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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en">Cone Beam Computed Tomography Assessment of the Maxillary Incisive Canal and Foramen: Considerations of Anatomical Variations When Placing Immediate Implants</title><author><name sortKey="Al Amery, Samah M" sort="Al Amery, Samah M" uniqKey="Al Amery S" first="Samah M." last="Al-Amery">Samah M. Al-Amery</name><affiliation><nlm:aff id="aff001"><addr-line>Dept. of Diagnostic and Integrated Dental Practice, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></nlm:aff></affiliation></author><author><name sortKey="Nambiar, Phrabhakaran" sort="Nambiar, Phrabhakaran" uniqKey="Nambiar P" first="Phrabhakaran" last="Nambiar">Phrabhakaran Nambiar</name><affiliation><nlm:aff id="aff001"><addr-line>Dept. of Diagnostic and Integrated Dental Practice, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></nlm:aff></affiliation></author><author><name sortKey="Jamaludin, Marhazlinda" sort="Jamaludin, Marhazlinda" uniqKey="Jamaludin M" first="Marhazlinda" last="Jamaludin">Marhazlinda Jamaludin</name><affiliation><nlm:aff id="aff002"><addr-line>Dept. of Community Oral Health and Clinical Prevention, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></nlm:aff></affiliation></author><author><name sortKey="John, Jacob" sort="John, Jacob" uniqKey="John J" first="Jacob" last="John">Jacob John</name><affiliation><nlm:aff id="aff001"><addr-line>Dept. of Diagnostic and Integrated Dental Practice, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></nlm:aff></affiliation></author><author><name sortKey="Ngeow, Wei Cheong" sort="Ngeow, Wei Cheong" uniqKey="Ngeow W" first="Wei Cheong" last="Ngeow">Wei Cheong Ngeow</name><affiliation><nlm:aff id="aff003"><addr-line>Dept. of Oro-Maxillofacial Surgical and Medical Sciences, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></nlm:aff></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">PMC</idno><idno type="pmid">25679505</idno><idno type="pmc">4332502</idno><idno type="url">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4332502</idno><idno type="RBID">PMC:4332502</idno><idno type="doi">10.1371/journal.pone.0117251</idno><date when="2015">2015</date><idno type="wicri:Area/Pmc/Corpus">000412</idno><idno type="wicri:explorRef" wicri:stream="Pmc" wicri:step="Corpus" wicri:corpus="PMC">000412</idno></publicationStmt><sourceDesc><biblStruct><analytic><title xml:lang="en" level="a" type="main">Cone Beam Computed Tomography Assessment of the Maxillary Incisive Canal and Foramen: Considerations of Anatomical Variations When Placing Immediate Implants</title><author><name sortKey="Al Amery, Samah M" sort="Al Amery, Samah M" uniqKey="Al Amery S" first="Samah M." last="Al-Amery">Samah M. Al-Amery</name><affiliation><nlm:aff id="aff001"><addr-line>Dept. of Diagnostic and Integrated Dental Practice, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></nlm:aff></affiliation></author><author><name sortKey="Nambiar, Phrabhakaran" sort="Nambiar, Phrabhakaran" uniqKey="Nambiar P" first="Phrabhakaran" last="Nambiar">Phrabhakaran Nambiar</name><affiliation><nlm:aff id="aff001"><addr-line>Dept. of Diagnostic and Integrated Dental Practice, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></nlm:aff></affiliation></author><author><name sortKey="Jamaludin, Marhazlinda" sort="Jamaludin, Marhazlinda" uniqKey="Jamaludin M" first="Marhazlinda" last="Jamaludin">Marhazlinda Jamaludin</name><affiliation><nlm:aff id="aff002"><addr-line>Dept. of Community Oral Health and Clinical Prevention, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></nlm:aff></affiliation></author><author><name sortKey="John, Jacob" sort="John, Jacob" uniqKey="John J" first="Jacob" last="John">Jacob John</name><affiliation><nlm:aff id="aff001"><addr-line>Dept. of Diagnostic and Integrated Dental Practice, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></nlm:aff></affiliation></author><author><name sortKey="Ngeow, Wei Cheong" sort="Ngeow, Wei Cheong" uniqKey="Ngeow W" first="Wei Cheong" last="Ngeow">Wei Cheong Ngeow</name><affiliation><nlm:aff id="aff003"><addr-line>Dept. of Oro-Maxillofacial Surgical and Medical Sciences, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></nlm:aff></affiliation></author></analytic><series><title level="j">PLoS ONE</title><idno type="eISSN">1932-6203</idno><imprint><date when="2015">2015</date></imprint></series></biblStruct></sourceDesc></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en"><sec id="sec001"><title>Introduction</title><p>The maxillary incisive canal connects the roof of the oral cavity with the floor of nasal cavity and has the incisive and nasal foramina respectively at its two opposite ends. Its close proximity with the anterior incisors affects one’s ability to place immediate implants in ideal position.</p></sec><sec id="sec002"><title>Objective</title><p>To avoid causing complication, variations in their dimensions were studied.</p></sec><sec id="sec003"><title>Material and Methods</title><p>Images of ninety Mongoloids patients examined with i-CAT Cone Beam Computed Tomography were included. The sizes of the nasopalatine foramen, the incisive canal and foramen, and anterior maxillary bone thickness were measured. The direction and course of the canals were assessed.</p></sec><sec id="sec004"><title>Results</title><p>The mean labiopalatal and mesiodistal measurements of the incisive foramen were 2.80mm and 3.49 mm respectively, while the labiopalatal width of the nasal foramen was 6.06mm. The incisive canal was 16.33mm long and 3.85 mm wide. The anterior maxillary bone has an average thickness of 7.63 mm. The dimensions of the incisive foramen and incisive canal, and anterior maxillary bone thickness demonstrated gender differences with males showing greater values. The anterior maxillary bone thickness was affected by age but this difference was not observed in canal dimensions. The majority of subjects have a funnel shape-like incisive canal with the broader opening located at its superior. They seem to have a longer slanted-curve canal with one channel at its middle portion and a narrower incisive foramen opening than those reported elsewhere.</p></sec><sec id="sec005"><title>Conclusions</title><p>This study found that gender is an important factor that affected the characteristics of the IC and the amount of bone anterior to it. Male generally had bigger IC and thicker anterior bone. In addition, the anterior maxillary bone thickness was affected by aging, where it becomes thinner with increased age even though the subjects were fully dentate.</p></sec></div></front><back><div1 type="bibliography"><listBibl><biblStruct><analytic><author><name sortKey="Sarandha, Dl" uniqKey="Sarandha D">DL Sarandha</name></author><author><name sortKey="Hussain, Zu" uniqKey="Hussain Z">ZU Hussain</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Scheid, Rc" uniqKey="Scheid R">RC Scheid</name></author><author><name sortKey="Woelfel, Jb" uniqKey="Woelfel J">JB Woelfel</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Drake, R" uniqKey="Drake R">R Drake</name></author><author><name sortKey="Vogl, Aw" uniqKey="Vogl A">AW Vogl</name></author><author><name sortKey="Mitchell, Awm" uniqKey="Mitchell A">AWM Mitchell</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Ghom, Ag" uniqKey="Ghom A">AG Ghom</name></author><author><name sortKey="Ghom, A G" uniqKey="Ghom A">A.G Ghom</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Glickman, Gn" uniqKey="Glickman G">GN Glickman</name></author><author><name sortKey="Cohen, S" uniqKey="Cohen S">S Cohen</name></author><author><name sortKey="Burns, R C" uniqKey="Burns R">R. 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<front><journal-meta><journal-id journal-id-type="nlm-ta">PLoS One</journal-id><journal-id journal-id-type="iso-abbrev">PLoS ONE</journal-id><journal-id journal-id-type="publisher-id">plos</journal-id><journal-id journal-id-type="pmc">plosone</journal-id><journal-title-group><journal-title>PLoS ONE</journal-title></journal-title-group><issn pub-type="epub">1932-6203</issn><publisher><publisher-name>Public Library of Science</publisher-name><publisher-loc>San Francisco, CA USA</publisher-loc></publisher></journal-meta><article-meta><article-id pub-id-type="pmid">25679505</article-id><article-id pub-id-type="pmc">4332502</article-id><article-id pub-id-type="doi">10.1371/journal.pone.0117251</article-id><article-id pub-id-type="publisher-id">PONE-D-14-27903</article-id><article-categories><subj-group subj-group-type="heading"><subject>Research Article</subject></subj-group></article-categories><title-group><article-title>Cone Beam Computed Tomography Assessment of the Maxillary Incisive Canal and Foramen: Considerations of Anatomical Variations When Placing Immediate Implants</article-title><alt-title alt-title-type="running-head">CBCT Assessment of Maxillary Incisive Canal for Implant Placement</alt-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Al-Amery</surname><given-names>Samah M.