Anterior Tooth Form and Formation: A Systematic Approach

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Maxillary anterior teeth have functional and esthetic components.  Because of this esthetic value, there are countless theories, courses, and presentations to explain and teach the intricacies of maxillary anterior teeth. When we consider color, texture, rotations, spacing, and many more topics it is easy to get lost in the details. This post will not focus on the details.  Before I focus on the details I ALWAYS follow this systematic approach for anterior tooth arrangement.  Just like building a house, the framework or foundation must be constructed first. After the framework is completed, the details are then added to make each tooth unique.  Following these exact steps on every case will save a tremendous amount of time and will also allow for the variability of nature. These steps are followed whether I do one unit or six. The same steps are used for wax-ups, temporaries, or definitive restorations, digital or analog. The goal is developing efficiency by following the same protocol time after time. This protocol allows the technician or dentist tremendous variability for adding the details after the foundation is completed.

The Steps

Figure1-interpupillary

Fig 1

1)  When creating multiple anterior teeth, the starting points are always the midline and the labial incisal edge of the central incisors.  The midline is determined by facial landmarks.  A horizontal line can be drawn connecting the glabellum, apex of the nose, and the center of the chin.  A second interpupillary line (fig.1) can be drawn which is perpendicular to the facial midline.  The labial incisal edge of the central incisors will be parallel with the interpupillary line. The midline and labial incisal edge should be predetermined prior to the definitive restorations. If the dentist has done the temporaries a model of the correct midline and incisal edge position should be provided to the lab.

Figure2-contact-points

Fig 2

Figure3-contact-points

Fig 3

2)  The contact points come next.  As the contact areas move from the centrals to the canines they move cervically. (red line fig.2,3)

 

 

Fig4-function

Fig 4

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Fig 5

3)  The next step is the most critical step, the lingual surface.  Since all teeth exist within a masticatory system it is impossible to shape teeth without addressing how they interact with the antagonist tooth, or teeth.  The incisal edge of the tooth is more accurately an incisal ridge2.  The ridge consists of the labial incisal edge (red line in fig.4,5) and the lingual incisal edge (blue line in (fig.4,5).  These two incisal edges form the boundaries of the incisal ridge.  The lingual edge, which is often ignored, is the functional component that is dictated by the mandibular incisors and how a person chews.  The labial edge is the esthetic incisal edge that is seen when a person speaks and smiles. The maxillary lingual incisal edge is the most critical part of the ridge with regard to function. The lingual edge cannot be ignored or placed arbitrarily without consideration of the mandibular incisors.

The location, or placement of the labial edge is mostly determined by facial esthetics and phonetics. This edge can be lengthened or moved as long as it does not affect function with the mandibular incisors, speech, and facial esthetics.

The incisal ridge is rarely symmetrical and the two edges are rarely parallel. (fig.4,5)

In short, the lingual function and contour are addressed prior to the labial contour.

Figure6-mesial

Fig 6

4)  The mesial line angle is created next. (black line fig.6)  When viewed directly from the facial the central, lateral, and canines are divided in segments vertically (fig.3). The central is divided in thirds.  The lateral and canine are divided in half. The mesial line angle of the central will start near the contact point and terminate in the cervical portion of the tooth at the mesial third of the tooth. This line angle should match the mesial line angle of the adjacent central incisor as closely as possible.

The lateral mesial line angle starts at or above the contact point and terminates in the cervical portion at the middle half of the tooth.

The mesial line angle of the canine starts above the contact point and angles towards the middle of the tooth.

Figure9-mesial-distal

Fig 7

5)  The distal line angles come next (fig.7), always moving from the central to the canine. Whenever possible, the distance between these line angles should closely mimic the contralateral tooth. The width of the contralateral teeth is not always the same, but they can be optically matched more easily if the line angles match.

