Research that matters: debunking the myth of the “fracture resistance” of root filled teeth

There is no topic within Endodontics that causes more controversy and interest than the mechanical failure of root filled teeth. Although such failures present in scenarios ranging from cuspal fractures to vertical fractures, all involve development cracks (Rivera & Walton 2007). As a result microbial contamination, these fracture lines can trigger endodontic symptoms or periodontal bone loss (Ricucci et al. 2015). In some cases, outcome many structural are catastrophic unrestorable leading inevitable extraction teeth (PradeepKumar 2016). The term “fracture resistance” often used research; however, materials science engineering, has specific meaning, is: increase toughness with crack extension, which material property. What dental researchers do most without really understanding difference measure “load capacity” restored tooth, property structures consisting components made different materials. reader acknowledge, there currently standards for testing have undergone canal treatment. Many use static loading prove disapprove various hypotheses effect intracanal antimicrobials (Andreasen 2002, Dotto 2020) access cavity designs (Rover 2017, 2020, Sabeti 2018) on However, it must be emphasized tests load capacity not resistance. information might obtained using this approach, studies lack fundamental biomechanical support their results. More importantly, fact only very limited test rarely acknowledged, consequence readers misled about results implications study. During last 40 years, Dentistry progressively moved ductile (e.g. gold) brittle rely adhesion restore A similar trend occurred high-temperature engineering when engineers switched metals ceramics, needed change methods design against failure. Therefore, approaches should adopted during restorations. Even though restorative sciences started move clinically relevant 20 years ago (Braemet 1994), clearly consensus amongst how tooth tested mechanically. first step towards improving research avoiding confirmatory bias area understand nature restorations service. With exception traumatic substantial evidence subsequent modes (cracked fracture, split fracture) develop as cyclic form mastication over period time (Mireku 2010, Kishen 2015, Pradeepkumar 2016, Arola 2017). By definition, fatigue occurs due application fluctuating stress much lower required cause monotonically increasing (Drummond 2008, Campbell Taha 2014, approximately 90% caused by (Campbell 2008); remaining 10% early inadequate designs, manufacturing faults accidental loads. chewing delayed after phase oral function indicates comprehension essential ensuring longevity (Arola taken number cycles (N) reduces exponentially amplitude (σ), i.e. , where σ0 strength α life reduction factor. Thus, equally important experiment. This leads concept tool analyzing failure, stress-life curve; see Figure 1. Published experiments regards provide critical one cycle, unlikely adequate long-term prediction. consists several tissues, interfaces, each curve. Further, under masticatory loading, region subjected amplitude. vulnerable necessarily highly stressed, but shortest expectancy. best optimum individual level will give them same Teeth relatively nature, means they stronger compression tension, may demonstrate large variation service (Kinney 2003, Park 2008). standardized samples terms dimensions (such CAD/CAM restorations) fail at test. mechanics theory states enamel dentine) because unstable extension pre-existing flaws range sizes orientations samples. Interestingly, specimen largest flaw weakest if located oriented direction stressed (Fok Chew, 2020). Crack size orientation occur randomly, why predictions need expressed probability. instead simply designing restoration certain time, contain uncertainty, its probability specified, significant variable compatible clinical For analysis purposes, weakest-link coupled Weibull’s power used. If repaired restored, relaxed maybe acceptable. could lead loss, stricter requirement well necessary, example less 5% 5 Environmental effects been into consideration past. Dental interfaces degrade through corrosion, wear hydrolysis. properties, including curve, constant time. classic “corrosive fatigue”. degradation combined action corrosion loading. (See Fig. 2). general “environmental cracking” “environmentally assisted field, tissues interact complex environment includes chemical (pH variations), physical (cyclic fatigue, parafunction) biological challenges biofilm colonization (Zhang Not loads already degrading additional accelerate (Carrera example, composite-dentine interface low pH enzymatic attack plaque accumulation rapidly compared working an inert air (Orrego Whilst factors contribute evaluated separately, considered simultaneously assess any synergistic future These variables direct resin composite debonding increases flexure leaving occurrence events (Taha 2014). It opinion authors who seeking take following topics consideration: (1) clinically, subcritical capacity. loading; (2) important; (3) report time; (4) ideally aged before testing. steps help community properly evaluate irrigants medicaments, microcracks generated instrumentation, minimally invasive procedures expected They therefore representative methodology studying influencing factors, detection treatment cracked context, recommendations based solely performed load. longer Knowledge also re-evaluating assessing validity previous study designs.