cone-beam computed tomography evaluation of alveolar ridge … · 2017-12-22 · treatment and...

ORIGINAL ARTICLE

Cone-beam computed tomography evaluationof alveolar ridge width and height changes afterorthodontic space opening in patients withcongenitally missing maxillary lateral incisors

Flavio Uribe,a Soumya Padala,b Veerasathpurush Allareddy,c and Ravindra Nandad

Farmington, Conn, Columbus, Ohio, and Cambridge and Boston, Mass

aAssoof CraUnivebPostStatecInstrHarvaBostodProfeChair,All auPotenAddreConnFuribeSubm0889-Copyrhttp:/

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Introduction: The purpose of this studywas to evaluate the alveolar bone dimensional changeswith cone-beamcomputed tomography after space-opening procedures for an endosseous implant in patients with unilateral orbilateral maxillary lateral incisor agenesis.Methods: A pilot retrospective cohort study was conducted of 11 pa-tients (13 sites) in whom the canines had erupted less than 2mmdistally to the central incisors. Pretreatment andposttreatment scans obtained from 3 private practice offices were evaluated for changes in alveolar bone width,height, and labial concavity. A fiducial line representing the ideal location of the longitudinal axis of anendosseous dental implant was used as a reference for the spatial location of the alveolar bone at the lateralincisor site in reference to the adjacent tooth roots at posttreatment. The posttreatment width and height mea-surements scans were compared with normative data from the contralateral incisor in patients with unilateralagenesis (n5 6). Results: Alveolar bone width was significantly decreased on average from 17% to 25% alongthe height of the ridge (2-10 mm) (P\0.05). The labial concavity was significantly increased compared with theinitial dimensions (P\0.05). No significant changeswere found in alveolar bone ridge height.Conclusions:Sig-nificant alveolar bone width decreases and increases in labial concavity were found after implant ridge develop-ment in patients with maxillary lateral incisor agenesis. The alveolar bone ridge was located more lingually thanthe adjacent teeth, suggesting a need for bone grafting to achieve proper fixture placement. (Am J OrthodDentofacial Orthop 2013;144:848-59)

Dental implants are commonly used to replacecongenitally missing maxillary lateral incisorsonce skeletal maturity has been reached. The

restorative treatment for these patients is often chal-lenging for the surgeon and the restorative dentistbecause the 3-dimensional (3D) morphology of the

ciate professor and program director, Division of Orthodontics, Departmentniofacial Sciences, Charles Burstone Professor, School of Dental Medicine,rsity of Connecticut, Farmington, Conn.rgraduate resident, Division of Orthodontics, College of Dentistry, OhioUniversity, Columbus, Ohio.uctor and director of predoctoral orthodontics, School of Dental Medicine,rd University, Cambridge, Mass; cleft and craniofacial orthodontics fellow,n Children's Hospital, Boston, Mass.ssor and head, Department of Craniofacial Sciences, Alumni EndowedSchool of Dental Medicine, University of Connecticut, Farmington, Conn.thors have completed and submitted the ICMJE Form for Disclosure oftial Conflicts of Interest, and none were reported.ss correspondence to: Flavio Uribe, Division of Orthodontics, University ofecticut Health Center, 263 Farmington Ave, Farmington, CT 06030; e-mail,@uchc.edu.itted, February 2013; revised and accepted, August 2013.5406/$36.00ight � 2013 by the American Association of Orthodontists./dx.doi.org/10.1016/j.ajodo.2013.08.017

alveolar ridge might be less than ideal. Inadequate alve-olar bone width can require surgical bone augmentationto ensure ideal implant positioning and adequate threadcoverage. An alternative to grafting is the developmentof the alveolar ridge through orthodontic movement ofan adjacent tooth through the deficient dentoalveolarsite.

Ridge development procedures aimed to achieveadequate alveolar ridge dimensions have been reportedto be successful when the maxillary canine erupts adja-cent to the central incisor and thereafter is distalizedwith orthodontics to its proper location.1,2 As the rootof the canine is displaced distally, new bone isdeposited, establishing adequate buccolingual widthand vertical height of the edentulous ridge site. Arecent study found that the ridge of the maxillarylateral incisor is well preserved in the short and longterms, with insignificant clinical losses in width andheight, right after alveolar ridge development iscompleted.3 However, conflicting results were found inanother study that measured bone volume in the lateralincisor site in the short and long terms. A significant

Delta:1_given name

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http://dx.doi.org/10.1016/j.ajodo.2013.08.017

Carlos Peña Gutierrez

Uribe et al 849

volume deficiency was observed immediately after ridgedevelopment in the site of the missing lateral incisor.4

Similarly, another recent study also reported 13% to15% ridge width decreases in patients when the caninewas distalized after erupting close to the central incisor(\2 mm).5 Furthermore, the authors of this study foundthat the labial concavity of the alveolar ridge in thelateral incisor site was on average 1.5 mm deep afterthe canine was distalized.

These conflicting results might be related to variedmeasurement techniques, which were not consistent inall the studies. Furthermore, all these studies used stonemodels to evaluate ridge changes that do not reflect theexact underlying alveolar bone changes, which are ofprimary interest when considering an implant fixtureplacement. Thus, the objective of this study was to eval-uate the alveolar bone dimensional changes with cone-beam computed tomography (CBCT) in patients withunilateral or bilateral maxillary lateral incisor agenesiswhen the canines erupted less than 2 mm distally tothe central incisors. The null hypothesis was that thereare no significant dimensional alveolar bone changesin the lateral incisor site after distalization of a caninethat erupted close to the central incisor.

