Stabilization of mandibular complete dentures by four mini implants: Impact on masticatory function

Abstract

Objectives

The frequent instability of mandibular removable complete dentures causes an alteration of mastication. An innovative therapeutic strategy involves placing four symphyseal mini implants. This study aimed at assessing the development of masticatory parameters and the impact on quality of life in subjects that underwent this procedure.

Methods

Eleven edentulous subjects (mean age 72 ± 11 years) with unstable mandibular complete dentures were followed-up before (T0) and two − three months after (T1) mini implant setting. Physiological parameters (number of cycles, duration of sequence and frequency of mastication) during the mastication of food models and the bolus median particle size (d50) of carrot were evaluated at each time. Quality of life was assessed at T0 and T1 using the Global Oral Health Assessment Index (GOHAI). Parametric tests were used to test relationships between mastication, quality of life variations and mini implant setting, and to compare each parameter mean value at times T0 and T1.

Results

More subjects were able to chew carrot after setting the mini implants (8 subjects compared to 4 at T0). This improvement was accompanied by changes in kinematic parameters when chewing carrots, soft and hard model food, and by an improvement of their quality of life. However, the particle size values observed in the bolus remained higher than for normal dentate subjects (9.2 ± 2.8 mm).

Conclusions

These results indicated that the placement of mini implants as retentive elements for mandibular full dentures had a positive impact on patients’ masticatory function and quality of life.

Clinical significance

The placement of mini implants has a positive impact on the masticatory function and oral health quality of life. The results suggest that this alternative procedure can be used as a treatment option for patients unable to receive conventional implants.

Introduction

A report from the World Health Organization (WHO) in 2003 revealed that the prevalence of complete edentulous persons between the ages of 65 and 74 ranges from 12.8% to 69.6% in Europe . The trend toward more total tooth loss occurring later in life than in the past poses a major challenge for dentists.

Maxillary and mandibular complete denture is one of the treatments proposed for these edentulous persons. However, most subjects wearing such dentures complain about the poor stability of their mandibular prosthesis . Tools such as the Geriatric Oral Health Assessment Index (GOHAI) questionnaire and the Oral Health Impact Profile (OHIP) questionnaire were used to determine that patients’ Oral Health Related Quality of Life (OHRQL) was particularly affected by problems of discomfort, change in eating habits, and avoidance of social interactions, to name but a few . Indeed, it has been shown that impaired mastication of denture wearers is similar to that of persons with neuromotor deficiencies . Furthermore, Mishellany-Dutour et al. reported that ageing and tooth loss hinder mastication that is not compensated by wearing a complete denture . In this context, placing implants can be proposed as an alternative treatment to stabilize the mandibular complete denture. The Mc Gill consensus prescribed the use of an overdenture supported by two implants as the minimal treatment for complete mandibular rehabilitation . However, this treatment option is limited in several populations due to medical, anatomical or/and economic reasons. Indeed, edentulous patients are often very old, toothless for a long time, subject to many diseases and the placement of two symphyseal implants is not always possible. Consequently, the dental unit of the University Hospital of Clermont-Ferrand proposes a new protocol for geriatric patients using four monolithic small implants (mini implants) to improve mandibular complete denture stabilization. However, the term “mini implants” used by some authors may have a negative connotation while the term “Narrow Diameter Implants” does not emphasize its specific use in geriatric patients. Therefore the term “Geriatric Slim Implant” (GSI), as proposed previously , seems more accurate regarding their use in this procedure. Previous studies showed a positive impact of GSI placement on patients’ perception of their oral quality of life, especially concerning oral function and comfort. However, the real physiological impact of this kind of rehabilitation on mastication has not been evaluated.

Mastication is considered as the first step in the process of digestion, giving legitimate importance to this function. A mastication sequence starts with the introduction of a piece of food into the mouth and ends with swallowing. The food is fragmented into small size particles and lubricated to form a plastic and cohesive bolus ready to be swallowed. Each mastication sequence is constituted by a succession of chewing cycles, formed by one jaw-opening movement followed by one jaw-closing movement, in a time course .

