CHARACTERISTICS OF IMPLANTS AND PROSTHETIC TECHNIQUES
Vincenzo Bucci Sabattini, Francesca Bucci Sabattini
“Implantology is not a surgical discipline, but a surgically-supported prosthetic discipline” U. Pasqualini (Lezioni di gnatologia, 1977).
Medicine as a whole, and therefore dentistry too, changed radically in the wake of the Second World War. However, it is perhaps true to say that the most radical change of all has been due to the evolution and spread of prosthetic implant therapies.
The dream of being able to replace body parts lost as a result of injury or disease is one that dates back to antiquity, as indeed does the practice of fabricating functional, or at least partly functional, prostheses.
In the different areas of clinical practice, prostheses more or less fit for their intended purpose, have always been fabricated. In literature, Peter Pan’s great enemy regained some of the functions of his lost hand through a hook.
The dream of being able to replace lost teeth is, too, one that dates back centuries. However, it was not until around the 1970s that it became one that could be fully realised.
The implant that paved the way for all the subsequent developments seen in this field was Formiggini’s intrabone implant with drive screw. This was, indeed, the starting point for the whole process that has led us, in stages, to the full range of dental implantology possibilities available to us today.
Professor Zampetti, in the opening chapter of this book, described implantology’s long and difficult evolution.
More than just a fascinating historical account, his chapter serves a very important purpose, as it gives us the background knowledge we need in order to appreciate and understand the latest technical and scientific developments within this discipline.
Today, immediate loading is the new frontier of implantology. In truth, however, it is not so much a new frontier as a return to its own roots.
After Zampetti’s account, it is not necessary, here, to look back over the whole cultural and technical journey that has brought us to where we are today.
However, for the sake of clarity, it is worth dividing, broadly, the recent history of implantology and prosthetic implants into three periods.
It is reasonable to say that the history of implantology began, roughly, with the birth of Formiggini’s intrabone screw. After this, the first real change came with Branemark, while the current period can be said to have started in the 1990s.
Fig. 3.1 •
From the end of the Second World War through to the 1970s/1980s, implantology was a field for pioneers who were armed with enormous enthusiasm and intelligence, but lacked the technical and financial resources available to their successors.
The advances made in this period, which were numerous, were due almost entirely to the inventiveness and clinical observation skills of the various professionals who devoted themselves to this discipline.
Although their efforts were contested in many quarters, primarily by almost the whole of the academic world, not only in Italy but worldwide, they worked with great courage and passion.
These were years in which anyone who practised implantology was, at best, labelled a dangerous charlatan, or even accused of dishonesty.
Implantology owes its evolution not to research carried out in institutional settings (universities, etc.), which in most cases actually opposed it, but to the growing wellbeing of the population, which led to citizens starting to request this kind of treatment.
A little historical knowledge and imagination is all that is required in order to understand this.
In the aftermath of the Second World War, with Europe divided between East and West, Asia reeling from the nuclear destruction of its leading nation (Japan), and other parts of the world still largely under colonial rule, the societies that were managing to get themselves back on their feet were dominated, as regards their economies and social frameworks, by US money and US models.
Indeed, the Second World War marked the end of the era in which the world was dominated by European culture and social models, and the start of the American one.
You might well ask: “What does this have to do with implantology?”
Well, the fact is that this transition determined everything that happened from 1945 onwards; so much so that it triggered the evolution of a whole new way of life and a new conception of what life means. One need only think of old European novels and films to realise that up until around the 1970s, European society was still characterised by levels of inequality so great as to be almost unimaginable to anyone growing up in the decades since then.
Thanks to the importing of “American” democracy, based on the “American dream”, social classes stopped being seen as rigidly impermeable, and the concept of social mobility was born.
All this was accompanied by the leap towards today’s consumer economy, and thus towards the consumption of health – health understood not as absence of disease, but as psychophysical wellbeing, which includes aesthetic and relational wellbeing.
In short, social change helped to determine therapeutic demands.
When most of the population accepts that it is normal to die at 70 years of age, that people are old at 50, and may well have lost their teeth by 40; when most people are poor and, since soap is expensive, take a bath (if they can at all) only on a Saturday; when most people have no money for dentists, whom they go to only for extractions or, at best, for sets of dentures, then there is clearly no demand for other treatments, and thus no money invested in researching other treatments.
Formiggini was a groundbreaker, as was Jules Verne, a genius who proposed things that are now increasingly returning to the fore as research progresses. He was a man ahead of his times.
It was only with the global economic recovery of the early 1960s (the boom years) that there emerged a level of demand, albeit among a minority, sufficient to inject fresh impetus into research in the sphere of personal wellbeing and aesthetics.
In this new setting there grew up, worldwide (but mainly in Italy, thanks to Formiggini’s visionary studies), schools of thought and clinical practice ideas on dental implantology.
Given that it is normal to remember only those personages who, for various reasons (scientific rigour, organisational skills, brilliant insights, etc.), remain most deeply impressed in people’s minds, we here recall Prof. Ugo Pasqualini, who provided the world’s first histological demonstration of bone-implant ankylosis, later to be termed osseointegration, Prof. Stefano Tramonte, who was the first (in the world) to identify titanium as highly biocompatible and, thus, as the ideal implant material, and Prof. Giordano Muratori, organiser of a meeting in Bologna that was for many years the most important platform for implantology worldwide.
Together with them, there were “…a hundred flowering buds and a hundred disputing schools…”. In Italy, to name but a few, it is right to recall Apolloni, Garbaccio, Foscarini, Ballavia, Mondani, and Gnalducci. Implant systems and machines (e.g. the intraoral welder) devised by some of these individuals are today marketed under different names, and without even the courtesy of acknowledging their true origin.
I am sorry not to be able to mention every single one of the pioneers whose work made possible all that we know and have today. However, I wanted to cite at least some of them in order to convey something of the wealth of thought that abounded in that period in Italy and that made Italy a main birthplace of implantology.
In truth, this period saw the emergence of dedicated schools and clinical proposals throughout the world. The most important include, among others, those of Linkow (who heralded the split crest), the implants developed in Tubingen in Germany (which gave excellent aesthetic results), and those of Dr Shalom, in France (which made it possible to restore anatomical situations characterised by severe bone atrophy using extremely low-invasive surgery).
The biological principles, including the material of choice (titanium), were all identified at that time; furthermore, considering the techniques and procedures developed in that period, one is easily led to conclude, as already said, that progress in implantology today is actually more implantology returning to, and modernising, its own roots.
Most of the implantologists of that time were all-round dentists. Specialists in specific branches of dentistry were still (almost) unheard of. Dentistry, as a whole, was just one small specialty within the sphere of medicine and surgery.
This situation made it possible to tackle certain situations arising in clinical practice: most dentists had surgical know-how, but also knowledge of prosthetics and prosthetic possibilities. The lack of technical resources encouraged a flexible, imaginative approach, and in prosthetics, numerous, often very useful blockable connectors were proposed.
However, not all dentists attempting the implant route were up to the task.
Implants, at that time, were mainly monophasic and inserted transmucosally. They needed immediate prosthetisation. Therefore, they had to have high primary stability and required specific knowledge of prosthetics and occlusion.
Implant prosthetics was, in truth, a difficult and risky discipline and, inevitably, many failures were recorded among those attempting it. Hence the aversion to this discipline on the part of most dentists, but even more so on the part of universities and other culturally blazoned settings. For many years, they criticised and condemned implantology out of hand, without even attempting to study the topic in any detail.
