Quantitative analysis of participants



Baseline data



Satisfaction survey



Periodontal pocket depth and alveolar bone height

[1]Zhu HW. Clinical effect of study Ball-cap attachments in the rehabilitation of dentition free deletion based on the treatment of 37 patients suffering from severe periodontal disease. Zhongguo Shiyong Kouqiangke Zazhi. 2011;4(7): 433-434. [2]Boeckler AF, Morton D, Ehring C. Mechanical properties of magnetic attachments for removable prostheses on teeth and implants. J Prosthodont. 2008;17(8):608-615. [3]Zinner ID, Miller RD, Panno FV. Clinical management of abutments with intracoronal attachments. J Prosthet Dent. 1992;67(6):761. [4]State Council of the People’s Republic of China. Administrative Regulations on Medical Institution. 1994-09-01. [5]Cao CF. Periodontology. Beijing: Renmin Weisheng Chubanshe. 2001:87,90,94. [6]Liu W. Effect observation of the curative effect of magnetic attachment in mandibular denture. Xiandai Yiyao Weisheng. 2010;26(6):849-850. [7]Jiang Y, Liu HC, Li HB, et al. Application of single complete overdenture with magnetic attachments in the elderly. Kouqiang Hemian Xiufuxue Zazhi. 2012;13(2):79-82. [8]Wu XX, Zhang XM, Zhang Y, et al. Clinical application of Magnetic attachment in restoration of removable partial denture. Zhonghua Laonian Kouqiang Yixue Zazhi. 2009; 7(1):39-41. [9]Wang PZ, Xia L, Wang GP, et al. Clinical effects of complete mandibular overdenture with magnetic attachments. Kouqiang Hemian Xiufuxue Zazhi. 2005;6(2):121-123. [10]Wu LJ, Wang X, Zhang GY. Clinical research of complete mandibular overdentures with magnetic attachments. Kouqiang Yixue. 2010;30(2):103-105. [11]Vere J, Deans RF. Tooth-supported, magnet-retained overdentures: a review. Dent Update. 2009;36(5):305-308, 310. [12]Zheng XJ, Wei HW, Huang JJ. Magnetic precision attachment in mandibular denture in the coverage application. Shiyong Linchuang Yixue. 2010;11(6): 90-91. [13]Zhu S. Clinical observation of body overdenture elderly edentulous magnetic attachment. Kouqiang Yixue. 2010;30(9):571-572. [14]Tsuchida F, Suminaga Y, Takishin N, et al. A new retainer using magnetic attachment.Nihon Hotetsu Shika Gakkai Zasshi. 2008;52(4):559-561. [15]Preiskel HW, Preiskel A. Precision attachments for the 21st century.Dent Update. 2009;36(4):221-224, 226-227. [16]Zeng D, Jiao LP, Liu G, et al. Clinical evaluation of magnetic attachment retained over-denture and traditional removable partial denture. Kouqiang Hemian Xiufuxue Zazhi. 2010; 3(11):84-86. [17]Zeng D, Jiao LP, Liu G, et al. Clinical observation of magnetic attachment overdenture restoration for patients with advanced periodontitis. Zhonghua Laonian Kouqiang Yixue Zazhi. 2010;8(2):88-92. [18]Liu LY, Jiang T, Feng HL. Fatigue test of retention force of magnetic attachment and stud-type attachment. Shiyong Kouqiang Yixue Zazhi. 2008;24(5):635-638. [19]Kuang H, Wang H, Huang XH, et al. Magnetic attachment for observation of the elderly's dentition defect repair effect. Gannan Yixueyuan Xuebao. 2012;32(2):218-219. [20]Xiong YR, Feng D, Pang JL. Clinical application of magnetic attachments in complete overdentures in elder patients. Zhongguo Zuzhi Gongcheng Yanjiu. 2012; 16(12):2273-2276. [21]Li MJ, Liu AG. Clinical application and common problems of magnetic attachment of overdenture. Gguangdong Yabing Fangzhi. 2010;18(8):443-446. [22]Zhong AX, Pan XB, Peng LH, et al. Clinical application of SD ball attachment dentures. Guangxi Yike Daxue Xuebao. 2008;25(6):904-905. [23]Deng SN. Comparative study of masticatory efficiency between attachment dentures and clasp removable partial dentures. Xiandai Yiyao Weisheng. 2008;24(10): 1459-1461. [24]Saito M, Miura Y, Notaniet K, et al. Stress distribution of abutments and base displacement with precision attachment- and telescopic crown-retained removable partial dentures. J oral Rehabil. 2003;30(5):482-487.

