Comparison of masticatory performances between immediately loaded
and conventionally loaded mandibular two-implant overdentures withmagnetic attachments
Watanabe M1, Kanazawa M1, Miyayasu A1, Shimada R1，Negoro M1，Uehara Y1, Sato D2 , Sato Y1,Minakuchi S1

１Gerodontology and Oral Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo

Medical and Dental University
２

Oral Implantology and Regenerative Dental Medicine, Graduate school of Medical and Dental Sciences,

Tokyo Medical and Dental University

AbstractPurpose
The aim of this study is to compare the masticatory performances between immediately loaded andconventionally loaded mandibular two-implant overdentures with magnetic attachments.
Material and Method
Nineteen participants with edentulous mandibles were randomly assigned to an immediately loaded
group or a conventionally loaded group. In the immediately loaded group, a magnetic attachment
was applied on the same day as implant surgery, and in the conventionally loaded group, a magneticattachment was applied 3 months after implant surgery. Both masticatory performances, measured
by a color-changeable chewing gum and a gummy jelly, and maximum occlusal force were assessedat baseline and at 1, 3, 6, 12, 24, 36 and 48 months after implant insertion.
ResultAt the 6‐month evaluation time‐point, the immediately loaded group exhibited a significantly
higher gummy jelly score than the conventionally loaded group. There were no significant
differences in masticatory performance measured by the color‐changeable chewing gum between thetwo groups at any evaluation time‐point.
Conclusion
The masticatory performance, measured by a gummy jelly, is improved by 2-IOD of immediateloaded at an earlier time-point than of conventional loaded.

Introduction
The McGill consensus suggested that two-implant overdenture(2-IOD) should become the first
choice of treatment for the edentulous mandible1). Furthermore, to recover MP, 2-implant
overdentures (2-IODs) were introduced as a standard treatment option for edentulousindividuals2). However, no reports are available regarding the MP of 2-IODs retained bymodified magnet attachments. Moreover, no reports are available regarding comparison of MPs
between immediately loaded 2-IODs and conventionally loaded 2-IODs.

Objective
The aim of this study is to compare the masticatory performances between immediately loaded
and conventionally loaded mandibular two-implant overdentures with magnetic attachments.

Materials and Methods
1. Study design
This study was a randomized unblinded parallel-group trial.
2. ParticipantsParticipants were recruited by telephone from among patients who had previously visited theDental Hospital of Tokyo Medical and Dental University. All participants were given oral andwritten information regarding the study and provided written informed consent. The Ethical
Review Committee of the Faculty of Dentistry, Tokyo Medical and Dental University, approved
the study protocol. The following inclusion criteria were applied:
1. A completely edentulous mandible and any opposing maxillary occlusion status.
2. Adequate bone volume in the anterior mandible for the placement of two implants withminimum dimensions of 4.0 × 10.0 mm.
3. No requirement for bone augmentation.
4. Commitment to undergo at least 4 months of healing after extraction.
5. Good oral hygiene.
The following exclusion criteria were applied:
1. Uncontrolled systemic disease that could compromise implant surgery.
2. History of chemotherapy or radiography in the head and neck region.
3. Heavy smoker status.

4. A history of taking bisphosphonate.
3.Surgical and prosthetic procedure
Each participant received new appropriate mandibular complete dentures (CDs). When theadjustment is finished, computed tomography (CT) scans was gotten using this denture as aradiographic guide. From the obtained CT image, the implant planting position is simulated on asimulation software and produce surgical guides. Two implants (Nobel Speedy Groovy RP 4×10–
18 mm, Nobel Biocare, Gothenburg, Sweden) were inserted in the inter-foraminal area of eachparticipant according to the manufacturer’s protocol for a flapless surgical procedure by the same
experienced implantologist. In the immediately loaded group, magnetic attachments (Magfit, Aichi
SteelCo, Aichi,Japan) were applied to the implants on the same day as implant surgery, and in theconventionally loaded group, healing abutments were applied. The conventional group was fittedwith magnetic attachment, three months after implantation. After surgery, the participants wereinstructed to keep wearing their dentures 24h a day for 7 days except for denture cleaning toprevent swelling of the mucous tissue and making it difficult to wear dentures. The equivalent partof the implant on the denture mucosal surface was sufficiently relieved so as not to apply stress tothe implant.
4.OutcomeMP was evaluated using a color changing gum, gummy jelly, and occlusion force meter. Gum wasevaluated for mixing ability, gummy for biting ability, and occlusal force meter for maximum
occlusal force. As for each measurement method, the mixing ability was freely chewed 60 times, andthe amount of color change was calculated. Then I evaluated how many times the color change wasequivalent to the number of mastication. Gum jelly (UHA Mikakuto, Japan) was chewed 30 times,
and the bite fragments were evaluated on a 1-10 scale. The maximum occlusal force was measured
when the occlusion force meter was occluded as long as possible for several seconds. The evaluation
period is preoperative, 1, 2, 3, 6,12,24,36,48 months after the operation.
5.Statiscal analysis
The baseline characteristics of the participants in both groups were compared by using thenon-paired t-test and the chi-square test. The Mann-Whitney U test was used to analyze differencesin MP and maximum occlusal force between the two groups at baseline and each evaluation
time-point after implant insertion. Steel's test was used to compare MP and maximum occlusal force

at baseline with MP and maximum occlusal force at each evaluation time-point after implant
insertion within each group. All statistical analyses were performed by using the statistical software
JMP ver.13 (SAS Institute, North Carolina). Statistical significance was set at P < .05 for all tests.