Although there were some worthy exceptions, it was really only with Branemark that the discipline gained acceptance as a field worthy of study and application. Thus opened the second stage in its development.
What did Branemark do to bring about this epochal change?
Branemark made implantology an approach accessible to all (or almost all) dentists, regardless of their level of skill and training.
Thanks to his introduction of a strict and extremely detailed surgical protocol (whose main purpose, rather than the consideration of real requirements, was to allow even the less skilled to operate safely and with confidence), and also to his submerged implants requiring very long waiting times, it became possible to obtain very high success rates, albeit at the cost of biological damage nevertheless considered minor.
Flapless implant installation, or in any case insertion of an implant without preparing a full flap, demands specific skills. It is, indeed, very easy to fenestrate the cortical bone and place the implant submucosally.
The Branemark protocol therefore demanded extensive skeletisation of the site, to allow visual monitoring.
To obtain an implant with a primary stability of 35/40 Ncm, or preferably more, and then to load it immediately with a superstructure that does not subject it to inappropriate stress is certainly a very difficult undertaking.
For this reason, the Branemark protocol required implants to be left submerged for extremely long periods of time.
Fixed, implant-supported prostheses are difficult to apply and the greatest difficulties are encountered in the upper jaw. Therefore, Branemark’s protocol proposed screw-retained prostheses, lifted from the gingiva and almost always destined for the lower jaw.
Analysing very large numbers of cases treated in this way – in the early years, all users were required to submit, to the manufacturer, data on all interventions carried out –, Branemark was able to gather statistically significant data testifying to the success of the protocol.
In this way and thanks to this method, the Branemark company quickly became the world leader in implantology and Branemark himself a “prophet”, for many years considered indisputable.
For too many years, though, implantology, recalling the unsupported assertions of the pre-Galilean period, remained a discipline in the non-scientific ambit. In fact, today very little of Branemark’s “decalogue” remains.
Indeed, it has since been seen that many of the principles were useless, and even harmful, and were proposed only in order to ensure the working of an implant actually considerably worse than all those proposed previously, being placed surgically using methods liable to result in iatrogenic damage, or in the best-case scenarios, to delay healing.
However, the past 15 years have seen a more than 100% increase in the number of reliable scientific papers dealing with immediate loading in implantology, the first and most important including Richard Lazara’s studies of post-extraction implants.
Both the surgical and the prosthetic aspects of Branemark’s protocol have been reviewed and revised and the macro- and micromorphological characteristics of the implants have also been modified.
Thus we enter the third phase in this fascinating story, the one in which we find ourselves today.
Of all that Branemark said, his indications on the need for sterility – implants must be absolutely sterile, while the working environment and operating field must be thoroughly treated to obtain the maximum possible sterility – remain absolutely correct and fundamentally important. Practically everything else has been revised. There has been a return to less invasive surgery, it has been shown that immediate and/or early loading increases bone-implant contact, and waiting times for definitive prosthetisation of the patient have been drastically reduced. Implantology today is more difficult for the operator, but more respectful of the patient and more in line with modern biology and biological approaches. The fact that dogmas deriving from Branemark’s “decalogue” still survive is, unfortunately, an indication of widespread poor professional updating and of the power of marketing. Today, clinical and research data are highlighting the possibility, and even the advantages, including biological ones, of immediate implant loading.
Numerous experimental studies show, in accordance with Wolff’s law, that immediate functional loading of implants results in highly significant increases in bone-implant contact and better and more rapid bone-implant integration.
Fig. 3.2 • Percentage increase in the number of publications dealing with immediate loading in implantology between January 1998 and December 2007.
However, an inappropriate load, especially if applied very early, is one of the main risk factors liable to jeopardise the survival of the implant.
The problem, therefore, is not with the load itself, but with its application.
But before taking a close look at what are considered the most reliable immediate loading procedures, it is crucial to draw attention to a few basic concepts, which unfortunately are still not as clearly understood as they should be, and need to be.
Unfortunately, as a result of various factors including, primarily, the strong marketing campaigns conducted by many companies, there is a tendency not to pay enough attention to the things that are absolutely essential for a successful implant outcome, or to those that are useful, even though not absolutely essential. Too often, complete faith, totally undeserved, is placed in manufacturers, especially those that, through advertising, are particularly well-known.
There thus follows a brief, but clear and exhaustive, presentation of the foundations of implant prosthetics. We will look at the factors determining long-term implant success, and at the factors that are useful to this end, both the clinician-dependent ones and those inherent in the different implant systems currently present on the market.
It is simply not true that all implants are useful and efficacious to the same degree. It is simply not true that it makes little difference which surgical and prosthetic protocols are used.
While the main differences may not be apparent straight away, over time they certainly emerge. In the context of immediate or even just early loading, differences in implant macro- and micromorphology, which are what determine the speed of bone healing and the duration of the delicate “window period”, are extremely important factors determining the success of the intervention, even only in the short term.
Implant surgery: necessary conditions and conditions contributing to success, preparation of the field and ensuring sterility, of both the operating field and the working environment
In addition to the characteristics of the bone tissue, there exist other factors that contribute to or are necessary for successful and long-lasting implant osseointegration.
Three factors necessary for a successful clinical outcome
- Primary stability
- An adequate blood supply to the site
Other factors contributing to a successful implant:
- Biomechanical factors
- Biological factors: patient’s clinical conditions, healing mechanisms
- Surgical techniques
- Chemical factors
Before beginning to examine the different implant techniques and characteristics, we consider it useful to highlight several aspects of two of the necessary conditions listed above; in so doing, we draw on scientifically valid concepts and are driven by a desire for intellectual honesty.
Fig. 3.3 •
Francesca Bucci Sabattini, Vincenzo Bucci Sabattini
With a view to ensuring patient and operator safety, there has emerged, also in the field of dentistry, the need for a document containing indications on correct sterilisation procedures, which constitute the main means of preventing possible infectious complications. Sterility of the operating field, of the instrumentation and of everything else used in implant surgery is one of the essential conditions determining the predictability of a successful outcome. The use of set procedures and written protocols allows us to identify, measure and document the quality of the sterilisation process, and this is necessary not only in order to respect ethical codes of practice towards patients, but also to avoid possible medical-legal consequences of incorrect use and handling of medical equipment and to reduce the risk of failures, particularly in implantology. The term sterilisation refers to a series of physical and/or chemical processes, involved in standardised and clearly defined methodologies, able to destroy all types of microorganism present and/or all pathogens, both vegetative and spore forms; the aim of sterlisation is sterility, i.e. that state in which a microorganism is highly unlikely to survive. Spaulding’s idea that sterilisation and disinfection procedures should be classified according to the level of risk of infection carried by reusable medical devices and instruments (critical, semi-critical, non-critical) remains valid.
The transmission of infectious agents (viruses, bacteria, fungi) between healthcare workers and patients and from patient to patient in a clinical setting is called cross-contamination, and the term refers to diseases that can be contracted when an instrument that has been in contact with the blood, saliva, or other bodily fluids of an infected person comes into contact with the blood of another person; such instances are termed cross-contaminations because of the pattern of transmission between subjects (patient-healthcare worker-patient). They are a major public health problem, widely documented in dental practice. The only strategy for prevention is to adhere to procedures and behavioural practices of scientifically proven and recognised efficacy that, presented in the form of practical recommendations easily applicable in all dental settings, allow work to be carried out in “safe and protected” environments.