</given-names></name><xref ref-type="aff" rid="aff001"><sup>1</sup></xref></contrib><contrib contrib-type="author"><name><surname>Nambiar</surname><given-names>Phrabhakaran</given-names></name><xref ref-type="aff" rid="aff001"><sup>1</sup></xref></contrib><contrib contrib-type="author"><name><surname>Jamaludin</surname><given-names>Marhazlinda</given-names></name><xref ref-type="aff" rid="aff002"><sup>2</sup></xref></contrib><contrib contrib-type="author"><name><surname>John</surname><given-names>Jacob</given-names></name><xref ref-type="aff" rid="aff001"><sup>1</sup></xref></contrib><contrib contrib-type="author"><name><surname>Ngeow</surname><given-names>Wei Cheong</given-names></name><xref ref-type="aff" rid="aff003"><sup>3</sup></xref><xref rid="cor001" ref-type="corresp">*</xref></contrib></contrib-group><aff id="aff001"><label>1</label><addr-line>Dept. of Diagnostic and Integrated Dental Practice, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></aff><aff id="aff002"><label>2</label><addr-line>Dept. of Community Oral Health and Clinical Prevention, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></aff><aff id="aff003"><label>3</label><addr-line>Dept. of Oro-Maxillofacial Surgical and Medical Sciences, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia</addr-line></aff><contrib-group><contrib contrib-type="editor"><name><surname>Tuukkanen</surname><given-names>Juha</given-names></name><role>Academic Editor</role><xref ref-type="aff" rid="edit1"></xref></contrib></contrib-group><aff id="edit1"><addr-line>University of Oulu, FINLAND</addr-line></aff><author-notes><fn fn-type="conflict" id="coi001"><p><bold>Competing Interests: </bold>The authors have declared that no competing interests exist.</p></fn><fn fn-type="con" id="contrib001"><p>Conceived and designed the experiments: PN WCN. Performed the experiments: SMA. Analyzed the data: SMA PN MJ WCN. Wrote the paper: SMA PN WCN JJ.</p></fn><corresp id="cor001">* E-mail: <email>ngeowy@um.edu.my</email></corresp></author-notes><pub-date pub-type="epub"><day>13</day><month>2</month><year>2015</year></pub-date><pub-date pub-type="collection"><year>2015</year></pub-date><volume>10</volume><issue>2</issue><elocation-id>e0117251</elocation-id><history><date date-type="received"><day>9</day><month>7</month><year>2014</year></date><date date-type="accepted"><day>20</day><month>12</month><year>2014</year></date></history><permissions><copyright-year>2015</copyright-year><copyright-holder>Al-Amery et al</copyright-holder><license xlink:href="http://creativecommons.org/licenses/by/4.0/"><license-p>This is an open access article distributed under the terms of the <ext-link ext-link-type="uri" xlink:href="http://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution License</ext-link>, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited</license-p></license></permissions><self-uri content-type="pdf" xlink:type="simple" xlink:href="pone.0117251.pdf"></self-uri><abstract><sec id="sec001"><title>Introduction</title><p>The maxillary incisive canal connects the roof of the oral cavity with the floor of nasal cavity and has the incisive and nasal foramina respectively at its two opposite ends. Its close proximity with the anterior incisors affects one’s ability to place immediate implants in ideal position.</p></sec><sec id="sec002"><title>Objective</title><p>To avoid causing complication, variations in their dimensions were studied.</p></sec><sec id="sec003"><title>Material and Methods</title><p>Images of ninety Mongoloids patients examined with i-CAT Cone Beam Computed Tomography were included. The sizes of the nasopalatine foramen, the incisive canal and foramen, and anterior maxillary bone thickness were measured. The direction and course of the canals were assessed.</p></sec><sec id="sec004"><title>Results</title><p>The mean labiopalatal and mesiodistal measurements of the incisive foramen were 2.80mm and 3.49 mm respectively, while the labiopalatal width of the nasal foramen was 6.06mm. The incisive canal was 16.33mm long and 3.85 mm wide. The anterior maxillary bone has an average thickness of 7.63 mm. The dimensions of the incisive foramen and incisive canal, and anterior maxillary bone thickness demonstrated gender differences with males showing greater values. The anterior maxillary bone thickness was affected by age but this difference was not observed in canal dimensions. The majority of subjects have a funnel shape-like incisive canal with the broader opening located at its superior. They seem to have a longer slanted-curve canal with one channel at its middle portion and a narrower incisive foramen opening than those reported elsewhere.</p></sec><sec id="sec005"><title>Conclusions</title><p>This study found that gender is an important factor that affected the characteristics of the IC and the amount of bone anterior to it. Male generally had bigger IC and thicker anterior bone. In addition, the anterior maxillary bone thickness was affected by aging, where it becomes thinner with increased age even though the subjects were fully dentate.</p></sec></abstract><funding-group><funding-statement>This study was supported by the Ministry of Education, Malaysia Grant (UM.C/HIR/MOHE/DENT/19). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.</funding-statement></funding-group><counts><fig-count count="8"></fig-count><table-count count="5"></table-count><page-count count="16"></page-count></counts><custom-meta-group><custom-meta id="data-availability"><meta-name>Data Availability</meta-name><meta-value>All relevant data are within the paper and its Supporting Information files.</meta-value></custom-meta></custom-meta-group></article-meta><notes><title>Data Availability</title><p>All relevant data are within the paper and its Supporting Information files.</p></notes></front><body><sec sec-type="intro" id="sec006"><title>Introduction</title><p>The maxillary incisive papilla is an important landmark in prosthetic dentistry for setting up teeth as it helps to ensure that the arrangement and alignment conforms to the midline of the anterior maxillary ridge [<xref rid="pone.0117251.ref001" ref-type="bibr">1</xref>]. It is also an important landmark when it comes to the administration of local anesthesia in the anterior palate [<xref rid="pone.0117251.ref002" ref-type="bibr">2</xref>]. This is because the maxillary incisive foramen (IF) that is located beneath it marks the exit of the nasopalatine (incisive) nerve that supplies the palatal region of the anterior palate. This foramen is the inferior opening for a passage (the maxillary incisive canal) that connects the oral cavity to the nasal cavity [<xref rid="pone.0117251.ref003" ref-type="bibr">3</xref>].</p><p>The IF is an oval-shaped opening that faces the posteroinferior side of the palate. It has a diameter of 2 mm to 1 cm [<xref rid="pone.0117251.ref004" ref-type="bibr">4</xref>–<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>], with a position that varies from just above the crest of the alveolar ridge to the level of the apices of the central incisors [<xref rid="pone.0117251.ref008" ref-type="bibr">8</xref>].</p><p>The maxillary incisive canal (IC) is a Y-shaped passage that is between 4 and 26mm in length, depending on the surrounding maxillary bone height [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>, <xref rid="pone.0117251.ref009" ref-type="bibr">9</xref>]. It develops from the fusion of the right and left IC respectively with the anterior palatine canal to form the common IC [<xref rid="pone.0117251.ref008" ref-type="bibr">8</xref>]. It is located about 12–15 mm from the anterior nasal spine, usually closer to the nasal septum [<xref rid="pone.0117251.ref009" ref-type="bibr">9</xref>]. It connects the roof of the oral cavity with the floor of nasal cavity [<xref rid="pone.0117251.ref008" ref-type="bibr">8</xref>]. The IF and the incisive fossa form the inferior part of this canal while superiorly, the nasal septum in the nasal floor divides the opening into 2 foramina, namely the nasopalatine foramen or the foramen of Stensen [<xref rid="pone.0117251.ref010" ref-type="bibr">10</xref>,<xref rid="pone.0117251.ref011" ref-type="bibr">11</xref>]. Two accessory minor openings, termed the foramina of Scarpa are sometimes seen. These additional canals may also transmit the nasopalatine nerve [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>]. Nasal foramen (NF) is the collective term that is usually used to describe the nasal openings located on the nasal floor. In addition to nerve bundles, the naso-(spheno) palatine artery also shares a course along this canal to supply the oral cavity [<xref rid="pone.0117251.ref008" ref-type="bibr">8</xref>]. The maximum width and standard deviation of the NF was reported to be 4.9 (1.2) mm [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>].</p><p>In general, no serious clinical complication has been reported to result from surgical intrusion to the content of the IC [<xref rid="pone.0117251.ref012" ref-type="bibr">12</xref>], although a case hematoma formation 1 week after surgical removal of an impacted supernumerary tooth in the maxilla has been reported [<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>]. Neurosensory changes that usually happen following surgical transection of the nasapalatine nerve is felt the most during the first week, but return to normal within a month [<xref rid="pone.0117251.ref012" ref-type="bibr">12</xref>].