Bone map’ for a safe placement of miniscrews generated by computed tomography

Objectives: The aim of this manuscript is to provide a bone map that can be used as a general guide to determine the areas where miniscrews can be safely anchored.Materials and Methods: Twenty-one computed tomographies (CTs) of maxilla and mandible

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  ‘Bone map’ for a safe placement ofminiscrews generated by computedtomography L. C. Herna´  ndezG. MontotoM. Puente Rodrı´  guezL. Galba´  nV. Martı´  nez Authors’ affiliations: L. C. Herna´  ndez , Department of Morphology andCell Biology, University of Oviedo, Oviedo, Spain G. Montoto, M. Puente , Department ofOrthodontics, University of Oviedo, Oviedo, Spain L. Galba´  n , Department of Dentistry, University ofSalamanca, Salamanca, Spain V. Martı´  nez , Quiron Hospital, Madrid, Spain Correspondence to: Martı´  n Puente Rodrı´  guez C/Vı´ctor Quintanar,4 Bajo 33013Oviedo (Asturias)Espan˜aTel.:  þ 985270607Fax:  þ 985270607e-mail: Key words:  anchorage, bone map, computed tomography, miniscrew, safe areas Abstract:Objectives:  The aim of this manuscript is to provide a bone map that can be used as ageneral guide to determine the areas where miniscrews can be safely anchored. Materials and Methods:  Twenty-one computed tomographies (CTs) of maxilla andmandible were taken by the imaging centre ORTOSCAN s and two measures were taken: -First, the interradicular space in the mesiodistal plane of the maxillary and mandible teethwith slices taken at 3, 6, and 9mm from the alveolar crest, in the palatine and vestibularslices. -Second, the interradicular space in the vestibular–lingual direction. Results:  We can see that the greatest amount of mesiodistal bone is between the first andsecond inferior molars on the vestibular side and between the second and first inferiormolars on the lingual side, whereas the least amount of bone on the mesiodistal plane isbetween the inferior incisors on the vestibular side. To determine the length of theminiscrew, we must take into account that the greatest amount of vestibular–lingual boneis between the first and second inferior molar, whereas the least amount is between thecentral and lateral inferior incisors. Conclusions:  Mesiodistal values in vestibular are those that must be considered wheninserting the microscrew so as not to damage the dental tissue. Mesiodistal measurementstaken in palatal–lingual do not present problems when inserting microscrews. Thestability oftheanchorageunitisofkeyimportance in orthodontic anchorage con-trol. Creeckmore & Eklund (1983) werethe first to report the clinical insertion of atemporary anchoragedevice. Since Kanomifirst used this kind of material in ortho-dontic treatments (Kanomi 1997), manyprofessionals have used microscrews as analternative method for orthodontic ancho-rage. The choice of microscrew to be usedwill depend on the area where it is to beplaced and the interradicular or bone spaceavailable for it to be properly implanted(Huja et al. 2005).Possibleplacesformicroscrewanchoragechange depending on patient anatomicalcharacteristics (Ohmae et al. 2001; Mainoet al. 2003; Dias de Silva et al. 2004;Roberts et al. 2004; Schnelle et al. 2004;Carano et al. 2005; Cousley 2005; Melsen2005).In the maxilla, these potential sites foranchorage placement comprise the areabelow the nasal spine, the palate, thealveolar process, the infrazygomatic crest,and the retromolar area, in the mandible,they are the alveolar process, the retro-molar area, and the symphysis.Microscrew length and diameter willvary from one brand to another (Cheng-YiLin & Jein-Wein Liou 2003; Kyung et al.2003; Maino et al. 2003; Melsen 2005). Date: Accepted 15 July 2007 To cite this article: Herna´ndez LC, Montoto G, Puente M, Galba´n L,Martı´nez V. ‘Bone map’ for a safe placement ofminiscrews generated by computed tomography. Clin. Oral Impl. Res .  