The risk of transmission of pathogenic agents during dental work arises in various situations: when using (intra- or extra-orally) sharp and/or pointed instruments contaminated with saliva or blood, both potential vehicles of pathogenic agents; or when using ultrasound devices and high-speed rotary instruments, the latter generating aerosols containing saliva, blood and microorganisms that can be inhaled and can contaminate the skin or mucous membranes, as well as the surfaces of the working environment; in addition, the problem of incorrect and inadequate cleaning and disinfecting procedures is not to be underestimated.
The surfaces of a dental studio can contribute to instances of cross-contamination. The guidelines issued by the Centers for Disease Control and Prevention (CDC) classify the surfaces in a dental office as housekeeping surfaces, i.e. those least likely to enter into the infection transmission chain (floors, walls, basins) or clinical contact surfaces, i.e. those that can be contaminated directly by the patient’s secretions (surfaces of the chair and accessories) or because they are touched by the operator (lamp handle, control panel, drawer knobs or handles, radiographic equipment, etc.) and are thus at high risk of transmitting microorganisms.
The cleaning and disinfecting of the working environment and medical devices is, therefore, a fundamental part of preventing infections.
Methods of sterilisation can be classified into different types according to the sterilising agent used. In dentistry the best known and most widely used sterilising agent is heat, particularly in the humid form of steam. Steam, under pressure, can reach temperatures higher than 100°C, and in these conditions can sterilise penetrable materials and surfaces exposed to the infecting agent. Steam is the safest, quickest, most economical and most innocuous method of sterilisation.
STAGES IN THE STERILISATION PROCESS
Used medical devices and instruments, before being sterilised, are put through a series of stages: collection, decontamination, washing, drying, checking, maintenance, dispatch, possible acceptance and selection.
Through these stages, the aim is to obtain a device or instrument that has a low bacterial load and is suitable for the sterilising system being used. This is achieved through:
- reduction of the microbial load present on the device (decontamination and washing)
- removal of all soiling matter from the surfaces of the device (washing and rinsing)
- verification of the suitability of the device for the chosen sterilisation process (rinsing, maintenance, possible acceptance and selection)
- a functional check of the treated instruments (functional check)
The exposure, or potential exposure, of operators to biological agents begins with the collection of used items (various materials, instruments and devices), given that these are, or may be, contaminated. For this reason, operators should avoid handling these items before the subsequent decontamination stage, or should handle them only when wearing appropriate personal protection devices.
PREPARATION OF ITEMS: DECONTAMINATION AND WASHING
Fig. 3.4 • Chemical decontamination: immersion in an ultrasonic tank containing disinfectant.
Decontamination is a procedure designed to reduce microbial load, both environmental and on reusable items, and also to reduce the operator’s risk of coming into contact with pathogenic agents while preparing them. As such it constitutes a preventive measure. One of the requirements of Italian law 626/94, it is a collective safety measure that must be performed prior to washing by immersion in an appropriate liquid. This safety measure contributes to the protection of operators involved in the sterilisation process, particularly those responsible for transporting and washing items. This aspect was, in fact, already taken into account in the Italian Health Ministry decree dated 28 September 1990 (on protecting workers against HIV infection), which, in art. 2, para. 2, states: “…Reusable instruments and devices, after use, must immediately be immersed in a chemical disinfectant of proven efficacy against HIV; this must be done prior to disassembly or cleaning operations carried out in preparation for sterilisation”.
Instruments must be immersed in a decontamination tank containing a suitable disinfecting fluid, as indicated by the manufacturer; furthermore, depending on the quantity of items treated, it may even be necessary to replace the fluid on a daily basis.
Medical instruments must be washed before they are sterilised.
Washing is essential as it serves to reduce the level of microbial contamination by over 90% and to remove organic matter that, if left, could prevent the sterilising agent from acting properly and thus render the whole process vain.
The washing stage involves: manual washing, automatic washing (in medical equipment washing machines), and ultrasonic washing.
Manual washing is preferably carried out using hot or warm water. The items are immersed in a liquid detergent solution, which helps to remove soiling matter, and they are scrubbed with special brushes.
Particular care must be taken with sharp or pointed objects and with those that have screws or articulations, which must be opened and cleaned inside.
It can be difficult to clean absolutely every part of an instrument, particularly the surfaces of very small instruments and those that have many anfractuosities; in these cases, it is advisable to use medical equipment washing machines and ultrasonic washing.
Automatic washing is carried out using medical equipment washing machines that automatically wash, rinse and dry the instruments. This method is to be preferred as the high temperatures reached (around 95°C) guarantee not only thorough washing, but also heat disinfection; it also reduces the amount of direct contact the operator has with contaminated surfaces and thus the risk of accidents to personnel; furthermore, medical equipment washing machines, like autoclaves, can be validated.
Fig. 3.5 • Rinsing.
Fig. 3.6 • Preparing the instrument tray for heat decontamination.
Fig. 3.7 • Heat decontamination in medical equipment washing machine.
Ultrasounds are sound waves emitted at a frequency that cannot normally be detected by the human ear alone. Through the use of “ultrasonic tanks”, they are able to decontaminate and clean dental instruments.
It is important to ensure that ultrasounds are applied correctly for this purpose: the tanks must be kept covered to prevent aerosolisation of the solution; the process must be carried out using an appropriate detergent solution and the cycle must last the time specified by the manufacturer; after the treatment the instruments must be drained and rinsed.
Appropriate personal protection devices must be worn when washing instruments and devices: head covers, strong gloves, disposable face masks, protective visors and waterproof overalls.
Before beginning the sterilisation process, it is essential to check that the equipment washed is completely dry, as any residual water could jeopardise the efficacy of the heat sterilisation process; for this reason, compressed air should be used to dry hollow items, or such items can be left standing on end.
Packaging is the procedure meant to guarantee that packaged materials and items, providing they are assembled, sterilised, stored, transported and used in accordance with the manufacturer’s instructions, remain sterile from the time of sterilisation until the moment of use, or until the use-by date is reached.
Before beginning the packaging process, it is necessary to check that the item to be packaged is complete, clean, and dry; any constituent parts must be disassembled, stoppers must be removed and the tips of needles and sharp objects must be protected; it is also necessary to check that all the surfaces will be directly exposed to the sterilising agent.
As a rule, instruments and devices are packaged singly, or in sets of equipment needed for specific procedures. In dentistry, the preferred packaging materials are sterile paper-polymer pouches, medical paper and small metal containers.
The European reference standard is UNI EN 868, which is divided into 11 parts; the first is introductory while all the other sections are given over to descriptions of material types, technical and chemical characteristics and physical tests that must be passed.
Packaging materials must, therefore, have the following characteristics: they must be compatible with the sterilising processes used, with the article/s contained in the package and with the labelling system used; they must not contain chemical agents whose toxicity could constitute an exposure risk at any time during the sterilising process, performed as stipulated, and/or that could contaminate the items being sterilised; they must be biocompatible; and they must be able to maintain the sterility of the packaged item(s).
Fig. 3.8 • Drying and maintenance.
Fig.s 3.9-3.10-3.11-3.12 • Different stages in instrument packaging.
STERILISATION BY STEAM UNDER PRESSURE
Sterilisers, also referred to as autoclaves, are units in which steam can be pressurised; they have leakproof chambers and are able to withstand high pressures.
Stream sterilisation is obtained through a combination of four factors:
Pressure: necessary to increase the boiling point of the water, hence the sterilising temperature increases in proportion to increases in the pressure.
Temperature: must be high enough to guarantee the destruction of microorganisms.
Time: the temperature is effective only if it is kept constant for specific times. The higher the temperature, the shorter the sterilisation time.
Fig. 3.13 • Autoclave.
