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Table of Contents
ORIGINAL ARTICLE
Year : 2011  |  Volume : 1  |  Issue : 2  |  Page : 64-74

Pre-evaluation of implant sites by Dentascans


1 Department of Oral Medicine and Radiology, MGV Dental College and Hospital, Panchavati, Nashik, India
2 Dr. D.Y. Patil Dental College and Hospital, Mahesh Nagar, Pimpri, Pune, India
3 Dental Surgeon, Maharashtra, India

Date of Web Publication30-Dec-2011

Correspondence Address:
Prashant P Jaju
7, Nilgiri Housing Society, Datta Mandir Stop, Nashik Road, Nashik - 422 101, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0974-6781.91282

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   Abstract 

Objectives: To study the efficacy of pre-evaluation of implant sites by Dentascans.
Materials and Methods: Twenty five patients between age groups of 15 -and 80 years requiring implant placement were selected for this study. The computed tomography (CT) scan machine used for this study was Siemens Somatom Sensation 64. This has multidetector technology with 32 detector array and 64 data channels. Dental software used was Syngo Dental CT 2006 A-W VB20B-W. Axial, paraxial and panoramic images obtained were evaluated for available ridge height and width at implant sites, proximity to maxillary sinus and inferior alveolar canal, easy identification of inferior alveolar canal, radiographic presence of bony concavities and density at implant sites.
Results: Dentascan was an effective software in pre-evaluation of available height and width at the implant sites. There was a co-relation between the available bone at the implant sites and region of jaw, sex and age of patients. Proximity to maxillary sinus and inferior alveolar canal was clearly demonstrated by Dentascans. Inferior alveolar canal was identified in 85.71% cases. Bony concavities were identified in 22.95% cases. Dentascans provide subjective evaluation of bone density in Hounsfield units (symbol HU).
Conclusion: Dentascans are a rapid, time saving, effective, safe and indispensable procedure in dental implantology. Dentascans determines the available bone at the implant sites accurately without any magnification or distortion that is observed in panoramic radiography. Osseous morphology variations like knife edge ridges, which cannot be demonstrated on conventional radiography, could be appreciated on Dentascans. Bony concavities may not be observed on panoramic radiography; Dentascans provide the opportunity to appreciate such details. Critical anatomical landmarks can be clearly demonstrated on Dentascans. Dentascans provide a subjective evaluation of the density at the implant site.

Keywords: Bone density, bone morphology, dental CT


How to cite this article:
Jaju PP, Suvarna PV, Subramaniam AV, Jaju SP. Pre-evaluation of implant sites by Dentascans. J Dent Implant 2011;1:64-74

How to cite this URL:
Jaju PP, Suvarna PV, Subramaniam AV, Jaju SP. Pre-evaluation of implant sites by Dentascans. J Dent Implant [serial online] 2011 [cited 2019 Dec 11];1:64-74. Available from: http://www.jdionline.org/text.asp?2011/1/2/64/91282


   Introduction Top


Conventional dental imaging techniques include periapical and panoramic views, which is taken for implant site evaluation; however, it loses the battle for its lack of perception in the third dimension. Buccolingual width, angulation, unanticipated bony undercuts, undulating concavity of the maxillary sinus cannot be visualized in these conventional radiograph techniques, and coupled with its inherent distortion factors, these techniques do not allow precise measurement of the available ridge height. [1],[2],[3],[4] Newer generations of radiologic technology like computed tomography (CT) provides better visualization of the jaws than other radiographic methods. Multislice spiral CT is a significant advance in the technology of X-ray computed tomography, which increases the speed of data acquisition. It involves simultaneous translatory movement of the patient while the X-ray source rotates, so that continuous data acquisition and archiving occurs as the entire volume of interest is scanned in a minimum time. Special algorithms allow multiplanar computer-reformatted two-dimensional (2D), three-dimensional (3D) and panoramic reconstructions. Dentascan is a dedicated post-scanning image evaluation software for the teeth and the jaw, which creates panoramic and paraxial views of the upper and lower jaw. Typical applications are pre-surgical planning for implants, information about the structure of the jaw bones and proximity to the critical anatomical structures at proposed implant sites like the mandibular canal, nasal cavity, incisive foramen, maxillary sinus. This technique provides a wealth of diagnostic information that is accurate, detailed and specific. The use of CT scans in conjunction with special reformatting software, Dentascan, readily meets the pre prosthetic imaging objectives i.e. identify disease, determine bone quality, quantity, implant position and implant orientation, and surpasses the short comings of conventional radiographic technique with detailed accuracy and reliability. James J. Abrahams, in his comprehensive review on dental CT, reiterated that the dental CT programs have been successfully used to evaluate implants, cysts, tumors and surgical procedures. They have created not only a new modality for viewing the jaw but also a new partnership between dentists and radiologists. [5] Advocates of cross-sectional imaging argue that this imaging provides essential information both anatomically and quantitatively and that in its absence, the implant would be placed at unfavorable angles making functional rehabilitation difficult. Rothmall L et al. (1988) studied that buccal and lingual bone heights may differ, resulting in inaccuracies with conventional radiographs. The reformatted CT view allows the surgeon to accurately evaluate available bone height and bone mineralization in all areas of the ridge. [6],[7]

