12

Decision Making in the Anterior Esthetic Region

Compared to standard protocols, implant placement in the esthetic field requires increased precision and predictability of augmentation thickness and height over long periods of time to provide a reliable basis for subsequent soft tissue attachment and pink esthetics. One desires a permanent 1- to 2-mm thick labial bone wall up to the implant shoulder to avoid the gray color of the titanium showing through the gingiva. Recession due to graft resorption is counterproductive. Prosthetic gingiva, ie, pink ceramic, or vestibular acrylic shields as gingival substitutes are a second choice but can usually be avoided by correct bone augmentation. The gingival transition of mandibular teeth is usually not in the direct view of others, but because patients can look directly at their own mandibular anterior teeth and the associated gingiva in the mirror, patient satisfaction should also be promoted here by an esthetic replacement.

12.1 Special Anatomical Features of the Anterior Maxilla

The oblique position of the superior alveolar process has consequences (Fig 12-1). Implant axes placed in the direction of the bone usually create a screw opening on the labial surface or require prosthetic compensation. Implant axes placed in the prosthetic direction, with the screw channel on the palatal surface of the crowns, then require augmentation. Vertical bone atrophy always has a sagittal component due to the oblique position of the alveolar process, which leads to recession of the atrophied alveolar ridge. In order to compensate for occlusion, the implant axes and the denture are often tilted forward in a fan shape, resulting in a mechanically unfavorable canting of the prosthetic denture (ridge lap design). This compensation results in eccentric implant loading. Therefore, the bone should be augmented vertically and horizontally to achieve an esthetic and functionally resilient result. In general, sagittal discrepancies such as pseudoprognathism and true dysgnathia cannot be compensated prosthetically, not even with the help of dental implants. In healthy patients, surgical correction by augmentation and, if necessary, jaw realignment is the best option. Furthermore, unlike in the posterior region, vertical losses cannot simply be compensated by long dental crowns. If the latter aspects are not taken into account, the result is so-called horse teeth: long anterior crowns that, starting from the small apical base of the maxilla, fan out and tilt forward.

Fig 12-1 The atrophied edentulous maxilla has two disadvantages: vertical loss and the recession of the alveolar ridge causing an anterior oblique angle. If these problems are not recognized, long protruding anterior crowns (ie, horse teeth) will result.

12.2 Anatomical Features of the Anterior Mandible

The anterior partially edentulous mandible very often shows an extremely narrow apical base with a bulb shape in sagittal section. While in the posterior region a certain buccolingual angling of the implant axes to adapt to the opposing dentition is usually possible, this is rarely possible in the anterior mandible because of the narrowness of the apical region. CBCT diagnostics and, if necessary, navigated implant placement is also advantageous because of the narrow tooth gaps (Fig 12-2). Problems are sometimes caused by a very prominent incisive nerve, injury to which should be avoided because neuropathic pain conditions associated with dental implants are known in this area (Fig 12-3).¹

Fig 12-2 Digital volume tomogram with ampullary mandibular cross-section with an indentation inferior to the anterior teeth.

12.3 Gingival Biotype

According to clinical experience, thick and thin gingival biotypes² mainly influence the bone thickness of the facial lamella and the recession tendency of the gingiva^3,4 on the dental implant, even though this cannot be proven with certainty on the basis of scientific data.⁵ The soft tissue thickness figures given in chapter 7 were quoted without taking the gingival type into account and must therefore be individually adjusted.⁶ A thick gingival type is more forgiving of deficiencies in bone augmentation than a thin biotype. In short gaps, the gingiva of the thick biotype hangs like a stiff curtain, attached to the adjacent periodontium. The problems of the thick biotype are scarring at incisions of the gingival margin and the tendency to pockets with associated peri-implantitis risk, which can remain unnoticed for a long time. The thin biotype responds to deficiencies in bone augmentation with recession and exposed implant margins. Undesirable gray discoloration of the metal implant is also possible. Therefore, there is an increased need for bone and soft tissue augmentation to reinforce the gingiva of this biotype. On the other hand, the risk of peri-implantitis is lower because the gingiva “moves away” from the infection and does not form pockets with pathological bacterial flora in the first place.

Fig 12-3 Digital volume tomogram. The incisive nerve can be seen in the anterior interforminal mandible, which would be at risk in the event of implant placement.