Humidity: for the sterilisation process to be effective, the steam must be saturated (100% relative humidity).
The temperature of steam under pressure increases progressively in proportion to increases in the pressure of the steam.
Steam pressure and temperature are directly proportional to one another: a higher pressure corresponds to a higher temperature.
This relationship between these two parameters is valid only if the steam is saturated, i.e. not mixed with air.
The presence of air in the chamber is the factor most likely to prevent a correct steam sterilisation process.
If the air is not completely extracted from the steriliser, there will be differences in temperature inside the chamber and some of the material loaded for sterilising may find itself submitted to lower temperatures.
Autoclaves are equipped with special devices for eliminating the air present in the sterilisation chamber.
Sterilisation time and temperature are inversely correlated parameters: increasing the temperature increases the speed at which microorganisms are destroyed, thereby reducing the necessary exposure time.
In the same way, with longer sterilisation times it is possible to use lower temperatures. Safety is not increased by exceeding the indicated exposure times.
Phases in the saturated steam sterilisation process
1. Extraction of air from the chamber
2. Filling of chamber with steam
3. Steam is taken to temperature and penetrates the load
6. Baric balancing
Types of steam steriliser
Technological progress has allowed considerable advances in steam steriliser design and production.
The European Committee for Standardisation (CEN) divides steam sterilisers into two types:
a) Small steam sterilisers
These sterilisers (reference standard UNI EN 13060: 2005), designed for the sterilisation of medical articles, are used mainly in dentistry and in outpatient settings.
Because small sterilisers, like large ones, are classified as “medical devices” the manufacturer is obliged to declare their “intended use”.
The user is responsible for incidents occurring as a result of any use other than that specified by the manufacturer.
Although the intended use is stated, compulsorily, in the user manual, it should really be requested, and thus officially declared, during the negotiation stage, i.e. prior to the actual purchase of the steriliser; in this way, the purchaser, informed beforehand of any limits of use, is enabled to make the right choice.
Small sterilisers are divided into three subcategories according to the type of materials they can sterilise; according to the quantity and type of instrumentation requiring sterilisation, the following criteria (see table) must be taken into consideration.
b) Large steam sterilisers
Sterilisation using saturated stream sterilisers must be considered the method of choice for materials whose integrity is not jeopardised by the physical conditions created by the sterilisation cycle, given that it is regarded as the most rapid and economical method, and also that there exist indications for its validation (UNI EN 285, UNI EN 554).
These sterilisers can be used to sterilise articles in non-thermolabile rubber, medical textiles, surgical instruments, metallic instruments and glassware. Conversely, hydro-insoluble substances (oily substances and powders) and all thermolabile materials cannot be submitted to steam sterilisation.
Each type of material, depending on the difficulties it presents when exposed to saturated steam, requires a specific type of autoclave (class B, N or S as specified by EN directive 13060); the different types of material are:
- solid materials without hollow spaces (e.g. instruments with solid handles);
- porous materials; complex loads that retain air before the sterilisation cycle and remain damp at the end of it (e.g. coats, gowns, sheets);
- type A hollow loads: items with deep, narrow, hollow spaces (e.g. cannulas, handpieces, turbines);
- type B hollow loads: items with shallower, wider hollow spaces (e.g. tubes, containers).
This classification is based, in part, on how readily their surfaces can be exposed to the steam, which in turn is due to their retention of air and to the different degrees to which different materials retain moisture at the end of the cycle.
Fig.s 3.14-3.15-3.16 • Different stages in autoclave loading.
Basic procedure for loading steam sterilisers
One factor influencing the efficacy of steam sterilisation is the way in which the chamber is loaded. The instruments should not be packed too tightly: the steam must be able to reach all the parts of the load and it is necessary to avoid the presence of residual air. The sterilising agent is the steam that, under pressure, reaches very high temperatures, and it can only sterilise the material with which it comes into contact. The steam is introduced at the top of the autoclave chamber, while the air, which is heavier, is eliminated at the bottom. Therefore, the load must be distributed in such a way as not to impede the extraction of the air, or prevent full penetration of the steam. This is achieved by distributing the packages vertically, at a distance of at least 5 cm from the sides of the chamber and arranging them so as not to block the steriliser outlet. The smaller packages must be positioned above the larger ones, in order to prevent the formation of pockets of air that the steam cannot easily replace; similarly, lighter packages must be positioned above heavier ones, so as not to impede the diffusion of the steam within them..
The sterilisation process itself
The sterilisation cycle begins with repeated extraction of the air that is present in the autoclave chamber and in the load it contains, interspersed with the immission of steam (fractional vacuum system). This is followed by exposure of the load to the sterilising agent for a given time, which depends on pre-determined physical parameters (pressure and temperature). The sterilisation process itself ends with the dying of the load, which is necessary to remove most of the condensed steam, as a damp or wet load would easily be re-contaminated by environmental microbes. The drying phase is part of the autoclave’s automatic programme.
Choice of cycle. The choice of sterilisation cycle, i.e. of the set of physical parameters required for the particular load, depends on the type of material to be sterilised. The parameters to check are: exposure time, temperature and pressure. It is usual to use a 121°C cycle (pressure of 1 atm) for items in rubber and plastic with a low melting point and a 134°C cycle (2 atm) for all heat-proof materials, surgical instruments, fabrics and dressings.
Exposure time. The duration of exposure to the sterilising agent depends on the temperature of the steam: if the temperature of the steam is increased, the exposure time can be reduced, and vice versa. According to experimental studies, it is possible to obtain sterilisation using steam at a temperature of 121°C (1.1 bar pressure) for at least 15 minutes or 134°C (2.1 bar pressure) for at least 3 minutes and the choice of parameters (or sterilising cycle) depends on the material to be treated. The relationship between the three parameters (time, temperature and pressure), which are shown in the following table, is accepted by European standards applied in the hospital setting (EN 285, EN 554).
Safety is not increased by exceeding the exposure times indicated. It is, on the other hand, essential to adhere to the validations performed by the manufacturer when the autoclave was installed. Parameter values different from the pre-established ones may be used only if they are first validated by the manufacturer.
Unloading the steriliser. The person unloading the steriliser must wear adequate protection devices in order avoid coming into direct contact with the load, which will be extremely hot. The unloaded packages must be laid on a clean, dry rack or trolley, and must not be handled for at least 10 minutes. At the end of the sterilisation cycle, the physical sterilisation parameters must be checked by the person responsible before the devices can be deemed useable.
The packaging around sterilised material forms an antimicrobial barrier, but this barrier can be impaired by various environmental factors, such as the presence of dust, humidity, contaminated air, and factors linked to the package itself, i.e. it may be damaged, or the operator may not open or handle it in the correct way. It is therefore necessary to ensure good environmental and structural conditions in order to guarantee the best possible storage conditions, choosing clean dry rooms, with easy-to-clean floors and walls; doors and windows should be kept closed and there should be limited access to the rooms. The ambient humidity and temperature should be less than 50% and between 18° and 22°C, respectively. Any shelving must be positioned in such a way as to ensure that the material placed on it does not come into contact with the walls (stainless steel shelving 20-25 cm from floor level, 40-50 cm from the ceiling and 15-20 cm from the wall is recommended), even though it is far better to place the material in closed, scrupulously clean cupboards, well away from heat sources. It is important not to underestimate the importance of a series of essential organisational measures: hands must be washed before handling packages; packages must not be handled unnecessarily; sterilised material must be stored in such a way that it is used sequentially, in the order in which it was sterilised, so that packages are not allowed to pass their use-by date; elastic bands must not be used to bundle packages together as this could result in microdamage to the biological barrier; the amount of material stored should be compatible with requirements. Dropped, wet or damaged (torn, open, perforated) packages must be considered contaminated. They must be opened and their contents must be prepared to undergo a new sterilisation cycle. When sterilised instruments are used, their sterilisation batch numbers must be noted in the patient’s clinical records, thereby archiving an important datum that links the patient with the sterilisation treatment session and with the “state” of the instruments used. At the end of the treatment, it will thus be possible, if necessary, to provide the patient with the list of sterilisation batch numbers of the instruments used in each session. This is a good policy, which also helps the patient to appreciate the quality of the intervention.
