Dr. Mamaly Reshad, et al take a look at the diagnostic factors that affect the predictability of peri-implant aesthetics
Achieving aesthetics with implant restorations is significantly more challenging than that with conventional restorations. Diagnosis and appropriate treatment planning are critical in obtaining a successful outcome. Many manufacturers will identify their systems as aesthetic; from an objective perspective components in of themselves are not aesthetic. There is not a single component available that would be the ideal replacement for a maxillary central incisor. Aesthetic outcomes are based on many variables. It is not the speci c implant design, surface characteristics or type of abutment that will guarantee an aesthetic result. It is the time spent on data collection in reaching a correct diagnosis that pays dividends in terms of function and aesthetics (Sullivan, 2001).
Figure 1: Laboratory photograph of implant in poor position angled labially
Root form cylindrical implants placed following surgical techniques described by Branemark et al have proven to be a predictable method for anchoring replacement teeth to the jawbone (Branemark et al, 1990; Naert et al, 1992). Today, clinicians can prescribe the use of implants with the knowledge and confidence that they will predictably integrate into the jawbone. The successful integration of an implant, however, is not sufficient to declare success, implants placed in poor restorative positions result in unaesthetic restorations that provide little satisfaction for the clinician or the patient. Figures 1-3 demonstrate the complexity of implant use in aesthetic zones and the importance of proper treatment planning prior to implant placement.
Providing an aesthetic outcome requires understanding of the objective and subjective criteria related to hard and soft tissue aesthetics (Belser, 1982). Both dental and gingival aesthetics act together to provide a smile with harmony and balance. The clinician must be aware of parameters related to gingival morphology, form and dimension, characterisation, surface texture and color (Magne, Belser, 2002) (Figure 4). Ceramists can often produce restorations to match adjacent teeth in terms of color, however, if the surrounding tissues are not reconstructed, an aesthetic outcome is not likely (Figures 5a and 5b). The ultimate aim is for the implant restoration to harmonize into the frame of the smile, face and, more importantly, the individual.
Treatment planning must address hard and soft tissue deficiencies and combine this with precision in implant placement: only with this approach can implant restorations be indistinguishable from the adjacent teeth (Figure 6).
Recreating what nature provided can be a formidable challenge. The physiology of wound healing after tooth extraction creates an unfavorable soft tissue complex. The remaining mucosa often recedes palatally and apically. Often this results in a restoration that appears long and this is compounded by the absence of interdental papilla (Figure 7).
Figure 2: Smile view of restoration fabricated for implant in Figure 1
Figure 3: Labial view of restoration for implant in Figure 1. Pink ceramics utilized to disguise poor implant position
Figure 4: Restoration of implants must satisfy objective and subjective aesthetic criteria. There should be sufficient inter-radicular space for placement of the implant and sufficient inter-tooth distance for fabrication of an aesthetically pleasing restoration
Figure 5a: Implants in lateral incisor position placed too buccally. Note how position of implant affects position of gingival margin
Figure 5b: Cemented implant restorations placed on custom abutments. Note asymmetrical gingival margins
Figure 6: Implant restoration on right lateral incisor in harmony with the existing hard and soft tissue
Figure 7: Wound healing following extraction of a tooth can result in apical and palatal migration of the interdental papilla
The predictability of the aesthetic outcome of an implant restoration is dependent on many variables including, but not limited to:
1. Patient selection and smile line
2. Tooth position
3. Root position of the adjacent teeth
4. Biotype of the periodontium and tooth shape
5. The bony anatomy of the implant site
6. The position of the implant
1. Patient selection and smile line
Patients who are candidates for replacement of an anterior tooth with an implant-supported restoration must understand its benefits. They must also understand the additional length of time required for treatment and additional costs that will be incurred. The clinician must also understand the patient’s desires. In most cases the patient’s primary demand is an aesthetic tooth replacement, with this in mind it is important to establish sound clinical concepts with clearly defined parameters that lead to successful aesthetics with long-term stability of the peri-implant tissues.
The major indication for a single tooth implant restoration is preservation (non-preparation) of one or more of the adjacent teeth (Figure 8), and reduction in the rate of alveolar resorption. Additional indications would be restoration of a missing tooth to maintain a diastema and preservation of extensive fixed restorations that are intact.
A patient’s aesthetic expectations must also be evaluated together with their lip activity and lip length. In an average smile, 75-100% of the maxillary incisors and the interproximal gingiva are displayed. In a high smile line, additional gingival tissue is exposed. Less than 75% of the incisors are exposed in a low smile line (Figures 9-11) (Tjan, Miller, The, 1984). The clinician should be aware that the patient who presents with unacceptable tooth health, shade or position may not give a full smile when asked. Previous photographs may aid in determining the natural position of the patient's lip when smiling.
