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2013 92: 195S originally published online 24 October 2013J DENT RES

V. Chappuis, O. Engel, M. Reyes, K. Shahim, L.-P. Nolte and D. BuserRidge Alterations Post-extraction in the Esthetic Zone: A 3D Analysis with CBCT

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DOI: 10.1177/0022034513506713. University of Berne, Freiburgstrasse 7, Berne, 3010, Switzerland; *corresponding author, [email protected]

A supplemental appendix to this article is published electronically only at http://jdr.sagepub.com/supplemental.


V. Chappuis*, O. Engel, M. Reyes, K. Shahim, L.-P. Nolte, and D. Buser

Ridge Alterations Post-extractionin the Esthetic Zone: A 3DAnalysis with CBCT

CLINICAL INVESTIGATIONS

Abstract:Dimensional alterations ofthe facial bone wall following toothextractions in the esthetic zone have

a profound effect on treatment out-

comes. This prospective study in 39

patients is the first to investigate three-

dimensional (3D) alterations of

facial bone in the esthetic zone dur-

ing the initial 8 wks following flapless

tooth extraction. A novel 3D analysis

was carried out, based on 2 consec-

utive cone beam computed tomogra-

phies (CBCTs). A risk zone for signif-

icant bone resorption was identifiedin central areas, whereas proximal

areas yielded only minor changes.

Correlation analysis identified a facial

bone wall thickness of 1 mm as

a critical factor associated with the

extent of bone resorption. Thin-wall

phenotypes displayed pronounced ver-

tical bone resorption, with a median

bone loss of 7.5 mm, as compared

with thick-wall phenotypes, which

decreased by only 1.1 mm. For the first

time, 3D analysis has allowed for doc-

umentation of dimensional alterationsof the facial bone wall in the esthetic

zone of humans following extrac-

tion. It also characterized a risk zone

prone to pronounced bone resorp-

tion in thin-wall phenotypes. Vertical

bone loss was 3.5 times more severe

than findings reported in the existing

literature.

Key Words:bone remodeling, boneresorption, three-dimensional imaging,clinical trial, dental implants, maxilla.

Introduction

Esthetics poses a challenge in clinicalpractice and is critical for successfulimplant-supported prostheses in the

anterior maxilla (Belser et al.,2009). Akey prerequisite for esthetic outcomes isadequate three-dimensional (3D) osseousvolume of the alveolar ridge, includingan intact facial bone wall of sufficientthickness and height (Buser et al., 2004;Grunder et al.,2005). Deficiency of facialbone anatomy has a negative impacton esthetics and is a critical causativefactor for esthetic implant complicationsand failures (Chen and Buser, 2009).Experimental studies on caninemandibular premolar sites revealed

substantial structural and dimensionalalterations to the facial bone wall of theextraction socket (Cardaropoli et al.,2003; Araujo and Lindhe, 2005). Thesecatabolic changes are initiated byresorption of the bundle bone that linesthe extraction socket. They are correlated

with the disruption of blood supply from

the periodontal ligament and significantosteoclastic activity (Cardaropoliet al.,2003; Araujo and Lindhe, 2005).Importantly, experimental findings onfacial bone resorption in extraction sitesof canine mandibular premolars havenever been confirmed for the estheticzone in humans, since ethical concernsprohibit histological studies being carriedout. Alternative, non-invasive techniquesmust be adopted. Recently, cone beamcomputed tomography (CBCT) has

become a commonly accepted diagnostictool (Tyndall et al.,2012). Current CBCTtechnology offers extremely accurate3D diagnostics allowing for small Fieldsof View (FOV), good image quality,and low radiation doses (EuropeanCommission, 2011).