The autoclave must have the following requisites:
Conformity with the intended use of the device (93/42 CEE – Italian law 46-1997): therefore, the manufacturer must specify (in the user manual or similar document) what instruments can be sterilised in that particular autoclave, and in what types of packaging.
Declaration of conformity (89/336 CEE – 93/42 CEE – 73/23 CEE): this is a document that certifies the autoclave’s conformity with certain requisites, particularly with regard to safety. This document must always be kept in the studio or laboratory where the steriliser is located.
Validation (EN 554): checks to be carried out by the manufacturer/specialised technical staff and checks to be carried out by the user.
Checks to be carried out by the manufacturer/specialised technical staff: inspection; installation; periodic calibration.
Checks to be carried out by the user: checks of physical parameters; vacuum test; Bowie-Dick test, Helix test; biological test.
In accordance with the indications contained in European directive UNI EN 554: 1996, sterilisers, both large and small, are subject to periodic, systematic tests and checks.
The programme of systematic checks should include sufficient tests and checks (also indicating the frequency with which they should be carried out) to guarantee that the sterilisation cycle parameters are always within the limits determined in the performance qualification.
Fig.s 3.17-3.18 • Instrument storage.
CHECKS TO BE CARRIED OUT BY THE USER: PHYSICAL PARAMETERS
The checks carried out by the user serve to verify the correct functioning of the autoclave. It is necessary to carry out the following: vacuum test, Bowie-Dick test, Helix test; biological test.
None of these tests can replace the checks of the physical parameters, which are part of the equipment functioning checks; they are carried out using measurement instruments supplied with the steriliser, namely: manometers, thermometers, chart recorders, electrical and acoustic indicators which signal the various physical parameter values reached during the phases of the sterilisation cycle.
CHAMBER AIRTIGHTNESS TEST
The vacuum test is carried out before starting each day’s cycles. Serving to evaluate the airtightness of the chamber, it involves monitoring the chamber pressure.
The test is valid if, during the 10-minute test time during which the vacuum is maintained, loss of pressure does not exceed 13 mbar; if this condition is not met, then the autoclave cannot be used and an extraordinary maintenance intervention must be requested.
STEAM PENETRATION TEST
Fig. 3.19 • Sterilisation cycle validity test.
The Bowie-Dick test must be performed daily on turning on the steriliser. The test pack, which must be the right way up (not overturned), must be placed in the centre of the autoclave, on the lower level of the vacuum chamber (in these conditions there will be a greater amount of air to be removed and the test will be more critical).
Select the pre-set programme. The sterilising action of the steam autoclave is strictly dependent on the ability of the saturated steam (i.e. not mixed with air) to reach all the parts of the load. In the event of inadequate extraction of the air, the steam introduced under pressure will push the residual air towards the centre of the pack, where it will form an air bubble or cold area.
The presence of air in the pack prevents the sterilising agent from penetrating completely.
Using the Bowie-Dick test, it is possible to verify the extraction of air contained in porous loads (gauzes and fabrics). A positive result means that the steam has penetrated the inside of the test pack rapidly and correctly. A negative result (failure) indicates inefficient extraction of the air.
The Bowie-Dick test must be conducted in compliance with the description given in the UNI EN 285 directive. The test is carried out using a single-use or reusable test pack into which a special sheet of paper is inserted; this paper is impregnated with ink (chemical indicator) which will change colour evenly from the edges to the centre.
Reading the test:
At the end of the test cycle, check that the ink-impregnated paper has changed colour evenly, i.e. with the same intensity, from the edges to the centre. This result indicates that the sterilisation cycle has taken place correctly. If, on the other hand, the pre-vacuum conditions were not efficient and there was air still present when the steam was introduced, the pressure of the steam pushes this air to the centre of the pack where it collects as a bubble.
Thus, the presence of a lighter area in the centre of the sheet shows that the autoclave is not functioning correctly.
Class-B autoclaves (as defined by the prEN13060 standard) can be submitted not only to the Bowie-Dick test, but also to the Helix text, which is even more selective than the Bowie-Dick in evaluating the performance of the machine; the Helix test is used to verify the conditions in steam autoclaves used to sterilise hollow instruments (e.g. dental handpieces) and the test kit comprises a 1.5-m tube with a cross-section of 2 mm, at the end of which is a closed capsule in which is inserted an indicator that changes colour if the steam, at the sterilisation temperature, has managed to penetrate as far as the capsule.
Fig. 3.20 • Test to confirm that sterility has been correctly obtained.
Fig.s 3.21-3.22 • Loading process of the hollow instruments test (Helix Test).
Chemical indicators are used to monitor the presence or achievement of one or more of the variables (time, temperature, presence of saturated steam and relative humidity) necessary in order to obtain effective sterilisation.
They may either be solutions in test tubes or “strips” that gradually change colour according to the conditions of the sterilisation process; they must be used with every load and they are an effective form of control. The most important characteristic distinguishing chemical tests from microbiological ones is the fact that their results can be read immediately, without the need for incubation or culture media.
The commercially available indicators may be sensitive to several variables or only to one. Indicators sensitive to only one variable cannot be used alone: it is essential that they be used together with other indicators.
Strips are chemical indicators meeting requisites governed by the UNI EN 867 directive. The class to which they belong is specified on the package or on the technical data sheet. It is essential to use class D multi-variable indicators for validation of the sterilisation process. The use of class C indicators is not recommended as they are sensitive to a single variable: sterilising temperature (single-parameter calibrated).
Fig. 3.23 • Indicator strip used to confirm that sterility has been correctly obtained.
The performance (times and modalities) of routine biological tests is a debated topic; their results are normally read 48 hours after the sterilisation process (the incubation period). This testing method is based on the use of biological indicators, namely bacterial strains of known identity and population. Commercial preparations are used that consist of test tubes (technologically advanced systems) containing heat-resistant spores of Bacillus Steathermophilus which are placed in the part of the autoclave least easily penetrated by the steam. The spores can also be placed on strips of paper (classical systems). At the end of the cycle, the spores are brought into contact with a liquid which changes colour if the spores are not dead and the specimen is then cultured in the laboratory as specified by the manufacturer. The biological indicators used in dentistry are normally solid materials which may already contain, internally, culture media with which the spores are brought into contact after the sterilisation process; the inoculation of culture media must be performed manually. Adding a special pH indicator to the culture medium may make it possible to detect the growth of spores by means of colour changes.