A high smile line poses considerable challenges when planning for implant-supported restorations in the aesthetic zone because the restoration and gingival tissues are completely displayed. In these types of clinical situations maximal efforts towards maintaining peri-implant tissue support throughout the planning, provisional, surgical and restorative phases will be required.
The low smile line is a less critical situation because the implant restoration interface will be hidden behind the upper lip. However, this cannot be assumed and the patient’s input must be sought to confirm this.
Figure 8: A perfect indication for a dental implant is non-preparation of the adjacent teeth
Figure 9: Low smile line
Figure 10: Average smile line
Figure 11: High smile line. The colour and contour of the restorations and associated hard and soft tissues becomes very visible to the observer
Figure 12: The right lateral incisor has been treatment planned for an implant restoration. The level of the soft tissues mimic that of the contra lateral tooth
2. Tooth position
The tooth needs to be evaluated in three planes of space: apicocoronal, faciolingual and mesiodistal. The existing tooth position will significantly influence the presenting gingival architecture. In many instances, teeth with a poor prognosis are thoughtlessly extracted. These teeth can significantly influence both the hard and soft tissue configuration.
Apico-coronal
On assessment of the apico-coronal position of the tooth, it may be more apical, more coronal or ideal and mimic the level of the adjacent gingival margin (Figure 12). Numerous authors have shown that following extraction and insertion of an ovate pontic there is likely to be up to 2mm of gingival recession, and on extraction and placement of an implant immediately the migration of the gingival margin is likely to approximate 1mm (Kois, 1998; Saadoun et al, 1999).
The implications this has is that if there is a hopeless tooth positioned ideally or apically and this is extracted, the gingival margin is likely to migrate apically. Restoratively, long clinical crowns, pink porcelain or visible metal margins will compromise the aesthetic outcome. These
Figure 13: Immediate extraction of the right lateral incisor would result in apical migration of the soft tissue. Orthodontic extrusion will allow the clinician to position the tissue more coronally so that on extraction there is a margin of error
teeth can benefit from orthodontic extrusion (Figure 13) prior to extraction, which will serve to position the gingival level at a more harmonious level (Kois, 2004; Salama, Salama, Kelly, 1996).
Facio-lingual
In this dimension, the tooth position may present with different concerns. The tooth may be positioned too far facially; this often results in very thin or non-existent labial bone. These teeth are not good candidates for orthodontic extrusion because of inadequate underlying bone. Extraction of these teeth results in significant vertical bone loss and collapse of the gingival architecture. This type of situation would benefit from bone augmentation procedures prior to implant placement. A tooth positioned more lingually would benefit from the presence of an increased amount of facial bone. This situation is more favorable prior to extraction since the resultant discrepancy in the facial free gingival margin may be minimal (Kois, 2004).
Mesio-distal
The proximity of the adjacent teeth necessary to provide proximal support and volume of interdental papillae should be evaluated. Ideally, the mesiodistal tooth width should be equal to that of the contra lateral tooth so that an aesthetic outcome can be achieved (Figures 14 and 15). Excess or deficiencies in this dimension should be addressed through the use of orthodontics, enameloplasty or restorations. For patients with diastemas, it is imperative that the decision to maintain or close the space be made prior to implant placement. If the patient refuses the above options to close the space and insists on closing the space with the implant restoration there is a likelihood that a black triangle may ensue. This results from inadequate support from the adjacent tooth to maintain the papilla. It is important that the clinician discusses this with the patient ahead of time so disappointment with the final outcome is avoided (Figures 16 and 17).
Figure 14: The mesiodistal width of the tooth requiring replacement must equal that of the contra lateral tooth
Figure 15: Implant restoration replacing the right central incisor
Figure 16: Excessive mesiodistal space in the region of the tooth requiring an implant restoration
Figure 17: Implant restoration in the region of the right central incisor. Note absence of interdental papilla as a result of inadequate support of the soft tissue by the restoration
3. Root position of the adjacent teeth
Part of the diagnostic work for patients who need implants is a periapical radiograph, as often root position will preclude placing of implants. Many of these patients can benefit from orthodontics to reposition malposed teeth. If the patient illustrated in Figures 18 and 19 desired implant restorations to replace congenitally missing maxillary lateral incisors, orthodontic therapy would be necessary to move the roots of the cuspid and central incisor to allow room for ideal implant placement.
