3i-Implant Innovations® system and aesthetic implant surgery: the rationale for selection

Introduction

Developments in modern implantology, based on our knowledge of osseointegration (^{Adell et al., 1981}, ¹⁹⁹⁰ ; ^{Jemt et al., 1989} ; ^{Laney et al., 1994} ; ^{Lazzara et al., 1996}), have permitted simplification of the surgical and prosthetic techniques (^{Buser et al., 1992}), a reduction in treatment times (^{Lazzara et al., 1998}) and, indeed, an improvement in the bone's response to rough titanium (^{Wong et al., 1995}).

At the same time these advanced technologies are of little value unless they can be applied to daily practice, especially in relationship to the aesthetics of implant-supported prostheses which is a permanent challenge to the profession.

The aim of this article is to assess the capacity of 3i-Implant Innovations^® to meet, in the most satisfactory way, all those clinical situations where success depends on the aesthetic result.

In general, irrespective of the implant system used, the aesthetic result is precisely linked to the following criteria (^{Garber and Belser, 1995} ; ^{Jansen and Weisgold, 1995}):

- the presence of well-developed gingival papillae on both sides of the implant crown ;

- the subgingival location of the crown margin ;

- the absence of discoloration of the gingival margin due to the grey metallic colour of the collar showing through ;

- production of a clinical crown, the length of which is the same as the tooth it replaces ;

- production of an emergence profile of the same shape as that of the missing tooth.

It seems logical to us that amongst the considerations to be taken into account before arriving at the 3i-Implant Innovations^® system, the greatest weight should be given to an appreciation of the effect that the surgical and prosthetic components have on the last of the criteria cited, i.e. the emergence profile. This is the essential determinant factor, common to all aesthetic restorations, irrespective of whether the implants are in the anterior or posterior segments.

Definition of emergence profile

The emergence profile corresponds to the shape of the abutment as well as the implant itself which, in the transgingival position, enables a transition between the diameter of the implant and the mesio-distal diameter of the artificial crown to reproduce that of the missing tooth.

The determinants of the emergence profile

In any clinical situation, the creation of an emergence profile depends upon the position in space and the size of the neck of the implant as well as the peri-implant soft tissue morphology. These three factors determine the height, the angulation, the width, the site, the contour of the finishing line and, finally, the means of screwing or bonding the definitive prosthesis in place (^{Chiche and Leriche, 1998}).

Selection of the implant in relationship to the aesthetic outcome

One of the major developments in implantology over the last 10 years has been the ability to adapt the diameter of implants to the dimensions of the bone into which they are inserted. 3i-Implant Innovations suggests submerged implants of commercially pure titanium with an external hexagon. They have screw threads and are produced in diameters of 3.25, 3.75, 4.0, 5.0 and 6.0 mm. Non-submerged implants with a morse-taper are produced in diameters of 3.25, 4.0 and 5.0 mm. From the point of view of osseointegration, this range of implants (of the same length but differing diameters) enables the operator to optimize the bone-implant contact as their diameters increase.

From the prosthetic point of view, the diameter of the implant at the level of its junction with the post represents the diameter from which changes to the emergence profile are possible. This principle is fundamental because it indicates that implants with an external hexagon are those that are the most adaptable for use ; the neck of the implant being submerged and positioned at the level of the bony crest. It is because of their great potential for adjustments and adaptation to the clinical situation that they are indicated mostly for use in the anterior segment.

Dimensions of implants and gingival papillae

The presence of a papilla is an essential aesthetic element for anterior implants (^{Salama et al., 1995}). The maintenance or the enlargement of papillae depend on four factors that must be taken into account from the surgical stage of treatment:

- in the case of a single tooth implant, the presence of bone in the interdental region ;

- the presence of radiologically visible peaks of bone in the form of a hemi-septum at the level of the adjacent teeth constitutes the best guarantee that the papillae will be present at the end of the prosthetic treatment (^{fig. 1}, ², ³ and ⁴ ) ;

- the presence of at least 1.5 to 2.0 mm space mesio-distally between the implant and adjacent tooth ;

- the presence of at least 2.5 to 3.0 mm space between two implants.

