ACKNOWLEDGEMENTWe are extremely thankful to all the staff members ofthe Department of Prosthodontics throughout ourclinical posting.The immense knowledge and experience of Dr.TejasviSaigal and his continuous help,support andencouragement has been extremely useful to us.We would like to thank Dr. Krishan Dudeja fortheir skillful and gentle support in the presentation ofcontent.Without their active participation and helpthis project would have been impossible to complete.
The posterior palatal seal is defined as, “the soft tissues along the junction of the hard and soft palates on which pressure within thephysiological limits of the tissues can be applied by a denture to aid in the retention of the denture”.
FUNCTIONS OF THE POSTERIOR PALATAL SEALThe function of the posterior palatal seal in the completed maxillary prosthesis is to :-- Maintain contact with the anterior portion of the soft palate during functional movements of the stomatognathic system (i.e mastication, deglutition and phonation). Therefore,the primary purpose of the posterior palatal seal is the retention of the maxillary denture. The posterior palatal seal that has been correctly diagnosed and incorporated into the prosthesis reduces the gag reflex.
Reduces food accumulation beneath the posterior aspect of the denture. Reduces patients’ discomfort when contact occurs between the dorsum of the tongue and the posterior end of the denture base,as the posterior denture border will closely approximate the soft palatal tissues. Compensate for the volumetric shrinkage that occurs during the polimerization of methyl methacrylate resin.
ANATOMIC AND PHYSIOLOGIC CONSIDERATIONSThe posterior palatal seal is divided into two separate but confluent areas based upon anatomic boundaries. The post palatal seal extends medially from one tuberosity to the other. Laterally, the pterygomaxillary seal extends through the ptrygomaxillary notch (hamular notch),continuing for 3 to 4 mm anterolaterally approximating the mucogingival junction.
A. Pterygomaxillary seal extends through the pterygomaxillary notch.B. Postpalatal seal extends medially from one tuberosity to the other.C. Posterior palatal area lies between the anterior and posterior vibrating lines.
ANTERIOR AND POSTERIOR VIBRATING LINESThe posterior palatal seal area lies between the anterior and posterior vibrating lines. The anterior vibrating line is an imaginary line located at the junction of the attached tissues overlying the hard palate and the movable tissues of the immediately adjacent soft palate. One way to locate the anterior vibrating line is to have the patient perform the Valsalva maneuver, which requires thet both nostrils be held firmly while the patient blows gently through the nose.
The anterior vibrating line can also be approximated by visualizing the area while instructing the patient to say “Ah” with short vigorous bursts. Due to the projection of the posterior nasal spine,the anterior vibrating line is not a straight line between both hamular processes. The anterior vibrating line is always on soft palatal tissues.
POSTERIOR VIBRATING LINEThe posterior vibrating line is an imaginary line at the junction of the aponeurosis of the Tensor veli palatini muscle and the muscular portion of the soft palate. It represents the demarcation between that part of the soft palate that has limited or shallow movement during function and the remainder of the soft palate that is markedly displaced during functional movements.
The methods used to mark the posterior palatal seal area are:- i. Conventional approach ii. Fluid wax technique iii. Arbitrary scraping of the master cast
CONVENTIONAL APPROACH This procedure is done after the impression is made and the master cast is poured. A trial base is fabricated using shellac base plate or a well-adapted self cure resin. The patient is asked to sit in an upright position and asked to rinse his mouth with some astringent mouth wash. The posterior palatal area is wiped with gauze. The “T” burnisher is used to locate the hamular notch by palpating posteriorly to the maxillary tuberosity on both sides.The full extent of the hamular notch is marked with an indelible pencil.
The hamular notch is marked using indelible pencilThe posterior vibrating line is marked between the movableand immovable soft palate,using an indelible pencil byasking the patient to say “Ah” in a non-vigorous manner
The line marked in the hamular notch is connected with the posterior vibrating line using an indelible pencil.This’ll form the posterior border of the denture. The trial base is inserted into the patient’s mouth so that the indelible markings are transferred to the trial base. The trial base is seated on the master cast to transfer the markings marked in the patient’s mouth to the cast.
The trial base is trimmed till the posterior border. The anterior vibrating line is marked in the patient’s mouth using an indeloble pencil.While recording the anterior vibrating line,the patient should perform the Valsalva maneuver.The markings are transferred to the master cast. The anterior vibrating line is marked at the junction of hard & soft palate using an indelible pencil.
The area between the anterior and posterior vibrating line is scraped in the master cast to a depth of 1 to 1.5 mm on either side of the mid palatine raphe.In the region of the mid-palatine raphe,it should be only 0.5 to 1mm in depth. The posterior border of the posterior palatal seal should be tapered so that it blends with the palatal tissues.The entire border of the post palatal seal resembles the shape of a Cupid’s bow. The markings of the anterior and posterior vibrating lines are transferred to the cast.The cast should be scraped to a depth of 1 to 1.5mm in the area between the two vibrating lines.
ADVANTAGES OF THE CONVENTIONAL TECHNIQUE. The trial base’ll be more retentive; this can produce more accurate maxillomandibular records. Patient’ll be able to experience the retentive qualities of the trial base. The new denture wearer’ll be able to realize the posterior extent of the denture.
