Complete tooth loss is an important oral-health issue, especially among older adults, and is linked to problems with chewing, speech, eating, oral comfort, and quality of life.[1] While there has been a reduction in the prevalence of edentulism in recent decades, it is clinically significant in the ageing population.[2] Data from the U.S. surveillance system show that about 15.2% of adults aged ≥65 years are edentulous, and the prevalence increases from 11.4% for adults between the ages of 65 and 74 years to 19.7% for adults ≥75 years.[3] A similar national analysis found that the prevalence of complete edentulism among adults ≥65 years in the U.S. decreased from 16.36% in 2012 to 13.54% in 2020, with significant socioeconomic differences remaining.[3] Therefore, the need for prosthetic rehabilitation remains an important aspect of oral care in completely edentulous patients.

Conventional complete dentures (CCDs) are the most widely available method for edentulism due to their low cost, the ease and imperceptibility of fabrication, and low cost.[4] Traditional dentures, however, sit on the oral mucous membranes and have poor retention and stability, especially for patients with advanced residual ridge resorption.[5] The implant-supported overdenture (ISO) has therefore emerged as an alternative to provide implant support and improve denture retention and functional performance without compromising the removable denture design.[6] Recent studies have shown improvements in functional and patient-reported outcomes with implant-supported overdentures, compared with conventional complete dentures.[7] However, the biological impact of these two approaches to prosthetics is not limited to retention and mastication, but can also extend into the oral environment to which the prosthesis is subject every day.

Saliva is an essential part of oral homeostasis and plays important roles in lubrication, protection by mucin, buffering, remineralization, antimicrobial function, and maintenance of the oral microbial ecosystem.[8] A range of factors, including age, systemic factors, medication, oral stimulation, and prosthetic rehabilitation, can affect salivary pH and flow rate.[9] These alterations can then influence the microbial colonization and the progression of denture-associated oral diseases. In clinical practice, we have previously shown that the pH of the saliva changes after fitting with both conventional and implant-supported dentures, which may be significant.[10] Likewise, the replacement of poor-quality complete dentures has been found to be correlated with salivary flow rate changes, both unstimulated and stimulated.[11]

The oral microbiota is another important determinant of prosthesis-related oral health.[12] The presence of dentures can also provide new surfaces and protected areas which can promote microbial adhesion and biofilm formation.[13] This is especially important for removable prostheses as microbial accumulation can lead to denture-associated stomatitis and to inflammation of the oral mucosa, bad breath and opportunistic infections. Systematic review evidence has recently revealed differences between dentate older adults, edentulous older adults, and complete denture wearers, which highlight the effect of tooth loss and the effect of prosthetic rehabilitation on the oral microbial ecosystem.[14]  Most of the literature has focused on patient-reported outcomes and prosthetic function, or on one biological parameter at a time, but not both the characteristics of the saliva and microbial load at the same time for various complete-denture designs.

Although implant-supported overdentures are becoming more popular, an important clinical question has been posed whether or not the functional advantages of overdentures have measurable differences in the biological oral environment more than conventional complete dentures. Measurement of salivary pH, salivary flow rate, and oral microbial load in the same study population would give a more comprehensive understanding of the interactions between prosthesis design and oral homeostasis and oral microbial ecology. This information could be used by clinicians when choosing and monitoring an edentulous patient's prosthetic rehabilitation, not just retention and patient satisfaction. Thus, the present study was planned to evaluate the difference in salivary pH, salivary flow rate, and oral microbial load of patients with conventional complete dentures and implant-supported overdentures.