Figure 18: Clinical presentation of patient with congenitally missing maxillary lateral incisors post orthodontic treatment
Teeth with root proximity also possess very little interproximal bone, this thin bone creates a greater risk of lateral resorption, which will decrease the vertical bone height after extraction or implant placement. When teeth are present the use of orthodontics serves as a valuable adjunct to create space. This can be advantageous for support of proximal gingival architecture (Tarnow, Cho, Wallace, 2000; Tarnow, Magner, Fletcher, 1992).
Figure 19: Radiograph of patient in Figure 18 revealing that there is insufficient inter-radicular space for implants
4. Biotype of periodontium and tooth shape
The position of the gingival tissue around a tooth is determined by the connective tissue attachment and by the bone level. Two different periodontal biotypes have been described in relation to the morphology of the interdental papilla and the osseous architecture – the thin scalloped periodontium and the thick at periodontium (Becker et al, 1997).
The thin scalloped periodontium, found in less than 15% of cases, is characterized by a delicate soft tissue curtain, a scalloped underlying osseous form and often has dehiscence’s and fenestrations and a reduced quantity and quality of keratinized mucosa. Generally, interproximal tissue does not completely fill the space between adjacent teeth. This form of gingiva reacts to insults by receding facially and interproximally. As recession occurs and the inter-root bone resorbs, the subsequent soft tissue loss compromises the overall aesthetic result (Figure 20).
The tooth form in this type exhibits a contact point towards the incisal third essentially triangular anatomic crowns and contact areas of teeth that are small facio-lingually and apicocoronally. Due to extreme taper of the roots, the bone interproximally tends to be thicker.
Characteristics of the soft tissue biotype will play a prominent role in final planning for the shoulder position of the implant. A thin biotype with highly scalloped tissue will require the implant body and shoulder to be placed more palatal to mask any titanium show through. When implants are placed toward the palate, a slightly deeper placement is required to allow for proper emergence profile.
Combining previous factors in a patient with a high lip line and a thin biotype is extremely difficult to treat. Patients who fit into these treatment categories should be made aware of the challenges involved in obtaining an aesthetic result before treatment begins.
The thick flat periodontal biotype is characterized by a denser more fibrotic soft tissue curtain, a flat thicker underlying osseous form and an increased quantity and quality of attached keratinized gingiva. This tissue often reacts to insults by pocket formation. Flat gingiva is associated with a tooth form that is more bulbous contact areas are located more toward the middle third of the tooth primarily square anatomic crowns and contact areas that are wide facio-lingually and apicocoronally (Figure 21).
Figure 20: Biotype 1 periodontium, note thin and scalloped tissue
Figure 21: Biotype 2 periodontium, not thick and flat tissues. Implant provisional restoration in the position of left central incisor
Figure 22: Loss of interproximal soft tissue in the presence of a triangular tooth form can result in unsightly black triangles
Figure 23: Over contour of the implant restoration as it emerges from the free gingival margin can result in apical migration of the soft tissues
The tooth morphology appears to be correlated with the soft tissue quality. The triangular tooth shape is associated with the scalloped and thin periodontium. The contact area is located in the coronal third of the crown, underlining a long and thin papilla. The square anatomic crown shape combines with a thick and at periodontium. The contact area is located at the middle third, supporting a short and wide papilla.
Loss of interproximal tissue in the presence of a triangular tooth form will display a wider black triangle than in a situation when a square tooth is present (Figure 21). In some cases when the adjacent teeth are to be restored, the crown form can be modified prosthetically to compensate for partial interproximal tooth loss.
The contact area of the prosthetic tooth is positioned more cervically, reducing the volume of the interdental space. The presenting tooth shape will also influence the implant restoration shape.
The implant restoration should mimic its contra lateral natural tooth coronal to the free gingival margin (Figure 22). However apical to the free gingival margin the implant restoration will not be an anatomic replica. A delicate balance must be developed that provides adequate support of the gingival architecture yet does not provide excessive pressure. Ideally, the facial contour should be slightly flatter than the contra lateral natural tooth to minimize apical displacement of the free gingival margin after insertion (Figure 23) (Phillips, Kois, 1998).
5. Bony anatomy of the implant site
For successful aesthetic restoration of implants, the bony housing must have a three-dimensional configuration that permits placement of an implant in a restoratively ideal position (D’Addona, Nowzari, 2000). If the bony anatomy is inadequate, a bone grafting procedure may be required to enhance the site.
When these situations are encountered the patient must be made to understand that a successful outcome will involve replacing more than just a ‘missing tooth’. The patient must also understand that the missing hard and soft tissue architecture will need to be rebuilt so that optimum aesthetics can be achieved.