MATERIAL AND METHODS

This study was a retrospective evaluation of patientrecords. The study aim and protocols were reviewed,and institutional board approval was obtained fromthe University of Connecticut (IRB number 11-030-1)before the study.

A pilot retrospective CBCT cohort study was conduct-ed to measure the changes in the maxillary alveolar bonedimensions in patients with lateral incisor agenesiswhere orthodontic ridge development was done throughdistalization of the adjacent canine. These patients'CBCT scans were obtained from 3 private orthodonticoffices (Dr Paul Rigali, Wallingford, Conn; and Dr CarlRoy, Virginia Beach and Chesapeake, Va) that routinelyuse this type of 3D imaging for diagnostic purposes.

The inclusion criteria were unilaterally or bilaterallycongenitally missing maxillary lateral incisors, mesiallyerupted permanent canines adjacent to the central inci-sors, space between the distal surface of the centralincisor and the mesial surface of the canine less than2 mm, a maxillary canine orthodontically distalized tocreate space for an endosseous dental implant in thelateral incisor site, no systemic health problems, goodperiodontal health, and a posttreatment CBCT scan.The exclusion criteria included presence of a deciduouslateral incisor, an impacted or unerupted permanentcanine, cleft palate or any other dentofacial deformity,and a history of periodontal disease.

American Journal of Orthodontics and Dentofacial Orthoped

Over 10,000 patient records were screened from the3 offices, and 60 records of patients with unilateral orbilateral maxillary lateral incisor agenesis were obtainedthat included a posttreatment CBCT scan taken within2 months of appliance removal. Among these 60patients, only 19 had an endosseous dental implantrestoration as part of the treatment plan. Finally, only11 patients' records met the strict inclusion criteriadelineated by this study. The final sample comprised7 male and 4 female subjects with mean ages of 16.456 5.76 years (range, 11.3-28 yeas) at the beginning oftreatment and 18.68 6 5.79 years (range, 13.6-30.3years) at the end of treatment (Table I). Orthodontictreatment lasted on average 2.4 6 0.6 years.

Three-dimensional CBCT scans were previouslyobtained using an i-CAT Classic scanner (ImagingSciences International, Hatfield, Pa). Each scan wasacquired with a 20-second scan time with a 16-cm(diameter) 3 13-cm (height) field of view at a resolu-tion of 0.3-mm voxels. All images were collected at120 kV(p) and 3-8 mA. Raw data were reconstructedand exported as 12-bit depth DICOM files using Xoran(i-CAT software, version 2.1.22). The DICOM files wereimported into Dolphin 3D (version 11; Dolphin Imag-ing and Management Solutions, Chatsworth, Calif) forfurther analysis. The CBCT scans were taken at 2 times,before orthodontic treatment (T1) and at the end oforthodontic treatment (T2). All offices had the sameCBCT unit and used the same method to acquire thescans.

Twomethods were used to evaluate the alveolar bonewidth changes at the maxillary lateral incisor site on theCBCT scans. The first method was used to evaluate thealveolar bone widths at T1 and T2. The second methodwas used to evaluate the available labial and palatalbone to a fiducial line representing the longitudinalaxis of an ideal location of an endosseous dental implantin the lateral incisor site at T2 only.

In method 1, the scans were oriented after drawing aline that bisected the angle formed by the longitudinalaxes of the maxillary canine and the central incisor me-siodistally and buccolingually. Alveolar bone width mea-surements were made along the sagittal reference planeat 2, 4, 6, 8, and 10 mm apically to the alveolar bonecrest. Additionally, alveolar width measurements parallelto this sagittal plane were made at the same heightsapically to the cementoenamel junction at the middleof the central incisor and the canine (Fig 1).

For the second method, 2 lines were used for orien-tation of the scans. The first line bisected the angleformed by the longitudinal axes of the adjacent maxil-lary central incisor and the canine mesiodistally. Anotherline perpendicular to this reference line and tangent to

ics December 2013 � Vol 144 � Issue 6

Fig 1. Scan at T1 illustrating method 1 used to assessalveolar bone width changes: A, coronal slice; B, sagittalslice; C, axial slice. T1 and T2 scans were oriented afterdrawing a line that bisected the angle formed by the lon-gitudinal axes of the maxillary canine and the centralincisor mesiodistally (red line) and buccolingually (greenline). Alveolar bone width measurements were madealong the sagittal reference plane at 2, 4, 6, 8, and 10mm apical to the alveolar crest (blue line). Additionally,alveolar width measurements parallel to this sagittalplane were made at the same heights apical to the ce-mentoenamel junction at the middle of the central incisorand the canine.

