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Keywords:

  • bone micro-architecture;
  • bone resorption;
  • complete edentulism;
  • implant overdenture;
  • median-palatal region;
  • micro-CT

Abstract

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Conclusion
  7. Acknowledgements
  8. Conflict of interest
  9. References

Introduction

Atrophy of the alveolar bone is an irreversible multifactorial phenomenon, the rate of which varies between individuals and between the jaws. This atrophy of the alveolar ridges presents severe limitations for the oral rehabilitation of the edentulous patients and poses a clinical challenge to the prosthodontists and implant surgeons. The present research aimed to investigate whether the median-palate of elderly edentulous subjects is anatomically suitable for implant placement.

Materials and methods

A total of 32 samples were harvested from the maxillae of 16 human cadavers. One dentate male subject was included for contrast. Bone quality and quantity were analysed at two regions: the median-palate and the edentulous maxillary alveolar ridge. Samples were scanned through micro-CT, and the region of analysis (ROA) identified and dissected. Bone volume to tissue volume ratio (%BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular separation (Tb.Sp) and trabecular bone pattern factor (Tb.Pf) were evaluated for the two regions using Skyscan CTAn®.

Results

The results of bone volume fraction obtained from CTAn® of the median-palatal region show higher values than the respective premolar sites in 12 of 15 (80%) edentulous samples. However, this difference was statistically non-significant (= 0.06). Similarly, the trabecular number for 10 of 15 samples (66.6%) from the median-palate shows greater values than the respective premolar site (= 0.07). Trabecular thickness of 10 of 15 (66.6%) premolar samples is larger than in the median-palatal region. However, these differences were also statistically non-significant (= 0.25). Statistically significant difference (= 0.04) was found between the Tb.Sp values of the two regions.

Conclusion

The results indicate that the anterior median-palate is structurally better than their respective maxillary premolar region in elderly edentulous persons, and an implant can be placed to anchor an overdenture. The best site for a wide-body implant was established to be 6–8 mm posterior to the incisive foramen in elderly edentulous patients.

Loss of teeth leads to irreversible atrophy of the alveolar bone, the rate of which varies between individuals and between the jaws (mandible and maxilla) (Atwood 1979; Ulm et al. 1999, 2009). Alveolar ridge atrophy limits the oral rehabilitation of edentulous patients and thus poses a clinical challenge to prosthodontists and implant surgeons. One of the most significant paradigms in implant dentistry is to improve the quality of life of edentulous elders (Awad et al. 2003; Petersen & Yamamoto 2005). Dental implants offer a predictable treatment modality for oral rehabilitation, with implant-supported overdentures having been proposed as the standard of care in the rehabilitation of edentulous patients with its resultant improvement in the quality of life (Mericske-Stern 1998; Feine et al. 2002; Awad et al. 2003; Stanford 2007). Whilst much attention has been paid to the implant design features such as length, diameter and surface, novel implant sites and the quality of bone at these sites have received relatively less attention.

Implant treatment in the edentulous posterior maxilla may be complicated by an inadequate quantity of bone due to horizontal and vertical ridge resorption, antral pneumatisation or poor bone quality (also categorised as type III or IV, low-density trabecular bone) (Jemt 1993; Kronström et al. 2006). Structural bone quality is thought to play an important role with respect to both initial osseointegration and long-term implant survival (Rozé et al. 2009). This is of particular importance in the maxilla where bone is predominantly cancellous, with a less densely structured cortical plate than that of the mandible (Ulm et al. 1999, 2009).

The quest to improve the success rates of maxillary implants has lead researchers to place implants in areas other than the more traditionally employed edentulous alveolar ridge. Such approaches represent attempts to overcome the limitations of the maxillary bone structure, morphology and anatomy. For example, implants have been placed in the zygomatic buttress, mid-palatal region or incisive foramen in an attempt to achieve greater anchorage for overdentures (Scher 1994; Aparicio et al. 2006; Machado et al. 2008).