The definitive implant restoration needs to be surrounded by a hard and soft tissue environment that is in harmony with the surrounding dentition. It is not only the amount of bone and soft tissue present prior to implant surgery but also the precision of surgical execution that leads to an overall favorable outcome. Several key analyses need to be performed prior to commencing with implant placement. A diagnostic wax-up, which highlights tissue deficiencies and final tooth positioning, can assist in the planning process (Figures 1a and 1b).
Faciolingual ridge anatomy should be evaluated to determine if there is sufficient crest width to house the implant. Deficient alveolar crest width will require a bone augmentation procedure to allow the implant to be placed in the ideal position (Figure 2). Clinical sounding techniques or sophisticated radiographic techniques such as tomograms or CT scans can assist in diagnosing deficiencies in this dimension (Figures 3, 4 and 5).
Mesiodistal space should be equal to that of the contralateral tooth; excess or deficiencies in this dimension need to be addressed through orthodontics, enameloplasty or restoration either prior to or after implant placement.
Figure 4: Bone augmentation of the site pictured in Figure 3
Figure 1a: A diagnostic wax-up can highlight the deficiency of the hard and soft tissue and can indicate to the surgeon how much augmentation is required
Figure 1b: Pink ceramics utilized to disguise soft tissue deficiency
Figure 2: A deficient alveolar crest will not allow the implant to be placed in an ideal position. There will be insufficient bony housing to accommodate the fixture
Figure 3: Clinical slide of inadequate buccolingual width for implant placement
Figure 5: Ideal implant placement, note adequate ridge contours
The most critical dimension remains the apicocoronal dimension. Deficiencies in this dimension can result from periodontal disease, trauma, atrophy and infection. Vertical grafting is complex and the site may require several surgeries to achieve an optimal configuration.
The most efficient method to evaluate this dimension is through the use of a diagnostic template, highlighting the proposed gingival margin of the implant restoration.
Two anatomic structures are important in determining predictability of soft tissues after implant placement. The first is the height and thickness of the facial bony wall and the second is the bone height of the alveolar crest in the interproximal areas.
Height and thickness of facial bony wall
The position of the osseous crest is an important predictor for gingival levels. In a survey of 100 patients, Kois (2001) classified patients as having high, normal or low crests. This was based on the vertical distance of the osseous crest to the free gingival margin. The greater the distance from the osseous crest to the free gingival margin, the greater the risk of tissue loss after an invasive procedure. Kois proposed that if the total vertical distance of the total dentogingival complex on the mid facial aspect is 3mm, a slight apical loss of tissue up to 1mm is anticipated after extraction and immediate implant placement. Greater or lesser than 3mm indicates the change will be relatively negligible to more than 1mm.
Measuring the distance from the free gingival margin to the osseous crest prior to extraction is an important diagnostic predictor of the anticipated final position of the free gingival margin.
Height of bony crest in the interproximal area
The interproximal bony crest plays a critical role in the presence or absence of peri-implant papillae. A clinical study around teeth measured the distance from the interproximal contact to the vertical height of bone and observed how frequently the interproximal space would be filled completely by soft tissue (Tarnow, Cho, Wallace, 1992). When the contact point to the bone was 3.5mm,papilla always filled the space. When the distance was 6mm papilla was absent 45% of the time and with a distance of 7mm, papilla did not fill the space 75% of the time.
Figure 6: If attachment of adjacent teeth is deficient it is unlikely that the interdental papilla will be maintained
Figure 7: Black triangles are likely to result between the implant restoration and adjacent teeth
Figure 8: Diagnostic sounding of the bone inter-proximally is a good clinical indicator in predicting post-treatment papilla levels
A difference of 1-2mm is significant in obtaining soft tissue aesthetics. This has been confirmed with implant supported restorations (Choquet et al, 2001; Kan et al, 2003) that have also shown that the height of peri-implant papillae in single tooth gaps is independent of the proximal bone level next to the implant but is dependent on the interproximal bone height of the adjacent teeth. From a diagnostic perspective, sounding from the tip of the papilla to the (Figures 6 and 7) interproximal bone crest of the adjacent tooth would be an important predictor. If this distance is 5mm or less there is an increased likelihood that the interproximal tissues will be predictably maintained following implant placement and restoration. If the distance is greater than 5mm the papilla cannot be predictably maintained after surgical intervention (Figures 7 and 8).
6. Implant position
Aesthetic implant placement is driven by both a restorative and biological philosophy. Aesthetically, the implant should be placed to satisfy the parameters of contour so that the restoration is pleasing. Biologically, it should be placed to allow maintenance of both hard and soft tissue architecture. If the tooth to be replaced has not yet been removed, several determinations should be made prior to the extraction (Salama, Salama, Kelly, 1996; Kois, 2004).
