A study of masticatory efficiency influenced by mandibular residual ridgeshape in complete denture wearers in south canara population

INTRODUCTION

The geriatric population has been growing rapidly over the last quarter of century and will increase further probably by at least one third within next 20 years.¹ Despite the advancements in the field of dentistry, 75% of the older persons around the world were using complete dentures in at least one jaw in last decade.²

Edentulism (partial or total) is an indicator of the oral health of a population. It may also be a reflection of success of various preventive and treatment modalities put in place by the health care delivery system. Many patients also regard edentulism as self-mutilating and may be a strong incentive to seek dental treatment. While the rate of total edentulism is decreasing in developed countries, the reverse is the case with developing countries and this had been attributed mainly to the high prevalence of periodontal disease and caries. Studies have also shown that several non-disease factors such as attitude, behaviour, routine checkup, characteristics of health care system and sociodemographic factors play important roles in the etiopathogenesis of edentulism. It is also reported that the incidence of edentulism correlated with educational levels and income status, with those in the lower levels exhibiting higher risks of becoming totally edentulous.³

Recent years have witnessed a shift from restorative orientation to a preventive approach. Many studies predicted that treatment of patients with complete denture would continue to decline in future. However, some very compelling points must be understood.2 Documented evidence reveals that despite projections of declining edentulism, the unmet need for complete denture treatment will remain high. Predictions from several surveys regarding a healthy elderly population indicate that a high percentage of older people will be edentulous. Therefore, the effective demand for prosthetic care for this population is likely to increase.

Clinical experience suggest that, the cumulative consequences of biological and chronological aging will likely confront the dentist with a significant increase in the number of difficult edentulous mouths that require treatment.¹ Dental prosthesis thus remains as an indispensable means for functional and aesthetic rehabilitation of an edentulous patient to improve his/her oral health along with the relative quality of life.⁴ However, the reduction in masticatory efficiency may lead to changes in dietary selection with risk of impaired nutritional status in the elderly complete denture wearers.⁵

One of the main treatment goals in dentistry is to achieve an acceptable masticatory function by restoration of natural teeth or the replacement of missing teeth. This treatment goal is considered to be the basis for proper digestion and absorption of nutrients. The maintenance of masticatory function for subjects who wear complete dentures is especially important because of the inherent limitations with these natural teeth replacements.⁶

Mastication is the first phase of the digestive process and it is considered as an essential function of the stomatognathic system. Chewing breaks down food that will be swallowed and digested. The effectiveness of the enzymatic processing of food depends on the mechanical breakdown of the food during chewing.⁷

Chewing requires muscular coordination to perform mandibular movements and generate enough force to cut, crush, and grind the food to keep it on the occlusal surface of tooth. As masticatory efficiency reduces, some patients avoid foods that are difficult to chew, including stringy foods like beef or steak, crunchy foods like raw carrots and dry, solid food like crusty bread. Patients with poor oral health status can as a consequence, suffer from impaired intake of fruits and vegetables, dietary fibre and some key nutrients.⁷

The impact of masticatory efficiency on food selection is likely to be compounded by food preparation. A person with reduced chewing capability may overcook or over prepare fresh foods (e.g., removing all skin from fruits and vegetables) to make them easier to eat. A wide range of nutrients are affected by these actions, including food constituents that are thought to be important for preventing cancer and cardiovascular disease (i.e., non-starch polysaccharides or dietary fibre) and for cellular defence and combating the effects of aging (i.e., the anti-oxidant micronutrient vitamins C and E).⁷

The masticatory efficiency in complete denture wearers is influenced by many factors. The factors can be grouped into two main categories: factors related to proper design and fit of prosthesis (denture related factors), and factors related to morphologic, physiologic, and psychological parameters (patient related factors).⁸

This study aimed to evaluate the influence of mandibular residual ridge shape on masticatory efficiency in complete denture wearers and to elucidate which factors regarding shape of the mandibular residual ridge (area, height, and volume) have the greatest influence on masticatory efficiency.

MATERIALS & METHODS

Twenty-eight complete denture wearers with age group 45-65 (mean age 55.75, Standard deviation 5.99;16 males,12 females) who received their complete dentures in the Department of Prosthodontics and Crown & Bridge, KVG Dental College and Hospital, Sullia, India and had no complaints in daily use were selected. Their period of edentulousness ranged from 6 months to 1 year. Dentures were with semi anatomic teeth in non-balanced articulation. Informed consent was obtained from all the subjects participating in this study.