</p><p>However, there is concern over the long term outcome of implants when being in contact with the content of the IC. Two studies suggested that more care should be taken with females and younger patients during the immediate implant placement due to natural root proximity to the IC at the mid-root level of the maxillary central incisor [<xref rid="pone.0117251.ref014" ref-type="bibr">14</xref>, <xref rid="pone.0117251.ref015" ref-type="bibr">15</xref>]. Taking into consideration future apicolingual resorption, surgeons tend to place implants more palatally. This approach again increases the risk of it encroaching into the IC. As a consequence, there may be a loss of osseointegration at a wall of the endosseous implant [<xref rid="pone.0117251.ref016" ref-type="bibr">16</xref>]. To overcome this problem, Artzi et al reported a novel surgical approach using a configurated cortico-cancellous block graft core to fit the foramen, while its soft tissue content was pushed back posteriorly [<xref rid="pone.0117251.ref017" ref-type="bibr">17</xref>]. This process ensures that solid bone is present around the entire length of the endosseous implant. Nevertheless, preoperative assessment using conventional radiographs may not show the exact anatomy of the IC.</p><p>A thorough understanding of variation in sizes of these structures is very important to avoid complications during and following implant insertion. It is therefore, the aim of this study to determine the norms and variations in the location and dimension of the IF and IC in 2 Mongoloid groups, namely the Chinese and Malays. The objective of this study was to determine the variations in (1) the IF size (2) NF size (3) IC length and width (4) the number of channels at the middle portion of the IC and (5) the direction and course of the IC. In addition, the amount of bone present labial to the Nasopalatine (NP) canal was measured. For the purpose of this study, this bone width was termed anterior maxillary bone thickness. The effect of gender and age of the subjects toward these findings were also analyzed.</p></sec><sec sec-type="materials|methods" id="sec007"><title>Materials and Methods</title><p>The study was approved by the Faculty of Dentistry University of Malaya Medical Ethics Committee (IRB approval no.DF DP 1302/0013[P]). The board of ethics was aware that this was a retrospective study and the facts that this study was undertaken using patients’ data / records / radiographs. As this is a teaching institution, all patients seeking treatment at the Faculty of Dentistry are informed and verbal consent taken for all forms of their records to be used for teaching and/or research purposes, with the assurance that their identity will remain anonymous.</p><sec id="sec008"><title>Image selection</title><p>One hundred consecutive cone beam computed tomography (CBCT) images recorded with i-CAT imaging system (Imaging Sciences International, Inc. Hatfield, USA), taken at the Oral & Maxillofacial Radiology Division, Faculty of Dentistry, University of Malaya were selected for this study. All images were taken retrospectively but following a standardized protocol for patient positioning, exposure parameter (120 KvP, 3–7 mA, 20 sec) and image acquisition at 0.3 mm voxel size by the same radiographer. These images were reconstructed from the CBCT data using proprietary i-CAT image reconstruction software. For this study, all the patient images were anonymized and de-identified prior to analysis. Patients with suspected pathological lesions in the anterior maxillary region and images of low quality were excluded from this study. A total of 6 records were excluded at this stage.</p></sec><sec id="sec009" sec-type="materials|methods"><title>Methods</title><p>In general, various measurements were made to determine the dimensions of the IC and corresponding anterior maxillary bone thickness (Figs. <xref rid="pone.0117251.g001" ref-type="fig">1</xref> and <xref rid="pone.0117251.g002" ref-type="fig">2</xref>). The number of channels at the middle portion of the IC was counted and the course and direction of the IC was determined based on the criteria described by Song et al [<xref rid="pone.0117251.ref006" ref-type="bibr">6</xref>].</p><fig id="pone.0117251.g001" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.g001</object-id><label>Fig 1</label><caption><title>Measurement of incisive foramen (blue line), nasal foramen (red line), incisive diameter (green line), and the incisive foramen location (yellow line).</title></caption><graphic xlink:href="pone.0117251.g001"></graphic></fig><fig id="pone.0117251.g002" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.g002</object-id><label>Fig 2</label><caption><title>Measurement of the incisive canal length (green line) and anterior maxillary bone thickness at 3 levels (yellow, orange & pink lines).</title></caption><graphic xlink:href="pone.0117251.g002"></graphic></fig><p>Figs. <xref rid="pone.0117251.g001" ref-type="fig">1</xref> and <xref rid="pone.0117251.g002" ref-type="fig">2</xref> illustrate various points of measurement at a sagittal-cross section of a CBCT image. This image was obtained using the MPR screen at the middle of the IC. The diameter of the NF was measured at the nasal entrance of the IC while the diameter of the IF was measured at the oral entrance of the canal (<xref rid="pone.0117251.g001" ref-type="fig">Fig. 1</xref>). The canal diameter was measured at the midpoint between these two levels (<xref rid="pone.0117251.g001" ref-type="fig">Fig. 1</xref>). Using two other images captured at both right and left sides of the IC, the length of the NP canal was measured as a distance from the nasal opening to the palatal opening (<xref rid="pone.0117251.g002" ref-type="fig">Fig. 2</xref>).</p><p>The anterior maxillary bone thickness (labial to the canal) was assessed at three levels—at level of the nasal spine, at the level of the most anteroinferior point of the cortical plate of maxilla and at the midpoint between these two levels. The measurement was performed as a perpendicular distance from the outer canal wall to the outer cortical plate of anterior maxillary bone (<xref rid="pone.0117251.g002" ref-type="fig">Fig. 2</xref>). An average was calculated based on these three measurements, similar to that reported by Mraiwa et al [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>]. Lastly, the location of IF was determined as a distance between the IF and the most anteroinferior point of the cortical plate of the labial bone of the maxilla (<xref rid="pone.0117251.g001" ref-type="fig">Fig. 1</xref>), as described by Liang et al [<xref rid="pone.0117251.ref018" ref-type="bibr">18</xref>].</p><p>The number of channels in the middle portion of the canal was determined by using an axial cross-section view that showed the middle portion of the NP canal (<xref rid="pone.0117251.g003" ref-type="fig">Fig. 3</xref>). The term “channel” here refers to separate small canaliculi within the NP canal and is adopted from the term used by Song t al [<xref rid="pone.0117251.ref006" ref-type="bibr">6</xref>].</p><fig id="pone.0117251.g003" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.g003</object-id><label>Fig 3</label><caption><title>Representative images showing different number of channels seen at mid incisive canal.</title></caption><graphic xlink:href="pone.0117251.g003"></graphic></fig><p>The IC was then classified according to their sagittally viewed direction in relationship to the nasal floor which was regarded as the horizontal plane. Based on a vertical line drawn perpendicular to the horizontal plane, IC which changed course by more than 10° from vertical was regarded to be “slanted”. Subsequently the course of the IC was classified as either being straight or curved (<xref rid="pone.0117251.g004" ref-type="fig">Fig. 4</xref>), as described by Song et al [<xref rid="pone.0117251.ref006" ref-type="bibr">6</xref>]. The Simplant software version 13 was used for this purpose.</p><fig id="pone.0117251.g004" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.g004</object-id><label>Fig 4</label><caption><title>Representative images showing different classifications of the direction and course of the incisive canal.</title></caption><graphic xlink:href="pone.0117251.g004"></graphic></fig><p>Using the same screen, the shape of the anterior maxillary bone labial to the IC was classified as either being (a) straight (b) concave or (c) convex. Examples of the straight and concave appearance are shown in <xref rid="pone.0117251.g005" ref-type="fig">Fig. 5</xref>.</p><fig id="pone.0117251.g005" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.g005</object-id><label>Fig 5</label><caption><title>Sagittal view shows the typical appearance of a (a) flat and (b) concave alveolar maxillary bone labial to the incisive canal.