DENTAL IMPLANTS

Trabecular Bone Microarchitecture in the Median Palate and Maxillary Premolar Alveolar Sites of Edentulous Elderly Cadavers Allauddin Siddiqi, BDS, PDD, MSc, PhD,* Jules A. Kieser, BSc, BDS, PhD, DSc, FLS FDSRCS(Ed), FFSSoc,y Rohana K. De Silva, BDS, FDSREPS (Gls), FFDRCS (Ire), FDSRCS (Eng),z Andrew McNaughton, MAppliSci,x Sobia Zafar, BDS, MSc, PhD (Cand),jj and Warwick J. Duncan, ED, MDS, PhD, FRACDS (Perio){ Purpose: The median palate has been proposed as an alternative site for implant placement supporting maxillary overdentures. The aim of our research was to compare the histologic bone microarchitecture of the median palatal and the maxillary premolar alveolar ridge in edentulous elderly human cadavers. Materials and Methods:

The bone quality and quantity were analyzed at two regions of analysis (ROA) in 16 maxilla of human cadavers: the median palate (ROA I) and edentulous maxillary alveolar premolar ridge (ROA II). Histomorphometry of the scanned images was performed using image analysis software (National Institutes of Health ImageJ). The bone volume/tissue volume ratio, trabecular thickness, trabecular separation, and trabecular number were evaluated for the two regions.

Results: The bone volume fraction of the median-palatal region (ROA I) was greater than at the respective premolar sites (ROA II) in 10 of 15 samples (66.6%), with mean values ranging from 19.3-61.3%. However, the results were not statistically significant (P = .151). Similarly, the trabecular number of ROA II showed greater values than that for ROA II (mean TbN for ROA I, 1.03 mm1 and for ROA II, 0.96 mm1). However, these differences were not statistically significant (P = .454). Conclusions:

These results have indicated that the anterior median palate is structurally similar to the corresponding maxillary premolar region in elderly edentulous persons. Therefore, it can be used as an implant site to anchor a maxillary overdenture in patients with atrophic maxillary ridges. Ó 2013 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 71:1852.e1-1852.e11, 2013

Alveolar bone resorption of older individuals can result in denture-related problems and, consequently, can also compromise their quality of life.1 Agerelated bone decline has been attributed to a decrease

in the number of stromal cells with the capacity to differentiate into osteoblasts (osteoblastogenesis) and an increase in the capacity of stromal cells to support differentiation of osteoclasts from hematopoietic cells

*Department of Oral Sciences, Sir John Walsh Research Institute, University of Otago Faculty of Dentistry, Dunedin, New Zealand.

Address correspondence and reprint requests to Dr Siddiqi: Department of Oral Sciences, Sir John Walsh Research Institute,

yDirector, Sir John Walsh Research Institute, University of Otago Faculty of Dentistry, Dunedin, New Zealand.

University of Otago Faculty of Dentistry, PO Box 647, Dunedin 9054, New Zealand; e-mail: [email protected]

zAssociate Professor, Oral Diagnostic and Surgical Sciences, University of Otago Faculty of Dentistry, Dunedin, New Zealand.

Received February 27 2013 Accepted July 17 2013

xDepartment of Anatomy and Structural Biology, University of Otago School of Medical Sciences, Dunedin, New Zealand. jjDepartment of Oral Sciences, Sir John Walsh Research Institute,

Ó 2013 American Association of Oral and Maxillofacial Surgeons 0278-2391/13/00926-9$36.00/0 http://dx.doi.org/10.1016/j.joms.2013.07.019

University of Otago Faculty of Dentistry, Dunedin, New Zealand. {Associate Professor, Department of Periodontics, University of Otago Faculty of Dentistry, Dunedin, New Zealand.

