The Influence of Maximum Bite Force on Patient Satisfaction and Quality of Life of Patients Wearing Mandibular Implant Overdentures

Retention and stability problems of the mandibular complete dentures often cause complaints of oral function in edentulous patients. Mandibular implant overdenture treatment is a successful treatment modality in this group of patients. Older individuals would even prefer an implant-supported overdenture to implant-supported fixed prostheses if given the choice.^1,2  This clearly indicates that implant-supported overdenture treatment should not be considered a substandard treatment, and mandibular 2-implant supported overdentures opposing conventional complete maxillary dentures have been proposed as the standard of care for edentulous patients.³  Improvement of oral function after implant support not only eliminates the movement of the mandibular denture; in addition, the bite force magnitudes of subjects with mandibular implant-supported overdentures have been found to be 60%–200% higher than those of subjects with conventional complete dentures.^4–6  Patient desire for improved masticatory function is often given as one of the primary reasons for treatment with implant-supported dentures.^5,6 

The most commonly used measure for assessing the impact of dental treatments on quality of life is the Oral Health Impact Profile (OHIP), which is a disease-specific measure of an individual's perception of the social impact of oral disorders on their well-being. Its validity and reliability have previously been established.^7–9  The full-length OHIP consists of 49 questions covering 7 domains: functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability, and handicap.¹⁰  The OHIP-14, a shorter and patient-friendly version, consists of 14 questions in the same domains.¹¹  Responses for each item are on a 5-point Likert scale (0 = “never” to 4 = “very often”). Lower scores represent higher oral health–related quality of life (OHRQL).

It has been clearly established that implant-supported mandibular overdentures have more positive outcomes in terms of general satisfaction and OHRQL than conventional complete dentures, although the magnitude of the effects remains uncertain.¹²  The present study was conducted for assessing the effect of maximum bite force (MBF) on patient satisfaction and OHRQL of edentulous patients treated with mandibular implant-supported overdentures.

This retrospective study sample involved edentulous patients rehabilitated with implant-supported mandibular overdentures at a university clinic between 2004 and 2007. Patient inclusion criteria were as follows: absence of any systemic disease that was likely to compromise implant outcome, absence of obvious signs of bruxism, and ability to read and sign the informed consent.

Sixty-two patients who fulfilled the inclusion criteria and agreed to participate were enrolled (32 females, 30 males; average age: 64.03; range: 42–90 years). The patients provided informed written consent with regard to treatment and measurement procedures, and approval from the university ethics commission was duly obtained. Patients were wearing various types of mandibular overdentures supported by 2 implants with ball or locator attachments, 3 implants with ball or bar attachments, and 4 implants with bar attachments. A clinical examination, including evaluation of prosthetic parameters such as occlusion, tissue adaptation, and condition of the retentive mechanism, was performed by 2 qualified prosthodontists who were blinded to the treatment. If the denture base adaptation was not acceptable, a relining was performed. Occlusion was checked for premature contacts due to wear and eliminated. Loosened abutments or occlusal screws were tightened. Loosened retentive mechanisms were either changed or tightened. In case of corrections, the patients were required to use their dentures for an extra 1-month period prior to measurements.

After the previously mentioned corrections were finished, MBF was measured bilaterally by the same examiners, in the first molar region, using a device with 2 strain gauges (Measurements Group Inc, Micro-Measurements Division, Type EA-06-125MW-120, Raleigh, NC) connected to a strain gauge measurement system (Vishay Micro-Measurements, Strain Indicator and Recorder, Model P3, Serial 159 606, Raleigh, NC; Figure 1). The measurement was repeated 3 times for each of the left and right sides (Figure 2). The highest values were recorded while patients were biting as hard as possible, as instructed; the mean of the left- and right-side values was taken as 1 value. A 10-minute relaxation period between each bite was required in order to obtain a reliable MBF value. It was important to determine whether the dentures caused pain during biting and to eliminate any pressure spots in order to avoid diffidence on the part of patients.

After the MBF measurements, the subjects were asked to grade their mandibular overdentures on a visual analog scale (VAS) ranging from 0 to 100 mm^13,14 on 2 separate factors: general satisfaction and chewing satisfaction. Each subject was asked to place a dot on the scale. The higher the score, the more satisfied the subject.¹⁵ 

Additionally, all subjects were asked to complete the Turkish version OHIP-14, which had been determined to be valid and reliable.¹⁶  Each subject was asked to place a dot on the 5 categories of response for every 14 items, which were “never, hardly ever, occasionally, fairly often, and very often.” Items were scored on 5-point scales ranging from 0 = “never” to 4 = “very often.” Achievable OHIP-14 scores ranged from 0 to 56, and lower scores represented higher OHRQL.^10,11 

For the statistical analysis of the results, the NCSS (Number Cruncher Statistical System) 2007 and PASS 2008 Statistical Software (Kaysville, Utah) were used. The Spearman rho test was used to determine the correlations between OHIP scores and MBF and between VAS scores and MBF.