Mastication is considered as efficient when the individual can form a correctly reduced cohesive and viscous mixture ready to be swallowed . Previous studies showed that masticatory parameters can be evaluated using electromyography or video .

When using video recording, mastication parameters can be defined as the number of chewing cycles, chewing time, chewing frequency , and food refusal. Many factors, such as the type of food (size, hardness and rheological behavior) and the individual characteristics (age, gender, dental status) influence these masticatory parameters . It has been shown that healthy mastication is characterized by the ability of chewing to adapt to increasing food hardness. In healthy mastication, this adaptation results in an increased number of cycles and chewing time, without modifying chewing frequency . Adapting masticatory parameters to food hardness is an efficient means of assessing the level of chewing efficiency. Reductions of the number of residual teeth, occlusal force and salivary flow are risk factors for masticatory dysfunction in older adults . Impaired mastication leads to the alteration of the ability to disrupt the food matrix and to form the food bolus. Masticatory deficiency may be detrimental for general health with nutrient intake alterations and gastrointestinal disorders . Thus it is crucial to distinguish between subjects with normal mastication and those for which it is impaired. To do this, it is necessary to examine their masticatory performance, i.e. the capacity to reduce food in small particles suitable for swallowing. The evaluation of masticatory performance can be performed by analyzing food matrix disruption by the granulometric examination of a food bolus collected at the end of mastication when the desire to swallow is perceived . A previous study set the median particle size (d50) for the bolus of “raw carrot” test food at 4 mm, which is considered as the Masticatory Normative Indicator (MNI). This represents the cut-off value to produce a safe and easy to swallow bolus and is used to distinguish patients with normal mastication from those with impaired mastication .

The aim of this study was to evaluate whether the placement of GSI to stabilize mandibular complete dentures changes mastication parameters in terms of kinematics and improves bolus granulometry. The evolution of patients’ OHRQL before and after GSI placement was also assessed with a GOHAI questionnaire.

Material and methods

Study design

The prospective observational study was conducted at the Dental Department of the University Hospital of Clermont-Ferrand, France over a 3-year period (2012–2015), and was approved by the local Ethics Committee (CECIC- GREN-06-12).

Study sample

Edentulous patients received new maxillary and mandibular complete denture within the 6 months prior to this study. All new dentures, anatomical posterior teeth with 20° angle cusp manufactured by Ivoclar ® (SR Orthotyp PE) were used with bilateral balanced occlusion scheme. This occlusal scheme was employed because it provides comfort for the patient, protects tissues and improves retention. If they reported oral function difficulties following a prosthetic adaptation period, they were proposed for mandibular complete denture stabilization using GSIs 2.7 mm in diameter and 9–15 mm long made of grade V titanium from Eurotecknica ® . Implant rehabilitation consisted in the placement of four symphyseal GSIs using a flapless procedure, followed by immediate loading of the GSIs with the O-ring prosthesis attachment. The entire clinical protocol was previously described by Huard et al. . The initial complete denture became an implant-supported overdenture.

The following inclusion criteria were used: cooperating adult patient, able to understand and participate in the study, wearing new, adapted complete dentures with an unstable mandibular denture, and for whom rehabilitation with “standard implants” is not possible due to medical, anatomical or/and economic reasons. Patients who could not speak or read French fluently, with cognitive disability according to their medical questionnaire (in case of doubt, the MMSE (Mini Mental-State Evaluation) was used), and with no social security cover were excluded. Eleven subjects, nine women and two men, were included (mean age 72 ± 11 years) and assessed before and after GSI placement for their quality of life and chewing efficiency.

The number of subjects needed was estimated from a pilot study that showed 50% refusal for chewing the carrot sample before implant rehabilitation. No refusal was observed after implantation. Furthermore, the required number of subjects was calculated in unilateral comparison (procedure of comparing two observed proportions) (α = 5%, β = 10%). Calculations using the epiR package 0.9-30 indicated the need for 11 subjects (α = 5%, β = 10%).