19 , 2008; 576–581doi: 10.1111/j.1600-0501.2007.01507.x 576  c   2008 The Authors. Journal compilation  c   2008 Blackwell Munksgaard  The literature dealing with this subjectadvises the use of RX before microscrewanchorage, the most common and well-known techniques being orthopantomogra-phy and periapical RX, although computedtomography (CT) isthemostefficient, asityields more accurate, distortion-free dataregarding the anatomic structures for thethree space levels. Poggio et al. (2006) andFreudenthaler et al. (2001) recommendusing CT before miniscrew insertion.Although microscrews are a good meansof anchorage, they can present several pro-blems such as:   Screw breakage : depending on theamount of load it must support andpatient bone quality (Marti et al. 2004).   The risk of damaging certain struc-tures : dental roots ,  blood vessels, ornerves (Liou et al. 2004; Asscherickxet al. 2005).Theaimofthepresentstudy istoprovidea bone map that can be used as a generalguide for determining the safest areas forminiscrewplacement.Weseektogenerateaguidethatthecliniciancanuseinwhichweprovide mesiodistal measurements (be-tween dental roots and between teeth) andvestibular–lingualmeasurements. Thus, ac-cording to where we want to anchor themicroscrew, we will choose the appropriatelength and diameter. Material and methods Data acquisition A sample of 50 volunteers aged 17–21years was obtained. Those who had miss-ing teeth, severe crowding, or who hadundertaken orthodontic treatments wereexcluded from this group.Of the 50 volunteers, 29 were excluded:   seven presented severe crowding(>6mm discrepancy between bone andtooth),   seventeen had undergone prior ortho-dontic treatment,   five had at least one missing tooth.Oncethestudy hadbeenapprovedby theEthics Committee of the University, eachparticipant signed an informed consentdocument. Of the 21 subjects admittedinto the study, 14 were males and sevenwere females.Data were obtained from 21 CTs – 21images were taken of the maxillae and 21of the mandible in order to take the mea-surements that will subsequently be ex-plained.These images were taken at the centerfor diagnostics, ORTOSCAN s (Oviedo,Spain). The equipment used was a HiSeepDual CT (General Electric Medical Sys-tem, Farfield, CT, USA) and the studieswere performed according to the followingprotocol: pitch 1:1, matrix 512  512,field of view 13.8, 120Kvp and 100mA.The effective radiation doses, were 304.5micro Sv in the mandible and 324.9 microSv in the maxillae. Data were obtainedusing the Dental Scan software takingorthogonal slices up to the planned line inaxial, panoramic slices and 3D reconstruc-tions. Measurements Mesiodistal measurements For each interradicular space ,  from thesecond right upper molar to the left side,the mesiodistal distance was measured at3, 6, and 9mm from the alveolar crest.These measurements were taken with tworeference planes, one for the palatal sideand one for the buccal side.Thirty-nine values were obtained in or-der to establish these measurements ineach patient in the vestibular referenceplane and another 39 values were obtainedin order to measure along the