This study was undertaken with the aim and objective of unraveling the importance and indispensable role of Dentascans in pre-evaluation of implant site.

The aim of this study was to examine the multi-planar assessment of maxilla and mandible for implant placement by Dentascans (a specialized CT image reformatting software).

Various objectives included were:

  1. To evaluate the available ridge height and width of the implant site and to categorize ridge sites for acceptable treatment modification.
  2. To identify and visualize proximity to maxillary sinus prior to implant placement and thereby categorizing treatment procedure.
  3. To identify and visualize proximity to mandibular canal prior to implant placement using the same criteria as in (b).
  4. To assess radiographically the presence or absence of bony undercuts.
  5. To assess the ease of identification of mandibular canal at the implant site.
  6. To measure the bone density Hounsfield units (symbol HU) value at the sites of implant placement.



   Materials and Methods Top


The selection of the patients was done randomly irrespective of sex, race, religion and socioeconomic status. The age group of the patients was kept between 15 and 80 years. Twenty five patients were included for this study. Patient reporting to outpatient department of the college or at the private clinics were clinically examined by taking detailed history to arrive at the clinical diagnosis. The CT scan machine used for this study was Siemens Somatom Sensation 64. This has multidetector (MDCT) technology with 32 detector array and 64 data channels, Mumbai, Maharashtra, India. Dental software used was Syngo Dental CT 2006 A-W VB20B-W. A consent form was signed by the patient after the complete explanation of the dental scan procedure. Dental CT slice was of 0.75 mm with reconstruction increment of 0.5 mm, along with an effective mAs of 90 and 120 kilovoltage. Image acquisition of 64 × 0.6 mm with rotation time of 1 s and slice collimation and width of 0.6 mm and 0.75 mm, respectively. During the procedure, the patient was placed in supine in the gantry, using a head holder, chin strap and sponges on either side of the head to prevent motion. The patient head was oriented in the center of the scan field with the use of lateral laser light marker for positioning. A lateral digital scout view was then obtained to define the upper and lower limits of the study and to determine if the scan plane was parallel to the alveolar ridge. In case of upper jaw, the angulation is along hard palate and in lower jaw it is along inferior border of mandible or the mandibular occlusal plane. Once the scan plane is corrected, 0.6 mm × 64 mm contiguous scans with pitch of 0.9 were obtained using a bone algorithm, 15 cm field of view, 512 × 512 matrix, 120 kV and 90 mAs. Axial images were acquired and then these images were processed with the dental CT reformatting program. Images were transferred on 14 × 17 inch size AGFA films, and these data were set to actual scale without magnification. The films were developed on Agfa Dry star 5300 processor. A scale was given against each image; which allows measurement using our routine measurement scale and confirms measurements on film. These data sets were also available to be viewed on any PC as these data are burned with DICOM reader.

Measurement of the height and width of the available alveolar ridge

Measurement was done both on the life-size images obtained on the films and on personal computer from the compact disk with help of vernier caliper. For maxillary anterior region, the height of the available ridge was calculated from the crest of ridge to inferior border of nasal fossa. For maxillary posterior region, the height of the ridge was calculated from the superior border of crest of ridge to the inferior border of maxillary sinus. For mandibular anterior region, the height of the ridge was calculated from the crest of ridge to inferior border of mandible. For mandibular posterior region, the height of the ridge was calculated from the crest of ridge to superior border of inferior alveolar canal. Buccolingual width of the ridge was calculated from the inner buccal and inner lingual cortical plates from the crest of ridge [Figure 1].
Figure 1: Measurement of height, width and density at the implant sites

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Visibility of mandibular canal

At the implant site, the visibility of the mandibular canal was interpreted and graded into three groups.