Experimental design

With their new and adapted complete dentures, at T0 (before GSI placement) and at T1 (two or three months after GSI placement), each subject chewed and swallowed two samples of each model food (one soft and one hard) and three samples of raw carrot of which the first was swallowed for training and the following two were expectorated in a container when the subjects felt it was ready to be swallowed. In order to evaluate their Oral Health Related Quality of Life (OHRQL), each subject answered the GOHAI questionnaire at T0 and T1 ( Fig. 1 ). The subjects were evaluated at T1, two or three months after GSI placement, depending on their availability.

Fig. 1
Experimental procedure.

Assessment tools

Kinematic parameters of mastication

Masticatory function was assessed during the chewing of a model food (viscoelastic gel allowing standardization of the oral stimuli) and a natural food (raw carrot).

The model foods used were viscoelastic gels differing in hardness (one soft and one hard) but identical in size and shape (2 cm diameter, 1 cm thickness cylinders) prepared in the laboratory from commercially available sweets (Haribo “Les Schtroumphs”™) supplemented with increasing quantities of gelatin (Rousselot, 250 blooms, Degussa Texturant Systems, Baupte, France) and water.

Carrots were bought fresh at a local market and cut in cylindrical samples (2 cm diameter; weight 4 g ± 0.05) just before the experiment.

Kinematic parameters were evaluated before (T0) and after GSI placement (T1), by positioning a digital camera in front of the subject (face-on). The method had previously been validated for healthy fully dentate patients and for denture wearers . For each mastication sequence, the number of cycles (CC) and the chewing time (CT) were measured by an experimenter who viewed the video, and the number of food refusals (inability to chew the proposed food) was reported. Chewing frequency (CF) was calculated as the CC/CT ratio.

For each recording sequence, the subjects were asked to chew and swallow two samples of each model food (replicates) without changing their usual practice. Three samples of raw carrot were then presented for mastication, the first was swallowed and the two following samples were expectorated in a container when the desire to swallow was perceived. The two expectorated samples were stored at −20 °C until granulometric analysis and considered as replicates. During the chewing tests (4 model foods and 3 carrot samples), subjects could take a break and a glass of water when they felt fatigue. Subjects could have all the recovery time they needed between each mastication.

Granulometric analysis of raw carrot bolus

After gentle thawing at room temperature, the food bolus was rinsed with a hand shower in a 100 μm sieve to eliminate saliva, and placed in a drying-oven at 80 °C for 30 min. Dried carrot particles were spread onto a transparent A4 sheet that was scanned to produce a 600-dpi image (Epson perfection 4990 photo™). This image was processed to evaluate food particle size and distribution (Powdershape ® , Innovative Sintering Technologies, Switzerland) . For each food bolus, the results were expressed in terms of the d50 value, characterizing the theoretical sieve size that allowed 50% of the particles to pass through. Therefore the d50 value decreased as the food boluses contained more small particles. As defined in a previous study, subjects forming a food bolus of carrot with a d50 value higher than 4 mm are considered to have impaired mastication .

Oral health related quality of life

The French version of the GOHAI questionnaire was used to assess the subjects’ OHRQL . It was filled in before (T0) and after (T1) GSI placement.

This questionnaire provides a score based on the answers to twelve items grouped in three fields: the functional field (item 1–4), the psychosocial field (items 6, 7, 9, 10 and 11 concerns relational discomfort, and appearance), and the pain or discomfort field (items 5, 8 and 12 concern drugs, gingival sensitivity, and discomfort when chewing certain foods). A summary score (GOHAI-Add score) of each item (1 = always to 5 = never) was calculated.

The maximum GOHAI score is 60 (20 = functional field; 25 = psychosocial field; 15 = pain or discomfort field). In this study however, subjects did not reply to the 12th item relating to dental sensitivity to heat and cold because they were edentulous. The maximum score of 5 was therefore attributed to each subject for this item to obtain “adjusted GOHAI-Add” and “adjusted discomfort field” scores. According to Atchison et al. , a score between 57 and 60 is regarded as high and corresponds to a satisfactory OHRQL. A score from 51 to 56 is regarded as average, and a score below 50 is regarded as low, reflecting a poor OHRQL.

