Load‐related bone modelling at the interface of orthodontic micro‐implants

Abstract

The purpose of this study was to determine the interface reaction of two different titanium micro-implant systems activated with different load regimens. A total of 200 micro-implants (100 Abso Anchor and 100 Dual Top) were placed in the mandible of eight Göttinger minipigs. Two implants each were immediately loaded in the opposite direction by various forces (100, 300 or 500 cN) through tension coils. Three different distances between the neck of the implant and the bone rim (1, 2, 3 mm) were used. The loads provided by superelastic tension coils (which are known to develop a virtually constant force) led to a range of tip moments 0-900 cN mm at the neck of implants. Non-loaded implants were used as a reference. Bone tissue responses were evaluated by histology, histomorphometry and scanning electron microscopy after 22 and 70 days of loading. Implant loosening was present in the groups where the load reached 900 cN mm. No movement of implants through the bone was found in the experimental groups, for any of the applied loads. A direct bone-to-implant contact to various extents was observed at differently loaded implants. Ultrastructural analysis confirmed the clinical and histological finding that implants (except when loaded at 900 cN mm) were well osseointegrated after 22 days. An increase in the bone-to-implant contact ratio was observed during the experimental period in the coronal part of the implants in most experimental groups. The difference reached a level of statistical significance at 500 cN mm (Abso Anchor) and 600 cN mm (Dual Top). We conclude that micro-implants can not only be loaded immediately without impairment of implant stability but many enhance bone formation at the interface when the load-related biomechanics do not exceed an upper limit of tip moment at the bone rim.

Microdamage in Cortical Bone due to the Overtightening of Orthodontic Microscrews

“…Low-grade microdamage or microcracks are physiologically present in loaded bone [28]. The continuous loading of bone induces active bone remodeling [6,16]. Traumatized bone tissue is thus replaced by newly-formed replacement bone.…”

“…logischen Belastungen des Knochens kontinuierlich neu auf und konnten histologisch auch nach längerer klinischer Verweildauer einer Mikroschraube in situ in direkter Nachbarschaft zum Schraubengewinde nachgewiesen werden [4]. Sie induzieren -zumindest in vitalem Knochen -den aktiven Knochenumbau [6,9,16,17]. So wird solch traumatisiertes Knochengewebe physiologischerweise wieder durch neu gebildeten Ersatzknochen substituiert.…”

“…It keeps occurring in response to physiological stresses on the bone; it has also been histologically identified adjacent to microscrews following long-term therapy in situ [4]. Microdamage induces active bone remodeling (in vital bone at least) [6,9,16,17]. Bone tissue thus damaged is then replaced physiologically by newly-created replacement bone.…”

Measurement of mini-implant stability using resonance frequency analysis

“…[31][32][33][34][35] In particular, the contact with the compact bone seems to be important for implant stability. 36 A correlation could found between the bone to implant contact rate and RFA.…”

A healing period increases mini-implant stability in growing rats

“…Fluorescent microscopic images are also useful for confirming bone formation in the area surrounding implants (22,23,(30)(31)(32). Deguchi et al (23) used fluorescent and polarized microscopic to evaluate growing dogs and found that mini-implants were able to function as rigid osseous anchors during orthodontic loading for 3 months.…”