Preparation Guidelines

Design. Deliver. Support.

Preparation Guidelines6 resources that will improve your tooth preparation


Learn more at ddslab.comCall or chat online with our technical support team.

(877) 337-7800

Index

Introduction ..................................................................................1

Bur sizes and selection for optimum preparations..........................2

Three unit all-ceramic preparation guidelines .................................8

Tooth preparation for all-ceramic crowns .....................................14

Tooth preparation guidelines for PFM crowns .............................. 17

Tooth preparation guidelines for zirconia crowns ......................... 21

All-ceramic chairside preparation guide for IPS e.Max® .................26

Final Thought ..............................................................................28



(877) 337-78001

Although the average person enjoys good dental health, tooth loss is still very common. Due to the growing lifespan of a person, more elderly adults need dental restorations to eat their favorite foods and smile with continued confidence. The demand for long-term solutions for tooth loss continues to grow.

Patients are demanding dental restorations that provide excellent aesthetics and functionality. There are many different types of restorations and materials on the market. Depending on the patient’s needs, a clinician should be equipped to prepare different types of tooth restorations with complete accuracy and efficiency. Achieving a successful restoration depends on the clinician’s ability to select the appropriate material and follow the right preparation and cementation protocols.

Often times it can be difficult for dental students or young doctors

to prepare a tooth correctly. Unlike other human tissue, dental tissues don’t have a regenerative capacity. Therefore, the removal of dental biological material should be planned and executed with supreme attention. Tooth preparation involves several distinct steps which require careful preparation and execution. This resource contains tooth preparation guidelines for an array of restoration types and materials.

In this guide we will discuss:

• Bur sizes and selection for optimum preparations

• Three-unit all-ceramic preparations guidelines

• Tooth preparation for all-ceramic crowns

• Tooth preparation guidelines for PFM crowns

• Tooth preparation guidelines for Zirconia crowns

• Anterior composite restoration: materials, preparation, techniques

Introduction


2

Bur sizes and selection for optimum preparationsArticle by Daniel Williams | Removable Technical Consultant

Burs are one of the most frequently used mechanical devices in any dental office. Selecting the correct size and type of bur is essential for clinical success.

Burs

A bur consists of three parts: the head, the neck, and the shank. The burs used in handpieces are usually fabricated from tungsten carbide but they could also be made with diamond particle coatings. The coating has varying degrees of roughness depending on the nature of the treatment. Ceramic and zirconia burs are increasingly utilized. Ceramic burs are suitable for caries removal and are used in restorative procedures.

A wide range of sizes and configurations are available, and the bur selected by the clinician will depend on individual preference, the type of procedure, and the bur’s effectiveness in a given clinical situation. Selecting the most appropriate bur is critical for safely and effectively removing dental hard tissues. Choosing the correct type of bur also increases ergonomics for the clinician and reduces discomfort for the patient.

Image: Bur Sizes Source: Strauss Diamond Instruments



(877) 337-78003

Tungsten carbide and diamond coated burs

Tungsten carbide burs have blade-shaped heads to produce the desired cutting action. These cutting properties vary according to the blade’s degree of angling and positioning.

Some of these properties are outlined below:

• A bur with a more obtuse angle produces a negative rake angle, increasing the longevity and strength of the bur. These type burs are excellent for producing smooth curved lines and for chamfer or shoulder margins; as they virtually will do the work for you.

• Burs with more acute angles produce positive rake angles, so cutting is quicker, but the bur will become blunt sooner. The diamond coated varieties are great for initial reduction of enamel, and are invaluable for veneers preps. Again; they practically do the work for you, both sub-gingivally as well as supragingival

• Crosscuts or additional cuts across the blades increase cutting efficacy. Crosscut burs are faster due to less debris build-up.

• Flute angles and cutting characteristics in burs are designed for each specific task.

• Cavity preparation burs have wider and deeper flutes that cut into enamel more efficiently and quickly.



(877) 337-78004

• Operative burs are crosscut or have straight blades that cut more slowly but smoothly.

• Diamond coated burs create a smooth shape, and the level of smoothness achieved depends on whether you select a fine, medium, or coarse-coated bur.