12.4 Gingival Height and Reverse Planning

The esthetics and height of the gingiva of an implant restoration in the anterior region should be clearly planned by anticipating the final result digitally or in a wax-up and discussing it with the patient (Figs 12-4a and 12-4b). Reverse planning is the calculation backwards from this treatment objective. In other words, the prospective gingival morphology is first determined in the wax-up on the basis of the esthetic proportions and the gingival height of existing neighboring teeth. The decisive factor for the subsequent attachment and pattern of the gingival attachment is the bone, because the soft tissue follows the bone passively.

Fig 12-4 a. Trial set-up of a maxillary anterior dentition. b. Transfer to a drilling template by duplicating in clear acrylic. c. Starting from the drilling template, the average numbers shown here can be used to precalculate the required bone height and then generate it by augmentation.

As a rule of thumb, the soft tissue height (chapter 7) in the edentulous region is 1.5 mm. If the gingiva can rest on one side against a crown on the vestibular surface, it rises to 3 mm, which corresponds to the average value of the biologic width (Fig 12-4c). If the gingiva can support itself between two teeth on both sides, then with a probability of 95% it rises about 6 mm coronal to the bone.⁷ However, between two adjacent dental implants only 3 to 4 mm of soft tissue height can be expected, which is why this situation should be avoided as much as possible in the anterior region by inserting pontics or bridge attachments. These dimensions are therefore subtracted from the specified prospective gingival height, which gives the bone level required for the reconstruction. The bone is precisely built up to this height by augmentation using autogenous blocks.⁸ In augmentation procedures such as guided bone regeneration (GBR), which are prone to height resorption, the amount of shrinkage must be factored in and compensated by overcorrection.

12.5 Precise Augmentation by Avoiding Resorption

Especially when augmenting simultaneously with implant placement, precise and low resorption healing of the augmentation is required to accurately adjust the labial soft tissue height with the bone graft. Resorption protection of bone block grafts was discussed in chapter 2 and consists of using hard bone graft types such as external oblique ridge blocks, membranes, and bone graft substitutes such as xenogeneic bone graft substitute to cover the block graft. In contrast to the former methods, the additional use of a bone graft substitute in the wound also has disadvantages because it increases the amount of foreign material and creates infection risks due to interfaces for possible biofilm formation directly under the suture.

12.6 Implant Positioning

Vertical

As a rule, implants with a raised rough-smooth border and platform switching, so-called bone-level implants, are used in the esthetic field. However, this name does not suggest that the implants are placed at the level of the existing bone, but rather at the level of the prospective bone after augmentation. The implants are therefore planned with their rough-smooth border in the vertical plane at the prospective bone height corresponding to the prospective gingival height. There is little tolerance in the vertical dimension. It is true that dental technicians like to place the implant somewhat more apically, because a longer emergence profile can then better compensate for implant misplacements. However, if the implant is placed too deep, the biologic width will be violated. In a single-tooth gap, where the gingiva is attached to the healthy adjacent periodontium, an implant placed too apically would create a pseudopocket and a loss of attachment to the adjacent periodontium because the body strives to comply with the law of biologic width. Thus, an implant placed too apically in a single-tooth gap will produce iatrogenic damage to the adjacent tooth. In a larger gap, if the implant is placed too apically, the entire gingival margin will be established more apically, resulting in interdental black triangles and food retention.

Mesiodistal

The implant diameter should be selected so that there is a 1.5- to 2-mm distance from the neighboring teeth in a gap. If one places the implant closer to the neighboring tooth, the soft tissue attachment apparatus will not have enough space. The so-called biologic width should actually be called biologic height, but this structure also has a space requirement in its width. If this space requirement is not met in the mesiodistal direction, iatrogenic damage occurs due to loss of attachment to the neighboring teeth with the formation of a more apical papilla tip. If the horizontal minimum distances are not observed between two implants, the papillae also lose height with the formation of interdental black triangles. In very narrow gaps, for example, in mandibular anterior teeth and some maxillary lateral incisors, eg, in the case of gaps caused by agenesis, it is sometimes necessary to go slightly below these minimum distances. If at least one platform-switched implant is used, the distance of the platform switch can be added to the horizontal biologic width. This results in a minimum gap width of 5 mm for a 2.9-mm implant with a 2.2-mm abutment diameter, for example. If the gap is even smaller, one should rather think about the option of the single retainer resin-bonded prosthesis.