It is known that the palatal shelf of the maxilla varies regionally from a relatively thin sheet of simple lamellar bone to a rather thick plate consisting of two cortical tables that enclose a middle cancellous diploe (the spongy, porous, bony tissue between the hard outer and inner bone layers of the cranium) (Ferguson 1988; Shuler 1995). Also, a growing body of literature now exists on the suitability of the mid-palate in young dentate subjects for narrow diameter orthodontic implants (Wehrbein et al. 1999; Bernhart et al. 2000; Männchen & Schätzle 2008; Wehrbein 2008, 2009). Taken together, the mid-palatine region has become an area of interest to implant dentistry (Table 1). However, insufficient palatal bone height at the implant site can jeopardize implant osseointegration as well as create a risk of perforation of the nasal mucosa. When compared to the para-median region of the palate, the median-palatal region is thicker with a denser cortical bone (Bernhart et al. 2000; Kang et al. 2007). Wehrbein (2009) evaluated palatal bone characteristics in human cadavers and found that the median-palate was a suitable site for mini-implant placement because it had a relatively compact bone that provided good primary stability. Similarly, Männchen & Schätzle (2008) in a prospective longitudinal study concluded that the survival and success rates of palatal orthodontic implants were comparable to those of implants placed for dental prostheses. Although research to date has focused on short implants in the palatal region in young adults rather than investigating this region for elderly edentulous patients for anchoring maxillary prosthesis, Machado et al. (2008) reported success with a strategically positioned palatal implant to increase the retention and stability of a maxillary implant overdenture. These authors used a triangular prosthodontic design, with two conventional implants placed in the canine areas of the maxillary ridge and a single implant in the mid-palatal region.

Table 1. Literature on palatal bone height
InvestigatorType of study (human/animal)Age range (years)NumberInvestigation toolBone heightKey findings
  1. Lat rad, lateral radiograph; CBCT, cone beam computed tomography; lat ceph, lateral cephlogram; SD, standard deviation.

Jung et al. (2011)Retrospective clinical (human)12–6391Lat rad/CBCT98% had bone > 4 mmCT/CBCT is only required in borderline cases
Jung et al. (2012)Human skullsNot stated18Lat rad/CBCT

Lat rad/mean 6.6 mm

CBCT/mean 8.98 mm

Later ceph provides a reliable assessment of the vertical bone height of the palatal region
Stockmann et al. (2009)Human cadavers (maxillae)15–2010

Histology and histomorphometric

• First premolar

• Second premolar

• First molar

Canine- 6.3(1.2 SD)

1st premolar-5.1 (1.5 SD))

Second premolar- 5.2 (0.7 SD)

1st molar-4.5 (1.6 SD)

Sufficient amount and quality of bone is available (anterior palatal midline)
Wehrbein (2009)Human cadavers (maxillae)18–6322 (19 male and three females)

Histomorphometric

• Anterior part of the median palate (first premolar)

• Middle part of the median palate (2nd premolar)

• Posterior part of the median palate (first molar)

Mean hard tissue fraction/total bone vol = 68.88%

Mean bone marrow fraction/total bone vol = 21.38%

Mean soft tissue fraction/total bone vol = 9.53%

No statically significant differences with the older age group were found
Baumgaertel (2009)Human skulls (no more than 3-teeth missing)19–5030 (26 male and four females)CBCT

Canine-first premolar = 8.70 (2.30 SD)

First and second  = 8.68 (3.77 SD)

Second premolar and first molar = 4.26 (3.24 SD) 1st molar and second mol = 2.71 (1.40 SD)

Sufficient bone depth and cortical bone thickness of palate at first and second premolar were found
Jung et al. (2008)Human 15 Patient (mid-palatal18–6318 (nine male and nine females)Histology and histomorphometric (implants were removed with a trephine drill)4–6 mm availableBone to implant contact at the endosseous level was 68.22% (14.35 SD)
Machado et al. (2008)Case report401 (male)

1 year clinical success

Lateral radiograph

6 mmSuccessful use of mid-palatal implant to anchor maxillary implant overdenture
Wehrbein (2008)Human cadavers18–6322 (19 male and 3 females)

Histology

5–10 mm behind the incisive foramen (anterior median palatal region)

Mid-palatal and 3 mm bilateral to the midline were assessed

High bone quantity

C I. Palatal bone consists of almost compact bone

C II. Broad compact bone in the mid-suture area >3 mm C III. Thin compact bone <3 mm