Statistical analysis

Statistical analysis was performed using SPSS ® (IBM, v20) software. Statistical significance was set at p < 0.05. After checking for the normal distribution of the data, parametric tests were used to obtain the results. For the subjects unable to chew the carrot sample, an indicative value was calculated for each mastication parameter (CC, CT, CF and D50) as follows: the average value of all the participants able to chew the carrot sample to which the standard deviation was added twice. Four indicative values were then obtained, one for each mastication parameter. All the values were expressed as mean ± SD.

To evaluate the impact of GSI placement on mastication parameters, the mean CC, CT and CF values measured during the mastication of model foods were compared at T0 and T1 using paired sample t -tests. The same analysis was performed for the carrot test food, including the d50 parameter.

The subjects’ ability to adapt to the different hardnesses of the viscoelastic gels was evaluated independently at T0 and T1, by observing changes in the mean values of CT, CC and CF using a paired t -test.

The mean values of the GOHAI-Add scores recorded before (T0) and after (T1) GSI placement were compared by the paired t -test.

The analysis of chewing efficiency by observing the number of food refusals (inability to chew the proposed food) was performed by a Wilcoxon test.

Material and methods

Study design

The prospective observational study was conducted at the Dental Department of the University Hospital of Clermont-Ferrand, France over a 3-year period (2012–2015), and was approved by the local Ethics Committee (CECIC- GREN-06-12).

Study sample

Edentulous patients received new maxillary and mandibular complete denture within the 6 months prior to this study. All new dentures, anatomical posterior teeth with 20° angle cusp manufactured by Ivoclar ® (SR Orthotyp PE) were used with bilateral balanced occlusion scheme. This occlusal scheme was employed because it provides comfort for the patient, protects tissues and improves retention. If they reported oral function difficulties following a prosthetic adaptation period, they were proposed for mandibular complete denture stabilization using GSIs 2.7 mm in diameter and 9–15 mm long made of grade V titanium from Eurotecknica ® . Implant rehabilitation consisted in the placement of four symphyseal GSIs using a flapless procedure, followed by immediate loading of the GSIs with the O-ring prosthesis attachment. The entire clinical protocol was previously described by Huard et al. . The initial complete denture became an implant-supported overdenture.

The following inclusion criteria were used: cooperating adult patient, able to understand and participate in the study, wearing new, adapted complete dentures with an unstable mandibular denture, and for whom rehabilitation with “standard implants” is not possible due to medical, anatomical or/and economic reasons. Patients who could not speak or read French fluently, with cognitive disability according to their medical questionnaire (in case of doubt, the MMSE (Mini Mental-State Evaluation) was used), and with no social security cover were excluded. Eleven subjects, nine women and two men, were included (mean age 72 ± 11 years) and assessed before and after GSI placement for their quality of life and chewing efficiency.

The number of subjects needed was estimated from a pilot study that showed 50% refusal for chewing the carrot sample before implant rehabilitation. No refusal was observed after implantation. Furthermore, the required number of subjects was calculated in unilateral comparison (procedure of comparing two observed proportions) (α = 5%, β = 10%). Calculations using the epiR package 0.9-30 indicated the need for 11 subjects (α = 5%, β = 10%).

Experimental design

With their new and adapted complete dentures, at T0 (before GSI placement) and at T1 (two or three months after GSI placement), each subject chewed and swallowed two samples of each model food (one soft and one hard) and three samples of raw carrot of which the first was swallowed for training and the following two were expectorated in a container when the subjects felt it was ready to be swallowed. In order to evaluate their Oral Health Related Quality of Life (OHRQL), each subject answered the GOHAI questionnaire at T0 and T1 ( Fig. 1 ). The subjects were evaluated at T1, two or three months after GSI placement, depending on their availability.

Jun 19, 2018 | Posted by in General Dentistry | Comments Off on Stabilization of mandibular complete dentures by four mini implants: Impact on masticatory function
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