</title></caption><graphic xlink:href="pone.0117251.g005"></graphic></fig><p>The collection of data was done by the first author. Reliability of the measurements was performed by re-evaluating randomly 10% of samples twice after one week interval and without any knowledge of previous measurements. Intra-class correlation coefficients of 0.97 were achieved showing reproducibility of the evaluation of the categorical data, namely the number of channels seen and the shape and of the IC and the anterior maxillary bone labial to it was good. A kappa figure of 0.92 was achieved when comparing the numerical data, again showing good reliability of results obtained.</p></sec><sec id="sec010"><title>Statistical analysis</title><p>Data was entered and analysed by using SPSS 12.01 for Windows (SPSS Inc., Chicago, USA). Descriptive statistic was employed where appropriate. Mean and standard deviation was obtained for all measurements. Differences in measurements between gender were compared using independent <italic>t-test</italic>. Differences in the location of the IF in patients of various age groups were analyzed using analysis of variance (ANOVA). Corresponding non-parametric test (Mann-Whitney U test or Kruskal-wallis test) were used if the distribution of the data was not equal or when the number of the samples was small. In addition, chi-square test was used to compare the differences in the number of channel and the course and direction of the IC. The significance level for all the tests was set at <italic>P < 0.05</italic>.</p></sec></sec><sec sec-type="results" id="sec011"><title>Results</title><p>Ninety images of 46 males and 44 females between the ages of 15 to 75 years were included into this study. Images of four edentulous persons were excluded from the analysis as it was feared that it may have a negative effect on the morphology of the IC. Twenty of subjects whose images were used in the study were aged between 15–25 years old, 17 were 26–35 years, while 19 each were in the 36–45, 46–55 and 56–75 years old category respectively. Their gender distribution in each age group was almost at 1:1 ratio (range 0.9 to 1.13).</p><p>On average, the mean labiopalatal and mesiodistal sizes of the IF was 2.80mm and 3.49mm, respectively (<xref rid="pone.0117251.t001" ref-type="table">Table 1</xref>). This means that it has an elliptical shape with the wider part closer to the adjacent central incisors. There was a significant gender difference in the labiopalatal width (Independent <italic>t-test</italic>; <italic>P</italic> = 0.003) where the male subjects had larger foramen (3.03mm) than female subjects (2.56 mm), but no such significant difference was detected with regards to the mesiodistal width. Female subjects also presented with a wider range in the labiopalatal size (0.95–5.10mm) when compared to the mesiodistal size (1.28–4.80mm).</p><table-wrap id="pone.0117251.t001" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.t001</object-id><label>Table 1</label><caption><title>The mean dimensional measurement of the incisive and nasal foramina.</title></caption><alternatives><graphic id="pone.0117251.t001g" xlink:href="pone.0117251.t001"></graphic><table frame="hsides" rules="groups"><colgroup span="1"><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col></colgroup><thead><tr><th rowspan="3" align="center" colspan="1">Landmarks</th><th rowspan="3" align="left" colspan="1">Overall average size (SD) & range in mm</th><th colspan="2" align="center" rowspan="1">Gender</th><th rowspan="3" align="left" colspan="1"><italic>P</italic> value</th></tr><tr><th colspan="2" align="center" rowspan="1">Average size (SD) & range in mm</th></tr><tr><th align="left" rowspan="1" colspan="1">Male (n = 46)</th><th align="left" rowspan="1" colspan="1">Female (n = 44)</th></tr></thead><tbody><tr><td colspan="2" align="left" rowspan="1">Incisive foramen (IF)</td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td rowspan="2" align="center" colspan="1">Labiopalatal width</td><td align="left" rowspan="1" colspan="1">2.80 (0.82)</td><td align="left" rowspan="1" colspan="1">3.05 (0.77)</td><td align="left" rowspan="1" colspan="1">2.56 (0.80)</td><td rowspan="2" align="left" colspan="1">0.003<xref rid="t001fn001" ref-type="table-fn">*</xref></td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">[0.95–5.10]</td><td align="left" rowspan="1" colspan="1">[1.28–4.80]</td><td align="left" rowspan="1" colspan="1">[0.95–5.10]</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td rowspan="2" align="left" colspan="1">Mesiodistal width</td><td align="left" rowspan="1" colspan="1">3.49 (1.00)</td><td align="left" rowspan="1" colspan="1">3.55 (1.05)</td><td align="left" rowspan="1" colspan="1">3.44 (0.96)</td><td rowspan="2" align="left" colspan="1">0.624</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">[1.50–6.60]</td><td align="left" rowspan="1" colspan="1">[1.80–6.60]</td><td align="left" rowspan="1" colspan="1">[1.50–5.70]</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td rowspan="2" align="left" colspan="1">Distance to labial alveolus</td><td align="left" rowspan="1" colspan="1">12.05 (3.07)</td><td align="left" rowspan="1" colspan="1">11.92 (2.76)</td><td align="left" rowspan="1" colspan="1">12.19 (3.38)</td><td rowspan="2" align="left" colspan="1">0.686</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">[3.45–18.45]</td><td align="left" rowspan="1" colspan="1">[4.9–16.27]</td><td align="left" rowspan="1" colspan="1">[3.45–18.45]</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td colspan="2" align="left" rowspan="1">Nasal foramen (NF)</td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td rowspan="2" align="left" colspan="1">Labiopalatal width</td><td align="left" rowspan="1" colspan="1">6.06 (3.00)</td><td align="left" rowspan="1" colspan="1">6.54 (3.18)</td><td align="left" rowspan="1" colspan="1">5.56 (2.72)</td><td rowspan="2" align="left" colspan="1">1.180</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">[1.26–16.03]</td><td align="left" rowspan="1" colspan="1">[1.26–16.03]</td><td align="left" rowspan="1" colspan="1">[2.42–15.60]</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td rowspan="2" align="left" colspan="1">Width on right NF</td><td align="left" rowspan="1" colspan="1">6.03 (2.97)</td><td align="left" rowspan="1" colspan="1">6.76 (3.31)</td><td align="left" rowspan="1" colspan="1">6.76 (3.31)</td><td rowspan="2" align="left" colspan="1">0.017<xref rid="t001fn001" ref-type="table-fn">*</xref></td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">[1.53–15.49]</td><td align="left" rowspan="1" colspan="1">[1.62–15.49]</td><td align="left" rowspan="1" colspan="1">[1.62–15.49]</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td rowspan="2" align="left" colspan="1">Width on left NF</td><td align="left" rowspan="1" colspan="1">5.93 (3.04)</td><td align="left" rowspan="1" colspan="1">6.45 (3.32)</td><td align="left" rowspan="1" colspan="1">5.39 (2.63)</td><td rowspan="2" align="left" colspan="1">0.098</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">[0.90–16.57]</td><td align="left" rowspan="1" colspan="1">[0.90–16.57]</td><td align="left" rowspan="1" colspan="1">[1.70–13.12]</td></tr></tbody></table></alternatives><table-wrap-foot><fn id="t001fn001"><p>* Independent <italic>t-test</italic>.</p></fn></table-wrap-foot></table-wrap><p>The IF was located 12.05 mm away from the most anteroinferior point of the cortical plate of the labial bone of the maxilla (<xref rid="pone.0117251.t001" ref-type="table">Table 1</xref>). However, there was a wide variation in the ranges of this distance, from 3.45 to 18.45 mm. There was no significant gender influence with regards to this distance, with the average for males being 11.92mm (range 4.97–10.27mm) and the average for females being 12.19 mm (range 3.45–18.45mm). However, one female subject presented with a minimal distance that was almost one-third of the average distance. The location of the IF was affected significantly by advancing age (ANOVA test; <italic>P</italic> = 0.008), where the canal becomes closer to the most anteroinferior point of the cortical plate of the labial bone in older subjects (<xref rid="pone.0117251.g006" ref-type="fig">Fig. 6</xref>). Subjects of 15–25 years age group presented with the IF almost 14 mm away from the anteroinferior point of the cortical plate, but this distance was just slightly above 10 mm for those aged more than 55 years. The difference between this two ends of different age-groups is statistically significant (Post Hoc Tukey; <italic>P</italic> = 0.004). Further analysis of dividing the subjects to those below and above 45 years old found that the distance in the former group (12.66 mm) in average, is 1.6 mm more than the latter group (11.06 mm). This difference is statistically significant (Independent <italic>t-test</italic>; <italic>P</italic> = 0.016).</p><fig id="pone.0117251.g006" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.g006</object-id><label>Fig 6</label><caption><title>Differences in the distance from the incisive foramen to the most anteroinferior point of the cortical plate of labial bone in subjects of different age groups.