• Bur shapes depend on the clinician’s preference and the patient’s required treatment. Configurations include tapered fissures, inverted cones, round, and pear-shaped. Each of these are available in a variety of sizes and diameters. Flat fissure, crosscut, and plain tungsten carbide burs all have the same cutting force when used in a traditional air-driven handpiece so their shape doesn’t appear to influence the cutting power of the bur.

More specialized restorative burs are used for specific tasks, including depth-cutting burs, which have horizontal ridges against the diamond fissures to guide the depth of the cut. End-cutting burs are used to shape the floor of mesial and distal tooth preparations for Class II cavities with smooth sides. These burs reduce the risk of affecting the surface of the adjacent tooth with the bur’s cutting surface. End-cutting burs can also be used to shape the pulpal floor of Class I and II cavities while avoiding the risk of a cutting surface meeting the prepared cavity walls.

More recently, tungsten carbide burs have been developed. These burs have a unique geometry because they are more sharply dentated compared with a crosscut bur. Tungsten carbide burs cut more quickly and efficiently through enamel, amalgam, composite, and metals, all while producing



(877) 337-78005

less vibration. The design of these burs helps reduce stress on the tooth and surrounding periodontal tissues because they require less pressure to initiate and complete a cut. Cutting is more accurate and generates less heat. Similarly, fine crosscut tungsten carbide burs are suitable for all types of restorative dentistry and can accomplish multiple tasks, saving time since there is no need to swap burs during a procedure.

Choosing the correct type of bur for specific clinical situations

Removing a dental crown

A diamond fissure bur is most effective when cutting through porcelain. After removing the porcelain, it’s easiest to remove the metal substructure using a tungsten carbide bur. The tooth structure underneath can be prepared with a tapered-fissure bur.

Removing an amalgam

A tungsten carbide bur is the most efficient and fastest way to remove an existing amalgam. Pear-shaped burs and fine crosscut burs are both good burs to select.



(877) 337-78006

Removing dental caries

Dental caries are removed using a round tungsten carbide bur at a slow speed. Good sizes to select are sizes two, four, six, or eight. Using a round tungsten carbide bur at a slower speed removes only a minimal amount of dental hard tissue while more effectively removing the softer areas of decay. Where cavities are deeper, it reduces the risk of pulpal exposure. Some clinicians may prefer to use a ceramic round bur. Once all signs of caries are removed, a finer and smoother diamond or carbide bur can complete the preparation before restoration.

Preparing for an all-ceramic restoration

All-ceramic restorations need a 90° exit angle but require a rounded internal angle. A modified-shoulder diamond bur provides a flat 90° exit angle and a rounded internal angle. When using any bur, it is possible to create a reverse margin inadvertently if the depth cut of the bur exceeds the diameter width at the tip. You often won’t notice this problem until a model is poured. One solution is to use an end-cutting bur or to choose a bur size that matches the desired depth of the preparation.

Finishing preparations

Finishing burs are made from tungsten carbide and have flutes that are closer together and shallower compared with operative burs. Tungsten carbide or diamond finishing burs remove excess composite and smooth the restoration



(877) 337-78007

before polishing. They create an optimal smoothness, reducing the potential for biofilm development on the restoration surface. It is important that you practice with the different types and evaluate for each phase of the preparation. This way; you may become familiar with what works best in the least amount of time and effort. Often you may be pushed to get an entire bur kit. This may not be needed. A pick and choose often works best and can save money.

Maintaining reusable burs

After completing the patient’s treatment, it is essential to examine the condition of the burs closely and discard any that are worn or damaged. Using a damaged bur will affect the quality of the preparation and could cause trauma to the hard tissues. Additionally, a damaged bur will cut less efficiently and may cause overheating of the handpiece as it increases power to compensate. After pre-soaking them to loosen debris, any burs suitable for reuse should be cleaned and sterilized. Diamond burs may be cleaned using an enzymatic cleaning solution that prevents the diamond coating from dulling during sterilization.



(877) 337-78008

Three-unit all-ceramic preparation guidelinesArticle by Mario Abreu | Fixed Technical Consultant

The introduction of stronger and more durable ceramics over the past few years has greatly increased the clinician’s choice of materials when fabricating an all-ceramic three unit bridge. The latest generation of zirconia is suitable for three unit bridges and can restore teeth anywhere in the mouth, and IPS e.max is suitable for anterior teeth.