Analysis of Shape of Residual Ridge: The mandibular residual ridge of each subject was evaluated by a replica of the mandibular ridge. Replica was obtained with silicone impression material (Aquasil soft putty/ regular set Dentsply, Germany) which was filled and rubbed off against the denture border onto the tissue surface of the subject’s mandibular denture (Fig 1). The basal seat area of each replica was measured by Cercon eye scanner (Degudent, Germany) (Fig 2). The volume and the height of each replica were also calculated using the formulas.

volume=Weight of replica / Specific gravity of impression material

height=volume / base area  ×2 basal area 

To compare the three parameters (basal area, volume, and height), the mean value of three parameters obtained from 28 replicas was represented by 100% respectively.

Measurement of Masticatory Efficiency: The masticatory efficiency in each subject was evaluated as follows. Each subject was instructed to masticate 3 g of peanuts 20 times on their habitual chewing side. This trial was repeated thrice. After specified number of chewing strokes, the chewed peanuts were expectorated into a collecting cup. The mouth was rinsed twice with water, and the rinsing was added to the cup. The denture was also washed and the particles were collected. The peanut particles collected were stirred with a glass stirrer to break up the clumps and then poured on a stalk consisting of 5-, 10-, 20-, and 40- sized mesh sieves. The particles which got collected in each sieve were transferred to different centrifugal tubes. The volume on each sieve was measured in centrifuge tubes after centrifugation for 3 minutes at 1,500 rpm. Masticatory efficiency was evaluated by the percentage of the particles that passed through the 5- sized mesh sieve.

masticatory perfomance% =volume of particles passing through 5-sized mesh sieve / total particle volume×100 

The results obtained from the above study were collected, tabulated and statistically analyzed using Karl Pearson’s coefficient of correlation.

RESULTS

The results of this study showed a very high significance between masticatory efficiency and basal area (r=.986, p<.001), volume (r=.896, p<.001) and height (r=.731, p<.001). (Table 1). Scattered diagram was plotted to show the correlation of masticatory efficiency percentage to basal area percentage, volume percentage and height percentage. It illustrated a positive correlation of all the three parameters (basal area, volume and height) to masticatory efficiency.(Fig. 3,4,5). When compared it was found that the masticatory efficiency was greatly changed by the value of basal area in comparison to the height and/or the volume (Fig. 6).

DISCUSSION

The shape of the residual ridge has an influence on the support and retention of complete dentures.² It is important to evaluate the denture foundation, which is defined as the oral structure available to support a denture, for predicting successful prosthodontics treatment,especially in complete denture wearers (GPT-8). The masticatory efficiency in complete denture wearers was limited by their own residual ridges.⁹

Masticatory function can be evaluated by questionnaires or personal interviews to assess an individual’s chewing ability, whereas clinical mastication tests can provide information about efficiency and performance. Questionnaires had been used in several epidemiologic surveys.⁶ Studies that used questionnaires or interviews for the assessment of masticatory function lack the necessary objectivity for repeatability and validity. Variation among subjects was a drawback with this method. An index system would possibly ease such problems and permit the assessment of the patient’s comfort or discomfort during mastication and speech. In turn, a questionnaire would allow the patient to judge comfort or discomfort when chewing. The use of a scale would be used with the highest value representing a very good, subjective feeling of comfort when chewing, whereas the lowest value would indicate discomfort or great difficulties in chewing. A universally accepted approach is needed for investigators and clinicians to evaluate masticatory function by questionnaire method.⁶

The objective evaluation of masticatory function is possible with chewing tests, and this approach was used effectively by investigators as the method is standardized. Fractional sieving as a technique of separating the food after chewing for a given time period has been used since 1924, and is still considered to be a viable method.⁶ The test foods have varied widely in chewing tests and have included artificial food such as standardized sizes of formalin-hardened gelatin, round tablets of silicone impression materials, and various natural foods. Japanese investigators often use a special fishcake called “Kamaboko”, whereas American and European investigators have preferred peanuts, almonds, and carrots. Ham, coconut, pineapple, olives, lettuce, apples, rice were used by some investigators.⁶