 

Figure10-height-of-contour

Fig 8

cervical_height_contour_Illustrator3

Fig 9

6)  The cervical height of contour (white line fig. 8,9) closely follows the contour of the soft tissue (pink). This is why it is important to do this step with a soft tissue model, or solid model. The apex of the CEJ on the central incisor is at the distal third.  The apex of the lateral and canine are at the middle of the tooth (red dots in fig.8).

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Fig 10

Figure13-Kois-waxing-Guide

Fig 11

8)  The last step for the basic framework is the labial incisal edge. The shape of the labial edge (red line fig.10) can be highly variable as long as it is not in the pathway of the mandibular incisors during chewing.  Typically, the labial edge of the centrals and the canines will follow the same line when viewed on a horizontal plane. In this case, the Kois Waxing Guide (fig.11) from Panadent is used to show how the central incisors and canines are on the same incisal plane.

anterior-frame-4contour--incisal-edge

Fig 12

When the framework is shown without teeth (fig.12) the basic shapes become apparent. From this point forward attention can be paid to filling in the lines, or connecting the dots. After the basic framework is completed the individual esthetics can be completed. The individual esthetics varies from person to person, but the basic framework is always the same and the same steps are always followed.

 

Figure15-canine-not-in-view

Fig 13

When the teeth are viewed facially the distal half of the canine is not in view (fig.13) or barely in view. The arch form can be broadened simply by making the distal half of the canine more in view.

Conclusion

Creating esthetic anterior tooth contours that function properly requires a tremendous amount of skill and knowledge. Tooth morphology, facial esthetics, soft tissue contour, and occlusion all play a role. When creating a framework it is important to not get locked in to a specific tooth form or design. The framework should follow the basic commonalities of teeth and allow room for the variability of details. Having a consistent repeatable protocol for the basic framework will save tremendous amounts of time.

 

 

 

category_dentalUniversity of Washington Affiliation

easter-quadMany thanks to the University of Washington School of Dentistry, especially Dr. John Townsend, for awarding me the Affiliate in Medical/Dental Practice.  It is an incredible honor to be granted this affiliation.  Over the past 20 years I have had an ongoing relationship with the Graduate Prosthodontic Program. I have taught classes, worked on literature review,  and assisted the graduates with their laboratory work.  It is very much appreciated that my work has been acknowledged and I look forward to future involvement.

category_articleCharacteristics of Teeth:  A Review of Size, Shape, Composition, and Appearance of Maxillary Anterior Teeth

CCEDV37N3_Cover_4th.inddCompendium of Continuing Education in Dentistry was kind enough to publish my article in their March 2016 Issue.  This article explains the very basics about anterior maxillary teeth.  Most of this article also appears in Personality of Teeth: A Visual Encyclopedia.

Characteristics of Teeth:  A Review of Size, Shape, Composition, and Appearance of Maxillary Anterior Teeth  [pdf]

 

 

category_dental

The Optical Properties of Teeth

Restorative dental materials have physical and optical properties that attempt to mimic the properties of teeth. Many modern monolithic ceramic materials have defined predictable crystalline structures that do not scatter light in the same way as a natural tooth.  To compensate for these esthetic properties, the dental technician must layer different colors and opacities of material.  Light scattering within homogenous monolithic materials makes the replication of teeth very difficult.  The natural tooth section on the right is .55mm thick.  From this cross section it is easy to see the optical complexities of tooth structure.  The feldspathic ceramic cross section on the left is 1.5mm thick.  This cross section shows the different layers of material that are necessary to mimic natural teeth.  The sample in the center is a replica of the left sample.  It is made from monolithic zirconia.  The zirconia cross section shows the optical challenges the dental technician faces when using this material to match teeth.  Monolithic materials have gained in popularity, but present many esthetic challenges.

category_scienceEmerging Material Research

Denry-kellyThis fantastic article addresses many critical issues with today’s new ceramic systems for dentistry.  It is essential for dental laboratories to know why materials are used, and how to properly use them.  Drs. Denry and Kelly also mention emerging ceramic systems which will be fun to follow.  Thank you to Dr. Kelly for kindly sharing their research with me.

category_dental

The Personality of Front Teeth

Fig12-Central-set20e

One of the most basic and valuable subjects necessary for dental professionals is dental anatomy.  A fundamental component of dental anatomy is tooth morphology.  There are many well known dental anatomy textbooks that tackle the complex topic of tooth form.  In many cases these textbooks use artist’s renderings of teeth.  They assign average measurements in an attempt to create a standard tooth shape for each tooth in the mouth.  Artist or computer renderings of tooth shapes give basic information but don’t fully convey the rich diversity of sizes, shapes, colors, and textures.