</title></caption><graphic xlink:href="pone.0117251.g006"></graphic></fig><p>As for the NF, it showed a larger dimension with a mean labiopalatal width of 6.06 mm which is more than double the width of the IF. The NF however, presented with a wide range of widths, from a minimum of 1.26 to as wide as 16.03mm. Further analysis showed that there was no significant difference between mesiodistal widths of the right and left NF (Independent <italic>t-test</italic>; <italic>P</italic> = 1.14). However, there was gender influence on the size of the right NF (Independent <italic>t-test</italic>; <italic>P</italic> < 0.001), with the mesiodistal width for males (6.70mm) being significantly larger than for the females (5.28mm).</p><p>The IC has an average width of 3.85mm (<xref rid="pone.0117251.t002" ref-type="table">Table 2</xref>). The canal of male subjects was found to be significantly larger than the female subjects (Independent <italic>t-test</italic>; <italic>P</italic> = 0.015, and when this result was analyzed together with those found for the IF and NF, it suggests that there was gender difference in the size of the IC beginning from its inferior opening until its mid-length.</p><table-wrap id="pone.0117251.t002" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.t002</object-id><label>Table 2</label><caption><title>The mean dimensional measurement of the maxillary incisive canal.</title></caption><alternatives><graphic id="pone.0117251.t002g" xlink:href="pone.0117251.t002"></graphic><table frame="hsides" rules="groups"><colgroup span="1"><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col></colgroup><thead><tr><th rowspan="3" colspan="2" align="center">Incisive canal</th><th rowspan="3" align="left" colspan="1">Overall average size (SD) & range in mm</th><th colspan="2" align="center" rowspan="1">Gender</th><th rowspan="3" align="left" colspan="1"><italic>P</italic> value</th></tr><tr><th colspan="2" align="center" rowspan="1">Average size (SD) & range in mm</th></tr><tr><th align="left" rowspan="1" colspan="1">Male (n = 46)</th><th align="left" rowspan="1" colspan="1">Female (n = 44)</th></tr></thead><tbody><tr><td rowspan="2" colspan="2" align="left">IC width</td><td align="left" rowspan="1" colspan="1">3.85 (1.32)</td><td align="left" rowspan="1" colspan="1">4.17 (1.45)</td><td align="left" rowspan="1" colspan="1">3.51 (1.09)</td><td rowspan="2" align="left" colspan="1">0.015<xref rid="t002fn001" ref-type="table-fn">*</xref></td></tr><tr><td align="left" rowspan="1" colspan="1">[1.50–7.20]</td><td align="left" rowspan="1" colspan="1">[1.51–7.20]</td><td align="left" rowspan="1" colspan="1">[1.50–6.14]</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td rowspan="2" colspan="2" align="left">Overall IC length</td><td align="left" rowspan="1" colspan="1">16.33 (4.43)</td><td align="left" rowspan="1" colspan="1">17.96 (3.96)</td><td align="left" rowspan="1" colspan="1">17.49 (4.18)</td><td rowspan="2" align="left" colspan="1"><0.001<xref rid="t002fn001" ref-type="table-fn">*</xref></td></tr><tr><td align="left" rowspan="1" colspan="1">[4.51–30.24]</td><td align="left" rowspan="1" colspan="1">[10.64–30.24]</td><td align="left" rowspan="1" colspan="1">[10.26–31.71]</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td rowspan="2" align="left" colspan="1">Right IC length</td><td align="left" rowspan="1" colspan="1">16.66 (4.52)</td><td align="left" rowspan="1" colspan="1">18.44 (4.12)</td><td align="left" rowspan="1" colspan="1">14.80 (4.20)</td><td rowspan="2" align="left" colspan="1"><0.001<xref rid="t002fn001" ref-type="table-fn">*</xref></td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">[4.84–28.77]</td><td align="left" rowspan="1" colspan="1">[9.84–28.77]</td><td align="left" rowspan="1" colspan="1">[4.84–23.24]</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td rowspan="2" align="left" colspan="1">Left IC length</td><td align="left" rowspan="1" colspan="1">16.00 (4.80)</td><td align="left" rowspan="1" colspan="1">17.49 (4.18)</td><td align="left" rowspan="1" colspan="1">14.45 (4.95)</td><td rowspan="2" align="left" colspan="1">0.002<xref rid="t002fn001" ref-type="table-fn">*</xref></td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">[4.18–31.71]</td><td align="left" rowspan="1" colspan="1">[10.26–31.71]</td><td align="left" rowspan="1" colspan="1">[4.18–31.70]</td></tr></tbody></table></alternatives><table-wrap-foot><fn id="t002fn001"><p>* Independent <italic>t-test</italic>.</p></fn></table-wrap-foot></table-wrap><p>The IC was 16.33mm in average length, with the right canal being slightly longer than the left canal. There was a wide range in the lengths of this canal (4.51–30.24mm). This variation is greater in females who presented with differences in length that is almost six-folds between the shortest and longest canal (4.15–23.97 mm). Males, in contrast presented with a three-fold difference between the longest and shortest canal of 10.64 and 30.24 mm respectively. Further analysis showed that the IC length was significantly longer in male subjects (Independent <italic>t-test</italic>; <italic>P</italic> < 0.001). Interestingly, the age of the patients did not influence the IC length and width (ANOVA test; <italic>P</italic>>0.05).</p><p>A majority of the IC presented with 1 channel (64.4%) with the remaining 34.4% having 2 channels. Only 1 IC had 3 channels. The gender of the subjects did not correlate with the number of channels present (chi-square test; <italic>P</italic> = 0.304). There was also no correlation between the length and width of the IC with the number of channels present.</p><p>There was a wide variation in the direction and course of ICs when examined in the sagittal view. The slanted type dominated the direction of IC. The most commonly found IC direction and course was the slanted-curve type, accounting for 65.2% in males and 63.6% in female (<xref rid="pone.0117251.t003" ref-type="table">Table 3</xref>). However, there was no significant difference between gender in its direction and course (chi-square test; <italic>P</italic> = 0.382).</p><table-wrap id="pone.0117251.t003" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.t003</object-id><label>Table 3</label><caption><title>Distribution of the different directions and courses of the ICs in males and females.</title></caption><alternatives><graphic id="pone.0117251.t003g" xlink:href="pone.0117251.t003"></graphic><table frame="hsides" rules="groups"><colgroup span="1"><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col></colgroup><thead><tr><th rowspan="2" align="left" colspan="1">Direction & course</th><th colspan="2" align="center" rowspan="1">Gender n (%)</th><th rowspan="2" align="left" colspan="1">Overall</th></tr><tr><th align="left" rowspan="1" colspan="1">Male</th><th align="left" rowspan="1" colspan="1">Female</th></tr></thead><tbody><tr><td align="left" rowspan="1" colspan="1">Slanted-curve</td><td align="left" rowspan="1" colspan="1">30 (65.2%)</td><td align="left" rowspan="1" colspan="1">28 (63.6%)</td><td align="left" rowspan="1" colspan="1">58 (64.4%)</td></tr><tr><td align="left" rowspan="1" colspan="1">Slanted-straight</td><td align="left" rowspan="1" colspan="1">15 (32.6%)</td><td align="left" rowspan="1" colspan="1">14 (31.8%)</td><td align="left" rowspan="1" colspan="1">29 (32.2%)</td></tr><tr><td align="left" rowspan="1" colspan="1">Vertical-straight</td><td align="left" rowspan="1" colspan="1">0 (0%)</td><td align="left" rowspan="1" colspan="1">0 (0%)</td><td align="left" rowspan="1" colspan="1">1 (1.1%)</td></tr><tr><td align="left" rowspan="1" colspan="1">Vertical-curve</td><td align="left" rowspan="1" colspan="1">0 (0%)</td><td align="left" rowspan="1" colspan="1">2 (4.5%)</td><td align="left" rowspan="1" colspan="1">2 (2.1%)</td></tr><tr><td align="left" rowspan="1" colspan="1">Total</td><td align="left" rowspan="1" colspan="1">46 (100%)</td><td align="left" rowspan="1" colspan="1">44 (100%)</td><td align="left" rowspan="1" colspan="1">90 (100%)</td></tr></tbody></table></alternatives></table-wrap><p>There was a wide range in anterior maxillary bone thickness. The anterior maxillary bone was the thickest at the nasal spine level (10.75mm), and was the narrowest at lower labial alveolus (5.7mm), giving it a tapering appearance superior-inferiorly. Objective study of the shape of the anterior labial bone anterior to the IC found that they were equally distributed between straight and concave type. None of the bone was convex in shape. Their distribution is shown in <xref rid="pone.0117251.g007" ref-type="fig">Fig. 7</xref>. Ethnicity and gender of the subjects did not affect the shape of this bone (Chi-square test: P>0.05).</p><fig id="pone.0117251.g007" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.g007</object-id><label>Fig 7</label><caption><title>Distribution showing alveolar bone shape anterior to the incisive canal in subjects of different gender and ethnicity.