Table I. Sample demographics and characteristics

Characteristic ValueSexMale 7Female 4

Age and SD (y)T1 mean 16.45 6 5.76Range 11.3-28T2 mean 18.68 6 5.79Range 13.6-30.3

SitesTotal number of sites 13Number of patients with unilateralagenesis

6

Total sites meeting inclusioncriteria

6

Number of patients with bilateralagenesis

5

Total sites meeting inclusioncriteria

7

Distribution of sites in patientswith bilateral agenesis

2 patients 3 2 sites 5 4 sites3 patients3 1 site5 3 sites

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the anterior contours of the pulp canals of the centralincisor and canine was drawn. Alveolar width measure-ments, palatal and labial to this fiducial line at 2, 4, 6,8, and 10 mm from the alveolar bone crest weremeasured in the sagittal plane (Fig 2). This methodwas only used to evaluate the scans at T2. This fiducialline was based on the average location of the longitudi-nal axis of a maxillary lateral incisor (Fig 3).

Two methods were used to evaluate alveolar boneheight changes. In method 1, the scans were orientedafter drawing a line that bisected the angle formed bythe longitudinal axes of the maxillary canine and thecentral incisor mesiodistally and buccolingually. A lineconnecting the incisal edges of the canine and the cen-tral incisor (best fit), perpendicular to these lines, wasused to measure the height of the alveolar bone crest.Measurements were taken from this line to the alveolarbone crest on the coronal slice: (1) distally to the centralincisor, (2) at the middle of the ridge, and (3) mesially tothe canine (Fig 4). For method 2, the same reference linesfor method 1 were used. A reference line connecting thecementoenamel junctions of the maxillary canine andthe central incisor (best fit), on the coronal slice, wasused to measure the changes in alveolar bone heighton the middle of the ridge (Fig 5).

The changes in the labial concavity were evaluated byorienting the scans with a line that bisected the angleformed by the longitudinal axes of the maxillary canineand the central incisor mesiodistally and buccolingually.The distance from the deepest concavity observed be-tween the central incisor and the canine to a reference

December 2013 � Vol 144 � Issue 6 American

line tangent to the most prominent labial aspect of these2 teeth was recorded at 2, 4, 6, 8, and 10 mm apically tothe alveolar crest in the axial slice (Fig 6).

Incisor inclination changes as a result of space openingwere evaluated bymeasuring the angulation of the central

Journal of Orthodontics and Dentofacial Orthopedics

Fig 2. Method 2 for alveolar bone width analysis in T2scans: A, coronal slice; B, sagittal slice; C, axial slice.Two lines were used for orientation of the scans. The firstline bisected the angle formed by the longitudinal axes ofthe adjacent maxillary central incisor and the canine me-siodistally (red line). Another line perpendicular to thisreference line and tangent to the anterior contours ofthe pulp canals of the central incisor and the caninewas drawn. Alveolar width measurements, palatal andlabial to this fiducial line (green line) at 2, 4, 6, 8, and 10mm from the alveolar bone crest (blue line), weremeasured in the sagittal plane.

Uribe et al 851

incisor to the palatal plane. In addition, all measurementsof alveolar bone width and labial concavity where themaxillary lateral incisor was present (control side) in pa-tients with unilateral agenesis (n 5 6) were comparedwith the contralateral developed alveolar sites at T2.


Statistical analysis

T1 and T2 scans were collected from 11 patients withunilateral or bilateral lateral incisor agenesis. Measure-ments were taken in the sites with lateral incisor agenesisand in the contralateral side in patients with unilateralagenesis. A total of 13 sites in these 11 patients wereexamined, and the unit of analysis was each site. Mea-surements were made by the same examiner (S.P.).Data were imported into SPSS software (version 20;SPSS, Chicago, Ill) for analysis. Means, standard devia-tions, and 25%, 50% (median), and 75% quintileswere reported for all T1 and T2 variables. Because ofthe small sample size and because the data were not nor-mally distributed, nonparametric tests were used tocompared outcomes. A Wilcoxon signed rank test wasused to analyze T1 and T2 differences for the treatmentside, and to compare the posttreatment changes with thecontrol side in patients with unilateral agenesis. All sta-tistical tests were 2-sided, and a P value of\0.05 wasdeemed statistically significant.

All variables were remeasured to assess measurementerror and reliability. Intrarater reliability was estimatedusing the Cronbach alpha coefficient.

RESULTS

The Cronbach alpha for double measurements for theselected data points ranged from 0.65 (T2 bone width at2 mm in the middle of the ridge) to 0.99 (Table II). On thetreatment sites, the space for the lateral incisor wasopened to a width of 6.63 6 1.24 mm from an averagespace of 0.956 0.74 mm at T1. This final space dimen-sion was similar to the contralateral incisor in patientswith unilateral agenesis, where the mesiodistal widthwas 6.78 6 0.86 mm. The space was opened throughdistalization of the canine and labial tipping of theincisor reflected by an increase of the incisor's inclina-tion to the palatal plane by an average of 6.43�

(P \0.05) (Table III). Alveolar bone height changeswere not significant for either measurement methodwith treatment.

The alveolar bone width was reduced at the lateralincisor site from 17% to 25% at the different heights;these changes were significant (P \0.05) at allmeasured levels (Table III). Interestingly, the centralincisor and the canine that were displaced mesiallyand distally, respectively, also had reduced alveolarbone widths with treatment; this was significant atevery level for the incisors and at 2 and 4 mm fromthe cementoenamel junction for the canines. However,the average alveolar bone width decrease was greater atthe level of the lateral incisor, averaging 1.37 mm for allmeasured heights. The width changes for the central


Fig 3. T2 scan depicting the ideal location of the longitudinal axis of a maxillary lateral incisor in thecontrol side of a patient with unilateral agenesis:A, coronal slice;B, sagittal slice;C, axial slice;D, volu-metric view. In the axial slice, the longitudinal axis of the lateral incisor lay in the same plane to a linetangent to the labial contour of the pulp canal of the central incisor and canine. This reference was usedto trace the fiducial line in the toothless ridge. Red, blue, and green lines represent the sagittal, axial,and coronal slices, respectively.

