Its Clinical Significance on Guiding Implant Restoration

Mingxu Sun1Fang Gu1Hongwei Qin1Chenyuan Zhou1Jianjun Yang

（1Qingdao university medical college266000；2The affiliated hospital of Qingdao university266000）【Abstract】Purpose： Provide reference basis for the clinical implant restoration to select implant diameter through measuring each data of 7 teeth in the dental neck of bilateral upper and lower jaws of the young volunteers with normal dentition.

Methods： Select 30 healthy young volunteers with complete dentition but no malocclusion， take cone beam CT （CBCT）， apply mimics 10.0 to measure the mesiodistal and buccolingual distance of the tooth root at 1.5mm from 14 teeth （bilateral upper and lower jaws） to alveolar crest， adopt Photoshop CS3 to trace out the outline of each tooth neck in this layer， calculate the cross sectional area and roundness of each tooth neck according to pixel value calibration， and then carry out statistical processing.

Results： Complete the data collection and processing of mesiodistal length， buccolingual width， cross sectional area， and cross sectional roundness of the dental neck at 1.5mm from these seven teeth of the bilateral upper and lower jaws to the alveolar crest of 30 volunteers， and calculate the mean value， variance， and reference value range of medical science of each index.

Conclusion： CBCT can effectively obtain the image information of the cross section of the dental neck. Through mimics 10.0 and Photoshop CS3， it is possible to accurately calculate the dental neck length and width， and cross sectional area of each tooth according to CBCT image information. This result can provide reference basis for the implant restoration of the clinical teeth to select implant diameter and restoration base.

【key words 】Implant，CBCT，Measurement， Natural teeth

【CLC】R722.12 【Document code】B【Article No.】1004-4949（2015）03-0481-01

Introduction

The tooth is an important organ of human body. It undertakes the function of chewing， pronouncing， beauty， etc. After the loss of tooth， how to better select the restoration method to restore its function is the work emphasis and pursuit target of the dentists all along. At present， with the constant deepening of the implant-support false tooth basis and clinical research， its simulation and long-term effect have aroused great concern in this circle. The natural teeth can be divided into incisor， canine， premolar and molar based on the function. They form and function is uniform. Therefore， when restoring the lost implant-support false teeth， it is necessary to take the crest， neck and root form of the teeth in different parts into full account. When selecting the implant and restoration abutment， it is important to refer to the form and size of the natural dental neck. To discuss the dental neck form of different tooth position and its relation with the tooth aesthetics[1，2]， the author designs this research subject. It is aimed at guiding the clinic to rationally select implant and restoration base through the data from this research， and realizing the ideal and perfect restoration of the implant-support false tooth.

Material and method

1.1 Select healthy young volunteers with complete dentition， no malocclusion， no endodontics， and periodontal disease， at the age from 18 to 25. There are 15 males and 15 females. When taking CBCT， they adopted erect position and made the Ala-tragus line parallel to the horizon. Besides， the teeth of upper and lower jaws were in intercuspal occulusion. The scanning range is from the Frankfort plane to the superior border of the thyroid cartilage. The thickness of the scanning layer is set into 0.3mm. Each volunteer gained 255 images， and copied the data into the disc.

1.2 Data measurement and processing

1.2.1 Measurement of mesiodistal distance and buccolingual diameter

Through NNT Viewer built in NewTom VGG CBCT， directly transform into DICOM] format data of international standard of medical image， export and lead in mimcs 10.0， select the image of the horizontal scanning layer in the operation window， magnify and position to the plane as the plane of the alveolar ridge crest that the mesiodistal part of the target dental neck is just surrounded by the alveolar ridge ； take this plane as the standard， and move five planes towards the root， i.e. gain the plane that is 1.5mm away from the root of the alveolar ridge crest ， apply Measure Distance function in Tools menu of mimics， select proper amplification factor in Zoom Factor， and measure the buccolingual distance and mesiodistal distance of each tooth according to the form of the dental arch and tooth.

1.2.2 Measurement of cross sectional area and roundness

Save the selected dental neck plane image into JPEG format， lead in Photoshop CS3 and open it， apply the function of setting measurement proportion in the analysis menu， calibrate the pixel value of the corresponding length according to the length data measured by mimics. In this way， it is feasible to get the actual length of the pixel per unit ， and then use the polygon lasso tool in the toolbar to trace out point-by-point outline of the dental neck of each tooth according to 15-25 points of the outline tracing， establish selection area， and record the cross section selection data of each tooth through the recording measurement function in the analysis menu. This function can calculate the area， perimeter and roundness of the corresponding selection area according to the pixel quantity in the area.

1.3 Statistical analysis

Depict， measure and calculate CBCT images of 30 volunteers； carry out statistics on the mesiodistal and buccolingual distance， cross sectional are and roundness of 840 teeth in 14 tooth positions （the tooth on the right and left with the same name is regarded as a tooth position） of the upper and lower jaws. The statistical magnitude of each tooth position is 60. Sort out the data， lead in SPSS17.0， describe the statistical magnitude， and get the statistics information of the mesiodistal and buccolingual distance， roundness and cross sectional area where the dental neck of the upper and lower jaws is 1.5mm away from the alveolar ridge crest root.