Standard-dev-chartsIn order to quantify this diversity I have sorted, cleaned, photographed, and measured 600 extracted maxillary incisors; 200 centrals, laterals, and cuspids.  I have compiled my data in an article that has been submitted for publication.  If and when this gets accepted, I will post the full article.

Gallery of article images.

category_dental

  Personality of Teeth: A Visual Encyclopedia

personality-coverSeveral years ago I was given thousands of extracted teeth. These teeth were collected during volunteer work at clinics in the southeast of the US.  This collection of teeth changed hands several times before they were given to me.   It has been very helpful for me to study and photograph these teeth and I have always wondered if I could find a way to share this collection with others.  A diverse collection of teeth is a treasure filled with useful information.  About a year ago I decided to document these teeth with photography.  The result is Personality of Teeth: A Visual Encyclopedia.

This electronic book has taken over a year to complete.  For each type of tooth (maxillary central incisor, for example) there were hundreds of samples to choose from.  Each tooth is photographed from five perspectives.  In total, there are over 2,000 views of more than 500 teeth. I spent several weeks photographing these teeth from different views using various light sources.  I finally settled on a technique that would best convey the form, color, and texture of these teeth.  There are also study pages that describe landmarks and a glossary of terms.

packaging-presentationThe analyzing, sorting, cleaning and photographing of these teeth took hundreds of hours.  I have learned so much from viewing these teeth through my macro lens, and blown up on my computer screen. I believe this project has elevated my work and has given me a new appreciation of the diversity of nature.

category_scienceSlow cooling protocol improves fatigue life of zirconia restorations.

Slow cooling protocol improves fatigue life of zirconia crownsOne of the newer restorative materials used today in dentistry is zirconia.  Zirconia has been used as a biomaterial for over 25 years.  What Future for Zirconia as a Biomaterial? Although much has been written about zirconia, there is surprisingly little clinical research in the field of dentistry.  The lack of research has created some challenges with understanding this material.

 As mentioned, zirconia has a long history of use in the medical field but is relatively new to dentistry.  Why has zirconia become popular in dentistry?  There are some driving factors behind the increased popularity of zirconia. 

In dentistry the standard of care for dental restorations has been gold and gold alloys.  Gold alloys can have porcelain veneered to the outside to make tooth colored restorations.  Gold prices have skyrocketed recently which has caused dentists to seek out less expensive alternatives.

gold-chart

The use of CAD/CAM technology has increased within dentistry.  Dentists and labs are increasingly turning to this technology to replace tasks that were traditionally done by hand. Zirconia can be milled (CAM=computer aided milling) easier than other restorative materials. Zirconia  milled for industrial applications has been used since the late 1970’s,  with widespread use since the 1990’s.  The mills used today for dental applications were originally developed for industrial uses.  These industrial machines and methods have been adapted to suit the dental profession.  Millions of zirconia dental restorations have been fabricated worldwide using machines and methods based on industrial technology and experience. 

This excellent article addresses some of the common problems with zirconia restorations.  Understanding the problems associated with zirconia allows me to use this material more comfortably in the proper situation.  This can be said for all the restorative materials I use.

I cautiously use zirconia restorations.  Like all of the restorations I make, I want to be aware of current research so I can be comfortable using newer materials.  I never want to use a material solely because it is popular.  I want to make sure my choice is evidence based.

Slow cooling protocol improves fatigue life of zirconia restorations. [pdf]