palatineplane. The same measurements were de-termined in the lower arch.Figures 1 and 2 present the referenceplanes of the vestibular and palatine slicesof the maxilla and mandible, respectively.Thesemeasurementswillgiveusanideaofthe diameter of the microimplant weshould choose. Buccolingual measurements Bone thickness was measured in the ves-tibular–lingual direction at 3, 6, and 9mmfrom the alveolar crest in the upper andlowerarchesstartingwiththeseconduppermolar from right to left in each of the 21patients (Fig. 3).All measurements were recorded inde-pendently bytwooftheauthorsonseparate Fig.1 . Vestibular and palatine reference planes formeasuring the mesiodistal distance in the superiormaxillary bone. Fig.2 . Vestibular and lingual reference planes formeasuring the mesiodistal distance in the mandible. Fig.3 . Slice showing the vl measurement at 3, 6, and 9mm. (a) Orthogonal slice of the upper maxillary bone.(b) Orthogonal slice of the mandible. Herna´ndez et al . ‘Bone map’ for a safe placement of miniscrews generated by computed tomography c   2008 The Authors. Journal compilation  c   2008 Blackwell Munksgaard  577 |  Clin. Oral Impl. Res.  19 , 2008 / 576–581  occasions to ensure validity. Results fromthe study underwent statistical analysis.The mean and standard deviation wereobtained for the measurements per-formed in the 21 CTs of the maxilla andmandible. Results The results are shown in Tables 1 and 2.The values were taken from 3-, 6-, and9-mm-thick slices on both vestibular andpalatine sides. Other values were obtainedby measuring the buccolingual distance inthe same slicesat 3, 6, and 9mmas shownin Tables 3 and 4. Mesiodistal measurements Lower arch Lingual side   On the lingual side, the greatestamount of mesiodistal bone was lo-cated between the first and second leftlower molars ( m ¼ 6.5mm; SD 2.9),between the second premolar and firstleft lower molar ( m ¼ 6.5mm; SD 1.9),and between the first and second rightlower molars ( m ¼ 6.5mm; SD 2.1) at9mm.   On the lingual side, the smallestamount of mesiodistal bone wasfound between the left central incisorand left lateral incisor in the 3mm( m ¼ 2mm; SD 0.4) and 6mm slices( m ¼ 2mm; SD 0.5); between theright lateral incisor and canine in the3mm slice ( m ¼ 2mm; SD 0.7), andbetween the canine and first rightpre-molar in the 6mm slice( m ¼ 2mm; SD 1.4). Table1 . Mesiodistal measurements in themandible (mean and standard deviation) Interradicular space Slice level3mm6mm9mm37–36 Buccal M 5 4.5 6SD 1.5 1.9 2.7Lingual M 5 4.5 6.5SD 1.7 1.9 2.936–35 Buccal M 3.5 4 5.5SD 0.8 0.9 1.6Lingual M 4 5 6.5SD 1 1.4 1.935–34 Buccal M 3 2.5 3.5SD 0.4 0.6 0.9Lingual M 3.5 3 3SD 0.4 0.6 0.734–33 Buccal M 2.5 3 4SD 1 1.6 2.6Lingual M 4 3 2.5SD 0.6 1.2 1.233–32 Buccal M 2.5 3 4SD 0.4 0.4 0.6Lingual M 3 2.5 3SD 0.5 0.7 0.932–31 Buccal M 2 2.5 3SD 0.2 0.4 0.6Lingual M 2 2 3SD 0.4 0.5 0.631–41 Buccal M 2 2.5 3.5SD 0.5 0.5 0.7Lingual M 3 2.5 3SD 0.6 0.8 0.941–42 Buccal M 2 2.5 3SD 0.4 0.5 0.7Lingual M 3 2.5 3.5SD 0.4 0.6 0.842–43 vestibular M 2.5 2.5 3SD 0.6 0.7 0.9Lingual M 2 3 3.5SD 0.7 0.8 143–44 Buccal M 2.5 3 3SD 1 1.2 1.6Lingual M 2.5 2 3.5SD 0.9 1.4 1.944–45 Buccal M 3 3 3SD 0.5 0.6 0.6Lingual M 3 2.5 3.5SD 0.7 0.8 0.845–46 Buccal M 3 4 5SD 0.9 1.1 1.3Lingual M 4.5 4 5SD 1.2 1.4 1.646–47 Buccal M 4.5 4 5SD 1.4 1.7 1.9Lingual M 5 4.5 6.5SD 1.7 1.9 2.1 Values in blue indicate measurements  2.5mm.SD, standard deviation. Table2 . Mesiodistal measurements in themaxillae (mean and standard deviation) Interradicular space Slice level3mm 6mm 9mm17–16 