【正文】 Lateral/horizontal screw retained to abutment。Dental implantationHistory and Development of Dental implantPrevious nonintegrating forms of implants may have been anchored to bone by means of a surrounding sheath of pseudoperiodontal ligament, but this fibrous sheath was a poorly differentiated layer of scar tissue. In most cases, loading and gradual widening of this led to loosening of the implant and subsequent implant failure.Implants consist of three main parts.The three ponents include Implant,abutment and superstructure.Most contemporary dental implants are made of mercially pure titanium, which has been shown to have excellent biopatibility. Titanium is a light metal. When exposed to air, a surface oxide is rapidly formed. This layer of oxide determines the biological response. Commercially pure titanium is also highly resistant to corrosion. ImplantsOther metals have been used for osseointegration, including zirconium, gold and titaniumaluminiumvanadium alloys. These alloys may strengthen the implant but have been shown to have relatively poor bonetoimplant contact.ImplantsImplant design has a great influence on the stability and subsequent function of the implant in bone. The main parameters are implant shape, implant length, implant diameter and surface characteristics. ImplantsRootform implants, such as screws and cylinders, are the dominating implant designs todays. Screw implants are considered to be superior to cylindrical ones in terms of initial stability and resistance to pression and tension stresses under loading . AbutmentA dental abutment is typically a machined or custommade ponent that connects the final prosthesis to the implant. The abutment may be made from a variety of materials.A machined abutment is typically manufactured from titanium, gold or ceramic. The advantages are that it is simple to use, requires minimal chairside and laboratory time and has a predictable precision fit and good retention.AbutmentA customised abutment may be prepable, custommade in the laboratory or puteraided designputeraided manufacture(CADCAM) designed. A prepable abutment is generally supplied by the manufacture as a blank in titanium or ceramic to be modified by the clinician at the chairside or by the dental technician on the master model. AbutmentCustomisation in the laboratory typically involves waxing to the required design and casting. A CADCAMdesigned abutment is produced with specialised puter software and a milling machine. AbutmentThe selection and use of an abutment is determined by a number of factors, including implant angulation and orientation, depth of soft tissue from implant body to gingival cuff, aesthetic demands, interocclusal space and preference for a cement or screwretained prosthesis. SuperstructureA final prosthesis It may be connected to the implant There are several ways to connect the final prosthesis to the implant: screw retained direct to the implant。Screw retained to the abutment。Cement retained to abutmentPatient Assessment and TreatmentPlanning Clinical AssessmentThe first part of the assessment To define the patient’s requirements and expectations. Unrealistic expectations need to be identified and discussed. particularly important when significant hard and soft tissue has been lost. when the placement of multiple implants is critical to a successful aesthetic oute. Medical HistoryA full medical history is taken. In addition to the usual contraindications for surgery, it is important to pay particular attention to the following:? smoking?uncontrolled diabetes? facial pain?psychological problems Smoking In patients that smoke, failure rates are considerably higher , with the probability that the failure rate increases with the extent of smoking. ●The risks need to be evaluated and carefully explained to the patient. Ideally he or she should be encouraged to stop smoking.Diabetes Implants can be placed in patients with diabetes if the condition is controlled. Un