DISADVANTAGES It is not a physiologic technique and therefore depends upon accurate transfer of the vibrating lines and careful scraping of the master cast. The potential for overcompression of the tissues is great.
FLUID WAX TECHNIQUE This technique is done immediately after marking the wash impression and before pouring the master cast. Zinc oxide eugenol and impression plaster are suitable impression materials for this technique as fluid wax adheres well to them. The anterior and posterior vibrating lines are marked as described in the conventional technique.These lines are marked in the patients’ mouth immediately after making the wash impression.
The markings are transferred to the secondary or wash impression by reseating the impression in the mouth. The wash impression is painted with fluid wax. Commonly used waxes are Iowa wax (white) by Dr.Smith, Korecta wax no:4 (orange) by Dr.O.C.Applegate, Adapted wax(green) by Nathan.G.Kaye and H-L physiologic paste (yellow-white) by CS Harkins. The wax should be painted only within the margins of the palatal seal marked on the impression.Usually it is applied in excess and cooled below mouth temperature so that it gains resistance to flow.
These waxes soften at mouth temperature and flow intraorally during impression making. The patients’ head should be positioned such that the Frankfort’s horizontal plane is 30o below the horizontal plane.It is only at this position that the soft palate is at its maximal downward and forward functional position.Flexion of the head also helps to prevent aspiration of the impression material and saliva. The patients’ tongue should be positioned such that it is at the level the mandibular anteriors.This action helps to pull the palatoglossus anteriorly.
In completely edentulous patients’,the handle of the maxillary custom tray should be designed such that it acts like the lower anteriors to guide the tongue during impression making. After positioning the head and the tongue,the impression tray is inserted into the mouth and the patient is asked to make rotational movements of his head without altering the plane to record the functional movements of the palate. The impression is removed after 4-6 minutes and examined. In contrast to green stick compound, glossy areas, show tissue contact. Dull areas show areas which were not in contact with the tissues. The impression should show uniform tissue contact. Areas which appears dull,are added with more wax and the procedure is repeated.
Every time the impression is reinserted, the impression should be held for 3-5 minutes under gentle pressure and 2-3 minutes under firm pressure applied in the mid-palatine area. The procedure is repeated till even tissue contact is achieved. After achieving even tissue contact, the impression is removed and reexamined. The wane in the region of the anterior vibrating line should have a knife-edge margin. Blunt edge margins indicate improper flow and the impression should be repeated. Fluid wax extending beyond the posterior vibrating line should be cut with a hot knife. The impression is redefined again till feather-edge margins are produced.
ADVANTAGES OF FLUID WAX TECHNIQUE Its is a physiological technique. Chances of overcompression of tissues are less. Increased retention of the trial base and convenience in jaw relation.
DISADVANTAGES Handling of the material is very difficult. Increased chair-side time during patient appointment.
ARBITRARY SCRAPPING OF THE MASTER CASTIn this technique, the anterior and posterior vibrating lines are visualized by examining the patient’s mouth and approximately marked on the master cast. Scrapes 0.5 to 1mm of stone in the posterior palatal seal area of the master cast and fabricates the denture.This technique is inaccurate and not physiological and should be avoided.
ERRORS IN RECORDING THEPOSTERIOR PALATEL SEALThe following errors can occur while recording the posterior palatal seal.Underextension:- Most common cause. May be produced due to following reasons. When the denture does not cover the foveapalatina, the tissue coverage is reduced & the posterior border of the denture is not in contact with the denture border during functional movements. Improper delineation of the anterior and posterior vibrating lines.
Excessive trimming of the posterior border of the denture by the dental technician. There are patients who inform the dentist on the very first visit for complete denture therapy that they are gaggers. The dentist intentionally leave the posterior borders underextended in order to reduce the patients’ anxiety in gagging…OVEREXTENSION:- Overextension of the denture base can lead to ulceration of the soft palate and painful deglutition.Covering of the hamular process can lead to sharp pain in that region.In order to relieve these areas ,indelible pencil markings are made on them (hamular process, ulcers, etc) and transferred to the denture.These regions are trimmed and polished.
UNDERPOSTDAMMING:- This can occur due to improper head positioning & mouth positioning, eg:- When the mouth is wide open while recording the posterior palatal seal the mucosa over the hamular notch becomes taut.This’ll produce a space between the denture base and the tissues. Inserting a wet denture into a patient’s mouth and inspecting the posterior border with the help of a mouth mirror can identify underdamming.. If air bubbles are seen to escape under the posterior border,it indicates underdamming. In order to correct underdamming,the master cast can be scraped in the posterior palatal area or the fluid wax impression can be repeated with proper patient position.
OVERPOSTDAMMING:- This commonly occurs due to excess scraping of the master cast.It occurs more commonly in the hamular notch region. Mild overdamming in the hamular notch region can lead to tissue irritation of the mucosa and excessive postdamming produces downward displacement of the denture posteriorly. Selective reduction of the denture border with a carbide bur, followed by lightly pumicing the area while maintaining its convexity will remedy the problem.