Introduction
Clinical and technical needs exist for excellent, accurate records that are essential for the success of any dental procedure using either digital or conventional techniques. This is no truer than with Denture prostheses. A review therefore of the anatomical landmarks which must be included in the impressions is important since without this inclusion of these mandatory elements, the expected successful outcome will predictably fail.
Prosthetic Principles
Regardless of the advances in technology, the basic principles governing the fit, function, comfort and retention of complete dentures are the same. These principles have existed without change for over a hundred years. Alfred Gyri published literature outlining these fundamental principles in 1918 and they have formed the guidelines used today in the fabrication of complete dentures. As modern techniques including both digital and conventional modalities have evolved, the principles and guidelines established over time have remained constant. Some of these principles are governed by the establishment of a prosthesis which covers and fits edentulous anatomy in such a way as to be functionally compatible, and comfortable with adequate retention as to allow the patient an excellent chance of constant use. It must be mentioned that of all dental procedures, complete denture fabrication and proper fit is extremely difficult and non-forgiving. Excellent training by individuals who have mastered these skills is a start. However, all masters of this craft admit that nothing makes up for the experience of doing many cases and applying these principles over time, gaining wisdom as they go. There are no short cuts. Much like an artist whose paintings improve by putting in the time and effort and eventually his or her “art miles” cause an improvement and increase in excellence over time, so it is with the skill in mastering denture procedures.
Anatomical Landmarks
Complete dentures begin with an understanding of the oral anatomy upon which the denture prosthesis will rest. The pictures shown in Illustrations 1 and 2 show how this anatomy appears in situ.
Illustration 1 Maxillary Arch
Illustration 2 Mandibular Arch
The maxillary landmarks are shown in diagrams 3 and 4 and include the following:
- Hamular notches
- Tuberosities
- Fovea palatini
- Labial and buccal frenums
- Palatal midline suture
- Post dam area
See below in Diagram 3
Diagram 3
The mandibular landmarks include:
- Retromolar pads (Pear shape pads)
- Mylohyoid
- Sublingual crescent
- Lingual frenum
- External oblique / buccal shelf
- Buccal frenum
- Mentalis muscle
- Labial frenum
See Below in Diagram 4
Diagram 4
Whether utilizing digital or conventional impressions, these landmarks must be passively included. This is illustrated in the perfect impressions below in Illustrations 5 and 6:
Illustration5 and 6 Maxillary and Mandibular Impression2
Illustration 7 Maxillary Model
Illustration 8 Mandibular Model
The models which are poured with dental stone are shown above in Illustrations 5 and 6. If digital scans are utilized, a three-dimensional model is fabricated which will then be used in the same way. It has been observed by many dentists and lab technicians that one problem that exists is getting proper passive impressions of the areas in which the borders of the denture will fit peripherally without pulling the tissues, tongue and cheeks out of the way too much as to stretch and distort these areas. This is more difficult with digital scans than with well fit denture trays which are border molded or utilizing a putty and wash technique.
Understanding the biology and function of oral anatomy will definitely improve clinical and technical communication. And it can’t be stressed enough that good communication and understanding must exist between dentist and laboratory technician using the basic knowledge of the edentulous oral environment and essential requirements for proper fit and success of the case. Having a common “language” for this knowledge is requisite for collaboration.
Understanding the Oral Environment
A prosthodontist once said, “If I could specialize in anything, it would be upper dentures!” I is true that between the two, upper dentures fit more securely and seem easier to fabricate for patient satisfaction than lower dentures. The advent of denture attachments such as Zest or Novaloc overdenture systems have vastly improved denture procedures as they allow the denture to snap in place rather than resting merely on the ridges as with the lower denture or relying on suction alone as with the upper denture. This suction is achieved on the upper denture by placement of ideal borders which are neither over or under extended and with a posterior sealed called a post dam that is placed in the denture by the dental technician. Care must also be taken not to over or under extend the posterior of the denture to prevent looseness or gagging. The ideal placement is at the vibrating line between the hard and soft palate and to include the fovea palatini. Because the lower denture retention is reliant on the patient learning to hold it in with tongue and cheek muscles, it is sometimes referred to as a “floater”. The denture rests on the bony ridge and retromolar pad (pear shape pad). If the lower denture is short posteriorly and doesn’t rest on the retromolar pad, it will dig into the ridge and be painful to the patient when they masticate or otherwise bites down. Special care is taken to extend the borders into the mylohyoid and lingual crescent and buccal areas. These areas are somewhat more arbitrary and less defined as the upper denture but must not be over or under-extended for the particular patient for whom the denture is being made. Both upper and lower dentures must not constrict or press on the frenum and muscle attachments. The dentures must be adjusted if any pain or ulcerations occur on delivery and subsequent wearing of the dentures.
Conclusion
As more dental laboratories branch out and expand their product offerings to include removable prosthetics and as more dentists begin sending digital imagery for their final edentulous impressions, effective communication is a must. Analyzing impressions both digitally and conventionally for the purpose of anatomical inclusions during denture fabrication and communicating using the language of removable prosthodontics will affect productivity and reduce redos. Check out the slide presentation on the “Putty and Wash Technique using Adjust-a-Trays™” on this website.