Implants in Clinical Dentistry (PDF)

detected. Ridge mapping is advocated by some clinicians. In this technique the area under investigation is given local anaesthesia and the thickness of the soft tissue is measured by puncturing it to the bone, using either a graduated periodontal probe or specially designed callipers.

The information is transferred to a cast of the jaw that is sectioned through the ridge. This method gives a better indication of bone profile than simple palpation but is still prone to error. Whenever the clinician is in doubt about the bone width and contour, it is advisable to request a radiographic examination to achieve this (see section on sectional tomography). One of the most important assessments is measurement of the tooth space at the level of the crown, at the soft-tissue margin and between the roots. The first is important for the aesthetics and is best judged by measuring the width of the crown in comparison to the contralateral natural tooth, if present. The available width at the root level determines whether an implant and abutment can be accommodated without compromising the adjacent tooth roots and soft tissue.

A commonly quoted minimal dimension is 6 mm, both in the mesiodistal and buccolingual plane. This allows for an average implant of 4 mm in diameter to have a margin of 1 mm of bone surrounding it. The mesiodistal dimension is commonly compromised in the maxillary lateral incisor region and the lower incisor region, where the natural teeth are small (Figures 3.2 and 3.3). In the case of young patients with developmentally missing maxillary incisors, it is advisable to liaise with the treating orthodontists to agree space requirements and to check that adequate space has been achieved before removal of the orthodontic appliance. The adjacent root alignment can sometimes be palpated but usually requires verification radiographically.

Spaces that are 5 mm wide mesiodistally may be amenable to treatment with a narrow-diameter implant/abutment (e.g. 3.3 mm rather than 4 mm in diameter) provided that the forces it is subjected to are not too high. For example, utilization of narrow implants would be contraindicated in a patient with a parafunctional activity such as bruxism. On the other hand, patients with a spaced dentition have excess mesiodistal space. Provided that the ridge has an adequate buccolingual width, the clinician could plan to place a wider diameter implant that more closely matches the root of the tooth that is being replaced (Figures 3.4 and 3.5). The selection of the most appropriate implant diameter has a great bearing on the aesthetics and surgery. This is dealt with in more detail in the surgical section (Chapter 9), which also compares some of the implant systems available.