852 Uribe et al

incisor and the canine averaged decreases of 0.9 and0.37 mm, respectively.

The trend for labial concavity was increased in theapical direction at both T1 and T2. The labial concavitywas deepest at the 8-mm level from the cementoenameljunctions of the adjacent teeth at T1 and T2. With treat-ment, the labial concavity increased significantlybetween T1 and T2 at all heights (P\0.05) (Table III)except at 4 mm. The average increase ranged from 0.3to 2.8 times the original labial concavity.

When the alveolar width at T2 was compared with thenormative side on patients with unilateral agenesis, nosignificant differences were found between sides at thecentral incisor, the canine, or the middle of the ridge.However, when the alveolar bone ridge was dividedinto palatal and labial bone by a fiducial line, the labialbone was significantly reduced compared with thenormative side at all heights except at 8 and 10 mm(P\0.05) (Table IV). The palatal bone was significantlyincreased only at 10 mm (P\0.05). Most of the boneavailable after ridge development was palatal to thisreference line, with an average of 64% to 80% of theof the total alveolar bone width on that side.

The labial concavity measurements at T2 comparedwith the normative data reflected the findings observedwhen compared with the T1 dimensions. The labialconcavity was significantly greater at 6 and 8 mm(P \0.05) (Table IV). Additionally, a significant


difference was found in alveolar bone height in themiddle of the crest for method 1 between the T2 andthe normative values.

DISCUSSION

The evaluation of the changes in the alveolar ridgewidth in patients with maxillary lateral incisor agenesisafter ridge development procedures has produced con-flicting results. Some studies reported minimal alveolarbone width losses,3,6 whereas others have shownsignificant decreases in alveolar ridge dimensionsimmediately after orthodontic treatment.4,5 Soft-tissuevariations might account for the differences; thus, anoninvasive method to evaluate alveolar bone ridgechanges with space-opening procedures is necessary toevaluate whether adequate dimensions for an endo-sseous dental implant are achieved.

Currently, one of the most accurate methods to eval-uate the alveolar bone dimensions is the use of CBCTimages. The recent literature has reported a high degreeof accuracy in measurements of buccal bone height andthickness between CBCT and direct measurements.7,8 Bymeasuring the alveolar bone at different heights alongthe ridge, the actual osseous response to ridgedevelopment can be measured. This method eliminatesthe confounding factor of the soft-tissue variationsbetween patients and their response to space-openingprocedures.


Fig 5. Method 2 used to evaluate bone height changesfrom the cementoenamel junction: A, coronal slice; B,sagittal slice. The same reference lines for method 1ridge-height analysis were used. A reference line con-necting the cementoenamel junctions of the maxillarycanine and the central incisor (blue line, best fit), on thecoronal slice, was used to measure the changes in thealveolar bone height on the middle of the ridge. Redand green lines represent the reference sagittal and cor-onal slices, respectively, which bisect the angle betweenthe longitudinal axes of the central incisor and the caninemesiodistally and buccolingually.

Fig 4. Method 1 used to evaluate alveolar bone heightchanges: A, coronal slice; B, sagittal slice. The scanswere oriented after drawing a line that bisected the angleformed by the longitudinal axes of the maxillary canineand the central incisor mesiodistally (red line) and bucco-lingually (blue line). A line connecting the incisal edges ofthe canine and the central incisor (blue line, best fit),perpendicular to this line (red line), was used to measurethe height of the alveolar bone crest. Measurements weretaken from this line to the alveolar bone crest on the cor-onal slice: (1) distally to the central incisor, (2) at the mid-dle of the ridge, and (3) mesially to the canine.

Uribe et al 853

In this study, we set strict inclusion criteria bylimiting the T1 space between the incisor and the canineto no more than 2 mm. This ensured that the alveolarbone ridge width was developed as the canine and thecentral incisor were separated along the arch. The ridgewas opened to a width that was comparable with thecontralateral incisor and to what has been publishedfor a normal size of a lateral incisor.9

The space was developed through labial tipping ofthe incisors; this is consistent with previous findings.4

Labial incisor movement is not surprising and shouldbe expected in a nonextraction approach because theclinical presentation in patients whose canine has erup-ted close to the central incisor is often a maxillarymidline deviation to the agenesis side, a midline dia-stema, and space distal to the canine. When space open-ing for an endosseous dental implant is planned, thecentral incisor is moved mesially and labially to correctthe midline deviation and close the diastema as thecanine is distalized.


This study showed significant alveolar bone widthchanges with the space-opening procedures for thecongenitally missing lateral incisor. There was a 17%to 25% decrease in bone width at the level of the lateralincisor from the alveolar crest down to 10 mm apically.The trend was for the edentulous alveolar bone ridgeto become wider in an apical direction. However, theaverage difference from the most coronal measurementat 2 mm from the alveolar crest to the most apical mea-surement was approximately 1.1 mm. Moreover, therewas greater variability as the measurements were mademore apically.