Standard implants

Consideration of the above dimensions directly affects the choice of which implant diameter to use from the prosthetic and gingival points of view. The minimum mesio-distal space between two teeth required to place such an implant is 7.0 mm (^{Lekholm and Jemt, 1989}). This dimension corresponds to a standard screw implant with a neck diameter of 4.1 mm that must be 1.5 mm from the adjacent teeth in order to have sufficient space to maintain the interdental papillae. In the anterior segment, placement of a standard screw implant is possible in most cases because the mean mesio-distal diameter of a central incisor, a canine and even a premolar is between 7.5 and 9.0 mm (^{Reynolds, 1968}).

Small diameter implants

Particular attention must be paid to the replacement of upper lateral and lower incisors because, in the majority of cases, their mean diameter of 5.5 mm contraindicates the use of standard screw implants (^{Block and Kent, 1993} ; ^{Spiekermann et al., 1995} ; ^{Lazzara et al., 1996} ; ^{Buser et al., 1997}). However, the use of the Micro-Miniplant^® type implant with a neck diameter of 3.4 mm allows a space of 1 mm each side of the implant. Nevertheless, a minimum distance of 5.5 mm between the teeth is required for a Micro-Miniplant^® implant with a neck diameter of 3.4 mm ( ^{fig. 5}, ⁶, ⁷ and ⁸).

Large diameter implants

Large diameter implants, originally developed for use in the wider posterior ridges, are available in diameters of 5.0 and 6.0 mm at the neck as well as the threads (^{Chiche and Missika, 2000}). They are also indicated in the anterior segment, in the case of immediate replacement after extraction of one or two upper central incisors, providing the essential spacing requirement between implant and tooth or between two implants is met. Usually, a 5.0 mm implant is used, or an XP implant with a neck diameter of 6.0 mm and a body diameter of 5.0 mm (see later).

Large diameter implants are less frequently used in the anterior region when the sockets have completely healed because of resorption from the outer aspect of the ridge tends to displace it in an antero-posterior direction and hence to reduce the mesio-distal distance between the lateral incisors.

Implants that are oversized at the neck

Grouped under the label XP, these implants have a larger diameter at the neck to support the prosthesis compared with the « surgical » diameter at the threads. They are indicated in all situations where the thickness of the ridge, or the presence of buccal concavity necessitates the use of an implant, the neck of which is of a small diameter compared with the mesio-distal diameter of the future crown. The emergence profile is instantly assured by the oversized implant neck that, after the surgery, is usually located above the crest.

Emergence profile and implants with an external hexagon

Implants of the 3i-Implant Innovations^® type, with an external hexagon, where the diameters at the level of the neck are 3.4, 4.1, 5.0 and 6.0 mm are the basis on which to map out the emergence profile of the prosthesis. However, faced with the differing possibilities of submerging the implant, it seems necessary to define which location of the neck allows the most reproducible aesthetic result to be achieved.

Location of the neck

The basis of the concept for the placement of standard implants, described by Swedish workers, consists of submerging the implant threads in such a way that the external hexagon is located slightly below the level of the crest (^{Adell et al., 1981}). This aims to avoid micro-movements of the implant that are likely to occur during osseointegration because of pressures from a prosthesis through the thin overlying mucosa or operculum.

This is also the method of choice to be applied whenever aesthetics is a prime consideration (^{Parel and Sullivan, 1989}). In this position the neck is placed more apically compared with the gingival margin thus offering a greater possibility of flaring the post as well as locating the finishing line of the crown subgingivally.

In parallel with this technique, ^{Davarpanah et al. (2000)} have shown that by placing the neck of the implant in a supra-crestal position, one can increase the number of threads that are submerged in bone in such a way as to increase anchorage. This option may be of benefit in the posterior segments, where the height of available bone is often limited, but it is not indicated in the anterior segments because it restricts the extent to which corrections can be made to establish an ideal emergence profile.

Selection of the post in relation to the aesthetic result

The debate over the concept of a screw-fitted or cemented prosthesis is not new. The supremacy of either one of these concepts has not been demonstrated, the selection of the type of retention having to be made for each clinical case by balancing the following alternatives: for a screw-fitted prosthesis, its ease of removal versus complexity, and for a bonded prosthesis, its difficulty of removal versus its simplicity of construction because of the techniques used closely resemble those of prostheses on natural teeth.

However, the construction of a crown that is cemented on to a post or screwed flanged abutment is, at present, a standard method for prostheses on implants.

The absence of occlusal screws also enables an ideal morphology to be achieved whilst reducing the risk of fracture of the porcelain. The absence of a « black hole » also improves the chances of meeting the patient's aesthetic requirements. In most cases, porcelain to metal bonded crowns are attached with temporary cement.