Results
The flow of participants in the study is shown in Figure 1. Nineteen participants with edentulous
mandibular arches were recruited into the study. There were a total of 6 dropouts. In theconventional load group, one patient lost the implant within 3 months after the operation, and theremaining five patients were unable to continue the study due to the circumstances of theparticipants. The final analysis was carried out for a total of 13 people, 7 in the immediate loadgroup and 6 in the normal load group, 4 years after implantation.
Figure1 The flow of participants
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 !& %$$$$$ %+ - ,There were no significant differences in MP measured by the color-changeable chewing gum
between the two groups at any evaluation time-point (Table 1). At the 6-month evaluation time-point,
the immediate group exhibited a significantly higher gummy jelly score than the conventional group(Table 2). There were no significant differences in maximum occlusal force between the two groups
at any evaluation time-point (Table 3).
MP measured by the color-changeable chewing gum was significantly higher than baseline at the36-month evaluation time-point and 48-month evaluation time-point in the immediate group, andthere were significantly higher differences at 48-month time-point. From the 3-month evaluation
time-point to the 36-month evaluation time-point, MP measured by gummy jelly score wassignificantly higher than baseline in the immediate group; however, in the conventional group, thegummy jelly score did not differ significantly from baseline at any evaluation time-point (Table 4).
Maximum occlusal force was significantly higher at the 12-month evaluation time-point in theimmediate group, compared with base- line, but there were no other significant differences in eithergroup at any time-point (Table 4).
TABLE1 Masticatory performance scores measured by a color-changeable chewing
gum in the two groups from baseline to the 48-month time-point
MedianBaseLine

1 month

3 months 6 months

12 months 24 months 36 months 48 months

Imediaete

60.0

66.8

59.1

75.7

73.7

87.2

104

129

Convetional

53.3

60.2

48.8

59.3

73.5

82.8

110

134

P value

.689

.399

.198

.307

.962

.689

1.00.721*P value <.05.

TABLE2 Masticatory performance scores measured by a gummy jellyin the two groups from baseline to the 48-month time-point
MedianBaseLine

1 month

3 months 6 months

12 months 24 months 36 months 48 months

234

4.5

4

4.5

5.5

5.5

Conventional 1

1.5

3.5

3

3.5

5

4

4

P value

.433

.504

.034*

.617

.890

.319

.428

Immediate.784*P value <.05.

TABLE3 Maximum occlusal force in the two groups from baselineto the 48-month time-point
MedianBaseLine

1 month

3 months 6 months

12 months 24 months 36 months 48 months

Immediate

165

198

185

268

350

303

286

139

Convetional

53.360.248.8

59.3

73.5

82.8

110

191

P value

.859

.12

.143

.79

.414

.824

.772

.830

*P value <.05.

TABLE4 The P values for differences in masticatory performancemeasured by color-changeable chewing gum and gummy jelly andmaximum occlusal force between baseline and each evaluation time-point
P value
1 month

3 months 6 months 12 months 24 months 36 months 48 months

Color-changeable chewing gum
Imediaete

.737

.993

.192

.267

.098

.004*

.002*

Convetional

.910

.994

.963

.603

.138

.083

.005*

Imediaete.504.042*.002*.003*

.003*

.031*

.070

Convetional

.914

.266

.331

.205

.159

.407

.253

Gummy jelly

Maximum occlusal force
Imediaete

.515

.570

.098

.032*

.098

.087

.098

Convetional

.999

1.00

.383

.174

.065

.182

.128

*P value <.05.

Discussions
MP measured by the color-changeable did not differ significantly between two groups at any
evaluation time-point. In contrast, MP measured by the gummy jelly increased significantly at the6-months evaluation time-point. These results suggest that the biting ability improves early after
surgery. The reason that no significant difference in the mixing ability between two groups was thatthe color-change gum was soft to chew easily for CDs wears.
In within-group comparisons, there was no significant difference in MP measured by thecolor-changeable chewing gum between the immediate load group and the conventional load group
before 36-months time-point. The reason for this is that gum texture and increased occlusal contact
area due to artificial tooth wear.
There was a significant difference in gummy jelly score in the immediate load group from3-months time-point to 36-months time-point. This suggests that biting ability has improved
compared to preoperatively. On the other hand, the gummy jelly scores in the conventional group
did not differ significantly from the baseline score at any time-point after implant loading. This lackof a significant increase may be related to variation in data.
There were no significant differences in maximum occlusal force between the two groups at any
time-point, and in within-group comparisons of maximum occlusal force compared to baseline inboth groups, only the score at 12-months in the immediate group was significant. And, the maximum
occlusal force showed a decreasing trend after one year. The reason was thought to be due to theaging of the participants.

Conclusions
Within the limitations of the clinical research, the MP measured by a gummy jelly is improved by
immediately loaded mandibular 2-IODs with magnet attachments at earlier time-point than ofconventional loaded. Therefore, immediate loading of 2-IODs retained by magnet attachments isrecommended with regard to MP.

References
1. Feine JS, Carlsson GE, Awad MA, Chehade A, Duncan WJ, Gizani S, et al. The McGillconsensus statement on overdentures. Mandibular two-implant overdentures as first choicestandard of care for edentulous patients. Montreal, Quebec, May 24–25, 2002. Int J Oral
Maxillofac Implants 2002;17:601–2.
2. Thomason JM, Kelly SA, Bendkowski A, Ellis JS. Two implant retained overdentures—areview of the literature supporting the McGill and York consensus statements. J Dent.
2012;40:22-34.