The study was designed as a comparative analytical cross-sectional study in the Department of Prosthodontics, Lahore Medical and Dental College, Lahore. The study was carried out over 6 months from October, 2025 to April, 2026. Salivary pH was chosen as the primary outcome, and a sample size was calculated using the OpenEpi sample size calculator for comparing two means. The calculated sample size was 51 for each group with a 95% two-sided confidence level and 80% power, based on the previously reported mean values of salivary pH for conventional complete-denture users (6.94 ± 0.22) and for those receiving an alternative complete-denture design (7.04 ± 0.12).[15] The final sample size, after adding around 10% to compensate for incomplete data not being complete and the loss of some participants, was increased to 114 participants, 57 of whom were assigned to the conventional complete denture group and 57 to the implant-supported overdenture group. A non-probability consecutive sampling technique was used. Patients were included if they were completely edentulous and had used either conventional complete dentures or implant-supported overdentures for at least three months and were either male or female. The participants should possess clinically acceptable and functional prostheses, regular usage, and willingness to give oral microbial and saliva samples. Those patients in the implant-supported overdenture group had to have clinically stable implants with no clinical evidence of peri-implant infection. Patients with active oral infection, oral candidiasis, periodontal or peri-implant disease, salivary-gland disorder, and clinically apparent oral mucosal diseases or lesions were excluded. Patients who were taking medications that cause significant xerostomia, uncontrolled diabetes mellitus, or systemic diseases that significantly affect salivary secretion were also excluded. Patients who recently used antibiotics, antifungal medications, or antiseptic mouthwashes in the last four weeks were excluded, as this would affect the oral microbial load. Patients who did not follow the instructions for saliva collection, had fractured dentures or dentures that were very ill-fitting, had recently had their dentures changed, or could not follow the instructions for care were also not included. After obtaining ethical approval from the institutional research ethics committee and written informed consent, eligible participants were interviewed using a structured data-collection form. Demographic data, length of edentulism, length of time wearing prosthesis, type of prosthesis, frequency of denture wearing, denture cleaning habits, and pertinent medical and medication history were documented. A clinical examination was conducted to evaluate the condition of the oral mucosa, denture fit, and denture hygiene and, in the presence of implants, the peri-implant tissues. To reduce the diurnal variations, unstimulated whole saliva was collected between 9:00 AM and 11:00 AM. The participants were asked not to eat, drink, smoke, chew gum, or perform oral hygiene procedures for at least 2 hours prior to sampling. Participants were seated comfortably with their heads slightly bent forward and asked to allow saliva to collect in their mouths and then spit it into a sterile graduated collection tube at regular intervals after first rinsing with water. The collection was standardized, and the volume collected was recorded. The volume of saliva collected was divided by the collection time to determine the salivary flow rate, which was recorded as mL/min. Immediately after collection, the pH of the saliva was measured using a calibrated digital pH meter. Measurements were performed on the instrument after it had been calibrated as per the manufacturer's instructions. Microbial samples were collected from unstimulated whole saliva by providing a sterile container and then promptly sent to the microbiology laboratory under proper conditions. Oral microbial count was estimated by serial dilution and culture on suitable non-selective agar media after incubation under standard laboratory conditions. Colony-forming units (CFU/mL) were quantified. Standard microbiological identification procedures were employed, if necessary, with representative colonies. The same protocol was used in all laboratories to evaluate the same prosthetic groups. SPSS version 26 was used for data collection and analysis. All of the study variables were analyzed for descriptive statistics. The Shapiro-Wilk test was used to check for normality of continuous variables such as age, duration of prosthesis use, pH of the saliva, flow rate of the saliva, and microbial load. Continuous variables were presented as a mean ± standard deviation, and non-normally distributed variables were presented as the median and interquartile range. Categorical variables were described in terms of frequencies and percentages. The difference in the mean salivary pH and salivary flow rate between the two groups was evaluated by an independent-samples t-test for normally distributed data and by the Mann-Whitney U test for non-normally distributed data. The distribution of the data allowed comparison of oral microbial load between the two groups. Categorical variables were analyzed using the chi-square and fisher's exact test. A two-sided p-value <0.05 was considered statistically significant.

A total of 114 patients were included in the study, half with conventional complete dentures and half with the implant-supported overdenture group. Demographic characteristics, the duration of edentulism, the duration of prosthesis use, and denture cleaning practices were not significantly different between the two groups. No statistically significant differences were found between the two groups in terms of their demographic characteristics, duration of edentulism, duration of prosthesis use, frequency of prosthesis use, or denture cleaning practices. The clinical and prosthetic parameters were also quite similar in both groups (Tables 1 and 2).