The ridge width decrease was consistent with thefindings of Uribe et al,5 who observed a 13% to 15%decrease when measuring at 2.5 mm from the gingivalmargin. This measurement corresponds approximatelyto the 2-mm measurement from the cementoenameljunction used in this study. However, these findingsare in contrast to those of Novackova et al,3 who foundonly a 4% decrease with ridge opening. Three reasons


Fig 6. A, Method used to evaluate labial concavity of the alveolar bone ridge. A line that bisected theangle formed by the longitudinal axes of the maxillary canine and the central incisor mesiodistally(red line) and buccolingually was used for orientation of the scans. The distances from the deepest con-cavity observed between the central incisor and the canine to a line tangent to the most prominent labialaspect of these teeth (green line) were recorded at 2, 4, 6, 8, and 10 mm apically to the alveolar crest inthe axial slice (blue line).B, Axial slice representing a measurement of the labial concavity at 6 mm fromthe alveolar bone crest.

854 Uribe et al

might explain this discrepancy. First, the patientsincluded in that study did not have set inclusion criteriafor the pretreatment minimal amount of space betweenthe central incisor and the canine. The space between thecentral incisor and the canine had a range of approxi-mately �2 to 6 mm. As a result, a greater pretreatmentseparation of the roots would have a less likely chanceof affecting the toothless ridge by the movement ofthe canine, resulting in minimal width changes. Second,inconsistencies between the studies could be related tothe different methods used to measure alveolar bonewidth. For example, 1 measurement used by Novackovaet al to evaluate alveolar width changes was taken at agingival level and might reflect not the real osseouschange but a minimal soft-tissue change. In this study,the osseous changes were recorded every 2 mm alongthe height of the alveolar ridge to evaluate the changes


along the height of the future implant site. These multi-ple measurements were recorded because it wasobserved that the widths could vary significantly withina patient along the alveolar bone ridge (Fig 7). Third, No-vackova et al measured only the soft-tissue changes andinferred the underlying osseous changes. There could beminimal soft-tissue changes with space-opening proce-dures that do not reflect the marked osseous widthchanges. Furthermore, it has been reported that thereare significant variations in the soft-tissue depthscovering the alveolar bone ridge; thus, measurementson a stone model do not reflect the real osseouschanges.10

It is interesting that alveolar bone width changes alsooccurred at the levels of the incisor and the canine,although to a lesser extent than the changes observedalong the edentulous ridge. These changes might have


Table II. Reliability analysis for pretreatment (T1) andposttreatment (T2) measures: Cronbach alpha values

Outcome

Cronbach alpha

T1 T2Space between incisor and canine 0.96 0.87Height method 1 (mesial crest) 0.93 0.86Height method 1 (middle crest) 0.96 0.81Height method 1 (distal crest) 0.96 0.82Height method 2 0.87 0.68Bone width at 2 mm central incisor 0.82 0.77Bone width at 4 mm central incisor 0.86 0.90Bone width at 6 mm central incisor 0.95 0.96Bone width at 8 mm central incisor 0.94 0.97Bone width at 10 mm central incisor 0.82 0.84Bone width at 2 mm middle ridge 0.84 0.65Bone width at 4 mm middle ridge 0.97 0.69Bone width at 6 mm middle ridge 0.99 0.95Bone width at 8 mm middle ridge 0.98 0.93Bone width at 10 mm middle ridge 0.96 0.97Bone width at 2 mm canine 0.92 0.90Bone width at 4 mm canine 0.97 0.88Bone width at 6 mm canine 0.98 0.94Bone width at 8 mm canine 0.99 0.93Bone width at 10 mm canine 0.99 0.97Labial concavity at 2 mm 0.87 0.92Labial concavity at 4 mm 0.75 0.93Labial concavity at 6 mm 0.91 0.93Labial concavity at 8 mm 0.90 0.78Labial concavity at 10 mm 0.87 0.73Incisor inclination 0.90 0.96Palatal bone width at 2 mm — 0.97Palatal bone width at 4 mm — 0.98Palatal bone width at 6 mm — 0.97Palatal bone width at 8 mm — 0.97Palatal bone width at 10 mm — 0.97Labial bone width at 2 mm — 0.68Labial bone width at 4 mm — 0.68Labial bone width at 6 mm — 0.73Labial bone width at 8 mm — 0.83Labial bone width at 10 mm — 0.80

Uribe et al 855

resulted from the type of toothmovements achievedwithspace opening. The osseous width changes were moresignificant at the level of the incisor, and this could berelated to the labial tipping we observed. A recent CBCTstudy evaluating bone width changes with labial tippingalso found a significant reduction in alveolar bone widthat the middle of the roots of the mandibular incisors.11

The labial concavity also increased with treatment atall measured height levels of the ridge. This change hasonly been evaluated previously in 1 study that foundan average of a 0.5-mm increase in the labial concavity.5

Our findings mirror those reported changes because weobserved a significant increase in the labial concavity.Moreover, this increase in concavity might also be relatedto the finding that most of the alveolar bone was located


palatal to a fiducial line based on the normal location ofthe longitudinal axis of a lateral incisor, again reflectingthe more palatal location of the alveolar bone with treat-ment. The clinical implication of this finding is importantbecause this might require a more lingual placement ofthe fixture to be able to engage the alveolar bone.