0. Mandibular canal could not be identified.

1. The mandibular canal was visible, but had diffuse borders.

2. The mandibular canal was clearly visible.

Evaluation of bone density

Dentascan software provided the means for assessing the subjective evaluation of available bone density at the implant site. This was done only on the computer with help of pixels tools present in the software. A circle was formed at a height of 7 mm from the crest, touching both the inner buccal and palatal/lingual cortical plates. [8]

After the formation of circle, with the help of software, a circle histogram was plotted, which demonstrated the minimum and maximum pixel values. Along with it a standard deviation was also given. So the minimum and maximum values were recorded. They were divided into five subdivisions based on HU values.

Bone density based on HU values given by Misch: [8]

D1: >1250 HU

D2: 850-1250 HU

D3: 350-850 HU

D4: 150-350 HU

D5: <150 HU

Proximity to maxillary sinus

Proximity to the maxillary sinus at the proposed implant site was measured according to the criteria given by Misch [Table 1]. [8]
Table 1: Criteria for proximity to maxillary sinus

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Proximity to inferior alveolar canal

Similar criteria as above were used to evaluate the proximity to the inferior alveolar canal [Table 2].
Table 2: Criteria for proximity to inferior alveolar canal

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Division of available bone

Depending upon the available height and width at the proposed implant site, availability of bone was divided into four categories according to the classification given by Manuel Chanavaz, a French professor who presented volumetric bone classification at Paris in 1986 [Table 3]. [9]
Table 3: Chanavaz and Donazzan French volumetric classification

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Statistical analysis and computation procedures were performed. Data collected was entered into MS-Excel worksheet and use of statistical package for social sciences (SPSS) software was done and results were represented in the form of tables and graphs. The results were expressed in the form of number and percentages for the following objectives:

  1. Available bone at the implant sites would be correlated with the zone in the jaw, followed by its correlation with the sex and age groups of the patients.
  2. Proximity to the maxillary sinus and inferior alveolar canal.
  3. Visibility of the mandibular canal.
  4. Presence of radiographic bone concavities at the implant sites.


Mean (minimum and maximum) density of the bone at the implant sites would be correlated with the sex of the patients, individual jaw and zone in the jaw, independent 't' test would be applied and 'P' value would be determined at 95% confidence limits. Also mean (minimum and maximum) density of the bone would be evaluated according to the side of the jaw and ANOVA test would be applied followed by Turkey test.


   Results Top


Available bone type at implant sites

This study revealed a total of 61 implant sites in 25 patients. Depending upon the available height and width at the proposed implant sites, it was divided into four categories based on Manuel Chanavaz's French volumetric classification.

Relationship between available bone type at implant sites and anterior/posterior region of jaw

Study revealed a total of 16 sites of type A bone (26.22%); 39 sites of type B bone (63.93%) and 6 sites of type C bone (9.83%). Maxillary anterior region revealed a combination of type A and type B bone whereas mandibular anterior region had type B and type C bone. A total of 48 implant sites were present in posterior region. The maxillary posterior region had more type A bone (20%) followed by type B bone (16.66%) and type C bone (2.08%). Mandibular posterior region showed more type B bone (50%) followed by type A bone (8.33%) and type C bone (2.08%) [Table 4].
Table 4: Relationship between available bone at implant sites and anterior/posterior region of jaw

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Relationship between available bone type at implant sites and sex of the patient

The results showed interesting values. Both the sexes had type A, B and C bone without type D bone. Male and female patients both had maximum type B bone at the implant sites. But male patients had greater implant sites of type A bone while female patients had more of type C bone [Table 5].
Table 5: Relationship between available bone type at implant sites and sex of the patient

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Relationship between available bones according to age groups

With increasing age the nature of available bone changed from type A to type C bone.

