Single mandibular implant study (SMIS) − masticatory performance − results from a randomized clinical trial using two different loading protocols

Abstract

Objectives

This multi-centre randomized controlled trial was conducted to investigate, whether the masticatory performance of elderly edentulous patients is improved by placement of a single implant in the midline of the edentulous mandible, and whether improvements differ with respect to the loading protocol, i.e., implant is loaded either directly or three months later after second stage surgery.

Methods

Edentulous seniors aged 60–89 years were screened according to inclusion and exclusion criteria and 163 underwent implant placement. Of those, 158 were randomly assigned either to the direct loading group A (n = 81) or the conventional loading group B (n = 77). Chewing efficacy was obtained before treatment, one month after implant placement during the submerged healing phase (only group B) and 1 and 4 months after implant loading.

Results

The masticatory performance increased over time in both groups. Four months after loading, a significant increase was observed for both groups compared to the baseline data without implant (p ≤ 0.05). However, between the two groups, chewing efficiency did not differ significantly at any point in time (p > 0.05).

Conclusions

A single midline implant in the edentulous mandible increases masticatory performance significantly, independently from the loading protocol.

Clinical significance

A single midline implant in the edentulous mandible increases masticatory performance. The loading protocol has no influence.

Introduction

Many edentulous patients are very dissatisfied, especially with their complete mandibular denture, and complain about insufficient stability . Masticatory performance with complete dentures is reduced to between one-forth and one-seventh compared to adults with a natural dentition . Complete denture wearers often start adapting their dietary habits changing to a softer diet with less proteins, minerals and vitamins resulting in malnutrition or undernutrition . Although mandibular implant-retained and implant-supported overdenture treatment has a minor influence on dietary choices and nutrition, it considerably improves masticatory performance .

According to a systematic literature review on the effect of implant-supported or retained overdentures (IOD) on masticatory performance, the combination of an IOD in the mandible and a maxillary conventional complete denture provides significant improvement in masticatory performance compared to conventional complete dentures for patients, having persistent functional problems with a conventional mandibular denture due to a severely resorbed mandible .

Several more recent studies have shown that at least two implants in the edentulous mandible improve masticatory performance significantly, compared to conventional dentures . In contrast, information on the influence of a single mandibular implant in the edentulous mandible on masticatory performance is scarce in the literature. Grover et al. provided 10 edentulous patients with a single mandibular implant and a magnetic attachment . An early loading protocol was chosen and all implants were loaded 7 days after implant placement using dentures with either conventional complete denture arches or shortened dental arches. After 3 months, a significant improvement of masticatory performance was achieved in both groups with a greater improvement in the conventional complete denture arch group.

In another investigation with a cross over trial design the masticatory performance of single implant retained mandibular overdentures using either a stud or a magnetic attachment was evaluated . Fifteen patients received one implant, which was loaded 10 weeks later after a transmucosal healing period with either the stud or the magnetic attachment. The masticatory performance was evaluated after 3 months, the attachment system was exchanged, and another 3 months later, the masticatory performance was evaluated again. The masticatory performance increased significantly in both groups and the perceived chewing ability performed better in the stud attachment group. However, no significant difference was observed between the two attachments regarding masticatory performance. Although most studies on single mandibular implants used ball attachments none of those evaluated the masticatory performance.

So far it has never been investigated whether the loading protocol influences masticatory performance when single mandibular implants with ball attachments are used. Therefore, the present study evaluated as a secondary outcome whether the masticatory performance is improved by placement of an implant in the midline of the edentulous mandible and also whether improvements differ with respect to the loading protocol, i.e., implant is loaded either directly or three months later after second stage surgery with a submerged healing period. The primary outcome of the present clinical trial was to show that implant success is not compromised by immediate loading when one median implant in the edentulous mandible is used to retain a complete denture.

Materials and methods

The Institutional Review Boards of all participating centres of this multi-centre randomized controlled trial approved the study design and the trial was registered at Deutsches Register Klinischer Studien (German register of clinical trials) under DRKS-ID: DRKS00003730. All study participants gave their informed written consent.