Immediately placing the implant after extraction helps to shorten the treatment time and may reduce the amount of ridge width reduction that accompanies tooth extraction. In addition, if bone deficiencies are present, orthodontic eruption of the tooth prior to extraction can help to increase the amount of hard and soft tissue in the future implant site (Neale, Chee, 1994; Chee, 2001; Chee, 2003).
The need for precision in implant placement varies according to each individual case. For example, in the edentulous mandible there is need for precision only in the faciolingual direction. The need for precision to the extraction (Salama, Salama, Kelly, 1996; Kois, 2004).
Immediately placing the implant after extraction helps to shorten the treatment time and may reduce the amount of ridge width reduction that accompanies tooth extraction. In addition, if bone deficiencies are present, orthodontic eruption of the tooth prior to extraction can help to increase the amount of hard and soft tissue in the future implant site (Neale, Chee, 1994; Chee, 2001; Chee, 2003).
The need for precision in implant placement varies according to each individual case. For example, in the edentulous mandible there is need for precision only in the faciolingual direction. The need for precision increases in the partially edentulous jaws according to the teeth treated and the positions of the neighboring and opposing teeth. The most challenging is the anterior maxilla where a malposition of less than 1mm can jeopardize the overall treatment outcome.
In most situations involving a single anterior implant restoration, the aesthetic considerations are more important than functional considerations. As such, axial loading is not as critical as it is with posterior implant restorations. Implant position is critical to the final aesthetic outcome and needs to be considered in all three dimensions and in relation to
the adjacent teeth. Misalignment of the implant in the prosthetic space can have adverse aesthetic consequences.
Apicocoronal placement
Apicocoronal positioning appears to be the most critical aspect. Deficient tissue in this dimension can result from several factors. This type of tissue needs to be addressed during treatment planning. Because of the complexity of vertical hard and soft tissue grafting, these patients are placed in a high-risk group.
Most often tooth loss is followed by bone loss of minor or major importance. It is necessary to evaluate the discrepancy between the bone level at the proposed implant site and the level at the adjacent teeth. Too large a difference represents a risk to both periodontal and peri-implant tissue health. Facing this, the surgeon should consider reconstructing the ridge prior to implant placement.
The apicocoronal positioning of the implant is the vertical discrepancy between the occlusal surface of the implant and the peaks of the bony septa proximal to the adjacent teeth; the most pleasing aesthetic result occurs when this discrepancy is minimal.
To obtain appropriate apicocoronal positioning of the implant a diagnostic wax-up needs to be completed and from this a surgical guide is made. The emergence profile and the shape of the restoration are reproduced on the guide to verify the implant positioning on placement.
Figure 9: Radiograph of Figure 8, the right lateral incisor has been treatment planned for an implant restoration. Due to attachment loss on the adjacent canine it is unlikely that the interproximal papilla will be maintained
Figure 10: Ideal implant placement for central incisor. Implant should be placed 3-4mm apical to the existing free gingival margin. Adequate room is required for transition from the head of the implant to the point where the restorations exits the free gingival margin. Note minimal bone discrepancy between the implant and the adjacent teeth
Figure 11: Laboratory slide depicting ideal implant placement and transition required
Figure 12: Occlusal view of implant restoration shown in Figure 11
Figure 13: Lateral view of implant restoration in Figure 11 showing fill of interproximal soft tissue
Figure 14: Facial view of implant restoration in Figure 11 showing aesthetic harmony
Figure 15: Placement of an implant too shallow will result in inadequate space for transition and a short restoration in length
A maxillary central incisor measures on average 7-8mm mesiodistally and 6mm faciolingually at the emergence from the soft tissue. A 4.0mm implant needs to be placed 3-4mm apical to the gingival margin of the contralateral tooth to allow the restoration to emerge with a natural profile. A vertical distance of 3-4mm is needed for gradual transition from the 4mm diameter of the implant platform to the 7-8mm dimension at the gingival margin. If a lateral incisor is being replaced, the implant would not have to be placed so apically since the average diameter of the crown at the gingival margin is 5mm and less room is required for transition (Figures 10-14).
There are also situations in which there is excess tissue height and these require attention as well. In these types of patients, a bone scalloping procedure is required to allow placement of the implant shoulder in a subgingival position; once again the most efficient way to examine this is through a surgical guide highlighting the proposed gingival margin.
Errors in apicocoronal implant placement can have serious aesthetic and biomechanical implications. An implant placed too coronally will not allow adequate transition from the head of the implant to the point where the restoration exits from the free gingival margin. The restoration will look short in comparison to the contralateral tooth. The only prosthetic 'bailout', for this type of situation
is to provide a ridge-lapped restoration with contours that are pleasing to the observer’s eye (Figures 15 and 16).