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(osteoclastogenesis).2,3 With increasing age, the edentulous posterior maxillary alveolar process changes into loosely structured bone with no more than a thin layer of cortical bone.4,5 Significant differences have been noted in the bone mineral density of the maxillary and mandibular alveolar sites.5 Similarly, the bony microstructure of the maxillary crestal and buccal sites was reported to be less dense than that in the hard palate.4,6 Edentulism influences both general and oral healthrelated quality of life and remains a well-known public health issue.7 Oral rehabilitation of completely edentulous individuals becomes more challenging for the clinical team when the patients are frail and elderly, mainly because of the age-related decline in the bone volume. The compelling benefits of implantsupported prostheses have made this the standard of care in the rehabilitation of edentulous patients. Implant-supported overdentures offer a significant advantage from psychosocial, structural, and functional viewpoints compared with conventional complete dentures.8 However, in the maxilla, compromised bone quality and quantity are limiting factors in achieving greater implant success rates.5,9,10 Numerous innovative attempts have been made to improve the success rate of implant treatment in the maxilla. These have included sinus lift surgery, diverse grafting techniques, modified implant biomaterials and surfaces, and the use of different numbers and distribution of implants to support the prosthesis.11-13 Sinus elevation and augmentation procedures have frequently been used in compromised bone height and width situations. The published data on implant success in augmented sinuses have been equivocal.14,15 A recent comparative study noted an increased failure rate of implants placed in augmented sinuses.14 The complexity of the surgical procedure and the morbidity of the donor site, especially in elderly persons, pose a health risk and are limiting factors for this option. Alternative remote implant sites, such as the pterygomaxillary region and zygomatic buttress, have also been used to rehabilitate patients with a severely resorbed maxilla.16,17 Previous work regarding the bone density of the zygomatic process has been rather inconsistent, with some suggesting it to be an unfavorable site unless transcortical stabilization has been obtained.18 Others have reported a high success rate and a 96-100% survival rate in the rehabilitation of the atrophic maxilla.16,19 These sites are not without complications and pose a clinical challenge to the prosthodontist and implant surgeon. Additionally, long transmucosal abutments and palatine emergence have been reported to cause increased peri-implant bleeding and hygiene problems.20,21 Other sites such as the nasopalatine canal and the mid-palatal region have also been used for retention of implant-supported over-

dentures.12,13,22,23 The use of the mid-palate for implant dentistry dates from Wehrbein et al,24 who designed a screw-shaped, surface-treated implant (Orthosystem) for orthodontic anchorage. No clinical complications with regard to implant mobility and peri-implant soft tissues were found in their study.24 Since then, the philosophy of temporary anchorage devices has been widely adopted, and a considerable amount of data have been published discussing intraoral hard and soft tissue depths and the relevant safety issues for their placement.25-28 Palatal implants have also been used successfully for prosthetic reasons in isolated case reports.13,29 Bone histomorphometry is a well-established technique for studying the structural qualities and measuring trabeculae in cancellous bone and is considered the reference standard for the assessment of bone quality and quantity.30 Recent histologic studies of the mid-palatal bone in human subjects have documented the presence of compact bone with sufficient bone height to obtain good primary stability of dental implants in these sites.27,28 These studies mainly focused on young adults receiving orthodontic anchorage devices. Micro-computed tomography (CT) and histomorphometry are two comparable tools for measuring the bone quality and quantity.31 Recently, in a micro-CT investigation, our research team compared the mid-palatal bone microstructure with the maxillary premolar alveolar site in elderly edentulous subjects.32 The results of micro-CT indicated that the anterior median palate is structurally better than the respective maxillary premolar sites. We have proposed that the anterior median palate is a suitable alternative surgical site for placement of implants to retain implant overdentures in elderly edentulous subjects. In the present study, we hypothesized that maxillary posterior edentulous alveolar ridges differ in trabecular structure compared with the anterior median palate because of skeletal adaptations to reduce function after edentulism. Our aim was to compare the bone microarchitecture of the median palatal and maxillary premolar alveolar ridge in edentulous elderly human cadavers using histomorphometry.

Materials and Methods STUDY DESIGN AND SAMPLE DEMOGRAPHICS

Sixteen complete maxillae from human cadavers were obtained from the Department of Anatomy, University of Otago School of Medicine (Otago, New Zealand). The decision regarding the number of samples (edentulous elderly cadavers) was based on the number of cadavers available for the study. An analysis of the body donor records for the cause of death showed that six subjects had died of metastatic