Buccal M 4 3 5SD 0.9 1.2 1.4Palatal M 3 3.5 4SD 0.8 1 1.216–15 Buccal M 3 3 4SD 1 1.2 2.2palatal M 4 4 4.5SD 0.6 0.9 1.315–14 Buccal M 3 3 4SD 0.8 1.2 1.4Palatal M 3 3 3.5SD 0.6 0.8 1.114–13 Buccal M 3 3 4SD 0.8 0.9 1.2Palatal M 3 3 4SD 0.9 1.2 1.513–12 Buccal M 2 2 3.5SD 1.5 1.8 2.5Palatal M 2.5 3 3.5SD 2 2.2 2.812–11 Buccal M 2.5 2.5 3SD 1 1.4 1.8Palatal M 2.5 3 3.5SD 1.5 1.8 211–21 Buccal M 4 4 4SD 1 1.5 1.8Palatal M 3 4 4.5SD 1.2 1.5 1.921–22 Buccal M 2 2 3SD 1 1.5 1.9Palatal M 2.5 3 3.5SD 1.4 1.6 1.822–23 Buccal M 3 3 3.5SD 1.5 1.9 2.6Palatal M 2.5 3 4SD 2 2.3 2.823–24 Buccal M 3 3 3.5SD 0.9 1.4 1.6Palatal M 3 4 4SD 0.9 1.2 1.424–25 Buccal M 3 3.5 4SD 0.9 1.2 1.3Palatal M 4 3.5 3.5SD 0.7 0.8 125–26 Buccal M 3 3 4SD 0.9 1.1 1.4Palatal M 4.5 5 5.5SD 0.8 1 1.426–27 Buccal M 4 3 3.5SD 1 1.1 1.5Palatal M 4 4.5 5SD 0.7 1 1.2 Values in blue indicate measurements  2.5mm.SD, standard deviation. Table3 . Buccolingual measurements in themandible (mean and standard deviation) Interradicular space Slice level3mm 6mm 9mm37–36 M 15 16 17SD 1.4 1.6 1.836–35 M 15 15 14SD 1.3 1.7 2.235–34 M 11 12 14SD 2.1 2.3 2.534–33 M 8 10 12SD 1.8 1.9 2.233–32 M 8 8 11SD 2.2 2.3 2.532–31 M 7 9 10SD 2.7 2.1 2.431–41 M 8 9 11SD 2.8 2.7 2.441–42 M 8 9 11SD 2.3 2.5 2.642–43 M 10 12 13SD 2 2.1 2.343–44 M 10 12 13SD 1.6 1.8 1.944–45 M 12 13 14SD 1.2 1.2 1.345–46 M 15 16 16SD 1 1.3 1.446–47 M 14 16 16SD 1.5 1.6 1.2 Values in red indicate measurements  10mm.SD, standard deviation. Herna´ndez et al . ‘Bone map’ for a safe placement of miniscrews generated by computed tomography 578 |  Clin. Oral Impl. Res.  19 , 2008 / 576–581  c   2008 The Authors. Journal compilation  c   2008 Blackwell Munksgaard  Vestibular side   The smallest measurements found onthe vestibular side that could representa risk given that they were  o 2.5mm(shown in the table in blue) are thefollowing:   Between the first and second left pre-molars in the 6mm slices( m ¼ 2.5mm; SD 0.6); between thecanine and first pre-molars on the leftand right in the 3mm slices( m ¼ 2.5mm; SD 1); between the ca-nineandleftlateralincisorinthe 3mmslices ( m ¼ 2.5mm; SD 0.4) and rightin the 3 and 6mm slices ( m ¼ 2.5mm;SD 0.6 and 0.7, respectively); betweenthe left central and lateral incisors inthe 3mm slices ( m ¼ 2mm; SD 0.2)and between the right central and lat-eral incisors in the 3 and 6mm slices( m ¼ 2mm; SD 0.4 and  m ¼ 2.5; SD0.5). Finally, the least amount of bonewas found between the central incisorsin the 3mm slice ( m ¼ 2mm; SD 0.5)and 6mm slice ( m ¼ 2.5; SD 0.5). Superior dental arch The measurements of the interradicularspaces of the maxillary obtained in themesiodistal plane are reported in Table 2.Palatal side. The narrowest space wasfound in the 3mm between the canineand right lateral incisor ( m ¼ 2.5mm; SD2), between right lateral incisor and centralincisor ( m ¼ 2.5mm; SD 1.5), as well asbetween the left lateral incisor and thecentral incisor ( m ¼ 2.5; SD 1.4), and,finally, between the canine and left lateralincisor ( m ¼ 2.5; SD 2).Vestibular side. A mean distance of 2mmwas found on the slices on the vestibularside and between the canine and the rightlateral incisor in the 3- and 6-mm-thickslices (SD 1.5 and 1.8, respectively) andbetween the left lateral and central incisorsalso on the 3- and 6-mm-thick slices (SD 1and 1.5, respectively).Dangerous areas in the mesiodistal di-rection are shown in Figures 4 and 5. Vestibular–lingual measurements The dangerous areas where special atten-tion to microscrew length must to be paidare shown in Tables 3 and 4.The figuresinredindicatelengths oflessthan 10mm from pre-molar to pre-molarin both arches. Discussion Itistruethattakingexactmeasurementsisimportant particularly when taking thevestibular slices, because many risks canarise when placing these devices at thatpoint which is one of the most commonlyused.No data are available regarding howmuchboneisnecessary betweenthedentalroots and the miniscrews. Poggio et al.