Good primary stability

Gracco et al. (2008)Human10–44162Digital volumetric tomographsThickest bone 4–8 mm was found in the anterior part of the palate, at the suture and in the para-median areasThe anterior region is the thickest part, but posterior region is also suitable for screws of appropriate diameter and length
Kang et al. (2007)Rerecord base (CT)18–35 (mean 26.8)18 (nine male and nine females)CTWide-rangeThe thickness decreases laterally and posteriorly
Kim et al. (2006)Human cadavers49.5 (mean age)23 (16 male and seven females)Specimens were digitally scanned and then measurements were made with a software (image-pro plus)

Palatal cortical between 1st and second premolars = 6 mm apical to CEJ

Second premolar and 1st molar = 2 mm (apical to CEJ) 1st and second molar = 6 mm (apical to CEJ)

Palatal mucosa-1 mm thick (posterior to the incisive papilla)
Gracco et al. (2008)Human10–1552 (28 male and 24 females)Digital volumetric tomographyThickest part is the anterior palate (4–8 mm from the incisive foramen both at the suture and at the median areas)The highest values are always found corresponding to suture
King et al. (2006)Human10–19183 (59 male and 124 females)CBCTIncreased palatal height at the level of the 1st permanent molarAge and palatal morphology are not applicable predictors of bone height (in the para-median palate)
Knaup et al. (2004)Human palates18–6322Histology

Median sutural width in young patients (<25) = 211.20 um

Older age group = 161.16 urn

The proportion of ossified tissue in the entire suture was low in all cases
Gahleitner et al. (2004)Human12–49 (mean 26, 11 male and 21 females)32CT maxillaeOverall mean bone height = 5.01 mm (2.60 SD)Great individual variation in the vertical bone vol i.e. up to 16.9 mm was noted.
Henriksen et al. (2003)Human skullsNot stated25Lateral cephalometric technique

Theoretical amount of bone (average) 8.6 ± 1.6 mm

The actual amount of bone (average) = 4.3 ± 1.6 mm

The horizontal width of the incisive canal (average) = 2.5 ± 0.6 mm

6 mm implant should be used with caution
Schlegel et al. (2002)Cadavers12–5325 (20 male and five females)Histology of suture Palatine medians (Bone cylinders with a diameter of 0.5 × l cm)Bone quality and quantity were variableAbsolute ossification of the suture palatine median is uncommon before the age of 23 years
Bernhart et al. (2000)Human13–4822 (four male and 18 females)Dental CTSuitable implant placement is 6–9 mm posterior to incisive foramen and 3–6 mm para-median. Vertical bone volume greatly varied 
Wehrbein et al. (1999)Human15–3912 (6 male and six females)Late ceph4–6 mm implants can easily be placedVertical bone height is 2 mm more than appear on the cephalogram and a safety region (2 mm) should be left while placing implants

This paper investigates whether the median-palate of elderly edentulous subjects is anatomically suitable for implant placement to assist in the support of a maxillary prosthesis. The study compares the micro-architecture of the median-palate to conventional oral implant sites in the posterior maxillary edentulous alveolar ridge. Our hypothesis is that the anterior median-palatal bone is dimensionally and anatomically equivalent to the maxillary residual alveolus of the premolar region, for the purposes of placing an oral implant. To the knowledge of authors, this is the first time two potential implant sites (in the median-palate and the maxillary edentulous ridge) have been compared using micro-computed tomography (μCT) scans.

Material and methods

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Conclusion
  7. Acknowledgements
  8. Conflict of interest
  9. References

Study design/sample demographics

Sixteen complete maxillae of human cadavers (six female and 10 male) were obtained from the Department of Anatomy, School of Medicine, University of Otago, New Zealand. The mean age of cadavers was 80 years (age range, 65–94 years). Analysis of the body-donor records for cause of death showed that six subjects died of metastatic carcinoma, five of pneumonia/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 as shown in Fig. 1a). For ethical reasons, clinical dental data regarding the length of time that these anonymous body donors had been edentulous and the quality of their maxillary prostheses were not available. We also included a palate from one dentate cadaver sample, to give an indication as to whether differences exist in the bone micro-architecture of dentate and non-dentate individuals. Research on the cadaveric samples was conducted in accordance with the regulations of the Institutional Review Board of the University of Otago, New Zealand.

image

Figure 1. Sampling sites: schematic illustration of the palate and magnified view of the trabecular bone.