Suitable materials for three-unit all-ceramic bridges

Options include high translucent (HT) zirconia for anterior three-unit bridges and layered zirconia. Zirconia Solid is an extremely strong material suitable for restoring posterior teeth, and it can be an excellent choice when the patient has bruxism or tooth grinding issues. IPS e.max is a lithium disilicate ceramic that provides exceptional esthetics. It is suitable for three unit anterior bridges and for posterior bridges where the second premolar is used for an abutment tooth. IPS e.max lacks the structural strength required for bridges extending past the second premolar.

If you are unsure which material will provide the best treatment outcome for the patient, contact the dental lab to discuss the case with experienced



(877) 337-78009

technical staff. Once you have selected the appropriate material for the patient’s restoration, it is essential to prepare the abutment teeth correctly. Tooth conservation is always an important consideration; preserving the maximum amount of healthy tooth structure is one of the main aims of modern dentistry.

With all bridge preparations for all-ceramic restorations, incisal and occlusal edges must be rounded. There should be no undercuts, the walls of the preparation must be parallel. The abutment teeth must not diverge or converge, preventing a clear path of insertion. The minimum thickness for the walls of a bridge preparation is 0.5 mm. During tooth preparation, the minimum connector cross-section for an anterior restoration should be 7 mm2, while a posterior restoration should have a connector cross-section of 9 mm2.

Three-unit all-ceramic preparation for layered zirconia and HT zirconia bridges

Layered and high translucency zirconia bridges can provide the patient with an extremely high quality restoration. The high strength of zirconia means that it handles similarly to PFM restorations. Supragingival margins are acceptable, because of the tooth-colored framework. Zirconia margins make it simple to maintain excellent gingival esthetics, even after these restorations have been in the mouth for a long time.

Image: Zirconia Layered Source: DDS Lab



(877) 337-780010

Ideally, when preparing teeth for a layered or HT Zirconia bridge, ensure that the preparations have a continuous and easily visible chamfer around the entire circumference of the tooth. Avoid bevelling. The vertical and horizontal preparation must have an angle of at least 5 degrees.

When shaping anterior teeth ensure that:

• The anatomical shape is evenly reduced by between 1 and 1.5 mm.• The incisal third of the crown should be reduced by 1.5 mm, and the incisal

edge should be reduced by between 1.5 and 2 mm.

When shaping posterior teeth then ensure that:

• The anatomical shape is evenly reduced by between 1 and 1.5 mm.• The occlusal surface should be reduced by between 1.5 and 2 mm

Three-unit all-ceramic preparation for zirconia solid

Frequently, the patient requiring Zirconia Solid restorations will have a well-documented history of nighttime grinding and may have previously broken the cusps on molar or premolar teeth. Monolithic, or solid, zirconia is an extremely strong material that provides an excellent fit. The material exhibits opacity which causes it to be unsuitable for selecting a proper shade for anterior restorations. Tooth preparation for solid zirconia restorations will be similar to high-




(877) 337-780011

translucent zirconia: it is recommended to be more liberal during preparation, even in cases that the manufacturer advises to prep like a full cast.

There should be 1 to 1.5 mm occlusal clearance, with a 3 to 4 mm axial wall height. A 0.5 mm chamfer is preferable and preparations should have a 4 to 8 degree taper. Once the teeth are prepared, check that the margins are clearly visible and that the design allows for easy insertion. When the margins are supragingival, they are easier to identify, and an impression is more efficient to capture.

Three-unit all-ceramic preparation for IPS e.max®

IPS e.max is a good material to select when minimal restoration thickness is important. It provides good biocompatibility, high mechanical strength, and optimum translucency.

When preparing teeth for IPS e.max, the following guidelines apply:

• Tooth preparations should have no sharp angles or edges• The shoulder preparation must have rounded inner edges

When shaping anterior teeth ensure that:

• The anatomical shape is evenly reduced while adhering to the correct minimum thickness required.