Younger age group patients i.e. between 15 and 20 years had type B bone but thereafter there was a combination of type A and type B bone. Only one site of type C bone was present before the age group of 50 years. Beyond 50 years of age there were five implant sites of type C bone. Maximum implant sites belonged to type B bone (63.93%) followed by type A bone (26.22%) then by type C bone (9.83%).There was no type D bone present [Table 6].
Table 6: Relationship between available bone according to age groups

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Proximity of the maxillary posterior implant sites to the maxillary sinus

Out of 12 maxillary posterior implant sites, 10 implant sites belonged to Subantral (SA) SA1 group (83.33%). In these sites conventional implant procedure was recommended. Remaining 2 maxillary posterior sites belonged to SA3 group (16.66%). Here the height was between 5 and 10 mm from the floor of the maxillary sinus. Sinus lift procedure was recommended prior to implant placement [Table 7].
Table 7: Proximity of the maxillary posterior implant sites to the maxillary sinus

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Proximity of mandibular posterior implant sites to the inferior alveolar canal

There were in total 28 mandibular implant sites. But in case number 5 there was removal of mandible due to tumor and was replaced by iliac bone graft. Hence only 27 implant sites are considered. Twenty three implant sites (85.18%) had height beyond 12 mm from the superior surface of the canal. Three implant sites (11.11%) were between 10 and 12 mm from the mandibular canal. Only one implant site (3.70%) were between 5 and 10 mm from the mandibular nerve. No implant site height was less than 5 mm from the canal [Table 8].
Table 8: Proximity to mandibular posterior implant sites to the inferior alveolar canal

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Visibility of mandibular canal

In 28 mandibular posterior implant sites, visibility of canal was assessed. Canal was not visible in two sites (7.14%). But in this group, case number 5 was included wherein iliac bone grafting was done, subsequently canal was not visible. So effectively there was only one site at which the canal was not visible. In two implant sites (7.14%), the canal was diffusely visible. In 24 implant sites (85.71%), the canal was clearly visible [Table 9] [Figure 2].
Table 9: Ease of visibility of mandibular canal

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Figure 2: (a) Canal not visible, (b) Canal diffusely visible, (c) Canal distinctly visible

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Presence of bony concavities at implant sites

Out of 61 implant sites, bony concavities were present in 14 implant sites (22.95%). Ten concavities were present in mandibular implant sites and only four concavities were present in maxillary implant sites. In 47 implant sites no concavities were present [Figure 3].
Figure 3: Presence of bony concavities

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Bone density values in Hounsfield units at implant sites

There were totally 61 implant sites that were assessed. No implant site belonged to D1 category. D2 category had two implant sites, with a maximum mean value of 1134 HU. D3 category had the maximum implant sites. A total of 46 implant sites were present in this category. In this category the HU value ranged from 350 to 850 HU. The highest value in this category was 799.5 HU, while the lowest value was 354 HU. D4 category had total of 10 implant sites with lowest value of 156 HU and highest value of 341.5 HU. D5 category had a total of 3 implant sites with a lowest value of 124.5 HU and highest value of 146.5 HU [Table 10].
Table 10: Bone density at implant sites in Hounsfield values

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Density and the relation of sex of the patients

A total of 25 patients were present in which 13 were males and 12 were females. In females the minimum mean density was 6.8750 HU with a standard deviation of 198.1502. In males the minimum mean density was -48.3846 HU and standard deviation of 151.7015 HU. In females the maximum mean density was 1063.37 HU with a standard deviation of 294.4543. In males the maximum mean density was 975.6262 HU with a standard deviation of 274.9293. 'P' value revealed that there was no significant correlation between maximum and minimum density in both the sexes [Table 11].
Table 11: Maximum and minimum bone density according to sex of the patient

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Relationship between the bone density at implant sites and jaws, bone density correlation with zone of implant placement in the jaws and relationship between side of jaw for implant placement and bone density is shown in [Table 12], [Table 13] and [Table 14].
Table 12: Maximum and minimum mean bone density relating to the jaw

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Table 13: Bone density at implant sites according to zone in the jaw

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Table 14: Minimum and maximum bone density according to side of the jaw

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   Discussion Top


The present study was carried out on 25 completely or partially edentulous patients. Patients wanted to replace their teeth with implant placement.

A thorough case history and clinical examination of the patients was conducted and then a pre-evaluation of the implant site was performed using special reformatting software (Dentascan) on Siemens Somatom Sensation 64, CT scan machine. This study was undertaken with the main aim of understanding the competency and efficacy of Dentascan software and its usefulness in pre-evaluation of the proposed implant site.

Present study evaluated the available ridge height and width at implant sites, its proximity to maxillary sinus, nasal cavity and inferior alveolar canal.

Also the presence of concavities, which could not be detected clinically or on conventional imaging were noted. Finally the density of the available bone at the implant sites was also studied.

