Knowledge and understanding for root canal system anatomy serve to influence and guide predictably successful endodontic treatment outcomes. Predictable endodontic treatment begins with an effective access preparation that enables locating any given orifice, which in turn, promotes negotiating, securing, and shaping the canal, 3D disinfection, and filling this root canal system. Missed canals hold pulp tissue and at times bacteria and related irritants, which oftentimes contribute to clinical symptoms and lesions of endodontic origin. 
Radiographic Diagnostics: Since an x-ray is a two-dimensional representation of a three-dimensional object, it can be helpful to take periapical x-rays in 3 different horizontal planes: straight-on, mesial-oblique, and distal-oblique. Cone Beam Computed Tomography (CBCT) imaging is a major advancement in radiographic diagnostics, revealing anatomy.
If you can’t see it, you can’t treat it. Lighting equals vision. Magnification loupes and headlamps are fundamentally necessary to effectively see pulpal and radicular anatomy.
Surgical Length Burs: Surgical length burs move the visually- obstructive head of the handpiece further away from the occlusal table. Long-length cutting instruments improve the line of sight along the shaft of the bur, promoting safety while encouraging the preservation of tooth structure when searching for canals.
Access Cavities: The completed access cavity should enable the operator to look in a mouth-mirror into a furcated tooth and visualize all of the canal orifices without moving the mirror. Orifice exposure is often diminished by the presence of enamel shelves that can be removed by judicious use of long, fine, thin diamond burs.
Endodontic Access: Cavity preparation is designed to gain access to the pulp chamber and the underlying root canal system. Endodontic access is the first mechanical step that will significantly influence a series of subsequent steps that serve to guide each case to a successful conclusion. With a thoughtful plan, the mechanical objectives are to penetrate, funnel, and create straight-line access to any given orifice. Upon identifying an orifice, the internal axial walls should be flared, flattened, and finished. Importantly, coronal interferences are eliminated to improve radicular access. 
An effective access preparation allows files to be easily inserted directly into orifices, reagents to be strategically dispensed, and, regardless of the obturation method, root canal systems to be filled. In furcated teeth, the access preparation is widest on the cavo surface of a tooth and progressively funnels toward the pulpal floor. All unsupported dentin and enamel should be removed, as leaving this hard tissue has not been shown to strengthen teeth. Leaving trapped tissue, debris, or residual sealer within the access preparation is well-known to contribute to staining and discoloration of the clinical crown following treatment.
The goals of endodontic access and the concept of MIE are compatible and should coexist. Namely, access cavities should not be needlessly restrictive or excessively large; rather, the outline form and preparation should be just right. Ideally, access objectives are confirmed when all the orifices in furcated teeth can be visualized without moving the mouth mirror (Figure 11). The concept of minimally invasive endodontics encourages maximizing healthy tissue, but, and this is most important, MIE does not mean compromising the endodontic treatment goals. To use a car engine analogy, it is illogical to repair the engine through the tailpipe, rather than simply lifting the hood. 
Figure 11. Left: is photograph demonstrates the access preparation and the “white line” connecting the MBI to a more mesially positioned MBII orifice. Right: is image shows initial access and the “red line” of blood emanating from the anatomical grooves o the MB and DB orifices. 
The presence of a second (mesio-buccal (MB)) (MB2) canal in the MB root of the maxillary molars has been the subject of many discussions and studies.
The landmark study of Hess and Zurcher in 1925 showed the mesial root of the mandibular first molar, and the MB root of the upper molars had the most ramifications of any teeth. The results of these studies have shown from 18.6% (2l to 96.1% (3) occurrence of the fourth (MB2) canal in maxillary first molars, depending on which method was used. The literature shows both clinical (in vivo) and laboratory (in vitro) results (1-14) and that more MB2 canals can be found in the laboratory than were found clinically (4). In short, the incidence varies widely, depending on the method used: whether done with or without dye penetration, radiographically, various sectioning techniques, record reviews, different social groups, different age groups, with or without magnification, etc. These studies are important; however, they do not necessarily relate to the routine, daily observations in the clinical practice of endodontics
The results of this 8-year study showed MB2 canals were present in 802 (73.2%) teeth, 665 (82.9%) were filled to their terminus, 300 (45.1%) were deter- mined to join the MBI canal, 365 (54.9%) had separate portals of exit and 137 (17.1%) were unable to be completely instrumented (filled). 
The essential and daunting take away from this rather ancient article is that more than likely there is an MB II in the majority of first molars we treat and that those with separate portals of exit can lead to reinfection. The following case example comes from one of the offices in which I function as an itinerant endodontist. Support given me in terms of proper scheduling, staffing, and supplies enables me to treat Synergy office patients while maintaining high standards.
This patient presented with a chronic lesion associated with a necrotic pulp. The patient came in for treatment to address her inability to chew without experiencing pain in her upper right first molar. The tooth was positive to percussion and tender to palpation. There were no significant periodontal findings. A l.e.o. can be seen on the x-ray.
Diagnosis: chronic apical periodontitis, necrotic pulp.
Prognosis: very good
Completed Root Canal
The concepts discussed were applied. Creation of a rhomboid-shaped access with parallel walls enabled location and treatment of MBII canal.
All images are the property of Stephen Kane, D.D.S.