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Over-denture repair is a common treatment means for elderly denture and denture retention is important for its normal functions. As a retention device, attachment can replace the clasp and its biting force conduction is close to abutment tooth long axis, thus effectively avoid the adverse effects of clasp lateral force and torsional forces on the abutments. The attachments have many advantages, such as good retention and stability, beautiful appearance, and small feeling of foreign body, which contribute to meet patients aesthetic, comfort, and functional requirements, therefore it has been increasingly used in dental treatment ^[1-2] . Also, retaining dental root can reduce the loss of alveolar bone, maximize the alveolar bone height and thickness, and is highly conducive to maintain the denture stability and to improve chewing efficiency. The commonly used attachment can be divided into magnetic attachment, ball-cap attachment and ERA attachment. Magnetic attachment and ball-cap attachment are dominant in the mandibular complete denture. SD ball-cap attachment is simple, easy to clean, convenient to use, and widely used in clinical practice. The positive part of the attachment is a spherical body, which contacts with the negative cap-like part of the attachment, through a slight rotation between the spherical surface, the attachment can buffer the lateral torsional forces caused by denture. There is a flexible soft plastic layer present between positive and negative parts, and the layer is located in the negative part, which can play a tampon role between the attachment contact surfaces. It can withstand the vertical and horizontal forces on the abutments. As the chewing forces increase, denture sink and attachment structure adheres closely to the denture base and alveolar crest. At this time, both abutment teeth and alveolar crest bear the biting force, to protect abutment teeth. Magnetic attachment refers to adsorb the denture on the abutments using the magnets on the abutments, to stabilize and fix partial denture. It is characterized by good appearance, strong fixation and constant retention, simple operation, easy to wear, and easy to clean. Magnetic attachment has been widely used in complete denture, partial denture, denture implantation and restoration, as well as orthodontic treatment. Magfit magnetic attachment is a commonly used attachment type, due to long-term, stable retention, especially it can improve mandibular complete over-denture retention. Magnetic attachment is composed by an armature placed in the dental root residues and a closed circuit placed on the prosthesis substrate, the prosthesis can be tightly retained on the alveolar ridge by means of magnetic attraction between the two components. The closed magnetic circuit design allows to generate the four-fold retention force of opening magnet, and to ensure magnetic field leakage in a safe arrangement. This design provides the lasting constant retention, significantly improves denture retention and stability, reduces the absorption of alveolar ridge, improves chewing efficiency and repair effect. By the use of dental root retention and crown cross-sections to improve crown root ratio, magnetic attachment reduces the burden on the abutments. Magnetic attachment attraction is only the strongest in the vertical direction, and significantly decreases when the magnet and the armature laterally shift or dislocate to form an angle, thereby reducing the torsional and lateral forces on the abutments, and effectively protecting abutment teeth. At the same time, natural dental root is preserved, and periodontal proprioceptors are retained, which is conducive to health of periodontal tissue and prevention of alveolar bone absorption. Therefore, as the socio-economic level and modern dental technology is developing, precision attachment can attract increasingly attention in the repair of removable partial denture due to great advantage in aesthetics, comfort and wide application range in clinical practice. In this study, 45 patients subject to mandibular overdenture restoration were treated with magnetic attachments and traditional removable partial dentures were observed for 3 years in follow-up. The patient’s satisfaction and periodontal tissue conditions were surveyed. The advantages and shortcomings of these three kinds of attachments were compared, to explore the difference of precision attachment and traditional clasp retainer in removable partial dentures especially in mandibular overdenture restoration.