Height and width available at the implant sites

Available bone is the amount of bone in the edentulous area considered for osseointegration of the implant. As a general guideline, a distance of 1.5 mm is maintained for surgical error between the implant and any adjacent landmark.

Based on Chanavaz French Volumetric bone classification (1986), the available bone height and width was divided into four categories i.e. category A, B, C and D. Study revealed a total of 61 implant sites comprising of 16 sites of type A bone (26.22%); 39 sites of type B bone (63.93%) and 6 sites of type C bone (9.83%).No type D bone was present in this study.

[Table 4] showed the relationship between the available bones at the implant site in the anterior/posterior region of the jaws. Maxillary anterior region showed two implant sites of type A bone while mandibular anterior did not show any. Type C bone which included inadequate bone for implant placement was seen in four mandibular anterior implant sites (30.76%). Female patients with age above 70 years in completely edentulous mandible showed type C bone in the anterior region taking in consideration the basic architecture of the bone in this region. The changes in anterior maxilla ridge dimension can be very dramatic both in height and width i.e. up to 70% especially when multiple extractions are performed. [10] The residual ridge shifts palatally in the maxillary and lingually in the mandible as related to tooth position at the expense of buccal cortical plate in all areas of jaw. [11] In posterior implant sites, type A bone was present at 10 implant sites in maxillary jaw and only 4 implant sites in mandibular jaw. This may be attributed to early loss of mandibular molars. Atrophy of the maxillary arch proceeds at a slower rate than in the mandible. The posterior mandible resorbs approximately four times faster than the anterior mandible. The original height of available bone in the mandible is twice that of maxilla. [12] Type D bone was not seen in any of the implant sites. Panoramic images are 2D views and cannot demonstrate the buccolingual width of the alveolar ridge. Dentascan provides a 3D environment to visualize the buccolingual width of the alveolar ridge. In patients with triangular-shaped cross-section, osteoplasty was advised to obtain greater width of bone, although of reduced height. This rule was not applied in anterior maxilla as most edentulous ridges exhibited a labial concavity in the incisor area resulting in a hour glass configuration. For every 0.5 mm increase in width there is an increased surface area ranging between 10 and 15%. Since the greatest stresses are concentrated at the crestal region of implant, width is more significant than the length for an implant design. Buccolingual ridge pattern cannot be viewed on 2D radiographs, but Dentascan provides with advantage of appreciating the type of alveolar ridge pattern present. Similarly loss of cortical plates was seen in paraxial images, which cannot be seen on conventional radiography. [13] Following rapid initial resorption the rate decreases and then continues at about 0.1 mm per year in male and about 0.4 mm per year in female. [Table 5] showed relationship between the sex of the patients and the available bone type at implant sites. According to the findings, type A bone was seen in 13 implant sites in male patients (81.25%) and only 3 (18.75%) implant sites were present in female patients. This can be attributed to the decreased estrogen level in female patients. A total of 4 female patients were above the menopause age. Females are more prone to osteoporosis and subsequently there is faster resorption of bone. Hence adequate height and width may not be present. Female patients had 4 type C bone (66.66%) whereas only 2 male patients had type C bone (33.33%).

The age-associated bone loss is about 1% in women and 0.5% in males annually. Women represent a greater percentage of patients with residual ridge resorption than men. [Table 6] showed relationship between age groups of the patients and type of available bone at implant sites. In younger age group (10-20 years), lower anterior implant sites were considered for implant placement. Dentascan revealed knife-edged ridge pattern with bone having decreased bone density, which was not appreciated on panoramic view. Trabecular pattern were decreased with only few horizontal trabeculae. Available bone in this peculiar case belonged to type B.

