The histological behaviour of bone tissue and mucous membranes in italian school immediately loaded “one-piece” implants

INTRODUCTION

This work aims to investigate the intimate relationship between host tissue (bone and mucosa) and Italian implantology school titanium endosseous implants.
Modern implantology (Formiggini 1947) began with immediate prosthetic loading of post-extractive implants. In recent years, clinical practice in implant prosthetics has increasingly moved towards the adoption of immediate loading, even by the School which had dogmatically adopted the ‘philosophy’ of deferred loading.
In 1962, a university research by Ugo Pasqualini scientifically resolved the issues relating to the biocompatibility of implant materials, their osseointegrative potential, communication with the external environment and occlusal load.
In 1963, after years of research, Stefano M. Tramonte developed his grade 2 titanium wide-spiral self-tapping screw – the first in the world to use titanium in implant prosthetics. In 1972, Dino Garbaccio patented a self-tapping screw, also made of grade 2 titanium, introducing the concept of bicorticalism in screw implantology, taken from Scialom’s needles (1963). The Italian School was the first to have and use Mondani’s intra-oral welding machine since 1978, a tool that is capable of welding titanium directly in the mouth and making immediate functionalisation of retainers possible and predictable (1).
At present, several international authors have also presented one-piece implants similar to those of the Italian School (2-4).
Analysing the results of some of the various histological studies carried out on these implant types, we have a clear picture of the excellent behaviour of the bone tissue and peri-implant mucous membranes.

MATERIALS AND METHODS

Histological research used “block sections” of post-mortem examined implants, implants removed from living humans for traumatic fractures after years of function and sections taken from experimental animals.

The preparation methods for studying the behaviour of the contact zone between alloplastic structures and host tissues used in this research were: the abrasion technique to obtain histological preparations comprising bone and metal in well-coloured sections just a few microns thick, which allows simultaneous analysis of the alloplastic material and the hard tissues surrounding it, a method improved by Prof. Karl Donath of Hamburg University in the 1980s (5,6).

Mucosal peri-implant samples were analysed using the classic method: fixed in 5% formalin and then embedded in paraffin, prepared in 4 mm serial sections and stained with haematoxylin-eosin at progressive magnifications up to a maximum of 400x. Mucosal biopsy research was used to progressively assess and control the histological behaviour of the epithelium and submucosal corium at the level of the epithelial connective attachment. The samples were divided into two parts examined in the two typical cutting sections: orthogonal or parallel to the axis of the implant emergence.
The total number of sections examined was 2,400 – Fig.1 (7).

HISTOLOGICAL RESEARCH / 1

Karl Donath, Professor at the University of Hamburg, made it possible to obtain sharp and precise ground sections of the metal inclusions and their surrounding tissue. These show that osseointegration does not require macroscopic retention since it is organised through a process of osteoanchylosis even along the smooth surfaces of submerged titanium structures (8).
Piattelli and collaborators of the University of Chieti, using both Donath’s original technique and their own techniques, confirmed similar bone-implant interface results (9,10). antaggiato, Iezzi and Piattelli described Donath’s technique in demonstrating the long-term osseointegration of three one-piece screw implants (11). Using another “ground” technique, Vito Terribile, Wiel Marin, Piero Passi, and Antonino Miotti of the University of Padua documented a similar bone apposition on a Tramonte’s screw that had been under load for years before fracturing (12). Andrea Bianchi of the San Raffaele University of Milan carried out extensive research into how peri-implant bone adapts in terms of density and architectural organisation in response to the functional prosthetic stresses to which implants in living bone were subjected. Bianchi considered also the term “functional ankylosis” between the bone tissue and the enclosed osseointegrated implant more accurate and in line with the results of his scanning electron microscope (SEM) research (13). This definition was confirmed by the studies of Professor Carlo Zerosi of the University of Pavia, who defines ankylosis as the relationship between bone and implant, commonly referred to as osseointegration (14,15).
In order to study the metal-including bone interface of a screw implant, Bianchi adds that “between the peri-implant bone and the titanium screw surface there was an almost constant empty space of about one micron, where it was never possible to find fibrous tissue or other non-mineralised soft tissue, even at maximum magnification (SEM 250x)”. – Fig 2,3,4,5 (16).

LA RICERCA ISTOLOGICA / 2

Histological research on the behavior of the so-called “epithelial attachment” marginal to the abutments of one-piece implants has shown that the epithelium around implants behaves the same way as the epithelium around healthy natural teeth. The serial sections of the mucous membrane (2400 sections) attached to the neck of the screws are histologically similar: the external mucous membrane always appears protected by a keratin layer, while the internal mucous membrane, facing the metal, is always devoid of a keratin layer with progressive loss of the cellular layers up to the mono-stratification of the basal cells only. Underneath is a normal corium. (fig.) The 1972 work by Camera and Pasqualini U of the University of Modena was republished after further scientific confirmation in 2009 (17).
Histological analyses prove that the above-crestal soft tissues around one-piece implants are similar to the gingival soft tissues surrounding healthy teeth. – Fig. 6,7.

CONCLUSIONS

The histological studies have proved the ability of Italian School single-phase one-piece immediately loaded implants with a thin emerging neck (abutment) and a reduced diameter compared to the body of the coils (fixture) to realise an adequate epithelial seal (Platform Switching) (18,19); a necessary condition for the bone to heal perfectly, achieving osseointegration.
The biopsy samples show that the soft tissue sections at the neck of the screws feature a physiological pocket with a depth of approximately 1.5 mm, similar to that observed around the collar of healthy human teeth. It has been also proved the perfect placement of healthy newly formed bone, both compact and spongy, around all the metal structures of the various morphologies of the one-piece implants without the interposition of collagen fibres.

Acknowledgements

Figures 2, 3, 4 e 5 – Courtesy of Andrea Bianchi, taken from the book Implantologia e Implantoprotesi, Torino: UTET; 1999.