• A shoulder is prepared around the entire circumference of the tooth with a chamfered edge or rounded inner edges and with an angle of



(877) 337-780012

approximately 10 to 30 degrees. The overall width of the shoulder or the chamfered edge must be at least 1 mm.

• The tooth is reduced incisally by at least 1.5 to 2.0 mm. The oral or vestibular area should be reduced by at least 1.5 mm.

• For successful bonding to, the preparation height should be at least 4 mm and have retentive surfaces.

The preparation guidelines for posterior teeth are similar. You must ensure that:

• The anatomical shape is evenly reduced and the correct minimum thickness is achieved.

• The prepared tooth has a circular shoulder with rounded inner edges. Alternatively, it may have a chamfer with a 10 to 30 degree angle. The width of the shoulder or chamfer must be at least 1 mm.

• The occlusal surface of the tooth is reduced by at least 1.5 mm.

• The buccal, palatal, or lingual surfaces are reduced by at least 1.5 mm for lithium disilicate e.max bridges. If e.max zirconium oxide is chosen, then at least 1.5 mm must be removed from these surfaces.

• The preparation has adequate retentive surfaces and is at least 4 mm in height for successful self-adhesive or conventional cementation.



(877) 337-780013

Ensuring that the pontic width is acceptable

For three unit bridges, the maximum width of the pontic differs for anterior and posterior bridges. For anterior bridges up to the canine, the width of the pontic shouldn’t be more than 11 mm. For posterior bridges up to the second premolar, the pontic width should be no more than 9 mm. Once an impression is taken of the abutment teeth, check that all the details are captured before sending it to the dental lab.

Mario’s recommended resource

Free downloadable

All-ceramic restorations

In this eBook we talk about:• Preparation for all-ceramic

restorations• Parameter for reduction of tooth

structure• And more...

Download the book here:https://go.ddslab.com/all-ceramic-restorations-free-white-paper



(877) 337-780014

Tooth preparation for all-ceramic crownsArticle by MaryLeigh Dempsey | Implant Manager

All-ceramic crowns can create some of the most aesthetically-pleasing restorations available today. Using a no metal substructure allows light to be transmitted through the crown, closely replicating the translucency of a natural tooth. An all-ceramic crown also promotes good tissue response, and only mild reduction of the facial surfaces is required. However, significant tooth reduction is necessary on the lingual and proximal surfaces.

Wear may also develop on the functional surfaces of natural teeth opposing the all-ceramic crown. All-ceramic crowns may not be suitable for discoloured teeth or teeth with enamel defects, teeth with bilateral or unilateral decay. During fitting, the appearance of the restoration can be modified by the colour of the luting agent. To be successful, an all-ceramic crown should have a relatively-even thickness circumferentially. There are only minor differences in preparation between the various all-ceramic crown materials. Proper design is critical for ensuring the mechanical success of the restoration.

Ensuring the preparation has a 90° cavosurface angle helps to prevent unfavourable distribution of stresses and minimises the risk of the crown fracturing. The preparation must be designed to provide the correct support for the porcelain along its entire incisal edge, unless an all-ceramic crown with a strong core (i.e. zirconia) is chosen.



(877) 337-780015

The tooth should have a relatively intact coronal structure that will provide sufficient support for the restoration, particularly in the incisal area. Ideally, this area shouldn’t exceed a thickness of 2 mm. Otherwise more brittle all-ceramic restorations may fail. When preparing posterior restorations, the occlusal load should be evenly distributed, so that contact is in an area where the porcelain is supported by the tooth structure.

For an IPS Empress or e.max crown, and for zirconia anterior crowns, a tooth must be reduced by between 1 mm and 1.5 mm to create an aesthetically-pleasing restoration. Facial reduction should be between 1 mm and 1.5 mm, while incisal edges should be reduced between 1.5 mm and 2 mm to ensure sufficient incisal translucency can be created.

To reduce the facial surface, depth orientation grooves should be placed at 0.8mm deep; after they are finished, this depth will become 1mm. Once placed, the area between the grooves should be reduced and facial reduction should extend around to the facial-proximal angles. Margins must be precisely prepared with a 1-mm-wide circumferential shoulder or chamfer with rounded inner edges. To reduce the incisal edges, three depth grooves of 1.3mm should be created and the tooth structure between them should be carefully reduced. Care should be taken to avoid creating undercuts at the junction of the shoulder finish line and the axial walls. Feather edges and sharp transitions must be avoided and the shoulder should be as smooth as possible. A football-shaped bur can be used to reduce and shape the lingual surfaces.




