Alveolar Ridge and Socket Preservation Techniques for Implant Therapy

Maintaining optimal alveolar ridge dimension and socket preservation following tooth extraction are key goals in implant therapy. Once the tooth is extracted, hard and soft tissue remodeling is part of the normal physiologic healing process that occurs to the remaining edentulous ridge. This remodeling negatively affects the ridge dimensions in the buccolingual and apicocoronal aspects. For premolar and molar sites, Schropp et al¹ report ridge width reductions up to 50% (an average loss of 6.1 mm) within the first year post-extraction. With respect to anterior and premolar sites, a systematic review described an average loss of 3.87 mm in ridge width, and 1.67 to 2.03 mm in ridge height.² Considering these ridge alterations may hinder optimal implant placement, compromise esthetics, and create unfavorable defects around neighboring teeth and prostheses, minimizing this bone-resorptive process has been extensively researched. For clinicians, the goal is to provide treatment that preserves the natural tissue contours of the ridge following tooth extraction.

Alveolar socket preservation has been used to describe “a technique in which completely contained extraction sockets are filled with a bone substitute material and/or sealed with membranes, whereas in alveolar ridge preservation, damaged extraction sockets are also included.”³ Conversely, some review articles consider the terms interchangeable and mainly use alveolar ridge preservation, which has been described as “any procedure developed to eliminate or limit the negative effect of postextraction resorption, maintain the soft and hard tissue contour of the ridge, promote bone formation within the socket, and facilitate implant placement in a prosthetically driven position.”⁴ The term alveolar ridge preservation will be used throughout this article, and the reviewed literature will involve intact or mild-to-moderately damaged extraction sockets, rather than severely compromised sockets. This paper will also present a visual clinical comparison of two socket preservation cases (Case 1: Figures 1 through 11B; and Case 2: Figures 12 through 22B).

Ridge preservation is indicated in situations in which immediate or early implant placement is not possible due to patient- or site-specific reasons.⁵ In these scenarios, the main significance of ridge preservation lies within limiting alveolar ridge contraction over the healing period. A systematic review by Avila-Ortiz et al⁶ reports alveolar ridge preservation was effective with a clinical magnitude of 1.89 mm in terms of buccolingual width, and 2.07 mm for midbuccal height. Maintaining adequate ridge dimensions may help achieve prosthetically driven implant therapy, while avoiding or minimizing the need for additional ridge augmentation at the time of implant placement. A systematic review by Weng et al⁷ notes “the need for hard tissue augmentation at implant placement was five times higher if no socket preservation/ridge preservation was performed on the day of tooth extraction.” This agrees with a more recent systematic review by Mardas et al⁸ noting that in comparison with unassisted socket healing, alveolar ridge preservation procedures significantly decrease the need for further ridge augmentation during implant placement.

PRESERVATION TECHNIQUES

It is established that tooth extraction is a traumatic procedure causing severance of the soft tissue and periodontal ligament attachment, along with disruption of vascular structures within the socket walls.⁹ Therefore, the first critical step is the use of minimally invasive techniques and instruments — such as tooth sectioning, periotomes and vertical extraction systems¹⁰ — to prevent additional trauma during extraction (particularly fractures and expansion of socket walls). Following extraction, ridge preservation techniques can be divided into the surgical aspect and material selection aspect.

Surgical Considerations: These mainly relate to the extent of soft tissue manipulation surrounding the extracted tooth. A flapless approach generally means no soft tissue manipulation or only limited undermining was performed to allow for extension of the barrier material under the tissues beyond the defect, and no primary closure was attempted. In comparison, a flapped approach usually involves vertical-releasing incisions, flap reflection and coronal advancement to achieve primary closure.^11,12 Studies report mixed results when comparing flap and flapless approaches in alveolar ridge preservation; some authors describe more pronounced ridge resorption when flap reflection is performed to achieve primary closure,¹² while others note no significant difference between the two approaches.^13,14 However, one of these studies found significantly higher postoperative discomfort associated with the flapped group, and a more coronally displaced mucogingival junction as a result of the associated tissue release for primary closure.¹³ Additional studies also report no major adverse outcomes and favorable ridge preservation results, despite the fact no primary closure was attempted and treated sockets were left exposed to the oral cavity.^15–17

Material Selection: Alveolar ridge preservation procedures have been extensively tested with numerous materials and combination of materials, such as:

• Bone grafting alone (including autografts, allografts, xenografts and alloplasts)
• Membrane alone (including resorbable or nonresorbable)
• Combinations of membrane and bone grafting