Problems can also result when implants are placed too apically. Clinically, if an implant is placed too apically with excessive countersinking procedures, an unnecessary amount of bone loss will occur (Figure 17). Because this bone loss takes place circumferentially it will affect not only the proximal bone structure but also the height of the facial bone wall and can lead to undesirable soft tissue contours (Buser, Martin, Belser, 2004).
A practical problem in placing an implant too deeply is access for instrumentation. Making an impression of a deeply placed implant can be a difficult experience (Figure 18) – the soft tissue tends to collapse, there is tissue impingement when trying to locate the head of the implant and seating is difficult to evaluate. This is specific to external hex systems.
If an implant is placed too deep, a screw-retained restoration is the treatment of choice. The literature shows that removing all the cement when an implant is placed so deeply can prove to be a difficult endeavour. Agar et al (1997) found that when six experienced investigators were asked to remove cement there was a surprising amount of cement left behind; this can lead to serious soft tissue complications.
Figure 16: A prosthetic bailout for too shallow implant placement is to ridge lap the restoration onto the tissues
Figure 17: Too deep an implant placement can result in bimechanical problems. Note level of bone around implant in relation to adjacent teeth. This deep a placement can result in fistula formation and constant post-operative maintenance problems.
Figure 18: Too deep an implant placement can result in soft tissue collapse and difficulty in instrumentation
Mesiodistal placement
Improper mesiodistal positioning of implants can also have a substantial effect on the generation of interproximal papillary support as well as on the osseous crest of the adjacent tooth. An implant should be placed 1.5mm-2mm from an adjacent tooth. Placement too close to the adjacent tooth can cause resorption of the interproximal alveolar crest to the level of that on the implant (Thilander, Odman, Jemt, 1999). With this resorption comes a reduction in papillary height. Restorative problems exist as well. Poor embrasure form and emergence profile will result in a restoration with a long contact zone and compromised clinical outcomes.
The loss of crest height on adjacent teeth is caused by bone saucerisation routinely found around the implant shoulder in implants. This has two dimensions a horizontal and vertical. Radiographs only demonstrate the horizontal aspect of bone saucerisation; the proximal bone saucerisation measures 1-1.5mm from the implant surface. This distance needs to be respected on implant placement to prevent vertical bone loss on adjacent teeth (Esposito, Ekestubbe, Grondahl, 1993).
Faciolingual placement
The crest width needs to be examined to determine the presence or absence of bone atrophy.
Placement will vary depending on the mechanism of retention of the final restoration (screw retained versus cement-retained).
Deficient alveolar crest width may require augmentation so that the implant can be positioned in the correct faciolingual position.
Computerized tomographic scan techniques are useful in assisting to determine width. The amount of bone available should be at least 1mm greater than the implant diameter on each side. Hence a 4mm diameter implant would require 6mm of bone. The single implant placed in the maxillary anterior region should be situated palatal to an imaginary line that outlines the curve of the arch formed by the facial surfaces of the adjacent teeth (Figure 19) (Chichem, Leriche, 1998).
Implants placed too palatally complicate development of hygienic contours. Biomechanical complications can also arise as a result of cantilever forces on the screw joint of external hex systems (Figures 20, 21 and 22). Implants are often mistakenly placed too facially. This error results in excessive resorption of the supporting osseous structure, resulting in a restoration that will appear long in comparison to the contralateral tooth. Placement of a restoration such as this in the aesthetic zone is certainly unlikely to meet the patient’s desires (Figures 23 and 24).
Figure 19: Ideal implant placement should be palatal to an imaginary line that outlines the curvature of the teeth. (Modified from Parel, Sullivan, 1989)
Figure 20: Too palatal an implant placement
Figure 21: The restoration for the implant placement in Figure 20 would require an excessive facial cantilever
Figure 22: Profile of restoration in Figure 21 illustrating a biomechanical and hygienic compromise
Figure 23: Too facial an implant placement
Figure 24: Too facial an implant placement will result in facial bone resorption and apical migration of the soft tissue. The resulting restoration will appear long in comparison to the contra lateral tooth
Considerations for multiple implants
Patients with extended edentulous spaces present greater anatomic and aesthetic challenges, making it even more difficult to obtain an aesthetic result with certainty.
Following extraction and wound healing of two adjacent teeth, the ensuing apical and faciolingual resorption results in an edentulous segment that is flattened. The same diagnostic considerations need to be addressed as when looking at single tooth edentulous sites.