The study population consisted of edentulous male und female patients in the age of 60 to 89 years, who were satisfied with their maxillary complete denture but dissatisfied with their mandibular denture, despite technical acceptability. Two hundred and twenty four patients were screened according to inclusion and exclusion criteria and 163 received one implant (3.8 × 11 mm; Promote plus, Camlog Biotechnologies, Basel, Switzerland) in the midline of their edentulous mandible. After implant placement, 158 patients could be randomly assigned either to the direct loading group (group A) or to the conventional delayed loading group (group B) by opening a sealed envelope ( Fig. 1 ).

Fig. 1
Study flowchart.

The trial statistician using block randomization with variable block size and an allocation ratio of 1:1 performed the central randomization. Stratification took place according to the patient’s residual bone height (Class II or III according to McGarry et al.) as well as the study centre. Blinding was not possible, due to the obvious differences between the two treatment groups.

A ball attachment (Dalbo-Plus Elliptic, Cendres Métaux, Biel, Switzerland) was used to connect all implants to the existing denture bases. The matrices were integrated into the denture base intraorally using a self-curing bis-acrylate resin (LuxaPick-up, DMG, Hamburg, Germany). The surgical approach, the randomization process and the prosthodontic procedure have been described in detail elsewhere .

The masticatory performance was assessed before implant placement (baseline) as well as 1 and 4 months after implant loading. Patients from group B performed an additional masticatory performance test 1 month after implant placement during the submerged healing phase.

All patients chewed an artificial standardized test food (Optocal), which is based on a silicon impression material (Optosil, Bayer) . The test food particles were fabricated centrally under standardized conditions following the protocol for production of a chewable material for masticatory function tests . All ingredients were weighed and mixed homogenously. The mixture was pressed into molds with an edge size of 5.6 mm and stored in an electrical stove for 16 h at 65 °C to ensure complete polymerization. All study participants chewed 17 cubes (approximately 3 cm 3 ) with 40 chewing cycles, counted by the examiner, following a protocol described in previous studies . They were seated upright in a dental chair and advised to chew normally. After chewing, the test food was collected in a plastic cup and disinfected with alcohol. The test food dried for 24 h and was sent to the University of Kiel, Germany, where it was centrally sieved to ensure equal sieving conditions with a standardized sieving protocol. A sieve apparatus (Retsch, Haan, Germany) with 5 sieves of different sizes (4 mm, 2 mm, 850 μm, 425 μm, 180 μm) was used and the test food particle parts on each sieve were weighed using a laboratory scale (Analytic, Sartorius, Göttingen, Germany). The percentage share of each of the 5 sieve capacities was calculated resulting in 100% for the whole test food of each chewing sample.

Sample size and statistical analysis

The sample size was calculated based on the primary endpoint of the study, the survival rate of the single median implant after 24 months. This is a binomial random variable and the implant survival probability was assumed to be 97% in both treatment groups. An inferiority of 7% of the survival rate in the direct loading group compared to the conventional loading group was considered clinically tolerable taking into account the advantages of an immediate loading, such as avoiding a second stage surgery. Under these assumptions, a one-sided test of binomial parameters at a 2.5% significance level has a power of 80% to reveal the non-inferiority of the immediately loaded implant if the sample size is 148 (74 per group). Taking into account a loss to follow-up rate of app. 20% a total of 180 patients (90 per group) was considered necessary.

The statistical analysis was performed using the Wilcoxon signed-rank test and Wilcoxon rank-sum tests as well as the Friedman-test. Additionally, a linear interpolation was used to identify a theoretical sieve, through which 50% of the chewed test food would pass. The software IBM SPSS Statistics, Version 22 and R, Version 3.2.3 (R Foundation for Statistical Computing) was used for analysis.

Materials and methods

The Institutional Review Boards of all participating centres of this multi-centre randomized controlled trial approved the study design and the trial was registered at Deutsches Register Klinischer Studien (German register of clinical trials) under DRKS-ID: DRKS00003730. All study participants gave their informed written consent.

