牙冠-植體高度比的改變對於植體周圍骨質應變之影響

Abstract

實驗目的: 牙冠對植體的高度比(CIR)可能影響植體治療較長期的預後。本研究的目的是使用電阻應變計，評估不同高度的牙冠受水平靜力時，對植體周圍骨質所產生應變的影響。希望探討的問題包括:當補綴物受到水平力的時候，CIR的改變(包括改變牙冠的高度、或是改變植體的長度) 對植體周圍骨質的應變(strain)是否會有不同的影響;以及當CIR比例改變時， 植體周圍骨頭應變的比例是否會隨著CIR的增加而增加。 實驗方法: 選用三組Branemark MK III RP 的人工植體，每組使用直徑為4.0mm，長度分別為 10mm，13mm及15mm各一支，分別將植體包埋在寬高長分別為12x22x70 mm的環氧樹脂塊之中，僅露出平台的部分。三組電阻應變計(EA-00-031CE-350)分別黏貼於植體平台周圍的近心，舌側及遠心的樹脂表面，之後選用Branemark Goldadapt engaged abutment鑄造出一個16mm高，四角柱形的金屬冠，並在金屬冠的頰側面從邊緣以上做出五個刻度，分別為6mm，7mm，9mm，12mm以及15mm。三組不同的水平靜力(10N ;30N ;50N)則施予在已固定在植體的金屬冠的頰側標記上，以模擬不同的牙冠植體高度比在受力時的情形。每一組力是在同一個刻度上持續五秒並重複五次，而從應變計上面得到的資料加以紀錄及分析。 實驗結果: 水平靜力的大小以及牙冠高度的改變和舌側面應變計的輸出數值呈現強烈的線性關係(r²>0.99);而從線性回歸可以得知，當牙冠高度愈高、或CIR愈大時，不論植體長度是否相同，標準化的應變百分比的確存在逐漸增大的趨勢(r²>0.99)。 結論:實驗結果顯示當植體長度固定，而牙冠高度或是水平靜力增加時，植體周圍骨質的應變量也呈現線性的增加;而當牙冠高度愈高、或CIR愈大時，標準化的應變值的確存在愈大的趨勢。因此當CIR比例改變時，植體周圍骨頭應變的確會隨著CIR的增加而增加。未來的研究可著重於當CIR固定時，植體長度的變化亦或是牙冠高度的改變何者對植體周圍骨質所產生的應變的影響更大，期能更瞭解牙冠對植體的高度比對植體周圍骨質所產生的應變的影響。

Objectives: The crown-implant height ratio (CIR) has been considered to affect the long term prognosis of implant therapy. The purpose of this study was to evaluate the effects of different crown heights and implant length on the peri-implant bone strain, with strain gauge technique, under a horizontal static load. Methods: Three groups of Branemark MK III RP implant, &ouml; = 4.0mm with different length of 10mm, 13mm and 15mm, were embedded in a 12 x 22 x 70 mm (width x height x length) epoxy resin block. Three strain gauges (EA-00-031CE-350) were bonded on resin surface adjacent to the mesial , lingual , and distal side of the implant platform. A 16 mm height tetragonal column casting crown was fabricated with a Branemark Goldadapt engaged abutment and 5 marks were made at buccal crown surface with different distances from the margin: 6mm , 7mm , 9mm , 12mm and 15mm. Three different horizontal forces (10N; 30 N; 50N) were applied to the different marks of the connected crown of the buccal side to represent the relative crown-implant ratio. Each force was repeated 5 times at each mark and data from the strain gauge were recorded and analyzed. Results: The output from the lingual strain gauge had a strong linear correlation with the amount of horizontal force (r&sup2;>0.99). From the linear regression model, we could see the greater the crown height, or the larger the CIR ratio, the increase tendency of the standardized strain gauge output would be obtained(sig<0.05); Similar trend could be observed from results of different implant length. Conclusions: The data suggested that increase of the crown height, or the increase of the applied, lateral force may increase the peri-implant bone strain linearly as the implant length is fixed. The greater the crown height, or the greater the CIR ratio, the increase tendency of the standardized strain gauge output would indeed be obtained. Further study is needed to compare the relative roles of implant length and the crown height on the peri-implant bone stress, thus the effect of crown-implant ratio on peri-implant bone stress could be better understood.