What are Mini Implants, Micro implants, Mini screws, Skeletal Anchorage devices, Orthodontic implants or Micro screws, Temporary Anchorage devices

What are Mini Implants?

Mini Implants are the anchorage devices required to fulfil the need for absolute anchorage. It is used in conditions for moving of large segment of the tooth without any counter-movements. But these counter-movements are seen using other orthodontic or orthopaedic appliances. It cannot be used in all patients, because it depends upon various factors including the bone sites, anatomical sites located adjacent to the anchorage site, cortical bone quantity and quality, age, gender and Mini Implant factors including length, diameter, material, and surface.

The term "Mini Implants” is interchangeably used with Micro implants, Mini screws, Skeletal Anchorage devices, Orthodontic implants or Micro screws, and Temporary Anchorage devices (TAD).

 

TYPES OF MINI IMPLANTS

 

Classified according to the

• Method of Placement

SELF TAPPING	SELF DRILLING
Used in the small diameter mini implants	Used in large-diameter mini-implants
1st drill is made and then a mini implant is inserted	The mini implants itself drilled into the bone while inserting

• Exposure of the Implant head

OPEN METHOD	CLOSED METHOD
The mini-implant head is exposed to the oral cavity	The mini-implant head is not exposed to the oral cavity
It is used in places where there are immoveable soft tissues such as Attached gingiva	It is used in places where there are moveable soft tissues

• Angle/ Path of Insertion

OBLIQUE DIRECTION	PERPENDICULAR DIRECTION
The mini implant is inserted at an angle of 30- 60 degrees to the long axis of the tooth	The mini implant is inserted at an angle of 90 degrees to the long axis of the tooth
It is used when the Inter-radicular bone is narrow	It is used when there is sufficient inter-radicular bone

(a) Perpendicular, Open method (b) Perpendicular, Closed method (c) Oblique

SITES FOR PLACEMENT OF MINI-IMPLANTS

MAXILLA	INDICATION
Maxillary tuberosity	For retraction of maxillary posterior teeth
Infrazygomatic crest area	For retraction of the maxillary anterior & intrusion of maxillary posteriors
Bucally between maxillary 1st & 2nd molars	For retraction of maxillary anterior & intrusion of maxillary molars
Bucally between maxillary 1st molar & 2nd premolar	For retraction of the maxillary anterior & intrusion of buccal teeth
Bucally between maxillary canine & 1st premolar	Mesial and Distal movements of maxillary molars & intrusion of maxillary buccal teeth
Labially between maxillary incisors	Intrusion and Torque control between maxillary incisors
Palatally between 2nd premolar & 1st molar	Retraction of maxillary anterior & intrusion of maxillary molars
Midpalatal area	For correction of unilateral crossbite

MANDIBLE	INDICATION
Retromolar region	For uprighting mandibular molars & retracting mandibular teeth
Bucally between 1st & 2nd molars	Intrusion & Distal movement of mandibular molars and retraction of mandibular anterior
Bucally between 1st molar & 2nd premolars	Intrusion of mandibular molars & retraction of mandibular anterior
Bucally between mandibular canine & premolars	Protraction of mandibular molars
Facially in the symphysis region	For intrusion of mandibular anterior

SIZE OF MINI IMPLANTS

The mini implants are easily inserted into the various parts of the maxilla and mandible due to their small size in diameter and length. The size of mini implants ranges from 6-12mm in length & 1.2mm- 2mm in diameter. The length of the mini implant inserted into the bone ranges from 4 mm to 6 mm. The procedure for the insertion of mini implants is slightly invasive and requires only topical anaesthesia. Most times the mini implants are inserted through the gingival and into the bone with the help of a hand driver. In cases of thick soft tissues and dense cortical bone the mucosal punch and pilot drill are done which helps in guiding the insertion of the mini implants. These mini implants are retained  mechanically to the cortical bone and loaded immediately.

ANGLE OF INSERTION OF MINI IMPLANTS

In the maxilla, the mini implants are inserted at an angle of 30-40 degrees, and in the mandible, it is inserted at an angle of 20-60 degrees to the long axis of the tooth. The rationale for the above recommended angles is to engage the mini implants with cortical bone and away from the root structure.

Maxillary & Mandibular mini implants

MORPHOLOGY OF MINI IMPLANTS

The shape of mini implants includes four types are Screw, Plate, Disk and Blade. The screw and plate-shaped mini implants are most commonly used . It consists of head, neck, collar and body. The central core of the mini implants comes in different shapes cylindrical and tapered. In the tapered type, there is a gradual decrease in shape from head to tip while it is the the same taper in cylindrical form.

(a) Screw (b) Plate (c) Disk (d) Blade

(a) Cylindrical (b) Taper

CHARACTERISTICS OF ORTHODONTIC TADs

The central core of TADs made up of one of the three materials: Titanium, Stainless steel and Vitallium. The ideal properties of the material must be biocompatible with oral tissues. Vitallium-based mini implants are replaced by titanium due to poor biocompatibility. Titanium is the most frequently used one, however, there are no significant differences between titanium and stainless steel-based mini implants.

MECHANICAL CHARACTERISTICS OF ORTHODONTICS TADs

TADs obtain retention by engaging the alveolar bone. The engagement between threads of the mini implants and cortical alveolar bone provides mechanical retention which is achieved as soon as the insertion. It is called Primary Stability. After insertion, bone remodeling takes place results new bone apposition which has increased strength. It is called Secondary stability. After some time, the primary stability gradually decreases and secondary stability increases. Clinical stability is the sum of the primary and secondary stability. It is important for the success of the mini implants.

COMPLICATIONS OF ORTHODONTIC MINI IMPLANTS (TADs)

The complications include fracture of mini implants, soft tissue inflammation, root contact or penetration, and failure of orthodontic TADs.

Root contact or penetration is caused by inadequate inter-radicular spaces, incorrect inclination of the insertion, and failure in analyzing the bone thickness and distance between the bone and roots. Soft tissue inflammation is due to inadequate oral hygiene and presents as redness and swelling. Fracture of TADs is due to over-torque during insertion or removal. It can be reduced by proper insertion techniques and the selection of correct-sized TADs. Failure of mini implants is due to decreased clinical stability which causes the loosening of mini implants. The solution is the removal of old mini implants and replacement with new mini implants.

The image shows mini-implant failure caused due to loosening by displacement of elastics.