Maximum implant sites over a wide age group belonged to type B (63.93%). This was due to delay in replacing the teeth following its loss. Hence resorption took place in this interim period. Beyond age group of 50 years, five implant sites showed type C bone reiterating the fact that prolonged loss of teeth without replacement cause disuse atrophy of alveolar bone. Literature states that the decrease in bone begins in the fourth decade and is linear. [13] Type C bone was present in patient who underwent iliac graft augmentation following surgical excision of tumor. There was only one implant site showing type A bone as observed in maxillary anterior region. Patient was a denture wearer and hence it can be considered that resorption had been slowed down due to functional stimulation. Amount of bone loss occurring the first year after the tooth loss is 10 times greater than the following years. [14] Although atrophy of the maxilla is generally not as pronounced as that of the mandible, narrowing of ridges in a buccolingual direction may present a problem for implant placement. Bone is also not as dense in the maxilla as in the mandible and Dentascan allows precise preoperative evaluation of these structures. This study reiterates the point that cross-sectional reformations provide the best assessment of the shape and contour of the ridges as believed by Rothman et al. [7] Similarly, Mcginvney et al. and Schwartz et al. concluded that Dentascan images more accurately reflected the true osseous topography and considered it as a valuable diagnostic aid. [15],[16] In case of compromised jaw bone, in terms of quality and/or quantity of bone, the panoramic technique is an inefficient imaging tool. This dictates additional imaging in 2D/3D, especially when there is risks and doubts about treatment outcome, Dentascan may prove indispensable.

Dentascans is the modality of choice in the evaluation of diseases of nose and paranasal sinuses. Pathoses appeared as mucosal thickening and it was diagnosed preoperatively and treatment could be provided prior to implant placement. Mucosal thickening in the maxillary sinus was seen clearly on Dentascans [Figure 4]. Dentascan provides information regarding the cortical bone in the floor of the nasal cavity and maxillary sinuses prior to implant placement. Proximity to maxillary sinus of the implant sites was assessed using Dentascan software. According to the height criteria given by Misch, four groups were formed and subsequently the implant sites were advised SA treatment option [Table 7]. Twelve maxillary posterior implant sites were assessed, 83.33% belonged to SA1 treatment option, which is conventional division A root form placement. 16.66% implant sites belonged to SA3 treatment option, which includes lateral wall approach sinus graft with delayed division A root from implant placement. Dentascans are expensive investigation but provides a 3D information at an early stage with precise measurement and exclude patients not suitable for implants for technical reasons and thus save time and money both for the patient and the surgeon. Thus Dentascans of the upper alveolar process justifies its place in the pre-surgical evaluation of the edentulous patient who is in need of implants. [17]
Figure 4: Insufficient height available, sinus lift required

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Inferior alveolar canal is the deterministic factor for implant placement in the mandibular posterior region. During treatment planning prior to mandibular implant surgery, it is important to determine the location of the mandibular canal. In the application of an implant system to the partially edentulous distal portion of the mandible, the inferior alveolar nerve is a vital anatomic structure that must be avoided.

Canal may not be visible on conventional radiographic methods; it is probably related to the fact that the inferior alveolar neurovascular bundle is not always surrounded by an ossified canal. The bony sheath seems to disappear anteriorly toward the mental foramen. Similarly, in edentulous patients, the diameter of the artery is smaller compared to dentate patients and hence the visibility of the canal may be affected. [18]

The mandibular nerve may course diagonally from a lingual location posteriorly to a buccal location in the area of the mental foramen. The neurovascular bundle may loop downward, forward and medially before exiting from the foramen in a posterior-superior direction. In older edentulous patients with resorbed ridges the foramen was near and in some cases emerged on the alveolar crest.

Routine radiographs provide information only about the distance of the inferior alveolar canal from the alveolar crest but are unable to delineate its buccolingual dimension. The buccal-lingual position of the nerve can only be seen in either axial or cross-sectional views of the mandibular ridges. Paraxial slices provide consecutive sections, which depicts the course of the inferior alveolar nerve up to the mental foramen and beyond it. Visibility of the mandibular canal was assessed on cross-sectional images of Dentascans. Out of 28 mandibular posterior implant sites, in two cases canal was not visible (7.14%). In two implant sites (7.14%), mandibular canal was diffusely visible. Both sites were in male patients above age group of 40 years. This may be due to the fact that with increasing age there is decrease in cortication around the mandibular canal. In 85.71%, the canal was distinctly visible on the cross-sectional images of Dentascans [Table 9].

In the present study the mandibular posterior implant sites were present in 15 patients. The findings of this study were consistent with work done by Klinge et al., [18] Lind et al., [19] Todd et al., [20] and Sonick et al., [3] which emphasized that mandibular canal is best demonstrated on Dentascans. Dentascans does not produce any magnification as compared to panoramic radiography. Hence accurate measurements are possible from the canal. In 85.18% (23 implant sites), it was found that the canal was situated at a distance greater than 12 mm from the crest of the ridge. In 11.11% cases (3 implant sites), the canal was placed between 10 and 12 mm distances from the crest of the ridge and only 3.07% cases i.e. single implant site was present at a distance between 5 and 10 mm [Table 8].