The salivary profile was much better for those who used implant-supported overdentures. There was a significant difference in both salivary pH and unstimulated salivary flow rate between the prosthetic groups. The number of participants with low unstimulated flow was also significantly larger in the conventional complete-denture group (Table 3).

The oral microbial assessment showed a significant difference between the two groups, with the implant-supported overdenture group having less microbial burden overall. The incidence of high microbial load was also significantly different among the groups (Table 4).

There were significant relationships between denture hygiene practices, denture wearing practices, and microbial outcomes. The individuals who had a moderate or poor denture hygiene and who wore their dentures while sleeping had higher numbers of microorganisms. Significant differences were found in salivary pH and microbial load with overnight prosthesis use, while the duration of daily prosthesis use was significantly associated with the microbial load, but not with salivary pH (Table 5).

The salivary and microbiological parameters showed significant correlations. Salivary flow rate was inversely proportional to the microbial burden, and salivary pH was also inversely correlated with the microbial load. There was a positive correlation between salivary pH and flow rate (Table 6).

Table 1. Demographic and baseline characteristics of study participants

Table 2. Clinical and prosthetic characteristics of participants

Table 3. Comparison of salivary parameters between the two prosthetic groups

Table 4. Comparison of oral microbial load between the two groups

Table 5. Association of prosthetic and behavioral factors with salivary and microbial outcomes