The aim of the present prospectivestudy was to investigate dimensionalalterations of the facial bone wall fol-lowing tooth extraction in the estheticzone. A novel 3D method utilizing digitalmodel superimpositions based on 2 con-

secutive CBCTs was used to characterizethe extent of bone loss and to identifyrisk zones and the respective modulatingfactors for facial bone resorption. Thisstudy should provide a better under-standing of underlying tissue biologyand facilitate the selection of an


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appropriate treatment protocol to achieveesthetic outcomes.

Materials & Methods

Study Sample

Thirty-nine patients were consecutivelyenrolled in this prospective case seriesstudy. All patients were referred tothe Department of Oral Surgery at theUniversity of Berne (Switzerland) witha need for a single-tooth replacementin the anterior maxilla, subsequent toan inevitable tooth extraction. Exclusioncriteria were systemic diseases that couldalter bone and soft-tissue healing,pregnancy, and participants < 18 yrsof age (Buser et al., 2000). The studywas approved by the standing ethical

committee of the state of Berne,Switzerland (Number 079/09) and wasconducted as a prospective clinicaltrial in accordance with the HelsinkiDeclaration (Version 2008) and theSTROBE statement guidelines.

Surgical Procedure

Prior to extraction, the patients rinsedwith a 0.1% chlorhexidine solution for1 min. Following the administration oflocal anesthesia, tooth extraction was

performed without flap elevation bymeans of a low-trauma technique. Theextraction sockets were thoroughlydebrided to remove all soft andgranulation tissues. A collagen spongewas placed into the socket to stabilizethe blood clot (Tissue ConeTM, Baxter,Chicago, IL, USA). Medication prescribedto all patients included analgesics anda chlorhexidine mouthwash (0.1%). Aremovable prosthesis was inserted andadapted to avoid any direct pressureto the underlying soft tissues. Patients

were recalled at 2, 4, 6, and 8 wks formonitoring of the healing progress.

Radiographic Examination

Two consecutive CBCTs were obtained,one immediately post-extraction and thesecond after 8 wks (3D Accuitomo XYZSlice View Tomograph, Morita, Kyoto,Japan). The smallest FOV of4 4 cm with a voxel size of 0.125 mmwas used with an exposure setting of 5.0

mA/80 kV and a scanning time of 17.5sec. The DICOM data (Digital Imagingand Communications in Medicine)were segmented by digital imagingsoftware (Amira, FEI VisualizationSciences Group, Hillsboro, OR, USA).

Based on the result of segmentation,a surface mesh model was generatedaccording to conventional marching cubealgorithms (Lorenson and Cline, 1987),followed by automated surface meshmodel generation (Fig. 1). The eight-week mesh model was superimposedon the baseline mesh model and rigidlyaligned by anatomical landmarkswith the help of Di2Mesh software(Institute for Surgical Technology &Biomechanics, Bern, Switzerland) (Fig.1). The distance between the 2 surface

meshes was presented as color-codedfigures to identify zones of facial boneresorption (Kim et al.,2010) (Fig. 1).Baseline facial bone thickness wasmeasured at distances of 1, 3, and 5mm from the most coronal point of thebone crest (Araujo and Lindhe, 2005).The analysis was performed in central(c) and proximal sites (a) oriented at a45 degree angle, with the tooth axisas a reference (Fig. 2A). A horizontalreference line was traced connecting the

facial and palatal crest for standardizedmeasurements (Fickl et al.,2008). Thepoint-to-point distance between the2 surface meshes with the respectiveangle to the reference line was obtainedfor each sample, and the vertical andhorizontal bone losses were calculatedaccordingly (Fig. 2C).

Statistical Analysis

All data were expressed as median,mean values ( standard error),minimum, and maximum values. To

test whether there was a statisticalsignificance between/among the groups,we used a non-parametric Wilcoxonsigned-rank test. Multivariate linearregression was applied in the centralmeasurements to identify modulatingfactors (Oja, 2010). Age, gender, andbaseline central wall thickness were usedas explanatory variables. Differenceswere considered statistically significantat *p 10 cigarettes/day). The extraction sitesincluded 29 central incisors, 8 lateralincisors, and 2 canines.