The detection of mandibular canal is more difficult with increased slice thickness and slice interval with reduced tube current. [21 ] Present study clearly detected the mandibular canal by changing the above parameters. Visualization of the location of mandibular canal in posterior mandibular region is of paramount importance for implant placement. There were times when portions of the canal or even the entire canal may be difficult to visualize on the cross-sectional images. In this situation the following methods were helpful in locating the canal. On panoramic radiographs, the appearance of the mental foramen changes with the positioning of the mandible in the focal trough. Increased film density increases the difficulty in detecting the mental foramen. It is suspected that it might not be true mental foramen but a portion of the mental canal after it leaves the mandibular canal. [22]

In all patients who underwent scan for mandibular arch showed mental foramen in the paraxial images. The mental foramen exited on the buccal cortical plates except for a single patient in whom it exited on the alveolar ridge This study thus demonstrates that Dentascans is the radiographic method of choice to depict mental foramen. Presence of bony concavities alters the pathway of implant placement. Its presence warns the surgeon to alter the orientation of implant to avoid cortical plates' perforation and be ready with augmentation procedures. Conventional radiography cannot predict the presence of bony undercuts/concavities. Dentascans detects these concavities clearly and helps the surgeon in planning the treatment. In 14 implant sites (22.95%) concavities were detected radiographically. Ten implant sites were present in mandibular region and only 4 implant sites were present in maxillary region. In remaining cases the concavities were absent.

Bone density at implant sites

Density of available bone in an edentulous site is a determining factor in treatment planning, implant design, surgical approach, healing time and initial progressive bone loading during prosthetic reconstruction. Literature suggests that the anterior mandible has greater bone density than the anterior maxilla. The posterior mandible has poorer bone density than the anterior mandible. The poorest bone quality in the oral environment typically exists in the posterior maxilla and it is associated with dramatic failure rates. Periapical or panoramic radiographs are unhelpful when determining bone density because the lateral cortical plates often obscure trabecular pattern. In addition the more subtle changes of D2 to D3 cannot be quantified using these radiographs. CT is currently the only diagnostically justifiable imaging technique that allows at least rough conclusion about the structure and density of the jaw bones. Bone density can be evaluated using Hounsfield units (HU), which are directly related to tissue attenuation coefficients. The Hounsfield scale is based on density values for air, water and dense bone, which are assigned arbitrarily values of −1000, 0 and +1000, respectively. Techniques such as histomorphometry of bone biopsies or densitometry, quantitative ultrasound, dual photon absorptiometry, quantitative computed tomography, although reliable, and quantitative measures of bone density are not routinely feasible for the practice of implant dentistry. The most critical region of bone density is the crestal 7 to 10 mm of bone. This determines the treatment protocol. [8] In the present study, bone densities were divided into five categories based on HU values. 75.40% values were in D3 group, 16.39% in D4 group, 4.95% in D5 and 3.27% in D2 group. Highest mean HU value was 1134 [Table 10]. Highest mean HU value in anterior maxilla was 727.5 while in anterior mandible it was 1134. Similarly highest mean HU value in posterior maxilla was 781 and in posterior mandible it was 764.5. The HU value in this study ranged from −233 to 2146. It is possible that higher HU values were reported because of slight inclusion of cortical plates. Statistical analysis did not show any significant relationships between HU values and demographic data like gender, jaw, side and zone in the arch [Table 11], [Table 12], [Table 13] and [Table 14]. These findings are consistent with similar study done by Shapurian et al. [23] However, in their study significant difference of P <0.001 was observed in the anterior and posterior values. Previous studies using different approaches have shown discrepancies linked to hormonal factors and masticatory muscle strength. Kribb et al. failed to show an age-related difference in mandibular bone mineral density between normal and osteoporotic women. [24] Only a single study conducted by Shapurian et al. evaluated the bone density using the Hounsfield scale in relation to age and gender. [23] It is important to note that based on the limited information available from the dental implant and orthopedic literature there is no absolute contraindication for implants in osteoporotic bone. [25] The density decrease in the jaws is related to the length of time the region has been edentulous and not loaded appropriately. Dentascans provide the clinician with Hounsfield values as an objective method of evaluating bone density for a proposed implant site. Haldun et al. advocated use of CT for determining bone quality and quantity. [26] Absolute guidelines on these HU values cannot be provided as the density observations will be scanner dependent and vary according to the particular exposure settings and window level applied. It is obvious that HU variation observed in the same jaw scan reflect local bone density variations with lower HU values for poor bone quality. [27] Variability in values can alert the surgeon to modify the treatment plan so that primary stability in bone of less density is ensured and a longer healing period can then be planned. [28]

