The fate of the alveolar ridge after tooth extraction

Emilio Couso-Queiruga

doi:10.25820/etd.006555

This thesis consisted of five studies. The objectives of the individual studies that constitute this project were: (1) To analyze the evidence pertaining to post-extraction dimensional changes in the alveolar ridge after unassisted socket healing (USH); 2) To assess the effect that specific periodontal phenotypic characteristics have on the remodeling of the alveolar ridge after non- molar tooth extraction; (3) To determine the amount of bone grafting material and approximate dimensions of barrier membrane employed in alveolar ridge preservation (ARP) therapy based on root morphology and the socket orifice dimensions; (4) To evaluate the efficacy of ARP therapy following tooth extraction of non-molar teeth compared with USH in reducing the need for ancillary bone augmentation procedures; (5) To evaluate the healing outcomes of non-molar post-extraction sockets grafted with deproteinized bovine bone mineral with collagen (DBBM-C) as a function of time.Study 1 is a systematic review aimed at analyzing the evidence pertaining to post-extraction dimensional changes in the alveolar ridge after unassisted socket healing. The protocol of this PRISMA-compliant systematic review (SRs) was registered in PROSPERO (CRD42020178857). A literature search to identify studies that fulfilled the eligibility criteria was conducted. Data of interest were extracted. Qualitative and random-effects meta-analyses were performed if at least two studies with comparable features and variables reported the same outcome of interest. Twenty-eight articles were selected, of which 20 could be utilized for the conduction of quantitative analyses by method of assessment (i.e., clinical vs radio- graphic measurements) and location (i.e., non-molar vs molar sites). Pooled estimates revealed that mean horizontal, vertical mid-facial and mid-lingual ridge reduction assessed clinically in non-molar sites was 2.73 mm (95% CI: 2.36–3.11), 1.71 mm (95% CI: 1.30–2.12) and 1.44 mm (95% CI: 6 0.78–2.10), respectively. Mean horizontal, vertical mid-facial and mid-lingual ridge reduction assessed radiographically in non-molar sites was 2.54 mm (95% CI: 1.97–3.11), 1.65 mm (95% CI: 0.42–2.88) and 0.87 mm (95% CI: 0.36–1.38), respectively. Mean horizontal, vertical mid- facial and mid-lingual ridge reduction assessed radiographically in molar sites was 3.61 mm (95% CI: 3.24– 3.98), 1.46 mm (95% CI: 0.73–2.20) and 1.20 mm (95% CI: 0.56–1.83), respectively. A variable amount of alveolar bone resorption occurs after unassisted socket healing depending on tooth type. Study 2 is a case series study aimed at assessing the effect that specific periodontal phenotypic characteristics have on alveolar ridge remodeling after tooth extraction. Patients in need of extraction of a non-molar tooth in the anterior maxilla were enrolled. Baseline phenotypic characteristics (i.e., mid-facial and mid-palatal soft tissue and bone thickness, and supracrestal soft tissue height [STH]) were recorded upon extraction. A set of clinical, linear, volumetric, and patient-reported outcomes were assessed over a 14-week healing period. A total of 42 subjects completed the study. Linear and volumetric bone changes, as well as vertical linear soft tissue and volumetric alveolar ridge contour variations, were indicative of a marked dimensional reduction of the alveolar ridge over time. On the contrary, horizontal linear soft tissue gain was observed. Thin facial bone (<1mm) upon extraction, compared with thick facial bone (>1mm), was associated with greater linear horizontal (-4.57±2.31mm vs -2.17±1.65mm, P=0.003), and vertical mid-facial (-0.95±0.67mm vs -4.08±3.52mm, P<0.001) and mid-palatal (-2.03±2.08mm vs -1.12±0.99mm, P=0.027) bone loss, as well as greater total (-34±10% vs 15±6%, P<0.001), facial (-51±19% vs 28±18%, P=0.040), and palatal volumetric bone reduction (-26±14% vs - 8±10%, P<0.001). Aside from alveolar bone thickness, it was also observed that STH is a predictor of alveolar ridge resorption since this variable was inversely correlated with volumetric 7 bone reduction. Patient-reported discomfort scores progressively decreased over time and mean satisfaction upon study completion was 94.5±0.83 out of 100. Alveolar ridge remodeling is a physiologic phenomenon that occurs after tooth extraction. Post-extraction alveolar ridge atrophy is more marked on the facio-coronal aspect. These dimensional changes are more pronounced in sites exhibiting a thin facial bone phenotype.Study 3 is an ex-vivo study aimed to aimed to characterize extraction sockets based on indirect digital root analysis. The outcomes of interest were estimated socket volume and dimensions of the socket orifice. A total of 420 extracted teeth, constituting 15 complete sets of permanent teeth (except third molars), were selected. Teeth were scanned to obtain STL files of the root complex for digital analysis. After digitally sectioning each root 2.0 mm apical