人工植體頸部型態的差異對周圍骨質應變之影響

Abstract

實驗目的：在人工植牙的臨床應用上，牙醫師經常會面對不理想的骨質和骨量，造成治療上的困難，而植體的生物機械特性，就成為改善人工植牙預後的重要因素。學者進一步提出“功能性表面積”的想法來解釋在骨頭–植體交界面的應力傳導，然而，目前的研究對這個區域的細節還沒有全盤了解。本實驗的研究目的即希望能進一步釐清這個區域的範圍，並了解它是如何對應力分散造成影響。 材料與方法：本實驗中採用兩種不同設計的植體：Brånemark（Mk III，瑞典）植體的尺寸分別為直徑3.75或5.0 mm，長度8.5或10.0 mm。Astra Tech（OsseoSpeed，瑞典）植體的尺寸分別為直徑4.0S、5.0S或5.0 mm，長度9.0或11.0 mm。每種尺寸的植體有兩個樣本， 每支植體被包埋在聚甲基丙烯酸甲酯樹脂塊（ 85×20×30 mm）中，藉以模擬上顎無牙區的低密度骨質。每支植體表面上黏有四個微型應變計（KFG-02-120-C1，Kyowa，日本)，測量點分別在植體平台以下1.0、2.0、4.0及5.0 mm的位置。在模擬支台齒的鈦金屬塊（8 × 8 × 8 mm）上施以30度，50牛頓的定力，每個模型6次，並記錄四個測量點的應變值。 實驗結果：所有植體平均應變值（MSV）的最大值皆出現在植體平台以下1.0 mm處，且較其他3個測量點達到顯著差異（P < 0.05）。Brånemark組的MSV最大值出現在3.75*8.5 mm的植體上，Astra Tech 組的MSV最大MSV值則出現在4.0S*9.0 mm的植體上。當植體的直徑增加，或長度增加時，MSV有減少的現象，在兩組不同設計的植體上， 直徑和長度的影響力並不相同。此外，植體的設計，包括微螺紋或外展等，都會對測量到的MSV造成影響。 結論：在本實驗的條件限制下，無論植體的直徑、長度或設計，最大的應力集中都發生在植體平台以下2.0 mm的範圍。因此可以推論， 有一個主要支持區在這個範圍，並且承擔了大部分植體受力時傳導下來的應變。而植體在這個區域內若有良好的設計，將會對應力分散給予更多的好處。

Objectives: During the clinical practice of implant treatment, dentists are usually bothered by facing unfavorable bone quantity and quality. The implant biomechanic characteristics become important to improve the prognosis of implant placement. Therefore, the idea of “functional surface area” was brought up to explain more about stress transfering at bone-implant interface. Unfortunately, we did not really understand the details of this area. The aim of the present study was to identify this area and how it influences the stress distribution. Methods: Two different designs of dental implants were included in this study. The sizes of Brånemark (Mk III, Sweden) implants were 3.75 or 5.0 mm in diameter and 8.5 or 10.0 mm in length. The sizes of Astra Tech (OsseoSpeed, Sweden) implants were 4.0S, 5.0S or 5.0 mm in diameter and 9.0 or 11.0 mm in length. There were two implants of each size. Each implant was embedded in a polymethyl methacrylate resin block (85 X 20 X 30 mm), simulating a maxillary edentulous region with low-density bone. Four miniature strain gauges (KFG-02-120-C1, Kyowa, Japan) was attached to each implant where the measuring points were at 1.0, 2.0, 4.0 and 5.0 mm below the platform on the external surface of the implant. A 30-degree oblique static load of 50N was applied 6 times on a Ti block (8 X 8 X 8 mm) screwed on the implant of each model and bone strains at the four measuring points were recorded. Results: All implants showed the largest mean strain value (MSV) at 1.0-mm site below the platform which was statistically higher (P < 0.05) than the other 3 measuring sites. For Brånemark implants, the largest MSV was observed in 3.75*8.5 mm implant. For Astra Tech implants, the largest MSV was observed in 4.0S*9.0 mm implant. MSV dereased when the implant length increased and when the implant diameter increased. However, difference existed between two implant designs in the effect of implant length and implant diameter on MSV. The outspreaded or microthreaded design also affected the MSV. Conclusion: Within the limitation of this in-vitro study, we concluded that MSV concentrated mostly at 2.0 mm below platform of implants in different diameters, lengths or designs. Therefore, there was a primary supporting area in peri-implant bone where received most strain from implants during loading. Well design in this area would give more benefits in stress distribution.