For this study each subject was instructed to masticate 3 g of peanuts 20 times on their habitual chewing side, and all particles were then collected in a cup. This trial was repeated three times, and all particles were sieved by 5-, 10-, 20-, and 40- size mesh sieves. The volume on each sieve was measured in a centrifuge tube after centrifugation for 3 minutes at 1,500 rpm. Masticatory efficiency was calculated by the percentage of the particles that passed through the 5- sized mesh sieve.⁹

Graphical methods were used earlier to find the surface area of the residual ridge.10 In this method extension of denture base was marked on the cast and scrapped. A rubber-based impression material is placed on the cast and once it sets it is removed from the cast and placed on a graph paper and outline is marked. The squares included in each outline were counted and the area is found out in square inches. But this method is time consuming and the conversion of a three-dimensional body onto a two-dimensional graph sheet may not be always accurate.¹¹

Most often, mandibular atrophy and residual bone are measured and classified on the basis of radiographic analysis.⁹ Soft tissue morphology and structure may be as important as bone shape in edentulous patients. Wical and Swoope reported the use of panoramic radiographs for evaluation of the mandibular residual ridge. However, it is difficult to determine the soft tissue morphology from radiographic evaluation. Hence evaluation in their method is limited only to one part of the mandible and merely represents the height of the residual ridge.¹²

In the present study the mandibular residual ridge of each subject was evaluated by a replica of the ridge that was obtained with silicone impression material filled and rubbed off against the denture borders in the tissue surface of the denture. The basal area of each replica was measured by a CAD scanner system (Cercon eye scanner). The volume and the height of each replica were also calculated. By this method the whole denture foundation and the area, height, and volume of the residual ridge can be evaluated. To discuss the influence of the shape of the residual ridge on masticatory function in complete denture wearers, it is necessary to obtain the maximum area of the residual ridge without interfering with the health of the tissues.⁹

The results obtained from the study were statistically analysed using Karl Pearson’s coefficient of correlation to estimate the correlation between masticatory efficiency and shape of mandibular residual ridge (basal area, volume and height).

Total 28 subjects participated in the study; 16 males and 12 females. While analysing the result for all 28 subjects in total, significant correlations were observed between masticatory efficiency and basal area (r=.986, p<.001), volume (r=.896,p<.001) and height (r=.731, p<.001). While comparing correlation of basal area, volume and height to masticatory efficiency it was found that the masticatory efficiency was greatly changed by the value of basal area in comparison to the height and/or the volume.

In this study significant correlations were observed between masticatory efficiency and basal area (r=.986, p<.001), and masticatory efficiency and volume (r=.896,p<.001). This result supports thestudy done by Koshino et al9 comparing the mandibular residual ridge shape and masticatory ability in complete denture wearers by questionnaire method which showed statistically significant correlation between the basal area of the residual ridge and the masticatory score (r=0.366, p<0.01), and also the volume of residual ridge and masticatory score (r=0.314, p<.01).

Another study by Koshino et al to find the influence of mandibular residual ridge shape on masticatory efficiency in complete denture wearers by sieving method showed significant correlations between the masticatory efficiency and the measurements of the basal area (r =.64; P < .01), the volume (r = .49; P < .01), and the height (r = .39; P <.05) represented by percent, respectively.¹² While comparing correlation of basal area, volume and height to masticatory efficiency it was found that the masticatory efficiency was greatly changed by the value of basal area in comparison to the height and/or the volume.¹² This result is in accordance with results obtained from our study.

Hirai T in his study showed that there was no significant correlation between residual ridge height using panoramic radiographs and masticatory performance using the sieving method with peanuts. This result was contradictory to the present study, were a significant correlation (r=.731, p<.001) was obtainedbetween masticatory efficiency and basal ridge height.¹² This difference might have occurred because it was difficult to determine the soft tissue morphology from radiographic evaluation. Evaluation by panoramic radiograph method is limited only to one part of the mandible and merely represents the height of the residual ridge. On the other hand, method used in present study can evaluate the whole denture foundation and the area, height, and volume of the residual ridge without interfering with the health of the tissues.

CONCLUSION

Within the limitation of this study it can be concluded that,

• There is a significant correlation between the masticatory efficiency and basal area of mandibular residual ridge.
• There is a significant correlation between the masticatory efficiency and volume of mandibular residual ridge.
• There is a significant correlation between the masticatory efficiency and height of the mandibular residual ridge.
• The basal area showed the strongest correlation than volume and height to masticatory efficiency