Assessment of Dental Implant Site Dimensions And Alveolar Bone Density in The Mandible Using Cone Beam Computed Tomography

Background: The quantity and the quality of available bone, influence the clinical success of dental implants surgery. Cone beam Computed tomography is an established method for acquiring bone images before performing dental implant. Cone beam computed tomography is an essential tool for treatment planning and post-surgical procedure monitoring, by providing highly accurate 3-D images of the patient's anatomy from a single, low-radiation scan which yields high resolution images with favorable accuracy. The aim of study is the Measurement of alveolar bone (height and buccolingual width) and density in the mandible among Iraqi adult subject using CBCT for assessment of dental implant site dimensions. Material and method: The study sample include (60) Iraqi subjects (30 male and 30 females) aged between 20-65 years, sagittal view of Cone beam computed tomography was obtained to measure the height ,width and alveolar bone density of the mandibular anterior area, while coronal view was used to measure the height ,width and alveolar bone density assessment of the mandibular premolar and molar areas. Measurement of mandibular bony height and width was in(mm)and each of the three mandibular areas were represented by seven consecutive measurements for bony height and width and these seven stations were set using an average distance of 2 mm apart while the bone density in Hounsfield unit (HU) with point of measurement represent the mean of density to the area located between the height and buccolingual width. Results:The Statistical analysis of linear measurements of mandibular bone which include the bony height , width and density showed that the mean values of all three measurements are significantly higher in males than females also there was statistically significant difference in the mean bone density of mandibular areas which was highest in anterior area and lowest in the molar area followed by premolar area among both gender, mandibular bony height showed a statistically insignificant very weak negative linear correlation with age in all the three examined mandibular areas while the effect of age on bucolingual width was significantly higher among subjects older than 50 years compared to those younger than 50 years old. Conclusion: The mean bony height was highest in anterior area and lowest in premolar area followed by molar area, while the mean bony width was lowest in anterior area and highest in molar area followed by premolar area , finally the mean bone density was highest in anterior area and lowest in molar area followed by premolar area.


INTRODUCTION
Provision of dental implants for patients who have lost their teeth is a common practice.Anatomic structures and the surrounding bone must be assessed both clinically and radiographically before placing implants. (1)resurgical dental implant planning requires specific and accurate data to assess the implant site so that dental implants can be placed where they have the greatest chance of success.Anatomic considerations such as determination of bone height and width, determination of bone density, identifying and localizing internal anatomy, determining jaw boundaries, and detecting pathologies are the principal determinants in selecting an optimal implant site. (2)ne quantity can be defined as the amount of bone height and the width of the alveolar crest at an edentulous site.Areas of lesser bone quality have higher failure rates and weaker primary stability values. (3)The introduction of CBCT, in 1998, provided a new form of 3D evaluation, and several studies have shown that CBCT provides high quality, accurate cross-sectional images with low dose exposure. (4,5)CBCT has proven to capture structures with high contrast, have excellent image acquisition of such structures as the inferior alveolar nerve canal, and has proven more reliable than medical CT (6) .In the current study the dental implant site dimensions were evaluated including the height and width of the mandible with the measurement of alveolar bone density using CBCT.

MATERIAL AND METHOD:
A

RESULTS
The mean of these seven measurements would be un-biased estimate of the bony height and width in each of the three areas.The errors in each measurement station of bony height and width ranged between a maximum decrease or increase of 0.1 mm.These errors were unbiased since their mean was zero.In addition, the average coefficient of variation for these errors reached a maximum of 0.5%, which is very small and can

Vol. 30(2), June 2018 Assessment of
Oral and maxillofacial Surgery and Periodontics 36 be neglected.

Comparison between anterior, premolar and molar areas. 1.Bony height
The mean bony height was highest in anterior area (17.2 mm) and lowest in premolar area (13.2 mm) followed by molar area (13.5 mm).The effect of changing from anterior to premolar area with average reduction of 4 mm in bony height, which is evaluated as a strong effect Similarly, the molar area was less in bony height by an average of 3.7 mm compared to anterior area, which is also a strong effect.Finally, the change observed in bony height when moving from premolar to molar area is of 0.3 mm, which was of small effect size.Table 1.

2.. Bony width:
The mean bony width was lowest in anterior area (5.5 mm) and highest in molar area (7 mm) followed by premolar area (6.1 mm).The effect of changing from anterior to premolar area is with a mean increase of 0.6 mm in bony width, which is evaluated as a moderately strong effect.The effect of moving from anterior to molar area was a strong one and associated with a mean increase in bony width of 1.5 mm.Similarly, the molar area was associated with a higher mean bony width compared to premolar area by an average of 0.9 mm, which was also evaluated as a moderately strong effect.Table 2.

Bone density:
The mean bone density was highest in anterior area (931.3HU) and lowest in molar area (571.8HU) followed by premolar area (730.6 HU).Table 3.

