29.28	28.95	28.92
8	27.28	26.92	26.04
9	28.39	27.68	26.75
10	29.23	28.53	27.44
Sample mean	27.21	25.86	25.47

Table 2 . Retention force of ball attachment housing at baseline and after immersion in Listerine Cool Mint chemical oral rinse at 360 (3 months) and 720 (6 months) insertion-removal cycles in Group II

Sample No.	Retention force values (N)
	At base line	360 cycles (3 months)	720 cycles (6 months)
1	26.90	26.03	25.78
2	23.06	21.85	22.20
3	25.66	23.46	22.90
4	27.87	26.43	25.47
5	27.89	24.03	23.62
6	26.56	24.76	22.80
7	27.48	25.74	24.62
8	24.28	22.95	21.91
9	23.23	21.82	21.75
10	25.48	23.86	22.67
Sample mean	25.84	24.09	23.37

Table 3 . Retention force of ball attachment housing at baseline and after immersion in Colgate Vedshakthi oil based herbal oral rinse at 360 (3 months) and 720 (6 months) insertion-removal cycles in Group III

Sample No.	Retention force values (N)
	At base line	360 cycles (3 months)	720 cycles (6 months)
1	26.42	24.19	24.22
2	21.86	17.48	17.89
3	24.37	20.13	19.77
4	27.79	22.68	21.29
5	25.70	21.21	20.61
6	25.39	22.99	21.84
7	26.96	22.15	21.68
8	24.52	21.46	21.10
9	27.28	23.62	22.88
10	26.32	22.84	22.72
Sample mean	25.66	21.87	21.40

Table 4 . Comparison of the mean retention force of the test samples at baseline, 360 (3 months) and 720 (6 months) insertion-removal cycles within Groups I, II and III using Repeated Measures ANOVA test

	Number of cycles	Sample No.	Mean (N)	SD	P-value
I	Base line	10	27.2130	1.60611	<0.001**
	360	10	25.8620	2.20986
	720	10	25.4790	2.03919
II	Base line	10	25.8410	1.81937	<0.001**
	360	10	24.0930	1.64432
	720	10	23.3720	1.45311
III	Base line	10	25.6610	1.74301	<0.001**
	360	10	21.8750	1.95158
	720	10	21.4000	1.75943

If P-value is between 0.000 to 0.010 then denoted by **, it implies Significant at 1% level (Highly Significant).

Table 5 . Multiple comparison of the mean retention force of the test samples at baseline, 360 (3 months) and 720 (6 months) insertion-removal cycles within Groups I, II and III using Post hoc Analysis

Group	Number of cycles	Mean	SD	P-value
I	Base Line-360	1.351	0.271	0.002**
	Base Line-720	1.734	0.258	<0.001**
	360∼720	0.383	0.231	0.316
II	Base Line-360	1.748	0.261	<0.001**
	Base Line-720	2.469	0.344	<0.001**
	360∼720	0.721	0.211	0.023*
III	Base Line-360	3.786	0.313	<0.001*
	Base Line-720	4.261	0.378	<0.001**
	360∼720	0.475	0.169	0.061

If P-value is between 0.000 to 0.010 then denoted by **, it implies Significant at 1% level (Highly Significant). If the P-value is between 0.011 to 0.050 then denoted by * it implies Significant at 5% level (Significant).

Table 6 . Comparison of the mean retention force of the test samples at baseline, 360 (3 months) and 720 (6 months) insertion-removal cycles among Groups I, II & III using One-Way ANOVA test

Number of cycles	Group	Sample No.	Mean (N)	SD	P-value
Base line	I	10	27.2130	1.60611	0.108
	II	10	25.8410	1.81937
	III	10	25.6610	1.74301
360	I	10	25.8620	2.20986	<0.001**
	II	10	24.0930	1.64432
	III	10	21.8750	1.95158
720	I	10	25.4790	2.03919	<0.001**
	II	10	23.3720	1.45311
	III	10	21.4000	1.75943

If P-value is between 0.000 to 0.010 then denoted by **, it implies Significant at 1% level (Highly Significant).

Table 7 . Multiple comparison of the mean retention force of the test samples at 360 (3 months) and 720 (6 months) insertion-removal cycles between Groups I, II and III using Post hoc Analysis

Number of cycles	Group	Mean	SD	P-value
360	I∼II	1.76900	0.87162	0.124
	I∼III	3.98700	0.87162	<0.001**
	II∼III	2.21800	0.87162	0.043*
720	I∼II	2.10700	0.79017	0.033*
	I∼III	4.07900	0.79017	<0.001**
	II∼III	1.97200	0.79017	0.048*

If P-value is between 0.000 to 0.010 then denoted by **, it implies Significant at 1% level (Highly Significant). If the P-value is between 0.011 to 0.050 then denoted by * it implies Significant at 5% level (Significant).