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Sample preparation

Bone quality and quantity were analysed at two regions: the median-palate and the edentulous maxillary alveolar premolar ridge. Samples were radiographed, and the region of analysis (ROA) identified and dissected as follows:

  • Median-palatal region (ROA. 1): A tissue block sectioned antero-posteriorly from the incisive foramen to the posterior palate cantered on the sagittal suture and extending least 4 mm either side of this suture (Fig. 1b).
  • Edentulous maxillary alveolus (canine-premolar region) (ROA. 2): Tissue blocks measuring 10 × 15 mm, extending posteriorly from the canine eminence to the second premolar region just before the maxillary antrum and medio-laterally to encompass the entire residual alveolar ridge (Fig. 1c) were removed with an autopsy blade (Feather Safety Razor #170, Osaka, Japan) with soft tissue intact and stored in 10% neutral buffered formalin.

Anatomical analysis

The anatomical micro-architecture of the mid-palatal region was described with particular reference to the mid-palatal bone (ROA 1) and the mid-palatal suture.

Volumetric radiography

Cadaveric specimens were scanned using a desktop micro-computerised tomography (μCT) machine (Skyscan 1172 X-ray Micro-tomograph, Antwerp, Belgium®) consisting of a sealed x-ray tube at 100 kV/100 μA and a precision object manipulator for moving the sample translationally in two dimensions as well as rotational movement. The specimens were positioned on the scanning platform using plasticine. Using the PC-based Skyscan® software, a preview image was obtained. Each specimen was adjusted until the highest possible magnification was achieved in the desired field of view. Transmission x-ray images were set for 400 views through 180 degrees of rotation to give 0.45 degrees rotational increment, using a 0.5-mm aluminium filter to minimize beam hardening. The camera was set to its medium resolution to provide an 8-μm pixel resolution. The CT stack was measured with an axial spacing of 8 μm and a pixel size of 8 μm in each plane providing an isotropic voxel resolution of 8 μm. The total scanning time per specimen was approximately 150 min for the mid-palatal region and 50 min for the maxillary premolar region. The image data set was processed using Skyscan's NRecon® software to produce a working data set of approximately 900 tomographic slice images, each measuring 1024 × 1024 pixels with a sixteen-bit Gray level; file sizes were approximately four megabytes per image. Images were calibrated, and measurements were taken using Skyscan's proprietary image analysis software (CT-An®). From the reconstructed 3D ROA, cortical and cancellous bone areas were identified in each specimen. The vertical bone height at 4, 6, 8 and 10 mm posterior to the incisive foramen in mid-sagittal line was also measured using CT-An (Skyscan micro-CT analyzer, Kontich, Belgium). The comparative radiographic anatomy of the mid-palatal and edentulous ridge regions was described with reference to the morphology, apparent bone density and (for ROA-1 only) the width, interdigitations and ossification of the median-palatal suture.

Trabecular bone morphometry

Bone microstructure was assessed using μCT according to the guidelines presented by the American Society for Bone and Mineral Research (Bouxsein et al. 2010). Bone volume to tissue volume ratio (%BV/TV) is a fundamental parameter that represents the density or lack of porosity of bone (Parfitt et al. 1987). This was calculated by summing the total number of voxels in the segmented image that represent bone, divided by the total volume. Indirect parameters including trabecular thickness (Tb.Th), trabecular separation (Tb.Sp) and trabecular number (Tb.N) were also evaluated for the two regions ROA-1and ROA-2. Trabecular thickness (Tb.Th-mm) and trabecular separation (Tb.Sp-mm) were calculated from direct measurements of the 3D data. Trabecular number (Tb.N-mm) represents the number of trabeculae per unit length. This parameter provided an estimate of the number of the trabeculae within a volume of bone, whereas Tb.Th and Tb.Sp provided the trabecular size (width of trabeculae) and marrow spaces (distance between the trabeculae), respectively. Trabecular bone pattern factor describes the relationship between the convex and concave elements. A well-connected structure contains abundant concave surfaces, whilst a loosely connected structure has more convex surfaces (Hahn et al. 1992). The trabecular bone pattern factor decreases as network connectivity increases, that is, the lower the TbSp value, the denser the bone.