</title></caption><graphic xlink:href="pone.0117251.g007"></graphic></fig><p>The average anterior maxillary bone thickness was calculated by obtaining an average of measurements made at three different levels; this was found to be 7.63 mm (<xref rid="pone.0117251.t004" ref-type="table">Table 4</xref>). On the whole, the labial bone thickness in males (8.16mm; range = 4.20–12.18 mm) was significantly larger than in the females (7.08mm; range = 3.92–9.84 mm) (Independent <italic>t-test</italic>; <italic>P</italic> < 0.001), at all the levels of measurement.</p><table-wrap id="pone.0117251.t004" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.t004</object-id><label>Table 4</label><caption><title>Anterior maxillary bone thickness.</title></caption><alternatives><graphic id="pone.0117251.t004g" xlink:href="pone.0117251.t004"></graphic><table frame="hsides" rules="groups"><colgroup span="1"><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col></colgroup><thead><tr><th colspan="2" align="center" rowspan="1">Level</th><th align="left" rowspan="1" colspan="1">Mean (SD); range in mm</th><th align="left" rowspan="1" colspan="1"><italic>P</italic> value</th></tr></thead><tbody><tr><td colspan="2" align="left" rowspan="1">Nasal spine</td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">Male</td><td align="left" rowspan="1" colspan="1">11.48 (2.14); 6.64–16.80</td><td rowspan="3" align="left" colspan="1">0.001<xref rid="t004fn001" ref-type="table-fn">*</xref></td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">Female</td><td align="left" rowspan="1" colspan="1">10.00 (1.88); 6.35–14.09</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">Average</td><td align="left" rowspan="1" colspan="1">10.75 (2.14); 6.35–16.80</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td colspan="2" align="left" rowspan="1">Mid Incisive canal</td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">Male</td><td align="left" rowspan="1" colspan="1">6.73 (1.90); 2.72–10.60</td><td rowspan="3" align="left" colspan="1">0.002<xref rid="t004fn001" ref-type="table-fn">*</xref></td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">Female</td><td align="left" rowspan="1" colspan="1">5.86 (1.55); 1.58–8.22</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">Average</td><td align="left" rowspan="1" colspan="1">6.31 (1.78); 1.58–10.60</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td colspan="2" align="left" rowspan="1">Lower labial alveolus</td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">Male</td><td align="left" rowspan="1" colspan="1">6.19 (2.06); 1.05–9.41</td><td rowspan="3" align="left" colspan="1">0.055</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">Female</td><td align="left" rowspan="1" colspan="1">5.36 (1.99); 1.53–8.99</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">Average</td><td align="left" rowspan="1" colspan="1">5.78 (2.06); 1.05–9.41</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td colspan="2" align="left" rowspan="1">Overall average</td><td align="left" rowspan="1" colspan="1">7.63 (1.61); 3.92–12.18</td><td align="left" rowspan="1" colspan="1"></td></tr></tbody></table></alternatives><table-wrap-foot><fn id="t004fn001"><p>* Independent <italic>t-test</italic>.</p></fn></table-wrap-foot></table-wrap><p>Age affected significantly the average anterior maxillary bone thickness, whereby it was noted to be thicker in young patients e.g. 8.54 mm in 15–25 years, but reduced 24% to 6.49mm when compared to subjects above 55years (<xref rid="pone.0117251.g008" ref-type="fig">Fig. 8</xref>; <italic>ANOVA</italic>; <italic>P</italic> < 0.001). When the data was further analyzed by grouping the subjects into those ≤ 45 years and > 45 years, it was found that the labial bone thickness at the nasal spine was almost equal, but the older patients had significantly narrower anterior maxillary bone thickness at lower labial alveolus and the mid IC level (Independent <italic>t-test</italic>; <italic>P</italic> < 0.001; <xref rid="pone.0117251.t005" ref-type="table">Table 5</xref>). There is a significant positive correlation between the overall location of the IF with the anterior maxillary bone thickness (Pearson’s correlation 0.581; <italic>P</italic> < 0.001).</p><fig id="pone.0117251.g008" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.g008</object-id><label>Fig 8</label><caption><title>The reduction in anterior maxillary bone thickness with an increase of age.</title></caption><graphic xlink:href="pone.0117251.g008"></graphic></fig><table-wrap id="pone.0117251.t005" orientation="portrait" position="float"><object-id pub-id-type="doi">10.1371/journal.pone.0117251.t005</object-id><label>Table 5</label><caption><title>Differences in average anterior maxillary bone thickness between those aged above and below 45 years.</title></caption><alternatives><graphic id="pone.0117251.t005g" xlink:href="pone.0117251.t005"></graphic><table frame="hsides" rules="groups"><colgroup span="1"><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col><col align="left" valign="middle" span="1"></col></colgroup><thead><tr><th align="left" rowspan="1" colspan="1">Level</th><th align="left" rowspan="1" colspan="1">Age</th><th align="left" rowspan="1" colspan="1">Mean (SD) mm</th><th align="left" rowspan="1" colspan="1"><italic>P</italic> value</th></tr></thead><tbody><tr><td align="left" rowspan="1" colspan="1">Nasal spine</td><td align="left" rowspan="1" colspan="1">≤ 45 years</td><td align="left" rowspan="1" colspan="1">10.96 (2.27)</td><td rowspan="2" align="left" colspan="1">0.227</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">> 45 years</td><td align="left" rowspan="1" colspan="1">10.35 (1.87)</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td align="left" rowspan="1" colspan="1">Mid Incisive canal</td><td align="left" rowspan="1" colspan="1">≤ 45 years</td><td align="left" rowspan="1" colspan="1">6.93 (1.61)</td><td rowspan="2" align="left" colspan="1"><0.001</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">> 45 years</td><td align="left" rowspan="1" colspan="1">5.28 (1.57)</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td align="left" rowspan="1" colspan="1">Lower labial alveolus</td><td align="left" rowspan="1" colspan="1">≤ 45 years</td><td align="left" rowspan="1" colspan="1">6.43 (1.79)</td><td rowspan="2" align="left" colspan="1"><0.001</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">> 45 years</td><td align="left" rowspan="1" colspan="1">4.71 (2.05)</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1"></td></tr><tr><td align="left" rowspan="1" colspan="1">Average bone thickness</td><td align="left" rowspan="1" colspan="1">≤ 45 years</td><td align="left" rowspan="1" colspan="1">8.13 (1.54)</td><td rowspan="2" align="left" colspan="1"><0.001</td></tr><tr><td align="left" rowspan="1" colspan="1"></td><td align="left" rowspan="1" colspan="1">> 45 years</td><td align="left" rowspan="1" colspan="1">6.80 (1.38)</td></tr></tbody></table></alternatives><table-wrap-foot><fn id="t005fn001"><p>* Independent <italic>t-test</italic>.</p></fn></table-wrap-foot></table-wrap></sec><sec sec-type="conclusions" id="sec012"><title>Discussion</title><p>Implant restoration of the upper incisors is a challenging task due to its aesthetic and functional requirement, amid the limitation that results from the resorption of alveolar bone following tooth extraction, and a variation in the dimension and location of the IC and the IF [<xref rid="pone.0117251.ref019" ref-type="bibr">19</xref>,<xref rid="pone.0117251.ref020" ref-type="bibr">20</xref>]. The former has been addressed by many researchers through various bone graft technique and materials used [<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>]. However, anatomic limitation arising from the close proximity of the IF and large IC limits one’s ability to immediately place implants in the ideal position.</p><p>Although the IC is discussed in the literature, there are only a handful of studies describing the morphology and morphometric variations of this canal [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>,<xref rid="pone.0117251.ref015" ref-type="bibr">15</xref>,<xref rid="pone.0117251.ref018" ref-type="bibr">18</xref>,<xref rid="pone.0117251.ref021" ref-type="bibr">21</xref>–<xref rid="pone.0117251.ref026" ref-type="bibr">26</xref>] of which only three involved Asian subjects[<xref rid="pone.0117251.ref006" ref-type="bibr">6</xref>,<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>,<xref rid="pone.0117251.ref027" ref-type="bibr">27</xref>]. Most other studies focused on IC pathology and their management [<xref rid="pone.0117251.ref028" ref-type="bibr">28</xref>–<xref rid="pone.0117251.ref030" ref-type="bibr">30</xref>]. As such, the authors feel that it is timely to further evaluate the variations in dimensions of IF and IC of two Mongoloid groups, namely the Chinese and Malay.</p><p>This current study shows that the IC presents with a wide variation of dimension and course and direction that is not affected by age, but their sizes were influenced by the gender of the subject. This finding is in agreement to that reported by several authors [<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>, <xref rid="pone.0117251.ref015" ref-type="bibr">15</xref>, <xref rid="pone.0117251.ref024" ref-type="bibr">24</xref>, <xref rid="pone.0117251.ref025" ref-type="bibr">25</xref>]. Although the average dimensions may not be much different from those reported in the literatures (<italic>see below</italic>) their specific variations should be taken into account when placing endosseous implant in the anterior maxilla. The following parts of this section discuss the norm and variations found.