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carcinoma, five of pneumonia and/or chronic obstructive respiratory disease, and four of cardiac failure. A total of 32 bone blocks were harvested from the maxillae (two sample blocks from each maxilla; Fig 1). For ethical reasons, the clinical dental data regarding the period these anonymous body donors had been edentulous and the quality of their maxillary prostheses were not available. The sample set consisted of 15 fully edentulous maxillae (six female and nine male) and one maxilla from one male dentate cadaver. The latter was included to give an indication regarding whether differences exist in the bone microarchitecture of dentate and nondentate individuals. The dentate palatal sample was not intended as a control but, rather, to

gain perspective regarding the effect of edentulism on the palatal sites in our edentulous samples. A detailed comparison of the mid-palatal region of edentulous versus dentate elderly human subjects was outside the scope of the present investigation, but could be worthy of consideration for future studies. The cadaveric samples were used in accordance with the regulations of the institutional review board of the University of Otago (New Zealand). SAMPLE PREPARATION

The bone quality and quantity were analyzed at two regions: the median palate and the edentulous

FIGURE 1. Sampling sites. A, Maxilla of human cadaver. B, Region of analysis (ROA) I, median palatal region, occlusal view. (Fig 1 continued on next page.) Siddiqi et al. Histomorphometric Analysis of Median Palate and Maxillary Premolar Bone. J Oral Maxillofac Surg 2013.

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FIGURE 1 (cont’d). C, ROA I, sagittal view. D,E, ROA II, maxillary premolar site. F, Magnified view of the bone microarchitecture. TbN, measure of the average number of trabeculae per unit length, shown in numbers; TbTh, mean thickness of trabeculae; TbSp, mean distance between trabeculae. Siddiqi et al. Histomorphometric Analysis of Median Palate and Maxillary Premolar Bone. J Oral Maxillofac Surg 2013.

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maxillary alveolar premolar ridge. The regions of analysis (ROAs) were identified and dissected as follows: Median palatal region (ROA I): A tissue block was cut anteroposteriorly from the incisive foramen to the posterior palate, centered on the sagittal suture and extending at least 4 mm on either side of this suture (Figs 1B,C). Edentulous maxillary alveolus (canine premolar region; ROA II): Tissue blocks measuring 10 mm  15 mm, extending posteriorly from the canine eminence to the second premolar region just before the maxillary antrum and mediolaterally to encompass the entire residual alveolar ridge (Figs 1D,E), were removed with an autopsy blade (Feather Safety Razor no. 170; Feather Safety Razor, Osaka, Japan) with the soft tissue intact and stored in 10% neutral buffered formalin.

SPECIMEN PREPARATION

All specimens were fixed in 10% formalin in a phosphate buffer at pH 7.4 (HT501128, Sigma-Aldrich, St Louis, MO) and then dehydrated in ascending grades of alcohol and embedded in methylmethacrylate according to a standardized embedding protocol.33 Subsequently, 80 to 100-mm-thick ground sections were prepared, and a minimum of four slides from the median palate (ROA I) and two slides from the maxillary premolar alveolar site (ROA II) from each cadaveric maxilla were selected and stained with MacNeal’s tetrachrome and toluidine-blue solution using a standardized protocol.34 HISTOLOGIC ANALYSIS

The slides were digitally scanned using a flat-bed scanner (Epson Perfection V700 Photo; Epson New Zealand, Wellington, New Zealand) at 1400 pixels per inch and 1:1 magnification. We used the software SilverFast (LaserSoft Imaging AG, Kiel, Germany) on an iMac computer running Mac OS X 10.6.8 (Apple, Cupertino, CA) with postscan processing using Adobe Photoshop CS3, version 10 (Adobe Systems, New York, NY). The two ROAs were described histologically and then analyzed using the BoneJ plug-in for the image analysis software ImageJ (available at: http://rsb.info.nih.gov/ij/). The threshold for the images was initially set to select only the bone component in the image according to their gray scale distribution. Binary images were then generated using ImageJ and used for subsequent analysis in BoneJ. The regions of interest were cropped, and BoneJ was used to measure the bone volume fraction, thickness, separation, and connectivity, which can be interpreted as the trabecular number (TbN), as described by Doube

et al.35 The TbN represents the number of trabeculae per unit length. This parameter provided an estimate of the number of trabeculae within a volume of bone. In contrast, the trabecular thickness (TbTh) and TbSp provide the trabecular size (width of the trabeculae) and marrow spaces (distance between the trabeculae), respectively. All samples were calibrated using a standardized protocol. STATISTICAL ANALYSIS

Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS, version 18; IBM New Zealand, Wellington, New Zealand) and GraphPad PRISM, version 5.04 (GraphPad Software, La Jolla, CA). Wilcoxon’s signed rank test was used for paired comparisons of the bone microarchitecture in the median palatal and premolar region in the same cadaver. P < .05 was considered statistically significant. Spearman’s correlation was used to quantify the association among the variables (bone volume/tissue volume [%BV/TV] ratio, TbTh, TbSp, and TbN) and between the two different ROAs. The measurement error was determined by repeat measurements by the same examiner of 10 slides selected at random, using Dahlberg’s formula: s = OS (x1  x2)2/2n, where (x1  x2) is the difference between the first and second measures, and n is the sample size that was remeasured.36 The error of reproducibility was in the range of 0.01 to 0.63.

Results A total of 96 scanned bone images of 16 elderly cadavers (ROA I, 64 and ROA II, 32) were analyzed using image analysis software National Institutes of Health ImageJ (plugin BoneJ). The research compared the mean values of the median palatal region (ROA I) of each cadaver with that of the mean values of the premolar region (ROA II). The mean age of donor cadavers at death was 80 years (range 65 to 94 years). HISTOLOGIC DESCRIPTION

ROA I was bound by the nasal floor superiorly and the palate inferiorly and was bisected in the midline by the vertical portion of the palatine process of the maxilla (anteriorly) or palatine bone (posteriorly; Fig 1). In the median palatal region, a thick layer of keratinized fibrous mucosa covering a compact layer of palatine bone was observed. In the maxillary premolar region, the bone in most of the samples was finely trabeculated and spongy in appearance, with a thin outer layer of compact bone. HISTOMORPHOMETRY

The histomorphometric results of bone volume fraction of the median palatal region showed higher values

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than the respective premolar sites in 66.6% of samples, with the mean values ranging from 19.3-61.3%; however, the difference between the two regions was not statistically significant (P = .151; Table 1, Fig 2). The greatest %BV/TV value was measured in the median palatal region (ROA I) of a male aged 76 years, and the lowest value (19.7%) of the same region was noted for a female aged 85 years. The %BV/TV correlated positively with the TbTh and TbSp, because the two variables increase together (rs = 0.721 for ROA I, and rs = 0.375 for ROA II). For ROA I, this correlation was statistically significant (P = .002); however, this was not the case for ROA II (P = .168). Similarly, the correlation between TbSp and TbTh was positive in ROA II only (P = .017). TbTh correlated negatively with TbN (for ROA I, rs = 0.811, P = .0002; for ROA II, rs = 0.920, P = .00001). No differences were observed between the male and female specimens for any of the variables. In the present study, age-related differences were not observed. The single dentate sample showed a lower bone volume fraction and TbN in the premolar region (ROA II) than the median palatal region (ROA I). Measurements of all variables from both regions of this single dental sample lay within the ranges recorded for edentulous subjects (Table 1). It is possible that the characteristics of oral bone from the two different regions would be closely related in response to other variables (eg, the

duration of the edentulous period, duration and quality of the prosthesis, the presence or absence of osteoporosis). However, only %BV/TV showed a weak positive correlation between the two ROAs (rs = 0.44, P = .30). The remainder of the variables showed no significant correlation, suggesting that in this edentulous population, the two potential implant sites can be considered relatively independent of each other.

Discussion The present study compared the histomorphometric parameters of bone quality between two potential implant sites in the maxillae of elderly edentulous cadavers. The bone density or quality of the median palatal region was comparable to the respective premolar site. With some minor differences, the results of the present histomorphometric analysis were comparable to the micro-CT analysis of the same cadaveric samples conducted previously.32 Similar to the histomorphometric findings, the micro-CT analysis found no significant differences between ROAs I and II in the % BV/TV, TbN, and TbTh. Micro-CT analysis found a statistically significant difference in the TbSp of the two regions, showing loosely connected bone in the premolar region compared with the median palatal bone. Although not significant, a similar trend was observed in the histomorphometric analysis.32

Table 1. QUANTIFICATION OF HISTOMORPHOMETRIC PARAMETERS OF EACH REGION OF ANALYSIS

%BV/TV Sample No.

