Influence of implant number on the movement of mandibular implant overdentures.
BACKGROUND
The rotational movement of an implant overdenture (IOD) has a negative effect on the perceived masticatory ability of the denture wearer. However, the influence of implant number on the movement of IODs has not been investigated.


OBJECTIVE
The purpose of this in vitro study was to evaluate the denture movement of mandibular IODs anchored by different numbers of implants.


METHODS
An edentulous mandibular test model with artificial mucosa and 5 experimental overdentures (N=5) was fabricated. The locator attachment system with blue nylon inserts was chosen for this study. Three implant positions were prepared: anterior midline (1-IOD), bilateral lateral incisor regions (2-IOD), and anterior midline and bilateral canine regions (3-IOD). Vertical loads of 50 N were applied to the mid-anterior region, the left canine region, the left premolar region, and the left first molar region. The vertical and horizontal displacements at the right distal edge and the vertical displacements at the loading point were measured. The displacement values were statistically analyzed using a 1-way analysis of variance and the post hoc Tukey honest significant difference test with the implant number as a factor. In addition, the values of the vertical and horizontal displacements at the distal edge of the overdenture were statistically compared using a paired t test, and the values of the vertical displacement at the distal edge of the overdenture were statistically analyzed by a repeated measures analysis of variance and the post hoc Tukey honest significance difference test with the loading point as a factor (a=.05).


RESULTS
Upon anterior loading, the 2-IOD showed significantly larger vertical displacements at the right distal edge than the 1-IOD or 3-IOD (P<.01). The horizontal displacements at the right distal edge were small compared with the vertical displacements at the same point, although the displacement of the 2-IOD was significantly larger than that of the 1-IOD upon anterior loading (P=.03). The magnitude of the vertical displacement at the loading point of the 2-IOD was significantly larger than that of the 3-IOD upon anterior loading (P<.01). No statistically significant differences were shown under the other conditions for each loading (P>.05).


CONCLUSIONS
Within the limitations of this in vitro study, the following conclusions were drawn: During mastication with the anterior teeth, the use of 2 implants for anchoring an IOD increased the rotation of the denture base more than the use of 1 or 3 implants. The horizontal movements of the IODs were small compared with the vertical movements. Denture movement under the occlusal force in the molar region was smaller than that in the anterior region.
Graduate student, Gerodontology and Oral Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Yushima, Bunkyo, Tokyo, Japan.
Ken
K
Oda
Assistant Professor, Gerodontology and Oral Rehabilitation, Tokyo Medical and Dental University, Tokyo, Japan. Electronic address: m.kanazawa.gerd@tmd.ac.jp.
Manabu
M
Kanazawa
Resident, Gerodontology and Oral Rehabilitation, Tokyo Medical and Dental University, Tokyo, Japan.
Shin
S
Takeshita
Professor, Gerodontology and Oral Rehabilitation, Tokyo Medical and Dental University, Yushima, Bunkyo, Tokyo, Japan.
Shunsuke
S
Minakuchi
D000704:Analysis of Variance; D001732:Bite Force; D015921:Dental Implants; D003764:Dental Materials; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis; D003819:Denture Bases; D003779:Denture Design; D003781:Denture Retention; D003826:Denture, Complete, Lower; D003828:Denture, Overlay; D006801:Humans; D066298:In Vitro Techniques; D007575:Jaw, Edentulous; D008334:Mandible; D008409:Mastication; D055595:Mechanical Phenomena; D009068:Movement; D013997:Time Factors
D015921:Dental Implants; D003764:Dental Materials