**2. Classification as a systematic approach for communication and planning**

A classification is a systematic approach in which the items or units are categories in groups or subgroups according to specific criteria. This approach facilitates the

*Strategic Implants under Existing Partial Removable Dentures, Why, How Many, and Which… DOI: http://dx.doi.org/10.5772/intechopen.100191*

discussion regarding the most suitable treatment options, eases the communication between the dentist and the technician. The classification also allows for visualization and differentiation between the RPD support types: tooth-supported, tooth tissuesupported, tissue-supported, implant-supported, implant tissue-supported, and implant tooth-supported.

#### **2.1 Kennedy classification system**

In 1925 Dr. Edward Kennedy introduced his approach of categorizing partially edentulous arches into four classes. He categorized the partially edentulous arches in a way that considered the edentulous area position in the arch and if it was surrounded with teeth or not. This approach was beneficial in visualizing the cases and reaching the decisions regarding the RPD designs.

The following is the Kennedy classification:

Class I: Edentulous free-end areas located on both sides (bilateral), posterior to the remaining teeth (**Figure 1**).

Class II: Edentulous free-end area located on one side (unilateral), posterior to the remaining teeth (**Figure 2**).

Class III: Edentulous bounded area with natural teeth remaining both anterior and posterior to it (**Figure 3**). The area is located on one side (unilateral).

**Figure 1.** *Class I maxillary arch.*

**Figure 2.** *Class II maxillary arch.*

**Figure 3.** *Class III maxillary arch.*

**Figure 4.** *Class IV maxillary arch.*

Class IV: Edentulous bounded area with natural teeth remaining posterior to it. The area is located anteriorly and crossing the mid-line (**Figure 4**).

In 1965 Applegate's added eight rules to the classification. The rules can be summarized by the following: The categorization (classification) is always determined by the most posterior edentulous region (or regions). Any additional edentulous area (other than those that define the categorization) is considered a modification (**Figures 6** and **7**). If the teeth posterior to the edentulous area are not used to support the RPD, the edentulous area is classified as a free end (**Figures 5** and **7**), and vice versa (**Figures 6** and **7**). If the posterior free end edentulous region is not going to receive artificial teeth, it will not be considered in the classification (**Figures 6–8**), and vice versa. Putting the design and the structure of the RPD into consideration is a cornerstone in giving the correct RPD classification. Subsequently, the classification will be the start point making the best clinical decision regarding the number and the position of strategic implants under the RPD.

#### **2.2 Steffel classification**

In 1962 Steffel described six support possibilities that can be encountered in RPD [2]. He labeled the classification categories from A to F based on the fulcrum, and the number and distribution of the abutments, **Figure 9**. The fulcrum line is a hypothetical line formed between abutments, teeth or implants. The RPD may rotate somewhat around the fulcrum during function.

*Strategic Implants under Existing Partial Removable Dentures, Why, How Many, and Which… DOI: http://dx.doi.org/10.5772/intechopen.100191*

#### **Figure 5.**

*No rest is going to be costructed on # 38 or 37* → *the arch has two free end areas* → *Class I mandibular arch.*

#### **Figure 6.**

*Direct retainer is going to be constructed on 37. No artificial teeth is going to replace 46, 47 or 48* → *no free end* → *Class III mod 1 mandibular arch.*

#### **Figure 7.**

*No artificial teeth is going to replace, 48. Direct retainer is going to be constructed on 37 but not on 47* → *one free end* → *Class II mod 3 mandibular arch.*

In this chapter, we suggest a modification to this classification to simplify the communication and decision-making regarding the strategic implant under the existing RPD. In the modification, B, C, and D will be labeled together.

#### **Figure 8.**

*No artificial teeth is going to replace, 38, 37, 36, 47 or 48. Class IV mandibular arch.*

**Figure 9.** *Steffel classification.*

The following is the *modified Steffel classification:*


#### *Strategic Implants under Existing Partial Removable Dentures, Why, How Many, and Which… DOI: http://dx.doi.org/10.5772/intechopen.100191*

Providing the patient with a stable prosthesis is a crucial target for the dentist. However, the RPD is not rigidly attached to the intraoral hard (teeth) and soft (mucosa) tissues, which have different levels of compressibility and mobility. Subsequently, the chewing and occlusal forces may generate different levels of tissue stress and prosthesis mobility. Both (stress and mobility) should be within the physiological level and cause no harm or trauma. Achieving this critical goal depends on the clinician's understanding of the biomechanics and the different design solutions. The RPD design should consider the unique nature of each clinical case and counter the expected RPD movement in response to loading. The design also should minimize the potentially destructive forces that may affect the supporting tissues; teeth, mucosa, and bone. That can be achieved by avoiding a long lever system, good selection for the RPD supporting elements, and wide symmetrical distribution of the functional forces [3, 4]. Many of the previous points (if not all) can be achieved (fully or partially) by delivering an RPD with quadrangular-support type.

According to the modified Steffel classification, there are four types of prosthetic support: punctual, linear, triangular, and quadrangular. The RPD support improves gradually as the classification change from I to IV. Classification IV provides the best support to the RPD with the highest resistance of rotation. The strategic implant aims to change the prosthetic support type to a more favorable configuration. *Delivering an RPD with a better support type can be considered the start point in a multifactorial process for deciding the number, type, and position of strategic implants.*