Baseline MeasurementsThe facial bone wall in central sites revealed

a mean thickness of 0.8 0.5 mm (range,0-1.7), whereas in proximal sites themean facial thickness was 1.0 0.6 mm(range, 0-1.9) (Fig. 2A). The difference infacial bone thickness between central andproximal sites was statistically significant(p< .0001). The frequency distributionanalysis yielded a facial wall thicknessof 1 mm in 69% of central sites and in59% of the proximal sites (Fig. 2B). The

multivariate regression analysis revealedno correlation between ridge alterationsand age or gender.

Dimensional Changes andIdentification of Risk Zonesfor Bone Resorption

Central sites yielded progressive boneresorption, with a median vertical boneloss of 5.2 mm or 48.3% of the originalbone wall height (range, 0.7-12.2 mm or5.5-99.6%) and a median horizontal boneloss of 0.3 mm or 3.8% of the original

bone wall width (range, 0-3.4 mm or0-49.5%) (Figs. 2C-2E). In proximalsites, there was significantly less boneresorption, not only vertically but alsohorizontally (p< .0001). Proximal sitesrevealed a median vertical bone loss of0.5 mm or 4.5% (range, 0.1-1.1 mm or1.0-12.7%) and a median horizontal boneloss of 0 mm or 0% (range, 0-0.4 mmor 0-5.9%) (Figs. 2C-2E). These resultsindicated that central sites were of special


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interest from a clinical point of view, andwere further analyzed.

Characteristic Bone ResorptionPatterns and Correlation Analysisin the Central Risk Zone Area

The superimposed color-coded figuresshowed characteristic resorption patterns(Fig. 3). A critical facial bone wallthickness of 1 mm was identified (Fig.4A). A thin-wall phenotype exhibiting

a facial bone wall thickness of 1 mmshowed a median thickness of 0.7 mm(range, 0.4-1.0 mm; Appendix Fig. 1). Athick-wall phenotype, with a facial bonewall thickness of > 1 mm, revealed amedian thickness of 1.4 mm (range, 1.1-1.7 mm; Appendix Fig. 2). Significantbone resorption was associated with athin-wall phenotype, showing medianvertical bone loss of 7.5 mm or 62.3%(range, 0.8-12.2 mm or 8-99.6%), and

median horizontal bone loss of 0.8 mm,or 10.5% (range, 0-3.4 mm or 0-49.5%;Fig. 3A, Fig. 4B, Appendix Fig. 1). Aless pronounced resorption patternwas associated with facial bone wallthickness of > 1 mm at baseline. Thethick-wall phenotype displayed a medianvertical bone loss of 1.1 mm or 9.1%(range, 0.7-3.2 mm or 5.5-38.6%), and amedian horizontal bone loss of 0 mm or0% (0-1.5 mm or 0-21.2%; Fig. 3B, Fig.

4B, Appendix Fig. 2). The difference ofvertical bone loss in sites with a thinor thick phenotype was significant (p 1 mm,

exhibited a less-pronounced bone resorption pattern after 8 wks of healing.

understanding of tissue biology and theassociated 3D changes in facial bonearchitecture. In the mid-2000s, the mech-anisms of bone resorption and model-ing post-extraction were characterized incanine mandibular premolar sites over aninitial eight-week healing period, result-ing in a mean facial bone wall resorptionof 2.2 mm (Araujo and Lindhe, 2005).