Statistical analysis

Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS® version 18 – IBM New Zealand Ltd, Wellington, New Zealand) and GraphPad PRISM® (version 5.04, GraphPad Software, Inc. La Jolla, CA, USA). Each ROA (which was in the form of a rectangular section of bone sample) was divided by the number of slices and voxel height, that is, Tt.Ar = Tt.V/(number of slices × voxel height). Wilcoxon's signed rank test was used for paired comparisons of the bone micro-architecture in median-palatal and premolar region in the same cadaver. A P-value of < 0.05 was calculated to be statistically significant. Measurement error was determined by repeat measurement by the same examiner of four micro-sections selected at random, using Dahlberg's formula inline image as reported in earlier studies (Kang et al. 2007; Jung et al. 2011). The mean error was non-significant, that is, <1.

Results

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Conclusion
  7. Acknowledgements
  8. Conflict of interest
  9. References

Region of analysis 1 has an overall inverted T-shape towards the incisive foramen, becoming a flattened lozenge-shaped rhombus as one moves progressively more posteriorly. This bony region is bounded by the nasal floor superiorly and the palate inferiorly and is bisected in the midline by the vertical portion of the palatine process of the maxilla (anteriorly) or palatine bone (posteriorly) (Fig. 1b). This fusion is visible radiographically as a serpentine radiolucent line, the mid-palatal suture. The mid-palatal strut is flanked by a pair of radiolucent, sparsely trabeculated, equilateral triangular regions with the base towards the mid-palate and the apex towards the aleveolar process; these represent the non-fused diploe of the palatal process. Morphological analysis of the midline suture between the incisive foramen and the termination of the bony palate reveals a convoluted zigzag pattern of mid-palatine suture in μCT scans (Fig. 2). The scans also show that mid-palatal suture ossification occurs at the posterior part of the palate, and the suture is wider in the anterior region.

image

Figure 2. Cross-sectional radiographic images of bone architecture and vertical bone height in the median-palatal region using CT An® (a) Screenshot of the mid-sagittal view (CT An®) extending from the alveolar ridge in the maxillary incisal region to the posterior hard palate. Vertical arrows represent coronal sections through the 3D data set, as shown in figures (b–f). Colours indicate relative densities of bone as derived from the original greyscale data. (b) Cross-section at incisive foramen (IF). (c) Cross-section taken 4 mm posterior to the IF. (d) Cross-section taken 6 mm posterior to the IF (e) crosssection taken 8 mm posterior to the IF. (f) Cross section taken 10 mm posterior to IF. (g) Snapshot of the Ct An® window in which false colour image reperesents the different thickness of the trabeculae.

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Radiomorphometric analysis

The results of bone volume fraction obtained from CTAn® of the median-palatal region (ROA.1) show higher values than the respective premolar sites (ROA. 2) in 12 of 15 (80%) edentulous samples (Table 2). However, this difference was statistically non-significant (= 0.06) (Fig. 4). Similarly, the trabecular number for 10 of 15 samples (66.6%) from the median-palate shows greater values than the respective premolar site (= 0.07). Trabecular thickness of 10 of 15 (66.6%) premolar samples (ROA. 2) is larger than in the median-palatal region. However, these differences were also statistically non-significant (= 0.25). Statistically significant differences (= 0.04) were found between the Tb.Sp values of the two regions. The premolar region showed higher values than the respective median-palatal region that represents a loosely connected bone structure in the premolar region. The trabeculae of the median-palatal region is more compact than those of the premolar site, in other words the median-palatal bone appears to be more densely trabeculated than the premolar site. Whilst these data suggest that the median-palatal region has a denser bone than the premolar region, over all these differences are not statistically significant for%BV/TV, Tb.N, Tb.Th and Tb.Pf. No statistically significant difference is noted between male and female subjects with respect to%BV/TV, Tb.N, Tb.Th, Tb.Sp and Tb.Pf.

Table 2. Quantification of 3D trabecular morphometric parameters of each region of analysis (median-palatal (ROA. 1) and maxillary premolar site (ROA. 2) using CT An®
Samp #AgeSexBV/TV (%)Tb.N (1/mm)Tb.Th (mm)Tb.Sp (mm)Tb.Pf (1/mm)
ROA. 1ROA. 2ROA. 1ROA. 2ROA. 1ROA. 2ROA. 1ROA. 2ROA. 1ROA. 2
  1. Bone volume to tissue volume ratio (%BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), trabecular bone pattern factor (Tb.Pf).