Age (yr)

1 93 85 2 3 69 4 94 5 87 6 65 7 72 8 70 9 76 10 85 11 89 12 91 13 82 14 75 15 70 Mean  SD 80.2  9.7 Dentate 76 sample

Gender F M F M M M F F M M M F M F M — M

ROA I

ROA II

Mean TbTh (mm)

Mean TbSp (mm)

Mean TbN (mm)

ROA I

ROA I

ROA I

ROA II

ROA II

ROA II

42.5 25.5 0.30 0.89 12.6 13.9 1.34 0.28 19.7 25.2 0.15 0.23 1.26 1.68 1.27 1.09 33.5 25.7 0.33 0.78 11.7 9.31 1.03 0.33 57.8 56.5 0.42 0.84 11.0 9.6 1.38 0.67 46.1 40.4 0.40 0.64 8.98 10.4 1.17 0.63 29.6 50.0 0.48 0.47 4.28 7.44 0.62 1.06 26.0 34.0 0.15 0.20 1.26 0.74 1.73 1.68 45.5 35.5 0.57 0.41 6.05 13.9 0.80 0.87 61.3 49.6 0.53 0.38 11.7 17.6 1.15 1.29 60.3 51.5 0.95 0.74 1.22 6.01 0.63 0.69 43.7 41.6 0.55 0.78 6.57 15.3 0.79 0.53 21.9 28.7 0.19 0.18 1.07 0.98 1.18 1.57 50.8 30.1 0.45 0.44 12.2 7.73 1.13 0.69 53.0 57.1 0.68 0.62 8.73 6.32 0.78 0.92 52.3 19.3 0.56 0.08 13.7 0.50 0.93 2.41 42.9  13.8 38.1  12.5 0.4  0.2 0.5  0.3 7.5  4.7 8.1  5.6 1.1 0.3 1.0  0.6 36.6 28.95 0.41 1.5 10.41 17.02 1.36 0.25

%BV/TV, bone volume to tissue volume (ratio); ROA, region of analysis; TbN, trabecular number; TbSp, trabecular separation; TbTh, trabecular thickness. Siddiqi et al. Histomorphometric Analysis of Median Palate and Maxillary Premolar Bone. J Oral Maxillofac Surg 2013.

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FIGURE 2. Scattered plots illustrating comparisons among the two regions of analysis (ROAs). The bone volume fraction of the median palatal region (ROA I) was greater than at the respective premolar sites (ROA II) in 10 of 15 samples (66.6%) with the mean value ranging from 19.3% to 61.3%. However, the results were not statistically significant (P = .151). Similarly, the number of the trabeculae of ROA II showed greater values than those in ROA II, but the difference was not statistically significant. Siddiqi et al. Histomorphometric Analysis of Median Palate and Maxillary Premolar Bone. J Oral Maxillofac Surg 2013.

In comparative studies, researchers have investigated the microarchitecture of maxillary and mandibular bone of edentulous cadavers using histologic and micro-CT techniques.10,31,37,38 The present study was designed to investigate the bone microarchitecture of the median palate and maxillary premolar alveolar sites using histomorphometric analysis and to compare the findings from these two sites. This comparative approach has not been previously reported using histomorphometric analysis. We found a greater bone volume fraction, more trabeculae, and reduced

trabecular separation (indicating more compact bone structure) in the median palatal site; however, none of these differences were statistically significant. We did not analyze all the potential implant sites in the maxilla. We chose to investigate the maxillary premolar site, because of the findings from a human clinical trial currently being conducted by our research group, with a novel distribution of four implants in the maxilla (bilateral premolar sites, the lateral incisor region, and a median palatal implant). The rationale for this configuration was that it

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FIGURE 3. Representative microphotographs of histologic specimen of median palatal region. A,B, An example of loosely connected cancellous bone surrounded by a thick layer of cortical bone in the median palatal region of a 93-year-old female. C,D, Maxillary premolar region of a 72-year-old female with good interconnectivity, thick cancellous bone, and a well-structured dense cortical layer. A,C, Histologic sections (original magnification 2) stained with MacNeal’s tetrachrome; B,D, binary images of the same sections. Siddiqi et al. Histomorphometric Analysis of Median Palate and Maxillary Premolar Bone. J Oral Maxillofac Surg 2013.

provides a wider anteroposterior spread of the implants and thus a more stable mechanical distribution of the loads. We suggest that future investigations consider other commonly used maxillary edentulous ridge sites, such as the lateral incisor and canine regions.