The study population consisted of edentulous male und female patients in the age of 60 to 89 years, who were satisfied with their maxillary complete denture but dissatisfied with their mandibular denture, despite technical acceptability. Two hundred and twenty four patients were screened according to inclusion and exclusion criteria and 163 received one implant (3.8 × 11 mm; Promote plus, Camlog Biotechnologies, Basel, Switzerland) in the midline of their edentulous mandible. After implant placement, 158 patients could be randomly assigned either to the direct loading group (group A) or to the conventional delayed loading group (group B) by opening a sealed envelope ( Fig. 1 ).

Fig. 1
Study flowchart.

The trial statistician using block randomization with variable block size and an allocation ratio of 1:1 performed the central randomization. Stratification took place according to the patient’s residual bone height (Class II or III according to McGarry et al.) as well as the study centre. Blinding was not possible, due to the obvious differences between the two treatment groups.

A ball attachment (Dalbo-Plus Elliptic, Cendres Métaux, Biel, Switzerland) was used to connect all implants to the existing denture bases. The matrices were integrated into the denture base intraorally using a self-curing bis-acrylate resin (LuxaPick-up, DMG, Hamburg, Germany). The surgical approach, the randomization process and the prosthodontic procedure have been described in detail elsewhere .

The masticatory performance was assessed before implant placement (baseline) as well as 1 and 4 months after implant loading. Patients from group B performed an additional masticatory performance test 1 month after implant placement during the submerged healing phase.

All patients chewed an artificial standardized test food (Optocal), which is based on a silicon impression material (Optosil, Bayer) . The test food particles were fabricated centrally under standardized conditions following the protocol for production of a chewable material for masticatory function tests . All ingredients were weighed and mixed homogenously. The mixture was pressed into molds with an edge size of 5.6 mm and stored in an electrical stove for 16 h at 65 °C to ensure complete polymerization. All study participants chewed 17 cubes (approximately 3 cm 3 ) with 40 chewing cycles, counted by the examiner, following a protocol described in previous studies . They were seated upright in a dental chair and advised to chew normally. After chewing, the test food was collected in a plastic cup and disinfected with alcohol. The test food dried for 24 h and was sent to the University of Kiel, Germany, where it was centrally sieved to ensure equal sieving conditions with a standardized sieving protocol. A sieve apparatus (Retsch, Haan, Germany) with 5 sieves of different sizes (4 mm, 2 mm, 850 μm, 425 μm, 180 μm) was used and the test food particle parts on each sieve were weighed using a laboratory scale (Analytic, Sartorius, Göttingen, Germany). The percentage share of each of the 5 sieve capacities was calculated resulting in 100% for the whole test food of each chewing sample.

Sample size and statistical analysis

The sample size was calculated based on the primary endpoint of the study, the survival rate of the single median implant after 24 months. This is a binomial random variable and the implant survival probability was assumed to be 97% in both treatment groups. An inferiority of 7% of the survival rate in the direct loading group compared to the conventional loading group was considered clinically tolerable taking into account the advantages of an immediate loading, such as avoiding a second stage surgery. Under these assumptions, a one-sided test of binomial parameters at a 2.5% significance level has a power of 80% to reveal the non-inferiority of the immediately loaded implant if the sample size is 148 (74 per group). Taking into account a loss to follow-up rate of app. 20% a total of 180 patients (90 per group) was considered necessary.

The statistical analysis was performed using the Wilcoxon signed-rank test and Wilcoxon rank-sum tests as well as the Friedman-test. Additionally, a linear interpolation was used to identify a theoretical sieve, through which 50% of the chewed test food would pass. The software IBM SPSS Statistics, Version 22 and R, Version 3.2.3 (R Foundation for Statistical Computing) was used for analysis.

Results

Eighty-one patients were randomly assigned to group A and 77 patients were allocated to group B, while 5 patients could not be randomized due to inadequate primary implant stability. During the first four months, nine implants failed in group A and one implant failed in group B. One patient from group B was excluded from the study due to medical conditions before second stage surgery . Finally, the masticatory performance of 68 patients from group A and 69 patients from group B were obtained at each recall visit during the first four months of observation and statistically analyzed. The descriptive statistics are shown in Table 1 . Over time, a statistically significant increase of the masticatory performance could be observed in both groups, indicated by higher proportions of particles with smaller size at follow-ups ( Table 2 ). Furthermore, 4 months after implant loading, a significant increase compared to the baseline masticatory performance, could be observed in both groups ( Table 3 ). One and 4 months after implant loading, no statistically significant differences could be observed between the two treatment groups. The theoretical sieve size through which 50% of the chewed test food would pass decreased significantly over time in both groups, but there was no statistically significant difference between the two groups at all follow-ups ( Fig. 2 ).