Results

Through the statistics， get the mean value and standard deviation of mesiodistal diameter， buccolingual diameter， cross sectional area and roundness where 14 dental neck parts of the upper and lower jaws is 1.5mm away from the alveolar ridge crest root （Table 1）.

Table 1. The detailed results of mean value and standard deviation of mesiodistal diameter， buccolingual diameter， cross sectional area and roundness where 14 dental neck parts of the upper and lower jaws is 1.5mm away from the alveolar ridge crest root.

Mean ± SD

mesiodistal diameter buccolingual diameter cross sectional area roundnessUpper 7 7.31±0.57 10.62±0.42 82.11±5.24 0.81±0.018Upper 6 6.96±0.32 10.51±0.59 76.50±4.74 0.80±0.018Upper 5 4.35±0.26 7.95±0.35 35.34±2.53 0.76±0.045Upper 4 4.37±0.25 8.45±0.47 36.15±2.84 0.74±0.044Upper 3 5.36±0.36 7.85±0.39 44.59±4.00 0.82±0.045Upper 2 4.31±0.23 6.10±0.64 28.22±3.06 1.09±1.621Upper 1 5.03±0.34 6.71±0.58 40.75±3.38 0.81±0.025Lower 7 9.09±0.52 7.69±0.50 65.95±12.98 0.83±0.027Lower 6 8.85±0.41 7.64±0.49 72.70±6.98 0.82±0.027Lower 5 4.67±0.27 6.88±0.41 34.68±3.58 0.83±0.027Lower 4 4.58±0.30 6.74±1.15 33.97±3.96 0.82±0.029Lower 3 5.14±0.27 8.04±0.31 38.47±3.32 0.81±0.021Lower 2 3.61±0.24 6.55±0.32 26.19±4.65 0.76±0.036Lower 1 3.28±0.14 6.01±0.57 21.38±3.61 0.78±0.039Discussion

The implant neck has the same function as the natural dental neck. The ideal implant should be designed into root form， so as to realize the unification of the form and function. However， the current mainstream implant has been designed into conicalness， which still has great difference from the natural tooth root form. To realize the aesthetic restoration of the tooth implantation， it is necessary to make the implant form get closer to the natural tooth as possible， and then reach the clinical effect of supporting the radian and fullness of the gingival， and maintaining the form of the inter-dental papilla. So far， there is no consensus on how to select implant diameter for the tooth implantation and restoration. Clinically， due to the incorrect selection for the implant diameter， it always leads to black triangle from the interproximal clearance after implant restoration， which not only affects the beauty and gives rise to horizontal food impaction [3， 4]， but also exerts great influence on the masticatory function， and even speeds up the bone resorption around the implant due to the non-axial force， and reduces the service life of the implant false teeth （Figure 1）.

Figure 1 Comparison on interproximal clearance and stress distribution of thick and thin implant diagram.

The cross section of the natural dental neck shows different forms， while the cross section of the mainstream implant is round. Such design makes the insufficient bone mass or clearance on any direction of the agomphosis limit the implant diameter. Therefore， when selecting the implant diameter， it is necessary to take the minimal natural mesiodistal and buccolingual diameter as the reference basis. The data from this research indicates that， the mesiodistal diameter of the first and second molar of the lower jaw is bigger than the buccolingual diameter， so it is necessary to mainly refer to the buccolingual diameter of the dental neck when selecting the diameter of the implant； in addition to this point， the buccolingual diameter of other teeth is larger than the mesiodistal diameter， so it is necessary to mainly refer to the buccolingual diameter of the dental neck when selecting implant diameter . To make the implant restoration to perform good short and long-term function and aesthetic restoration effect， the author provides the following suggestion according to the measurement on the dental neck and the clinic application： select the implant with the diameter of 4.0-5.0mm for the maxillary central incisor； select the implant with the diameter of 3.5-4.5mm for the maxillary lateral incisor； select the implant with the diameter of 3.0-3.5mm for mandibular incisor； select the implant with the diameter of 4.0-4.5mm for dentes premolars of the upper and lower jaws； select the implant with the diameter of 6.0-7.0mm for the molar of the upper and lower jaws . It is necessary to note that， to ensure the union of the implant and surrounding sclerotin， the bone thickness surrounding the implant should be more than 1.5mm； otherwise， the implant with small diameter should be selected. The author suggests that， the implant with the thick diameter of 6-7mm should be selected for the molar. However， up to June， 2014， there were only a minority of implantation system produced the implants with the thickness of 6mm and even thicker diameter， which prompts that each implant manufacturers should produce implants with different types so as to meet the clinical demands.

Conclusion

CBCT can effectively collect the information of the tooth and jaw； by virtue of mimics， Photoshop and other software， it is feasible to accurately measure the mesiodistal diameter， buccolingual diameter， roundness， and cross sectional area of the healthy dental neck. According to this data and clinical research， the following suggestion is put forward： select the plant with the neck diameter of 4-5mm for maxillary central incisor； select the plant with the neck diameter of 3.5-4.5mm for maxillary lateral incisor； select the plant with the neck diameter of 3.0-3.5mm for the mandibular incisor； select the plant with the neck diameter of 4-4.5mm for the dentes premolars of the upper and lower jaws； select the plant with the neck diameter of 6-4.5mm for the molars of the upper and lower jaws.

References

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