Radiation dose

Dentascan gives a radiation dose of 14.10 mGy for a total scan period of 7.98 s at 90 kV and 120 mAs. This radiation dose is comparatively less compared to radiation dose give by dental CT in the past where values above 200 mGy was calculated. [29],[30],[31],[32] This radiation dose can be further reduced by decreasing the kilovoltage, milliampere seconds, and increasing the slice thickness. The disadvantage of changing these parameters would be that it would decrease the image resolution thereby affecting the image quality. Conventional radiographic techniques have a low radiation dosage but they do not furnish the osseous details as impeccably as Dentascans do and so by providing such accurate details it increases the success rate thereby reducing the chances of failure of implants. Additional information gained from Dentascans were about cystic lesions in the jaw, relation of impacted lower third molar with inferior alveolar nerve and pathologies of maxillary sinus.


   Conclusion Top


Successful implant imaging must be individualized to the particular needs of each patient and must recognize that the imaging as well as the implant process is prosthetically driven. When adequate bony support is not available it is usually possible to modify or augment the chosen site. The choice of an imaging modality to evaluate the implant sites should be weighed carefully. It is a disservice to the patient to use or recommend imaging tests based on only considerations of radiation dose, cost. Dentascans are a rapid, time saving, effective, safe and indispensable procedure in dental implantology. Dentascans determined the available bone height at the implant sites accurately without any magnification or distortion which is observed in panoramic radiography. Buccolingual width of the available ridge is determined by Dentascans. Osseous morphology variations like knife edge ridges, which cannot be demonstrated on conventional radiography could be appreciated on Dentascans.

Bony concavities may not be observed on panoramic radiography, Dentascans provides the opportunity to appreciate such details. Critical anatomical landmarks can be clearly demonstrated on Dentascans. Bone density at the implant sites dictates the successful osseointegration of the implants. Dentascans provides a subjective evaluation of the density at the implant site.

Technological advances have resulted in the development of clinically relevant and state of the art CT techniques. Further advances will undoubtedly improve medical imaging so that a consistent level of image quality and reproducibility can be attained. New and improved algorithms may offer the clinicians a wide range of options for patient examination. As the technique becomes more widely acceptable, a probable reduction in cost should be anticipated. In the present scenario, Dentascans provides more precise information than conventional radiographic techniques so that the patient is placed at minimal risk in the reconstruction of completely or partially edentulous jaws. With the continued research the disadvantages of Dentascans should be minimized, enhancing patient comfort, further decreasing radiation dose, scanning time and cost factor.

Hence, in nutshell it can be concluded that the vision of the third eye gifted to us by Roentgen enlightens the pitfalls and the abyss of complications, which a clinician can entangle himself in this blind procedure of implant dentistry if he has not taken the help of newer generations of advanced imaging modalities in Radiology.

 
   References Top

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3.Sonick M, Abrams J, Faiella RA. A comparison of the accuracy of periapical,panoramic, and computerized tomographic radiographs in locating the mandibular canal. Int J Oral Maxillofac Implants 1994;9:455-60.  Back to cited text no. 3
    
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7.Rothmall SL, Chafetz N, Rhodes ML, Schwartz MS. CT in the preoperative assessment of the mandible and maxilla for endosseous implant surgery. Radiology 1988;168:171-5.  Back to cited text no. 7
    
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9.Chanavaz M, Donazzan. Maxillo-mandibular bone reconstruction and implantology bone and biomaterials. French classification of available bone for implantology. Paris: The book of 30 th Congress of Stomatology and maxillofacial Surgery; 1986. p. 189-204.  Back to cited text no. 9
    
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32.Clark DE, Danforth RA, Barnes RW, Burtch ML. Radiation absorbed from dental implant radiography: A comparison of linear tomography, CT scan, and panoramic and intra oral techniques. J Oral Implantology 1990;16:156-64.  Back to cited text no. 32
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11], [Table 12], [Table 13], [Table 14]



 

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