9

Alternatives and Adjuncts to Standard Augmentation Techniques

The innovative power of dentists, surgeons, and manufacturing companies worldwide is great. Numerous procedures and modifications are published almost daily in the literature, so that the modifications and additions to the standard techniques presented here represent only an incomplete selection. What most of the procedures in this chapter have in common is that they work in the hands of good surgeons in special situations and have been documented in small case series but have not been comparatively tested multicenter in larger studies.

9.1 Titanium Mesh Technology

Bone grafts require contour and stability for healing, especially when working beyond the alveolar envelope. Both requirements can be met by a titanium mesh. There are 10-year data on mesh technology with 94.1% implant survival.¹ Meshes have a long history in reconstructive surgery, for example, in the treatment of orbital fractures or for cranial vault reconstruction.

However, it is difficult to shape the rigid mesh structure in three dimensions, and material removal is difficult because the mesh becomes entangled in the soft tissue scar. For three-dimensional shaping, companies in the pre-digital era devised special mesh structures (eg, Micro Mesh, KLS Martin) that can yield in two directions and the clinician can shape spherically in three dimensions with the aid of pincers in a similar way to a building a car body (Fig 9-1). With a little experience, any desired rounding of the alveolar process can be created chairside. For the less experienced, this step is now facilitated by additively building up the meshes layer by layer in a patient-specific shape by means of selective laser melting (SLM) after electronic preliminary planning on computed tomography (CT) or CBCT data (Yxoss CBR, ReOss). Clinically, the fitting accuracy is often impressive. The mesh is clinically underfilled with bone chips obtained as sterilely as possible (via bone mill or scraper) and, if necessary, mixed with bone substitute material in a 50/50 ratio. The mesh can be fixed to the bone with screws. It usually has to be surgically removed before implant placement because the mesh structures block implant placement and because there is a risk of mesh exposure later in the life of the patient. The processing technology of meshes is well developed on the engineering side.

Fig 9-1 Mesh technology a. The Micro Mesh has special bars that facilitate spherical shaping. The pincers allow spherical curves in two planes. b. Shaped mesh in situ for vertical defect in the maxillary right central incisor to canine area after trauma. It is filled with autogenous iliac crest cancellous bone. c. Panoramic image shows the placement of the mesh. d. Regenerate after mesh removal 4 months later. The implants have primary stability, but the bone regenerate is not yet mature.

The problem, as with all overlay bone grafts, is the 3- to 4-mm limit of neoangiogenesis and biofilm formation. The soft tissue of an overlay bone graft must be mobilized three times (see chapter 8), which creates flap tension, and the material lies under the suture. Premature exposure of the meshes due to biofilm formation is common depending on the defect size and buildup height and has been reported in studies with individually prefabricated meshes as being between 37%² and 66%.^3,4 The working group of Ghanaati has therefore proposed a way to allow the meshes to heal openly in critical cases from the outset, covering them only with collagen membranes and leukocyte- and platelet-rich fibrin (L-PRF) membranes.⁵ Successful open, uncovered healing of bone graft substitutes has been reported in other fields such as ridge preservation. In CAD/CAM meshes that initially healed without problems for a few weeks, later exposure after 6 to 8 weeks is often observed. The portion of material not incorporated by angiogenesis is secondarily rejected via biofilm. Mesh implantations above 3- to 4-mm buildup height could therefore also be described as a partial loss strategy (Figs 9-2 to 9-3).

Fig 9-2 Customized mesh technique. a. The panoramic tomogram shows a bilateral free-end situation in the maxilla with a fissured alveolar ridge 9 months after tooth extractions as the initial situation. b. The mesh is virtually preplanned based on data from a CBCT, showing a buildup of the ridge height to the level of the canine. c. Occlusal view of the preplanning of the printed customized mesh (Yxoss CBR). d. Panoramic with the meshes in situ, each filled with a mixture of 50% xenogeneic bone substitute and 50% autogenous bone from the scraper; 1.5-mm Micro Screws (KLS Martin) were used for fixation. Sinus floor augmentations were performed at the same time. e. For osteosynthesis material removal on the occasion of implant placement 4 months after mesh insertion, the mesh must be completely excised from the scar, which requires a wide soft tissue opening. f. The regenerate after 4 months still has a granular structure and is not yet completely remodeled bone. Nevertheless, it provides sufficient support for the dental implants.

Fig 9-2 Customized mesh technique. g. The dental implants in situ, which healed unloaded for 3 months. In the mandible, short implants of 6-mm length were used. h. Panoramic tomographic image of the completed prosthetic restoration.