Interestingly, when the width of the edentulous alve-olar bone ridge was compared with the contralateral sidein the patients with unilateral agenesis, we found that thedifference was not significant. However, when the labialconcavity and the labial bone availability were comparedwith the normative data, there was a significant differ-ence. The labial concavity was increased, especially inthe middle portion of the ridge, and the labial bone avail-ability was significantly reduced compared with the con-trol side. This is consistent with the study of Beyer et al,4

who found primarily buccal volume loss of the toothlessalveolar ridge after ridge development.

It has been reported that the crown dimensions ofthe teeth in patients with unilateral agenesis are re-duced.12,13 This could also translate to the dimensionsof the root and alveolar bone; thus, this might explainwhy there was no difference in alveolar bone ridgewidth with the contralateral side for most widthmeasurements. However, the final alveolar bone ridgewidth dimensions could be more clinically relevant ifadequate position and remnant bone covering thefixture are desired to achieve good esthetic results.

The range of bone width measurements in the lateralincisor site along the ridge at T2 varied from 4.58 mm atthe 2-mm ridge height to 5.68 mm at 10 mm. It can beobserved that based on an average 3.75-mm endosseousimplant fixture width, there is little room for error in thesurgical placement, especially if adequate bone coverageof the fixture is expected. Moreover, the surgeon mightneed to sink the implant more apically to achieveadequate dimensions to house the fixture and reducethe fixture diameter, or it might be necessary to graftthe labial surface to ensure adequate bone width foracceptable esthetic results in the short and long terms.Based on this reduced osseous width, 3D surgical plan-ning could be indicated in patients with maxillary lateralincisor agenesis before implant placement to ensurecoverage along the entire fixture surfaces.

One of the most important aspects in implantesthetics is adequate osseous coverage of the fixtureto prevent translucency of the metal and labial boneloss in the long term. To achieve this, a minimum of 2mm of bone labial to the fixture has been recommen-ded.14-16 Based on the alveolar bone width after ridgedevelopment in this study (\5 mm on the coronalaspect), it would be impossible to achieve this amountof bone labial to the implant without grafting in


Table III. Means, standard deviations, and differences (mm) before and after ridge development for the treatment sidefor the 11 patients (13 sites)

Outcome

Pretreatment PosttreatmentPosttreatment –pretreatment

P valueMean SD

Percentile distribution

Mean SD


Mean difference25th 50th 75th 25th 50th 75thSpace between incisor andcanine

0.95 0.74 0 1.10 1.65 6.63 1.24 5.45 6.80 7.30 5.68 0.001y

Height method 1 (mesialcrest)

8.48 0.94 7.95 8.10 8.75 8.18 1.28 7.40 8.30 9.20 �.30 0.420

Height method 1 (middlecrest)

8.50 0.97 8.00 8.30 8.70 8.44 1.68 7.55 8.50 9.45 �.06 0.834

Height method 1 (distalcrest)

8.55 1.23 7.90 8.20 8.75 8.25 1.52 7.70 8.20 9.15 �.30 0.439

Height method 2 1.41 0.91 0.55 1.20 2.15 1.32 0.90 0.60 1.30 2.05 �.09 0.624Bone width at 2 mmcentral incisor

7.05 0.59 6.55 7.00 7.55 6.60 0.52 6.30 6.60 6.85 �.45 0.031*

Bone width at 4 mmcentral incisor

7.42 0.78 6.75 7.20 8.05 6.87 0.77 6.35 6.60 7.25 �.55 0.006y


7.46 1.02 6.55 7.20 8.35 6.58 1.22 5.90 6.20 7.20 �.88 0.012*


7.69 1.17 7.00 7.40 7.95 6.34 1.27 5.45 6.00 6.95 �1.35 0.006y


8.24 1.75 6.80 7.70 10.40 6.95 1.52 5.70 7.20 7.40 �1.29 0.036*

Bone width at 2 mmmiddle ridge

5.55 2.01 4.85 5.70 7.10 4.58 1.02 3.95 4.60 5.05 �.97 0.046*


6.82 1.28 5.70 7.00 7.85 5.31 1.05 4.45 4.90 6.05 �1.51 0.001y


6.84 1.71 5.45 6.50 8.30 5.48 1.42 4.65 5.40 5.95 �1.36 0.002y


6.78 1.84 5.45 6.20 7.85 5.42 1.84 4.55 5.50 6.30 �1.36 0.003y


7.34 2.04 5.65 6.80 8.55 5.68 1.93 4.60 5.50 6.50 �1.66 0.002y

Bone width at 2 mmcanine

8.42 1.12 7.40 8.60 8.90 7.62 1.23 7.00 7.70 8.40 �.80 0.017*


8.89 1.17 8.20 8.50 9.70 8.22 1.09 7.35 8.10 9.05 –.67 0.002y


8.64 1.46 7.65 8.20 9.90 8.35 0.89 7.60 8.50 9.20 �.29 0.53


8.39 1.60 7.35 8.00 9.85 8.38 1.19 7.40 8.60 9.25 �.01 0.875


8.39 1.69 7.10 7.70 9.80 8.32 1.47 7.30 8.50 9.30 �.07 0.727

Labial concavity at 2 mm 0.3 0.48 0 0 0.85 0.84 0.83 0 1.00 1.35 .54 0.011*Labial concavity at 4 mm 0.68 0.61 0 1.10 1.20 1.05 0.83 0.25 1.10 1.45 .37 0.058Labial concavity at 6 mm 0.97 0.63 0.30 1.10 1.45 1.39 0.81 1.00 1.50 1.85 .42 0.016*Labial concavity at 8 mm 1.13 0.67 0.65 1.20 1.65 1.58 0.77 1.05 1.90 2.10 .45 0.028*Labial concavity at 10 mm 0.87 0.54 0.60 0.80 1.30 1.22 0.68 0.80 1.40 1.70 .35 0.049*Incisor inclination 110.71 6.91 107.3 109.0 117.4 117.14 8.28 110.0 116.0 123.5 6.43 0.010*