Design

How to achieve good retention effects of the denture in abutments and to make patients satisfied with the denture aesthetics and comfort are puzzling the clinicians^[7] . The denture retention is very important for the elderly patients with complete denture patients and with flat alveolar crest^[6] . Precision attachments are characterized by strong retention, good appearance, comfort and durability, thus being widely used in complete denture restoration^[8-11] . Some scholars believe that complete over-dentures are more aesthetic than conventional dentures, it can improve chewing efficiency and effectively prevent alveolar bone resorption^[12-15] . In this study, patients were highly satisfied in denture aesthetics, retention, chewing function, and comfort after two precision attachments, which was consistent with previous studies^[16-17] . In terms of aesthetics, two precision attachment groups were better than traditional clasp retention group, because there is no buccal and lingual exposure on precision attachments. In terms of retention, precision attachment also shows some advantages because closed magnetic circuit can significantly increase denture retention, and the cathode-anode padlock capacity in ball-cap attachment also increased denture retention. These designs make the precision attachments are more balanced and stable than clasp retainer. It is reported that the initial retention force of magnetic attachments is lower than that of ball-cap attachment, but small retention forces allows good stability and long-term efficacy^[18] . In addition, magnetic attachment is more suitable for one or two abutment teeth^[7] . Among patients underwent ball-cap attachment, two cases appeared negative component detachment and three cases showed a decline of binding force between positive and negative components, resulting in a decreased subjective feeling of retention. These phenomena cannot be observed in magnetic attachment group, which further illustrate the superiority of magnetic attachment in the retention and long-term efficacy. In traditional clasp retention group, four patients had a decrease in retention between the clasp and the abutment, and two cases appeared clasp breakage. This is possibly explained that, traditional clasp retainer functions through friction between the clasp and natural tooth, as well as the clasp arm. Once the metal clasp tends to be broken as the repeated wearing number of removable dentures, there is a gap formed between clasp arm and abutment teeth, thus decreasing retention force. Traditional removable partial dentures are often poorly stable, inefficient in chewing, less comfortable and aesthetic. For the patients with only one or two abutment teeth, the abutments may be eradicated due to loosening at 2-3 years after restorative treatment^[19] . Our findings showed that, chewing function in magnetic attachment group was higher than in the conventional clasp retention group, but was not different from ball-cap attachment group, suggesting that precision attachment overdenture restoration can improve chewing efficiency. When the denture functions, the patients can feel the force direction and size, even distinguish food shape and hardness through force stimulation transferred into the central nervous system via periodontal proprioceptors, thus improving chewing efficiency. Periodontal health is a contributing factor for the removable partial denture restorative effects, periodontal disease-caused tooth mobility can easily lead to overdenture failure. In this study, gingival health was the best in magnetic attachment group and the worst in traditional clasp retention group. Screw cap-shaped magnetic attachment is tightly casted on the dental root and the surface is polishing, which is difficult to produce plaque accumulation, in addition the material is good compatible to gingival tissue and produce less periodontal inflammation. We used MagfitEX magnetic attachment which can provide lasting retention and reduce plaque accumulation, as well as easy to clean; in addition, the armature materials are biocompatible to gingival tissue, thus minimizing marginal gingivitis and further maintaining periodontal health. In clinical test pf gingival index, we also noted that all patients presented varying degrees of gingival inflammation, with gingival bleeding on probing as the main clinical manifestation. This phenomenon is related with personal oral hygiene care. Although magnetic attachment has many advantages, there is still a risk for abutment periodontal disease. The gingivitis is the contributing factor affecting the service life of magnetic attachment. The oral health maintenance and periodic check after the restoration can maintain abutment health and sustain long-term treatment effects. In clinical practice, the denture should not directly press gingival margin. Before the crown with an armature is fixed, tissue surface must be highly polished to avoid plaque adhesion^[20] . Abutment tooth mobility in two precision attachment groups was lower than the control group, suggesting that the abutment health was poor in traditional clasp retention group. Clasp retainers have some friction forces on abutments, and the clasp-caused torsional force on abutments when chewing food also damages periodontal tissue. The advantages of magnetic attachment is its low requirement on the crown root ratio^[21] and protective effect on the abutments, mandibular overdenture with magnetic attachment can shift for a short distance along the root plane when subjected to lateral forces, thus reducing lateral forces. Ball-cap attachment is exracoronal stud attachment, with its power distribution perpendicular to the tooth long axis, and has some stress-buffering effects. It fits mucosal support or hybrid supported denture and its elastic cap can be adjusted according to different retention forces, thus avoiding damage to the abutment and protecting the abutment. However, ball-cap attachment indications are not wide as magnetic attachments, it requires high crown root ratio, mandibular overdenture with cap attachment cannot produce adjustable movement when subjected to lateral forces, and may produce torsional force on the abutment teeth, and the protection effect for abutment periodontal tissue is not good as magnetic   attachments^[22] . In this study, periodontal pocket depth in magnetic attachment and ball-cap attachment groups was increased slightly, but there was no significant difference between two groups. This evidence suggested that, in the mandibular denture restoration process, periodontal pocket formation is not related with types of attachments, it is closely associated with personal oral health. However, periodontal pocket depth in control group was higher than magnetic attachment and ball-cap attachment groups, suggesting that traditional clasp-retained mandibular removable partial denture is more susceptible to periodontal pockets. Presumably it is due to repeated wearing of clasp retainer denture, and the gap between clasp arm and the abutment teeth leads to food impaction^{[23 ]} . X-ray measurement results showed that, alveolar bone height in magnetic attachment denture group was higher than ball-cap attachment, with significant differences. This evidence suggested that magnetic attachment exhibited less influence on the alveolar bone vertical height than ball-cap attachment. Patients treated with magnetic attachment may have less alveolar bone resorption, no or less occlusal trauma in abutments, and more healthy periodontal tissues. Alveolar bone height in two precision attachment groups was higher than the control group, suggesting precision attachment is more conducive to periodontal health than traditional clasp retainer. Saito et al ^[24] found that, the abutments provided strong supports for the attachment of removable partial denture, while alveolar ridge gave a weak support; in clasp denture, abutments provided less support forces, and the support of alveolar crest mucosa was dominant, so alveolar bone resorption is obvious. The connection between the ball-cap attachment is a kind of spherical elastic connection, the gap between elastic connection and attachment components is 0.5-   1.0 mm, so that the denture allows a little vertical movement of base plate to reduce load and to make better occlusal force dispersed in abutment and alveolar ridge. The magnetic attachments may lower the crown root ratio, produce even force on the abutment roots, reduce lateral forces and torsional forces, decrease alveolar bone absorption, and ensure periodontal health.
In summary, magnetic attachment shows great advantages in mandibular removable partial dentures. The denture has good retention and healthy periodontal tissue, minimums alveolar bone absorption and makes patients satisfied. The disadvantage is high cost, which restricts clinical application. Magnetic attachment and ball-cap attachment for the overdenture is superior to traditional clasp retainer for removable partial dentures.