Table 8 . Percentage loss of the mean retention force of the test samples at 360 (3 months) and 720 (6 months) insertion-removal cycles in Group I

Number of cycles	Mean % retention	Percentage loss
0∼360	95.04	4.96
0∼720	93.63	6.37

Table 9 . Percentage loss of the mean retention force of the test samples at 360 (3 months) and 720 (6 months) insertion-removal cycles in Group II

Number of cycles	Mean % retention	Percentage loss
0∼360	93.18	6.82
0∼720	90.59	9.41

Table 10 . Percentage loss of the mean retention force of the test samples at 360 (3 months) and 720 (6 months) insertion-removal cycles in Group III

Number of cycles	Mean % retention	Percentage loss
0∼360	85.25	14.75
0∼720	83.4	16.60

On multiple comparison of the mean retention force of the test samples at 360 (3 months) and 720 (6 months) insertion-removal cycles between Groups I, II and III:

At 360 cycles, the mean retention force exhibited with Group I test samples is higher than that of Group II test samples and the difference was found to be statistically not significant (P-value=0.124). At 360 cycles, the mean retention force exhibited with Group I test samples is higher than that of Group III test samples and the difference was found to be statistically significant (P-value <0.001). At 360 cycles, the mean retention force exhibited with Group II test samples is higher than that of Group III test samples and the difference was found to be statistically significant (P-value=0.043).

At 720 cycles, the mean retention force exhibited with Group I test samples is higher than that of Group II test samples and the difference was found to be statistically significant (P-value=0.033). At 720 cycles, the mean retention force exhibited with Group I test samples is higher than that of Group III test samples and the difference was found to be statistically significant (P-value<0.001). At 720 cycles, the mean retention force exhibited with Group II test samples is higher than that of Group III test samples and the difference was found to be statistically significant (P-value=0.048).

The surface topography of the attachments were qualitatively assessed initially and after immersion in their respective oral rinses after 720 insertion-removal cycles using stereomicroscope. Representative images showing surface topography of the three test groups obtained were represented in Fig. 5A, B, C.

Figure 5. (A) Stereomicroscopic picture representative of Group I before retention force testing, observed at 40× magnification (left image). Stereomicroscopic picture representative of Group I after retention force testing, observed at 40x magnification (right image). (B) Stereomicroscopic picture representative of Group II before retention force testing, observed at 40× magnification (left image). Stereomicroscopic picture representative of Group II after retention force testing, observed at 40× magnification (right image). (C) Stereomicroscopic picture representative of Group III before retention force testing, observed at 40× magnification (left image). Stereomicroscopic picture representative of Group III after retention force testing, observed at 40× magnification (right image).

Fig. 6 shows the reduction in mean retention force from baseline to 360 cycles to 720 cycles in all three groups.

Figure 6. Comparison of the mean retention force of the test samples at baseline, 360 (3 months) and 720 (6 months) insertion-removal cycles between Groups I, II & III.

Conventional dentures have been the primary treatment choice for the rehabilitation of completely edentulous arches^11,12). Gotfredsen et al.¹³⁾ compared ball and bar attachments in mandibular overdentures revealed that the bar group had a significantly higher number of complications and/or repairs compared to ball attachments.

Implant supported overdentures require meticulous hygiene and cleansing procedures irrespective of the attachment system. Patients should combine both brushing and soaking in cleansers according to the American college of Prosthodontists (ACP) guidelines. Chemical denture cleansers include alkaline peroxides, alkaline hypochlorite, acids, enzymes and disinfectants. These chemical denture cleansers are found to be more effective than mechanical methods¹⁴⁾. Sodium hypochlorite (NaOCl) is an another commonly used denture cleanser which is bactericidal, fungicidal and removes stains by dissolving organic substances that accumulates on the denture¹⁵⁾.

According to Wichmann and Kuntze, attachment systems undergo wear during movements of insertion and removal as well as during functional load¹⁶⁾. This wear is due to friction between the base and attachment leading to decreased retention values. This occurrence has also been mentioned in many previous studies. Some studies have evaluated the amount of wear of the attachments resulted during retention testing¹⁷⁾. In the present study, Water, Listerine Cool Mint and Colgate Vedshakti were used for immersion of the prosthetic test samples for 45 hours, assuming an immersion period of 15 minutes per day simulating 6 months of clinical use in accordance with the previous studies. Assuming an immersion period of 15 minutes per day. The test samples have been divided into three groups, Group I, Group II and Group III. Group I had prosthetic test samples immersed in water, Group II had prosthetic test samples immersed in Listerine Cool Mint chemical oral rinse and Group III had prosthetic test samples immersed in Colgate Vedshakthi oil based herbal oral rinse.

Retentive force was measured previously by various methods like dental mastication simulator, cyclic fatigue machine (load cell), CS-dental testing machine, Imada device and universal testing machine (UTM)^2,18).the test samples were subjected to 720 insertion-removal cycles which corresponds to 6 months of clinical usage of dentures, considering an average of four removals per day in accordance with previous studies and the retention force was measured at baseline, 360 and 720 insertion-removal cycles¹⁷⁾.

