Ridge augmentation for implant procedures has been shown to be highly successful. There are several techniques available to the dentist, but they require some degree of surgical expertise and experience. No particular technique has been shown to be superior. This article presents the indications, techniques, and complications of the various procedures for alveolar ridge augmentation. This information will educate the general dental practitioner of the techniques available and provide information on the surgical procedures that could be used to discuss with patients when they are being referred to a specialist.
Key points
- •
The ideal position of a dental implant should not be compromised in the setting of a deficient maxillary or mandibular alveolar ridge. Overall, bone augmentation techniques can be highly predictable and can provide significant horizontal and vertical gain.
- •
Since there is currently no true consensus in the literature on which bone grafting technique or material is strictly indicated for each clinical scenario, dental professionals can benefit from gaining an understanding on the various methods to achieve horizontal and vertical augmentation of the deficient alveolar ridge.
- •
The surgical techniques presented in this article for the augmentation of the deficient alveolar ridge can vary from simple to advanced and require proper training for successful outcomes and minimizing complications.
Introduction
The loss of alveolar bone is a common phenomenon linked to various systemic and local factors. Systemic factors include age, nutrition, osteoporosis, and other skeletal disturbances, and local factors include the premature loss of teeth, trauma, pathology, and periodontal disease. In the United States, partial edentulism affects the majority of the population and the number of partially edentulous individuals is expected to increase to more than 200 million in the next 8 years. The increased focus in preventative dental care over the past years has positively impacted tooth retention and thus a decrease in fully edentulous individuals is expected. Interestingly, the premature loss of permanent teeth remains correlated with an increase in age. The growth of a more socially active and more esthetically demanding aging population in the United States has increased the demand for more comfortable, functional, and esthetic dental prosthetic solutions. The placement of dental implants broadens the treatment options for these individuals. Prosthetically driven implant restorations may not only significantly improve the patient’s treatment outcomes by improving the esthetics, occlusion, phonetics, retention, and stability of the prosthesis, but also preserve the remaining alveolar bone. The atrophy of the maxillary and mandibular alveolar arches is a common occurrence that can pose many challenges for the rehabilitation of these patients, both surgically and restoratively. In contemporary implant dentistry, a practitioner may choose between the use or augmentation of the remaining bone based on the clinical and radiographic presentation. In this article, we discuss the various indications and techniques for the vertical and horizontal augmentation of the deficient maxilla and mandible for endosseous implant placement. Ridge preservation and socket augmentation procedures are beyond the scope of this article.
Patterns of bone loss
The classic study by Cawood and Howell demonstrated there are predictable patterns of progressive horizontal and vertical anatomic changes following the loss of teeth ( Box 1 ). The loss of teeth induces the progressive loss of alveolar bone until completely resorbed. , In addition, the loss of basal bone from ill-fitting dentures or occlusal overloading can further contribute to the atrophy of the ridge. Identifying the various patterns of bone loss can facilitate the treatment planning and increase the predictability of the rehabilitation of atrophic ridges.
When teeth are lost prematurely, it can lead to a decrease in the alveolar ridge’s volume owing to the lack of functional stimulus necessary to preserve its vertical and horizontal dimensions. Function influences the delicate balance that exists at the cellular level between bone resorption and bone formation. When permanent teeth are loss prematurely, the loss of stimulus from the forces of mastication in the area lead to a shift to bone resorption.
Generally, the loss of teeth in the maxilla tends to occur before the loss of teeth in the mandible and mandibular anterior teeth are commonly the last teeth remaining in the mouth. However, the rate of resorption of the alveolar crest of the mandible is 4 times the average rate of resorption of the maxilla. The rate of resorption occurs more rapidly within the first 6 months after the loss of teeth. Combination syndrome is a well-documented condition seen in patients with a completely edentulous maxilla and a partially edentulous mandible with preserved anterior teeth. This syndrome leads to a classical pattern of severe resorption of the anterior maxilla and posterior mandible, overgrowth of the maxillary tuberosities, papillary hyperplasia of the hard plate, and extrusion of the lower anterior teeth. The treatment for combination syndrome with dental implants has made it possible for the rehabilitation of posterior occlusion, the redistribution of the forces of mastication, and the prevention of further bone loss.
The loss of teeth can also be attributed to the body’s response to the presence of bacterial biofilm in the oral cavity or trauma from occlusal forces. Periodontal disease can lead to the permanent destruction of supportive periodontal structures, alveolar bone, and ultimately the teeth involved. Without treatment, the resulting inflammatory reaction leads to an average bone loss per year of approximately 0.2 mm for facial surfaces and 0.3 mm for proximal surfaces, with a radius of 1.5 to 2.5 mm from the site of bacterial biofilm formation. In addition, bone destruction caused by persistent occlusal trauma results in a widening of the periodontal ligament and resorption of adjacent bone. These changes to the adjacent bone can lead to tooth mobility and when paired with inflammatory reactions to the bacterial biofilm can result in vertical bone loss or unusual bone loss patterns. The most prevalent form of bone loss caused by periodontal disease is horizontal bone loss, whereas vertical or angular bone loss tends to occur in areas of greater bone volume.