The aim prior to implant placement is to have a three- dimensional configuration of hard and soft tissue, which will allow placement of implants in an ideal position. The placement of two missing central incisors poses an additional challenge. Following surgical placement, an additional peri-implant bone remodeling takes place. In the frontal plane, two processes occur – one between the implant and the adjacent natural tooth and one between the two adjacent implants.
On the tooth implant side, the predictability of the interdental papilla is governed by the height of the interproximal bone crest of the tooth. If this height is favorable there is a good certainty that the interdental papilla will be maintained following implant placement. The bone crest between the two implants is likely to undergo further resorption in an apical direction. This is accompanied by a loss of inter- implant soft tissue that, in the case of multiple edentulous sites, will result in black triangles between the adjacent restorations.
Many clinicians have sought after the ideal implant
distance required to maintain the interdental papilla. Tarnow et al (2000) performed a radiographic study to address this clinical problem. Radiographic measurements were taken at a minimum of one and three years after implant exposure. All radiographs were taken with a paralleling technique.
Radiographs were computer scanned imaged and magnified for measurement. The following measurements were taken:
1. Lateral distance from the crest of the inter-implant bone to the implants
2. Vertical crestal bone loss
3. Distance between the implants at
the implant/abutment interface. When implants were placed too close together the bone remodeling overlapped to a great degree and consequently resulted in loss of vertical bone height and this subsequently had soft tissue implications.
When implants were placed 3mm and greater, lateral bone loss from the adjacent implants did not overlap with minimal resultant crestal bone loss.
They concluded that it is more difficult to create or maintain papilla between two adjacent implants than it is between an implant and a natural tooth. Their recommendation was that when two implants are placed adjacent to each other in the aesthetic zone a minimum of 3mm of bone should be retained between them at the implant/ abutment level (Figures 1 and 2).
Figure 1: When implants are placed 3mm and greater apart the bone loss from the adjacent implants does not overlap, resulting in minimal crestal bone loss (modified from Tarnow et al, 2000)
Figure 2: When implants are placed too close together, bone loss from adjacent implants overlaps, resulting in additional loss of the crestal bone (modified from Tarnow et al, 2000)
Figure 3: Bone loss is circumferential around the implants. When implants are placed too close together the vertical and horizontal components of bone loss compromise the peak of the interproximal bone and thus the resulting soft tissues.
Figure 4: Ideal implant theoretically will maintain the interproximal peak of bone, however there are no long-term studies to support this
Figure 5: If implants are placed too facially this will compromise the thickness of the facial bony plate, which can eventually resorb. This will result in apical migration of the soft tissue
Figure 6: Ideal implant placement will allow fabrication of restorations with ideal contours
This particular study addressed bone loss between the implants. It should be remembered that the bone saucerisation has two dimensions – a horizontal and vertical. Radiographs only demonstrate the horizontal aspect of bone saucerisation. Bone loss occurs circumferentially around the implant and when two implants are placed adjacent to each other, facial bone loss also occurs (Figures 3 and 4). This has implications in terms of stability of the facial gingival margin. If the implants are placed too far forward there will be less facial bone and this will ultimately result in apical migration of the free gingival margin (Figure 5).
Placement of adjacent implants is also critical for restorative contours, placing implants too close together makes it dif cult for the laboratory technician to fabricate restorations with pleasing aesthetic contours.
Tarnow et al (2003) also performed a study to determine the height of the soft tissue to the crest of the bone between two adjacent implants. This was done independent of the location of the contact point.
They looked at 136 inter-implant papillary heights in 33 patients by eight examiners. A standardized periodontal probe was used and placed from the height of the papilla to the crest of the bone.
They found that the mean height of papilla between two adjacent implants was 3.4mm with a range of 1-7mm.
Although this was a retrospective study and there were many variables such as operator, implant type, placement and so forth it did give us information that soft tissue
"One common error published in the literature is the placement of four implants to replace lateral incisor to lateral incisor."
between two adjacent implants in the aesthetic zone is not a predictable procedure. The patient must be aware of this when treatment planning or alterations must be made in the treatment plan to provide an aesthetic result.
Recreating interdental papilla between two adjacent implants is a formidable task. Restoratively, clinicians alter the position of the contact point to give the illusion of papilla. The thin spicule of bone remaining between the implants may be sufficient to maintain the papilla during the first few years of the restorations service. However, there are no clinical studies with long-term results presented to date to illustrate the predictability of papilla between two adjacent implants.
Another clinically challenging situation is replacement of a maxillary canine and adjacent lateral incisor. This becomes clinically more challenging because the edentulous space is smaller and the inter-implant soft tissue tends to be less voluminous. Consideration in this instance should be given to placement of a single implant in the canine region and cantilevering a lateral incisor from it. Placement of the implant should follow all the principles discussed previously.