169F26.918.22.51.50.10.10.91.0−35.5−23.3
272F26.034.11.71.70.20.21.30.7−17.5−18.1
391F21.928.71.21.60.20.21.11.0−3.1−13.6
470F27.819.01.30.90.20.21.01.5−6.7−6.7
593F15.713.10.90.60.20.21.21.5−1.5−4.2
665M27.423.61.92.50.10.10.90.8−15.0−29.9
789M25.818.84.11.50.10.10.51.1−28.8−25.4
882M21.719.21.81.20.10.21.11.4−29.5−24.1
976M27.820.61.01.40.30.21.91.6−9.2−26.8
1085M20.720.02.30.60.10.30.91.2−19.7−2.8
1187M28.627.91.01.50.30.21.21.1−2.7−19.9
1285M19.725.21.31.10.20.21.31.7−3.0−11.5
1394M38.521.62.21.10.20.20.51.7−15.2−17.8
1470M29.013.52.20.70.10.20.82.1−21.9−13.0
1575F27.927.51.51.40.20.20.71.1−2.8−7.8
1676M23.839.22.41.30.10.31.11.0−38.6−10.7

The results for the single dentate sample show comparatively denser bone with high bone volume fraction and trabecular number in the premolar region (ROA-2) compared with the median-palatal (ROA-1), which is supported by the analysis of respective trabecular pattern factors. The average vertical height of the median-palatal bone 4 mm posterior to the incisive foramen is 9 mm, whilst at 6, 8 and 10 mm posterior, it is 7.5 mm, 5.6 mm and 4 mm, respectively.

Discussion

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Conclusion
  7. Acknowledgements
  8. Conflict of interest
  9. References

This cadaver study suggests that the anterior median-palate in elderly edentulous subjects may have a better quality of bone when compared to their respective maxillary premolar alveolar sites. The median-palatal bone appeared to have a greater bone volume fraction and interconnectivity although these differences were not statistically significant. Statistically significant differences were found in the trabecular separation values of the two regions. This is in accordance with other reported studies where age-related increase in bone porosity was correlated with reduced number of trabeculae (Stauber & Muller 2006).

The study also explored the vertical bone height of the mid-palate as a suitable site for a wide-body implant. Mid-palatal vertical bone height was greatest in the anterior region of the median-palatal bone (4 mm posterior to the incisive foramen in the sagittal plane), whereas the lowest vertical height was noted 10 mm posterior to the incisive foramen. In contrast to other studies (Table 1), our subjects truly represent the elderly population as the mean age was 80 years. Gender-specific differences as reported in other studies were not observed in our investigation (Ulm et al. 1999, 2009).

We did not analyse all the potential implant sites in the maxilla. We chose to investigate the maxillary premolar site based on a human clinical trial currently being conducted by our research group, with a novel distribution of four implants in the maxilla (bilateral premolar sites, lateral incisor region and a mid-palatal implant). The rationale for this configuration was that it provides a wider anterior–posterior spread of implants and thus more stable mechanical distribution of loads. We suggest that future investigations consider other commonly used maxillary edentulous ridge sites, such as lateral incisor and canine regions.

Trabecular bone architecture and interconnectivity are important aspects of cancellous bone that influence bone quality. They describe bone strength and are recognized as key factors in implant osseointegration (Ulm et al. 2009). Bone strength varies depending on anatomical location and functional demands; bone also undergoes constant adaptational changes in response to local forces and stress distribution (Pearson & Lieberman 2004). Compromised bone quality and severe bone resorption have been associated with poor implant outcomes (Van Steenberghe et al. 1990; Jemt 1993). We hypothesized that the bone micro-architecture of the median-palatal region will not be the same as in the maxillary premolar site due to the loading pattern of the alveolar ridges. This is the first study that has compared the bone quality of the edentulous anterior median-palate and maxillary premolar bone region of an elderly population using μCT scans.

Analysis of bone morphology and density provides useful information regarding bone quality, quantity, geometry and phenotypes of the skeleton (Pearson & Lieberman 2004; Bouxsein et al. 2010). Feldkamp et al. (1989) directly examined the three-dimensional bone structure in an in vitro model based on high-resolution computed tomography (CT) and introduced this technique in 1989. Micro-CT has the potential to overcome some of the limitations histomophometry generates. The exclusive characteristics and wide applications of μCT have made it the standard technique for quantifying bone architecture in animal and ex vivo models (Swain & Xue 2009; Bouxsein et al. 2010). There is no literature available which has compared the trabecular bone micro-architecture of the median-palatal bone with the respective premolar regions. However, the literature has discussed the bone histology and radiology of the median-palatal bone using histomorphometry, CT/CBCT, lateral cephalometric technique and occlusal radiographs (Table 1).