Orofacial

Augmentation success and also long-term preservation of the alveolar process is initially best achieved within the envelope. There are augmentation techniques that can offset the envelope, such as extended splitting or a long bone block. But for the single implant position, the goal should be that it should always be within the buccal contour line of the alveolar process. If the opposing dentition suggests a different implant positioning, eg, in the case of dysgnathia or pseudoprognathism, then it should be remembered that dysgnathia should not be compensated prosthetically but skeletally by appropriate surgery. If the reason is pseudoprognathism, then the occlusal height must be corrected and not the orofacial implant position (see chapter 14). Basically, a simple rule applies to the orofacial implant position in both jaws. Place the implant in contact with the palatal wall. The prerequisite is that this wall has been clearly visualized by soft tissue detachment and can be assessed intraoperatively. If this wall is missing, it should be built up by augmentation (see section 11.4 Defect Stage 3/4 in chapter 11).

Fig 12-5 Esthetic complication management. a. Infraocclusion due to implant placement at young age before the pubertal growth spurt. Vestibular fistula. b. Panoramic radiograph with approximately 7-mm infraocclusion, after an attempt at compensation by an overlong abutment. c. Bone defect largely concealed by the soft tissue after explantation. d. After opening, the extent of the bone defect is shown. e. Treatment of the bone defect by autogenous bone block from the external oblique ridge. f. Panoramic radiograph showing osteosynthesis screws.

12.7 Augmentation for Dental Agenesis and Adolescents

The alveolar process grows throughout life by further eruption of the teeth. This growth can be seen when an anterior implant moves into infraocclusion with the adjacent teeth over time, especially in patients with a vertical growth pattern (Fig 12-5).

The greatest growth is to be expected in childhood up to 12 years of age, with up to 23.7 mm vertical growth, which results from the deepening of the palatal arch (dentoalveolar growth) and the drift of the maxilla in the vertical development (craniofacial growth) of the midface^9,10 (Table 12-1). An ankylotic dental implant would not follow this drift and would therefore be in infraocclusion by this amount in relation to the occlusal plane. In adolescence from 12 to 18 years, the addition of dentoalveolar and craniofacial growth results in mean infraocclusions of about 3.1 mm for an implant placed in adolescence, but in the most unfavorable individual case, taking into account the observed data spread, up to 7.9 mm.¹¹ Beyond the age of 18, no further craniofacial growth can be assumed, but there is still a vertical development of the alveolar process by eruption of the teeth, with a mean 1.7-mm and maximum 5.8-mm infraocclusion of a dental implant. Beyond the age of 31, there are data of a mean of 0.3 mm of further infraocclusion, which is probably clinically tolerable. However, in individual cases, in 6.25% of patients, the infraocclusion was significant enough that crowns had to be remade. No exact values have been reported in studies,^12,13 but the author assumes that crown remaking is performed for an infraocclusion >1 mm, which is considered to be the maximum value for the older adult age group.

Fig 12-5 Esthetic complication management. g. Soft tissue contour after healing of the bone block. h. Reentry. The bone block had partially integrated 4 months later. i. Panoramic view after implant placement in the bone block. j. Implant uncovering as an interim outcome. k. Documentation of stability 7 years later. The patient has moved to another location and kindly took a photo with his cell phone camera.

Table 12-1 Mean and maximum infraocclusion and implant survival in the maxillary anterior region with implant placement during growth14,16

M, male; F, female.

Contrary to what may have been initially expected, implant prognosis improves with age, which may be related to the improved bone supply and reduced immune response of the elderly to foreign bodies.14

Girls go through the pubertal growth spurt, recognizable by menarche, at around 13 years of age, and boys later at around 15 years of age. After that, alveolar process growth slows down. If an implant restoration is planned, then waiting for the pubertal growth spurt is the best compromise between the threat of implant infraocclusion and increased psychologic stress.¹⁵ Taking into account the individual psychologic stress, augmentation and implantation can then also be performed before the age of 18 according to the Association of Scientific Medical Societies in Germany (AWMF) guidelines, if necessary with 1 to 2 mm epicrestal positioning as a secutity surcharge, because further growth of the adjacent dentition can be expected until the age of 30 years and beyond.¹⁶

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