The correlation of VAS and OHIP scores with MBF values of 62 patients treated with implant-supported mandibular overdentures opposing full maxillary dentures (32 females, 30 males; average age: 64.03; range: 42–90 years) have been evaluated in this study.

The MBFs of patients ranged from 60.5 to 305 N (mean 137 N). VAS general satisfaction scores ranged from 10 to 100 (mean 90.5), whereas chewing satisfaction scores ranged from 44 to 100 (mean 90.5). OHIP scores ranged from 0 to 28 (mean 5.6). All the obtained VAS and OHIP scores together with the MBFs are presented in the Table.

No statistically significant correlation was found between MBF values and VAS general and chewing satisfaction scores (P = .748 and .777, respectively). These correlations are shown in Figures 3a and 3b. The correlation between OHIP scores and MBF values was also found insignificant (P = .801; Figure 3c).

Mastication is very important for the improvement and preservation of general health status, especially in elderly people.¹⁷  MBF is 5–6 times greater in the dentate subjects than in the complete denture wearers.¹⁷  Edentulous persons are very handicapped in masticatory function, and even clinically satisfactory complete dentures are poor substitutes for natural teeth.¹⁸  The efficacy of dental implants for the rehabilitation of edentulism in terms of MBF has been well documented in previous studies.^4–6,15,19  This study was conducted to investigate the possible effect of MBF values obtained from implant-supported mandibular overdentures on patient satisfaction and life quality. This issue has received little attention in the literature.

In the present study, we were unable to find a positive correlation between bite force magnitudes and general satisfaction, chewing satisfaction, and life quality scores in the 60–305-N MBF range. Subjective measures like patient satisfaction and quality of life have been shown to be multifactorial, and the lack of correlations established in this study indicates that raising the bite force magnitude does not necessarily create more satisfied patients or increase the quality of life. Closer inspection of the literature about the correlation between patient satisfaction and MBF has shown dissimilar results.^15,20,21 

Rismanchian et al²⁰  found a positive correlation between bite force magnitude and patient satisfaction in a cross-sectional study of 75 patients comparing the bite forces of complete denture and implant-supported mandibular overdenture wearers. Lassila et al,²¹  in a study of 89 patients comparing the bite forces of 3 denture groups (which did not have implant support), concluded that satisfied patients had a higher bite force than dissatisfied ones only in the group of complete denture wearers. In both of these studies, the examined groups involved complete denture wearers who were not highly satisfied with their dentures. It is well known that patients who undergo mandibular implant overdenture treatment are more satisfied than patients who receive conventional complete dentures without implant support.^1,2,7  This may be the reason why we achieved contrary results. Most of the patients in the present study showed high satisfaction scores (Table). In a crossover clinical trial comparing the MBF and patient satisfaction of 3 different implant attachment types on 18 subjects, Cune et al¹⁵  was not able to find a correlation between MBF and patient satisfaction, which is in agreement with our results.

It should be noted that in the present study, all the involved patients reported high satisfaction as well as quality-of-life scores, which could have masked a possible association just like in the study of Cune et al.¹⁵  When all the satisfaction scores are high, it is not possible to draw reliable conclusions on correlations. A high degree of individual variance in MBFs was observed in the present study (60.5–305 N), which is in accordance with the results of van Kampen et al.¹⁹ 

The uniqueness of the present study is the evaluation of the influence of MBF not only on general satisfaction like the previously mentioned studies^15,20,21  but also on chewing satisfaction and quality of life. One notable finding is that the patient with the highest MBF showed the lowest general satisfaction score in the present study (Table). General satisfaction scores depend not only on chewing ability but also on esthetics and expectations of the level of retention for implant-supported overdentures.^21,22  It is valuable to analyze the possible effect of MBF on chewing satisfaction in addition to general satisfaction, which was performed in the present study.

Furthermore, the previously mentioned studies^15,20,21  referred to the influence of MBF on patient satisfaction as additional information. However, this study was conducted solely to examine the effect of MBF on life quality and patient satisfaction. Besides, as far as the authors know, this is the first report investigating the effect of MBF on the life quality of mandibular-implant supported overdenture wearers.

In conclusion, generally high scores of satisfaction and life quality from mandibular implant-supported overdenture wearers were observed across the entire range of MBF values. Therefore, we do not have evidence of an association between MBF and patient satisfaction or between MBF and life quality.

MBF

maximum bite force

OHIP

oral health impact profile

OHRQL

oral health–related quality of life

VAS

visual analog scale