Figure 7: Implants placed too close together will result in compromised restorative contour
Figure 8: Placement of adjacent implants compromises the inter-implant peak of bone, resulting in resorption and soft tissue loss
Figure 9a: It is easier to develop illusion of papilla between an implant and an adjacent pontic. Implant placement philosophy should take advantage of such techniques
Replacement of several missing teeth with implants allows for the use of fixed partial dentures and the opportunity to utilize ovate pontics to help support the soft tissue and give an illusion of papillae.
The authors have encountered many situations where a one implant per tooth philosophy is espoused to. This can be particularly detrimental in the aesthetic zone. The literature is quite clear that maintaining papillae between implants is not predictable. Even with the advent of scalloped type implants there are no long-term studies showing papilla maintenance. For an aesthetic outcome, it is more predictable to place implants away from each other so that the intervening soft tissue can be sculpted to give the illusion of papilla. One common error often published in the literature is placement of four implants to replace lateral incisor to lateral incisor. This philosophy of implant placement will not yield an aesthetic outcome (Figure 8). Placement of two implants in both lateral incisor regions and fabrication of a fixed partial denture, sculpting the intervening tissue with ovate pontics is likely to produce an illusion of papilla, which will be more pleasing to the observer’s eye (Figures 9a, 9b and 9c). This placement philosophy can also be reserved for extended edentulous spans where aesthetics is of paramount importance (Figures 10-15).
"Implants used to replace missing teeth in the aesthetic zone have many advantages from preservation of unrestored adjacent teeth, halting the resorption of edentulous space and providing support."
Placement of implants in multiple edentulous spaces must follow the same principles as for single tooth situations, placement must follow appropriate diagnosis and treatment planning, which includes a diagnostic wax-up and fabrication of a surgical guide to facilitate implant placement.
If these techniques are not followed it is all too easy to find implants in the wrong position where prosthetic strategies have to be utilized to satisfy the patient's demand for aesthetics. In situations like these patient expectations are unlikely to be met (Figures 12, 13 and 14.)
Figure 9b: Patient suffered trauma. This patient has been treatment planned for extraction of the lateral incisors, root banking of the central incisors, and placement of implants in lateral incisor region to support a four-unit bridge
Figure 9c: Four unit bridge on two implants in lateral incisor region. Note how tissue in central incisor region has been sculpted. Also note how buccal contours of tissue in central incisor region has been maintained
Figure 10: Clinical slide showing dental implant placement so that illusion of papilla can be developed
Figure 11: Facial view of slide in Figure 10
Figure 12: Intraoral photograph depicting placement of two implants in upper right lateral incisor and upper left canine region
Figure 13: Laboratory slide illustrating a five-unit splinted screw retained bridge with pontics designed to compress tissue and provide illusion of interproximal papilla
Figure 14: Lateral view of five-unit screw retained zirconia bridge. Note how soft tissue has been redeveloped
Figure 15: Buccal view of bridge depicting sculpting and maturation of soft tissue to give appearance of interproximal papilla
Conclusion
When a patient has a missing anterior tooth and desires replacement, a decision must be made by the dentist and patient as to the method of replacement. Common choices would include a conventional fixed partial denture, a resin bonded fixed partial denture or an implant borne restoration. Each has its advantages and disadvantages.
The conventional fixed partial denture has the advantages of being an established treatment procedure, having predictable aesthetics, and being expedient. It has the disadvantage of requiring preparation of adjacent teeth and potential risk for periodontal and pulpal tissue.
The resin bonded partial denture has the advantages of preserving tooth structure, having predictable aesthetics and reduced cost. It has the disadvantages of being technique sensitive for the dentist and technician and often losing retention, which may lead to decay.
Implants used to replace missing teeth in the aesthetic zone have many advantages from preservation of unrestored adjacent teeth, halting the resorption of edentulous spaces and providing support. However, at present, it has the disadvantages of long treatment time,
Much effort is being directed at shortening the treatment time and making delivery of the service more
Much effort is being directed at shortening the treatment time and making delivery of the service more time efficient.
Immediately loading implants is one direction that many researchers and clinicians are taking – however, the parameters to when immediately loading implants is possible have not been established and, until that time, immediately loading implants must be made on an individual and case-by-case basis, taking into account all the factors that affect loading of the initially non-osseointegrated implants.
Even with all the disadvantages listed, the implant supported single tooth restoration can be successfully executed when all the factors discussed in this series of articles are addressed. When one or more of the adjacent teeth are unrestored or in need of only a minor restoration, the single tooth implant should be considered the restoration of choice.