A possible explanation for the observed differences in the bone structure is that the resorption pattern in the median palatal bone is quite different from that of the alveolar ridges.39 In addition, functional loads have also reported to play a key role in bone structure and density.40

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FIGURE 4. A, Binary image (ImageJ) of an undecalcified histologic specimen from the maxillary second premolar and median palatal region of an 89-year-old male with moderately connected thick cancellous bone surrounded by a thin layer of cortical bone. B, Binary image of median palatal region of a 91-year-old female with a dense, well-connected cancellous bone with greater trabecular number and thickness surrounded by a well-demarcated dense cortical layer. Median palatal region represented a better quality of bone than the maxillary premolar region. B, buccal; N, nasal cavity; P, palatal; V, vomer. Siddiqi et al. Histomorphometric Analysis of Median Palate and Maxillary Premolar Bone. J Oral Maxillofac Surg 2013.

Previous work has noted that regional and/or structural differences in human bone can be influenced by age or ancestry and genetics,41,42 although we found only a weak correlation between the two sites in the same cadaver. It has generally been accepted that mandibular bone has comparatively denser bone than the maxillary alveolar bone.5 Differences also exist in the anterior and posterior regions of the jaw, and the posterior maxilla was found to have low bone mineral density.6,10,37,43 This might be due to the differing amounts of trabecular bone in the maxilla and mandible. It also depends on how well the trabeculae are connected or separated from each other. Ulm et al10 analyzed 52 edentulous maxillae of human cadavers and noted a wide range of variations in the trabecular bone volume (6.7% to 51.9%) in the lateral incisor, first premolar, and first molar regions. A recent comparison of micro-CT and conventional stereologically based histomorphometry also reported a wide range of %BV/TV (mean 48.7%  17.8%).38 Moon et al38 analyzed the 3-dimensional microstructure of trabecular bone in the dentate mandible (10 specimens, 7 males and 3 females) and reported similar results, with the %BV/TV ranging from 2.568.0%. Our samples were relatively homogenous, ranging from a minimum bone volume fraction of 19% to a maximum of 60% in the premolar and median palatal regions. The mean for the two regions (premolar 38.1  12.5; median palate 42.9  13.8) was similar to those previously reported. These results have shown great variations in the structural morphology of the individual regions (Figs 3 to 5). When the data were examined by gender, the samples

from the female cadavers showed lower values of bone volume than the male samples, with a reduced thickness and TbN. The main limitation of the research was the small sample size. The present research did not involve a formal power study; rather, a pragmatic approach was dictated by the availability of the edentulous cadavers. However, a post hoc power analysis based on the observed differences for the %BV/TV ratio (and with a level of 0.05 and 0.08 power to detect such a difference) would have required approximately 100 cadavers in each group. Finding such a number of edentulous elderly cadavers

FIGURE 5. Binary image (from ImageJ) of the median palatal region with a high bone volume and high trabecular connectivity representing a dense, well-connected cancellous bone surrounded by a compact layer of cortical bone. Siddiqi et al. Histomorphometric Analysis of Median Palate and Maxillary Premolar Bone. J Oral Maxillofac Surg 2013.