Fig 9-3 Premature mesh exposure. a. Panoramic with non-salvageable maxillary right lateral incisor to left first molar and a significant vertical bone defect at the pontic. b. 3D model of the defect area based on CBCT data. c. Virtual planning of the customized mesh (Yxoss CBR). d. Defect situation after unfolding via midcrestal incision.

Fig 9-3 Premature mesh exposure. e. Fitting of the prefabricated patient-specific mesh. This requires a wide flap of the soft tissue. f. Mixture of 50% scraper bone and 50% bone graft substitute and venous blood. g. The mixture is filled into the mesh in excess. h. The mixture is compacted in the mesh. i. The mixture is further compacted by pressing it onto the bone. The mesh is fixed with a microscrew (KLS Martin 1.5 mm system, Tuttlingen, Germany). j. A Bio-Gide (Geistlich) collagen membrane is cut to size in the dry state. k. The membrane is placed neatly under the palatal and buccal soft tissue flaps. Afterward, the collagen membrane is rehydrated by saline solution.

Fig 9-3 Premature mesh exposure. l. The rehydrated membrane adheres to the support by capillary forces and therefore does not require additional fixation. m. Meanwhile, the remaining maxillary incisors were extracted, and the sockets were restored by ridge preservation. A temporary dental implant (IPI, Nobel Biocare) was placed in the interdental septum between the lateral incisors and canines to support the provisional prosthesis and prevent pressure on the soft tissue superior to the mesh. n. The panoramic view shows a correct fit of the mesh in the planned position. o. The soft tissue has healed without interference, and the midcrestal incision has healed without irritation. A soft tissue dehiscence occurs in the vestibule after 8 weeks, in an area that was not in contact with the provisional prosthesis. There is an additional dehiscence in the maxillary left second premolar region. p. The mesh continued to heal open for another 8 weeks under local disinfecting measures. Here, clinically hard bone is seen after mesh removal with placement of the bone graft substitute particles. q. The panoramic radiograph shows that there is a bone gain of about 3 to 4 mm compared to the initial position, but not a complete filling of the defect. After partial loss, the portion of the bone graft close to the bone has healed; the rest has been rejected (see the discussion of neoangiogenesis in chapter 2).

9.2 Partial Tooth Extractions

Loading of the Sharpey fibers stimulates the alveolar bone and can prevent its resorption or even build up new bone. There have been different approaches suggested for leaving root remnants in place during the initial tooth extraction. The socket-shield technique is a form of ridge preservation to prevent resorption of the facial bundle bone after tooth extraction (Fig 9-4). At the level of retrospective case series, good results were shown, especially for the preservation of buccal bone.⁶ However, fistulae or rejection reactions starting from the root remnant occurred in 18% of the cases.⁷

Bone can be developed vertically by forced eruption of a root remnant; for this purpose, the tooth to be extracted is reduced to the gingival level and extruded with orthodontic brackets and wires; this process is repeated several times if necessary.⁸ The Tissue Master Concept goes one step further than the socket-shield technique by replanting a slice of an extracted tooth and extruding it crestally with the attached bone.⁹ This method is biologically well designed. Similar to distraction osteogenesis, new bone forms in a crestal direction, resulting in a vertical augmentation (see also section 10.8 in chapter 10).

9.3 Implant Site Preparation by Condensation, Bone Expansion Screws, Conical Implants, and Bone Spreaders

The maxilla, in contrast to the mandible, has a thin compact bone layer, a peripheral blood supply type via multiple periosteal vessels, and a fine-mesh cancellous internal bone structure. Therefore, special surgical procedures have evolved for the maxilla to stretch, micro-fracturing and reshaping the cancellous bone. If the bone is then compressed by cylindric condensers of ascending size, the primary stability of an implant in the usually loose cancellous bone of the maxilla (eg, Misch type D4 bone) can be improved. The technique can be made more comfortable by replacing the tapped condensation instruments with expansion implants (ie, bone expansion screws), which are screwed into the jaw with high torque. The condensation techniques have in common that nutrition is maintained over the fractured bone portions via an intact soft tissue attachment. Because of the minimal surgical access and the lack of soft tissue incisions, the condensation techniques are usually well tolerated by patients. However, there is evidence that bone, especially in the mandible, reacts to the strong pressure during condensation with increased peri-implant bone resorption of up to 2 mm¹⁰ and that implants with high insertion torque (>50 Ncm) develop soft tissue recession.¹¹

Fig 9-4 Principle of partial tooth extraction. In the socket-shield technique, part of the tooth root is left with an intact periodontal ligament so that the vestibular bone is not lost (see chapter 10).

A normal dental elevator is well suited as a spreader (Fig 9-5

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