</p><p>The mean labiopalatal and mesiodistal widths of the IF were 2.80mm and 3.49mm respectively. This is close to the average of 2.90mm reported for the Caucasians/Arabs [<xref rid="pone.0117251.ref026" ref-type="bibr">26</xref>] and 3.49mm for the Koreans [<xref rid="pone.0117251.ref027" ref-type="bibr">27</xref>] on the same parameters measured. However, it is lower than the 3.8mm size for labiopalatal width and 3.7mm for mesiodistal width reported for the Japanese [<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>]. Further comparison shows that even larger diameter (4.45–4.6 mm) has been observed in Caucasians [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>,<xref rid="pone.0117251.ref024" ref-type="bibr">24</xref>]. The difference in the size of IF between male and female has been inconclusive. Mraiwa et al [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>], Bornstein et al [<xref rid="pone.0117251.ref024" ref-type="bibr">24</xref>] and Güncü et al [<xref rid="pone.0117251.ref025" ref-type="bibr">25</xref>] reported that male had significantly larger mean canal diameter as compared to female. The authors found that gender difference was only true for the labiopalatal width, but not applicable to the mesiodistal width. We are unable to explain this finding.</p><p>In comparison to the IF, the NF has a wider size of 6.06mm. This width of NF is larger when compared to the Caucasians’ and Koreans’ who only presented with a mean diameter of 3.49–4.9mm [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>,<xref rid="pone.0117251.ref024" ref-type="bibr">24</xref>,<xref rid="pone.0117251.ref027" ref-type="bibr">27</xref>]. Although the size of the NF in male patients was bigger than the females’, this difference was not statistically significant. This finding concurs with that reported by Mraiwa et al [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>], but is in contrast to that reported by Güncü et al [<xref rid="pone.0117251.ref025" ref-type="bibr">25</xref>].</p><p>The mean IC width of 3.85mm was slightly larger than those reported by Liang et al [<xref rid="pone.0117251.ref018" ref-type="bibr">18</xref>], who reported variation between 3.3 mm in cadavers to 3.6 mm when examining different samples using CT scans. This measurement is however larger than those reported in dentate Japanese, whereby the labiopalatal width was 2.8 mm and the mesiodistal width was 3.3 mm [<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>]. The narrowest canal diameter was 1.5mm and the widest was 7.2mm. This range is close to that reported by Song et al [<xref rid="pone.0117251.ref006" ref-type="bibr">6</xref>] and is within the threshold of 1cm, where any size bigger is suspected to have the presence of a pathology. The IC was significantly larger in male than female, a finding that concurs with those reported by several other researchers [<xref rid="pone.0117251.ref018" ref-type="bibr">18</xref>, <xref rid="pone.0117251.ref025" ref-type="bibr">25</xref>, <xref rid="pone.0117251.ref031" ref-type="bibr">31</xref>, <xref rid="pone.0117251.ref032" ref-type="bibr">32</xref>]. However, compared to the current finding, Güncü et al [<xref rid="pone.0117251.ref025" ref-type="bibr">25</xref>] reported smaller mean canal diameter of 2.79mm in male, and 2.4 mm in female.</p><p>Taken together, the measurements obtained for the 3 diameters of the IC suggested an appearance of a funnel shape like passage between the superior (wider NF opening), middle (intermediate IC width) and inferior (narrower IF opening), similar to that reported by Mraiwa et al [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>] and Kim et al [<xref rid="pone.0117251.ref027" ref-type="bibr">27</xref>]; but this finding is in contrast to that reported by Asaumi et al [<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>] who found the opening to be broader at the oral cavity side. Mardinger et al [<xref rid="pone.0117251.ref015" ref-type="bibr">15</xref>] and Tözüm et al [<xref rid="pone.0117251.ref026" ref-type="bibr">26</xref>] on the other hand, found the middle part of the canal to be the narrowest.</p><p>The mean length of IC has been reported to range between 8.1mm and 11.96mm in Caucasians [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>,<xref rid="pone.0117251.ref015" ref-type="bibr">15</xref>,<xref rid="pone.0117251.ref018" ref-type="bibr">18</xref>,<xref rid="pone.0117251.ref024" ref-type="bibr">24</xref>–<xref rid="pone.0117251.ref026" ref-type="bibr">26</xref>]. In contrast, Song et al [<xref rid="pone.0117251.ref006" ref-type="bibr">6</xref>] reported longer mean length of 12.0mm and 15.87mm respectively in Koreans. In this study, the IC was found to have mean length of 16.33mm which is close to that reported by Kim et al [<xref rid="pone.0117251.ref027" ref-type="bibr">27</xref>] who also performed their study using CBCT. The IC has been reported to be 1.32–1.57mm significantly longer in male than female Caucasians [<xref rid="pone.0117251.ref024" ref-type="bibr">24</xref>,<xref rid="pone.0117251.ref025" ref-type="bibr">25</xref>]. The current study however, found an even higher difference of 3.27mm. One unique feature is noticeable when the findings for the IF and NF above are combined with this IC length. The Mongoloids in this study seem to have a longer IC with narrower IF opening similar to that reported by Kim et al [<xref rid="pone.0117251.ref027" ref-type="bibr">27</xref>] in Koreans, compared to literatures describing the Caucasians as having shorter canal with wider IF opening.</p><p>Several authors described the effect of the age on the length and width of the IC [<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>,<xref rid="pone.0117251.ref015" ref-type="bibr">15</xref>,<xref rid="pone.0117251.ref018" ref-type="bibr">18</xref>,<xref rid="pone.0117251.ref024" ref-type="bibr">24</xref>,<xref rid="pone.0117251.ref033" ref-type="bibr">33</xref>]. They found that with aging the NP canal diameter increases due to the bone resorption. At the same time, the IC length decreases. However, this study did not find any significant difference in the canal dimensions in patients of different age-groups. This is because there were only four edentulous patients included into this study. Such an observation is consistent to the dimensional stability reported for the fully dentate control group in the study by Mardinger et al [<xref rid="pone.0117251.ref015" ref-type="bibr">15</xref>]. This finding suggests that the presence of teeth ensure stability in the size and length of the IC.</p><p>In a cross-sectional study among Koreans, it was found that 87% of IC at the side of nasal fossa have one channel, 10.4% have two channels, and 2.6% have three channels, but these canals merged into one canal in the middle portion of palate [<xref rid="pone.0117251.ref027" ref-type="bibr">27</xref>]. Similar features of multiple channels, with a maximum of 4 channels at the NF have also been reported in Caucasians [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>,<xref rid="pone.0117251.ref018" ref-type="bibr">18</xref>]. In contrast, this study found that multiple channels were present even at the middle portion of the palate, a finding similar to that reported by Song et al [<xref rid="pone.0117251.ref006" ref-type="bibr">6</xref>]. A majority of the IC presented with 1 channel (63.8%) with the remaining being mainly 2 channels (35.1%). Only 1 IC had 3 channels. In comparison, Song et al [<xref rid="pone.0117251.ref006" ref-type="bibr">6</xref>] reported a lower percentage of patients presenting with 1 channel (42.9%) but higher percentage of patients presenting with 3 channels (25.0%). They also reported finding 8.9% patients with 4 channels, a finding that was not observed in this study.</p><p>The majority of the Mongoloid population in this study have slanted-curve canal with one channel at the middle portion of the IC. Although this result was in agreement with Song et al [<xref rid="pone.0117251.ref006" ref-type="bibr">6</xref>] with regard to the number of the channels, the direction and course of their IC was however, mainly of the vertical-straight type.</p><p>The funnel shaped IC is described as having a Y-shape because it is made up of at least two nasal orifices on each side of nasal septum that forms a right and left canals which eventually unite to form a common canal in the incisive fossa region. Comparisons were done to get more information regarding their length and as a result of, the authors can safely say that the right canal is longer than the left canal in both males and females. The reason for this developmental variation is still unknown.