Dimensional Soft and Hard Tissue Alterations Following Single Tooth Extraction in the Anterior Maxilla - A Prospective Clinical Study

Overview

Bone modeling after tooth extraction has a major consequence on implant therapy, in particular in the esthetic zone. In esthetic sites, no tissue loss should occur if an optimal esthetic outcome is expected. Recent experimental studies in dogs have shown that neither an immediate implant insertion nor ridge preservation techniques can prevent this bone modeling process.

Background The alveolar process is a tooth dependent tissue and develops in conjunction with the eruption of teeth. The size and the form of the tooth, the axis of eruption and eventual inclination determine the local volume as well as the shape of the alveolar process. It has been shown that after removing all teeth in humans, the alveolar ridge undergoes a process of resorption and atrophy. In a recent animal study, Cardaropoli et al. (2003) assessed the healing events occurring in the extraction socket following tooth removal. The findings of this study demonstrated that the healing of an extraction socket involved a series of events including the formation of a coagulum that was replaced by a provisional connective tissue matrix, woven bone and lamellar bone and bone marrow. On day 30, mineralized bone occupied 88% of the socket volume. Hard tissue formation had started already after 2 weeks of healing, and then, after a month, the socket was filled with woven bone. Later, the woven bone was gradually replaced by lamellar bone and bone marrow. After 3 months of healing, a hard tissue bridge was consistently found to cover the crestal portion of the extraction site, which was formed by woven bone and lamellar bone. Araújo et al. (2005) analysed in an experimental study in dogs the ridge alterations following the extraction of premolars in the mandible. The authors observed that the resorption of the buccal and lingual walls occurred in two overlapping phases. Phase 1: The bundle bone - that lost its function and blood supply - was resorbed and replaced with woven bone. Vertical resorption was considerably greater on the buccal aspect of the alveolar crest, since this bone wall was much thinner then the lingual wall and was primarily comprised of bundle bone. Phase 2: An additional resorption occurred from the outer surfaces of both bone walls. The reason for this additional resorption has not been clearly ascertained. The hypothesis could be: Impaired superficial vascularisation by raising a mucoperiosteal flap; adjusting to the lack of continuous function; or the reestablishment of the ridge shape, which is genetically determined in the absence of teeth. A recent animal study confirmed that flap elevation plays an important role for a more pronounced superficial bone resorption following extraction , therefore, it seems critical that tooth extraction should be carried out without elevation of a mucoperiosteal flap. Even ridge preservation techniques are not able to prevent the contour changes after tooth extraction. Objective The aim of the present clinical study is to examine the dimensional changes of the alveolar ridge following single tooth extraction in the anterior maxilla of patients, in particular on the facial aspect of the alveolar ridge. These horizontal and vertical changes will be sequentially documented up to 8 weeks of healing before an implant is inserted using the concept of early implant placement. The study will also provide information about the anatomic situation of the facial bone wall in the anterior maxilla at the time of extraction, and the prevalence and extent of bone deficiencies on the facial aspect, when teeth need to be extracted. Methods To document these changes over time, two methods will be applied. Firstly, two cone beam computed tomographies (CBCT) will be obtained, one directly after tooth extraction, the other one at 8 weeks of socket healing prior to implant placement. The two CBCT's will be analyzed with a novel software program (InVivo Dental). Secondly, consecutive impressions will be made at day 0 (day of extraction), day 14, 28, 42, and 56 to digitally produce virtual 3D study models. These models can be analyzed with another software program (Geomagic) to document the variations of the soft tissue in the extraction site.

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