The traceability system is a long-term control system that, through a series of data present on the packaging, makes it possible to identify and, if necessary, trace a sterilised device at any point in its pathway (from removal from the autoclave to use), and also to identify the operator responsible for the process. The traceability system must also extend to the sterilisation process itself, through recording, on special forms, of the type of load and the cycle programme chosen (which corresponds to the temperature, pressure and exposure time established by the manufacturer). Records must be kept of all packages submitted to sterilisation and all sterilisation cycles performed, noting data making it possible to identify the sterilisation batch, in particular: the date of sterilisation; the number of the autoclave used; the number of the sterilisation cycle. It is also obligatory to enter in the sterilisation register data relating to the material sterilised (or sets of instruments sterilised), the batch identification references, and data relating to the sterilisation process checks, as indicated below. The following documents must be kept in the sterilisation folder: machine data sheet (description, serial number, manufacturer, date of inspection, etc.); technical specifications; validation checks; user manual; maintenance register; register of processes and sterilised loads; documents relating to systematic checks.
According to the UNI EN 556 directive, sterilisation is a special process in that the sterility of the end product cannot be verified directly; hence the need to apply documented procedures that certify the validity of the process itself: these procedures, taken together, are defined validation. This means that, for the whole process to be deemed validated and safe for both operators and patients, it must be carried out in accordance with high quality standards, the checks carried out focusing on the suitability of the environments used and the performance levels of individual machines, determined in accordance with the technical standards of the sector.
The main standards take the form of legislative decrees, technical standards (UNI – Italian National Standards Institute), and guidelines.
REGULATIONS: Italian law decree n. 46 of 24 February 1997 (implementation of 93/42/CEE on medical devices): the sterilisation process is considered a critical process and must therefore meet the essential requisites set out in Attachment I of the aforementioned decree; “devices supplied in sterile state must be produced and sterilised using a validated and appropriate method”.
GUIDELINES: Issued by the Center for Disease Control (CDC) in Atlanta, by the Association for the Advancement of Medical Instrumentation (AAMI/USA) – the Guideline for Moist Heat Sterilisation of Medical Products – and by the Association of Operating Room Nurses (AORN).
TECHNICAL STANDARDS: (UNI – Italian National Standards Institute). These are the technical standards of reference for countries that are members of the European Committee for Standardisation (CEN).
Below is the complete set of technical standard relating to sterilisation.
- UNI 10384-1:1994. Equipment and processes for sterilisation of hospital waste. General requirements.
- UNI EN 1174-1:1996. Sterilisation of medical devices. Estimation of the population of microorganisms on product – Requirements
- UNI EN 1174-2:1998. Sterilisation of medical devices. Estimation of the population of microorganisms on product – Guidance
- UNI EN 1174-3:1998. Sterilisation of medical devices. Estimation of the population of microorganisms on product – Guide to the methods for validation of microbiological techniques
- UNI EN 13824:2005. Sterilisation of medical devices. Aseptic processing of liquid medical devices. Requirements
- UNI EN 552:1996/A1:2000. Sterilisation of medical devices. validation and routine control of sterilisation by irradiation
- UNI EN 285:1998. Sterilisation. Steam sterilizers. Large sterilisers
- UNI EN 550:1996. Sterilisation of medical devices. Validation and routine control of ethylene oxide sterilisation
- UNI EN 552:1996. Sterilisation of medical devices. Validation and routine control of sterilisation by irradiation
- UNI EN 552:2002. Sterilisation of medical devices. Validation and routine control of sterilisation by irradiation
- UNI EN 554:1996. Sterilisation of medical devices. Validation and routine control of sterilisation by moist heat
- UNI EN 556:1996. Sterilisation of medical devices. Requirements for medical devices to be labelled “Sterile”
- UNI EN 556:2000. Sterilisation of medical devices. Requirements for terminally sterilised medical devices to be labelled “Sterile”
- UNI EN 556-1:2002. Sterilisation of medical devices. Requirements for medical devices to be designated “STERILE” – Requirements for terminally sterilised medical devices
- UNI EN 556-2:2005. Sterilisation of medical devices – Requirements for medical devices to be designated “STERILE” – Part 2: Requirements for aseptically processed medical devices
- UNI EN 866-1:1998. Biological systems for testing sterilisers and sterilisation processes. General requirements
- UNI EN 866-2:1998. Biological systems for testing sterilisers and sterilisation processes. Particular systems for use in ethylene oxide sterilisers
- UNI EN 866-3:1999. Biological systems for testing sterilisers and sterilisation processes. Particular systems for use in moist heat sterilisers
- UNI EN 866-4:2001. Biological systems for testing sterilisers and sterilisation processes. Particular systems for use in irradiation sterilisers
- UNI EN 866-5:2001. Biological systems for testing sterilisers and sterilisation processes. Particular systems for use in low temperature steam and formaldehyde sterilisers
- UNI EN 866-6:2002. Biological systems for testing sterilisers and sterilisation processes. Particular systems for use in dry heat sterilisers
- UNI EN 866-7:2001. Biological systems for testing sterilisers and sterilisation processes. Particular requirements for self-contained biological indicator systems for use in moist heat sterilisers
- UNI EN 866-8:2001. Biological systems for testing sterilisers and sterilisation processes. Particular requirements for self-contained biological indicator systems for use in ethylene oxide sterilisers
- UNI EN 868-2:2002. Packaging materials and systems for medical devices which are to be sterilised. Sterilisation wrap. Requirements and test methods
- UNI EN 868-6:2002. Packaging materials and systems for medical devices which are to be sterilised. Paper for the manufacture of packs for medical use for sterilisation by ethylene oxide or irradiation. Requirements and test methods
- UNI EN 868-7:2002. Packaging materials and systems for medical devices which are to be sterilised. Adhesive coated paper for the manufacture of heat sealable packs for medical use for sterilisation by ethylene oxide or irradiation – requirements and test methods
- UNI EN 868-8:2002. Packaging materials and systems for medical devices which are to be sterilised. Re-usable sterilisation containers for steam sterilisers conforming to EN 285. Requirements and test methods
- UNI EN ISO 10993-7:1997. Biological evaluation of medical devices. Ethylene oxide sterilisation residuals
- UNI EN ISO 11140-1:2005. Sterilisation of health care products – Chemical indicators – Part 1: General requirements
- UNI EN ISO 11737-2:2001.Sterilisation of medical devices – Microbiological methods – Part 2: Tests of sterility performed in the definition, validation and maintenance of a sterilisation process
- UNI EN ISO 14160:2000. Sterilisation of single-use medical devices incorporating materials of animal origin – Validation and routine control of sterilisation by liquid chemical sterilants
- UNI EN ISO 14161:2002. Sterilisation of health care products. Biological indicators. Guidance for the selection, use and interpretation of results
- UNI EN ISO 14937:2002. Sterilisation of health care products. General requirements for characterisation of a sterilising agent and the development, validation and routine control of a sterilisation process for medical devices
- UNI EN ISO 15882:2003. Sterilisation of health care products. Chemical indicators. Guidance for selection, use and interpretation of results
- UNI EN ISO 17664:2005. Sterilisation of medical devices. Information to be provided by the manufacturer for the processing of resterilisable medical devices.
Guidelines express the position, on a specific issue or question, of the organisation or body that issues them and they are not binding. However, when the issuing body enjoys a certain degree of prestige (nationally or internationally) they assume considerable significance and, in the absence of other sources of reference, can be accepted as indications on correct behaviour. Some of the most prestigious international guidelines on sterilisation are those issued by the CDC (Center for Disease Control) in Atlanta, by the AAMI/USA (Association for the Advancement of Medical Instrumentation), with its Guideline for the Moist Heat Sterilization of Medical Products (1987), and by AORN (the Association of Operating Room Nurses). Also valid as a guideline is the Circular n. 56 issued by the Italian Ministry of Health on 22 June 1983: “Use of toxic ethylene oxide gas”, which contains, among other things, suggestions on the packaging and storing of materials that can also be applied in the context of steam sterilisation. Publications, articles in the specialised press and reports presented at national and international congresses can also provide guidance on excellent operating procedures, providing they are produced by authors, health organisations and associations that are recognised as authorities in the sector.