Difference was calculated by subtracting pretreatment measurements from posttreatment measurements; significance of the difference wasassessed with Wilcoxon signed rank tests.*P\0.05; yP\0.01.

856 Uribe et al

lateral incisor sites. Furthermore, since the bone appearsto be located more palatally, considerable labial crowncompensation might be needed in the restoration to beadequately positioned along the arch.


The alveolar bone height did not change with treat-ment in this study. This is consistent with the findingsof previous studies that found these changes negligible.Uribe et al5 found a significant 6% to 12% decrease in


Table IV. Comparison between T2 and normative values

Outcome

T2 (n 5 6) Normative value (n 5 6)Normative

– T2

P value(Wilcoxon signed

rank test)Mean SD


Mean SD

Percentile distributionMean

difference25th 50th 75th 25th 50th 75thSpace between incisor and canine 6.78 1.18 5.47 7.00 7.60 6.78 0.86 5.95 6.90 7.58 .00 0.917Height method 1 (mesial crest) 8.40 0.71 7.85 8.35 8.97 8.30 0.69 7.88 8.10 8.83 �.10 0.500Height method 1 (middle crest) 8.65 0.49 8.25 8.60 8.97 7.92 0.47 7.50 7.75 8.45 �.73 0.028*Height method 1 (distal crest) 8.40 0.58 7.77 8.50 8.92 8.03 0.76 7.48 8.10 8.68 �.37 0.225Height method 2 1.82 1.03 1.05 2.05 2.70 1.47 1.31 0.38 1.40 2.23 �.35 0.500Palatal bone width at 2 mm 3.10 1.55 1.87 2.70 4.12 2.67 0.59 2.23 2.70 3.18 �.43 0.917Palatal bone width at 4 mm 3.87 1.70 2.65 3.65 4.87 3.03 0.66 2.28 3.15 3.70 �.84 0.462Palatal bone width at 6 mm 4.20 2.06 2.50 3.85 5.82 3.28 0.87 2.43 3.55 3.98 �.92 0.279Palatal bone width at 8 mm 4.68 2.21 3.20 4.25 6.00 3.45 0.85 2.55 3.60 4.13 �1.23 0.207Palatal bone width at 10 mm 5.47 2.44 3.52 4.95 7.55 3.55 1.30 2.28 3.55 4.68 �1.92 0.028*Labial bone width at 2 mm 1.77 0.61 1.30 1.70 2.20 2.52 0.67 2.05 2.25 3.10 .75 0.027*Labial bone width at 4 mm 2.15 0.54 1.67 2.10 2.50 3.08 0.49 2.70 2.95 3.40 .93 0.046*Labial bone width at 6 mm 1.52 0.66 0.95 1.35 2.20 2.70 0.62 2.30 2.60 3.05 1.18 0.046*Labial bone width at 8 mm 1.12 0.69 0.47 0.95 1.92 2.22 0.39 1.95 2.30 2.53 1.10 0.074Labial bone width at 10 mm 1.45 0.75 0.97 1.35 2.12 2.10 0.47 1.75 2.20 2.45 .65 0.168Bone width at 2 mm central incisor 6.65 0.65 6.17 6.60 7.10 6.48 0.48 6.13 6.70 6.80 �.17 0.752Bone width at 4 mm central incisor 7.05 1.09 6.00 6.85 8.05 6.58 0.37 6.28 6.50 6.95 �.47 0.752Bone width at 6 mm central incisor 6.93 1.55 5.95 6.20 8.40 6.53 0.49 6.18 6.50 6.98 �.40 0.753Bone width at 8 mm central incisor 6.58 1.71 5.15 6.20 7.87 6.68 0.71 5.93 6.85 7.33 .10 0.750Bone width at 10 mm central incisor 7.37 1.96 5.92 7.20 8.67 7.03 1.23 5.95 6.65 8.48 �.34 0.917Bone width at 2 mm middle ridge 4.30 1.06 3.42 4.40 5.22 5.68 1.11 4.75 5.60 6.53 1.38 0.075Bone width at 4 mm middle ridge 5.10 1.03 4.22 4.80 6.22 6.13 1.06 5.23 6.00 6.88 1.03 0.207Bone width at 6 mm middle ridge 5.38 1.27 4.25 5.40 6.32 6.02 0.79 5.28 5.85 6.88 .64 0.345Bone width at 8 mm middle ridge 5.17 1.46 4.07 5.45 6.35 5.70 0.82 4.88 5.65 6.40 .53 0.753Bone width at 10 mm middle ridge 5.73 1.11 4.55 6.05 6.72 5.88 1.06 5.10 5.60 7.13 .15 0.917Bone width at 2 mm canine 7.58 1.74 6.27 7.75 9.07 7.43 0.68 6.95 7.30 7.80 �.15 0.893Bone width at 4 mm canine 8.37 1.38 7.40 8.00 9.95 7.95 0.88 7.30 7.55 8.75 �.42 0.600Bone width at 6 mm canine 8.60 0.85 7.60 8.75 9.42 8.08 0.95 7.10 8.10 8.83 �.52 0.528Bone width at 8 mm canine 8.48 1.17 7.55 8.25 9.55 7.82 0.99 6.80 7.90 8.73 �.66 0.400Bone width at 10 mm canine 8.32 1.62 6.97 8.30 9.65 7.47 1.61 6.23 7.70 8.88 �.85 0.463Labial concavity at 2 mm 1.10 1.01 0 1.25 1.72 0.15 0.37 0.00 0.00 0.23 �.95 0.068Labial concavity at 4 mm 1.13 1.11 0 1.20 1.80 0.08 0.20 0.00 0.00 0.13 �1.05 0.068Labial concavity at 6 mm 1.47 1.03 0.60 1.45 2.32 0.20 0.32 0.00 0.00 0.55 �1.27 0.043*Labial concavity at 8 mm 1.60 0.83 0.75 1.65 2.32 0.52 0.29 0.30 0.60 0.73 �1.08 0.027*Labial concavity at10 mm 1.27 0.74 0.60 1.55 1.77 0.92 0.40 0.58 0.80 1.35 �.35 0.246