(2006) assumed that 1mm of alveolarbone around the screw is sufficient forgood periodontal health.Figure 6 shows two possible places formicroimplant insertion in the mandible,one in the incisal area and one in themolar area, as well as the relation tocortical bone.A recent study showed that a high man-dibular plane angle and inflammation ofthe tissue surrounding the implant follow-ing insertion were risk factors for screwmobility. However, they could not detect asignificant association between thesuccessrate and the following variables: screwlength, type of surgical placement, im-mediate loading, implant location, age,gender, crowding of teeth, anteroposterior Fig.4 . Panoramic image of the maxillae taken by computed tomography (CT). Green spaces are dangerousareas ( o 2.5mm). The red lines indicate the slice thickness (3 or 6mm). Table4 . Buccopalatal measurements in the maxillae Interradicular space Slice level3mm 6mm 9mm17–16 M 13 15 16SD 1.6 1.3 1.916–15 M 12 14 15SD 1.2 0.9 1.615–14 M 11 12 12SD 1.9 1.6 2.314–13 M 9 11 11SD 2.4 2.5 2.113–12 M 9 9 9SD 0.9 2.2 2.412–11 M 7 9 10SD 0.8 1.1 1.511–21 M 9 8 8SD 1.6 1.6 1.821–22 M 8 9 10SD 2 2.1 2.322–23 M 8 9 9SD 1.7 1.3 1.923–24 M 9 10 11SD 1.9 2.1 2.224–25 M 11 12 13SD 0.8 0.7 1.725–26 M 13 15 17SD 1.7 1.6 1.926–27 M 14 16 17SD 1.6 1.8 1.9 Values in red indicate measurements   10mm.SD, standard deviation Herna´ndez et al . ‘Bone map’ for a safe placement of miniscrews generated by computed tomography c   2008 The Authors. Journal compilation  c   2008 Blackwell Munksgaard  579 |  Clin. Oral Impl. Res.  19 , 2008 / 576–581  jaw base relationship, controlled perio-dontitis, and symptoms of temporoman-dibular disorder (Miyawaki et al. 2003).Thestudy ofthebonemaprevealslessofa safety margin on the mesiodistal side dueto the variability of tooth angles and rootmorphology. Vestibular–lingual measure-ments are safer in determining microscrewlength. Although we have attempted toprovide a standardized osseous guide, thenumerous variations patients present mustalways be factored into any decision.There is only one article published onthis subject (Poggio et al. 2006) where ananatomic study is undertaken using com-puterized tomography; nevertheless, thereare several differences between our studyand Poggio’s work. Patient age ranges from20 to 40 years and no mention is made asto whether the patients examined had un-dergone orthodontic treatment, what couldresult in different measurements, espe-cially mesiodistal measurements. Vestibu-lar–lingual and mesiodistal measurementsin the study were taken at 2, 5, 8, and11mm and they did not measure the ante-rior teeth, whereas in our study we tookmeasurements at 3, 6, and 9mm aftermeasuring every single tooth. Poggio andco-workers also took mesiodistal measure-ments differing in vestibular and palatineonly from the first superior molar to thefirst superior pre-molar on both sides.Be that as it may, when comparingresults we can see that there are no greatdifferences even after considering thosealready mentioned.Generally speaking, it is recommendedthat microimplants be placed