(877) 337-780016

For posterior crowns, occlusal surfaces should be reduced between 1.5mm and 2mm, with a 1.5mm axial reduction. Internal line angles should be rounded and a tapered, flat-ended diamond should be used to create a good shoulder margin.

When preparing teeth for all-ceramic crowns, a uniform reduction will help result in optimal ceramic strength. Ensuring sufficient tooth structure is removed will lead to better aesthetics. The smoother the edges, the lower the stresses placed on the porcelain crown which in turn decreases the potential for fracturing. Additionally, scanners can read smooth preparations more accurately.

MaryLeigh’s recommended resource

Free downloadable

Preparation and cementation for all-ceramic restorations

This table will provide you with guidelines for:• Prep Design• Occlusal Clearance• Axial Reduction• Cementation


Preparation and cementation table for all-ceramic restorations

Lithium Disilicate (IPS e.Max®) Empress Layered Zirconia Solid Zirconia (Bruxzir®)

Prep Design

Smooth w/ roundedangles and deep(1-1.5mm) shoulder orchamfer at margins



Smooth w/ roundedangles and chamfer,shoulder, or knife-edgemargins

Occlusal Clearance 1.5 - 2 mm 1.5 - 2mm 1.5 - 2 mm 1.5 - 2 mm

Axial Reduction 1 - 1.5 mm facial, lingual;1mm proximal

1 - 1.5 mm, facial, lingual;1mm proximal

1 - 1.5 mm all around foroptimal esthetcis &strength of porc/zirconiainterface

.5 mm - 1.5 mm all aroundfor maximum strength

Adjusting Highly recommended to adjust AFTER cementation to avoid fractures & micro cracks in all-ceramicrestorations. Always use waterspray, fine diamond bur and a light touch restorations.

Cementation

Self etching/self adhesive:Multilink Automix, MaxCem Elite, Nexus NX3, SpeedCEM TotalEtch: Variolink II; Calibra, Rely, Rely X, Rely X Veneer

Variolink Veneer, Multilink, Rely X , Rely X Veneer, Nexus, NX3

*Do not use glass inomer on Empress material

Multilink Automix, Variolink II, MaxCem, Elite, Nexus NX3, Duo-Link, Zinc Phosphate

Multilink vvAutomix, Variolink II, Maxcem Elite, Nexus NX3, Duo-Link, Zinc Phosphate


(877) 337-7800

Download the book here:https://go.ddslab.com/preparation-and-cementation-table-for-all-ceramic-restorations



(877) 337-780017

Tooth preparation guidelines for PFM crownsArticle by Mary Hochwarter | Technical Consultant (Fixed)

Porcelain-fused-to-metal (PFM) crowns are among the most popular and reliable restorations. Using a cast metal substructure that is veneered with porcelain, this material closely mimics the appearance of a natural tooth. For this restoration to be successful, the tooth must be properly prepared and often substantial tooth reduction is required. The crown must be sufficiently thick enough to hide the metal substructure and the opacious porcelain used to mask this alloy. When preparing a tooth, a systematic and organized approach helps to ensure the prep is correctly shaped. Tooth preparation involves several distinct steps which include, creating the guiding grooves for incisal or occlusal reduction, reducing the labial or buccal surfaces and axial reduction of the lingual and proximal surfaces. After those chosen steps are complete, all prepared surfaces can be finished.



(877) 337-780018

Preparing anterior teeth for PFM crowns

For good aesthetics, an anterior tooth should be reduced by at least 1.2 mm on its labial surface, although 1.5mm is the preferable size. Lingual surfaces are reduced by 1 mm and incisally by 2 mm using a rotary instrument. To successfully prepare the labial surface, a central cervical groove should be made parallel to the path of placement along the long axis of the tooth. Two further secondary grooves are made on either side. Incisal edge reduction grooves are placed and these must be approximately 1.8 mm deep. The depth of these grooves can be verified using a periodontal probe, they then should extend halfway down the labial surface.