The difference in bone structure and morphology of maxillary and mandibular bone has been extensively discussed in the literature. Both compact and trabecular bone is affected by age but at different rates and with different starting times (Sharpe 1979). Stockmann et al. (2009) presented higher%BV/TV values (40–60%) in 10 human cadavers. This is probably due to the fact that the samples were harvested from younger cadavers (15–20 years of age). In terms of median-palatal bone height, the results of the present study are consistent with those of Henriksen et al. (2003) and Baumgaertel (2009). These authors studied dry human skulls and suggested that the optimum vertical height for mini-implants was the first premolar region. Most of these studies were in adolescents for the application of temporary orthodontic appliances (King et al. 2006; Kang et al. 2007; Männchen & Schätzle 2008). In the present study, the vertical bone height, 6–8 mm posterior to the incisive foramen, was found 7.6 mm, which is considered to be optimum for a wide-bodied implant to anchor a maxillary overdenture (Fig. 3).

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Figure 3. Illustration of a wide-bodied implant (red) in the median-palatal region (scanned image).

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Figure 4. Graphical representation of the comparison in bone micro-architecture of two regions of analysis (ROA-1 represents median-Palatine and ROA-2 represents maxillary premolar region of the cadaver) using Wilcoxon's signed rank test. The %BV/TV, Tb.N, Tb.Th and Tb.Pf in the median-palatal region showed better quality of bone as compared to the maxillary premolar site; however, the difference is statistically non-significant. (a) Bone volume fraction (= 0.06). (b) Trabecular number (= 0.07). (c) Trabecular thickness (= 0.25). (d) Trabecular separation showed significant difference between the two regions (= 0.040. (e) Trabecular separation factor (= 0.42).

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Denture design and the type and time-course of load borne by full dentures affect the pattern of bone resorption of residual alveolar ridges (Palla 1997; Carlsson 2004); it would therefore have been useful to know the clinical details of edentulism and prosthetic reconstruction for each of the donated bodies that we sampled. A limitation of our study was that details of the prosthodontic rehabilitation or treatment records for the bequeathed bodies were not accessible and could not be obtained. In New Zealand, bequest of bodies for anatomical study is governed by the Human Tissue Act 2008; medical and dental historical data for donated bodies are 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 influence the bone microstructure.

Our study aimed to investigate an alternate site for implant placement where atrophic maxillary ridges compromise the long-term success of oral implants. The μCT data provided an insight to the bone quality and vertical height in the anterior region of the median-palate. In our opinion, these data support the use of the anterior median-palatal region (6–8 mm posterior to the incisive foramen) as an alternate site for an implant placement in the oral rehabilitation of severely resorbed maxillary alveolar ridges.

Conclusion

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Conclusion
  7. Acknowledgements
  8. Conflict of interest
  9. References

The results indicate that the anterior median-palate is structurally superior to corresponding maxillary premolar region in elderly edentulous persons and could accommodate an implant placed to anchor an overdenture. The best site for a wide-body implant was established to be 6–8 mm posterior to the incisive foramen in elderly edentulous patients.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Conclusion
  7. Acknowledgements
  8. Conflict of interest
  9. References

This study was kindly supported by a grant from The New Zealand Dental Research Foundation. We would like to thank Mr. David Styles from the Department of Anatomy and Structural Biology, University of Otago for providing the human cadavers and Mr Matthew Blair for the graphic illustrations. Special thanks to Dr. Sobia Zafar for her statistical guidance and support. This article is dedicated to the participants who bequeathed their bodies to science, and we are truly indebted to them for their magnanimous final act.

Conflict of interest

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Conclusion
  7. Acknowledgements
  8. Conflict of interest
  9. References

The authors declare that they have no conflict of interest.

References

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  3. Material and methods
  4. Results
  5. Discussion
  6. Conclusion
  7. Acknowledgements
  8. Conflict of interest
  9. References
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