Partial vs Full Coverage Restorations Part 1
Shifting from the Traditional View
You have to choose whether to prepare a partial or full coverage restoration for a patient rather frequently as a restorative dentist. The optimal option for a specific patient will depend on a variety of criteria, including the severity of the tooth damage, the patient's oral health, and their cosmetic objectives.
Both types of restorations offer pros and cons.
One factor that makes the decision making process lengthy is the traditional viewpoint that ‘full coverage is stronger.’ Usually the standard protocol was that an endodontically treated tooth had to be crowned or run the risk of a catastrophic fracture.
Nickel Chromium crown delivered in 2017. Minimal preparation, sub gingival margin distally, no esthetic demand. Most importantly it was full coverage. But what would be next if that crown failed?
Dr Miguel Ortiz recently opened the discussion on why crowns would be indicated as a line of treatment. According to a large study, crowns had the shortest track to extraction after MOD Amalgam-treated teeth.
To many it was a lightbulb moment. After all, our job is to save teeth, not make our restorations live as long as possible. What made me as an MProsth holder giddy about that discussion was how avoiding crowns was constitutional since holding a teaching position. On day 1 of the three year course of specialty prosthodontics, we’d teach that unless the tooth is so damaged it needs an MOD Amalgam, the only indication for a crown is replacing an older crown. After all, the 2018 British dental Journal paper Dr Ortiz was quoting was part of our source material in studying and teaching for the Membership in Restorative Dentistry.
When understanding this more streamlined decision making, we need to shift the lens from ‘crown strong, onlay weak’ or ‘crown invasive, composite conservative,’ or the absolute worst: ‘vertiprep best.’
Classifying Indirect Restorations
The concept of minimally invasive dentistry suggests defect oriented
preparations. Put simply, you prepare the defect plus the minimum thickness
of material needed to repair that specific effect. There is no longer an
indication to prepare a restoration outline then resistance and retention form
as needed for conventional crowns or amalgam restorations. Thus,
restorations are more appropriately classified as follows:
A restoration retained using conventional dental cements in combination with tooth preparation features designed to prevent disruption of the cement and displacement of the restoration. The first thing that could come to mind is amalgam, which is retained specifically by its preparation features
Regarding indirect restorations, the purest form of a conventional restoration is the full crown. Resistance and retention form depend on factors such as preparation height and taper. If a partial coverage solution was to be prepared with the same conventional principles, retention features such as grooves and boxes would be needed to counteract the lack of resistance and retention form.
Let’s move on to the second category
A restoration retained using adhesive technology, often resin based for strength and chemical bonding. The advent of adhesion opened the venue for indirect materials to chemically bond with tooth substrate via resin cement and surface treatment. Adhesive restorations are divided into:
Conventional preparation
Conventional restorations luted adhesively. Think crowns on short or over tapered teeth holding on better with resin cement
Minimal preparation
Preparation that does not depend on geometric features for resistance and retention. The purest expression of this is the porcelain laminate veneer. Only enough preparation is done for the layering
ceramic, and the retention depends purely on resin cement bonding the porcelain to the enamel substrate.
The same principle is done for posterior indirect restorations. The minimal
preparation technique applies to ceramic and metal.
Rehabilitation delivered in 2016 with posterior adhesive metal onlays to treat caries and wear. Upper left lateral incisor is an implant retained crown and the adjacent canine is full coverage ceramometal on an endodontically treated tooth
Now that we shifted the categorization from full vs partial to categories of retention and what preps are needed for said retention, we’ll look next at how teeth are estimated to survive and how preparation affects this.
See you soon!
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won't be disappointed.