to the cementoenamel junction (CEJ), root volume was measured in mm3 and converted to cc. Subsequently, a horizontal section plane was drawn at the most zenithal level of the buccal CEJ, and the surface area (in mm2) and buccolingual and mesiodistal linear measurements of the socket orifice (in mm) were computed. Maxillary first molars exhibited the largest mean root volume (0.451 ± 0.096 cc) and mandibular central incisors the smallest (0.106 ± 0.02 cc). Surface area analysis demonstrated that mandibular first molars presented the largest socket orifice area (78.56 ± 10.44 mm2), with mandibular central incisors presenting the smallest area (17.45 ± 1.82 mm2). Maxillary first molars showed the largest mean socket orifice buccolingual dimension (11.08 ± 0.60 mm), and mandibular first molars showed the largest mean mesiodistal dimension (9.73 ± 0.84 mm). Mandibular central incisors exhibited the smallest mean buccolingual (5.87 ± 0.26 mm) and mesiodistal (3.52 ± 0.24 mm) linear dimensions. Findings from this study can be used by clinicians to efficiently plan extraction-site management procedures (such as alveolar ridge 8 preservation via socket grafting and sealing) and implant provisionalization therapy, and by the industry to design products that facilitate site-specific execution of these interventions.Study 4 is a retrospective study aimed at evaluating the efficacy of ARP therapy after tooth extraction compared with USH in reducing the need for ancillary bone augmentation prior to or at the time of implant placement. Adult subjects that underwent non-molar single tooth extraction with or without simultaneous ARP therapy were included in this study. Cone beam computed tomography scans obtained prior to tooth extraction and after a variable healing period were used to record the baseline facial bone thickness and to virtually plan implant placement according to a standard method. A logistic regression model was used to evaluate the effect of facial alveolar bone thickness upon tooth extraction and baseline therapy (USH or ARP) on the need for additional bone augmentation, adjusting for several covariates (i.e., age, sex, baseline KMW, and tooth type). One hundred forty subjects that were equally distributed between both baseline therapy groups constituted the study population. Implant placement was deemed virtually feasible in all study sites. Simultaneous bone augmentation was considered necessary in 60% and 11.4% of the sites in the USH and ARP group, respectively. Most of these sites (64.2% in the USH group and 87.5% in the ARP group) exhibited a thin facial bone phenotype (<1mm) at baseline. Logistic regression revealed that the odds of not needing ancillary bone augmentation were 17.8 times higher in sites that received ARP therapy. Furthermore, the need for additional bone augmentation was reduced 7.7 times for every 1mm increase in facial bone thickness, regardless of baseline therapy. Based on a digital analysis, ARP therapy, compared to USH, and thick facial alveolar bone largely reduce the need for ancillary bone augmentation at the time of implant placement in non-molar sites. 9 Study 5 is a randomized clinical trial aimed at evaluating the healing outcomes of non-molar post-extraction sockets grafted with deproteinized bovine bone mineral with collagen (DBBM-C) as a function of time. Patients in need of non-molar tooth extraction were randomly allocated into one of three groups according to total healing time (A: 3 months, B: 6 months, C: 9 months). Post-extraction sites underwent alveolar ridge preservation therapy (ARP) via socket grafting using DBBM-C and socket sealing with a porcine collagen matrix (CM). The effect of healing time was assessed based on a panel of clinical, digital, histological, implant-related, and patient-reported outcomes. A total of 42 subjects completed the study. Histomorphometric analysis showed a continuous increase in the proportion of mineralized tissue with respect to non-mineralized tissue, and a decrease in the proportion of remaining xenograft over time. All volumetric bone and soft tissue contour assessments revealed dimensional reduction of the alveolar ridge overtime, affecting mainly the facial aspect. Linear regression analyses revealed that baseline buccal bone thickness is a strong predictor of bone and soft tissue remodeling. Ancillary bone augmentation at the time of implant placement was needed in 16.7% of the sites (A:2; B:1; C:4). Patient-reported discomfort and wound healing index scores progressively decreased over time and was similar across groups. Healing time influences the proportion of histologic tissue compartments in non-molar post-extraction sites grafted with DBBM-C. A variable degree of alveolar ridge atrophy, affecting mainly the facial aspect, occurs even after performing ARP therapy. These changes are more pronounced in sites exhibiting thin facial bone (≤1mm) at baseline.

The fate of the alveolar ridge after tooth extraction

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