Vertical bone loss was classified by Goldman and Cohen on the basis of the number of osseous walls present in the defect ( Fig. 1 ). Consequently, various defect patterns can arise after dental extractions. Furthermore, Misch and Dietsh classified the resulting extraction socket defects based on the amount of remaining bony walls and provided recommendations on the appropriate graft materials and techniques to be used for the restoration of such defects ( Fig. 2 ). The 5-wall defect results from extraction sockets or cystic cavities. Bone grafting is optional in these defects owing to the tendency of 5-wall defects to fill in with bone without additional surgical interventions. For this reason, the use of inexpensive materials is recommended when considering socket preservation procedures. The 4-wall defect typically consists of missing labial and occlusal walls, whereas the 2- and 3- wall defects present a larger area for bone augmentation and require the use of autogenous bone. Moreover, the 1-walll defect is the most challenging to augment and, thus, block grafts are usually recommended for the restoration of the ridge’s volume.
Deteriorating changes to the quality of the soft tissue architecture can also occur owing to the loss of alveolar bone. The alveolus is typically protected by a strong layer of keratinized attached gingiva. Upon the loss of alveolar bone, the soft tissue can be replaced with a less keratinized oral mucosa, allowing for the area to be more easily traumatized upon normal function. The loss of keratinized mucosa can add to the challenges in placing dental implants in the esthetic zone.
Horizontal and vertical requirements for implant placement
A successful treatment outcome in relation to dental implants depends the restoration of the patient’s function, comfort, speech, and esthetics. Alveolar bone atrophy in the vertical or horizontal dimensions may obstruct the surgeon’s ability to place endosseous implants in the desired position for the prosthetic rehabilitation of the arch. The development of advanced techniques has allowed for the achievement of these outcomes despite the patient’s level of maxillary or mandibular atrophy. Owing to the predictability of bone augmentation procedures, the practitioner should avoid compromising the ideal position of the implant when adequate bone width and height are not available. Nonetheless, the fact remains that the greater the loss of teeth and bone volume, the more challenging the process of achieving a functional and esthetic outcome. Careful treatment planning must take into account the 3-dimensional position of the implant in the bone and the horizontal and vertical requirements for implant placement.
A cone beam computed tomography scan offers the most accurate measure for the available bone structure in the mesiodistal, buccolingual, and apicoronal planes. To minimize damage to adjacent teeth, the ideal distance from the implant to adjacent tooth should be at least 1.5 mm. However, to achieve soft tissue health, the distance between the neck of the implant and the crown of the adjacent tooth should be increased to at least 2.0 mm. In addition, if the coronal distance between the implant and the tooth exceeds 4.0 mm, the cantilever effect would lead to bone loss, magnified occlusal forces, and ultimately possible restoration and/or implant failure. After implant placement, the width of the remaining bone should be at least 2.0 mm on the facial aspect and 1.0 mm or more on the lingual or palatal aspect to prevent bone recession owing to a lack of blood supply. It is widely accepted that, to determine the horizontal dimension required for implant placement, the practitioner must follow the formula: Implant diameter + 2.0 mm facial bone + 1.0 mm lingual bone. Therefore, the horizontal dimension of the available bone should be at least 3.00 mm or greater than the diameter of the implant.
As opposed to calculated measurements, the vertical dimension requirements depend on soft tissue height, prosthetic needs, and proximity to vital structures. The ideal depth of placement of a dental implant is 2.0 to 4.0 mm apical to the adjacent cemento–enamel junction or free gingival margin to allow for adequate prosthetic crown soft tissue emergency profile. The fabrication material of the final prosthesis should be taken into account. Typically, a space of 15 mm is suggested from the crest of the alveolar ridge to the incisal edge of the prosthesis. The specific crown height space (CHS) requirements depend on the selected material for the final restoration. If the interocclusal space is deemed insufficient or excessive, it can be detrimental to the survival of the prosthesis and additional procedures should be considered. Vital structures should be identified in the treatment planning phase with the assistance of 3-dimensional imaging studies or computer-generated models. To prevent traumatic injury to the nerve, implants should be positioned at least 2.0 mm away from the inferior alveolar nerve canal or mental foramen. Moreover, bleeding and other iatrogenic complications can result from the penetration of the dental implant through the inferior border of the mandible or border of the maxillary sinus and nasal cavity and, thus, great care should be taken to avoid these structures ( Box 2 ).
| Mesiodistal | |
| Implant–tooth (apical) | >1.5 mm |
| Implant–tooth (coronal) | >2.0 mm, <4.0 mm |
| Implant–implant | >3.0 mm |
| Buccolingual/faciopalatal | |
| Facial/buccal thickness | >2.0 mm |
| Lingual/palatal thickness | >1.0 mm |
| Apicocoronal | |
| Implant platform- cemento–enamel junction/free gingival margin | 2–4 mm |
| Distance from vital structures | |
| Inferior alveolar nerve canal or mental foramen | >2 mm |
| Inferior border of the mandible | Avoid cortical bone perforation |
| Nasal cavity | Avoid cortical bone perforation |
| Inferior border of maxillary sinus | Without bone grafting, can penetrate approximately 1–2 mm into the sinus |
| Interocclusal/CHS | |
| Alveolar ridge–incisal edge of prosthesis | <15 mm |
There is no consensus in the literature in regard to strict guidelines on which technique or material is indicated for each bone deficiency or clinical scenario. , Rather, the decision should be made after careful consideration and treatment planning. The combination of different techniques and materials is encouraged to achieve optimal treatment outcomes.