Next, the incisal edge is reduced and proximal contact is broken while maintaining a lip of enamel which protects the adjacent tooth from damage. Ideally, the incisal edge on an anterior tooth should be reduced by 2 mm, as this will allow for adequate material thickness, enabling the ceramist to create a crown with good incisal translucency. The proximal contacts are reduced and a 0.5-mm lingual chamfer is created. The tooth structure in between the depth grooves is removed, creating a cervical shoulder that should be approximately 1 mm wide. It should extend into the proximal embrasures. The easiest way to shape the lingual surface of an anterior tooth is using a football-shaped diamond. Generally, for anterior teeth, a single guiding groove is placed in the central lingual surface. Preparation is completed with a fine grit diamond bur.




(877) 337-780019

Preparing posterior teeth for PFM crowns

When preparing posterior teeth for PFM crowns, depth holes are created in the occlusal surface to facilitate the creation of occlusal depth cuts. Once these depth cuts have been completed, the occlusion can be reduced and a lingual chamfer and a buccal shoulder are created. The buccal shoulder preparation should extend at least 1mm lingually to the proximal contact. The preparation should extend slightly further mesially than distally, as it is more visible. The occlusal surfaces of posterior teeth generally require 1.5 to 2 mm of clearance. Occlusal reduction may be less if the crown is fabricated with a metal occlusal surface or with a metal bite stop.

All margins should be distinct and continuous circumferentially. All other angles must be rounded and the finished preparation should not have any obvious bur marks. Areas that are frequently missed during finishing include the incisal edges of anterior preparations and the transition from axial wall to occlusal in posterior preparations. Margins should be finished with diamonds or with hand instruments.

The design of the shoulder does depend on the chosen margin. For example, a porcelain margin requires proper support and a 90° angle is preferable. This shoulder is also suitable for crowns with conventional metal collars, allowing the collar to the kept narrow and unobtrusive. However, bevelling the margin or sloping it allows for the porcelain to be better supported.



(877) 337-780020

Mary’s recommended resource

Free downloadable

Crown and bridge comparison chart

This chart will help you:• Decide which materials are best• Know the difference between crown and bridge products• Know all the benefits and features of each product.

Benefits and Features

Strength strong superior 1200 MPa strength superior

strong 600-780 MPa strength 400 MPa strength 160 MPa strength

Durability durable most durable highly durable durable durable durable durable

Longevity up to 30 years* lifelong* 30 years* 20-30 years* 20-30 years* 20 years* 20 years*

Marginal fit good fit better fit precise fit precise fit precise fit exceptional fit precise fit

Tissue response healthy, good excellent, especially gold

healthy response healthy response healthy response healthy response healthy response

Free from metal

Translucence good none opaque life-like very natural very natural very natural

Versatilityanywhere in mouth, all

bridgesanywhere except smile anywhere in mouth anywhere in mouth anywhere in mouth anywhere in mouth as

crown or veneerveneers anterior crown

Integrity level good high high good high high good

Shade matching good n/a good opaque very good very good exceptional exceptional

Plaque resistance high high high high high high high

Biocompatibility good good exceptional exceptional exceptional exceptional exceptional

Opalescence can be good n/a n/a can be good n/a can be good can be good

Esthetic level good notesthetic

notesthetic

very high very high excellent excellent

Extras non precious is most affordable

full cast gold most durable

cost effective alternative to full

cast crown

alternative to zirconia HT or e.max for

long span bridges

cosmetic cosmetic cosmetic

PFM Full cast Zirconia solid Zirconia layered IPS e.Max IPS EMPRESSZirconia

high translucent

Crown and bridge - which material is best?

*Depending on patient oral hygiene



(877) 337-7800

Download the book here:https://go.ddslab.com/crowns-and-bridges-material-guide



(877) 337-780021

Zirconia crowns preparation guidelinesArticle by Bill Warner | Technician, and Former Laboratory Owner

Since its emergence into the dental arena, Zirconia has increasingly become the material of choice for clinicians who wish to provide their patients with the most technologically advanced metal-free restorations. Zirconia has improved significantly with the introduction of a wider array of available milling pucks which allow for greater shade variation and translucencies that closely resemble natural dentition. In addition to improved esthetics, the Zirconia physical properties allow for durability, strength, and precision-fitting restorations. To maximize on the success of seating Zirconia restorations, and minimizing chair time, it is essential to ensure that proper preparation guidelines are being followed.