Difference was calculated by subtracting pretreatment measurements from posttreatment measurements; significance of the difference wasassessed with Wilcoxon signed rank tests.*P\0.05.

Uribe et al 857

alveolar height. However, the magnitude was 0.6 mm,which is considered clinically insignificant. When theposttreatment height was compared with the contralat-eral incisor in patients with unilateral agenesis, a signif-icant difference was observed in the middle of the crestwith method 1. This difference was less than 0.7 mm,which is also considered clinically insignificant.

Further studies should assess the frequency that pa-tients with maxillary lateral incisor agenesis who havespace-opening procedures for ridge development stillrequire grafting of the labial alveolar bone. Another


study should concentrate on a long-term follow-up toevaluate the esthetics of endosseous implants in lateralincisor sites with and without grafting after space-opening procedures.

This study was the first to assess the 3D osseousridge changes in patients with lateral incisor agenesisafter orthodontic ridge development. CBCT scans,instead of stone models, were used to evaluate the un-derlying osseous changes. Thus, an ethical dilemmaemerges regarding the use of this technology for pa-tients with lateral incisor agenesis. A recent position


Fig 7. Sagittal slice depicting the irregular shape of thealveolar bone ridge at the lateral incisor site. Alveolarbone width dimensions are approximately 5 mm at thecoronal level and only 2.5 mm at 10 mm in this T2 scan.Green and blue lines represent the respective coronaland axial planes of orientation.

858 Uribe et al

statement by the American Academy of Oral andMaxillofacial Radiology discourages the routine pre-treatment use of CBCT scans.17 Based on our results,scans at T2 might be justified for patients withcongenitally missing lateral incisors undergoing ridgedevelopment to ensure adequate ridge dimensionsbefore implant placement, and to evaluate the needfor additional grafting procedures.

This study was a retrospective evaluation of patientcharts. Consequently, it has several limitations, and thefindings should be interpreted keeping these inperspective. We examined an association and not anactual cause-and-effect relationship between the inde-pendent and outcome variables. There could be errorsin tracing the data points, even though we made everyeffort to minimize such biases by conducting a reli-ability analysis, and our analyses showed excellent reli-ability of measurements. Furthermore, the actual ridgechanges were not evaluated with a 3D superimpositionmethod, which could have provided insight into theprecise ridge changes and explained the increasedlabial concavity and reduced alveolar ridge width.Our sample size was small, and the study might nothave been appropriately powered. However, we usedstrict criteria to select our subjects by reviewing thecharts of almost 10,000 patients. Finally, our samplewas obtained from 3 private offices, and it is not clearwhether this sample represents the population of in-terest; hence, the generalizability and external validityare questionable. However, our results indicate thatthere could be scope for conducting prospectivestudies using samples drawn from several more officesand demonstrating generalizable findings.


CONCLUSIONS

The alveolar bone ridge width was significantlyreduced with the space-opening procedure for acongenitally missing lateral incisor.

Alveolar bone width changes occurred not only at thetoothless ridge level. To a lesser extent, width changeswere also observed on the adjacent canine and centralincisor.

Labial concavity was significantly increased withalveolar bone ridge development.

Alveolar ridge dimensions at T2 in the toothless sitewere smaller but not significantly different from thecontralateral incisor in patients with unilateral agenesis;however, the labial concavity was significantly increasedcompared with the normative data at 6 and 8 mm.

The bone labial to a fiducial line representing thenormal location of the longitudinal axis of a lateral incisorwas significantly reduced at T2 comparedwith the norma-tive data at 2 to 6 mm, reflecting a labial ridge deficiency.

No changes in alveolar bone ridge height wereobserved with space opening.

ACKNOWLEDGMENTS

The authors thank Dr Paul Rigali, Wallingford, Conn,and Dr Carl Roy, Virgina Beach and Chesapeake, Va, forproviding the data for this study.

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