Australasian Dentist Issue 93

CATEGORY AUSTRALASIAN DENTIST 39 LINICAL According to Park (2002) Table 1 Difference between Bone screws and miniplates Table 2 Fig 31 Implantation site for maxilla and mandible (Blue – Safe Zone) (Red – Danger Zone) Fig 32a For maxillary molar distalization Host factors 1. Systemic disease 2. Bone quality and quantity 3. Amount of attached gingiva vs. movable soft tissue available 4. Age and physical condition 5. Oral microflora, salivation, mouth breathing, etc Implant factors 1. Choice of implant material 2. Implant surface type 3. Shape of implant screw Ways to avoid failure: See Figure 30. u Also torsional strength is proportional to the cube of the core diameter, a very small enhancement of core diameter can greatly increase the strength of a screw. u The mini-type diameter should not be used where cortical bone is comparatively thick. u To prevent fractures, predrilling through cortical bone is obligatory, particularly in areas where accessibility is poor and cortical bone is very hard, such as the mandibular posterior buccal alveolar area, buccal shelf area, and midpalatal suture area. A short implant is recommended for these areas for prevention of fracture. u Modifications of the design, proper manipulation, and use of the predrilling procedure can minimize implant fracture. II. CONCLUSION Skeletal anchorage will become an integral part of daily orthodontic practice. careful planning and consideration of the risk factors are important when choosing the patient, the site, and the mini-implant. Skeletal anchorage should be used to widen the spectrum of orthodontics, no replace the rational application of biomechanics III. SUMMARY Design factors for Bone screws Related to stability and success u Pitch of screw threads: tight, not loose u Length of screw – Alveolar bone, approximately 6 mm o Palatal or mandibular bone, approximately 4 mm – Base of zygomatic bone, 6 to 8 mm u Diameter of screw – Minimum 1.3 mm – Maximum 2.0 mm u Shape of screw: conical preferred u Form of tip: thread-cutting preferred u Bicortical versus monocortical: monocortical preferred – Minimal stability advantage for bicortical – Decreased ease of use Related to Ease of Use u Pilot hole: better if not necessary u Soft tissuepunch: better if not necessary u Insertion torque: better if low u Insertion device: better if simple u Direct versus indirect anchorage: both acceptable A) For maxillary molar distalization, the insertion position is location1 to 2 mm distal to the imaginary central line between the two teeth. C) For molar protraction, the insertion position is placed 1 to 2 mm mesial to the imaginary central line.