Technical standards are developed, approved and published by a standardisation body whose aim is to establish sets of rules, specifications, procedures and/or technical characteristics relating to given products or processes. The technical standard on medical devices, valid for all countries that are members of the European Committee for Standardisation (CEN), is Directive 93/42/CEE. In Italy, this directive, which regulates the entry onto the market of all medical devices, was adopted through law decree n. 46 of 24 February 1997 (ordinary supplement to the Gazzetta Ufficiale n. 54 of 6.03.97).
The harmonised standards relating to methods of sterilising medical devices using steam are:
- UNI EN 554 Sterilisation of medical devices. Validation and routine control of sterilisation by moist heat
- UNI EN 556 Sterilisation of medical devices. Requirements for medical devices to be designated “STERILE”
- UNI EN 285 Sterilisation. Steam sterilisers. Large sterilisers
- UNI EN 866-1 Biological systems for testing sterilisers and sterilisation processes
- UNI EN 866-3 Biological indicators for testing sterilisers and sterilisation processes
- UNI EN 867-1 Non-biological systems for use in sterilisers. Part 1: general requirements
- UNI EN 867-2 Non-biological systems for use in sterilisers. Part 2: process indicators
- UNI EN 867-3 Non-biological systems for use in sterilizers. Specification for Class B indicators for use in the Bowie and Dick test.
- UNI EN 868-1 Packaging materials and systems for medical devices which are to be sterilised.
Of these standards, UNI EN 556, UNI EN 285 and UNI EN 554, deserve particular attention.
UNI EN 556: this standard reiterates that the safety of a sterilised product, free of viable microorganisms, can be established only in terms of the probability of microorganisms surviving. It is generally accepted that a product can be defined sterile when the chance of a single viable microorganism being present is equal to or less than 10-6.
UNI EN 285: this standard refers to sterilisers defined “large” i.e. those with a sterilisation chamber having a volume of at least 1 module (that is, a volume of 30x30x60 cm), or multiples thereof, and it describes in detail:
- the design principles relating to dimensions, materials, instruments to be installed and safety;
- the characteristics of the regulation/monitoring/registration devices;
- the tests to which they must be submitted, divided into tests on the prototype, manufacturer’s tests, installation tests;
- the methods of performing these tests, the reference loads to use, the minimum results that must be obtained;
- the minimum requisites of the fluids used (steam/water/air);
- the documentation that the manufacturer must supply to the customer.
UNI EN 554: this standard describes the methods for the validation and routine control of steam sterilisation. These latter two standards allow validation of the sterilisation process as required by Italian law decree n. 46 of 24-2-97. Validation is a global procedure that is performed at several levels: in acceptance for service and in performance qualification. The latter, in turn, comprises physical qualification and microbiological qualification. In detail: – acceptance for service: this is the procedure for obtaining and documenting the evidence that the equipment has been supplied and installed in conformity with the specifications and that it works within predetermined limits when used in accordance with the instructions for use; – performance qualification: this is the procedure for obtaining and documenting the evidence that the equipment, as accepted for service, when it is used in accordance with the process specifications, will be able to provide an acceptable product; – physical qualification: this procedure is designed to verify the reproducibility, in each cycle, of the parameters necessary to achieve sterilisation; – microbiological qualification: this is a further safety guarantee based on the effectiveness of the sterilisation cycle.
ORGANISATION IN TRAYS
In all fields of activity, and particularly in dentistry, ergonomics is a factor central to ensuring that work is carried out work rapidly, effectively and in the best way possible.
Having at one’s disposal an adequate supply of the necessary instruments, no more no less, organised so as to facilitate their use for their given purpose, contributes to the achievement of better results.
In the surgical field this factor is particularly crucial.
Speed of action is one of the significant factors for achieving quality in surgery.
Reduction of operating times means less morbidity, a more straightforward post-operative course and less stress for the patient: overall, a better quality result.
This is why all surgeons, once they have mastered the operating techniques, endeavour to reduce operating times progressively and significantly.
A key factor in achieving this objective is correct organisation of the instruments.
Implant surgery is divided into two distinct phases:
- first, a phase of normal stomatological and/or periodontal surgery;
- second, a phase of bone and implant surgery proper.
Fig.s 3.24-3.25-3.26 • Examples of organised surgical trays.
This distinction between these two operating phases is important, as the first is normally highly contaminating and will, as a result, necessarily result in considerable contamination of the surgical instruments.
We might consider, for example, the case of post-extraction implants in a patient with periodontal disease.
Even after pre-surgical treatment has been carried out, the periodontal tissues will never be completely restored to health, therefore the surgical instruments at the end of the first phase of the operation will inevitably be highly contaminated.
This is why it is recommended to prepare two different trays of surgical instruments: one for the first phase and another, which is kept absolutely sterile, to be used only for the phase in which we prepare the surgical alveolus and insert the implants.
The first kit must contain, in addition to the instruments required for any extractions (syndesmotome, levers and clamps), a Columbia retractor, a P24G elevator, a Prichard curette, a curved Cocker Mosquito clamp, a scalpel blade holder, preferably cylindrical, a 7/8 Younger-Good curette.
The second: a Columbia retractor, a CP 12 periodontal probe, a Prichard curette, a needle holder, suture scissors, surgical tweezers.
THE STERILE OPERATING FIELD
For the above reasons, there is no point preparing a sterile field prior to every single step in the surgical process. Indeed, it is best first to complete the creation of the flap and/or the extraction phase (should this be necessary) and only then to prepare a new sterile field on the implant-bearing surfaces, scrub up and put on a sterile gown and gloves. At this point, and only having prepared the field, the new instrument kit is opened and the instruments (handpiece, motor and cable, tube and whatever else is needed) are removed from the sterile package. In this way it is easy to obtain and maintain the greatest possible level of sterility in the critical phase of the implant operation.
Vincenzo Bucci Sabattini
Primary stability is the sine qua non of obtaining optimal healing of tissues generally. In the case of a skin lesion, in order to obtain the best possible scar aesthetically, which may even be almost invisible, it is crucial to ensure that the flaps are completely stabilised by appropriate sutures. If this condition is not met, there will be healing by second intention, which will result in the formation of tissue markedly different, both mechanically and aesthetically, from normal skin. In the same way, failure to join two bone fracture fragments in a precise and, above all, stable way will result not in bone union, but in pseudoarthrosis: a fibrous layer will form between the ends of the bone fragments, thereby culminating in negative repair due to a process of healing by second intention.
For these reasons, correct healing of the socket around the surgical implant, which leads to osseointegration, demands absolute stability of the implant. Thus, primary stability is the first crucial condition for obtaining dental implant osseointegration.
Primary stability depends on many factors including, fundamentally, the quality of the bone and, according to this, the preparation of the surgical socket, and finally the implant macromorphology and microphology.
Numerous factors contribute to creating the conditions necessary for osseointegration, and to determining the quantity of bone-implant contact. These include asepsis, the blood supply to the site and the macro- and micromorphology of the implant. Together with these, other extremely important factors playing a key role in surface treatment are related to the implant threads: their shape, depth in relation to the osteotomy line, angle, and reciprocal distance.
In this regard, it must be appreciated that there cannot exist a single implant site preparation protocol and type of implant suitable for all different anatomical situations.
