Tooth decay is the most common disease affecting children and adults worldwide. If left untreated, acid produced by bacteria in the dental plaque or biofilm forms cavities or holes in the teeth. A number of techniques and a variety of materials can be used to restore or fill teeth affected by decay. One of these materials is tooth-colored, resin-based composite or RBC. This material is increasingly used as an alternative to amalgam (a mixture of mercury and metal alloy particles).
Since the 19th century liners have often been placed in cavities in the teeth under the filling material. The liners are thought to protect the living pulp of the tooth from filling materials themselves and also from their potential to allow more heat or cold through than the natural tooth would. Although RBC filling materials are thought to be similar to the natural material of teeth in terms of how they conduct heat, sensitivity to temperature change is sometimes still an issue for people after treatment.
What was the research?
A systematic review to assess the effects of using liners under tooth-colored resin fillings in cavities on the biting surface (Class I) and the biting surface and side(s) (Class II) of permanent teeth in the back of the mouth in children and adults.
Who conducted the research?
The research was conducted by a team led by Andrew B. Schenkel from New York University College of Dentistry, on behalf of Cochrane Oral Health. Analia Veitz-Keenan was also on the team.
What evidence was included in the review?
Eight randomized controlled trials, with over 700 participants, were included. Two studies were conducted in the USA, two in Thailand, two in Germany and one each in Saudi Arabia and Turkey. The studies compared the use of liners under tooth-colored resin fillings (RBC) in permanent teeth at the back of the mouth to no liners for Class I and Class II fillings. One of the two studies in the USA took place in dental practices, the others in university-based dental schools. All participants were over 15 years of age.
What did the evidence say?
Very little evidence was found to show that a liner under Class I and II RBC fillings in permanent teeth in the back of the mouth reduced sensitivity in adults or children 15 years or older. No evidence was found to show that there was any difference in the length of time fillings lasted when placed with or without a cavity liner. No adverse events were reported in any of the included studies.
How good was the evidence?
The body of evidence identified in this review does not allow for robust conclusions about the effects of dental cavity liners. The quality of the evidence identified in this review is low and there is a lack of confidence in the effect estimates. Furthermore, no evidence was found to demonstrate a difference in how long restorations last when placed with or without dental cavity liners.
What are the implications for dentists and the general public?
There is inconsistent evidence regarding the difference between resin-based composite restorations placed with liners and those placed without liners when considering postoperative hypersensitivity. There is no evidence of a difference between the use of liners or not with regard to restoration failure. Despite the low quality of the evidence, we feel that this evidence is applicable when placing routine composite-based restorations in adult posterior teeth and that placing a liner is an unnecessary step. Any cost savings can be passed along to the public. Even without any cost savings, the evidence does not currently support including the unnecessary step of placing any lining material underneath routine composite-based restorations in adult posterior teeth.
What should researchers look at in the future?
If new liner materials are developed then future clinical trials should be undertaken to determine if the new liner materials are of any benefit in terms of postoperative hypersensitivity and restoration failure. Any additional research on calcium hydroxide or resin-modified glass ionomer liners should focus on their use as pulp capping materials rather than on their use as dental cavity liners under routine composite-based restorations.
Future trials should be well-designed randomized controlled trials (with adequate sequence generation and allocation concealment methods, blinding of participants and outcome assessors) reported according to the Consolidated Standards of Reporting Trials (CONSORT) Statement (www.consort-statement.org).
The trials included in the current review used a variety of methods for assessing postoperative hypersensitivity that precluded pooling in some instances. It would be helpful if future studies use agreed, standardized outcome assessment methods, as recommended by the Core Outcome Measures in Effectiveness Trials (COMET) Initiative (www.comet-initiative.org), to allow for greater comparison of results across studies. Better reporting of adverse events is required and the planning and conducting of an economic analysis alongside future clinical trials would also be beneficial.
Schenkel AB, Veitz-Keenan A. Dental cavity liners for Class I and Class II resin-based composite restorations. Cochrane Database of Systematic Reviews 2019, Issue 3. Art. No.: CD010526. DOI: 10.1002/14651858.CD010526.pub3.