Many studies evaluated the retentive force of overdenture attachments in different dislodgment speeds (900 cm/min to 0.5 mm/min domain). (0.5 mm/min to 150 mm/sec), 120 mm/min. Sarnat proposed a crosshead speed of 50 mm/min and said that it is as close to the speed of the movement of real overdenture removal from its retention elements when vertical force is applied and therefore it was used in the present study¹⁹⁾. The retention force test was carried out with the above mentioned parameters. The retention force obtained for all the test samples in Group I, Group II and Group III were tabulated and statistically analysed.

The overall percentage loss of retention force after 720 cycles in Group I, Group II and Group III was 6.37%, 9.41% and 16.60% respectively. You et al.⁴⁾ reported the retention force values of pink Locator attachments after immersion in water (control), Efferdent, Polident Overnight, sodium hypochlorite and Listerine mouthwash simulating 6 months of clinical usages reported a percentage of retention loss of 53±12% in water, 49±9% in efferedent, 34±18% in Polydent overnight, 42±11% in Naocl and 29±9% in Listerine respectively. The percentage loss of retention in the present study was lower than those observed in previous studies^3,4). This might be due to variations in the company of the nylon cap employed or might be due to the composition of Listerine Cool Mint chemical oral rinse and Colgate Vedshakti oil based herbal oral rinse. However, this needs to be evaluated further in the future studies.

Previous study have reported that, the retention force of about 5 to 7 N was enough to stabilize the overdentures during function. In the present study all the test samples have retention force values more than the above mentioned value and therefore it was considered satisfactory to stabilize the overdenture. However, reduced retention characteristic may be desirable in some patients with poor manual dexterity who may have difficulty during insertion and removal of overdenture. Therefore, under such specific situations, matching the retentive level of the attachments to the physical condition and required needs of the patient should be considered while planning treatment⁴⁾.

The test samples immersed in Water showed a significantly highest retention values followed by the test samples immersed in Listerine Cool Mint chemical oral rinse and the least by the test samples immersed in Colgate Vedshakti oil based herbal oral rinse. The decreased retention force in test samples immersed in Listerine Cool Mint chemical oral rinse might be due to the interaction of active ingredients like thymol, eucalyptol, menthol and methyl salicylate present in Listerine Cool Mint oral rinse with the O-ring attachments thereby lowering the retention force. Colgate Vedshakti herbal oral rinse is mainly composed of sesame oil, clove, eucalyptus, basil and lemon oil. The oil based composition of Colgate Vedshakti herbal oral rinse might have a lubricating action on the surface of the O-ring thus causing increased retention loss when compared to Listerine Cool Mint chemical oral rinse. The reason for this retention loss following immersion in Colgate Vedshakti herbal oral rinse needs to be explored further in future studies. In the present study it is difficult to interpretate whether it was oil based action which caused retention loss. Studies evaluating the effect of Colgate Vedshakti herbal oral rinse on overdenture attachments are lacking in literature to enable further comparisons.

The percentage loss in retention from baseline to 720 cycles was highest in Group III, followed by Grroup II and Group I. In the present study, irrespective of the oral rinses used for immersion, there was a gradual decrease in retention values in all the groups tested as seen in Fig. 6. Both oral rinse immersion, insertion and removal cycle of the attachment had caused decrease in MRF. According to previous studies, most of the attachment systems showed a common trend toward a reduction in the retention force^3,4,8). Felipucci et al.⁹⁾ evaluated the effect of Listerine on O-ring after a simulation of 90 overnight immersions and concluded that there was a gradual loss of retention force values which is not significant clinically. Arora and mittal also concluded that ball attachments lose retention after simulation of 1 year of clinical usage^4,20). Therefore, repeated insertion-removal cycles led to a gradual and continuous loss of retention as mentioned in the above studies. In a previous study, the wear of components of ball attachments was found to be responsible for a decrease in the retention of the attachments, and leading to the eventual fracture of the attachment components¹⁰⁾. The test samples immersed in Colgate Vedshakti oil based herbal oral rinse exhibited highest surface topographic changes followed by the test samples immersed in Listerine Cool Mint chemical oral rinse and the least by the test samples immersed in Water.

The present study had some limitations. Factors like temperature of saliva and its composition and the presence of food residues may influence the parameters tested above which are difficult to simulate in vitro. Under clinical conditions, the forces exerted on the attachments are more complex, with tridimensional forces often occurring. Further studies are needed to evaluate the retention force after immersion in different denture cleansing solutions, simulating longer periods of clinical usage, by comparing single implants or two implants or by comparing different attachment systems.

There is a significant decrease in mean retention force in all three groups after immersion in oral rinses and following six months of insertion and removal cycles. The test samples immersed in Colgate Vedshakti oil based herbal oral rinse had highest surface topographic changes which corroborates with the lesser retention obtained followed by the test samples immersed in Listerine Cool Mint chemical oral rinse and the least surface topographic changes in the test samples immersed in water corroborates with the greater retention obtained. it can be concluded that, both insertion and removal cycles and different types of oral rinses had significant effect in reduction of retention and surface topography of the overdenture attachment.