Finally, the use of a gold screw, torqued to 32 ncm using a torque wrench allows for possible removal of the post or implant abutment at a later date. The 3i-Implant Innovations^® system offers two types of screwed posts according to the different diameters of the implant.

The UCLA gold post

• Description

This post is composed of two elements:

- the main element is composed of machined precious-metal alloy with an internal hexagon that fits the external hexagon of the implant. Upon this is mounted a sheath made from combustible resin which serves to support a wax addition so that the final shape can be decided before over-casting ;

- a gold attachment screw, located within this element, to attach the assembly to the implant.

This post offers a number of advantages.

• Advantages associated with machining

Being machined, this component, which is intended to be over-cast, offers the best guarantees of precision and reproducibility and can be modified to suit the implant (^{Lewis et al., 1988} ; ^{Lewis, 1992}).

The main element is precious-metal alloy and possesses an internal hexagon that fits the external hexagon of the implant. The interlocking of the hexagons ensures that rotation of the post does not occur and also a single implant crown to be fitted (^{Binon, 1995}).

• Advantages associated with over-casting

The main significance of this component is to be able to adapt the emergence profile of the post in relation to the mesio-distal diameter of the tooth being replaced. Sometimes there is a significant difference between the mean diameter of an upper central incisor (9.0 mm) and that of a standard implant in the Brånemark system^® (4.1 mm). The possibility of modifying the shape of the post by over-casting provides this system with great flexibility. All that is needed is to add more or less wax at the stage of making the model in order to establish the ideal mesio-distal contour for the replacement tooth. The thickness of the peri-implant gingiva represents the transition space within which correction of the diameter of the implant and that of the future prosthesis can be made.

The amount of divergence of the sides of the post can be varied according to the height of the gingiva. If the gingiva is thin and the tooth to be replaced is large, the divergence will be more severe. This situation can cause major problems because of plaque accumulation and the difficulty of cleaning. If the gingiva is thick, the divergence will be more gentle, avoiding this « spiky » effect and enabling better plaque control.

For the health of the peri-implant tissues, the transgingival component must be as smooth as possible in all cases.

This prosthetic component, unlike the non-adjustable machined titanium abutments, allows for the finishing line to be more accurately located according to the position of the implant and its environment. If the finishing line must be subgingival, it is possible at the wax stage to create a 1.5 mm collar following the buccal gingival margin at a depth equivalent to that of the interdental papillae. This margin could possibly be subgingival on the palatal aspect. By overcasting it is possible to achieve a flanged post that is truly anatomical on all aspects.

This ease of adaptation to local conditions is a very valuable asset because the gingival profile may be very uneven. In this situation the depth of the sulcus on the proximal aspect is as great as the slope between the crests of the papillae and the most apical part of the buccal gingival margin. By using an over-cast flanged post upon which is mounted a bonded metal crown, one can more easily remove excess cement because the margins have been set at a depth no greater than 2 mm around the whole periphery no matter how deep the sulcus. Finally, although being fixed, there is considerable scope for angulating the cast post in order to correct the axis of the future crown in relationship to the implant (^{fig. 9}, ¹⁰, ¹¹, ¹², ¹³, ¹⁴, ¹⁵ and ¹⁶).

The GingiHue post

GingiHue posts are made from machined titanium coated with titanium nitride and coloured gold. They are the shape of a flattened cone and have collar heights of 2 or 4 mm from the junction with the implant. In addition three different diameters (5.0, 6.0 and 7.5 mm) are available for each size of collar height.

Adjustments are made with a diamond or tungsten carbide bur. One can reduce the height of the post according to the inter-arch space available as well as adjust its walls in order to alter the general axis of the post. When the axis of the implant and that of the crown are very divergent, it is preferable to use an angulated 15° post.

In contrast to the gold UCLA post, the machined section is circular at the level of the collar and cannot be shaped to the triangular form of a central incisor or the trapezoidal form of a molar.

However, it is possible to change the position of the finishing line as well as its contour, in order to place it subgingivally according to the aesthetic requirements of each clinical case.

The GingiHue post offers total compatibility with the titanium of the implant and allows the freedom to over-cast. The layer of titanium nitride that is deposited on the surface eliminates the risk of the grey titanium showing through a thin gingiva. Finally, where there is gingival recession, it reduces the adverse effect on aesthetics when the titanium post is at the gingival margin or supragingival.

The advantages of screwed posts

There are various types of these posts which, in the case of problems, can simply be removed by unscrewing them.

