Oral stereognosis is defined as the ability to sense the form or shape of an object in the mouth by means of touch. ¹ Oral perception can be evaluated by oral stereognostic ability (OSA) which is widely used in many studies reported in the literature. ¹ Grossman ¹ was probably the father of this concept and paved the way to assess oral perception by means of stereognosis tests.

OSA score is a good yardstick to infer the oral perception of the patients. It has a direct relationship with denture performance. High score in OSA indicates that the complete denture wearers could perceive full and accurate information about what is going on in his mouth and could exhibit more complaints in the postinsertion phase. Most importantly, the patient knows where the foreign body and what is doing so that they can control it properly. Low score indicates their perception about anything to their mouth and patients have fewer or no complaints in the insertion phase. ¹ , ²

Much work had been done in the past in studying the OSA of complete denture wearers with respect to age, gender, duration of edentulism, and satisfaction with denture using several methods. ³ However, the effect of systemic diseases, particularly diabetes mellitus, has not been evaluated yet with OSA of complete denture wearers.

The common problems observed with diabetic patients are reduced salivary flow and/or xerostomia, altered saliva composition, inflammation, loss of sensation, changes in taste perception, numbness, burning mouth syndrome, and lesions of oral mucosa and tongue. ⁴ It is widely assumed that diabetic neuropathy and microcirculatory disturbances also lead to alterations, particularly sensations in the oral cavity. Histopathologic and histochemical changes also occur in the denture bearing mucosa that supports masticatory pressure. ⁵

Due to prolonged diabetics, the complete denture wearers may be greatly affected by clinical challenges such as denture adaptation problems and lack of awareness of developing ulcers. ⁵ However, to date, there is no comprehensive study available in literature to measure the OSA in diabetic complete denture wearers.

The objective of the present study is to compare the OSA in diabetic and nondiabetic complete denture wearers. The null hypothesis was there is no difference in OSA between diabetic and normal subjects.

In this in vivo study comprised of seventy edentulous subjects (thirty six males and thirty fourfemales), aged from thirty five to eighty four rehabilitated with complete dentures, at the Department of Prosthetic Dentistry of Rajah Muthiah Dental College and Hospital, Annamalai University, Chidambaram. Among them, thirty five were diabetic complete denture wearers and thirty five subjects were nondiabetic complete denture wearers. All complete dentures were fabricated and inserted by the postgraduate students of our department. They had an average denture wearing experience of >3 months at the time of the study. All patients who visited the clinic for a recall appointment were examined. The patients chosen were free from acute or chronic pain that might relate to the stomatognathic apparatus, without lesions of the oral mucosa, or problems of a neuromuscular nature. All subjects gave written informed consent for participation in this study. The following information about the patients was obtained such as age and sex, duration of the period of edentulism, number and wearing period of dentures, blood glucose level, and duration of diabetes and associated diseases.

For assessing OSA, tests were conducted following the method of Garrett et al. ⁶ and Hirano et al. ⁷ The test pieces comprised of 12 shaped forms, which included circle, ellipse, semicircle, square, rectangle, and triangles of both large (12 mm × 12 mm × 3 mm) and small (8 mm × 8 mm × 2 mm) sizes. ⁷ The test pieces were prepared with base plate wax corresponding to each shape. Their size was verified with the digital vernier caliper (zoom digimatic caliper) and processed by clear acrylic resin (DPI-RR cold cure, Dental Products of India, a division of the Bombay Burmah Trading Corporation Limited, Mumbai, India, ISO 9001; 2008 certified) with intrinsic staining. Twenty sets of test pieces were prepared and these were disinfected with 2% glutaraldehyde solution after each use.

The test was carried out in a quiet environment where the subject was seated comfortably in an upright position. The test pieces were kept out of the subjects' sight during the test. Before the OSA test, the procedures were explained to the subjects and the enlarged pictures of all test pieces were shown to them on a chart, and they were instructed to point out the corresponding picture for each shape at the time of testing. Subjects were told that they should use their tongue and palate to identify the shape. The object was placed on the middorsal surface of the tongue by tweezers Figure 1. They were instructed to respond as quickly as possible and to avoid biting on the test pieces and pushing it against the lips and cheeks. To prevent learning effect, no practice trials were held. The test was done with and without denture for each patient Figure 2. Each of the 12 pieces was presented twice. The 24 presentations were made in random order, and the same order was used for each test. Participants were not informed of the correct answers at any point during testing. Figure 1

Test pieces kept in mouth – with denture.

In this study, diabetic complete denture wearer got the mean OSA score of 12.43 ± 3.93 without dentures, which was lower than nondiabetic complete denture wearer group (14.82 ± 4.44). When comparing these groups, there was a significant difference (P = 0.020*) in the identification of test pieces. With dentures also, diabetic complete denture wearer got the mean OSA score of 13.89 ± 4.04, which was lower than nondiabetic complete denture wearer group (15.71 ± 5.39). However, it was not statistically significant (P = 0.269).