Bone loss was histometrically analyzedin the mid-facial areas of the extractionsockets. In the present study, dimensionalchanges were examined not only in cen-tral, but also in proximal areas. The 3Danalysis identified the central zone to beat higher risk for bone resorption, witha median bone loss of 5.2 mm verticallyand 0.3 mm horizontally. Proximal areasrevealed only minor changes of 0.5 mmand 0 mm, respectively (Fig. 2D-E). The

minimal bone resorption in proximal areasshowing at 8 wks post-extraction providesa favorable two-wall defect morphologyat early implant placement. This is con-sidered relevant for predictable regener-ative outcomes (Buser, 2009). The regen-erative potential of a peri-implant bonedefect has been attributed to the ratiobetween the area of exposed bone mar-

row and the defect volume to be regener-ated (Schenk et al., 1994). Flapless extrac-tion appears important for achieving afavorable 2-wall defect morphology, andavoids additional superficial bone resorp-tion in proximal areas due to open flapelevation (Fickl et al., 2008).

The maintenance of facial bone architec-ture has been related to a facial bone wallthickness of 2 mm in an experimental dogstudy (Qahash et al.,2008). In the ante-

rior maxilla, the facial bone wall is usuallythinner than 2 mm, as demonstrated inseveral CBCT studies (Braut et al., 2011;Januario et al.,2011; Vera et al., 2012b).In the present study, none of the cen-tral areas revealed a facial wall thick-ness of 2 mm. Central facial wall thick-ness was 1 mm or less in 69% of sites (Fig.2B). Correlation analysis of the central risk

zone revealed a facial bone thickness of 1 mm to be a critical factor for severebone resorption. Thin-wall phenotypesresulted in a median vertical bone loss of7.5 mm in the central risk zone, whereasthick-wall phenotypes showed a medianvertical bone loss of only 1.1 mm (Figs.3, 4). Therefore, thin-wall phenotypesexperienced a 3.5-times-greater bone lossthan documented in experimental studies(Araujo and Lindhe, 2005). Even thick-wall


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phenotypes exhibited bone loss of morethan 1 mm, which could affect estheticsnegatively. Efforts have been made to pre-vent these dimensional changes followingtooth extraction, but neither immediateimplant placement nor ridge preserva-tion techniques were able to maintain thefacial osseous architecture (Araujo et al.,2005; Ten Heggeler et al., 2011).

The clinician must select an appro-priate time point for post-extractionimplant placement, to achieve a predict-

able regenerative and esthetic outcome,and to avoid complications. The conceptsof immediate and early implant place-ment were developed in the 1990s toreduce overall treatment time for post-extraction implant therapy (Hmmerleet al.,2004). The most recent systematicreviews clearly demonstrate that imme-diate implant placement increases therisk of significant mucosal recessions ifthis approach is not applied with strictinclusion criteria (Chen and Buser, 2009,2013). The present study supports these

findings, since even thick phenotypesproduced a median vertical bone loss of1.1 mm. Two recent clinical studies per-forming consecutive CBCTs, the first atimplant placement and another 1 yr later,confirmed that significant mid-facial ver-tical bone resorption occurred in imme-diate implant cases (Roe et al., 2012;Vera et al., 2012a). Therefore, it is rec-ommended that immediate implants

be carried out only in ideal sites with athick-wall phenotype and thick gingivalbiotype (Morton et al.,2013).

There are some limitations of the pres-ent study. First, since only sites in theanterior maxilla were involved, the resultscan be applied exclusively to extractionsites in the esthetic zone. Second, thestudy was limited to an eight-week heal-ing period, since this is standard for earlyimplant placement (Buser et al., 2008). Alonger healing period could potentially

produce different results.In conclusion, biological understand-ing of dimensional alterations of thefacial bone wall following extraction aidsin the selection of the appropriate surgi-cal protocol needed to achieve estheticresults. The present study clearly showedthat facial bone resorption also occurs inpost-extraction sites in the anterior max-illa, and that the facial bone wall thick-ness in central areas determines theextent of resorption. In addition, theobserved dimensional alterations in thin-

wall biotypes are much more severethan has been documented in pre-clini-cal studies.

Acknowledgments

The study was supported by the ITIFoundation (Basel, Switzerland; No.624_2009). The authors declare no poten-tial conflicts of interest with respect to

the authorship and/or publication of thisarticle.

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