They are retained on the implant by a gold screw torqued to 32 ncm using a torque wrench. The device is sufficiently reliable to eliminate the need for any kind of cement or composite at the subgingival junction of the post and implant, irrespective of the thickness of the mucosa.

Once screwed to the implant, this component acts as a conventional post and can receive a bonded porcelain crown, fixed with temporary cement (Temp-Bond^®). The screw may be fitted on the buccal or palatal side and does not affect the occlusion, or the final aesthetic result, because it is covered by the crown.

This « screwed-cemented » concept has the advantage of being able to be totally dismantled. This can easily be done by incorporating a notch on the palatal side of the crown into which a crown remover can be inserted.

Emergence profile of non-submerged TG implants

From 1998, 3i-Implant Innovations have developed a monobloc implant designated TG (Trans-Gingival) in parallel with those with an external hexagon. This implant is produced in diameters of 3.25, 4.0 and 5.0 mm and takes the form of a titanium screw upon which there is a collar available in two heights, 1.8 and 2.8 mm. The collar has a fixed diameter of 5.0 mm irrespective of the diameter of the implant and contains an internal morse-taper within the prosthetic connector.

This implant is especially indicated in the posterior regions for the replacement of single teeth, and other types of tooth loss, as long as the patient submits to certain constraints: not to wear a removable denture during the period of bone healing, not to eat with the implants during this period and to ensure excellent plaque control of all the teeth and implants.

Localisation of the collar

In parallel with the two-stage technique, Swiss workers (^{Schroeder et al., 1976}) have described another protocol that does not require the implant to be submerged following the first surgery. This one-stage technique simplifies and reduces the stages of treatment ; elimination of a second intervention means that the length of the prosthetic treatment can be shortened to 1.5 months which represents the time taken for the gingiva to heal before the impression can be taken (^{Buser et al., 1992}).

The surgical placement of TG implants strictly follows the one-stage protocol which involves not submerging the prosthetic collar under the gingiva. At the end of the surgical stage, the margin of the collar is slightly subgingival. The best aesthetic results are obtained by using a TG implant with a 1.8 mm high polished collar. This lower height collar is generally sufficient to allow the future crown margin to be placed subgingivally. In those cases where the thickness of the soft tissues is greater, it is preferable to use a TG implant with a short collar and to use a taller cover screw to avoid the collar becoming buried at the end of the intervention.

The limited ability to make corrections to non-submerged monobloc implants means that great care must be taken with their positioning at the surgical stage. Mastery of the aesthetic result depends on the angulation of the implant whose long axis must conform to that of the future prosthesis as well as being parallel with any other implants in the same reconstruction. Equally, it is possible to bury the implant beyond the first thread if the mucosa is so thin that there is a risk of the finishing line of the final restoration becoming supra-gingival.

Emergence profile of monobloc posts

Changes to the emergence profile are made from the same dimensions irrespective of the diameter of the implant that is present, i.e. from a 5 mm diameter collar located at the gingival margin. Posts compatible with the morse-taper are made of titanium monoblocs, the screw being firmly attached to the body. They are screwed and locked together to prevent rotation at 32 ncm using a torque wrench. Unscrewing is prevented by friction between the sides of the post and the morse-taper.

The emergence profile is no longer provided by the post, the diameter of which is indicated on the neck of the collar, but by the shape of the crown at the laboratory stage. The degree of flare is established either at the wax stage before casting the core, or at the porcelain stage.

These screwed posts, available in three heights (4.0, 5.5 and 7.0 mm), facilitate the attachment of the prosthesis with no screws on the occlusal surface. They meet the mechanical, functional and aesthetic requirements of each patient (^{fig. 17}, ¹⁸, ¹⁹, ²⁰, ²¹ and ²²).

Conclusion

The diversity of clinical situations capable of being treated by means of dental implants has been considerably extended in recent years. In response to recently acquired data, 3i-Implant Innovations^® offer two types of implant characterised by the means of attachment of the prosthesis: the large group of implants with an external hexagon and monobloc implants with a morse-taper. The carefully considered use of implants of various diameters at the surgical stage, and of the subsequent prosthetic components associated with them, provides a functional as well as aesthetic solution in all clinical situations, thanks to the ability to produce the ideal emergence profile.

Prostheses constructed by Laboratoire Oral Concept/Marc A. Leriche.

Demande de tirés à part

Frédéric CHICHE, 133, boulevard Haussman, 75008 PARIS - FRANCE.

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