Cd-report.docx

POLISHING AND TRIMMING TRIMMING AND POLISHING (Laboratory Procedures & Materials)  

POLISHING is a process of removing scratches. Polishing consists of making the dentures smooth and glossy without changing the contours. Principles of polishing: a. The tissue surface of a denture is never polished as a polishing destroys the details necessary for good fit and retention. b. The polished surface extends just over the border, but the borders are not reduced in height and width during polishing. c. Care must be taken when using pumice (it should be used as wet slurry) as this material is very abrasive and may obliterate the details placed on the denture when they were waxes (festooned). d. Resin teeth have approximately the same hardness as the denture base, so polishing a denture with resin teeth requires some precautions not necessary with porcelain teeth. e. When polishing, only the denture base and not the teeth are polished. f. During the finishing and polishing we should minimize the reduction of bulk because this cause warpage.

EQUIPMENT AND MATERIALS 1) Maxillary and mandibular complete dentures separated from the master casts.

2) Dental lathe machine 

A machine that rotates a workpiece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, and turning, with tools that are applied to the workpiece to create an object with symmetry about that axis.

3) Pumice  

Recommended as a cleaning and polishing aid to finish acrylic denture moulds. It is used in a slurry form to assist dental technicians obtain a smooth surface.

4) Brushes and rag wheels suitable for polishing

5) Polishing compound     

Tripoli Polishing Compound is great for removing scratches and preparation of denture materials. Also works well on metals prior to final polishing. Yellow High Shine Polishing Compound is for exceptional high gloss on denture materials. White Diamond Polishing Compound is a clean, dry, fast pre-polish on plastics. Green Plate Polish is a high shine polishing compound for use on acrylic denture materials. Shure-Shine Plate Polish is bestselling polish for acrylic denture materials.

6) No. 6 or 8 round bur

7) Carbide acrylic burs

PROCEDURE 1. Using a carbide acrylic bur in the lathe, remove any acrylic flash and bulk produced when sealing the trial dentures to master casts. 2. Place small black bristle brush in the polishing lathe on low speed. Place pumice and disinfectant into pan. Using a generous amount of pumice, polish the stippled areas, the portion of the denture base near the cervical portions of the teeth and the rugae area. Never polish the tissue surface of a denture. 3. Place a large black bristle brush in the polishing lathe on high speed. Using generous amounts of pumice, polish the lingual flanges of the mandibular, the posterior of the maxillary denture and the lingual festooning adjacent to the denture teeth. 4. Wet a rag wheel designated for use with pumice. At high speed with generous amounts of pumice, Polish all denture base areas. 5. Rinse off the pumice and dry. Check areas that are not polished and re-polish until smooth 6. When you have achieved a uniformly smooth denture base surface, dry the denture thoroughly. Place the rag wheel designated for high shine in the lathe at low speed and polish the denture with polishing compound. 7. Place the dentures in the general purpose (blue) solution in the ultrasonic cleaner for a few minutes to remove any polishing compound. RESULT: You have finished and polished your complete dentures. You must now make remount casts and remount the maxillary dentures in preparation for your next patient visit. On receiving the processed complete denture from the laboratory BEFORE THE DELIVERY APPOINTMENT YOU MUST a. make maxillary and mandibular remount casts and; b. mount the maxillary remount cast on the articulator using the face bow remount jig. This must be done before the denture placement appointment because you will not have sufficient time to complete the denture delivery procedures if you do not plan ahead. The remount casts, occlusal index, and processed dentures must be graded by your faculty prior to your patient visit for denture delivery.

REMOUNT PROCEDURE Causes of Errors in Occlusion 1. Incorrect registration of centric occlusion a. During jaw relation, when occlusal rims are brought together cause uneven pressure due to premature contact in the 2nd molar or incisor region b. Imperfectly fitting record bases can cause movement of rims while recording centric i. The dentures will have slight inaccurate centric occlusion relation and will tend to move on the ridges, causing soreness c. The models may not be placed accurately on the articulator while mounting 2. Irregularities in Teeth Setting a. Difficult to set perfectly even contact in teeth arrangement leading to some heavy contacts / pressure b. Wax has certain resiliency, permits tooth movements to occur when interferences are encountered unlike hard acrylic in denture c. Wax can contract and move causing irregularities in teeth setting 3. Tooth movement while Flasking and Packing a. Tooth movement while de-waxing b. Excesive packing pressures results in, the artificial teeth being forced into the investing plaster c. If the acrylic resin has reached an advanced dough stage d. Normal packing pressures when the investing mix is weak can break the mould e. Incomplete flask closure f. If pressure on the flask is released during the curing cycle g. Separation of the two halves of the flask by a layer of excess resin which should have been removed during trial closure of the flask (flash) 4. Articulator Wear a. All articulators are subjected to wear i. Older and more worn the articulator is, the greater will be the error in occlusion and articulation b. Every piece of mechanical apparatus exhibits some play in its moving part and when this becomes easily detectable, the bearing should be replaced 5. Other factors a. Overheating during polishing procedures b. Inevitable dimensional changes in the denture material during and after polymerization c. Expansion of the acrylic resin due to water absorption i. Shrinkage in denture makes the cuspal position change in turn increasing vertical dimension