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within the period available would have been impossible. Another limitation of our study was that the details of the prosthodontic rehabilitation or treatment records for the bequeathed bodies were not accessible and could not be obtained. In New Zealand, the bequest of bodies for anatomic study is governed by the Human Tissue Act 2008. Thus, medical and dental historical data for donated bodies is limited to the information provided with the consent of the deceased’s relatives. We acknowledge that it would be useful to know how those factors might influence the bone microstructure. Peterson et al44 investigated the cortical thickness, density, and elastic properties of 15 dentate freshfrozen maxillae of human cadavers and found that the cortical bone from the body of the maxilla was thinner, denser, and stiffer than that in the palatal region. It was also intermediate in some features but, overall, more similar to the cortical bone in the alveolar region.44 More recently, Dechow et al45 evaluated the thickness and density of the edentulous maxillae (15 cadavers). They concluded that the loss of occlusal loads could have contributed to the change in the material properties, because the maxillae presented with a reduced directional orientation of the principal axis of stiffness.45 A considerable body of orthopedic data has been published on iliac crest, spine, hip, and limb bone biopsies investigating the bone microstructure and density using histomorphometric, micro-CT, dual-energy x-ray absorptiometry, and magnetic resonance imaging.46-50 These studies have presented a wide range of values of bone structure that varies according to the anatomic region, age, and gender. A structural comparison of different bones (eg, iliac, spine, hip, wrist) with that of the maxillary or mandibular bone would be of limited value owing to the diverse morphologic characteristics and loading conditions.10,45 Furthermore, the published data have also shown discernible differences among the methods (ie, histomorphometry, micro-CT, dualenergy x-ray absorptiometry, magnetic resonance imaging) used to investigate the bone microarchitecture of the same regions and have suggested they should be used in combination for more convincing results.44,47,48 Others have reported similar results with micro-CT and histomorphometry.36,51,52 Gielkens et al51 described similar concordance between microCT and histomorphometry when bone-grafted sites and bone graft donor sites from the angle of rat mandibles were compared using the two techniques (although their study used demineralized histologic sections). M€ uler et al53 compared cadaveric iliac crest bone biopsies using micro-CT and un-demineralized resin-embedded sections. They noted similar issues to those we encountered in matching the location of the histologic sampling to the micro-CT slices obtained

from the 3-dimensional volume of interest. They also used fully automated image analysis for micro-CT versus semiautomated image analysis for histomorphometry. However, we used the same fully automated computer program for both data sets. Nonetheless, M€ uler et al53 still concluded that the results from the 3-dimensional analysis are in excellent agreement with the indexes assessed from conventional histomorphometry. The results from our cadaver study have suggested that the anterior median palate in elderly edentulous subjects has comparable bone quality to maxillary premolar alveolar sites in the same individual. This finding has important implications regarding potential dental implant sites in edentulous patients with atrophic maxillary ridges, for whom both the quantity and the quality of the remaining bone will be poor. We suggest that our results provide indirect support for the use of the median palatal bone site as an alternate implant site for anchoring overdentures. A detailed consideration of the mid-palatal as a potential implant site will add pertinent and significant information to human trials that use this site for the construction of implant prostheses. In conclusion, the results of the histomorphometric analysis have indicated that the anterior median palate is structurally similar to the corresponding maxillary premolar region in elderly edentulous persons and, therefore, could be useful as a site for dental implants to anchor an implant-supported overdenture. However, the results warrant a need for additional histologic and anatomic evidence to support this finding. Acknowledgments We would like to thank Mr David Styles from the Department of Anatomy and Structural Biology, University of Otago for providing the human cadavers, Dr Eric Lord for his guidance to obtain funding for this trial, and Professor Murray Thomson for statistical advice. Our study is dedicated to the participants who bequeathed their bodies to science, and we are truly indebted to them for their magnanimous final act.

References 1. Awad MA, Locker D, Korner-Bitensky N, Feine JS: Measuring the effect of intra-oral implant rehabilitation on health-related quality of life in a randomized controlled clinical trial. J Dent Res 79: 1659, 2000 2. Glowacki J: Cellular models of human aging. In: Rosen CJ, Glowacki J, Bilezikian JP, (eds). The Aging Skeleton. (ed 1). San Diego, CA: Academic Press, 1999 3. Mueller SM, Glowacki J: Age-related decline in the osteogenic potential of human bone marrow cells cultured in threedimensional collagen sponges. J Cell Biochem 82:583, 2000 4. Ulm C, Tepper G: Structure of atrophic alveolar bone. In: Watzek G, (ed). Implants in Qualitatively Compromised Bone. (ed 1). London: Quintessence, 2004 5. Jaffin RA, Berman CL: The excessive loss of Branemark fixtures in type IV bone: A 5-year analysis. J Periodontol 62:2, 1991 6. Devlin H, Horner K, Ledgerton D: A comparison of maxillary and mandibular bone mineral densities. J Prosthet Dent 79:323, 1998 7. Petersen PE, Yamamoto T: Improving the oral health of older people: The approach of the WHO Global Oral Health Programme. Commun Dent Oral Epidemiol 33:81, 2005

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