Effect of gender on the bony height:
The mean bony height was obviously higher among males compared to females in all the 3 areas examined.The effect of gender was evaluated as a strong one (Cohen's d>0.8) in the anterior area.The gender effect in premolar and molar area was evaluated as a moderately strong effect.Table 4.

Effect of age on the bony height:
The mean bony height showed no obvious or statistically significant difference between subjects <50 years old and those older in both premolar and molar areas.No association was examined among subjects in the anterior area, since none of them were younger than 50 years of age.Table 5.
Effect of gender on the mean bony width : The mean bony width was obviously higher among males (6 mm) compared to females (5.1 mm) among subjects in the anterior area group, and was evaluated as a strong effect .The gender effect on bony width in premolar and molar area was evaluated as a moderately strong effect.In these two areas males had a slightly lower mean bony width than females.Table 6.
Effect of age on the mean bony width: The mean bony width was higher among subjects older than 50 years compared to those younger than 50 years old in the premolar and molar areas.No association was examined among subjects in the anterior area, since none of them were younger than 50 years of age.Table 7.

Effect of gender on bone density:
The mean bone density was significantly higher among males (1144.7 HU) compared to females (717.8HU) in the anterior area group.The effect of gender was evaluated as a strong one in the anterior area.The effect of gender was very small in the premolar area.Finally, the gender effect in molar area was evaluated as a moderately strong effect (Cohen's d between 0.3 and 0.8).Table 8.

Effect of age on bone density:
The mean bone density was slightly higher among older age group in the premolar a and molar area.Table 9.

DISCUSSION
Prior to implantation, an investigation of the planned implant site is required to visualize the available bone and surrounding anatomical structures and augmented areas that could be affected.For this process, CBCT data is critically important in planning for the insertion of not only single implants, but also in the surgical treatment planning for multiple implants.(7).
 comparison between (anterior, premolar and molar) area.1-Bone height :According to present study in table (1), the mean bony height was highest in anterior area and lowest in premolar area followed by molar area.this result is similar to that reported by Mercier et al (8) that found the residual ridge resorption is usually more rapid in the premolar and molar region than the anterior region of the mandible because of the lower position of the reversal line in the posterior region.
2-Bone width : as shown in table(2) the mean bony width was lowest in anterior area and highest in molar area followed by premolar area.These results agree with many authors (9,10,11) 3-Bone density: In this study, the mean bone density was highest in anterior area and lowest in molar area followed by premolar area as demonstrated in table (3) ,this result agree with Norton and Gamble (12) recorded that the mean bone densities in the anterior mandible was (970) HU and the posterior mandible was(669)HU. (12)he effect of gender on bony height, width and density.
In the present study as shown in table(4) the mean bony height was obviously higher among males compared to females in all the 3 areas examined.In the study done by Ortman et al (13) reported that the decrease in the height of the edentulous mandible was more pronounced in female than in male. (13),this result agree to what reveled by the present study.From the results shown in table(6), the mean bony width was obviously higher among males compared to females among subjects.Sandring et al (14) who state that there's no significant differences in bone width were determined between ethnic and age groups and, in spite of a normal anatomical trend for thicker male than female bone.the mean bone density was significantly higher among males compared to females in as shown in table (8), this result is similar to that found by many authors that found the bone density is more in males than females. (15,16,17)ffect of age on the bony height ,width and density: In the present study in table (5), the bony height showed a statistically insignificant very weak negative linear correlation with age in all the three examined mandibular areas, such findings come in agreement with Güler et al ( 18) .From the results shown in table(7) the mean bony width was significantly higher among subjects older than 50 years compared to those younger than 50 years old in the premolar area.
In the molar area, the mean bony width showed no obvious difference between the two age groups.Allen et al., 2007 (19) In the present study as shown in table(9) the mean bone density was slightly higher among older age group in the examined areas .But this result disagreed with that found by Froum et al (20) who stated that there was a decrease in bone density of jaws which was more pronounced in the 70-74 years age.this disagreement may be due to differences in sample size.
In conclusion the mean bony height was highest in anterior area and lowest in premolar area followed by molar area, while the mean bony width was lowest in anterior area and highest in molar area followed by premolar area, and the mean bone density was highest in anterior area and lowest in molar area followed by premolar area.The effect of age on bony height showed no obvious or statistically significant difference between subjects <50 years old and those older, Male gender was associated with a statistically significant increase in bony height compared to females.The effect of age on bony width was as strong as that changing the mandibular area examined from anterior to premolar and molar .being on older age (+ 50 years old) is associated with a statistically significantly increase in bony width compared to younger age group less than 50 years old.Male gender associated with bony width higher than females.The effect of age on bone density was as strong as that changing the examined area from anterior to molar.being an older age is associated with statistically significant increase in bone density when compared to younger age ,Male gender associated with bone density higher than females.

( 1 )
Master student (2) Assistant Professor, Department of oral Diagnosis, College of Dentistry, University of Baghdad.