When to Do Remounts? 1. Wax-Up ▫ If the wax-up occlusion is different in mouth compared to the articulator 2. Processed ▫ After processing the VDO is increased ▫ To get back to the original VDO

3. Delivery ▫ Inaccurate occlusion from all previous steps not eliminated in prior remount Occlusal Errors can be corrected by A. Direct Correction in the Mouth a. Articulating Paper  It will not give an accurate indication of premature contacts because of resiliency of supporting tissues that allows the denture to shift producing marking which are frequently false b. Use of central bearing plates c. Occlusal waxes  Adhesive wax is added on the mandibular denture  Points of penetration are observed and relieved  Advantage: can locate interference in functional movements  Disadvantage: can give false reading due to shift of underlying soft tissues d. Abrasive Pastes  Should only be used to refine occlusion after selctive grinding on articulator  Disadvantages: (1) shifting bases cause premature contacts (2) cusps maintaining vertical dimension might be destroyed B. Laboratory Remounting C. Clinical Remounting Laboratory Remounting o

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Purpose o To correct errors in processing o To return dentures to the correct vertical dimension o To restore centric and bilateral balanced occlusion It is done after processing Advantages o Helps in achieving centric balance by selective grinding o Correction of occlusal errors is done before denture delivery

Clinical Remounting    

It consists of remounting the finished dentures on an articulator by using new inter-occlusal records in the patient’s mouth Purpose is to accommodate the errors made during centric relation records It is done after denture delivery Advantages o Reduces the patient’s cooperation because it is done in the articulator rather than in the patient’s mouth o Easier to spot and correct errors in the articulator than in the patient’s mouth o Absence of saliva makes markings more accurate o It will provide stable base when correcting rather than the resilient tissues inside the mouth

BALANCE OCCLUSION o

Is the simultaneous contacting of the maxillary and mandibular teeth on the right and left side and in the posterior and anterior occlusal areas in centric and eccentric positions, developed to lessen or limit tipping or rotating of the denture bases in relation to the supporting structures

Types of Balanced Occlusion  Unilateral Balanced Occlusion o This is a type of occlusion seen on occlusal surfaces of teeth on one side when they occlude simultaneously with a smooth, uninterrupted glide. o This is not followed during complete denture preparation. o It is more pertained to fixed partial dentures.  Bilateral Balanced Occlusion o This is a type of occlusion that is seen when a simultaneous contact occurs on both sides in centric and eccentric positions. o Bilateral balanced occlusion helps to distribute the occlusal load evenly across the arch and therefore helps to improve stability of the denture during centric, eccentric or parafunctional movements.  Protrusive Balanced Occlusion o This type of balanced occlusion is present when mandible moves in forward direction and the occlusal contacts are smooth and simultaneous anteriorly and posteriorly. o There should be at least three points of contact in the occlusal plane. o Two located posteriorly and one anteriorly. o Absent in natural dentition.  Lateral Balanced Occlusion o There will be a minimal simultaneous three point contact present during lateral movement of the mandible. o Absent in natural dentition o Teeth should be arranged such that there is simultaneous tooth contact in balancing side and working side. Mechanics of Balanced Occlusion 

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In natural teeth, when the mandible is protruded so that the incisal edges of the upper and lower teeth contact, there is a gap between the upper and lower posterior teeth, this is termed as “Christensen’s phenomenon” But this occlusion could cause tipping of the denture in the posterior region. Thus, simultaneous anterior and posterior contacts are required when mandible is protruded.

Concepts of Balanced Occlusion 1) Gysi’s concept o He proposed the first concept towards balanced occlusion in 1914 o He suggested arranging 33 degree anatomic teeth could be used under various movements of the articulator to enhance the stability of the denture 2) French’s concept o He proposed lowering the lower occlusal plane to increase the stability of the dentures along with balanced occlusion o He arranged upper first premolars with 5 degrees inclination, upper second premolars with 10 degrees inclination and upper molars with 15 degrees inclination o He used modified French teeth to obtain balanced occlusion 3) Sear’s concept o He proposed balanced occlusion for non anatomical teeth using posterior balancing ramps or an occlusal plane which curves anteroposteriorly and laterally 4) Pleasure’s concept o He introduced a pleasure curve or the posterior lateral curve to align and arrange posterior teeth in order to increase the stability of the denture 5) Frush’s concept