The choice of implant socket preparation procedure and of implant morphology is dictated by the type of bone: different types of bone need specific implants that differ from one another not only in terms of diameter and length, but also in terms of morphology and threads; accordingly, the surgical socket preparation procedure will also differ.
In very low-density, highly vascularised bone tissue, it is best to under-prepare the surgical socket and use a self-tapping implant with a wider collar and more aggressive thread design. For example, if we use a Ø 2.5 drill, we can insert an implant that has a apical end of the same Ø, but that is conical in shape and has cutting threads up to Ø 4 at the collar. In this way it will be extremely easy to achieve primary stability of, or greater than, 50 Ncm, even in D4 bone.
Conversely, in the presence of very dense and poorly vascularised bone tissue, it will be necessary to use an implant with less aggressive threads, and also to use all the drills up to the one compatible with the chosen implant Ø. For example, in D2 bone it could be useful to choose a conical implant, 4.3 Ø, and to use the whole sequence of dills provided by the manufacturer: the pilot drill, the Ø 2.5 drill, the Ø 2.8 drill and all the subsequent drills up to the one corresponding to the implant.
In this way, the desired torque is reached without excessively compressing the bone tissue. Excessive compression of dense and poorly vascularised bone could cause ischaemic damage, possibly severe (leading to loss of the implants and bone necrosis). However, if the above premises are respected it is relatively easy to obtain adequate primary stability and, as a result, bone-titanium integration in a physiological period of time (4/6 weeks): this is considerably shorter than the time envisaged by the Branemark protocol.
Implants, once inserted in the bone tissue at a torque able to guarantee sufficient primary stability (preferably 35 Ncm or more), are able, without sustaining damage, to withstand the application of loads that are directed along their long axis. Conversely, when they are subjected to tangential forces (vestibular-lingual and/or mesio-distal) the bone marrow-derived perivascular pluripotent mesenchymal cells, which are recruited to the site after the surgical procedure, instead of differentiating towards the osteoblastic cell line differentiate towards the fibroblastic and/or adipogenic lines. The mature osteoblasts already present are unable to achieve integration and the result is the formation of fibrous tissue around the implant, which leads to implant failure.
It is essential to have a good understanding of this phenomenon before performing an immediate loading prosthetic implant rehabilitation procedure.
With the aim of obtaining better implant stability and of promoting osseointegration, many forms of implant have been proposed over the years. The objective pursued has always been that of conferring on the implant the necessary immediate stability.
Over the years we have also seen an extremely wide range of implant designs.
Of the various morphologies proposed, all that remains today is the screw. But even screws differ.
It is well known that the threads, but also the morphology of the body of the implant, will differ depending on the density of the bone being treated. Indeed, in orthopaedics, too, there exist screws of at least two types: cortical bone screws and cancellous bone screws.
A tightly threaded screw with very closely positioned threads (e.g. iron-type screw) is undoubtedly more suitable for a site of dense bone tissue, such as the interforaminal region of the mandible.
Fig. 3.27 • 1960s: Dr Linkow’s Vent-Plant.
Instead, for upper maxillary bone it is certainly better to use a wood-type screw or, in any case, a self-tapping screw with threads that cut the cancellous bone trabeculae without crushing them.
Many studies have been performed to evaluate implant macromorphology.
Implant macromorphology, which influences the speed of osseointegration and the possibility of directing the occlusal forces along the axis of the implant, could be a factor able to contribute to more predictable outcomes of immediate and early loading.
The macromorphology of the screw, too, has been shown to be crucial both to the achievement and the maintenance of osseointegration, and to the quantity of bone-implant contact that can be obtained. In this regard, while the angle of the threads and the distance between the osteotomy line of the surgically prepared socket and the shank of the screw remain stable, the dimensions of the threads themselves and their reciprocal distance can vary.
A space left between the implant and the bone wall acts as a “bone chamber” and speeds up the formation of new bone tissue.
In summary: the aspects of implant morphology to be considered extremely important are: a form that increases immediate stability and limits bone compression.
Thread characteristics (orientation, angle etc.) that allow the occlusion forces to be directed along the axis of the implant, eliminating the tangential forces that would result in cell differentiation unfavourable to bone-implant integration.
Fig. 3.28 • Berlungdh T, Abrahamsson I, Lang NP Lindhe J. De novo alveolar bone formation adjacent to endosseous implants. A model study in the dog. J Clin Oral Impl Res, 14, 2003, 251-262.
Fig. 3.29 •
“The maximum micro-movement to allow for a differentiation in bone cells is 28 microns. A movement superior to 150 μ will induce differentiation into fibrous cells.”
Pilliar, Lee, Maniatopoulos, 1986, Clin. Orthop.
THE AIM OF AN IMPLANT SCREW DESIGN: TO CONVERT CUTTING FORCES INTO COMPRESSION FORCES DIRECTED ALONG THE IMPLANT AXIS
– IS BONE HEALING A FUNCTION OF IMPLANT MACROMORPHOLOGY?
– YES !
Fig. 3.30 • F1: TANGETIAL FORCE, F2: COMPRESSIVE FORCE, F: AXIAL FORCE.
Here we show some extremely significant images taken from an experimental study in beagles carried out by Dr Paulo Coelho of New York University.
The aim of the study was to ascertain whether or not the macro design of the implant influenced bone healing, in terms of both quality and time.
Implants were inserted into the animals’ tibial plates and after 48 hours it was possible to observe early bone remodelling corresponding to the compression areas.
At 72 hours, the investigators, both by means of polarised light microscopy and tetracycline labelling, observed the absence of necrotic spots in the area near the cervical part of the implant and, in a broader field, apposition of new, vascularised bone adjacent to the implant surface.
On the basis of current knowledge, which is also supported by the study just cited, it can be affirmed that the bone healing process, certainly as far as healing times are concerned, is a function of the implant macomorphology, and of the surface treatment.
In dental clinical practice, and in prosthetic implantology particularly, the materials and instruments chosen are often crucial to the quality of the outcome.
For this reason, the authors of the present volume, in the light of research findings and the results of independent studies, and also on the strength of their considerable clinical experience, which includes the follow up of a great number of resolved cases, and reassured by literature data, decided to focus, here, on the Intra-Lock® implant system.
In choosing this method, they have avoided merely adapting to what is available on the market. Well aware of the characteristics that an implant must have in order to constitute what might be deemed the best option, both in relation to the biology of surgical healing and the ergonomics of the prosthetic procedures, they chose, among the various good quality implant systems available internationally, the ones produced by Intra-Lock International®.
Intra-Lock®, among other features, allows the clinician to choose between many different implant sizes and, above all, shapes, each designed for different conditions, anatomical, dimensional and bone density, that may be encountered.
All the implants are supplied with the unique OsseanTM surface treatment.
Choosing an implant is probably more difficult than using a one-for-all implant designed for all situations.
It undoubtedly demands, in addition to the obviously essential prosthetic skills, a better and greater knowledge of physiology and of bone and soft-tissue biology, but these “difficulties” must be weighed up against the possibility of obtaining optimal results, because one is using the best means: the most suitable for the single case.
Intra-Lock International® offers users continuous and timely updating, based on the latest research data. It has recently proposed a series of new implant models: CT, which is for low-density bone, has a different macromorphology from DT, which is for dense bone (usually mandibular); in addition, there is the more recent Blossom model, as well as large-diameter, short length systems for the replacement of molars close to high-risk anatomical structures.
The extent to which implant macromorphology influences the healing of the surgical site, the speed of osseointegration and the quantity of bone-implant contact has already been explained, but is here reiterated, albeit briefly.