BONE GRAFTS

Although autografts were considered the gold standard for augmentation procedures, an animal study was conducted to evaluate its efficiency in ridge preservation. The re­searchers compared autogenous bone chips to anorganic bovine bone and, after three months of healing, significantly more resorption was noted in the autogenous group. The authors attribute this to rapid resorption associated with autogenous bone, which was de­monstrated by minimal remaining autogenous chips in the histologic analysis.¹⁸ On the other hand, two of the most commonly used grafting materials for alveolar ridge preservation are allografts and xenografts, which were recently compared in a hu­man study that revealed no significant differences in vertical and horizontal dimensional changes after six months of healing.¹⁹ With regard to allografts, they are available in mineralized and demineralized forms, and studies comparing the two in ridge preservation have not found one superior to the other.²⁰ Finally, alloplasts — such as hydroxyapatite, tricalcium phosphate, calcium sulfate and bioactive glass polymers — are common examples discussed in the literature. These grafts have shown mixed results in studies, with some authors noting favorable ridge preservation abilities,²¹ while others report inferior outcomes.²²

BARRIER MEMBRANES AND SOCKET SEALING

Clinicians can choose between resorbable and nonresorbable membranes, and both types have been extensively discussed in the literature. Lekovic and colleagues^23,24 published some of the earlier studies on the use of membranes alone for ridge preservation. When compared to unassisted socket healing, they found less bone resorption when resorbable or nonresorbable membranes were used. That noted, the use of membranes alone is not widely discussed in the current literature because the focus has chiefly centered on combination approaches in which a graft acts as a socket filler, and either a membrane or socket seal is used to cover the material.

When used in combination with bone grafts, resorbable^15,19 and nonresorbable^16,25 membranes have shown positive results in ridge preservation. With regard to the use of socket sealers in conjunction with bone grafts, a recent study compared four groups: bovine graft with soft tissue punch (from the palate); bovine graft without soft tissue punch; bovine graft with absorbable collagen membrane; and unassisted socket healing as a control. The researchers reported significantly less ridge width loss with the soft tissue punch and membrane groups, as compared to the other two.²⁶ It is generally accepted that covering the underlying bone graft is beneficial. In fact, studies have shown favorable ridge preservation by simply covering the graft material with various collagen wound dressing materials (either tape or plugs).^20,27–31

CONCLUSION

It is accepted that ridge preservation procedures are beneficial in limiting alveolar bone resorption following tooth extraction. The buccal plate is usually thin in nonmolar sites,^32,33 and when its thickness is < 2 mm, ridge dimensions are more prone to resorption³³ — thus, some form of alveolar ridge preservation is advised. Although ridge preservation may not be advisable in molar sites with a thick buccal plate,³⁴ studies have reported that sinus pneumatization may occur, especially after extraction of second maxillary molars.³⁵ One study showed alveolar ridge preservation in the posterior maxilla may reduce the need for sinus augmentation for implant placement.³⁶ In addition, as noted earlier, alveolar ridge preservation has generally reduced the need for further augmentation at the time of implant placement.^7,8

In situations in which immediate or early implant placement is not possible due to patient- or site-specific reasons, alveolar ridge preservation is indicated.⁵ However, the 2012 Osteology Consensus Conference³⁷ and recent systematic reviews^3,38 have not demonstrated clear superiority regarding technique or choice of biomaterials. With respect to the surgical aspect, it seems prudent to choose a ridge preservation technique that involves the least tissue manipulation and surgical trauma, as this will speed healing, while minimizing patient discomfort and postoperative complications. Even so, flap elevation may still be justified for adequate tooth removal and extraction site management.³⁴

In terms of material selection, operators may choose from biomaterials that have been well documented in the literature, taking into account handling characteristics, as well as clinician and patient preference. Ultimately, the choice of technique and material is based on the individual patient and specific clinical situation.

KEY TAKEAWAYS

• The clinical goal in implant therapy involving tooth extraction is to provide treatment that preserves the natural tissue contours of the alveolar ridge, as alterations may hinder optimal implant placement.
• The chief significance of ridge preservation is to limit alveolar ridge contraction over the healing period.
• Compared to unassisted socket healing, alveolar ridge preservation procedures significantly decrease the need for further ridge augmentation during implant placement.
• When used in combination with bone grafts, resorbable^15,19 and nonresorbable^16,25 membranes have shown positive results in ridge preservation.
• Recent systematic reviews^3,38 have not demonstrated clear superiority regarding a specific technique or choice of biomaterials.

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The authors have no commercial conflicts of interest to disclose.

From Decisions in Dentistry. October 2018;4(10):42–46.