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He advised arranging the teeth in a one dimensional contact relationship, which should be reshaped during try in to obtain balanced occlusion Hanau’s Quint o Rudolph L. Hanau proposed nine factors that govern the articulation of artificial teeth. They are:  Horizontal condylar guidance  Compensating curve  Protrusive incisal guidance  Plane of orientation  Buccolingual inclination of tooth axis  Sagittal incisal guidance  Tooth alignment  Relative cusp height o “Laws of Balanced Articulation” o Hanau later condensed these nine factors and formulated five factors which are commonly known as Hanau’s Quint:  Condylar guidance  Incisal guidance  Compensating curves  Relative cusp height  Plane of orientation of occlusal plane Trapozzano’s concept of occlusion o He reviewed and simplified Hanau’s Quint and proposed his Triad of Occlusion o He said that plane of occlusion could be shifted to favor weak ridges, hence its location is not constant and is variable within the inter arch distance  Condylar guidance  Incisal guidance  Relative cusp height Boucher’s concept o Boucher proposed the following three factors for balanced occlusion: o Orientation of the occlusal plane, the incisal guidance, and the condylar guidance o The angulation of the cusp is more important than the height of the cusp. o The compensating curve enables one to increase the height of the cusp without changing the form of teeth Lotts concept o The greater the angle of the condylar path, the greater is the posterior separation during protrusion. o The greater the angle of the overbite, the greater is the separation in the anterior and posterior regions irrespective of the angle of the condylar path. o The greater the separation of the posterior teeth the greater or higher must be the compensating curve. o Posterior separation beyond the balancing ability of the compensating curve can be balanced by the introduction of the plane of orientation. o The greater the separation of the teeth, the greater must be the height of the cusps of posterior teeth. Levin’s Concept o He named the four factors of occlusion as the QUAD o The condylar guidance is fixed and is recorded from the patient. o The incisal guidance is usually obtained from patients esthetic and phonetic requirements o The compensating curve is the most important factors in obtaining occlusal balance o Cusp teeth have the incline necessary for balanced occlusion but nearly always used with a compensating curve.

Factors influencing Balanced Occlusion

a) Thielemann’s formula b) Condylar Guidance o Mandibular guidance generated by the condyle and articular disc traversing the contour of the glenoid fossa o This is the only factor which can be recorded from the patient o It is registered using protrusive registration and transferred to the articulator as the condylar guidance o This factor cannot be modified  Horizontal condylar guidance - guides the forward movement for protrusive balance  Lateral condylar guidance - guides the sideward or lateral movement of the mandible o Posterior slope of the articular eminence represented by the condylar tract of articulator c) Incisal Guidance o The influence of the contacting surfaces of the mandibular and maxillary anterior teeth on mandibular movements o It is determined by the dentist and customized for the patient during anterior try in o It acts as a controlling path for the movements of the casts in an articulator o It should be set according to the desired overjet and overbite planned for the patient o If overjet is increased, the inclination of the incisal guidance is decreased o The incisal guidance has more influence on posterior teeth than condylar guidance d) Plane of occlusion or occlusal plane o An imaginary surface which is related anatomically to the cranium and which theoretically touches the incisal edges of the incisors and tips of occluding surfaces of the posterior teeth o It is not a plane in the true sense of word but represents the mean curvature of the surface o It is established anteriorly by the height of the retromolar pad o It is usually parallel to Camper’s line e) Compensating curves o The anteroposterior and lateral curvatures in the alignment of the occluding surfaces and incisal edges of artificial teeth which are used to develop balanced occlusion o 2 types of curves o Anteroposterior curves o Lateral curves Curve of Spee o

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Anatomic curvature of the occlusal alignment of teeth beginning at the tip of lower canine and following buccal cusps of natural premolars and molars, continuing to the anterior border of ramus It is seen in the natural dentition and should be reproduced in a complete denture The significance of the curve is that, when the patient moves his mandible forward, the posterior teeth set on this curve will continue to remain in contact

Monson’s Curve o o

The curve of occlusion in which each cusp and incisal edges touches or conforms to a segment of a sphere of 8 inches in diameter with its center in the region of glabella Only if teeth are set following Monson’s curve will there be lateral balance of occlusion

Wilson’s Curve o o o

A curve of occlusion which in transverse cross section conforms to a line which is convex upward except for last molars This curve runs from palatal cusp of the first premolar to the distobuccal cusp of second molar The second molar gives occlusal balance and the second premolars gives lever balance

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Cuspal angulation o The angle made by the average slope of a cusp with the cusp plane measured mesiodistally and buccolingually o The cusps on the teeth or the inclination of the cuspless teeth are important factors that modify the effect of plane of occlusion and the compensating curves o The mesiodistal cusps lock the occlusion, such that the repositioning of teeth does not occur due to settling of the base o To prevent the locking of occlusion, the mesiodistal cusps are reduced during occlusal reshaping.