Diabetic complete denture wearer group took less mean time for the identification of all shapes with denture (100.73 ± 42.99 sec) than the nondiabetic denture wearer group (109.00 ± 43.12 sec), which was not statistically significant (P = 0.424). Without dentures also, there was no significant difference between these groups (P = 0.583).

In this study, diabetic complete denture wearers showed lower OSA score than nondiabetic complete denture wearer. This finding substantiated the fact that the diabetic subjects possess altered sensation due to diabetic neuropathy and microcirculatory disturbances which may be predisposed to clinical challenges such as denture adaptation problems. This would also emphasize on the amount of care required for the fabrication of dentures to the diabetic complete denture wearers. It was also found that the diabetic complete denture wearers showed statistically significant difference in OSA score while not wearing dentures (P = 0.020*) Table 1. Even though the diabetic denture wearers obtained lower OSA scores than nondiabetic denture wearers with dentures, it was not statically significant. This was due to wide variation in the denture wearing period of the sample group studied and smaller sample size.{Table 1}

However, Shinkai et al. ⁵ found that the diabetic subjects showed slightly superior intraoral sensitivity compared with nondiabetic adults at the posterior tongue and soft palate sites, which was not significant statistically.

In this study, the overall OSA score of both diabetic and nondiabetic complete denture wearers' groups without dentures was lesser than with denture Table 1. For edentulous subjects, the oral sensorimotor function may be influenced by the quality of dentures and denture-wearing period because they lose their teeth and the sensory endings within the periodontal tissues that play a fundamental role to recognize foods. In this study, denture wearing improved the OSA score like Ikebe et al. ⁹ However, Mantecchini et al. ³ reported that more score was obtained by the subjects without dentures. Oral discrimination depends primarily on the anterior lingual area. Covering the palate with denture may exclude the palatal mucosa from sensorial mechanism. So by practice, complete denture wearers may use this as rigid support against which the tongue can manipulate the object to be identified.

In this study, nondiabetic complete denture wearers needed more time than diabetic complete denture wearers to identify test pieces Table 2. This might be a factor ascribed to personal character as well as oral sensorimotor ability to determine the response time. Without dentures, both groups needed more identification time than with dentures (104.1 ± 53.4, 111.1 ± 52.7, and 100.72 ± 42.9, 109.00 ± 43.12) like previous studies done by Ikebe et al., ⁹ van Aken, ¹⁰ Mantecchini, ³ and Garret et al. ⁶ This is thought to be the result of a sudden change in the oral environment.{Table 2}

As reported previously by van Aken ¹⁰ and Mantecchini, ³ large test pieces showed higher OSA score than small pieces Table 3while wearing dentures in both diabetic and non diabetic groups. However in subjects without dentures the OSA scores were similar with large and small test pieces in both diabetic and non diabetic groups. Both diabetic and nondiabetic complete denture wearers needed more identification time for larger shapes than small shapes Table 4. Hirano et al. ⁷ also found the same results except for triangles.{Table 3}{Table 4}

In this study, test pieces of different sizes measuring 12 mm × 12 mm × 3 mm and 8 mm × 8 mm × 2 mm, with different shapes such as square, rectangle, circle, semicircle, ellipse, and triangle were used. The selected shapes in this study provided sufficient difficulty, which was evident from a wide range of discrimination among complete denture-wearing groups. Only one nondiabetic subject could identify all test pieces correctly. None of the diabetic complete denture wearer correctly identified all shapes. Highest score of diabetic complete denture wearer with and without denture was twenty two. This would suggest that the test was valid.

We recorded the health status of all diabetic and nondiabetic complete denture wearers. While ten of them in diabetic complete denture wearers group and five of them in nondiabetic complete denture wearers had hypertension and take a daily medication. In nondiabetic complete denture wearers, two asthmatic patients and one cardiac patient in diabetic complete denture wearers were found. However, there was statistically no significant difference in OSA score or response time was found relative to chronic general diseases in this study population like Shinkai et al. ⁵

From the results of this stereognosis tests with and without complete dentures, we found that correct rehabilitation is a determinant in improving the OSA in edentulous patients. Litvak et al., ¹¹ Garrett et al., ⁶ and Ikebe et al. ⁹ found an enhancement of stereognostic ability in denture wearers with their dentures in place. Grossmann ¹² reported that oral discrimination depends primarily on the anterior lingual surfaces, whereas the mucosa covering the hard palate acts mainly as a rigid support against which the tongue can manipulate the object to be identified. However, Mantecchini ³ found increased OSA score in patients without denture.

Limitation of the study

We used a relatively small number of convenient individuals who were healthy and able to visit a clinic by themselves. Consequently, the results reported here may be specific to this study sample and should not be generalized until these associations have been confirmed in other studies of a similar population.

Similarly, studies are needed to investigate the process that reduced sensory function in diabetic complete denture wearers in a large population.

Within limitations of this study, diabetic complete denture wearers showed decreased OSA than nondiabetic subjects, particularly it was statistically significant while not wearing dentures. With this source of information, the dentist may educate the patient about the prognosis of the prosthesis, and we can mentally prepare the patient about its limitations.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Personally financed by the authors of the study.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or nonfinancial in this article.