Table 1
Descriptive statistics group A and B before implant placement and at all recall visits.
Baseline
Group A (N = 68) Sieve 1 Sieve 2 Sieve 3 Sieve 4 Sieve 5
Means 50.8 32.6 13.9 2.1 0.6
Standard deviations 33.4 21.6 12.2 2.8 0.9
Minimum 0.0 0.0 0.0 0.0 0.0
1 st quartile 25.0 7.0 2.0 0.0 0.0
Medians 36.0 41.0 12.0 1.0 0.0
3rd quartile 91.0 50.3 23.0 3.3 1.0
Maximum 99.0 62.0 51.0 16.0 4.0
Group B (N = 69)
Means 43.6 37.1 16.0 2.7 0.6
Standard deviations 29.4 17.7 11.9 3.1 0.9
Minimum 0.0 0.0 0.0 0.0 0.0
1 st quartile 22.0 28.0 5.0 1.0 0.0
Medians 37.0 42.0 16.0 2.0 0.0
3rd quartile 65.0 49.0 22.0 3.0 1.0
Maximum 100.0 64.0 46.0 14.0 3.0
1 month after implant placement (only group B, N = 69)
Means 43.2 38.6 15.4 2.2 0.6
Standard deviations 32.6 20.7 12.0 2.3 0.9
Minimum 0.0 0.0 0.0 0.0 0.0
1 st quartile 16.0 23.0 6.0 1.0 0.0
Medians 32.0 45.0 13.0 1.0 0.0
3rd quartile 71.0 56.0 24.0 3.0 1.0
Maximum 100.0 69.0 46.0 10.0 4.0
1 month after implant loading
Group A (N = 68)
Means 35.4 42.2 18.5 2.9 1.0
Standard deviations 29.9 18.3 11.9 3.0 2.3
Minimum 0.0 1.0 0.0 0.0 0.0
1 st quartile 14.0 37.0 9.8 1.0 0.0
Medians 26.0 48.5 19.5 2.0 1.0
3rd quartile 46.8 53.3 26.0 4.0 1.0
Maximum 99.0 66.0 45.0 15.0 18.0
Group B (N = 69)
Means 30.3 43.9 21.4 3.4 1.0
Standard deviations 28.7 16.0 12.6 2.7 1.0
Minimum 0.0 0.0 0.0 0.0 0.0
1 st quartile 7.0 36.0 10.0 1.0 0.0
Medians 22.0 49.0 22.0 3.0 1.0
3rd quartile 47.0 54.0 31.0 5.0 2.0
Maximum 100.0 69.0 47.0 10.0 4.0
4 months after implant loading
Group A (N = 68)
Means 24.7 47.6 22.8 3.9 1.1
Standard deviations 25.2 15.2 12.2 3.4 1.1
Minimum 0.0 1.0 1.0 0.0 0.0
1 st quartile 5.8 42.8 14.0 2.0 0.0
Medians 16.5 50.5 22.5 3.0 1.0
3rd quartile 33.5 58.0 32.0 5.3 2.0
Maximum 98.0 69.0 54.0 16.0 5.0
Group B (N = 69)
Means 20.4 50.4 23.9 4.1 1.2
Standard deviations 18.9 11.2 11.2 3.4 1.3
Minimum 0.0 18.0 4.0 1.0 0.0
1 st quartile 6.0 46.0 14.0 2.0 1.0
Medians 13.0 52.0 23.0 3.0 1.0
3rd quartile 38.0 58.0 32.0 5.0 2.0
Maximum 77.0 74.0 55.0 18.0 8.0
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Jun 17, 2018 | Posted by in General Dentistry | Comments Off on Single mandibular implant study (SMIS) − masticatory performance − results from a randomized clinical trial using two different loading protocols
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