at 30 1  withrespect to the tooth’s axis. A recent studyhas shown that in the maxilla, mini-im-plants should be inserted apically at anoblique angle. In the mandible, the screwshould be placed as parallel to the roots aspossible if there are teeth present (Melsen2005).The aim of the present study is to pro-vide a bone map to aid in placing micro-screws at a safe site, although no studieshave been performed in relation to thedifferent ages of the patients taking intoaccount the variations that can exist interms of the amount and quality of thebone, as well as variations that mightappear in edentulous areas. This issuecould be solved in future studies. Conclusions We can conclude that the vestibular spaceis smaller than the palatal–lingual one.   The values presented in the tables bymesiodistal in vestibular are those thatmust be taken into account when in-serting the microscrew so as to avoiddamaging dental tissue.   Insofarasvestibular–lingualthicknessisconcerned, there are no problems withshorter microscrews (minor to 7mm),albeit they could pass through the cor-tical bone at some points but withoutdamagingany vasculonervousstructure.Nevertheless, longer microscrews(greater than 7mm) can injure the innercortical of the maxillaries at any time.Nonetheless, no anatomic structure ofinterest would ever be affected.   The study of the bone map is lessreliable in mesiodistal due to the varia-bility of tooth angle and root morphol-ogy. Vestibular–lingual measurementsare safer, and this can be helpful whenchoosing microscrew length. References Asscherickx, K., Vannet, B.V., Wehrbein, H. &Sabzevar, M.M. (2005) Root repair after injuryfrom mini-screw.  Clinical Oral Implants Re-search  16 : 575–578.Carano, A., Velo, S., Leone, P. & Siciliani, G. (2005)Clinical applications of the miniscrew anchoragesystem.  Journal of Clinical Orthodontics  39 :9–24.Cheng- Yi Lin, J. &Jein-Wein Liou, E. (2003) A newbone screw for orthodontic anchorage.  Journal of Clinical Orthodontics  37 : 676–681.Cousley, R. (2005) Critical aspects in the use oforthodonticpalatalimplants.  American Journalof Orthodontics and Dentofacial Orthopedics  127 :723–729.Creekmore, T. & Eklund, M.K. (1983) The possi-bility of skeletal anchorage.  Journal of ClinicalOrthodontics  17 : 266–9.Dias da Silva, J., Peres, F.R. & Amorim, P.(2004) Implantes y ortodoncia.  Implante palatino. Periodoncia y osteointegracion  14 :371–384.Freudenthaler, J.W., Haas, R. & Bantleon, H.P.(2001) Bicortical titanium screws for criticalorthodontic anchorage in the mandible: a preli-minary report on clinical applications.  ClinicalOral Implants Research.  12 : 358–63.Huja, S.S., Litsky, A.S., Beck, M., Johnson, K.A. &Larsen, P.E. (2005) Pull-out strength ofmonocortical screws placed in the maxillae andmandibles of dogs.  American Journal of Ortho-dontics and Dentofacial Orthopedics  127 :307–313. Fig.6 . Placement of 9 and 11mm microscrews andtheir relationship to cortical bone in the mandible.(a) Orthogonal slice of the mandible in the incisalregion. (b) Orthogonal slice of the mandible in themolar region. Fig.5 . Panoramic image of the mandible taken by computed tomography (CT). Green spaces are dangerousareas ( o 2.5mm). The red lines indicate the slice thickness (3 or 6mm). Herna´ndez et al . ‘Bone map’ for a safe placement of miniscrews generated by computed tomography 580 |  Clin. Oral Impl. Res.  19 , 2008 / 576–581  c   2008 The Authors. Journal compilation  c   2008 Blackwell Munksgaard
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