Table 6. Correlation of salivary parameters with oral microbial load

The present study found that patients with ISODs had significantly higher mean salivary pH and salivary flow rate and significantly lower total oral microbial load than CCD patients. Poor denture hygiene, long-term wearing of the denture, and overnight use of the denture were also related to increased microbial load. The salivary environment has also been correlated with microbial load; a significant inverse relationship was seen, which may indicate that the salivary environment could play a role in microbial control in edentulous denture wearers. The significantly higher salivary pH in the ISOD group (7.08 ± 0.18 versus 6.94 ± 0.22; p<0.001) indicated a better oral chemical environment for the implant-supported overdenture patients. The clinical significance of this finding is that saliva buffers and has antimicrobial properties, and changes in the physicochemical features could affect microbial colonization. In 2022, Madana et al. conducted a randomized clinical trial to compare the mean salivary pH levels of conventional and Biofunctional Prosthetic System (BPS) complete dentures, with values of 6.94 ± 0.22 and 7.04 ± 0.12, respectively, which were not statistically different. The direction of the difference in their study was therefore similar to that found in the present study, and these differences were statistically significant, and possibly, the larger biological difference between the conventional denture and implant-supported overdenture was more likely due to two different conventional-denture designs.[15] The present findings may also be evaluated based on the review presented by Alshahrani et al., 2022, who highlighted that salivary pH, although an important parameter in the field of removable dental prostheses and denture-base materials, tends to be one of the parameters that are less studied. The review also revealed significant differences in the experimental conditions of pH in saliva and how this may affect prosthetic materials.[16] Therefore, the difference observed in the present study could be due to the fact that it may be related to the prosthetic design as well as the accumulation of oral biofilm, stimulation of saliva, prosthesis-mucosa interaction, and hygiene habits. In addition, unstimulated salivary flow rate increased significantly among ISOD users (0.48 ± 0.16 mL/min) vs. CCD users (0.39 ± 0.14 mL/min) (p=0.002). This result indicates that the implant-supported rehabilitation can have a more positive functional response for saliva. Previous clinical studies have shown that prosthetic rehabilitation affects salivary output, and more recent studies have consistently highlighted the role of saliva in complete denture wearers. A study published in 2023 that explored the effect of using a CPP-ACP product on salivary response to acid challenge in removable-denture wearers showed an improvement in salivary response to the acid challenge; however, there was no statistically significant increase in salivary flow.[17] While it was a different intervention than the one currently compared, it reinforces the idea that prosthodontic/denture factors can alter saliva. The most notable finding was the microbial material. In the present study, the median total microbial counts were significantly lower in the ISOD group than in the CCD group (p=0.003), with 68.4% of those with conventional dentures having counts >2 × 10⁶ CFU/mL, whereas only 40.4% of the ISOD group had counts >2 × 10⁶ CFU/mL. Recent literature has confirmed that the denture surface is another ecological niche for microbial adhesion and biofilm formation, which is consistent with the results obtained in this study. According to a 2023 study assessing removable dental prostheses, Candida albicans, Staphylococcus aureus, and Streptococcus spp. were frequently isolated from the prostheses, with C. albicans found in 63.3% of samples. The authors were also able to observe that microorganisms can take up residence on prostheses within a relatively short period of use, and stressed the need for oral hygiene to control the growth of microorganisms.[18, 19] The lower microbial burden in the ISOD group was also confirmed by the results of the geotextiles in the study by Zhao et al. (2024) who specifically studied the microbial biomass on implant-supported overdenture surfaces. Their experimental investigation showed that the adhesion ability was different depending on the type of attachment, and some of the attachment systems exhibited higher adhesion and were harder to clean. The lowest biomass residues occurred when both ultrasonic and chemical cleaning methods were used. The present results are significant when considering the findings presented above, as these suggest that implant-supported overdentures are not necessarily microbiologically superior and that the microbial profile of overdentures can be influenced by the design of the prosthesis, the type of attachment, the surface characteristics, and the cleaning method.[20] In the same way, a 2023 pilot study conducted by Veseli et al. compared the levels of red-complex bacteria in completely edentulous patients that were obtained before and after the denture was inserted. The study was able to show that the introduction of a removable prosthesis (rehabilitation of the denture) had an influence on the oral bacterial environment, which supports the theory that the oral microbiota of the edentulous mouth is altered by the introduction of a removable prosthesis. The present study goes further by comparing two types of prosthetic rehabilitation instead of analyzing the changes in microorganisms before and after insertion of the conventional dentures.[20] In recent years, evidence has been accumulating that the changes in the microbial ecosystem caused by dentures are not due to any one microbe. In a 2025 systematic review and meta-analysis of 32 studies, the authors found that the oral microbiome of denture wearers varies depending on their edentulous status, denture material, denture design, and length of use. Progressive changes were also observed in Candida albicans, Streptococcus mutans, etc., during long-term use of dentures, and a dysbiosis of microorganisms was reported in denture stomatitis. These findings are in line with the present finding of an association of more microorganisms with a long period of prosthesis use and poor hygiene.[21] The general results indicate that implant-supported overdentures showed higher salivary pH, unstimulated salivary flow, and lower microbial load than the conventional complete dentures. Critically, the findings also showed that factors related to the prosthesis and patient practice, such as the care of the dentures and overnight wearing, were linked to the microbial outcomes. The observations are in line with recent studies that highlighted the effects of denture design, attachment configuration, surface characteristics, hygiene, and length of time in use on microbial colonization. The present study, however, involved a comparative cross-sectional study design; therefore, the results must be interpreted as associations and not as evidence that the use of implant-supported overdentures leads to an improvement in salivary physiology or microbial load. Further longitudinal studies involving species-specific culture or 16S/metagenomic sequencing methods would be able to identify if these findings are indicative of stable biological effects of the design of a given prosthetic or if the differences are more driven by hygiene, type of attachment, duration of use, and patient-related factors. There were several limitations to the study. The cross-sectional design precluded the ability to determine the causal association between the type of prosthesis and alteration of salivary or microbial variables. The research was carried out in one dental institution and may not be applicable to other populations. Selection bias could have occurred with the use of consecutive sampling. Differences in individual bacterial or fungal species could not be determined as the microbial load in the mouth was assessed using the total number of colony-forming units (CFU). Even after the exclusion criteria were applied, dietary habits, oral hygiene, systemic conditions, medication, duration of prostheses use, and attachment design might have affected salivary parameters and/or microbial load. Lastly, the relatively brief study period and small sample size could have restricted the identification of smaller differences between groups.

Salivary pH and flow rate were found to be significantly higher, and overall oral microbial load was lower in implant-supported overdenture users compared to conventional complete-denture users. Poor denture hygiene and overnight denture use were also related to higher microbial burden, and vice versa; higher salivary flow was related to lower microbial load. The results indicate that prosthetic rehabilitation can have a biological effect on the oral environment, as well as a functional effect. Longitudinal multicenter studies incorporating species-specific microbial analysis are warranted to clarify these associations.