Ross Cutts touches upon Cement versus Screw Retained Abutments
Until the introduction of CADCAM abutments, traditional screw retained crowns and bridges were only available by using Cast UCLA type abutments. The cost prohibitive nature of expensive customised abutments has meant the wider use of stock abutments and therefore cement-retained restorations. This carries the risk of cement inclusion in particularly deep restorations – something completely avoided by using a screw-retained option. (Figure 1 – cement inclusion on crown)
However implants do not have a Periodontal Ligament which in conventional crown and bridgework can act as a tension buffer – ensuring long term passive fits because the teeth will move in the first couple of days. If there is a lack of implant passivity at insertion, these forces are transferred through the super structure onto the underlying crestal bone. This can result in simple screw loosening within the restoration through to advanced crestal bone loss, leading to further periodontal tissue problems. Thus it is imperative we capture a truly passive fit if we are going to screw retain.
Unfortunately available quantity of bone does not allow us to screw retain restorations due to the path of the screw hole access emerging through unfavorable positions in the anatomy of the restorations – especially in the anterior zone – without the need for adjunctive grafting procedures that have a much greater rate of morbidity. However the emergence of Angle correction abutments – where we can correct misaligned implant fixtures up to 25 degrees to allow us to utilize screw retained restorations – enables clinicians to utilise screw retention for the vast majority of cases whilst avoiding complex grafting procedures. (Fig 2 – fixture angulations)
Dr Ross Cutts, B.D.S. (Lond) Dip Imp Dent RCS (Eng)
Principal of Cirencester Dental Practice & Stow-on-the-Wold Dental Practices
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