Preparation guidelines for an anterior zirconia crown

When prepping a tooth for an anterior Zirconia crown, you will need to ensure that there is sufficient room for the internal zirconia wall thickness to have a minimum of 0.3 mm and ideally between 1.0 mm and 1.5 mm, or 1.8 to



(877) 337-780022

2.0 mm incisal reduction. There should be a clearly visible and continuous circumferential chamfer with a reduction of at least 0.5 mm at the gingival margin. The horizontal and vertical preparation of the tooth should have an angle of approximately 5° and a bevel is not advisable. A deep chamfer or shoulder prep is required for optimal esthetics. All the incisal edges should be rounded. never sharp or abrupt line angles.

Preparation guidelines for a posterior zirconia crown

When prepping a tooth for a posterior Zirconia crown, you will need to ensure that there is sufficient room for the wall thickness to have a minimum of 0.5 mm and ideally between 1 mm and 1.5 mm or 1.5 to 2 mm occlusal reduction. The prep should be tapered between 4°and 8°. It will also need to have a clearly visible and continuous circumferential chamfer and a reduction of at least 0.5 mm is required at the gingival margin. Just as with the preparation for an anterior crown, a bevel is not recommended. Ensure that all occlusal edges should be rounded.

Although the Shoulder and Chamfer preparations are the most ideal, Feather edge preparations are typically not recommended, but can be acceptable for Z irconia crowns. Check with your dental laboratory to see if their fabrication process will allow for this form of prep, as different types of Zirconia do have different guidelines.



(877) 337-780023

Factors that may make a crown preparation unacceptable for a zirconia restoration

To be acceptable for a Zirconia crown restoration, the preparation should not have any undercuts and it should not have a gutter preparation. A 90° shoulder is also unacceptable as are parallel wall preparations. Sharp incisal or occlusal edges are not suitable for a zirconia restoration.

Layered or monolithic restorations

For Zirconia restorations within the esthetic zone or “smile zone”, a zirconia restoration layered with porcelain, or a High Translucent zirconia restoration will usually provide optimal results. A Zirconia crown layered on the facial, will provide optimal results. Over the past few years layering porcelain and techniques have improved significantly so a Zirconia substructure that has been layered with porcelain is unlikely to chip or fracture on the occlusal or incisal. However, if maximum strength is required because a patient has bruxism, a heavy bite or where there is only limited occlusal clearance, a monolithic crown may be a better solution. Monolithic restorations are providing an increasingly aesthetic result with the introduction of High Translucency Zirconia or the DDS Lab product reference, Zirconia HT.



(877) 337-780024

Cementing and finishing zirconia restorations

Quite often marginal finishing is required when fitting and cementing Zirconia restorations. Excess cement must be removed to avoid plaque formation which can lead to tooth sensitivity and periodontal disease. Gingival margins can be finished using non-cutting, safe-end finishing burs that will protect the soft tissues. Although these adjustments may slightly roughen the surface of a Zirconia restoration, it should be easy to polish, creating an exceptionally smooth surface.

If adjustments are required it is important to use an appropriate diamond bur which is suitable for a Zirconia restoration. It is also important to use as little pressure as possible. Less pressure will reduce heat which can cause the Zirconia to fracture. Using water while adjusting will also help keep the restoration cool.



(877) 337-780025

Bill’s recommended resource

Free downloadable

Why your peers choose zirconia over PFM crowns

In this eBook we talk about:• Disadvantages and Advantages of Zirconia • Why your peers choose Zirconia over PFM• Layered, Solid, and High Translucent Zirconia Applications compared• Zirconia High Translucent: Benefits, Wear Properties and Selection Process • Zirconia Dental Implants • Zirconia Crown Preparation Guidelines• Parameter for reduction of tooth structure

Download the book here:https://go.ddslab.com/all-ceramic-restorations-free-white-paper