下颌可摘局部义齿临床修复治疗中固位体类型的选择存在一定争议，试验旨在比较磁性附着体、球帽附着体和传统卡环固位体在下颌可摘局部义齿修复中的临床效果。

可摘局部义齿修复治疗后基牙的牙周健康状况是影响义齿修复效果的主要因素，尤其是牙周疾病导致的基牙松动极易导致覆盖义齿失败。试验中磁性附着体修复组牙龈健康状况最好，传统卡环固位修复组牙龈健康状况最差。磁性附着体钉帽状铸接覆盖于牙根表面，密合性较好，并且表面抛光，不易产生菌斑堆积，此外该材料与牙龈组织相容性较好，较少产生牙周炎症。试验中采用的MagfitEX磁性附着体能够提供持久的固位力，钉帽高度抛光，减少菌斑堆积，易于清洁；且衔铁材料与牙龈组织的生物相容性较好，最大程度地减少边缘性龈炎的发生，从而进一步保持基牙牙周组织的健康状态。在牙龈指数临床检测结果中我们还注意到，3组患者的基牙均有不同程度的牙龈炎症发生，主要临床表现为牙龈探诊出血。此现象的发生于个人口腔卫生护理情况有关。虽然磁性附着体具有很多优点，但是基牙仍然存在发生牙周疾病的风险。对基牙颈部龈炎的控制是影响磁性附着体寿命的重要因素。修复后的口腔健康维护和定期复查是保持基牙健康和维持长期治疗效果的重要保障。在临床治疗上，要求义齿就位后避免直接压迫龈缘，对与龈缘接触的组织面进行缓冲，缓冲区应在1mm以内。且在含有衔铁的桩核被粘固之前，组织表面一定要高度抛光，避免菌斑附着。基牙松动度临床检测结果表明，两组精密附着体组基牙松动程度均低于对照组,提示传统卡环固位义齿的基牙牙周健康状况欠佳。卡环固位体对基牙产生一定的摩擦力，咀嚼食物时卡环对基牙产生一定的扭转力等都会对基牙牙周组织造成一定的损伤。而磁性附着体的优点在于对基牙冠根比例要求较低，对基牙具有保护作用，带有磁性附着体的下颌全口义齿在受到侧向力时可沿根面板平面产生少量移动，减少基牙所受的侧向力。球帽型附着体为冠外卡抱式附着体，其力量分布垂直于牙体长轴并有一定的应力缓冲作用，适用于黏膜支持式或混合支持式义齿修复，根据需要可选择不同固位力大小的弹性帽，可轻易调节固位力，避免了对基牙的损坏，利于牙周病基牙的保护。但是球帽附着体适应证较磁性附着体窄，基牙冠根比例要求较高，带有球帽附着体的下颌全口义齿在受到侧向力时不能产生可调节式移动，对基牙产生一定的扭力，较磁性附着体对基牙牙周组织健康保护程度稍差。

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