Dentoalveolar ridge preservation after tooth extraction: biological events (Part I)

This article has been written by Dr Roberto Sacco and Dr Alessandro Acocella

The requirements for any successful implant therapy are:

  • integration of the implant
  • ideal implant position
  • appropriate hard and soft tissue contours

However, following dental extraction, alveolar ridge resorbs creating potential challenges for implant therapy, resulting in inadequate bone volume and unfavourable ridge architecture.

Over the past decades, researchers have been increasing their interest in a concept called “dentoalveolar ridge preservation”. This was defined as “any surgical method undertaken at the time of, or following, a dental extraction that is designed to decrease socket bone resorption”.

What is happening biologically?

Following a dental extraction, the surrounding bone structure changes. These histological changes have been described in dog studies (Cardaropoli et al. 2003). In this study, on day 1 after a dental extraction, the socket was plugged by a coagulum; this coagulum contained mainly erythrocytes and platelets that were imprisoned in a fibrous matrix. In direct contact with the coagulum, and adjacent to the hard tissue wall, there was the “bundle bone” and fibers from periodontal ligament (Sharpey’s fibers). On day 3, the coagulum was replaced by a vascularised granulation tissue. On day 7, newly formed blood vessels were distinct in the primary matrix. Various kinds of leukocytes and collagen fibres were replacing the residual periodontal ligament as well as the granulation tissue. On day 14, most of the bundle bone had dissolved, and instead, “woven bone”, adjacent to the newly formed blood vessels, started to deposit from the old bone of the socket walls toward the centre of the socket. On day 30, woven bone underwent resorption, suggesting that the remodeling process had started. On day 60, hard tissue bridges separated the marginal mucosa from the socket, and bone marrow replaced woven bone at the centre of the previous socket. On day 90, woven bone was replaced by lamellar bone. On days 120 and 180, most of the woven bone had been replaced by lamellar bone.

What is the changing dimension?

In a recent systematic review, Tan et al.  analysed the dimensional alterations in the hard and soft tissues of the alveolar process up to 12 months following tooth extraction (Tan et al. 2012). The final outcome was that after 6 months of healing, the vertical resorption of the alveolar bone was 11–22%, whereas the horizontal resorption of the alveolar bone was 29 –63% of the initial residual bone. When soft tissue was included together with the hard tissue in the dimensional assessments after 3 months of healing, there was even an increase of 0.4 mm in the vertical dimension. After 12 months of healing, the vertical resorption of the alveolar ridge was 0.8 mm. Horizontally, resorption of the soft and hard tissue together was 1.3mm and 5.1mm after 3 and 12 months of healing, respectively representing unfavourable conditions for implant placement.

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