26

e

All-Ceramic Chairside Preparation Guide for IPS e.max®

Anterior chairside preparation guide

Full-coverage 3-unit bridge restorations

Veneers Thin Veneers

Shoulder margin 1.0 mm reduction at the gingival margin

1.0 mm to 1.5 mmfacial reduction

1.5 mm to 2.0 mmincisal reduction

1.5 mm lingualcontact clearance

Shoulder margin

Rounded internalline angles

Football-shaped finishingbur for lingual reduction

Shoulder margin



1.0 mm reduction at the gingival margin

1.5 mmaxial

reduction

Anterior crown preparation 3-unit bridge preparation

A medium grit, round-ended, diamond bur is used to remove a uniform thickness of facial enamel by joining the depth-cut grooves.

IPS e.max can be pressed to as thin as 0.3 mm for veneers. If sufficient space is present, IPS e.max can be placed over the existing teeth without the removal of any tooth structure. Depending on the case requirements, however, some teeth may need to be prepared to accomodate for the thickness of the ceramic and to ensure for proper contour and emergence profile.

The diamond bur is angled tobevel back the incisal edge.

Depth cuts of 0.6 mmto 0.8 mm*


*Please note: For additional masking capabilities and/or layering techniques, further reduction may be necessary. Contact your laboratory for further information. © 2021 DDS Lab. All rights reserved.

27

Posterior chairside preparation guide

All-Ceramic Chairside Preparation Guide for IPS e.max®

Inlays/Onlays

3-unit bridge restorations

Full-coverage restorations

Shoulder margin

1.5 mm to 2.0 mm isthmus width

Inlay preparation

1.5 mm-depth at isthmus

1.0 mm- to 1.5 mmwide gingival floor


Shoulder margin

1.0 mm- to 1.5 mmwide gingival floor

Occlusal reduction of1.5 mm to 2.0 mm

3-unit bridge preparation

Posterior crown preparation

1.5 mm axial reduction

1.5 mm to 2.0 mmocclusal reduction



Shoulder margin

1.0 mm reduction atthe gingival margin


1.5 mm axialreduction

Conventional cementation preparation

Taper between 4° and 8°

Shoulder preparationof at least|1.0 mm proximalreduction

Occlusal reduction of at least 2.0 mm in contact area

Coronal lengthat least 4.0 mm


A flatended, tapered diamond isutilized to establish a shoulder margin

1.0 mm reduction atthe gingival margin margin

1.5 mm axial reduction




(877) 337-780028

Final thoughtDental restorations must be planned and designed to ensure that they are conducive to maintaining good periodontal health. Preparing tooth restorations properly will increase the success of your practice and well-being of your patients.

It is important to remember that every tooth loss case is different so you must cater to the specific needs of each individual patient. There are many factors that affect tooth preparation including the occlusal relationship, pulpal and periodontal status, direction of enamel rods, size and position of pulp, and the relationship of the affected tooth to its supporting tissues. Additionally, patient factors such as age, health issues, and esthetic needs factor into the decision. Selecting the right restoration solution and accurately preparing the affected area could mean all the difference between a blissful patient who will recommend your services to others, and a dissatisfied patient who needs hours of clinical support to try and fix the issue.

Having the right dental laboratory to assist you with your dental implant treatments can be invaluable. Our experienced technical team is always willing to discuss any case with you and our in-depth technical knowledge will enable you to make the right treatment choices. We can liaise closely with you through the entire treatment, ensuring your patient is satisfied.


Use our virtual RX system, MyDDSLab.com, online or through our mobile app

Use MyDDSLab.com to...

• Submit prescriptions online

• Track cases and receive email order notifications

• Manage UPS case shipments

• View account balance and pay invoices online

• View impression reports and scores

Learn more at ddslab.com

29


Crown and Bridge Prescription

Next

(877) 337-7800© 2021 DDS Lab. All rights reserved.

About DDS Lab:DDS Lab is a NBC member and full-service Certified Dental Lab (CDL) located in Tampa, FL. DDS Lab specializes in serving group practices and provides the perfect balance between quality products and competitive pricing. For more information, contact DDS Lab at ddslab.com or at 877-337-7800.

Additional free resources can be found at: dslab.com/free-resources

Documents

Preparation Guidelines