</p><p>Equally important for immediate implant placement is the anterior maxillary bone thickness. Similar to that reported by several researchers [<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>,<xref rid="pone.0117251.ref024" ref-type="bibr">24</xref>–<xref rid="pone.0117251.ref026" ref-type="bibr">26</xref>], the bony dimensions demonstrated an increasing thickness from crestal to apical measurements. The basal bone does not change its shape significantly [<xref rid="pone.0117251.ref034" ref-type="bibr">34</xref>], and the current study corresponds with this finding, whereby the anterior maxillary bone thickness at the anterior nasal spine area was not different between the young (10.96mm) and the old (10.35mm) subjects. This thickness is however slightly lower than the average of 12–15 mm reported in Caucasians [<xref rid="pone.0117251.ref009" ref-type="bibr">9</xref>] but is higher than that reported for the Japanese [<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>]. The mean thickness of 7.54mm as obtained by averaging the measurements at 3 levels was close to the average reported by Mraiwa et al [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>] and Asaumi et al [<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>] but lower to that reported for the Chinese [<xref rid="pone.0117251.ref035" ref-type="bibr">35</xref>]. The range of 3.92–12.18mm was also not much different from those reported by Mraiwa et al [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>], and because of this, the precautionary advice by Mraiwa et al [<xref rid="pone.0117251.ref007" ref-type="bibr">7</xref>] on the need to carefully examine each variation in patients preoperatively must be followed for Mongoloid subjects too.</p><p>This study found that the anterior maxillary bone thickness in male was more than female, a finding in agreement with those reported by several researchers [<xref rid="pone.0117251.ref018" ref-type="bibr">18</xref>,<xref rid="pone.0117251.ref024" ref-type="bibr">24</xref>–<xref rid="pone.0117251.ref026" ref-type="bibr">26</xref>]. Such a finding indicates that female patients need more precautions during surgical procedures. Furthermore, researchers [<xref rid="pone.0117251.ref015" ref-type="bibr">15</xref>,<xref rid="pone.0117251.ref017" ref-type="bibr">17</xref>,<xref rid="pone.0117251.ref026" ref-type="bibr">26</xref>] reported that aging causes anterior maxillary bone thickness to reduce and some relate this to the fact that these patients most likely lose the anterior teeth as their age increases. An unusual finding in this study was that even in fully dentate patients, the anterior bone width became less (a 24% reduction) as the age of the subjects increase. The cause is unknown even though it may be related to bone remodeling and structural loss with advancing ages.</p><p>Although there is no significant difference in the location of the IF between males and females, in general males exhibited closer position to the most anterioinferior point of the cortical plate of the labial bone of the maxilla (mean = 11.92mm) while for female, the mean was 12.19mm. Both measurements were higher than those reported by Liang et al [<xref rid="pone.0117251.ref018" ref-type="bibr">18</xref>], who found an average of 10.6 mm in their dentate group. This current study revealed a possible effect of aging on the location of the IF when the anterior maxillary bone thickness and the distance to the most anteroinferior point of the cortical plate of labial bone become reduced with increase in age. These changes will make the procedure of dental implantation become more complex for aged patients. In such cases, this problem can be overcome by surgical intervention where the soft tissue contents in the canal is either curreted or pushed back, and the IF obturated by bone graft [<xref rid="pone.0117251.ref017" ref-type="bibr">17</xref>,<xref rid="pone.0117251.ref036" ref-type="bibr">36</xref>,<xref rid="pone.0117251.ref037" ref-type="bibr">37</xref>]. In fact, Peñarrocha et al [<xref rid="pone.0117251.ref037" ref-type="bibr">37</xref>] even used the IC as an anatomic buttress for implant placement.</p><p>In this study CBCT and the SimPlant interactive software were used to visualize the anterior maxilla for cross-sectional imaging. This technique confirms the benefit for replacing multi-detector CT scans in order to obtain accurate diagnosis and evaluation of structures in this area. CBCT machines generate less radiation with high-quality images sufficient for invasive procedures such as implant insertion and also bone grafting [<xref rid="pone.0117251.ref013" ref-type="bibr">13</xref>,<xref rid="pone.0117251.ref024" ref-type="bibr">24</xref>].</p><p>The clinical implication of this study reveals the fact that there is great variability in the sizes of the nasopalatine foramen, the incisive canal and foramen, and anterior maxillary bone thickness, even within subjects of the same Mongoloid origin. These differences appear to be gender and age related rather than of ethnic difference. Nevertheless, this study provides a detailed anatomic location of the IC and the sizes of the adjacent structures that shall become a useful reference in centers where CBCT is not available. It is recommended that clinicians make use of CBCT to overcome the shortcomings observed in conventional radiography, where possible.</p></sec><sec sec-type="conclusions" id="sec013"><title>Conclusion</title><p>This study clearly showed wide variations in the IF widths, IC dimensions and anterior maxillary bone thickness with significant difference between gender, where male patients showed larger and longer IC dimensions. This anatomical variability in the dimensions may be clinically important during surgical procedures especially in immediate implant placement. The findings from this study suggest that gender is an important factor that can affect the characteristics of the IC and the amount of bone anterior to it. In addition, the anterior maxillary bone thickness and the location of the IF are affected by aging. Lastly, Chinese and Malay subjects appear to have a funnel shape-like IC with the broader opening located at its superior. They seem to have a longer slanted-curve IC with one channel at its middle portion and a narrower IF opening than those reported in other population.</p></sec><sec sec-type="supplementary-material" id="sec014"><title>Supporting Information</title><supplementary-material content-type="local-data" id="pone.0117251.s001"><label>S1 Datasheet</label><caption><title>Combined file of supporting tables.</title><p>Table S1: Measurements of the incisive canal structure, number of channel at the middle of the canal, course and direction of the canal and the anterior bone thickness in Malay males. Table S2: Measurements of the incisive canal structure, number of channel at the middle of the canal, course and direction of the canal and the anterior bone thickness in Malay females. Table S3: Measurements of the incisive canal structure, number of channel at the middle of the canal, course and direction of the canal and the anterior bone thickness in Chinese males. Table S4: Measurements of the incisive canal structure, number of channel at the middle of the canal, course and direction of the canal and the anterior bone thickness in Chinese females.</p><p>(DOCX)</p></caption><media xlink:href="pone.0117251.s001.docx"><caption><p>Click here for additional data file.</p></caption></media></supplementary-material></sec></body><back><ref-list><title>References</title><ref id="pone.0117251.ref001"><label>1</label><mixed-citation publication-type="book"><name><surname>Sarandha</surname><given-names>DL</given-names></name>, <name><surname>Hussain</surname><given-names>ZU</given-names></name> (<year>2008</year>) <article-title>Textbook of Complete Denture Prosthodontics</article-title>. <publisher-name>Jaypee Brothers, Medical Publishers</publisher-name></mixed-citation></ref><ref id="pone.0117251.ref002"><label>2</label><mixed-citation publication-type="book"><name><surname>Scheid</surname><given-names>RC</given-names></name>, <name><surname>Woelfel</surname><given-names>JB</given-names></name> (<year>2007</year>) <article-title>Woelfel's Dental Anatomy: Its Relevance to Dentistry</article-title>. <publisher-name>Lippincott Williams & Wilkins</publisher-name><comment>doi: <ext-link ext-link-type="uri" xlink:href="http://dx.doi.org/10.1093/jxb/erm028">10.1093/jxb/erm028</ext-link></comment></mixed-citation></ref><ref id="pone.0117251.ref003"><label>3</label><mixed-citation publication-type="book"><name><surname>Drake</surname><given-names>R</given-names></name>, <name><surname>Vogl</surname><given-names>AW</given-names></name>, <name><surname>Mitchell</surname><given-names>AWM</given-names></name> (<year>2009</year>) <article-title>Gray's Anatomy for Students</article-title>. <publisher-name>Elsevier Health Sciences</publisher-name></mixed-citation></ref><ref id="pone.0117251.ref004"><label>4</label><mixed-citation publication-type="book"><name><surname>Ghom</surname><given-names>AG</given-names></name> (<year>2008</year>) <article-title>Normal Radiographic Anatomy</article-title>. 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