Horizontal augmentation
Advanced horizontal bone augmentation procedures are indicated when the bone volume available in the proposed implant site is deemed to be insufficient for the prosthetically ideal placement of the dental implant. The final decision on which bone augmentation technique is adequate for each clinical scenario remains the responsibility of the clinician because there are no clear set protocols in the literature. Clinicians should be familiar with the various options for restoring the deficient alveolar ridge ( Table 1 ). Some of the most predictable surgical techniques available are:
- •
Tunnel technique using particulate bone
- •
Guided bone regeneration (GBR)
- •
Onlay block grafting
- •
Ridge splitting or expansion technique
- •
Distraction osteogenesis
| Technique | Indication | Potential Bone Gain | Recommended Time to Implant Placement |
|---|---|---|---|
| Tunnel technique | 2-wall defect Satisfactory vertical height <4 mm ridge width A ridge that widens as it approaches the basal bone |
1–4 mm | 4 mo |
| GBR | 2-wall defect, 3-wall defect, 4-wall defect | 3–6 mm | 9–12 mo |
| Onlay bone grafting | 1-wall defect <3 mm ridge width |
4 mm Ramus 3–4 mm Symphysis 4–6 mm |
4–6 mo |
| Ridge Split/Expansion | 3–4 mm ridge width | 2–3 mm | Immediate or 4 mo |
| Distraction Osteogenesis | >5 mm horizontal deficiency | Not reported | 3–4 mo |
Tunnel Technique Using Particulate Bone
The placement of particulate bone under the periosteum using a tunneling technique for space maintenance has shown to successfully increase the width of the alveolar ridge. This technique is minimally invasive, simple, and can be more cost effective than other augmentation procedures. In an article by Block, the reported indications for the procedure are (1) satisfactory vertical height, (2) a lack of at least 4.0 mm of bone width, and (3) widening of the ridge as it approaches the basal bone. The ideal defect type for this procedure is the 2-wall defect.
The technique described starts with a crestal incision on the superior aspect mesial to the site of the defect running inferior in a vertical fashion. The blunt end of a periosteal elevator is used to create a subperiosteal tunnel posterior to the incision site. At the crest of the ridge, the periosteum is elevated over the ridge. Excessive lingual dissection should be avoided. Using a TB-type syringe, the particulate material is deposited in a posterior to anterior direction, directly against bone and removed at an angle to create a bevel. Digital pressure is then used to mold the graft until the desired shape is achieved. The incision is then closed using interrupted resorbable sutures. The recommended bone grafting particle sizes range from 350 to 500 μm and the volume from 0.5 mL to 1.5 mL. A healing period of at least 4 months is recommended before implant placement. Overall, the use of allogenic or xenogeneic grafting materials seems to result in a higher potential for horizontal gain, compared with the use of synthetic materials. The potential bone gain of this technique has not been widely reported in systematic reviews, however, case studies show a 2.0- to 4.0-mm augmentation after 4 months of healing time.
A retrospective cohort study by Deeb and colleagues compared the treatment outcomes between 21 patients treated by the tunnel technique and 31 treated with the open technique. After a 6-month healing period, their data showed no significant difference between the outcomes of the tunnel technique versus GBR using a titanium-reinforced polytetrafluoroethylene membrane for the augmentation of horizontal ridge augmentation. The tunnel technique provides a minimally invasive option for patients for the rehabilitation of the deficient alveolar ridge.
Guided Bone Regeneration
GBR is one of the most common and predictable methods for the treatment of horizontal bone defects. Space maintenance can be provided by nonresorbable and resorbable membranes preventing the migration of undesired soft tissue and guiding the growth of bone into the grafted site. There is evidence to support the use of GBR for horizontal augmentation at the time of implant placement for ridges measuring approximately 4 mm or as a staged procedure in preparation for implant placement for residual crests measuring less than 3 mm. Nonresorbable membranes include titanium mesh, expanded polytetrafluoroethylene, and titanium-reinforced expanded polytetrafluoroethylene membrane. Resorbable membranes include collagen, polylactic acid, amniotic membrane, pericardial membrane, and dura mater. The barrier material seems to have little effect on horizontal ridge augmentation and although there are more complications reported with the use of titanium meshes (ie, dehiscence), the conclusion on recent systematic reviews has not shown the data to be statistically significant ( Figs. 3–5 ).
